Research On Single-tube Resonant Single-stage Photovoltaic Micro-inverter

At present,most of the micro-inverters on the market use a flyback topology as a basic circuit.The circuit topology has problems such as one-way excitation of the transformer,low utilization of the magnetic core,and low power.To this end,a single-stage photovoltaic micro-inverter based on a single-tube resonant circuit and its control method are studied,which effectively solves these problems.The specific work is as follows:In this paper,the home distributed photovoltaic micro-inverter is the main research object.Firstly,the characteristics of the flyback circuit,the forward circuit and the singletube resonant circuit are compared and analyzed.The leakage inductance in the flyback circuit affects the efficiency of the circuit.And power,forward mode requires flux reset windings,and single-tube resonant circuit can improve these shortcomings,and finally determine the single-stage photovoltaic micro-inverter structure based on single-tube resonant circuit.The characteristics and working process of the single-tube resonant circuit are systematically analyzed,and the equivalent model is established.The most important LC resonant circuit in the circuit is analyzed in detail.Based on the analysis of the characteristics of the main circuit,the main parameters of the main circuit,including the switching frequency,the resonant circuit and the energy storage type high frequency transformer,are designed and calculated.Aiming at the characteristics of single-tube resonant circuit,an MPPT control method combining PWM and PFM and a novel SPWM control method are proposed.Based on dsPIC30F2020,the control circuit and its partial sampling circuit are designed,including the voltage and current sampling circuit of the photovoltaic panel,the voltage and current sampling circuit of the grid,the analysis of the ADC and PWM modules used and the microinverter control structure.The final software control flow and the overall control block diagram of the circuit.A comprehensive comparison of different simulation software was carried out.Finally,PSIM was used as the main simulation software,and the main control methods were simulated and analyzed,including MPPT control and SPWM control methods,and some programs were annotated.The PCB was drawn and a simple experimental platform was built.The program was programmed,and the off-grid experiment was carried out.The experimental results were analyzed to verify the feasibility of the circuit topology and control method proposed in this paper.