| I never said the transformer had to be 50/60. Take the line, rectify it,
| then invert it at high frequency and drive the primary of a *small*
| transformer. Take the secondary, rectify it and drive a power inverter at
| 50/60. Complete isolation and no 'big transformer'.
What is the efficiency of all this conversion to and from a higher frequency?
|> So how can you produce a "grounded center tap" system with a "single,
|> larger" inverter?
|
| Ah, for that you *would* use a large 50/60 transformer as the output stage.
| Drive at 240 and have center-tapped secondary. At least that's one way.
| There may be others.
An "other" way I have in mind is a pair of synchronized 100-120 V inverters
wired in series. Ground would be connected to the center when/where that
kind of system is needed or desired.
| So that would be a compromise of either a big bulky 50/60 transformer or
| more-difficult/ less-reliable inverter design.
Are 100-120 V inverters less reliable? For a given UPS capacity this would
involve 2 inverters at half the capacity, of course.
|> If the derived system is _not_ a "grounded center tap" type system,
|> then that
|> would complicate the bypass switching, because that would mean a
|> sudden shift
|> in grounding relations when the bypass is engaged.
|
| If the service is for a grounded center tap, then simply ground the center
| of the inverter output (either center-tap of power 50/60 transformer or leg
| between your two-inverter design). With *just* a ground connection on the
| secondary side, there isn't any interaction with the mains.
|
| Obviously if the unit is to be used in a variety of service, the exact
| grounding of the output has to be user configurable. But if the output is
| isolated from input using either a high-frequency or low-frequency
| transformer, you can ground any *one* point of the output with no
| ill-effects.
|
| (well, grounding one side of a power inverter so it 'looks' like a
| grounded-on-one-side UK supply, *may* cause some noise issues and EMI that
| affects other equipment, but the basic inverter would still be operational).
The goal I'm looking at is a UPS that can be connected to either kind of power
system. In the case of single ended, either end might be grounded (so it can
be used in continental Europe and similar places with reversable plugs). In
the case of center tap grounded, only the 2 hot wires are coming in, and the
neutral is not (pure 240V American style). The output should match the input
system, and it should be automatically done correctly and safely. That means
the grounding conductor would be connected at the appropriate point on the
output. In the case of American center tapped 240V, the point between the
two inverters would be grounded, but no neutral grounded conductor would be
needed since the intent is to provide 240V (200V in Japan) the same way it is
available from the supply. In the case of single ended, the correct output
conductor has to be grounded such that when the bypass switch is engaged, the
grounding status does not change. There should be NO "ground shift". That
would mean opening the grounding conductor and closing the neutral conductor
at the same time. But should this be an open transition to ensure there is
no issue with "downstream double bonding"?
| then invert it at high frequency and drive the primary of a *small*
| transformer. Take the secondary, rectify it and drive a power inverter at
| 50/60. Complete isolation and no 'big transformer'.
What is the efficiency of all this conversion to and from a higher frequency?
|> So how can you produce a "grounded center tap" system with a "single,
|> larger" inverter?
|
| Ah, for that you *would* use a large 50/60 transformer as the output stage.
| Drive at 240 and have center-tapped secondary. At least that's one way.
| There may be others.
An "other" way I have in mind is a pair of synchronized 100-120 V inverters
wired in series. Ground would be connected to the center when/where that
kind of system is needed or desired.
| So that would be a compromise of either a big bulky 50/60 transformer or
| more-difficult/ less-reliable inverter design.
Are 100-120 V inverters less reliable? For a given UPS capacity this would
involve 2 inverters at half the capacity, of course.
|> If the derived system is _not_ a "grounded center tap" type system,
|> then that
|> would complicate the bypass switching, because that would mean a
|> sudden shift
|> in grounding relations when the bypass is engaged.
|
| If the service is for a grounded center tap, then simply ground the center
| of the inverter output (either center-tap of power 50/60 transformer or leg
| between your two-inverter design). With *just* a ground connection on the
| secondary side, there isn't any interaction with the mains.
|
| Obviously if the unit is to be used in a variety of service, the exact
| grounding of the output has to be user configurable. But if the output is
| isolated from input using either a high-frequency or low-frequency
| transformer, you can ground any *one* point of the output with no
| ill-effects.
|
| (well, grounding one side of a power inverter so it 'looks' like a
| grounded-on-one-side UK supply, *may* cause some noise issues and EMI that
| affects other equipment, but the basic inverter would still be operational).
The goal I'm looking at is a UPS that can be connected to either kind of power
system. In the case of single ended, either end might be grounded (so it can
be used in continental Europe and similar places with reversable plugs). In
the case of center tap grounded, only the 2 hot wires are coming in, and the
neutral is not (pure 240V American style). The output should match the input
system, and it should be automatically done correctly and safely. That means
the grounding conductor would be connected at the appropriate point on the
output. In the case of American center tapped 240V, the point between the
two inverters would be grounded, but no neutral grounded conductor would be
needed since the intent is to provide 240V (200V in Japan) the same way it is
available from the supply. In the case of single ended, the correct output
conductor has to be grounded such that when the bypass switch is engaged, the
grounding status does not change. There should be NO "ground shift". That
would mean opening the grounding conductor and closing the neutral conductor
at the same time. But should this be an open transition to ensure there is
no issue with "downstream double bonding"?