Page 170 - Electrical Engineering Dictionary

control structure essentially the same as to uncertainty in the envisaged behavior of
the control system; this term is used when the controlled process and, eventually, there
one wants to indicate that the controller is is uncertainty concerning the internal behav-
composed of several decision units, suitably ior of the controlled process; in particular
interlinked; decision units of a control struc- when the forecasted scenarios of the future
ture usually differ in their tasks, scope of au- free input values tend to appear to be largely
thority and access to information; depending different from the actual future free input re-
on the context one speaks of a control struc- alization.
ture or of a decision structure; decentralized
control, multilayer control, hierarchical con- controllability (1) the property of a sys-
trol are examples of control structures. tem that ensures the existence of bounded
control inputs to drive any arbitrary initial
control surface any of the movable parts state to any arbitrary final state in finite time.
such as tabs, panels, or wings that control For linear systems, an algebraic condition
the depth of a submarine or the attitude of that involves system and input matrices can
a flight vehicle moving through the atmo- be used to test this property.
sphere. For example, the yaw angle of an (2) the ability to establish the required test
airplane is controlled by the rudder, the pitch stimuli at each node in a circuit by setting
angle by the elevators, while the roll angle appropriate values on the circuit inputs.
by the ailerons. In fuzzy logic community,
control surface may mean a plot of a typi- controllability at a given time a charac-
cal fuzzy logic controller output as a func- teristic of some dynamical systems. A linear
tion of its two inputs. The inputs to a typical dynamical system is said to be controllable
fuzzy logic controller are the error between at a given time if there exists a finite time t 1 ,
the desired and the actual plant output, and such that it is controllable in a time interval
the change-in-error. [t 0 ,t 1 ].

control system (1) the entity compris- controllability condition for nonstation-
ing the controlled process and the controller. ary discrete system a condition found
Control system is influenced by the environ- in some dynamical systems. A linear dy-
ment of the process both through the free in- namical nonstationary discrete-time system
puts to the process itself and through any cur- is controllable in an interval [k 0 ,k 1 ] if and
rent information concerning the behavior of only if the controllability matrix
these free inputs that is made available to the
controller. k 1 −1
X
T
T
F (k 1 ,j + 1) B(j)B (j)F (k 1 ,j + 1)
(2) an arrangement of interconnecting ele-
ments that interact and operate automatically j=k 0
to maintain a specific system condition or is nonsingular. See also dynamical linear
regulate a controlled variable in a prescribed nonstationarydiscrete-timefinite-dimensional
manner. system.
control transformer a step-down trans- controllability in a fixed interval a char-
former used to provide power to the control acteristic of some dynamical systems. A dy-
portion of a power or motor circuit. namical discrete system is said to be control-
lable in an interval [k 0 ,k 1 ] if for any initial
n
control under uncertainty operation of state x(k 0 ) ∈ R and any vector x 1 ∈ R n
the control system in a situation when there is there exists a sequence of admissible con-
a significant uncertainty regarding current or trols u(k), k = k 0 ,k 0 +1,...,k 1 −2,k 1 −1
future values of the free inputs, which leads such that the corresponding trajectory of the

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