Micro-step position control with a simple voltage controller using low-cost micro-processor

This paper presents micro-step operation of low power step motor for dashboard using a direct connection of low cost micro processor. The micro-step operation of stepper motor is very important in an indicating instrument such as speed and tacho meter. The proposed system uses a PWM output and digital output pin of micro processor per phase winding for low cost implementation. In order to perform smooth positioning for suitable application, a simple low pass filter and modified sine data table are introduced to reduce low frequency harmonics. The modified sine data table is produced by the injected harmonics to reduce the practical harmonics of phase voltage. Furthermore, S-curve function for smooth position reference and amplitude control of phase voltage according to acceleration and deceleration are proposed in this paper. The proposed voltage amplitude controller can change the phase voltage according to motor speed to compensate the back emf of high speed and to reduce the torque ripple in the low speed region. The proposed system is designed by the low cost 8-bit micro processor without any external memory and power devices. The effectiveness of the proposed control scheme is verified by the practical dashboard system.