Application of the double fed asynchronous motor (DFAM) in variable-speed drives

For high power industrial applications requiring high dynamic performance even far in the field-weakening range (such as spindles used to coil up laminated steel sheets), the wound rotor asynchronous motor with both its stator and rotor fed by a frequency converter possibly offers an interesting solution. Due to the high flexibility of the DFAM (four degrees of freedom) flux, torque, slip and power factor of the motor can be controlled independently. And since, in the case of wound rotors, the rotor currents are observable, the computation of the flux vector does not require knowledge of the (highly temperature dependent) rotor resistance. This fact, and the better field distribution of the wound rotor induction motor as compared with cage induction motors, leads to a more precise open loop torque control. This paper describes the design of the vector controller for an induction motor fed by two IGBT PWM inverters. Results of computer simulations are included