A direct current machine is a rotating electrical machine that converts DC electrical energy into mechanical energy (DC motor) or converts mechanical energy into DC electrical energy (DC generator). It is a motor that converts DC power and mechanical energy to each other. When it is used as a motor, it is a DC motor that converts electrical energy into mechanical energy; when the generator is running, it is a DC generator that converts mechanical energy into electrical energy. The structure of the DC motor should consist of two parts: the stator and the rotor. The part of the DC motor that is stationary during operation is called the stator. The main function of the stator is to generate a magnetic field. It consists of a base, a main pole, a commutating pole, an end cover, a bearing and a brush device. The part that rotates during operation is called the rotor. Its main function is to generate electromagnetic torque and induced electromotive force. It is the pivot of energy conversion of DC motor, so it is usually called armature. It is changed by shaft, armature core, armature winding, and It consists of a transmitter and a fan.
Electromotive force generation: When the armature is driven by the prime mover at a constant speed and rotated in the counterclockwise direction, the right hand rule can be used to determine the direction of the induced electromotive force generated by the magnetic flux lines cut by the coils ab and cd, and the loop formed by the load and the coil. A current Ia is generated in the same direction as the electromotive force direction. The current flows from the brush A and flows back from the brush B.
Reversing: When the armature is turned to the position shown on the right, the direction of the induced electromotive force in the coil changes, but since the commutator rotates with the same rotation, the brush A always touches the wire under the N pole, and the brush B always touches the wire under the S pole, so the current still flows back from A to B, and the direction does not change.
Three-phase motor refers to the three-phase stator winding of the motor (each phase difference is 120 degrees electrical angle). After three-phase alternating current is applied, a rotating magnetic field is generated, which rotates the rotor winding to generate an induced current in the rotor winding. (The rotor winding is a closed path).
The current-carrying rotor conductor generates electromagnetic force under the rotating magnetic field of the stator, thereby forming electromagnetic torque on the motor shaft, driving the motor to rotate, and the motor rotating direction is the same as the rotating magnetic field. The motor is also called (commonly known as a motor) and is represented by the letter "M" (the old standard is "D") in the circuit. Its main function is to generate driving torque. As a power source for electric appliances or various machines, the motor is fully enclosed, external fan-cooled, and squirrel-cage structure.
When the three-phase stator windings of the motor (each phase difference of 120 degrees electrical angle), after three-phase alternating current is applied, a rotating magnetic field is generated, which cuts the rotor windings, thereby generating an induced current in the rotor windings (the rotor windings are closed paths) The current-carrying rotor conductor generates an electromagnetic force under the rotating magnetic field of the stator, thereby forming an electromagnetic torque on the motor shaft, driving the motor to rotate, and the motor rotating direction is the same as the rotating magnetic field. 3.1 The electromagnetic torque of an asynchronous motor is generated by the interaction of the stator main flux and the rotor current. 3.2 However, the stator main flux of an asynchronous motor is not stationary, but is rotated at a certain speed. 3.3 The necessary condition for generating the rotor current is that the rotor winding cuts the magnetic field lines of the stator magnetic field. Therefore, the rotor speed must be lower than the speed of the stator field (ie "asynchronous").
The difference between DC motor and AC motor:I use the simplest and most understandable way to talk about the working principle and difference between DC motor and AC motor.
The picture above is the simplest physical model of a DC motor.
working principle:1. The DC power supply current flows along the positive pole of the power supply to the left side of the brush. The brush and the commutator rub against each other. The current passes through the left commutator (also called the commutator. This motor has two left and right commutator segments). Flow into the coil, flowing out from the right side of the coil, through the right commutator and the right brush back to the negative pole of the power supply, forming a closed loop.
2. Since the coil is in the magnetic field of the main magnetic pole (N and S in the figure), the coil will be subjected to electromagnetic force. The two sides of the coil are different in direction of current (the current on the left flows inward, and the flow on the right) Therefore, the two coil sides are subjected to electromagnetic forces of opposite magnitude and opposite directions. These two electromagnetic forces just form an electromagnetic torque, and the coil starts to rotate under the pulling of the electromagnetic torque. In the DC motor, the coil is embedded in the rotor slot and the motor starts to rotate.
3. The left and right reversing pieces rotate with the rotating shaft, and the brush is fixed. After one rotation, the right coil is to the left, and the left coil is to the right, but due to the existence of the commutator, it is now in the left coil. The current direction flows in the same direction as the current of the coil that is originally on the left side, so the direction of the electromagnetic force received is the same, and the right side is also the same. Therefore, from the perspective of space, the direction of the electromagnetic force received at the coil side of the same position is constant, which ensures the cyclic rotation of the motor.
4. However, a coil, because the magnetic field is different when the coil is turned to different positions, the electromagnetic force of the coil is also constantly changing, so the coil is unstable and slow. Therefore, it is possible to ensure uniform and stable stress on the coil by installing a plurality of coils.
So there is such a thing,
Even such a motor model.
In addition, the two outer magnetic poles are actually electromagnets generated by excitation coils. There are permanent magnets in small motors, and electromagnets are used in slightly larger ones.
The model is a model, but the real motor rotor is like this.
AC motors are divided into synchronous and asynchronous motors. Synchronization is mainly used as a generator, and asynchronous is mainly an electric motor. I mainly talk about asynchronous motors. Because of their simple structure, low price, easy maintenance and reliable operation, asynchronous motors have been widely used.
Although the AC motor has a simple structure, the working principle is actually more complicated than that of the DC motor. If it is to be understood clearly, it is more difficult.
A three-phase symmetrical alternating current is applied to the stator of the alternating current motor. As shown in the above figure, the stator does not move, and only a change in current can generate a rotating synthetic magnetic field, which is like a magnet that rotates around the stator.
With this rotating magnet, everything is easy to handle. A closed coil is placed inside the stator. In this closed coil, the electromotive force and current are induced, and electromagnetic force is generated. The closed coil will rotate.
It can also be understood that there is a rotating magnet on the stator. The rotor closing coil is actually an electromagnet due to induction charging. When the outer electromagnet is rotating, it will turn with the electromagnet inside, so the AC motor The rotor turned.
The rotational speed of the stator magnetic field is called synchronous speed. The inner rotor is actually driven by the stator magnetic field, so its rotational speed will be slower than the stator magnetic field, so it is called asynchronous speed. So there is the name of the asynchronous motor.
The rotor of an AC motor is such a simple closed coil, or a closed conductor, like a rat cage, so it is also called a 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 called an induction motor. Therefore, the names of three-phase asynchronous motors are quite numerous: AC motors, asynchronous motors, induction motors, all of which are said to be names from different angles.
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