A Adjustable Frequency Drive (VFD) is a type of electric motor controller that drives a power engine by varying the frequency and voltage supplied to the electric motor. Other titles for a VFD are adjustable speed drive, adjustable quickness drive, adjustable frequency drive, AC drive, microdrive, and inverter.
Frequency (or hertz) is directly linked to the motor’s velocity (RPMs). In other words, the faster the frequency, the faster the RPMs go. If a credit card applicatoin does not require an electric motor to run at full acceleration, the VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor velocity requirements change, the VFD can merely turn up or down the electric motor speed to meet up the speed requirement.
The first stage of a Variable Frequency AC Drive, or VFD, is the Converter. The converter is definitely comprised of six diodes, which are similar to check valves used in plumbing systems. They enable current to circulation in only one direction; the path shown by the arrow in the diode symbol. For instance, whenever A-stage voltage (voltage is comparable to pressure in plumbing systems) is definitely more positive than B or C stage voltages, then that diode will open up and allow current to circulation. When B-phase becomes 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 adverse aspect of the bus. Hence, we obtain six current “pulses” as each diode opens and closes. That is called a “six-pulse VFD”, which is the regular 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 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 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 program. This capacitor absorbs the ac ripple and delivers a soft dc voltage. The AC ripple on the DC bus is typically less than 3 Volts. Thus, 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 engine load, the impedance of the power program, and any reactors or harmonic filters on the drive.
The diode bridge converter that converts AC-to-DC, may also be just referred to as a converter. The converter that converts the dc back again to ac can be a converter, but to distinguish it from the diode converter, it is normally known as an “inverter”. It is becoming common in the market to refer to any DC-to-AC converter as an inverter.
When we close among the top switches in the inverter, that phase of the motor is linked to the positive dc bus and the voltage on that stage becomes positive. When we close one of the bottom level switches in the converter, that phase is linked to the adverse dc bus and becomes negative. Thus, we are able to make any stage on the motor become positive or adverse at will and can thus generate any frequency that we want. So, we can make any phase be positive, negative, or zero.
If you have a credit card applicatoin that does not need to be run at full velocity, then you can cut down energy costs by controlling the engine with a adjustable frequency drive, which is one of the advantages of Variable Frequency Drives. VFDs permit you to match the rate of the motor-
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14.6 UDL performance table for UDL Series Rate Variator (N1=1400R/MIN)
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