Design Of Push-pull Micro Photovoltaic Inverter

In distributed photovoltaic power generation system,the micro inverter that can track the maximum power point of a single photovoltaic cell greatly improves the overall power generation efficiency of the system,but the micro grid-connected photovoltaic inverter on the market generally has a power of about 500 W.In this paper,a micro grid-connected photovoltaic inverter with fixed power of 700 W is designed for the photovoltaic modules with power level of 600 w to 800 W newly appeared in the market.The common DC-DC topology and DC-AC topology are studied,the push-pull boost transform topology is selected for the front stage,and the full-bridge inverter topology is selected for the rear stage.The working principles of the two topologies are analyzed,and the feasibility of the topology is verified by the simulation model.In commonly used maximum power point tracking（MPPT）control method is studied,and the variable step disturbance observation method increased the integral element,on the basis of the guarantee system dynamic response speed and eliminate the power oscillation near the maximum power point,establish simulation model,by comparing three kinds of disturbance observation method,the control effect is verified to increase integral link of variable step disturbance observation method is feasible.The design method of high-frequency push-pull transformer is studied,the key parameters of front and back main power circuits are calculated,the components needed for hardware circuit are selected,and the schematic diagram and PCB of main power circuit and control system circuit are designed.The mathematical model of the main power circuit of the front and back stages is established,the voltage and current double closed-loop control algorithm of the push-pull converter is designed,the MPPT control algorithm is designed,and the phase-locked algorithm based on the second order generalized integrator is designed.The feasibility of the algorithm is verified by the simulation model.The control algorithm is written by CCS6.1.3,and the experimental prototype is designed and built based on DSP28335.The oscilloscope is used to observe the output voltage and current waveform of the main circuit of the front and rear stages,which is consistent with the simulation results,proving the feasibility of the design.