Research On Control Strategy Of Soft-switching Photovoltaic Grid-connected Inverter Based On LC Resonance

In recent years,as environmental problems have become increasingly serious and the demand for clean energy has increased,among many new energy sources,photovoltaic power generation has high development potential because it is not restricted by resources and the environment,so it has been favored by people.Photovoltaic inverters,as the core components of photovoltaic arrays and power networks,are the key to the research.Among them,non-isolated grid-connected inverters have great application prospects due to their light weight and high power density.This paper takes miniaturization,high efficiency,and low leakage current as the research goals,and proposes a soft-switching photovoltaic grid-connected inverter based on LC resonance.The front-stage DC/DC converter realizes soft switching operation through the resonance of the line inductance and the DC capacitor;the latterstage DC/AC converter uses the high-frequency pulsed DC voltage generated by the previous stage as the input,and adopts the sliding mode-discrete pulse modulation strategy to complete the The grid connection of the converter reduces the leakage current at the same time.This paper proposes a DC/DC converter based on LC resonance for the front stage of a two-stage non-isolated photovoltaic grid-connected inverter.First,it introduces the front-end topology Boost converter of the traditional two-stage structure,and briefly analyzes its advantages and disadvantages.Secondly,the operation mode of the DC/DC converter proposed in this paper is analyzed,and then the maximum power point tracking(MPPT)control strategy of photovoltaic cells based on sliding mode variable structure algorithm is introduced in detail,and compared with the traditional disturbance observation Method for comparative verification.Finally,the simulation shows that the structure and control method can realize the soft switching function and MPPT control of the front stage of the photovoltaic grid-connected inverter.This paper proposes a sliding mode-discrete pulse modulation strategy for the latter stage of the two-stage non-isolated photovoltaic grid-connected inverter.Firstly,the reason and mathematical model of the leakage current of the subsequent DC/AC converter are introduced,as well as the influence of the modulation strategy on the leakage current of the single-phase full-bridge structure.Secondly,it analyzes the working process of soft-switching operation and grid connection of the DC/AC converter under the condition of high-frequency pulsed DC voltage as input.Then the back-stage topology of this article uses LCL-type grid-connected inverters,and inserts a common mode inductor on the DC side;the back-stage control method is a sliding mode-discrete pulse modulation strategy,which can achieve unity power factor gridconnected,and the inverter’s Soft switching operation and reduced leakage current.Finally,a simulation model is built for the front and rear two-stage converters to verify the correctness of the proposed photovoltaic grid-connected inverter structure and the effectiveness of the control strategy.Finally,an experiment platform was built to design the hardware circuit and software program.The experimental waveforms of the soft-switching photovoltaic grid-connected inverter based on LC resonance proposed in this paper are basically consistent with the simulation results.Compared with the traditional two-stage nonisolated photovoltaic grid-connected inverter,the topology and control strategy proposed in this article can reduce the DC side inductance and capacitance,and realize soft switching operation,reducing losses and leakage current.Meet the development requirements of miniaturization,high efficiency and safety of photovoltaic gridconnected systems.