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| 12/8/2011 7:29 AM | |
Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12316 Rating:
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Hello Deepstra; Thyristors and IGBTs are based on different technologies, but can be used for similar applications. The basic difference is that the thyristor is based on a 4-layer bipolar transistor, while the IGBT is based on a 4-layer MOSFET design, See here, on Wikipedia: http://en.wikipedia.org/wiki/Thyristors http://en.wikipedia.org/wiki/IGBT IGBTs and thyristors both have a control "gate" that controls the firing angle of the output current, and can withstand high-power levelsused to control theoutput signal of a VFD. See the explanations on this article: http://en.wikipedia.org/wiki/Variable-frequency_drive All VFDs use their output devices (IGBTs, transistors, thyristors) only as switches, turning them only on or off. Using a linear device such as a transistor in its linear mode is impractical for a VFD drive, since the power dissipated in the drive devices would be about as much as the power delivered to the load, The inverter circuit is probably the most important section of the VFD, changing DC energy into three channels of AC energy that can be used by an AC motor. The usual method used to achieve variable motor voltage is pulse-width modulation (PWM). With PWM voltage control, the inverter switches are used to construct a quasi-sinusoidal output waveform by a series of narrow voltage pulses with pseudosinusoidal varying pulse durations,(Note: this is the part of the VFD where thyristorsor IGBTs circuitsare required). As new types of semiconductor switches have been introduced, these have promptly been applied to inverter circuits at all voltage and current ratings for which suitable devices are available. Introduced in the 1980s, the insulated-gate bipolar transistor (IGBT) became the device used in most VFD inverter circuits in the first decade of the 21st century. Hope this helps, Daniel Chartier |
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| 12/9/2011 5:19 PM | |
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Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12316 Rating:
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Hello Deep; Thank you for your compliments, however undeserved they are. I only looked for information to complement my working experiences, so you could find your own answers. I don't feel very confident about answering your new questions either. My experience has often been that with HV drives you tend to find more manufacturers using thyristors in their powerswitching sections. My most marking memory was working with (inside of?) a Robicon drive, rated for 10 MW (yes, that was kind of impressive! it occupied a 50 meters square floor print) where all the rectification and switching stages were built on "hockey-pucks", 10 cm diameter SCRs (thyristors). When I asked the technician from Robicon why they chose this technology, he said that it was because at these power levels the thyristors were more resiliant, and when they blew (and it did happen a lot during commissioning) they were cheaper and easierto replace than IGBTs. In any case, have a look at this document discussing and comparing different technologies of switching transistos for MV and HV drives. It might just give you somedetails on the differences between technologies. http://w5jgv.com/hv-ps1/pdf/MV_AC_Drive_Topology_Analysis.pdf Hope this helps, Daniel Chartier |
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| 5/18/2012 7:45 AM | |
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Posts: 165 Rating:
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hello dchartier Nice job you have done!! Regards Mothilal |
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