High-speed motors possess advantages such as high efficiency, high specific power, high power factor, high reliability, and ease of maintenance. In advanced industrialized countries, high-speed motors are widely used in the aviation, aerospace, and mold industries. my country's high-speed motor industry began in the 1990s, with products continuously developing from low-end to high-end, and the market size constantly expanding.
How to define a high-speed motor
There is no clear-cut definition of what constitutes a high-speed motor. Generally, motors exceeding 10,000 r/min can be considered high-speed motors. Another definition uses the linear velocity of the rotor; the linear velocity of a high-speed motor is typically greater than 50 m/s. The centrifugal stress of the rotor is proportional to the square of the linear velocity, thus classifying motors by linear velocity reflects the complexity of rotor structural design. Some international scholars define high-speed motors by multiplying the speed by the square root of the power. This classification considers both the complexity of the rotor design and the energy output of the motor, making it more scientific and reasonable. According to this standard, high-speed motors can be divided into two main categories: high-speed and ultra-high-speed.
The difference between high-speed motors and ultra-high-speed motors lies in the product of power and speed. We'll use three examples to understand this concept:
▷ Case 1 is the Dyson hair dryer motor, a very famous small appliance. This motor has a speed of 110 kr/min and a power of 1600 W. The product of its power and speed is 1.39 × 10⁵. In the diagram above, it is below the high-speed/ultra-high-speed dividing line and belongs to the high-speed motor category.
▷Case 2 is an automotive drive motor developed by Integral Powertrain, with a speed of 20 kr/min and a power of 450 kW. The product of its power and speed (square root) is 4.24 × 10⁵. The larger this product, the greater the speed and the more difficult it is to achieve.
▷Case 3 is Honeywell's aircraft drive motor, 20 kr/min, 1000 kW. Its power-speed product is 6.3×10⁵, which falls into the category of ultra-high speed motors, and it uses more advanced technology.
In terms of high-speed operating point alone, the difficulty of motor operation increases stepwise with the product of power and speed. Therefore, we can use this indicator to evaluate the degree of high-speed motor operation.
Applications of high-speed motors
The applications of high-speed motors are expanding explosively, and the following are some of the applications ordered by speed.
01 Power Tools
The image below shows Westwind's EDM product, 200 W, 300 kr/min. It uses a coreless PCB winding process and integrates the control chip, making it very compact. This type of EDM can also be used in dental and other medical equipment.
02 Molecular Pump
Molecular pumps are commonly used physical devices for obtaining high vacuum and can also be used to separate air to obtain highly clean air. For this application, the motor speed can reach 32 kr/min and 500 W, and can be designed using either an induction motor or a concentrated-winding permanent magnet motor.
03 Separate energy storage flywheel
There are many sub-sectors of energy storage, including flywheel energy storage used in aircraft and flywheel energy storage used in power plants. The example below is a flywheel energy storage product for automotive applications. Its concept is similar to battery energy storage or supercapacitor energy storage in hybrid vehicles. When the car needs to generate power, the flywheel energy storage motor can act as a generator to supply electricity to the power source. The energy storage motor shown below has a power of 30 kW and a speed of 50 kr/min. It uses an induction motor design, and the rotor is a solid iron block.
04 Turbocharged
Electric turbocharging is a relatively new technology that uses boost pressure on car engines at low speeds to reduce eddy lag and increase torque output. The image below shows a 10 kW, 100 kr/min product developed by BorgWarner, employing a 2-pole, 24-slot permanent magnet motor structure. Due to the high operating temperature, in addition to high speeds, the design of this type of motor also requires controlling magnet losses and temperature rise.
05 Micro Gas Turbine
The micro gas turbine is truly a legendary product. A machine roughly the size of a pencil can generate 50 kW of power. It's said that its application in automobiles could reduce engine size by 95%. Besides automobiles, many other devices require this small engine. Its working principle is shown in the diagram below, requiring a permanent magnet synchronous motor to convert the kinetic energy generated by combustion into electrical energy. This motor uses a 2-pole, 6-slot structure.
06 High-speed air compressor
High-speed air compressors utilize high-power, high-speed motors, typically operating at speeds of tens of thousands of revolutions per minute and with power ranging from 100 to 700 kW. They generally employ magnetic levitation bearings, using a motor to drive a turbine or blades to compress air. High-speed direct-drive motors replace the traditional low-speed motor + speed increaser system, offering advantages such as compact structure and high reliability. Common types of these motors include surface-mount permanent magnet synchronous motors and induction motors; relevant manufacturers are shown in the diagram below.
The centrifugal fan in the example below can also be considered a type of high-speed air compressor, employing a 4-pole, 24-slot SPM motor. Using a permanent magnet motor can improve efficiency and reduce size.
07 Automotive drive motor
Automotive drive motors remain the hottest field, with mainstream passenger car motors operating at speeds below 16,000 r/min, while higher-speed motors are under development. The image below shows a 25,000 r/min, 225 kW induction motor developed by a certain company. It has an outer diameter of 290 mm, a stack height of 230 mm, a maximum torque of 358 N·m, and uses a water-cooled structure.
To improve power density, Integral Powertrain developed a 20,000 r/min, 450 kW permanent magnet motor system with a maximum torque of 900 N·m and a weight of only 28 kg. It employs advanced technologies such as winding oil spray cooling, stator radial cooling, and rotor axial cooling. Its controller is based on the SiC platform.
Coincidentally, AVL's next-generation 20,000 r/min drive motor also adopts oil-cooled permanent magnet motor technology, with a motor power of 230kW and a corresponding weight of 45 kg.
08 aircraft drive motor
As aircraft become increasingly electrified and semi-electrified, the demand for high-power, high-speed motors is also rising. The image below shows a 300 kW, 35 kr/min permanent magnet motor, which uses a concentrated winding permanent magnet motor design and weighs 28.4 kg.
Higher-power aviation motors are used in hybrid aircraft as the core of similar range-extended hybrid architectures. These motors generally adopt a forced air cooling structure to utilize high-speed airflow. Honeywell's motors can reach a power of 1 MW. To improve efficiency, permanent magnet motors are used more often than induction motors.
