High-Quality PWM Scheme for High-Speed Electric Drives

A pulsewidth modulation (PWM) scheme is presented for three-phase high-speed electric drives using coupled inductors with a very low series output inductance that generate multilevel output voltages with an elevated PWM frequency. Two inverter legs are used in each phase, connected in parallel using coupled inductors with magnetic cross-coupling. The PWM switching of the inverter legs is controlled using carrier signals 180° apart. Rather than changing these carrier signals on the zero crossovers of the three-phase reference signals to improve the PWM line voltage, the reference signals are modified instead:
enhanced PWM control
. This approach allows the use of compensation signals to eliminate flux jumps in the magnetic cores commonly associated with carrier switching. Hence, the flux in the magnetic cores follows predictable patterns, with the peak flux reduced considerably. This, in turn, allows the inductor design to be reduced in size and weight. The
enhanced PWM control
described is also shown to reduce the load current THD
_f
and the load voltage harmonic volt-seconds. The feasibility of the
enhanced PWM control
is verified using both simulations and experimental results of a 10-kW (208 V/28 A, 300 V
_dc
) laboratory prototype.