Eduard Eitelberg

A regulating and tracking PI(D) controller

Traditionally, PI controllers operate solely on the reference error signal (modified reference error in the case of PID controllers) in the forward path of the classical feedback loop. They are designed either as regulating (e.g. to reduce process disturbances) or as tracking controllers (e.g. to follow reference changes). If both characteristics are important then a compromise design has to be found. Here a special ‘connection’ of the classical PI(D) controller is proposed, which allows a greater degree of independence in the design and practical tuning of the regulating and tracking features.

Model reduction by minimizing the weighted equation error

A method for model reduction is proposed which minimizes the equation error and yields a stationary exact model. With this model, the desired state variables, or their physically meaningful linear combinations, are reproduced. This approach to the reduction problem leads to linear equations; thus no search routines are needed. Moreover, a time-varying weighting matrix is introduced, so that even unstable linear time-invariant models can be reduced. Especially, the characteristics of very low order reduced models depend highly on the weighting matrix. The reduction for a distillation column of the 45th-order is carried out.

Estimating Synchronous Machine Electrical Parameters from Frequency Response Tests

A method of obtaining synchronous machine d and q axis impedances by test as a function of frequency of d,q components has recently been proposed by de Mello and Hannett [1]. Their proposal ends by determination of the numerical values for the operational inductances Ld(j2w), Lq(j2w) or impedances Zd(j2w), Zq(j2w) at different values of W, the speed of the machine at which the tests are conducted; however, they do not show how the values of actual parameters such as inductances and time constants are to be obtained from the curves of operational inductance versus frequency.

Technical Communique: Quantitative feedback design for tracking error tolerance

The feedback system tracking error is related rigorously to the sensitivity function S=1/(1+L). A two design degrees of freedom design procedure is presented that guarantees frequency-domain tracking error tolerances despite uncertainties in the feedback and feed-forward components of the system. This procedure is solidly based on and fits into the general framework of the Quantitative Feedback Theory of Horowitz (1991, International Journal of Control 53(2), 255-291; 1993, Quantitative Feedback Design Theory (QFT). Boulder: QFT Publications).

Continuous-time system representation with exact macro-difference expressions

A macro-difference equation representation is proposed which is a mixture of finite-difference quotients and integrals over finite time intervals. The choice of the micro or sampling interval length (for the numerical integration accuracy and representation bandwidth) and the choice of the macro interval length (for numerical conditioning/accuracy of the difference quotients and of the resulting equations) are independent. This approach does not need the assumption (which in practical situations is quite unnatural) of zero initial conditions.

Comments on model reduction by minimizing the equation error

Minimization of the equation error is a well-known and powerful tool, which has been introduced to the reduction of time-invariant linear systems independently by Obinata and Inooka [1], [2] and by Eitelberg [3]-[5]. The purpose of this note is to examine critically the methods in [1], [2] and to propose to the readers of IEEE TRANSACTIONS ON AUTOMATIC CONTROL an altenative formalism, which has been tested successfully on systems of high order [3]-[5].

Stabilizing SSR oscillations with a shunt reactor controller for uncertain levels of series compensation

The authors demonstrate how frequency-domain techniques based on I. Horowitz et al.s (1986) quantitative feedback theory can be applied to the design of fixed-parameter controllers in power systems where the plant parameters have large uncertainties. They present the design of a controller for a shunt reactor to eliminate torsional shaft oscillations in a turbogenerator susceptible to subsynchronous resonance (SSR). The considered parameter uncertainty is the series capacitor compensation level, which has been assumed to vary between 12% and 76%. Simulated transients results of the uncontrolled/controlled system are depicted. >

Sampling rate design based on (1 − sT/2)

A digital controller design technique must yield all controller parameters, including the sampling rate 1/T, as functions of (continuous-time) specifications. It will be shown that, under certain conditions, sampling is modelled by a continuous-time (1 -sT/2) in the loop transfer function.

Optimal output feedback design of a shunt reactor controller for damping torsional oscillations

Abstract Suppression of the torsional oscillations of a turbogenerator by means of a shunt reactor placed at the turbogenerator terminals has been proposed by others and would appear to be the most promising of all the counter-measures suggested so far. This paper investigates the damping of subsynchronous resonance (SSR) oscillations by using such a shunt reactor stabilizer and placing it at the high voltage instead of the low voltage side of the generator step-up transformer. It shows how the shunt reactor controller (SRC) is designed by employing optimal output feedback techniques. A digitally computed step-by-step solution of the 31 non-linear differential equations yields the transient response of the non-linear system and illustrates the stabilizing effect of the shunt reactor controller, even for an initially unstable plant.

Load sharing in a multivariable temperature control system

Abstract The general multivariable feedback control is related to load sharing. In particular, the problem of interaction is shown to be very closely related to the fundamental load sharing notion of the supply cross sensitivity . An application of some of the load sharing control theory to an industrial 2×2 temperature control problem is reported.