Analysis And Simulation Study Of Inverter Parallel System Based On Droop Control

As the high-speed development of the economy and society,the requirement for the power supply quality is much higher among the industrial production and social activity,and the huge demand of the computer and the equipment with high precision makes it much harder than before.On the one hand,it needs the power system with high reliability to ensure the supply.On the other hand,hopefully it can obtain a larger power capacity to enhance the operation ability for the whole power supply system.With respect to the single power supply with large capacity,using multi-module parallel system can effectively improve the reliability and security for the entire system,which makes it one of the most mainstream trends of the power supply technology.Among all of them,the research for the multi-module inverter parallel system is of high value,and the most important part for it is the circulating current restraint and the power sharing.To begin with,the module of the single-phase full-bridge inverter is established.The LC filter is well studied in different modulation systems,including the single-polarity modulation,double-polarity modulation and single-polarity double frequency modulation.For the control strategy of the inverter,the inductor current and output voltage double-loop control with load feedforward is applied and the parameters of the double-loop PI controller are determined through the pole-placement method with high veracity.Also,the LC filter and the double-loop control system are all modeled in MATLAB/Simulink to test its dynamic performance and static performance carrying changing linear load and unlinear load,whose result verifies the theoretical analysis presented above.Next,the basic module of the multi-module inverter parallel system is studied,toghter with the cause and influence of the circulating current.Furthermore,it researches using the tradition droop control to restrain the circulating current.But due to the reason that the impedance characteristic of the circuit is simplified as inductive while using the tradition droop control,the applicable occasion for the tradition droop control is limited.Thus,the tradition droop control requires to be enhanced.Given that the resistive part of the low voltage power supply system can not be simply ignored,the improved droop control is applied to accommodate the circuits with various impedance characteristic.Meanwhile,the SOGI is applied to the virtual impedance on the basis of the improved droop control to make further performance advance for the entire parallel system in front of diverse output and load occasion.Finally,the inverter parallel system consist of two single inverter modules is modeled in MATLAB Simulation platform,and the two different droop control strategies,plus with the virtual impedance,are tested.The result shows that the improved droop control has better performance on the power sharing under different circuit's impedance characteristics.The test for the virtual impedance mainly concentrates on the output performance and power distribution while carrying unlinear load and changing load,or switching single inverter module.The result illustrates that using the virtual impedance can obtain favourable circulating current restraint and power sharing.The THD of the output voltage is pretty low carrying unlinear load,and the response is rapid even with the changing load.The power sharing and system stability can be acquired as well.This thesis mainly studies the single-phase SPWM inverter parallel system with droop control,and the result shows that the system researched above can achieve the stable operation and power sharing.It has certain meaning for making better inverter with higher reliability and stronger capacity.