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What is a Variable Frequency Drive

Variable frequency drive (VFD) is an adjustable speed drive used for motor drive system, control the speed and torque of the AC motor by changing the electromechanical input frequency and voltage. Also termed variable speed drive, AC drive or frequency inverter. The VFD is a device that converts an industrial frequency power supply (50 Hz or 60 Hz) into an AC power source with various frequencies to realize varying speed operation of the motor.

VFD control circuit completes the control of the main circuit, the rectifier circuit converts the alternating current into direct current, and the direct current intermediate circuit smoothes the output of the rectifier circuit, and the inverter circuit reverses the direct current into alternating current. The VFD achieves the purpose of speed regulation by changing the power supply frequency of the stator winding of the motor.

Reasons for Using VFD

Adopt VFD to meet the requirements of improving productivity, improving product quality, improving equipment automation, and improving living environment. The second is to save energy and reduce production costs.

1.Soft Start Function
The starting current of a common cage motor is usually 5 to 7 times the rated current, which has a great impact to the power grid. With VFD variable pressure starting, the starting current is only about twice the rated current, and the starting torque is not lower than the rated torque, which can start smoothly and efficiently.

2.Stepless Speed Regulation and High Precision Speed Regulation
For example, in the production process of plastic machinery, due to the difference in plastic characteristics, various product specifications and different production process requirements, many cases require speed control of the production machinery. VFD's high reliability, high precision and smooth stepless speed regulation characteristics make plastic machinery automation level improve.

3. Intelligent control
VFD has many intelligent control functions: the analog and digital control interfaces are directly connected to computers, Internet devices, PLC program controllers, and touch screens, making it easy to control whether it is on-site touch operation or remote visual control.

4. Energy saving
After adopting VFD speed regulation, the energy saving effect of the fan and pump load is the most obvious, and the power saving rate can reach 20% to 60%. This is because the power consumption of the fan pump is proportional to the cube of the speed. When the average flow required by the user is small, the speed of the fan and the pump is low, and the energy saving effect is also considerable. When the traditional baffle and valve are used for flow regulation, the power does not change much. Since this type of load is about 20% to 30% of the total capacity of the AC motor, the energy saving of the VFD is very important.

5. Power factor compensation
Reactive power not only increases the line loss and heat of the equipment, but more importantly, the power factor is reduced, resulting in a decrease in the active power of the grid. A large amount of reactive power is consumed in the line, and the equipment is inefficient. After using the variable frequency drive, due to the internal filter capacitor of the VFD, the reactive power loss is reduced, and the active power of the power grid is increased.

Variable Frequency Drive Application

VFDs have been widely used in the production of light and heavy industries as well as people's daily lives. In steel, non-ferrous metals, petroleum, petrochemical, chemical, chemical fiber, textile, machinery, electronics, construction, coal, pharmaceutical, paper, injection, elevator, driving, urban water supply, central air conditioning, household appliances, etc. are commonly used.


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