Abstract: A procedure and apparatus for the control of solid-state switches in three-phase frequency converter and rectifier/inverter bridges is disclosed. Such control employs pulse width modulation. In this procedure, the modulation pulses of each phase are generated by comparing sinusoidal modulation references in an interval-by-interval manner to at least two triangular waves with a phase shift between them. The modulator unit for implementing the procedure incorporates one or more memory circuits storing the modulation reference curves, one or more D/A converters for converting the memory circuit outputs into analog form, and comparators for producing preliminary modulation pulses by comparing the sinusoidal modulation reference signals to at least two triangular waves shifted in phase relative to each other.

Abstract: A device for overvoltage protection of a rectifier bridge feeding a d.c. motor and implemented using fully gate-controlled solid-state switches without zero diodes, and for control of the d.c. motor during emergency braking is disclosed. To protect at least the switches of the rectifier bridge against overvoltages and to control the d.c. motor during emergency braking, the device incorporates a capacitor connected via diodes both to the d.c. circuit and the a.c. circuit and, connected in parallel with said capacitor, a series cirucit of a fully gate-controlled solid-state switch and a resistor, said solid-state switch being controlled by a control unit in such manner that, when the voltage between at least two connections in the a.c. or d.c.