Variable-speed drive for single-phase asynchronous motors

A circuit for controlling the speed of a single-phase asynchronous AC motor, comprising:

• a device for generating two sinusoidal AC voltages from supplied rectified AC voltages wherein a frequency of a second generated AC voltage is always the same frequency as that of the first generated voltage;
• said second generated voltage is shifted by exactly 90° with respect to said first generated voltage;
• said frequency of both generated voltages depends on a supplied control voltage;
• wherein the amplitude of the generated voltage decreases with decreasing frequency;
• said amplitudes of said generated voltages are not equal wherein an amplitude ratio of said voltages must correspond to a ratio of a number of turns of a working winding and an auxiliary winding, wherein;
• a smallest possible slip is obtained between said rotating magnetic field caused by said two generated voltages and said rotating rotor wherein a greatest possible efficiency is obtained, which may be achieved for a required operating state of the motor, whereby at a required torque and speed of the single-phase asynchronous motor as little energy as possible must be supplied to the motor together with a device, and thus at the required operating state of the motor as little energy as possible is converted into heat.