1
Modeling and Design of MPPT Controller for a
PV Module using PSCAD/EMTDC
Rajesh Gupta, Member, IEEE, Gaurang Gupta, Dharmendra Kastwar, Amir Hussain and Hars Ranjan
Abstract- This paper presents a modeling of photovoltaic (PV)
module in PSCAD/EMTDC and design of maximum power point
tracking (MPPT) using boost converter. The model can be used
for simulation studies of grid interface applications using voltage
source converter in the PSCAD. The validity of the PV model
developed has been verified using the set of data collected
experimentally. In order to extract maximum power from the PV
module the boost converter can be controlled through the Hill
Top algorithm. All the simulation study has been done in the
PSCAD/EMTDC simulation software.
Index Terms-- Boost Converter, Hill Top algorithm, maximum
power point tracking (MPPT), photovoltaic (PV) module,
PSCAD/EMTDC.
I. INTRODUCTION
P
OWER generation from environment friendly resources is
one of the major concerns today. Conversion of solar
energy through photovoltaic (PV) system has now reached
to the user end, where he can now contribute to the overall
protection of the environment. Recent growth in the power
semiconductor technology has made possible the clean and
efficient conversion of solar energy into electrical energy
through a PV cell. A PV module generally is a source of low
power DC that cannot be directly put the grid applications. A
power converter is required that converts the raw electrical
power generated by solar PV module into the usable electrical
power. The output power of the solar PV module is variable
for a fixed input condition of cell temperature and solar
insolation level. In addition the output power extracted from
the solar PV module is a function of electrical variable such as
current and voltage. There is a set of these variables at a
particular temperature, insolation level and load at which the
power drawn from the solar PV module is maximum.
Therefore a maximum power point tracker (MPPT) is required
which can extract the maximum power out of the PV module,
continuously. A power electronics converter is used that not
only converters the raw electrical power into usable electrical
power but can also extract maximum power. A DC-DC
converter can track the maximum power from the PV module
continuously.
With the increased penetration of solar PV system into the
distributed generation, this renewable source of energy is
taking the significant share of the overall power generation.
Authors are with the Department of Electrical Engineering, M. N.
National Institute of Technology, Allahabad-211004, India (e-mail:
rajeshgupta310@rediffmail.com, gauranggpt@yahoo.co.in, lucky16kastwar
@gmail.com, exploreamir@gmail.com, harsonly4u@gmail.com).
Study of the dynamic model of PV module and its
applicability is one of the important aspect of the PV system.
Generation of power from PV module and its supply to the
load or interface to the grid through various converter stages
require accurate modeling of the various characteristics of the
PV system.
The PSCAD/EMTDC is a simulation tool for the Power
System Computer Aided Design and Electromagnetic
transients for DC. This simulation package has become very
useful for various power system simulations and design
studies [1]. Integration of distributed power generation
resources such as solar PV module require a simulation tool
that can accurately model both the fast power system
dynamics and slow power generation dynamics of solar PV
module. There has been a recent proposal for modeling of
wind energy conversion system using PSCAD/EMTDC
simulation tool [2]. However PSCAD simulation package
lacks the valid simulation model. Extensive study of grid
interface of solar PV system requires accurate PV model in
PSCAD/EMTDC.
In this paper first a simulation model is developed for the
PV module in the PSCAD/EMTDC software that accurately
models the PV characteristics including the effect of
temperature and insolation level. Further an MPPT controller
is designed for the boost DC-DC converter using Hill Top
algorithm for the PV model developed in the
PSCAD/EMTDC. The simulation results are obtained that
verifies the proposed MPPT algorithm.
II. OVERVIEW OF A PHOTOVOLTAIC (PV) MODULE
A solar cell is the simplest component of a PV module that
generates current carriers when sunlight falls on it. The current
generated by these cells is very small. A solar module is a
combination of number of solar cells that are connected in
series and/or parallel to generate usable current and voltage.
A practical solar cell is current source, with an anti parallel
semiconductor diode as shown in Fig. 1, whose p-n junction is
exposed to light [3]. A solar cell also offers a series resistance
Rs due to contact resistance of the metal base with the p-type
semiconductor, the resistance of p and n bodies, the contact
resistance of the n layer with the top metal grid, and the
resistance of the grid [4]. Some generated current also goes as
leakage current due to the fabrication of the PV cell, which
gives rise to a shunt resistance Rsh. The resistances Rs and Rsh
are shown in Fig. 1. The value of Rsh is generally high whereas
that of Rs is low. An ideal solar cell doesn’t offers any series
and shunt resistance.
2
Ipv
Id
Rs
I PV = [I sc + K i (T − Tn )]
I
Ir
Rsh
V
Fig. 1 A solar cell model.
The basic equation that governs the relationship between
the solar cell current I and voltage V of a single ideal solar cell
is given by the following equation.
⎡ ⎛ q(V + I R s ) ⎞ ⎤ V + I R s
I = I PV − I o ⎢exp⎜
⎟ − 1⎥ −
αKT
R sh
⎠ ⎦
⎣ ⎝
⎛ 1 1 ⎞⎤
⎜⎜
− ⎟⎟⎥
⎝ Tn T ⎠⎥⎦
(4)
where, Ki is the short circuit current/temperature coefficient, G
is the solar insolation in W/m2 and Gn is the nominal solar
insolation in W/m2.
The dependence of the VI characteristic on the cell
temperature and radiation or insolation is shown in Fig. 3(a)
and Fig. 3(b), respectively. As the cell temperature of module
increases the open circuit voltage decreases keeping the short
circuit current almost constant whereas if insolation level
increases the short circuit current increases keeping open
circuit voltage almost constant.
(1)
where, IPV is the current generated by the incident light, Id is
the diode current, Io is the reverse saturation or leakage current
of the diode, Ir is the current through the shunt resistance, q is
the electron charge (1.6×10-19 C), K is the Boltzmann constant
(1.38×10-23 J/K), T is the temperature in Kelvin of the p-n
junction and α is the ideality factor which varies between 1.0
and 1.5. Equation (1) represents a basic Kirchhoff’s current
law equation. This is shown graphically in Fig. 2, where Fig.
2(a) shows IPV, 2(b) shows Id, and 2(c) shows I, that is the
current fed to the load assuming that RS is negligible and Rsh is
infinite.
The VI characteristic of the PV module shown in Fig. 2(c)
depends upon the internal parameters of the module, i.e., Rs
and Rsh, and on the external influences such as insolation level
and temperature of the cell.
The diode saturation current Io and its dependence on the
temperature may be expressed by the equation as shown below
[5].
3
⎡ qE g
⎛T ⎞
I o = I o,n ⎜ n ⎟ exp ⎢
⎝ T ⎠
⎢⎣ αK
G
Gn
2 (a)
2 (b)
2 (c)
Fig. 2 Kirchhoff’s current law I = IPV – ID in PV module (ignoring the RS and
Rsh), (a) IPV , (b) Id , and (c) I.
(2)
Fig. 3 (a) Variation of VI characteristic by varying the cell temperature.
where, Eg is the band gap energy of the semiconductor, Tn is
the nominal temperature (298 Kelvin) and Io,n is the nominal
saturation current given by the following equation. The
subscript n denotes the nominal conditions here.
I o,n =
I sc
⎛V
exp⎜⎜ oc
⎝ αVt
⎞
⎟ −1
⎟
⎠
(3)
where, Voc is the open circuit voltage of the PV module and Isc
is the short circuit current of the module and Vt is the thermal
voltage defined as, Vt = Ns KT/q. The symbol Ns is the number
of series cells in an array. The light generated current of the
module depends linearly on the solar radiation and is also
influenced by the temperature according to following
equation.
Fig. 3 (b) Variation of VI characteristic by varying the solar insolation.
3
III. MODELING OF PV MODULE USING PSCAD
Start
In this section PV module is modeled using
PSCAD/EMTDC. The PV characteristics are modeled using
FOTRAN programming to create the component in PSCAD.
The proposed algorithm for modeling of PV module is
described using a flow chart as shown in Fig. 4 and briefly
explained below.
The schematic of the PV module component created in
PSCAD is shown in Fig. 5. The component is embedded with
the FORTRAN code implementing the algorithm of Fig. 4.
In order to obtain the VI characteristic of the PV module,
the load is varied in steps. For a particular load the steady state
values of the current variable ‘I’ and intermediate voltage
variable ‘TEST’ are recorded. The simulation is repeated by
varying the load, temperature and the insolation level. The
sample simulation results are shown in Fig. 6. The parameters
chosen for modeling corresponds to the TATA BP solar
module as listed in Table I. The voltage V is considered
varying from 0 to open circuit voltage Voc corresponding to the
variation in current from short circuit current Isc to 0. Fig. 6 (a)
shows the VI characteristics with the variation in cell
temperature for a fixed insolation level of 600 W/m2. It can be
seen from the characteristics that the open-circuit voltage
decreases with the increase in cell temperature, while the short
circuit current Isc remaining constant. Similarly, Fig. 6 (b)
shows the VI characteristics with the variation in solar
insolation level at a constant cell temperature of 35 degrees. It
can be seen that the short circuit current increases with the
increase in insolation level, while with vary little change in the
open-circuit voltage.
The result clearly matches with the ideal results of Fig. 3.
The peak value of the product of V and I represent the
maximum power point (MPP) Pmax of the solar module. The
current and voltage of PV module at the MPP are denoted by
Imp and Vmp, respectively. The solar module should always be
operated in this region so as to extract the maximum power for
a given input conditions. For this purpose various algorithms
have been proposed in the literature that can be developed in
order to extract maximum power from the module.
In order to verify the model of PV module developed,
experiment was conducted in which the TATA BP solar
module was used and its VI characterstic were plotted by
varying load as shown in Fig. 7, under the assumption that the
temperature of the cell and insolation level were almost
constant having values, insolation level = 800 W/m2 and cell
temperature = 30 degree, with variable load resistance. A large
load corresponds to the short circuit current Isc = 4 A and no
load voltage corresponds to the open-circuit voltage Voc = 19
V (approx.). The experimental results are also compared with
the simulation results in Fig. 7 that verifies that the model
developed in PSCAD is in close approximation to the actual
one. Results at other operating conditions showed the similar
approximation.
The result in the Fig. 6 and 7 implies that the PV model
developed in PSCAD is in close approximation to the actual
charateristics and can be used for the design of a maximum
power point tracking (MPPT) for the given operating
conditions and load.
Specify the different parameters of the
PV module as given in datasheet
Input the temperature and insolation
level of the PV module
Calculate IPV,Io,n and Io
At,TIME = 0,
then, initialize I(k-1)=IPV, V(k-1) = 0,
TEST = V(k-1)
Calculate,
I(k) = f(V(k-1),I(k-1))
Increment,
V(k) = V(k-1) + 0.005
V(k-1)= TEST,
I(k-1) = I
TEST = V(k), I = I(k)
Sense TEST and I
if I(k) < 0 or I(k)>IPV
Yes
I(k) = IPV, V(k) = 0
No
Yes
if [V(k)/I(k)] < Rload
No
Take reading of
TEST and I
Stop
Fig. 4 Flowchart for the PV module simulation algorithm.
Fig. 5 Model of PV module built in PSCAD based on the algorithm shown in
Fig. 4.
Table I
Parameters of TATA BP SOLAR
Parameter
Imp
Vmp
Pmax
Isc
Voc
KV
Ki
Ns
Rs
Rsh
Value
4.608 A
17.655 V
81.360 W
5.078 A
21.827 V
-0.1230V/K
1.141 mA /K
36
0.502 ohm
644.13 ohm
4
L
O
A
D
MPPT
System
PV
Module
Fig. 8 Block Diagram of a typical MPPT system.
Fig. 6 (a) VI characteristic of the developed model of the PV module at
different cell temperature and constant insolation of 600W/m2.
The peak power is reached with the help of a dc/dc
converter by adjusting its duty cycle such that the load
impedance corresponding to the peak power is obtained as
shown in Fig. 9. Various algorithms have been developed in
past to implement the MPPT controller [6], namely Hill Top
algorithm, Perturb and observation, etc. In this paper, Hill Top
algorithm has been implemented in PSCAD/EMTDC
environment in order to extract the maximum power from the
PV module [7].
V. HILL TOP ALGORITHM
Fig. 6 (b) VI characteristic of the developed model of the PV module at
different solar insolation and constant cell temperature of 35 degree.
As the name of the hill climbing method states, this
process works by increasing or decreasing the duty cycle of
the buck or boost DC to DC converter and observing its
impact on the module output power. This current value of
power is compared to its previous value and according to the
result of the comparison, the sign of the “slope”, which is a
program variable (slope ∈{1,-1}), is either complemented or
remains unchanged [8]. As a result, the PWM output duty
cycle or duty ratio is changed accordingly. Fig. 7 shows the
flowchart for the hill climbing method as it is implemented in
controlling the switch position of the switching device used in
the DC-DC converter.
Current
Sensor
A
PV
MODULE
L
Voltage
V Sensor
C
Cout
L
O
A
D
MPPT
Controller
Fig. 7 Comparison of simulation and experimental PV module characteristic.
IV. MAXIMUM POWER POINT TRACKING
The output power of the solar PV module changes with
change in direction of the sun, change in solar insolation level
and change in temperature. Also there is a single maximum
power point in the PV characteristics of the PV module for a
particular operating condition. It is desired that the PV module
operates close to this point, i.e., output of the PV module
approaches near to MPP. The process of operating PV module
at this condition is called as maximum power point tracking
(MPPT). Maximization of PV power improves the utilization
of the solar PV module. The load and the PV module are
interfaced with each other through a dc/dc converter (step
up/step down) that serves the purpose of transferring
maximum power from the solar PV module to the load as
shown in Fig. 8. By continuously changing the duty cycle, the
maximum power is transferred to the load.
Fig. 9 Circuit for the MPPT using DC-DC boost converter.
In order to implement hill-top algorithm, a controller is
designed in the PSCAD as shown in Fig. 9. In this figure, the
source for the converter is the PV model as built earlier in the
PSCAD. The voltage and current output of the PV module is
continuously fed to the MPPT controller that drives a DC-DC
boost converter. The variable L and Cout represents the boost
converter inductance and capacitance respectively. The
capacitor C holds the input DC voltage for the boost converter.
In the MPPT controller the algorithm shown in Fig. 10 is
embedded. The output of the controller is a duty cycle. This
duty cycle varies between 0 and 1. It is then compared with a
sawtooth signal whose amplitude is 1.0 V. The comparator
output is high if duty cycle is greater than the carrier signal
and low when duty cycle is less than the carrier signal. The
controller continuously adjusts the duty cycle so that the
maximum power is extracted from the PV module. Fig. 11
shows the schematic of the PV model, boost converter and
MPPT controller developed in PSCAD 4.2.
5
compared in Fig. 16 and Fig. 17. The load resistance is
directly proportional to the voltage. Therefore Fig. 16 and 17,
indirectly holds the relationship between the power and
voltage. The schematic in Fig. 11 was run for different
insolation with the open loop and close loop (MPPT) control
of the converter. The duty cycle in both the cases was
initialized to 0.7. In open loop case, the duty cycle was fixed,
whereas in the close loop case the duty cycle was set to vary
by the MPPT controller. The results are compared in Fig. 18.
The power with the open loop control is less as compared to
the close loop control, hence the MPPT controller operation
and PV model developed in PSCAD/EMTDC is justified.
Start
Slope = 1
Sense module's
Voltage V(k), Current I(k)
Calculate Power
P(k) = V(k).I(k)
P(k) > P(k-1)
No
Yes
Complement Slope
Duty Ratio = Duty Ratio + slope*step size
Fig.10 Hill Top Algorithm.
Fig. 12 Duty cycle variation.
Fig. 11 Schematic of the PV model, boost converter and MPPT controller
developed in PSCAD.
Fig. 13 Switching signal for boost converter switch.
VI. SIMULATION RESULTS
The proposed schematic was simulated in the
PSCAD/EMTDC environment at the cell temperature of 30
degree and insolation level of 800 W/m2. Duty cycle was
initialized to 0.7 and step size was taken as ½8. Fig. 12 shows
the variation of the duty cycle with time. It changes itself in
order to extract the maximum power from the PV module.
When the maximum power point is achieved it settles down
finally at a steady state. Fig. 13 shows the switching signal for
the power switch (sa1 shown in Fig. 11) used in the DC-DC
boost converter. Fig. 14 and 15 shows the output voltage
across the PV module and the load. The figure clearly shows
that the output of the module and the load settles up after
sometime when the maximum power point is tracked. In order
to verify the results, the schematic was simulated at different
temperatures and insolation levels and the results are
Fig. 14 Voltage across the model of PV module.
6
chargeable battery supported DVR which compensates for
sags and swells in the event of their occurrences. Other
example includes supply of power from the battery supported
inverter to the grid connected loads in the event of main grid
failure. In both the above cases the battery is continuously
charged from the PV module. The model of PV module
proposed in this paper can easily be combined for the
applications involving multiple PV modules to produce PV
array, multi-string PV system and distributed PV system
support to the grid.
VII. CONCLUSIONS
Fig. 15 Voltage across the load.
Fig. 16 Output PV power verses load resistance at 30º temperature for
different insolation level in W/m2.
This paper presented the modeling of a PV module in
PSCAD/EMTDC and design of the MPPT controller. The
validity of the model of the PV module developed in the
PSCAD/EMTDC has been verified by comparing its VI
characteristics with the actual data set collected
experimentally. The comparison showed the close
approximation of the model characteristics with the actual
characteristics. Furthermore, the VI characteristics of the PV
model has been studied with the variations in insolation level
and temperature and found to be in close approximations to
the ideal characteristics. The application of the PV model has
been shown through the MPPT using DC-DC boost converter
based on the Hill Top algorithm in the PSCAD/EMTDC
environment. It is shown that the MPPT algorithm extracts the
maximum power from the PV model under all conditions of
insolation level and temperature. Also the results are shown
for the operation of the converter under open loop and close
loop control at different insolation and it has been observed
that more power is extracted when the MPPT controller is
used. This verifies the operation of MPPT controller for the
PV model. The model for the PV module developed in the
PSCAD/EMTDC can be used for the simulation studies of the
PV supported grid interface applications. This includes multistring PV system, distributed PV system etc.
VIII. REFERENCES
[1]
[2]
Fig. 17 Output PV power verses load resistance at 20º deg for different
insolation level in W/m2.
[3]
[4]
[5]
[6]
[7]
[8]
Fig. 18 Comparison of power extraction for open loop and closed loop control
of the converter at different insolation.
The model of PV module and MPPT controller developed
in PSCAD/EMTDC software can easily be implemented in the
grid interface simulation studies. The simple example include
[9]
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