Research On Advanced Control Strategy Of Brushless DC Motor Servo System

Brushless DC Motor (BLDCM) has small volume, long running life-time and little coupling between electrical torque and fluxes;it is used in servo system more and more. But the electrical torque varies especially when current exchanges between two phases, and load torque and parameters variations exist. In order to realize better performance, higher performance drive and control strategy is expected.At first, the principle of BLDCM is explained. The mathematical model and the MATLAB simulating model of BLDCM are presented.Combing with a pulse width modulation mode, the source of electrical torque variation is analyzed quantitatively. To reduce electrical torque variation, a new current control strategy is developed: control effort is used to hold on the electrical torque when exchanging phases, and follow the reference current quickly when not exchanging phases. Experiments show that the proposed current control strategy provides smaller torque variation than general control strategy.The principle of a sensorless technique, phase voltage crossing zero detecting, is explained, the measurement error source is analyzed and compensation method is presented. This sensorless technique is simple but useful.Variable-structure control strategy is insensitive to uncertainties including parameter variations and external load disturbance. To overcome two main problems with variable-structure control, i. e. the assumption of known uncertainty bounds and chattering phenomena in the control effort, an adaptive and variable-structure fuzzy controller of brushless DC motor position servo system is developed. The controller is composed of Linear Quadratic Regulator (LQR) and fuzzy sliding mode adaptive regulator. By adjusting the center of membership function, the adaptive regulator minimizes linear quadratic objective function which is also the Lyapunov objective function. The experiment results show that the proposed controller provides good performance in case of disturbance rejection and parameter mismatch and the position signal tracked the reference position quickly and smoothly.BLDCM servo system is developed based on digital signal processor (DSP). Three main parts i.e. signal measurement and A/D conversion, driving and protecting circuit, were presented.