Electric vehicle powertrains are completely different from traditional internal combustion engine vehicles. The power system is not composed of an engine, clutch, transmission, differential, etc., but consists of an energy storage device (ESS) that stores electrical energy, which outputs energy to a converter and a power control module (PEM). The PEM uses control sensors to sense the driver's operating needs and road conditions to drive the motor . Because of the complexity and precision of its power system, electric vehicles are more like electronic devices.
Recently, the first batch of Tesla Model 3 vehicles were delivered to owners, and electric vehicles have once again become the focus of attention.
Electric vehicles use electricity to propel the car forward, and this process does not produce harmful gases, making them the most promising alternative to traditional fuel-powered vehicles.
But did you know that the powertrain of an electric vehicle is completely different from that of a traditional internal combustion engine vehicle? The power system is not composed of an engine, clutch, transmission, differential, etc., but consists of an energy storage device (ESS) that stores electrical energy, which outputs energy to a converter and a power control module (PEM). The PEM uses control sensors to sense the driver's operating needs and road conditions to drive the motor. Because of the complexity and precision of its power system, an electric vehicle is more like an electronic device.
In the field of drive motors, the two most representative types currently used in small cars are Tesla's AC asynchronous motors and BYD's rare-earth permanent magnet motors . Today, we'll briefly introduce some knowledge about rare-earth permanent magnet motors.
The Development History of Rare Earth Permanent Magnet Motors
The world's first electric motor appeared as early as the 1820s, and its rotor was a permanent magnet used to generate an excitation magnetic field. However, the permanent magnet material used at that time was natural magnetite (Fe3O4), which had a very low magnetic energy density. Motors made from it were bulky and were soon replaced by electrically excited motors.
With the development of technology, there have been many choices for permanent magnet materials. Among them, rare earth materials are the best. Therefore, motors that use rare earth permanent magnet materials are also called rare earth permanent magnet motors.
Mechanism and Principle of Rare Earth Permanent Magnet Motor
From a structural perspective, rare earth permanent magnet synchronous motors are mainly composed of components such as rotor, end covers, and stator.
Generally speaking, the stator structure of a permanent magnet synchronous motor is very similar to that of an ordinary induction motor, but the unique structure of the rotor is what distinguishes it from other motors.
The biggest difference between it and the AC induction asynchronous motor used by Tesla is that it has high-quality permanent magnet poles (rare earth) on the rotor.
Because there are many options for the placement of permanent magnets on the rotor, permanent magnet synchronous motors are generally classified into three main categories: embedded, surface-mounted, and plug-in.
Their working principles are roughly the same. Three-phase current is passed through the stator winding of the fixed motor. After the current is passed through, a rotating magnetic field is formed in the stator winding of the motor. Since permanent magnets are installed on the rotor, and the magnetic poles of the permanent magnets are fixed, according to the principle that like poles attract and unlike poles repel, the rotating magnetic field generated in the stator will drive the rotor to rotate.
Technical bottlenecks of rare earth permanent magnet motors
1. Control issues
Permanent magnet motors can maintain their magnetic field without external energy after being manufactured, but this also makes it extremely difficult to adjust and control their magnetic field from the outside. Permanent magnet generators are difficult to adjust their output voltage and power factor from the outside, and permanent magnet DC motors can no longer adjust their speed by changing the excitation.
2. Cost issues
Because rare-earth permanent magnets are currently relatively expensive, the cost of rare-earth permanent magnet motors is generally higher than that of electrically excited motors. This higher cost needs to be compensated by their high performance and lower operating costs. Therefore, permanent magnet motors are suitable for low-power applications.
3. Demagnetization problem
Rare earth permanent magnet motors have stringent requirements for the working environment. Rare earth permanent magnet materials will experience irreversible demagnetization and failure when the temperature exceeds 180°C. They are prone to breakage under severe vibration or large temperature differences. The materials are easily oxidized and corroded, and surface coating is required before use. Rare earth permanent magnet motors are very sensitive to overload, and overload will cause demagnetization of the permanent magnet materials.
Meanwhile, rare-earth permanent magnet motors have very high electromagnetic loads, and their magnetic fields are difficult to adjust after fabrication, making their power control systems far more complex than those of induction motors. Traditional motor design theories, calculation methods, and motor control systems are inadequate for the development requirements of high-performance motors.
In conclusion, the development of rare-earth permanent magnet motors faces numerous challenges. However, just as one cannot see a rainbow without experiencing storms, the tireless efforts of automotive engineers in the face of air disasters will eventually break through the bottlenecks, allowing the public to benefit from the convenience brought by technology.
