Research And Implementation Of Parallel Inverters In Photovoltaic Generation System

With the development of society and economy, humanity’s demand for electricity isincreasing while the energy crisis and environmental pollution are aggravating day by day, soit promotes the humanity to the new power generation technology research. Photovoltaictechnology has the advantages to become one of the dominant ways of the future powergeneration. And its development prospect is so large that it has been a research hotspot inrecent years. However, the installation position of photovoltaic power generation is restrictedto natural conditions and geographical area, and the capacity of distributed power generationsinstalled are not the same, then the parallel inverters are required to complete the task oftransmission power from the distributed power generation devices to the grid or the loads.This paper takes the technology for parallel inverters in photovoltaic generation systemas the research object, starts from the traditional technologies of parallel inverters, analyzesthe control strategy of parallel inverters based on the droop control. It takes aparallel-inverters system including two distributed generation units as an example, proposesthe expressions of droop characteristic when the equivalent output impedance of the inverteris inductive and the expression of output impedance for the voltage and current dual-loopcontrol inverter. In this section, a method to change the equivalent output impedance of theinverter by introduction of inductive virtual impedance is briefly introduced.Next, focuing on the characteristics that the line resistance is greater than the linereactance in low voltage photovoltaic distributed generation, the solution that making theequivalent output impedance of the inverter to be resistive is proposed. The analysisdemonstrates that the output impedance of the inverter can be designed to be resistive bettervia the introduction of appropriate virtual-impedance. So, the big circulating currentresult from the difference of electrical parameters was reduced.Finally, the design of the hardware and software based on the DSP control system isintroduced. Through the Matlab/Simulink simulation and prototype experiments, itdemonstrates that the proposed control strategy based on virtual complex impedance canreduce circulating current and improve the system performance of parallel inverters. It alsoverify that the proposed method is correct and effective.