Fault diagnosis in voltage-fed PWM motor drives based on discrete voltage states

This paper presents a new approach for diagnosis of short circuit Insulated Gate Bipolar Transistor (IGBT) faults in a three-phase voltage-fed motor drive. The three-phase Pulsewidth Modulated (PWM) voltage signals are monitored and digitised into two discrete levels. The combination of discrete voltage levels of the three phases composes eight voltage states. For a healthy Sinusoidal PWM (SPWM) motor drive, all eight states are monitored within one carrier period. However, when a fault occurs certain states cannot be obtained. A fault signature set is defined for each switch fault. By comparing the monitored states with the fault signature sets, the faulty switch is detected and isolated. A PWM voltage source inverter that feeds a threephase Permanent Magnet Synchronous motor with IGBT switch faults is simulated and the fault diagnosis algorithm is applied. The results show that the faults can be diagnosed within tens of microseconds. The robustness of the proposed fault diagnosis and isolation (FDI) approach to the load changes is tested by connecting the motor to a variable mechanical torque.