Ferro-Resonant UPS-Inverter Unstable Phase/Frequency

[psapengineer]

Lately our legacy backup UPS has been slipping in and out of lock with the alternate line. After much investigation we have found that the legacy Ferro-Resonant design is not compatible with newer switching power supplies that employ active power factor correction.

Essentially the active power factor correction "bucks" the phase and frequency of the resonate design making it unstable with respect to phase and frequency. So, as the inverter's frequency and phase shifts it slips in past the phase and frequency of the alternate line. As it does this the alternate line becomes unavailable and the internal alarm is activated.

I'm told that the only solution to this is to replace the legacy unit with a newer technology PWM or DSP design inverter or UPS.

Has anyone else suffered through this problem and if so, what was your solution?

Thanks in advance, Bob

[SlimBob]

That's just f'in brilliant. At my last job, I took a power meter and balanced the UPSes by hand to make sure that the power factor was evenly distributed. Oh well... life goes on.

[thebigphish]

how old is that Ferro-Resonant PS? Was it's time up anyway?