I had the chance to take this Eaton Powerware 30 kVA / 27 kW (9355-30-N-7-2x9Ah) uninterrupted power supply apart to look for parts worth salvaging for future reuse in other projects.
Looking up the type on the Eaton website we learn that it is a UPS using double conversion topology that provides isolation from all input anomalies on the output side. Double conversion means that there is AC to DC converter that is connected to the battery pack and the DC to AC converter, a total of two power conversions.
The use of 432 VDC battery pack makes the whole construction smaller and more light weight, the higher voltage avoids the use of step-down or step-up transformers, large switches to handle high current at low voltages but it also adds another danger element as a high voltage battery is not as easy to service and failures can be more catastrophic. This design is called transformer free design, but apparently they do not count in the large choke transformers in the inverters.
The following schematic shows the block diagram of a double conversion UPS.
Viewed from the side we can see the four compartments for batteries, with this rather small battery stack this unit is only able to keep up for 7 minutes at its rated load of 27 kW.
In the close up picture of the circuit board, we can basically see the complete controls of this unit. Out to the far right is the CPU board, top of it connects out to the inverter modules and at the bottom its outputs for relays / switch timing on the large main circuit board.
All wiring was unfortunately cut off when I got to the unit, but looking at the amount of cable shoes still sitting in the bolts, I can safely assume that the PFC connects our to the left side terminals, one inverter module connects at the top terminals and at the bottom near the three black current transformers two inverter modules have been connected in parallel.
Four 230 VAC 15 Watt fans ensure the cooling of the IGBT switches and chokes.
Below the fans we can see the three identical inverter modules, they were easily pulled out when the copper busbars was disconnected. The copper busbars is the battery rails between the the input conversion and output conversion.
At the following pictures of one of the modules it can be seen that they are very generic, not meant for a very specific task, but is merely a dumb inverter module that is connected to a control bus for input signals.
The IGBT modules Semikron Skiip 25AC125V10 are ultra fast NPT IGBTs, rated for 1200 V and 100 A pulsed, combined switching time is a mere 600 ns. Each of the IGBT switches has its own output choke.
The circuit board contains a few ICs at the data bus connector, three isolated power supplies for the six gate drive circuits. From the number of drive circuits and tracks to the IGBT gates it is clear that these 3 phased bridge IGBTs are driven with the three upper dies in parallel as the same for the 3 lower dies of the brick. The four electrolytic capacitors are connected two in series and two of those strings in parallel for 3000 uF at 900 VDC rating.
The PFC circuit board has three SKKT 122/16E thyristor half-bridge modules, rated at 1700 V and 130 A. In the lower left of the close up picture we can see PFC controls which consists of normal logic ICs and a PIC processor that is connected to the CPU on the main circuit board through the RJ22 connector.
On the upper left side of the circuit board is the various house keeping power supplies for all of the control circuitry and networking interfaces of the UPS unit.
A very modular design that was easy to take apart, but unfortunately not that great on collecting useful parts. The lack of large IGBT bricks and capacitors is the worst let down of this unit.