The theory of comparative advantage.

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Give a short summary of text 5.

21.Give derivatives of the following words from Text 6 and translate them into Russian:

Representation, loading, failure, complexity.

22.Give the Russian equivalents of the following terms. When necessary, look them up in a dictionary:

To offset, torque, shaft, altitude, to deliver, sensor, actuator.

23. Supply synonyms for the following words:

Meet, to take place, because of, as regards, breakdown, to consider

24. Analyse the grammatical structure of the following sentences and translate them:

1. The reference signal to be tracked is usually not known beforehand.

2. The load torque on the shaft of an electric motor, whose speed is to be maintained constant, can be regarded as a disturbance.

25.Translate Text 6:

Text 6. The uncertainties

The uncertainties encountered in control systems are both in the environment and within the system. In the first place the reference signal to be tracked is usually not known beforehand. Then there are disturbance signals tending to offset the tracking. For example the load torque on the shaft of an electric motor, whose speed is to be maintained constant, can be regarded as a disturbance.

As far as the system is concerned the main source of uncertainty is the behaviour of the plant. These uncertainties can occur, for example, due to changes of operating points, as in an aircraft flying at various altitudes and loadings, or a power system delivering power at differing load levels. Large changes can also occur in an uncontrolled fashion for example, when sensor or actuator failures occur. The complexity of even the simplest plants is such that any mathematical representation of the system must include significant uncertainty.

(from S.P.Bhattacharyya, H. Chapellat, L.H.Keel. Robust Control. The Parametric Approach)

Make a list of terms from Text 6 referring to control and memorize them.

Read and translate Text 7.

Text 7

There are several ways in which systems can be uncertain, and the main three are:

· The initial conditions of a system may not be accurately specified or completely known.

· Systems experience disturbances from their environment, and system commands are typically not known a priori.

· Uncertainty in the accuracy of a system model itself is a central source. Any dynamical model of a system will neglect some physical phenomena, and this means that any analytical control approach based solely on this model will neglect some regimes of operation.

The major objective of feedback control is to minimize the effects of unknown initial conditions and external influences on system behavior, subject to the constraint of not having a complete representation of the system. This is a formidable challenge in that predictable behavior is expected from a controlled system, and yet the strategies used to achieve this must do so using an inexact system model. The term robust refers to the fact that the methods which are pursued will be expected to operate in an uncertain environment with respect to the system dynamics.

(from G.E. Dullerud, F.G.Paganini. A Course in Robust Control Theory. A Convex Approach )