Q.What are the factors against which the power semiconductor devices and converters must be commonly protected?

Power converters run from the utility mains and are exposed to switching transients and load faults, so several protection schemes are built in. A power device must be protected against over-current, an excessive rate of rise of current $(di/dt)$, voltage spikes and over-voltage, an excessive rate of rise of voltage $(dv/dt)$, excessive temperature rise, and gate over-current and over-voltage. The standard methods are:

• Over-current: a semiconductor fuse coordinated with a fast circuit breaker in series.
• $di/dt$: a series inductor to limit the rate of rise of current.
• Voltage spikes / over-voltage: a Metal Oxide Varistor (MOV) across the device.
• $dv/dt$: an R-C snubber circuit across the device, which also absorbs switching spikes and prevents false triggering.
• Excessive temperature: a heat-sink to conduct heat away.
• Gate over-current: a series gate resistor $R_G$. …