Research On Single-phase Full-bridge Grid-connection Photovoltaic Inverter With Low Leakage Currents

In the era of rapid development of human society,the reduction of fossil energy reserves,environmental pollution and other problems cannot meet the needs of human energy.The characteristics of solar power generation with clean,sustainable and large scale development have become an important way to solve human energy.As an energy converter,PV grid connected inverter is the most important part in the photovoltaic power generation system.The non-isolated PV grid connected inverter has the characteristics of small size,light weight,low cost and high efficiency.In the absence of electrical isolation of the transformer,the inverter will produce common mode leakage current causing potential damage to workers and equipment.In this paper,in order to improve the common mode leakage current characteristics and improve the efficiency of the inverter,this paper makes a thorough study.Firstly,the development of inverter in photovoltaic power generation system is outlined,and the mechanism of common mode leakage curre nt in non-isolated PV grid connected inverter is analyzed,and the common mode equivalent circuit of single-phase full bridge inverter is deduced.The equivalent circuit model is used to analyze the common mode leakage current characteristics of PV generat ion system with different PWM modulation strategies,and the way to suppress common mode leakage current is also pointed out.The simulation is carried out through the full bridge circuit.Secondly,the working principle of the typical H5 topology and the Heric topology and the common mode leakage current characteristics are analyzed.The derivative topology with their characteristics is compared and analyzed,and a new type of six switch topology is proposed.Through the derivation and working mode analysis of the new topology,it has better ability to suppress the common mode leakage current and work efficiency than the H5 and Heric topology.Then,through the analysis of the parasitic capacitance and parameters of the typical topology,this paper cannot ensure that the common mode voltage is completely constant by constructing a new continuous current loop.Due to the charge and discharge of the parasitic junction capacitance at high frequency,there is a high frequency pulse in the common mode voltage of the inverter in the state of the current flow.In order to ensure that the common mode voltage of the inverter is constant,it is necessary to improve the structure of the circuit by clamping.The new topology of the new topology proposed in this paper is improved by the clamp method,and the improvement effect of the common mode leakage circuit characteristics is verified by simulation.Finally,through the theory application of grid connected inverter system,a prototype platform of non-isolated photovoltaic grid connected inverter is designed and completed.By comparing experiments,we verify the common mode characteristic and efficiency of the new topology.