Research On Parallel Issues For PV Inverter

With the development of society, energy and environmental issues become more andmore prominent. The development of Photovoltaic system was faster and faster as anemerging industry. Grid-connected PV system is one of the most popular development trendin the photovoltaic field. Single inverter module is limited by its unreliability andextendibility in practical applications. The design of multi-module inverters parallel systemhas been more and more important because of the increasingly requirements for high powercapacity.There were many control methods with different complexity and different performanceof equal-distributed load current in inverter parallel system. These could be divided into wiredparallel control methods and wireless parallel control methods according to the existence ofinterconnection line in different modules. The parallel system will be more reliable and moreintelligent with the technology getting refined. The frequently used wireless parallel controlstrategy is droop control method. The output voltage could be adjusted by detecting the outputactive power and reactive power.Firstly, the current issues of national energy and the significance of photovoltaic powergeneration was described in this article. PV inverter’s important role for PV system wasintroduced in the text. Main circuit structure and working principle of the inverter wasstudied.Secondly, create a mathematical model of the inverter. The reason why circulationcurrent generated in the parallel system was analyzed in the text. The impact of loop currentin parallel system caused by control parameter could be studied from the simulation results.Thirdly, it has been proved that the distributed logic control strategy could make goodeffects on parallel system according to research on the deduced control formula and thesimulation results.Finally, a parallel control strategy based on voltage droop control was introduced in thistext. Then the circulation features of inverter parallel system was analyzed. The simulationanalysis for the parallel system which uses the droop method was finished in the paper. Theresults illustrate that the droop method could make current sharing and power sharing in thesystem, but it also changed output characteristic into soft. The differential signals of activepower and reactive power are added into droop control formula to improve dynamicperformance. The results of simulation indicate that the improved droop method could restrictcirculation and make the system more stability.