Research Of Parallel Inverter System

For a long time, the main characteristics of electric power system's production patterns are high voltage, large power, which is called centralized power generation mode. However, with the rapid development of modern society, the requirement of power quality is increasing constantly. Thus the centralized generation model does not meet the need of power quality. Meanwhile, worldwide electricity crisis, energy crisis and blackout accidents in large areas have speeded up the reform process of electric power system. Distributed generation system can be flexible to get and installed near the users, thus it becomes an auxiliary way of centralized power generation. To expand supply capacity and improve reliability of power, inverters in parallel have become the development direction of distributed generation. Wireless control strategy for parallel inverter attracts much attention for its high redundancy and flexibility.This article sets two inverters in parallel as the research object, the single phase full bridge inverter system with independent operation is analyzed. The principle of operation and the causes of circulating current are analyzed. Two main factors which influence the circulating current are given, that is output voltage difference and equivalent impedance. In order to decrease the circulating current, two control algorithms are proposed, which is droop control method and virtual impedance method. This paper analyzes the regulating process of droop power and finds a method of choosing the droop coefficient. Meanwhile the fact that position change of zeroes and poles of equivalent impedance effects steady and transient performance is proposed. A novel method to optimize the coefficients of virtual impedance is put forward. Steady and transient performance of parallel inverter is improved.At last, the model of inverters in parallel is established by Matlab/Simulink simulation software. The simulation experiments are operating in the steady state, transient state and different parameter form to observe the steady and dynamic performance separately. The results show that circulating current among the inverters is reduced and the dynamic response has speeded up, the feasibility and correctness of the algorithm and parameter is verified.