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Abstract

An inverter control unit having a bridge circuit provided with controllable semiconductor switches in upper and lower circuit arms, which bridge circuit converts a direct voltage to be fed to the inverter into an alternating voltage of variable frequency and amplitude, said control unit controlling the semiconductor switches by pulse-width modulation (PWM) to generate an inverter output voltage, and said control unit comprising a first control section (21) at ground potential and a second control section (22) at the potential of the semiconductor switches, galvanically isolated channels being provided between said sections for serial transmission of control data from the first control section to the second control section and of feedback data from the second control section to the first control section. A modulation circuit controlling the semiconductor switches is disposed in the second control section (22) at the potential of the semiconductor switches, and the modulation circuit forms the time integral of the difference between the reference and actual values (U.sub.uref, U.sub.uact) of the phase voltages of the inverter, compares this difference to positive and negative limits (L.sub.+, L.sub.-) and when the time integral exceeds the positive or the negative limit, drives the phase switch in the upper or lower arm of the phase in question into conduction.

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First Claim