A Adjustable Frequency Drive (VFD) is a type of electric motor controller that drives an electric motor by varying the frequency and voltage supplied to the electrical motor. Other names for a VFD are variable speed drive, adjustable speed drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly related to the motor’s rate (RPMs). Quite simply, the quicker the frequency, the quicker the RPMs go. If an application does not require an electric motor to perform at full speed, the VFD can be utilized to ramp down the frequency and voltage to meet up certain requirements of the electric motor’s load. As the application’s motor velocity requirements alter, the VFD can merely arrive or down the motor speed to meet the speed requirement.
The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is usually made up of six diodes, which are similar to check valves used in plumbing systems. They enable current to flow in only one direction; the direction shown by the arrow in the diode symbol. For example, whenever A-phase voltage (voltage is comparable to pressure in plumbing systems) is more positive than B or C stage voltages, after that that diode will open and allow current to circulation. When B-phase 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 detrimental aspect of the bus. Therefore, we obtain six current “pulses” as each diode opens and closes. That is called a “six-pulse VFD”, which may be the standard configuration for current Adjustable Frequency Drives.
Let us assume that the drive is operating on a 480V power system. The 480V rating is “rms” or root-mean-squared. The peaks on a 480V system are 679V. As you can 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 style to a reservoir or accumulator in a plumbing program. This capacitor absorbs the ac ripple and delivers a easy dc voltage. The AC ripple on the DC bus is normally significantly less than 3 Volts. Hence, the voltage on the DC bus becomes “around” 650VDC. The real voltage depends on the voltage level of the AC range feeding the drive, the amount of voltage unbalance on the 
power system, the electric motor load, the impedance of the energy system, and any reactors or harmonic filters on the drive.
The diode bridge converter that converts AC-to-DC, is sometimes just referred to as a converter. The converter that converts the dc back again to ac is also a converter, but to distinguish it from the diode converter, it is usually known as an “inverter”. It has become common in the industry to refer to any DC-to-AC converter as an inverter.
When we close one of the top switches in the inverter, that phase of the electric motor is connected to the positive dc bus and the voltage upon that stage becomes positive. Whenever we close one of the bottom level switches in the converter, that phase is linked to the bad dc bus and turns into negative. Thus, we are able to make any stage on the engine become positive or unfavorable at will and can therefore generate any frequency that people want. So, we can make any phase be positive, negative, or zero.
If you have an application that does not need to be run at full velocity, then you can decrease energy costs by controlling the engine 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 tools to the strain requirement. There is no other method of AC electric motor control that allows you to do this.
By operating your motors at the most efficient speed for your application, fewer mistakes will occur, and thus, production levels increase, which earns your company higher revenues. On conveyors and belts you get rid of jerks on start-up enabling high through put.
Electric motor systems are responsible for a lot more than 65% of the energy consumption in industry today. Optimizing electric motor control systems by setting up or upgrading to VFDs can decrease energy intake in your service by as much as 70%. Additionally, the utilization of VFDs improves item quality, and reduces production costs. Combining energy effectiveness tax incentives, and utility rebates, returns on purchase for VFD installations is often as little as six months.
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