Is PFC worth it?? - Page 1
Forum section: electronics / beginners

author: aboubkr90
author_rank: Contributor
timestamp: September 23, 2024, 01:55:53 pm
content: PFC has become the standard now, a requirement actually. But no matter how much I tried I just can't wrap my head around that mosfet switching to ground.I mean, What if we don't. Mains bulge? noise?We still have to deal with noise and nobody lost 10% of the world's energy dealing with noise!!Maybe because I come from software where efficiency outweighs functionality sometimes, But I find it really hard to accept that much wasted energy.I believe that PFC should be restricted to medical and voltage sensitive devices. I personally don't mind the lighting flickering.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 23, 2024, 02:02:30 pm
content: https://www.us.lambda.tdk.com/resources/blogs/20080208.htmlso yesi would say for critical / sensitive / or precise stuff / long term stabilityand getting rid of harmonics is very important too, telecomm / communications ..

author: Wolfram
author_rank: Frequent Contributor
timestamp: September 23, 2024, 02:25:51 pm
content: From a legal perspective, PFC is required for loads above 100 W or so, due to limits on harmonic current drawn from the mains grid.From a technical perspective, power factor correction introduces typically 1 - 10 % loss depending on power level and the technology used, while reducing input current between 25 and 50 %. For higher power loads, this puts much less of a burden on the power network, while introducing manageable losses within the product, so I suspect it would be common even in the absence of legal requirements. PFC stages also usually provide the following stage with a fixed voltage, greatly simplifying their design, and enabling efficient LLC converters to be widely used for fixed output voltage applications, while also allowing universal mains voltage input.There's also the subject of harmonics. Non-PFC loads with a capacitor input filter draw significant low frequency harmonics, leading to voltage distortion in the mains network. The overall level of harmonic currents in the supply network have to be limited in order to not induce gross mains voltage distortion, which can pose challenges for other loads on the grid.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 23, 2024, 03:04:34 pm
content: My practical experience shows that PFC-power-supplies are 50% more expensive than the cheapest non-PFC-modules but practically as efficient and mostly of much better engineering quality. I´ve seen quite a few non-PFC-modules that really had terrible EMI-emissions (especially LED drivers...) but so far most PFC-designs have been well filtered.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 23, 2024, 04:01:36 pm
content: PFC not worth it? ....this question means that you don't understand the implications of a low power factor in the electrical generation and distribution industry.For a given amount of generated, transformed and conductedvolt-amps, the amount ofwattswhich are the real power that actually performs useful work, decreases with a decreasing power factor.This fact was immediately recognized when AC power generation and distribution became mainstream. This is the reason that all utilities severely penalize the user with a low power factor load.(*)For decades, the #1 reason for a low power factor was caused by electric motors. But in the last decades, electronic loads have become ubiquitous, and the traditional rectification and filtering methods create a low power factor situation. Additionally it generates harmonic distortion which itself produces a series of very significant headaches.Think of the PFC circuit as similar to your car's catalytic converter. Yes, it may rob the engine of some power, but would you rather live with the air pollution?(*)In many countries, small users i.e. homes, are exempt.

author: MrAl
author_rank: Super Contributor
timestamp: September 24, 2024, 09:14:26 am
content: Quote from: aboubkr90 on September 23, 2024, 01:55:53 pmHi,Power factor is a smooth operation if the voltage and current are both sinusoidal. A low power factor in that case is still not too good because it draws more current than would be needed to produce the required power. Correcting the PF would lower that current.The problem here is that all the lines that bring that power in have to handle more current, and wire with more current dissipates more energy which loads the grid more than necessary, and on top of that, the power company does not get paid for that extra current. That's with pure AC loads.With non sinusoidal loads, the situation is even worse. That's because then we have currents that are not sinusoidal anymore. I good example I think is with a full wave bridge rectifier and capacitor filter. The current is almost like a pulse rather than a sinusoid, and that means high distortion as well as high peak current. Fixing that reduces the distortion as well as allows the capacitor to last longer.The formula for power factor for pure AC loads is:PF=cos(theta), where theta is the angle of lead or lag.The formula for any load is:PF=Pavg/(Vrms*Irms), where Pavg is the average power and Vrms is the RMS voltage and Irms is the RMS current.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 24, 2024, 12:03:23 pm
content: The main task of PFC is to make load looking like being pure resistive.If in 3 phase supply system you have the same resistive load at each phase their currents add up in zero wire, but as they have phase shift the sum is 0 (they are shifted by 1/3 of the period). If load in phases are not the same some current flows in zero wire but a maximum (0 load at one phase, or 0 load at two phases) is the same as in phase wires.If you have bridge+capacitor load than you get high current pulses far different than sinus. Such pulses have a big 3-th harmonic component. These harmonics adds in zero wire as previously but this time they are 'in phase' as shift by 1/3 of the main frequency period means shift for the 1 period of 3-th harmonic.To avoid fire the zero wire in all distribution should have 2..3 times the cross-section of phase wires or loads having big 3-th harmonic should be avoided. And PFC does this job.

author: madires
author_rank: Super Contributor
timestamp: September 24, 2024, 01:32:02 pm
content: Quote from: Wolfram on September 23, 2024, 02:25:51 pmIEC 61000-3-2 Ed. 5.1: PSUs >75W and LED drivers >25W

author: coppice
author_rank: Super Contributor
timestamp: September 24, 2024, 02:17:58 pm
content: Quote from: madires on September 24, 2024, 01:32:02 pmThis is probably the reason 23W and 24W LED luminaires are so very popular.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 24, 2024, 02:19:56 pm
content: I say this PFC stuff is a whole lot of bollocks that governments do just because they can.The apparent and imaginary powers are real, but that does not mean you should shove it into the faces of consumers. My vote is that the electricity company has much better opportunities to do this in an efficient way. For example by putting FPC correctors on sub stations. But also, I do not know anything about mains power instabilities and oscillations. I once talked to a guy working in the high voltage distribution stuff, and apparently it was quite difficult to keep the harmonics on the distribution net under control. (Yeah, I know, harmonics are not PFC, but bad power factor (for example triac dimmers) are a big generator of harmonics).Another idea is to let (industrial) customers pay for apparent power, instead of real power. This gives them a choice to whether they want to do PFC themselves, or let the power company do it for them. This would not work for consumers, mass produced gadgets are cheap ("price sensitive") and no house wife (or guy) is going to pay attention to the power factor of their latest gadget.Doing PFC on a house-by-house basis instead of for each individual gadget is probably also a much better solution, and cheaper in the long run, but who is going to pay for and install all those PFC boxes in each house.Edit: Coppice (below) is right, and I formulated my remark about PFC / harmonics differently.

author: coppice
author_rank: Super Contributor
timestamp: September 24, 2024, 02:31:24 pm
content: Quote from: Doctorandus_P on September 24, 2024, 02:19:56 pmEr, no. If all the harmonics in the current and voltage line up, you have a PF of 1, with a large amount of real harmonic energy. The chances of all of them lining up might be low, but the statement above is wrong.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 24, 2024, 07:44:50 pm
content: Quote from: Doctorandus_P on September 24, 2024, 02:19:56 pmOk, see how that sounds dumb?QuoteIt's been this way for decades. All industrial consumers pay for poor power factor.QuoteNobody is making individual consumers care about power factor correction. That would indeed be crazy. That's exactly why there are regulations for device manufacturers.QuoteIt seems unlikely that adding a 50 kW power supply to every house would be cheaper than devices building it in as needed.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 24, 2024, 07:54:15 pm
content: Is there anyone who is annoyed by the PFC-obligation beside manufacturers of cheap battery chargers?I can't see that PC-power supplies have got much more expensive. Yes, maybe they would be €5 cheaper without PFC, but does any private PC buyer care about this?

author: Wolfram
author_rank: Frequent Contributor
timestamp: September 25, 2024, 11:12:53 am
content: Quote from: madires on September 24, 2024, 01:32:02 pmIs that what the standard says? I'm not sure I've read the latest version, but from my memory the limits are on absolute harmonic currents and not on a given power level. Practically, capacitor input filters will fail above a certain power level in that range, but the exact value depends on smoothing capacitor sizing and ESR, so the exact transition point is not clearly defined. But if they changed the way in which this was specified, that's definitely interesting. As an example, induction stoves don't use PFC but also use very little smoothing capacitance across the bus, staying within the IEC-61000-3-2 (or -3-12 for hard-wired units above 16 A) at power levels above 2 kW.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:17:43 pm
content: Sorry for the late reply. There are a million ways to get rid of harmonics that doesn't cost 10% efficiency.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 25, 2024, 12:22:19 pm
content: Why do you assume PFC costs 10% efficiency?Modern PC power supplies keep around 90% total efficiency over a wide range of loads. Do you think all 10% of losses only account on the PFC-circuit?

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:22:55 pm
content: Fixed voltage is important for voltage sensitive device. I like it as well. But not on every device. I mean, a 4kw split-ac doesn't need it enough to lose 40-400w on it. And that's my point.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:24:53 pm
content: That's implication dependant. The extra e-waste I'm ok with. It falls into our hands and we play with it.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:32:04 pm
content: I don't agree with the correlation between power and power factor.Pollution kills people. CMI doesn't kill circuits. It reduces their stability. what I'm asking, Is stability as important to every device? Do we need to lose energy for the stability of a battery charger for example? It's dead stable, and it doesn't mind the noise.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 25, 2024, 12:33:25 pm
content: Ah AC inverters...Let´s try to see it on a wider scale: The losses of all house cabling and also of the grid transformers are generated by the apparent and not by the active power that is drawn by the devices.That means, if you improve the power factor of an AC inverter by the PFC circuit from 0.45 top 0.9 then you reduce the supply losses to their half. It depends on your cabling and grid connection how much losses there are, but it´s easily possible that the overall consumption of a house goes down by using PFC.That´s no big oil conspiracy that´s just physics.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:39:58 pm
content: Ok everyone!Your are explaining why we PFC. I know why we PFC.I'm saying there are other ways that doesn't have much impact on the efficiency of our devices. Like ferrite beads. The rest of the slow CMI spectrum, if ignored, will become white noise that will average to zero (not exactly, but close).For critical devices, where a human could die if it goes wrong, there we can PFC. and it will regulate the stable voltage the device needs to operate safely.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 12:46:06 pm
content: If I may add. I also know that mains frequency will double if we do that.Still okay.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 25, 2024, 02:05:26 pm
content: Quote from: aboubkr90 on September 25, 2024, 12:39:58 pmNo, ferrite beads do not affect power factor.I believe you are confusing power factor with EMI. They are two very different things.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2024, 02:22:12 pm
content: Simple explanation to beginners:Poor power factor means pulling large amounts of power during short moments. It can (but not necessarily) also mean of pushing some power back into grid (alternatively "borrowing" and "giving back" for no reason).Someone has to generate (in a loose way, e.g. time-shift by bidirectional storage) and transfer this power at those exact right moments your crappy contraption decides to want it. It is not that this could not be done, but more that it makes more sense to just design products in a way that such special snowflake power delivery for them is not needed.Analogy: try asking your employer to pay whole year of salary upfront and see how they like the idea. Of try asking them to pay for two year's salary in advance and promise to pay one year worth back after a while.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 25, 2024, 03:00:28 pm
content: Quote from: aboubkr90 on September 25, 2024, 12:39:58 pmWhat you propose is like have hope that car shock absorber (absorbs ms range pulses) will ensure your car be traveling strictly horizontally when you drive through hills (hour range pulses).Ferrite beads work at 100MHz..GHz while PFC eliminates 150Hz, 250Hz ,.. from 50Hz (the ratio between these frequencies is 1000000 times).

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 05:03:48 pm
content: @Andy CMI not power factor. In this post I'm trying to separate the power factor from other properties of PFC to see if the power factor specifically is worth 5-10% of the world energy.

author: aboubkr90
author_rank: Contributor
timestamp: September 25, 2024, 05:06:52 pm
content: @PGPG What I'm proposing is that the car doesn't need to move strictly horizontally.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 25, 2024, 05:09:48 pm
content: Your statement does not get true by repetition. From the power plant to the consumer the system with PFC is more efficient than without. Because transmission losses are indirect proportional to the power factor.

author: Andy Chee
author_rank: Super Contributor
timestamp: September 25, 2024, 05:43:33 pm
content: Quote from: aboubkr90 on September 25, 2024, 05:03:48 pmfor the energy generators, power stations, and power companies, it is definitely worth it.for the individual home consumer, not worth it.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 25, 2024, 05:56:01 pm
content: Simply put, the power factor has to be correctedsomewhere. This is the classic distributed vs. centralized discussion. Distributed PFC (every device having decent power factor) avoids creating a problem to begin with. Poor power factor at devices might have a tiny cost saving at the device but then the PFC has to be placed elsewhere. Classic "somebody else's problem", which is why legislation gets involved.Yes, grid-level power factor correctors are a real thing. In the past with simple linear phase-shift errors, they were simply switched capacitor banks (because inductive motor and transformer loads dominated). Nowadays more advanced semiconductor-controlled stuff because today's poor PF is a completely different thing than phase shift between current and voltage. And using home PV inverters to participate in a distributed way is a recurring discussion which has some reality in it.It is usually a good idea to avoid creating the problem in the first place. I could accept exceptions but they need to be rationalized with real calculations for total costs (including grid level power factor correction and higher transmission losses).

author: ejeffrey
author_rank: Super Contributor
timestamp: September 25, 2024, 06:23:25 pm
content: Quote from: aboubkr90 on September 25, 2024, 12:17:43 pmOf course. That includes PFC corrected power supplies. The idea that PFC costs 10% or even 5% is just wrong. For instance, the Meanwell UHP-200-24:https://www.meanwell.com/webapp/product/search.aspx?prod=UHP-200(R)is 94% efficient. You would be hard pressed to find a non PFC power supply of similar power and voltage with better than say 96% efficiency. In fact, if you look through meanwell's product line, their non-PFC power supplies are generally targeted at low cost. They actually have worse efficiency than their PFC products (more like 86-90%). I might as well claim that PFC improves efficiency by 5%! That would of course be wrong, the difference is not intrinsic to PFC vs non-PFC, it's just how the device is designed.Basically the whole premise of your claim is flawed, PFC isn't significantly less efficient even measured strictly at the point of use. When considering the generation and distribution costs PFC improves overall efficiency for medium and high power loads at least.

author: madires
author_rank: Super Contributor
timestamp: September 25, 2024, 07:06:01 pm
content: https://en.wikipedia.org/wiki/Power_factor#Importance_in_distribution_systems

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 25, 2024, 08:46:35 pm
content: Quote from: aboubkr90 on September 25, 2024, 12:39:58 pmAgain; your arguments demonstrate that you haven’t the foggiest idea how a large power generation and distribution network operates. Why don’t you research World Power Quality Standards instead of writing platitudes?A perfect example of the Dunning-Kruger effect.EDIT: I see that you registered only 2 days ago. So essentially you registered with the sole purpose of starting a controversy.

author: PGPG
author_rank: Frequent Contributor
timestamp: September 26, 2024, 09:33:13 am
content: Quote from: aboubkr90 on September 25, 2024, 05:06:52 pmI have only give a suggestive image showing how proposed by you ferrite beads are related to what PFC does.I understand that you didn't suggest that car in my example has to move strictly horizontally, specially that you suggested to use tools (car shock absorber in my example) that can't do that.

author: aboubkr90
author_rank: Contributor
timestamp: September 26, 2024, 10:12:01 am
content: @phill I'm not repeating to make it true I'm repeating so you would understand my point. 'cause nobody answered my question.@ejeffrey And some go as low as 2%. If they follow normal distribution they would average to 5%. But I can assure you they don't. The majority will be around the 10% area.@schmitt I didn't join to star a controversy, I joined to ask a question.

author: aboubkr90
author_rank: Contributor
timestamp: September 26, 2024, 10:14:24 am
content: Conclusion. After siwastaja's previous comment I imagined some local devices forming a star connection, like a brushless motor, and yeah that's insane ('cause some of them started oscillating since it is not a real star and there is no core).

author: Andy Chee
author_rank: Super Contributor
timestamp: September 26, 2024, 10:25:43 am
content: Quote from: aboubkr90 on September 26, 2024, 10:12:01 amYour question was answered multiple times.Is PFC worth it? For the power station generator, yes, it is worth it.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 26, 2024, 11:05:41 am
content: Quote from: aboubkr90 on September 26, 2024, 10:12:01 amIn the first place you repeatedly stated that PFC causes losses. That´s just not true in general. PFC creates some losses at your site, but prevents mostly larger losses somewhere else in the grid. Yes, PFC is a burden for the consumer because it makes devices a little more expensive and marginally increases the accounted power consumption. But in the end the power plant needs less fuel or can supply more customers.

author: MrAl
author_rank: Super Contributor
timestamp: September 26, 2024, 11:44:17 am
content: Hello again,One of the things that has not been directly mentioned yet is what power factor correction actually does, what it affects.First, we can view a PFC circuit as being between the power line and the product. That means it acts as an intermediary between the line and the product such as a power supply. If we look at what it does for the product, it does not do much. That's because it's not really made for improving the product, it's made for improving something about the line itself. If we look at how it affects the line, we see that it has an important function and it affects the line by a significant amount.This is why one method of correcting the power factor is done by placing a capacitor across the input line. If we think about this, the capacitor does nothing for the sine voltage, so the product does not see anything different. The line however has to constantly supply current to that capacitor and so the line gets affected by the change in current demand.In the simplest case, the capacitor just has to change the phase angle of the current from the line. That means the impedance the line sees changes, but the product does not see any change.

author: madires
author_rank: Super Contributor
timestamp: September 26, 2024, 02:06:30 pm
content: PFC also helps the device/load by optimizing the power consumption. Any reactive power created by loads has an impact on the mains installation of your building/home, i.e. you could run into wiring/breaker limits sooner than with an optimal power factor.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 26, 2024, 02:36:55 pm
content: I don't like the term PFC used as widely as it is. It refers to power factor correction as if poor power factor is a necessity and then correcting it is clearly a separate component. Sometimes this is the case, but I like the more generic concepts like "good power factor design". Requiring designs to not pull operating current in nonoptimal spikes is a sane requirement and it helps everyone.As such, I don't know any legislation which mandates use of PFC. Never heard of such requirement. They do however mandate some certain power factor (among MANY other things). You are not allowed to manufacture and sell any random crap design.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 26, 2024, 03:48:04 pm
content: @Siwastaja: Of course - I think the term "PFC" comes from AC-DC SMPS like computer power supplies where PFC generally required either a bulky and quite lossy LC-filter or an additional voltage conversion step of the kind of a power/voltage controlled step up converter before the buffer cap. These building blocks now are called "PFC".Many other appliances like induction hobs, VFDs or probably even AC inverters (roughly just a VFD with a more complicated user interface) can have a more integrated design. They either need no buffering, like the induction hob that just delivers no power during the mains zero crossings, or are designed to work with a non completely stabilized buffer voltage.Just out of curiosity: What was the power factor of an old style 3phase mercury vapour rectifier???

author: Andy Chee
author_rank: Super Contributor
timestamp: September 26, 2024, 04:14:18 pm
content: Quote from: Phil1977 on September 26, 2024, 03:48:04 pmI think the term "PFC" might even pre-date SMPS. Old fashioned inductor ballast fluorescent light tubes often had power factor correction capacitors fitted to them, particularly in factories, multi-level office buildings and shopping malls, where hundreds of fluoro tubes were used for general lighting.Multiply those installations by the hundreds in an average city and the power factor losses add up. Of course, lighting technology has since evolved to more efficient lumens per electrical watt.The type of loads imposed on power grids has changed markedly compared to, say, 1970. Fewer inductive ballasts, more capacitive SMPS.

author: coppice
author_rank: Super Contributor
timestamp: September 26, 2024, 04:23:15 pm
content: Quote from: Andy Chee on September 26, 2024, 04:14:18 pmThe term PFC predates semiconductors, going back to the earliest days of AC power engineering.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 26, 2024, 04:36:33 pm
content: Yes, thanks... In my perception PFC was always this smoothing of rectifier inputs, but of course there have been these capacitor or inductor banks for shifting phases. In german language these devices were often called "Phasenschieber <🥞> phase shifter, I first heard the term "PFC" together with SMPS.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 26, 2024, 05:17:48 pm
content: Quote from: Phil1977 on September 26, 2024, 04:36:33 pmRemember that power factor itself was defined directly from phase shift, PF = cos(phase_shift). That definition of course had to change a long time ago* so that the concept of PF could still remain valid with many forms of modern loads which can draw current peaks at any arbitrary point in time.But the concept is simple: if you try to pull a lot of current while voltage is at low point, you are transferring less power yet transferring all that current. Optimally the instantaneous current should be directly proportional to instantaneous voltage. This gives PF=1, and this gives same RMS current as if were a DC distribution system with the same RMS voltage. Running at less than PF=1 is then equivalent of running a DC distribution at lower voltage, meaning higher current and more resistive losses.*) or maybe for old-timers, it feels like it was recently

author: MathWizard
author_rank: Super Contributor
timestamp: September 26, 2024, 08:55:57 pm
content: I've made DC-DC buck and boost converters on a breadboard with all discrete parts, (except maybe a 555timer) . One of these days I want to use a small transformer like 24V, and try to make a PFC stage and forward converter type SMPS, just on a breadboard. IDK what the transistor count would be, so I might want to use some real op-amp's, and timer/counter's.

author: ejeffrey
author_rank: Super Contributor
timestamp: September 26, 2024, 09:01:21 pm
content: Quote from: aboubkr90 on September 26, 2024, 10:12:01 amI challenge you to find one in in production, general purpose power supply where you can demonstrate the use of power factor correction decreases the point of use efficiency by 10%. I don't believe they exist, and I think your are just making it up, or repeating something you heard from somebody else making it up. As an average, that is completely absurd.Also, it is 100% categorically wrong that power factor correction increases total energy use. Overall it definitely decreases energy use. We burn less fuel and install less copper and iron because large loads are required to be power factor corrected.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 26, 2024, 09:28:24 pm
content: Quote from: MathWizard on September 26, 2024, 08:55:57 pmYou may find this of interest,https://www.eevblog.com/forum/projects/power-factor-correction-discrete-control-circuit-(for-bcm)/msg4405327/#msg4405327Tim