Design of 1500V solar inverter stack beyond megawatt in NPC1 topology

This paper describes a design concept of NPC1 power stack for 1500VDC megawatt level solar inverter. This stack uses three latest half-bridge IGBT modules with highest power density and operation junction temperature, which enable realization of power level beyond 1MW without paralleling. Critical design concept on loop inductance is explained. Dynamic characteristics are verified by double-pulse test. Thermal characteristics and output power limits are verified by thermal test. Temperature-sensitive component on PCB as output power constraint is identified. Different PCB repositioning solutions are tested to give the overall output power thermal derating curves, which enable output power of 1.15MW at $T_A=55^{\circ}C$ with $15^{\circ}C$ thermal margin. The power stack characteristic and performance change under different thermal environment is further analyzed.