**3.1. MPPT from the dc-dc converter point of view**

The operating point of a photovoltaic system is defined by the I-V generation and load curves intersection. For understanding how it occurs, firstly considerer a PV module sup‐ plying a resistive load, as depicts Figure 8.

**Figure 8.** PV module supplying a resistive load.

The load curve is accomplished by the Ohm's Law, in accordance with (6), while the genera‐ tion curve is related to the PV I-V curve. Both curves are represented at Figure 9.

An Optimized Maximum Power Point Tracking Method Based on PV Surface Temperature Measurement http://dx.doi.org/10.5772/51020 97

**Figure 9.** Definition of the system operating point by the I-V and load curves intersection.

by the solar radiation and temperature levels, it may randomly vary along the I-V plan, as

Thus, in order to dynamically set the MPP as operation point for a wide range of solar radia‐ tion and temperature, specific circuits, known at the literature by Maximum Power Point

In this chapter the studies concerning MPPT are grouped in two categories: the first is relat‐ ed to hardware, in which the influence of the dc-dc converter and load-type on the tracking quality is investigated, and the second refers to the software, where tracking accuracy and

The operating point of a photovoltaic system is defined by the I-V generation and load curves intersection. For understanding how it occurs, firstly considerer a PV module sup‐

The load curve is accomplished by the Ohm's Law, in accordance with (6), while the genera‐

tion curve is related to the PV I-V curve. Both curves are represented at Figure 9.

**Figure 7.** MPP across the I-V plan considering solar radiation and temperature changes.

illustrates Figure 7.

96 Sustainable Energy - Recent Studies

Trackers (MPPT), are employed.

**3.1. MPPT from the dc-dc converter point of view**

plying a resistive load, as depicts Figure 8.

**Figure 8.** PV module supplying a resistive load.

speed are targeted.

Even when the load resistance is chosen for both curves intercept each other exactly on the MPP, it is impossible to ensure the maximum power transfer for long time intervals, once when solar radiation or temperature change, the MPP is relocated on the I-V plan.

For solving this problem, in order to maintain the system always operating on the MPP, the load curve should be modified according to solar radiation or temperature changes. For ex‐ ample, from Figure 10, if the PV generation curve is *I-V 1* and the load curve is *Load 1*, the system operating point is given by *MPP 1*. Now, considering a solar radiation and tempera‐ ture change, the generation curve comes from *I-V 1* to *I-V 2*. In this situation, keeping the same load curve (*Load 1*), the system operating point is established at *X2*, i.e., out of the MPP. However, if the load curve is modified from *Load 1* to *Load 2*, the system backs to oper‐ ate on the MPP, in this case, *MPP 2*.

**Figure 10.** I-V and load curves intersection for defining the PV system operating point.

Evidently, modifying the load curve in accordance with the solar radiation and temperature changes is not a suitable solution, since the load is defined by the user. Nevertheless, if a dcdc converter is interposed between the PV module and the load, it is possible to control the converter duty cycle in order to emulate a variable load from the PV terminals point of view, even when a fixed load is employed. The arrangement presented at Figure 11, com‐ posed by a PV module, a dc-dc converter and a load, defines the hardware of a maximum power point tracking system.

*VR* =*RIR* (7)

http://dx.doi.org/10.5772/51020

*<sup>G</sup>* <sup>2</sup> (10)

*<sup>G</sup>* <sup>2</sup> *IPV* (11)

*<sup>R</sup>* ) (12)

(8)

99

(9)

Taking into account a literal dc-dc converters static gain *G*, the input system variables (*V PV*

An Optimized Maximum Power Point Tracking Method Based on PV Surface Temperature Measurement

Isolating *V <sup>R</sup>* in (8) and *I <sup>R</sup>* in (9) and substituting the found results into (7), it is possible to

<sup>=</sup> *<sup>R</sup>*

The term *V PV /I PV* describes the effective resistance *R eff* obtained from the PV module termi‐ nals. In other words, the dc-dc converter emulates a variable resistance, whose value can be modulated in function of the converter static gain *G*. This conclusion allows redesigning Fig‐

and *I PV*) can strictly be associated to the output ones (*V <sup>R</sup>* and *I <sup>R</sup>*), through (8) and (9).

*<sup>G</sup>* <sup>=</sup> *VR VPV*

*G* = *IPV IR*

*VPV IPV*

*VPV* <sup>=</sup> *<sup>R</sup>*

<sup>θ</sup>=atan( *<sup>G</sup>* <sup>2</sup>

θ, given by 12, is modified according to the converter static gain *G*.

When plotted on the I-V plan, equation (11) results in a straight line whose inclination angle

obtain (10).

ure 12 as Figure 13 and writes (11).

**Figure 13.** Effective resistance obtained from the PV module terminals.

**Figure 11.** Maximum point tracker system.

It is important to emphasize that the tracking system will present distinct behaviours de‐ pending on the dc-dc converter and load-type features. Here, buck, buck-boost, boost, Cuk, SEPIC and zeta converters will be analyzed in association with resistive or constant voltage loads-type.
