Working principle of three-phase asynchronous motor control circuit

The concept and working principle of three-phase asynchronous motor

The three-phase asynchronous motor is a common AC motor. Its working principle is based on the principle of a single-phase induction motor. It is powered by a three-phase AC power supply, which generates a rotational force between the rotor and stator inside the motor to achieve mechanical energy conversion.

Specifically, the rotor of a three-phase asynchronous motor is equipped with a winding, also known as an induction coil. When the three-phase AC power supply is connected, the current will generate an alternating magnetic field in the induction coil inside the rotor. This magnetic field will interact with each other, forming a rotating magnetic field on the rotor.

At the same time, the stator of the motor is also equipped with a coil, also called a stator coil. The stator coil is connected to a three-phase AC power supply to form a three-phase AC magnetic field. The size and direction of this magnetic field are stable and unchanged.

Because the rotating magnetic field inside the rotor and the AC magnetic field in the stator coil are not synchronized, a difference in magnetic field is generated between them, which generates a torque between the rotor and the stator. This torque causes the rotor to start rotating until it rotates to the adjacent position of the stator magnetic field.

The working principle of the three-phase asynchronous motor is based on the principle of magnetic induction. It generates torque through AC power supply, rotating magnetic field, AC magnetic field and the difference between them to achieve the conversion of mechanical energy.

Wiring method of three-phase asynchronous motor

The wiring methods of three-phase asynchronous motors include star connection and delta connection.

1. Star connection

The star connection is to connect one terminal of each motor winding together to form a three-phase intersection, and the other terminal is grounded or connected to the phase line of the power supply. This connection method reduces the voltage of the motor by 1/√3, increases the current by √3 times, and the power and torque remain unchanged.

2. Triangle connection

The triangle connection is to connect the two terminals of each motor winding to each other to form a closed triangle. At this time, the voltage of each phase is equal to the line voltage, and the current and power remain unchanged. However, the starting current of the motor becomes larger, which is not conducive to starting.

Generally speaking, when the rated power of the motor is small, star connection is used, while when the rated power is large, delta connection is mostly used. This can reduce the starting current of the motor when starting, and protect the safety of the power supply system and the motor itself.

Basic control circuit of three-phase asynchronous motor

The basic control circuit of a three-phase asynchronous motor includes a starting circuit and an operating circuit.

1. Starting circuit: A large starting current is required when starting a three-phase asynchronous motor. Commonly used starting circuits include direct starting, star-delta starting and auto-coupling starting.

Direct starting: Connect the three-phase power supply directly to the three wires of the motor. The current is large when the motor starts, but the efficiency is low. It is generally used for small power motors.

Star-angle starting: Connect the three-phase power supply to three fixed positions in sequence. The current is small when the motor starts, but the effect is better than direct starting. It is suitable for medium and low power motors.

Auto-starting: Based on the star-delta starting, an auto-transformer is added to make the motor starting current smaller and the effect better. It is suitable for larger power motors.

2. Running circuit: After the motor starts, the speed and direction of the motor need to be adjusted through the running circuit.

Voltage speed regulation: The speed of the motor is controlled by changing the voltage. Common methods include adjusting the transformer, which can achieve constant torque or constant power speed regulation.

Frequency speed regulation: The motor speed is controlled by changing the power supply frequency. The commonly used method is frequency converter, which can achieve wide range speed regulation and good speed regulation performance.

Phase sequence control: Change the rotation direction of the motor by adjusting the phase sequence of the three-phase power supply. The commonly used method is to control the phase sequence with an AC contactor to achieve forward and reverse control.

In summary, the basic control circuit of a three-phase asynchronous motor consists of two parts: a starting circuit and an operating circuit. The details of the control circuit of different motors will have different design schemes.

Working principle of three-phase asynchronous motor control circuit

The three-phase asynchronous motor control circuit mainly consists of power supply, control circuit and motor. When the motor is powered on, the AC power of the power supply will first enter the control circuit, which generates the voltage and frequency signals required by the motor by rectifying, filtering and controlling the voltage conversion. These signals are connected to the three windings of the motor through the terminals of the motor starter to form a rotating magnetic field to make the motor rotate.

The control circuit is generally controlled by an integrated circuit or a single-chip microcomputer. Its main functions are to detect the running status of the motor, adjust the speed and direction of the motor, and protect the motor from abnormal conditions such as overload or overheating. The control circuit can be programmed as needed and can achieve a variety of functions, such as start-stop control, speed control, direction control, positioning control, etc.

Wiring method of three-phase asynchronous motor control circuit

The wiring method of the three-phase asynchronous motor control circuit usually includes the main circuit and the control circuit.

Main circuit wiring method:

1. Connect the three wires of the three-phase mains power to the three-phase terminals of the motor respectively.

2. Connect the three neutral wires from the motor to the neutral wire of the power source.

3. Connect a three-phase circuit breaker and a fuse to protect the motor and circuit.

4. Connect the motor's ground wire to the ground terminal.

Control circuit wiring method:

1. Connect a main contactor to control the starting and stopping of the motor.

2. Connect a time relay or star-delta converter to control the starting mode of the motor.

3. Connect an overload protector to protect the motor from overload.

4. Connect an inverter to change the direction of the motor's rotation.

5. Connect a current interlock to ensure that the motor is not overloaded.

6. Connect a temperature protector to prevent the motor from overheating and damage.

The above are common wiring methods for three-phase asynchronous motor control circuits. The specific wiring methods need to be adjusted according to actual conditions and design requirements.