Research Of Grid Connected Photovoltaic Inverter Based On Direct Power Control

Photovoltaic(PV) grid inverter is the core of PV grid power generation equipment, thus improving the reliability of the inverter device, safety and efficiency of PV power generation become one of the research hot spot. In this paper, the grid connected PV inverter based on direct power control is studied and the PV grid system model, PV cells MPPT method, the instantaneous power theory, the direct power control principle are analyzed. The MPPT tracking method and the direct power control strategy are studied deeply in this paper, and improvements on this basis to improve system performance are suggested.This paper studies the maximum power tracking algorithm of PV cells, puts forward a new kind of variable step disturbance observation method. In the Matlab/Simulink environment, the simulation model is established, and the simulation results show that the algorithm can improve the tracking speed and precision of the maximum power, and also can restrain the oscillation phenomenon at the maximum power point.To improve the dynamic performance of pv grid inverter, the paper based on the theory of instantaneous power establish the mathematical model of the inverter circuit and study the direct power control strategy based on the power of hysteresis comparator. Analyzed the principle of hysteresis comparator, and the influence of hysteresis width of the output power. Switch table according to the power output of the hysteresis comparator and the vector Angle of the grid voltage vector give the PWM signal, and then adjust the output power. Analyzed the traditional principle of the structure of the power switch table, discusses the control inverter output power of its rapid limitations. A new type of switch table are presented, and simulation results in Matlab/Simulink environment. Experimental results verified the new switch table performance than traditional switch table performance improved.This paper also studies the direct power control strategy based on virtual flux. Based on the analysis of the virtual flux observer based on the low pass filter, an improved virtual flux observer is proposed. Under the environment of Matlab/Simulink simulation, the simulation results show that the modified virtual flux observer tracking virtual flux circular faster and better.