A New Power Conversion Strategy for a Uni-Polar Stepper Motor Drive

Uni-polar, stepper motors with bifilar windings are often used in the industry. Condenser or zener suppressors are often used to protect the stepper-driver circuit from over voltage due to stored magnetization energy. Faster magnetization and demagnetization of windings enhances the torque capability of the motor. Although faster, the zener suppressor is inefficient. On contrary, the efficient condenser suppressor is slower. Therefore, researches have resorted to dual-rail systems for synchronous reluctance and stepper motor drives. The proposed driver circuit is derived from the power topology. In the proposed arrangement, the power circuit and the motor are integrated and the system uses additional diodes to take demagnetization energy. As for the control a feedforward voltage loop is introduced, and it is shown that the input capacitor charging is accelerated due to the loop, along with its output control. The demagnetization energy of the outgoing winding is transferred to the input of the power supply. The energy feedback to the input is done under a fairly larger clamp-voltage. Therefore, a shorter current tail is made possible. Hence the torque performance is enhanced. Since the demagnetizing energy is recovered the system is efficient. All the other advantages of a dual rail-power supply with regard to reluctance motors are retained. In addition, the power supply works off the utility, yet it uses a capacitor rated at much lower voltage and current. Experimental waveforms are presented