Research On Single-phase Inverter Parallel System With Droop Control Based On Virtual Impedance Method

With the progress of human industrial civilization,the demand for power is also increasing,and high power and large capacity inverters have become the current development trend.However,with the increase in capacity,the cost will increase correspondingly and the reliability will be greatly reduced.Therefore,the modular parallel technology of inverter power has become a hot research topic in the power electronics industry.In the fields of UPS,all-electric aircraft,large ship power supply,high-speed railway and so on,the modular parallel technology of inverter power has been widely used.Firstly,in this paper,single-phase inverters are taken as the research object,and the working characteristics of single-phase inverters are analyzed in detail.Furthermore,the mathematical model is built in the static coordinate system and the control structure block diagram is drawn on this basis.The mathematical model and structural block diagram based on rotating coordinate system are also established.The controller uses voltage and current dual-loop control.The MATLAB/Simulink simulation model proves that single-phase inverter under the control of using dual closed-loop can output the voltage of standard sine wave in the cases of any load,with high steady precision and fast dynamic response.Then,the paper studies the parallel connected inverters system and build the mathematical model of the circulation.The droop control strategy is introduced,and the simulation model is carried out in paper.In view of the problem that the traditional droop control strategy could not distribute unevenly the reactive power under composite impedance transmission line.The virtual impedance method was introduced to improve the droop control strategy.The simulation model verifies the results that the introduced virtual impedance method has a good circulating current suppression effect for any parallel system of transmission lines.Finally,according to the technical parameters,this paper builds an experimental prototype by selecting reasonable components.The design of the circuit of hardware and the control algorithm of software were introduced minutely in this paper.The experimental waveforms of single inverter,traditional droop control and droop control based on virtual impedance method are obtained,and the validity and correctness of the double closed-loop control strategy based on rotating coordinate system and the droop control strategy based on virtual impedance method are verified by the experimental waveforms obtained.