A Variable Frequency Drive (VFD) is a type of engine controller that drives a power electric motor by varying the frequency and voltage 
supplied to the electric motor. Other names for a VFD are adjustable speed drive, adjustable swiftness drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly related to the motor’s acceleration (RPMs). Basically, the faster the frequency, the quicker the RPMs proceed. If an application does not require an electric motor to run at full rate, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electrical motor’s load. As the application’s motor velocity requirements change, the VFD can merely turn up or down the engine speed to meet the speed requirement.
The first stage of a Adjustable Frequency AC Drive, or VFD, is the Converter. The converter is certainly made up of six diodes, which act like check valves used in plumbing systems. They enable current to circulation in only one direction; the path proven by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is similar to pressure in plumbing systems) is usually more positive than B or C stage voltages, after that that diode will open and invite current to flow. When B-stage becomes more positive than A-phase, then the B-phase diode will open up and the A-phase diode will close. The same is true for the 3 diodes on the unfavorable part of the bus. Therefore, we get six current “pulses” as each diode opens and closes. That is known as a “six-pulse VFD”, which is the regular configuration for current Variable Frequency Drives.
Why don’t we assume that the drive is operating upon a 480V power program. The 480V rating is certainly “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can plainly see, the VFD dc bus has a dc voltage with an AC ripple. The voltage operates between approximately 580V and 680V.
We can get rid of the AC ripple on the DC bus with the addition of a capacitor. A capacitor functions in a similar fashion to a reservoir or accumulator in a plumbing system. This capacitor absorbs the ac ripple and delivers a simple dc voltage. The AC ripple on the DC bus is normally significantly less than 3 Volts. Hence, the voltage on the DC bus turns into “approximately” 650VDC. The actual voltage will depend on the voltage level of the AC range feeding the drive, the level of voltage unbalance on the energy system, the electric motor load, the impedance of the energy program, and any reactors or harmonic filters on the drive.
The diode bridge converter that converts AC-to-DC, is sometimes just known as a converter. The converter that converts the dc back to ac can be a converter, but to tell apart it from the diode converter, it is generally known as an “inverter”. It is becoming common in the market to make reference to any DC-to-AC converter as an inverter.
When we close among the top switches in the inverter, that stage of the engine is connected to the positive dc bus and the voltage upon that phase becomes positive. When we close among the bottom switches in the converter, that phase is linked to the bad dc bus and turns into negative. Thus, we can make any stage on the electric motor become positive or adverse at will and will hence generate any frequency that we want. So, we are able to make any phase be positive, negative, or zero.
If you have an application that does not need to be operate at full acceleration, then you can decrease energy costs by controlling the motor with a variable frequency drive, which is one of the advantages of Variable Frequency Drives. VFDs enable you to match the speed of the motor-driven products to the strain requirement. There is no other approach to AC electric engine control that allows you to do this.
By operating your motors at the most efficient speed for the application, fewer mistakes will occur, and therefore, production levels increase, which earns your firm higher revenues. On conveyors and belts you get rid of jerks on start-up permitting high through put.
Electric engine Variable Speed Drive systems are accountable for more than 65% of the power consumption in industry today. Optimizing electric motor control systems by installing or upgrading to VFDs can decrease energy usage in your facility by as much as 70%. Additionally, the use of VFDs improves item quality, and reduces production costs. Combining energy performance taxes incentives, and utility rebates, returns on investment for VFD installations can be as little as six months.
