Seamless Transfer For Operation Mode Of Grid-connected PV System Based On Virtual Synchronous Generator

Abstract:Solar photovoltaic power generation is low-cost, non-polluting and renewable, and has become an important source of renewable energy. While the photovoltaic power output characteristics under the influence of light and other natural conditions, its output power need to be conducted before transforms to the grid, and the mode transfer between grid-connected and isolated island operation is need because of system failure or human factors, so it is necessary to study and control the output characteristics of the PV system.This article takes the grid-connected systems as the research object, studying on the PV system for seamless transfer by the inverter control technology of Virtual Synchronous Generator (VSG). This paper establishes the mathematical models of the component of the PV system, such as the photovoltaic power unit, inverters, controllers and the overall system, and refers the mathematical model of synchronous generator to make the inverter simulates the synchronous generator’s advantages of large impedance and inertia. And then, the power unit with inverter gets the output characteristics of synchronous generator, meets the operation requirement of the system. The paper designs several system controllers, such as V/f controller, auto-reclosure unit, to make the PV system prevents larger mutations of voltage and frequency fluctuations when transfer between grid-connected and isolated island mode with Virtual Synchronous Generator control method contains energy storage system. That makes the system more stable and reliable.This paper introduces the research background and the necessity for the research at first, analyses and discusses the algorithm theory and the mechanism of composition of the virtual synchronous generator (VSG) control in the follow, and establishes mathematical model of the VSG. And then, to test the effect of the control algorithm, we study the transient response of the PV system when it transfer between grid-connected and isolated island mode with VSG control method contains energy storage system. Finally, the system’s Matlab/Simulink simulation model is built based on the control arithmetic for simulation and analysis. The simulation result demonstrates the feasibility and accuracy of control algorithms.