What Are the Working Principles of a Variable Frequency Drive (VFD)?

Saving money and developing a solid company reputation can be achieved by reducing energy costs. When installed in the appropriate application, Variable Frequency Drives (VFD) help save energy, which cuts costs and increases revenue.

For an electric AC motor, there are fixed speeds. This type of motor works best for applications in which there is the need for a constant output speed. However, roughly 50% of all motor applications have demand for a varying speed, which includes processes for precision tools, winding reels, and moving liquids and air.

Specific to applications that need more precise speed control, it was common for hydraulic couplings and Direct Current (DC) motors to initially be used. However, for other applications, speed control was provided by dampers that open and close, valves, pulleys, gears, and various other similar devices. As an alternative, Variable Frequency Drives first appeared during the 1980s and 1990s. By principle, the electrical supply going to an AC motor is adjusted using a corresponding voltage and frequency. As a result, the output of motor torque and speed changes.

When a Variable Frequency Drive (VFD) is implemented, motor speed and process requirements of the machine are closely matched. Today, VFD technology is extremely advanced. As such, it has been widely adopted and used with AC motors. These drives are also versatile, and they provide a high degree of control. With a VFD, the motor speed is more accurately varied, going from 0 RPM to more than 100% of the rated speed.

Based on the exact application, there are different options for a Variable Frequency Drive. For instance, the basic design is commonly used for simple applications, including pump and fan control. In comparison, complex versions of the Variable Frequency Drive are required to achieve precise control over torque and speed. Some of the common applications for the more complex VFD include materials forming and multiple winders.

There are also different sizes of a Variable Frequency Drive. These start out at 0.2 kilowatts and go up to several megawatts. Typically, a VFD is used as a standalone device. In this case, the drive connects to the electrical supply of the motor. Now, for smaller designs, usually those that are 15 kilowatts or less, they are actually built onto the motor. Therefore, they become an integrated product of the motor drive.

To achieve a significant reduction in the cost of energy, variable speed control works extremely well in many applications. Especially in pump and fan applications, Variable Frequency Drives are highly effective. For these applications, the drive replaces the output regulation of a more traditional method, which leads to a better relationship between machine output and the amount of energy used.

Regardless of the variation in design, the functionality of Variable Frequency Drives is much the same. This drive works by converting incoming electrical supply or fixed voltage and frequency into a variable voltage and frequency, which is the motor’s output with a corresponding change in torque and speed. Considering the low cost for a Variable Frequency Drive and the tremendous benefits, the choice is obvious.

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