There are many kinds of rotor magnetic circuit structure of permanent magnet brushless DC motor. The different uses, price and performance requirements determine the customer's choice of different structures.

According to the placement of permanent magnets on the rotor in different ways, can be divided into surface mount type, embedded permanent magnet (Inset PM) and built-in permanent magnet (IPM), today we mainly talk about the advantages and disadvantages of these three structures.

Surface mount structure:

Its main advantage is simple structure, thus reducing manufacturing costs. In addition, under the same size and the same power, the permanent magnet material used by the surface mount design of the motor is less than the built-in structure. This is because the built-in structure always has more magnetic leakage. The main disadvantage is that permanent magnets are easy to be demagnetized by armature.

Embedded structure:

The permanent magnet of this structure is embedded from the surface of the rotor core, so it combines the advantages of the surface mount type and can generate magnetoresistive torque because of the presence of the core salient pole.Compared with the surface mounted structure, the obvious advantage of IPM lies in the demagnetization of reducing the armature reaction and the protection of centrifugal force at high speed. More importantly, the PM structure is suitable for the weak magnetic control of the motor.

Built-in structure:

It is the permanent magnets embedded inside the rotor core. Its advantage is that the permanent magnet is protected well by the periphery ,so that prevent the armature effect of demagnetization and mechanical reaction from being affected, and has a magnetic agglomeration effect, which will concentrate the magnetic flux generated by the permanent magnet, so as to obtain a high air gap magnetic flux density. In addition, the presence of a core pole in the built-in structure can generate magnetoresistive torque. It also enables constant power operation over a wide speed range. Therefore, it is often used in the sine wave drive mode where weak magnetic control is required.

The built-in type also has W-shaped permanent magnet rotor structure, multi-layer magnet rotor structure and other structural forms.

Six different type structures of brushless motor rotor permanent magnet display:

(a) Surface mount type (b) diskette type (c) magnetic ring type

(d) Bread type (e) Bread type (f) embedded type

(g) Built-in tangential type (h) built-in radial type (i) built-in V-shaped radial type

Among these type, the surface mount structure is the most commonly used one, that is, the structure of the curved sheet magnet (neodymium segment magnet or ferrite segment magnet) pasted on the surface of the rotor magnetic core, and the inner and outer circles of the sheet magnet can be designed with different cores to form an unequal width air gap, so that the back electromotive force waveform is close to the sine wave.

Our company is a professional motor permanent magnet manufacturer, we can provide motor magnets which commonly used, such as ceramic ferrite segment magnets, rare earth neodymium arc/rectangle magnet, injection neodymium/ferrite, bonded neodymium ring magnet, etc.. If you have any question, welcome to your custom drawing, or provide magnet specifications and inquiry sample and quotation

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