Research On Control Strategy Of Parallel Inverter Based On Circulation Feedback

In recent years,the parallel operation of inverters has become more and more widely used in distributed generation systems.However,for parallel inverter systems,the circulation generated between the parallel inverters will cause the inverter's operating efficiency to decline.At the same time,when the nonlinear loads is connected,the harmonic content of the output current of the inverters will increase,which will seriously affect the output current quality of the parallel inverters and also affect the operating efficiency of the inverters.According to the above problems,this paper uses a parallel inverter control strategy based on loop feedback to improve the system's operating efficiency.Inverter parallel system consists of lots of single-phase inverters.The stable operation of a single inverter directly affects the operation of the entire parallel system.Therefore,this chapter firstly analyzes and designs the single-phase full-bridge inverter circuit,Then,the filter parameters are selected by the ripple inductor current,finally completes the design of the entire single-inverter control strategy.Then,analyze the size of the circulation between two parallel inverters.For the problem that the PI controller can not realize error-free tracking which lead to circulation is increased,the PR control theory is analyzed,and the parameters of the PR controller are adjusted to complete the design of the quasi-PR controller.Finally,the simulation verifies that the quasi-PR controller can realize the error-free tracking of the output voltage of the inverter to the AC reference voltage,so this strategy can effectively reduce the size of the circulating current between parallel inverters.At the same time,the traditional parallel inverter control strategy based on output current feedback is analyzed.According to the problem that the output impedance of the inverter under this strategy can not effectively suppress the circulation,a control strategy based on loop feedback is used to increase loop impedance and effectively suppresses the circulation.Finally,the effectiveness of the control strategy is verified by simulation and experiment.In addition,the existing method for suppressing the output current harmonics of the inverter by changing filter parameters is analyzed.According to the deficiency of this method,a method of suppressing harmonics by changing the size of the virtual resistor is proposed.This method can achieve good results in both the suppression of the size of the circulating current between the parallel inverters and the reduction of the output current harmonic content of the inverter.Finally,the output current harmonics and spectrum of the two inverters with different resistance ratios are simulated and analyzed.The simulation results verify the effectiveness of the proposed method.