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Controlling the torque-speed characteristics of a polyphase induction motor using a switched rotor ballast network

This paper describes the development and experimental demonstration of a solid-state switching network that actively modifies the performance characteristics of a wound-rotor induction motor, enabling real-time impedance matching with its mechanical load. This switching network manipulates the rotor currents of the motor to modify the torque and efficiency characteristics as a function of rotor speed. Perturbation and simulation studies establish the active range of induction motor torque that rotor resistance can control. Analytical control strategies are developed that enable the motor to operate at peak torque at all speeds. For implementation, a switched ballast network is inserted into the rotor circuitry of a wound-rotor induction motor. The modified motor was tested and the experimental results confirm the viability of this approach.