A Novel Three-Phase Transformerless Cascaded Multilevel Inverter Topology for Grid-connected Solar PV Applications

Abstract

Nowadays, multilevel inverters (MLIs) are gaining huge popularity for the high power transformerless PV applications. Among the traditional MLIs, the CHB MLI accommodates lower voltage rated input DC sources, which reduce the voltage stress across the devices. However, the CHB MLI requires multiple PV sources as separate DC link voltage sources which create more paths for leakage currents. Therefore, it is a challenging task to deal with the leakage currents in the case of CHB MLIs. In this paper, a novel three-phase transformerless inverter topology for grid-connected solar PV application is introduced. This proposed inverter topology has six switches per phase, and it has the combined advantages of dc-bypass and ac-by pass circuit configurations. A new modulation strategy is developed for the proposed topology; it is based on a sine triangle pulse width modulation technique combined with the dedicated logic functions. The gate pulses for all switches are provided by using these dedicated logic functions. The switching pulses obtained from the dedicated logic functions control all the switches of the inverter in such a way that the variation of common-mode voltage (CMV) is constant during the operation of the inverter. This results in reduced leakage current throughout the operation of the inverter. The theoretical analysis and simulations are presented to validate the concept of proposed topology for a 3kVA grid-connected system. All the major results are included in the paper. The experimental work is underway.