Balanced parallel instantaneous position control of PMDC motors with low-cost position sensors

This paper presents an advanced parallel position control scheme for dual permanent DC (PMDC) motors based on a low-cost and low-resolution Hall sensor, which decreases the control performance and accuracy due to the insufficient resolution and slow response in the low-speed range. To balance and improve the position control performance of both PMDC motors, an instantaneous position compensation based on operating time and a current model speed observer with an adaptive sliding mode observer based on the back electromotive force (EMF) constant are presented in this paper. The insufficient resolution and low dynamic response of the Hall sensor can be improved by the advanced current model reference adaptive observer using the back EMF bias calculation and the sliding mode observer of the back EMF constant. From the proposed sensor–sensorless combined estimation method, precise continuous speed and position information can be estimated at every sampling period. To compensate for speed and position estimation errors, the back EMF constant can be adjusted with the average speed error between the speed observer and the actual speed obtained from the Hall sensor. For the balance control of parallel PMDC motors, instantaneous position and speed reference control based on the operating time is presented. In the proposed control method, the speed reference is determined by the time-based speed reference, the instantaneous position error and the position error between two motors. Smooth balancing can be achieved from the compensation term of the balanced position error. The control performance of the proposed scheme for a dual PMDC motor system is verified by comparative simulations and experiments. In both simulations and experiments, the proposed method shows a significant improvement in the position control when compared to that of the conventional control method.