Adaptive asymptotic disturbance attenuation for a permanent magnet DC motor

The problem of speed control of a permanent magnet DC motor with unknown parameters and unknown external load torque is formulated in the form of an adaptive control problem based on the design requirement of asymptotic command following with simultaneous asymptotic disturbance attenuation. The adaptive design scheme is indirect and it is based on RLS (recursive least squares) identification. The key point of the disturbance attenuation approach is to identify the system without knowledge, estimation or measurement of the unknown disturbance. This way the variations of the disturbance influence the estimation of the system parameters and consequently the choice of the controller parameters. The identification can be initialized on the basis of arbitrary initial estimation. The present results are successfully applied to a 75 Watt DC motor (35NT2R82-426SP) where a significantly varying external torque and rotor voltage noise of about 1% are considered to be applied. The present design scheme is compared to those of a traditional open loop feeding system and a PID (or PI, or P) controller designed on the basis of the first Ziegler-Nichols method.