Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rectification questions

  1. Feb 18, 2016 #1
    Hello, I am new here so forgive any noob-ness,

    I am doing a study on Thyristor rectification and have a few questions:

    A single-phase, half controlled bridge rectifier cannot be an inverter?

    -Unless it is connected to an inductive load, then it can?

    A single-phase, half controlled bridge rectifier connected to an inductive load acts like a current generator as the stored inductor current means the thyristors wont turn off when the voltage changes direction?

    Those are the questions and the main question to all of them is "are those statments correct?"

  2. jcsd
  3. Feb 18, 2016 #2

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    A picture would sure help.
    Your words paint a picture in my mind but how am i to know it's the same picture as in your mind?

    So i am reluctant to venture a guess.

    My answer would be - "can't rightly say."

    I can say this
    As ambiguous as the labeling is on this chart we can glean something from it that relates to your questions

    Simplify your thinking and go one step at a time:

    At time α the SCR gets fired. Assume it's fired by a brief pulse so we dont have to worry about gate timing any more..
    Current commences to flow in the load, PUSHED clockwise by Vs . That is building stored energy in the inductor.
    Current's phase lags voltage because of inductance.
    At time pi, when Vs has returned to zero, and shortly thereafter, note we still have current and in same direction.
    That current is now being PULLED clockwise by inductance.
    Stored energy of inductor is partly dissipated in the resistor and partly returned to the source.
    When that energy is spent current ceases and SCR "commutates", that is it turns off.

    So while it looks at first glance impossible, current does actually flow briefly opposite Vs and the SCR remains forward biased.

    It's a beautiful demonstration of the laws of Ohm Kirchoff and Lenz. It's exactly how we move the rods in my nuke plant(well, actually we have 3 phase half wave , no different though).

    A question well stated is half answered. I hope above helps you rephrase yours.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook