Patent ID: 8390227

Claim:
A method comprising: continuously determining an applied armature voltage supplied to a polyphase synchronous machine having a pull-out torque, the armature voltage being supplied from a power source via one of a plurality of taps of a regulating transformer, each of the plurality of taps supplying a voltage at a different level; and changing the armature voltage being supplied from the power source to the synchronous machine by selecting one of the voltage levels from the plurality of taps of the regulating transformer, the selecting one of the voltage levels being based on the determined applied armature voltage to minimize power consumption of the machine while ensuring based on a predetermined confidence level that the pull-out torque of the synchronous machine will not be exceeded; wherein the predetermined confidence level corresponds to a probability distribution indicative of at least one operating characteristic of the polyphase synchronous machine; wherein the predetermined confidence level that a pull-out torque of the machine is not exceed is applied to computed statistics of the time varying mechanical load applied to the machine, and wherein the method further comprises: detecting a slip of the polyphase synchronous machine; and increasing the margin of the pull-out torque upon slip detection.