4 February, 2014


Why are IGBTs used instead of SCRs in VFDs? Why? Source please. After speaking to others on the web, I found the answer. SCRs were used in VFDs until transistors became available with sufficient voltage and current ratings for motor control use. When SCRs were used, the most common design was to use a six-SCR controlled rectifier converter to provide variable voltage DC input to a six-SCR inverter circuit. The SCRs in the inverter circuit required commutation circuits to supply the reverse voltage required to turn them off. The most common commutation circuit design used six SCRs and three L-C circuits to generate commutation pulses. In addition, six power diodes were connected inverse parallel to the inverter SCRs. All together, that is 24 individual power semiconductors. There were several designs used at various power levels, but they all had more complicated and less efficient power circuit topologies than today's IGBT PWM designs. Re "Source please????" This has less detail but touches on several of the points mentioned above: Here are any related Wikipedia articles:

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1 Comment

  1. J. Smith36 February 3, 2014 at 9:33 am #
    A VFD requires power switches that may be turned on and off with a control signaal. This is the case for IGBTs. However, SCRs, once on, won't turn off until the current through the main terminals drops below the holding current.