Study On The Grid-connection Control Of Two-stage Photovoltaic System Based On Virtual Synchronous Generator

In recent years,with the fast development of microgrid technology,the traditional power system structure dominated by centralized generation and unidirectional power flow is currently faced with challenges from the Distributed Generation(DG).The concept of Virtual Synchronous Generator(VSG)has been raised in the last decade as a reliable approach for power electronics converters to integrate the controllability and stability features of classical synchronous machines.The main contents of this paper are as follows:In Chapter 2,the physical model of a two-stage photovoltaic microgrid system is established,and the basic control strategy of the important components of the PV system is presented.The model and simulation of the photovoltaic cell are established.The model of the PV inverter based on LCL filter is established.,And the mathematical derivation and detailed analysis of the model,the decoupling control strategy of the inner loop voltage and current double loop control of the photovoltaic inverter is studied.Chapter 3 analyzes the MPPT control strategy of DC / DC converter based on admittance increment method,simulates the inertia frequency regulation principle of synchronous generator,adds the virtual rotor motion characteristic link after dropping the control output reference frequency,simulates the synchronous generator excitation system,The design of reactive power and voltage control of photovoltaic inverter power supply,and the improvement of reactive power control strategy based on the characteristics of two-stage photovoltaic system,proposed PVP and virtual synchronous control strategy based on PVP,PV grid-Can be stable in the constant active power output and active FM mode and active power reserve mode.In chapter 4,we discuss the current characteristics and power distribution control strategy when two PV inverters are connected in parallel as an example,and propose a combination of sag control and virtual impedance method to solve the parallel circulating and reactive power Proportion allocation problem.The method can realize decoupling control of active and reactive power,distribute the power according to the proportion of capacity,and can suppress the circulating current,and realize the control goal of multi-inverter coordinated and controllable parallel.