I have 2 1000W non-limited grid tie inverters. I need to at times limit the AC they output to my home grid (so i dont back feed) Yes i could just buy GTV w/ limiter but whats the fun and learning from that? So thought process go something like limit the DC input to do this!!! When less sun is shining on the panels i get less DC input and less AC output. Thinking a basic mosfet set up PWM controlled by an Arduino uno or any controller that can do PWM with probably some smoothing capacitor(s) to smooth the output? The issues are the inverters say the have an MPPT function built into them so will that cause problem?
Current set up is 4-5 panels connected in parallel to each inverter
Inverter specs DC input 20-45 VDC with MPPT built in
panel specs 250W 24V ... OCV 37.2V ....SSC 8.07A
then the system is operating as it normally does (med sun like today) i am seeing between 23-25V and 13-17 A at the DC input terminals of the inverter
Basically what i want is a throttling circuit on the DC input side of the inverter that i can have an Arduino vary to limit the input.
What specs of mosfet? capacitors? gate resistors? etc might i need to complete this?
PS this will be my 1st Arduino project so as much help as i can get is MUCH appertained I always say if i learned how to fly an airplane i can learn how to "____"
What is Your education and experience regarding those things?
Sending PWM into an inverter looks really off to me. Know that PWM technic does not give a nicely varying DC, like a toy train transformer.
brandonoh777:
I have 2 1000W non-limited grid tie inverters. I need to at times limit the AC they output to my home grid (so i dont back feed) Yes i could just buy GTV w/ limiter but whats the fun and learning from that? So thought process go something like limit the DC input to do this!!! When less sun is shining on the panels i get less DC input and less AC output. Thinking a basic mosfet set up PWM controlled by an Arduino uno or any controller that can do PWM with probably some smoothing capacitor(s) to smooth the output? The issues are the inverters say the have an MPPT function built into them so will that cause problem?
Current set up is 4-5 panels connected in parallel to each inverter
Inverter specs DC input 20-45 VDC with MPPT built in
panel specs 250W 24V ... OCV 37.2V ....SSC 8.07A
then the system is operating as it normally does (med sun like today) i am seeing between 23-25V and 13-17 A at the DC input terminals of the inverter
Basically what i want is a throttling circuit on the DC input side of the inverter that i can have an Arduino vary to limit the input.
What specs of mosfet? capacitors? gate resistors? etc might i need to complete this?
PS this will be my 1st Arduino project so as much help as i can get is MUCH appertained I always say if i learned how to fly an airplane i can learn how to "____"
Brandon
Playing around with high dc voltages and mains supply not recommended, regardless of how you consider your ability.
There are no-feedback relays especially designed for grid tie systems which must be installed by registered electrician and their install inspected and passed by one from the local supply authority.
There are warnings on the use of Arduino around any possible life threating situation and this is one of them.
Railroader:
What is Your education and experience regarding those things?
Sending PWM into an inverter looks really off to me. Know that PWM technic does not give a nicely varying DC, like a toy train transformer.
IS that not how a charger controller steps up/down voltage ? and the capacitors on the output would smooth out the ripple.
bluejets:
Playing around with high dc voltages and mains supply not recommended, regardless of how you consider your ability.
There are no-feedback relays especially designed for grid tie systems which must be installed by registered electrician and their install inspected and passed by one from the local supply authority.
There are warnings on the use of Arduino around any possible life threating situation and this is one of them.
One thing you gootta love about internet blogs are (people who im sure mean well, or at least i hope that do) telling you not to do something or play with things that are not toys. I am not playing around with mains voltage i am working around it very cautiously and slowly with as much knowledge as i can get/already have. As far as the DC voltages side its a 24/36 or at max will be 48V system with exception if i go with a slightly dif inverter which can handle up to about 90V DC of which i would treat with the same caution and respect as i do any other voltages of those number ranges.
brandonoh777:
IS that not how a charger controller steps up/down voltage ?
Search for literature regarding how such equipment is made. Your question sounds like quite some fantasy and less of knowledge.
I once got a master degree in electronics an more. To qualify for electrical experiments in various higher courses the one year course in measuring technic had to be passed. During the first lesson history told that one pupil died in a electrical lab. The highest voltage available was "only" 35 volt!
and you can die in a car going 35 MPH but your much more likely to at 150V/MPH...if we go through life saying i cant do/try/learn about this because of the what if's nothing will be accomplished....Now that we have covered all of the why you shouldnt's can we please get back to the electrical theory and physics?
you say Search for literature regarding how such equipment is made... I have and came up mostly come empty handed this is why i originally made the post here on the topic. You say feeding a PWM dc signal to an inverter is a bad thing? and i asked isnt that exactly how a solar charger controller "conditions" the energy it then passes from the solar panels to the batteries/inverters? isnt that how almost all switch mode DC power supplies regulate there outputs? of coarse through further smoothing capacitors on the output side to smooth out the ripple
I would recommend you do not do it. You have several control loops that will interact with each other. Your PWM loop will probably cause big problems with the Inverter control. It is more then likely using PWM as well. Why not simply switch panels in and out, that would be much safer. The BTS660 would make a nice high side switch. I do not know for sure if they will tolerate a back feed but I think they will. You should check into this first. Of course there is the old fashioned relay.
TomGeorge:
Hi,
If you have Grid-Tie, doesn't the excess energy that you don't use get pumped into the grid and you get paid for it?
What do you mean by "non limited"?
Can you explain what you mean by "back feed"?
Thanks.. Tom..
Only if u are set up for net metering..and by non limiting i mean the inverter will put out whatever it can on the AC side regardless of the demand of the house.... example house is only demanding 15 amps if the inverter can produce more than 15 amps it will and you will be backfeeding through the meter on the side of your house....a Grid tie inverter w/ limiter monoters the amp demand at the mains coming into your house and will "limit" its AC production to not exceed that
Hi,
Hmm, how did you get Grid-Tie and not a meter to measure both ways?
I would be very careful throttling back a PV panel output like that as a PV is not a voltage source but a current source.
Your inverter may not be happy with PWM current supply.
If I was you I would be DIVERTING the energy from your PV or output of inverter to another load, the energy is free.
Batteries, pre heating hot water as an example.
You could preheat water from the mains side of the inverters, so no interference needed to the source or the PV.
Another solution is to just switch out a panel or two when "over production" occurs.
You have 5 x 250W panels to each inverter.
Say 1000W max, (250W is a laboratory conditions spec), inverter efficiency say 95%.
So inverter output power 1000 * 0.95/110 = 8.6A (assuming 110V mains).
Two inverters = 17.2A max on a good day.
How much does your home consume on an average day that needs to have the power production throttled back?
TomGeorge:
Hi,
Hmm, how did you get Grid-Tie and not a meter to measure both ways?
I would be very careful throttling back a PV panel output like that as a PV is not a voltage source but a current source.
Your inverter may not be happy with PWM current supply.
If I was you I would be DIVERTING the energy from your PV or output of inverter to another load, the energy is free.
Batteries, pre heating hot water as an example.
You could preheat water from the mains side of the inverters, so no interference needed to the source or the PV.
Another solution is to just switch out a panel or two when "over production" occurs.
You have 5 x 250W panels to each inverter.
Say 1000W max, (250W is a laboratory conditions spec), inverter efficiency say 95%.
So inverter output power 1000 * 0.95/110 = 8.6A (assuming 110V mains).
Two inverters = 17.2A max on a good day.
How much does your home consume on an average day that needs to have the power production throttled back?
Tom....
Tom those are good ideas.. i have considered using the extra energy to run one of the 2 elements in my electric hot water tank. The thing i dont understand is why so many people say PWM to an inverter is bad... is this not how a solar charge controller regulates its DC conversions/outputs? PWM?
When the load is a passive load, like a heater, a motor etc., PWM can be used to vary the power delivered to the load.
Don't try to make a Pc run slower by feeding it with PWM. A Pc is an active device containing logic circuitry, as an inverter does.
brandonoh777:
Tom those are good ideas.. i have considered using the extra energy to run one of the 2 elements in my electric hot water tank. The thing i dont understand is why so many people say PWM to an inverter is bad... is this not how a solar charge controller regulates its DC conversions/outputs? PWM?
When a controller uses PWM it is using MPPT, Maximum Power Point Tracking, into a battery bank, that basically smooth's the PWM for any load that is using the PV energy.
A grid- tie inverter is usually designed for PV supply and no batteries.
The PV is a current source and most if not some of the inverters use MPPT internally on their inputs as part of their control system.
Supplying them with PWM is not what they are designed to see coming from the panels.
TomGeorge:
When a controller uses PWM it is using MPPT, Maximum Power Point Tracking, into a battery bank, that basically smooth's the PWM for any load that is using the PV energy.
A grid- tie inverter is usually designed for PV supply and no batteries.
The PV is a current source and most if not some of the inverters use MPPT internally on their inputs as part of their control system.
Supplying them with PWM is not what they are designed to see coming from the panels.
OK yes i am starting to see your points and i never said this was the most efficient way to do what i am trying to do its not there are somewhere around 30% losses when i have done it this way but it does work! I guess the big question is how do the grid tie inverters with internal limiters do the "limiting" if i better understand that i can better try to duplicate it electrically. I have seen 3rd party add on box limiters fore non limiting GTI's. My 2 1000W GTI's do say MPPT so they have some sort of MPPT function built into the DC side of them
Railroader:
When the load is a passive load, like a heater, a motor etc., PWM can be used to vary the power delivered to the load.
Don't try to make a Pc run slower by feeding it with PWM. A Pc is an active device containing logic circuitry, as an inverter does.
This all came about when i was looking at wanting to use ALL or as much as i can of the energy produced at the time it is produced and only store the extra at any given moment. I was originally told just use a battery bank in between the panels (through an mppt charge controller) and the inverters. This would somewhat work if im useing a GTI w/ limiter if not the inverters would just run full blast till the bat is depletded. Also i see the other problem is is, lets say the batt is depleted and the house has high demand at that time energy will still be going into the bat where i ONLY want the extra energy going into the bat. It may not fully charge the batt and thats ok i just wait till it is charged up and then use whatever extra energy in the batt at night till they are down to there cutt off voltage.
As a water analogy i want a valve on the flow form the PV-inverter "pipe" diverting energy to the bat ONLY the excess not demanded by the house load
I always say if i learned how to fly an airplane i can learn how to "____"