Three phase common-mode winding voltage elimination in a three-limb five-level coupled inductor inverter

In three phase converters that use interleaved switching, coupled inductors between modules can be used to create a multi-level PWM output. To save weight, these coupled inductors can be integrated together to use a single three-limb core, but the presence of common mode voltages across the three-phase windings significantly reduce the converter performance. In this paper, a space vector based approach is used to eliminate these common mode winding voltages, allowing efficient three-limb coupled inductor operation at standard industrial switching frequencies, e.g. 3 kHz. This modulation approach is applied to a five-level neutral point clamped coupled inductor inverter (NPC-CII) and is intended to allow the use of lower frequency, higher powered devices. The proposed approach is compared against an interleaved modulation scheme that does not incorporate common mode winding elimination, and a 10 kW NPC-CII experimental prototype is used to confirm operation.