A Clamped Three-phase Transformerless Inverter For Restraining The Leakage Current

With the elimination of the transformer part for electrical isolation,the transformerless photovoltaic inverters can reduce the volume and weight effectively,as well as improve the efficiency of the inverter system.Therefore,the study of transformerless photovoltaic inverter has received more and more attention of scholars.And the research of transformerless photovoltaic inverter is more and more deeply.Due to the PV inverter connected with the grid directly,scholars have found that the common mode leakage current in the inverter would harm the power grid and endanger personal safety.So,based on the three-phase transformerless photovoltaic inverter topology,this paper proposed a new clamped three-phase transformerless inverter with a freewheeling switch.The proposed inverter topology can suppress the change of common mode voltage and reduce the leakage current effectively.A freewheeling circuit and a clamping circuit to reduce the common-mode voltage variation during the inverter work have been added into the proposed improved topology.First of all,this paper introduces several transformerless three-phase inverter topologies which can suppress common mode leakage and several frequently-used control methods of the inverters.Secondly,it introduces reasons of generating common mode leakage current by the modeling and analysis of transformerless inverters.The control method of suppressing the leakage current is given.Then an improved topology is proposed which is based on the simulation and analysis of the general three-phase transformerless inverter topology.At the same time,corresponding inverter control method is given.The simulation result shows that the improved topology has better suppression capability of the leakage current.Next according to the requirements,the main circuit,control circuit,drive circuit and signal generator circuit of the inverter are designed in detail.And the control circuit uses a voltage and current double closed-loop control network.Finally,a prototype which has 600 W rated power is fabricated and tested.The experimental results agree with the simulation results,which proves the correctness of the proposed topology and the capability of suppressing the leakage current.