Single DC Source Based Three Phase High Resolution Transformerless Multilevel Inverter

A transformer less high-resolution hybrid asymmetrical multilevel inverter is proposed in this paper. The proposed topology is a hybrid of Level Doubling Network (LDN), cascaded H-bridge (CHB) and neutral point clamped (NPC) multilevel inverter (MLI). Objective of the proposed work is to utilize TNPC to merge all the three dc buses of main bridge to reduce the dc-bus capacitor requirement and inter array leakage current. The main challenge with this hybrid transformerless converter topology is balancing the capacitors of TNPC with corresponding LDN operation. For capacitor balancing of TNPC, one extra non-isolated buck-boost converter of low rating and a closed loop current control is used which will finally helpful to remove a bulky and expensive transformer. It will help to reduce both capital cost and running cost, as the rating of additional converter is just 7% to 8% of transformer rating. This topology offers high power quality, reliability and efficiency with less number of components than other asymmetrical MLI topologies with same resolution at output voltage. Simulation is done using MATLAB/Simulink model and simulation results matched well with the theory.