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164 CHAPTER 5 DMPPT PV System: Modeling and Control Techniques

given set of operating conditions. Many Maximum Power Point Tracking (MPPT)
techniques have been presented in the literature [1e8]. Nevertheless, the Perturb
and Observe (P&O) and Incremental Conductance (INC) techniques are widely
used [8], especially for low-cost implementations. In case of mismatching operating
conditions of the PV modules of a given PV array (because of the effects of clouds,
shadows of neighboring objects, dirtiness, manufacturing tolerances, different orien-
tation of parts of the PV field, dust, uneven aging, thermal gradients etc.), the PeV
characteristic of the PV field may exhibit more than one peak, because of the pres-
ence of bypass diodes and/or of PV cells that work in reverse bias conditions, and
MPPT algorithms can fail. As a result, a marked reduction of the overall system ef-
ficiency occurs [9e14]. Moreover, the absolute maximum power of a mismatched
PV field is lower than the sum of the available maximum powers that the mis-
matched modules would be able to provide if each of them could operate in its
own MPP. Therefore, it is evident that the adoption of a PV system architecture
able to allow each PV module of the array to operate in its own MPP is highly desir-
able. Such an architecture can be obtained by choosing one of the two possible
following options. The first option is represented by the possibility of using
module-dedicated DC/AC converters, often called microinverters, carrying out the
MPPT for each PV module [15e25]. Microinverters have their output ports directly
connected in parallel to the grid. The second option is represented instead by the pos-
sibility of using module-dedicated DC/DC converters, often called microconverters
or power optimizers or module maximizers, carrying out the MPPT for each PV
module [26e44]. Indeed, as discussed in [44], each bypass diode of a given PV mod-
ule should be substituted by a microconverter to avoid the drawbacks associated to
mismatching operating conditions among strings of cells belonging to the same PV
module and put in parallel to different bypass diodes. This chapter is devoted to an
in-depth description of exact and approximate modeling techniques of PV systems
adopting microconverters. Such modeling techniques are very useful to properly
design control techniques allowing the extraction of the maximum available power
from PV systems adopting microconverters.

2. CENTRAL MAXIMUM POWER POINT TRACKING AND
DISTRIBUTED MAXIMUM POWER POINT TRACKING
In this chapter, the term Distributed MPPT (DMPPT) technique will be used with
specific reference to an MPPT technique simultaneously acting on the output of
each PV module representing the source of each microconverter. Hereafter, a system
composed by a PV module equipped with microcontroller will be called self-
controlled PV unit (SCPVU). In the following analysis, without any loss of general-
ity, reference will be made to Lossless SCPVU (LSCPVU). The term “lossless”
means not only that all losses occurring in the power stage of DC/DC converters
(conduction losses, switching losses, iron losses, etc.) are neglected in the following,
but also that, in the sequel, the MPPT efficiency of the DMPPT controllers is