A Study on the Speed Control of a Blac Motor by Back-Emf Feedforward Compensation

Abstract

A PI controller is used to control the speed of a motor, but the gain of the PI controller is limited according to the system. Thus, the PI controller alone cannot meet the control performance requirements of the motor. A method involving back-electromotive force (back-EMF) compensation can solve this problem. Here, a feedforward compensation method based on the speed is used to compensate for the back-EMF. However, it is difficult to measure speed in the extremely low speed range, so it is difficult to compensate the back-EMF. In addition, the rate of the back-EMF compensation is modified by adjusting the gain. This proposed method of the back-EMF compensation is proven by simulation and experiment. The root mean square (RMS) value for the speed error is measured when the back-EMF is compensated for, when the back-EMF is not compensated for and when the gain of the back-EMF compensation is adjusted. The study confirms that the proposed algorithm is superior in the RMS value of the speed error.