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

The emergence of microgrid has improved the ability of distributed power sources to absorb locally.However,due to the lack of inertia and damping characteristics of traditional microgrid inverter control strategies,it is difficult to maintain the stable operation of the system when distributed power sources are connected in a high proportion.For this reason,an inverter control strategy that simulates the operating characteristics of a synchronous generator-Virtual Synchronous Generator(VSG)came into being.VSG can not only participate in frequency and voltage regulation,but also increase system inertia and damping.The large-scale integration of distributed power sources into micro-grids provides a new idea.This paper studies the control strategies of microgrid inverters using VSG technology.(1)Construct the VSG control algorithm based on the second-order stator and rotor equations of the synchronous generator,analyze the bottom double closed-loop control with the help of the Bode diagram;use the step response to analyze the influence of the moment of inertia and the damping coefficient on the VSG;finally,the established VSG model is simulated and verified,Lay the foundation for follow-up research.(2)In order to increase the capacity of the microgrid and the stability of the system,the VSG built in the previous article was extended from a single machine to multiple machines in parallel operation.Aiming at the problem that the line impedance affects the parallel power sharing of the VSG,an integral link and a voltage compensation link with the AC bus voltage as a global variable are constructed in the reactive loop,and a variable virtual impedance term is added on the basis of the fixed virtual impedance to make the power It can achieve accurate equalization according to the capacity,and can effectively suppress the voltage amplitude drop and reduce the system circulation;finally,it is verified by simulation.(3)In order to realize the smooth switching of VSG island and grid-connected,the vector rotation idea of phase-locked loop is used for reference,and a presynchronization control strategy without phase-locked loop is improved on the basis of reconstructing the voltage loop in the previous article.First,perform simulation verification under a single VSG grid connection,and then extend the strategy to multiple VSG grid connection.In order to ensure that multiple VSGs can obtain the same amount of secondary compensation at the same time,a method is proposed to control multiple VSGs with a single VSG secondary compensation at the same time.Synchronous control strategy;finally design a variety of working conditions for simulation verification.(4)Focus on the DC side of the VSG and combine the AC side control described above to construct a complete optical storage VSG coordinated control system.Considering the nonlinear output characteristics of photovoltaic cells,an improved MPPT control algorithm is given;for the hybrid energy storage unit composed of supercapacitors and batteries,an energy management strategy based on a second-order low-pass filter is improved;finally,a complete the optical storage VSG coordinated control system realizes the coordinated control between "source-network-load-storage",and designs a variety of working conditions for simulation verification.