Forced commutation is used to turn-off or commutate a thyristor.


When a thyristor is turned on, it remains conducting until the current flowing through it becomes zero. This is because the thyristor is a latching device that requires a negative gate current or a reverse blocking voltage to turn off.

To turn off or commutate a thyristor, we need to interrupt the current flowing through it. This can be achieved by using forced commutation techniques.

Forced commutation techniques:

1. Commutation by source: In this technique, a separate source is used to provide a reverse voltage across the thyristor when it needs to be turned off. This reverse voltage helps in reducing the current flowing through the thyristor and eventually turns it off.

2. Commutation by auxiliary circuit: In this technique, an auxiliary circuit is used to divert the current away from the thyristor when it needs to be turned off. This is achieved by providing an alternate path for the current to flow, bypassing the thyristor.

3. Commutation by resonant pulse: In this technique, a resonant circuit is used to generate a high-frequency voltage pulse across the thyristor. This high-frequency pulse helps in reducing the current flowing through the thyristor and turns it off.

Importance of forced commutation:

Forced commutation is essential to control the operation of a thyristor-based circuit. It allows us to turn off the thyristor when required, enabling precise control over the circuit's operation.

Without forced commutation, the thyristor would remain conducting indefinitely, leading to a loss of control and potential damage to the circuit.

Therefore, forced commutation techniques are used to turn off or commutate a thyristor and regain control over the circuit's operation.