Research On Circulation Suppression Method Of Photovoltaic Inverter Parallel System

The photovoltaic inverter is the core equipment of the photovoltaic power generation system,which can invert the direct current generated by the photovoltaic array into alternating current for load use or grid connection.In practical applications,multiple inverters are often required to operate in parallel.Although parallel operation can increase the output power of the system,it is easy to form a circulating current between the inverters,and the circulating current will not only reduce the efficiency of the inverter,but also affect the efficiency of the inverter.The service life of the inverter can lead to the collapse of the entire system in severe cases,which makes the research on the parallel operation control strategy of the inverter has important practical significance.In this paper,the double-closed-loop control theory of voltage and current for a single inverter is studied.Based on the analysis of the control theory of a single inverter,the equivalent model of parallel operation of two inverters is established.The output voltage and the equivalent impedance of the transformer are inconsistent.The most used in the suppression method of the circulation is the traditional droop control.The principle is to calculate the active and reactive power through the power calculation unit,and then obtain the command value of the voltage amplitude and frequency according to the droop control equation,and then adjust the inverse through the feedback control.The respective voltage amplitudes and frequencies of the transformers are such that the amplitudes and frequencies of the output voltages of the inverters are consistent,thereby achieving the purpose of suppressing the circulating current.Since the traditional droop control ignores the resistance component in the equivalent impedance of the inverter and its droop coefficient is constant during the control process,the conventional droop control has certain limitations.Based on the traditional droop control,this paper proposes three improvements for its limitations: a power decoupling control strategy for adjusting the amplitude and phase of the output voltage with active and reactive power is proposed for the power coupling problem of the traditional droop control.The problem of contradiction between voltage drop and power sharing accuracy is proposed.The adaptive droop control strategy of droop coefficient with power variation is proposed.The control strategy of increasing power differential term is proposed for slower system response speed.Finally,a decoupled adaptive droop control strategy with power differential term is obtained.Finally,a model of two inverters running in parallel was built on the MATLAB/Simulink platform and related simulations were carried out.The simulation results verify that the improved droop control strategy can improve the output voltage quality of the system,suppress the circulation of the parallel system,and achieve the power sharing of the parallel system.Figure[56] table[2] reference[61]...