Comparison and analysis of starting performance of PMSM with different rotor structures

In this paper, the electromagnetic fields of PMSM with four different rotor structures are analyzed by the finite element method, and the distribution of magnetic field lines is compared. Then the asynchronous starting process of PMSM is studied. The starting process of four kinds of permanent magnet synchronous motors with no load and load is simulated and analyzed, and the characteristics of speed, torque, and phase current are obtained. These studies can provide references for the starting design of permanent magnet synchronous motors in practical applications. Therefore, a more reliable and efficient motor starting process is realized, which provides a basis for further structural design of permanent magnet synchronous motor.


Introduction
The initial stage of a permanent magnet synchronous motor can be divided into two stages: asynchronous starting stage and synchronous traction stage.In the asynchronous starting stage, the motor is started and connected to the power grid.The motor slowly accelerates from a stationary state.When the speed approaches synchronous speed quickly, the speed will reach or exceed the synchronous speed due to the pulse rotation torque of the permanent magnet, which is the phenomenon of speed overshoot.Finally, after the speed oscillates for a certain time, the motor is pulled to a synchronous state.
The mechanical motion equation with load is as follows: where J is the moment of inertia of the motor and load, and L T is load torque.
The motor in the electromechanical system is coupled with the mechanical device, so the movement of the motor and the mechanical part occurs simultaneously and affects each other.When studying electromechanical systems, it is necessary to consider the interaction between electromagnetic field equations and mechanical motion equations to obtain accurate results [1][2][3][4] .
This paper will compare and analyze the magnetic field distribution and starting performance of four types of PMSM.

Distribution of magnetic field lines for four types of PMSM
The simulation models of four types of PMSM with rotor structures of tangential type, radial type, Vtype, and U-type are built [5][6] .The following is the magnetic field line distribution diagram of the four types of motors.Through the magnetic field line distribution diagram, it is possible to intuitively understand the uniformity of the internal magnetic field distribution of the motor and determine whether there is an uneven magnetic field.Uneven magnetic field distribution can cause vibration and noise during motor operation, while also reducing the efficiency and lifespan of the motor.The simulation results in Figure 1 are beneficial for comparing the electromagnetic performance of four different rotor structures of permanent magnet synchronous motors, providing a basis for subsequent design and research.

No-load starting performance for four types of PMSM
The load torque of the motor is set to 0 N in Maxwell.The speed is set to 1500 RPM.Then the variation curve of each quantity of motor with time can be obtained under no-load conditions.

No-load starting performance of motor 1
The no-load starting performance of motor 1 is as follows: As shown in Figure 2, the motor tends to run stably after a startup process of about 0.06 s.The maximum torque of motor 1 is about 23 N.m when it is unloaded.The starting current amplitude of the motor is about 24 A when it is unloaded, and the current amplitude is about 15 A when it is running at synchronous speed.

No-load starting performance of motor 2
The no-load starting performance of motor 2 is as follows: As shown in Figure 3, the motor tends to run stably after a startup process of about 0.075 s.The maximum torque of motor 2 under no load is about 21 N.m.The starting current amplitude of the motor is about 13.5 A when it is unloaded, and the current amplitude is about 4.5 A when it is running at synchronous speed.

No-load starting performance of motor 3
The no-load starting performance of motor 3 is as follows:  As shown in Figure 4, the motor tends to run stably after a startup process of about 0.2 s.The maximum torque of motor 3 under no load is about 18 N.m.The starting current amplitude of the motor is about 11 A when it is unloaded, and the current amplitude is about 2.5 A when it is running at synchronous speed.

No-load starting performance of motor 4
The no-load starting performance of motor 4 is as follows: As shown in Figure 5, the motor tends to run stably after a startup process of about 0.14 s.The maximum torque of motor 4 under no load is about 19 N.m.The starting current amplitude of the motor is about 11.5 A when it is unloaded, and the current amplitude is about 4 A when it is running at synchronous speed.

Load starting performance for four types of PMSM
The load torque of the motor is set to 4 N in Maxwell.The speed is set to 1500 RPM.Then the variation curve of each quantity of motor with time can be obtained under load conditions.

Load starting performance of motor 1
Load starting performance of motor 1 is as follows:  As shown in Figure 6, the motor tends to run stably after a startup process of about 0.08 s.The maximum torque of motor 1 is about 28 N.m when it is loaded.The starting current amplitude of the motor is about 22 A when it is loaded, and the current amplitude is about 14.5 A when it is running at synchronous speed.

Load starting performance of motor 2
Load starting performance of motor 2 is as follows: As shown in Figure 7, the motor tends to run stably after a startup process of about 0.2 s.The maximum torque of motor 1 is about 28 N.m when it is loaded.The starting current amplitude of the motor is about 13 A when it is loaded, and the current amplitude is about 5 A when it is running at synchronous speed.

Load starting performance of motor 3
Load starting performance of motor 3 is as follows: As shown in Figure 8, the motor tends to run stably after a startup process of about 0.22 s.The maximum torque of motor 1 is about 25 N.m when it is loaded.The starting current amplitude of the motor is about 10.3 A when it is loaded, and the current amplitude is about 3.1 A when it is running at synchronous speed.As shown in Figure 9, the motor tends to run stably after a startup process of about 0.2 s.The maximum torque of motor 1 is about 24 N.m when it is loaded.The starting current amplitude of the motor is about 11.2A when it is loaded, and the current amplitude is about 3.8 A when it is running at synchronous speed.
By observing the simulation curve, it can be seen that the torque generated by the permanent magnet pulse causes a certain degree of fluctuation during the stage of continuously increasing speed.As the motor approaches the synchronous speed, the pulling torque comes into play, making the speed reach or even exceed the synchronous speed.Then, under the combined action of synchronous torque and damping torque, the motor successfully achieved stable synchronous speed.The simulation results indicate that the starting process of motor 1 is short and the response speed is fast.However, in the rated state, the phase current amplitude is large and the load performance is poor.Motor 2, motor 3, and motor 4 have long start-up times.However, in the rated state, the phase current amplitude of the three types of motors is relatively low.The phase current amplitude of motor 4 is the lowest.

Conclusion
This paper conducts simulation analysis on the electromagnetic field distribution and starting characteristics of PMSM.The main research content is as follows: 1) Through simulation analysis of magnetic field lines, the internal magnetic field distribution of four types of motors is obtained.Motor 2, motor 3, and motor 4 have uniformly distributed magnetic fields.2) When the rotor structure and input conditions are the same, motor 1 has a short startup time.
3) When the load torque of the motor is set to 4 N in Maxwell, the phase current amplitude of motor 4 is lowest, and the phase current amplitude of motor 1 is highest.

Figure 1 .
Figure 1.Magnetic field line distribution of four motors.Through the magnetic field line distribution diagram, it is possible to intuitively understand the uniformity of the internal magnetic field distribution of the motor and determine whether there is an uneven magnetic field.Uneven magnetic field distribution can cause vibration and noise during motor operation, while also reducing the efficiency and lifespan of the motor.The simulation results in Figure1are beneficial for comparing the electromagnetic performance of four different rotor structures of permanent magnet synchronous motors, providing a basis for subsequent design and research.

Figure 3 .
Figure 3. No-load starting performance of motor 2.As shown in Figure3, the motor tends to run stably after a startup process of about 0.075 s.The maximum torque of motor 2 under no load is about 21 N.m.The starting current amplitude of the motor is about 13.5 A when it is unloaded, and the current amplitude is about 4.5 A when it is running at synchronous speed.

Figure 7 .
Figure 7. Load starting performance of motor 2.As shown in Figure7, the motor tends to run stably after a startup process of about 0.2 s.The maximum torque of motor 1 is about 28 N.m when it is loaded.The starting current amplitude of the motor is about 13 A when it is loaded, and the current amplitude is about 5 A when it is running at synchronous speed.

Figure 8 .
Figure 8. Load starting performance of motor 3.As shown in Figure8, the motor tends to run stably after a startup process of about 0.22 s.The maximum torque of motor 1 is about 25 N.m when it is loaded.The starting current amplitude of the motor is about 10.3 A when it is loaded, and the current amplitude is about 3.1 A when it is running at synchronous speed.

6 4. 4 Figure 9 .
Figure 9. Load starting performance of motor 4.As shown in Figure9, the motor tends to run stably after a startup process of about 0.2 s.The maximum torque of motor 1 is about 24 N.m when it is loaded.The starting current amplitude of the motor is about 11.2A when it is loaded, and the current amplitude is about 3.8 A when it is running at synchronous speed.By observing the simulation curve, it can be seen that the torque generated by the permanent magnet pulse causes a certain degree of fluctuation during the stage of continuously increasing speed.As the motor approaches the synchronous speed, the pulling torque comes into play, making the speed reach or even exceed the synchronous speed.Then, under the combined action of synchronous torque and damping torque, the motor successfully achieved stable synchronous speed.The simulation results indicate that the starting process of motor 1 is short and the response speed is fast.However, in the rated state, the phase current amplitude is large and the load performance is poor.Motor 2, motor 3, and motor 4 have long start-up times.However, in the rated state, the phase current amplitude of the three types of motors is relatively low.The phase current amplitude of motor 4 is the lowest.