What Are Variable Frequency Drives (VFDs)?

When Nikola Tesla patented the original three-phase alternating current (AC) motor in 1888, the invention was a major breakthrough in electrical engineering. The only problem was that this early electric motor could only operate at one speed. After a century of research and experimentation, scientists finally developed a viable solution — variable frequency drives (VFDs). 

Today, the VFD market is growing steadily thanks to the drive’s high versatility and increasing usefulness in various industrial and commercial sectors. Understanding what a VFD is and how it can benefit your operations can help you enhance business processes and cut costs.

What Is a Variable Frequency Drive?

First invented in the 1980s, a VFD is a type of electric motor controller that enables users to adjust motor speed by varying the supplied frequency and voltage. 

Based on your specific application, the type of VFD you need might change. The most common drive types include:

• Pulse-width modulation (PWM): This type of VFD repeatedly switches the drive’s inverters on and off to generate the required root-mean-square (RMS) voltage levels for your application. The drive may use either standard transistors or insulated-gate bipolar transistors (IGBTs), depending on the unit.
• Voltage-source inverter (VSI): Another common type is the VSI, which essentially operates in reverse of the standard VFD. This type takes in direct current (DC) electricity and converts it to the proper AC for precise control over electric motor speed.
• Current-source inverter (CSI): This VFD type uses field-effect transistors (FETs), which have a higher switching speed than drives using IGBTs. As a result, CSIs can handle high-speed applications better than other drives.

How Do VFDs Work?

While each different type of VFD operates slightly differently, they all follow the same basic workflow:

1. Rectifier: Also known as the AC-DC converter, this component consists of six diodes that convert incoming AC to direct current (DC).
2. DC bus: The newly converted DC often has an AC ripple that can impact throughput, so it passes through a series of capacitors and filter inductors as it moves along the DC bus. These capacitors eliminate the AC ripple to ensure stable output and high performance.
3. Inverter: Finally, the inverter converts the DC back to variable frequency AC, which provides power to the electric motor. It accomplishes this conversion through a connected series of IGBT switches that control the electrical flow until it reaches the motor.

The Benefits of VFDs 

Installing a VFD in your industrial applications can enhance operations in various ways, such as:

• Safer working environments: Adjusting the frequency that’s traveling to an electric motor can lower noise levels in loud machine parts like fans and pumps, which reduces the risk of noise-related injuries and simplifies compliance with Section 5 of the Occupational Safety and Health Act (OSHA) of 1970.
• Extended machine life spans: A VFD enables you to optimize your drive’s torque, power and speed according to your application’s process requirements, which reduces mechanical stress on startup and slows wear on an electric motor’s internal parts.
• Energy savings: Optimized power output helps you reduce overall energy consumption, boosting your energy efficiency and lowering peak energy consumption during times of high grid demand. These savings are especially dramatic compared to direct-on-line (DOL) operation, which runs the electric motor at full speed regardless of operational requirements.
• Tighter process controls: Operating electric motors at the most effective speed for your specific application enhances productivity and reduces the risk of errors, boosting revenue generation and minimizing operating costs.
• Low maintenance requirements: While preventive maintenance is essential for keeping electrical equipment in peak condition, VFDs require less intensive maintenance than other electric motor controllers.

That said, it’s always important to mention some of the drawbacks of using VFDs:

• High upfront costs: Although VFDs have been around for decades, they are still a significant investment. However, the cost savings and productivity boosts you can gain from improved energy efficiency can help you generate a strong return on investment (ROI). 
• Installation challenges: It’s critical to ensure your VFD is installed properly, as errors in installation can significantly increase your risk of malfunctions and other issues.
• Temperature control: VFDs require more heat dissipation equipment than other drives, which can impact operating costs in some cases.

Common Industrial and Commercial Use Cases for VFDs

VFDs can efficiently power a wide variety of devices and equipment, such as:

• HVAC systems: Because VFDs reduce mechanical stress and boost energy efficiency, they’re excellent for controlling the speed of internal HVAC components like fans and pumps.
• Conveyor belts: Manufacturing plants often need to adjust conveyor speed according to the production phase, and VFDs can help control conveyor speeds for maximum efficiency.
• Machine tooling: CNC machines can use VFDs for more precise control over spindle speeds and feed rates, which can help improve accuracy and minimize tool wear.
• Pressure booster pumps: The energy and cost savings VFDs provide make them effective alternatives to pressure control valves in large commercial and industrial buildings.
• Hybrid systems: VFDs make energy-efficient power converters for hybrid systems that use battery storage. 
• Mixing and agitating: VFDs enable you to precisely control agitating and mixing machine speeds, which is critical for consistent production in industries like food and beverage.

Basic VFD Maintenance Practices

While VFDs are generally considered low-maintenance equipment, regular preventive maintenance is critical for ensuring high performance and preventing downtime. A thorough visual inspection before each maintenance interval will provide the insight you need to determine the most suitable actions.

Key areas to inspect include:

• The drive’s surface and ambient conditions.
• Drive fan and cooling system function.
• Internal connections.
• Ribbon and fiber optic cables.
• Fault logger.
• Device parameters.
• Prevention of unexpected startup circuits.

Following your inspection, your operators should clean the VFD while following electrostatic discharge protection protocols. Investing in a high-quality electrical safety training program can help you ensure your team keeps themselves and your equipment protected.

Functional testing is also required to ensure the system works as intended. You can conduct a functional assessment by monitoring the VFD’s performance under typical operating conditions. If it seems to be under- or overperforming, you may need to call a professional to make on-site repairs.

Finally, it’s a good idea to always have a spare VFD on hand to minimize unplanned downtime resulting from malfunctions or emergency repairs. 

Call on Industrial Electrical Company for VFD Maintenance Services

VFDs are excellent devices for achieving precise control over any industrial equipment that operates at various speeds. Maintaining and protecting your VFD is essential for ensuring high performance and a long equipment life span.

At Industrial Electrical Company, we offer professional VFD installation and maintenance services to ensure efficient operation and help you extend your electrical equipment’s working life. We also provide 24-hour emergency support, so you can count on us to pick up anytime you need assistance. 

Contact us today to learn more about how our VFD preventive maintenance services can help you keep your drives in optimal condition.