www.elsevier.com/locate/solener

Solar Energy 81 (2007) 31–38

Theoretical assessment of the maximum power pointtracking efficiency of photovoltaic facilities

with different converter topologies

J.M. Enrique a,*, E. Duran a, M. Sidrach-de-Cardona b,1, J.M. Andujar a

a Departamento de Ingenierıa Electronica, de Sistemas Informaticos y Automatica, Universidad de Huelva, Spainb Departamento de Fısica Aplicada, II, Universidad de Malaga, Spain

Received 16 May 2005; received in revised form 1 March 2006; accepted 15 June 2006Available online 24 August 2006

Communicated by: Associate Editor Hansjorg Gabler

Abstract

The operating point of a photovoltaic generator that is connected to a load is determined by the intersection point of its characteristiccurves. In general, this point is not the same as the generator’s maximum power point. This difference means losses in the system per-formance. DC/DC converters together with maximum power point tracking systems (MPPT) are used to avoid these losses. Differentalgorithms have been proposed for maximum power point tracking. Nevertheless, the choice of the configuration of the right converterhas not been studied so widely, although this choice, as demonstrated in this work, has an important influence in the optimum perfor-mance of the photovoltaic system. In this article, we conduct a study of the three basic topologies of DC/DC converters with resistiveload connected to photovoltaic modules. This article demonstrates that there is a limitation in the system’s performance according to thetype of converter used. Two fundamental conclusions are derived from this study: (1) the buck–boost DC/DC converter topology is theonly one which allows the follow-up of the PV module maximum power point regardless of temperature, irradiance and connected loadand (2) the connection of a buck–boost DC/DC converter in a photovoltaic facility to the panel output could be a good practice toimprove performance.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Photovoltaic module; DC/DC converter; I–V curve; Maximum power point tracker; Losses

1. Introduction

DC/DC converters are widely used in photovoltaic gen-erating systems as an interface between the photovoltaicpanel and the load, allowing the follow-up of the maximumpower point (MPP). Its main task is to condition the energygenerated by the array of cells following a specific controlstrategy (Hua and Shen, 1998; Hussein et al., 1995;

0038-092X/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.solener.2006.06.006

* Corresponding author. Tel.: +34 959 21 7374/7655/7671/7656; fax:+34 959 017304.

E-mail addresses: juanm.enrique@diesia.uhu.es (J.M. Enrique), msi-drach@ctima.uma.es (M. Sidrach-de-Cardona).

1 Tel.: +34 952132722/23; fax: +34 952131450.

Masoum et al., 2002). The DC/DC conversion processimplies in turn an associated effect of impedance transfor-mation, i.e., the input impedance shows a dependence ona number of parameters such as load resistance, duty cycle,etc. In this sense, converters are similar to transformerswhen they are used as impedance adaptors, except that inconverters the adaptation parameter is not the turns ratiobetween the secondary and primary ones, but the dutycycle d, which can be governed electronically (Singer,1991; Jingquan et al., 2001; Tse et al., 2002, 2004), a factthat corresponds to the maximum power point trackingsystem (MPPT). This effect, which is the basis of MPPTsystems, also shows an odd property: certain input imped-ance values can be either reached or not, depending on the

Nomenclature

d duty cycleg MPP-tracking efficiencyA ideality factor of PN junctionC capacitanceI current supplied by the photovoltaic arrayIL photo-current generated by solar radiationIMPP maximum power point currentK Boltzmann constant (1.38 · 10�23 J/K)L inductancenP number of parallel-connected cellsnS number of series-connected cellsP power supplied by the photovoltaic arrayPMPP power of the maximum power point

q electron charge (1.602 · 10�19 coulombs)Ri input resistanceRL load resistanceRMPP maximum power point impedanceRP intrinsic parallel resistanceIS reverse saturation currentRS intrinsic series resistanceT temperatureTC conmutation periodV voltage supplied by the photovoltaic arrayVMPP maximum power point voltage

32 J.M. Enrique et al. / Solar Energy 81 (2007) 31–38

type of converter used, which significantly affects the pho-tovoltaic system’s performance.

MPPT is used in PV power systems to force the PV mod-ule operating at MPP. In this way the PV module producesthe maximum power output. For this operating point, itovercomes the disadvantages of high initial installation costsand low energy conversion efficiency. Previously-used meth-ods of achieving MPPT include: (1) incremental conduc-tance (IncCond); (2) perturbation and observation (P&O);(3) neural network and (4) curve-fitting (Hua et al., 2003).

At present there are numerous works aimed at designingMPPT systems (Bahgat et al., 2004; Enslin et al., 1997; Gar-cıa and Alonso, 2000; Hua et al., 2003; Kitano et al., 2003;Masoum et al., 2002; Neto et al., 2000; Schilla et al., 2000;Veerachary et al., 2002, 2003; Yu et al., 2004), where the effi-ciency of each of them is shown and comparatives of the dif-ferent methods of MPP tracking are established underdifferent operating conditions. However, the choice of theappropriate DC/DC converter for the implementation ofboth the MPPT system and its integration in the facilityarray has not been explicitly studied, despite its affecting sig-nificantly the optimum operation of the photovoltaic system.

The aim of this work is to make a comparative of thephotovoltaic system performance using the three basictopologies of DC/DC converters and MPPT tracker, sothat it may be possible to make a decision on the best con-figuration to be used. This work is divided into the follow-ing sections: Sections 2 and 3 present some characteristicsand properties of photovoltaic modules and DC/DC con-verters, especially as regards the input impedance that theypresent under certain operating conditions. The analysisand results for each configuration are shown in Sections 4and 5. Finally, some conclusions are drawn in Section 6.

2. Theoretical models of solar arrays

A simplified exponential expression (Gow and Manning,1999) describes the relationship between voltage (V) andcurrent given by a module, Eq. (1).

I ¼ nP IL � I s eq V

nSþIRS

nP

� �.AKT� 1

" #�

VnSþ IRS

nP

RP

" #ð1Þ

P ¼ I � V ð2Þ

P ¼ nP � V � IL � I s eq V

nSþP �RS

V �nP

� �.AKT� 1

" #�

VnSþ P �RS

V �nP

RP

" #ð3Þ

dPdV

� �MPP

¼ 0 ð4Þ

The nP and nS parameters indicate the number of cellsconnected in parallel and in series, respectively; RP and R

S, are the intrinsic parallel and series resistances associatedto the panel; K is the Boltzman constant (1.38 · 10�23 J/K)and q is the charge on an electron. Factor A determines thedeviation of the characteristics of an ideal p–n junction,and IS is the reverse saturation current, which presents adependence on the panel temperature. IL represents thecurrent (photo-current) generated by solar radiation (G).Such a current shows a linear relation with regard to radi-ation and temperature.

Eq. (1) (considering the dependence of its parameters onT and G) provides the so-called I–V curves of a photovol-taic panel, and the multiplication result of both magnitudesprovides the supplied power: Eqs. (2) and (3). This curvechanges depending on the incident irradiance and the celltemperature. Each curve presents a maximum power point(MPP, point of coordinate VP), which provides the optimaloperation point for an efficient use of the panel (Hohm andRopp, 2002; Hua and Shen, 1998).

The MPP is calculated solving Eq. (3) with the condition(4). This calculation is tedious and slow, since these expres-sions do not have an analytical solution, and therefore,they have to be solved by numerical methods (i.e., New-ton’s method). Other two important points of this curveare the open-circuit voltage (Voc) and the short-circuit cur-rent (Isc). The voltage in an open circuit represents themaximum voltage given by the panel to a zero current(without load), while the short circuit current represents

Fig. 1. Panel–converter connection.

Table 1Ri values for converters in Fig. 4

Converter Kcrit Ri (CCM) Ri(DCM)

Buck 1 � d RL

d2 RL

4 � 1þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4K=d2

q� �2

Boost dÆ(1 � d)2 RLÆ (1 � d)2 4�RL

ð1þffiffiffiffiffiffiffiffiffiffi1þ4d2p

=KÞ2

Buck–boost (1 � d)2 RL �ð1�dÞ2

d2K�RL

d2

With K ¼ 2Leqv

RLT CDCM happens for K 6 Kcrit

J.M. Enrique et al. / Solar Energy 81 (2007) 31–38 33

the maximum removable current of the panel (short-circuitload).

There are other models of photovoltaic generators(PVG) apart from the one mentioned above. Akbaba andAlataawi (1995) proposed a simple model which is namedthe Akbaba model (Akbaba et al., 1998). Its accuracy, flex-ibility and simplicity are demonstrated by comparing thismodel with the traditional diode junction model for aPVG whose parameters are given in Appelbaum (1986).But the existing version of the Akbaba model is not com-plete, since the values of its model parameters are solar radi-ation-dependent and they need to be evaluated at each solarradiation level. This adds additional computational burdenand hence full advantage of the model cannot be utilized.

In this work, we use the model described in Eq. (1) inorder to implement the theoretic model used in thesimulation.

3. DC/DC converters as variable resistance emulators

DC/DC converters are used in applications where anaverage output voltage is required, which can be higher orlower than the input voltage. This is achieved by governingthe times in which the converter’s main switch conducts ordoes not conduct (PWM technique) usually to a constant fre-quency. The ratio of the time interval in which the switch ison (TON) to the commutation period (TC) is called duty cycle

(d) of the converter. Both in the continuous conductionoperational mode (CCM)2 and the discontinuous conduc-tion mode (DCM),3 the three basic converter topologiescan be compared to a continuous current transformer,where the transformation ratio can be electronically con-trolled varying the converter’s duty cycle d in the range [0,1].

Fig. 1 shows the diagram of a solar panel connected to aDC/DC converter, where the resistance shown at the con-verter’s input is represented by Ri (RL is the converter’sload resistance). In relation to the photovoltaic module,the converter is its Ri value load resistance. Assuming con-verters without losses, the ratio of input resistance to loadresistance is shown in Table 1, both for CCM and DCM(Tse et al., 2002).

The converter’s operational mode is defined by the con-stant K given in (5), where Leqv is the inductance equivalentto the converter, RL its load resistance and TC the commu-tation period (reverse to the operating frequency).

K ¼ 2Leqv

RLT C

ð5Þ

2 CCM (Continuous Conduction Mode): DC/DC converter operationalmode, where the current intensity that circulates through the inductance ofthat converter is not cancelled out at any interval of the TC commutationperiod.

3 DCM (DCM, Discontinuous Conduction Mode): DC/DC converteroperational mode, where the current intensity that circulates through theinductance of that converter is cancelled out during an interval of the TC

commutation period.

If K value is lower than or equal to another one calledKcrit, the converter will operate in DCM. Conversely, if K

exceeds the value of Kcrit, the converter will operate inCCM. As observed in Table 1, the value of Kcrit is differentfor each type of converter.

Fig. 2 shows the three basic converters which providethe different conversion ratios given in Table 1, togetherwith a graphic representation of the input resistancereflected according to the duty cycle d for CCM (Andujaret al., 2004; Enrique et al., 2005).

4. Theoretic analysis

Fig. 3 shows the I–V curve for a given module connectedto a converter. Let us take any curve point, for example A.The photovoltaic module will operate in A provided thatthe output voltage and current match the voltage andcurrent of point A (VA, IA). Thus, we will call the quotientVA/IA impedance of the operating point A (RiA).

Assume that B is the maximum power point, thereforeRiB = RMPP = VMPP/IMP. The system will then operate atthe maximum power point (MPP) provided that Ri =RiB = RMPP. In general terms, a maximum power pointtracking system tries to vary impedance at the photovoltaicmodule output (Ri) in order to take it to the RMPP value.As has been mentioned above, the I–V curve of a photovo-ltaic module varies according to the incidental temperatureand radiation, so VMPP, IMPP and RMPP will vary depend-ing on how these variables do.

4.1. Analysis of the module-buck converter-load

configuration

The following expressions are deduced from Table 1 forthe buck converter:

Fig. 2. DC/DC converters commonly used and their input resistance. (a) Buck Converter; (b) boost converter; (c) buck–boost converter; (d) inputresistance versus d in CCM; (e) input resistance versus d in CCM and (f) input resistance versus d in CCM.

Fig. 3. Location of the operation point of a photovoltaic module.

34 J.M. Enrique et al. / Solar Energy 81 (2007) 31–38

limd!0

Ri-CCM ¼ limd!0

RL

d2¼ 1 ð6Þ

limd!1

Ri-CCM ¼ limd!1

RL

d2¼ RL ð7Þ

limd!0

Ri-DCM ¼ limd!0

RL

4� 1þ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4K

d2

r !2

¼ 1 ð8Þ

Ri-DCM ¼RL

4� 1þ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4K

d2

r !2

P RL ð9Þ

limd!1

Ri-DCM ¼ limd!1

RL

4� 1þ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4K

d2

r !2

ð10Þ

In DCM K 6 Kcrit ¼ ð1� dÞ, then:

limd!1

Ri-DCM 6 limd!1

RL

4� 1þ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4ð1� dÞ

d2

s0@

1A

2

¼ RL ð11Þ

From (9) and (11) we have:

limd!1

Ri-DCM ¼ RL ð12Þ

Being the expressions of Ri continuous in d, for a scan-ning of the converter’s duty cycle d 2 [0,1], Ri takes valuesthat belong to the interval [RL,1), being RL the load resis-tance. If RMPP does not belong to the set of values allowedfor Ri, the capture of MPP will not be possible, thus

Fig. 4. Chart of MPP tracking with buck DC/DC converter. Fig. 5. Chart of MPP tracking with boost DC/DC converter.

J.M. Enrique et al. / Solar Energy 81 (2007) 31–38 35

defining a ‘‘non-capture zone’’ for RL > RMPP values.Fig. 4 shows the effect graphically. The impedance at theinput of a buck converter is always a version scaled by afactor greater than or equal to 1 (see Table 1) of the imped-ance connected to its output (in our case RL). Therefore,the MPP capture will only be possible for RL 6 RMPP

values.

4.2. Analysis of the module-boost converter-load

configuration

The following expressions are deduced from Table 1 forthe boost converter:

limd!0

Ri-CCM ¼ limd!0

RL � 1� dð Þ2 ¼ RL ð13Þ

limd!1

Ri-CCM ¼ limd!1

RL � 1� dð Þ2 ¼ 0 ð14Þ

limd!0

Ri-DCM ¼ limd!0

4 � RL

1þffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4d2

K

q� �2¼ RL ð15Þ

limd!1

Ri-DCM ¼ limd!1

4 � RL

1þffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4d2

K

q� �2ð16Þ

In DCM K 6 Kcrit, therefore K 6 dÆ(1 � d)2. Taking thiscondition in Eq. (16) into account, it is deduced that:

limd!1

Ri-DCM 6 limd!1

4 � RL

1þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4d2

Kcrit

q� �2

¼ limd!1

4 � RL

1þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ 4d2

d�ð1�dÞ2

q� �2¼ 0 ð17Þ

Given that Ri-DCM cannot be negative, it is clear that,when d! 1, the limit matches Ri-DCM = 0. Being theexpressions of Ri continuous in d, both for CCM andDCM, it is deduced that Ri can only be at the interval[0,RL]. The maximum power point tracking system willmodify the value of Ri, trying to get Ri = RMPP. However,this will not be possible if RMPP does not belong to the setof values allowed for Ri, that is, the system will not reachthe MPP if RL<RMPP. The behaviour is clearly oppositeto that mentioned in the previous section, and therefore

there is an inversion of zones with respect to the buck con-verter. Fig. 5 shows this effect. The impedance at the inputof a boost converter is always a lessened version in a factorlower than or equal to 1 (see Table 1) of the impedanceconnected to its output (RL in our case). Therefore, theMPP capture will only be possible for RL P RMPP values.

4.3. Analysis of the module-buck/boost converter-load

configuration

The following expressions are deduced from Table 1 forthe buck–boost converter:

limd!0

Ri-CCM ¼ limd!0

RL � 1� dð Þ2

d2¼ 1 ð18Þ

limd!1

Ri-CCM ¼ limd!1

RL � 1� dð Þ2

d2¼ 0 ð19Þ

limd!0

Ri-DCM ¼ limd!0

K � RL

d2¼ 1 ð20Þ

limd!1

Ri-DCM ¼ limd!1

K � RL

d2ð21Þ

In DCM K 6 Kcrit, therefore K 6 (1 � d)2. Taking thiscondition in Eq. (21) into account, it is deduced that:

limd!1

Ri-DCM 6 limd!1

Kcrit � RL

d2¼ lim

d!1

ð1� dÞ2 � RL

d2¼ 0 ð22Þ

Given that Ri-DCM cannot be negative, it is clear that thelimit, when d! 1, matches Ri-DCM = 0. For this configura-tion, in accordance with the results from (18)–(22), andknowing that Ri is a continuous function in d, a scanningof the duty cycle, d 2 [0, 1], allows all values of Ri, i.e., Ri

can take any value between 0 and 1. Consequently, theimposed restrictions for the two previous converter topolo-gies do not affect the buck–boost converter, and thereforethere is not ‘‘non capture zone’’. Fig. 6 shows this effect.This allows the photovoltaic solar facility to achieve theMPP regardless of the value of RL, thus obtaining a higherpower point tracking efficiency.

5. Examples

To support the theoretic results analysed in the previoussection, we have simulated four photovoltaic systems

Fig. 6. Chart of MPP tracking with buck–boost DC/DC converter. Notethat this converter allows MPP tracking in both directions.

Fig. 7. Temperature and irradiation values for a clear day in Malaga(Spain).

Table 2Photovoltaic module ‘SX60’ parameters

A = 1.2 Ideality factor of PN junctionEg = 1.12 eV Band gap energynp = 1 Number of parallel-connected modulesns = 36 Number of series-connected cellsPmax = 60 W Maximum power at standard conditionsa

Vmax = 16.8 V Voltage at the maximum power pointImax = 3.56 A Current at the maximum power pointNOTC = 47 �C Nominal Operating Cell TemperatureIsc = 3.87 A Short-circuit current at standard conditionsVoc = 21.06 V Open circuit voltage at standard conditionskv = � 80 mV/�C Voc temperature coefficientki = 0.065%/�C Isc temperature coefficient

a Standard conditions: 25 �C and 1000 W/m2.

Fig. 8. Maximum power point voltage VMPP(t) and current IMPP(t)trajectories for the ‘SX60’ (BP) module for a clear day in Malaga (Spain).

36 J.M. Enrique et al. / Solar Energy 81 (2007) 31–38

(using MATLAB). Three systems use a DC/DC converter(each one of a different type) with MPP tracking system,and a fourth one uses a direct connection photovoltaicmodule-load. Experimental values of cell temperature andglobal irradiation corresponding to a clear day have beenused as input metereological data.

The aim is to evaluate the MPP-tracking efficiency ofeach of the systems, calculated according to expression(23):

g ¼R t

0 P instðtÞ � dtR t0 P MPPðtÞ � dt

ð23Þ

where Pinst is the instantaneous power in the operatingpoint of the system and PMPP is the available power atthe photovoltaic module maximum power point under a gi-ven cell temperature and irradiance (Hohm and Ropp,2002). Given that according to (23) MPP-tracking effi-

ciency is the quotient between the areas under each curve,the closer the real curve to the PMPP(t) trajectory, the betterefficiency.

The meteorological data used for the study have beenmeasured in the laboratory of photovoltaic systems ofthe University of Malaga (Spain).The measure of the celltemperature was carried out by means of a PT100 coupledto the later face of the module. The incident global irradi-ation has been measured by means of a reference solar cellinstalled in the same plane that the photovoltaic module.Both signals were taken from the weather station withone minute intervals from the data acquisition system,Hydra (Fluke). The measured values for the day 3rd ofOctober of 2002 are shown in Fig. 7. The ‘SX60’ (BP)model was selected as photovoltaic generator for the simu-lation. Table 2 shows its parameters.

Fig. 8 shows the calculated trajectories of VMPP, andIMPP, for the cited day for the SX60 module. It can beobserved that the IMPP is directly proportional to the inci-dent irradiance while the VMPP varies depending on the celltemperature. The variation of the impedance in the maxi-mum power point, RMPP, throughout the day is shown inFig. 9. In this case, we obtained a daily average RMPP valueof 9 X. To guarantee the achievement of information onthe system’s behaviour when it operates with resistive loads

different from RMPP, in our analysis we have differentiatedbetween loads higher and lower than average RMPP (specif-ically, 5 X and 20 X).

Due to its simple and easy implementation, the maxi-mum power point tracking in this work was made on thebasis of the well-known method ‘‘Perturbation and Obser-

Fig. 10. Maximum power point power trajectory PMPP(t) and powersupplied P(t) to the 5 X and 20 X loads, without DC/DC converterbetween the photovoltaic module and the load.

Fig. 11. Maximum power point power trajectory PMPP(t) and powersupplied P(t) to the 5 X and 20 X loads, with buck converter between thephotovoltaic module and the load.

Fig. 9. Maximum power point impedance trajectory RMPP(t) for the‘SX60’ (BP) module for a clear day in Malaga (Spain).

Fig. 12. Maximum power point power trajectory PMPP(t) and powersupplied P(t) to the 5 X and 20 X loads, with boost converter between thephotovoltaic module and the load.

Table 3MPP-tracking efficiency obtained for each DC–DC converter configura-tion and load

Load Withoutconverter(%)

Buckconverter(%)

Boostconverter(%)

Buck–boostconverter(%)

RL = 5 X 88.5 97.2 91.2 99.9RL = 20 X 40.2 40.3 99.7 99.9

J.M. Enrique et al. / Solar Energy 81 (2007) 31–38 37

vation P&O’’ (Hohm and Ropp, 2002; Hua and Shen,1998; Hussein et al., 1995).

Fig. 10 shows the trajectories of the power supplied by theload and the MPP power for the two different values of RL.It is observed that when the panel is directly connected to theresistive load, without inserting any DC/DC converter, thesystem will only operate at the maximum power point whenRMPP and RL match (see Fig. 9). If a buck converter isinserted between the panel and the load (Fig. 11), we canobserve that the system is only able to follow the maximumpower point for not very high irradiation values (dependingon RL), i.e., when the maximum power point impedanceRMPP is relatively high. At maximum solar irradiationhours, RMPP reaches its minimum values, and so the systemis unable to achieve the MPP. This is even more evident thatthe higher RL is in relation to RMPP. When it is used a boostconverter, (Fig. 12), the system is able to reach the maximumpower point only at maximum irradiation hours (lowRMPP), with a remarkable loss of MPP-tracking efficiencyat the initial and final hours of the day.

Finally, when a buck–boost converter is used thePMPP(t) and P(t) trajectories are graphically equal, withvalues of 0.999 for the MPP-tracking efficiency. Ri can takeany value with this converter. This allows the photovoltaicsolar system to reach the MPP regardless of the existingirradiation level and RL, achieving a higher MPP-tracking

efficiency. Note that the MPP can be tracked for any RL

value, regardless of its relationship with RMPP.In Table 3, a comparative of the MPP-tracking effi-

ciency provided by each of the configurations for the con-cerned day of study is given. Observe that in all cases, the

38 J.M. Enrique et al. / Solar Energy 81 (2007) 31–38

configuration with buck–boost converter is the one thatpresents the highest efficiency.

6. Conclusions

In this work we aimed at revealing the importance of thecorrect choice of the DC/DC converter in a photovoltaicfacility in order to obtain its highest MPP-tracking effi-

ciency. In this article we demonstrate that only the buck–boost DC/DC converter is able to manage the facility tofollow the photovoltaic panel maximum power point atall times, regardless of cell temperature, solar global irradi-ation and connected load.

It is important to remark that the result obtained in theanalysis is independent from the MPP tracking system, i.e.,however efficient this system may be, the DC/DC converterconfiguration imposes restrictions on it that it cannot sidestep.

‘‘Despite the fact that the study carried out in this workis theoretical, it is important to note that from a practicalapproach, the buck and boost converters are the most effi-cient topologies for a given price. While voltage flexibilityvaries, buck–boost and Cuk (Cuk is a type of structurederived from the buck–boost topologies) converters arealways at efficiency or, alternatively, price disadvantage.Nevertheless, there are already configurations of buck–boost and Cuk converters where both the MOSFET andthe inductor are of a very low resistance, achieving efficien-cies as regards input power higher than 95% and hardly 2or 3% lower than the buck and boost topologies.’’

According to the performed analysis, we dare to suggestthat a good practice could be including a buck–boost DC/DC converter in photovoltaic solar facilities at the PVarray output and then connecting, after the converter, therest of the facility elements (load). This practice guaranteesthe photovoltaic panel maximum power point tracking forany solar irradiation, cell temperature and load conditions,which could undoubtedly redound to the facility’s highersystem efficiency.

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