As per my understanding,
- In the case of NMP, the system responds in the opposite direction of the steady state.
- Internal stability
- Problem in phase response
- Limitation of control bandwidth, which result into limited disturbance rejection.
- The non minimum phase systems has a slower response.
- The value of phase angle is greater than 90 degree.
Let me know, if any correction or updation is required.
Thanking You,
Hi Pritesh.
When dealing with NMP systems (let us assume continuous-time systems), the problems you may encounter are due to zeros characterized by positive real part.
In this case you have to deal with the following problems:
x) inverse response;
x) reduced phase margin that implies limited bandwidth and slower closed-loop response (a positive zero is somehow similar to a delay);
As long as the phase angle is concerned, it largely depends on the other singularities of your transfer function.
Regarding the disturbance rejection capabilities, it depends on wether you consider low-freq. disturbances or high-freq. disturbances. Since your bandwidth will be limited you should not have problems with high-freq. disturbances. On the other hand you may have problems rejecting low-freq. disturbances, but this largely depends on the low-freq. shape of the modulus Bode diagram of your trasfer function. More in depth, the higher the modulus is in the disturbances freq., the better the rejection will be.
I agree with Matteo. Another issue not in your list is robustness when the system is moreover unstable: if an unstable zero is not very far from an unstable pole, the controller will have a poor robustness whatever the control design.
For non-minimum phase systems, it is called unstable zero. This type of systems is deemed difficult to control. These systems are often associated with an inverse response at a step change of the input. It is possible to stabilize, to replace the term "integral" by a term "derivative" and use the Routh criterion or the Nyquist diagram for the stability margin analysis.
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