A Single-Phase T-Type Transformerless NPC- MLI for Grid-Connected PV Power System

Abstract

Transformerless (TL) inverter topologies have elicited extra special treatment in photovoltaic (PV) based power generation system as they provide high efficiency and low cost. Conversely, for the successful TL grid-tied PV inverters implementation, the shoot-through problem of bridge legs and leakage current should be considered prudent. Neutral point multilevel inverter (NP-MLI) topologies based transformerless (TL) are being immensely used in high-power medium voltage grid connected applications due to their better performance as compared to two-level voltage source inverter (VSI). Unfortunately, these topologies such as neutral point clamped-MLI (NPC-MLI), full-bridge inverter with dc bypass (FB-DCBP) suffer from the shoot-through problem on the bridge legs, which affect the reliability of the implementation. Literature confirms that the T-type Neutral point Multilevel inverter (TNP-MLI) rallies better performance compared to NPC-MLI, with its own clamping diode free circuit structure. Based on the aforesaid credits, a novel Transformerless TNP-MLI (TL-TNP-MLI) is offered to be an alternative which can be applied in the medium power low-voltage grid-tied PV systems. The proposed TL-TNP-MLI topology ensures no switching frequency common-mode voltage, leakage current, and shoot-through burden. This paper initially analyzes the switching states, commutations, and common-mode characteristic of TL-TNP-MLI and compares with other reported NP-MLI based on its PV tied grid conn