The introduction of AC motor

The introduction of AC motor

(1) Main components and functions of AC motor

1: Stator core; Magnetic conductivity (made by laminating octagonal silicon steel sheets), which acts as a base.

2: The stator core with winding (the stator core after wire embedding) is powered by three-phase sinusoidal alternating current. Generating rotating magnetic field: connecting support: connecting the stator core of the motor part and the brake stator core, and installing the blower, which is also a mounting part with foundation.

3: Front and rear end covers: fix stator iron core and brake, and install sliding bearing (rotor bearing platform and sliding bearing are equipped in sliding mode).

4: Sliding bearing: plays the role of supporting the rotor.

5: Rotor: the motor generates induced current. After rotation, the torque is output to drive the tractor, and the brake part plays the role of over-current braking.

6: Rotating shaft: the grid motor rotates on the iron core, and the brake rotates on the iron core. It is also matched with the sliding bearing to connect the load. It is the main structural member of the rotating part.

7: The eddy current brake turns the iron core: eddy current is generated, and the principle of electromagnetic induction is used to generate braking torque.

8: Coil; The main conductive part is the component unit of the winding. The stator winding of the motor, the fixed coil of the brake and the rotor winding are respectively provided with a squirrel cage guide bar.

9: Blower: for forced ventilation.

10: Junction box: for motor outgoing line.

(2) There are several speed regulating methods for AC motor

1. Speed regulation method of pole changing logarithm: change the red connection method of stator winding to change the number of stator poles of cage motor to achieve speed regulation.

2. Variable frequency speed regulation method: use the frequency converter to change the frequency of motor stator power supply, so as to change its synchronous speed.

3. Cascade speed regulation method: Cascade speed regulation refers to adding adjustable additional electromotive force in the rotor circuit of wound motor in series to change the slip of motor to achieve the purpose of speed regulation.

Most slip power is absorbed by the additional potential of series connection, and then used to generate additional devices to return the absorbed slip power to the grid or convert energy for use. According to the slip power absorption and utilization mode, cascade speed regulation can be divided into motor cascade speed regulation, mechanical cascade speed regulation and thyristor cascade speed regulation, which are mostly adopted.

4. Speed regulation method of winding motor rotor with resistance in series: the rotor of the linear asynchronous motor is connected with additional resistance in series, so that the slip of the motor is increased and the motor operates at a lower speed. The greater the series resistance, the lower the motor speed. This method is simple in equipment and convenient in control, but the slip power is consumed on the resistance in the form of heating. It belongs to stepwise speed regulation, with soft mechanical characteristics.

5. Stator voltage regulation and speed regulation method: when the stator voltage of the motor is changed, different speeds can be obtained. Because the torque of the motor is proportional to the square of the voltage, the maximum torque decreases a lot, and its speed regulation range is small, making it difficult to apply the general cage motor. In order to expand the speed regulation range, cage motors with large rotor resistance value shall be used for voltage regulation and speed regulation, such as torque motors specially used for voltage regulation and speed regulation, or frequency sensitive resistors shall be connected in series on wound motor.

(3) Classification of AC motor and application of each motor

1. Servo motor

Servo motor is widely used in various control systems. It can convert the input voltage signal into the mechanical output on the motor shaft and drag the controlled components to achieve the control purpose.

Servo motor can be divided into DC motor and AC motor. The earliest servo motor was a general DC motor. In the case of low control accuracy, the general DC motor was used as the servo motor. The current DC servo motor is a small power DC motor in structure. Its excitation mostly adopts armature control and magnetic field control, but usually adopts armature control.

2. Stepping motor

Stepping motor is mainly used in the field of NC machine tool manufacturing. Because stepping motor does not need A/D conversion and can directly convert digital pulse signal into angular displacement, it has been considered as the most ideal actuator of NC machine tool.

In addition to its application in CNC machine tools, the stepping motor can also be used in other machines, such as the motor in the automatic feeder, the motor as a general floppy disk driver, and the printer and plotter.

3. Torque motor

The torque motor has the characteristics of low speed and large torque. Generally, AC torque motor is often used in textile industry, and its working principle and structure are the same as single-phase asynchronous motor.

4. Switched reluctance motor

Switched reluctance motor (SRM) is a new type of adjustable speed motor. It has a very simple and solid structure, low cost, and excellent adjustable speed performance. It is a strong competitor of traditional control motors and has strong market potential.

(4) Advantages and disadvantages of AC motor and DC motor

1. DC motor

Advantages: 1. DC motor has good starting characteristics and speed regulation characteristics. 2. The torque of DC motor is relatively large. 3. Maintenance is relatively cheap. 4. The DC of DC motor is more energy-saving and environment-friendly than the AC motor.

Disadvantages: 1. The manufacturing of DC motor is expensive 2. There are carbon brushes

2. AC motor

Advantages: simple structure, convenient manufacture, low price and convenient operation.

Disadvantages: lagging power factor, low light load power factor, poor startup and speed regulation performance.