Research On GaN High-efficiency And High Power Density Single-phase Inverter Based On TCM Modulation

Photovoltaic power generation has become the fastest-growing form of various renewable energy sources.In recent years,the residential photovoltaic system has developed steadily and is expected to become an important role in China achieving carbon emissions peak and carbon neutrality as scheduled.In the residential photovoltaic system,the single-phase photovoltaic inverter is an intermediate link connecting electrical equipment,photovoltaic cells,and the external power grid.Improving the efficiency and power density of the single-phase inverter is beneficial to improving the user’s power utilization rate and reducing installed costs.The Gallium Nitride(GaN)inverter based on Triangular Current Modulation(TCM)is a current research hotspot.In order to optimize the efficiency and power density of the TCM-based single-phase inverter,the efficiency improvement of the main power inverter circuit,the DC secondary ripple suppression circuit,and the compact design method of the Electromagnetic Interference(EMI)filter is discussed respectively,in this paper.The switching frequency range of TCM modulation is too high in the symmetric H-bridge inverter topology,resulting in excessive losses.The published methods for limiting frequency have problems such as waveform distortion,partial hard switching,and excessive conduction losses.Therefore,a hybrid modulation method based on the principle of optimal efficiency is proposed to limit the frequency in this paper.Firstly,the loss is optimized based on the accurate GaN loss model and the inductor loss model.And then the influence of the hybrid TCM modulation ratio on the loss of the single-phase inverter is analyzed.It is found that there is an optimal hybrid modulation ratio with the highest efficiency.The lower switching frequency and higher efficiency are guaranteed in the full load range.Finally,the efficiency improvement of the optimized H-TCM modulation is verified by building a 1 k W single-phase inverter,whose power density reaches 120 W/in~3,peak efficiency is 98%,and light-load efficiency is 0.8%higher than that of TCM.The DC side parallel Buck circuit can realize the DC side secondary ripple suppression with a small volume and weight.The modulation s of this circuit currently given in the literature mainly include Continuous Current Mode(CCM),Discontinuous Current Mode(DCM)and TCM modulation.The efficiency and power density of this circuit are not comprehensively optimized.In this paper,the law of the efficiency and power density of the parallel Buck circuit with the decoupling capacitance,the initial capacitor voltage,the decoupling inductance and the energy storage margin under different modulation methods is analyzed at first.The preliminary analysis shows the potential of TCM modulation to achieve high efficiency and high power density is the highest.And then an efficiency-optimized hybrid TCM strategy is used to optimize the light-load efficiency.Finally,a parallel Buck decoupling circuit is built for the 1-k W single-phase inverter.The power density of the inverter including the Buck decoupling circuit reaches 88 W/in~3.the peak efficiency reaches 98.6%,and the light load efficiency is 1.2%higher than that of the TCM modulation,which verifies the efficiency improvement of the hybrid TCM modulation.After adopting the TCM modulation with the switching frequency variation,the method based on the envelope detection model of the EMI receiver needs to be used for EMI noise prediction and filter design.However,the prediction range of the existing prediction methods is all lower than 1 MHz,and the prediction error in the high-frequency range is very large.In this paper,an improved EMI noise prediction method is proposed.By establishing an accurate drain-source voltage model considering the TCM resonance process,a noise gain model considering the parasitic parameters of passive devices,and a more accurate EMI receiver envelope detector model,the predictable frequency range can be expanded,and the rapid iteration of the EMI noise analysis of the TCM modulation converter at high switching frequency is realized,which effectively saves the time cost of filter design.Finally,an output EMI filter is designed for a 1 k W single-phase inverter built above.The offline EMI prediction can improve the space utilization rate of the converter.In the converter design stage,both the filter and the circuit can be considered together to achieve a compact layout.After adding the EMI filter,the power density of the inverter also reaches 88 W/in~3.Relevant EMI tests show that the inverter can meet the conducted EMI standard EN55022 class B under all load conditions.