There is a certain relationship between the size of the motor magnet and the motor power, especially in the design of permanent magnet synchronous motor (PMSM) and brushless DC motor (BLDC), the size, shape and magnetic properties of the magnet directly affect the motor output power, efficiency and volume. Specifically, the relationship between the size of the motor magnet and the power can be described by the following aspects:
1. The volume of the magnet and the motor power
The power of the motor is directly related to the volume of the magnet on the rotor (i.e. the size of the magnet). A larger magnet volume usually means more magnetic flux, which can produce a larger motor output power.
Under the same motor design (such as the same speed and current density), increasing the volume of the magnet can increase the torque output of the motor, thereby increasing the power.
2. The magnetic energy product of the magnet and the power
The magnetic energy product (BH) max: The higher the magnetic energy product of the magnet, the greater the magnetic flux that the magnet can provide per unit volume, which directly affects the power density of the motor. For high power density motors, such as drive motors in electric vehicles, NdFeB magnets with higher magnetic energy products are usually selected.
Under the same volume of magnets, materials with high magnetic energy product (such as NdFeB) can provide more magnetic flux, thereby improving the efficiency and power output of the motor.
3. Magnet shape and power
The shape of the motor magnet (such as bar, curved or tile shape) affects the distribution of the magnetic field and the path of the magnetic flux, which in turn affects the efficiency and power output of the motor. For example, in high-power motors, tile-shaped magnets can effectively utilize the magnetic field and provide more uniform magnetic flux, thereby improving the performance of the motor.
Magnets with reasonable shapes can make the magnetic flux density more uniform, reduce losses, and help improve the power output of the motor.
4. Rotor size and power
The size of the rotor (including the size of the magnet) determines the maximum torque that the motor can provide. If the magnet is too small, the magnetic field generated is insufficient, which may cause the motor to be unable to provide sufficient torque and the power output will be limited.
For example, in electric vehicle applications, in order to provide higher power density, larger rotors and magnets are usually required. Larger magnet volume can provide more magnetic flux to meet high speed and high power requirements.
5. Motor power and magnet configuration
For low-power motors (such as tens of watts to several kilowatts), the volume of the magnet is relatively small, and a small amount of high-performance magnets (such as neodymium iron boron) can usually meet the power requirements.
For medium and large power motors (such as several kilowatts to hundreds of kilowatts), a larger magnet volume is required to provide sufficient magnetic flux and high torque output. In this case, in addition to the volume of the magnet, the layout of the magnet (such as multiple magnet blocks in series or parallel) and the optimization design of the magnetic field need to be considered.
For ultra-high power motors (such as wind turbines, large industrial motors), larger rotors and multiple magnet segments may be used to ensure motor performance.
6. Relationship between speed and power
The speed of the motor is also closely related to the size of the magnet. For high-speed motors, smaller magnet sizes may be more suitable, because at high speeds, larger magnets will cause higher centrifugal forces, which will affect the stability and efficiency of the motor.
For low-speed, high-power motors, larger magnets can provide higher torque and power output.
Practical examples:
Small power motors (tens of watts to a few kilowatts): In this type of motor, the size of the magnet is relatively small, and high-performance NdFeB magnets are usually used to provide sufficient magnetic flux and power output. The diameter and length of the magnet may be between tens of millimeters and hundreds of millimeters.
Medium power motors (several kilowatts to tens of kilowatts): For medium power motors, the volume of the magnet will increase significantly, and magnets of several hundred grams to several kilograms may be required. The rotor volume and magnet layout are usually optimized to ensure power output and efficiency.
High power motors (tens of kilowatts to hundreds of kilowatts): For this type of motor, the volume and weight of the magnet are very large, and a more complex design is required to ensure sufficient magnetic flux and good thermal stability. For example, the drive motor of an electric vehicle or an industrial high-power motor, the magnet volume may exceed several kilograms, and higher quality NdFeB or SmCo magnets are required to cope with the needs of high power and high efficiency.
Summary:
Small motors: The magnet size is small and the power is low, and high magnetic energy product materials (such as NdFeB) are usually used to increase the power density.
Medium and large motors: As the magnet size increases, the power demand increases, and the magnet shape, layout, and material selection need to be optimized to provide high power output and high efficiency.
Ultra-high power motors: require a larger magnet volume and optimize the magnet configuration, and often use high-quality magnets to ensure motor performance.
The size and performance of the magnet are closely related to the power of the motor. Reasonable design can effectively improve the power density, efficiency, and overall performance of the motor.
