New MRAC load torque observer for the position control of BLDC motor

A new control method for the robust position control of a brushless DC (BLDC) motor using an asymptotically stable adaptive load torque observer is presented. A precision position control is obtained for the BLDC motor system, approximately linearized, using the field-orientation method. An application of the load torque observer using a fixed gain has been published by Jong Sun Ko et al. (1993). However, the flux linkage is not exactly known for a load torque observer. Therefore, a model reference adaptive observer is considered to overcome the problem of the unknown parameter in this paper. A stability analysis is carried out using the Lyapunov stability theorem. As a result, an asymptotically stable observer gain can be obtained without affecting the overall system response. The load disturbance detected by the asymptotically stable adaptive observer is compensated by feedforwarding the equivalent current having the fast response.