Simplified Synchronous Machine - Speed Regulation

I am simulating simulink from this website "https://www.mathworks.com/help/physmod/sps/examples/simplified-synchronous-machine-speed-regulation.html"

I got the desired waveform and tried to adjust the load to 1MW and 500kW together. I got the following waveform

Heres the question. at rotor speed and mechanical torque from 0.2s, why isnt it a straight line like when both loads are 800KW?

Answer 1

[John Noon]

This model has a PI speed regulator. What you are seeing at 0.2 seconds is the dynamics of this PI regulator. The regulator is changing the mechanical torque to "regulate" the speed to its original value. As time goes to infinity, these will be a straight line again, but when you introduced the step response in power the torque and speed must regulate. If you search "PI controller step response" you will find similar looking waveforms.

[Mark Hamill]

How about from 0 to 0.2s? In the previous simulation i got a straight line. For this, i got a slight increase in rotor speed and slight decrease in mechanical torque.

[John Noon]

The synchronous machine has initial conditions, so if any of the operting points were changed then these initial conditions will no longer be the steady state value so there will be some transient response resulting in a waveform that isn't quite straight.

[Mark Hamill]

Alright. I understand. 1 last question, what are the initial conditions? Are they the parameters of the generators or others? Thanks

[John Noon]

The generator has an initial condition, and the PI regulator has an initial condition too. The PI regulator's initial condition is the same as the Tmec block in the model since that is the steady state torque for the condition at the start.