IPM vs SPM Electric Motors

A comparison between interior permanent magnet (IPM) and surface permanent magnet (SPM) motors. 

Which advantages you can get using this type of motors on construction, agricutlural and industrial machines?

Electric Vehicles make use of permanent magnet synchronous traction motors for their high torque density and efficiency. The main result of the proposed analysis is to put in evidence the different behavior of IPM and SPM motors.

A permanent magnet motor (PM) can be separated into two main categories: interior permanent magnet (IPM) and surface permanent magnet (SPM). Both types generate magnetic flux by the permanent magnets affixed to or inside of the rotor.

IPM Motor vs SPM Motor

Courtesy of KEB AG

IPM Motor

A type of motor that has a rotor embedded with permanent magnets is called IPM (interior permanent magnet).

SPM Motor

A type of motor in which permanent magnets are attached to rotor circumference is called SPM (surface permanent magnet).

Electric solutions for constructions

Perhaps the biggest advantage of IPM designs, one that gives them an edge in vehicle applications like traction motors, is the high-speed performance. The power versus speed curve for SPM motors is roughly hyperbolic, rising to a region of quasi-constant power over a narrow speed range, then falling off.

For decades, surface permanent-magnet (SPM) motors dominated the market for permanent magnet motors. In recent years, however, the emerging hybrid and electric vehicle market, have boosted demand for interior permanent magnet (IPM) motors. With advantages like near-constant power over a broad speed range and a magnet-retaining design, IPM motors provide a good solution for applications like traction and auxiliary motors.

For vehicle applications IPM technique provides big benefits compared to SPM motors. The IPM configuration allows more control over the magnetization of the magnetic circuit.

IPM motors, in contrast, provide a much broader region of more or less consistent torque. Using a technique called field weakening, designers can apply current to modify performance. Field weakening essentially involves tuning the magnetic field of the stator to partially oppose the effect of the permanent magnets.

Power Compariosn Chart

Why you should choose an IPM motor instead of a SPM

High Torque

High torque is achieved by using reluctance torque in addition to magnetic torque.

Energy Saving

IPM motors consumes up to 30% less power compared to conventional SPM motors.

High Speed

It can respond to high-speed motor rotation by controlling the two types of torque using vector control.


Mechanical safety is improved as, unlike in a SPM, the magnet will not detach due to centrifugal force.

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