Page 135 - Decision Making Applications in Modern Power Systems

100 Decision Making Applications in Modern Power Systems

devices for improving power quality can play an effective role under these
conditions. By using distributed configuration, these devices have required
flexibility to work with various loads and generation technologies. Advanced
control methods are also implemented in order to integrate these devices into
conventional networks and provide the required degree of power quality. In
this regard a detailed discussion about the third generation of PQI devices is
presented in the following section to help the researchers build the missing
bridge between the power quality issues of conventional electrical systems
and the power quality issues of smart electricity systems.

4.3.4 Third generation of power quality improvement devices
The third generation of PQI devices is the pioneer in emerging smart grid
technologies into PQI devices. These devices are mostly multifunctional,
capable of performing several tasks at a time without adding any hardware
to the structure of the device, which leads to increased cost-effectiveness
besides being effective and reliable. Smart impedance, ES, and MFDGs are
the main devices included in this category [30,31].

4.3.4.1 Smart impedance
A PQI device, which has the characteristics of all abovementioned second-
and first-generation PQI devices, is named “smart impedance.” From the
physical point of view, smart impedance is a combination of an APF, a cou-
pling transformer, a capacitor bank, and an appropriated control strategy.
Smart impedance can solve the tuning process of passive filters, while
compensating harmonic currents, harmonic unbalances, improving quality
factor, tuned and displacement power factor (DPF). Smart impedance can
improve voltage regulation and stability in weak systems such as small
microgrids (smart grids), in which the source impedance is not negligible.
Smart impedance, which is controlled by a proportional resonant (PR) con-
trol method, could perform as a series APF, shunt active filter, a tuned pas-
sive filter, a capacitor bank, and a combination of an active and passive
filter to reduce the capacity of the filters. Smart impedance is able to miti-
gate the selected harmonics of interest, it can act as a short circuit (zero
impedance) for load current harmonics, while acting as infinite impedance
against undesired harmonics. Fig. 4.3 shows a simple view of smart imped-
ance topology [32]. The power circuit of mart impedance includes a capaci-
tor bank, which is connected to a power converter via a transformer. Three
phase control blocks are on the basis of the proportional resonant (PR) con-
verter to mitigate system current harmonics without need for phase-locked
loop (PLL). The harmonic control block is used to eliminate harmonics
using a PR controller. DPF block is controlling the injected reactive power