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fail prematurely, or not operate at all. Therefore, PQ analysis attracts many multidis-
ciplinary researchers in this provocative field [5].
The PQ events which majorly occur in a distribution system can be classified into
slow voltage variations, short duration under voltages, rapid voltage changes, har-
monic distortions, and switching transients [6]. These are discussed to understand
their effects in a smart grid. The PQ issues with the penetration of renewable energy
sources integrated to the distribution system in terms of microgrids are explained. The
microgrids which are classified into AC microgrids and DC microgrids are also dis-
cussed. The PQ concerns in each type of microgrids are discussed. Also the PQ issues
with respect to the demand side management (DSM) are discussed along with the new
PQ indices established are discussed in this chapter.

2 Microgrids in a smart grid

Environmental concerns that were witnessed in recent years gave the path for the pro-
motion of sustainable activities in power sector [7]. This leads to the development of
distributed power generation with the help of renewable energy technologies. With the
penetration of renewable sources, the functioning and controlling of existing power
system have become a tedious job. Hence, in order to manage the power system ef-
fectively, a systematic approach is adopted by integrating all the distributed generating
station into a micro power system referred to be microgrids [8]. As said earlier, these are
tiny power systems embedding various power generating units, energy storage devices,
and loads. In microgrid, all these embedded components works together, which embed
various components such as controlled and uncontrolled loads, DG units and storage
devices operating together in a coordinated manner with controlled power electronic
devices (active and reactive power flow controllers, frequency and voltage regulators),
which are integrated with protective devices [9]. They can be operated based on the
principles of the AC power systems (i.e., AC microgrids) or DC power systems (i.e.,
DC microgrids). Thus, the architecture of the future energy system will eventually look
very different from that of the conventional energy system along with the microgrids
expected to be the main building blocks [10]. In this context, the future energy system
that is “The smart grid” is anticipated to have the following features [11]:
• Energy efficiency, sustainability, and RESs inputs.
• Reliability, security, ESSs, and DG units (renewable based).
• Sensing, measurements, and advanced control methods.
• Load usage awareness, real-time EMS, and advanced load components (e.g., electric
vehicles, heaters, and industrial motor drives).
• Integrated information and communication infrastructures full of cyber-security

2.1 Power quality concerns in AC microgrids
In low-frequency AC (LFAC) microgrids, the DERs devices are typically interfaced
to the grid via a power electronics interface, with the exception of conventional rotat-
ing machines. In such cases, it is possible to have both directly connected, as well as