Flux and torque decoupling control for field-weakened operation of field-oriented induction machines

One of the primary advantages of field-oriented induction machines for high-performance applications is the capability for easy field weakening and thus full utilization of the voltage and current ratings of the invertor to obtain a wide dynamic speed range. This attribute has not been widely developed, however, because of the difficulty in actually knowing the flux magnitude and the effective rotor time constant at each operating point as needed for indirect field-oriented controllers. A straightforward approach is presented for estimating and fully decoupling the rotor flux and rotor time constant terms in indirect field-oriented controllers. This approach is based on a combination of both the intrinsic magnetic linearity of the field-weakened machine and the fully decoupled stator current and voltage equations which result from the use of delta-modulator current regulators