Publish Time: 2023-11-06 Origin: Site
The history of electric motors dates back to 1820, when Hans Christian Oster discovered the magnetic effect of electric current, and a year later Michael Faraday discovered electromagnetic rotation and made the first A primitive DC motor. Faraday discovered electromagnetic induction in 1831, but it wasn't until 1883 that Tesla invented the induction (asynchronous) motor. Today, the main motor types remain the same, DC, induction (asynchronous) and synchronous, all based on theories developed and discovered by Alstead, Faraday and Tesla over a hundred years ago.
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Advantages of induction motors over other motors
Speed limit control of induction motors
Since the invention of the induction motor, it has become the most widely used electric motor today due to its advantages over other electric motors. The main advantage is that induction motors do not require an electrical connection between the stationary and rotating parts of the motor, therefore, they do not require any mechanical commutators (brushes) and they are maintenance free motors. Induction motors also have the characteristics of light weight, small inertia, high efficiency, and strong overload capacity. Therefore, they are cheaper, stronger, and do not fail at high speeds. Also, the motor can work in an explosive atmosphere without sparking.
Considering all the advantages mentioned above, induction motors are considered to be perfect electromechanical energy converters, however, mechanical energy is usually required when changing gears, and speed control systems are no easy task. The only effective way to generate infinitely variable speed is to supply the asynchronous motor with a three-phase voltage of variable frequency and amplitude. The rotor speed depends on the speed of the rotating magnetic field provided by the stator, so frequency conversion is required. Variable voltage is required to reduce motor impedance at low frequencies, and current must be limited by reducing supply voltage.
Before the advent of power electronics, speed-limiting control of induction motors was achieved by switching the three stator windings from a delta to a star connection, which reduced the voltage across the motor windings. Induction motors also have more than three stator windings to allow changing the number of pole pairs. However, motors with multiple windings are more expensive because the motor requires more than three connection ports and only specific discrete speeds are available. Another method of speed control can be achieved using a wound rotor induction motor, in which the rotor winding ends are brought onto the slip rings. However, this approach apparently removes most of the benefits of an induction motor, while also introducing additional losses that can degrade performance by adding resistance or reactance in series across the stator windings of an induction motor.
At that time, only the above methods could control the speed of induction motors, and DC motors already had continuously variable speed drives, which could not only operate in four quadrants, but also have a wide power range. They are very effective and have proper control and even good dynamic response, however, its main disadvantage is the mandatory requirement for the brush.
Over the past 20 years, semiconductor technology has made tremendous progress, providing the necessary conditions for the development of suitable induction motor drive systems. These conditions fall into two broad categories: cost reduction and performance improvement in power electronic switching devices. Possibility to implement complex algorithms in new microprocessors. However, suitable methods must first be developed to control the speed of induction motors, the complexity of which is particularly important in terms of their mathematical structure (multivariate and nonlinear) compared to their mechanical simplicity. For more information, please connect https://www.hzxhldj.cn/.