Research On The Control Technology Of Parallel Inverter

The parallel of inverters can expand capacity and realize redundancy in power supply system. So it is now considered as one of the most important research in the field of inverter technology. The capacity expanse of parallel-inverters can greatly improve the power system's flexibility.Then the system's volume and weight can be remarkably reduced. The current stress of the power switch is considerably lessened which means higher reliability, lower cost and higher power density.This paper firstly analyzes the impact of inverter parameters on the output impedance and output voltage steady error with current hysteresis control. Circulating current characteristic is analyzed through the equivalent model of paralleled inverter. The theory basis of the droop strategy is introduced according to power flow theory.Secondly the droop current-sharing method is verified through wireless parallel system made up of two half-bridge inverters, and the software and hardware circuit are given.Based on the small signal model of parallel system, the influences of system parameters such as frequency droop coefficient on system stability and dynamic performance are researched by means of root locus of characteristic equation. The power distribution of parallel system is discussed when the line inductances are differernt and output voltage mismatches between paralleled inverters. The reason why the reactive power can not be shared is analysed, and the ways to reduce the reactive power error are introduced.At last the parallel system based on average current sharing strategy, which is composed of two full-bridge inverters is researched. The equivalent math model of system deduced indicates that the performance of parallel system is similar with that of single inverter. The output voltage characteristic and current-sharing performance of the parallel system with and without load current compensation are compared. The imbalance of current feedback coefficient and output filter capacitor between inverters are the main factors to lead to circulating current.