Electric power steering device

Abstract

There is provided a electric power steering device which can perform torque control through a simple arithmetic process using a synchronous reluctance motor having a nonlinear current/torque characteristic. A target torque is transmitted from an EPS control unitto a motor control unit. The motor control unitcalculates a target-current effective value I and a target-current phase θ from the input target torque. Based on the calculated target-current effective value I and target-current phase θ, calculation is changed whether to perform calculation so that the maximum torque (the maximum torque obtainable at the minimum current effective value) can be obtained, or to perform calculation so that the maximum output (the maximum output obtainable at the minimum current effective value) can be obtained in accordance with a duty ratio of an output by a PWM converting unitcomprising a three-phase inverter. Next, a three-phase biaxial converting unitcalculates a target q-axis current Iq and a target d-axis current Id from the target-current effective value I and the target-current phase θ, and the PWM converting unitperforms duty control in order to control the torque of a motor