Abstract: A method and apparatus for selecting one of several different modulating signals for use with a system including a PWM controller and an inverter to generate low frequency alternating voltages on three motor supply lines, modulating signals selected as a function of a modulating index to minimize harmonic distortion in the alternating voltages, minimize switching losses, maximize overall system gain at high modulating index values and maximize the linear range of system operation.

Abstract: A method and apparatus for eliminating greater than twice motor over voltage by altering modulating signals provided to a PWM controller which in turn provides firing pulses to a PWM inverter. The modulating waves are altered by either tying them to positive or negative DC buses or limiting their maximum magnitudes when their instantaneous characteristics are known to cause greater than twice overvoltage. The modulating waveforms are altered in a symmetrical fashion so that the resulting fundamental terminal voltages remain essentially unchanged.