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214 CHAPTER 6 Flexible Power Control of Photovoltaic Systems

Maximum Power Point
(MPP)
PV power P pv (kW) P limit Power curtailment

dv pv dP pv High dP pv/dv pv
Low dP pv/dv pv
PV voltage v pv (V)
FIGURE 6.5
Possible operating points of the photovoltaic (PV) system in powerevoltage curve of the
PV arrays with the PV power below the maximum available power.

(i.e., MPPT algorithm). This offers a cost-effective solution in terms of component
cost, as there is no extra component (such as battery or dump load). In addition, the
reduced number of components in the system also results in a benefit in the reli-
ability aspect because of the lower number of possible failure components in the sys-
tem. Nevertheless, the shortcoming of this approach is the reduction in the PV
utilization as a result of the loss of PV energy yield during the power curtailment
because the PV energy is not being stored or used. In some cases, the economic
loss because of the reduction in the PV energy yield may overcome the benefit of
the reduced equipment cost, which has to be carefully designed [31,35,36].

4. POWER CONVERTER TECHNOLOGY AND CONTROL FOR PV
SYSTEMS
4.1 SYSTEM DIAGRAM OF GRID-CONNECTED PV SYSTEMS
A general system diagram of grid-connected PV systems is shown in Fig. 6.6 and
consists of three main components: PV panels (or arrays), power converters (PV in-
verters), and ac grid. As the power generated by the PVarrays is dc power, the power
converter, which is a power electronic-based technology, is required to convert the
dc power from the PV arrays to the ac power [37]. In other words, power converter
plays an important role in controlling the power delivery and at the same time
ensuring a proper integration between the PVand the grid. Additionally, other spec-
ifications are imposed by the grid requirements to make grid-connected PV systems
more resilient and grid-friendly: (1) reliable or secure the power supply; (2) flexible
control of active and reactive power; (3) dynamic grid support per demands; (4) sys-
tem condition monitoring, protection, and communication; and (5) high efficiency
and reliability, low cost, and small volume [38e40].