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how does a ac drive control speed

  • 2021-08-19 10:17:38
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The ac drive controls the speed of the pump and fan by changing the electrical energy supplied rather than damping the air- or water flow. It is like reducing the speed of a car by pressing less on the accelerator instead of using the brake to slow down the speed. The payback time of an ac drive is typically one year or less.


Other benefits of using ac drive to control the speed of fan or pump are:


Smooth ramp up and down causes less stress to the mechanics of fans and pumps and to air ducts and water piping. Slowing down the speed rather than damping the output will result in lower noise levels.


AC motors are used in a variety of applications, particularly within industrial settings where motors are needed to power heavy duty machinery.  In plants where accuracy and timeliness are extremely crucial for the operation, the actual AC motors need to be controlled.  Therefore, various methods and/or products may be used to control the motor’s speed and frequency.


There are several ways to control the speed, such as changing the number of poles in very small increments, changing the slip of the motor, and changing the frequency of the AC signal.  The method of changing the poles is rarely used because it’s inefficient for continual control needs in demanding operations.  The method of changing the AC motor’s rotor slip is best used when the motor is designed for high slip.  With this method, the motor must be matched to the load, and one should make sure that the change in power results in the correct change in load speed.  Also, the load should have substantial inertial components.


The most common way of controlling AC motor speed is changing the motor’s frequency.  With this method, variable speed AC motor drives are used to adjust the speed.  These are often called variable frequency drives (VFD), AC inverters, or adjustable speed drives (ASD).  The AC frequency can be adjusted using a six-step inverter, vector flux or pulse-width-modulation.  A six-step inverter or variable voltage inverter rectifies the AC power to DC power, and then switches to imitate a sine wave.  With pulse-width-modulation, DC voltage is swiftly changed to match “area under curve.”


Consider these methods of AC motor speed control if you operate a plant or facility where AC motors are used to power pumps, fans, etc.  These applications require preciseness to keep an operation running smoothly.  The easiest method is to install reliable AC drives designed  to control the speed accurately.  These come with a variety of control settings, mounting options and more so you can easily find controls to meet your application needs.  Advantages include acceleration control, machines operate most smoothly, ability to adjust production rates, tension control capabilities, and energy savings.


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