The transformer-less grid connected inverters are gaining more popularity due to their high efficiency, very low ground leakage current and economic feasibility especially in photovoltaic systems. The major issue which surfaces these systems is that of common mode leakage current which arises due to the absence of an electrical transformer connected between the inverter and the utility grid. Several topologies have evolved to reduce the impact of common mode leakage current and a majority of them have succeeded in eliminating the impacts and have well kept them within the limits of grid standards. This paper compares and analyses the impact of the common mode leakage current for four popular inverter configurations through simulation of the topologies such as H5, H6, HERIC and FBZVR inverters.

Current source inverters (CSI) is one of the widely used converter topology in medium voltage drive applications due to its simplicity, motor friendly waveforms and reliable short circuit protection. The current source inverters are usually fed by controlled current source rectifiers (CSR) with a large inductor to provide a constant supply current. A generalized control applicable for both CSI and CSR and their extension namely current source multilevel inverters (CSMLI) are dealt in this paper. As space vector pulse width modulation (SVPWM) features the advantages of flexible control, faster dynamic response, better DC utilization and easy digital implementation it is considered for this work. This paper generalizes SVPWM that could be applied for CSI, CSR and CSMLI. The intense computation involved in framing a generalized space vector control are discussed in detail. The algorithm includes determination of band, region, subregions and vectors. The algorithm is validated by simulation using MATLAB /SIMULINK for CSR 5, 7, 13 level CSMLI and for CSR fed CSI.