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Key Points and Prospect of Microgrid Operation and Control Technologies XU Hailiang,ZHANG Yufeng,NIE Fei,MENG Zhiyuan,LI Zhi Journal of Electrical Engineering    2020, 15 (1): 1-15.   DOI: 10.11985/2020.01.001 Abstract （1370）   HTML （173）    PDF （6682KB）（1818）       Knowledge map    In recent years, microgrid technologies have been widely concerned as an important technical means to improve the stability and reliability of new-energy connected system. The latest development in microgrid operation and control is presented, with the relevant research domestic and abroad summarized. The technical difficulties are fully discussed, such as the topology variety, uncertainty in both source and load, power conversion diversity and communication mode design. Meanwhile, the key issues in microgrid control are explored in detail, including coupling design between the control strategy and planning scheme, stability in a single microgird and between each other, virtual synchronous control and frequency regulation, and power converter control as well. Then, the typical technologies on microgrid operation and control are analyzed. Finally, the research trend of microgrid operation and control is discussed, so as to show the latest works and provide a prospect of this technology. Table and Figures | Reference | Related Articles | Metrics

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Study on Transient Stability of Islanded Microgrid with Induction Motor Load YI Xiangtong,ZHAO Feng,CHENG Huijie,SHUAI Zhikang,SHEN Zheng Journal of Electrical Engineering    2020, 15 (1): 16-22.   DOI: 10.11985/2020.01.002 Abstract （855）   HTML （68）    PDF （3611KB）（1063）       Knowledge map    Microgrid is a complex power supply network with various load types. A large number of dynamic loads (such as induction motor) access will inevitably have a significant impact on the transient stability of microgrid. A simple islanded microgrid system is taken as an example to study the influence of induction motor load on its transient stability. Based on the introduction of the microgrid models, the transient instability process of induction motor with different mechanical load types is analyzed. The corresponding simulation model is built in PSCAD/EMTDC, and the critical clearing time of induction motor is obtained through time domain simulation. It is found that the system with induction motor load has already lost transient voltage stability compared with the equivalent constant impedance load in the same fault duration. Moreover, the influence of different parameters on critical clearing time and multiple induction motor on the transient stability of microgrid are analyzed by simulation. Table and Figures | Reference | Related Articles | Metrics

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Generalized Sag Control Strategy for Isolated Island Microgrid Clusters Based on Rotation Coordinate Transformation ZHANG Ruixuan,ZHOU Niancheng,MENG Xiaoxiao Journal of Electrical Engineering    2020, 15 (1): 23-28.   DOI: 10.11985/2020.01.003 Abstract （672）   HTML （13）    PDF （8193KB）（255）       Knowledge map    The microgrid clusters is composed of multiple power supply and load clusters, and its control design is complicated. The influence of tie line impedance between isolated island microgrid clusters on their interactive power control is analyzed. In view of the infeasibility of using generalized droop control strategy directly for microgrid clusters, an improved generalized droop control strategy based on microgrid clusters structure transformation is proposed in consideration of simplified microgrid clusters structure and tie line impedance constraint. Based on the coordinate rotation theory, this strategy can realize power decoupling control, frequency adjustment and active power equalization under arbitrary line impedance ratio, thus ensuring the stability of the operation of the microgrid clusters and improving the dynamic response of the system. Finally, the proposed control strategy is simulated and analyzed, and the simulation results prove the feasibility of the proposed control strategy. Table and Figures | Reference | Related Articles | Metrics

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Instability Mechanism and Control Measures of Reactive Compensation in Islanded Microgrid Based on Droop Control SHI Yunjie,FENG Xiayun,WANG Fei,ZHANG Lijun,LI Yufei Journal of Electrical Engineering    2020, 15 (1): 29-35.   DOI: 10.11985/2020.01.004 Abstract （689）   HTML （11）    PDF （12461KB）（121）       Knowledge map    For the line economical operation and lower transmission loss requirements, on the part of reactive compensation of islanded microgrid, resonance problems among droop control inverter and the reactive compensation capacitor are studied. Firstly, output impedance of droop control inverter is obtained by small signal method, it is disclosed that droop control inverter especially Q-U control factor is mainly factor, which would affect the output impedance value at lower frequency band. Then, the stability of islanded microgrid is analyzed by impedance-based specifications when reactive power capacitors are emulated for reactive power compensation. It is shown that the grid is unstable if the reactive power capacitor is existed for reactive compensation. Finally, harmonic suppression method based on capacitor current feedforward control at current inner loop is proposed, which reshapes the output impedance of droop control inverter, and a 3 kW droop control inverter is designed for verified the effectiveness of the output impedance model and harmonics damping mothed. Table and Figures | Reference | Related Articles | Metrics

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Microgrid Model with Renewable Energy and Energy Storage System and Its Optimal Operation Simulation DING Yujie Journal of Electrical Engineering    2020, 15 (1): 36-40.   DOI: 10.11985/2020.01.005 Abstract （874）   HTML （17）    PDF （3687KB）（816）       Knowledge map    With the wide application of new energy power generation, the economic interest of microgrid is the key factor to achieve an environment-friendly power supply. Scholars have done a lot of research on microgrid models, but the existing models fail to show the importance of renewable energy in microgrid operation. Therefore, a microgrid generation and storage model based on renewable energy and energy storage system is proposed. In order to minimize the cost and the carbon dioxide emissions, the generation and storage as well as the production costs of electric energy in microgrid are analyzed in detail. The microgrid consists of a photovoltaic power plant, a wind turbine, a diesel, and a gas generator as a power generation equipment, a battery energy storage system as an energy storage equipment and a small hydraulic reservoir. The simulation of the power production and storage process of the microgrid in the distribution network is carried out by using the FICO Xpress programming optimization tool. The result shows that the use of the energy storage system can greatly reduce the generating capacity of thermal power units, and also help to reduce the operating cost of thermal power units. In addition, the simulation results are in accordance with the proposed model for analyzing power production and storage in the microgrid. Table and Figures | Reference | Related Articles | Metrics

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Microgrid Stability Control Based on Adaptive Rotating Inertia VSG ZHU Zuobin,HUANG Shaoping Journal of Electrical Engineering    2020, 15 (1): 41-47.   DOI: 10.11985/2020.01.006 Abstract （698）   HTML （10）    PDF （8783KB）（438）       Knowledge map    In order to deeply analyze the mechanism of adaptive rotary inertia virtual synchronous generator (VSG) control on frequency stability of microgrid, based on the mathematical model of conventional VSG, using the power-angle characteristic curve of synchronous generator and the period curve of rotor angular velocity oscillation, the mechanism of adaptive rotary inertia on frequency stability of microgrid is analyzed, and the control strategy of adaptive rotary inertia VSG is proposed. The key parameters are tuned and designed. The results show that the system stability and dynamic performance of VSG control strategy with adaptive rotating inertia are better under load disturbance. Compared with the conventional VSG control strategy, the frequency fluctuation and output power overshoot are significantly suppressed. Finally, the simulation model of adaptive rotary inertia VSG control strategy is established, and the effectiveness of the method is verified by simulation. Table and Figures | Reference | Related Articles | Metrics

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Droop Control Method Based on Dynamic Virtual ComplexImpedance for Microgrid FAN Bishuang,WEI Guoqiang,LI Zeyang,YAO Ganzhou Journal of Electrical Engineering    2020, 15 (1): 48-54.   DOI: 10.11985/2020.01.007 Abstract （547）   HTML （6）    PDF （17609KB）（81）       Knowledge map    Output power sharing and circulating current suppression have been the main subjects for parallel inverters. The equivalent output impedance of the inverters is designed to be resistive using dynamic virtual complex impedance, which can improve applicability of selected PV-QF droop control and decouple the active power and reactive power. The dynamic virtual complex impedance method is proposed to further suppress the circulating current and improve performance of the power sharing and dynamic response after analyzing the generation and influencing factors of the circulating current. The feasibility of the proposed method is verified by the simulation. Table and Figures | Reference | Related Articles | Metrics