Field weakening control of synchronous reluctance motor for electric power steering

A calculation method of current reference for maximum torque per voltage control of synchronous reluctance motor in a characteristic region is proposed. To use the electric motor to power a steering system, it is necessary to control torque instantaneously in wide speed range, and it is also necessary that torque reference must be limited under maximum output capacity of the motor. Generally, motors for the electric power steering system have low rated voltage level, low output power and low rated speed. Consequently, they have larger stator resistance value relatively. In this case, stator resistance value must be included in calculation of the current reference for torque control, and so this paper proposes a calculation method of current reference including stator resistance value. The proposed method is verified by computer simulation and experiment.