Research On Power Compensation Of Grid-Connected PV Systems

With the rapid increase of global fossil energy consumption, the world-wide energy crisis has already arrived. The large-scale exploitation and utilization of fossil energy also wreak havoc on the natural environment that we are living in. The energy has becoming the bottleneck problem of social progress, economic development and ecological conservation. Under this circumstance, the development and utilization of renewable energy have caught the worldwide attention. With some merits such as inexhaustible supply, wide distribution, non-pollution, the photovoltaic (PV) has becoming an important green energy to resolve the problems of energy crisis and environment pollution. When PV is utilized, the grid-connected PV system is the most efficient way to utilize solar power.A novel grid-connected PV system is constructed in this thesis, which can realize the function multiplexing, improve the power quality, reduce the system loss, and save the equipment investment. The emphasis of his thesis is focused on some key theoretical and technical problems in the active and reactive power compensation control of the designed grid-connected PV system, such as the maximum power point tracking (MPPT) based on least squares support vector machine (LS-SVM), active power stabilization based on the hybrid energy storage system consisted of super-capacitor and battery, the integrated control of power generation and reactive power compensation based on space vector pulse width modulation (SVPWM). Based on the presented theory and technology, the simulation and experiment are carried out, whose results show the efficiency of the designed topology and control strategy. The detailed contents and achievements are as follows:(1) A novel two-stage schedulable grid-connected PV system is presented and designed based on the analysis of grid-connected PV topology and operation-feature comparison of different systems. The operation principle and mathematical model of main components are also studied.(2) A simplified mathematical model of PV component is presented. The current-voltage and power-voltage characteristics of PV component under different solar radiations and working temperatures are also studied.(3) A MPPT strategy and method is presented based on LSSVM. To overcome the incapability of coordinating stability, mis-tracking, multiple peak values, a novel LSSVM-based MPPT control strategy is presented. The simulation comparison among constant-voltage control, perturb&observe method, and LSSVM method is carried out, whose results shows the superiority of LSSVM tracking strategy.(4) A novel active power stabilization strategy based on hybrid energy storage system consisted of super-capacitor and battery is presented. To fully take the advantages of super-capacitor and battery and improve the power output capability, this stabilization strategy is presented and the corresponding stabilization system is constructed based on the analysis of model and performance characteristics. The simulation and experiments are also made, whose results show the superiority of the presented method.(5) An integrated control strategy is presented based on SVPWM. To expand the functions of grid-connected invertor, an integrated control strategy of power generation and reactive power compensation is presented based on the analysis of main circuits of grid-connected invertor and static synchronous compensator (STATCOM). The four-quadrant running principle is analyzed and SVPWM generation procedure is studied. The calculation and allocation method of switch-on time of switch tubes are also researched. The integrated control system of power generation and reactive power compensation is constructed and the corresponding simulation is carried out.(6) The simulating platform of grid-connected PV system is constructed and the grid-connected PV digital control system is designed based on DSP and FPGA. The concerned hardware and software are designed. The experiment is also carried out and the results show the correctness of the design and control strategy. The conclusion and perspective are given at the end of the dissertation.