System and method for ground fault detection and protection in adjustable speed drives

摘要

A system and method for detecting ground faults in an AC motor drive is disclosed. A fault detection and protection system for an AC motor drive includes current sensors to measure first and second phase output currents, a voltage sensor to measure a DC link voltage, and a desaturation control circuit to determine a voltage and associated current across PWM inverter switches for a third phase of the output. A controller compares the first and second phase currents, the measured DC link voltage, and the voltage across the PWM inverter switches on the third phase, to a plurality of thresholds. The controller detects a ground fault on one of the first, second, and third phases of the three phase output to the AC motor based on the comparisons of the first and the second phase currents, the DC link voltage, and the voltage across the switches to the thresholds.

主权项

1. An AC motor drive having an input connectable to an AC source and a three phase output connectable to an input terminal of an AC motor, the AC motor drive comprising:
a pulse width modulation (PWM) inverter having a plurality of switches therein to control current flow and terminal voltages in the AC motor; and a fault detection and protection system connected to the PWM inverter, the fault detection and protection system comprising:
a pair of current sensors to measure a current on a first phase and a second phase of the AC motor drive output;a voltage sensor to measure a DC link voltage on a DC link of the AC motor drive;a desaturation control circuit configured to determine a voltage and associated current across switches of the PWM inverter corresponding to a third phase of the three phase output; anda controller configured to:
compare the current measured on the first phase and the second phase of the three phase output to a first threshold;compare the measured DC link voltage to a second threshold;compare the voltage across the switches of the PWM inverter on the third phase to a third threshold; anddetect a ground fault on one of the first, second, and third phases of the three phase output to the AC motor based on the comparisons of the first and the second phase currents, DC link voltage, and voltage across the switches on the third phase, to the first, second, and third thresholds.