1. The document presents an improved maximum power point tracker system for photovoltaic energy systems. The system consists of a DC-DC boost converter, PWM inverter, and MPPT control system. 2. The MPPT control system adjusts the duty cycle of the boost converter to force the PV array to operate at its maximum power point. It also controls the modulation index of the PWM inverter to transfer maximum available power from the PV array to the grid. 3. Simulation results show the control system efficiently tracks the maximum power point and achieves a clean power interface with the grid, demonstrated by the high quality sinusoidal grid current waveform.

1. 1
An Improved Maximum Power Point Tracker for
Photovoltaic Energy Systems
Ali M. Eltamaly* *P. N. Enjeti** H. H. El-Tamaly*
*Electrical Engineering Dept.
Faculty of Engineering
Elminia University,
Elminia, Egypt
E-mail: eltamaly@yahoo.com
**Power Electronics & Power Quality Laboratory
Electrical Engineering Dept.
Texas A&M University
Collage Station, TX. 77843-3128
E-mail: enjeti@tamu.edu
Abstract: In this paper, A combined low cost, high efficiency inverter and peak power tracker has been
presented. Interfacing of photovoltaic and fuel cell energy systems requires a wide operating
range of DC to AC power conversion to utilize the available power in these energy sources. The
maximum power point tracker system consists of DC-DC boost converter and PWM voltage
source inverter as a utility interface unit. PWM generates high quality sinusoidal line current. By
the data supplied to the control system, it will generate a control signal to the PI controller to
generate suitable duty ratio for the boost converter and suitable value for the modulation index of
PWM inverter. The suitable duty ratio for the boost converter will force the PV to work around
the optimum voltage. The control system adjusts the modulation index of PWM inverter to
transfer the maximum power available from PV to the electric utility. Simulation results from
PSIM computer program has been presented in this paper. Results from analysis shows the
superiority of the Maximum Power Point Tracker system and clean power utility interface has
been achieved.
1. Introduction
The Power Voltage (P-V) characteristics and the locus of maximum power points are shown in
Fig.1. From this figure it is clear that when the radiation varies, the operating voltage varies
linearly with it. If the PV array forced to operate around maximum power point, 20 to 30%
increase in the output power from Photovoltaic arrays [1]. Maximum Power Point Tracker
(MPPT) has been used to force the PV array to work around the maximum power point. For this
reason, the MPPT is required to track the maximum power available in the PV array. The MPPT
operates by periodically incrementing the terminal voltage of the PV array and continuously seek
the peak power point as shown in Fig.2.
2. System Configurations
The proposed system consists of PV array, DC-DC boost converter, PWM inverter and the
MPPT as shown in Fig.3.The radiation and temperature are used to calculate the maximum PV
array output power and PV array terminal voltages. The MPPT operates by periodically
incrementing the terminal voltage of the PV array and continuously seek the peak power point as
shown in Fig.3. The control flowchart of the MPPT is shown in Fig.4. The control system adjusts
the boost converter as well as the PWM inverter taking into account to seek maximum power
point of PV array. A comparison between the terminal voltages (actual and optimum) will
control the duty ratio of boost converter. Changing the modulation index of PWM converter
according to the error signal between the maximum and actual power will pass the maximum
power available from PV to the electric utility.

2. 2
0 .2 0 .4 0 .6 0 .8 1
0
0 .2
0 .4
0 .6
0 .8
1 00 0W /m
2
8 00 W /m
2
6 00 W /m
2
40 0W /m
2
20 0 W /m
2
M a xim u m p o w e r c urve
O u tp u t P ow er, pu
T erm in al V oltage, pu
Fig.1 P-V charactristics of PV module
DC
Link
Constant Frequency
PWM Converter
Three Phase
utility
Lo
PV
Simulator
PI
+
S
PI
PIS
+
+
+
Temperature
Radiation Pmax
Vopt
Pact
+
-
+
-
S
+
-
Vdc
Vdc
*
DC-DC boost
ConverterPV array
Current
controller
Fig.2 The proposed approach and its Control system.
The terminal voltage and terminal current are taken as initial values for the PV simulator in
Fig.2. By calculating the terminal voltage and output power from V-I characteristics shown in
equations (1) and P-V characteristics shown in equation (2) respectively and by comparing those
values according to the program logic (Fig.4) we get the maximum power (Pmax) and the
corresponding optimum terminal voltage ( *
TV ). A comparison between actual and reference
values for PV terminal voltage and maximum power available from PV array will control the
duty ratio of boost converter and modulation index of PWM inverter respectively.
The PV simulator uses the radiation, temperature and output current from PV to determine the
corresponding PV curve by using equation (2) and as shown in Fig.1. The output power from PV
is the result from multiplying PV terminal voltage and PV output current. The power output from
PV modules is shown in (2).

3. 3













 −
+=
sat
TPH
satT
I
II
LnI
q
KT
V (1)








−=
− )(
**
satT IV
KT
q
satPHTT eIIVP (2)
)(
*
satT IV
KT
q
satPHT eIII
−
−= (3)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Pmax
P
P
Terminal current
∆VT
Terminal Voltage
I, P
Fig.3 The operating principle of PV simulator.
If
PT
(n+1)-PT
(n)<
VT(n)=VT(n+1)
VT
(n+1)=VT
(n+1)+ V
If
PT
(n+1)-PT
(n)>0
If
VT
(n+1)-VT
(n)>0
If
VT
(n+1)-VT
(n)>0
∆
Yes
Yes
Yes Yes
No
No No
No
εPmax=PT(n+1)
VT=VT(n)








−=
− ))(
)(
(
*)(*)()(
satT InV
nKT
q
satPHTT eInInVnP
Start
Measure VT
(n), IT
(n), T(n), IPH
(n)











 −
+=+
sat
TPH
satT
I
nInI
LnI
q
nKT
nV
)()()(
)1(








−+=+
−+ ))1(
)(
(
*)(*)1()1(
satT InV
nKT
q
satPHTT eInInVnP
VT(n)=VT(n+1)
VT
(n+1)=VT
(n+1)- V∆
VT(n)=VT(n+1)
VT
(n+1)=VT
(n+1)- V∆
VT(n)=VT(n+1)
VT
(n+1)=VT
(n+1)+ V∆
To DC-DC
converter
END
Fig.4 Control flowchart of PV simulator

4. 4
The control system compares the terminal voltage ( TV ) with optimum terminal voltage ( *
TV ) to
determine the duty cycle of boost converter. Also the control system compares the actual power
(Pact) with the maximum power (Pmax) to get the modulation index (mai) for PWM inverter to
control the power flow to the utility grid.
Input data for control flowchart of Fig.4 is the terminal voltage, PV output current, PV
temperature and radiation. The results from this program is the maximum power (Pmax) and
reference terminal voltage ( *
TV ) corresponding to input data. The error signal between reference
and actual values of terminal voltage controls the boost converter. Also, error signal between the
maximum power (Pmax) and actual output power (Pact) controls the modulation index of PWM
inverter.
The relation between the PV terminal voltage and DC voltage is shown in (4). From (4), at
constant DC-link voltage, Vd the PV terminal voltage, VT will change with the duty ratio (D) of
boost converter.
dT VDV *)1( −= (4)
The relation between active, reactive power going to utility grid and utility grid voltage are
shown in equations (5) and (6). Also, the relation between modulation index of PWM inverter
(mai) and phase voltage at the leg of PWM inverter is shown in equation (7).
UG
iiconvUG
o
X
VV
P
δsin**
*3
,
= (5)
UG
iiconvUGoconv
o
X
VVV
Q
δcos**
*3
,
2
, −
= (6)
22
,
dai
iconv
Vm
V = (7)
Substituting (7) into (5) and (6) we get direct relation between PWM active and reactive power
and modulation index as shown in (8) and (9).
UG
idUG
aio
X
VV
mP
δsin**
*
22
3
*= (8)
UG
iiconvUGiconv
o
X
VVV
Q
δcos**
*3
,
2
, −
= (9)
To reduce harmonic contents of utility line current we have to keep the modulation index in
linear region (mai<=1). According to this assumption DC reference, voltage can be obtained.
By using the site data (radiation and temperature) and the module data, the maximum power
and terminal voltage have been calculated from equations (1) and (2). By connecting the PV
module with, three phase electric utility the DC voltage can be calculated from (10).
ai
LL
m
V
Vd
3
22*
≅ (10)
3 Design Example
The market available Siemens SM100 PV array has been considered in the design of 10 kW
PV system. The electric characteristics of this PV module are shown in Table (1).
The PV array consists of several modules in series (Ns) and parallel rows (NP). In case of a 10
kW output, 200 V, PVES we need 6 modules in series and 17 string in parallel. (i.e. Ns =6 and
NP=17). By considering actual radiation data from Elminia city, Egypt [2], the system has been
designed.

5. 5
Table (1) The electric characteristic of SM100 Siemens PV module.
Rated Power 100W
Rated Voltage 34V
Rated Current 2.95A
Nominal Temperature 20o
C
Rated Saturation Current 0.00405 A
The PV terminal voltage varies between 138 and 200 V. the DC voltage of the DC-link
depends on the electric utility voltage. By connecting the PV module with 220, three phase
electric utility the DC voltage can be calculated from (10).
4. Simulation Results
The proposed control scheme has been simulated using PSIM Program linked with visual C
language. The radiation and temperature were fed to the PV simulator (Fig.3) to calculate the
optimum voltage and the maximum power. The error signal between the actual and optimum
value of PV terminal voltage were used to control the boost converter. To increase the system
stability, the error signal between the actual power and the maximum power output from PV
simulator were used to change the modulation index. The control system of the proposed
approach is shown in Fig.1. Fig.4 shows the terminal voltage of the PV arrays. Fig.6 shows the
actual and maximum power obtained from PV simulator. From this figure, we can see the control
system efficiently tracks the maximum power at any time. Fig.6 shows the terminal voltage of
the PV arrays (in Volt). Fig.7 shows the DC-link voltage. Fig.8 shows the three phase utility line
current and its FFT components which presents high quality utility line current. Fig.9 shows the
utility line current and the utility phase voltage.
0.1 0.2 0.3 0.4 0.5 0.6
ti ( )
200
195
190
185
182.5
12k
10k
8k
6k
4k
2k 0.1 0.2 0.3 0.4 0.5 0.6
time (sec.)
MaximumPower
Actual Power
. Fig.5 Terminal voltage of the PV arrays
(in Volt).
Fig.6 Actual and maximum power obtained
from PV simulator (in kW).
400
300
200
100
0 140 160 180 200 220
Fig.7 DC-link voltage (in Volt).

6. 6
60
40
20
0
-20
-40
-60
460 480 500 520 540
time (ms)
0 1.00 2.00 3.00 4.00 5.00
Frequency (kHz)
40
30
20
10
0
Fig.8 Three phase utility line current and its FFT components (in Ampere).
200
100
0
-100
-200
460 480 500 520 540
time (ms)
Utility Line current, A
Utility phase voltage, V
Fig.9 Utility line current (in Amp.) and the utility phase voltage (in Volt).
5 Conclusions
In this paper a combined low cost, high efficiency inverter and peak power tracker has been
proposed. This converter operates close to the maximum power point of the photovoltaic array
and forms a DC to AC inverter. Simulation and experimental results are shown. This system
shows a wide operating rage of DC to AC power conversion to utilize the available power in the
photovoltaic and fuel cell energy systems.
References
[1] D.B Snyman; J.H.R. Enslin ”Simplified maximum power point controller for PV installations
“ Photovoltaic Specialists Conference, 1993., Conference Record of the Twenty Third IEEE ,
1993 , Page(s): 1240 –1245.
[2] Meteorological Authority of Egypt.
List of Symbols
IT Array output current. Vd DC link voltage.
VT Array output voltage. VLL Line to line voltage.
VT
*
Reference output voltage. mai Inverter modulation index.
PT Array output power. Po Output power
Pmax Maximum output power. Qo Output reactive power
Isat Array saturation current. VUG Utility grid voltage per phase.
T Array temperature in Ko
. Vconv,i Phase voltage at the leg of inverter.
IPH Light generated current. δI Power angel at inverter side.
K/q Boltsman’s constant. XUG Impedance of the utility grid.

7. 7