An instantaneous speed observer for low speed control of AC machine

This paper presents a control method for AC machines in the low speed range with an instantaneous speed observer. When a low resolution pulse encoder is used for the speed detection, only the average speed during the interval of the encoder pulses can be obtained. Under low speed conditions, in particular, where the interval between the pulses is wider than a speed control period, detection dead time readily makes the speed controller unstable. In this paper, a new instantaneous speed observer is proposed, including a disturbance observer based on the full state observer algorithm. Simulation and experimental results show that the performance of speed estimation and control at very low speed is greatly improved with this scheme.