Research On Modulation Methods And Common Current Suppression Of GaN-Based Transformerless Inverter

With the increasingly severe energy consumption and environmental pollution,renewable energy power generation technology has become a hot spot in modern applications.Among them,photovoltaic power generation has attracted much attention.At present,photovoltaic inverters on the market are mainly divided into two types: transformer and transformerless.Transformerless inverter has become a research hotspot because of small size,light weight,high efficiency,and low cost.However,the presence of parasitic capacitance of the photovoltaic array in the transformerless inverter causes common mode current in the circuit,which reduces the safety and reliability of the system.In order to effectively suppress the common mode current and meet the requirements of high power density and high efficiency of modern inverter systems,it has become a new trend in the research of transformerless inverter.Based on this background,this paper conducts the following research on GaN-based transformerless inverter.Firstly,this paper analyzes the operation characteristics of two mainstream types of GaN devices,E-Mode and Cascode GaN.Based on the LTspice software,the switching performance of two GaN devices is analyzed.In addition,the first quadrant and the third quadrant characteristics of two GaN devices are compared and analyzed in detail.To reduce the conduction loss during the third quadrant operation,it is given that sufficient driving voltage should be applied to ensure that the GaN device can be the best operation point.The analysis provides a theoretical basis for the application of GaN devices.Secondly,based on full-bridge inverter topology and from the perspective of the modulation methods,the operation principle of full-bridge inverter based on different modulation methods is analyzed in detail,and the high-frequency common-mode equivalent models are established.A high-frequency common-mode equivalent model of unipolar single-arm chopping modulation method based on single-inductance filtering is proposed,and the modulation methods is adapted and optimized by considering high efficiency and low common-mode current.Aiming at the problem that thermal stress of high-frequency switches of full-bridge inverter based on unipolar single arm chopping,same arm complementary modulation method,a carrier phase shift control based on the unipolar dual-arm chopping and complementary modulation method of the same arm is researched for the single-phase interleaved full-bridge inverter topology.The operation principle,common-mode current characteristics and current ripple characteristics are analyzed in detail.Then,the hardware design process of the GaN-based full-bridge inverter is explained in detail,and a 2k W experimental prototype is built to verify the feasibility and correctness of theoretical analysis.Finally,a improved Dual-Buck inverter topology is proposed,and a unipolar asymmetric modulation method based on carrier phase shift control is proposed.Theoretical and simulation analysis shows that the circuit topology effectively improves the utilization of the inductor,reduces the current ripple,and has good common-mode current characteristics.The theoretical analysis is verified by a 1k W improved Dual-Buck inverter simulation prototype.