Research On Integrated Control Strategy Of PR And MPPT For Single-stage Photovoltaic Grid-connected Inverter

With the growing urgency of the global energy situation, photovoltaic generation hasbeen developing rapidly as one of the most feasible way to effectively alleviate the energypressure. In recent years, grid-connected PV systems have become a research hotspot inboth domestic and overseas, which relates to the maximum power point tracking control,grid connected inverter control and islanding detection, etc. This thesis mainly investigatesthe integrated control strategy of PR and MPPT for single-stage photovoltaicgrid-connected inverter.Firstly, this thesis highlights the importance of developing renewable energy byanalyzing the pattern of world energy and various environment problems caused by thefossil fuel; summarizes the development status and trend of grid-connected PV system athome and abroad, as well as topologies of the system in common use at present andexisting typical control techniques of PV inverter.Secondly, the overall structure block diagram of a single-stage grid-connected PVsystem is presented, the working principle of the PV cells is analyzed and the engineeredmathematical model of photovoltaic cells is given; the mathematical model of thesingle-stage photovoltaic grid-connected inverter is established, moreover, its outputharmonic is also analyzed and the output filter is designed; transmission lines and gridmodel which are necessary for grid-connected system is illustrated briefly.Next, based on the mathematic model of the inverter system established under α-βcoordinates, an integrated control strategy for single-stage photovoltaic grid-connectedinverter, which combines PR control with MPPT control and is of outer power loop andinner current loop, is put forward in this thesis to achieve both zero error maximum powerpoint tracking (MPPT) and unity power factor control. The parameter design method of thePR controller, which combines the root locus and frequency characteristics methods, isgiven and its parameters have been designed; The current-searching based variable-stepincremental conductance method for MPPT of PV arrays is put forward, and the singlesynchronous reference frame–phase locked loop (SSRF-PLL) is designed for thisapplication. At last, the simulation model for a single-stage grid-connected PV system of10kW isestablished in the Matlab/simulink environment, and the simulation study is carried out.Simulation results show that under the conditions of standard illumination，illuminationchanges and whole day illumination, the integrated control strategy can fast trackillumination changes, and achieve zero error maximum power point tracking(MPPT) andunity power factor control so that the system has obtained excellent dynamic and staticperformance.