In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. Electric motors (or electric machines) are finding an increasing number of applications in the automotive industry due to the electrification of the automotive drive system. Electric and/or hybrid vehicles utilize electric motors as either primary or supplemental torque sources in the automotive drive system. These electric motors are expected to function over extreme operating conditions for an extended period of time with high reliability. However, over time, the operating stresses applied to the electric motor may degrade the condition of the stator windings. For example, thermal stress and/or voltage stress may lead to insulation breakdown, which in turn, may result in partial short-circuiting and/or open-circuiting of individual turns of the stator windings. When motors are fed from pulse-width modulated (PWM) inverter drives, the high-frequency switching of the power semiconductors increases the voltage stress on the stator windings.
Some prior art techniques attempt to diagnose the stator winding inter-turn faults by computing the negative sequence component of the motor currents which is caused by a fault condition in the stator windings. However, field-oriented control (FOC) and other closed-loop current-regulated control techniques widely employed in electric and/or hybrid vehicles preserve symmetrical and balanced current waveforms in the electric motors. Therefore, even when a fault condition exists in the stator windings, there is no negative sequence component present in the motor currents because the motor currents are adjusted to remain balanced and symmetrical. Some other prior art techniques involve extensive computations, for example, Fast-Fourier series analysis, which are often inadequate for non-stationary transient motor operating conditions where torque and speed are constantly changing. In addition, an incipient fault condition in the stator windings can rapidly increase in severity, and thus, the computational delays impair the ability to identify and respond to an incipient fault condition within a limited amount of time.