Author Topic: High Voltage Inverter Design with PWM control for battery charger  (Read 1068 times)

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mrpackethead

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Hi all, i'm quite new to this game, and i've been playing a bit.. i've got a few questions that some of you may be able to answer, but first some backgroudn.


I've been tinkering with some Fisher Pakeyl Motors, and since they are cheap, readily available and mechanically easy to work with, i want to continue with them..  both for hydro and wind.  


I immediately was quite suprised with what most peopel seem to do, which is rewire the stator, and convert them to low voltage..  I figured that the high voltage output was considerably better as i would get less loss in cables / slip rings etc.    I also was quite taken back that most people just attached their batterys to some retified DC from the mill..  It works.. but not particually efficently..


I read in some other postings that people have tryed using PC power supplys, with Universal inputs, to produce a constant voltage output from the so called 'wild' AC that they get from their mill.   That concept quite appealed.. as it used cheap and easy to get components..       Of course i realised that i would need to control the current flow into the batterys.. A simple PWM switching solution sorts that out.. I used a reflashed linksys wrt54gs running openwrt ( www.openwrt.org ) and a few one wire devices to read the frequency of the incoming ac, and set the width of a PWM chopper on the ouputs of the ATX powersupplys ( one per phase ), 5V outputs wired in series to get 15V which works quite well as a charger.


What is good about using the ATX power supplys with the Universal input is that they deal with my 'wild' AC pretty well..  ( no smoke as yet )..


Today, i went looking for some bigger power supplys, so i could perhaps run a bigger mill..   It seems that theres not really anything much larger than 300W, with a universal input..  Most of what i looked at was universal to about 100W, and then it was a manual switch to deal with two ranges.. ( 120V / 230V +/- a bit ) ...


Why is this?? Is there some problem with dealing to such a wide voltage input at higher voltages??   Alternatively does anyone know of a design or supply of a SMPS that will cope with my 'wild' AC source..  Ideally i'd like to get rid having to have three differnt p/s, so i don't mind building somethign.. ( if it is possible )


It also made me think.. Perhaps this design is not really that efficent.. Are universal input Switch mode power supplies not good for efficency.. At 3W for your cellphone charger i guess its not a problem, if you run at 50%.  


I look forward to any help anyone can offer..

« Last Edit: November 21, 2006, 04:26:16 AM by (unknown) »

Flux

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Re: High Voltage Inverter battery charger
« Reply #1 on: November 20, 2006, 11:46:53 PM »
These things have been developed for specific needs, mainly computer power supplies.


They are concerned mainly with small size, weight and low cost. Reduction of heat is important, absolute efficiency may not be a high priority.


Once you go beyond the needs of the mass market things are not readily available, development cost is too great.


Probably if you want something in the 1kW range you are going to have to build it, then you find out where the development costs come from, but you can probably adapt the existing technology for small increases in size.


You can change the thing to do what you want, you certainly don't want a voltage regulated output, you need to track your output so that the input power to the F & P follows the prop output.


If you are up to building these things, go ahead and share it with us, otherwise leave well alone and save the smoke.

Flux

« Last Edit: November 20, 2006, 11:46:53 PM by (unknown) »

Opera House

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Re: High Voltage Inverter Design with PWM
« Reply #2 on: November 21, 2006, 03:57:47 AM »
With a mill you would have the best luck with the PWM monitoring the input voltage.  You could then set the cut in speed.  As you draw more power the speed slows and the input voltage drops.  The voltage just won't change that much, over 2:1.  Adjusting the gain slope will optomize the output power.  Dont worry about the output, just think of it as a current source. A second input of the PWM can shut it down if battery voltage gets too high.  A diverter or shunt on the input will be needed for input over voltage and overspeed if the PWM shuts down.  Support or this technology is very weak on this board.
« Last Edit: November 21, 2006, 03:57:47 AM by (unknown) »

Nando

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Re: High Voltage Inverter battery charger
« Reply #3 on: November 21, 2006, 05:26:20 AM »
FLUX;


You hit the nail, right on center, the development cost is TOO great.


Just recently, I needed a power supply capable of 48 Volts at 1 KW, the quantity just below 125 units, analyzing the development cost and time to get it to produce the power at a reasonable quality, is was decided to buy the units.


The price varied from about 800 to 1000 dollars, and these units had PFC input to allow variable input voltage that with the addition of a small circuit, the supply acquired MPPT capabilities if necessary.


So, for the initial message sender, they are available up to several kilowatts but one pays for them in "hard" cash and not in the "soft" cash for the popular supplies that many times are available in the "surplus" market.


Nando

« Last Edit: November 21, 2006, 05:26:20 AM by (unknown) »

inode buddha

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Re: High Voltage Inverter battery charger
« Reply #4 on: November 21, 2006, 12:21:31 PM »
Perhaps some of the power supplies on this page


http://www.surpluscenter.com/sort.asp?UID=2006112115180516&catname=electric&keyword=EPPD


would do the trick? I kinda want to play with those big ones myself... let alone some of the transformers.

« Last Edit: November 21, 2006, 12:21:31 PM by (unknown) »

mrpackethead

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Re: High Voltage Inverter Design with PWM
« Reply #5 on: November 21, 2006, 02:38:07 PM »
Hi Opera.. Thats pretty much what i'm doing now..    I'm just using stuff that was readily available..


Using a easy to program micro-controller ( openwrt on a linksys wrt54g ) gives me a pretty high level envirometn to mess with things.. ( my control code is written in perl and shell scripts so far! )..


in terms of what to monitor, for calculating the width of the pwm, i have found that the voltage at the mill, is proporitional to the frequency.. So measuring either gives the same end result.      Using PWM effectively changes my fixed voltage supply to a varible current course.

« Last Edit: November 21, 2006, 02:38:07 PM by (unknown) »

mrpackethead

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Re: High Voltage Inverter battery charger
« Reply #6 on: November 21, 2006, 02:40:03 PM »
Hi Nando.. At $800-$1000 i'd be keen to find out what that ps you are talking about is.
« Last Edit: November 21, 2006, 02:40:03 PM by (unknown) »

scottsAI

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Re: High Voltage Inverter for battery charger
« Reply #7 on: November 21, 2006, 04:31:01 PM »
Hello mrpackethead,


Sorry to bring you bad news.

Most of the lower cost ATX supplies list at 65 to 70% efficiency at full load, drops at lower power.


I have 18 SETI computers, along with a $125/mo electric bill, spent several months looking to improve their efficiency. By spending as much as I paid for the whole computer I could find 80% supplies. I calculated years before payback. Still using original supplies.


Now, I shutdown during summer, dislike paying twice for the power. AC bill dropped 71% this summer.

Have fun,

Scott.

« Last Edit: November 21, 2006, 04:31:01 PM by (unknown) »

mrpackethead

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Re: High Voltage Inverter for battery charger
« Reply #8 on: November 21, 2006, 06:49:26 PM »
You know what.. I like a hard problem.

« Last Edit: November 21, 2006, 06:49:26 PM by (unknown) »

scottsAI

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Re: High Voltage Inverter for battery charger
« Reply #9 on: November 22, 2006, 07:41:04 AM »
Hello mrpackethead,


Great, then you have started out on something that is a hard problem!


You mentioned your new. So I will give a quick summery of a "hard problem."


What you need to make is a MPPT for wind. Max Power Point Tracker from solar.

To get the max power out, you must load the wind turbine based on available wind power.

Properly loaded wind turbine spins at half the speed of a non loaded blade.

The "why" people worry about having a proper load on the generator. (At least in high winds!-)


I have spent some time thinking about this solution.

Looks like the wind speed must be measured, dia, RPM of the blade, and TSR.

The proper loading can be figured and applied. Control can be as simple as keeping RPM based on wind speed! I see the need of a microprocessor?

Sound like fun?


Have fun,

Scott.

« Last Edit: November 22, 2006, 07:41:04 AM by (unknown) »

mrpackethead

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Re: High Voltage Inverter for battery charger
« Reply #10 on: November 22, 2006, 02:26:01 PM »
yes, a MPPT is needed. This is not a hard problem.


The hard problem is trying to use easy to get, cheap components, in a way that they where not intended for.

« Last Edit: November 22, 2006, 02:26:01 PM by (unknown) »

scottsAI

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Re: High Voltage Inverter for battery charger
« Reply #11 on: November 22, 2006, 03:55:46 PM »
Hello mrpackethead,


MPPT is not problem? !!

Then I don't understand why your trying to use existing electronics.

They will be a compromise at best, designed from individual parts will result in a much more efficient system and much lower cost.


When covering a large power range I find the magnetics are best split into a couple power ranges. Saves on power losses, simplifies support electronics etc.

What do you think?

Have fun,

Scott.

« Last Edit: November 22, 2006, 03:55:46 PM by (unknown) »

Nando

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Re: High Voltage Inverter battery charger
« Reply #12 on: November 23, 2006, 06:12:25 AM »
Since You asked and the analysis I did was a few years old, I was going to do a search and how fortunate You were, I got a small advertisement in the mail with power supplies from Astrodyne.


Visist www.astrodyne.com and look for - all must be with PFC & choose the output voltage model -- You will need to ask questions to see if the supplies are the proper one for You.


PSP1000 AROUND $500


PSP1500 AROUND $826


RSP1500 AROUND $807


To convert for battery charging one needs to know some electronics, also, to convert for a wind mill charger controller additional changes are required.


Input needs to be Universal INPUT without input switching from low to high voltage ( doubler rectifier to full wave rectifier).


Need to add 3 phase rectifier to the input.


You need a small circuit to read the input voltage to modify the current detector profile of the PFC.


Then a MPPT circuit to regulate the output current of the converter by taking the input voltage, the battery voltage, the PWM duty cycle and a square wave at low frequency to modulate the MPPT circuit.


This way the supply will reduce the output current as defined by the input power.


Go to my files and down load the : 2IFD_MPPT_.PDF


It is a basic battery charger that has MPPT capabilities that may give You the MPPT circuit section to implement for your high power.


Nando

« Last Edit: November 23, 2006, 06:12:25 AM by (unknown) »

mrpackethead

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Re: High Voltage Inverter battery charger
« Reply #13 on: November 28, 2006, 12:14:52 PM »
Thanks Nando, for your links.. I'll digest and come back on this soon.
« Last Edit: November 28, 2006, 12:14:52 PM by (unknown) »