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3. Possible Solutions for Flexible Power Control of PV Systems 213

but it is being utilized by the actual loads, which can be flexibly controlled, and they
are referred to as “smart load” [28,29].
This solution has been widely discussed with the context of smart grid, where
communication network and coordination control between different components
are the main focus [29]. However, the requirement of communication network
and coordinate control are also shortcomings of this method, which may increase
the cost and the complexity of the overall system.

3.3 MODIFYING THE CONTROL ALGORITHM OF THE POWER
CONVERTERS
With the recent technology advancement in power electronics, more and more
advanced control functionality has been developed for power converters [16,30].
This gives a possibility for the PV system to take the benefit of the advanced control
in power converters, which are the key components to control the power delivery of
PV systems, to achieve the flexible power control functionality. Conventionally, the
MPPT control strategy is implemented in power converters of PV systems for maxi-
mizing the energy yield from the PV arrays. However, the MPPT control scheme
cannot provide the flexible power injection, as the PV systems under this control
scheme always try to extract the maximum available PV power during the operation.
In other words, the PV power production with the MPPT control can be fluctuating
following the dynamic of the solar irradiance and ambient temperature (e.g., during
the cloudy day).
To enable the power control flexibility of the PV systems, the conventional
MPPT control algorithm needs to be modified as shown in Fig. 6.4. Instead of always
tracking the Maximum Power Point (MPP) of the powerevoltage (PeV) curve of
the PV arrays, the operating point of the PV system may need to be regulated below
the MPP, corresponding to the required amount of output power for certain active
power control functionality [31e34]. The operational principle of the modifying
MPPT algorithm is illustrated in Fig. 6.5, and this approach is also called active po-
wer curtailment in literature.
In this approach, the flexible active power control functionality is realized
through the modification of the inherent control algorithm of the power converter

FIGURE 6.4
Flexible active power control solution for grid-connected photovoltaic system by modifying
control algorithm of the power converters.