What is the principle and operation of the machine control circuit of an induction motor?

Induction motor, also known as ‘asynchronous motor’, is a device in which the rotor is placed in a rotating magnetic field, and under the action of the rotating magnetic field, a rotating torque is obtained, and thus the rotor rotates. The rotor is a rotating conductor, usually in the form of a squirrel cage. Invented by electrical engineer Nikola Tesla in 1887. The entry describes the concept, inventor, principle of operation, basic structure, mode of operation, braking method, asynchronous characteristics, specifications, and fault checking of induction motors. Induction motor is also called ‘asynchronous motor’, which means that the rotor is placed in the rotating magnetic field, and under the action of the rotating magnetic field, it obtains a rotating torque, and thus the rotor rotates.

The rotor is a rotating conductor, usually in the shape of a squirrel cage. The stator is the non-rotating part of the motor, whose main task is to generate a rotating magnetic field. The rotating magnetic field is not achieved mechanically. Instead, alternating current is passed through several pairs of electromagnets, so that the magnetic poles of the nature of the cycle change, so it is equivalent to a rotating magnetic field. This kind of motor is not like a DC motor with brushes or collector rings, according to the type of AC used in single-phase motors and three-phase motors, single-phase motors are used in such as washing machines, electric fans, etc.; three-phase motors are used as power equipment in factories.

The basic working principle of induction motor

Induction motor is a kind of motor that generates torque between rotor and stator by inducing electric current. The basic principle of operation is that according to the law of electromagnetic induction, an alternating magnetic field generates an induced current in the stator coil, which creates a rotating magnetic field in the rotor, thus generating torque and driving the motor to rotate.

An induction motor usually consists of two parts: the stator and the rotor. The stator is the stationary part of the motor and consists of the stator core, windings, and end caps. Three-phase staggered winding coils are distributed in the winding, and when three-phase power is connected to the winding, a rotating magnetic field is formed in the winding.

The rotor is the rotating part of the motor and usually consists of a rotor core and conductor bars. The conductor bars of the rotor are usually made of aluminium, copper and other good conductive materials and are fixed on the rotor core. When the rotating magnetic field passes through the rotor conductor bars, the induced electromotive force will generate a current inside the conductor bars, and the rotor will be subjected to a certain amount of torque because the current inside the conductor bars is subjected to electromagnetic force.

Depending on how the magnetic field is generated, induction motors can be classified into two types, which are asynchronous motors and synchronous motors. An asynchronous motor is the most common type of induction motor, in which the rotor rotates at a slightly lower speed than the magnetic field, called slip. Synchronous motors, on the other hand, are motors whose rotational speed is exactly the same as the rotational speed of the magnetic field.

In summary, the basic operating principle of an induction motor is to form a rotating magnetic field in the stator coil through the principle of electromagnetic induction, thereby generating a rotating magnetic field within the rotor, which drives the motor to rotate through the torque generated by the induced current. This type of motor has the advantages of simple structure, high reliability and stable operation, and is one of the main types of motors widely used in various industrial and civil fields.

Induction motor is a type of motor that generates torque between the rotor and stator by induced current. The basic working principle is to generate an induction current in the stator coil through an alternating magnetic field according to the law of electromagnetic induction, which causes a rotating magnetic field in the rotor, thus generating a torque and driving the motor to rotate.

An induction motor usually consists of two parts: the stator and the rotor. The stator is the stationary part of the motor and consists of the stator core, windings, and end caps. Three-phase staggered winding coils are distributed in the winding, and when three-phase power is connected to the winding, a rotating magnetic field is formed in the winding.

The rotor is the rotating part of the motor and usually consists of a rotor core and conductor bars. The conductor bars of the rotor are usually made of aluminium, copper and other good conductive materials and are fixed on the rotor core. When the rotating magnetic field passes through the rotor conductor bars, the induced electromotive force will generate a current inside the conductor bars, and the rotor will be subjected to a certain amount of torque because the current inside the conductor bars is subjected to electromagnetic force.

Depending on how the magnetic field is generated, induction motors can be classified into two types, which are asynchronous motors and synchronous motors. An asynchronous motor is the most common type of induction motor, in which the rotor rotates at a slightly lower speed than the magnetic field, called slip. Synchronous motors, on the other hand, are motors whose rotational speed is exactly the same as the rotational speed of the magnetic field.

In summary, the basic operating principle of an induction motor is to form a rotating magnetic field in the stator coil through the principle of electromagnetic induction, thereby generating a rotating magnetic field within the rotor, which drives the motor to rotate through the torque generated by the induced current. This type of motor has the advantages of simple structure, high reliability and stable operation, and is one of the main types of motors widely used in various industrial and civil fields.

Working mode of induction motor

Induction motors work according to the law of electromagnetic induction, using a rotating magnetic field to generate an induced current in the rotor, which causes the rotor to rotate and drive the load movement.

An induction motor usually consists of two parts: a stator and a rotor. The stator is the stationary part of the motor and consists of the stator core, windings and end caps. Three-phase staggered winding coils are distributed in the winding, and when three-phase power is connected to the winding, a rotating magnetic field is formed in the winding.

The rotor is the rotating part of the motor and usually consists of a rotor core and conductor bars. The conductor bars of the rotor are usually made of a good conducting material such as aluminium or copper and are fixed to the rotor core. When an alternating current is applied to the stator winding, a rotating magnetic field is generated in the winding, which passes through the rotor core and induces an electromotive force in the conductor bars. Since the resistance inside the conductor strip is not zero, currents are generated in the conductor strip. These currents are in the opposite direction to the rotor magnetic field, so they interact with the rotating magnetic field to produce torque. The rotor turns in the same direction as the rotating magnetic field, so the relative velocity between them is small.

Induction motors are also known as asynchronous motors due to the presence of induced currents in the rotor because the rotor rotates at a speed slightly lower than the speed of the rotating magnetic field, and this speed difference is known as slip. When the load resistance increases, the rotor decelerates and the slip increases, resulting in a greater torque. This characteristic enables the induction motor to automatically adjust its output power under large load variations and has good load adaptability.

In conclusion, the induction motor works by using a rotating magnetic field to generate an induced current in the rotor, which generates torque and drives the load to rotate. This kind of motor has the advantages of simple structure, high reliability, stable operation, etc. It is one of the main types of motors widely used in various industrial and civil fields.

Measurement method of operating characteristics and parameters of induction motor

The working characteristics and parameters of induction motor can be measured by the following methods:

Rated voltage and rated power: these parameters can be found on the nameplate of the motor or calculated by measuring the winding resistance and no-load current of the motor.

Speed: The speed of an induction motor can be determined by measuring the speed of the motor output shaft or by using a tachometer.

Torque: The torque of an induction motor can be determined by measuring the output shaft torque of the motor directly or by using a torque transducer.

Efficiency: The efficiency of the motor can be calculated by measuring the input power and output power.

Power Factor: The power factor can be calculated by measuring the active and apparent power of the motor.

Rotor resistance: It can be calculated by measuring the winding resistance of the motor using a low-voltage meter and by measuring the impedance of the motor during operation.

Damping ratio: The damping ratio can be calculated by measuring the winding impedance of the motor during operation.

Slip: The slip can be calculated by measuring the speed of the motor during operation.

Skeleton Current: The skeleton current of the motor can be measured by installing a current sensor outside the motor.

Motor control circuits are circuits used to control an electric motor by varying parameters such as voltage, current and frequency to control the speed, steering and stopping of the motor. Motor control circuits typically consist of a power supply, a controller, a feedback element, a sensor, and an actuator.

Common motor control methods include DC motor control, AC motor control, and stepper motor control. DC motor control circuits can use PWM controllers to change the speed and direction of the motor, while AC motor control is usually implemented using inverters or motor soft starters. In stepper motor control circuits, each stepper motor needs to be controlled individually, and commonly used control methods include full-step, half-step and micro-step control.

Motor control circuits are used in a wide range of applications, including home appliances, industrial automation, machinery and equipment, and transport. In industry, motor control circuits can be used to control the operation of equipment such as conveyor belts, machine tools, fans, pumps and compressors.

How motor control circuits work

Motor control circuits are electrical systems that control motor start/stop, forward/reverse rotation, and speed regulation. The principle of operation mainly involves motor motion control and protection.

The working principle of motor control circuit includes the following aspects:

1. Motor start-stop control

Motor start-stop control can be achieved by directly controlling the power supply. For example, controlling the contactor or circuit breaker switch state of the motor, or controlling the relay or switch state of the motor. In this case, the motor start-stop state is determined by the switch of the motor control circuit.

2. Motor forward and reverse control

Motor forward and reverse control can be achieved by changing the wiring of the motor, such as changing the relative wiring position between the power supply and the motor. In this case, the motor forward, reverse and stop functions are controlled by the switch of the motor control circuit.

3. Motor speed control

Motor speed control can be realised by changing the size and frequency of the power supply voltage. For example, by changing the size of the power supply voltage, the torque of the motor can be changed; by changing the frequency of the power supply, the speed of the motor can be changed. At this time, the motor speed regulation is determined by the voltage and frequency issued by the motor control circuit.

4. Motor protection control

Motor protection control can be achieved by using fault detectors. For example, the safe operation of the motor can be protected by the motor control circuit using an overload protector and a short circuit protector. In this case, the fault detector will detect the operation status of the motor, and once abnormalities are detected, alarms or protective measures will be triggered.

In summary, the working principle of motor control circuit mainly involves motor start and stop, forward and reverse rotation, speed regulation and protection, and its control can be achieved by switching, voltage and frequency.

Structural composition of motor control circuit

The motor control circuit is mainly composed of the following parts:

1. power supply part: it is responsible for providing current and voltage, and ensuring the power conditions required for normal operation of the motor.

2. Signal input section: responsible for receiving the operation signals and converting them into signals that can be recognised by the control circuit.

3. control unit: responsible for controlling the motor, including starting, stopping, speed regulation, reversing and other control operations.

4. Protection part: responsible for overload protection and over temperature protection of the motor to ensure the safe operation of the motor.

5. Sensor: It is used to detect the running status of the motor, such as motor speed, current, temperature and other parameters, and feedback these parameters to the control circuit through the control unit.

6. interface part: responsible for conducting the commands output from the controller to the motor to achieve motor control.

Motor control circuit design scheme

Motor control circuit design can use different schemes according to the needs of the application. The following are some of the commonly used schemes:

1. DC motor control circuit design:

(1) Unipolar adjustable DC power supply control: adjustable regulated power supply or one-way chopper voltage regulator circuit can be used to achieve current control of DC motor.

(2) Bipolar adjustable DC power supply control: H-bridge circuit can be used to control two half-bridges respectively to achieve forward and reverse rotation and speed control.

2. AC motor control circuit design:

(1) Frequency converter control: use AC frequency converter to regulate the frequency and voltage of AC motor to achieve speed and torque control.

(2) Three-phase bridge rectifier circuit control: the AC power supply is converted into DC power supply through three-phase bridge rectifier circuit, and then the torque and speed are controlled by PWM.

(3) Soft start control: avoid high current impact and prolong motor life by controlling AC motor starting current.

In short, the motor control circuit design needs to be selected and adjusted according to the specific application requirements, while the stability, safety and reliability of the control circuit needs to be considered.