Design Of Single Phase Non-isolated Photovoltaic Grid-connected Inverter Based On H6 Bridge

Photovoltaic grid-connected inverter is the core device for power conversion and control in photovoltaic power station.In order to achieve higher power conversion efficiency,the research on topology of photovoltaic grid-connected inverter is gradually flourishing.A non-isolated and non-transformer topology becomes the mainstream.The first problem solved by this topology is to suppress common mode current.Therefore,this paper studies a new type of single-phase non-isolated photovoltaic grid-connected inverter with H6 structure to effectively suppress the common mode current.Firstly,this paper studies the MPPT control method,which is based on the Simulink simulation of photovoltaic cells,after analyzing the P-V and I-V characteristic curves,a MPPT control algorithm based on Hermite interpolation calculation is proposed;Secondly,taking H4 full bridge inverter circuit as the research object,the generation principle of common mode current is analyzed,and the influence of unipolar and bipolar PWM modulation on common mode current is simulated and compared.Through the analysis of common mode current suppression,this paper selects Boost topology and H6 topology respectively,and verifies that H6 topology can suppress common mode current better through Matlab2018a/Simulink simulation tool;At the same time,the H6 topology is mathematically modeled,combined with the grid-connected current control strategy,and the Bode diagram is used to judge the response of the system.The PI,PR and QPR controllers are compared respectively.The comparison results show that this paper chooses the grid-connected current control based on QPR control.The technology can realize signal tracking without static error and strong anti-disturbance ability.Finally,the hardware and software circuit of H6 bridge photovoltaic grid-connected inverter is designed by taking DSP of TI company as the main control chip.The hardware design analyzes in detail the selection of the switch tube,the design of the grid-connected filter,the design of AC and DC sampling circuits and the design of the drive circuit;the software design mainly analyzes the design of the main program,the program design of the SPWM algorithm,and the design of the digital phase-locked loop.;And set up an H6 bridge non-isolated photovoltaic grid-connected inverter experimental platform in the laboratory for experimental research,and verify the feasibility of the design in this paper through experimental results.