Introduction:
Class E commutation is a technique used in power electronics to switch off a thyristor or a power semiconductor device without relying on an external pulse. It is commonly used in applications where rapid commutation is required, such as in inverters, motor drives, and power supplies. Class E commutation is a form of forced commutation technique.

Forced Commutation:
Forced commutation refers to the process of turning off a thyristor or a power semiconductor device by applying a specific voltage or current waveform across its terminals. This is necessary because these devices are naturally latching and require an external means to interrupt the current flowing through them.

Class E Commutation:
Class E commutation is a type of forced commutation technique that can be used to turn off a thyristor or a power semiconductor device. It does not rely on an external pulse to achieve commutation, hence it is also known as external-pulse commutation technique.

Line Commutation:
Line commutation is a technique that uses the natural commutation process of the AC line voltage to switch off a thyristor or a power semiconductor device. It takes advantage of the zero-crossing points of the AC waveform to interrupt the current flowing through the device. Class E commutation is not a line commutation technique.

Load Commutation:
Load commutation is a technique that uses the load current to switch off a thyristor or a power semiconductor device. It involves connecting an inductor or a capacitor across the device to create a high voltage or current spike that forces the device to turn off. Class E commutation is not a load commutation technique.

External-Pulse Commutation:
External-pulse commutation, also known as class E commutation, is a technique that uses a resonant circuit to generate a high voltage pulse across the terminals of the thyristor or power semiconductor device. This high voltage pulse forces the device to turn off. The resonant circuit consists of an inductor and a capacitor, and it is tuned to the switching frequency of the device. When the device needs to be turned off, a control signal activates the resonant circuit, causing a high voltage pulse to be applied across the device. This pulse interrupts the current flowing through the device and switches it off.

Conclusion:
Class E commutation is an external-pulse commutation technique used to switch off thyristors or power semiconductor devices. It relies on a resonant circuit to generate a high voltage pulse that forces the device to turn off. It is not a line commutation or load commutation technique.