A Variable Frequency Drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor. Other titles for a VFD are adjustable speed drive, adjustable velocity drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly related to the motor’s quickness (RPMs). Put simply, the 
faster the frequency, the quicker the RPMs move. If an application does not require a power motor to run at full quickness, the VFD can be utilized to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements modify, the VFD can simply arrive or down the motor speed to meet up the speed requirement.
The first stage of a Adjustable Frequency AC Drive, or VFD, may be the Converter. The converter is certainly comprised of six diodes, which are similar to check valves found in plumbing systems. They enable current to stream in only one direction; the direction demonstrated by the arrow in the diode symbol. For instance, whenever A-phase voltage (voltage is comparable to pressure in plumbing systems) is certainly more positive than B or C stage voltages, after that that diode will open and allow current to circulation. When B-phase turns into more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same holds true for the 3 diodes on the negative side of the bus. Therefore, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which may be the standard configuration for current Adjustable Frequency Drives.
Why don’t we assume that the drive is operating on a 480V power system. The 480V rating can be “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can see, the VFD dc bus includes 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 operates in a similar fashion to a reservoir or accumulator in a plumbing program. This capacitor absorbs the ac ripple and provides a even dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Therefore, the voltage on the DC bus becomes “approximately” 650VDC. The real voltage will depend on the voltage level of the AC collection feeding the drive, the amount of voltage unbalance on the energy system, the 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, may also be just known as a converter. The converter that converts the dc back again to ac is also a converter, but to tell apart it from the diode converter, it is usually known as an “inverter”. It is becoming common in the industry to refer to any DC-to-AC converter as an inverter.
Whenever we close among the top switches in the inverter, that stage of the electric motor is connected to the positive dc bus and the voltage on that stage becomes positive. Whenever we close among the bottom level switches in the converter, that phase is linked to the detrimental dc bus and becomes negative. Thus, we can make any stage on the motor become positive or bad at will and may hence generate any frequency that people want. So, we are able to make any phase maintain positivity, negative, or zero.
If you have an application that does not need to be run at full quickness, then you can decrease energy costs by controlling the electric motor with a variable frequency drive, which is among the advantages of Variable Frequency Drives. VFDs permit you to match the quickness of the motor-driven tools to the strain requirement. There is no other method of AC electric electric motor control that allows you to accomplish this.
By operating your motors at most efficient velocity for the application, fewer mistakes will occur, and therefore, production levels will increase, which earns your business higher revenues. On conveyors and belts you remove jerks on start-up enabling high through put.
Electric motor systems are accountable for more than 65% of the energy consumption in industry today. Optimizing motor control systems by installing or upgrading to VFDs can reduce energy consumption in your service by as much as 70%. Additionally, the use of VFDs improves product quality, and reduces production costs. Combining energy efficiency taxes incentives, and utility rebates, returns on purchase for VFD installations can be as little as 6 months.
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