Research On Leakage Current Suppression Technology Of Three-phase ZVR Inverter With Different Clamping Modes

As the core part of photovoltaic power generation technology,photovoltaic inverter determines the development of photovoltaic power generation technology.The isolated photovoltaic inverter with transformer has the disadvantages of large volume,heavy weight,high cost and low conversion efficiency,while the non isolated photovoltaic inverter,because the removal of transformer as electrical isolation,causes leakage current in the inverter system,which endangers the safety of operators and equipment,so the leakage current must be restrained within the allowable range.Based on the improvement and innovation of the traditional three-phase inverter,this paper proposes a topology and modulation strategy of three-phase ZVR inverter with different clamping modes.The new three-phase inverter proposed in this paper is to add a continuous current circuit at the AC side of the inverter.The continuous current circuit is composed of a switch tube and three-phase uncontrolled rectifier bridge in parallel.At the same time,three partial voltage capacitors are introduced at the DC side of the inverter.The input voltage is divided into four potential points:0,1/3,2/3 and 1.Two clamping switches are added at 1/3 and 2/3 potential points to make the common mode voltage of the inverter It can be clamped at 1/3 or 2/3 of DC input voltage in the whole inverter cycle.With the increase of auxiliary circuit,compared with the traditional three-phase inverter,the common mode voltage of the new inverter is reduced from the original four changes to two changes,and the change range of the common mode voltage is reduced from 0?U_PV(U_PV is the DC input voltage)to U_PV/3?2U_PV/3,which reduces the amplitude of the common mode voltage and thus plays the role of restraining the leakage current of the system.At the same time,there are two different clamping modes for the two clamped switches:forward clamping mode and reverse clamping mode.In the forward clamping mode,the common mode voltage frequency is the switching frequency,while in the reverse clamping mode,the common mode voltage frequency is three times of the switching frequency,which increases the common mode loop impedance.Therefore,the reverse clamping mode is better than the forward clamping mode in the effect of suppressing the leakage current of the system method.In this paper,the common mode equivalent model of the non isolated three-phase inverter is analyzed firstly,and two methods to suppress the leakage current of the system are obtained.Secondly,the topology and working principle of the new three-phase inverter are introduced in detail,and the theoretical simulation results are given.Finally,a principle prototype of single-phase output 200W is designed.The overall structure of the prototype and the design process of each circuit parameter are introduced The correctness of the theoretical analysis is verified by the prototype experiment.