The carrier - based PWM method to reduce common-mode voltage for three - level T - type neutral point clamp inverter

Common-mode voltage (CMV) is responsible for overvoltage stress to the winding insulation and bearing damage of an AC motor. High dv/dt of CMV causes leakage currents, which create noise problems to the equipments installed near the converter. This paper proposes modulation strategy for three-level T-type NPC that substantially eliminates CMV. The principles of selecting suitable triangle carrier signals for the T-type NPC is described. The proposed method can mitigate the peak value to 50% as compared to the conventional sinusoidal pulse width modulation method. The proposed modulation can be easily implemented in software without any additional hardware modifications. Both simulation and experimental results are shown to demonstrate that the new carrier-based PWM method can generate good performance of the output waveforms and provide CMV reduction.