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 considering the requirements of high current ratings, low stray inductance and standardized housing with widespread availability. Therefore a smart solution for the 1500VDC 3-level central PV inverters is needed.
In general a problem occurs when 3-level NPC topologies are developed using several standard half bridge power modules. A series connection of IGBT modules results 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 usage of the active neutral point clamp (A-NPC) topology in combination with a smart modulation scheme which enables the utilization of half bridge IGBT modules such as the new defacto standard (the LV100 modules) without the problem of switching overvoltages caused by high commutation inductances.
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