The Study On Modulation Scheme Of Single Phase Zero-Voltage-Switching Inverter

With the development of distributed generation, low-power PV inverter will be widely used. Due to the low-power photovoltaic inverter installed in residential, urban commercial buildings, it is desirable to minimize the weight and volume of the low-power photovoltaic inverter, while increasing conversion efficiency of the PV inverter is still the pursued goal. In this paper, the household small power photovoltaic inverter is selected as the research subject. And the attention is paid on the startup problem and ground current suppression problem during grid connected operation of the single phase Compound-Active-Clamping (CAC) Zero-Voltage-Switching (ZVS) inverter.The classification of the single-phase PV inverter and the mainly single-phase inverter topology are introduced in the first chapter. The common-mode voltages of these topologies with corresponding modulation are analyzed. The single-phase CAC ZVS inverter topology is described in details. The ground leakage current safety rules and the methods to suppress the ground leakage current are introduced at last.The soft switching inverter startup stage problem is analyzed in the second chapter and the reason of the high voltage stress of the auxiliary switch in the startup stage is presented. Three different clamping capacitor pre-charge methods and corresponding voltage stress suppression effects are described. Theoretical and experimental results show that the optimized pre-charge method can effectively reduce the voltage stress of auxiliary switch in the startup stage.In the third chapter of this paper, the common mode equivalent model of the soft switching inverter is established. The possible switch combinations of the soft switching inverter in grid-connected PV application are analyzed. The similarities and differences between the ZVS inverter and hard switching full-bridge inverter of the common mode characteristic are analyzed. The bipolar soft switching PWM modulation scheme is chosen as the research subject. The working principle of the ZVS inverter circuit is analyzed and the corresponding soft-switching conditions are calculated. According to the obtained common-mode equivalent circuit and the common-mode circuit parameters, the grid ground current with bipolar soft switching modulation of the CAC ZVS inverter is calculated. The ZVS on of all the power devices and grid-connected operation with the bipolar PWM scheme are realized on the hardware platform of a3kW inverter. The ground leakage current waveforms are measured and its suppression effect is analyzed.Theoretical and experimental results show that compared with the conventional soft switching modulation, soft-switching inverter grid ground current can be effectively suppressed by using soft switching bipolar modulation scheme.The calculation of the loss is analyzed in the fourth chapter the paper by using bipolar soft switching PWM Modulation scheme. The efficiency is calculated and tested. The loss distribution and efficiency between bipolar zero voltage switching modulation scheme and traditional double frequency zero voltage switching modulation scheme are compared. Analysis shows that, by using bipolar zero voltage switching modulation scheme, the resonant inductor current effective value is greater and then the loss of auxiliary branch is greater. Then the conversion efficiency is lower with the same parameters.