Page 133 - Decision Making Applications in Modern Power Systems

98 Decision Making Applications in Modern Power Systems

i s i L L ac i s i L L ac
V S Nonlinear load V S Nonlinear load
i f i f

(A) (B)
L
L ac
i s i L
V in C C V out
V S Passive Nonlinear load
L
filter
i f
(D)
(C)
Critical
load
Main
grid
3rd 5th 7th
L Filter
o
a Energy VSI
storage source
d
(e) (F)
(E)
FIGURE 4.2 First and second generation of PQI devices: (A) shunt APF, (B) series APF, (C)
hybrid APF, (D) passive filter, (E) DVR, and (F) SVC. APF, Active power filter; DVR, dynamic
voltage restorer; PQI, power quality improvement; SVC, static VAR compensator.
effective as the first generation of devices, but they have more functionalities
in comparison with the first generation. PQI devices, such as DVR, static
volt amperes reactive (VAR) compensator (SVC), STATCOM, the automatic
voltage regulator (AVR), and UPS, are categorized in the second generation
of PQI devices, since they have more complex controllers. Since bringing a
full definition and application case of these devices is out of the purpose of
this chapter, it seems enough to give a brief explanation and refer the
researchers to more detailed papers to read about these devices [14].
DVR is a power electronic based device that includes an energy
source, an isolated transformer, and a power electronic converter. It is con-
nected in series with sensitive loads to protect them against voltage unba-
lances. For compensating voltage harmonics, it also needs an energy
storage source such as a capacitor, an ultracapacitor, superconductor energy
storage, or flywheel. Researching on improving the performance and
emerging this technology with novel storage device technologies is popular
among researchers [25,26].
AVR is a device that changes the output voltage that would be applied to
critical loads to keep it at a sufficient voltage level. It could change the volt-
age using transformer taps continuously using servo motors or in a discrete
way using power electronic relays. Although power electronic device based
AVRs are faster in comparison with rotary AVRs (servo motor based), they
have less precision due to the discrete output voltage levels.