importance of capacitor voltage and inductor current instead of cap volt and ind curr

[nepdeep]

Hi, started studying power electronics recently. They rarely mention inductor voltage and capacitor current. Most of the cases, they say the voltage acorss the capacitor is changing or the inductor current is changing.

From my understanding the current in the capacitor is also changing, and the voltage in the inductor is also changing? why inductor current and capacitor votage is important?

 

[crutschow]

It's certainly true that both current and voltage are involved in the operation of inductors and capacitors. But in may applications it's the capacitor voltage and inductor currents that are of most interest so they are mentioned more frequently.

 

[keith1200rs]

For a capacitor Q = CV and i = C dV/dT where T is time. So the voltage depends on current and time. If you try to force a voltage across a capacitor the current will theoretically be infinite and the voltage will instantly jump to the applied voltage. This isn't the real situation. There will always be a finite current and therefore a finite rate of voltage rise. So, you tend to think in terms of applying a current and seeing the voltage rise.

The same us true of inductors but trying to instantaneously change the current is impractical, rather than an instantaneous voltage change in a capacitor.

Keith