Abstract: Battery powered variable speed motor drives typically control the speed of the motor in accordance with a speed command. If the battery discharges to a point where the speed command is greater than that speed which can be supported by the battery voltage, the current drawn from the battery by the motor increases, thereby accelerating discharge of same. This problem is obviated by a control for an AC motor drive according to the present invention which includes means for deriving a signal from the output of the battery representing the maximum motor speed which the battery voltage can support, means for summing the maximum motor speed signal with the speed command signal to derive an error signal and means for summing the error signal with the speed command signal when the commanded speed is greater than that speed which can be supported by the battery voltage to reduce the speed command to the inverter and thereby maintain a predetermined voltage to frequency relationship in the inverter output.

Abstract: AC motor drives which include static inverters typically are operated by inverter controls that are designed according to certain criteria so that the inverter is operated in an efficient manner. Generally, it is desirable to design such a control to reduce as much as possible losses in the motor windings and losses associated with the inverter switches. However, inverters switching losses cannot be reduced without increasing motor losses, and vice versa, since motor losses decrease with increasing PWM frequency while inverter losses decrease with decreasing PWM frequency. In order to overcome this problem, a control system according to the present invention for controlling an inverter which converts DC power into variable frequency AC power for energizing a motor in accordance with an input command includes circuitry coupled to the input command for generating a plurality of waveforms at different frequencies, each frequency being an integer multiple of the frequency of the AC output.