VHDL Based Maximum Power Point Tracking of Photovoltaic Using Fuzzy Logic Control

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 7, No. 6, December 2017, pp. 3454~3466
ISSN: 2088-8708, DOI: 10.11591/ijece.v7i6.pp3454-3466  3454
Journal homepage: http://iaesjournal.com/online/index.php/IJECE
VHDL Based Maximum Power Point Tracking of Photovoltaic
Using Fuzzy Logic Control
Doaa M. Atia1
, Hanaa T. El-madany2
Department of Photovoltaic Cells, Electronics Research Institute
Article Info ABSTRACT
Article history:
Received Oct 18, 2016
Revised May 30, 2017
Accepted Jun 15, 2017
It is important to have an efficient maximum power point tracking (MPPT)
technique to increase the photovoltaic (PV) generation system output
efficiency. This paper presents a design of MPPT techniques for PV module
to increase its efficiency. Perturb and Observe method (P&O), incremental
conductance method (IC), and Fuzzy logic controller (FLC) techniques are
designed to be used for MPPT. Also FLC is built using MATLAB/
SIMULINK and compared with the FLC toolbox existed in the MATLAB
library. FLC does not need knowledge of the exact model of the system so it
is easy to implement. A comparison between different techniques shows the
effectiveness of the fuzzy logic controller techniques. Finally, the proposed
FLC is built in very high speed integrated circuit description language
(VHDL). The simulation results obtained with ISE Design Suite 14.6
software show a satisfactory performance with a good agreement compared
to obtained values from MATLAB/SIMULINK. The good tracking
efficiency and rapid response to environmental parameters changes are
adopted by the simulation results.
Keyword:
Maximum power point tracking
(MPPT)
Photovoltaic (PV)
Fuzzy logic controller (FLC)
Very high speed integrated
Circuit hardware description
language (VHDL)
Copyright © 2017 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Hanaa T. El-madany,
Departement of Photovoltaic cells,
Electronics Research Institute,
ElTahrir Str., Dokki, Giza, Egypt.
Email: hanaa_tolba@eri.sci.eg
1. INTRODUCTION
At present worldwide have an energy crisis so that renewable energy is a necessary solution to
conventional resources problems [1]. Photovoltaic (PV) energy is highly recommended in electrical power
applications. It is crucial to operate the PV systems near the maximum power point to increase the PV system
efficiency.However, the nonlinear nature of PVarray depends on the array terminal operating voltage.
Therefore, the tracking control of the maximum power point is a complicated problem. To overcome these
problems, many conventional tracking control strategies have been proposed such as perturb and observe
[2],[3], incremental conductance [4], parasitic capacitance [5], constant voltage [5], the hill climbing strategy
[6]. Intelligent MPPT controller techniques, such as neural network (NN) and fuzzy logic (FL) methods, have
been developed [7]-[18].
Using Fuzzy logic methods for maximum power point determination of a solar array has a good
stability and a high response rate. Nowadays, fuzzy based [6],[7] researches have been published due toits
good performance andhigh accuracy. Field programmable gate arrays (FPGAs) are digital integrated circuits
that contain several millions of programmable logic blocks connected together with
configurable interconnections. FPGA is used for hardware implementation for many applications especially
FLC because of the required high speed and parallel processing of fuzzy logic applications [19],[20].
The paper is organized as follows. In section 2, the stand-alone PV system is presented which
describes the PV system and the DC–DC boost converter mathematical modeling and design. Then, proposed

IJECE ISSN: 2088-8708 
VHDL Based Maximum Power Point Tracking of Photovoltaic Using Fuzzy Logic Control (Doaa M. Atia)
3455
MPPT control strategies are reported in section 3 which explains the perturb and observe, incremental
conductance, and fuzzy logic control approach. The simulation results and discussion are illustrated in
section 4 and section 5 respectively. Finally, Section 6 contains a conclusion of this work.
2. MPPT IN STAND-ALONE PV SYSTEMS
The PV stand-alone system comprises of PV module, MPPT control unit, DC/DC converter and the
required load as shown in Figure 1. The PV module under test has 75W as a maximum power, 4.4A as a
maximum current and 17.7V as a maximum voltage. The DC/DC boost converter is used where the proposed
system operates at 48 DC voltage. Perturbation and observation, Incremental conductance, and Fuzzy logic
control method are known as MPPT algorithms for PV systems which are widely used.
Figure 1. PV stand-alone system scheme
2.1. Photovoltaic generator model
A solar cell converts energy in the sunlight photons into electricity. PV modules consist of group of
PV cells connected in series. PVmodules are interconnected in a series-parallel configuration to form PV
arrays. The equation that descripes the I-V charateristics of PV array can be expressed as follws [21]:








 1
)(
exp
t
S
oLPV
V
IRV
III (1)
where IPV is the output current of PV (A), IL is the light generated current (A) , Io is the revese saturation
current at operating temperature (A),V is the output voltage of PV (V) and Vt is the thermal voltage. The solar
insolation variation effect on PV module is studied in Figure 2.
Figure 2. IV characteristic curve of PV module
2.2. Boost Converter
For PV systems, DC-DC converter is used to regulate DC voltage. The regulation is normally
achieved by pulse width modulation technique using MOSFET or IGBT as a switching element. By adjusting
DC/ DC
Converter Load
MPPT
Control unit

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IJECE Vol. 7, No. 6, December 2017 : 3454 – 3466
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the PWM duty cycle, maximum power will be changed and the maximum power point is reached. The
mathematical modelling of the converetr in a continuous conduction mode is given by [22]:
DV
V
i
o


1
1 (2)
𝐿 =
𝑉 𝑖 𝐷
𝑓𝑠 𝐶𝑅𝐹
(3)
𝐶 =
𝐼 𝑜 𝐷
𝑓𝑠 𝑉𝑅𝐹
(4)
where CFR is the current ripple factor, VRF is the voltage ripple factor, fsis the switching frequency, and D is
the duty cycle. By designing of proposed DC-DC boost converter under the maximum power 75W, the value
of inductor and capacitor are 5 mH and 100 µF respectively.
3. MPPT CONTROL STRATEGY
There are many MPPT algorithms have been developed and implemented by researchers [2]-[18].
The MPPT algorithms used in this work are Perturb and Observe method (P&O), incremental conductance
method (IC), and fuzzy logic method. These methods will be discussed below in detail.
3.1. MPPT control with perturb and observe method
The main concept of perturb and observe method is to drive the system to operate in the direction of
increasing PV output power. If the output power increases, then the perturbation of the voltage is made in
the same direction otherwise perturbation against the original direction should be made. Figure 3 shows the
flowchart of P&O technique. The following equation describes the strategy of the P&O technique [2].
𝑖𝑓
𝑑𝑃
𝑑𝑉
> 0; 𝐷 = 𝐷𝑖 + dD (5)
𝑖𝑓
𝑑𝑃
𝑑𝑉
< 0; 𝐷 = 𝐷𝑖 − dD (6)
Figure 3. Flowchart of P&O algorithm
Start
Measuring V(n), I(n)
Calculate Power P(n)
P(n) - P(n-1) = 0
P(n) - P(n-1) > 0
V(n)-V(n-1) < 0 V(n)-V(n-1) > 0
D =D+ΔD D = D-ΔDD = D-ΔDD = D+ΔD
Return
YNNY
YN
N
Y

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3.2. MPPT control with incremental conductance
The incremental conductance MPPT algorithm flowchart is shown in Figure 4. The incremental
conductance algorithm as cleared in Eq. (7) is based on the PV power differentiation with respect to PV
voltage and setting the result equal to zero as given below [4]:
𝑑𝑃
𝑑𝑉
= 0; 𝑎𝑡 MPP (7)
𝑑𝐼
𝑑𝑉
= −
𝐼
𝑉
; 𝑎𝑡 MPP (8)
𝑖𝑓 (
𝑑𝐼
𝑑𝑉
> −
𝐼
𝑉
); 𝐷 = 𝐷𝑖 + dD (9)
𝑖𝑓 (
dI
dV
< −
I
V
) ; D = Di − dD (10)
Figure 4. Flowchart of IC algorithm
3.3. MPPT control with fuzzy logic
Fuzzy logic based MPPT control contains mainly from three steps which are fuzzification, rule-
base, inference and defuzzification. Two simulation methods are proposed to build FLC in
MATLAB/SIMULINK. The first one focused on FLC toolbox in MATLAB library; on the other hand, the
mathematical modeling of FL technique is built using MATLAB/SIMULINK. The proposed FL MPPT
control has two inputs and one output. The two inputs of FLC are the error E (k) and change of error CE (k)
as defined below [18]:
𝐸(𝑘) =
𝑃(𝑘)−𝑃(𝑘−1)
𝑉(𝑘)−𝑉(𝑘−1)
(11)
𝐶𝐸(𝑘) = 𝐸(𝑘) − 𝐸(𝑘 − 1) (12)
Start
Read V(n), I(n)
ΔI= I(t)-I(t-Δt)
ΔV= V(t)-V(t-Δt)
ΔV=0
ΔV /ΔI=-I/V
V(n)-V(n-1) < 0
V(n)-V(n-1) > 0
Increase D Decease DDecease DIncrease D
Return
ΔI=0
I(t-Δt)=I(t)
V(t-Δt)=V(t)
Y
Y
Y
Y
Y N
N
N
N

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The FLC input variables are represented by seven fuzzy sets; Negative Large (NL), Negative
Medium (NM), Negative Small (NS), zero (Z), Positive Small (PS), Positive Medium (PM) and Positive
Large (PL). The rule base is presented in Table 1. Figure 5 gives the membership function of FLC input and
output.
Table 1. Rule base of fuzzy logic controller
Change of error (Ce)
NL NM NS ZE PS PM PL
Error(e)
NL NL NL NL NL NM NS ZE
NM NL NL NL NM NS ZE PS
NS NL NL NM NS ZE PS PM
ZE NL NM NS ZE PS PM PL
PS NM NS ZE PS PM PL PL
PM NS ZE PS PM PL PL PL
PL ZE PS PM PL PL PL PL
Figure 5. Membership function for fuzzy inputs and output
The mathematical modeling of triangle membership function is given by [7]:
𝜇𝑀(𝑥) = 𝑚𝑎𝑥(𝑚𝑖𝑛 (
𝑥−𝑥1
𝑥 𝑇−𝑥1
,
𝑥2−𝑥1
𝑥2−𝑥 𝑇
) , 0) (13)
The fuzzification step consists of seven membership tringle function connected together and min/
max opereator is used to achieve this step. Due to the seven membership tringle function there are 49 rules in
total. The defuzzification step used the center of the area method. The mathematical expression of this
method is shown by Eq.14 [18].
𝑧 =
∑ 𝜇(𝑧 𝑗). 𝑧 𝑗
𝑛
𝑗=1
∑ 𝜇(𝑧 𝑗)𝑛
𝑗=1
(14)
4. SIMULATION RESULTS
In order to show the effectiveness of the MPPT, a comparison between the different control
techniques has been carried out. The value of solar radiation variation levels which used for different
controllers is the same. Figure 6 shows the total system design using MATLAB SIMULINK. The system
consists of PV unit, P&O, IC and FLC MPPT unit using toolbox, FLC subsystem using Simulink and boost
converter unit. The PV power and voltage are the input signals to MPPT unit and duty cycle is the output
signal. The detailed block diagrams of control subsystem using different MPPT control technique such as
P&O, IC and FLC MPPT unit using toolbox, FLC subsystem using Simulink are shown in Figure 7 to Figure
10 respectively. Figure 11 clarify the detailed model of the fuzzy subsystem. The Simulink model of tringle
membership function is shown in Figure 12. The detailed simulink model of the fuzzification stage is
presented in Figure 13. It consists of seven membership tringle functions connected together and min/ max
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Error
DegreeofMembership

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opereator is used to achieve the fuzzification step. Due to the seven membership tringle function there are 49
rule base in total as seen in Figure 14.
Figure 6. Total system SIMULINK
Figure 7. Control subsystem using P&O
Figure 8. Control subsystem using IC

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Figure 9. Control subsystem using FLC toolbox
Figure 10. Control subsystem using FLC
Figure 11. Fuzzy subsystem implementation in MATLAB
Figure 12. Tringle Membership function SIMULINK

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Figure 13. Fuzzification subsystem
Figure 14. Rule base simulation using MATLAB
5. RESULTS AND DISCUSSION
The control unit is tested at variable solar radiation and constant air temperature degree as given in
Figure 15. Simulation is carried out by giving an irradiation changes from 500 W/m2
to 1000 W/m2
and
constant temperature at 25°
C. The different MPPT techniques are tested to check its ability to track the PV
maximum power. Figure 16 gives the PV power, current and voltage waveforms simulated using P&O
algorithm. The performance of IC technique is cleared in Figure 17. The two different FLC techniques give
the output power of PV module equal to 74.4 W at 1000 W/m2
and 34 W at 500 W/m2
as shown in Figure 18
and Figure 19.

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Figure 15. Variable solar radiation and constant air temperature
Figure 16. Power, voltage and current of PV for P&O technique
Figure 17. Power, voltage and current of PV for IC technique

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Figure 18. Power, voltage and current of PV for FLC toolbox
Figure 19. Power, voltage and current of PV for FLC Simulink
The FLC should be selected for its higher performance compared to the other controllers. FLC has
better response time, less oscillation and much more accurate tracking at each step. The two different
techniques of FLC have the same output response. So the mathematical model representation of FL is
selected due to its simplicity for conversion to VHDL code. The first procedure in the conversion process
from MATLAB SIMULINK to VHDL code is indicated in Figure 20. Once the FLC block diagram built in
MATLAB/SIMULINK, it is converted to VHDL code, the converted VHDL code of the FLC subsystem is
obtained in Fig. 21. Also, the VHDL code of the fuzzification, defuzzification, and rule base is shown in
Figure 22, Figure 23 and Figure 24 respectively. The ISE Design Suite 14.6 software has been used for
simulating the proposed architecture of FLC based on the VHDL as shown in Figure 25. The obtained results
has been verified and compared with MATLAB. The simulation results approximately coincide with the
simulation MATLAB results. In future the implementation of the proposed architecture will be implemented
on FPGA chip.

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Figure 20. Conversion process from MATLAB SIMULINK to VHDL code
Figure 21. VHDL code of the global subsystem of
the FLC
Figure 22. VHDL code of the Fuzzification process
Figure 23. VHDL code of the deuzzification process Figure 24. VHDL code of the Rulebase

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Figure 25. VHDL simulation of FLC subsystem
6. CONCLUSION
Photovoltaic stand-alone system simulation using Matlab/SIMULINK with a maximum power point
tracking approach was presented in this paper. Also, several maximum power point tracking (MPPT)
controller techniques were presented and implemented in Matlab/Simulink environment such as Perturb and
Observe method (P&O), Incremental Conductance method (IC), and Fuzzy logic controller (FLC). The
simulation results of FLC provided satisfactory results in extracting the MPP of PV compared with the other
proposed controller techniques. The complete FLC was built in ISE design suite 14.6 software using very
high speed integrated hardware description language to extract maximum power of the PV module. The
simulation results validated the programs before downloading them on the FPGA. In future the
implementation of the proposed architecture will be developed and implemented on FPGA chip.
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