UPSs and active PFC - A potential compatability problem

[Mark R]

I was thinking about PFC circuits - active and passive, and one thing that struck me was their inherently inductive nature.

When combined with a relatively high impedednce, regulated voltage source (such as the output of the UPS) this forms a loop which could potentially become unstable. A sudden change in load (e.g. loading a program, moving the mouse, etc.) could induce oscillations in the power supply due to inadequate compensation - leading to very poor voltage regulation in the supply, or possibly even damaging the UPS or PSU.

I wonder if this is worse for active PFC, because many popular ICs use a control method which leaves a significant undamped resonance at half the mains frequency. Potentially using one of these systems with a UPS with a ferro-resonant transformer PFC could spell disaster as the two devices oscillate together.

I've no idea if these problems actually occur, and I haven't even formally analysed the circuits - it's just some random thoughts before I do the math (or rather learn to do the math). Does anyone know if this is actually a problem, and if it is what it's impact is? Do designers of UPSs try to compensate for loops which are potentially out of their control?

 

[JSSheridan]

Passive power factor correction is simply achived by using a capacitor connected between the power line and neutral to bring a lagging PF closer to unity PF. This wouldn't be inductive in nature. I've never heard of leading PF to be an issue, but you would correct that by placing an inductor in series between the line and the load. I haven't studied active PFC, nor am I familiar with how they operate. Also, I'm really not a person who you should ask for a final opinion, but PFC circuits are safe to the best of my knowledge. Peace.