A motor controller known as a variable frequency drive (VFD) controls an electric motor by adjusting the power generator’s voltage and frequency. The VFD may accordingly regulate the motor’s slope and ramp-down during start and stop.
We frequently refer to the process as speed regulation even though the drive regulates the voltage and frequency of the power generated by the PV system since the end consequence is a change in motor speed.
We could want to change the motor speed for a variety of reasons.
- Reduce energy use and enhance system performance
- Change power in hybridized applications
- Align the drive’s speed with process demands
- Align a drive’s torque or power with the demands of the process.
- Increase the quality of the workplace
- Reduced noise levels, such as those made by fans and pumps
- Lessen mechanical strain on machinery to increase its lifespan
- Reduce peak usage to avoid price spikes and the necessary motor size.
Modern drives also have networking and diagnostic features to improve performance control and boost productivity. Therefore, using a VFD as the regulator in any motor-driven system is brilliant for three reasons: energy savings, intelligent motor control, and decreased peak current drawn.
Controlling fans, pumps, and compressors is the most frequent use for a VFD, making up over 75% of any drives in use worldwide.
Other, less advanced varieties of motor controllers include soft starters or across contactors. When starting an electric motor, a sensitive starter, a solid-state device, gradually ramps up the speed.
An electric motor can get the entire line voltage through a motor controller called almost across the contactor.
What benefit does using a VFD mostly offer?
To conserve energy or optimize energy use, an adjustable speed drive can use VFD control to change the power supplied to fit the energy requirements of the driven equipment.
The drive can significantly lower energy usage compared to direct-on-line (DOL) performance, in which the motor runs at incredible speeds regardless of the requirement.
Power or fuel efficiency of 40% is typical when using a drive. Because of the roll-on effect, installing drives also decreases the CO2 footprint & NOx emissions of the installations in which they are installed.
What’s the process of a variable frequency drive?
Knowing the rectification, DC bus, and inverter—the device’s three fundamental components—is necessary to comprehend the basic concepts underlying variable frequency drive functioning.
A sine wave-like pattern can be seen in the rise and decrease of the energy on an alternating (AC) power source. Current moves in one direction when the voltage is positive and reverses when the voltage is negative. Massive amounts of energy can be efficiently delivered across long distances using this kind of power system.
Incoming ac power is transformed into direct current (DC) power by the rectifier in a VFD. Only after the voltage is positive will one rectifier permit the passage of energy. Only when the voltage is negative will a second rectifier help power to pass through. Each cycle of power requires two rectifiers.
Use of rectifier
There will be a minimum of 6 rectifiers because the most significant power sources are three-phase. A motor with six rectifiers is called “6 pulses”. A VFD can be “12 pulses,” “18 pulses,” or “24 pulses,” depending on how many rectifier sections it has and how many rectifiers there are in each area.
After passing through the rectifiers, the energy will be stored on such a dc bus (or dc link). Capacitors are present on the dc bus to receive power from the rectification, store it, and then transmit it using the inverters section. Inductors, dc connections, chokes, and other similar components that contribute inductance to the dc bus may also be present. This smoothes the incoming power source to the dc bus.
An “inverter” is the name given to the VFD’s last component. Transistors found in the inverter provide the motor with power. The “Insulated Gate Bipolar Transistor” (IGBT) is a popular option in contemporary VFDs. The IGBT can accurately control the energy sent to the motor by turning it on and off thousands of times every second.
The IGBT simulates a current sinusoidal waveform at the required wavelength for the motor using a technique called “pulse width modulation” (PWM).
- Control the motor’s speed with the aid of an induction generator.
- Decreases the number of energy motors used to reduce demand and power consumption.
- Reduce mechanical stress caused by pressure spikes by starting and stopping directly online.
- Lower the motor’s starting current.
- Use the motor’s inbuilt protection features to keep it safe.
- Better process control
- Built-in power-factor rectification
- The potential to bypass in an emergency
- deciding which variable frequency drive to use
- The following standards must be understood while choosing the drive:
- The motor’s type (three-phase asynchronous motor)
- Input voltage equals the motor’s rated working voltage (3 AC400V).
- Motor rated voltage (guide value, dependent on the circuit type and the supply voltage)
- Torque at load (quadratic, constant)
- Initial torque
- The resistance temperature detector, which is rated at 122°F (50°C)
How does a VFD function?
Drives using Pulse Width Modulation and Variable Frequency. AC induction motors are fixed-speed machines powered by a constant frequency source (typically 60Hz). A variable frequency drive manages an AC motor’s speed by altering the frequency fed to the motor.
Why do variable frequency drives use IGBTs?
IGBT is an electronic-actuated, high-speed semiconductor switch. The current is permitted to flow from a collection point to an emitter’s point by introducing a small positive voltage between the IGBT’s gate & emitter points. VFDs have IGBT switching rates ranging from 2 to 15 kHz.
Therefore, it is impossible to produce a current that switches quickly between on and off without the IGBT.
Frequently Asked Questions
- What does a VFD do?
A motor controller known as a variable frequency drive (VFD) controls an electric motor by adjusting the power supply’s frequency and voltage. The VFD may also regulate the motor’s ramp-up & ramp-down during start and stop accordingly.
- Why does a VFD convert AC to DC?
DC power or signals can be stored, whereas AC signals cannot. Therefore, we must transform the electrical power into DC to keep it. Additionally, since digital devices demand consistent voltages or DC levels, we must use rectifiers to convert AC into DC to obtain those levels.