Imagine that we could control the pressure in a water line by turning the valve on and off at a high rate of speed. Thus, the average voltage is half of V or V. By pulsing the output, we can achieve any average voltage on the output of the VFD. If you have an application that does not need to be run at full speed, then you can cut down energy costs by controlling the motor with a variable frequency drive, which is one of the benefits of Variable Frequency Drives.
VFDs allow you to match the speed of the motor-driven equipment to the load requirement. There is no other method of AC electric motor control that allows you to accomplish this. Additionally, the utilization of VFDs improves product quality, and reduces production costs. Combining energy efficiency tax incentives, and utility rebates, returns on investment for VFD installations can be as little as 6 months.
By operating your motors at the most efficient speed for your application, fewer mistakes will occur, and thus, production levels will increase, which earns your company higher revenues. On conveyors and belts you eliminate jerks on start-up allowing high through put. Move Items to Quote. Skip to Content Have questions? Call us at Compare Products. Variable Frequency Drives. Electric Motors. Medium Voltage VFDs. Medium Voltage Motors.
Power Quality Products. VFD Panels. Industrial Controls. Mitisubishi Electric. US Motors - Nidec. What is a Variable Frequency Drive? VFD Buying Guide. VFD Panel. How to Read a Motor Nameplate. VFD How to Videos. How to Wire a VFD. Craig Hartman. Complete the form at the bottom of the page, or call us at to get your technical questions answered.
We know motors and drives! JANE Ming. September 12, at pm. September 8, at am. August 18, at pm. Piyush Patel. August 2, at am. Thank You so much for the deep information regarding variable frequency drive as I was seeking like this deep information about VFD.
Somehow I landed on your blog and got these informative things. I wanna know about this because in a week I am going to buy Honeywell Buildings VFD so it became very important to me to check it out briefly. Darius Baker. June 1, at am. I have a telescoping antenna tower. It has a 1 hp motor and the original control panel has "timer" limit switch controls. Can you build or do you have a control panel that will allow me too raise and lower the tower incorporating the limit switch relays, I have the limit switches.
I simply do not possess the knowledge to construct one myself. January 23, at pm. Way cool! Some extremely valid points! Bell A. January 13, at am. Great article. January 12, at am. Mats Lindqvist. June 4, at am. How fast can a VFD respond to torque changes of the load? I have an application with a roughly sinusoidally fluctuating load, and I would ideally like to motor to slow down when the torque goes up and vice versa.
Can a VFD be set to run at "constant torque" rather than "constant speed" and adjust the frequency this fast? May 30, at am. I was wondering if anyone could tell me if this could work on a turntable. I have a vintage turntable of more than 50 years old with an AC motor. Speed of the platter is determined by the frequency usually 50hz. I would need a device which absorbs v - 60hz from the mains and output v this reduces vibrations in the AC motor even further.
The device would need to be adjustable for voltage and frequency. The power consumption of the AC motor is only 16w tops. Can anyone help? These components have only been available at reasonable cost and reliability in the past thirty years or so, therefore AC drives are a relatively modern industrial product.
Figure 5 shows a three phase rectifier consisting of six diodes connected to a capacitor and a resistor as a simple load. The diodes conduct in one direction only in the direction that they point ; the capacitor stores energy a little like a battery, the resistor acts as a load.
In steady state, the voltage on the capacitor will sit pretty near to the peak of the input sine wave voltage. Now the diodes are conducting only when the input voltage is higher than the voltage on the capacitor.
However, we now have a relatively smooth DC voltage on the capacitor. If we take away the resistor, and connect an inverter instead, it begins to look like a variable frequency drive figure 6 The DC part is sometimes called the DC link as it joins the rectifier and inverter. Now to the business part. These function as very fast power switches. They have diodes in parallel with them for reasons that will become clear.
We can now switch on an upper and lower IGBT and provide a current path through any two motor connections. To turn an IGBT on, we simply apply a few volts to the gate shown here unconnected.
Then the IGBT conducts in the direction of the arrow. Depending on which IGBTs we turn on, we can create a positive or negative current path though the motor. Hence we can make AC from DC. If instead we turn on and off IGBTs in a carefully controlled sequence, we can build up a three phase current in the motor windings. If we vary the time that we switch the IGBTs on and off for, we can control this current. This, of course is what we want to do to control the motor speed.
Using the same technique, we can control the effective voltage, which in turn controls the magnetic field. This on off time control is called Pulse Width Modulation PWM , and is shown simplistically in Figure 7; switching the six IGBTs on and off provides current paths to the motor and allows a three phase sine wave current to flow, turning the motor at the desired speed. If we switch our IGBTs several thousand times a second usually between 4 and 16kHz we can build up quite a nice current waveform as shown in figure 8.
Notice that the output voltage consists of lots of pulses rather than a nice sine wave. However, the motor is happy with the jagged current and turns at the required speed. So what are the diodes doing in the inverter? The diodes automatically provide this current path by switching on, or commutating, the current. Hence the name commutation or flywheel diodes. Variable frequency drives not only offer adjustable speeds for accurate and precise control applications but also have more benefits in terms of process control and conservation of energy.
Some of these are given below. Both magnitude and frequency control technique to vary the speed consumes less power when variable speed is required by the motor. So a great amount of energy is conserved by these VFDs. VFD allows accurate positioning of the motor speed by continuously comparing with reference speed even at changes in the loading conditions and input disturbances like voltage fluctuations.
Induction motor draws current which is 6 to 8 times the nominal current at starting. Due to low frequency, the motor draws less current and this current never exceeds its nominal rating at starting as well as operating. It offers smooth operations at starting and stopping and also reduces thermal and mechanical stress on motors and belt drives. The inbuilt power factor correction circuit in the DC link of VFD reduces the need for additional power factor correction devices.
The power factor for the induction motor is very low for particularly no-load application, while at full load, it is 0. Low power factor results in poor utilization of power due to high reactive losses. Pre-programmed and factory wired VFDs offer an easy way for connection and maintenance. I hope that you have been provided with precise and ample knowledge about the working of VFDs in our article.
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Variable Frequency Drives by emainc. Basic parts of VFD by machinedesign. Working of VFD by cfnewsads.
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