Asymptotically stable adaptive load torque observer for precision position control of BLDC motor

A new control method for the precision robust position control of a brushless DC (BLDC) motor using the asymptotically stable adaptive load torque observer is presented. A precision position control is obtained for the BLDC motor system approximately linearised using the field-orientation method. DC motors have been graduallj replaced by the BLDC motor, since the intiustry applications require more powerful actuators in small sizes. Many of these motor system:; have BLDC motors to obtain high power rates. On the other hand, the disadvantages are the high cost and more complex controller caused by the complex driving principle of BLDC motors, and the load torque disturbance is directly affected to a motor shaft. The application of the load torque observer using fixed gain has been published (KO et al, 1993). However, the flux linkage is not exactly known for a load torque obszrver. There is a problem of uncertainty of obtaining very high precision position control. Therefore, a model reference adaptive observer was considered to overcome the problem of the unknown parameter and torque disturbance (KO et al, 1994), but this is a case of BIBO stability. A new model reference adaptive observer is considered and stability analysis is carried out using the Lyapunov stability theorem. As a result, asymptcltically 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 feecl-forwarding the equivalent current having the fast response.