US Patent 8643319 Control of a brushless motor

A method of controlling a brushless motor that includes rectifying an alternating voltage to provide a rectified voltage, and exciting a winding of the motor with the rectified voltage. The winding is excited in advance of predetermined rotor positions by an advance period and is excited for a conduction period over each electrical half-cycle of the motor. The length the advance period and/or the conduction period is defined by a waveform that varies periodically with time. The method then includes adjusting the phase of the waveform relative to the alternating voltage in response to a change in one of motor speed and RMS value of the alternating voltage. Additionally, a control system that implements the method, and a motor system that incorporates the control system.