The permanent magnet synchronous motor rotor is a vital component in the motors used in new energy vehicles. Without it, whether for Tesla or BYD, your electric vehicle simply cannot start.
Definition of Permanent Magnet Synchronous Motor
A permanent magnet synchronous motor mainly consists of the rotor, stator, bearings, windings, and end caps.
As the stationary part of the motor, the stator is composed of two main components: the stator core and the windings. The stator core is typically made from stacked silicon steel sheets, which helps reduce eddy current losses and enhance magnetic conductivity. The stator windings consist of insulated copper wires wound around the core’s slots in a specific pattern to form three-phase windings.
When three-phase alternating current is introduced into these three symmetrical windings, varying magnetic flux is generated by electromagnetic induction laws. Due to the phase differences in the three-phase currents over time, as well as the spatial arrangement of the windings, this magnetic flux interacts, creating a rotating magnetic field that rotates at synchronous speed in the space between the stator and rotor.
Definition of Permanent Magnet Synchronous Motor Rotor
The rotor of a permanent magnet motor mainly consists of permanent magnets, the rotor core, and the shaft.
Kinds of Permanent Magnet Synchronous Motor Rotor
The rotor of a permanent magnet synchronous motor has three main forms:
| Surface Mounted Rotor: Permanent magnets are mounted on the circumferential surface of the rotor core, referred to as surface-mounted rotors.
| Surface Embedded Rotor: The magnetic poles of the permanent magnets are embedded in the surface of the rotor core, known as surface embedded rotors.
| Internal Embedded Rotor: More commonly used in larger motors, this form has permanent magnets embedded inside the rotor, referred to as internal embedded rotors. The permanent magnets are installed within the rotor core, with slots created in the core for mounting the magnets. Each form may also utilize multiple layers of permanent magnets in combination.
Role of Neodymium Magnets in the Permanent Magnet Synchronous Motor Rotor
| Power Density: The magnetic energy product of neodymium-iron-boron (NdFeB) magnets is ten times that of traditional magnets, significantly enhancing the power density of permanent magnet synchronous motors. For instance, the Model 3 rear-wheel drive motor weighs only 47 kg yet delivers 275 horsepower, equivalent to a V6 engine.
| Energy Efficiency: Permanent magnet motors consume 15% less energy than induction motors, extending their range by an additional 50 kilometers.
Quantity of Neodymium Magnets in Permanent Magnet Synchronous Motor Rotor
Main Drive Motor: In Tesla’s permanent magnet synchronous motor, 48 pieces of neodymium magnets are required to form a circular array capable of withstanding high temperatures of 150°C and intense vibrations.
The cost of NdFeB magnets constitutes 30% of the motor’s total cost.
Strength Analysis of Neodymium Magnets in Permanent Magnet Synchronous Motor Rotors
NdFeB magnets are a widely used high-performance permanent magnetic material in permanent magnet motors. This material performs well in terms of magnetic properties and compressive strength but has relatively poor tensile strength, especially under high-speed rotation, where the rotor’s permanent magnets are subjected to significant centrifugal forces.
To ensure the reliable operation of the motor, effective fastening measures must be implemented to meet the structural strength and dynamic requirements of the rotor. In the design of surface-mounted rotors, they can be further classified based on the casing materials used into non-magnetic alloy steel-cased rotors and carbon fiber composite-cased rotors.
Structural Design of Permanent Magnet Synchronous Motor Rotors
| Slot Design: The rotor structure of permanent magnet motors has specific designs and functions. The rotor mainly consists of multiple stacked silicon steel plates, which not only make up the rotor’s primary structure but also help reduce eddy current losses, enhancing overall motor efficiency. Inside the rotor, multiple slots are designed, each serving different functions. The outer slots, known as V-slots, are primarily used to secure the permanent magnets, ensuring their stability during high-speed operation.
| Lightweight Design: The design of the permanent magnet synchronous motor rotor must also consider the need for lightweight construction. By carefully designing the slots and selecting appropriate materials, the rotor’s weight can be reduced while maintaining sufficient structural strength, thereby lowering the moment of inertia and improving the motor’s response speed.
| Pole Skewing Structure Design: Techniques for graded pole skewing, including conventional skewing, V-shaped skewing, and crossed skewing, primarily aim to reduce harmonics, improve cogging torque, and decrease torque fluctuations, effectively minimizing vibrations and noise induced by radial electromagnetic forces.
| Spatial Design: The rotor structure must ensure that, after the installation of permanent magnets, stability is maintained even under high-speed working conditions, preventing deformation. Additionally, the structure must provide sufficient space for the permanent magnets to accommodate more or larger-sized magnets, thereby enhancing motor performance. Furthermore, the rotor’s dimensions should be adaptable for optimization to meet the requirements of different vehicle models and performance needs.
Supporting Design for the Stator of Permanent Magnet Synchronous Motors
New energy vehicles commonly utilize built-in permanent magnet synchronous motors, owing to their exceptional performance and unique structural advantages. In the design of built-in motors, configurations can be divided into distributed and centralized forms based on the arrangement of windings. New energy vehicles tend to choose distributed winding motors over centralized ones for several reasons:
Distributed winding motors, through precise pole-slot fitting, can optimize the distribution of electromagnetic force, reduce harmonic generation, and effectively enhance NVH (noise, vibration, and harshness) performance, which aligns closely with the application requirements of new energy vehicles.
The stator structure of distributed winding motors avoids the design of protruding poles, instead utilizing one or more coils arranged according to specific patterns to form a coil group. This design provides flexibility in the diversified design of the motor rotor, allowing it to meet various operational conditions.
Magnetization of Permanent Magnet Synchronous Motor Rotors
Permanent magnet synchronous motor rotors employ an integrated magnetization technology. The core principle involves subjecting the completed product to a strong magnetic field using specific magnetization equipment and techniques to achieve overall magnetization. During this process, the product is placed in a powerful magnetic field, where the internal magnetic material is magnetized to achieve the desired magnetic characteristics.
This integrated magnetization technology ensures that the magnetic field distribution remains stable during the magnetization process, enhancing the performance and reliability of the product. After employing this technology, the motor’s magnetic field distribution becomes more uniform, reducing additional energy consumption caused by uneven magnetic fields. Furthermore, the stable process of integrated magnetization significantly lowers the product failure rate, providing greater value to customers.
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