How to Combine Two AC Inputs for Load Sharing up to 2KW With Priority Switching?

Hello Everyone,


I would like to make a device that can take two different AC input and give the summing output.

For eg. both AC input can provide maximum 1KW of power individually, if we have the load less than or equal to 1KW then only AC1 should power the load. If the load is 1.2KW then AC1 should give 1KW and AC2 should give 0.2KW to its load.
Suggestions are most welcome.
Thank you

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Hi Abdul-This is easier to do with DC than with AC.Are the two sources in phase with each other?  What is the load? If the two sources are not synchronized and precisely in phase, than the only way I can think of would be to rectify and filter both sources and then convert back to AC. Even then, the sources will share equally and not take 1KW  from one source and .2KW from the other source (assuming that the input voltages are equal).-Rick

Hi Rick,Thanks for the reply, both the input voltage AC1 and AC2 is the same. I am trying to make a device for an on-grid solar system that can utilise 100% solar energy instead of feeding it to the grid.If the system can be made in AC then it's better otherwise DC will work.For eg (for DC load only), in a building, DC load is of 30 KW and the rooftop solar system can feed its 25KW of power to the respective building DC load and the power management device takes the 5KW of power from the grid to sum up the 30KW to its load.Regards,Abdul Rasheed

Abdul, reading the above your requirements are varying wildly, starting from 1KW and now 30KW.What you seem to be trying to do would be satisfied by a standard solar inverter, they provide power up to their maximum and only feed back into the grid when the load is less than their output.The power management is in the solar inverter, it maintains its output voltage very slightly higher than the grid input voltage so it supplies as much power as possible up to its maximum output. This is a tried and proven technology.If this does happen often (ie load < solar output) then you can put in a battery storage system which will charge on the excess solar power and then feed back the power when the solar output is low.  30 KW is a lot to do this with but it can be done.  Some battery systems do have a current sensing transformer on the grid feed in so they can sense the power being taken from or fed to the grid.If this is not what you want to do, can you state your requirements more clearly?

Abdul- Try doing a search on "grid tie inverters".  These are ingenious devices that take the DC from your solar array and when they convert it to AC they carefully synchronize with the power grid. The facility where the inverter is located will still have its electrical loads connected directly to the grid with the inverter paralleled across it. By carefully adjusting the voltage and phase relationship with the grid, the inverter seamlessly powers all of the local loads (assuming enough solar power is available), and any extra flows back to the electric utility. It is almost always a requirement to notify the electric utility that you plan to do this. This is because they will install a special power meter that keeps track of power flow in both directions.  The metering arrangement will often include a protective device that will prevent power from flowing out to the grid in case of a grid outage.  This is necessary to avoid electrocuting linemen who are working to restore service.In some countries, like here in the United States, you can get a rebate from the government for generating power from alternative energy sources.One last thing-  Be aware that most electric utility companies sell you power at one rate, but they buy it back at a lower rate.   -Rick

Hello David, thank you for the reply.The requirements I have mention is just for the illustration purpose. As you have mentioned about the inverter, in case of grid tie when the load is low excess solar power is fed to the grid and when the grid is off the inverter trips off the solar power to avoid feeding its power to the grid, so we can't use grid power and also the solar power during day. I want the device to utilise the solar power and do not feed it to the grid in any case, also not the battery.

Hi Abdul, Ok I see your problem, you want the functionality of a grid-connect inverter but one that will keep working when the grid is off.I think there are systems that will do this but they are few and far between.  It's not so much that you don't want to feed power back to the grid (why not, if you have excess?) but that you want your inverter to work with no grid power.  This would imply some kind of contactor and control system to disconnect the grid if it senses loss of grid power (usually by your inverter getting a large feed back to the grid) and also an inverter that will keep generating in such circumstances.I don't know of such systems offhand but I will look around and advise if I find any.  Anyone else know of anything that does this?One way I can think of doing it is to feed your building direct from an inverter, using either solar power or grid power (via a rectifier and smoother) to power the inverter.  Since most inverters are built to use batteries it wouldn't hurt to use some of them too.  But you are looking at less than optimum efficiency in some ways.This would be a nice project for using a microcontroller of a PLC, to sense currents and voltages and switch on the grid power to the inverter if the solar is not enough.

Hi David, the reason why I don't want solar power to be fed to the grid is, in India solar power plants (rooftop and on the ground) have increased a lot and they are feeding their excess power to the grid which in return causing a damage to the grid due to overload. I believe there is a way in which we can develop a system that could help us utilise 100% solar energy.I am very thankful for your effort.  I will be discussing about it further as this is one of my startup projects.
Thank you.

Hi Rick, we do have the similar system in India, what if we could develop a system using a microcontroller or the PLC that will open the contact when the sensor senses the zero input power from the grip as mention by the David in the comment section. 
When the grid is on the system must give priority to solar power and when the load require more power than solar can feed in that case system should take in the extra required power from the grid to fulfil the load requirement.
Thank you Rick for your effort and time.

I generate with solar Photo Voltaic tied to the grid. However I divert most of my excess daily generation to a battery bank or hot water tank, I use an I-Boost to do this link to I-Boost .When the grid is off then I have a battery inverter kick in and use what I have stored in the storage battery. You do need to make sure that your battery inverter will sync  with the grid so you get no disruptions. Suppose you can consider the system to be a big UPS with two alternative power supplies with solar being the dominant supply when avaiable.

Abdul ok, see your problem.  Apart from my suggestion above of converting the grid to DC and using that and solar DC to power an inverter, Conrad Mannering's suggestion below of the IBoost is a good one.  This has a current sensor in the grid line and as soon as it senses you are exporting any power it will switch on a local load like a hot water system to use the solar power.  But you still have the option of using grid power if your solar is not working.  This might be the device you are looking for.

Hi Conrad,I will check for the similar device as I-Boost in India, I will discuss about the same topic later.Thank you so much for your time.