ENERGY SYSTEMS IN MODERN SOCIETY

Katushabe Sergius_202175093

What is the microgrid control issue? How can we fix these issues??

Due to the energy transition from fossil fuels to renewable energy and the global agenda towards a carbon-free economy (Net Zero) alongside the emerging electric-based transport system, new challenges in architecture, control, and management of the electrical grid will be manifested. This creates a need to establish future electricity grids schemes with easy integration of distributed generation, demand response, and energy storage systems. A microgrid is a solution for it operates within an energy market environment managed by an energy service company ESCO acting as an aggregator of various distributed sources/ multiple microgrids

Microgrid control issues revolve around unstable voltage/ frequency, active and reactive power, load consumption and shedding, and load starts. Ideally,?as a shift to renewable energy takes shape, we see problems like system parameter (voltage, frequency) synchronization, system failure due to variations in voltages, overloaded distribution or transmission networks, demand-related issues, off-peak hour redundancy, intermittence thus storage challenges among others.

This calls for effective energy management within microgrids to achieve the needed efficiency benefits through heat, gas, and electricity optimized production and consumption. A microgrid is called to operate in an energy market possibly coordinated by an ESCO, who will act as an aggregator of various distributed sources and probably a number of them.

This creates a need to highly ensure voltage and frequency controls, active and reactive power controls, load use and shedding management and controls, security monitoring, load and renewable energy sources (RES) forecasting, and black start as they can be implemented in the following ways.

During a normal operation, the local control functionalities can be performed using a single distribution generation (DG), storage or controllable load, protection functions, primary voltage/frequency control, primary active/reactive power control, battery management.

Sophisticated computer and information and technology entailing state of the art software, microprocessors, communication networks for sufficient bandwidth, and internet of energy will control complex microgrid challenges.

Putting appropriate microgrid infrastructure (architecture) in place to effectively achieve primary control level (based on the droop control method applied to various Distributed energy resources-DERs), and restore the voltage frequency and amplitude deviations (Management level) as well as full deployment of centralized and decentralized controls to tertiary issues of economic dispatch.

Using centralized to achieve proper operation during grid-connected and island modes, using the real-time data and decentralized control schemes to specify the maximum power generated by the micro-sources, and at the same time taking into account the capability of micro-grid to support the consumer and enhance power export to the grid for market sharing. This gives a balance of market participation and local needs

Forecasting of the electricity demand, heat demand, generation from renewable power sources, and external electricity prices, for the next few hours will be required by both centralized and decentralized control approaches to face unsafe situations and to optimize production costs and in general to maximize revenues of the production process in the marketplace

To manage active distribution networks, we can use state estimation?(SE) as it can be applied to a wider area of the distribution network including single or multiple microgrids and DGs linked at the MV level, and provides to the Distribution System Operators (DSO) overall the system operating conditions. In this way, it allows the DSO to identify appropriate control plans to be adopted in case the need arises.

Using effective power stabilization tools helps to control unexpected shutdowns of large consumers by regulating the generation of electricity and stabilizing consumption.

Using reliable fast controllers can help to instantly respond to any changes in the network to avoid losses that can lead to the unprofitable microgrid.

?Investigate the centralized and decentralized control of microgrids and compare them?

?????Centralized controls: The centralized control uses the microgrid central control (MGCC) to maximize the microgrid value and the optimization of its operation. Based on grid security and ancillary service requests by the DSO, the MGC?using market prices of electricity and gas costs determines the amount of power that the microgrid should import from the upstream distribution system, optimizing local production or consumption capabilities by controlling the micro sources and controllable loads within the microgrid by sending control signals to the field under actual active and reactive power units monitoring.

?????The fundamental feature a centralized control has is that at the MGCC level is where the microgrid operator or ESCO takes decisions about the operation of the DER. The MGCC is equipped with scheduling routines that provide optimal set points to the MCs, based on the overall optimization objectives. The locally distributed energy sources, acting either as individual market players or as one coordinated market player, provide energy and ancillary services by bidding in energy and ancillary markets, based on the prices provided by the system

?????Merits of Centralized controls are: They provide a high operation knowledge, where the main goals are identified and achieved; they can provide global optimal solutions; they allow an easy synchronization to the main grid, and they can effectively use real-time signals for online operation.

?????Demerits of centralized controls are: they have high communication necessities leading to additional costs; they are computationally expensive and time-consuming for they run an optimization problem that takes into account a large number of distributed generation units, loads, and storage elements.

?????Decentralized controls: In the decentralized control strategy, each distributed energy source (generation or capacity) works freely utilizing measured local signals (Natarajan et al., 2018). In the decentralized control structure, all subsystems of the plant are separately controlled by their own LCs.

?????According to Mohammed et al.?(2019), there may be some interactions between the subsystems so fewer interactions may lead to being closer to the suboptimal condition. In a decentralized scheme, the role of all controllable agents and their LCs are the same, and none of them has a more important role.

?????This system is designed and developed on foundations of Multi-Agent System theory (describes the coordination algorithm, the communication between the agents, and the organization of the whole system) in a sense that autonomous control process is assumed by each controllable element, namely inverters, DGs, or loads. They can improve LCs’ level of intelligence through transferring decision-making ability to the elements on the local side. Here, the communication system does an important role since the local decision-making is dependent on data received from the environment of the respective element and its adjacent devices. The decision-making is locally processed, and the energy management system must perform information sharing/coordination. This scheme has advanced reliability and offers the highest independence for the controllable agent so that each agent has its LC, which functions based on its local measurements' responses. This means that breakdown in each of the controllable agents or LCs will not result in the collapse of the whole plant.

?????Merits of decentralized controls are; They are suitable for fast-changing infrastructures; they are easily expanded because of their plug-and-play capabilities; they have high reliability?for they can operate further even after the loss of MGSC/EMS; they provide a suitable framework for plug-and-play functionality, which is important for the application of plug-in hybrid electric vehicles (PHEVS)

?????Demerits of decentralized controls are: they are very complex concerning multi-ownership and competition among the various actors who may pursue to attain their objective, such as profit maximization.

Comparisons between Centralized and Decentralized controls

Similarities

i.?They are all techniques used to achieve the coordinated control of a large number of DERs

ii.?They are all used in the operation and control of virtual power plants

iii.?Determining the approach of choice (centralized or decentralized) for microgrid control is based on the key intentions and the special features of the controlled microgrid and the available or affordable personnel and equipment

iv.?Forecasts of the electricity demand, heat demand, generation from renewable power sources, and external electricity prices, for the next few hours are a requirement in both centralized and decentralized control approaches.

Investigate about Virtual Power Plant (VPP) including its concept, operation, role, organization, coordination, business model, etc.

The concept of VPP

?????VPP is defined as a single big power plant that connects, controls, and envisions dispersed generators via an information communication technology (ICT) structure. In other words, it is a cluster of Distributed Energy Resources (conventional power plant replacement) that is collectively operated by a central control entity. It is highly efficient and more flexible.

?????According to Wikipedia, VPP is a cloud-based distributed power plant that aggregates the capacities of heterogeneous Distributed Energy Resources (DER) to enhance power generation, as well as trading power on the electricity market. Virtual power plants today exist in the United States, Europe, and Australia.

?????VPP was conceptualized in 1997 (Awerbuch.S,1997) as Virtual Utility (a flexible collaboration of independent, market-driven entities that offer efficient energy services demanded by the user without necessarily owning the corresponding assets).

?????VPP concept has become popular as a way used for the integration of DERs for energy system operation and energy market transactions. VPP interpretation varies from combinations of DGs, fixed and variable loads integrated via communication links and real-time control techniques to Energy Management System (EMS) acting as a real power plant in the electricity market which is consistent with Bai. H, (2015). VPP manages units independently, this is due to EMS that assists to launch the link between distributed power units from centralized to decentralized control modes.

?????The main importance of VPP include; Dispatch and optimization, Management and control, and Integration of DGs and renewable energy resources

?????The concept of the Virtual Power Plant (VPP) is entering the world power sector to facilitate the integration and management of distributed power units relying on real-time communication and uniform control. The motivation behind VPP is to solve the problem of variable profile and uncertainty of power generated by DG untargeted is found to be challenging when building a reliable DG-assisted power plant.

?????The application of the VPP concept boosts the reconciliation of discontinuous sustainable power sources, settling their stochastic power output as it optimizes the present energy framework and upgrades grid performance.

The structure of VPP

VPP components are not necessarily located on the same physical network, but they can be coordinated using networking infrastructure, to operate as one market entity

Operation of VPP

?????A VPP can be operated and controlled through 2 main approaches. These are (i) centralized or (ii) decentralized ways.

?????VPP operation under centralized control: The principles for VPP operation under centralized control are based on a central controller, Virtual Plant Central Controller (VPCC), not necessarily physically installed in one of the controllable sites. VPCC optimizes the energy supply of the members which comprise the VPP by selecting which DG units will operate and which flexible loads will be served. The orders to the local controllers (LC) are simple (ON/OFF) control activities and are calculated based on the expected electrical and heat/cooling demand of each site, the DER characteristics, the electricity, and fuel market prices, and the existing flexible loads.

?????This operation adopts two-way communication among the LC and the VPCC. LCs send at frequent intervals their operation cost or they bid for curtailing flexible loads. At this point, this information is taken into account by the VPCC that sends energy market prices and the setpoints. Such information exchange is basic to decide the price above which flexible loads are curtailed and the DER production.

?????VPP operation using decentralized control:?The principle of VPP operation using decentralized control adopts distributed management of information for taking similar decisions on DER operation and flexible loads. A common implementation of this approach is by Multi-Agent Systems (MAS).

Roles of VPP

?????A VPP may bring significant benefits in terms of transition to more efficient and environmentally friendly energy generation.

?????A Virtual Power Plant (VPP) is useful in the development of RES and increasing their contribution to net power generation. This can address the ever-increasing electricity demand and primary energy sources depletion.

?????A VPP constitutes an interesting option for the aggregation of Distributed Energy Resources (DER) increasing the participants’ benefits. This is useful in presence of disconnecting ability of some flexible load for a very short time.

Specifically, the benefits of VPP include the following.

i.?Offering considerable savings on primary energy and reduction in the emission of pollutants.

ii.?Energy loss is minimized during electricity transmission and distribution which results in additional energy saving.

iii.?Facilitating the integration of intermittent generation technologies based on renewable energy resources like wind power or Photovoltaic (PV), etc. by stabilizing the stochastic power output

iv.?Enabling the delay of investment on enforcing the electrical infrastructure as implementing the VPP requires relatively little modification to existing infrastructure.?

v.?Providing value-added services like ancillary services to power system operation through centralized/coordinated control strategies to both maintain the reliability, security and to increase the flexibility of electricity supply.

vi.?Increasing the participation of the end-users in both electricity market transactions and power system operations with more degrees of freedom.

vii.?Representing a wide range of options towards a future smart grid.

viii.?Other roles of VPP include; Dispatch and optimization, Management and control, and Integration of DGs and renewable energy resources

Organization of VPP

?????It’s organized to work remotely by combining several independent energy resources from disparate locations into a network that provides reliable power 24 hours a day

?????It employs software-based technology that relies on the smart grid as it utilizes planning, scheduling, and bidding of distributed energy resources (DER) to create the network that provides this reliable power.

Coordination of VPP

?????All VPP networked assets are efficiently monitored, coordinated, and controlled by the central control system. Control commands and data are conveyed through protected data connections which are shielded from other data traffic due to encryption protocols. The control system keeps key data to calculate the optimal operation schedules for electricity producers and consumers. Examples include; actual power, the readiness of the power plant or the power consumer, performance range for balancing energy, gas, or heat storage, the actual temperature in case of a cold store, water levels for an industrial pump.

?????In addition to operating every individual asset in the VPP along with an optimized schedule, the central control system has a special algorithm that it uses to adjust to balancing reserve commands from transmission system operators. The bidirectional data exchange between the individual plants and the VPP enables the transmission of control commands and provides real-time data on the capacity utilization of the networked units

The business model of VPP

?????There is a rapidly growing market for the Virtual power plant across the globe (North America-world leader in the gross value VPP market with share, Europe, Asia Pacific and Rest of the world-mainly Middle East and Latin America) with projections showing market growth significantly by 2030. As power networks become increasingly dependent on renewable (energy transition) and distributed energy systems from centralized generation, the need to control and optimize those systems reliably and profitably becomes a priority for cloud-based energy management systems.

?????Virtual power plants and virtual power pools are efficient and effective solutions for various applications - small-scale producers, microgrids and municipal energy systems, large-scale energy-intensive industries, and multi-unit conventional power plants. They can turn the otherwise disrupting effects of multi-source distributed power generation into an efficient and profitable business model.

The purpose of a VPP operator is to run its pool of units optimally and produce maximum revenues for its participants by bidding smartly on the energy trading market.

VPP operators participate in the market mainly in 3 categories which include;

i.?Provide balancing power to the transmission grid operator during peak demand periods.

ii.?Trade their power production on the energy market, by using weather and load management forecasts and real-time and historic data to regulate bidding and commitments

iii.?Daily unit control production and commitments in response to price signals from the market

?????Various aspects are considered during the design of the VPP as a basis. They include; the type of market participation selected, the target customers (small-scale producers, businesses, or industrial sites), and all the categories of generation and storage that make up the virtual power plant pool.

This means that no off-the-shelf software solution is available to cover such a broad variety of requirements hence, the control and optimization system must be tailored to the requirements of each VPP operator.

?????Regardless of the business model, the key component of a VPP is the plant’s control and optimization system and it must conform to the following parameters.

i.?It must have high availability to comply with the strict requirements for providing grid services.

ii.?It must be highly scalable so that the VPP operator can rapidly grow the network without complication or disruption.

iii.?It must meet top cyber security standards for transmitting set points and balancing power release calls from the control system to field units since connections to the units are IP-based.

iv.?It must perform day-ahead, intra-day, and real-time optimization using historical production, climate, and meteorological data for temperature, wind direction, and wind speed to forecast production capacity and load demand within a time horizon stretching from 1 hour to several days.

v.?With these forecasts, the VPP calculates optimal unit commitment and communicates the schedules to each unit in the pool, always updating the forecasts and commitment schedules and communicating changes to the concerned units.

vi.?It must provide spontaneous decision support for trading, as well as alarm and event management, historical data archiving, and other standard control and optimization features.

System control and optimization have to ideally be modular, comprising a chain of building blocks for forecasting, control, optimization, trading, portfolio management, and invoicing.

Modularity offers system agility and adaptability to changing market conditions and future business models.

Digitization of VPP in industry

?????VPP entails integrated technology infrastructure of software service that forecasts, analyses, monitors, and optimizes a system to create true value for effectual DER software. Digital technologies offer ideal solutions to integrate renewable energy sources into power grids already in existence and allow the flexibility required to integrate renewables into electricity networks on a large scale. This is because digital systems monitor and efficiently manage generation, distribution, and consumption from different dispersed energy sources for covering the end-users fluctuating demand.

Basic requirements of VPP

a)?Reliable and standardized communication means

In VPP operations, communication plays a vital role in proper operation. This means that there is a need for consistent and dependable communication language and the modest exchange of information among VPP, measurement systems, market, and the system operator. The way each party can communicate with each other is different and is defined concerning standard procedures.

b)?Operating within a unified Energy Management System

?To ensure the control center contains the data about the real-time status of each unit of the system VPP is operated within unified EMS. In this way, it provides the correspondence infrastructure for information stream and exchange.

An exuberant number of nodes connected with the EMS can back off the operation of the system or cause overstress in the communication medium. Due to that, a portion of the information from units should not be transmitted individually to the EMS. Obtained data has to be in a predetermined format and sent utilizing identified protocol. Assurance of a reconcilable information stream from various units and further extension of the system should be guaranteed.

c)?Power scheduling

It is important to properly manage power unit scheduling in addition to the establishment of proper communication links between players. This is essentially critical for the estimation of power demand in case of critical situations, day-to-day forecast of power supplied by actors, and optimum market participation. Well-coordinated power operation units contribute to a smoother profile and reliable functioning by expedient power scheduling.

The VPP system should sustain a local character, have the least delay, and can augment newly entering devices. Based on the number of units, the hierarchy structure of the infrastructure can be changed.

?Challenges common with VPP

Continuous need to update of storage servers; data security?issues?Availability and interoperability issues?and lack of off-the-shelf software solution that can cover a broad variety of requirements based upon developing a VPP

Bibliography

i.?Awerbuch.S (1997), The Virtual Utility: Accounting, Technology& Competitive Aspects of the Emerging Industry

ii.?Bai. H, Miao.S, Ran. X (2015), “Optimal dispatch strategy of a virtual power plant containing battery switch stations in a unified electricity market”, Energies, 8(3), 2015.

iii.?Mohammed. A, S. S. Refaat, S. Bayhan and H. Abu-Rub, (2019). "AC Microgrid Control and Management Strategies: Evaluation and Review," in IEEE Power Electronics Magazine, vol. 6, no. 2, pp. 18-31, June 2019, DOI: 10.1109/MPEL.2019.2910292.

iv.?Jiajia. Y, Fengji. L, Weicong. K, Zhao Y. D, (2021). Load forecasting in the short-term scheduling of DERs. Distributed energy resources in local integrated energy Systems optimal operation and Planning. Editors: Giorgio Graditi and Marialaura Di Somma

v.?Natarajan. P, AmalorpavarajRini, A. J, Ehsan. N, Kaliannan. P (2018). An overview of control techniques and technical challenges for inverters in a microgrid. Hybrid-Renewable Energy Systems in Microgrids. Integration, Developments, and Control. 1st Edition- June 2, 2018. Editors: Hina Fathima, Prabaharan N, Palanisamy K, Akhtar Kalam, Saad Mekhilef, Jackson Justo.?A volume in Woodhead Publishing Series in Energy.

vi.?Nikos. H, (2014). Microgrid Architectures and Control. First Edition. Published by John Wiley & Sons, Ltd -IEEE press.

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