Research On Soft Switching Photovoltaic Grid-Connected Inverter Based On Intermediate Pulsating Voltage

Since the 21 st century,the energy crisis and environmental pollution have continuously promoted the rapid development of the new energy industry represented by photovoltaic power generation.As a bridge connecting photovoltaic cells and power grids,photovoltaic grid-connected inverters have always been research hotspots,and Their power conversion Performance plays a crucial role in the stable operation of the system.In this paper,With high efficiency and miniaturization as the research goal,a new type of DC/DC converter structure-Magnetic Energy Recovery Switch will be adopted in two-stage non-isolated photovoltaic grid-connected inverter,which can effectively reduce the grid-connected inverter volume,realize the soft-switching operation of the switch tube by using the resonance of the capacitance and line inductance of the MERS structure,and generate high-Frequency DC on the intermediate DC side.The pulse voltage is used as the input of the inv erter.The tri-state DPM(DisCrete pulse Modulation)current hysteresis tracking modulation strategy is used to control the on/off of the inverter switch tube in the zero-crossing interval of the high-frequency pulse voltage to realize the soft switching of the inverter bridge.In the paper,the DC/DC boost side of the two-stage photovoltaic grid-connected inverter is studied firstly.The MERS-based DC/DC converter structure and soft-switching operating characteristics are introduced.The simulation proves the resonance process and soft-Switching operating characteristics of MERS.Several commonly used Maximum Power Point Tracking(MPPT)techniques are analyzed.Based on this,a photovoltaic-MERS simulation model based on the optimal gradient method is built.The simulation results achieve maximum power point tracking and MERS Switching devices.It is in the soft switch operation state.Secondly,the DC/AC inverter side of the two-stage PV grid-connected inverter is studied.Based on the DC high-frequency pulse voltage output from the former MERS converter,the Hysteresis-loop tracking control strategy based on tri-state DPM Is proposed,which used in soft-switching grid-connected inverter,the working process of the tri-state DPM grid-connected inverter is analysed detaily and construction of the simulation model for analysis and verification is builted,the simulation waveform verified the basic working The overall control method of the tri-state DPM inverter,further Ground,the MERS converter and the tri-state DPM inverter are cascaded to form a soft-switching photovoltaic grid-connected inverter based on the intermediate ripple voltage.The system is proposed and the simulation model is built for analysis.The simulation results show that the proposed grid-connected inverter has good grid-connected performance and MPPT tracking performance,and the front-end power tubes operate in soft-switched state,which verifies the theoretical correctness of the system.Finally,the hardware design of the system is introduced,including the design of the main circuit and the control circuit.The experimental platform is built for experimental verification.The experimental waveforms and data are basically the same as simulation results,indicating the Correctness of the proposed topology and the effectiveness of the proposed control method.Compared with the traditional two-stage photovoltaic grid-connected inverter,the full-power devices in the novel structure proposed in This paper operate are in the soft-switching state,and greatly reduce the volume of DC-side capacitance,further adapting to therequirement for miniaturization and efficiency of the photovoltaic grid-connected system.