Microgrid Control Strategy (original) (raw)
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In recent years, integrating renewable energy sources (RESs) has achieved significant attention due to the growing demand for sustainable energy solutions. Inverter-interfaced Islanded Microgrids (IGs) have appeared as an advantageous approach to integrating RESs into the power grid. Grid-forming inverters (GFIs) are a critical component of IGs, and their synchronization is essential for stable and reliable operation. The literature has widely proposed soft transition, pre-synchronization, and re-synchronization to synchronize IGs to the main grid. However, methods for synchronizing GFIs in the islanded microgrid are restricted. Parallel operation of GFIs is required to guarantee the high-power demand of IG and improve voltage-frequency stability. For parallel operation, GFIs must be synchronized with each other. In the conventional synchronization control systems that are highly nonlinear, the linear proportional-integral (PI) controllers are commonly used in synchronization loops without considering the nonlinearity resulting from the initial condition dependency and cross-coupling. Thus, conventional synchronization methods can be exposed to concerns of stable operation, narrow operation area, and performance degradation. This study proposes a new linearized synchronization control system for GFIs in IGs. In this way, it is possible to analytically design robust linear controllers and ensure a stable operation, high performance, and wide (full) operation area. In addition, a new soft-commissioning method is proposed to deactivate synchronization loops and soft-start the synced GFI. The proposed system has been tested in real-time and CHIL hardware setups for two 550 kW GFIs operating in parallel, and the results in the perfect agreement are presented in this study. INDEX TERMS Commissioning, control hardware-in-the-loop (CHIL), grid-forming inverter, islanded microgrid, load sharing, microgrid, synchronization. ÖZHAN ATMACA received the B.Sc. and M.Sc. degrees from Sakarya University, Sakarya, Turkey, in 2015 and 2018, respecively. In 2017, he joined as a Research and Development Engineer with the Elkon Marine and Electric Technologies Research and Development Center, Elkon Elektrik San. ve Tic. A.Ş, where he has been a Lead Research and Development Engineer, since 2020. He is also the Co-Founder with REGBES, Amsterdam, The Netherlands, a company that develops autonomous charging systems and shore power systems for e-ferries, cruises, and other marine vessels. His current research interests include power converters, electric drives, wind energy systems, and microgrids.
A synchronization technique for microgrid reclosing after islanding operation
IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society, 2012
The future electric grid concept will cover some small parts to be disconnected and work in an autonomous way isolated from the main utility. Control of microgridscomposed by the couple distributed sources-local loads -with the competence of operating in grid-connected and island mode is a trending research area. The presence of an efficient algorithm for synchronizing the microgrid with the main grid every time the recIosure is allowed is crucial for assuring a safe operation. The synchronization system presented in this work is compounded by two elements: Dual Second Order Generalized Integrator (DSOGI) and stationary reference frames phase locked loop (SRF-PLL). Besides, the voltage control of the microgrid plays a great role in the synchronization system performance.
IET Smart Grid, 2018
This study presents a fully distributed control paradigm for secondary control of islanded AC microgrid (MG). The proposed method addresses both voltage and frequency restoration for inverter-based distributed generators (DGs). The MG system has droop controlled DG units with predominantly inductive transmission lines and different communication topologies. The restoration scheme is fully distributed in nature, and the DGs need to communicate with their neighbours using a sparse communication network. The proposed control scheme is efficient to provide quick restoration of the voltage and frequency whilst accurate power-sharing is achieved despite disturbances. Further, convergence and stability analysis of the proposed control scheme is presented. The proposed algorithm avoids the need for a central controller and complex communication structure thereby reducing the computational burden and the risk of single-point-failure. The performance of the proposed control scheme has been verified considering variations in load and communication topologies and link delay by pursuing an extensive simulation study in MATLAB/SimPowerSystem toolbox. The proposed control scheme supports plug-and-play demand and scalability of MG network. The proposed control scheme is also compared with the neighbourhood tracking error based distributed control scheme and observed that the former exhibit faster convergence and accurate performance despite disturbances in MG network.
Synchronization Control of A Microgrid Using Network Based Co-Ordination Control Technique
A microgrid comprises of multiple distributed generators (DGs) and typically operates in parallel with this main grid. In certain cases this operation might fail and a microgrid may operate in an islanded mode. Synchronization occurs when such an islanded microgrid changes its operational mode back to grid connected operation by reconnection to the grid. Synchronizer used for synchronization of a single machine but a large microgrid which operates with multiple DGs and loads traditional synchronizer cannot be used to control it. This problem needs to be handled properly as it requires DGs to be controlled in a coordinated way to achieve synchronization. This paper presents work done on an active synchronizing control scheme which follows the network-based coordinated control of multiple DGs. Simulation results using Matlab/Simulink prove that the scheme is efficient enough to provide reliability in the reconnection of the microgrid. I. Introduction A combination of on-site distributed generators (DGs) along with loads is typically classified as a microgrid [1-2]. Many of these DGs are nearer to the load demand and may consist of one or many renewable energy sources. This can prove energy efficient system and thus microgrids are considered as the future of power systems. A lot of research has been conducted in this area in the last few years [2-6]. As advantages of microgrid are numerous, its stability and reliability is a major area of research. Traditionally for parallel operation of ac alternators the values of its difference of its voltage magnitudes, frequency and phase-angle are necessary to be kept as minimum as possible which is called its synchronizing criteria. A three phase breaker switch is given a make command when it is found that these conditions match. It is very important to satisfy this criterion as an out of sync generator can lead to a short-circuit condition and may cause mechanical vibrations of the generator shaft ultimately leading to trip condition. Furthermore it can lead to damage of equipment or ultimate blackout in the system which is economically not feasible for the growth of any country. Earlier an operator would command a close signal relying on the synchroscope reading and a relay. Later an autosynchronizer was introduced to automatically control voltage magnitude and speed/frequency of the generator to be able to connect to the electric power system. Synchronization of a microgrid is more complex than a single machine as it consists of many elements which may be unpredictable in nature such as renewable sources or sudden varying loads. Therefore due to above reasons an autosynchronizer is not adequate for synchronization of the microgrid as it works only for controlling single machine [8]. Most commonly manual method is used even today for synchronizing of a microgrid as the operator waits until the synchronizing criteria are satisfied, but always reliable results cannot be guaranteed [15]. Researchers have shown keen interest and are continuously providing promising solutions for the microgrid synchronization problem [7-12]. This paper focuses on one such method of automatically synchronizing a microgrid with the electric power system based on network-coordinated strategy to actively control multiple DGs to adjust its voltage and frequency to satisfy the synchronization criterion. Simulation results show the effectiveness of the approach to solve the problem of synchronization.This paper is divided in five sections. Section I gives a brief introduction about the problem of synchronization. Basic control scheme is given in Section II. Section III contains the simulation study and its various components and gives an idea of system under observation. Sections IV discuss the results of the system under study and comments on the same providing proof of effectiveness of the proposed control strategy while in Section V paper is concluded.
Energy Conversion and Management, 2015
This paper describes a control technique for enhancing the stable operation of distributed generation (DG) units based on renewable energy sources, during islanding and grid-connected modes. The Passivity-based control technique is considered to analyse the dynamic and steady-state behaviours of DG units during integration and power sharing with loads and/or power grid, which is an appropriate tool to analyse and define a stable operating condition for DG units in microgrid technology. The compensation of instantaneous variations in the reference current components of DG units in ac-side, and dc-link voltage variations in dc-side of interfaced converters, are considered properly in the control loop of DG units, which is the main contribution and novelty of this control technique over other control strategies. By using the proposed control technique, DG units can provide the continuous injection of active power from DG sources to the local loads and/or utility grid. Moreover, by setting appropriate reference current components in the control loop of DG units, reactive power and harmonic current components of loads can be supplied during the islanding and grid-connected modes with a fast dynamic response. Simulation results confirm the performance of the control scheme within the microgrid during dynamic and steadystate operating conditions.
IET Renewable Power Generation, 2018
This paper describes a novel strategy for microgrid operation and control, which enables a seamless transition from grid connected mode to islanded mode, and restoration of utility supply, without loss or disruption to loads sensitive to frequency or phase angle dynamics. A simulation study is conducted on a microgrid featuring inverter connected renewable generation, and power electronic interfaced loads. Therefore, the microgrid inherently has low inertia, which would subsequently affect the dynamic characteristics of the microgrid, in particular during mode transition. The microgrid is controlled by means of synchrophasor data to achieve synchronous island operation, enabling the microgrid to track the utility frequency and phase angle. The simulation includes synchrophasor acquisition and telecoms delays, allowing for detailed investigation of the microgrid dynamics under various mode transition scenarios, including the risk of commutation failure of the inverter sources. The proposed method is demonstrated to successfully maintain a microgrid in synchronism with the main utility grid after the transition to islanded mode without significant impact on various equipment connected to the microgrid. Thus, synchronous island operation of low inertia microgrids is feasible. This study also showed that utility supply could be seamlessly restored if the microgrid is operated as a synchronous island.
Soft Synchronization of a Microgrid
In today's energy scenario microgrid concept has emerged as an extremely important as it is expected to provide multiple advantages such as financial and environmental along with power reliability and superiority of power system. Inverter based distributed generation is yet to prove a lot but alternator-based CHP and diesel plants have been established and are high in terms of reliability and efficiency. However it is necessary to match the synchronization criteria (i.e. difference of voltage phase-angle and frequency of the grid system and alternator output) and control the breaker. In such cases traditional synchronization may generate high short circuit current, vibrations and may ultimately lead to trip condition if there is any operator malfunction. In this paper, an alternative to traditional synchronization is proposed. A case study of a local sugar industry is taken up and effectiveness and applicability of the proposed algorithm is proved with results. A test system is simulated and studied using MATLAB/Simulink and SimPowerSystems. Traditional methods of synchronization are studied and compared and advantages of the proposed strategy are highlighted using results from MATLAB.
IEEE Transactions on Smart Grid, 2015
Microgrids can operate in both grid-connected and islanded modes. In order to seamlessly transfer from islanded to grid-connected modes, it is necessary to synchronize microgrid voltage, frequency and phase to the main grid. However, since the microgrid is often based on power electronics converters, the synchronization process is quite different compared to the quasisynchronism control in conventional power systems. Firstly, in order to address this concern, the microgrid synchronization criteria are derived. Based on these criteria, a novel distributed active synchronization strategy is proposed, which takes into account not only the fundamental component but also positive and negative sequences of the harmonic components. This way a seamless reconnection to the main grid can be performed. The proposed method is implemented in the secondary control level of a hierarchical control structure. Real-time hardware-in-the-loop results show the feasibility of the proposed technique.
Review of Active Synchronization for Renewable Powered Microgrid
International Journal of Engineering & Technology, 2019
Microgrid can operate in dual mode; grid-connected and islanded mode. In order to seamless transfer from islanded microgrid to grid connected mode, it is necessary to voltage, frequency and phase of microgrid to synchronize with main grid to prevent severe consequence. However, microgrid has to be controlled in a coordinated way to achieve a synchronization. This paper present a review on the existing active synchronization approach with their control strategies. There are three approach for grid-connected synchronization; active synchronization, passive synchronization and open transition transfer. However, only active synchronization approach provides the reliable reconnection for microgrid. Active synchronization approach associates with control structures and control strategies. There are three control structures of microgrid under active synchronization; centralized, decentralized and distributed and three control strategies available in the literature which are phase locked loop (PLL), droop control, and frequency locked loop (FLL). The most applicable control strategy for active synchronization is phase locked loop because of its simplicity, robustness, and effectiveness in various main grid condition. Furthermore, between three control structures of active synchronization, decentralized control is becoming more favorable by the researches based on its advantages over the other structures.
Journal of modern power systems and clean energy, 2023
In this paper, the synchronization stability challenges of same-rated frequency interconnected microgrids (IMGs) with fully inverter-based generation units are studied. In this type of weak power grid with low X/R ratios and low line impedances, no strong source with a high-inertia rating exists with which other generation units can be synchronized. Two IMGs controlled using a pinning consensus-based control architecture are considered. The inrush power flow at the beginning of the interconnection process is modeled and analyzed. This power flow is affected by the voltage/phase/frequency difference of the IMG points of common coupling. A small-signal model of the IMGs is obtained that includes a synchronization control unit, and small-signal stability is analyzed based on sensitivity analysis of the most important control and operational parameters. In addition, the transient stability of a nonlinear model of the IMGs under study as implemented in SimPowerSystems/MAT-LAB is investigated. Stable synchronization is more challenging than the synchronization of multi-area strong power grids and grid-connected MGs. However, synchronization can still be performed by selecting more limited ranges for the control gains and threshold values of the synchronization algorithm. Nevertheless, different disturbances such as high load conditions can cause synchronization instability.