How DC Motors Work
The DC power current flows along the positive pole of the power supply to the brush on the left, the brush and the commutator rub against each other, and the current passes through the commutator on the left (also called the commutator, this motor has two commutators on the left and right) It flows into the coil, flows out from the right side of the wire, and flows back to the negative pole of the power supply through the commutator on the right and the brush on the right, forming a closed loop.
2. Since the coil is in the magnetic field of the main magnetic poles (N and S in the figure), the coil will be affected by electromagnetic force, and the two sides of the coil will have different current directions (the current on the left flows inward, and the current on the right flows outwards). ), so the two coils are subjected to electromagnetic forces of the same magnitude and opposite directions. These two electromagnetic forces just form an electromagnetic torque. Under the pulling of the electromagnetic torque, the coils start to rotate. The coils in the DC motor are embedded in the rotor slots. , the motor starts to turn.
3. The left and right commutator segments move with the shaft, and the brushes are fixed. After one turn, the coil on the right goes to the left, and the coil on the left goes to the right. However, due to the existence of the commutator segment, it is now in the country on the left. The direction of the current is the same as the direction of the current changed by the coil on the left, so the direction of the electromagnetic force is unchanged, and the same is true on the right. Therefore, from a spatial point of view, the direction of the electromagnetic force on the side of the coil at the same position is the same. Yes-straight invariant, which ensures the cyclic rotation of the motor.
4. But for a coil, since the magnetic field is different when the coil is rotated to different positions, the electromagnetic force on the coil is also constantly changing, so the coil turns unstable, sometimes fast and slow. Therefore, it can be installed by multiple installations. Several coils are used to ensure uniform and stable coil force.
Let's talk about the working principle of AC series motor:
AC motors are divided into synchronous motors and asynchronous motors. Synchronous motors are mainly used as generators, and asynchronous motors are mainly used as motors. Let's talk about asynchronous motors. Because of their simple structure, low price, convenient maintenance, and reliable operation, asynchronous motors have been widely used.
Although the structure of the AC motor is simple, its working principle is actually a little more complicated than that of the DC motor, and it is more laborious to understand it clearly.
The three-phase symmetrical alternating current is connected to the stator of the AC motor. As shown in the figure above, the stator does not move, and a rotating synthetic magnetic field can be generated only by the change of the current. This magnetic field is like a magnet that rotates around the stator.
With this rotating magnet, everything is easy to handle. Just put a closed coil inside the stator. In this closed coil, electromotive force and current will be induced, electromagnetic force will be generated, and the closed coil will rotate.
It can also be understood that there is a rotating magnet on the stator, and the closed coil of the rotor is actually electrified due to induction. In fact, it also becomes an electromagnet. When the electromagnet on the outside is rotating, it will rotate with the electromagnet inside, so the AC motor The rotor turns.
The rotational speed of the stator magnetic field is called the synchronous rotational speed, and the rotor is actually pulled by the stator magnetic field to rotate, so its rotational speed will be slower than the rotational speed of the stator magnetic field, so it is called asynchronous rotational speed. Hence the name asynchronous motor.
The rotor of the AC motor is such a simple closed coil, or closed conductor, like a squirrel cage, so it is also called squirrel cage asynchronous motor.
In addition, since the electromotive force and current inside the rotor are induced by the stator magnetic field, the asynchronous motor is also called an induction motor. Therefore, there are many names of three-phase AC series motors: AC motors, asynchronous motors, and induction motors.
