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ltopower Regular Member Joined: 08/03/2019 Location: United KingdomPosts: 64
Posted: 12:20am 08 Mar 2019
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Like the concept.
One thought, if you could design the DC level so that the MPPT voltage was say 5% above the rectified DC from the grid the system would then load share closer to the optimal mppt voltage level and get the most out of the solar panels. Potentially using a step down transformer if the grid voltage is too high for the inverter design ?
LadyN Guru Joined: 26/01/2019 Location: United StatesPosts: 408
Posted: 12:38am 08 Mar 2019
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ltopower, WELCOME to the board!
Are you interested in building a Warpverter? We will be beginning a build shortly and it will be a lot of fun doing it with you too!
Load sharing would be something I will be spending a lot of time developing.
To answer your question, we/I control the output of the boosting microinverter/mppt controller and it would typically ride higher than the rectified DC from the grid, yes.
What I am unfortunately clear less about is when a load comes in and solar power is not enough to satisfy the load.
Then we reduce the output of the mppt controller until its output voltage is <= rectified DC from the grid.
At that point, how do we STILL ensure that output of the mppt controller gets blended in with the rectified DC from the grid.
Tony says it will work, but unfortunately I dont understand it (and am upset that I dont understand it).
I really want the output of the mppt controller to get blended in with the rectified DC from the grid. I will be very sad if at this point, because the output from both systems are very close, the rectified DC "wins" most of the time.
AFAIK, the output of the mppt controller will have to be VERY CLOSE to the output of the rectified DC from the grid to stop it from reverse biasing the diode.
If this DOES NOT happen and the reverse biasing happens when I don't want it to, I would have to then think about active switching.
I have tabled this for later when I will have to address it if it comes upEdited by LadyN 2019-03-09
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:45am 08 Mar 2019
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People seem to have a real phobia about MPPT, but its not really a sharp power peak, its more of a very broad shallow hump.
If you pull it down say ten or twenty volts below the peak, the voltage falls, but the current still increases. Yes the power does drop off slightly, but its not as dramatic as many people seem to think.
If you have 6Kw of panels and are only pulling 500 watts to drive your refrigerator, some lights, and a computer or two, its never going to come close to the maximum power loading point anyway.
Now if there is some kind of power limiting system, all that can do is crash the 230v coming out of the inverter, and you are really no better off. No type of control system can add power that is just not there to be had.
Cheers, Tony.
ltopower Regular Member Joined: 08/03/2019 Location: United KingdomPosts: 64
Posted: 01:46am 16 Mar 2019
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Triggered by warpspeeds solar and high voltage inverter grid mix, I was looking at an old post I did asking if a VSD could be used as an inverter.. Now, taking the solar input directly into the DC bus line of the VSD.... just needs the PWM smoothing out ?
I realise the VSD units have a lot of motor parameters, but a fair few of the parameters can be changed to force the output stability.
Was just a thought after reading this and then 1+1 = 7.. hmmm...
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:52am 16 Mar 2019
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The problem with modern VSDs is that they are just too clever.
The load has to be exactly balanced between all three phases, or the microcontroller will assume that the "motor" has some very serious problems. It will just refuse to do anything and bring up an error message.
They are pretty useless for anything except driving induction motors unfortunately.Cheers, Tony.
tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438
Posted: 03:54pm 16 Mar 2019
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Bought this way back to test a 3-phase multiple triac device that is sensitive to noise on the sine waveform, it needs to sense exact zero crossing.
The output is unfiltered PWM which probably does not affect intended induction motor loads. It was very difficult to filter.
I still have not used it for testing, there are still noise spikes.Edited by tinyt 2019-03-18
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:14pm 16 Mar 2019
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The high frequency noise has almost no effect on an inductive load like a motor. Trying to filter it will be difficult but not impossible.
One slight problem will be that there is no neutral wire, three phase motors only have three wires without any neutral connection.
Another even bigger problem will be that the current sensors in the VFD will detect any slight unbalance in load between the three phases, and will shut down and just refuse to work.Cheers, Tony.
tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438
Posted: 04:21pm 16 Mar 2019
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This one can be used on single phase but when I was trying to filter the output, stupid me modified the current sensor circuit and blew it. The power chip alone cost $36 for one piece. So bought another one from aliexpress but have not touched it since then.
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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