Microprocessor-based sinusoidal stepper motor control with data interpolation

This paper presents a novel microstepping control of low power stepper motor for automotive dashboard instrument application used with a direct connection of a low-cost microprocessor. The microstepping operation of the stepper motor is very important to indicating instrument applications of, for example, fuel meter, battery meter, speed meter, and tachometer. The proposed system uses pulse-width modulated output and digital output pins of a microprocessor for the low-cost implementation. In order to perform a smooth positioning operation for an indicator application, a simple low-pass filter (LPF) and modified sine data table are introduced. The modified sine data table is produced by the injected harmonics to reduce the low frequency harmonics of the motor phase voltage. Furthermore, the S-curve function for the smooth position reference and the amplitude control of motor phase voltage depending on motor acceleration and deceleration speeds are proposed. The S-curve function provides a smooth response while maintaining high acceleration. The proposed voltage amplitude controller can change the motor phase voltage according to the motor speed to compensate the back-electromotive force (EMF) at high speed and to reduce the torque ripple in the low speed region. The proposed system is implemented with a low-cost 8-bit microprocessor without any external memory and power devices. The effectiveness of the proposed control scheme is empirically verified by a practical automotive dashboard instrument system.