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However, I'm curious to know *IF* there is a circuit that is infinitely variable on the input side, and with a fixed voltage on the output side.
Example:
Wind turbine turning slowly might produce say 6 volts, and vary up to 50v at max RPM.
Is there any way to 'tie' the voltage output to a fixed amount - i.e. 55v
What I'm trying to achieve is constant power input into the Grid, no matter what the input voltage is (using a a Latronics PV Edge inverter).
If this is achievable, it should be possible to extract just about every watt produced by the turbine - even in low winds. True, the current may be very LOW - but would add up over time.
Is this feasible ?
Regards, Greg.
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 05:52am 06 May 2009
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Hi Greg,
WRT your posting.
The link you provide is for voltage multipliers as typically found in an older style CRT display unit.
The circuit with an infinitely variable input with a fixed output is similar in function to a buck or boost type regulator. These are the type of ccts that manufacturers would akin to suit a wind MPPT. Don't see too many out there that will work on a DIY windmill.
The constant power input to grid. Where is the variable voltage/variable current that a windmill produces being stored, so that constant power is supplied to the grid? Maybe you mean a battery?
The Latronics, as well as most other grid connect inverters, consume between 10 and 30W when actually connected to the grid. Not much of a problem with a 1-3kW array driving things. The windmill in light winds may only produce 0-20W. The volts and current change in proportion to the winds, as we know. Latronics use a system like mine to maintain grid connection when the input voltage falls to a point below which windmill power is exported to the grid. The connection is maintained, barring grid disturbance, for up to 15mins. If there is sustained insuffficient power, the inverter will then disconnects from the grid. I had discussed this approach with latronics and it is now incorporated in their later firmware design. The system is reset when sufficient power is supplied by the windmill.
The voltage doubler link you gave is for a series multiplier arrangement. This is a high impedance unit and is unsuitable for windmill applications, but is useful in Jacobs ladder type examples, or providing a low current biasing voltage, say in a CRT application as I mentioned above.
The arrangement I have presented is a parallel 3phase full bridge design, with low impedance, and is suitable for windmills.
With a batteryless grid connect system it is important to only power up the inverter when there is sufficient power to offset the power required to maintain the grid connection.
I have spent a few years now working on PWM type arrangements to load my windmills in a way that the output closely follows the available wind energy. The capacitor multiplier arrangements I have presented are the most reliable and give the best matching of the alternator to the available wind energy. The operating windspeed range of a typical windmill is extended. A combination of upper and lower power range is expected.
I believe a manufacture is looking into testing of the voltage multiplier with the potential of adopting it into their own windmill designs. This will not necessarily help a DIY.
G'Day Gordon.
Sorry mate - I'm a newbie, just trying to fathom what is & isn't possible.
This has given me something else to look at (thanks).
No, I didn't mean storing the power. My intention was to 'use' every watt produced as it was generated (without batteries). For example, if the WT is only generating say 6 volts at 3m/s we MAY get say 50 watts. If we could boost that 6v to 54v (enough to trigger the PV Edge) then we should be able to 'use' the 50w produced (less losses etc). As wind speed increases, and the watts increase, the output would still be fixed at 54v (going into the PV Edge), but have more watts to pump into the system.
This is a bit of a worry. Am I to assume that with the Latronics consuming up to 30w itself, (which seems very high) anything LESS THAN 30w produced by a WT is effectively negated. In a low wind area, by the sounds of it, the Inverter could end up using more energy that a WT might produce. (Or am I on the wrong track?)
Sorry, I didn't know the circuit was not suitable.
No worries, however, from what I understood of the Caps / Voltage Doubler, it would not be able to do what I'm suggesting re 'fixing' output voltage at a sustained 54v - no matter what the input voltage was (or am I wrong ?)
Yes, I can see why now - with the inverter using the 10w to 30w of power. Potentially, a considerable drain.
So... How can we do it right ?
I'm not familiar with PWM.
Sorry if I sound like a complete idiot Gordon. I'm still trying to wrap my head around how this stuff all works.
Maybe I should just forget it & go back to 'consuming' power.
Regards, Greg.
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 12:37pm 07 May 2009
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Hi Greg,
My Latronics PVEdge 1200 consumes 18W or so when grid connection is made, and various lesser amounts when attempting to grid connect. My SMA 1100W is around 15W, and SMA 1700W about 20W. I believe Faronius have a technology that reduces switching components with load, and this reduces losses, with increased electronic complexity.
The key with grid connection of a windmill is to turn OFF the grid connection when the wind cannot sustain the power. I used a 10 minute timing window, with an auxillary power supply that was switched ON and OFF to maintain the required amount of power. If the windmill supplied insufficient power for 10 consecutive minutes, then the assisting power supply stayed OFF, and the grid connection was broken. This was an empirically determined solution, by looking at my own windmill. The F&P windmill, with cogging, requires more wind energy to get going, so the cutin and supply problem is not as great. In the last week, my F&P mill has only turned a couple of times. If the unit was directly connected to the grid, then the inverter would never have connected. My AxFx windmill however has turned and produced power on most days. If this had been directly grid connected, then this would require the smart system to help maintain the connection when there was sufficient winds. Latronics use an auxillary winding within the inverter as part of the smart system, without the need of an auxillary power supply.
The capacitors form an automatic variable voltage gain boost cct once cutin is reached and loading occurs. It is very important to have voltage limiting on the input of a grid connected inverter, especially with a voltage doubler, as the unloaded voltage could exceed system maximums. The problems I have seen 1st hand, with an expensive non warranty repair.
The 50W at 3m/s is highly optimistic. The wind energy would be 12W/m^2 of blade area. The shaft power may be 3W/m^2 and the output power may only be 2W/m^2. A 25m^2 windmill area would have about 3m blades.
A cct to give a 10x voltage range is a tall order without multiple stages. I have achieved 3x with high efficiency with a single stage. Commercial units are usually around 2x, or less. You may do it, but effficiency goes out the window.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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