Practical Commutation Circuits
In this tutorial, we will learn about SCR Turn OFF Methods By Practical
Circuits. There are several ways to properly implement the SCR Turn OFF
methods like Natural, Forced. In Forced Commutation, there are again several
sub-categories like Class A, B, C, D, E. We will learn about all these different
methods to properly turn OFF an SCR, different classes of Commutation and
also the Dynamic Turn OFF Characteristics of SCR.
Forced Commutation
In case of DC circuits, there is no natural current zero to turn OFF the SCR. In
such circuits, forward current must be forced to zero with an external circuit
(known as Commutating Circuit) to commutate the SCR. Hence the name,
Forced Commutation.
This commutating circuit consist of components like inductors and capacitors
and they are called Commutating Components. These commutating
components cause to apply a reverse voltage across the SCR that
immediately bring the current in the SCR to zero.
Depending on the process for achieving zero current in the SCR and the
arrangement of the commutating components, Forced Commutation is
classified into different types. They are:
Class A – Self Commutation by Resonating the Load
Class B – Self Commutation by Resonating the Load
Class C – Complementary Commutation
Class D – Auxiliary Commutation
Class E – Pulse Commutation
such as class A, B, C, D, and E. This commutation is mainly used in chopper
and inverter circuits.
