Abstract: The converter protection device has a number of controlled semiconductor elements. A control unit is connected to the semiconductor elements of the converter for forming firing pulses for the controlled semiconductor elements. Reference blocking intervals for the semiconductor elements are set and actual blocking intervals of the semiconductor elements are set and controlled. A comparator receives and compares the reference and actual blocking intervals. There are also provided a read-only memory for storing the reference blocking intervals, an event counter for counting disturbances detected by comparison of the reference and actual blocking intervals, a memory stage being connected to the event counter and being set if the event counter reaches a predetermined count, and a time-base device connected to the event counter and memory stage for resetting the event counter if the memory stage is not set at the end of a predetermined base time.

Abstract: Method for controlling the speed and torque of an asynchronous machine fed through a static frequency changer with impressed intermediate current link, a control variable for the frequency of the current delivered by the frequency changer being formed from an electrical variable corresponding to a slip frequency value and an electrical variable corresponding to actual value of a frequency proportional to the rotor speed of the asynchronous machine which includes operating the asynchronous machine with constant flux in a region of constant maximal torque, and adjusting the flux in the machine, in a region of constant maximal power, as a function both of voltage at commutating capacitors of a self-commutating inverter and of a respective load condition of the asynchronous machine.