Latched-up IGBT:
An Insulated Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device that is commonly used in high-power switching applications. However, under certain conditions, an IGBT can enter a latched-up state where it remains conducting even when the gate voltage is removed. This latched-up state can lead to excessive power dissipation and potential device failure.

Forced Commutation:
Forced commutation is a technique used to turn off a power semiconductor device, such as an IGBT, by actively manipulating the current or voltage. In the case of a latched-up IGBT, forced commutation of current is the most effective method to turn off the device.

Explanation:
When an IGBT latches up, it enters a state where the parasitic thyristor structure within the device turns on and holds the IGBT in the conducting state. This condition can occur due to excessive voltage or current spikes, high dv/dt or di/dt rates, or inadequate snubber circuits.

Forced commutation of current:
By forcing the current through the latched-up IGBT to zero or a low value, the thyristor structure can be turned off, and the IGBT can be brought out of the latched-up state. This can be achieved by applying a reverse voltage across the IGBT or diverting the current through an external circuit.

Other options:
- Forced commutation of voltage: This method involves applying a reverse voltage across the IGBT to turn it off. However, in the case of a latched-up IGBT, the thyristor structure prevents the reverse voltage from turning off the device.
- Use of a snubber circuit: A snubber circuit is an additional circuitry connected in parallel with the IGBT to suppress voltage spikes and limit the rate of voltage change. While a snubber circuit can help prevent latching-up of an IGBT, it is not effective in turning off a latched-up IGBT.

Therefore, the correct answer is option 'A' - forced commutation of current, as it is the most effective method to turn off a latched-up IGBT.