A circuit to monitor AC line current through resistors employed to provide a `step start` in a power supply, including means to monitor the current flowing through the step start resistors, comprising a peak detector, a sample and hold circuit, an analog to digital convertor and a microprocessor. The output of the current monitoring circuit may be employed to abort starting if abnormalities are sensed. The circuit may also be used to identify when the step start resistors need longer cooling time, and to continuously monitor current at times other than during starting. A timing circuit is also incorporated, which senses zero crossings of the voltage input to the power supply, so as to control the timing of the current monitoring circuit. The discrete circuits employed may be replaced by either a digital signal processor integrated circuit or a general-purpose computer implementing the same steps in a suitable algorithm.
A system and method for starting and regulating a wound rotor motor especially during the period between inactivity and a speed determined by the voltage ratings of the drive system. In a first embodiment, a starting resistor and a starting bypass contactor are connected between the rotor of the motor and a low voltage source inverter. In an alternative embodiment, the arrangement of the first embodiment is altered by connecting a shorting contactor on one side to the junction of the voltage source inverter, the starting resistor and the starting bypass contactor so as to be short circuited on the opposite side of the shorting contactor.
