STATOR-FLUX-BASED VECTOR CONTROL OF INDUCTION MACHINES IN MAGNETIC SATURATION

In many variable-torque applications of induction machines, it is desi rable to operate the machine at high Aux levels, thus allowing the mac hine to produce higher torques. This can lead to saturation of the mai n flux path, introducing cross-coupling effects which can severely dis rupt the performance of controllers dependent on knowledge of the mach ine's magnetic parameters. Stator-flux-oriented torque-control schemes need not depend on the magnetic parameters of the machine and, hence, are potentially more robust and easier to implement in magnetic satur ation than rotor-flux-oriented control. In this paper, we present and analyze a stator-flux-oriented torque-control scheme. This controller only requires knowledge of the stator voltage, stator current, and sta tor resistance. An analytical expression for the maximum achievable to rque output of the machine using a linear magnetics model is compared with values calculated using a nonlinear magnetics model incorporating saturation of the main flux path and is shown to be a good approximat ion at high flux levels, when the main flux path is heavily saturated. Experiments carried out on a 3-hp 1800-r/min wound-rotor induction ma chine show smooth operation of the control scheme at torque levels up to at least four times rated torque.