The thyristor is deterred by reverse biasing the SCR or just by utilizing active or elements which are passive. Thyristor current are paid down up to a value underneath the value of holding current. Since, the thyristor is powered down forcibly its termed as a commutation procedure that is forced.
The products which can be electronic is basic electric elements such as for example inductance and capacitance are used as commutating elements for commutation purpose.
Forced commutation could possibly be seen while using the DC supply; hence it is also called as DC commutation. The circuit that is external for forced commutation procedure is recognized as as commutation circuit plus the elements employed in this circuit are called as commutating elements.
The Forced commutation is classified as-
a) Voltage commutation
b) Current commutation
1) Forced commutation requires external components to store energy & used to apply reverse voltage across SCR or reduce anode current below holding current.
2) Current commutation-SCR is turned off by reducing anode current below holding current.
3) Voltage commutation-SCR is turned off by applying large reverse voltage across it.
Classification of Forced Commutation Methods.
The forced commutation can be classified into different methods as follows:
1. Class A: Self commutated by a resonating load
2. Class B: Self commutated by an LC circuit
3. Class C: Cor L-C switched by another load carrying SCR
4. Class D: C or L-C switched by an auxiliary SCR
5. Class E: An external pulse source for commutation
6. Class F: AC line commutation