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FPGA Implementation of a Robust MPPT of a 

Photovoltaic System Using a Fuzzy Logic Controller 

Based on Incremental and Conductance Algorithm 
 

Mohamed Yassine Allani 

UR-LAPER, Faculty of Sciences of Tunis,  
University of Tunis ElManar, 

Tunis, Tunisia 

medyassine.allani@fst.utm.tn 

Fernando Tadeo 

Department of Systems and Automation Engineering, 

University of Valladolid, 
Valladolid, Spain 

Fernando.Tadeo@uva.es 

Dhafer Mezghani 

UR-LAPER, Faculty of Sciences of Tunis 
University of Tunis ElManar, 

Tunis, Tunisia 

dhafer.mezghani@fst.utm.tn 

Abdelkader Mami 

UR-LAPER, Faculty of Sciences of Tunis,  

University of Tunis ElManar, 
Tunis, Tunisia 

abdelkader.mami@fst.utm.tn 
 

 

Abstract—Climate dependence requires robust control of the 

photovoltaic system. The current paper is divided in two main 

sections: the first part is dedicated to compare and evaluate the 

behaviors of three different maximum power point tracking 
(MPPT) techniques applied to photovoltaic energy systems, 

which are: incremental and conductance (IC), perturb and 

observe (P&O) and fuzzy logic controller (FLC) based on 

incremental and conductance. A model of a photovoltaic 

generator and DC/DC buck converter with different MPPT 

techniques is simulated and compared using Matlab/Simulink 
software. The comparison results show that the fuzzy controller 

is more effective in terms of response time, power loss and 

disturbances around the operating point. IC and P&O methods 

are effective but sensitive to high-frequency noise, less stable and 

present more oscillations around the PPM. In the second section, 

the FPGA platform is used to implement the proposed control. 

The FLC architecture is implemented on an FPGA Spartan 3E 
using the ISE Design Suite software. Simulation results showed 
the effectiveness of the proposed fuzzy logic controller. 

Keywords-fuzzy logic controller; P&O; IC; MPPT; energy 

solar; buck converter; FPGA 

I. INTRODUCTION 

The electrical energy produced by photovoltaic systems is 
very interesting and a modern topic of power generation. 
However, the costs of PV arrays are relatively high, and the 
efficiency of the energy conversion is quite low. Therefore, the 
electric power generated by the PV arrays should be efficiently 
used. In a direct coupled (with no battery storage) PV system, 
the solar cell arrays are directly connected to the motor load 
couple. These systems are relatively simple and inexpensive to 
operate. A direct coupled system may include a maximum 
power point tracker (MPPT) to improve its performance at 

starting and at steady state operation whenever it is needed. 
Many researches on photovoltaic techniques [1-3] have been 
carried out in order to increase the efficiency of these panels, 
and to extract their maximum energy while designing reliable 
and stable systems. There are different methods of PPM 
tracking such as IC [4-6], parasitic capacitance method [7], 
P&O method [8], etc. They are based on the regulation of the 
current or voltage of the photovoltaic generator according to 
climatic conditions. As a result, the uncertainties associated 
with these conditions have decreased the reliability of these 
techniques, especially as a result of changes in sunlight and 
temperature. Artificial intelligence techniques such as neural 
networks [9] and fuzzy logic [10, 11] have the characteristics 
of adaptive and versatile mechanisms and are able to improve 
the performance of the control system in the presence of these 
uncertainties.  

In addition, a software implementation of the FLC 
developed on general purpose cannot be regarded as a suitable 
solution for such applications, especially when it is used as an 
MPPT controller for autonomous PV applications. In this case, 
FLC was usually implemented in microcontrollers [12] and/or 
in digital signal processors (DSPs) [13]. Simulation and 
experimentation results showed the advantages of FLC over 
conventional P&O. This proposed technique was able to reduce 
steady-state oscillations and improve the convergence speed of 
the operating point. These devices can provide considerable 
performance, but they do not offer the advantages that FPGA 
(field-programmable gate array) devices can offer for the 
implementation of certain commands. With the progress in 
microelectronics, real time applications use intelligent 
techniques and new hardware design solutions such as FPGA. 
They are suitable for the implementation of control algorithms 
such as fuzzy logic controllers. These circuits allowed the 

Corresponding author: Mohamed Yassine Allani



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reduction of the execution time by adopting parallel processing, 
rapid design prototyping and improved MPPT control of the 
photovoltaic panel quality by exploiting new digital system 
technologies [9, 15, 16]. From the results of these works, it can 
be deduced that the MPPT is reached quickly, especially under 
rapidly changing climatic conditions, the response time is 
improved, the exceedance and the oscillations are extremely 
reduced and therefore the energy losses are reduced. All these 
advantages of real time implementation form a necessity for 
MPPT control. 

II. MODELLING OF THE PV CONVERSION SYSTEM 

A. Modelling of the Photovoltaic Panel 

The PV module converts light into electricity. The electrical 
characteristics of the photovoltaic panel depend on the 
irradiation and the temperature. Figure 1 shows the complete 
system simulated in Matlab/Simulink. The photovoltaic cell is 
modeled by (1)-(6) [16-18] that define the static behavior of the 
P-N junction of a conventional diode. The electrical model of 
the PV cells is shown in Figure 2. 

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,-./�
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� � �� � �� �	
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>�?�@
�2�
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� * � 1� � '�?�
�2�2A *  (6) 
 

 
Fig. 1.  Simulink model of the photovoltaic conversion system  

 
Fig. 2.  Simulink model of the photovoltaic conversion system  

The PV parameters used in the model are summarized in 

Table I. 
 

TABLE I.  PARAMETERS OF THE PV PANEL KANEKA G-SA060 [16-18] 

Parameters of PV Values and units 

Pmax 60.3W 

Cells per Module 61 

Vpv at Pmax 67V 

Ipv at Pmax 0.9A 

Vo (open circuit voltage) 91.8V 

Is (short circuit current) 1.19A 

a 2.1922 

Rs (series resistance) 5.8Ω 

Rsh (shunt resistance) 254.8Ω 

 

B.  Modelling of the Buck Converter 

Buck converter is a DC-DC converter. It adjusts the energy 
transfer between the photovoltaic generator (PVG) and the DC 
load and allows the reduction of the voltage. The buck 
converter model is illustrated in Figure 3. The output voltage 
and current of the buck converter are expressed in: 

BC � D ∗ BF				    (7) 
�C � >1/D@ ∗ �F				    (8) 

where α is the duty cycle of the buck converter, 0<α<1. 

 

 
Fig. 3.  Electrical circuit model of the buck converter. 

The parameters of the buck converter connected to the PV 
generator are presented in Table II. 

TABLE II.  BUCK CONVERTER PARAMETERS AND VALUES 

Parameters of the buck converter Values and units 

Vin 61V 

Vout 24V 

L (inductance) 10µH 

Ce (input capacitor) 470µF 

Co (otput capacitor) 470µF 

F (switching frequency) 30kHz 

 

III. MPPT CONTROL 

Three methods are studied and developed in this work: 

A. MPPT Based Perturb and Observe 

Perturb and Observe (P&O) is one of the most popular 
MPPT techniques used in a photovoltaic power system. This 
method uses the current/voltage measurements delivered by the 
PVG to calculate maximum power. Figure 4 describes the 
operation of the algorithm (P & O). 

B. MPPT Based on Incremental and Conductance 

The IC method is often applied in photovoltaic systems. It 
tracks the MPP by comparing the instantaneous and 
incremental conductance of the source under consideration. 
The question asked of the IC method is similar to that of P&O. 



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The fixed step size is generally adopted, which determines the 
accuracy and speed of the MPPT response. Figure 5 illustrates 
the algorithm of the IC method. 

 

 
Fig. 4.  Methodology of P&O method 

 
Fig. 5.  Algorithm of the incremental and conductance method 

C. MPPT Based Fuzzy Logic Control (Based on IC) 

Recently, several methods have been used to extract 
maximum power of the PVG [4-11, 9, 14-24]. In order to 
design an MPPT controller not only efficient, but also able to 
operate properly under all variations, we used fuzzy logic 
control which is one of the most known control techniques of 
the MPPT [10, 11, 21-23]. In addition, the IC method is often 
applied in photovoltaic systems. It tracks the MPP by 
comparing the instantaneous and incremental conductance of 
the source under consideration. The issues of the IC method are 
similar to the ones of the P&O method. The fuzzy logic 
converges quickly, although it can operate with inaccurate 
inputs, and does not require a perfectly well-known 
mathematical model. Therefore, we have combined the IC 
method into a fuzzy logic controller. The fuzzy controller 
inputs are modeled by (9) and (10), the result of the 
incremental and conductance algorithm is presented in (8) [4-
6]. 

	
pv

pv

pv

pv

V

I

dV

dI
−=     (9) 

	
pv

pv

pv

pv

V

I

dV

dI
kE +=)(     (10) 

	 )1()()( −−= kEkEkdE     (11) 
The proposed control model simulated with the use of 

Matlab/Simulink is shown in Figure 6. 

 

 
Fig. 6.  Simulink model of the fuzzy logic controller 

Triangular membership functions for the fuzzification 
process are employed. For inputs E, dE and Duty output, 5 
belonging functions have been identified depending on the 
following linguistic variables: Grand negative (GN), Negative 
(N), Zero (Z), Positive (P) and Grand positive (GP). The range 
for the error is (0.02 to 0.2), for the error change is (-0.4 to 0.4) 
and for the duty cycle increment is (-0.1 to 0.1). The degree of 
membership function of the input and the output of the PV is 
described in Figure 7. 

 

(a) 

 

(b) 

 

(c) 

 

Fig. 7.  The membership function of duty cycle (c) and the two inputs of 

the fuzzy logic controller: (a) E, (b) dE. 

According to the choice carried out for the fuzzification of 
the input and the defuzzification of the output, there are 25 
inference rules on the fuzzy controller database. We use the 



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Mamdani method with Max-Min for the fuzzy combinations 
[11]. They are presented in Table III 

TABLE III.  INFERENCE RULES OF THE FUZZY CONTROLLER 

E\dE GN N Z P GP 

GN Z Z GP GP GP 

N Z Z P P P 

Z P Z Z Z N 

P N N N Z Z 

GP GN GN GN Z Z 

 

IV. SIMULATION OF THE SOLAR CONVERSION SYSTEM 

The solar conversion system is composed of four 
photovoltaic panels connected in parallel, a buck converter and 
a DC load. To guarantee maximum power delivered by the 
photovoltaic generator, a control based on the fuzzy logic is 
implemented (based on IC). This has two inputs (the voltage 
and the current delivered by the GPV) and allows the 
estimation of the duty cycle used to control the chopper. The 
solar radiation varies between 600 and 1000W/m

2
, and the 

temperature is considered constant during the simulation. The 
radiation, the output power and the duty cycle are plotted in 
Figure 8. It is worth noting that the duty cycle and the power 
vary according to the climatic conditions. We can notice the 
rapidity and the performance of the MPPT against the variation 
of the radiation. The profiles of the output voltage, the current 
and the power are shown in Figure 8. 

 

 

Fig. 8.  Variation of duty cycle, power and radiation of the PV 

When the radiation changes from 600 to 800W/m
2
, our 

control increases the duty cycle from 0.31 to 0.38 and the 
power from 160 to 206W. When the radiation decreases from 
1000 to 700W/m

2
, the power and the duty cycle also decrease. 

Hence, they vary according to the radiation behavior. Figure 9 
describes the output power profiles of the photovoltaic 
generator and the DC-DC buck converter for a progressive 
variation of the radiation starting from 600 to 800, 1000, 
700W/m

2
 to the value of 900W/m

2
. We note that the tracking 

of the maximum power point is efficient and without 

oscillations. In addition, the efficiency is optimal and the 
performance of the photovoltaic generator is greater than 94%. 
The simulation results proved the robustness of the proposed 
MPPT control against the variation of the solar radiation. In 
Figure 10, the variations of the current and the voltage are 
proportional to the variation of the power. 

 

 

Fig. 9.  Output power profiles of the photovoltaic generator and DC-DC 

buck converter. 

 
Fig. 10.  Profile of the output current, voltage and power delivered by the 

PVG. 

Figure 11 shows the simulation results of FLC, IC, and 
P&O algorithms, where the FLC is achieved with a fast 
response time and few oscillations. In terms of response time, 
the three algorithms gave the same rise time to optimal power 
during each sunshine variation. The oscillation around the MPP 
increased power losses and thus the efficiency of the PV 
system was reduced. The FLC operates with fewer oscillations 
around the MPP. The power difference between the FLC and 
the IC is about 3 and 6W compared to the P&O algorithm. 

V. SIMULATION AND IMPLEMENTATION OF THE FUZZY 
LOGIC CONTROLLER ON FPGA 

Researchers can increasingly optimize problems using 
suitable platforms. This work results from the need to 
investigate the fundamentals of electronic power control 
strategies, using fuzzy logic. In this section, we have to 
implement on the FPGA a FLC based on IC. It is applied to the 
photovoltaic conversion system. In some cases, the 



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characteristics and the performance of the real-time 
implementation unjustified and unsatisfied the calculation of 
some arithmetic operations. In addition, the wrong choice of 
values can sometimes exceed the overflow limits in the results 
and give incorrect values. For this, the fixed point 
representation was chosen. Moreover, we must define by 
calculating the number of bits (m) which designate the integer 
part and the rest forms of the fractional part (n) [24].  

 

 
Fig. 11.  Profile of the output power delivered by the PVG with FLC, IC, 

P&O and without MPPT. 

For more precision and to have a synthesizable code able to 
be implemented in the FPGA, it is necessary to change the data 
type to fixed point and to add the IEEE-proposed library. Table 
IV describes some functions used in the VHDL program. 

TABLE IV.  FUNCTIONS AND DATA TYPES USED IN THE 
IEE_PROPOSED LIBRARY 

Library added to the ISE Functions and types of data 

IEEE_PROPOSED 

Fixed_pkg_c.vhd 

Fixed_float_types_c.vhd 

Sfixed (m-1 downto n) 

Ufixed (m-1 downto n) 

Resize(fixed point resultat,m-1,-n) 

To_ufixed(std_logic_vector valeur, m-1,-n) 

To_sfixed(std_logic_vector valeur, m-1,-n) 

To_slv(fixed point value) 

 

A. Architecture of the fuzzy logic controller 

Mamdani’s implication is the most popular method 
dedicated for the FLC [4-6]. The fuzzy rule of this method is 
expressed in (12): 

	 )]]2(),1(max[min[)(
21

xxy kk
AAc

µµµ =  (12) 

where k=1, 2… 25. The various processes of the fuzzy logic 
controller are described in the functional diagram presented in 
Figure 12. 

The Mamdani method facilitates the hardware 
implementation thanks to the simple min-max structure. An 
overview of the internal structure of the controller is given by 
the functional diagram in Figure 12. Indeed, the fuzzification of 
the two input variables provides the linguistic values and the 
corresponding membership functions (B1... B5) and (B11… 
B15). In fact, the connection of the pairs of antecedents in the 
rule structure is based on an operator logical AND. Then all the 
rules are associated with a max operation using the bloc max of 
the diagram. Therefore, the weighted average method is 
considered as one of the defuzzification techniques, which is 

suitable for hardware implementation. Considering that the 
output membership functions are usually symmetrical, the 
average of the fuzzy sets can be employed as weightings for the 
defuzzification process. In addition, this technique contains two 
arithmetic operations: multiplication processes with a constant 
and a single division process. 

 

 

Fig. 12.  Functional diagram of the fuzzy logic control 

The inputs / outputs of the analog-to-digital converter ADC 
and the analog-to-digital converter DAC existing in the Spartan 
3E FPGA board are represented by 12 bits. Therefore, the size 
of the integer part and the decimal part of each input/output 
signal is chosen according to the actual value of the signal to be 
represented. For example, the input signals can be represented 
by a vector of 12 bits (m=7, n=5) because the value of the 
voltage cannot exceed the open circuit voltage which is equal 
to 92V. On the other hand, the output value varies between 0 
and 1, thus, we have represented the duty cycle by 12 bits. For 
more precision, we chose to represent the decimal part by 10 
bits. 

B. Simulation Results  

After having detailed our architecture, we have to simulate 
and implement it. The simulation results using the ISE 
Simulator are shown in Figure 13. 

 

 
Fig. 13.  Simulation results of the fuzzy logic controller 

After simulation, we notice that the output of the fuzzy 
logic controller d (duty cycle) tracked the variation of the input 
variables Vpv (voltage) and Ipv (current). In addition, the 
output PWM changes after any variation of the duty cycle d. 
The input variables Vpv and Ipv are represented by 12 bits: 7 
bits for the integer number and 5 bits for the fractional number. 
Thereby, the output variable d is designed by 12 bits: 2 bits of 
the integer number and 10 bits of the fractional one. Table V 
shows the simulation results of FLC inputs and outputs whose 
data are represented in real and hexadecimal numbers. 



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TABLE V.  SIMULATION RESULTS OF THE INPUTS/OUTPUTS OF THE 
PROPOSED CONTROLLER 

Ppv (W) Vpv (V) Ipv (A) d (real) d (Hexa) 

8,48 10.6 0.8 0.3339 156 

92.46 40.2 2.3 0.3574 16e 

195 60 3.25 0.3837 189 

12.6 10.5 1.2 0.3466 163 

241.2 67 3.6 0.373 17e 
 

C. RTL Architecture of the Proposed Control  

The proposed architecture shown in Figure 14 is a black 
box with inputs/outputs. The role of fuzzy logic is to process 
inputs and interpret them to give accurate outputs. This box is 
divided into different blocks that are interconnected with 
intermediate signals. The RTL architecture of the fuzzy logic 
controller obtained after the synthesis process by the Xilinx 
Synthesis Technology (XST) is illustrated in Figure 15.  

 

 
Fig. 14.  The behavioral description of the controller 

 
Fig. 15.  RTL architecture of the controller 

The FLC's RTL architecture is divided into 7 blocks. The 
role of the first block (Interface1_u) is the calculation of the 
controller inputs, the second block (fuzzify_u) plays the role of 
fuzzification. Then, the (infer_u) block is dedicated to creating 
fuzzy rules. The (defuzz_u) block allows reconverting the 
fuzzy output to the crisp output. Furthermore, the FPGA board 
card generates a frequency of 50MHz whereas the duty cycle is 
generated at a frequency of 30kHz. Therefore, the (divider_cl) 
block acts as a frequency divider. Indeed, the block (mux_D1) 
represents a flip-flop that puts the duty cycle to the controller 
output. The (mux_pwm) block is the intermediary between the 
control signal and the transistor component. 

D. SynthesisRreport 

To verify the architecture of the proposed system, 
simulations were performed using the ISE Design Suite, 
version 14.7. Information about the device utilization, after the 
synthesis process are given in Figure 16. The hardware 
resources used by the architecture of the proposed controller 
are negligible compared to the available ones on the chip. 

 

Fig. 16.  The synthesis report 

E. Comparison and Discussion 

Having obtained the proposed controller simulation results 
in real time, it is important to verify and justify these results. 
Thus, we compared the behavior of the fuzzy controller in both 
environments (Matlab/Simulink and ISE) for the following 
values of input variables (solar radiation between 600 and 
1000W/m

2
, temperature equal to 25°C) during 5s. We 

compared the results of simulation of the duty cycle presented 
in Figure 8 and the values obtained in Table V. Figure 17 
shows shows the coherent profile of the duty cycle carried out 
in both environments. 

 

 
Fig. 17.  Comparison of the two simulation results. 

The duty cycle varied between 0.33 and 0.4 for the same 
variation of the solar radiation (from 600 to 1000W/m

2
). It is 

optimally changed after the variation of the solar radiation to 
track a maximal power from the PV module. The effectiveness 
of this method is evaluated with different simulation studies 
under Matlab/Simulink and ISE Design Suite. The proposed 
architecture of the MPPT was proved to be effective. 
Moreover, the output simulation by the ISE Design Suite is 
approximately identical to the one carried out using 
Matlab/Simulink environment. This study shows that the 
FPGA circuit can be used to develop a cost-effective and 
adaptable implementation of the MPPT control. 

VI. CONCLUSION 

The difficulties and the non-linearity of PV systems are 
influenced by the solar radiation and the temperature 
conditions, resulting in power losses and reduced efficiency. In 
the present paper, we developed a PVG controlled by a fuzzy 
logic control based on the incremental and the conductance 
using Matlab/Simulink environment. The proposed MPPT 
algorithm was compared with the traditional methods for 
nonlinear systems (P&O and IC). The conventional P&O and 
IC algorithms work with accepted time responses, 
minimization of maximum power, and more oscillations, which 
reduce the overall efficiency of the PV system. The proposed 
FLC has reduced these disadvantages according to different 
values of solar radiation. The simulation results indicated that 



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the control with FLC is more efficient than the traditional 
methods. It has the advantage of reducing the disturbances 
when the PVG reaches its maximum power and as a result, the 
performance of the photovoltaic installation has been 
optimized. On the other hand, to reach a fast response time and 
to take into account the time constraints, we adopted a 
functional diagram to facilitate the VHDL programming and to 
make this control executable in real time. Thereby, the fuzzy 
logic controller based on the incremental and the conductance 
was developed and simulated in VHDL. The comparison of 
both results showed that the output parameters (duty cycle) 
reach all variations of the input parameters (voltage and 
current) of the GPV. Therefore, this study showed that the 
proposed architecture was an adequate solution for a real-time 
implementation. The implementation of FLC on FPGA 
increases the efficiency of MPPT control systems. In future 
works, we aim to apply the proposed strategy to other energy 
applications. 

NOMENCLATURE 

PVG Photovoltaic generator 

FPGA VHSIC Hardware Description Language 

I Output current of the PVG 

Iph Photocurrent of the solar panel 

Io Photovoltaic reserve saturation current diode 

a Ideality factor 

k Boltzmann constant 

kI Temperature coefficient in current 

T Temperature 

Tref Reference temperature 

q Elementary charge in Coulomb 

G Irradiance 

Gref Reference irradiance 

Egap The energy Gap 

 

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