Principle and application of frequency converter

Firstly, principle of inverter

What is a Variable Frequency Drive

Variable Frequency Drive (VFD for short) is a power conditioning device used for motor drive to control the speed of motor by changing the frequency of power supply. The basic principle is to convert the input signal of AC power supply to DC power, and then convert the DC power to adjustable frequency AC power through inverter to control the speed of motor.

Composition of inverter

Inverter is mainly composed of rectifier part, filter part, inverter part and control part.

(1) Rectifier section: The input AC power is converted into DC power by rectifier circuit.

(2) Filtering section: A filtering circuit is connected behind the rectifier circuit to reduce the output DC pulsation through filtering.

(3) Inverter section: converts the DC power to adjustable frequency AC power through the inverter circuit.

(4) Control part: control the frequency and voltage of the output of the inverter circuit through the control algorithm, so as to realize the precise control of the motor speed.

Working principle of inverter

The working principle of inverter can be divided into the following steps:

(1) Power input: AC power is fed into the inverter.

(2) Rectification: The AC power is converted into DC power by rectification circuit.

(3) Filtering and smoothing: The DC power is filtered and smoothed by the filtering circuit.

(4) Inverter Forming: Converts DC power to adjustable frequency AC power through inverter circuit.

(5) Control output: control the output frequency and voltage of the inverter circuit through the control section.

(6) Motor drive: supply the AC power from the control output to the motor to realize the precise adjustment of the motor speed.

Second, the application of frequency converter

Industrial field

Frequency converter has a wide range of applications in the industrial field, mainly used for motor speed control. Its application scope covers a variety of industrial equipment and machinery, such as fans, pumps, compressors, conveying equipment and so on. By adjusting the frequency and voltage output from the frequency converter, continuous stepless adjustment of the motor speed can be realized to improve the performance and efficiency of the equipment and achieve energy saving.

Air conditioning and refrigeration field

Frequency converter is also widely used in the field of air conditioning and refrigeration. By controlling the speed of the air conditioning compressor, it can regulate the cooling capacity and heating capacity of the air conditioner, realize more accurate temperature control and save energy. In addition, inverters can also be used in cold storage, cold chain and other fields to realize the precise control of refrigeration equipment, to ensure that the stored goods to maintain the required constant temperature.

Water treatment field

In the water treatment industry, the application of frequency converter is mainly focused on water pump control. By adjusting the rotational speed of the pump, the water flow and water supply pressure can be controlled, realizing the precise control of the water treatment process. This is of great significance in the fields of sewage treatment, water supply and drainage, agricultural irrigation, etc., and can effectively improve the utilization efficiency of water resources.

Elevator and lifting equipment

Frequency converters are commonly used in elevators and lifting equipment. By controlling the rotational speed of the drive motors of elevators and lifting equipment, precise operation control and smooth starting and stopping processes can be achieved, improving the comfort and safety of riding.

Other Application Areas

In addition to the above major areas, inverter can also be used in textile, paper, machine tools, food processing, petrochemical and other industries to achieve speed control of the motor in the production process. At the same time, with the progress of science and technology and the continuous innovation of inverter technology, its application areas are still expanding and expanding.

Third, the method of frequency converter speed control

Manually set the frequency

Frequency converter is usually equipped with a panel display and operating keys to adjust the motor speed by manually setting the frequency. The specific operation method is to select the corresponding frequency parameter through the panel display, and increase or decrease the frequency value by adjusting the operation key, so as to realize the regulation of motor speed.

Closed-loop feedback control

Closed-loop feedback control refers to the inverter measuring the actual motor speed and sending the feedback signal back to the control system to realize the automatic adjustment of motor speed by adjusting the output frequency and voltage. Generally, the inverter obtains the motor speed signal by installing a device such as an encoder or a speed sensor, and then compares it with the set speed and adjusts the output frequency and voltage by means of a control algorithm, so as to make the actual speed of the motor consistent with the set speed.

Using control signals

In addition to manual frequency setting and closed-loop feedback control, speed adjustment of the inverter can also be realized through external control signals. For example, signals can be sent to the inverter through control devices such as PLC (Programmable Logic Controller) or DCS (Decentralized Control System) to control its output frequency and voltage, thus realizing remote control and regulation of motor speed.

As a kind of power regulation equipment, frequency converter plays an important role in industrial production and life. By changing the power supply frequency, it can precisely control the speed of the motor, improve the performance and efficiency of the equipment, and realize the goal of energy saving and emission reduction. Its main application areas include industry, air conditioning and refrigeration, water treatment, elevator and lifting equipment, etc. Meanwhile, with the continuous progress of science and technology, the application range of frequency converter is still expanding and enlarging. As for adjusting the rotational speed of the frequency converter, it can be realized by various methods such as manual frequency setting, closed-loop feedback control and using control signals.