What is forced commutation in SCR?

Forced Commutation The thyristor can be turned off by reverse biasing the SCR or by using active or passive components. Thyristor current can be reduced to a value below the value of holding current. Since the thyristor is turned off forcibly it is termed as a forced commutation process.

What are the condition for commutation of SCR?

This external circuit is known as commutation circuit. To turn off an SCR / thyristor, it is required that its anode current should fall below the holding current and a reverse voltage should be applied across the SCR for the sufficient time so that it regains to forward blocking mode from forward conduction mode.

What is load commutation of SCR?

Load commutation of SCR is a forced commutation technique in which SCR is forced to turn off. Turning off an SCR essentially requires its anode current to fall below holding current and a reversed biased voltage must be present across SCR for sufficient time so that SCR may regain its blocking state.

How SCR can be turned off?

To turn OFF the conducting SCR, the anode or forward current of SCR must be reduced to zero or below the level of holding current, and then a sufficient reverse voltage must be applied across the SCR to regain its forward blocking state.

How is forced commutation of SCR used in DC Circuit?

Forced Commutation of SCR: Unlike natural commutation, an external circuitry is required to forcibly bring the SCR andoe current below holding current and keeping SCR reversed biased for a period more than the SCR / thyristor turn off time. This technique is applied for DC circuit.

What is the process of turning off a SCR?

This method of turning off an SCR / thyristor is called commutation process. There are mainly two types of SCR commutation techniques: Natural Commutation and Forced Commutation. Natural Commutation of SCR is the process of turning off an SCR without using additional commutation circuitry.

What are the 5 categories of forced commutation?

The Forced commutation technique is further divided into five categories which are Class A, B, C, D, and E. Natural Commutation occurs only in AC circuits, and it is named so because it doesn’t require any external circuit.

Why is forced commutation used in a chopper circuit?

It requires commutating elements like inductance and capacitance to forcefully reduce the anode current of the Thyristor below the holding current value, that’s why it is called as Forced Commutation. Mainly forced commutation is used in Chopper and Inverters circuits. Forced commutation is divided into six categories, which are explained below: