Application Of String Power Optimizer For MPPT In PV Plant Operation And Maintenance

During the operation of photovoltaic(PV)power station,there are various defects occurring in PV array in their lifetime,such as,huge power degradation,by-pass diodes failure,potential induced degradation(PID),local shadow,tilted angles mismatch,surface soiling,etc.It brings high challenge to the yield production and benefit of the PV power station.These defects can reduce the voltage of some local PV strings and lead to mismatch with normal PV strings,which results in a significant reduction in the power output of the whole PV array.It calls as “Barrel Effect” of the PV string in term.This paper introduces a special PV string power optimizer to separate the problematic strings from the normal strings.Then the problematic strings and normal strings can keep independent each other and work at respective maximum power output status based on maximum power point tracking(MPPT)technology.The first chapter presents the research status and development prospect of power optimizer.Simultaneously,the current development and difficulties of PV operation and maintenance(O&M)are introducing.Further,the significance and value of the research in this thesis are discussing.The second chapter introduces PV output characteristics and MPPT simulations by MATLAB/Simulink.Three popular algorithms are introducing particularly about respective characteristic.Through simulating comparison,this thesis studies relevant MPPT simulation of PV modules string with perturbing and observing method.The third chapter introduces power mismatch phenomenon caused by PV modules defects during the whole system operation period.Meanwhile relevant research and analysis on the whole power output are implementing.The results implicate that the great application value of string power optimizer based on MPPT technology in PV O&M for large-scale PV plant.The forth chapter mainly performs detailed analysis on the design of hardware and software and the implementation of string power optimizer.The function of circuit modules and the tool of software are introducing,and the design idea and operation process of the software are analyzing.Finally,PV simulation power supply and on-grid inverter constructs the experimental platform.The tests on the developed prototype comply with the design requirement.The last chapter does relevant analysis about actual application results of PV string power optimizer in large-scale PV plant.Especially,one example of 10 MWp PV plant application puts forward with PID issue,where power optimizer of PV string can eliminate voltage mismatch and maximize power output.