Forced Commutated Systems

forced commutated thyristor

hi everbody,

can anybody tell me what is forced commutated systems and why is it necessary in the usage of thyristors ? thank you

regards,
mengghee

force commutated thyristor circuits

Hi,

Forced commutation is used in order to force a thyristor to turn-off.
It is used mainly in thyristor circuits as thyristors can't be turned off by gate control " GTO is an improved limited application thyristor with can be commutated by negative gate pulse ".
Mainly, Forced commutation is done by "forcing" the Anode to Cathode voltage to reach a negative value resulting in stopping of current flow.
Various techniques are used employing a charged capacitor to supply the " commutating " voltage, while i think some others use resonance to sustain a certain time relationship with the main power circuit.
This is done as the thyristor naturally turn - off when its current " depending on its external power circuit " reaches a value lower than the thyristor hold current , which is higher than zero with an increment.
You can find detailed circuits in Power Electronics Handbook of Mohammed Rashid, and also Power electronics for W.Lander.
Regards,.