Research On Single-phase Grid-connected PV Systems

In recent years, the development of renewable energy has become a research hotspot, in order tosolve the problems of energy and environment facing humanity. Solar energy has been paid moreand more attention because of its own advantages.And it is expected to become the major energysource of human in the future. The establishment of large-scale gird-connected PV systems will bethe main way of using solar energy with the continuous development of power electronicstechnology. Some important issues of grid-connected PV systems are reaserched in the paper basedon the background.The topology of the system in the paper is determined by analysising several different structuresof the single-phase grid-connected PV systems.Solar cell is the carrier to convert solar energy into chemical energy, it is the core of the wholesystem. The solar cells are usually composed of photovoltaic modules and photovoltaic arrays bythe way of series and parallel for power generation. The mathematical models of solar cell,photovoltaic module and photovoltaic array are established through the equivalent model of solarcell. MATLAB/Simulink is used to study the output characteristics of photovoltaic array under theconditions of the changes of light intensity and temperature and partial shadow.Several conventional maximum power point tracking(MPPT) methods are analysised andcompared. In order to ensure accurately tracking, the improved incremental conductance method isused acrroding to the multimodal nature of the PV array outputs under the condition of partialshading. The improved algorithm achieves good results by the simulation.The double-loop control strategy based on bipolar SPWM modulation is proposed. The controlstrategy of voltage and current double closed loop and the settings of PI parameters are studieddetailedly. The Simulations of single-phase grid-connected PV system are used to verify thecorrectness of the double-loop control strategy.