⚡ electrical engineering

Interturn Short Circuit Fault Mitigation in PMSMs

This paper proposes a hardware-free, control-based mitigation strategy for interturn short circuits in permanent magnet synchronous motors that utilizes diagnostic signals to optimize current references and reconstruct feedback components, thereby significantly reducing resistive losses and enabling continued operation under progressive fault conditions.

Original authors: Lukas Zezula, Matus Kozovsky, Ludek Buchta, Petr Blaha

Published 2026-08-03

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Lukas Zezula, Matus Kozovsky, Ludek Buchta, Petr Blaha

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the electric motors powering your favorite gadgets, from the silent hum of an electric car to the precise whir of a factory robot arm. These aren't just simple spinning wheels; they are sophisticated machines called Permanent Magnet Synchronous Motors (PMSMs) that rely on a delicate dance of electricity and magnetism to create motion. Think of the motor's windings (the coils of wire inside) as a team of runners passing a baton. If one runner trips and their shoelace gets tangled with a neighbor's (a short circuit), the whole team's rhythm is thrown off. The tangled runner starts overheating, and the team's speed becomes jerky and uneven. In the past, the safest thing to do was to hit the emergency stop button immediately, shutting the whole system down to prevent a fire. But in a world where we need our robots and cars to keep working even when things go wrong, we need a smarter way to handle the stumble without stopping the race.

This paper tackles that exact problem: how to keep a motor running smoothly even when a tiny, dangerous short circuit develops inside its wiring. The authors propose a clever software fix that acts like a "smart coach" for the motor. Instead of shutting down, this coach watches the motor's heartbeat (its electrical signals), spots the trouble, and instantly recalibrates the instructions to the runners. It tells the healthy runners to adjust their pace so the tangled one doesn't overheat, while simultaneously smoothing out the jerky movements so the motor still feels powerful and steady. The result is a motor that can survive a fault, keep working, and even adapt as the problem gets slightly worse, all without needing any extra hardware or expensive repairs.

The Problem: The Tangled Shoelace

Inside these high-tech motors, the electricity flows through loops of wire called windings. Sometimes, the insulation between two loops wears down, and they touch. This is called an interturn short circuit. Imagine a garden hose where the inner lining rubs through, and water starts leaking out the side. In a motor, this "leak" creates a rogue current that doesn't help the motor spin; instead, it just heats up that specific spot, like a hot spot on a frying pan.

This rogue current causes two big headaches. First, it creates a localized fire hazard by heating up the wire. Second, it messes up the motor's balance. The motor's computer thinks it's pushing with a certain amount of force, but because of the leak, the actual push is wobbly and uneven, causing the motor to vibrate and lose efficiency. Traditionally, the only solution was to stop the motor immediately (a "fail-safe" approach). But for things like self-driving cars or industrial robots, stopping isn't an option. We need a "fail-operational" or "fail-degraded" mode, where the machine keeps working, even if it's not running at 100% perfection.

The Solution: The Smart Coach

The authors of this paper developed a new control strategy that acts like a smart coach for the motor. They didn't add any new wires or sensors; instead, they upgraded the motor's existing "brain" (its control software). This new brain uses two main tricks to handle the short circuit:

The Heat Limit: The coach constantly calculates how much heat the "tangled" wire is generating. If the heat gets too high, the coach automatically lowers the motor's power request to keep the temperature safe. It's like a parent telling a child to slow down on a hot day to avoid getting a sunburn.
The Balance Fix: The coach also realizes that the motor's sensors are seeing a distorted picture because of the leak. So, it mathematically "subtracts" the noise caused by the short circuit from the feedback loop. This allows the motor to control its speed and torque as if the short circuit didn't exist, keeping the ride smooth.

How It Works: The Discrete-Time Model

To pull this off, the researchers used a mathematical model that looks at the motor's behavior in tiny, split-second snapshots (called discrete-time steps). They realized that the short circuit creates a specific pattern of "rogue current" that behaves predictably. By tracking this pattern, the system can estimate exactly how much heat is being generated and how much the motor's balance is off.

The key innovation is a new way of setting the motor's target speed and power. Instead of just asking for "maximum power," the system asks for "maximum power without burning the wire." It finds a sweet spot where the motor is still strong, but the shorted wire isn't getting any hotter than it should. This is called an ISC-aware MTPA (Maximum Torque Per Ampere) strategy. It's like finding the perfect gear on a bicycle: you want to go fast, but you don't want to pedal so hard that you burn out your legs.

The Results: Keeping Cool and Moving Forward

The team tested this idea in a real laboratory setting using a motor with a special setup that allowed them to create controlled short circuits. They simulated a fault that got progressively worse by lowering the resistance of the short circuit (making the "leak" bigger) in steps.

The results were impressive. When the motor had the new "smart coach" software:

Less Heat: The heat generated in the shorted wire dropped by 18–27% compared to a motor without the fix.
Less Energy Waste: The total electricity the motor used dropped by 23–36%.
Smoother Ride: The motor didn't jerk or lose speed as much when the fault happened.

Even more importantly, the system could adapt in real-time. As the researchers made the short circuit worse (by changing the resistance), the software automatically adjusted the motor's settings to stay safe. In some cases, if the fault got too severe, the system would gently reduce the motor's power (a "fail-degraded" mode) to prevent damage, rather than shutting down completely.

What This Means

This paper shows that we don't always need expensive hardware upgrades to make machines safer and more reliable. By using smarter software that understands the physics of a fault, we can keep electric motors running even when they are damaged. The authors demonstrated that this method works in real-time, reducing energy waste and preventing overheating without needing extra sensors. While the system does have to make some trade-offs (like reducing maximum speed in extreme cases), it successfully keeps the motor alive and functional, turning a potential disaster into a manageable glitch. This is a big step toward making our electric vehicles and robots more resilient, ensuring they can keep going even when things go wrong.

Technical Summary: Interturn Short Circuit Fault Mitigation in PMSMs

Problem Statement
Interturn short circuits (ISCs) represent a critical failure mode in permanent magnet synchronous motor (PMSM) drives. Unlike catastrophic failures that necessitate immediate shutdown, ISCs often begin as minor insulation degradations that can rapidly escalate. Once established, the shorted path generates a fault current driven by back-electromotive force and inductive coupling. This phenomenon creates two primary issues:

Thermal Stress: The fault current causes localized resistive heating, accelerating insulation degradation and potentially leading to full phase-winding failure.
Electrical Asymmetry: The ISC distorts the stator currents, introducing torque ripples and degrading drive performance.

While "fail-safe" approaches (disabling the drive) are common, they are increasingly unacceptable in safety-critical applications (e.g., autonomous vehicles, industrial automation) where system availability is paramount. Existing fault-tolerant control (FTC) strategies often rely on hardware modifications (e.g., multi-phase machines) or separate control objectives (limiting losses vs. suppressing ripple), lacking a unified approach for standard three-phase drives that utilizes only standard control-loop signals.

Methodology
The authors propose a control-based mitigation framework that operates within a standard Field-Oriented Control (FOC) structure without additional dedicated hardware. The method relies on a universal post-ISC discrete-time model and integrates two primary mechanisms:

Diagnostic Integration: The system utilizes diagnostic features inferred from standard control-loop signals to estimate fault severity ( $\sigma$ ), short-circuit resistance ( $R_{sc}$ ), and fault location. These estimates are derived from a recursive algorithm that adapts motor parameters ( $R_s$ , $L_{eq}$ ) and identifies ISC-related parameters ( $\Theta_f$ ) using a Kalman filter-based approach.
Resistive-Loss-Limited Current Reference Generation: Unlike traditional Maximum Torque Per Ampere (MTPA) strategies, the proposed method generates current references ( $i^*_{d,h}, i^*_{q,h}$ ) that strictly adhere to a resistive loss constraint. The objective is to ensure that the total resistive power loss ( $p_{res}$ ), which includes both healthy copper losses and ISC-induced losses, does not exceed the thermal limit of a fault-free motor ( $3R_s I_{max}^2/2$ ). This results in an "ISC-aware MTPA" trajectory that balances fault-current reduction with natural stator losses, rather than aggressively minimizing the fault current alone (which could increase healthy copper losses).
Feedback Path Reconstruction: To prevent the torque ripple and current distortion caused by the ISC from affecting the control loop, the current controller operates on reconstructed, fault-free current estimates ( $\hat{i}_{d,h}, \hat{i}_{q,h}$ ) rather than the raw measured currents. This allows the torque-producing current component to remain stable despite the fault.

The mitigation strategy is activated only after diagnostic estimates stabilize to a required accuracy, ensuring robustness against transient estimation errors.

Key Contributions

Unified Framework: The paper presents a unified approach that simultaneously limits fault-induced thermal loading and suppresses torque ripple within a standard three-phase FOC structure.
Loss-Constrained Reference Generation: The derivation of a post-fault current reference generator that minimizes total resistive losses under a fixed torque demand, effectively creating a thermal-safe operating envelope.
Hardware-Free Implementation: The method achieves fault tolerance using only signals available in the standard control loop, avoiding the cost and complexity of hardware-assisted FTC (e.g., redundant windings or modified converters).
Real-Time Adaptation: The system demonstrates the ability to adapt to progressive fault aggravation (emulated by stepped changes in short-circuit resistance) in real-time.

Experimental Results
The method was validated on a PMSM testbench equipped with a Fault Insertion Unit (FIU) capable of emulating varying ISC severities. Key findings include:

Power Reduction: In the most severe fault scenarios, the proposed mitigation reduced the fault-induced increase in input power by 23–36% compared to the unmitigated baseline.
Local Thermal Reduction: The local resistive loss increase in the shorted segment was reduced by 18–27%, directly addressing the risk of thermal runaway.
Performance Stability: The reconstruction of fault-free current components successfully suppressed speed transients and torque ripples that typically occur when the outer speed loop attempts to compensate for distorted current feedback.
Fail-Degraded Operation: In scenarios where the thermal constraints made the original operating point infeasible (e.g., high speed and high load), the controller successfully derated the drive to maintain thermal safety, prioritizing protection over torque production.

Significance and Claims
The authors claim that this work addresses a gap in existing literature where thermal stress reduction and torque-ripple compensation are often treated separately. By combining these objectives into a single control strategy grounded in a discrete-time post-ISC model, the method enables "fail-operational" or "fail-degraded" regimes for standard PMSM drives.

The paper modestly notes that the approach relies on an equivalent inductance assumption (neglecting saliency), which is consistent with the diagnostic stage where steady-state operation often lacks sufficient excitation to reliably separate $L_d$ and $L_q$ . However, the experimental validation confirms that the method effectively reduces thermal loading and maintains drive stability without requiring additional hardware, making it a practical solution for enhancing the availability of electric drives in critical applications.

The Problem: The Tangled Shoelace

The Solution: The Smart Coach

How It Works: The Discrete-Time Model

The Results: Keeping Cool and Moving Forward

What This Means

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