Re: 3phase PFC

legg wrote:
On Fri, 16 May 2008 02:27:17 GMT, Jamie Morken <jmorken@xxxxxxx>
wrote:


Hi,

A bit off topic, but I also have a split phase inverter that has a similar technique of injection, but its with the 120VAC common:

"http://www.rocketresearch.org/new/split%20phase%20240VAC%20inverter/splitphaseinverter.jpg";

The red bar is a +440VDC rail, and then there are two half bridges to
give 120VAC/60Hz 180degrees out of phase, and they are centered around
~220VDC, which is the 120VAC common, held by the middle half bridge.

Will this setup work ok, and does it have the same CMRR problems
due to the series L in the common return? The L is quite small,
probably 20uH or less for the common.

Wait a minute.

Are you saying that you intend to connect one of your inverter outputs
to hydro neutral (ie ground) ?

Might I ask, why?

Yes, the halfbridge output that is connected to hydro neutral (ground)
is there as the current return for the two 120VAC outputs, it just holds
a constant DC voltage, which the two 120VAC phases are centered around,
since 120VAC loads run from phase to neutral.

cheers,
Jamie


Unless there is some galvanic isolation somewhere back in the power
train, this will look like a short to somewhere.

If there IS isolation, you'll be driving the entire system with the
inverter 'output' voltage, where driving interphase loads normally
will only induce hf and modulation balancing errors on the system
hardware.

RL
.

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