Abstract: A power steering device capable of obtaining a high rotary speed in the medium low torque range of an electric motor without incurring a drastic increase in manufacturing cost. The power steering device generates an auxiliary steering power by oil pressure that is generated by a pump which is driven by an electric power motor. The electric motor is a triple-phase brushless motor, with its angle of rotation being detected by the Hall sensors. The field coils are provided with the electric current from a drive circuit which is driven by a drive signal from the motor drive control part. The motor drive control part controls the electric motor by PWM control in the low medium speed rotation range and controls the electric motor by phase advance angle control, with PWM duty at 100 percent, in the medium high speed range.

Abstract: A method for reducing EMI emissions in the control of an electric motor supplied by a switching inverter fed by a DC bus comprising controlling a phase advance of a conduction angle period during which a phase of the motor is fed power by the inverter to control the conduction angle to control the speed of the motor, thereby to reduce the number of switching operations of the inverter and thereby reduce EMI.