real-time load shedding

One of the solutions is to have an active switch between to "heavy loads" (relative to "small" inverter).

For example, on a refrigerator + freezer circuit, connect the freezer thermostat to a NC/NO relay. When the "freezer" thermostat is calling for cooling, AC power is routed to the freezer. When the freezer thermostat turns off, then power is routed to the refrigerator (which turns on when the fridge thermostat calls for cooling).

More or less, this will work as long as no appliance calls for >50% operating cycle (i.e., 30 minutes per hour). If you have an appliance that draws 75% of run time, then the other better not draw more than 25% run time.

There are other solutions for options such as when the fridge is running, the inverter can start the freezer. But the inverter cannot start both freezer and fridge at the same time.

And for off grid/full time operation--You need to make sure that you do not hit a deadlock conditions (such as both appliances want to start at the same time, and this "resets" the inverter and your control circuitry (which defaults to allowing both to start at the same time).

Deadlocks may not happen often (if it takes 3.6 seconds to "start" a compressor, and there are 3,600 seconds in an hour, that is a 1:1,000 chance of both trying to start at the same time). What you don't want is to have the deadlock happen when you are not there (food spoils in both before you realize there is a problem)--Or somebody turns of power for a few minutes then flips the breakers both on--Now both fridge and freezer may want to start at the same time--And the other person may not realize what is happening with your "custom" configuration.

And, there are various "soft start" things that sometimes can be done (VFD--variable frequency drive, hard start kit for compressors, using NTC's negative temperature coefficient resistors in series with heavy starting current load, use a current transformer or shunt resistor to control an interlock relay which "inhibits starting" of 2nd load, etc.).

What are the details of the loads/system you want to run?

-Bill

My two cents--AC inverters are (usually) electronically "protected"--And so can make "decisions" on a 1/2 cycle or faster (1/120th of a second or faster).

There is nothing that, I can think of, that could make a load decisions that is going to be "faster" and/or "smarter" that those made by the inverter's electronics.

AC line power--There is no active protection (other than Ground and Arc Fault) that are fast enough to "do something". And for a simple 120 VAC 15 amp circuit, 45 amp surge current for a few cycles is not unusual.

-Bill

My guess is that the inverters just do not have surge capabilities (magnetics saturate, internal resistance drops voltages so much that regulation circuit cannot maintain voltages, etc.). So, from the AC outside (or DC input) measurements--It is difficult to see distorted wave forms (low voltage amplitude, poor power factor, clipped peaks, high instantaneous current peaks clipped) that are caused by arbitrary loads to predict when an inverter is going to fail to deliver (output so poor that loads will not operate correctly, or inverter will clip, or inverter will fault).

You could generate an IV (current/voltage) model for each load. And add them together to determine which "combination" of loads would be allowed vs not allowed. But that would require some sort of multi-control (separate AC branch circuits or possibly on the "control side" such as thermostat interrupt).

Say you make a "map" of allowed and prohibited appliances--How many would that be? One circuit that is 100% on (lights, computer, TV). And then (at least two or three, or more?) controlled circuits (refrigerator, freezer, washer, well pump, etc.). And you would need (possibly) a feedback circuit to know which loads are "pending".

Do you monitor 100% on loads (average current). See that a washing load is pending--And you know you need the well pump for water with that--so allow washer+pump and disallow fridge+freezer loads for 40 minute cycle? Do you map water fill times (wash fill, rinse 1 and rinse 2 fill) and let fridge OR freezer start during this time? What if somebody wants to shower/fill tub? What happens when a random portable load is used (hair dryer, vacuum, circular saw, etc.).

Many times, complexity is the enemy of the good enough... Do you simply time stuff? 8-10am irrigation+washer. 10am-12 noon for fridge+freezer, microwave+kitchen tools+well pump 12-1pm. etc...

I just do not see this as a practical/livable power plan/diet/rationing.

Looking at loads--You have "well behaved loads"--Which I would suggest are low surge and good PF. Induction motors are usually very poorly behaved loads. 5x running current as surge. And, typically, at best, an inverter+battery bank is capable of ~2x rated power for surge. I would be going back and looking at limiting surge current for big loads in the first place.

Using digitally controlled motors ("inverter" mini-split AC, servo motor/three phase well pump with VFD controller, "inverter controlled" refrigerator compressor, etc.).

The alternative of using two inverters--One for 100% powered "off grid friendly loads" and a second AC inverter sized to start induction motor loads and an interlock relay (refrigerator or freezer run). If you want--Technically, you only need to prevent two (or more) automatic demand appliances from starting at the same time. A little "wall outlet" controller--Monitor current flow--When the beginning of a surge is detected--allow it through if nothing else is starting. If outlet A detects a surge, "block" any other outlet from surging.

But for things with a "complex" power usage profile--Say a Frost Free refrigerator--You have 120 Watt compressor running, 600+ Watt (VA) surge, and possibly even 500 Watt heater (defrost heater). And with some "more expensive" refrigerators, you have a digital timer for the defrost cycle--If you cut AC power, the defrost timer resets to "start defrost cycle". And a defrost cycle runs 1-2 hours (I assume the defrost heater cycles/regulates on/off during the cycle).

I just do not see a "generic" solution. For limited applications with "simple" refrigerator/freezer (manual defrost--Such as a "Chest Fridge conversion" + 2nd chest freezer)--The A or B load with small inverter can work well. And choose an "off grid" friendly deep well pump (and/or cistern+small pressurization pump--Use genset to fill cistern once or twice a week).

But more than that--I think one is committed to a larger system (larger battery bank + larger AC inverter which forces a larger solar array). As the system is enlarged--The mix of smaller/surging load problem pretty much "goes away" (all surges are much smaller than overall system power capabilities--And much less chance that all smaller loads are going to "turn on" at exactly the same time).

-Bill