An apparatus for generating electromagnetic torque in an N-phase electric machine, N being a positive integer, includes N lines, each of the N lines including an input terminal, an output terminal, and a pair of thyristors, or of one thyristor and one diode pair. The N lines are connected between a mains and the electric machine. An apparatus is provided for repeatedly or continuously determining at least the sign of a voltage over the thyristor or diode-thyristor pair in at least one of the N lines, means are provided for repeatedly or continuously determining at least one parameter related to the electromagnetic field in the electric machine, and a control device is provided for controlling the operation of the thyristor or diode-thyristor pair of the at least one of the N lines.