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Pspice power system on an aircraft

  1. Feb 18, 2008 #1
    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.
  2. jcsd
  3. Feb 21, 2008 #2
    There is a function called .PARAM which allows you to put the values of particular elements. So your resistance is 5KW div by 28V or 22V. I am assuming you know before hand what your voltage is and hence you just have to change it in one place to 22V or 28V. Pspice will then calc the resistance for you.
  4. Feb 21, 2008 #3


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    Seems like a VCCS is what you want. You can parameterize it with a slope that will give you constant power. Can you explain more why you can't use it? What does it mean to be an "excitation?"

    - Warren
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