Motors & Engines
Description
In newer AC drives, the transistors may be replaced by insulated gate bipolar transistors (IGBTs). The IGBTs are used because they can be switched on & off at much higher frequencies -- aka the switch frequencies -- that don& acute;t conflict with other signals. The higher frequencies are also used outside of the audible range for humans, so the AC drive will not emit a hum that humans can hear. Typical switch frequencies are 3KHz to 4KHz. (With an older, SCR-based AC drive, switch frequencies are 250 to 500 Hz). As one can imagine, the higher the switch frequency, the smoother the output waveform & the higher the resolution. However, higher switch frequencies decrease the efficiency of the AC drive because of increased heat in the power devices.
The diagram below shows two pairs of IGBTs used to produce two phases of a typical output section for an AC drive using IGBTs instead of bipolar transistors. From this section one can see that one IGBT of each pair is connected to the positive bus & a second is connected to the negative bus. The IGBTs operate similarly to the transistors in that they are cycled on & off at high frequencies within the overall waveform of a sine wave.
Insulated gate bipolar transistors (IGBTs) connected to the output stage of the AC drive. The IGBTs are used instead of traditional bipolar motor transistors in newer drives. Image courtesy of Philips electronics. Follow AC drive on Facebook.
Read More
AC Drives Manufacturers
AC drives, Variable frequency drive
Address: No.2 Xuwu Gongle Xixiang, Bao'an District,
Shenzhen, Guangdong
China, 518000
Tel: 0086-755-28480223
Fax: 0086-755-28480221
