A method for speed control of a wound-rotor induction motor is described. The rotor is supplied from an inverter, with SCRs having the same output frequency as the rotor (sf1). The stator is connected to a 3-phase network with constant voltage and frequency. The motor works in the region s > 1, so that the rotor revolves against the rotating field. The inverter works at a higher frequency than that of the network. Part of the slip power is fed back to the network. With mechanical and inverter-power limitations, the device permits continuous speed control from zero to maximum allowable speed. Starting is smooth and the starting current is low. Feedback may be used for speed stabilization under variable load. The motor is noiseless in spite of harmonics.
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M.S. Erlicki (1965) studied this question.