The BLDC Motor Design for Current Industrial and Civil Applications

2.1 Theoretical basis for design research

BLDC motors are gradually replacing brushed motors in most consumer and industrial electronics: hard drives, fan drives, model aircraft, hand tools, industrial robots, Computer Numerical Control (CNC) metalworking machinery equipment, washing machines, industrial pumps/fans, personal vehicles such as electric vehicles, industrial robots, medical devices, smart home appliances (home washing machines), refrigeration compressors, HVAC (Heating, ventilation and air conditioning systems), etc.

In the industry, BLDC is ideal for motion control, industrial robots, CNC machine tools, thanks to the ability to control torque precisely, directly control torque during the control process, BLDC motors operate with a wide speed range and low maintenance and maintenance costs.

BLDC motors are designed with an internal rotor as shown in Figure 1, this type of structure is also called "Inrunner". With this design, the permanent magnets are located above the rotor inside, and this rotor rotates inside the stator coils. Besides, there is also another popular configuration called "outrunner", where the stator coil is located in the center and the rotor with permanent magnets rotates around the outside. With this type of structure, it is often used in Hub motors of electric vehicles, industrial and civil machine motors.

Figure 1. Some types of BLDC motor structures

(a) BLDC motor has rotor inside

(b) BLDC motor has rotor on the outside

Figure 2. Two types of BLDC motors are currently being researched

In the field of industrial machinery, brushless motors are preferred because of their ability to accurately control speed and position, and their ability to adjust torque much better than other motors. In Figure 2, both types of BLDC motors are being researched, designed, and manufactured for application.

From there, the authors researched the BLDC design as shown in Figure 3.

Figure 3. External rotor BLDC motor

Research on BLDC motors for industrial and civil use is an important and rapidly developing field: optimizing stator and rotor structures to reduce weight and size while still ensuring performance.

Figure 4. An example of the total force acting on a vehicle is the application of BLDC for electric bicycles

Select high quality materials for coils (copper, aluminum), permanent magnets (Neodymium - NdFeB) and laminated steel cores to reduce energy loss and increase efficiency. Control problem with trapezoidal electromotive force to optimize torque, reduce noise and increase energy efficiency, used for industrial machines, civil electric vehicles (see Figure 4).

For example, Figure 4 shows the forces acting on a vehicle when moving on a slope where Fa is the aerodynamic drag force, Frr the rolling resistance, Fc the climbing force, Ftrac the total drag force, g the acceleration of gravity, θ the slope angle. The reference vehicle is a two-wheeled vehicle with the parameters as shown in Table 1 below.

Table 1. The main parameters of BLDC

In today's industry, machines also need precise control, aiming for high quality work (Figure 5).

Figure 5. The BLDC motors used in industrial machinery and civil

BLDC are being widely used in electronic devices such as fans, computers, printers, hand-held cutting machines, air-conditioning fans, car air-conditioning fans, drones, as well as in the automation and robotics industry.

2.2 The BLDC motor design calculation in industrial and civil fields

The BLDC calculation research process is a complex process that includes many steps, from determining technical requirements to simulation and actual testing:

Rated torque is expressed through power Po and angular speed ω [3]:

$T=\frac{P_o}{\omega}$          (1)

The following formulas are referenced by the author in document [4]. Mechanical angular velocity:

$\vartheta_m=\frac{T}{\omega}$          (2)

Synchronous angular velocity of the motor:

$\vartheta_e=\frac{N_m}{2} \cdot w_m$          (3)

In which, N_m is the number of magnetic poles.

Basic electrical frequency:

$f_e=\frac{\vartheta_e}{2 \cdot \pi}$          (4)

Number of stator slots:

$N_s=N_{s p} \cdot N_{p h}$          (5)

In which, the component $\mathrm{N}_{\mathrm{sp}}=\frac{\mathrm{N}_{\mathrm{s}}}{\mathrm{N}_{\mathrm{ph}}} \geq \mathrm{N}_{\mathrm{m}}$ is the number of slots per phase. Number of phases N_ph = 3.

Number of slots per phase under one pole:

$N_{s p p}=\frac{N_{s p}}{N_m}$          (6)

where, N_m is the number of poles of the electromagnet.

The number of slots per pole is counted:

$N_{s m}=N_{s p p} \cdot N_{p h}$          (7)

Step coefficient:

$\alpha_{c p}=\frac{{int}\left(N_{s m}\right)}{N_{s m}}=\frac{\tau_c}{\tau_p}$          (8)

Extreme step angle:

$\theta_p=\frac{2 . \pi}{N_m}$          (9)

Groove step angle:

$\theta_s=\frac{2 . \pi}{N_s}$          (10)

Electric angle, groove step:

$\theta_{s e}=\frac{\pi}{N_{s m}}$          (11)

Stator pole step:

$\tau_p=R_{o s} \cdot \theta_p$          (12)

Winding step:

$\tau_c=\alpha_{c p} \cdot \tau_p$          (13)

Figure 6. Detailed dimensions of a part of the engine

Figure 6 shows the dimensions of the BLDC motor with d₁ being the height of the groove neck, w_si, w_sb components, upper and lower body width, h_s being the height of the groove, etc. Below is how to determine the dimensions of the BLDC motor studied in this study:

$d_2=\frac{w_{s i}}{2}$          (14)

$d_3=\frac{w_{s b}}{2}+h_s$          (15)

$w_t=\tau_c-w_s$          (16)

Inner radius of stator:

$R_{s i}=R_{s o}-d_s-w_{b i}$          (17)

In which, d_s is the outer radius of the rotor:

$d_s=d_1+d_2+d_3$          (18)

The inner radius of the rotor R_ri is:

$R_{r i}=R_{s o}+L_m+g$          (19)

where, $\mathrm{g}=\left(0,1+0,012 \cdot \sqrt[3]{\mathrm{P}_{\mathrm{o}}}\right) \cdot 10^{-3}$ [24].

Distribution coefficient:

$k_{d 1}=\frac{\sin \left(\frac{N_{s p p} \cdot \theta_{s e}}{2}\right)}{N_{s p p} \cdot \sin \left(\frac{\theta_{s e}}{2}\right)}$          (20)

Step coefficient:

$k_p=\alpha_{c p}$          (21)

Slope coefficient:

$k_s=1-\frac{\theta_{s e}}{2 \pi}$          (22)

Flux concentration coefficient:

$C_\phi=\frac{2 . \alpha_m}{1+\alpha_m}$          (23)

where, $\alpha_m=\frac{\tau_m}{\tau_p}$ fractional magnet coefficient, $\tau_m$ is the width of the magnet

Environmental constant:

$P_c=\frac{l_m}{g \cdot C_\phi}$          (24)

With, $l_m$ is the length of the magnet.

Figure 7. Demagnetization curve of permanent magnet

In Figure 7, the B axis is the magnetic flux density value in the steel core, and the µ_oH axis is the magnetic flux density value in the air, with the values B_r is the remanent magnetism, B_m the maximum magnetic flux value, µ_r µ_o the permeability of the steel core and the permeability of the air, H_c is the coercive force, H_m the maximum magnetic field strength.

$A_g=\frac{\tau_p \cdot L \cdot\left(1+\alpha_m\right)}{2}$          (25)

Initial air gap flux density:

$B_g=\frac{C_\phi}{1+\frac{\mu_R \cdot k_c \cdot k_{m l}}{P_c}} \cdot B_r$          (26)

In which, B_r is the residual magnetic density.

The air gap flux:

$\phi_g=B_g \cdot A_g$          (27)

Preliminary yoke width:

$\omega_{b i}=\frac{\phi_g}{2 \cdot B_{\max } \cdot k_{s t} \cdot L}$          (28)

Compression coefficient K_st = 0.95. B_max component of allowable magnetic flux density in the yoke $\mathrm{B}_{\max }=1.45 \mathrm{~T}$.

Preliminary tooth width:

$\omega_{t b}=\frac{2}{N_{s m}} \cdot w_{b i}$          (29)

Cross section of the slot containing the preliminary winding:

$A_s=h_s \cdot\left[\theta_s \cdot\left(R_{s o}-d_1-\frac{h_s}{2}-d_2\right)-w_{t b}\right]+\pi \cdot \frac{w_{s b}^2}{4}$          (30)

Maximum counter-electromotive force:

$e_{\max }=N_m \cdot k_d \cdot k_p \cdot k_s \cdot B_q \cdot L \cdot R_{r o} \cdot N_{s p p} \cdot n_s \cdot w_m$          (31)

Peak groove current:

$I_s=\frac{T \cdot w_m}{e_{\max }}$          (32)

Primary phase current:

$I_{p h}=\frac{I_s}{N_{p h} \cdot \sqrt{\frac{3}{2}}}$          (33)

Peak winding current density:

$J_c=\frac{I_s}{k_{c p} \cdot A_s}$          (34)

Number of fibers in 1 slot:

$u_r=\frac{1000000 \cdot 4 \cdot A_s}{\pi \cdot d \cdot d \cdot n_s}$          (35)

From the above analytical calculation expressions, we conduct simulation research to get the results in part three as follows.

Sundaram et al. [23] confirmed that the 51-slot/46-pole combination is the optimal configuration for in-wheel PMSM hub motors in two-wheeler electric vehicles due to its low cogging torque, reduced core losses, and superior overall performance

The mesh was generated with a total of 210,750 elements. The simulation was configured in transient mode over a time interval from 0 to 0.02 s with a fixed time step of 0.002 s. ANSYS Maxwell 3D was used for the electromagnetic analysis, and after the simulation was completed, the corresponding results were obtained.

This paper has successfully researched and designed a high-performance BLDC motor with great potential for application, especially in the field of industrial and civil machinery manufacturing. The main results show that the motor has achieved outstanding advantages, including: Stable performance and operation and high efficiency, up to 91%. The ability to generate large, stable starting torque (reaching 6.39 N.M in simulation), low maintenance and smooth operation, this issue shows good operating quality, meeting the requirements of new designs. In addition, optimizing materials and production costs: The use of high-performance NdFeB magnets not only improves performance but also helps reduce product costs, opening up opportunities for widespread commercialization. Practical applications: This design is optimized for green means of transport such as electric bicycles, electric vehicles, electric cars, and current industrial and civil machinery. Role of simulation: Application of ANSYS Maxwell software and finite element method (FEM) has demonstrated the reliability of the design.

Future directions: The study has laid a solid foundation for further steps, including design optimization using modern algorithms and motor application research for automatic control fields, especially in electric vehicles. Overall, this study has provided a feasible and efficient BLDC motor design, demonstrating strong application potential in the future, especially in the field of transportation in today's industrial and civil machinery.