Author Topic: MPPT  (Read 12425 times)

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Offline artv

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MPPT
« on: January 06, 2012, 09:28:24 pm »
Maximum Power Point Tracking..
I'm not even sure if thats right?
Could it be used to close a contact, when the coil is at max out-put?
I want the circut to engage just before peak output, then disengage , right after peak output..
I've been trying to do this by mechanical means .......
Just wondering if this is what MPPT does??
and so it goes on..........artv

Offline Bryan1

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Re: MPPT
« Reply #1 on: January 06, 2012, 09:54:30 pm »
G'day Artv,
                  Basically a MPPT uses a buck step down converter and the P channel fet is pulsed to get the maximum performance. I am working on a MPPT project and the pic below shows the barebones of the buck circuit.

Cheers Bryan

70-0

Offline Wolvenar

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Re: MPPT
« Reply #2 on: January 07, 2012, 05:41:38 am »
LOL no offence Bryan, but I can see a laymen say..
What the heck did he just say ?
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline artv

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Re: MPPT
« Reply #3 on: January 07, 2012, 03:51:28 pm »
Thanks for the reply Bryan1,
But like Wolvenar just said "what the heck"..
I don't know much of anything with electronics...
But your diagram basically splits the output of each phase , and feeds it to both sides of each bridge . I've never seen this before.
I will give it a try....
I found that by putting a diode parralel to the phase connection ,then connecting back to the dc out of the bridge ,gives about a 10 percent increase.
Kind of hard to explain.
When I can get my mechanical switch working right,(not very consistant),  it triples the output and only testing one phase.
here's a pic of my latest failure73-0
It didn't work.....artv

Offline rossw

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Re: MPPT
« Reply #4 on: January 07, 2012, 03:58:35 pm »
Art, Bryans example was a fairly specific case of MPPT.

MPPT is really a "concept", that may be implemented in a variety of ways. It stands for "Maximum Power Point Tracking", and it means exactly what it reads like.

It's a control system that adjusts itself to get the Maximum Power from a source, and it then Tracks as changes happen, to ensure it remains on the maximum power point.

Initially, this was most common on PV arrays, where the voltage changes with current drawn, but isn't linear. There's one point on the curve where you get maximum WATTS out. It's not the maximum current, and it's not the maximum volts, and it varies depending on temperature and illumination and other factors.

It's also finding favor now with wind turbines. Turbines are trickier though, as they change far more quickly than PV, and if you lose control with a PV, nothing happens much, whereas a turbine can easily fly apart.

Offline philb

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Re: MPPT
« Reply #5 on: January 07, 2012, 10:42:44 pm »
This is probably going to be a dumb question.

Are switch mode power supplies also MPPT? 

SWPS's take variable voltages on the input and keep the output voltage constant, as I understand.

Offline rossw

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Re: MPPT
« Reply #6 on: January 07, 2012, 11:06:02 pm »
Are switch mode power supplies also MPPT? 

SWPS's take variable voltages on the input and keep the output voltage constant, as I understand.

Most modern MPPT devices incorporate switch-mode power supply concepts and parts. But few SMPS will be capable of MPPT without modification.

Offline Bryan1

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Re: MPPT
« Reply #7 on: January 08, 2012, 02:09:14 am »
G'day ArtV,
                 Ok I did say that circuit was the barebones basically a pic32 running basic will control it, I am going to do this for my PV array first as it will be easier. Now for wind one will have cube the output for windspeed which will mean a total new algorithm.

Now if and when I can get this done I do feel it will be the Bees knees in stuff so I do doubt it will be public. But what the hell if guys want to come in on this lets do this project together and make it a real thing.

Programming in basic does seem easy and with these Duinomite boards it should be a breeze so keep tuned and stuff might happen.................

Cheers Bryan

Offline Burnit0017

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Re: MPPT
« Reply #8 on: January 08, 2012, 06:05:57 am »
 



This is a video that demonstrates the benefits of using a MPPT circuit with the system.
I was so inspired by the video that I start a project to determine if just a variable input volt buck converter would have the same benefits for just charging a battery bank. I have a basic circuit and now I am just trying to oscillate the MOSFET at a fixed frequency. Then test with the PMA at fixed RPM and than determine what kind of micro control is needed.   

Offline madlabs

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Re: MPPT
« Reply #9 on: January 15, 2012, 09:57:27 am »
Bryan,

DIY MPPT is kind of a holy grail for me. What power levels are you planning? I got a PV mppt going but after about 5 amps the FET got too hot. I wasn't driving it correctly and I was playing on perfboard.

I now have access to a CNC PCB machine. Trouble is I don't have the design skills to desing the circuit. Are you making schematics with a CAD? I'd love to find someone to collaborate with. While I am not an EE, I do have a scope or two, a decent sized PV array, good soldering and assembly skills.

I'd like to be able to make DIY mppt that can handle 20 or more amps.

Jonathan
Some people are like a Slinky - not really good for anything, but you still can't help but smile when you shove them down the stairs.

Offline MadScientist267

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Re: MPPT
« Reply #10 on: January 15, 2012, 10:13:15 am »
Quote from: artv
I've been trying to do this by mechanical means .......

Artv -

MPPT (and the core component, buck conversion) is done at speeds MUCH faster than what can be done with mechanical methods.

Buck converters are very "sensitive" in the sense that there are a lot of factors that determine how efficient they are. Not trying to shoo you away from the idea or anything, but understand what you will be up against when designing one. Even for those of us seasoned in electronics and experienced with the ideas involved, there can be a lot of "magic smoke" events and the like in the process of developing one...  :o

Steve
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Offline artv

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Re: MPPT
« Reply #11 on: January 15, 2012, 04:57:09 pm »
Hi Guys ,...Thanks for the replies..
Steve do you think maybe a dump load controller could switch fast enough??
I was thinking 15vdc engage ,12vdc disengage,....the mechanical switch I have now switches so fast , it is almost a constant connection, the wires keep burning up,..
they actually weld themselves together..
I figure let it build to 15vdc ,dump to battery ,disengage ,then repeat....
I don't know maybe it's impossible.......wish I had more time to learn this stuff...
I'll keep pluggin away......artv

Offline rossw

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Re: MPPT
« Reply #12 on: January 15, 2012, 05:05:07 pm »
Hi Guys ,...Thanks for the replies..
Steve do you think maybe a dump load controller could switch fast enough??
I was thinking 15vdc engage ,12vdc disengage,....the mechanical switch I have now switches so fast , it is almost a constant connection, the wires keep burning up,..
they actually weld themselves together..
I figure let it build to 15vdc ,dump to battery ,disengage ,then repeat....
I don't know maybe it's impossible.......wish I had more time to learn this stuff...
I'll keep pluggin away......artv

Nothing mechanical or electromechanical is going to come close to making it.
To give you an example: if you have a plate with a cam and a contact that makes and breaks the connection once every revolution, it would need to be spinning at 1,200,000 RPM to achieve the 20KHz switching discussed earlier (and/or on other threads about MPPT). Even if you could make and break a contact 4 times for each revolution, it would need to be spinning at 300,000 RPM.

Or, putting that another way - a shaft turning at 1000 RPM, with a contact to make and break once per revolution would make only 16Hz.

Mechanical things are *slow*.

Offline MadScientist267

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Re: MPPT
« Reply #13 on: January 15, 2012, 08:58:57 pm »
To add on to what Ross said:

For MPPT, it's not as simple as just turning it on and off proportionally to the speed. This is simply frequency modulation, and the duty cycle remains (roughly) the same throughout the range of operating speeds. This doesn't really do much good in terms of controlling the power going through the circuit. To control the power and convert it, the *duty cycle* must be modulated, which is the percentage of the time the switch is on vs. off, regardless of frequency.

The RPM of a shaft (in this case the rotor of the alternator) is typically sensed by something such as a hall effect sensor, a kind of solid state magnetic switch (which has no moving parts). More commonly, it is just picked up directly by the AC coming from the coils in the alternator, and translated from there. Either way, the point is, there are no moving parts associated with "reading" the RPM of the shaft.

The output from this is then in turn used by a microprocessor to compare the speed against a pre-programmed table, which the processor then uses to determine the proper PWM percentage to modulate the MOSFET (type of transistor, in the buck converter section) that turns the juice on and off to the inductor (which is where the "extra" energy gets stored in the process of converting it to another form).

This has to happen very quickly in order to be effective; ***MUCH*** quicker than can be done with anything mechanical.

In the DIY versions of a buck converter, the speeds that they can run at are typically restricted by design limitation (imposed by the materials and construction methods available to the average Joe). 20kHz is ok, and is probably typical, although a little too close to the audible range for my taste, but in terms of design, is sufficient to operate reasonably well with commonly available parts. Personally, I like 25-30kHz, just so I don't have to ask myself "what is that WHINING sound?" every so often... :)

Faster is better, to a point, at which time the switching losses (the time it takes the MOSFET to turn on and off) become excessive, and heat becomes a problem. Heat=Lost power.

There's a lot more to it than that, but this targets the point you're at right now. Hope it helps a little. ;)

Steve
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