Research Of A Grid Simulator Based On Three-phase Four-leg Inverter

In recent years,distributed wind power generation systems and distributed PV systems have become more popular.State Grid Electric Power Research Institute's report shows that China has become the largest producer of photovoltaic modules in the world,the total installed capacity of photovoltaic power generation in china by 2020 will reach 20 million kilowatts to 50 million kilowatts.The distributed generation system connects with the grid through the inverter,this would get challenges to the operation of the power system and make requests to optimize the allocation of resources of the power system.As the distributed generation systems are interconnected to the power system,there would be a variety of technical issues,such as power quality,voltage problem,islangding issues,protection issues,security and stability issues.The state grid developed specifications for the distributed generation system interconnected to the grid.Therefore we need to study distributed generation systems and improve detection capability.Under normal circustances,the power system provides symmetrical three-phase sinusoidal voltage,power grid failure situation is not common.In order to detect the features of the distributed generation connected to the grid,we need a grid simulator.Domestic study about grid simulator is not systematic,the foreign products with excellent performance are too expensive to use in the general tests.Therefore,the research of the grid simulator still has a very important significance.According to the requirements of the distributed systems connected to the grid,this paper summarizes the functions which the grid simulator needs to achieve,such as simulation of the normal operation of the grid,simulation of voltage sag,frequency offset,imbalance of three-phase voltage,grid voltage with harmonic components.This paper proposes to use the three-phase four-leg inverter in the grid simulator,and analyzes the advantages,mathematical model of the three-phase four-leg inverter,and three dimensional space vector modulation.For the functions of the grid simulator,the paper proposes the control strategy with proportional resonant regulator.By building simulation models in Matlab/Simulink,the validity of the grid simulator based on three-phase four-leg inverter using dual-loop control strategy with proportional resonant has been testified.Finally,this paper tests the validity of the control strategy on the 20 kVA grid simulator plarform.