Research On The Control Of Photovoltaic Grid-connected Three-Phase Four-Leg Inverter

With the serious energy crisis and environmental pollution,the new energy is particularly important.Solar energy has become an ideal alternative energy in the international community because of its unique advantages,making the grid-connected photovoltaic system become a hot research in the new energy development.In this paper,the photovoltaic grid-connected system as the research object,the characteristics of photovoltaic battery,the maximum power point tracking control technology,control strategy of grid-connected inverter system,islanding detection technology are deeply studied.In this paper,the engineering mathematical model of photovoltaic cells is analyzed,established the simulation model,analyzed three common algorithms and the conductance increment method is selected,and the effect of temperature and light intensity on the output power of photovoltaic system is analyzed.Then the control strategy of common grid-connected inverter is analyzed,and the method of the grid-connected current tracking of the hysteresis current control strategy is selected.According to the switching frequency of the common hysteresis current control strategy has great influence and great loss of current,two algorithms are proposed: the algorithm based on the integration method and the algorithm based on the least square method.Through the simulation model,it shows that the two algorithms have the advantages of maintaining the hysteresis current control algorithm and the stability of hysteresis switch frequency.Three-phase photovoltaic grid-connected system usually uses three-phase half-bridge topology grid-connected inverter to achieve grid-connected,but for unbalanced load,three-phase four-leg inverter can better power supply,the three-phase four-leg bridge arm inverter,three-phase four bridge arm each phase switch control still interference,so this system is difficult to use single-phase grid-connected system hysteresis current control algorithm.In order to apply the mature three phase three bridge arm control strategy to the four bridge arm.The simulation results show that the constant frequency hysteresis current control algorithm is feasible in the three-phase four photovoltaic grid-connected system,and can realize the high quality sine wave with the same frequency and same phase to the grid voltage.Finally,the two methods of island effect are simulated and verified,the two methods can meet the requirements,the application part of the GUI,can make the user more convenient calling system module,the observation results are analyzed.