This paper aims to evaluate the thermal feasibility and reliability implications of maintaining full nominal torque in a five-phase permanent-magnet synchronous motor (PMSM) under a single open-phase fault. It examines how post-fault current redistribution strategies affect copper losses, thermal behavior and insulation aging to assess whether high-performance fault-tolerant control can be achieved without compromising the machine’s operational lifespan.
A coupled electromagnetic–thermal workflow is adopted. Electromagnetic finite-element simulations compute spatial copper and iron losses for two post-fault strategies: Equal-Current redistribution and Copper-Loss-Minimization. These losses are then imported into a detailed 2D transient thermal finite-element model to calculate winding temperature rise, hotspot location and steady-state thermal gradients. The analysis focuses on the effect of asymmetric current loading and interphase thermal coupling when full torque must be preserved.
Both strategies restore full torque, increasing the winding hotspot from 105°C in healthy operation to approximately 130°C–131°C. The Copper-Loss-Minimization strategy reduces total copper losses but introduces thermal imbalance. Nevertheless, strong lateral thermal coupling within the stator redistributes heat effectively, leading both strategies to converge to nearly identical peak temperatures. Since insulation aging is governed by hotspot temperature, both approaches impose comparable insulation stress. However, the significant temperature rise accelerates aging, drastically reducing the machine’s lifetime. Consequently, full-torque fault tolerance is viable only as a short-term emergency state for mission completion rather than continuous long-term service.
The adopted 2D model inherently neglects axial heat transfer and end-winding effects, but it fully captures the radial and orthoradial thermal coupling that drives spatial heat redistribution across the stator. While the machine proves thermally robust, the findings suggest that the inverter, lacking such internal coupling, constitutes the true system bottleneck. Future research should therefore prioritize coupled machine–inverter thermal dynamics.
The study shows that a five-phase PMSM can sustain full-torque operation under an open-phase fault without immediate overheating, challenging the assumption that immediate post-fault derating is required. However, it demonstrates that such operation significantly accelerates aging, classifying it as an emergency state rather than a continuous mode. It further confirms that Copper-Loss Minimization control can be applied safely for short durations, as intrinsic thermal coupling limits hotspot escalation. The results indicate that inverter thermal limits, rather than motor heating, are more likely to constrain ultimate post-fault performance.
