Open Source MPPT controller

[GoVertical]

Hi, using the stock F&P at 20 % duty cycle 100 volts max with very little current at the output; at 30 %, 40 volts max with about 5 amps max at the output. I still have to test using a different PMA. I think I will get better results using a PMA with a lower internal stator resistance. 

[GoVertical]

Hi, approximate measured values:
RPM = 280

Current in = .7 time 3 I can only measure the current at the input of one buck converter, I am using 3 buck converters. Input Current = 2.1 amps DC

Vin=58 volts DC

duty cycle = 30 %

Vout= 12 volts

Current output = 7 amps

[definitionofis]

It would be interesting to measure stator resistance and manually find the maximum power point by varying the duty cycle and see if it matches V/I = R,
volts divided by amps.  Then do it again at another rpm and see if it again matches V/I.

I mention this because in the second last post you said the stator resistance might be too high.

[GoVertical]

Hi, where do you take the measure, center to end or end to end?

[definitionofis]

I think the correct resistance value is to measure across one pair of wires from the three wire output of the stator, without the rectifier attached.

Any pair should be equal to another pair.

[GoVertical]

Hi, I think the magnets in the rotor are effecting measurement. The meter reading is oscillating. I will have to take the F&P apart and measure again. This may take a few days. It is a good suggestion and I will do it. Thanks for the input.

[GoVertical]

Hi, I found the value in a old post. Phase to phase resistance is 37 ohms.

[GoVertical]

http://www.jameco.com/Jameco/Products/ProdDS/387268.pdf

Hi, I was checking the data sheet for the inductor I am using and I not sure what I am looking at.  There is a column for inductance value @ current. Is this the value that should be used to calculate the switching frequency for the buck converter?  Comments welcome

     

[definitionofis]

Maybe because it has a ferrite core, the inductance drops as you get up to peak current because the core saturates with magnetic flux at high current.
I would guess that the higher inductance value in that chart is likely true at lower current.

[GoVertical]

Hi, the controller is operating at 20 kHz. Using the inductance @ current value to calculate the switching frequency the value is 35 kHz. I am going to configure the controller to operate at 35kHz. It will take a few days, I will post results when available.

 

[definitionofis]

I figured out a way to do the wind cubed power curve with a 59 cent quad op-amp moving around your duty cycle, instead of a microcontroller. On the other hand, I suspect the best curve is not exactly cubed, because the stator resistance issue, which you mentioned, messes up the power transfer at the upper end of the curve.  I am waiting for wind (day 18) to see what my power transfer looks like at various wind speeds.

http://www.digikey.com/product-detail/en/TL084CNSR/296-7211-1-ND/378290

The circuit might need a lot of experimenting to figure out the correct part values and you still might want a microcontroller for power and wind speed monitoring and battery bulk/absorb/float timing. So maybe it is not the path you want to go. I did my circuit as power squared analog (not cubed) and I added a microcontroller option to push it around digitally, later if I want to add that feature.  Backshed was analog power squared, approximately, I think, if I interpreted it correctly.

[joestue]

@definition just take the rpm, square it, and then feed that to a current mode controlled buck regulator.
the output current will then follow the rpm squared.

edit: the current mode control needs to take the current from the turbine and wrap that around the pwm loop. the current into the battery doesn't actually have to be measured at all, so you don't have to compensate for the buck converter's losses.

[definitionofis]

.

[definitionofis]

@definition just take the rpm, square it, and then feed that to a current mode controlled buck regulator.
the output current will then follow the rpm squared.

edit: the current mode control needs to take the current from the turbine and wrap that around the pwm loop. the current into the battery doesn't actually have to be measured at all, so you don't have to compensate for the buck converter's losses.

I am not sure what you mean. I guess you mean to measure rpm and do the math with a microprocessor?

I need to look at a current mode controlled buck regulator circuit.

goVertical is doing his own buck circuit though, with a 555 timer.

[joestue]

@definition just take the rpm, square it, and then feed that to a current mode controlled buck regulator.
the output current will then follow the rpm squared.

edit: the current mode control needs to take the current from the turbine and wrap that around the pwm loop. the current into the battery doesn't actually have to be measured at all, so you don't have to compensate for the buck converter's losses.

I am not sure what you mean. I guess you mean to measure rpm and do the math with a microprocessor?

I need to look at a current mode controlled buck regulator circuit.

goVertical is doing his own buck circuit though, with a 555 timer.

my original idea which i posted here 2 years ago was to take the rpm, convert it to a voltage, then take that voltage and square it by using one of those 95 cent power factor pwm controllers which have a 4 quadrant multiplier on the chip.

this control voltage can then be sent to a buck regulator.

to avoid the need to measure the voltage, put the current sense resistor on the turbine side, and then configure the buck converter's control loop to keep the turbine current equal to the control voltage.

[GoVertical]

Hi, adding fourth stator. This will allow a 8 coil per phase configuration. I am hoping this will lower the voltage and increase the current when used with the buck converters. But I am not sure. I still have to attach the end cap.

Hi  joestue, your idea sounds intriguing. I am planning to add a micro to the buck converters. Before I can do that the circuit needs a voltage limiter at the input. The max rating for the mosfet is 500 volts. I am searching for a circuit that will trigger at 400 volts. Any help will be greatly appreciated. 
   
     

   

[definitionofis]

my original idea which i posted here 2 years ago was to take the rpm, convert it to a voltage, then take that voltage and square it by using one of those 95 cent power factor pwm controllers which have a 4 quadrant multiplier on the chip.

this control voltage can then be sent to a buck regulator.

to avoid the need to measure the voltage, put the current sense resistor on the turbine side, and then configure the buck converter's control loop to keep the turbine current equal to the control voltage.

That is interesting. I saw a power factor controller for the first time, here on EEVblob:
http://www.youtube.com/watch?v=MBQn6xpto6M

Do you mean to say the PWM feature is doing the buck mosfet pulsing?
I don't think you mean a separate buck regulator.

Did you build your circuit and use it?

I came up with the same analogue idea equating input current with a varied control voltage, except I did not do squaring math on the control voltage. Here is my circuit: http://www.opencircuits.com/MPPT_Solar_and_Wind_Power_Boost_Charge_Controller

I used a microcontroller varied potentiometer max5480 to improve the curve, because I think the practical wind blade power curve is not cubed nor squared.  The tricky part in my circuit is making the FB pin on the boost/buck IC LTC3703 vary the output voltage so as to influence input voltage/current at the same time as it is doing feedback from the output voltage.  I used an op amp to do integration math until the inputs hit equality. (Using the Imax pin is not the way to go, I think. I read the Imax pin elsewhere on this website.)

The idea I had for a squared version is Question 7: http://www.allaboutcircuits.com/worksheets/nonlin.html
fed to a similar integrator op amp.

My circuit works. I documented my first trials in those videos.

I better upload it to here, in case that site disappears some day. I think you can tell by the clutter it has many revisions before I got it to work. I am afraid to unclutter it and make a mistake. I will leave it.

[definitionofis]

Hi, adding fourth stator. This will allow a 8 coil per phase configuration. I am hoping this will lower the voltage and increase the current when used with the buck converters. But I am not sure. I still have to attach the end cap.

Hi  joestue, your idea sounds intriguing. I am planning to add a micro to the buck converters. Before I can do that the circuit needs a voltage limiter at the input. The max rating for the mosfet is 500 volts. I am searching for a circuit that will trigger at 400 volts. Any help will be greatly appreciated. 
   
   

Did you need a separate stator for each circuit or did you do that to run them in parallel to lower the voltage (and more amps) at the same mechanical load on the blade ?

I think we already posted limiting circuits.

[GoVertical]

Hi, before I learned about the benefits of add a MPPT to the system, I added the extra stators to reduce the internal resistance by connecting the stators in parallel. By having inputs and outputs for each phase on each stator allows a multiple of different configuration    possibilities . The additional stator will allow the PMA to be configured as a 3 phase,8 coil per phase. The down side is it is heavy, but it makes a great learning tool.

Until I find a voltage limiting circuit for the input of the buck converters, I am going reconfigure the  PMA to work within the limits of the circuit.

[GoVertical]

Hi, I found a crow bar circuit that may work for the voltage limiting at the input of the buck converter. ZD1 will be replace and a load can added between the Q1 and ground. When Q1 is triggered the load may act as brake for the turbine and reset the circuit. Comments welcome

http://www.wiringdiagrams21.com/2009/11/28/a-typical-crowbar-circuit-diagram

[DamonHD]

A modification of this circuit that I use:

http://www.earth.org.uk/wind-power-pilot-autumn-2007-MotorWind.html

using a MC3423 or similar may be suitable given that it's designed to be non-destructive, ie not just to blow a fuse, and specifically to let go again as the turbine slows and the voltage drops.

The response is fast, so can simply clip the tail end of each troublesome (part-) cycle.

Rgds

Damon

[GoVertical]

Hi,  do the resistors at the input effect the turbine speed. When using the buck converters the input voltage will very high, well above 12 volts. I am not sure but does placing a voltage divider at the input act as a load?

 This is a condition I am trying to avoid. The reason for using the buck converters is provide away to adjust the duty cycle and prevent turbine stall and reduce heat at the stator. If a load is added at the input the benefit is lost.

If a load is added between Q1 and ground the fuse would only open if there was a circuit failure. If the fuse is scaled correctly. 

[DamonHD]

The whole circuit draws a few milli-amps (mA) of which the resistor divider is a small small fraction, and that draw should not be relevant.

IMHO, you DO NOT want any fuse in there at all: if it blew you'd have no control over your turbine for example, and no power coming in.

Let the SCR reset / drop out / switch off when the voltage gets low and you can generate again automatically.

Rgds

Damon

[GoVertical]

Hi, thank you for information. I have ordered some parts for the circuit and I will post results when available. 
     

The biggest problem is all PMAs are not the same. Finding a solution that will work for all projects may not be possible. If I can get the system working for my project, maybe others can adjust the parameters for their project.
Thanks again, I hope you can enjoy the Olympics 

[DamonHD]

Note the max (supply) voltage for the MC3423 if you use that, and in any case of your SCR, and note that the two circuits are for the rectified side of the system, and upstream of another diode if need be to avoid attempting to crowbar a downstream battery resulting in fireworks!

Rgds

Damon

[GoVertical]

Hi, I found a solution that will work on the AC side of the bridge rectifiers and reset after it triggers.

http://www.vawts.net/t45566226/us-vawt-limiter/

I not familiar with Triac's or Diac's. I will have to do some reading, now that I know what I am looking for. Comments welcome

[bob g]

if i might be so bold as to ask, perhaps it has been answered earlier, but i really would like to know.

where do you guys get your background in power electronics?  what books do your recommend on the subject?

i assume there are a couple members that are engineers for inverter companies or other industrial drive manufactures,  some that are very good technicians that might work in the industry, many that are very good amateurs, and the rest with varying degree's of proficiency in electronics.

this mppt thing has been something i have been very interested in for many years, actually before it was really called mppt i guess. while i have some training in electronics, i know very little of power electronics and have spent a lot of time looking for textbooks that are directed at actual design of such and not just theoretical books which i have found most to be.

fwiw, i have found one book that is written with actual design in mind, it covers buck, boost and flyback converters with real numbers, components and how to. 

power electronics principles and applications
j. michael jacob  2002
isbn 0-7668-3018-7

i can't remember where i got it, i think used off of amazon, and it wasn't particularly cheap or terribly expensive if i recall correctly.
it has a lot of info that might help in the specific design and component selection for this project.

failing that, i am very interested in other books on the subjects, if anyone here can recommend another good one i would like to get my hands on it.

thanks
bob g

[boB]

if i might be so bold as to ask, perhaps it has been answered earlier, but i really would like to know.

where do you guys get your background in power electronics?  what books do your recommend on the subject?

Very few schools really  teach this stuff anymore,  for some reason.  U of Washington used to have a lot of classes I know but for some reason stopped doing much there.  I would say that most good power electronics engineers/techs get experience on the job even if the school they went to did teach power electronics...  There is some art to it of course.  It's is VERY hard to find power electronics engineers that know what they are doing.


Electronics troubleshooting also seems to be somewhat of a lost art.

boB

[bob g]

troubleshooting and diagnostic's is almost a lost art in many industries these days, the common directive is "change it out for a known good part" 

always loved that response when working on a heavy truck and the part they were talking of replacement was the ecm, at 3500bucks a pop and no return policy from the parts department left folks like me to develop my own diagnostic procedures... basically if it came down to me really thinking it was a faulty ecm,,, it got sent to the dealer for repairs!   they can afford to eat an ecm or explain to my customer why they needed to buy an unneeded ecm... either way i was not the bad guy.

when it comes to electronics in general, it seems the common response to either swap out a unit or scrap the who thing and just buy a new one.

why we put up with this as consumers i have no idea.

bob g

[joestue]

Power Electronics Handbook by M Rashid is certainly one of the authorities. he has a third edition out (2010) and most of it can be read on google books.

Its an art, its really that simple.
Recently someone with a PHD in electronics confessed in his obituary that he'd never graduated, they misfiled his AA as a PHD and he said "you have to admit my designs worked very well"

this free book is most excellent: http://homepages.eee.strath.ac.uk/~bwwilliams/book.htm

I think i have a stack of stuff about 2 feet high that i've printed out over the past 4 years but i don't know what you are looking for.

[boB]

I like M. Rashid's book and the stuff on Barry William's link too.

Here is a list of decent books, including Rashid's and Pressman, which I also have...

http://www.smpstech.com/books/best-power-supply-books.html

Many years ago I had the pleasure of going to one of Lloyd Dixon's magnetics seminars when
he was working for TI/Unitrode...  Here is just one of his papers.

http://www.ti.com/lit/ml/slup128b/slup128b.pdf

If you can find them, and they should be online at TI.com, there are also videos of his slideshows as well as more
PDFs.

some stuff at ON Semi...
http://www.onsemi.com/pub_link/Collateral/AN1679-D.PDF

Lots of application notes online at the various companies that do power management.

Here's another one.  Google finds this stuff easily...

http://www.ti.com/lit/an/slva061/slva061.pdf

boB

[bob g]

thanks for the links guys, it is appreciated

bob g

[Watt]

Power Electronics Handbook by M Rashid is certainly one of the authorities. he has a third edition out (2010) and most of it can be read on google books.

Its an art, its really that simple.
Recently someone with a PHD in electronics confessed in his obituary that he'd never graduated, they misfiled his AA as a PHD and he said "you have to admit my designs worked very well"

this free book is most excellent: http://homepages.eee.strath.ac.uk/~bwwilliams/book.htm

I think i have a stack of stuff about 2 feet high that i've printed out over the past 4 years but i don't know what you are looking for.

I have this book on my phone.  It is the third edition but shows 2011.  I bought it on Google books.  isbn 978-0-12-382036-5