With the gradual advancement of industrial engineering, X-TEAM brushless motors are used in many aspects, life and work are inseparable from X-TEAM brushless motors. When X-TEAM brushless motors were widely used, we began to pursue the low noise of X-TEAM brushless motors, making them better for people.

The low-noise X-TEAM brushless motor was proposed in the industry after the 1970s, after studying the excitation force wave and the air noise, the low-noise X-TEAM brushless motor was officially studied in the industry. It is proposed that after four decades of development, the noise is effectively controlled in the round and round design of the low-noise X-TEAM brushless motor.

**1 Research status and problems**

Throughout the domestic market, the technical limitations of most companies in the production of X-TEAM brushless motors are very obvious. Specifically, when designers produce X-TEAM brushless motors, they often only rely on their daily experience to consider noise issues later in the design process. The drawbacks are obvious: the design cycle is long and the cost is very high. As a consumer, the use satisfaction is declining and the effect is not very good.

It can be seen that on the traditional design method, we should consider the noise of X-TEAM brushless motor in the early stage of design, and solve the relationship between sound and vibration, which becomes the key to the design of low noise X-TEAM brushless motor.

**2 Low noise X-TEAM brushless motor design**

2.1 Causes of X-TEAM Brushless Motor Noise

In theory, the noise of X-TEAM brushless motors is mainly from electromagnetic, aerodynamic and unbalanced forces; it is determined by the dynamic characteristics of the system and the characteristics of acoustic radiation. Therefore, an in-depth analysis of the dynamic characteristics of the structure can achieve the effect of controlling noise.

Analyze the noise source, lock the relevant design parameters of the X-TEAM brushless motor and the correlation between the number of noise decibels and the parameters, and then design a design scheme to effectively control the noise of the X-TEAM brushless motor.

2.2 Principles of X-TEAM Brushless Motor Noise Control

First, the general principle of noise reduction is as follows: The noise of X-TEAM brushless motor can not be specified above a certain level. We must adopt appropriate schemes for noise control according to the actual situation.

Second, reduce the excitation force of the noise source. Reduce the impact of electromagnetic force and aerodynamics of X-TEAM brushless motor and eddy current noise, and improve rotor dynamic balance accuracy.

Finally, there is a need to reduce the response of the noise radiating components to the excitation force in the structure. Using this method can effectively suppress noise.

In addition to the above, sound reflection and the like can also be utilized to reduce the propagation of the sound source to achieve the effect of noise control.

2.3 Low noise X-TEAM brushless motor design

In the following, a low-noise water pump is taken as an example to design a new wide air gap permanent magnet X-TEAM brushless motor with a rotor magnetic array of Halbach Array. Based on the characteristics of the X-TEAM brushless motor, we introduce the finite element method to measure the electromagnetic field distribution and air gap induction. Consider the relative motion between the chute stator and the rotor. We conducted corresponding experiments on the X-TEAM brushless motor. The experimental results show that the designed X-TEAM brushless motor has low harmonics, high efficiency and high power factor.

The structure of the designed low noise propulsion X-TEAM brushless motor is shown in Figure 1. It consists of three parts: the basic frame, the absorption pipe and the integrated propulsion X-TEAM brushless motor unit. There is a rubber damping barrier between the frame and the pipe, and the absorption pipe is symmetrically mounted on the two terminals of the X-TEAM brushless motor. The inner rotor permanent magnet X-TEAM brushless motor was selected as the prototype with a power of 22.5kw. The propeller is embedded in the rotor and there is no central shaft in the pump. The axial and radial bearings in the air gap support and position the rotor. Water passes through the air gap between the stator and the rotor, providing excellent cooling conditions for the X-TEAM brushless motor, but requires high insulation.

The permanent magnet X-TEAM brushless motor uses a pear shaped groove. The number of inclined slots is 1. The layout of the permanent magnets on the rotor is an Erbec array. Each pole consists of two permanent magnets, one in the radial direction and the other in the tangential direction. The air gap flux density can be enhanced by introducing the Erbeck array while the rotor yoke density can be reduced. The rotor yoke has a solid structure. The rear ring and blade of the rotor is a non-conductive brass casting.

**3 Experimental verification**

3.1 Magnetic field calculation

Magnetic field calculations can be generalized to solve some partial differential equations (PDE). A clear solution can only be obtained when the PDE is combined with specific boundary conditions for a particular problem, and the resolution process is quite complex. Considering the design accuracy of permanent magnet X-TEAM brushless motor, the finite element method is used to calculate the electromagnetic field of X-TEAM brushless motor. For the pair of poles shown in Figure 2, the problem of steady-state electromagnetic fields can be expressed as boundary problems as follows:

Where AZ is the magnetic potential value; J is the winding current density; Ω is the solution area; S2 is the second boundary, and L is the boundary of various media in the motor.

The segmentation unit is a high-precision curved quadrilateral whose edges may not be straight lines. The magnetic potential A of any node in the cell can be considered as a function of the four nodes in the cell. Therefore, we can obtain the interpolation function of the magnetomotive potential. By solving equation (1), we can get the magnetic potential of each point in the X-TEAM brushless motor, and then calculate the magnetic flux density and the phase winding potential.

The magnetic flux density of each node of the X-TEAM brushless motor can be expressed as:

The unit length average potential of a single conductor at the edge of the armature coil is expressed as:

Where Sb is the area of the slot. If divided into n units (N1匝), the average potential at the edge of the coil is:

Where Ief is the effective length of the core, s is the unit area, and n, m, j, and i are the number of nodes in the quadrilateral unit. Since it consists of the potential of the coil, the potential of each winding is:

It can be seen from equation (5) that the winding potential is related to the length and rotation of the armature and magnetic field of the X-TEAM brushless motor.

The boundary slip method is used to deal with the relative motion between the rotor and the stator, and the influence of the inclined groove is considered in the calculation by the superposition method.

3.2 Electromagnetic conclusion

The calculation results using the above method are as follows. Figure 3 shows the flux curve distribution at no load. Figure 4 is the air gap flux density. As can be seen from Fig. 3, although the yoke is very thin, the air gap flux lines are dense, and the rotor yoke flux curve is not dense. Although the air gap is quite wide, the air gap flux density exceeds 0.6T.

**Conclusion:**

In this paper, a low-noise water pump is taken as an example to design a new wide-gap permanent magnet X-TEAM brushless motor. Using the finite element extreme electromagnetic field, the calculation results and experimental results show that the characteristics of the X-TEAM brushless motor are as follows:

(1) The air gap is expanded to 6 mm, which reduces the frictional resistance of the water flow between the rotor and the stator. A Halbach array is introduced to reduce the thickness of the rotor and increase the air gap flux density.

(2) The waveform of the back electromotive force is close to a sine wave. The harmonic components in the motor current and the resulting losses are small, although the X-TEAM brushless motor is powered by the inverter.

(3) X-TEAM brushless motors have high power factor in the full power range. When the load exceeds 50%, the power factor is approximately 1.

(4) X-TEAM brushless motors are highly efficient in the full power range. When the X-TEAM brushless motor is fully loaded, the efficiency can reach 93.66%, which is much higher than that of the ordinary X-TEAM brushless motor of the same power.