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3. Necessity of Joint Adoption of Distributed Maximum Power Point 171

Fast Estimate of Maximum Power Voltages (FEMPV) algorithm] and will be dis-
cussed in depth in the subsection “HMPPTF technique”.

3.1 HMPPTS TECHNIQUE
The HMPPTS technique adopts a Modified P&O technique as DMPPT technique
and a CMPPT technique, which is based on the periodic scan of the whole PeV
characteristic of the string of LSCPVUs. The aim of such a scan is represented by
the identification of the best operating value, from the energetic efficiency point
of view, of the bulk inverter voltage v b . Such a CMPPT technique will be indicated
in the following with the acronym CMPPTS. In subsection “Modified P&O DMPPT
technique”, the Modified P&O technique will be explained in detail, and in subsec-
tion “CMPPTS technique”, it will be shown how to properly optimize the CMPPTS
technique. In particular, it will be shown that, despite the seeming great simplicity of
the CMPPTS technique, much care is needed to avoid errors because of the peculiar
shape assumed, under mismatching operating conditions, by the PeV characteristic
of a string of LSCPVUs. Such a PeV characteristic, as seen before (Fig. 5.4), in case
of mismatching operating conditions may exhibit the presence of multiple peaks, flat
regions, and/or nearly vertical portions, which might easily lead the CMPPTS tech-
nique in error, and, consequently, to a more or less consistent waste of the potentially
available energy of the PV systems. Therefore, a proper choice of the parameters of
the CMPPTS technique is mandatory. In fact, if properly designed, the CMPPTS
technique is instead not affected at all by errors, whatever the shape of the PeV char-
acteristic, and therefore the optimization of the energetic performances of the whole
PV system is possible.
3.1.1 Modified P&O Distributed Maximum Power Point Tracking Technique
As shown in Fig. 5.1, the output signal of each DMPPT controller is a reference
voltage v pan ref , which is compared with the sensed PV module voltage v pan . The cor-
responding error drives a PV voltage compensator network. The working principle
of the P&O technique is based on the periodic perturbation of the reference voltage
v pan ref [1]. In particular, the sign of the perturbation of v pan ref at the (k þ 1)-th sam-
pling instant is decided on the basis of the following rule: v pan ref ððk þ 1ÞT a Þ¼
v pan ref ðkT a Þþ Dv pan ref $signðpððk þ 1ÞT a Þ pðkT a ÞÞ, where p(t) is the instanta-
neous power drawn from the PV module, Dv pan ref is the amplitude of the perturba-
tion of v pan ref , and T a is the sampling interval [1]. A suitable modification of the
standard P&O MPPT technique allows to avoid that the output voltage of one or
more LSCPVUs (those ones providing higher powers, see Eq. 5.1) exceeds V ds
max . Such a modification justifies the adjective “Modified,” which has been added
to the name of the technique and hence the acronym MP&O, which will be used
in the following to label the Modified P&O technique. The limitation of the output
voltage of the LSCPVUs, which is obtained by means of the MP&O technique, does
not require the adoption of additional control circuitries as it happens instead with
the output voltage limitation techniques proposed in Refs. [43,57]. The MP&O