Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Doctor of Philosophy in Electrical and Computer Engineering


Electrical and Computer Engineering

Major Advisor

Said Ahmed-Zaid, Ph.D.


Nader Rafla, Ph.D.


Thad Welch, Ph.D.


Variable-frequency drives (VFDs) are widely used for control of electrical machines such as induction motors (IMs) or permanent-magnet synchronous motors (PMSMs). Similar to other electrical devices, these drives are subject to failure. Several types of faults are associated with VFDs. For instance, faults such as an open-switch fault, a short-circuit switch fault are the two common faults in VFDs. These faults can yield catastrophic consequences if proper remedial action is not taken.

A unique remedial topology for the post-fault period and a new pulse width modulation (PWM) strategy are proposed so that not only the motor drive can continue the operation, but also this new method reduces the common-mode voltage of the three-phase inverter.

In this work, switch failures are investigated, and a new solution to detect open-switch faults are proposed using an algorithm based on current analyses. Extensive simulations are done to simulate a real system response during the post-fault phase on different operating points and at various torque loads. These simulation results were used to develop a detection algorithm. These results were also verified using an experimental setup. The proposed method offers an efficient solution for fault detection in VFDs. Firstly, a fast response detection of a failure in an inverter is possible. Second, it provides an alternative back-up method for fault detection in electric drive systems.