The difference between the principle of asynchronous motor and synchronous motor and its application field
The so-called synchronous motor means that the magnetic field rotation speed of the armature winding is the same as the rotation direction of the rotor, and the rotation speed is the same. Such a motor generally has the following structure: a winding on the rotor, a concentrated excitation winding; no winding on the rotor, and a permanent magnet structure; no winding on the rotor, no permanent magnets, teeth and slots. There are distributed windings on the stator. The use of such a structure is mainly to minimize the number of slip rings and brushes, and such a motor is also called a transition type motor. There are also structures that place the field windings on the stator for some special requirements. Such structures are generally referred to as pivoting (such as household ceiling fans).
The asynchronous motor is an alternating current motor in which a rotating magnetic field formed by a stator winding interacts with a magnetic field of an induced current in a rotor winding to generate an electromagnetic torque to drive the rotation of the rotor, and is also referred to as an “induction motor”.
Induction motors and synchronous motors actually have a big difference in working principle:
The synchronous motor works by “the magnetic field always goes along the shortest direction of the magnetic circuit”, taking the case of a lost field motor as an example. After the excitation on the rotor, the N and S poles appear; then the stator magnetic field rotates, and the mutual changes of the N and S poles always correspond to the magnetic poles on the rotor. So a synchronization is formed. More importantly, the number of poles of the stator and rotor must be the same, otherwise the motor will not operate.
The asynchronous motor relies on induction to achieve motion. The principle is that after the three-phase voltage is applied to the stator winding, a rotating magnetic field is formed, and the bar on the rotor generates an electric potential due to the cutting of the magnetic lines of force; and since the bars are connected, a current is generated. At this point, we thought of the junior high school – “the charged conductor will produce motion in the magnetic field.” Therefore, such a motor is called an “induction motor.” For asynchronous or induction motors, the number of poles of the rotor is automatically induced by the number of stator poles. It can also be said that the rotor has no pole number. (The above is an example of the armature winding on the stator). Asynchronous motors do not have a pivot/transition.
In addition, there is no winding on the rotor, no permanent magnet, no slot, and the motor with distributed winding on the stator should belong to one type of induction motor. Such motors are also commonly used on small or small or special large motors.
Of course, there are many differences between asynchronous and synchronous motors, such as process requirements, design issues, and so on.
Application field :
Synchronous motors are mostly used in large generators. Asynchronous motors are used almost exclusively in electric motors. The synchronous motor can flexibly adjust the voltage and current phase on the input side by excitation, that is, the power factor; the power factor of the asynchronous motor is not adjustable, generally between 0.75 and 0.85, so in some large factories, when the asynchronous motor is used more, it can be attached. A synchronous motor is used as a camera to adjust the power factor at the factory-to-grid interface. However, due to the high cost of the synchronous motor and the large maintenance workload, the capacitor compensation power factor is generally used now.