Research On Parallel Control Technology Of Inverter

With the rapid development of China’s economy,the excessive consumption of energy,energy crisis and environmental problems become increasingly prominent,the development of renewable energy based on distributed generation technology has become an inevitable trend.The distributed generation system is composed of many inverters in parallel to meet the different load demands.Therefore,the research on power allocation strategy for distributed parallel inverters has theoretical reference and engineering application value.Firstly,this paper introduces the system structure of the inverter,establishes its mathematical model and on the basis uses the single voltage closed loop control method.The influence of the control parameters and the transformer on the output impedance is analyzed.Finally,a set of control parameters are chosen which can make the output impedance mainly inductive.Then the mechanism of the circulating current in two single-phase inverters parallel model is analyzed.The expression of output power in different characteristics of output impedance is derived,and the relationship between output power and output voltage is analyzed.Then the realization principle of traditional power droop control method is analyzed,and a droop control strategy based on virtual inductance is proposed.Then the paper demonstrates the effectiveness of adding virtual inductance to improve power allocation.The formula of the virtual inductance formula to achieve DQ in the two-phase rotating coordinate system is deduced.On the basis of adding virtual inductance,an improved droop control strategy based on load voltage feedback is proposed.This control strategy eliminates the influence of the uncertainty of the line impedance on the power allocation in the distributed generation system,and stabilizes the output voltage within the specified range.Then the paper analyzes conditions required for control parameters in parallel inverters with the different capacity,It is proved that the improved droop control strategy is effective for the output power allocation in parallel inverters with different capacity.Finally,the simulation and experimental results are used to verify the control strategy used and the conclusions deduced by the paper.The results show that the proposed improved droop control strategy based on load voltage feedback can effectively suppress circulating current of the parallel inverters of the same or different capacity.