The difference and connection between DC motor and AC motor

Update:24-12-2020
Summary:

Both DC motors and AC motors have a wide range of appli […]

Both DC motors and AC motors have a wide range of applications. The basic principles of their work are the same, and both are the law of electromagnetic induction. Both have their own advantages and disadvantages. To analyze, DC motors or DC motors have commutators. This is also the main reason that determines the different working methods of DC motors and AC motors.
Take the motor as an example. If the motor wants to work, it must rely on the electromagnetic force induced by the rotor winding to drive the rotor to rotate. Therefore, in order to ensure the stable and continuous rotation of the motor, the induced electromagnetic force in the rotor winding must maintain the same direction. For the motor, the direction of the stator magnetic field is unchanged, so if the current in the rotor is not commutated, the direction of the electromagnetic force received by the rotor during the rotation will change, and the continuous rotation of the rotor cannot be guaranteed. That is, as long as the electromagnetic force in the rotor windings is in the same direction, the rotor can continue to rotate.

When the AC motor is working, it is ensured by changing the direction of the stator magnetic field instead of commutation. Because for the AC motor, the stator magnetic field is not fixed, but rotates according to a certain rule, so it can be guaranteed The direction of the electromagnetic force received by the rotor winding remains unchanged. As long as the stator coils of an AC motor are arranged in phases, a rotating magnetic field will naturally be generated to ensure the rotation of the rotor.

The working principles of DC and AC motors are both the law of electromagnetic induction, but there are also differences between the two, which can be understood through the different starting methods of the two. The rotation of the rotor of the DC motor (the armature winding movement or force) is because the energized armature winding receives electromagnetic force in the magnetic field, so the premise is that there is current in the armature, so the DC motor needs the armature current to start; and the AC When the motor starts, as long as alternating current is applied to the stator, a rotating magnetic field will be generated. Since this magnetic field is moving, the rotor winding will induce electromotive force. As long as the rotor winding can form a closed loop, current will be generated and electromagnetic will be induced The force drives the rotor to rotate, so the premise of the AC motor rotor movement is that the magnetic field is rotating, which is the difference between the two in the initial state of movement.

The starting process of a DC motor is: magnetic field + armature winding with current flow → electromagnetic force induced in the winding → drag the rotor to rotate; and the start of an AC motor is called: the stator is connected to three-phase alternating current → the stator rotating magnetic field → Make the rotor winding in the rotating magnetic field generate induced electromotive force → Since the rotor winding forms a closed loop (premise), current is generated in the rotor winding → the rotor winding generates induced electromagnetic force → drag the rotor to rotate.
Single-phase AC motors have only one winding, and the rotor is squirrel cage type.

Single-phase electricity cannot produce a rotating magnetic field. To make the single-phase motor can rotate automatically, we can add a start winding to the stator. The start winding and the main winding are spaced apart by 90 degrees. The start winding should be connected in series with a suitable capacitor so that the current between the main winding and the main winding The phase difference is approximately 90 degrees, which is the so-called principle of phase separation.

In this way, two currents with a 90-degree difference in time pass through two windings with a 90-degree difference in space, and a (two-phase) rotating magnetic field will be generated in space. Under the action of this rotating magnetic field, the rotor can automatically start.

Use a single-phase capacitor motor to explain: a single-phase motor has two windings, namely the start winding and the running winding. The two windings are 90 degrees apart in space. A large-capacity capacitor is connected in series with the start winding. When the running winding and the start winding pass through single-phase alternating current, the current in the start winding is 90 degrees ahead of the current in the running winding due to the action of the capacitor, and reaches the maximum first. value.

Two identical pulsed magnetic fields are formed in time and space, so that a rotating magnetic field is generated in the air gap between the stator and the rotor. Under the action of the rotating magnetic field, an induced current is generated in the motor rotor, and the current interacts with the rotating magnetic field to produce The electromagnetic field torque causes the motor to rotate.
A DC motor does not move the magnetic field and the conductor moves in the magnetic field; an AC motor rotates the magnetic field while the conductor does not move.

DC motors are divided into stator windings and rotor windings. The stator winding generates a magnetic field. When direct current is applied. The stator winding generates a fixed-polarity magnetic field. The rotor is subjected to force in a magnetic field through direct current. Then the rotor rotates under force in the magnetic field. The DC motor has a complex structure and high cost.

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