What is the difference between asynchronous motors and synchronous motors?

Electric motors are used in all walks of life. Among various types of electric motors, asynchronous motors are the most common power equipment. In some cases, synchronous motors are also used.They are both AC motors. What is the difference between asynchronous motors and synchronous motors?Today I will use this question to discuss with my friends the differences between these two types of motors.

Asynchronous motor

Let’s first talk about the most widely used asynchronous motor.Let’s first analyze the basic structure of an asynchronous motor. In fact, the structure of an asynchronous motor is relatively simple, mainly consisting of a stator part and a rotor part.When the motor starts, there will be two so-called rotational speeds. One rotational speed is the rotational speed that we cannot see with our eyes. This rotational speed is called the rotational speed of the electromagnetic field. It is a magnetic field rotational speed formed in the stator magnetic field of the motor when the motor is supplied with three-phase alternating current. It is generally represented by n0. This n0 is also called synchronous rotational speed. This rotational speed is not only related to the frequency of the power supply, but also related to the number of magnetic pole pairs formed by the stator winding of the motor.For example, the operating frequency of the three-phase alternating current we use is 50HZ. If the number of magnetic pole pairs of the motor is 1.Then according to the formula n0=60f/p=60x50/1=3000r/min, if the number of magnetic pole pairs of the motor is 2, then n0=60f/p=60x50/2=1500r/min.We cannot see the above speeds. What we can see is the rotation speed of the motor rotor. This speed is due to the fact that the rotor is cut by magnetic lines of force in the rotating magnetic field, which induces a current in the rotor. This induced current is in turn affected by electromagnetic force in the rotating magnetic field.Therefore, judging from the generation time of these two speeds, the stator rotates first and then the rotor rotates. We can also understand that the rotor speed of an asynchronous motor always lags behind the speed of the stator magnetic field of the motor, so we call this kind of motor an asynchronous motor.

Synchronous motor

We know that the use of synchronous motors is relatively rare. Its structure can also be divided into a rotatable part and a non-rotatable part. The rotary part of the rotor is called the magnetic pole, and the non-rotatable part of the stator is called the armature.Then this so-called synchronization means that there is no speed difference between the rotating magnetic field n0 formed by the stator and the rotor speed n, so their speeds are equal, that is, n0=n=60f/p. This is the origin of the name of the synchronous motor.

Since the rotation speed of the two is the same and there is no difference in rotation speed, how does it rotate?This starts with the structure of the synchronous motor. As mentioned just now, the stator of the synchronous motor is the armature and the rotor is the magnetic pole. When it works, three-phase alternating current is passed through the stator, and current is also passed through the rotor. This current is direct current.In this way, the stator of the synchronous motor will generate a rotating magnetic field, and the rotor will form a constant magnetic field because it is supplied with direct current. The two magnetic fields will attract each other, so the rotor of the synchronous motor will rotate due to the electromagnetic force.

Comparison of the advantages and disadvantages of asynchronous motors and synchronous motors