A Adjustable Frequency Drive (VFD) is a kind of motor controller that drives a power engine by varying the frequency and voltage supplied to the electrical motor. Other titles for a VFD are adjustable speed drive, adjustable rate drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly related to the motor’s velocity (RPMs). Basically, the faster the frequency, the quicker the RPMs go. If an application does not require an electric motor to run at full speed, the VFD can be used to ramp down the frequency and voltage to meet up the requirements of the electric motor’s load. As the application’s motor velocity requirements alter, the VFD can merely turn up or down the engine speed to 
meet up the speed requirement.
The first stage of a Variable Frequency AC Drive, or VFD, may be the Converter. The converter is usually comprised of six diodes, which act like check valves found in plumbing systems. They allow current to flow in only one direction; the direction proven by the arrow in the diode symbol. For example, whenever A-stage voltage (voltage is comparable to pressure in plumbing systems) is usually more positive than B or C phase voltages, after that that diode will open up and invite current to movement. When B-stage turns into more positive than A-phase, then your B-phase diode will open and the A-stage diode will close. The same is true for the 3 diodes on the bad part of the bus. Therefore, we obtain six current “pulses” as each diode opens and closes. That is known as a “six-pulse VFD”, which is the standard 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 “rms” or root-mean-squared. The peaks on a 480V program are 679V. As you can plainly see, the VFD dc bus includes a dc voltage with an AC ripple. The voltage runs between approximately 580V and 680V.
We can eliminate the AC ripple on the DC bus with the addition of a capacitor. A capacitor works in a similar fashion 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 less than 3 Volts. Hence, the voltage on the DC bus becomes “around” 650VDC. The actual voltage depends on the voltage degree of the AC range feeding the drive, the amount of voltage unbalance on the energy system, the engine 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 to ac can be a converter, but to tell apart it from the diode converter, it is usually referred to as an “inverter”. It has become common in the market to make reference to any DC-to-AC converter as an inverter.
When we close one of the top switches in the inverter, that stage of the motor is connected to the positive dc bus and the voltage on that phase becomes positive. Whenever we close one of the bottom switches in the converter, that phase is connected to the negative dc bus and turns into negative. Thus, we are able to make any stage on the engine become positive or harmful at will and may hence generate any frequency that we want. So, we can make any phase maintain positivity, negative, or zero.
If you have an application that does not have to be operate at full velocity, 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 allow you to match the velocity of the motor-driven apparatus to the load requirement. There is absolutely no other approach to AC electric motor control that allows you to do this.
By operating your motors at the most efficient rate for your application, fewer errors will occur, and therefore, production levels will increase, which earns your firm higher revenues. On conveyors and belts you eliminate jerks on start-up enabling high through put.
Electric motor systems are accountable for more than 65% of the power consumption in industry today. Optimizing motor control systems by installing or upgrading to VFDs can reduce energy usage in your service by as much as 70%. Additionally, the utilization of VFDs improves product quality, and reduces production costs. Combining energy effectiveness tax incentives, and utility rebates, returns on expenditure for VFD installations can be as little as six months.
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