Active power factor correction - Page 1
Forum section: electronics / projects

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 02:09:51 pm
content: Hi everyone,My father has installed a solar powered water pump system in community nearby and he is experiencing some problems with the 48VDC->220VAC inverter he is using. The system consists of 4x 350W solar panels, 4x 12V 120Ah lead batteries connected in series, a 48VDC->220VAC inverter, a single-phase -> three-phase frequency inverter and a 3HP three-phase water pump (block diagram attached).The 48VDC->220VAC inverter has a sinusoidal output and is rated for 3KVA continuos so in theory it would be enough for the 3HP (2237W) load. But as you may guessed, the frequency inverter has a pretty low power factor due to AC->DC rectification (~0.6) and it surpasses the power capability of the first inverter. I am trying to think a practical solution to this and these are what I got so far:Get rid of the 48VDC->220VAC inverter and replace it with a DC-DC boost converter;Modify some what the 48VDC->220VAC inverter to output a square wave;Design an external active power factor correction device for the frequency inverter.1) would be the best engineering solution, but designing and building such DC-DC converter wouldn't be easy or cheap, 2) is risky and could reduce the efficiency of the first inverter (it has a 60Hz laminated steel core transformer that might not like high frequency harmonics). I'm gravitating towards the 3) solution, but I don't have any experience designing active pfc systems (let alone for a 2.3KW load), do anyone know a good literature about this?If someone can think of a better solution do this I would appreciate.Thanks!

author: Siwastaja
author_rank: Super Contributor
timestamp: September 06, 2020, 02:14:53 pm
content: Boost 48V to the DC bus voltage (320VDC) of the VFD. 48->320 is such a high ratio that bog-standard boost won't be doable (or far from optimum), so you need a different topology such as center-tapped boost or flyback or half/full bridge transformer based, but the end result is still fewer components and less conversion losses than what you have now.Thinking about it, maybe your sine wave inverter does have this boost stage already? You could bypass the output inverter stage and directly connect the 320V-ish DC bus of the sine wave inverter to the rectified DC bus of the VFD.Any of this is far from effortless, of course.

author: TheMG
author_rank: Frequent Contributor
timestamp: September 06, 2020, 02:47:20 pm
content: Quote from: Siwastaja on September 06, 2020, 02:14:53 pmHe did mention the inverter has a 60Hz transformer so it's likely not a SMPS type, the 60Hz transformer does the stepping up from 48V PWMd sine to 220V, thus no high voltage DC buss to hook onto internally. Doing such a thing would also likely bypass any kind of over current protection the inverter may have.The best and easiest solution of course would be to replace the motor with a 48V DC equivalent. But I guess this is not feasible because you already have the 3-phase motor and motors that size aren't cheap.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 02:48:58 pm
content: Hi Siwastaja,Quote from: Siwastaja on September 06, 2020, 02:14:53 pmYes, I was thinking of using a coupled inductor boost converter so the PWM duty-cycle would be near 50%. A flyback topology would be a good bet too.Quote from: Siwastaja on September 06, 2020, 02:14:53 pmUnfortunately, this inverter uses a huge 60Hz transformer to step-up the voltage (48VDC -> 34VAC 60Hz -> Transformer -> 220VAC 60Hz) so I can't take this route.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 02:54:32 pm
content: Quote from: TheMG on September 06, 2020, 02:47:20 pmYes, unfortunately I don't think there are any off-the-shelf 3HP 48VDC motors were I live. Another concern is maintenance, DC motors require periodic replacement of its brushes, while induction motors are more robust in this regard.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 06, 2020, 04:20:50 pm
content: What kind of topology is this inverter using? How does it boost to 220V and them, does the AC switching?I've read you're running the motor with a VFD drive, so you could tap the high voltage dc of the inverter and feed the VFD straigh, you may have a DC+ and DC- in the VFD or just feed it through the AC terminals, would be fine.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 04:45:39 pm
content: Quote from: rvalente on September 06, 2020, 04:20:50 pmAs I said previously, the 48VDC->220VAC inverter doesn't generate high-voltage DC, it converts to low voltage AC (PWM) and feeds directly to a big 'n old 60Hz transformer that steps-up the voltage to 220VAC.

author: ConKbot
author_rank: Super Contributor
timestamp: September 06, 2020, 05:05:06 pm
content: Since your load is relatively fixed, an input inductor would do fine for improving power factor and making the input cirrent less spiky. Documentation for VFD line reactors should help you size one appropriately. It may not be the most ideal solution, but it is a known off-the-shelf solution.Given the equipment on hand, it may be the cheapest solution too.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 06, 2020, 05:09:58 pm
content: Adjusting the VFD settings to ramp up the pump more slowly, reducing maximum torque setting, and/or limiting maximum speed to a lower value, could let it run while still providing enough pumping action. Have you looked at this?

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2020, 05:56:30 pm
content: Quote from: Palmitoxico on September 06, 2020, 02:09:51 pmI'm not sure what theory you are using, but you need to re-examine that statement in practice. It looks to me like you are way underpowered. Many inverters are fine with power factor issues, especially the low-frequency transformer type. In some cases they may have a kVA rating and a separate, lower watt rating--you might check that first--but in any case, your 3HP pump likely draws a lot more power than you think, not even considering startup transients.You'd be best off measuring the actual power used by the pump under operating conditions, but you can get in the ballpark by taking into account theefficiencyof the motor and itsservice factor.I don't know your details, but a bog-standard pool pump motor (very common here in SoCal) might have an efficiency of 65% and a service factor of 1.5. So take your 2237W x 1.5 / 0.65 and you have 5162W maximum power, assuming the motor is loaded that much and has those specs. Your numbers will likely be different.Your square wave mod idea may have some merit--but it would certainly be an experiment, and sometimes experiments end in smoke. If you can use the motor drive inverter to slow down the motor, even from 60Hz to 50Hz, you may reduce the power requirement enough to allow the system to work. Fluid pumps have a third-power exponential rise in power with speed--cut the speed in half and the mechanical power needed goes down 8-fold. Going from 60Hz to 50Hz will lower the motor speed to 3000RPM (if it was 3600 to begin with) but save you 40% in power--in theory.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 06, 2020, 06:42:44 pm
content: Share the equipment manuals, maybe there is a way

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 06:52:31 pm
content: Quote from: Siwastaja on September 06, 2020, 05:09:58 pmWe already ramp the VFD (10s ramp) and have no problems at startup, then after ~3 minutes running the inverter shuts-down. Next week we will do some measurements (mosfets temperature, transformer temperature, more accurate power measures). We configured the VFD to deliver a 54Hz output reducing the pump power and it increases the running time to ~15 minutes. It may be that the thermal protection is not well adjusted because my father said it seemed not too hot upon first inspection, but we need to measure it.Quote from: ConKbot on September 06, 2020, 05:05:06 pmHumm, I will check that, maybe a passive PFC solution may be enough. I couldn't easily find a suppliers for such reactors, I may have to request some place to custom built it.Quote from: bdunham7 on September 06, 2020, 05:56:30 pmI'm pretty sure that the motor is 3HP rated and the efficiency would impact only the pumping capacity (3HP mechanical from the shaft, 2HP pumping power), but I would try to measure it more accurately with my oscilloscope and be very careful to isolate the ground and not blow up my probes (I don't have a proper power meter at hand).

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 06, 2020, 06:54:27 pm
content: Quote from: bdunham7 on September 06, 2020, 05:56:30 pm65% for the motor sounds really low (most motors of that size are in the 80s), but might be right for the motor+pump combo.Would it be possible to replace the motor with a BLDC?

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 07:10:57 pm
content: Quote from: rvalente on September 06, 2020, 06:42:44 pmWe only have the documentation of the VFD (WEG CFW500):https://static.weg.net/medias/downloadcenter/h21/h6b/WEG-CFW500-programming-manual-v3.2x-10006739425-en.pdfhttps://static.weg.net/medias/downloadcenter/hd7/h49/WEG-CFW500-user-manual-10001278006-en.pdfThe step up inverter is custom built, after we measure all parameters we will contact the manufacturer.Quote from: NiHaoMike on September 06, 2020, 06:54:27 pmIt would be relatively expensive to do it right now, I don't think we can easily source a powerful enough brushless motor here (we would probably need to import and pay insanely high taxes and fees).

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2020, 07:34:47 pm
content: Quote from: Palmitoxico on September 06, 2020, 06:52:31 pmIt doesn't work that way. A 3HP motor should produce up to 3HP (x the service factor if greater than 1) at the shaft. The amount of electric power in watts required to power the motor at a given mechanical power level determines the efficiency. So if your motor is loaded at 3HP and is drawing 3KW, it has an efficiency of 74.6% at that operating point. The efficiency will vary widely according to load, input voltage, etc. I think it is very unlikely that your motor would exceed 75% efficiency at full rated load, especially factoring in the losses in the VFD. It is possible, and even likely given that the system works at all, that the load of the pump is less than 3HP so that your motor is not fully loaded. It is still a marginal system as any change in pumping conditions could increase the load.

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2020, 07:46:00 pm
content: Quote from: NiHaoMike on September 06, 2020, 06:54:27 pmNot at full load, depending on the design and age. Replacing pool pump motors with more efficient designs as they come out is a big business here in SoCal. I have a two-speed one in the 80s, the one it replaced was 2HP and 65% at best. Now they have nice 3HP variable-speed models at about 90%--probably just what the OP needs. 3HP nameplate, 92% efficiency and it still needs 3.2kW supply.https://www.pentair.com/en/products/pool-spa-equipment/pool-pumps/intelliflo_vsf.html

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 08:15:28 pm
content: Quote from: bdunham7 on September 06, 2020, 07:34:47 pmHumm, I don't know exactly the VFD efficiency, but I imagined that a three phase motor of such power would be > 85% efficient at nominal power. Of course the pump efficiency would be significantly lower (it is a 3 stage pump, it needs to pump water up to > 50m + fluid viscosity losses). That said, I don't believe it needs to operate full power, but I need to do more measurements to confirm.

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2020, 08:24:58 pm
content: Quote from: Palmitoxico on September 06, 2020, 08:15:28 pmIs that 50m distance or height? Does the motor have a data plate?You really can't talk about pump efficiency in the same way you do motor efficiency. The amount of recoverable work in any pumping system is usually pretty low unless you go to great lengths to reduce losses--an energy storage system, for example. And many systems, like my pool, have 0% efficiency because there is no recoverable work done--the water stays in the pool--and all of the pumping energy is lost at one point or another. And, as far as your electrical system is concerned, the pump efficiency is irrelevant. You could be driving a friction brake with it and the motor/VFD/inverter/batteries would neither know nor care.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 08:43:30 pm
content: Quote from: bdunham7 on September 06, 2020, 08:24:58 pmSorry, I wasn't clear, 50m height (~400m distance). Yes, the total efficiency doesn't concern the inverter provided that its output is 3KVA maximum. Let me search for a photo of the motor data plate.

author: CoteRotie
author_rank: Contributor
timestamp: September 06, 2020, 09:23:46 pm
content: There are several topologies that could work, but a flyback is generally limited to maybe 200W max, and I wouldn't even go that high. Anything in the KW range is full-bridge or PSFB territory, though you could conceivable do a tapped inductor boost at relatively low frequency, and several other topologies could potentially work.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 06, 2020, 09:33:49 pm
content: Here is the motor plate (attached).REND: Rendimento = EfficiencyFS: Fator de Serviço = Service FactorFP: Fator de Potência = Power Factor

author: bdunham7
author_rank: Super Contributor
timestamp: September 06, 2020, 10:30:52 pm
content: That helps a lot. It is a brand new, very efficient motor, so going to a BLDC setup isn't going to help all that much. It's interesting that they list 50Hz specs, although there doesn't seem to be any real design involved--almost any 60Hz 3-PH motor would behave similarly. Note the 1.00 service factor at 50Hz.Does this motor come attached to the pump as a unit or are they two separate items that you have combined? If the pump/motor is sold as a unit, does it have specs for flow and head pressure?So I get 3288kVA and 2926W at full service factor load at 60Hz, not counting any VFD losses or tolerances in specs for the motor or the inverter--both of which could be rated optimistically. Better than my earlier estimates, but still either cutting it close or just too much, depending on the loading. The 0.6 PF of the VFD may not be helpful, but you're still at or near the limits. The fact that reducing the VFD frequency to 54Hz extended the run time seems to back that up.One other thought--you mentioned that the pump ran for 15 minutes at 54Hz. If the input to the inverter is, say 3.2kW, that is a roughly 66A load on the batteries, more than C/2. Have you checked to see how low the battery side of the inverter is going? That 120Ah is likely the C/20 rate, at more than C/2 you are pushing the limits there too.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 06, 2020, 11:09:43 pm
content: Also, what kind of lead acid battery?AFAIK there are 3 basic types of lead acid batteries: automotive, stationary and traction. As described, you're using 120Ah, so i believe they're automotive, right?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 06, 2020, 11:17:41 pm
content: Quote from: rvalente on September 06, 2020, 11:09:43 pmMost likely deep cycle.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 06, 2020, 11:55:55 pm
content: The CFW500 has a bunch of nice features, had you ever checked the motor power on the VFD to see how much do you really need?If yours have the plug-in card you can connect to the superdrive G2 software and monitor it.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 06, 2020, 11:56:31 pm
content: I'd say automotive, deep cycle batteries here are not common at all and if you could find stationary ones here they're pretty price

author: TheMG
author_rank: Frequent Contributor
timestamp: September 07, 2020, 12:29:49 am
content: Quote from: bdunham7 on September 06, 2020, 10:30:52 pmThat is definitely something to consider. At a discharge rate of C/2, the effective usable capacity becomes approximately half of the C/20 rating for most AGM deep cycle batteries. So about 60Ah is the most you're going to get out of a set of new, healthy, fully-charged 120Ah batteries. Less than an hour of pump run time with that setup, on brand new batteries (not accounting for input from the solar panels).

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 07, 2020, 12:41:54 am
content: Quote from: bdunham7 on September 06, 2020, 10:30:52 pmWe bought the pump + motor in a single unit, I've attached the flow / pressure relationship for our model (now I don't remember if the model we have is the ME-AL/BR 1630 or ME-AL/BR 1630V). Captions (attachment):Potência (cv) = Power (hp)Estágios = StagesMonofásico = Single-phaseTrifásico = Three-phaseØ Sucção (pol) = Ø SuctionØ Recalque (pol) = Ø Repression ??Pressão máxima sem vazão (m.c.a.) = Maximum pressure without flow (water column meter)Altura máxima de sucção (m.c.a.) = Maximum suction height (water column meter)Ø Rotor (mm) = Ø Rotor (mm)Altura Manométrica Total (m.c.a.) = Total manometric height (water column meter)Vazão em m³/h válida para sucção de 0 m.c.a. = Flow in m³/h valid for a 0m water column suctionThe load was split between the solar panel and the batteries at the time my father was testing, but the voltage was stable arround 47.5V running. This system will work only during the day intermittently, 40% max depth of discharge to extend the batteries' longevity.Quote from: rvalente on September 06, 2020, 11:56:31 pmNo, we bought stationary batteries from Moura. Automotive batteries would have a poor longevity. Yes those were more expensive but not by a huge margin.Quote from: rvalente on September 06, 2020, 11:55:55 pmI don't think we have the model with this plug-in card.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 07, 2020, 12:47:21 am
content: One correction, we are using4x400Wsolar panels, we measured a total output of 1500W at peak sun light. The total pump running time for the day should be about 3h at a reduced power (3HP is more than we need).

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 07, 2020, 12:48:35 am
content: Quote from: TheMG on September 07, 2020, 12:29:49 amSo in summary, either the pump is too big or the rest of the system is too small.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 07, 2020, 12:51:56 am
content: Nice, you've got yourself nice batteries.Check P0010, its motor power and see how much you're truly using.About the VFD, did you filled all the motors parameters P399 and so on...P202, V/F or VVF? The standard is V/F and it has a huge impact in current, specially at start-ups.Did you run the auto-tuning? P408?Have a look at Weg Pump genius technology, i'm not sure if your drive has such technology but is specifically made for reducing pumps power usage.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 07, 2020, 01:01:37 am
content: Quote from: rvalente on September 07, 2020, 12:51:56 amMy father has configured the VFD following a guide from WEG, I don't know what parameters he put at the V/F ramp. I don't think our VFD supports this 'WEG Pump Genius' but I may have a closer look.Nice to know about P0010, next time we will check it.

author: bdunham7
author_rank: Super Contributor
timestamp: September 07, 2020, 01:15:53 am
content: Quote from: Palmitoxico on September 07, 2020, 12:41:54 amDo you know what the actual output pressure at the pump is when it is running? Is there any significant inlet suction due to height or filtration?

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 07, 2020, 01:22:59 am
content: Quote from: bdunham7 on September 07, 2020, 01:15:53 amI'll ask my father these questions tomorrow, but I think he measured 6 bar at the pump output.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 07, 2020, 09:20:00 pm
content: As the thing is solar powered I assume intermittent use.A simple solution may be to adjust the settings of the 3-phase inverter.Just run your pumps at lower rpm, but for a longer time to do the same amount of work. this reduces the strain on the 48Vdc -> 220Vac inverter.I do not know what this would do to overall efficiency of the system though. It may get better or worse.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 07, 2020, 09:56:36 pm
content: Quote from: Palmitoxico on September 07, 2020, 01:22:59 amConfirmed, it is running with 6 bar at the pump ouput. The pump is placed about 1m in height from the aquifer, the filter is very coarse, so I don't think it interferes to much.Quote from: Doctorandus_P on September 07, 2020, 09:20:00 pmYes we will run at a lower rpm to limit the power requirement.My father contacted the manufacturer of the 48VDC -> 220VAC inverter today and the manufacturer told that the transformer temperature switch might be the problem by been too conservative. The power electronics, he said, should be fine because it was designed to handle up to 5KVA. He recommended placing the temperature sensor in a different location, so we'll try this next week probably.As soon as we get new data I'll post here.

author: bdunham7
author_rank: Super Contributor
timestamp: September 07, 2020, 10:15:44 pm
content: Quote from: Palmitoxico on September 07, 2020, 09:56:36 pmThat certainly is helpful--and more in line with margins that keep things reliable.Did you determine which model pump you have? I looked at the flow/pressure chart and I'm hoping you don't have the 'V' model, unless you might need more pressure at another time. Fluid pumps have a power/flow curve that varies with design, but max head pressure is not usually the highest power point--and in your case, the maximum pump load might be somewhere in those asterisks. Slowing it down will shift things to left.Another thought I had was that it might be easier and safer to check the inverter input current. You can then directly see how the various speed selections affect input power. I'm thinking if you can stay under 60A input you'd be in good shape.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 08, 2020, 05:41:32 pm
content: Quote from: bdunham7 on September 07, 2020, 10:15:44 pmConfirmed here it is theME-AL 1630model without the 'V' (AL stands for aluminium shaft and BR for bronze shaft).Is too late now to change our system but I came across an interesting product, it consists of a smart solar powered VFD, no batteries required:https://www.usfull.com/wp-content/uploads/2016/11/Fullwil-solar-pumping-system.pdfOf course, you need enough solar panels in series to provide the necessary DC voltage so the inverter can output 220VAC. From what I read, it controls the output power by changing the AC frequency, so it can do some sort of MPPT to better harness the solar panel power.And amazingly,I can buy it locally!

author: bdunham7
author_rank: Super Contributor
timestamp: September 08, 2020, 06:01:49 pm
content: Is this system an 'on demand' pump or an 'as available' system? If you get the inverter sorted, it actually seems a pretty good setup for only 4 panels.I'd suggest you characterize the pumping performance by measuring the actual flow at various speeds to see what is most efficient in liters per watt-hour.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: September 08, 2020, 06:24:43 pm
content: Quote from: bdunham7 on September 08, 2020, 06:01:49 pmIt is an 'as available' system. It pumps the aquifer water in to a reservoir for later use. It is intended to replace the previous gas powered pump (the gas pump will only be used when there isn't enough sun light to charge the batteries).Quote from: bdunham7 on September 08, 2020, 06:01:49 pmRight, we will try measure it.

author: Palmitoxico
author_rank: Regular Contributor
timestamp: October 04, 2020, 04:26:18 pm
content: Hi everyone!Just a quick update, we positioned the inverter's transformer temperature sensor in a different place as the manufacturer recommended and it has been working very well last 3 weeks. The pump is operating at 56Hz and 1.4 - 1.5 kW as showed by the VFD (parameter P0010). We couldn't measure the total flow yet (a water flow meter will be installed soon), but it seems enough for now.I attached some pictures of the system if you are curious.Thank you very much for all your suggestions!

author: rvalente
author_rank: Frequent Contributor
timestamp: October 07, 2020, 12:44:28 pm
content: It is great that it have been working for 3 weeks now.The good thing is, there are lots of room for improvements there.