With the increasing demand for electric vehicles, reliability in motor drives is an issue of growing importance. Over the years, various fault tolerant three-phase motor drive topologies have been introduced and their performances have been investigated. Evaluation of the post-fault power of a fault-tolerant drive should take into account both the post-fault torque and speed, which depend on both the post-fault current and voltage limits. Nevertheless, the post-fault motor voltage limits are usually omitted from discussion. Furthermore, current limit in induction motor drive is not as direct as that in permanent magnet motor drive, due to the presence of the flux current. In this paper, the performances of available fault tolerant three-phase induction motor drives have been reinvestigated, taking into account the impact of not just currents, but also voltage limits for both the inverter and machine. By deriving the post-fault machine voltage equations, the effects of machine parameters and operating point on voltage limit and hence speed limit are explained. Depending on the topology, the motor may be able to run above the rated speed to gain extra power. The analysis is verified through experiment results on a 1kW induction machine for four different fault tolerant drive topologies.

With the increasing proliferation of variable speed drive, the demand for the more reliable drive is also on the rise. Despite the growing interest on more advanced motors like permanent magnet and flux switching motors, three-phase induction motors (3ph-IMs) are still the main workhorse in the industry and hence fault-tolerant control of these motor drives remains an interesting and important topic. In this paper, a simple fault-tolerant field oriented control (FOC) technique for 3ph-IMs is presented. It is shown that by injecting zero-sequence compensation voltage in a feedforward manner, open-circuit faults can be effectively tolerated. Compared to the previous feedforward fault tolerant control methods, the proposed approach does not require the knowledge of the magnetizing inductance, which is tricky to be obtained in induction motors. Furthermore, the unified feedforward approach allows same control structure to be used for different fault-tolerant 3ph-IMs drive topologies, with minor modifications to the feedforward terms. In addition, the effect of inverter non-idealities on the performance of the proposed control method are also highlighted and addressed. The effectiveness of the proposed controller is verified using MATLAB simulation and further validated using experimental tests.

Fault‐tolerant drives have been gaining increasing attention due to the need to enhance the reliability and robustness of electric drive systems, particularly for safety critical applications. However, in postfault control, it is often necessary to derate the machine, that is to reduce the torque and/or flux currents, to satisfy the current constraints of the power electronic devices. For induction motors, there are different approaches to quantify the current components in postfault operation while maintaining a stable operation within the current constraints. The efficiency enhancement of a faulted drive through flux current reduction is one of the methods reported in literature, however, the details of power components, that is, achievable torque and speed, are not addressed. This study broadly investigates the effect of flux and/or torque current partitioning on postfault capability of polyphase (three and more phases) induction machines in terms of achievable torque and speed. It is demonstrated that the magnetising inductance characteristics, which depend on the machine design and its power rating, have a profound effect on the choice of postfault current partitioning, and hence the machine performance. Theoretical discussion is supported with experimental verification using three‐phase and symmetrical six‐phase induction motors.