Stirlingengineforum.com

Geoff V wrote:theropod2

I appear to have hit a nerve, good, I've been mislead for 30 years by authors publishing theories as to how the Stirling cycle functions, it wasn't until I disregarded these learned words and started to bench test every possible aspect of the design that I started to make some progress with these engines. It was the fine engineer Kieth Duckworth of Cosworth fame who wrote in his book 'it is better to be uninformed than misinformed' a sentiment I totally agree with. So I'm sorry if I have offended you, but if I can save other engineers from wasting time and money through following the untested theories of those who think they know better, I will.
snip...

Geoff V,

While I understand what you are saying you seemed to have missed the most important point I was attempting to make, and failed. My Bad!

My point was concerning the common misuse of the word theory. Those guys that mislead you were not presenting a theory. They were proposing a hypothesis. They were/are neither following the scientific method in their work or proposals (hypothesis). Try reading peer reviewed papers instead of books. Peer review demands empirical supporting evidence. Books demand to be sold.

You did not offend me. I just feel very strongly that the common misunderstanding of these terms should be corrected when I read them. There is no such thing as an untested theory, as such a thing is a hypothesis, and a weak one. Such authors are making assertions without empirical evidence and if they had one ounce of self respect they wouldn't publish a word without real world testing.

Here's an example of the kind of thing I'm talking about, and the format I use when referencing any peer reviewed material.

SOURCE

"Manufacturing and testing of a gamma type Stirling engine"
Renewable Energy: Volume 30, Issue 1, January 2005, Pages 57–6
Can Çinara and Halit Karabulut

Abstract
In this study, a gamma type Stirling engine with 276 cc swept volume was designed and manufactured. The engine was tested with air and helium by using an electrical furnace as heat source. Working characteristics of the engine were obtained within the range of heat source temperature 700–1000 °C and range of charge pressure 1–4.5 bar. Maximum power output was obtained with helium at 1000 °C heat source temperature and 4 bar charge pressure as 128.3 W. The maximum torque was obtained as 2 N m at 1000 °C heat source temperature and 4 bar helium charge pressure. Results were found to be encouraging to initiate a Stirling engine project for 1 kW power output.

See, this is how real science is done and how a theory is applied to real world settings with testing which returns repeatable empirical evidence.

Hopefully this clarifies my position and lowers the thermostat a couple degrees, and the above citation displays the methodology under which real science done.

R

Vamoose

I'm sorry to say I appear to have caused your thread to be hijacked by a discussion on the use of the English language, not intentional and unlikely to have any influence on achieving a SE that is of use to mankind. I'm sure you are quite wise enough to have understood the advise I was offering and I look forward to following your progress.

GeoffV

Tis all fun and games to me fellas, potato tomato whatever. Life’s way too short to get too serious IMHO. Its in part why I made the 'Funny Stirling Engines' thread (although not many others have taken up the 'flame'), plus it helps placate the little smart ass gremlin that 'mostly' resides in my internal dialogue.
I'm glad that people can even be bothered reading and sharing on topics that I’ve started, although I hope its more than general semantics that they find of interest in them.

Geoff, I have been busy running multiple computer type simulations on Stirling engines and hope my results are at least in the ball park, as the CPU I’ve been using is the one that the Gods (if your into that kind of stuff) gave me, and there are no returns or refunds on defective hardware and software for these specific units, no matter how hard one prays for it.
I feed all kinds of random garbage and inputs into mine, and get a whole lot of hard to decipher gobbledygook out most of the time. But occasionally I get a 'ding' and light bulb moment occurring, and if I’m lucky I get to scribble it down before my monkey brain has a walk through door event and it disappears back into the Ether.

vamoose

Now back to our regularly scheduled programming…

Sorry for no progress report as of late. Had to come up with a new laser controller concept, so had my brain filled with that. But I did get a chance to do some leisure reading. The Dingo controller post by Vamoose is a very interesting gadget and it got me to do yet more research...

Initially I entered this post and forum as I didn’t have the faintest clue of what a MPPT was, but from what I have read and experienced, wanted to suggest a method (Dither & Lock or D&L) that would capture the max of a bell shaped power curve and have gone a bit crazy myself (sorry!). The first MPPT controller researched was just a basic DC-DC converter that would help but not do a great job. I got to prove this with my TPS61202-EVM-179 experiments with a LED. Something in that Dingo manual made me redo my MPPT researches and I found there are four different types of MPPT controllers: Perturb and Observe, Incremental Conductance, Current Sweep Method & Constant voltage. See http://en.wikipedia.org/wiki/MPPT for more information on each mechanism.

Ok, I thought I was doing something novel with something very old. You know, teaching an old dog new tricks! And it looks like the solar lads have already done the hard part. It doesn’t mean we can’t use their toys to help improve our toys, or at least get the most out of them!

Though deflated a bit, I did yet more searches and found some very nice devices exist out there. And some of these off the shelf devices are relatively low cost. So I now truly believe there are MPPT devices that will work with stirling battery or stirling AC grid systems. I have no visions of grandeur, nor do I expect my toy JS002 will ever power more than a LED, but I am having fun! Would be interesting if I could get more than one to illuminate. So stay tuned…

Still, I wanted to see the curves, so my next stop in this adventure was to cobble up a basic PWM stage to help me measure the power out of the Toy JS002 SE setup in the previously posted photos and videos. I wanted to change the duty cycle of some relatively high frequency and apply that to a MOSFET to short out the motor. I could then measure the average current through the MOSFET and voltage on the motor with digital meters. Basically I am applying a variable resistance load to the DVD spindle motor/generator and measuring the power and RPM. Grabbing a simple function generator, I used an IRF3708 N-Channel FET as the PWM stage. My oscilloscope was used to measure/set the duty cycles. Here is a picture of the scope and function generator. The transistor was hooked to the motor with temporary spring J-Clip wires.

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I will admit I had a few failures here, as I first used a MOSFET that had too high of an on resistance. But I still got very encouraging results with an impact on PWM –v- RPM. It wasn’t linear, but I could at least have an impact on the RPM and saw that the power curve started to flatten.

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So using a more Manly-Manly transistor (very low on resistance) I was able to get the curve I was hoping to see; a bell shaped curve of RPM – v- Power.

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The power shows a roll over bell shaped curve as hoped and suspected. So I ran more tests all showing similar curves, just lesser peak powers with different Max Power Point (MPP) versus PWM/RPM points. This just further showed me how variable my toy SE setup is and how a MPPT might just improve things, or keep them at the optimum…

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So now I’m off to build a MPPT based on my new knowledge and discovery the JS002 Toy SE has a bell shaped power curve. Here is a close up run. The last curve shows the motor was starting to die off and needs another rebuild…

So why am I doing this? Lasers like SE are tools that are on the verge of not working. When I first heard of a laser in the late 60’s, they were “TOO LITTLE POWER” and “TOO LARGE”; sound familiar? Now days, I’m working around several watt lasers that can fit in the palm of your hands. I see the marriage of a MPPT (or VMPPT) w/ SE as beneficial; a tool to get more power out of a power limited tool, thus making it more useful. I can imagine the guys like Whispergen that sell Combined Heating and Power (CHP) or Waste Energy systems might be interested in getting the very max out of their electrical generation, especially if variable heating is used and especially when talking kWatts.

More to come!
-NerdyEE

P.S. English is a funny language. For example Ian used the word “FAG” for cigarettes or smokes. I live near San Francisco, and that word is a hate word. So now imagine the puzzlement of my first interpretation/read on that post…

NerdyEE, english sure is a bit odd at times, our English in NZ is different to that in Austrailia, I toured Britian and found from one end to the other just about a comptetely different language, I imagine there are major differences in the USA too. Mostly I think we understand whats going on. Ian S C

Here's a summary or few documents (pdf's) that may have some relevant info in them for consideration.
Its pretty much over my head on many levels, and hope i'm not perturbing anyone from reading, with too many links..
[hr]

Dynamic Response Analysis of Small Wind Energy Conversion Systems (WECS)
Operating With Torque Control versus Speed Control

http://www.icrepq.com/ICREPQ'09/378-gonzalez.pdf

Abstract: This paper encompasses the study of modelling and design of WECS, using a wind turbine with known dynamic characteristics and a permanent magnet synchronous generator with a back to back power converter topology. The dynamic modeling allows to know the response of the turbine generator system in the whole range of operation.

6.- Conclusion A control system for small wind turbines has been presented in this paper. The proposed control system has a variable structure depending on the operation region. In the MPPT region, a speed turbine control loop is used to follow the maximum available power point. In the nominal power region, a linear control is used to maintain the power close to a reference value in spite of high wind speeds. For this CP region, it has been shown that closing the power control loop by cascade compensation of the inner speed loop is preferred to use an inner torque control loop.
[hr]

Optimization of Perturb and Observe Maximum
Power Point Tracking Method

http://ecee.colorado.edu/~ecen4517/mate ... 6O2005.pdf

V. CONCLUSION
In this paper a theoretical analysis allowing the optimal
choice of the two main parameters characterizing the P&O algorithm
has been carried out. The idea underlying the proposed
optimization approach lies in the customization of the P&O
MPPT parameters to the dynamic behavior of the whole system
composed by the specific converter and PV array adopted. The
results obtained by means of such approach clearly show that
in the design of efficient MPPT regulators the easiness and
flexibility of P&O MPPT control technique can be exploited
by optimizing it according to the specific system’s dynamic
characteristics. As an example a boost converter has been
examined. The results obtained and the considerations drawn
can be extended to any other converter topology as well.
[hr]

Comparative Study of Maximum Power Point Tracking Algorithms
for Thermoelectric Generators

http://itee.uq.edu.au/~aupec/AUPEC%2020 ... s/p217.pdf

VII. CONCLUSION
This paper has compared the steady state performance of the P&O, INC and fractional ISC algorithms. The results show for the above TEG model and various fixed load resistances, the fractional ISC had the best steady state performance. Also unlike the P&O and INC, it required no extra error and/or tracking parameters to ensure correct operation, making it the easiest to develop. Due to the nature of the short circuit test, it is likely that the dynamic response of the fractional ISC is not as good as the P&O or INC. Due to the thermal mass of the TEG, the impact of this drawback should not be very significant, but further work is required to test for this.
[hr]

Low-Power Maximum Power Point Tracker
with Digital Control for Thermophotovoltaic Generators

http://www.google.com.au/url?sa=t&rct=j ... NnfGsqaGAA

V. CONCLUSION
We have demonstrated a power electronics architecture
suitable for TPV power generation. The proposed architecture
addresses challenges that are unique to the TPV application,
and enables a substantial increase in energy capture compared
to conventional methods. We incorporate low-power sensing
techniques and achieve high power conversion efficiency
and small size. A tracking efficiency above above 99% is
demonstrated. In addition, we have demonstrated a micro-TPV
system generating 150 mW with the MPPT converter. These
results pave the way towards a fully integrated, fully functional
micro-scale TPV power generator.
[hr]

Maximum Power Point Tracking methods for small scale
Wind Turbines

http://www.satnac.org.za/proceedings/20 ... 20Moor.pdf

Abstract
Power Point trackers for increased efficiency in the
power production of wind turbines are investigated.
The power point trackers are to be used for large scale
and small-scale systems. Two basic methods for
tracking are presented. The first method is
rudimentary load adjusting in sample steps. The
second method requires previous knowledge of the
parameters of the wind turbine to provide an optimal
look-up table. The loading of the wind turbines is
determined by these power point trackers and will be
implemented on a practical system by controlling the
rectification from the generator. Computer
simulations are performed on the proposed methods
and the results are presented in this paper. An
analogue model was also created and the preliminary
results are presented.
[hr]

A Novel Approach for Robust Maximum Power Point Tracking of PEM Fuel Cell Generator
Using Sliding Mode Control Approach

http://www.electrochemsci.org/papers/vol7/7054192.pdf


6. CONCLUSIONS
In this paper, a sliding mode based maximum power point tracking approach for PEM fuel cell
is presented and its characteristics, accuracy and performance is investigated via simulations. The analyses and simulations are performed on a system including of a PEMFC, boost DC/DC converter and a battery for both normal and time varying Fuel cell temperature and membrane water content operating conditions. Besides, the performance of the proposed method is compared with the P&O approach [10]. The results are indicative of the out performance of the proposed method. The main features of sliding mode MPPT method can be summarized as:
 High accuracy or equivalently low steady state tracking error;
 Fast response;
 Simple control law, low complexity and implementation cost.
[hr]

vamoose

This has nothing to do with anything stirling, but just watched it and now have a massive headache. Thought i might share it around...

http://www.abc.net.au/catalyst/stories/3618432.htm

Anyway off to the cupboard for some panadol
vamoose

Hello to all!
Below I demonstrate a MPPT chip development board with my JS002 Toy SE and DVD spindle generator setup. It allows me to pump x4 - x5 more current into a white LED load than the previous demonstration.

In researching other MPPT devices, here are some of the more interesting units. Vamoose mentioned the desire to do MPPT with an Arduino processor. See http://www.timnolan.com/index.php?page= ... ar-charger. Do a Google and you can find hundreds of off-the-shelf MPPT devices and kits available!

There are even chip solutions from many semiconductor manufacturers. Triune Systems offers some clever battery charging units w/ MPPT. TI offers impressive development kits and chips like the TMDSHVMPPTKIT that will even generate the inverted AC for 120 or 220VAC Power Co. back injection. IMHO, some of the more impressive chips are the SPV1020 and SPV1040, from ST Microelectronics, with the SPV1020 boasting over 300W capability and costing less than US$10 in quantities of one. But it was the specifications of the SPV1040 that really caught my eye as a perfect fit for the JS002 Toy SE setup. So I got a development kit (ST-Micro STEVAL-ISV006V2) from Mouser and hooked it up. The photo shows the motor is spinning at 925 RPM (3700/4), motor current is 25mA (.65V?) and 8.6mA is going into the 2.7V LED.

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To my first amazement, the motor didn’t stall but initially produced 1mA of current into the load and eventually increased to 5mA over time and warm-up. Post warm-up, the SE & generator voltage, current and RPM readings were nearly identical to the MPP readings I got with the curve taking, possibly a bit biased on the “I’m about to loose it” side of the curve (less RPM). But when I blew out the flame and saw that the output load current naturally reduced allowing the setup to run longer than previous non-MPPT runs, my jaw hit the floor!

Since then I have measured every conceivable voltage & current into and out of the MPPT evaluation board to try to figure out if it was at the ideal optimum level. It was when I connected my scope to the MPPT input (DC generator output) that I could see what was going on. Once the load demands more power than the MPPT receives, it enters its MPPT mode where the 100KHz based PWM varies the duty cycle and observes the average voltage and current. The average input voltage goes from open loop voltage to approx 0.2V in a saw tooth triangle waveform every 16 milliseconds, as shown in the picture below. I initially suspected the MPPT controller was oscillating but the average level was near the MPP. Or perhaps this action was this devices proprietary MPPT technology. Doing the same measurement on the built in solar panel, the waveform appears to be the devices MPPT process (see second photo below; same shape, less noise).

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Burn after burn, slight adjustments, rebuilds, adding friction to the flywheel, pushing on the displacer hot cap stopping the compression/expansion oscillations; all these subtle disturbances appear to get tracked out. I am able to produce more current into a LED load than ever before, all automatically. The max output current obtained so far was 10mA into the white led and super capacitor load post SE rebuild. I am very impressed!


So, does this saw-tooth MPPT process on the ST SPV1040 obtain actual MPP results? By using the white LED as a somewhat constant voltage ballast, I could measure the current drawn by the MPPT loads (LED & 0.22Farad Super Capacitor). Adjusting the output voltage potentiometer, I could easily transition the controller between voltage regulation mode and MPPT mode. What was observed was that just before the transition I could consistently obtain approximately 2.5mA more load current than obtained when running in MPPT mode.

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Even though this controller might not get the very max out of a SE (this could be a generator noise issue), it does appear to control it and doesn’t stall the SE setup when loads are greater than output power. There were a couple of times the setup would stall and I would get scared the MPPT was the reason. I found I had just forgotten to cool the setup after every burn and was getting the motor too hot again. Even the drag of the DVD motor disconnected would stall the setup.

Bumpkin wrote:Most Stirlings have a torque rise as R.P.M. drops that would approximate the amperage rise of P.V.s as voltage drops. If the Stirling alternator freewheels at a comparable voltage to an open circuit panel, a M.P.P.T for photovoltaic charging MIGHT work right off the shelf. Bumpkin

Though the VI curves of my SE and a P.V. cell look nothing alike, how correct you were sir, it does appear to work…

In summary, it appears as though a MPPT would be beneficial for a SE electrical generator as it is for a solar panel. The results of these latest experiments are very inspiring and validate the claim. In my first experiments, the Toy SE setup was barely able to illuminate a high efficiency red led with currents well under a milliamp. The second set of experiments with the DC-DC converter got a white light led to glow with current just over 1.25mA before the DC-DC converter would clobber the SE. With the MPPT development board, I am able to produce 5-6mA of current on average into the same white LED load; a factor of four increase in load current…

WOW!
-NerdyEE

So NerdyEE,
Just another lazy weekend then, hey.
I organised my sock draw, wow, what a mission (ok I didn't really).

But seriously, I applaud you for all the work you've put in and how you've shared it on the forum for everyone who wishes to read it. Big effort and 'Impressive Results!!'....
You've got me excited!!
Very Juicy...

vamoose

Hello to all!
If I had read some of claims like the above without some type of proof or evidence, I think I would have flamed that in-DUH-vidual. Since posting the above, I have expected/feared it from others. So hopefully I have a treat for those who are interested.

The most difficult task in all of this work has been data collection. I don’t have an automated data collection system other than digital volt/current meters and my eyes. As I discovered from previous measurements, visual averaging was very difficult. So, using a camera, I took pictures of the meters measuring input & output, voltage & current (4 meters total). Blowing out the alcohol lamp, photos were taken as quickly as possible. The data from the photos (if readable) was then entered into Excel and plotted. I was astonished to see a nearly linear set of dots of power input versus power output. So the treat I have is to share the data taken with over 260 photographs over a single burn…

The plot below shows the MPPT input and output power with respect to the data samples; basically time. From points 1 - 69, the MPPT is in STARTUP MODE waiting for the output voltage to go approximately 2.0V. From points 70 to 103, the device is operating in MPPT MODE. From 104 to 112, modes switch from VOLTAGE to MPPT.
At point 113, I changed the system to VOLTAGE mode and slowly increased the setpoint voltage, thus increasing power until the chip hopped to MPPT mode at point 127. At data point 130, the flame of my setup was moved out of optimal location and then back again. Finally, at point 191, the flame was blown out and motor runs to point 261.


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A view of the input voltage clearly delineates the various modes mentioned above. This voltage is also a good indication of speed, thus note how the MPPT controls the voltage as the heat is disturbed. Or is it how the MPP and RPM drift over time…

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Something I thought interesting was to plot the input versus output powers at various points of operation. Additionally, the slopes of the plots show the input/output efficiency (approx 70% and approx 80% Voltage Mode). One point to consider is that this chip uses the power it makes to get more power, and it is working with milliwatts of input power. Said chip was designed for 5W operations.

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So beyond all, I believe this MPPT chip controls my toy SE setup to obtain the max power harvesting. Maybe not at the very optimum of efficiency, but understand this may be due to system noise, low power operation, or the chips mechanism of preventing MPPT/Voltage mode oscillation. As can be seen from the first plot above, any change on input power shows on the output. This shows that this MPPT can track the MPP (or near the MPP) of the toy SE setup as the motor changes. Therefore this benefit can also apply to your SE setup…

Thank you for your time!
-NerdyEE

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NerdyEE, with such dramatic results the concern for scepticism is warranted, but putting it out there is much appreciated and the work is valued. A side note on photovoltaic MPPTs: your tests, as I understand, are loading down to zero, unlike charging a battery which only loads down to a certain voltage. There's a PV system for direct water pumping without a battery - the controller might be interesting for you to look at. Things like that are just black boxes to me. Bumpkin

Hi Bumpkin,

THANK YOU for your kind words, especially since I didn’t think a Solar MPPT would work at first! Dramatic results are an understatement. Now I didn’t’ really watch the input power at first, but will assume the output power from the SE engine has always been around 20-25mWatts max. So going from the red LED at less than 0.2mWatts of output, to the DC-DC giving just under 3mWatts, and finally the solar MPPT chip giving over 15mW is amazing!

Yes I ran this run from zero output volts to approx 2.7V. Part of this drop is a sleazy battery monitor circuit that comes with the development board. Typically the 0.22 Farad super cap “battery” will hold a charge for several hours, especially if I don’t parallel the super cap with a white LED (thus 2.7V). But for this test, I wanted to demonstrate how this chip can operate from near zero battery residual charge and come alive. To me that is a pretty darn cool feature! The MPPT chip can operate off of 0.3V inputs. See http://www.st.com/internet/analog/product/251161.jsp for more information...

I will edit this post with a plot of the output voltage over sample time. I would love to know more about the water pumping device mentioned! Do you have a URL???
Cheers,
-NerdyEE

Hi Again Bumpkin,

Here is a plot of the input and output voltage, current, and power. It is a bit cluttered! The legend shows the first three lines use the scale on the left, where the last three use the scale on the right. I called this the EVERYTHING PLOT as it is a plot of everything (nothing hidden)…

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Note how the output voltage ramps up due to the current, just like a battery would, but tops off with a soft knee at 2.7V due to the White LED starting to conduct the current…

I am welcome for test suggestions and/or setup recommendations!

Cheers,
-NerdyEE

NerdyEE, this place makes some of the aforementioned equipment, though in retrospect it looks like the technology depends more on pumps than controllers. I haven't looked too deep. http://www.sunpumps.com/ It's ironic in the investigation of Stirlings, that as I watch all those watts float up the chimney of my woodstove I have to limit computer time because my P.V.s are covered with snow. Bumpkin

Hey NerdyEE, Bumpkin (and all other interested parties),

Well stepping to the side of the controller for a second I guess we could look at the generator, from which it is receiving its input..
In my searching of Stirling engines I've seen countless random generators/motors tacked on to well made Stirling engines and often thought to myself that there is no way that most of those are really giving a true indication of power output.
I was considering how best to match generator sizes and windings with the load/charge voltage, so is why i started the 'MPPT for Stirling engine' thread . From the way I understand it there is only a, limited load and related RPM zone, where a generator and its windings are truly at their most efficient, when directly connected to a 'Fixed' output.
By using the MPPT we free the windings from the system voltage which allows them to run with a more suited, voltage and current that is free to dynamically change with different conditions, to get the best power output from that generator, again all regulated by the Maximum Power Point Tracker.

Some more points to consider about generator ineficiencies and losses are the different kinds of Copper losses, Magnetic losses and Mechanical losses.
http://www.powerelectricalblog.com/2007 ... -eddy.html

In essence I think that the smaller you go with the generator size the smaller the losses will be (until you go too small with the generator and it is overloaded, either electrically or mechanically).
Also for any Stirling engine/generator pairing, I think it would be interesting to alter and test the drive ratio incrementally and see how the power would chart over progressive runs (all whilst connected through the MPPT of course), I have a feeling even with the MPPT, there would be a Goldilocks zone for this with any pairing as well (due to aspects of the generator).

Just some thoughts
vamoose