Research On Low-Power Photovoltaic Grid-Connected Inverter

Distributed photovoltaic technology has been developed rapidly and becomes a hot research topic, in recent years. As the core part of distributed photovoltaic grid-connected system, low-power photovoltaic inverter with appropriate MPPT can greatly improve the efficiency of photovoltaic grid-connected system. This thesis focused on researching topology, MPPT technique, and the quasi proportional resonant control of low-power photovoltaic grid-connected inverter.This thesis studied output characteristics of photovoltaic module in single illumination and partial shading condition. And the Two-Step MPPT method was improved based on output characteristics when PV cells under the partial shading. The improved algorithm combined the advantages of both particle swarm optimization (PSO) and incremental conductance method (INC). When illumination changes the new method finds the range of the MPP using PSO, and then use INC to track the maximum power point.The thesis analyzed the working principle and control method of the inverter, used quasi PR control in the current inner loop, eliminated the interference brought by the grid voltage fluctuation, and improved the reliability of the system. By adding power feedforward control, the thesis improved the dynamic properties of photovoltaic system.In the end, this thesis designed the hardware of the low-power single-stage photovoltaic grid-connected inverter, including the inverter circuit, control circuit, signal sampling and conditioning circuit; at the same time, the paper designed the software, including the MPPT and the grid current control. And the feasibility of MPPT algorithm is verified by experiment. The THD of inverter output current met the grid requirements.