Power Electronics

Generally speaking two phase power is actually a single phase system. It takes 2 phases
in and produces single phase out.

Start with one phase -


Two phase -



Three phase -



So you build a truth table that passes DC source to load with the requisite
polarity maintained across load.

Hint, a three phase system requires 3 sets of H bridge switches since there are
3 phases out each at different angles. The switches for each phase controlled
by a phase shifted signal for each phase so that 120 degrees is maintained
between switches.


Regards, Dana.

danadak said:

Generally speaking two phase power is actually a single phase system. It takes 2 phases
in and produces single phase out.

Click to expand...

Household power is not correctly called two-phase.
It's called split-phase with one phase 180° out-of-phase with the other, (generated from a 220V center-tap transformer output with the center-tap as the neutral).

True two-phase has one phase 90° from the other, and three-phase has the phases 120° from each other.

crutschow said:

Household power is not correctly called two-phase.
It's called split-phase with one phase 180° out-of-phase with the other, (generated from a 220V center-tap transformer output with the center-tap as the neutral).

True two-phase has one phase 90° from the other, and three-phase has the phases 120° from each other.

Click to expand...

Agree the def is a problem. Problem is the electrician world normally refer to
220 by taking about multiple phases. Unlike 110 as single phase. I think any
two sources with a non zero phase, but same waveshape, is multiphase, not just
90 degrees.

Here is one def -

In electrical phase it is the expression of relative displacement between waves that have the same frequency. There are two different ways of looking at phases. First, it is when the voltages are out of phase with each other, as with three-phase power, and second, when the voltage is out of phase with the current.

Click to expand...

And this def over at Wiki - https://en.wikipedia.org/wiki/Phase_(waves)



Regards, Dana.

danadak said:

I think any
two sources with a non zero phase, but same waveshape, is multiphase, not just
90 degrees.

Click to expand...

I never said that it had to be 90° to be multiphase, only that 2-phase is normally 90°.
Also, household current is not multiphase, it is split-phase.