What is a Variable Frequency Drive (VFD)?
Variable Frequency Drives (VFDs) are an integral part of modern motor control, providing more precise control, more flexibility, and better performance in a wide range of applications. We’ll start with the basic principles and then explore the components that make up a variable frequency drive and how they contribute to improved motor control and reduced energy use.
Variable Frequency Drives (VFDs) Explained
A VFD (also known as an adjustable frequency drive or inverter) is an electronic device designed to control the speed and torque of an AC motor by altering the frequency and voltage supplied to the motor. Not surprisingly, but very significantly, this dynamic control provides energy savings, improved process control, and a more efficient use of the motor.
Variable Frequency Drive Components
The basic components of a VFD are:
Rectifier: This circuit converter incoming AC power into DC; it’s the DC that the inverter wants to see.
Inverter: The inverter is a key part of any VFD. It takes the DC voltage from the rectifier and inverts it back to AC voltage, but it’s AC with a constantly adjustable frequency and voltage. This adjustable output creates the dynamic control that, in turn, controls the speed of an AC induction motor.
Controller: The controller takes signals from the operator to adjust the frequency, voltage, and current to the motor. Once this adjustment is made, feedback signals from the motor tell the controller how it’s doing.
Human-Machine Interface (HMI): The HMI provides a keypad and/or display for the owner/operator to set parameters, monitor performance, and diagnose problems.
Variable Frequency Drive Operations
The operating principle of VFDs is fairly straightforward. They do a lot of things but typically less is more. VFDs control motor speed by varying the frequency of the power supplied to the motor. While this sounds simple, it’s a CPU that allows the VFD to do everything else. Higher frequencies result in higher speeds; lower frequencies mean lower speeds. More significant to energy savings, however, is that allowing the VFD to control the speed of the motor is that there’s no longer any need for mechanical controls such as throttling valves or dampers used to open and close to adjust flow and temperature.
Making the application of a VFD even more attractive is their controlling the speed when they start. The “soft” application of voltage to the motor means there are no hard start-up and sudden start-up torque shocks. These advantages are found under normal and overload conditions (stalling). And they are also attractions to motor manufacturers because they mean longer lives for their machinery.
Dynamic Braking: Some VFDs are able to perform a dynamic braking function where the motor will be brought to a controlled stop or deceleration without the use of any external braking. Applications of Variable Frequency Drives Industrial Processes: In industries such as manufacturing, VFDs are used to provide a precise control of conveyor belts, pumps and fans. manipulation in speed of this equipment will result in an increase in required production. HVAC Systems: VFDs are used to vary the speed of the motors which drive compressors, fans and pumps providing an energy efficient solution for heating, cooling and air handlers. Water Treatment: VFDs play an instrumental part in the water treatment processes to regulate the speed of pumps and blowers to meet the needs to supply water. Renewable Energy: VFDs are an essential component in renewable energy systems such as controlling the speed of motors in wind turbines and solar tracking systems.
Advantages of Variable Frequency Drives Energy Savings: The ability to only run a motor at the speed required for actual load results in significant energy savings. Reduced Mechanical Stress: Soft start and stop features reduce the wear and tear put on mechanical components reducing the need for future repairs and extend equipment life. Improved Process Control: Having precise control over the speed of a motor will increase the efficiency, accuracy and repeatability of an industrial process. Cost-Effective: Higher initial investment; but, with energy savings, cost-effective.
Conclusion In conclusion it is without question, Variable Frequency Drives are the way of the future for motor control. They offer unprecedented efficiency, control and flexibility. Whether it be industrial applications, HVAC systems or for renewable energy, VFDs will continue to perform a crucial role in optimizing performance to help create a more sustainable and cost-effective future.
