8. References


The MO (and therefore the MOMI) method optimises the closed-loop tracking performance (from the reference to the process output). This may lead to a degraded disturbancerejection performance, especially for lower-order processes. In order to improve the disturbance-rejection performance, the MO criteria have been modified. The modification was based on optimising the integral of the closed-loop transfer function from the process input (load disturbance) to the process output. Hence, the method is called the

The MOMI and the DRMO tuning methods have been tested on several process models and on one hydraulic laboratory setup. The results of the experiments have shown that both methods give stable and fast closed-loop responses. The MOMI method optimises tracking performance while the DRMO method improves disturbance-rejection performance. By using a two-degrees-of-freedom (2-DOF) PID controller structure, the optimal disturbance-rejection and improved tracking performance have been obtained

The MOMI and DRMO methods are not limited to just PID controller structures or stable (self-regulatory) processes. The reader can find more information about different controller structures and types of processes in Vrančić (2008), Vrančić & Huba (2011), Vrečko et al.,

The drawback of the MO method (and therefore the MOMI method and, to an extent, the DRMO method) is that stability is not guaranteed if the controller is of a lower-order than the process. Therefore, unstable closed-loop responses may be obtained on some processes containing stronger zeros or else complex poles. Although the time-domain implementation of the method is not very sensitive to high-frequency process noise (due to multiple integrations of the process responses), the method might give sub-optimal results if lowfrequency disturbances are present during the measurement of the process steady-state

The author gratefully acknowledges the contribution of the Ministry of Higher Education,

Åström, K. J., & Hägglund, T. (1995). PID controllers: Theory, design, and tuning.

Åström, K. J., Panagopoulos, H. & Hägglund, T. (1998). Design of PI Controllers based on

Ba Hli, F. (1954). A General Method for Time Domain Network Synthesis. IRE Transactions

Gorez, R. (1997). A survey of PID auto-tuning methods. Journal A. Vol. 38, No. 1, pp. 3-10. Hanus, R. (1975). Determination of controllers parameters in the frequency domain. Journal

Instrument Society of America Research Triangle Park (2nd ed.).

Non-Convex Optimization. Automatica, 34 (5), pp. 585-601.

– Circuit Theory, 1 (3), pp. 21-28.

Science and Technology of the Republic of Slovenia, Grant No. P2-0001.

"Disturbance-Rejection Magnitude Optimum" (DRMO) method.

(2001), Vrančić et al., (2001b) and in the references therein.

simultaneously.

change.

7. Acknowledgments

A, XVI (3).

8. References


Available on http://dsc.ijs.si/Damir.Vrancic/bibliography.html


**Multivariable Systems – Automatic** 

**Tuning and Adaptation** 

Whiteley, A. L. (1946). Theory of servo systems, with particular reference to stabilization. The Journal of IEE, Part II, 93(34), pp. 353-372. **Part 3** 
