controlcontrol systempid controller
I am trying to simulate PID controllers in MATLAB Simulink, but I am bit confused by the term "transient behaviour" in how its extreme highlighted forms (aggressive and robust) will affect the system response?
Here in this context, what will be the meaning of aggressive and robust?
The step is a stimulus to the system. The system is defined by the pole zero diagram irrespective of the stimulus and it looks like a 2nd order response so here's the math behind the poles: -
You have poles at co-ordinates -5 on the real part of the s-plane and +/-9 on the \$j\omega\$ of the s-plane. So you can say 5 = \$\zeta\omega_n\$ and 9 = \$\omega_n\sqrt{1-\zeta^2}\$. From this you can work out what \$\omega_n\$ and \$\zeta\$ are.
Because it looks like a 2nd order system you can use this to define the shape from the above values for \$\omega_n\$ and \$\zeta\$: -
Any particular reason you are considering implementing a D term? The reason I ask is while they are great in theory, providing a higher component for high error steps and smaller component for smaller error steps THEY are very prone to noise.
They are at the end of the day, differentiators. As a result they are usually not considered for practical implementations of control loops. If they are, it is small component or in the form of a lead-lag compensator.
For you specific example with an actuator hitting an end-stop, the issue isn't so much with hitting the end-stop, but with hitting it with "high velocity". One option to consider is at the output of your PI (maybe D) position loop, the output which is a speed demand into the next loop, is to include a dynamic saturation block.
The saturation limits are then dependent on the absolute position of the actuator. 100% rate for say... 90% of the stroke. then as the actuator comes closer and close to the end-stop, saturation limits are decreased so at... 98% IF there is any high speed demand out of the position loop for whatever reason (instability, noise, BAD command...) the actual speed limit is 10% of maximum
Best Answer
Robust means that your controller will be less affected by plant variations. For example, if your plant transfer function is a crude approximation, you should aim for a more robust controller. It is loosely related to the concept of robustness https://en.wikipedia.org/wiki/Robust_control
Aggressive means fast rise time. If your model is really accurate, your actuators strong an fast, you can aim for a fast rise time.