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Author Topic: Controlling a wind turbine  (Read 13412 times)
stephendv
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« on: July 08, 2014, 09:50:14 AM »


It's that time of year again where I uhm and ahh about adding a wind turbine to the solar PV system.  One of the complications is that I'm using a raspberry pi to control the midnite classic charge controller so that it doesn't do a full charge every day, instead if the battery SoC is high then it forces a float and it could go straight to float for 5 days in a row without doing a bulk+ absorb.  This means that the standard way of connecting a turbine to the battery + a diversion controller to the battery won't work, because I have no way of programmatically controlling the diversion controller to match the midnite classic.

So someone on the midnite forum suggested using a 3 phase SSR and connect it to 3 dump load resistors directly to the turbine's 3 phase output before rectifying.  Then having the built in relay on the classic turn on the SSR when the classic goes to float.
If the resistors are sized correctly, would there be any problems with instantly switching them on while the turbine is turning?
One of the classic's relays can also be configured for PWM output, so could I use this to directly control the SSR so that the resistors are powered on more gradually?

Any other ideas on how to control the turbine and prevent overcharging, but still allowing me to set custom charging modes via the rPi?

The turbine I'm considering is rated at 1kW at 10m/s and 1.5kW at 12m/s and the battery is 700Ah C5, so even at full tilt with no regulation it would only push 4% charging rate into the battery which is below the 5% that the battery manufacturer recommends for limiting absorb and EQ charging currents.



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« Reply #1 on: July 08, 2014, 10:05:38 AM »

Believe it or not Stepen,
                             I might be able to help but I am off out to play with my toys. I will get back to you later.
                                                           Biff
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« Reply #2 on: July 08, 2014, 10:37:55 AM »

Biff, I'll be waiting in antici






pation
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Eccentric Anomaly
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« Reply #3 on: July 08, 2014, 11:00:00 AM »

Couldn't the rPi turn on something more useful (perhaps an AC load) if it knows what's going on? It'd have to know the current coming from the turbine, of course, but adding some sensors for that shouldn't be too difficult. As you say, the turbine is not producing a huge amount compared with the capacity of the batteries so the load doesn't have to match terribly well.
« Last Edit: July 08, 2014, 11:09:24 AM by Eccentric Anomaly » Logged

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stephendv
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« Reply #4 on: July 08, 2014, 11:16:14 AM »

Couldn't the rPi turn on something more useful (perhaps an AC load) if it knows what's going on? It'd have to know the current coming from the turbine, of course, but adding some sensors for that shouldn't be too difficult. As you say, the turbine is not producing a huge amount compared with the capacity of the batteries so the load doesn't have to match terribly well.

Yes yes, absolutely.  I neglected to mention an important part of the Grand Plan  Grin 

The rPi will monitor loads and production and then turn on opportunity loads in the house.  The complication is that the house is about 300m away and has another media pc with ciseco RF controller and RF relays to control the loads. So from the rpi it's: wifi to media pc then RF to relays.  When the opportunity loads managed by the rpi all work as expected then everything is fine, but given the number of components in the system and the two wireless links there's scope for things to go wrong.  With a purely solar solution, when loads don't turn on it's really not a problem, but with a wind turbine it could be one.

The aux relay on the classic + SSRs (or some other system) will be mounted right next to the batteries and independent of any PCs/rpi and what not so it should be able to kick in and save the turbine and batteries if everything else fails.
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« Reply #5 on: July 08, 2014, 02:15:18 PM »

H,mmmmm,Well.
                 Well the first thing you have to realise is that 1kw of wind is going to spend the whole summer or sunny weather stopping and starting.The PV will control everything. At the moment the PV can allow your generator to start up if your voltage drops.Wind is fickle and is not as stable as pv or hydro,+ you can switch pv off but wind has to have an outlet or a dump load and that is  the catch. The dump load brakes the turbine.
  So if you send your little 1kw up on a sunny day,it will spend the whole day taking off at speed when the sun goes in behind a cloud but then  when the sun shines the turbine has to brake.
 I strongly suspect that my Yang-Shen,s bearings were helped on their way to the great bearing heaven in the sky by spending a good 10months stopping and starting non stop because I allowed it to stay up competing with the PV.It would have been fine if we had some where to put all the electricity so that it did not have to brake every second but lowering the turbine was the only answer. However, i faffed about until finally the bearing began to growl and then I lowered it. I have plans for a tilting tower,one that can send the lump up and down in seconds with one hand. I plan to have everything up and working by the end of September. The simplest method is the best.
 Keep your wind turbine well protected but ready for action and in the evening when the sun goes down,swing it up into position and relax.The big lads like Paul have more powerful wind turbines and the sun don,t get to shine quite as much on our latitude as it does down your way.
 Russ has a 1kw and he has a lot of trouble sorting out the control. If you have the constant demand that will keep the turbine loaded,then you do not have a problem but once the load goes off and they will,the problems rear their ugly heads.
       This has been my experience.I had excellent controllers and dump loads but I still managed to fry the grease out of the bearings.
  I know there are many who want to keep the wind turbine errect but I would argue that if your water is boiling hot and all the other dump load exits are occupied,lowering the turbine is the simplest and best answer as far as I can see.
   Perhaps you might be able to organise some way of controlling the lowering and raising from your laptop or mobile phone.
                                                    Biff
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billi
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« Reply #6 on: July 08, 2014, 05:55:22 PM »

Quote
Any other ideas on how to control the turbine and prevent overcharging, but still allowing me to set custom charging modes via the rPi?

The turbine I'm considering is rated at 1kW at 10m/s and 1.5kW at 12m/s and the battery is 700Ah C5, so even at full tilt with no regulation it would only push 4% charging rate into the battery which is below the 5% that the battery manufacturer recommends for limiting absorb and EQ charging currents.



Stephen,
Have i not a glue  what  a "rPi"  is  ..... but  why not dump AC power  via your Sunny Island  ?  

Also i hope you go for AC coupling with the turbine  ? Even those cheap  SUN G  GTI for wind  they have   a dump load relay  

I do not use this GTI dump relay  in my setup , cause i dump via the Victron AC Inverter  

I am quite pleased with my setup   to integrate a GTI  for  the turbine ( better than before with only charge controller )

Up to 600 watt  from my Turbine (1.5 kw rated) go via the GTI direct into the house  or back-feed by the Victron into the battery , all surplus on windy days goes then into the battery via charge-controller

But  i am sure you know  this ....



Regards
Billi




* system.jpg (119.94 KB, 992x780 - viewed 304 times.)
« Last Edit: July 08, 2014, 07:18:29 PM by billi » Logged

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« Reply #7 on: July 08, 2014, 07:04:18 PM »

an alternative view.  Could you not set up your control system so during the summer the WT always dumps its load somewhere (water heating or hot tub?) during the day, then at night let any power from the WT go to the charge controller.
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stephendv
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« Reply #8 on: July 08, 2014, 07:17:16 PM »

Biff, I'd really like to be able to control the turbine electrically- hoisting it up and down just because the dump loads are full won't fly around here- I want less work, not more!  Grin
So if dumping on the AC side of the turbine will cause too much starting and stopping, then I could instead dump on the AC inverter side as billi suggests.  Two ways to turn this dump load on would be through the midnite classic's relay or through the sunny island's relay.  But the SI has quite limited relay settings for this, e.g. it can turn a relay on based on battery SoC or based on whether Absorb is active, but not based on float!  I guess I could wire the two relays in parallel so it will turn on the dump either during absorb or when battery is more than 95% SoC.

Billi, thanks for mentioning the SUN G inverters, I didn't realise that they had a built in overvoltage and dump load facility.
I've been strongly considering the AC coupling route but have even more questions and doubts than the DC route:

- I don't know if it's possible to turn the Sunny Island's frequency shifting off or not.  Because if it's on, then it will kick out the GTI and the turbine will spin up and then engage the dump load so it might constantly switch between on and off and cause wear on the turbine.

- With AC coupling I can put the turbine in a much better spot which is on the top of a small hill and the highest point for a few hundred meters.  BUT I'm concerned about lightning and since it will be AC coupled a lightning strike would fry everything.  I suspect that if lightning hit a DC connected turbine it wouldn't be that bad (?).

- Are those Sun G inverters high quality enough to trust with a wind turbine?  If the inverter dies in a strong wind then it's likely that the turbine will too because there'll be no speed control.

And finally, AC coupling means buying the additional inverter whereas on the DC side I wouldn't need anything, not even a controller, just direct to the battery.  All of the non-chinese inverters I've seen also need a wind controller box, which then brings the price of the inverter+controller to more than the turbine itself!   But with the sun G it seems affordable, so there's just the lightning issue to think about.
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« Reply #9 on: July 08, 2014, 07:19:14 PM »

an alternative view.  Could you not set up your control system so during the summer the WT always dumps its load somewhere (water heating or hot tub?) during the day, then at night let any power from the WT go to the charge controller.

Yeah, that's the plan, but the control system is based on a computer and I don't trust it (or my own code) to stay working 100% of the time, so want a backup dumping solution in case it fails.
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« Reply #10 on: July 08, 2014, 08:05:44 PM »

It gets really complicated,
                            When you mix the wind turbine with the PV and generator.You could,If you liked,just apply the brake when the turbine stops in sunny weather.
                                      Biff
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« Reply #11 on: July 08, 2014, 10:10:30 PM »

If the resistors are sized correctly, would there be any problems with instantly switching them on while the turbine is turning?

It's not obvious to me how to pick the right size of resistor if it's a simple on/off condition and the turbine is to run for a long time in that state. Isn't it hard to avoid either stopping the turbine quite violently or leaving it turning at low speed but with high torque and current which might not be good for the windings? I'd have thought some sort of active switching of the resistors would be needed. A job for the rPi?

(Billi: rPi = Raspberry Pi).
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« Reply #12 on: July 09, 2014, 12:53:10 AM »

Exactly EA,
          I have had a year,s experience watching our turbine trying to get along with our PV. The Turbine is of course our 2kw with reduced blade area that will max at 1600watt instead of 2.5 (3kw +). the Pv amounts to just under 4kw.
  In the beginning I was quite taken with the idea of the Turbine being left up and looking after itself but the summerdays got longer and the turbine was forced to brake all day long.I have seperate controllers for pv and of course the turbine but the problem was and is,that the sunlight bursting on the pv can brake the turbine and stop it immediately.So in other words The turbine is being forced into extreme braking which in the long term (short term) can only result in premature wear and tear on the turbine.
                I don,t care how you do it. You can have as many pc and laptops working on your behalf but ,still none of them can forecast exactly how strong the sunlight is going to be and when exactly the suns rays will trigger the brake on the turbine.
  The answer to the problem has to be someway of stopping the turbine and delaying its restart set by voltage and a timer during peak daylight hours.
  This is a rather serious problem and needs to be addressed properly.I have excellent multiple controllers and dump loads with backup but our turbine was suffering under the constant braking.
 I am looking forward to installing our new baby.The present installation has been raised and lowered with a winch and joystick for years trouble free but now I think it is time we switched to a tilting tower. I may not have time this year for the tilting tower but I will have it up before next summer.
    A constant load on the ac side is fine until that load is sated, Our final excess dump was pumping the excess heat around the C/H system in our house. (That can get uncomfortable and counter productive).I know now that it is not good business to have the turbine fighting all day with the PV. I learned the hard way but still I learned.
                                                                        Biff
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« Reply #13 on: July 09, 2014, 01:30:51 AM »

EA  thanks for the details  ,....

Quote
(Billi: rPi = Raspberry Pi).

And ?  Raspberry Jam    is something i know ....

Quote
- Are those Sun G inverters high quality enough to trust with a wind turbine?  If the inverter dies in a strong wind then it's likely that the turbine will too because there'll be no speed control.


Upto now fine , and my turbine is connected to the battery as well , so best of both worlds ---- feed my home grid via Ac couppling  and attached to the battery .... even if this China GTI breaks  ....  still the battery is there to protect the turbine
...... my findings are , that Wind and PV are not easy to combine , so i switched the wind-turbine to AC coupling  to direct feed our grid and the outback controller with the PV  can finnish the full charge , if i would have left the turbine on its chagecontroller only , it would dump too early at related voltage , now i have a day an night AC wind souce  direct into the house


its late and after 7:1 against Basil   ... sleep now needed


Talk soon Stephen  Germany vs  Holland     hopefully soon

Billi
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« Reply #14 on: July 09, 2014, 07:37:36 AM »

                I don,t care how you do it. You can have as many pc and laptops working on your behalf but ,still none of them can forecast exactly how strong the sunlight is going to be and when exactly the suns rays will trigger the brake on the turbine.

Ok, so instead of braking the turbine what if you could turn on loads on the AC side to match the turbine output?  E.g. turbine is rated for maximum 1.5kW so there must be some dedicated dump load of 1.5kW that will _always_ be available, e.g. outdoor air heaters.  With the pc controlling everything it will first turn on the useful dump loads like water heating, space heating in winter and then if all of those are taken up it will fall back to turning on the air heaters.  Then there wouldn't be any problems with the solar coming on and off and the solar controller is clever enough to quickly match it's output to what's required.

To extend the turbine life, I could lower it during summer and just raise it during the low sun months perhaps?

Billi, when you say that your turbine is connected both to the battery and to the grid tied inverter, how is that wired?  The only way I can think of would mean that the batteries would also be powering the grid tie inverter when there's no wind.
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