Patent ID: 7102333

Claim:
A method for controlling the mains bridge of a four-quadrant PWM frequency converter provided with a DC intermediate circuit when the power is flowing in the direction towards the supply network, comprising: providing said frequency converter with an AC inductor to be connected to an alternating voltage source, a controlled mains bridge, a DC intermediate circuit and a controlled load bridge for feeding a variable-frequency alternating voltage into a load, and providing said mains bridge with controlled semiconductor switches and shunt diodes; and controlling the mains bridge so that the controlled semiconductor switch in the upper branch of the phrase having the highest supply voltage instantaneous value and the controlled semiconductor switch in the lower branch of the phase having the lowest supply voltage instantaneous value are conducting; advancing the control of the mains bridge semiconductor switch to be conducting next by a time sufficient to cause the current of the conducting phase turned from negative to positive before commutation, the size of the time being determined by the size of the current in said mains bridge.