Motors and Drives

Permanent Magnet Motors

With advantages such as high efficiency, compact size, and high torque density, permanent magnet (PM) motors are becoming increasingly competitive in many applications. PM motors use permanent magnets to create the magnetic field provided by the stator and rotor windings of other alternating current (AC) and direct current (DC) motors. Replacing part of the motor windings with permanent magnets eliminates the conductor losses associated with those windings, thus making the motor more efficient. While costs have decreased dramatically in recent years, PM motors are still more expensive than conventional motors.

The introduction of high energy density rare earth magnets such as neodymium-iron-boron (NdFeB), has dramatically increased the range of applications of PM motors. Typical applications of high-performance PM motors in the original equipment manufacturing (OEM) industry include floor cleaning equipment, elevators, forklifts and other types of lift and material handling equipment, power tools, golf carts, etc. Other applications include consumer appliance, automotive and other industries. The most common types of PM motors used in industry are

Brush PM Motors -- Conventional DC machines with mechanical commutators and brushes where permanent magnets provide the excitation field.
PM Synchronous Motors -- Conventional synchronous machines where permanent magnets replace the DC rotor winding.
Brushless DC Motors -- High power density permanent synchronous machines equipped with rotor position sensors and advanced controllers for electronically commutating the stator windings.
Line-start PM Synchronous Motors (sometimes called Hybrid Synchronous PM Motors) -- Synchronous machines equipped with squirrel-cage induction-type rotor winding for line starting. Permanent magnets embedded in the cage synchronize the motor.

For most applications in the OEM industry, there are as many PM motors to choose from as suppliers of these motors. One way of ensuring that the PM motors under consideration fit your specifications is to conduct testing of candidate motors to determine pertinent performance data such as rated torque, efficiency, temperature rise, reliability, etc.

Without proper protection, high temperatures, severe overloading and short circuit conditions can demagnetized permanent magnets and seriously impact motor operations. Therefore, it is important to ensure these motors meet the constraints of your motor application. OEMs frequently ask Advanced Energy to perform endurance, efficiency, torque speed curves, build and inspection analyses and several other tests that help select the lowest cost and most reliable motors for their applications. Special tests such as short circuit, voltage speed and voltage current tests can be performed to fully characterize the performance of PM motors and to determine magnetic circuit parameters. Please contact us to discuss your motor concerns.

For More Information

For information, contact David Berkowitz at dberkowitz@advancedenergy.org or (919) 857-9047.