symbolic dynamic models for highly varying power system loads

9
increasing or decreasing the value of load current. The principle for controlling the
current reference in this approach helps in stabilizing the load voltage. Thus the active
filter proposed by the authors, not only performs the filtering function for the higher
order harmonics but also exhibits the characteristic of a variable inductance, providing
additional stabilization.
In 1992, Carpita and Marchesoni conducted an experimental study of a power
conditioning system using sliding mode control [9]. Traditional techniques used for the
control of power conditioning system are harmonic elimination [10], optimal [11],
subharmonic [12], and pulse width modulation methods. These are the open loop
methods that require a close loop to maintain the desired value of output voltage.
According to the authors, control actions, which make use of RMS output voltage as
feedback, are not fully satisfactory because of their long settling times. The sliding mode
operation, discussed in this paper, is a particular phenomenon of variable structure
control systems (VSCS) theory. This scheme is reliable for the design of switching
regulators. Experimental and simulation results of this study show the high dynamics and
robustness of the implemented system and the authors validate the proposed approach for
power conditioning and UPS systems.
1.7 Symbolic Dynamics
Symbolic Dynamics is a branch of mathematics, which deals with spaces
consisting of infinite sequences of symbols. Invented by Hadamard in 1898, it was
developed in 1930s and applied to one-dimensional mapping since 1970s [13].