1-MW advanced T-type NPC converters for solar power generation system

A multi-level topology is one of the effective approaches to improve the efficiency of power converters. Recently, three-level converters are used not only in medium voltage converters but also in low voltage converters in order to improve the conversion efficiency. Advanced T-type NPC (AT-NPC) converter belongs to three-level converters and utilizes Reverse-Blocking IGBT (RB-IGBT) as a bi-directional switch. The AT-NPC topology is simple and enables low conduction losses of the converters. This time, the authors develop a 1-MW photovoltaic converter using AT-NPC topology. This photovoltaic converter is outdoor-type transformer-less single-stage converter, and consists of four 250-kW power units. In addition, to reduce EMI from the converter, the neutral point of the LC filter is connected to the medium point of the DC-link voltage. This paper describes the features of this solar power inverter, power units using AT-NPC IGBT modules connected in parallel and the evaluation results.