Strategies needed for operating parallel VAWTs

[GoVertical]

Hi, I am starting this post to discuss the strategies needed to operate VAWT's in parallel to gain a higher output current at low wind speeds.  A 4x8 foot VAWT at 10 MPH should produce about 5 amps using a 12 volt battery as a test load. So if four VAWTs are operating in parallel at 10 MPH wind speed the charge current would be about 20 amps. If your control circuitry is designed to operate safely at 20 amps there is no problem, at 12 MPH wind speed the current from the four VAWTs will rise far above the 20 amp limit.  I am searching for safe methods that can be used to avoid the stated problem.
Suggestions welcome

[ghurd]

Use a decent controller and a bigger dump load?

[GoVertical]

Hi, thank you for responding. Are there any dump controllers that will trigger from a increase of current.  I have limited control electronics experience.

[ghurd]

I mean if the controller is rated for 20A, add some external "trigger" parts to the existing dump load, and a dump load separate from the existing controller and dump load.

It's only a couple resistors, a mosfet, Schottky diode, and an additional dump load.

What dump load controller is rated for 20A?  Nothing rated at 20A comes to mind.
You are not thinking about using a solar controller are you?
G-

[Flux]

Can't help feeling there is confusion here.

What is the difference between 4 VAWTs producing over 20A or a single HAWT producing 100A.

The machines will logically be fed to the battery, the only control needed will be some wire and possibly 4 fuses.

You don't control battery charging from AMPS. The battery takes all it can get until fully charged, at this point it starts gassing and the voltage rises out of control. This is where the controller comes in, it lets the battery sit at a fixed voltage and any excess current over what is needed to maintain this is dumped by a dump resistor.

Standard controllers are typically available up to 60A. Usually if you want more you can add additional dump capacity with a relay or use more than one controller.

As Ghurd said you can increase the capacity of the controller but you use voltage as the reference not current. If you regulate for constant input current there is no way the battery will be kept in a controlled state of charge.

If as Ghrud suspects you are looking at a series solar controller, then forget it, series regulation is a disaster with wind as the machine runs away.

Flux

[GoVertical]

Hi, I have been testing with a  modified F&P as a PMA.  It produces a workable output if a MPPT circuit is used. I found that by setting the duty cycle to 35% of a power conversion circuit; buck converter;  the VAWT will produce a output that is allowed by wind speed and blade size.

I live in a low wind area so I am planning to operate multiple VAWTs in parallel.  I searching for a off the shelf buck converter that has a wide range input voltage that can charge a larger  capacitor that would supply a solar MPPT controller. I am not sure if the solar MPPT would track the voltage at the capacitor.  I am not sure if it would work without stalling the turbine. The other problem is over current when there are high wind speeds.

This is  just a experiment.  Some solar MPPTs are low cost and have a high current output. I have the buck converter circuit that I can fabricate. I also have a Crowbar circuit that I can fabricate, I just need to find at what voltage value the F&P PMA will output 5 amps then I can try the experiment.

If I can find low cost prefabricated parts I could try the experiment sooner.

[GoVertical]

Hi, for my project VAWTs are low cost, safe, and easy to fabricate. Multiple HAWTs or VAWTs, the problem is the same.

[OperaHouse]

I have limited control electronics experience.

"you're  a one eyed man in the kingdom of the blind."
Kurt Vonnegut, Player Piano

I've seen your projects and you have a dedication that makes me think you are capable of this.  Have you done
anything with the UNO you purchased?  A dump load would be a good starter for you.  Read the voltage, average
the values, and send out a proportional dump signal between a start voltGE and a full on voltage. That couldn't
be ten lines of simple code.  Built in functions do all the heavy lifting.

Next you could start keeping time.  With known voltage, dump resistance and PWM duty cycle the watt hours can
be logged.  When you get data, a lot is learnrd about a system that is never expected.

Then you can monitor that other dump.  I'm partial to the ACS712 current sensor they sell on ebay for about $3.
These are mounted on a board with connectors and are available from 5-30A.  These are a deal and you have total
isolation. I pity anyone who puts 30A through that chip.  I buy the 5A version and parallel it with a shunt or
6 inches of wire.  Even a couple of hundred counts is enough to make decisions with.  Only three wires to connect
to the UNO.  The A/D counter will sit at half.  Subtract out a little more than half to get rid of noise and you're
done.

Lots of festures can be added three lines of code at a time.  Control strategy is a tough one. At least any form
that doesn't work out can be quickly erased.  Look at the discussion of heating water.  Just turn on a SSR,
seperate inverter, or turn on an inverter for a period of time.  If only one inverter do you monitor the input
current to see how much capacity is being used.  You don't want to use 2KW inverter as a 1KW dump load when it
is already supplying 1600W to some other load.  The micro should be integrating the system together.

Early in mky career I was asked to make a machine run faster.  I made a number of improvments and the machine
"ran" twice as fast.  As part of the modifications I added counters and timers to get more dats.  What I found
shocked me.  In a 12 hour work day the machine actually only ran about three hours.  It didn't really matter how
fast the machine ran, production would only be improved if the material handline aspects were addressed.

RE is at that point right now.  A little focus on saving a few hundred watts heating water when a thousand is lost
somewhere else.  Scheduling energy usage and communication between devices will be the future.

[Flux]

Thanks for the clarification, I think I can see where you are coming from now.

If your converter is capable of dealing with one VAWT then the solution is to use 4 of them. one for each. Wind is so fickle that you can't realistically hope for any mppt converter to deal with multiple units. It may sort of work with your open loop approach but in the real world, one turbine one mppt converter.

I suspect you are not using it as a mppt converter but an impedance matching device, this is fine and easier than messing about with the motor windings and if it works well enough for each unit then it will all work together and you can use the dump controller to deal with the battery.

If you try to feed multiple machines to one converter you will never have the same conditions for all. With VAWTs at low level in normal environment you will probably see very large variations in current sharing and you may see the case where one machine is producing all the power. No mppt converter could untanglle this and even your open loop impedance matching approach will get way off it s best condition in these conditions.

There is also the case that small converters are easier to build so using 4 small ones makes perfect sense. In addition you have the redundeancy factor, loose one small converter and you have 3/4 output. Loose one big one and the system crashes.

If you have one working unit then really you are home and dry, just repeat it 4 times, feed all directly to the battery and use the dump load for battery management.

Flux

[GoVertical]

Hi, I contacted Harry Landis at intronics. He was to write new software that limits the duty cycle of the MPPT25 to stay below 50% and it prevents the turbine from stalling. I forgot to add the OVP circuit at the input and I had to send it back for repairs. Sometimes I make mistakes. 


I shelfed the UNO for a while because I have been bata testing the MPPT25 from intronics and the V3 MPPT from Steve Hansel @ windgen.org

I have noticed the MPPT's or a buck converter with the duty cycle set to 35 % will produce about the same results. I am still testing.

Thank you for all the suggestions.

[GoVertical]

Mppt25 update: The repairs have been made and the chip with the new software that limits the duty cycle to 35% is working. Using a modified F&P and manully operating the PMA with a hand crank the ouput max is about 7 amps into a 12 volt deep cell.

I finially made a basic drawing of maybe a new idea, I do not know. Use a power conversion circuit to convert the ouput of a wind turbine to simulate the output from a solar array. Then any MPPT solar converter could be used.  It may solve the problem of finding a low cost MPPT controller for a wind turbine.  Comments welcome.

[ghurd]

What happens when the battery is at regulation voltage?
That happens when the wind is high?

Usually, when the wind is high, the battey is already at regulation voltage from the incomming winds before the high winds get there, for MOST of us.

The high winds arrive.
The battery is at regulation voltage, because it has had an imbound current for a few hours.
The solar controller shuts off power to the battery.
The unloaded turbine turns faster, V/RPM, making more voltage.
Solar does not do that.
The high input voltage smokes the SOLAR controller.

[GoVertical]

Hi, the power conversion circuit I am planning on using has a over voltage protection circuit that would divert the current to load resistors and slow the turbine. This is very experimental and requires testing. It may take me a few months to set up and test. I will try to post results. Thanks for the input.

[GoVertical]

Hi, I fabricated the OVP and it will triggered at the voltage set by the zeners break down voltage. I have to replace the load resistors with higher wattage values, maybe a toaster heater element.