A Variable Frequency Drive (VFD) is a type of motor controller that drives a power electric motor by varying the frequency and voltage supplied to the electric powered motor. Other titles 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 speed (RPMs). In other words, the faster the frequency, the faster the RPMs move. If an application does not require a power motor to perform at full velocity, the VFD can be used to ramp down the frequency and voltage to meet up the requirements of the electrical motor’s load. As the application’s motor velocity requirements modify, the VFD can merely turn up or down the electric motor speed to meet the speed requirement.
The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is made up of six diodes, which are similar to check valves used in plumbing systems. They enable current to circulation in mere 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 phase voltages, after that that diode will open up and allow current to circulation. When B-stage turns into more positive than A-phase, then your B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the unfavorable side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is known as a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.
Let us assume that the drive is operating on a 480V power system. The 480V rating is definitely “rms” or root-mean-squared. The peaks on a 480V system 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 get rid of 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 system. This capacitor absorbs the ac ripple and provides a easy dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, the voltage on the DC bus turns into “around” 650VDC. The real voltage depends on the voltage degree of the AC collection feeding the drive, the amount of voltage unbalance on the power system, the engine load, the impedance of the power 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 normally known as an “inverter”. It is becoming common in the industry to refer to any DC-to-AC converter as an inverter.
When 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 connected to the unfavorable dc bus and becomes negative. Thus, we are able to make any stage on the engine become positive or adverse at will and may thus 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 need to be run at full acceleration, then you can decrease energy costs by controlling the engine with a adjustable frequency drive, which is one of the benefits of Variable Frequency Drives. VFDs permit you to match the acceleration of the motor-driven products to the strain requirement. There is absolutely no other method of AC electric electric motor control which allows you to do this.
By operating your motors at most efficient rate for your application, fewer errors will occur, and thus, production levels will increase, which earns your business higher revenues. On conveyors and belts you eliminate jerks on start-up permitting high through put.
Electric motor systems are responsible for a lot more than 65% of the energy consumption in industry today. Optimizing engine control systems by installing or upgrading to VFDs can decrease energy intake in your facility by as much as 70%. Additionally, the use of VFDs improves product quality, and reduces production costs. Combining energy efficiency tax incentives, and utility rebates, returns on expense for VFD installations is often as little as 6 months.

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