An asynchronous motor , also known as an "induction motor," is a motor in which the rotor is placed in a rotating magnetic field. Under the influence of the rotating magnetic field, the rotor obtains a torque, and thus the rotor rotates.
The rotor is a rotatable conductor, usually shaped like a squirrel cage. The stator is the non-rotating part of the electric motor , its main task being to generate a rotating magnetic field. This rotating magnetic field is not achieved mechanically, but rather by passing alternating current through several pairs of electromagnets, causing their magnetic poles to change cyclically, thus effectively creating a rotating magnetic field.
Depending on the type of alternating current used, there are single-phase motors and three-phase motors. Single-phase motors are used in appliances such as washing machines and electric fans, while three-phase motors are used as power equipment in factories.
01 Working principle of asynchronous motor
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The relative motion between the rotating magnetic field generated by the stator and the rotor windings causes the rotor windings to cut magnetic field lines, generating an induced electromotive force, which in turn induces a current in the rotor windings. The induced current in the rotor windings interacts with the magnetic field to produce electromagnetic torque, causing the rotor to rotate.
As the rotor speed gradually approaches the synchronous speed, the induced current gradually decreases, and the generated electromagnetic torque also decreases accordingly. When the asynchronous motor is operating in motor mode, the rotor speed is less than the synchronous speed.
Asynchronous motors are the most widely used in electric vehicles. Compared with DC motors, they have a wider range of speed adaptability, so even without a two-stage differential or gearbox, they can meet the needs of high-speed cruising.
An asynchronous motor has the ability to regulate speed by frequency conversion, which is equivalent to the relatively linear relationship between engine speed and vehicle speed when accelerating in a vehicle equipped with a continuously variable transmission.
Asynchronous motors also make it easier to recover kinetic energy. When the vehicle is coasting or braking, the wheels drag the motor to rotate. Under this condition, the motor can generate electricity and recover the electrical energy into the battery, thereby extending the vehicle's driving range.
The Tesla Model S uses an asynchronous motor, and this technology is also used in many other hybrid vehicles on the market, including the Roewe 550 Plug-in. The asynchronous motor was chosen because of its strong anti-interference capabilities and ability to operate in high-speed, weak magnetic fields; it also boasts high power output, a simple structure, and reliable operation.
02 Tesla Induction Motor Rotor Patent
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Tesla's induction motor rotor patent technology is the same as the welded squirrel cage technology, which involves inserting copper bars into the rotor slots. The result after insertion is shown in the image below:
The next step should have been to weld the end ring, but Tesla took a different approach and manufactured a set of silver-plated copper wedges. He then inserted these wedges into the gaps at the ends of the copper strips, thus completing the mechanical end ring.
After inserting the wedges, welding is performed between the wedges and the copper strips. This welding process is much less expensive and difficult than the induction brazing of the end rings in the other welding scheme. After welding, retaining rings (part 107 in the image below) are then attached to both ends.
This patent uses an ingenious solution to achieve low-cost, high-efficiency manufacturing of copper-core rotors, making it one of Tesla's core technologies.
03 Animated GIF of an induction motor
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▲Single-phase induction motor
The working principle of a single-phase induction motor is that the stator usually contains two windings and the rotor is a squirrel-cage type. Most single-phase induction motors operate in one direction because they are designed to rotate in one direction.
▲Single-phase induction motor
▲Single-phase induction motor
A three-phase induction motor is an AC motor that generates electromagnetic torque to drive the rotor to rotate by the interaction between the rotating magnetic field formed by the stator windings and the magnetic field of the induced current in the rotor windings. It is a type of induction motor.
For most fan and pump loads that do not require speed regulation, AC speed regulation can significantly save energy. Therefore, research on speed regulation and energy saving of induction motors is of great significance.
Three-phase induction motors are mainly used in computer peripherals, lathe systems, optoelectronic devices, valve control systems, nuclear reactors, surface grinders, CNC machine tools, automatic winding machines, electronic clocks and watches, and medical equipment.
