Constitution of V/f control for reducing the steady state speed error to zero in induction motor drive system

In order to extend the applicability of a voltage/frequency (V/f) controlled induction motor drive system, the problem of reducing to zero the steady-state speed error caused by load changes without using a rotor speed sensor is treated. The theoretical basis for this is given, and a scheme for constituting the control system is presented. The frequency of the stator voltage is controlled so as to compensate for the error, and this strategy is called the frequency compensation control (FCC). Transforming an induction motor into the corresponding idealized induction motor (IIM), which is defined as a motor having no stator resistance and leakage inductances, plays an essential role in realizing the FCC. The V/f control can exhibit excellent abilities when and only when it is applied to IIM, and is of the open-loop type in terms of the rotor speed. A well-known distinctive feature of Vf control, that it can generate a relatively large torque in the low-speed range to some extent, can be made use of with the maximum of ability. The proposed drive system is applicable to a part of the area in which the usual vector control equipped with a speed sensor has been utilized until now. In addition, as it has a detecting function for electromagnetic torque, torque monitoring is feasible.<>