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Hello, i am quiet new here. Now i learned something about the expressions. When i run DC it calculates 410mW, the same in AC, only time resolved. When i use P(Q1) in frequency-domain, it calculates ~30Watts!

How can this be?

Regards

Welcome to CL.

Could you publicise an example?

If Q1 is working into a reactive load, the power can go way up.

Understanding how the power calculation works in the frequency domain can be tricky. Two thoughts:

1) In the frequency domain, the power P(Q1) is a complex number for every frequency. You can also use expressions REAL(P(Q1)) or IMAG(P(Q1)) or MAG(P(Q1)) to explicitly select the real component, imaginary component, or overall magnitude of that complex quantity.

2) The frequency domain calculations are always relative to the input element, whether that's a voltage or current source, having a magnitude of 1 (zero-to-peak). If your actual input is 1mV instead of 1V, then essentially all of the voltages in the system need to be scaled down by 10^-3, and all of the currents are similarly scaled down by 10^-3. Therefore, the the power would have to be scaled down by 10^-6.

Post a circuit and we'll try to help interpret the results.