Adaptive Common-Mode Voltage Reduction Technique for Three Level NPC Inverters

Common Mode Voltage (VCOMO) created by space vector pulse width modulated inverters induces bearing currents that causes premature motor bearing failure, induces electromagnetic interference (EMI) and breaks down motor winding insulation. In this paper, an Adaptive Common Mode Voltage Reduction (ACMoR) method is proposed for space vector pulse width modulated three level neutral point clamped (NPC-3L) inverters. Common Mode Voltage Sense and Cascaded H-bridge power circuit system used in ACMoR reduces the VCOMO that arises between the motor neutral point and the dc link return of NPC-3L inverter, irrespective of the space vectors selected, thus enhancing the dc bus utilisation. Simulation results show a significant reduction in VCOMO with ACMoR method, when a three-phase load is driven by a NPC-3L inverter.