Torque notch minimization for five phase quasi square wave back EMF PM synchronous motors with voltage source drives

Quasisquare wave back EMF PM synchronous machines an be designed such that the angular extent (in electrical degrees) of the constant voltage portion of the back EMF waveform can exceed 150 degrees or more. In a five phase machine with voltage source drive each phase winding is nominally driven for only 144 degrees in each polarity. Thus there is an overlap period for these machines in which phase winding currents can be commutated while the phase winding back EMFs are constant. The torque notch suppression control scheme described functions during this constant back EMF overlap period. The difference of the drive voltages presented to the terminals of the incoming (turn-on) phase and the outgoing (turn-off) phase is held at a value needed to insure complete commutation of the outgoing phase within the overlap period. The sum of these two drive voltages is held constant at the precommutation value to insure constant torque production. The individual drive voltages presented to the remaining three phases of the machine are also held constant during the commutation period. Typical waveforms and switching speed requirements are presented and discussed.