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# Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

## Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

(OP)
Hello all,

Lately been struggling to get the answers to these questions,

Q.1 Does phase sequence/ phase shift in input AC supply affect rectified DC output in fully controlled rectifier?
Q.2 How does the triggering angle of rectifier change automatically in a practical fully controlled rectifier?
Q.3 Does its control circuit have some zero crossing detectors for input AC supply to determine its phase angle or to generate its triggering gate pulse?
Q.4 In the rectified DC output current to our battery I was able to measure the charging DC current as 2A and AC current as 18A. So I am guessing AC current which is due to the ripple needs to be minimum right? (and if not does it mean the capacitors need to be changed)?

Best!
Chris

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

1. Yes when the phases aren't 120 degrees apart.
2. It doesn't, the controller must change it for whatever reason it's programmed to change it.
3. Yes.
4. Not enough information to know.

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

(OP)
(a) But let's say if initially my phase sequence is R Y B, my triggering angle is 30 degree for T1 when R phase is connected to anode of T1. Now if I were to change my phase sequence to B R Y such that B phase is now connected to anode of T1. In the second case will the triggering angle of 30 degree for T1 give me same DC o/p as first case.

(b) Aren't the i/p ac phases always 120 degree apart? So what do you mean by your first reply.

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

Today's power distribution network is vast and interconnected, which means there are lots of things in the upstream part of the circuit, including transformers (if not m=between your ac "source" and power electronics, then almost positively between your "source" and the actual utility grid). All add their own little bit of modification to the pure AC waveform, including the possibility of non-uniform phase shift (i.e., phases are not always 120 degrees apart).

And since the zero crossings of a non-uniform phase shift don't happen equally spaced out (in time), you introduce distortion into the dc output.

Converting energy to motion for more than half a century

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

a. Changing the phase order won't affect the output waveform if the control circuit works right.

b. They should be, but aren't always.

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

On Q3: Good control units do not use zero crossing detectors, but PLL (phase locked loop)-circuits. The grid voltage might show multiple zero crossings leading to erroneous firing signals.

### RE: Does phase sequence/ phase shift in input AC supply affect rectified DC output ?

From the web, an example of a "fully controlled rectifier." is a new name for an old design of any multiple independent isolated Triacs with a shared controller and a shared ZCS. I did an 8 channel version of this back in the late '70's.

Q.1 Does phase sequence/ phase shift in input AC supply affect rectified DC output in fully-controlled rectifier?

Line and Neutral have some effects on some Triacs that prefer certain quadrants, so they may be labelled as such, otherwise, no.

Q.2 How does the triggering angle of the rectifier change automatically in a practical fully-controlled rectifier?

Yes, the control is done by changing the phase angle of Triac conduction.

Q.3 Does its control circuit have some zero crossing detectors for input AC supply to determine its phase angle or to generate its triggering gate pulse?

YES

Q.4 In the rectified DC output current to our battery I was able to measure the charging DC current as 2A and AC current as 18A. So I am guessing AC current which is due to the ripple needs to be minimum right? (and if not does it mean the capacitors need to be changed)?

The excessive AC current is an error, unless you were doing pulsed high current with low duty cycle.

I am making assumptions you know what you are doing with Triacs on chargers or any DC power supply, which normally do not go together well unless they are "dimmable". HALT! ACHTUNG!

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