Comparison, Induction Vs. PM Motors for EVs

AC induction motors tend to have slightly lower peak efficiency than comparable PM motors. This is because some input energy is always used to induce the rotor field (causing resistive (I²R) losses in the rotor). Moreover, a small amount of slip is required, which produces heat. In practice, well-designed induction motors for EVs can reach around 90–93% peak efficiency under optimal load. However, efficiency drops at partial load or low speeds, as the motor still draws magnetising current and incurs rotor losses even when not producing high torque. The need to create both stator and rotor magnetic fields leads to more losses across a broad operating range. One upside is that when an induction motor is not under load (for example, cruising with one motor inactive), the absence of permanent magnets means it can be essentially de-energised and freewheel with minimal drag losses, improving coasting efficiency.

Permanent magnet motors are known for their high efficiency, especially across varying loads. Because the rotor’s field is supplied by magnets, there are no rotor current losses and no slip. The motor can maintain synchronised rotation without wasted energy in the rotor. Efficiency ratings for PM traction motors can reach the mid-90s; modern designs achieve 95–97% peak efficiency. They also retain high efficiency at partial load, since no extra current is needed to sustain the magnetic field at low torque output. This superior efficiency (especially in stop-and-go or varying speed conditions) is a major reason why nearly all recent EV models have adopted PM motors, higher efficiency directly translates to better range. For instance, Tesla switched to a PM motor in the Model 3 primarily to improve range per battery charge. The trade-off is that a PM motor always has the magnet field present, so when the motor spins without a load it induces eddy currents and hysteresis losses in the stator (dragging on the rotation). In short, you can’t “turn off” a PM motor’s field, a PM rotor spinning freely will still generate some loss, meaning slightly less coasting efficiency. Overall though, under driving loads, PM motors’ efficiency advantage is significant, often giving a few percentage points better drivetrain efficiency than induction machines – a critical edge for EV range.

Induction motors generally have lower torque density (torque per unit weight or volume) than PM motors. Because the flux in an induction motor is limited by how much current the stator can induce into the rotor (and by magnetic saturation limits of the iron), achieving high torque requires a larger size or more current (which adds heat). Thus, for the same output torque, an induction motor tends to be bulkier and heavier than a PM motor. For example, one industry comparison noted a ~50 kW PM motor could weigh under 30 lbs, whereas an equivalent ~55 kW (75 HP) industrial induction motor might weigh several hundred pounds. While that is an extreme case, it illustrates the point – more of an induction motor’s volume is occupied by iron and copper to generate the same flux that a PM motor can with compact magnets. Induction motors can still produce high peak torque (they have historically been used in performance EVs like the original Tesla Model S), but they usually need aggressive current input to do so, and their continuous torque capability is limited by heating.

PM motors offer high torque and power density, meaning a smaller, lighter motor can produce the same (or greater) torque than a larger induction machine. The permanent magnets supply a strong flux in the rotor without bulk electromagnets, enabling a compact rotor design with high magnetic loading. Combined with high-energy magnet materials (e.g. NdFeB magnets with ~1.2–1.4 Tesla fields), this yields excellent torque in a small package. In fact, modern PMAC motors exceed the torque and power density of traditional AC induction designs. This is evident in high-performance EVs and motorsport: nearly all use PM motors for their superior power-to-weight ratio. For instance, iNetic Traction’s rEV Motor Range is specifically noted for its exceptional power-to-weight ratio, delivering up to 400 kW in a compact form factor suitable for demanding applications like racing and heavy commercial vehicles. Similarly, the smaller iFA and iPA series at iNetic focuses on optimal power density for applications like onboard hydraulics and fan applications. High torque density not only improves acceleration and performance but also helps with packaging in the vehicle, a lighter motor contributes to overall weight savings and potentially more interior or battery space.

One of the strongest points in favour of induction motors is typically lower cost for a given power rating. Induction motors use conventional materials; steel laminations and copper/aluminium – and do not require expensive magnets. In high-volume production, the active material cost of an induction machine can be ~20–30% lower than that of an equivalent PM motor. This is primarily because permanent magnets (especially rare-earth magnets used for high performance) are costly components. Induction motors also avoid reliance on rare-earth supply chains, which can be a strategic advantage if magnet material prices are volatile. For OEMs building cost-sensitive EVs (such as entry-level models or commercial vehicles where upfront cost is critical), an induction motor might offer savings. The simpler rotor construction can also reduce manufacturing complexity. However, it’s worth noting that induction motors still require a sophisticated inverter and control software (similar to PM motors), so electronics costs are comparable. And any cost advantage must be weighed against efficiency: a less efficient induction motor may require a larger battery to achieve the same range, potentially offsetting motor cost savings with battery cost.

PM motors generally have a higher initial cost due to the magnets. High-performance neodymium magnets and their assembly into the rotor add expense. Manufacturers also often invest in precise rotor balancing and magnet retention techniques, which can increase production costs. Estimates show that a comparable PM traction motor’s active components might cost ~25% more than an induction motor’s. Additionally, the control of PM motors can be a bit more complex (requiring rotor position sensors or sensorless algorithms and safeguards against demagnetisation), but in modern designs, this is largely a solved problem and similar in complexity to vector-controlling an induction motor. Despite higher upfront cost, the efficiency of PM motors can yield cost benefits over the vehicle’s lifetime – energy savings (especially for a vehicle used daily) may outweigh the initial price difference. Also, as EV production scales up, economies of scale and improved magnet technologies (or use of less rare-earth content) are steadily reducing the cost gap. Many automakers have deemed the efficiency and weight advantages of PM motors worth the cost in today’s EV market, which is why PM machines dominate current EV designs despite higher material costs.

Both induction and PM motors are low-maintenance by design; they are both brushless (no commutators or brushes to wear out) and have only a few moving parts (the rotor on bearings). In practice, the primary maintenance considerations for both are cooling system health and bearing replacement after long life. Induction motors have a reputation for ruggedness. The absence of fragile components like magnets means an induction rotor can tolerate mechanical and thermal stresses to a degree. For example, temporary overheating of an induction motor will mainly risk the insulation of windings (which is similar to a PM motor’s stator), but there’s no risk of permanently weakening a magnetic field. Induction rotors are basically solid metal forms; they generally either work or, if severely overstressed, might crack/break (which is rare outside extreme conditions). In most EV use cases, an induction motor’s reliability is excellent, Tesla proved this with the Roadster and Model S, logging many miles on induction machines.

PM motors are also very reliable, but there are a few additional considerations due to the magnets. Temperature is a critical factor; excessive heat can cause magnets to lose strength (a phenomenon accelerated if the motor exceeds certain temperature thresholds for the magnet grade). Most PM traction motors use high-temperature-rated magnets and have thermal management to avoid this. Nonetheless, sustained operation at very high temperatures can gradually demagnetise the rotor over time. Extreme overcurrent or a sudden short-circuit can also potentially demagnetise or physically damage magnets. If a PM motor’s magnets partially demagnetise, the motor will have permanently reduced performance and would require rotor replacement to fix, an unlikely failure in normal usage, but a point to note for abuse conditions. Another aspect is that the adhesive or mechanical retention for magnets must be robust, high-speed PM rotors need careful design to ensure magnets stay in place under centrifugal forces. Reputable manufacturers like iNetic Traction address these design challenges in their PM motors, testing for worst-case scenarios. In terms of general maintenance, PM motors don’t need any routine service different from induction motors (just keep them cool and the bearings lubricated). Both motor types are typically designed to last the life of the vehicle with minimal intervention. Overall, the reliability of PM motors in EVs has proven to be excellent, on par with induction machines, as long as the motor is operated within its design envelope (especially temperature and speed limits).

Induction motors have been produced in virtually every size and power, from tiny fractional-kW motors to multi-megawatt industrial drives. This scalability is an advantage in industrial contexts and was beneficial in early EV experiments. In the context of EVs, induction motors found use in some pioneering models (GM EV1, Tesla Roadster and Model S) and are still seen in certain applications. They can be a good choice for cost-sensitive EVs or those operating in extreme environments. For instance, an off-highway or high-performance vehicle that faces very high peak temperatures might opt for an induction motor to avoid magnet issues. Similarly, if an automaker wants to avoid reliance on rare-earth magnets due to supply chain concerns, induction is an alternative. Induction motors may also be considered in designs where a motor will often be spun without load or be shut off for efficiency (such as a multi-motor AWD setup where one axle’s motor can be deactivated at cruise). In fact, some dual-motor EVs use one induction motor alongside a PM motor to exploit this – the induction unit can be shut off and freewheel with virtually no drag when not needed, while the PM motor handles cruising efficiently. This strategy, used by Tesla in certain Model 3/Y configurations, highlights a niche strength of induction technology. Beyond cars, induction motors remain prevalent in heavy-duty applications (e.g. large electric trucks or buses in some cases) where initial cost savings and robustness might be prioritised over absolute efficiency (although as discussed, this can increase battery costs, leading to higher overview system costs).

PM motors have become the go-to solution for most modern EVs, from passenger cars to motorcycles to even heavy trucks, due to their superior efficiency and compact size. They scale well: designers can use multiple small PM motors for distributed drive (e.g. in-wheel motors or dual-motor setups) or build very large PM machines for buses and trucks (with appropriate magnet technology and cooling). Today’s magnet materials and motor designs allow PM traction motors to cover a wide range of power and torque. iNetic Traction’s product range is a good example of PM scalability – their sEV Motor Range addresses low-voltage and smaller EV needs (12 V up to 650 V systems, covering uses like e-bikes, fans and pumps), the iEV range spans mid-power applications (from ~5 kW up to 300 kW, suitable for mainstream automotive and marine uses), and the rEV series targets high-power applications (200–400 kW, for high-end passenger cars, motorsports, and heavy commercial vehicles). This demonstrates how PM motors can be engineered for everything from light urban mobility to high-performance racing. As EV adoption grows, the industry has largely standardized on PM motors for their blend of efficiency and performance. Even so, engineers must consider factors like magnet supply and operating environment. In some cases (e.g. a hypercar that might see repeated track abuse or a mining vehicle in extreme heat), they might add features like magnetic flux weakening or choose a different motor type if needed. Overall, PM technology continues to advance (for example, incorporating some reluctance torque to reduce magnet content), further extending its applicability. For most OEMs today, a PM motor is the first choice for an EV drivetrain, with induction reserved for special circumstances.