I am working on modeling a power system on an aircraft right now, the problem is that I have loads that are constant power drawing no matter the voltage. They will draw 5kilowatts no matter 28 volts or 22 volts. My problem is modeling them. I can model them at one particular voltage but I want a more dynamic approach to this. I was to be able to put in a resistive element, or black box that draws a certain power no matter the voltage. I have currently modeled it as resistive using the thevenin equivalents of each of the loads but this only works for one voltage and takes a bunch of time to recalculate for the loads. The relevant equations are v=ir and p=vi. I found something that does this an element online, cpwr but it is in a proprietary library that costs quite a bit. I thought about modeling it as a voltage controlled current source but this affects the rest of the circuit because it is an excitation. Thank you in advance and I will continue looking.