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Benefits of power Factor Correction between Load and Inverter?


MYBRIDH
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Hi Guys and Girls, Hope all is well.

A question I have after having a discussion about a system I need to install.  I have been advised to install , what essentially is a PFC between the inverter output and the loads.

( Device in question is a Turner Morris High Efficient Energy Saver. I would be interested to hear if anybody has any experience with these ........or has any alternate suggestions. Essentially a PFC so connected to households running older fridges, AC's, pumps , flourescent lights etc, I can see that there would be savings to be had, I will be looking into one of these.)

The gentleman advising me to do so is claiming that the inverter will be less susceptible to tripping on start up of inductive loads (and I suppose capacitive loads as well),  allowing higher base loads while maintaining reliable operation.

From the point of view of the grid supply to the inverter, I assume there wont be any real change if the inverter already does  PF correction with the inverter appearing to be a resistive load with a PF near 1.

It does make sense to me that adding the PFC before the inverter's loads would reduce the peak current demand seen by the inverter.

  • That being the case, we would see the above mentioned benefits, Right?....or am I missing something.
  • Another consideration, if the added PFC unit was more robust and capable of providing peak reactive power current  to the loads, doing the heavy lifting as it were, with the inverter only seeing the lower real power currents, would it not stand to reason that such a device could improve Inverters ability,  reliability and longevity? 

Would appreciate your thoughts guys.

 

Regards

 

 

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5 hours ago, MYBRIDH said:

From the point of view of the grid supply to the inverter, I assume there wont be any real change if the inverter already does  PF correction with the inverter appearing to be a resistive load with a PF near 1.

If it's an Axpert King in line mode (the usual mode for this model, unless you choose Eco mode), then yes, it has a PFC stage and will present a power factor of some 98% to the grid (there will always be a little distortion around the zero crossings, due to the required bridge rectifier).

But other Axpert models, and most other manufacturers' models, even those advertised as being "PF1.0", do not do this. "PF1.0" for these other Axpert models is mainly a marketing term. So for non-King models, or King models that are forced to bypass due to overload, the benefits of power factor correction will be seen at the grid connection as well. I don't know if there are many dual conversion models (using a PFC AC-DC converter followed by a DC-AC inverter) from other manufacturers.

5 hours ago, MYBRIDH said:

That being the case, we would see the above mentioned benefits, Right?

I wonder about that; it would possibly be worth a bit of research. Starting an induction motor takes about 7 x the run current, but the starting power factor is some 0.1 to 0.2. This suggests that most of the surge in apparent power is reactive, not real. So a power factor correcting machine, if capable of supplying the required start-up current, would presumably take most of the start-up load itself. (The instantaneous power would mostly flow to and from the PFC machine to the motor, and a relatively small proportion of the power would come from the input of the PFC machine). 

That does imply that the PFC device is an expensive machine, possibly more expensive than the inverter, and of course it adds its own efficiency penalties, requirements to space, maintenance, etc.

I'd be interested in the views of other, more industrially focused commentators.

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Coulomb, I appreciate your inputs thank you very much.

Considering the numbers you provided , being able to maintain unity PF should yield considerable reduction in peak current seen by the inverter......

Certainly seems like an avenue to be explored.

Does beg the question though.......if there is going to be such a benefit in the ability to curb peak start-up currents improving reliability and operation....why are inverter manufacturers not incorporating PFC's on their outputs?

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7 minutes ago, MYBRIDH said:

why are inverter manufacturers not incorporating PFC's on their outputs?

Cost, space, and weight, I would think. It basically puts two converters in the one cabinet, roughly doubling all three.

It would be on the AC input; you can't really PFC the output, without tripling the space, cost, and weight, and the benefit is to only one third of the equipment.

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True, it would add to cost space and weight.

The additional PFC would be incorporated on the output though in the sense that it is connected to the loads , correcting PF so that the Inverter itself  sees primarily resistive load. 

I dont know how susceptible inverts are to tripping or shutting down when encountering start-up currents  ,  I absolutely stand to be corrected here but sounds though it could be quite a common issue , which if curbed may allow for substantial increase in base load.

That all said assuming what I am suggesting does have merit in a theoretical sense......financial aspects aside.

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1 hour ago, MYBRIDH said:

The additional PFC would be incorporated on the output

But the PFC on the output would be an AC to DC rectifier/PFC stage, followed by another DC to AC inverter stage. Now you have the "main" inverter protected from surges, but you have another one that takes over those surges. What have you gained, apart from cost, space, and weight?

But putting it on the AC-in side, as with the Axpert King, makes sense, though it still adds cost etc.

Perhaps you're thinking about some sort of passive circuit, made up of large Ls and Cs. That can correct for current waveform distortions, but not for phase shift between voltage and current, or for surge currents, as far as I know.

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15 hours ago, Coulomb said:

 

Perhaps you're thinking about some sort of passive circuit, made up of large Ls and Cs. That can correct for current waveform distortions, but not for phase shift between voltage and current, or for surge currents, as far as I know.

Hi Coulomb. No, I am pretty certain it is a active device.

 

15 hours ago, Coulomb said:

But the PFC on the output would be an AC to DC rectifier/PFC stage, followed by another DC to AC inverter stage. Now you have the "main" inverter protected from surges, but you have another one that takes over those surges. What have you gained, apart from cost, space, and weight?

I absolutely see what you are saying, and that being the case, yes ........what is the point? 

 

So the only real gains to be had would be improving your smaller / existing inverters surge handling  ability to match that of a larger unit but at less of a cost of a larger unit or inverter upgrade.

Device label indicates 100A, which at this time I will assume to be a peak/surge rating judging by the small gauge of wiring I see in one of the images.

 

I will get back with more info, thanks Coulomb.

 

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