Research On Novel Droop Control Strategy For Parallel Photovoltaic Inverters System

The inverter is the core device of photo-voltaic power generation system,which converts the DC power generated by the solar energy into the alternating current we need.Due to the improvement of the capacity and the reliability as well as the demand of the high power load,the single inverter has been unable to meet the requirements of people.Parallel inverters system overcome the limit of the single inverter,which can increase or decrease the number of inverters to control the output capacity of the inverter flexibly,and achieves redundant power supply system.However,if the vector of the output voltage in parallel unit is different will lead to the formation of circulation between the inverters.The circulation between the inverters will lead to the overload of the inverter and destroy the parallel system.Therefore,the research on parallel inverters technology has a significant role on the development of photo-voltaic industry.Firstly,this paper analyzes the structure and mathematical model of the three-phase inverter.On the basis of the inverter mathematical model,a double closed loop regulator based on the capacitor voltage and the inductor current is designed to improve the dynamic performance of the inverter system.Then,this paper establishes the equivalent circuit diagram of two parallel inverters on the basis of a single inverter,analyzes the problems of power sharing and circulation in the parallel inverters system and introduce the traditional droop control method.The decoupling control based on the inherent limitations of the traditional droop control method is proposed to reduce the stability of the parallel system and improves the stability of the parallel system.On this basis,this paper adds the self-adaptive droop coefficient which adjusts according to the change of the load automatically.So that the parallel inverters system can achieve power sharing and reduce the circulation of system.Finally,this paper build the parallel inverters system model of the novel droop control in the Matlab/Simulink environment,and designs the hardware part and the software part of the parallel inverters system in detail.The simulation results show that the new decoupling control strategy can improve the voltage quality of the inverter parallel system,reduce the circulation of the parallel system,realize the power sharing of the parallel system and improve the dynamic performance of the parallel system.