What is an IGBT?

An Insulated Gate Bipolar Transistor (IGBT) is part of the setup of  a VFD (Variable Frequency Drive). If you look in more depth at a VFD, one easy way to analyse it is to think of it in three main parts: the bridge converter, DC link, and the inverter. An IGBT is the inverter element in a VFD, pulsing voltage at an extremely rapid rate.

Previously, IGBTs were slow at switching current on and off and often overheated. As with many parts, IGBTs have improved over time through innovation. They are now much quicker than their predecessors and have become highly reliable devices that can handle high voltage devices that can switch extremely quickly.

An IGBT is a semiconductor made up of three terminals, which act as a switch for moving electrical current. As the word “gate” suggests, when voltage is applied to the gate, it opens and creates a path for current to flow. If no voltage is applied to the gate, or if the voltage is not high enough, the gate remains closed and there will be no flow of electricity. An IGBT essentially acts as an on/off switch for current.

The number of pulses per second from the IGBTs is known as carrier frequency. Since carrier frequency is an adjustable parameter on most VFDs, you can set it at a bespoke level for your needs. One has to be careful to set it at the right frequency. Setting the carrier frequency too high will reduce the noise level produced from the VFD, but it will also shorten the VFD life due to increased heat. A higher carrier frequency can also overheat the motor and reduce its efficiency. On the other hand, setting the carrier frequency too low can create excessive motor noise. Some manner of testing at different levels is needed to see which works most efficiently and at the optimum noise level.

In a typical six pulse drive there are six IGBTs pulsing voltage up to 15,000 times per second. IGBTs play an important role in many modern day power electronics applications where speed and process control are needed and will continue to play a key roles in the advancement of technology.

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