Let's join Intech Group to learn more about the operating principles, structure and outstanding benefits of frequency converters in modern systems.

1.What is VFD?

VFD stands for Variable Frequency Drive or also known as frequency converter. This is an electronic device specialized in controlling the speed and torque of AC electric motors by changing the frequency and input voltage supplied to the motor. Thanks to this ability to change frequency, the motor can operate flexibly at many different speeds, suitable for each specific application in industry and civil use.

Other names for variable frequency drives (VFDs)

• VFDs are also known by many different names, including:
• Adjustable Speed ​​Drive
• Adjustable Frequency Drive
• AC Drive
• Inverter Drive
• Drive

No matter what name it is called, a VFD is a dedicated controller for electric motors, allowing users to easily change the rotation speed and control the torque to optimize operating performance.

2. Structure of VFD (Variable Frequency Drive)

VFD is an electronic device used to control the speed and torque of an AC motor by changing the frequency and supply voltage. Two outstanding features of VFD are the ability to flexibly adjust the speed and soft start/stop, which helps increase the motor's life and save energy effectively.

VFD consists of 4 main parts:

The rectifier has the function of converting alternating current (AC) from the grid power source into direct current (DC). Depending on the application requirements, the rectifier can be of the following types:

• Unidirectional: only allows current to flow in one direction.
• Bidirectional: allows current feedback in 4-quadrant motor control applications.

The components used in the rectifier include diodes, SCR (switchable thyristors), transistors and other electronic switching devices. In a three-phase power system, at least 6 diodes are usually needed to perform the conversion, called a six-pulse converter.

DC Link Circuit (DC Bus)

The DC Bus section is responsible for receiving DC power from the rectifier and smoothing the current, helping to stabilize the voltage before entering the inverter stage. This part includes: Capacitors and Inductors

Inverter

The inverter is a component that converts DC current back into AC current with adjustable frequency and voltage. Thanks to that, the rotational speed and torque of the motor can be flexibly controlled.

Commonly used electronic switching devices in the inverter include: IGBT (Insulated Gate Bipolar Transistor), transistors, thyristors, etc. The inverter uses PWM (Pulse Width Modulation) technology to generate an output AC signal that meets the motor's requirements.

Control Circuit

This is the center that processes and controls the entire operation of the inverter. The control circuit usually integrates:

Microprocessor to configure parameters, control speed and torque.

Functions to monitor operating status, warn of errors and protect the system.

Communication with other devices via protocols such as Modbus, Profibus, Ethernet...

The control circuit also receives feedback signals from the motor (such as speed, current...) to adjust the voltage/frequency ratio (V/Hz), helping to operate the motor accurately and stably.

3. Operating principle of VFD

VFD controls the speed of AC motor by changing the frequency and voltage of the power supply. The operation process consists of 4 main stages:

Rectifier

Converts the input AC power source into DC voltage. The rectifier uses diodes or SCRs to generate DC current, which is the first step in the processing chain.

DC Bus

The rectified DC power is filtered through capacitors and inductors to stabilize the voltage, reduce noise and store energy before moving to the inverter stage.

Inverter

Converts a stable DC power source into an AC power source that can change frequency and voltage. Uses components such as IGBTs combined with PWM technology to control the motor speed.

Control circuit

Controls the entire operation of the inverter, monitors operating parameters, sets configuration and handles alarms, and communicates with external control systems.

4. Advantages of using frequency converters

Energy saving and operating costs

In industry, the motor system accounts for more than 65% of total electricity consumption and integrating VFD can save up to 70% of energy. In addition, higher operating efficiency helps improve product quality and reduce production costs.

Soft and flexible control

VFDs allow motors to start, stop and change speed smoothly. This helps avoid jerks and shocks when starting, which is especially effective for conveyor systems, pump conveyors or fans, increasing stability and productivity.

Protect equipment, prolong service life

VFDs protect motors from problems such as overload, overvoltage, phase loss, etc., helping to start smoothly and reduce mechanical wear on belts, gears, bearings, etc. As a result, the equipment operates more durably and reduces maintenance and repair costs.

5. Disadvantages of inverters

High initial investment cost

Compared to traditional control methods (DOL, star-delta...), inverters are more expensive. However, the long-term benefits of saving electricity and reducing maintenance costs help pay for themselves quickly.

Complex configuration and operation

Installation, configuration or programming of inverters may require in-depth technical knowledge, requiring support from an electrical engineer or experienced specialist.

Harmonics and electrical noise

Inverters can generate harmonics that affect other electronic equipment in the system. Therefore, it is necessary to add harmonic filters or suitable anti-interference solutions.

Heat dissipation during operation

Inverters generate heat during operation. It is necessary to ensure an effective ventilation and heat dissipation system to ensure longevity and performance.

Derating the motor (De-rating)

In some cases, the motor needs to be derated when used with a frequency converter. Choosing the wrong power can affect the efficiency and durability of the system.

Electromagnetic interference (EMI)

The frequency converter can generate EMI, affecting nearby control devices. Proper shielding and grounding are necessary to limit this risk.

Electronic maintenance

Although less wear-resistant, the electronic components in the frequency converter still need to be periodically checked and maintained to ensure stable operation.

6. Classification of frequency converters (VFD)

Variable Frequency Drives (VFDs) are classified according to many different criteria, depending on the application and specific needs of the business. Below are the most common classification criteria today:

Size

The VFD (Variable Frequency Drive) market segment is divided into five size groups, based on rated power (in kW or HP). Specifically: Micro, Small, Medium, Large, Extra-large

In market analysis reports, micro to medium inverter lines are often used in light industry and commercial applications. High-power inverters focus on medium to very large products, serving heavy industries such as metallurgy, oil and gas, wastewater treatment, cement production, etc.

VFD Control Modes

VFD (Variable Frequency Drive) inverters can operate in different control modes, which optimize motor performance and meet the needs of precise speed control in industrial applications. One of the common control modes is Volts / Hertz (V / Hz), which is a traditional control method that maintains a constant voltage-frequency ratio. However, this mode has some limitations:

At low speeds, low voltage will result in low magnetizing current, causing torque loss.

V / Hz control cannot accurately adjust the change in slip between the rotor and stator when there is a change in frequency and load.

Input Voltage of VFD

Input voltage is an important factor in classifying VFDs. Power supply varies significantly with voltage, so classifying VFDs based on voltage range is necessary. Common voltage ranges of VFDs include:

• 115V to 240V
• 380V to 400V
• 460V to 480V
• 560V to 690V

DC Bus Configuration in VFDs

In applications that require multiple VFDs to operate simultaneously (such as conveyor belts or synthetic fiber production), using a single large DC power source (DC Bus) will reduce costs and improve brake energy regeneration. This configuration helps optimize energy efficiency and reduces the need for multiple independent VFDs.

VFD Hardware, Software, and Services

The VFD market includes not only hardware devices, but also software and support services that help meet users' engineering and project management requirements:

VFD Hardware: Standalone VFD devices have pre-programmed features, or can be reprogrammed to suit the specific needs of each application.

Peripheral Hardware: These products include control system components, enclosures, cabling, harmonic filters, and other accessories that are less valuable than the main drive.

Support Services: VFD users are increasingly looking for suppliers that offer additional support services such as training, installation, warranty, maintenance, and custom software development.

7. Benefits of Variable Frequency Drives (VFDs) in Industry

VFDs (Variable Frequency Drives) are important devices in many industrial applications thanks to their ability to optimize motor performance and bring many practical benefits. Below are the outstanding benefits that VFDs bring:

Energy Savings

VFDs are an effective solution to save energy. Instead of operating the motor at maximum speed continuously, VFDs precisely adjust the motor speed to suit the needs of use, helping to minimize power consumption.

Flexible Start and Stop

Unlike the fixed speed motor operation method, VFDs provide the ability to start and stop the motor smoothly, without causing sudden vibrations. Thanks to that, the life of the equipment is extended, and maintenance costs are also significantly reduced.

Precise Speed ​​Control

Variable speed drives provide very precise control of motor speed, which is especially important in applications that require consistent and precise speed. For example, in conveyor lines, the drive provides precise control of the conveyor speed, ensuring optimal product transfer without damage or errors.

Better Process Control

The ability of the Variable speed drive to precisely control motor speed improves manufacturing processes. In industries such as chemical processing, the drive can adjust pump speed to ensure a steady flow of liquid, helping to maintain consistent product quality.

Minimize Torque Fluctuations

Variable speed drives help minimize torque fluctuations that motors experience during operation. This results in smoother torque transmission, which improves machine performance and reduces stress on mechanical components, thereby extending the life of the equipment.

8. Applications of Variable Frequency Drives (VFDs) in industries

VFDs (Variable Frequency Drives) are devices that control the speed and torque of AC motors, helping to optimize system performance and save energy. Below are common applications of VFDs:

Material handling: VFDs are commonly used in conveyor systems to control the speed of material movement, helping to reduce energy consumption and improve operational efficiency.

Manufacturing: In machine tools, VFDs ensure precise speed control in processes such as cutting, drilling and machining, thereby improving product quality and labor productivity.

HVAC (heating, ventilation, air conditioning) systems: VFDs in HVAC systems help control temperature more effectively and reduce energy use.

Chemicals and petroleum: VFDs are used to control pumps, ensuring precise fluid flow in manufacturing processes.

Water and wastewater treatment: VFDs in water and wastewater treatment systems help optimize energy use based on actual needs, helping to reduce operating costs.

Building Automation: VFDs are used to control fans and pumps in buildings, improving occupant comfort and saving energy.

Renewable Energy: In renewable energy systems, VFDs are used in wind turbines to control the speed of generators, optimizing power generation based on wind conditions.

9. Common VFD Faults and Troubleshooting Tips

VFDs are important devices in many industrial applications, helping to control the speed and torque of AC motors. However, during operation, VFDs can encounter some problems.

Ground Fault

Fault: Grounding problem of the inverter or motor.

Cause: Loose grounding, broken ground wire, or grounding fault inside the motor.

Solution: Carefully check all ground points and ensure the ground wire is not damaged. Ensure the motor is properly grounded with the help of a qualified electrician.

Drive Overcurrent Fault

Fault: The motor is drawing more current than the drive is rated for.

Cause: Mechanical overload on the motor (e.g., a stuck bearing, a clogged conveyor belt), the drive setting is not correct for the motor specifications, or the motor winding is faulty.

Solution: Check the mechanical parts for any problems such as a stuck bearing or a clogged conveyor belt. Ensure the drive settings match the data on the motor nameplate (voltage, current, power).

Undervoltage Fault

Fault: The AC input voltage of the inverter is lower than the minimum required for operation.

Cause: Fluctuation in the power supply voltage or loose connection in the power supply wiring system.

Remedy: Check the power supply voltage and ensure it meets the technical requirements of the inverter. Tighten all connections in the power supply wiring system.

Overvoltage Fault

Fault: The AC input voltage of the inverter is higher than the maximum allowable voltage.

Cause: The power supply voltage suddenly increases or the voltage regulator in the inverter is faulty.

Remedy: Check the power supply voltage to ensure it does not exceed the allowable level. If a sudden voltage increase occurs, consult an electrician to determine the cause.

Communication Error

Fault: Communication problem between the inverter and other control systems (e.g., PLC, encoder).

Cause: Incorrect communication settings (baud rate, protocol), loose or damaged communication cable.

Solution: Recheck the communication settings in both the inverter and the control system to ensure they are compatible. Check the communication cable for problems such as damage or loose connections.

10. Popular VFD inverter manufacturers

VFD (Variable Frequency Drive) inverter is an important device in industries, helping to control the speed and torque of electric motors. In the Vietnamese market, there are many reputable and quality VFD inverter manufacturers from different countries. Here are some popular VFD inverter manufacturers:

Germany: Siemens, Rexroth, Lenze

Denmark: Danfoss

Japan: Mitsubishi, Yaskawa, Fuji, Omron, Panasonic, Hitachi, Toshiba, Nidec

Switzerland: ABB

France: Schneider

USA: Allen Bradley (Rockwell), Emerson, Parker, Sew-Eurodrive

Israel: Unitronics

Korea: LS

Taiwan: Delta, Shihlin

China: INVT, Kinco, Sinovo, Goodwe, Growatt, Sungrow, Inovance, Veichi, Gtake, Frecon, V&T, Powtran, Sinee, Delixi, Senlan, Enc, Zoncn, Sunfar, Sumo...

Frequently asked questions about VFD

1. What is VFD?
2. How are VFDs classified?
3. What are the popular VFD manufacturers?

For any questions about VFDs, please contact Intech Group via hotline 0966.966.103 / 0966 966 032 for quick and timely advice and support.