ELIMINATING COMMON MODE WINDING VOLTAGES FOR A 3-LIMB COUPLED INDUCTOR USED IN 3/5-LEVEL PWM VOLTAGE SOURCE INVERTERS

Three new PWM schemes are described for 3-phase dual inverter systems that allow a 3-limb coupled inductor to be used and produce 3/5 level pwm output voltages. A standard space vector pwm scheme is used to show that standard interleaved pwm techniques are not suitable to control the dual inverters: switching states exist that produce common-mode winding voltages. Special PWM techniques have to be used to align the inverter switching edges between phases. A useful rule to follow assumes that the sum of the winding voltages must sum to zero for all pwm switching states. Experimental and simulation results are used to compare the performance of the 3 schemes over the entire output voltage range and based upon the following performance criteria: average volt-seconds across the coupled inductor windings; average volt-seconds of the harmonics in the output line voltage PWM waveforms; inverter output current THD; inductor losses; common-mode inverter output voltage waveforms; inverter efficiencies.