Page 235 - Advances in Renewable Energies and Power Technologies

208 CHAPTER 6 Flexible Power Control of Photovoltaic Systems

FIGURE 6.1
Active power control strategies for grid-connected PV systems defined in the Danish grid

code (P pv : PV power, P avai : available power, P limit : the power limit level, R : the ramp-rate
r
limit, DP: the power reserve level) [17].

independent of fossil fuel by 2050 [3]. With these initiatives, the penetration level of
renewable energy such as solar and wind energy has been increasing considerably
during the last decades [4].
Among other renewable energy sources, photovoltaic (PV) systems have a poten-
tial to become a major source of electricity in the near future because of several
merits such as simple installation, modularity, and scalability. In fact, the installation
and component cost of PV systems, especially the cost of PV panel, has been signif-
icantly declining in the past years [5,6]. As a result, PV systems have been increas-
ingly installed and connected to the power grid during the recent years. However,
under a large-scale adoption of grid-connected PV systems, the integration of PV
systems into the power grid becomes important. Challenges like overloading of
the grid during the PV peak-power generation periods, severed grid voltage fluctu-
ations because of the intermittency of PV energy, and limited grid frequency regu-
lation capability because of more decentralized power generation units have been
witnessed in practice with a high-penetration level of grid-connected PV system
[6ae10].
To address the above issues and ensure a smooth integration of PV systems into
the grid, the grid requirements in some countries have been revised and updated
[11e17]. One of the recent requirements is the flexible active power control for
the PV system, where the active power generated by the PV systems has to be regu-
lated upon demands, e.g., during grid frequency deviation. An example of active po-
wer control strategies for PV systems introduced in the grid code is shown in
Fig. 6.1, where various power control functionalities have been defined as:

• Power-Limiting Control (PLC) (also called as Constant Power Generation
Control, Absolute Active Power Control): The maximum absolute active power