Electric AC motors operate at a fixed speed and are ideal for applications where a constant output is necessary. However, many motor applications have a level of varying speed demand. In the past, applications that needed precise speed control used expensive direct current (DC) motors or hydraulic couplings in machine speed regulation.
Other applications have relied on opening and closing dampers and valves or changing the output speeds with pulleys, gears, or similar devices while the motor runs at a constant speed. Fortunately, variable frequency drives (VFDs) emerged to offer an alternative method of control.
What is a VFD?
A variable frequency drive, also an inverter, AC drive, or Microdrive, is a type of motor controller that adjusts the electrical supply to an AC motor to vary the voltage and frequency of its power supply.
Although it controls the voltage and frequency of power, the outcome is an adjustment in the motor's speed, thus referred to as speed control. It is beneficial to all motors in that it improves the process and also contributes to saving energy. Besides, VFDs also help control the ramp-down or ramp-up during start or stop.
Why use VFDs?
1. Reduce Energy Costs
You can use the Variable Frequency Drives (VFDs) if you have an application that does not need to operate at full speed. That way, you control the motor and cut down energy costs. Considering that electric motor systems consume a lot of power in industries, optimizing the control system with VFDs helps reduce energy consumption. Besides, variable frequency drives reduce production costs and improve product quality.
2. Increase Production
You can use VFDs to increase production in your processes. Motors operating at the most efficient speed lead to fewer mistakes and generate more revenue for the company through increased production levels.
3. Extend Equipment Life
VFDs offer protection to the motor from issues such as overvoltage, under-voltage, electro thermal overloads, and phase protection. Therefore, your equipment can last longer without requiring maintenance.
How does a VFD Work?
The soft-start or stop and adjustable speed capabilities are the two main features of VFDs and make it a powerful controller to the AC motors. Electrically, you install a VFD in series between the main power supply and the motor.
Below is the working principle of VFDs.
The process begins in the rectifier, which converts AC power supplied from main to DC power. The section can be bidirectional or unidirectional depending on the application used, such as the four-quadrant motor operation. It uses transistors, SCR's, diodes, and other electronic switching devices. The converted DC power is uncontrolled if it uses diodes and varied by gate control if it uses SCR.
A rectifier unit is deemed as a six pulse converter since the three-phase conversion requires at least six diodes. The diodes function like check valves in plumbing systems and allow the current to flow in a single direction.
DC power flows to the DC link from the rectifier. This section has inductors and capacitors to store the DC power and smooth against ripples. The DC link function is to deliver, store and receive DC power.
The inverter consists of electronic switches such as thyristors, IGBT, transistors, etc. DC power flows from the DC link to the inverter and converts into AC before flowing to the motor. It uses modulation techniques such as pulse width modulation to change output frequency for the induction motor's speed control.
The control circuit has a microprocessor unit and performs different functions such as control, configuration, drive settings, and fault conditions. It gets a feedback signal as a current speed reference from the motor and regulates the voltage: frequency ratio to control motor speed.
Leverage the Benefits of VFDs!
Cutting down energy costs makes perfect business sense. It saves money, improves corporate reputation, and helps in fighting against climate change. Installing variable frequency drives in the right applications can help cut costs, save energy and increase profit margins.
At Mader Electric, we have experts ready to assist you with all your commercial and residential motor servicing needs.Contact us to talk with one of our team members.