Analog Computer Simulation of an Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

This paper deals with an analog computer simulation study of a complex drive system by making simplifying assumptions. The system incorporates a thyristor cycloconverter-type frequency-converter in the rotor circuit of a slip-ring induction motor for speed variation in subsynchronous as well as supersynchronous region by secondary voltage control. The action of the frequency converter is analogous to that of a normal commutator in a stator-fed ac commutator motor while the circuit behavior is similar to that of a cyclo-converter. A rotor position detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. Simulation involves solution of a set of generalized performance equations of an ideal induction machine in an appropriate reference frame under the control conditions imposed by the thyristor-commutator which is simulated using the parallel logic facilities of a modern analog computer. To simplify the simulation to study the system behavior, the thyristor units are represented by D/A switches available in the computer and the effects of source impedances are neglected. Results show very similar characteristics to the case when a pure sine-wave slip-frequency voltage is injected into the rotor as in the case of an ac commutator motr.