A Novel Vector Control Strategy For Bipolar Stepper Motor

The requirement of precise control in servo applications used in the digital systems led to the development of stepper motors. The precise and zero backlash operation of steppers extended its reach to various position control applications. The lack of requirement of sensors for position control applications was one of the main reasons for preferring stepper motors. Since the stepper motors were driven using digital pulses the motor moved in discrete steps of fixed angles and this caused torque pulsations in the machine. The advent of Micro-stepping strategy was a revolutionary change to this scenario, which helped to achieve a continuous smooth torque performance with reduced ripples, but this led to the requirement of a position sensor feedback for precise control. In robotic applications, continuous motion with a steady torque is preferred over stepped motion with pulsating torque. The paper proposes a novel control technique for stepper motors with reduced torque ripple and improved efficiency with the application of a vector control strategy analogous to PM Synchronous Motors. The proposed strategy was implemented and tested on a hybrid stepper motor. The proposed system can be used in position control applications, process automation, Robotics etc.