ONLINE TUNING OF THE ROTOR TIME CONSTANT FOR VECTOR-CONTROLLED INDUCTION-MOTOR IN POSITION CONTROL APPLICATIONS

The induction motor drive with an indirect field-oriented controller (IFO) exhibits excellent behavior in a low-speed region. Thus, the motor can be advantageously employed as an actuator in positioning servomechanisms [1]. The substantial sensitivity of IFO controller with respect to changes in the rotor time constant T(r)* calls for an adaptation mechanism, which should allow the tracking of the actual value of rotor time constant through the whole range of operation conditions. This paper proposes the adaptation scheme for the continuous on-line tuning of the parameter T(r)*, suitable for the environment of a position servo. The outlined analytical considerations and experimental results are focused on operation conditions characterized by the zero speed and a light load of the drive. The proposed adaptation scheme is based on the measurement of the terminal voltages that are used as an auxiliary information; then, the scheme is designed in such a way that stator resistance fluctuations and nonlinearities within the analog processing circuitry do not affect the estimated value of the rotor time constant. Experimental results show that the proposed scheme gives good results even in conditions at zero speed and dynamic loads that may be as low as 0.2 p.u.