Abstract

Conventional machine stator open-phase fault detection methods rely on the detection of current harmonics from the sensing of phase currents. Because the magnitudes of current harmonics are proportional to the machine load condition, it is a challenge for the phase fault detection at the light load condition when fault-induced current harmonics are too small to detect. This paper proposes an improved stator phase fault detection for permanent magnet (PM) machines based on the use of neutral point (NP) in Y-connected windings. It is shown that the first-order voltage harmonic is resultant once the open-phase fault occurs. Comparing with prior detection methods based on the current measurement, the fault detection using NP voltage is insensitive to the load condition, because the proposed fault signal is induced by the voltage unbalance as a result of the open phase. In addition, considering the fault tolerant control, a single-phase drive is developed by connecting the machine NP to one of the inverter legs. The machine can drive at the most efficient condition using standard three-leg inverters under phase fault. A 50-W PM machine with the accessible NP is used to evaluate the proposed open-phase fault detection and tolerant control method.

Introduction

Variable-frequency PM machine drives are applied in applications ranging from small fans and compressors to the large transportation systems. For the implementation of variable-frequency drives, high efficient real-time microcontrollers with advanced machine drive algorithms are typically used to control semiconductor switches and generate pulse-width-modulation (PWM) voltages. Due to the progress on the microcontroller, on-line condition monitoring and fault tolerant control can also be implemented by using the microcontroller as the fault monitor [1, 2]. For example, an adaptive controller is designed to detect faults in active suspension system [3]. A fault tolerant control is also developed to mitigate unknown actuator faults in the same system [4]. A nonlinear controller is implemented to improve the reliability in a hydraulic rotary actuator [5].