Asynchronous motor speed control method and device

Device for control of the speed of an asynchronous electric motor having a first branch of electrical windings and a second branch of electrical windings out of phase with the first branch, the device comprising

• first motor power supply means for running the motor at a rated speed, said first power supply means being operable to supply the first branch from a single-phase sine wave voltage source, and to supply the second branch from the same single-phase sine wave voltage source through a phase shifting capacitor,
• second and third motor power supply means supplying, respectively, the first branch of electrical windings by a first partialized voltage, and the second branch by a second partialized voltage, said first and second partialized voltages being formed from said single-phase sine wave voltage source for a half-period of the sine wave every uneven number ns of half-periods for running said motor at a speed reduced to 1/ns of the ratered speed thereof,
• means for generating control signals for said motor, and
• control means for sending activation signals alternately to said first and second power supply means upon reception of control signals requiring running of said motor at rated speed and reduced speeds, respectively.