Research On Control Strategy Of Microgrid Inverter Based On Virtual Synchronous Generator

With the large-scale distributed renewable energy access to the large grid leads to the reduction of system inertia,and the lack of frequency regulation ability when the load perturbation occurs,which makes the system frequency out of the normal range and endangers the safe and stable operation of the grid.The change of grid-connected operation mode will also produce the change of inverter control mode,making the system produce larger current shock,which is difficult to guarantee the safety and stability of micro-grid operation.As the key link connecting new energy and grid,the good or bad control strategy of inverter plays an important role in the scale of new energy grid-connected and stable operation of grid.In this paper,the virtual synchronous generator control strategy of the inverter is studied,aiming to reduce the shock caused by electricity when the microgrid is connected/off-grid and to improve the stable operation of the system,and the following aspects are mainly studied.(1)Analyze the topology and control system principle of Virtual Synchronous Generators(VSG),understand in detail the composition of VSG system,VSG control circuit principle and its components,analyze the principle and block diagram of active-frequency control,reactive voltage control and voltage and current double closed-loop control,explore the influence of rotational inertia J and damping coefficient D,and compare the anti-interference ability of the system under different regulation parameters through MATLAB/Simulink simulation,and derive the influence of rotational inertia and damping coefficient on the stability of the system,so as to lay the foundation for the subsequent research on the adaptive control strategy of rotational inertia.(2)Establish the function relationship between rotational inertia and frequency,design the rotational inertia adaptive control strategy,put forward the improved active-frequency control with VSG active-frequency control algorithm and rotational inertia adaptive control model.The effectiveness of the proposed adaptive control strategy is verified.The current prediction model in the inverter is established,and Model Predictive Control(MPC)is used to replace the voltage-current double closed-loop control link to generate the optimal inverter switching control signal,which is combined with the rotational inertia adaptive VSG control to establish the rotational inertia adaptive MPC-VSG control model,and analyze the effectiveness of VSG control,the rotational inertia adaptive VSG control,and the rotational inertia adaptive VSG control.The inverter output characteristics change due to load disturbance under VSG control,rotating inertia adaptive VSG control,MPC-VSG control,and rotating inertia adaptive MPC-VSG control strategies,and verify that both MPC and rotating inertia adaptive control strategies can effectively reduce system frequency fluctuations and improve system stability.(3)Analyze the operating characteristics of microgrid with rotational inertia adaptive MPC-VSG control strategy in both grid-connected and off-grid modes,build a simulation analysis of microgrid grid-connected operation and off-grid operation models,and observe the output characteristics of inverters in both operation modes;use constant differential regulation method to pre-synchronize the inverter frequency and voltage control,and use fast phase tracking link to shorten the phase synchronization The off-grid-to-grid switching process and the on-grid-to-off-grid process of the microgrid are analyzed,and the rotational inertia adaptive MPC-VSG control model with pre-synchronous control is designed to seamlessly switch the off-grid-to-grid and on-grid-to-off-grid processes of the microgrid.