Evaluation of a NPC1 phase leg built from three standard IGBT modules for 1500 VDC photovoltaic central inverters up to 800 kVA

This paper presents the concept and characterization of a NPC1 phase leg built up out of three PrimePACK™ 2 power modules with .XT and 1200 V IGBT5. The target application of such a topology is 1500 V solar central inverter. After a short description of the cosmic ray reliability issues leading to the NPC1 approach, different design concepts will be discussed. Double pulse measurements have been used to characterize the overvoltage during the long commutation in reactive power mode. The moderate stray inductance of the long commutation path within the design of the PrimePACK™ 2 NPC1 phase leg allows a safe turn-off without the need of clamping diodes in the driver. Furthermore the power conversion efficiency as well as the maximum power rating of a solar central inverter using the presented concept has been investigated by feeding the measured switching energies into simulations. It turns out that a power rating of more than 800 kVA can be reached due to the higher power density and more efficient switching thanks to the .XT and IGBT5 technology.