Rotors with permanent magnets

The principle of motors with permanent magnets (PMSM) is based on the interaction of the fixed magnetic field of the rotor with the rotating magnetic field of the stator. The rotating magnetic field of the stator is generated by electric current flowing through the three-phase winding of the stator, while the magnetic field of the rotor is generated by the bonded permanent magnets. The motors with permanent magnets achieve a higher efficiency than standard asynchronous motors, they do not require monitoring of the rotor position, and because they are in principle excited by permanent magnets, their design can exclude the excitation winding losses. The rotors with permanent magnets are smaller and lighter, thus the motor is capable of delivering the same or even a higher power with smaller overall dimensions. The manufacturing price of the motor decreases with its decreasing volume, and the use of permanent magnets increases its torque overload that can be ten times higher than that for all the other motor types. The permanent magnets increase the magnetic flux through the motor air gap and thus the total torque is considerably higher than that of the induction motors.

Magnet types in rotors:

The rare-earth magnets - neodymium, samarium and also ferrite permanent magnets, are used for the motors with permanent magnets. An application and price determine which of them is to be used. The neodymium-based permanent magnets have the highest magnetic flux and the highest energy product that determines the motor power, however their application is limited by a thermal class of the magnet. These magnets can be used for temperatures approx. up to 230°C and moreover they are sensitive to corrosion. The samarium magnets succeed the neodymium magnets where they are unsatisfactory. The samarium-based magnets have a high temperature resistance up to 350°C and an excellent corrosion resistance.

Manufacturing of rotors with magnets:

PZK BRNO realizes customized manufacturing of rotors with permanent magnets on the surface as well as with small and medium-size magnets buried (up to 50 kg). We focus on special applications having a high demand for the design quality. In our own testing laboratory, we test magnetic properties of individual magnets as well as products with them and also strength of bonded joints. We check dimensions on our own coordinate measuring machine (CMM) and perform balancing on our own balancing machine. Using the finite element method (FEM), we are able to design or optimize the most suitable solution.

We specialize in the following products:

• Rotors with permanent magnets on the surface
• Rotors with buried magnets
• External rotors of “outrunner” type
• Rotors with additional bandage (Polyglas, Kevlar, carbon)
• Rotors with protecting sleeve