Variable Frequency Drive Panels (VFD)

FAQ Guide

Over the years, some motor drive applications have faced challenges. In recent years, reliable power electronics have made it possible to control the speed of motors using variable frequency drivers.

VFD is now widely used in many applications. The main reason is that they are more functional and operable than conventional motor drivers when starting the motor.

1. What is a VFD panel?

A variable frequency drive control panel is made up of a frequency converter in the cabinet, as well as external controls, protections, displays, and other electrical components. It is a frequency conversion device for controlling three-phase AC motors (including fans). and pumps) to save energy. The VFD panel adopts a closed cabinet structure, and the protection level is generally IP20, IP21, and IP30. Some panels need to be weatherproof and waterproof in the application environment

Up to IP64, IP65, or even IP66. The surface of the panel is sprayed by the supplier, which is easy to install in parallel. The bus is configured on the top of the panel and the VFD keypad is wired to the door of the panel for direct operation. The frequency converter is a dedicated part of the electrical control panel, and the frequency convention and main characteristics of the panel depend on the configuration of the internal VFD and other components.

The frequency converter panel varies according to its different functions and applications and generally needs to be customized according to the specific operating environment, such as a constant flow water supply panel (one panel controls 1, 2, 3 water pumps, etc.), escalator control panel, Central air conditioning circulation pump panel, fan control panel.

2. Why choose the VFD panel?

The two main features of a VFD are adjustable speed and soft start/stop functionality. These two features make the VFD a powerful controller for controlling AC motors.

3. Benefits of VFD

In addition to providing accurate and precise control applications with variable speed, variable frequency drives also offer process control and energy savings.  Some of them are given below.

1) Energy saving

More than 65% of the electricity in the industry is consumed by electric motors. When the motor needs to change speed, the amplitude and frequency control techniques used to change the speed consume less power. Therefore, these VFDs save a lot of energy.

2) Closed-loop control

The VFD can accurately locate the motor speed by continuously comparing a reference speed even as load conditions and input disturbances such as voltage fluctuations change.

3) Limit the starting current

Induction motors draw 6 to 8 times the rated current when starting. VFD provides better results than traditional starters because it provides low frequency at the start. Because of the low frequency, the motor draws less current, and that current never exceeds its nominal rating when starting and running.

4) Smooth operation

Besides providing smooth starting and stopping, it also reduces thermal and mechanical stress on the motor and belt drive.

5) High power factor

Built-in power factor correction circuitry in the VFD DC link reduces the need for additional power factor correction equipment. The power factor of induction motors is very low, especially in no-load applications, and ranges from 0.88 to 0.9 at full load. Due to high reactive losses, low power factor results in poor power utilization.

6) Easy installation

Pre-programmed and factory-wired VFDs provide easy connection and maintenance.

Purge and pressurize panels

Fire and explosion-proof panel

SIL Safety PLC System

Distributed control system

IEC 61439 Type Test Assembly Panel

Typical applications: Water supply, air compressors, air conditioners, port machinery, machine tools, boilers, paper machinery, food machinery, etc.

4. Working principle of VFD

Using a rectifier bridge and capacitor bank to convert the AC voltage to DC, a variable frequency drive filters the DC with an inductor and capacitor bank then inverts the DC voltage back to AC and sends it out on the motor. desired frequency.

• Typically, a microprocessor or digital signal processor (DSP) communicates with the PLC, supervises motor operation, and checks for faults.
• The control circuit coordinates the switching of the power devices, activating the power elements in the correct order. Motor speed varies with the voltage and frequency supplied by the output device.
• A basic VFD maintains motor torque by keeping the voltage-to-frequency ratio constant. Advanced units use smarter and more adaptive algorithms to improve motor performance.

Simply put, a VFD converts one voltage and frequency to another to vary motor speed without loss of torque.

Three subsystems make up the VFD drive system:

• AC motors are most commonly three-phase induction motors, but sometimes single-phase or synchronous motors.
• Main drive controllers using solid-state power electronic conversion systems, including rectifier bridge converter, DC link or filter, and switch or inverter sections.
• Monitor and control interface that allows an operator or PLC to start, stop, adjust speed, and change the direction of a motor. The interface also provides information on motor operation, drive health, and more. Interfacing with PLCs can be accomplished through a variety of serial communication protocols, or through “old-fashioned” relay inputs and outputs combined with 4-20mA or 0-10V analog signals.

Variable frequency drives have gotten smaller over the decades, not least thanks to microprocessors replacing solid-state components. In many applications, the return on investment of the drive is usually higher than the price of the drive.

5. When to use a variable frequency drive

VFDs are used in systems run by AC motors in applications ranging from manufacturing to air conditioning. There are many reasons for choosing a system with a variable frequency drive.

• Precisely control the speed of the manufacturing process.
• Provides smooth starts and discreet acceleration to operating speeds.
• Achieve energy savings, especially in applications where load torque and power vary in a non-linear fashion. Variable torque fans and pumps are great options for saving money.
• Improve the process and quality of your application’s acceleration, flow, monitoring, speed, temperature, tension, torque, and pressure.
• Run the motor in a dedicated mode to minimize mechanical and electrical stress.

VFDs significantly reduce or eliminate the current surge required to start a motor “through the line”. In addition to a current surge of up to eight times the motor’s full load current, this start-up can damage mechanical components in the driven load.

6. Does your industrial facility need a VFD control panel

To answer this question, first consider how a VFD control panel works. The speed of the motor is controlled in two ways – voltage or frequency. Speed ​​control via frequency is the preferred option as it produces a constant flux density. This is where VFDs come into play. A VFD is like a power conversion device that converts input power of fixed frequency and voltage to output power of variable frequency and voltage.

What is the result of this effect? Therefore, using a VFD control panel provides adjustable speed for accurate control of the process. In addition, using a VFD control panel saves energy. Think about that too. Industrial facilities can draw excessive power if their equipment or devices are running at full speed all the time, even if they don’t have to be. This will consume a lot of power. So, in this case, using a VFD control panel is a good choice.

How can using this control panel help? Well, VFD control panels only draw power when needed. In other words, if the motor’s request changes, the control panel will vary the motor’s speed according to the request. This leads to massive conservation of energy. In addition, when the speed of the motor is adjusted as needed, its durability and lifespan are also significantly increased.

VFD control panels are AC drives. Therefore, these control panels are less expensive to maintain as there are no DC motors or transmissions involved. However, there is one caveat. what is it? These control panels emit a considerable amount of heat. Therefore, the location of the VFD control panel must have proper airflow. This prevents overheating of the components in this control panel. These control panels also ensure smooth operation.

This reduces thermal and mechanical stress on the motor and belt drive. So, does your industrial facility need a VFD control panel? Absolutely! We at Spike Electric would love to help you get one.

7. Conclusion

VFD stands for Variable Frequency Drive. These panels are primarily used to control the speed of electric motors and feed pumps used in various industrial facilities. To effectively monitor and control each motor, a separate control panel is required because they have different frequencies and voltages. VFD control panels centralize or combine motor control equipment and circuit protection equipment in one enclosure.

The control panel also protects these devices from moisture, corrosion, dust, and other damaging elements. VFD control panels are rated differently than NEMA. NEMA ratings include NEMA 1, NEMA 3R, NEMA 4, and NEMA 4X. What components make up a VFD control panel?

There are many components in a VFD control panel, such as VFDs, line reactors, circuit breakers, harmonic filters, cooling units, and some motor starters and bypasses. Why do VFDs need cooling? These control panels tend to generate a lot of heat; therefore, they also require integrated cooling. A VFD control panel contains many more components than those listed above.

Drilling, pumping, and applications involving large and heavy machinery, such as conveyors and compressors, commonly use these control panels. VFD control panels are also available in various power ratings.