Loss Calculation of NPC Three-Level Converter in Permanent Magnet Direct-Drive Wind Power Generation System

Permanent magnet synchronous generator with a full-scale converter is more attractive for large wind turbines at MW levels because of its low maintenance, reduced gearbox, high efficiency and power density, better low voltage ride through capability. As the increasing of converter’s capability, the device’s losses expand significantly, which directly affects the thermal design of the converters. In this chapter, a practical loss calculation method is derived based on the analysis of the conduction and switching principles of the NPC three-level converter at both generator and grid sides. Using thermal resistance equivalent circuit, the device’s junction temperatures are acquired. The infrared thermal imager is used to capture the temperature distribution of the converters and the thermal characteristics are analyzed in detail.