How Does a Varible Frequency Drive Convert AC to DC?
Variable Frequency Drive Basics AC, or alternating current, is electricity that switches direction many times every second. AC variable frequency drives, or VFDs, are used to control the speed of AC motors by changing the frequency of the current. Most VFDs are powered by AC current, which comes from the power lines. They need to turn that power into DC, or direct current before they can turn it back into variable frequency AC. Rectifying the Current The variable frequency drive uses a device called a rectifier to change the AC into DC. The most important parts of the rectifier are diodes — electronic one-way valves. One pair of diodes is attached to a positive outlet line and a second pair is attached to a negative outlet line. When the AC power coming in is positive, the positive diodes let it into the positive line while the negative diodes close. When the AC power cycles back to negative, the negative diodes open and let it through while the positive diodes close. Smoothing Out th
