Overcurrent fault detection device for electrical drive control system

An overcurrent fault detection device, comprising:

• an inverter that converts a DC current to three-phase AC currents in order to drive a motor;
• a DC voltage detector that detects a DC voltage value of a DC voltage flowing to the inverter;
• phase current detectors that detect respective phase current values of the three-phase AC currents;
• a rotational position detector that detects a rotational angle of the motor;
• a control circuit that controls a gate drive circuit, which controls output currents of the inverter at every predetermined cycle, based upon the phase current values provided by the phase current detectors, a motor rotational angle detection value provided by the rotational position detector and a speed command or a torque command issued by a higher-order control device;
• a decision-making circuit that detects an overcurrent based upon the phase current values detected by the phase current detectors at every predetermined cycle, wherein:
• the decision-making circuit includes a comparator with hysteresis provided with a predetermined hysteresis width, which carries out the frequency detection for any of the phase current values, and
• the decision-making circuit determines whether or not the phase current values exceed a predetermined amplitude threshold value by carrying out frequency detection for any of the phase current values exceeding the predetermined amplitude threshold value, and determines that an overcurrent has occurred upon detecting the frequency, and
• counters that count numbers of times of exceeding a predetermined amplitude for the phase current values respectively, by counting changes in output from the comparator with hysteresis, wherein:
• the decision-making circuit determines that an overcurrent has occurred upon detecting that any of the phase current values takes on a frequency of which amplitude exceeds a predetermined amplitude, based upon a count value having been counted on the counters.