How do I calculate phase angle for a power system with a changing frequency?

I'm trying to model an electrical power system with a generator and load. The generator is speed controlled and exhibits speed droop based upon loading. At no load the generator operates at 61.5 hz, and at full load the system would droop to 58.5 hz. The issue I am facing is that I can't get accurate phase angle readings out of the FFT block in Simulink. As soon as the frequency changes, the readings tend to become unstable, more so with changing loads and frequencies. I do know the frequency the system is operating at, but it does change throughout the simulation. Is there a way I can feed the frequency change back into the FFT block to get it deliver an accurate phase angle?

Answer 1

[Sebastian Castro]

Have you tried using a PLL block instead? PLLs are used for just this -- variable-frequency situations where you need to keep track of both frequency and phase angle.

http://www.mathworks.com/help/physmod/sps/powersys/ref/pll.html

- Sebastian