Research On MPPT And Grid-connected Operation Of Transformerless Photovolatic Power System

With the rapid development of the modern society,energy shortage and environmentpollution have the impact on people’s normal production and life,thus,people need to changetraditional energy thinking to search for cleaner energy instead of fossil energy.Photovoltaicgeneration is very popular for its merit of abundance,safety and no pollution,so more andmore experts have their efforts to research for more effective and secure photovoltaicgeneration technology. Under this background,the contents of the research in the paper are theefficient output of photovoltaic power,the grid-connected control of photovoltaic generationand the reliable transformerless topology.Based on analysis of working principle and control effect of traditional MPPT controlalgorithms, the problem that traditional algorithms can not balance between tracking speedand accuracy is pointed out.Through the research in output characteristic of photovoltaic array,a staged variable step size incremental conductance algorithm is proposed to solve the conflictbetween tracking accuracy and speed,and improve the output efficiency of the photovoltaicgeneration.In the aspect of grid-connected control of photovoltaic generation system, the newSPSVPWM-deadbeat control strategy is proposed,DC bus voltage as outer loop and gridcurrent as inner loop.Through the three points discrimination method,the new strategy cancarry out real-time inductance identification to overcome the flaw of traditional deadbeatcontrol depending on precise mathematical modelling,improve the accuracy control of outputcurrent under external changing conditions and ensure high quality of output current.To solve the potential safety hazard of common mode leakage current of transformerlessphotovoltaic generation system,firstly the cause of leakage current is analysed.On this basis,an improved Heric topology is researched that can keep high efficiency and improve thecapacity of leakage current suppression.Furthermore, based on the electrical specifications of3kW photovoltaic power system,hardware and software of the system are designed.The hardware part includes drive circuit,sample circuit,protection circuit and power supply circuit. The software part includes mainprogram, digital phase subprogram and PWM subprogram. At last, the new designedphotovoltaic generation system is verified by Matlab simulation and experiment.Results ofsimulation and experiment suggest that new control strategy and transformerless topology canmake the use of photovoltaic power in a safer,steadier and more efficient way.