For a full bridge phase shift converter I need to place a series capacitor to the bridge transformer . This will prevent dc current in the trnsformer core and avoid core saturation.
The bridge has a Bus voltage of 540VDC. The switching frequency is 50khz-100khz.
The capacitor triangle current is (+/-) 30A peak to peak.
In steady state the capacitor voltage is low. But if the duty cycle change in a short time is high ,the voltage on the capacitor rises for a short period of time.
The capacitor voltage rating is 800V-1000V. (regarding dynamic state and worst case with safety margin.). In steady state the voltage rating of the capacitor is very low.
I investigated film capacitors. But I noticed that they have a sharp decline of voltage rating versus frequency. For example a MKV polypropylene capacitor with a voltage rating of 1000VDC have only 25VDC voltage rating when driven by 10khz.
I am afraid that the only choice is the ceramic MLCC.
1- Which capacitor type would you prefer.
2- Is it more economic to limit duty cycle change range so that the voltage rating of the capacitor will be less. Is this method reliable enough? My regulation loop does not need fast response. So I can limit duty cycle change for a given time frame. This will introduce some problems for short circuits.
If I change my control scheme from voltage control mode to peak current control mode, I can get rid of the capacitor but I think that voltage mode control has more advantage and more easy to implement for my application (requires significant less engineering work)
Thanks for your input.