A Novel Three-phase Inverter With Leakage Current Attenuation For Transformerless PV Systems

More and more attention has been paied to solar power generation due to the serious envieonmental influence of fossil fuels.In PV power generation systems,photovoltaic inverters play an important role.The grid-connected PV inverters can be classified into two groups,namely with and without galvanic isolation.The galvanic-isolated PV systems typically suffer from low efficiency,large size and weight and high cost,mainly due to the isolated transformer.That is the reason why the transformerless PV systems are gaining more and more attentions in both academic and industry fields.However,the leakage current may arise due to lack of galvanic isolation.The undesirable leakage current causes the system losses,electromagnetic interferences,current harmonic distortion and safety troubles,which motivate many researchers to focus some attention on the method for leakage current elimination.In this paper,some classical topologies for single phase and three-phase are introduced and the mechanism of leakage current suppression has been explained.Based on one single phase inverter,a noverl three-phase three-level inverter for transformerless is derived.In order to suppress the leakage current in the novel inverter,the common mode loop model is presented firstly and the main factors and variables of the leakage current is discussed.Then the common mode characteristics with conventional modulation methods such as IPD and OPD are introduced,which fails to achieve the leakage current attenuation.So that a new single-carrier modulation method for the inverter is proposed to achieve constant common-mode voltage(CMV)and thus the leakage current can be suppressed.In order to operate the novel inverter with grid,the system mathematical model is established,and the current loop control scheme based on the Proportional Resonance controller is designed.Then the simulations with the tranditional modulation and new single-carrier modulation are conducted respectively.Finally,in order to futher verify the novel inverter;the experimental is implemented on the TMS320F28335 DSP + XC3S400 FPGA digital control hardware platform.Based on the comparison results of simulations and experiments,the inverter and the new modulation method to suppress the leakage current are proved to be effective.