BATTERY MANAGEMENT SYSTEM FOR ELECTRIC VEHICLES
vijay tharad
Director Operations at Corporate Professional Academy for Technical Training & Career Development
BMS Definitions & Glossary
The BMS Definitions & Glossary is an A to Z extension to our website that just gives you an alternative way of finding information.
Active Balancing – the idea here is to redistribute the energy across the cells. Give energy from the cells with the highest SoC to the cells with the lowest SoC. This is the ideal cell balancing
Active Mode – the BMS is on, communicating and monitoring all sensors.
Ah – Ampere-hour is the unit of cell capacity.
Balancing – all about the dissipation or movement of energy between cells. The aim being to align them all with respect to state of charge. Aligning the state of charge of all of the cells in a pack will allow the pack to deliver the most energy and power. This becomes more crucial as the pack ages and differences between cells become more significant.
Capacity – cell nominal capacity is defined as the quantity of charge, in ampere hours (Ah) that a cell is rated to hold.
Cell Matching – what level of cell matching do you do prior to assembling a battery pack? Assuming the battery pack will be balanced the first time it is charged and in use.?
Cell Voltage Delta – difference in resting voltage for cells at different points in a series string. A threshold maximum voltage difference will trigger cell balancing
Centralised BMS – long leads are required to connect the central control unit to every cell in the pack.
C - Rate – a measure of the rate at which a battery is charged or discharged relative to its capacity. It is the charge or discharge current in Amps divided by the?cell capacity?in Ampere-hours. An nC-rate is the constant-current charge or discharge rate that a cell can sustain for 1/n hours. This current (in A) equates to the cell nominal capacity (i.e. C Ah) multiplied by n h?1 i.e. i=nC. For example, a fully charged 20Ah cell should be able to deliver 10A for 1/n = C/i = 20/10 = 2hrs, or the c-rate is n=i/C = 0.5h-1?
Coulomb Counting – SOC Estimation
Current Derate – a reduced current charge or discharge capability.
DCIR – Direct Current Internal Resistance is the internal resistance of the cell. ?This is the resistance in charge and discharge to a direct current demand applied across the terminals.
De-Rate – when the charge or discharge current (power) limits communicated to the vehicle are reduced.
DoD – Depth of Discharge is equal to 1 – SoC
Insulation – use of a poor conducting material to restrict flow of current to almost zero.
Insulation Resistance – value of resistance between any two points.
Isolation – disconnection and separation of electrical equipment from every source in such a way that the disconnection and separation is secure.
Isolation Resistance – the value of resistance, measured at a specified voltage, between a HV bus and ground.
Kalman Filter – an estimator of information of a system from noisy (or uncertain) directly or indirectly related measurements.
Lossless Balancing – this approach switches cells in and out of the circuit during charging. This means we have a lot of switches and that these switches have to be designed to carry the full current.
Masterr and Slave BMS – a slave will monitor and control a sub-set/module of cells and communicate back to the master.Open Circuit Voltage (OCV) – is the potential difference between the positive and negative terminals when no current flows and the cell is at rest.
Open Circuit Voltage (OCV) – is the potential difference between the positive and negative terminals when no current flows and the cell is at rest.
Passive Balancing – simple form of balancing that switches a resistor across the cells. In the example shown with the 3 cells the balancing resistor would be switched on for the centre cell. Discharging this cell and losing the energy to heat in the balance resistor (typically 30Ω to 40Ω).
Precharge – when closing battery contactors onto a capacitor load there would be a very high current that could cause damage to the contactors or cells, or result in the fuse blowing. Thus a precharge resistor and contactor allows that maximum current to be controlled.
Remaining Useful Life (RUL) – a key function declared by the battery management system. A prediction of how many cycles the pack has before hitting the minimum requirements for operation.
Runtime Balancing – each cell is connected to an individual low DC-DC power converter, then each converter is connected in series. This then allows the power delivered and received by each cell to be completely controlled based on their capability.
Sleep Mode – the battery pack is isolated, there is no balancing, the BMS will be in a low power mode where it occasionally looks at sensor inputs and listens out for a communications request to wake.
State of Charge (SoC) – abbreviated as SoC and defined as the amount of charge in the cell as a percentage compared to the nominal capacity of the cell in Ah.
State of Health (SOH)– this is the total available charged capacity of the cell as a percentage compared to the nominal capacity in Ah when the cell was new.
Temperature – a critical parameter that you need to know before charging or discharging a cell. A cell is a 3 dimensional structure that is also inhomogeneous and hence you will observe temperature gradients within the cell. The temperature limits, gradients and heat rejection rate will define the overall power capability of the battery.
Temperature Gradient – the maximum temperature differential in a cell is normally specified as ~2°C to minimise the degradation in capacity of the cell. This requirement will drive the cell selection versus application along with the cooling system design.
The limits will also be blurred by the design of the battery and control system. One example is the maximum operating temperature for the cell.
Usable SoC Window – If we want a battery cell to last a lot of cycles, extend the life in a power application or to ensure the available power is consistent then we need to set a usable SoC window that is smaller than 100%.
Increasing the Usable SOC Window – If you are in a battery design role there is always pressure on increasing usable SoC window. Nobody wants to pay for and carry around unused battery capacity. However, there are some really good reasons to restrict that window.
Wireless BMS – one option for reducing the wiring complexity and weight in a battery pack is to use a wireless connection. Here the modules or cells report voltage and temperature signals back to the central control system in the battery wirelessly.
Battery Management System
A battery management system (BMS) is any electronic system that manages a rechargeable battery cell or battery pack , such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancing it. Protection circuit module (PCM) is a simpler alternative to BMS. A battery pack built together with a battery management system with an external communication data bus is a smart battery pack. A smart battery pack must be charged by a smart battery charger.
The electric vehicle drivetrain offers new freedom in terms of electric vehicle architectures while leading to new challenges in terms of meeting all requirements. Since electric vehicles have an electric motor and a battery instead of a combustion engine and a fuel tank, the architecture becomes simple and controllable at the component level. Modifications to locate the battery pack safe zone in an EV require extensive adoptions to integrate the battery safely.
?FUNCTIONS OF BATTERY MANAGEMENT SYSTEM
A BMS may monitor the state of the battery as represented by various items, such as:
Electric vehicle systems: energy recovery[edit]
Battery thermal management
Liquid cooling has a higher natural cooling potential than air cooling as liquid coolants tend to have higher thermal conductivities than air. The batteries can either be directly submerged in the coolant or coolant can flow through the BMS without directly contacting the battery. Indirect cooling has the potential to create large thermal gradients across the BMS due to the increased length of the cooling channels. This can be reduced by pumping the coolant faster through the system, creating a tradeoff between pumping speed and thermal consistency.
Computation
Additionally, a BMS may calculate values based on the items listed below, such as:
Communication
The central controller of a BMS communicates internally with its hardware operating at a cell level, or externally with high level hardware such as laptops or an HMI.
High level external communication are simple and use several methods:
Low-voltage centralized BMSes mostly do not have any internal communications.
Distributed or modular BMSes must use some low-level internal cell–controller (modular architecture) or controller–controller (distributed architecture) communication. These types of communications are difficult, especially for high-voltage systems. The problem is voltage shift between cells. The first cell ground signal may be hundreds of volts higher than the other cell ground signal. Apart from software protocols, there are two known ways of hardware communication for voltage shifting systems, optical-isolator and wireless communication. Another restriction for internal communications is the maximum number of cells. For modular architecture most hardware is limited to maximum 255 nodes. For high-voltage systems the seeking time of all cells is another restriction, limiting minimum bus speeds and losing some hardware options. Cost of modular systems is important, because it may be comparable to the cell price. Combination of hardware and software restrictions results in a few options for internal communication:
To bypass power limitations of existing USB cables due to heat from electric current, communication protocols implemented in mobile hone chargers for negotiating an elevated voltage have been developed, the most widely used of which are Qualcomn Quick Chargee and Media Tek Pump Express ."VOOC" by Oppo (also branded as "Dash Charge" with "OnePlus") increases the current instead of voltage with the aim to reduce heat produced in the device from internally converting an elevated voltage down to the battery's terminal charging voltage, which however makes it incompatible with existing USB cables and relies on special high-current USB cables with accordingly thicker copper wires. More recently, the USB Power Delivery standard aims for a universal negotiation protocol across devices of up to 240 watts.
Protection
A BMS may protect its battery by preventing it from operating outside its safe oerating area such as :over-charging
The BMS may prevent operation outside the battery's safe operating area by:
Battery connection to load circuit
A BMS may also feature a precharge system allowing a safe way to connect the battery to different loads and eliminating the excessive inrush currents to load capacitors.
The connection to loads is normally controlled through electromagnetic relays called contactors. The precharge circuit can be either power resistors connected in series with the loads until the capacitors are charged. Alternatively, a switched mode power supply connected in parallel to loads can be used to charge the voltage of the load circuit up to a level close enough to battery voltage in order to allow closing the contactors between battery and load circuit. A BMS may have a circuit that can check whether a relay is already closed before precharging (due to welding for example) to prevent inrush currents to occur.
Balancing
In order to maximize the battery's capacity, and to prevent localized under-charging or over-charging, the BMS may actively ensure that all the cells that compose the battery are kept at the same voltage or State of Charge, through balancing. The BMS can balance the cells by:
Battery Management System
A Battery Management System?(BMS), which manages the electronics of a rechargeable battery, whether a cell or a battery pack, thus becomes a crucial factor in ensuring electric vehicle safety. It safeguards both the user and the battery by ensuring that the cell operates within its safe operating parameters. BMS monitors the State Of Health (SOH) of the battery, collects data, controls environmental factors that affect the cell, and balances them to ensure the same voltage across cells.
A battery pack with a BMS connected to an external communication data transfer system or a data bus is referred to as a smart battery pack. It may include additional features and functions such as fuel gauge integration, smart bus communication protocols, General Purpose Input Output (GPIO) options, cell balancing, wireless charging, embedded battery chargers, and protection circuitry, all aimed at providing information about the battery’s power status. This information can help the device conserve power intelligently.
A smart battery pack can manage its own charging, generate error reports, detect and notify the device of any low-charge condition, and predict how long the battery will last or its remaining run-time. It also provides information about the current, voltage, and temperature of the cell and continuously self-corrects any errors to maintain its prediction accuracy. Smart battery packs are usually designed for use in portable devices such as laptops and have embedded electronics that improve the battery’s reliability, safety, lifespan, and functionality. These features enable the development of end products that are user-friendly and more reliable. For instance, with embedded chargers, batteries can have longer life cycles as the chargers charge the batteries to optimal, ideal specifications within the temperature limits. Accurate fuel gauges allow users to confidently discharge batteries to their limits and not worry about damaging the cell. GPIO, which stands for General Purpose Input/Output (GPIO), is an interface used to connect electronic devices and microcontrollers such as diodes, sensors, displays, and so on.
Primary function of EV-BMS
A BMS for an Electric Vehicle battery manages and controls the battery's charging and discharging, monitors its state of charge and health, and ensures safe operation. The BMS's safety features are critical for EV safety, preventing dangerous situations. The BMS monitors the battery pack constantly, taking action to prevent damage or danger, making EVs safe and reliable transportation.
The BMS has several safety features:
This is the primary function of a BMS. It monitors the state of a cell as represented by parameters such as:
2. Managing thermal temperatures
Temperature is the biggest factor affecting a battery. The battery’s thermal management system keeps an eye on and controls the temperature of the battery. These systems can either be passive or active, and the cooling medium can either be a non-corrosive liquid, air, or some form of phase change. Using air as a coolant is the simplest way to control battery temperatures.
Air cooling systems are often passive as they rely on the convection of the surrounding air or use a fan to induce airflow. However, the main drawback is the system’s inefficiency. Significant power is used to run the cooling system as compared to a liquid-based one. Also, in larger systems such as car batteries, the additional components needed for air-based systems such as filters can increase the weight of the car, further affecting the battery’s efficiency.
Liquid-cooled systems have a higher cooling potential than air because they are more thermally conductive. The batteries are submerged in coolant, or the coolant can freely flow into the BMS without affecting the battery. However, this indirect form of thermal cooling can create large temperature differences across the BMS due to the length of the cooling channels. But they can be reduced by pumping the coolant faster, so a tradeoff is created between the pumping speed and thermal consistency.?
3. Making key calculations
A BMS calculates various battery values based on parameters such as maximum charge and discharge current to determine the cell’s charge and the discharge current limits. These include:
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4. Facilitating internal and external communication
A BMS has controllers that communicate internally with the hardware at a cellular level and externally with connected devices. These external communications differ in complexity, depending on the connected device. This communication is often through a centralized controller, and it can be done using several methods, including:
Only a high-level voltage BMS has internal communication; low-level centralized ones simply measure cell voltage by resistance divide. A distributed or modular BMS must utilize a low-level internal cell controller for modular architecture or implement controller-to-controller communication for a distributed architecture. However, such communication is difficult, especially in high voltage systems, due to the voltage shift between cells. What this means is that the ground signal in one cell may be hundreds of volts higher than that of the next cell.
This issue can be addressed using software protocols or using hardware communication for volt-shifting systems. There are two methods of hardware communication—using an optical-isolator or wireless communication. Another factor hampering internal communication is the restriction of the maximum number of cells that can be used in a specific BMS architectural layout. For instance, for modular hardware, the maximum number of nodes is 255. Another restriction affecting high voltage systems is the seeking time (for reading voltage/current) of all cells, which limits bus speeds and causes loss of some hardware options.?
Optimal Energy Utilization
Battery management systems keep the battery safe, reliable, and increase the senility without entering a damaging state. Different monitoring techniques are used to maintain the state of the battery, voltage, current, and ambient temperature. The BMS communicates with the onboard charger to monitor and control the charging of the battery pack. It also helps maximize the range of the vehicle by optimally using the amount of energy stored in it. It is a crucial component in electric vehicles to ensure that batteries do not get overcharged or over discharged, thus avoiding damage to the battery and harm to occupants.
The battery is a fundamental component of the electric vehicle, which represents a step forward toward sustainable mobility. The battery management system is a critical component of electric and hybrid electric vehicles. Its chief purpose is to ensure safe and reliable battery operation. As an engineering services provider, Cyient works closely with industry experts through our focus areas of megatrends—Sustainable Energy Solutions and Electrification.
Why do we need a Battery Management System in Electric vehicles?
Lithium-ion batteries are the most favoured category among the batteries used in electric vehicles, owing to high power density, low self-discharge, and reasonably low cost. Nevertheless, along with the advantages, many safety risks are involved in making an electric vehicle with a lithium battery. Because, under unusual conditions, lithium-ion batteries may fail and even result in fire due to various reasons like overcharging/over-discharging, thermal runaway, age and wear. This pushes Automakers & OEMs to deploy effective Battery Management Solutions (BMS) to ensure EV batteries are under optimal safety limits to provide safer e-mobility. The section below explains what and how the BMS addresses EV battery operations.
In an electric vehicle, a battery amalgamates several modules, each a collection of individual cells. It is challenging to monitor battery pack performance since each cell in each module tends to charge and discharge at different rates. Also, each cell functions differently due to temperature, health status, and energy. Therefore, each battery cell must be independently observed for safer and more efficient operation. This is where BMS comes into play – it performs routine checks on the parameters, and if it detects any anomalies, it takes immediate corrective measures. This inspection ensures the battery’s safe and reliable operation, producing an efficient and safe electric vehicle for consumers.
Types of Battery Management Systems in Electric Vehicles
There are two types of Battery Management Systems – Centralized BMS and Distributed BMS.
A centralized BMS has one control unit managing all cells, which is cost-effective; however, it exposes the entire system to total failure in case of control unit malfunction. On the contrary, multiple control units are commissioned to enhance system resilience in a distributed BMS. Now, this comes with increased complexities and costs. Automotive brands choose the BMS system that best aligns with their needs and requirements, where price leans towards a centralized BMS and reliability goes for a distributed BMS.
Functions of Battery Management Systems in Electric Vehicles
The Battery Management System (BMS) plays several critical functions in electric vehicles, as in the following pointers.
Cell Monitoring:
The BMS fetches real-time data on fundamental battery parameters like voltage, temperature, and current. With these metrics, BMS closely monitors important performance parameters like State of Charge (SoC), denoting the amount of charge remaining out of the EV battery’s maximum capacity and State of Health (SoH), showing the overall status of battery pack health. SoC monitoring helps EV customers asses their disposable driving range and plan their charging station stops without worrying much about range anxiety. With SoH monitoring, EV manufacturers could practically assist their customers by providing heads-up on preventive maintenance, retaining healthy battery conditions and prolonged performance.
Thermal Management:
Electric Vehicle Batteries are sensitive to temperature variations, influencing their performance and lifespan. On this note, the BMS carefully regulates the thermal state of the battery through constant monitoring and control of battery temperature values to maintain optimal operation. For instance, this can involve utilizing heating-cooling mechanisms to keep the batteries within ideal temperatures to maximise their performance and lifespan.
Cell Balancing:
BMS includes a cell balancing process to make the energy cells perform uniformly. At a fully charged state, it equalizes the voltage and state of charge among the cells through two distinctive methods: active balancing – transferring energy from overcharged to undercharged and passive balancing – excess energy is discharged through dissipative bypass mechanisms. Hence, no one cell gets overcharged or under-charged. Cell balancing increases the efficiency and longevity of the battery pack in an electric vehicle.
Battery Optimization:
The BMS vigilantly monitors the multiple parameters of the battery packs since battery cells may lose their integrity as they naturally deteriorate over time. It has built-in protections for overvoltage, undervoltage, overcurrent, thermal management, and external overcharge/discharge incidents. In case of anomalies, the system will automatically regulate the pre-defined protection process, like optimized low voltage charging for damaged cells & balancing voltage variations due to oxidation to keep the battery performance optimal.
This makes the BMS an essential component as it ensures the functioning, reliability, and safety of batteries used in electric vehicles, thereby enhancing the growth of eco-friendly transport for your potential consumers.
Benefits of using a Battery Management System for EVs:
BMS has several significant advantages for electric vehicles. These benefits include:
Performance Optimization:
BMS helps derive the maximum performance of the battery packs to extend the driving range and battery longevity through automated mechanisms to resolve anomalies and malfunctions pertaining to the battery.
Safety and Reliability:
BMS has complete monitoring and safety mechanisms for overcharging, draining, and temperature abnormalities. This ensures the safety and durability of a battery, thus minimising accidents, or failures for EV buyers.
Real-time Data and Diagnostics:
BMS observes batteries in real time, records data for logs on battery health, and identifies malfunctions. This helps OEMs schedule proactive maintenance to rectify issues and significantly enhance customer satisfaction.
Current trends in BMS
Automotive OEMs consistently test new waters to evolve their BMS capabilities and strengthen their automotive offerings. Some notable developments in the BMS space include:
Intelligent BMS:
By employing advanced algorithms and machine learning techniques, BMS can optimize battery performance according to patterns of batteries’ utilization, environment conditions, and other dynamic scenarios. This advancement is valuable for automakers by reducing warranty claims and enhancing their reputation for reliability.
External Communication:
Wireless communication protocols can be seen increasingly leveraged with BMS, enabling them to have system enhancements at speed through Over-the-Air (OTA) updates. Meanwhile, with timely updates, Automotive OEMs can ensure their BMS functionality and performance are intact.
Advanced Predictive Algorithms:
Battery Management Systems in electric vehicles are being integrated with advanced predictive maintenance systems. These algorithms rely on real-time data to anticipate when battery components may require repair or replacement, reducing customer maintenance costs, improving vehicle reliability, and enhancing brand reputation.
Battery management system (BMS) is technology dedicated to the oversight of a battery pack, which is an assembly of battery cells, electrically organized in a row x column matrix configuration to enable delivery of targeted range of voltage and current for a duration of time against expected load scenarios.
The oversight that a BMS provides usually includes:
Here, the term “battery” implies the entire pack; however, the monitoring and control functions are specifically applied to individual cells, or groups of cells called modules in the overall battery pack assembly. Lithium-ion rechargeable cells have the highest energy density and are the standard choice for battery packs for many consumer products, from laptops to electric vehicles. While they perform superbly, they can be rather unforgiving if operated outside a generally tight safe operating area (SOA), with outcomes ranging from compromising the battery performance to outright dangerous consequences. The BMS certainly has a challenging job description, and its overall complexity and oversight outreach may span many disciplines such as electrical, digital, control, thermal, and hydraulic.
Battery Management System
Many different components contribute to the correct charging of electric cars, which we gradually address in our series Basics of Electromoobility. This time we will focus on the Battery Management System, or BMS.
The?battery is still the most expensive component of any electric car and, if mishandled, its service life can be considerably shortened and under unfavorable conditions, it also presents a safety hazard for the car itself and its crew. It is important to ensure the right conditions for individual battery cells and thus for the entire battery, which is what BMS takes care of.
An electric car and its components. Author: FirstEnergy Corp. (Licence CC BY-ND 2.0)
In this article we will summarize how batteries are designed, we will focus on what the external environment must be so that the battery can work optimally, how the BMS is designed, what are its main functions and at the end we will mention the main challenges in designing an effective BMS system.
Battery design
Although the electric car battery is talked about as a single thing, it actually consists of hundreds (and sometimes thousands) of battery cells that are connected in series or in parallel into battery modules. And these modules are then connected into a battery pack, or what everyone simply calls "a battery".
Thanks to this arrangement, it is possible to achieve the required capacity and energy, and at the same time it is easier to manufacture, install, but also to inspect and perform maintenance. We focus on the topic of batteries in more detail here.
battery cell, module and pack. Source: https://www.semanticscholar.org/
Every manufacturer makes the battery slightly differently, uses different chemical compounds, or makes battery cells of different shapes. But it is always a type of lithium battery, which is the most efficient technology that we have so far. These batteries are more or less (depending on the specific compound) sensitive to temperature changes, overcharging or discharging too much, and in order to prolong their life as much as possible, these quantities need to be carefully monitored and controlled.
Lithium batteries are also prone to temperature leaks, which can occur due to several errors, such as charging too fast or discharging too quickly. The following graphs show the so-called Safety Operation Area. The green box represents the conditions under which lithium batteries are safe and work the best. The temperature should be between -5 and 45 ° C, the voltage between 2 - 4 Volts and the current from 0-1A. It is paramount to carefully monitor and ensure that the battery is in this "safety operation area".Safety operation Area.
Source: Battery Management System For Electric Vehicle Applications.pdf
BMS Construction
The design of the BMS corresponds to a large extent to the design of the battery. It consists of a battery monitoring integrated circuit (BMIC), a cell management controller (CMC) and a battery management controller
(BMC).Sistema de gestión de batería. Autor: carrott (Licence: CC BY 2.0)
The BMIC monitors the individual battery cells and must be able to quickly - in a matter of microseconds - inform the CMC of the situation so that the CMC or BMC is able to react and, if necessary, correct an unfavourable situation. In order to prevent temperature leaks, the BMIC needs to notice immediately the battery cell that is overheating and send this information further on as quickly as possible. The BMC must decide how serious the situation is, how to proceed, and the overheated cell must be shut down if necessary. And all of this must happen in the blink of an eye.
The accuracy of the measurement and the ability to respond to adverse conditions depend primarily on the frequency of communication from the BMIC to the CMC and BMC, the more often they communicate, the greater the chance that they will successfully resolve a situation that could be risky. However, it is not at all easy to design an effective communication network in an electric car due to electrical noise.
Of course, before correcting the BMS tries to prevent any unfavorable situation, so apart from the BMIC, CMC and BMC modules it also consists of circuits that balance the energy loads of different cells, in this way all cells work more or less the same and do not tend to cause problems. The issue of leveling is so important that we will discuss it much more in detail later on.
Unused battery cells. Source:
Depending on how complicated the electric car is, several intelligent microcontrollers may be added to monitor and control various specific tasks. Each BMS must be able to monitor not only the battery but also itself and it must be able to determine if alarms or prompts are real and not fake.
Basic functions of BMS
From all of the above, the functions of BMS are more than obvious, but to recap, we will list them one by one and stop at each one of them for a moment.
1.?Discharge and charging control
Charging and discharging are the riskiest moments in the life of a battery. During AC charging , the charge control is partly taken care of by the on-board charger , which is responsible for converting AC current to DC, which is then sent in the required voltage to the battery. In the case of DC charging , the electric current goes directly to the BMS, which controls the charging and communicates with the DC station.
This function requires the whole system to be intelligent, because the parameters of the battery itself change over time (oxidation occurs at the terminals, changes in the capacity of the battery cells, etc.) and it is necessary that the charging always adapts to it in real time.
2.?Determination of the current state of charge (State of Charge)
This is one of the most important functions, thanks to which the BMS can tell the driver how much longer he can drive. But determining the state of charge is not nearly as simple as it might seem. It is actually one of the more complicated problems in the development of BMS systems.
The current state of charge is defined as the ratio of the available capacity to the total capacity of the battery and can therefore take any value from 100% to 0%. And since the 'discharging' of the battery is an electron flow, it would seem that the amount of charge or discharge can only be measured. However, consumption is affected by many variables, such as current temperature, temperature change during discharge, current load, and more, so taking into account all of them is far from easy.
"KIA Future Infotainment System - CES 2014 - (5) - SMADEMEDIA.COM Galleria" by THE SMADE JOURNAL is licensed under CC BY 2.0
Determining the right value of state of charge is also complicated by the fact that the methods of accurate measurement are either too computationally complex or insufficiently accurate, and in addition the state of charge depends also on the parameters of the whole battery that change during its life, i.e. it depends on the state of health of the battery, which is even more complicated to determine.
As accurate measurement is not possible or is extremely impractical, the current state of charge is based on computer battery models. It is an estimate, though a qualified one. In the next chapter, we will focus on battery models a little more thoroughly.
3.?Determination of State of Health
Battery health is defined as the ratio of the current full capacity to the full capacity of the battery at 0 kilometers. When you buy a battery, it has 100% health, which deteriorates with charging cycles.
Many studies agree that battery health is affected by temperature, battery charging current, number of charging cycles and other primary factors. However, not all processes in the battery are fully known, so there are no precise methods for determining battery health. As with determining the state of charge, it is necessary to rely on approximate computer models that take into account internal resistance, conductivity, self-discharge rate, capacity, energy received during charging, temperature during use, age, number of cycles, etc.
State of health of Nissan Leaf batteries over time.
So far, there is no exact agreement between individual manufacturers which variables enter into the calculations and which models are to be used. Research and development continues to focus intensively on these topics. And as mentioned above, determining the state of health correctly is crucial to be able to determine the state of charge as closely as possible.
4.?Charge balancing
Balancing the charge and discharge of individual cells is the last puzzle that every BMS must solve and which we have not yet sufficiently addressed, but it is actually one of the most important functions that the whole battery lifespan depends on. The same level of discharge and charge of each cell is important so that some cells are not overloaded and destroyed.
No two battery cells are ever exactly alike. Some always have a bit bigger or smaller capacity. Battery cells that have a slightly lower capacity discharge faster and are also destroyed faster, while the capacity of other cells remains unused. In the same way, during charging, the weakest cells are charged first and the others are only partially charged.
Balancing the charge and discharge of individual cells thus significantly increases the overall capacity, because it is not only determined by the weakest cells, and it also protects these weaker cells, so they are not damaged, shorted or leaked, which could damage the entire battery pack. In the section on BMS development, we will focus more deeply on active and passive balancing and different types of topology.
Active and Passive balancing.
5.?Recording and communication
Compared to the previously mentioned functions, recording and communication is a relatively easy function. Because the health of the battery is a relative quantity, the BMS needs to store data on what the battery's characteristics were at the beginning so that it can compare it with other values. Thanks to this, it enables the evaluation of the battery operation, as well as its diagnostics.
Equally important is communication between the BMS and other parts of the car such as the?on-board charger or charging station. The BMS also ensures that the driver's display shows how far he has traveled or when the car needs to be recharged. It is also possible to access the aforementioned history, which the BMS stores and processes.
BMS development
In order for each BMS system to be able to perform its functions correctly, several puzzles need to be overcome for its development. As we have said before, we will focus on two. The first is the Battery State Estimation. This is a value that is important both for the driver and for the system itself and its proper management.
The second is Battery Cell Charge Balancing. There are passive and active methods, as well as various active balancing topologies that need to be properly designed to optimize BMS properties.
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Battery State Estimation
The state of charge of the battery is absolutely essential information for the driver. Moreover, the use of the battery could be extended if it was possible to obtain an accurate value. However, this is a complicated problem. We have already explained why this quantity cannot simply be measured and why we have to rely on qualified estimates. Today, there are three basic estimation methods - the ampere-hour method, the open circuit voltage (OCV) method and model-based methods.
The ampere-hour method is simple and easy to implement. However, in order for it to function properly, it needs the original knowledge of the state of health (which is also only an estimate) and it is negatively affected by accumulated errors and measurement errors, and over time it becomes impractical. The open circuit voltage measurement method is also considered accurate. But it can be used only if the car has rested for a long time, so it is difficult to use it in normal operation.
Various methods determining battery state of charge. Author: Jack O'Grady. Source: https://www.jackogrady.me/battery-management-system/state-of-charge
Due to all the mentioned shortcomings, model-based methods are the most common solution. Both voltage and current measurements are used. The measured current is entered into the model and the voltage is calculated using the value of the current and / or past values and parameters. The difference between the calculated and measured voltage is then inserted into an algorithm that is able to cleverly update the estimated state.
The use of intelligent logarithms, fuzzy logic, artificial neural networks and other possibilities are being investigated. Due to their excellent ability to approach nonlinear functions, these methods can achieve very accurate estimates, but the learning process required to use these options is computationally complex, making it difficult to use them in the necessary applications.
Computer models of batteries
Creating computer models of batteries, according to which it would then be possible to calculate the charge level, is complicated because it is a strongly nonlinear system. There are basically two options. The first are electrochemical models that use the electrochemical properties of the battery. And although this method is relatively accurate, in practice it is computationally complex and so several equivalent circuit models are used instead. These circuit models are widely used to estimate battery status, but their problem is that they are not as accurate.
Current research focuses mainly on the development of more accurate models, or on a combination of the current ones (electrochemical and circuit) in such a way that they are not so computationally demanding and the goal is to eventually use them in electric cars.
Battery cell charge balancing
There are no two identical battery cells in the world (or two identical batteries). Differences can be in internal resistance, level of degradation, capacity, ambient temperature, and many more. These inevitable differences between cells can cause many problems, and overall capacity can be dramatically reduced. This imbalance then causes the individual cells to be over-discharged or over-charged, which is dangerous for the battery pack as a whole, and thus charge balancing between the individual cells is of paramount importance to maintain performance and extend battery lifespan.
Passive charge balancing methods
The passive method means that the cells that have more energy than others, are discharged by resistors and the excessive energy is dissipated as heat. By discharging the excess energy from the fuller cells, the battery pack can easily be balanced.
However, this method wastes too much energy and also complicates the thermal control of the entire battery. Moreover, in this case, only overcharged batteries work, and if one battery cell is significantly weaker than others, more energy is discharged during balancing than during driving.
Active charge balancing methods
Active switching circuits are used for active balancing, which are able to transfer energy between individual cells. Unlike passive methods, only a small amount of energy is wasted. But in order to achieve this, more components need to be built into the circuit, which not only leads to a higher cost, but also to reduced reliability.
Balanced and unbalanced battery pack. Source: https://www.ionenergy.co/resources/blogs/cell-balancing-better-performance/
Active balancing occurs through a variety of strategies called topologies, which take into account cost, complexity, and reliability. As always, there's a trade-off. With the simplest and therefore the most reliable topologies, a cell can only balance another cell that is right next to it, which is insufficient if the unbalanced cells are farther apart.
To effectively connect all the cells so that their alignment can be flexible, too many components are needed and thus become unreliable and expensive. The third method, which allows for a small number of components and flexibility, is too slow to be effective in practice, as two adjacent cells are gradually aligned until a homogeneous charge is achieved.
As this is a fundamental function of BMS, much effort is devoted to designing the most efficient topologies and using the best strategies, both passive and active balancing, using as few components as possible. We can surely expect many new things to come in these segments.
In conclusion
BMS is a part of electric cars, which we do not hear about as often as, for example, the battery, but its function is completely irreplaceable. It is the BMS that protects the battery from misuse and damage, prolongs battery life and ensures that the battery is always ready for use.
However, every design always brings the need to balance the price, efficiency and longevity of each system. The only value that is never discounted is security. All components must meet ISO 26262 security standards, so each BMS must be fail-safe and contain redundant resources, such as processor units, each of which must have its own dedicated devices, such as memory, and more.
In terms of the importance and safety of the car and crew, the BMS is definitely an underestimated part of the electric car and deserves the same attention as the battery itself (if not bigger).
Types of Battery Management Systems
1. BMS Depends on Topology
Battery management systems range from simple to complex and can embrace a wide range of different technologies to achieve their prime directive to “take care of the battery.” However, these systems can be categorized based upon their topology, which relates to how they are installed and operate upon the cells or modules across the battery pack.
Depending on the topology, the BMS is classified as
(1)Centralized BMS
(2)Modular BMS
(3)Distributed BMS
CENTALIZED BATTERY MANAGEMENT SYSTEM Has one central BMS in the battery pack assembly. All the battery packages are connected to the central BMS directly. The structure of a centralized BMS is shown in Figure provided.. The centralized BMS has some advantages. It is more compact, and it tends to be the most economical since there is only one BMS. However, there are disadvantages of a centralized BMS. Since all the batteries are connected to the BMS directly, the BMS needs a lot of ports to connect with all the battery packages. This translates to lots of wires, cabling, connectors, etc. in large battery packs, which complicates both troubleshooting and maintenance.
One of the main advantages of a centralized BMS is its ability to provide a comprehensive view of the battery pack, enabling effective control and management of the entire system. In centralized BMS, there is a single board comprising a centralized controller and a smart circuit for all the operations and internal communication. The centralized controller performs the functions of monitoring, maintaining battery voltages, temperature, and cell balancing by means of an instantaneous reference to each cell of the battery. The total board is commonly powered from battery output. The wire harness collected records related to battery state of health and state of charge are communicated internally and externally by the smart circuit board.
Modular BMS Topology
Similar to a centralized implementation, the BMS is divided into several duplicated modules, each with a dedicated bundle of wires and connections to an adjacent assigned portion of a battery stack. See Figure. In some cases, these BMS submodules may reside under a primary BMS module oversight whose function is to monitor the status of the submodules and communicate with peripheral equipment. Thanks to the duplicated modularity, troubleshooting and maintenance is easier, and extension to larger battery packs is straightforward. The downside is overall costs are slightly higher, and there may be duplicated unused functionality depending on the application.
Primary/Subordinate BMS
Conceptually similar to the modular topology, however, in this case, the slaves are more restricted to just relaying measurement information, and the master is dedicated to computation and control, as well as external communication. So, while like the modular types, the costs may be lower since the functionality of the slaves tends to be simpler, with likely less overhead and fewer unused features.
Distributed BMS Architecture
Considerably different from the other topologies, where the electronic hardware and software are encapsulated in modules that interface to the cells via bundles of attached wiring. A distributed BMS incorporates all the electronic hardware on a control board placed directly on the cell or module that is being monitored. This alleviates the bulk of the cabling to a few sensor wires and communication wires between adjacent BMS modules. Consequently, each BMS is more self-contained, and handles computations and communications as required. However, despite this apparent simplicity, this integrated form does make troubleshooting and maintenance potentially problematic, as it resides deep inside a shield module assembly. Costs also tend to be higher as there are more BMSs in the overall battery pack structure.
A system known as a distributed BMS is one in which each battery cell management system or module has its own BMS controller, which interacts with a master controller to regulate the entire system. This kind of BMS is frequently used in smaller-scale energy storage systems, including those in tiny electric vehicles or household energy storage systems.
The decision between a centralized and distributed BMS depends on a number of variables, including the overall complexity and size of the battery system, the level of fault tolerance and redundancy that is necessary, as well as the cost and wiring complexity limits. It is imperative to choose the best BMS for a particular application to aim for enhanced battery performance, durability, battery safety system and several other benefits.
2. BMS Depends on Design
In the design wise, the BMS is classified as follows:
(1)Production circuit model
(2)BMS
(1) Production Circuit Model. The primary protection circuits control all of the fundamental safety features: over-voltage, underneath-voltage, overcurrent, and on occasion over and under temperature. Additionally, maximum of the world class designs that we produce additionally include a secondary safety circuit which will safe-gaurd the battery cells as the primary protection unit.
The protection circuits are contained which is usually referred to as the protection circuit module (PCM).
The PCM is a part of the battery management machine (BMS) which manages the electronics of a rechargeable battery % by tracking its nation, reporting that data, balancing the cells together with protecting the battery, and controlling its surroundings.
Battery safety circuits for the maximum annoying packages are operated commonly by means of Integrated Circuits (ICs) typically using MOSFETS to replace lithium cells inside and outside of circuit. The over-present-day protection is commonly supplied while the IC detects the top present-day limit of the battery being reached which interrupts the circuit.
(2) Battery Management System. BMS is an extra sophisticated and intelligent shielding circuit. It includes extra modules like manipulate circuitry, control, and display modules. These modules other than controlling offer actual time records of the battery percent. It consists of a number of 2-wheeler, 3-wheeler, public and personal motors, stationary applications, and so on.
3. BMS Based on the Voltage
In BMS, battery pack is very important because battery is the main energy system in EV. This battery packs are classified into two ways:
(1)Low voltage
(2)High voltage
(1) Low Voltage BMS. Low voltage BMS supports 12 to 16 faucets depending on the required module and 8 temperature sensors. The number of cells is added through the cell interface.
(2) High Voltage BMS. HV-BMS has more advantages compared with LV-BMS. Here, the HV-BMS increases safety and reliability of battery. It prevented the damages for individual cells and batteries and increased the efficiency and lifetime of battery.
4. Advantage of BMS
(i)A BMS increases the life time of battery cells in EV
(ii)Easily measures the cells voltage
(iii)Finds any fluctuation and other disturbance very easily
(iv)Easily controls the performance of battery cells
(v)Controls the usage of energy from battery pack
(vi)Increases the reliability and stability
(vii)Increases the performance of EV
(viii)Reduces the usage of fossil fuels
(ix)Controls the charging and discharging produced depending on battery capacity
(x)Maintenance is low compared to fuel vehicle.
5. Disadvantages of BMS
(i)Battery charging time is long
(ii)Charging stations are not familiar to all places
(iii)In high loaded vehicles, the battery size is large
(iv)It required all time electric power for charging purpose
Battery Maintenance and BMS
Even though the BMS is designed to keep the battery functioning properly, routine maintenance is still required to maintain its longevity. In order to maintain a battery properly, it must be kept dry and clean, protected from high temperatures, and not overcharged or discharged. By providing data on the battery’s performance and warning the user of any problems that require attention, the BMS can help with battery maintenance as well.
For the efficient and secure operation of electric vehicles, lithium-ion Battery Management System is particularly crucial. Routine maintenance is still necessary for the battery to manage as long as feasible, even if the BMS is designed to retain the battery’s functionality.
BMS measures and monitors the speed of vehicle power usage from batteries of vehicle and power usage from the batteries. BMS also monitors state of change (SOC), state of health (SOH), temperature, over charging, and over discharging the battery.
When the battery over discharging process BMS give to signal to Electronics Control Unit. This unit produces control signal to converter and adjusts speed of motion. This process protects increase the life time of battery and increase the performance and efficiency of EV.
Topologies
BMS technology varies in complexity and performance:
BMS topologies fall in three categories:
Centralized BMSs are most economical, least expandable, and are plagued by a multitude of wires. Distributed BMSs are the most expensive, simplest to install, and offer the cleanest assembly. Modular BMSes offer a compromise of the features and problems of the other two topologies.
The requirements for a BMS in mobile applications (such as electric vehicles) and stationary applications (like stand-by UPSes in a server room) are quite different, especially from the space and weight constraint requirements, so the hardware and software implementations must be tailored to the specific use. In the case of electric or hybrid vehicles, the BMS is only a subsystem and cannot work as a stand-alone device. It must communicate with at least a charger (or charging infrastructure), a load, thermal management and emergency shutdown subsystems. Therefore, in a good vehicle design the BMS is tightly integrated with those subsystems. Some small mobile applications (such as medical equipment carts, motorized wheelchairs, scooters, and fork lifts) often have external charging hardware, however the on-board BMS must still have tight design integration with the external charger.
Various battery balancing methods are in use, some of them based on state of charge theory.
Major Components of BMS
Sensing Components
Sensing components are a crucial component of BMS. Sensing components are essential for monitoring and managing a battery's numerous properties. For the purpose of maximizing battery life, assuring safe operation, and improving performance, accurate sensing is essential. Voltage sensors, current sensors, and temperature sensors make up the majority of the sensing elements in BMS.
Voltage Sensors
Voltage monitoring devices are integral components for overseeing the voltage levels of individual cells within a battery. The maintenance of proper voltage levels stands as a paramount consideration for ensuring both the safety and efficiency of the battery. Typically, these devices gauge the potential difference across the terminals of each cell. This vigilant monitoring of cell voltages empowers the Battery Management System (BMS) to execute cell balancing procedures, guaranteeing uniform charge and discharge across all cells within the battery. Furthermore, it plays a pivotal role in computing the State of Charge (SOC) and serves as a preventive measure against overcharging or deep discharge, circumstances that could potentially inflict harm upon the battery.
Current Sensors
Current monitoring instruments find utility in the measurement of the electric current entering or exiting the battery. The monitoring of current assumes critical significance for multiple reasons. Firstly, it contributes to the computation of SOC by integrating the current over time, a technique known as coulomb counting. Secondly, it plays a pivotal role in the identification of abnormal conditions such as over-current or short-circuit incidents, thereby facilitating the implementation of protective measures. An array of current sensors is available, including Hall-effect sensors, shunt resistors, and current transformers. Among these, Hall-effect sensors hold widespread utility within BMS setups due to their versatility in measuring both AC and DC currents and their provision of electrical isolation between the sensor and the current-carrying conductor.
Temperature Sensors
Thermal sensors represent essential components tasked with monitoring the temperature conditions prevailing in a battery. The operation of a battery inherently generates heat, and the efficiency of the battery operation is profoundly influenced by its thermal environment. Furthermore, excessive heat can be detrimental, potentially leading to a hazardous state known as thermal runaway, which can result in battery malfunction or even fires. To combat these issues, temperature sensors, encompassing devices like thermocouples or thermistors, are strategically positioned at various locations within the battery pack. Their primary function is to track the temperature of individual cells and the ambient temperature surrounding the pack. The data gleaned from these sensors equips the Battery Management System (BMS) with the information required to make informed decisions. These decisions may involve the activation of cooling systems or the adjustment of charging and discharging rates to uphold safe thermal conditions.
Battery Controller
The battery controller unit stands as a pivotal element within the BMS framework. It assumes the role of the central processing unit and the decision-making hub for orchestrating a multitude of battery operations. This component processes data harvested from various sensing elements, formulates decisions based on predefined control algorithms, and carries out actions to ensure the battery's continued optimal performance and safety. The battery controller unit typically comprises a battery monitor and protector, a suite of control algorithms, and a microcontroller or digital signal processor (DSP).
Battery Monitor and Protector
The battery monitor is in charge of continuously monitoring the voltage, current, and temperature of the battery. The SOC, SOH, and overall operational state of the battery must be determined using this information. The battery protector functions in tandem with the battery monitor and responds whenever it notices an anomaly. For instance, the protector will take the appropriate actions, such as disconnecting the battery or altering the charge/discharge rates, to prevent harm if the battery voltage exceeds the safe limits.
Control Algorithms
Control algorithms represent a collection of rules and mathematical models harnessed by the Battery Management System (BMS) to make informed decisions. These algorithms can be intricate and are meticulously crafted, taking into account the precise battery chemistry, the intended application, and the desired performance characteristics. As an illustration, a control algorithm might dictate how the charging current should be dynamically adjusted as the battery approaches full charge to prevent overcharging. Another algorithm could be designated to gauge the State of Charge (SOC) by utilizing data from voltage and current sensors. The effectiveness of these algorithms stands as a linchpin, influencing the efficiency and safety of the battery's operation.
Microcontroller or Digital Signal Processor (DSP)
At the core of the battery controller lies a microcontroller or a digital signal processor (DSP). This component assumes the pivotal role of executing the control algorithms. Microcontrollers represent versatile, general-purpose processors that find widespread utilization owing to their adaptability and ease of integration. They boast the capacity to handle diverse tasks, encompassing data acquisition, communication, and the execution of control algorithms. Conversely, DSPs are specialized processors that excel in the numerical processing indispensable for intricate control algorithms. In specific applications, especially those demanding high-speed data processing, a DSP may emerge as the preferred choice. Ultimately, the selection between a microcontroller and a DSP hinges on the particular demands of the BMS and the application it serves.
Communication Interface
A crucial part of the BMS that enables information to be exchanged with other devices or systems is the communication interface. It is necessary for the battery system to be monitored and controlled effectively. The functionality for data logging and reporting is included in the communication interface, along with communication protocols.
Communication Protocols
The format and interchange of data between devices are governed by communication protocols in the context of a BMS. To make sure that devices can understand one another and communicate successfully, these protocols are necessary. Typical BMS practices include:
Controller Area Network (CAN): It is frequently utilized in automotive applications. It enables real-time communication and is renowned for its dependability and toughness in chaotic settings.
Inter-Integrated Circuit (I2C): In embedded systems, I2C is frequently used to link low-speed peripherals. Within a single device, it is straightforward and practical for short-distance communication.
Serial Peripheral Interface (SPI): Especially in embedded systems, SPI is utilized for short-distance communication. It is frequently used in applications where speed is essential because it is faster than I2C.
Modbus: Modbus is frequently utilized in industrial settings. It facilitates communication between numerous devices linked to the same network and is straightforward.
Bluetooth: Bluetooth is a wireless technology that can be used to communicate data to personal devices like computers or smartphones, particularly in portable devices.
Data Logging and Reporting
Recording data over time for analysis is known as data logging. Voltage, current, temperature, and SOC data are logged in a BMS. For trend and performance analysis, troubleshooting, and maintenance, this data may be crucial.
Sending this data to systems and devices outside of the reporting process. For instance, the BMS may transmit the SOC to the dashboard of an electric vehicle so that the driver may monitor the battery level. The BMS may provide data to a centralized control system for monitoring and control in an industrial application.
Monitoring the battery's performance and guaranteeing its dependable operation need data logging and reporting. They may also be essential for adhering to rules and specifications, particularly in situations when safety is of the utmost importance.
Protection Circuitry
A crucial part of a BMS that guarantees the security and dependability of battery systems is the protection circuitry. It continuously checks the battery's condition and adjusts or intervenes in real time to avoid potentially harmful or dangerous situations. Overcharge protection, over-discharge protection, short circuit protection, and heat protection are the main safety features found in a BMS.
Overcharge Protection
To stop the battery from being charged above its maximum voltage, overcharge prevention is crucial. The protective circuitry will either stop or redirect the charging current when the voltage hits a predetermined threshold, keeping the battery from receiving any further current. This safeguard is essential for the battery's longevity and safety as overcharging might result in a battery's catastrophic failure.
Over-Discharge Protection
In a parallel consideration to the risks of overcharging, discharging a battery below a specified voltage threshold can also inflict damage. The mechanism of over-discharge protection diligently monitors the battery's voltage as it undergoes discharge. In the event of a voltage drop nearing or surpassing a predetermined threshold, this safeguard intervenes by either disconnecting the load or implementing measures to prohibit the battery from discharging below the established limit. Such proactive measures hold paramount importance in forestalling capacity depletion, preserving the battery's well-being, and mitigating potential safety hazards.
Short Circuit Protection
Short circuit mitigation is an integral safety measure engineered to shield both the battery and the associated circuitry in the occurrence of a short circuit event. A short circuit materializes when the positive and negative terminals of the battery come into direct connection with minimal or negligible resistance in between, thereby triggering an exorbitant surge in current flow. This surge can induce the generation of heat, escalating the risk of fire or even explosion. Typically, short circuit mitigation encompasses the deployment of fast-acting fuses or circuit breakers. These protective elements function by expeditiously disconnecting the battery from the circuit in response to a detected short circuit event, thus averting potential catastrophic consequences.
Thermal Protection
Batteries exhibit sensitivity to temperature variations, and straying beyond a prescribed temperature range can prove detrimental to both operational performance and safety. Thermal safeguarding mechanisms are in place to continually monitor the temperature of the battery cells and intervene when the temperature exceeds the defined safe limits. In response to these temperature fluctuations, actions may include the initiation of cooling measures when the cells become excessively hot or, in the case of overly cold conditions, the imposition of restrictions on the charging current, as charging at too low a temperature can lead to damage.
Balancing Circuit
A fundamental constituent within the BMS framework is the balancing circuitry. Battery balancing stands as an imperative procedure, especially in battery packs composed of multiple cells, as it guarantees a uniform State of Charge (SOC) across all cells within the pack. This not only guarantees optimal performance but also augments the durability and dependability of the battery pack. Two primary balancing techniques come into play: passive balancing and active balancing.
Passive Balancing
Shunt balancing, sometimes referred to as passive balancing, is the process of dispersing extra energy from cells with higher SOCs as heat to lower-charged cells with a higher SOC. Typically, resistors are placed across each cell's terminals. The resistor is engaged when the voltage of a particular cell rises over a predetermined threshold, causing it to redirect some current and release the extra energy.
Passive balancing is less complicated and expensive than active balancing, but it is not more energy-efficient because the surplus energy is simply dissipated as heat. It is appropriate for systems where energy economy is not a major issue or applications where the difference in SOC between cells is not considerable.
Active Balancing
Active balancing, in contrast to passive balancing, seeks to redistribute the charge across the cells rather than letting it go. Active balancing techniques include employing DC-DC converters, inductors for energy transfer, and capacitors for energy transfer. Active balancing essentially involves the transfer of energy from cells with a higher SOC to those with a lower SOC.
Compared to passive balancing, active balancing is more energy-efficient, but it is also more complicated and generally more expensive. It is especially helpful in applications where energy usage efficiency is crucial or in setups with sizable battery packs where the variations in states of charge can be more obvious.
Roles of Battery Management Systems in Lithium-ion Batteries
Most lithium-ion batteries used in EVs are equipped with a BMS, due to the inherent risks associated with overcharging, over-discharging, overheating, or damage. The Battery Management System for electric vehicle protects the battery from various hazards by limiting the charging and discharging currents, maintaining the optimal temperature range, and balancing the cells to prevent uneven degradation. The Battery Management System for electric vehicle also optimizes energy utilization and prolongs the battery life by preventing excessive cycling and deep discharging.
For example, according to a study by the National Renewable Energy Laboratory (NREL), a Battery Management System for electric vehicle can improve the energy efficiency of an EV, by reducing the energy losses and increasing the usable energy of the battery. Another study by the Argonne National Laboratory (ANL) estimated that a BMS can extend the battery life by preventing capacity fade and power fade of the battery.?
Furthermore, a report by the National Highway Traffic Safety Administration (NHTSA) revealed that a Battery Management System for electric vehicle can prevent or mitigate 99.8% of the potential incidents of battery fires or explosions, by detecting and isolating the faulty cells or modules.
Many companies across a small variety of industries make BMS for electric vehicles. Some of them also make battery cells or modules, while others specialize in BMS hardware or software. These companies often provide comprehensive solutions, including battery design, integration, testing, and management.?
How Electric Vehicles Utilize BMS?
The Battery Management System for electric vehicle facilitates the energy flow between the battery and the vehicle’s systems. It ensures that the battery delivers sufficient power and torque to the motor and that the battery receives the correct amount of charge from the charger or regenerative braking. The BMS also monitors the state of charge (SOC), state of health (SOH), and state of power (SOP) of the battery, which indicate the amount of energy, capacity, and power available in the battery, respectively. The Battery Management System for electric vehicle uses these parameters to estimate the range, performance, and lifetime of the EV.
The functionality of BMS with electric vehicles can be demonstrated by some examples. For instance, when the EV is accelerating or climbing a hill, the BMS increases the power output of the battery to meet the demand of the motor. When the EV is braking or descending a hill, the BMS reduces the power output of the battery and enables regenerative braking, which converts the kinetic energy of the vehicle into electrical energy and stores it in the battery.?
When the EV is plugged into a charger, the Battery Management System for electric vehicle regulates the charging current and voltage to ensure the optimal and safe charging of the battery. When the EV is parked or idle, the BMS minimizes the self-discharge and parasitic loads of the battery and maintains the battery temperature within the desired range.
The Role of Battery Management System in Safety
The BMS plays a vital role in Lithium in battery safety by preventing thermal runaway, which is a chain reaction of increasing temperature and pressure that can cause the battery to explode or catch fire. Thermal runaway can be triggered by various factors, such as short circuits, overvoltage, overtemperature, mechanical damage, or external heat sources.?
The BMS detects any abnormal conditions, such as high or low voltage, high or low temperature, high or low current, or low impedance, and takes corrective actions, such as cutting off the power, activating the cooling system, or alerting the driver. The BMS implements various safety mechanisms, such as fuses, circuit breakers, contactors, relays, and isolation switches, to isolate the faulty cells or modules, and prevent the propagation of thermal runaway to the rest of the battery pack.
For example, when a cell or module experiences a short circuit, the BMS detects the sudden drop in voltage and increase in current and opens the circuit breaker or contactor to disconnect the cell or module from the battery pack. When a cell or module is overcharged or over-discharged, the BMS detects the deviation from the normal voltage range and balances the cell or module by bypassing or diverting the current.?
When a cell or module is overheated or overcooled, the BMS detects the deviation from the normal temperature range and activates the cooling or heating system to adjust the temperature. When a cell or module is damaged or punctured, the BMS detects the change in impedance or resistance and isolates the cell or module from the battery pack.
Software and Hardware Upgradability of EV BMS
The software of a Battery Management System for electric vehicle can be updated to improve the performance, efficiency, and reliability of the battery. The software update can include new or modified BMS algorithms, parameters, or settings, which can enhance the accuracy, robustness, or adaptability of the BMS. Some BMSs can be updated remotely via wireless communication, such as Bluetooth, Wi-Fi, or cellular, while others require a physical connection to the vehicle or the charger.
The hardware of a Battery Management System for electric vehicle can also be upgraded or replaced, but this may involve more cost and complexity. The hardware upgrade or replacement can include new or improved sensors, actuators, or control units, which can increase the effectiveness, precision, or speed of the BMS. However, the hardware upgrade or replacement would typically also require compatibility checks, calibration procedures, and safety tests to ensure the proper functioning and integration of the new BMS components.
Role of BMS in Electric Vehicle Fleet Management
The Battery Management System has a growing role in electric vehicle fleet management, as it can provide useful data and actionable insights for electric vehicle fleet operators. A Battery Management System for electric vehicle can monitor health, status, and location of batteries, and send alerts or notifications for maintenance, charging, or replacement.?
Battery Management Systems can help fleet operators to:
BMS Data Analysis and Research
The Battery Management System for electric vehicle serves as a valuable tool for data collection and research. It offers insights into the battery’s performance, behavior, and degradation. Researchers and engineers leverage this data to understand the factors that affect the battery’s life and efficiency, and to develop new technologies and solutions for improving the battery’s design, operation, and management.
The data collection and research contribution of BMS can be exemplified by some projects and publications. For example, the Battery Lifetime Analysis and Simulation Tool (BLAST) is a software tool developed by NREL, which uses BMS data to simulate and analyze the battery’s performance and degradation under different scenarios and conditions.
Another example is the Battery Health Management (BHM) project, which is a collaborative effort by NASA, ANL, and other partners, which uses BMS data to develop and test novel algorithms and methods for estimating and predicting the battery’s health and remaining useful life. Furthermore, many academic papers and journals have used BMS data to conduct experiments and studies on various aspects of battery science and engineering, such as modeling, optimization, diagnosis, prognosis, and control.?
Battery management systems are foundational to ensuring the safe, efficient, and prolonged operation of lithium-ion batteries in electric vehicles. It protects the battery from overcharging, over-discharging, overheating, or damage, and prevents thermal runaway in real-time. It facilitates and controls the energy flow between the battery and the vehicle’s systems, and optimizes energy utilization to maximize battery life and performance.
The Battery Management System for electric vehicle can be updated via software or hardware to improve its functionality and reliability. It also provides useful data and insights for electric vehicle fleet management and battery research and development. The battery management system is thus a key component in advancing the sustainable electrification of transportation and power infrastructure.
FREQUENTLY ASKED QUESTION ANSWERS
What is the EV battery management system?
A BMS monitors the temperatures across the pack, and open and closes various valves to maintain the temperature of the overall battery within a narrow temperature range to ensure optimal battery performance.
What is the battery management system method?
The main function of the battery management system (BMS) is to check and control the status of batteries within their specified safe operating conditions. BMS helps to monitor and control the charge. Demand from each cell in the chain ensures even distribution of SOC.
How do you manage an electric car battery?
Tips to maintain an electric car battery
How to design battery management system for electric vehicle?
What are the different types of battery management systems?
In order to maintain a battery's performance, lengthen its lifespan, and avoid safety risks, a BMS tracks and controls a number of battery parameters. BMS can be divided into two basic categories: distributed and centralized, with distributed BMS being more adaptable and simpler to operate.
What is BMS architecture in EV?
Understanding BMS architectures It manages the state of charge (SOC), state of health (SOH), and state of temperature (SOT), interfacing with the EV's main controller to maximize efficiency and performance. This includes optimizing acceleration and regenerative braking, and preventing thermal runaway.
What is the principle of BMS system?
A very basic BMS consists of software, a server with a database and smart sensors connected to an Internet-capable network. Smart sensors around the building gather data and send it to the BMS, where it is stored in a database.
Which software is used for battery management system?
Using Simulink, engineers can exercise the battery management system over a range of operating and fault conditions before committing to hardware testing. You can generate C code from Simulink models to deploy your control algorithms for rapid prototyping of systems or microcontrollers.
Does BMS limit charging current?
BMS's are not designed to "limit" charge current. That is not their job. A "Charger" limits charge current. The values of a BMS rating, say 100A, means that the BMS will be able to successfully disconnect a load/charger if the current flowing through the BMS is greater than 100A.
What is the best percentage to charge EV?
There are two reasons: charging performance and battery longevity. Most of the time you should only charge an EV to 80% because charging rates slow down dramatically past the 80% mark. And two, the long-term health of your vehicle's battery pack is improved when kept below 100%.
What is the best SOC for EV?
between 20% and 80%
The recommended SOC range for optimal battery health in electric vehicles (EVs) is between 20% and 80%.
What are the three levels of BMS?
## BMS system works with 03 levels; Management levels (Software programme), Automation level (Direct Digital Controllers) and Field Level (Sensors and Actuators)
How is BMS made?
Building Blocks of a BMS. A battery management system can be comprised of many functional blocks including: cutoff FETs, a fuel gauge monitor, cell voltage monitor, cell voltage balance, real-time clock (RTC), temperature monitors, and a state machine. There are many types of battery management ICs available.
What is the role of battery management system BMS in sustainable transportation?
The Role of the BMS in Electric Vehicles The BMS is typically an embedded system and a specially designed electronic regulator that monitors and controls various battery parameters (e.g. temperature, voltage, and current) to keep the battery cells within a safe working range.
What are the benefits of BMS system?
6 Advantages of a Building Management System (BMS)
What are the advantages and disadvantages of BMS?
Pros Of Building Management Systems
Does BMS prevent overcharging?
3. Charge Control: BMS optimizes charging parameters, such as voltage and current, to prevent overcharging, which can significantly impact battery lifespan. 4. Discharge Protection: BMS prevents excessive discharge, avoiding damage due to deep discharges that can shorten the battery's life.
Do all EVs have BMS?
For electric vehicles (EVs) and hybrid electric vehicles (HEVs) to operate safely and effectively, battery management systems (BMS) are necessary. Battery parameters like voltage, current, temperature, and state of charge are all under the BMS's supervision and control.
What are sensors in BMS?
For the purpose of maximizing battery life, assuring safe operation, and improving performance, accurate sensing is essential. Voltage sensors, current sensors, and temperature sensors make up the majority of the sensing elements in BMS.
Embedded Hardware design Engineer.
5 个月Too good sir
Doctor of philosophy(PhD)
6 个月Very good explanation about BMS.... Thank you so much for sharing this article...
We know how to switch since 1968
9 个月Outstanding and comprehensive Summary to understand what a BMS is. And why everyone dealing with batteries will need one. Do you plan to create a similar article for how to Validate and Test a BMS Design? Fyi Noman Hussain
Business Student
10 个月Gentle with that current you.