PV + wind + MPPT setup in Mozda, Gujarat, India

[domwild]

Hi,

Have lost link to this web page from a student project. But will try to add in the picture of the electric connections. If it does not work here, do not despair, I will work on it.

Just in case I cannot bring in the picture from the *.doc file, here are two questions:

1. 48V system, 1200 Watt, 10 foot dia prop, after rectifiers (3 x 35 Amps) and before the batteries is one 1000 uF, 160 V electrolytic capacitor. I suspect caps are used to smooth out the ripple BUT is there an increase in Watts one can squeeze out of a system by adding in a single cap?
   
2. This seems to be a rather large cap, one Millifarad, is there a rough formula perhaps depending on the wattage what size and sort of a cap should be used?
   
   

Picture will follow.

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[domwild]

Here is the picture, hope, hope:

HAVE A MERRY CHRISTMAS WITH SNOW AND NOT DURING 35 DEGREES CENTIGRADE!

[TomW]

dom;

You need to upload that picture with a name that does not contain spaces. Windows puts them in filenames and scoop gets confused.

Cheers.

TomW

[domwild]

Sorry, found the link again and here it is:

http://courses.ece.uiuc.edu/ece445/projects/spring2006/project3_appendix.doc

I will check if that works.

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dom

[domwild]

Tom,

Thanks for that. Here it is:

By the way, the link, that has been found should give the whole picture.

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[ghurd]

The doc file link works fine.

The setup looks... unusual to me. Proportionally and complexity speaking.

I hope they have a better use for the dump power, as the hysteresis and dumping at C/0.7 could suggest.

Maybe that's just me.

G-

[domwild]

Hi,

Here is the link to the final report, the link to the appendix is shown before.

http://courses.ece.uiuc.edu/ece445/projects/spring2006/project3_final_paper.doc

A few comments to Tom and whoever is interested:

1. The subject line is accepted on posting, but needs the word "India" removed, otherwise the posting fails.
   
2. Tried twice to insert the *.doc file with only the schematic included and that failed. The second time I had the blank removed from the filename.
   
   

Re the Buck converter:

1. Efficiency is claimed to be only 11%, is this common for DC-to-DC conversion?

I hope the electrical setup is of interest, the emergency brake seems to short all three phases. There has been a call to show a MPPT schematic and this is the first one I have seen before for wind. It is Buck only, so does not try to harvest energy via Boost when the voltage is below battery cut-in.

One hopes this is a web page of interest to all those with a greater knowledge of electronics who can offer a professional critique of the approach of three uni students.

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[Nando]

The 1000 Uf / 160 volts is used for a couple of reasons:

One : to even out the voltage excursions of the generator.

Two : To " Eliminate" the inductance of the cabling and the generator itself for the DC converter proper operation to work against a low AC Impedance.

For 1 Kw power source, I have used up to about 47,000 micro-farads to improve the DC converter efficiency at high current levels.

The capacitor should be close to the DC converter.

In power supplies, using 60 HZ, single phase, full wave rectification, a basic ripple reduction to 10 %, a 4000 Uf for 1 amp of load current.

For wind mills, 3 phase, where the frequency may be around 20 Hertz the capacitor may be calculated with the same 4000 Uf per amp of current.

Also, for wind mills that have such high variation on voltage, then one may assume that the capacitor is just swamping the inductance, so 1000 or so Uf is sufficient for most jobs.

Nando

[Nando]

To evaluate the design and the efficiency it is necessary to spend more time,it is illogical such 11 %.

To really know what is going on, a complete schematic of the converter is needed, I see one problem and it is handling of the basic power to the TL598 which has a limit of about 40 volts.

Another point is the driving of the MosFet, the isolation due to the high input voltage and the clamping of the diode.

If you can send the schematic to me, I can check the design and give you a basic report -- the design should have, at least, 85 % efficiency, so something major is not right in the design.

Another one thing, I noticed, is the small battery chargers that are linear and one is raised above 24 volts to limit the LM317T input voltage.

There are other IC with much higher voltage capabilities to connect directly to 48 volts and with PWM which makes the efficiency to around 90 % instead of the 50 % that the LM317 gives.

Another problem is the power MosFet, which requires proper evaluation and again the schematic is needed.

Nando

[Nando]

After examining the supplied basic schematic of the converter,

I have found the problems why the converter is so in-efficient and why the Power Mosfet is over heating, as well as, the lack of output voltage accuracy

The design is quite basic and the designers did not know what type of voltage isolation is needed to attain high efficiency, accurate output voltage and good high voltage dynamic operation.

-- 1) the power supply for the TL598 is formed by a Zener diode and a 500 Ohms 50 Watts resistor, same thing goes for the voltage for the MosFet driver.

-- 2 ) The voltage range of the input may go to 85 volts or even higher. and the TL598 is capable of 40 volts maximum

-- 3 ) The circuit bias supply voltage for the Mosfet driver is set to 12 volts, so it cannot swing the input voltage range to maintain proper gate voltage.

-- 4) the Feed back path goes into the error amplifier which was set as a pure DC gain amplifier and that is a NO, NO and NOT !. The amplifier requires limited AC gain and open DC gain for the loop to fully close to set the output voltage accurately.

Solutions: The Mosfet driver needs to have a high voltage offset type, IRF and many manufacturers do have many types, some from 100 to 600 volts capability and some with 2 or more Amps driving capabilities.

-- The power supply for the TL598 needs to be started with a low current source and once it starts to charge one can add a two chokes in series and a diode to charge the device supply with enough current capabilities, or the main choke can have an additional terminal that sets the voltage to a 1/4 of the battery voltage. or another additional circuit to connect the 12 volts lower battery to the device supply, lastly a small IC to produce the necessary voltages ( this is my preferred way).

Theses changes alone will bring the efficiency to the upper 80's or lower 90's and the output voltage accuracy is improved to a few millivolts range.

Also the high voltage detector is not needed allowing the converter to continue working with the higher volts, limited in this case by the breakdown of the Power MosFet.

Lastly, the linear charge regulators for the small amp-hour batteries are not the best solution, both should be changed to a better circuit using the same circuit for the high power converter to get better efficiency, as a matter of fact that should be the optimum solution because these circuits can be used to replace the main one in case the main is damaged -- I have done these with several systems.

Nando

[jimovonz]

Thanks Nando - If you could just make your suggested alterations to the schematic for us we can put the whole MPPT thinbg to bed.

[domwild]

Thanks Nando,

Now I know for the first time why Jerry and those three "Engineers without Borders USA" use one or several capacitors.

I remember someone once tried to decipher the schematic of the Air-X turbine which uses MPPT but he was unsuccessful.

Thanks for giving us the reasons for the low efficiency; those of us working on MPPT will surely find this web site interesting + the critique. The circuit is certainly not expensive.

I do not like the emergency brake; shorting all three phases could burn out the windings.

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[Nando]

This is a classical problem, giving to "newbies" in electronics; the assignment of a major project.

Clearly NOT good planning and not good definition of the problem with poor technical know how and lack of experience.

I wonder what the contact person for that project is, to see if this part of the design was implemented properly or still they have the problem.

The over all topology with the different pieces of equipment seems to be "too heavy" technology way with solutions that clearly are non-compatible with some of the charging procedures.

The charger does not have MPPT capabilities, so simple to add.

I do not like short circuiting emergency braking that most of the time this emergency is due to excessive RPM, for me it is a poor decision of how to protect the wind mill.

The proper way for emergency is the forced furling that can use the power of the generator itself to do it, though the right way to have a wind mill is to have one with PITCH control.

So many wind mills destroyed, blades broken, generators burnt, or towers falling with major loses just because the Furling did not work well when needed, Pitch control protects the wind mill, limiting the power out or the RPM if unloaded, of course many wind mills with furling have survived as well.

Nando