Low Commutation Inductance Using Standard Half Bridge IGBT Modules in High Power 3-Level (A)-NPC Inverters

Abstract:
In central PV inverter applications, 3-level neutral point clamp topologies based on 1200 V IGBTs are a popular approach. However, finding a suitable power module is often challenging. Central PV inverters operate at high power levels. Therefore, IGBT modules with high current ratings of 1000 A or more are required. A problem occurs when 3-level NPC topologies are developed using several standard power modules. A series connection of IGBT modules result in high stray inductances which in combination with high switching di/dt cause high switching overvoltages. IGBT modules with an integrated NPC topology phase-leg containing 4 IGBT and 6 diodes potentially have lower stray inductances but are not available for high current ratings and are more expensive due to the complex internal circuit. The solution is the change to the active neutral point clamp (A-NPC) topology in combination with a smart modulation scheme which enables the utilization of standard half bridge IGBT modules without the problem of overvoltages caused by high commutation inductances.