Closed-loop control of stepping motors: prediction and realisation of optimum switching angle

If a stepping motor is operated under closed-loop control, then, for maximum torque production, the switching angle must vary with the stepping rate. This variation is investigated theoretically for a variablereluctance stepping motor and a low-cost method of implementing a speed-dependent switching-angle control is described. Experimental results indicate that this type of control enables the motor to produce a high torque at low speeds, but to still operate at speeds up to the pull-out rate.