ELECTRIC POWER STEERING SYSTEM

摘要

An electric power steering system for assisting steering as follows. The system detects steering torque Ts applied to a steering member. According to detected steering torque Ts, the system determines q-axis current i*q and d-axis current i*d of a motor in the dq coordinate. The system determines q-axis voltage V*q and d-axis voltage V*d according to power supply voltage Ed so that the q-axis current i*q and d-axis current i*d thus determined flow to the motor. The system performs three-phase conversion of the q-axis voltage V*q and d-axis voltage V*d thus determined so as to determine three-phase voltages V^*u, V^*v, V^*w. The system drives the motor by applying the three-phase voltages V^*u, V^*v, V^*w thus determined. The system also includes a means for limiting the q-axis voltage V*q to v(3n²Ed²/8-Vd²)(n=1, 2 or 2/v3) or less.