Rare-earth permanent magnets have become the default assumption in EV motor design, but that default carries costs that go beyond the magnets themselves: volatile pricing, a concentrated supply chain and a heavy extraction footprint. The usual response is to accept those costs because removing the magnets is assumed to cost performance. This piece works through why that assumption doesn’t hold, starting with how magnetless machines actually generate torque and ending with why the engineering has to be treated as one system rather than a parts swap.
Understanding Magnetless Motor Technology
Magnetless traction motors replace a permanent magnet’s fixed rotor field with one of three mechanisms: induced rotor currents in induction machines, saliency torque in synchronous or switched-reluctance machines, or an electrically generated field in wound-field synchronous machines. In a permanent-magnet synchronous motor, rotor magnets interact directly with the stator’s rotating field; reluctance designs instead rotate toward the lowest magnetic-reluctance path, while induction designs generate rotor current electromagnetically [1].
These are distinct engineering choices, not one interchangeable category. Induction machines introduce rotor electrical losses, reluctance machines must extract torque from rotor geometry alone, and wound-field machines spend power establishing rotor flux. Efficiency in any of them depends on motor, inverter and duty cycle being designed as a set, not on the absence of magnets by itself. Current research identifies induction, synchronous-reluctance and wound-rotor machines as viable rare-earth-free EV alternatives [1], which sets up the real question: what does it cost to make that rotor field electrically, and can that cost be engineered away?
How Electrical Rotor Excitation Works
Wound-field synchronous machines answer that question by replacing a fixed magnetic field with a controllable one. Rather than relying on permanent magnets embedded in the rotor, the machine energises a rotor winding to create its field, and the stator’s three-phase currents interact with that field to produce synchronous torque. Unlike a permanent-magnet rotor, whose field strength is fixed by the magnet material, excitation current lets field strength be adjusted as operating conditions change.
That controllability is the design opportunity: field can be supplied where torque demands it and reduced when it doesn’t, rather than carrying a constant magnet field through every operating point, including the many low-torque moments where a permanent magnet’s field goes unused. The trade-off is real: creating rotor field consumes power and adds winding losses. The question that follows, and that the rest of this argument turns on, is not whether electrical excitation is free, but whether its controllability can be engineered to preserve performance without rare-earth magnets.
Identifying Core Limitations
Permanent-magnet traction motors deliver strong torque density, but that performance is inseparable from temperature control. Copper losses rise with current, and rotor magnets operate within fixed temperature limits that constrain sustained high-load operation, so cooling has to protect output and efficiency, not just prevent failure. The broader traction-motor literature identifies thermal management as a major determinant of global efficiency, particularly in high-performance BEVs [2].
It’s also a system-level burden: liquid cooling can meet demanding operating requirements, but it requires managing added cost and complexity [3], a complexity familiar from off-highway EV thermal and climate-management practice, where cooling architecture is already treated as a first-order design constraint (Webinar: Thermal and climate management for off-highway EVs). In traction motors specifically, the constraint isn’t only rejecting environmental heat, it’s preserving the motor’s electromagnetic operating margin under repeated, cyclic load.
Advantages of Magnet-Free Designs
Because rotor field is created electrically rather than fixed in a magnet, it can be regulated rather than merely endured. Electrical excitation lets torque-producing flux be reduced at high speed and restored when torque demand rises, avoiding the irreversible demagnetization risk that permanent magnets face under severe thermal or fault conditions. A direct EV comparison has assessed electrically excited and interior permanent-magnet machines across torque, power and efficiency [4].
The advantage is conditional: generating rotor field consumes power and can add copper losses, so magnet-free machines still require disciplined thermal design, the same discipline that off-highway EV programmes already build around as a core operating constraint (Webinar: Thermal and climate management for off-highway EVs). What controllable excitation adds is another variable engineers can use to protect performance under stress, rather than relying on a magnet’s fixed field to do it alone.
Cooled Motors: A Systematic Solution
Cooled Motors treats the magnetless motor as a system-design problem, not a component substitution. Its UESM electrically excites the rotor while retaining a standard three-phase inverter, avoiding the extra rotor power electronics commonly associated with separately excited machines. Rotor-field control, winding architecture and thermal paths are engineered together: higher current can raise I²R losses, so continuous output depends on removing heat as deliberately as torque is produced. [Cooled Motors Internal]
The result is a motor built to replace a permanent-magnet unit without requiring a new vehicle electrical platform. That approach targets the trade-off that usually accompanies magnet-free designs, gaining supply-chain resilience at the expense of packaging, cooling complexity or performance, by making excitation, control and manufacture mutually compatible from the start rather than adding them as afterthoughts. Other groups pursuing rare-earth-free motors, such as AEM Group, are similarly scaling manufacturing capacity around this shift, evidence that the industry is treating magnetless design as a systems problem worth investing in [5].
System-Level Thinking for Sustainable Solutions
A sustainable traction motor cannot be designed by swapping one material or component in isolation. Removing rare-earth magnets changes how torque is produced, where losses arise and which constraints govern continuous performance, so material choice, electromagnetic design and thermal architecture have to be evaluated together. Research on rare-earth substitution reaches the same conclusion: rare-earth-free traction motors are a system-level design problem, not a magnet-substitution exercise [6].
That integration carries its own discipline. Cooling protects continuous output but adds a circuit and integration complexity; electrical excitation avoids magnet dependence but demands careful control of copper losses. Neither trade-off disappears on its own. Sustainable designs earn their advantage only when materials, electromagnetic performance, structural requirements and efficiency are considered together rather than optimised separately [6].
Sources
- mdpi.com
- sciencedirect.com
- pmc.ncbi.nlm.nih.gov
- iieta.org
- Machinery Market — machinerymarket.co.uk
- uu.diva-portal.org