Working principle, functional characteristics and wiring method of three-phase motor control circuit

Concept of three-phase motor control circuit

The three-phase motor control circuit is an electrical device used to control the start, stop and direction of the three-phase motor. According to the control purpose and functional requirements of the three-phase motor, it can be divided into direct starting control circuit, step-down starting control circuit, star-delta starting control circuit, soft starting control circuit and other types.

Specifically, here are the four basic types of three-phase motor control circuits:

1. Direct start control circuit: The direct start control circuit has a simple structure, low cost, and easy installation. However, problems such as large current at the start moment, start impact, and line fluctuation need to be considered.

2. Dynamic braking control circuit: The dynamic braking control circuit can achieve the effect of turnover braking by controlling the electrical coil so that the motor can quickly eliminate its own mechanical energy when it needs to stop.

3. Frequency conversion control circuit: The frequency conversion control circuit uses a frequency converter to control the operation of the motor, which can achieve stepless speed regulation of the motor. It has the advantages of smooth start-up, high operating stability, energy saving, convenient adjustment, and high reliability.

4. Soft start control circuit: The soft start control circuit can slowly increase the starting current of the motor, so that the motor starts with a smaller current, thereby avoiding the damage of the starting impact to the power supply and the motor. It is suitable for use when the power supply voltage is unstable and the motor starting load is large.

In general, three-phase motor control circuits can achieve motor control and protection in a variety of ways. Choosing the right circuit type can improve motor utilization and extend the service life of the motor. It also plays an important role in safety protection.

The three-phase motor control circuit is a circuit that controls the operation of the three-phase motor. It has a variety of different control methods and wiring methods. Generally speaking, the three-phase motor control circuit includes the following parts:

1. Power interface: The three-phase power cable is directly connected to the motor power terminal box, usually a three-phase four-wire system, namely L1, L2, L3 and ground wire.

2. Starting protection device: including thermal relay, air switch, MCCB, etc., used to protect the motor from various abnormal conditions during operation, such as overload, short circuit, phase loss protection, etc.

3. Control interface: The external control signal is connected to the corresponding pins in the circuit junction box through the control cable, such as the start button, stop button, speed regulator, etc.

4. Converter: Convert three-phase fixed frequency AC into three-phase adjustable frequency AC, and adjust the output voltage and frequency to achieve motor output speed regulation.

5. Protection device: Provide protection for three-phase motors against overload, overheating, overcurrent, etc., such as thermal relays, circuit breakers, contactors, etc.

The power interface and starting protection device are the basic parts of the three-phase motor control circuit, while the control interface, converter and protection device are the key links for further regulation and protection of the motor operation. In actual use, other components such as filters, isolation transformers, grounding resistors, etc. can be added as needed to further improve the stability and safety of the equipment.

Working principle of three-phase motor control circuit

The three-phase motor control circuit is a circuit system that realizes motor control and speed regulation by adjusting the voltage and frequency of the three-phase power supply. The following is the working principle of the three-phase motor control circuit:

1. Three-phase power input: The three-phase power supply needs to be connected to the input end of the inverter for power conversion and regulation. The power enters from the input end and the voltage is reduced to the required voltage through the transformer. After entering the inverter, the inverter will rectify and invert the input three-phase AC power to obtain DC power or high-frequency power, and send the signal to the control circuit.

2. Control circuit: The control circuit is the core part of the three-phase motor control circuit. It controls the frequency, voltage, current and other parameters of the inverter output through the central processor. When running, the control circuit will set and control the output frequency and voltage of the three-phase motor within a given range according to the predetermined parameters and operating requirements to ensure the stability and controllability of the motor's speed and torque.

3. Output circuit: The output circuit is another basic structure in the inverter, which converts the instructions received from the inverter control circuit into information signals, and then controls the voltage and frequency output of the motor. Usually, the output circuit is composed of operational amplifiers, excitation units, output devices and other components, and uses a control program to control and change the speed of the motor, thereby achieving the desired control effect.

Through the above three steps, the three-phase motor control circuit realizes efficient, rigid and stable control of the motor. The parameter setting and circuit structure design in the control circuit can accurately control the key parameters such as the motor speed, torque, power and efficiency, thereby ensuring that the three-phase motor can effectively achieve stable and reliable operation under different loads and operating conditions. At the same time, the three-phase motor control circuit also has the advantages of high power density, fast response time and excellent efficiency, which makes it widely used in the fields of industrial automation control and motors.

Functional characteristics of three-phase motor control circuit

The three-phase motor control circuit is an electrical control device for three-phase motors, which has the following main functional features:

1. Start control function: The three-phase motor control circuit can control the start, stop and frequency conversion speed regulation of the motor through the start switch. The start switch can be manually or automatically controlled. Manual control can be achieved by the operator manually pressing the start button or turning the knob on the protective cover; automatic control can be achieved through contactor or PLC control.

2. Steering control function: The three-phase motor control circuit can also change the motor motion profile. By controlling the direction of the motor, it can make it rotate forward and reverse or forward and brake, and the delay time can be set to change the steering process. At the same time, the motor can also be started and stopped at multiple points through external jumper and other control devices.

3. Load control function: The three-phase motor control circuit can adjust and control the load by controlling the load of the motor. For example, in the fields of water pumps and conveyors, the speed and water pressure of conveying and water supply can be adjusted by controlling the size of the motor load to achieve a more effective and efficient production process.

4. Automatic control: The three-phase motor control circuit can realize automatic control of the motor by combining with sensors and controllers such as PLC, avoiding errors and negligence in manual operation. At the same time, a variety of automatic protection functions, such as undervoltage protection, overvoltage protection, overload protection, underload protection, etc. can also be realized.

In general, the three-phase motor control circuit can realize multiple functions such as start control, steering control, load control, automatic control, etc. according to different occasions and needs. It also has multiple protection measures to ensure the reliability and stability of the motor operation.

Wiring method of three-phase motor control circuit

There are usually two wiring methods for three-phase motor control circuits, namely: star connection and triangle connection. Specifically:

1. Star connection: The star connection of three-phase motors is also called Δ-Y starting. First, the three phase lines of the motor are connected into a triangle at an angle of 120 degrees, with one end being the common point, i.e. the grounding point. Then the other three phase lines are connected to the corresponding windings of the starting motor, so that the motor will be connected in a star shape when starting, and then in a triangle shape after running. This wiring method is suitable for low-power selection of three-phase motors, because the phase voltage and current drop to 1/3 during Δ-Y starting, so it cannot be used in equipment that requires large starting torque.

2. Delta connection: The delta connection of three-phase motors is also called Y-Δ starting. The three phases of the motor are first connected to the three phases of the power supply, and then the three phases of the motor are short-circuited in pairs to form a triangle connection when starting. Unlike the star connection, the delta connection has no common point. When the motor starts, the efficiency provided by the power supply to the motor is three times that of the star connection. Therefore, this wiring method is often used in situations where the power of the three-phase motor is relatively large.

It should be noted that, whether it is a star connection or a triangle connection, appropriate relays and protection devices need to be added to the circuit to ensure the safe operation and long-term stability of the motor. In addition, in order to adjust the motor speed, electrical devices such as frequency converters can be added to the circuit to achieve stepless speed control of the three-phase motor.