Inputs required to model BESS in Power System Simulation Softwares.

To model a Battery Energy Storage System (BESS) in power system simulation softwares, several inputs are required to accurately simulate the behavior of the BESS within a power system. These inputs help in defining the electrical, mechanical, and control characteristics of the system, ensuring that the model can replicate real-world performance. Here are the key inputs needed:

1. Battery Specifications

- Rated Power (kW/MW): The maximum power output or input capacity of the battery system.

- Energy Capacity (kWh/MWh): The total energy storage capacity, which defines how much energy the battery can store.

- State of Charge (SoC): The initial state of charge (as a percentage or in kWh), which indicates the current charge level of the battery.

- Charge/Discharge Rates: The rates at which the battery charges and discharges, typically expressed in kW or MW. You may also need to define the maximum C-rate (charge or discharge rate relative to capacity).

- Depth of Discharge (DoD): The percentage of the battery's capacity that can be discharged without affecting its lifetime or performance.

- Round-trip Efficiency: This is the ratio of energy output to energy input during a complete charge-discharge cycle, typically given as a percentage.

- Battery Type: Specify the type of battery technology, such as Lithium-Ion, Lead-Acid, Flow Battery, or other technologies. Each type has different characteristics such as lifespan, efficiency, and charging profiles.

2. Electrical Model Parameters

- Equivalent Circuit Model: This defines the electrical behavior of the BESS. The most common models include:

- Simplified Model: Considers battery as a constant power device.

- Detailed Equivalent Circuit Model: Includes resistance, capacitance, and inductance parameters for more accurate dynamic response simulation.

- Internal Resistance: Defines the internal losses during charge and discharge cycles.

- Open-Circuit Voltage (OCV): The voltage of the battery when it is not connected to any load, as a function of SoC.

- Series Resistance: The resistance in series with the battery that affects voltage drops during charging and discharging.

- Capacity Fade Model: Over time, battery capacity degrades. This model can take into account the degradation of the BESS over time, affecting the storage capacity.

3. Inverter/Converter Parameters

Since BESS typically interfaces with the grid via power electronics, you need to model the inverter (AC-DC converter) with the following parameters:

- Converter Rating (MW/kVA): The maximum power output of the inverter, which should match or exceed the rated power of the BESS.

- Converter Efficiency: Efficiency of the inverter during DC-AC and AC-DC conversions.

- Control Modes: Define the control strategies used by the inverter, such as:

- Active and Reactive Power Control: Controls to inject or absorb active (P) and reactive (Q) power.

- Voltage Control: Used to maintain voltage stability at the point of connection.

- Frequency Control: Participation in grid frequency regulation by adjusting power output.

- Power Factor Control: The inverter’s ability to control power factor by adjusting reactive power output.

- Dynamic Response Time: The time it takes for the inverter to respond to a change in control settings or grid conditions (e.g., load changes, faults).

4. Control System Settings

- Battery Management System (BMS) Control: The BMS regulates charging and discharging of the battery, manages SoC, and ensures that the battery operates within safe limits. Input parameters include:

- SoC Control Logic: How the BMS controls the SoC, such as target SoC, maximum and minimum SoC limits.

- Charge/Discharge Control Logic: Whether the battery charges or discharges based on grid conditions, SoC, or other control signals.

- Grid Support Functions:

- Frequency Regulation: Participation in grid frequency support by adjusting power output based on frequency deviations.

- Voltage Regulation: Voltage support at the point of common coupling (PCC) by adjusting reactive power output.

- Peak Shaving: Control settings for reducing demand during peak load periods.

- Droop Control: Defines the relationship between frequency deviation and active power output, or voltage deviation and reactive power output.

5. Connection Point (Grid Interface) Data

- Point of Common Coupling (PCC) Voltage: Voltage level at the grid connection point (e.g., 11 kV, 33 kV, or 400 V).

- Short Circuit Power at PCC: Defines the short-circuit power capacity of the grid at the connection point, which is used to model the strength of the grid.

- Grid Impedance: The impedance of the grid at the point of connection, which affects how the BESS interacts with the grid during voltage or frequency disturbances.

- Transformer Data: If a step-up or step-down transformer is required between the BESS and the grid, the transformer’s rated voltage, impedance, and other parameters need to be defined.

6. Dynamic and Time-Series Data

- Load Profiles: Time-series data showing the expected load variations over a period. This helps in determining how the BESS will charge or discharge based on load requirements.

- Generation Profiles: If the BESS is connected to renewable generation (e.g., solar or wind), you need time-series data on renewable generation output.

- Market Participation: If the BESS participates in electricity markets (e.g., arbitrage, frequency regulation), economic inputs such as electricity prices, regulation prices, and contract limits should be included.

7. Operating Constraints

- Operational Limits: Set minimum and maximum SoC levels, charge/discharge current limits, and thermal limits of the system.

- Cycling Limits: Define the number of charge/discharge cycles allowed, based on the expected lifespan of the battery.

- Ambient Temperature Effects: Include temperature-dependent performance characteristics if the battery's operation is sensitive to ambient conditions.

8. Fault Models

- Protection Settings: Define the protection mechanisms such as over-voltage, under-voltage, over-current, and thermal overload protection for the battery and inverter.

- Fault Ride-Through (FRT) Capabilities: Model how the BESS responds during grid disturbances like voltage dips or frequency deviations. G99 grid connection requirements in the UK, for example, require BESS to remain online during specific fault conditions.

9. Simulation Scenarios

- Steady-State Simulations: Define the steady-state scenarios, such as charging/discharging the battery under normal operating conditions, grid support modes, or islanded operation.

- Dynamic Simulations: Define dynamic scenarios such as fault conditions, voltage dips, frequency excursions, and BESS response to grid disturbances.

- Time Series Simulations: Provide inputs for long-term simulations to model the battery's operation over time, including periods of high load, low load, renewable generation fluctuations, and battery degradation.

Conclusion

Accurately modeling a BESS in DIgSILENT PowerFactory requires a combination of battery specifications, electrical model parameters, inverter/converter details, control system settings, and grid interface data. By incorporating these inputs, you can simulate the BESS's behavior under various operating conditions, optimize performance, and ensure compliance with grid requirements.