Research On Elimination Of Leakage Current For Transformerless Three-phase Six-switch Three-level Photovoltaic Inverter

Due to the increasing depletion of non-renewable energy and the environmental problems caused by the use of non-renewable energy,more and more attention has been paid to renewable energy.Solar energy is popular because of its large reserves,reliablity,safety and clean,and the solar power generation industry has been made rapid development in recent years.The inverter is an important part of the solar power generation.PV systems can be divided into isolated photovoltaic system and non-isolated photovoltaic system according to whether the inverter structure contains transformer or not.The transformer can achieve electrical isolation between the DC side and the AC side,but it will make many disadvantages of PV systems,such as large volume,high cost,high loss and low efficiency.Non-isolated photovoltaic systems can optimize the above deficiencies,but it will also cause leakage current problems because of the lack of the isolation role of the transformer.The leakage current will cause grid-connected current harmonic distortion,electromagnetic interference,additional system loss,and trigger potential safety hazards of equipment and personnel.Therefore,it is important to study the technology of leakage current suppression for non-isolated photovoltaic inverter.This paper first expounds the research and application progress of the leakage current of the non-isolated inverters at home and abroad and enterprises,and then determines that the main research content of this paper is the three-phase three level six switch inverter,and describes the operation mode of the topology,and it analyzes the working state of couple inductor and common-mode loop model of systems.The leakage current suppression of the Bidirectional Modulation Wave modulation scheme is analyzed.A new single carrier scheme is proposed based on the characteristics of the traditional scheme about the lack of suppressing leakage current.The problem of the charge-discharge balance of the coupled inductor in the topology is discussed and the corresponding measures are put forward.The current loop control scheme is designed based on the mathematical model of the system.The simulation is conducted.Finally,in order to further verify the effectiveness for the proposed leakage current suppression scheme,main circuit platform combining with TMS320F28335 DSP + XC3S400 FPGA digital control circuit is designed.The experiment is implemented and the experimental results prove the correctness of the theoretical analysis.