Abstract: A device for overvoltage protection of rectifier/inverter bridges employing gate-controlled solid-state switches without zero diodes is disclosed. To protect at least the solid-state switches of the rectifier/inverter bridge against overvoltages, the device incorporates one or two overvoltage protector units which are activated when the voltage between at least two protection connections exceeds the voltage across a storage capacitor of the overvoltage protector unit. Thus, a controllable switch connected in parallel with the storage capacitors is turned on when the voltage between two protection connections exceeds an excitation value and is turned off when the voltage falls below the excitation value, controlled by a control unit of the protector unit.

Abstract: Procedure for regulating the d.c. voltage of a pulse-width modulated rectifier bridge controlled by self-commutated semiconductor components and provided with filtering coils, in which procedure the phase voltages of the supplying three-phase mains and the d.c. voltage of the rectifier are measured. The modulation references needed for the pulse-width modulation are produced using pure sine and cosine curves synchronized with the mains voltages, with spatial vectors formed from them or with components of such vectors, by means of a phase-locked loop. The regulation is effected in a coordinate system tied to the spatial vector of the mains voltages.

Abstract: In a procedure for the selection of a bridge or bridge section in a rectifier bridge unit having a bridge or bridge section conducting in one direction and another bridge or bridge section conducting in the other direction, said bridges or bridge sections having solid-state switches, selection of the bridge or bridge section is based on the direction of the actual value of the current when the actual current has an essentially non-zero value, on the reference value of the current when the actual current value is essentially zero and the reference value of the current is essentially other than zero, or, when both the actual and reference values of the current are essentially zero, on a signal controlling the selection of the bridge or bridge section during the zero-current condition, which signal directs the bridge control signals alternatively to either bridge or bridge section. A bridge selector unit includes circuits for implementing this procedure.

Abstract: A method for controlling a frequency converter having multi-phase output is disclosed and a frequency converter for applying the method. In order to achieve a good waveform the currents of the frequency converter are controlled via modulation in such manner that the current modulation periods of each phase are interlaced with the modulation periods of the other phases.