Application of hybrid frame current regulators to multiphase vector controllers with missing phases

In order to provide enhanced tolerance to phase faults many critical applications are now using isolated phase motors where each phase is driven by a separate H-bridge. If a failure occurs in any one phase the current in the remaining phases can be adjusted to eliminate the pulsating flux, and the original vector controller can be made to function without any changes. This requires accurate control of the current phasors regulated in either stationary or synchronous frame If a stationary frame current regulator is used a PWM carrier in the 3 to 5kHz range is needed to have enough gain at the desired operating speed but with multi-megawatt drives the devices cannot operate at that switching frequency. This paper shows the design of a hybrid frame PI current controller which has good current response from dc to 60Hz with a carrier frequency of only 625Hz. It is also capable of controlling the required current phase shifts to eliminate the flux pulsations when one phase is missing.