Research On Parallel Control Technology Of Inverter

With the emergence of a variety of electrical equipment,the research on digital power supplies put forward higher requirements,such as reliability,redundancy and so on.The two important aspects of inverter power supply research are digital control and parallel technology.Inverter parallel technology can realize large-capacity and N+X redundant power supply,but the problem of power sharing and circulation suppression needs to be solved urgently.This dissertation mainly studies the parallel system composed of two inverters and its current sharing control strategy.First,a single inverter is modeled and analyzed,and the equivalent output impedance is derived based on its open-loop output characteristics.Because the output waveform quality of the inverter in the open loop is poor and the distortion is large,the voltage and current double closed loop control strategy is designed in this paper.Analyzes its closed-loop characteristics,derives the closed-loop transfer function,and calculates the parameters of the closed-loop regulator.Secondly,based on the previous theoretical analysis of a single inverter,the equivalent mathematical model of the inverter parallel system was established.Through the analysis of the parallel model,the causes of the circulation and the relationship among the output voltage amplitude,phase and output power are obtained.The characteristics of the circulation and output power of the system are analyzed in detail,A choke inductor is added to the output of the inverter to suppress the circulating current.Based on the analysis and study of the parallel control strategy without interconnecting lines,and compare with the traditional droop control method,for their existing problems,finally,an improved PQ drooping method is selected.It is a new type of droop control idea that adds a differential link to the control strategy,and the method of determining the droop coefficient is given and its droop control equation is deduced.And in MATLAB/Simulink,the single inverter and its parallel system were simulated and verified respectively.The simulation results show that the dynamic and static performance of the system is good,the average of the load power is well,and the ability to suppress circulation is stronger.Finally,on the basis of TMS320F28335 as the main controller,an experimental platform for the parallel system consisting of two 2kW inverters was built.And write the algorithm program in CCS,including SPWM generation,AD conversion,PI control algorithm,power calculation and adjustment and so on.The experimental results show that the parallel system has better circulation suppression capability,the current sharing accuracy meets the design requirements,and the load power can be evenly divided,further verifying the feasibility of the design scheme.