Frequency converter, method for its control and control of a motor by the frequency converter

The invention concerns a method and a device for converting one alternating voltage to another alternating voltage in accordance with a reference value and with a changed frequency and amplitude. The device comprises a rectifying bridge 1 and an inverting bridge 2 formed of controlled electrical couplers T1 . T6 with a resonance circuit 3 connected between them which consists of at least one condenser CR and a coil LR. In accordance with the invention under the influence of a control unit OE the output voltage of the rectifying bridge is connected in parallel across a resonance circuit 3 consisting of at least one condenser CR and a coil LR for a period of time equal to a half period of natural frequency of the resonance circuit using an electrical coupler T10 belonging to a controlled DC voltage circuit or alternatively the resonance circuit 3 consisting of at least one condenser CR and a coil LR is connected in parallel across the alternating voltage X2 of the inverting bridge 2 for a period of time equal to half the period of the natural frequency of the resonance circuit so formed via at least two electrical couplers T1, T5 belonging to the inverting bridge 2.