International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
Hybrid PV/Wind System Modeling &
its Control in Grid Connected Mode
S.Krishnaveni1(12HU1D5607), M.Balachandar2, R.Lakshmi3
1
M.Tech Scholar, Dept. of EEE, Chebrolu Engineering College, Guntur (A.P), India.
3
Asst. Prof, Dept. of EEE, Chebrolu Engineering College, Guntur (A.P), India.
ABSTRACT: This paper presents a modeling and
control of grid connected Hybrid wind
photovoltaic array. Hybrid energy system
consists of two or more renewable/nonrenewable
energy sources. In this paper the hybrid energy
system is formed by the combination of wind and
photovoltaic array. There are some constraints
in harnessing power from Renewable energy
sources like wind and photovoltaic power
systems. Variation in environmental condition
will cause variation of power output from
renewable energy sources. Power electronic
converters play a major role in utilizing these
RES. A proper control scheme is required to
operate power converters to match the up the
grid-connection requirements. This paper
consists of modeling and simulation of Hybrid
Wind/PV energy system inter-connected to
electrical grid through power electronic
interface. Power conditioning system is
implemented and modeled to control power
electronic interface. Performance of modeled
hybrid system is evaluated for different input
power levels and load variation.
chemical pollution. Thus connecting the PV
array and Wind directly to the Grid is a
method to make use of the energy that is
produced.
PHOTOVOLTAIC ARRAY MODULE
A photovoltaic system converts sunlight into
electricity. The basic device of a photovoltaic
system is the photovoltaic cell. Cells may be
grouped to form panels or modules. Panels
can be grouped to form large photo voltaic
arrays. PV arrays can either be designed as
stand-alone and grid-connected systems.
Mathematical modeling of PV array
INTRODUCTION
Hybrid Energy Systems
Inter-connection of two or more of
Renewable Generations like wind power,
photovoltaic power, fuel cell and micro turbine
generator to generate power to local load and
or connecting to grid/micro grid forms Hybrid
Energy Systems. Because of the characteristic
nature of the solar energy and the wind energy,
the electric power generation of the PV array
and the wind turbine are corresponding. The
reliability of combined power generation is
much higher when compared to the Power
generated by an Individual source. A sizable
battery bank is required for a load so that
maximum power is drawn from Wind and
Photovoltaic array. Nonetheless, the usage of
battery is not an environmental friendly and
there are some drawbacks like, heavy weights,
bulky size, high costs, limited life cycles, and
ISSN: 2231-5381
MATLAB/Simulink Modeling of PV
Array
A typical KC-200GT PV module is considered
here [Appendix (i)]. The module has 54 cells
in series. For desired output voltage and
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
current, the
generation
proposed
solar
PV
power
Where, ρ=Air density, Vwind=Wind speed,
A=Turbine swept area, =Tip speed ratio,
system (6kW) consists of 30 PV modules with
10x3 series-parallel arrangements. Each
module can produce 200W of DC electric
power. Typical electrical characteristics of a
KC-200GT PV module are shown in Table 1 at
solar radiation of 1000W/
and cell
R=Radius of turbine blades, Cp =Coefficient
of performance, =Mechanical output power, T
= Torque of wind turbine, ω =Angular
frequency of rotational turbine, β =Blade pitch
angle. The performance coefficient Cp (λ, β),
which depends on tip speed ratio λ and
temperature of 25ºC (STC).
MaximumPower (
)
200W(+10%/-5%)
MaximumPowerVoltage
(
26.3 V
)
MaximumPower Current
(
blade pitch angle β, determines how much of
the wind kinetic energy can be captured by the
wind turbine system. A nonlinear model
describes Cp (λ, β) as:
7.61 A
)
OpenCircuitVoltage(
)
32.9 V
ShortCircuitCurrent (
)
8.21 A
Where, C1=0.5176, C2=116, C3=0.4, C4=5,
C5=21and C6=0.0068
(Eqn.3.11)
Wind Turbine Modeling
The wind turbine (WT) converts wind energy
to mechanical energy by means of a torque
applied to a drive train. A model of the WT is
necessary to evaluate the torque and power
production for a given wind speed and the
effect of wind speed variations on the
produced torque. The torque T and power
produced by the WT within the interval
[
,
speed and
], where
is minimum wind
Modeling of PMSG:
is maximum wind speed, are
functions of the WT blade radius R, air
pressure, wind speed and coefficients
and
(Jitendra Kasera et al. 2012).
Is known as the power coefficient and
characterizes the ability of the WT to extract
energy from the wind.
coefficient and is related to
Is the torque
according to:
MATLAB/SIMULINKMODEL OF WECS
MODELING OF GRID TIE WIND/PV
HYBRID SYSTEM
Hybrid energy system usually consists oftwoor
more renewable / nonrenewable energy
sources. Presently two kinds of wind power
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
hybrid systems are in focus: wind power with
fuel cell and wind power with photovoltaic
power. The main purpose of such hybrid
power systems is to overcome the
intermittency and uncertainty of wind energy
and to make the power supply more reliable.
(Chen Wang et al. 2007).Wind power and
solar energy are always combined into a
hybrid system, especially for the power supply
for remote areas where the cost of transmission
line is too high. Also, another advantage of this
kind of hybrid system is that they are both
renewable energies, which is compatible to the
environment.
Table 4: Component parameters of the
Proposed Hybrid Energy System
Schematic of DC/DC Boost converter
The Proposed System Configuration
Configuaration for the proposed hybrid
system
The details of the system component
parameters are listed in Table 4
WIND TURBINE
Rated Power
Rated wind speed
Rated Rotor speed
Blade Radius
PMSG
Rated Power
Rated line Voltage
Stator phase inductance
Stator phase Resistance
No. of poles
Rated mechanical speed
PV
Module Unit
Module numbers
Power rating
20 kW
12 m/s
22.0958 rad/sec
2.7 m
20 kW
380.14 Vrms
22.0958 Mh
2.7 Ω
36
211 rpm
54
cells,
200
W@1kW/m2,25ºC
10*3=30
30*200
PI controller ofDC/DC Boost converter
DC/DC Boost Converter parameters of PV
system
Input voltage (Vin)
220-350 V
Power rating (P)
20 kW
Output voltage (Vout)
480 V
Switching frequency (f)
20 kHz
Output voltage
factor (Vr)
2%
ripple
Inductor (L)
0.004 mH
Capacitor (C)
12.41
Determination of DC Link Voltage :
6000 W
The dc bus voltage is mainly determined by
the inverter ac output voltage and the voltage
drop across the filter. A lower bound on the dc
bus voltage can be determined from the
following relation at a unity power factor
[N.Mohan et al.2003].
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
Where,
=Line-Line RMS voltage on inverter
side,
=Filter
Inductance,
value
of
=Maximum
possible
RMS
the
ac
load
current,
=Modulation Index of the Inverter.
Fig Power flow between a VSI and Grid
Parameters of Inverter
Three Phase Inverter:
The regulated DC output of boost
converter feeds the VSI which will then
connect to the grid through LC filter. The
inverter is of typical three phase six switch
pulse width modulation (PWM) voltage source
inverter. The VSI converts the power from the
dc voltage source to three phase ac outputs
with 120º phase displacement. PWM is
modulation technique used to control and
shape of the VSI output voltage. In order to
control the magnitude, phase angle and
frequency of the output voltage of VSI, PWM
is used to generate switching pulses to control
the six switches in VSI.In PWM three
balanced sinusoidal control voltages are
compared with the triangular voltages. The
triangular waveform is at a switching
frequency, which is generally much higher
than the frequency of the control voltages and
is called as carrier frequency. The three phase
sinusoidal control signals with the same
frequency are used to modulate the duty ratios
of switching pulses from the switches. The
Figure 4.5 shows power flow between a VSI
and grid, where the impedance represents the
combined filter, transformer and transmission
line inductance. The active and reactive power
flows from the converter are controlled by
magnitude and phase of the converter output
voltages relative with grid parameters. The
active power flow is controlled by varying the
phase difference and reactive power flow is by
varying the magnitude of inverter output. The
phase difference and amplitude are varied with
reference of constant grid voltage. The control
of modulation index controls amplitude, and
synchronization and phase angle control of
modulating sine wave controls the phase
variation. The real and reactive power
delivered to the utility is given by following
relations (Santhosha kumar A 2010).
Input Voltage
300-500V DC
Output Voltage
230 V AC
SwitchingFrequency
8 kHz
Modeling and
converter:
Control
of
Grid
side
Since the machine is grid connected the grid
voltage as well as the stator voltage is same,
there exists a relation between the grid voltage
and DC link voltage. The main objective of the
grid side converter is to maintain DC link
voltage constant for the necessary action. The
voltage oriented vector control method is
approached to solve this problem. The detail
mathematical modeling of grid side converter
is given below. The control strategies are made
following the mathematical modeling and it is
shown in Fig. 4.7. The PWM converter is
current regulated with the direct axis current is
used to regulate the DC link voltage whereas
the quadrature axis current component is used
to regulate the reactive power. The reactive
power demand is set to zero to ensure the unit
power factor operation [R.Pena et al.1996].
Fig. 4.6 shows the schematic diagram of the
grid side converter. The voltage balance across
the line is given by Eq. (4.8), where R and L
are the line resistance and reactance
respectively. With the use of d-q theory the
three phase quantities are transferred to the two
phase quantities.
Schematic diagram of grid side
converter
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
for the voltage loop. The plants for the current
loop and the voltage loop are given in below
equations.
For the grid side converter mathematical
modeling can be represented as
Where
and
are the two phase voltages
found from
using d-q theory.
Since the DC link voltage needs to be constant
and the power factor of the overall system sets
to be unity, the reference values are to be set
consequently.
The active and reactive power is controlled
independently using the vector control
strategy. Aligning the axis of the reference
frame along the stator voltage position is found
by Eq. (4.13), vq = 0, since the amplitude of
supply voltage is constant the active power and
reactive power are controlled independently by
means of id and iq in the following Equations.
The d and q reference voltages are found from
the below eqns.
MATLAB / Simulink Model of
WIND/PV Hybrid System
Control block diagram
converter
of
Grid
side
20 kW WIND Energy Conversion System
6 kW PV System
480 V DC Link Voltage
230 V 50 Hz Grid
The control scheme utilizes current control
loops for id and iq with the id demand being
derived from the dc-link voltage error through
a standard PI controller. The iq demand
determines the displacement factor on the grid
side of the choke. The iq demand is set to zero
to guarantee unit power factor. There are two
loops for the control design, i.e. inner current
loop and outer voltage loop to provide
necessary control action. Line resistance and
reactance decide the plant for the current loop,
whereas DC link capacitor is taken as the plant
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
RESULTS:
Model of wind turbine coupled with PMSG
and model of Photovoltaic energy system are
inter-connected with grid through full scale
power
electronic
devices
by
using
MATLAB/Simulink. The performance study is
done for the simulatedsystem under input
variations at RES’s and load variations.
Active Power distribution
Case-I: Constant Generation &
Constant Load
In this case the inputs like irradiation,
temperature, and wind speed are kept constant
with a constant ac load near Grid are
considered for simulation. The irradiation 900
W/m2, temperature 25ºC, for PV and wind
speed of 8 m/s are given as inputs to the
simulated Hybrid model and load parameters
as 7.5 kW active power, 5.0404 kVAR
Inductive reactive power connected to 230 V,
50 Hz Grid. The system is simulated for 1
second and load is connected through a breaker
which closes at 0.5 second. The results are as
follows:
Grid Voltage Case I
Grid current Case I
Load Current case I
DC Link Voltage case I
Power of Hybrid System case I
Inverter Output Voltage caseI
Inverter Output Current case I
ISSN: 2231-5381
Case-II: Variable Generation &
Change in Load
In this case both the inputs parameters
like irradiation and wind speed are varied with
a change in ac load near Grid are considered
for simulation. Change in Generation is
achieved by changing the irradiation of PV
system and Wind speed of WECS. In our
simulation we consider a change of irradiance
from 900 W/m2 to 600 W/m2 at 0.5 second,
Similarly for WECS the change in speed from
6m/s to 8m/s at 0.5 second. Change in Load is
illustrated by connecting a Load 1 of 7.5 kW
active power, 5.0404 kVAR Inductive reactive
power at 0.4 second, here the breaker 1 closes
and at 0.8 second the breaker is opened. Load
2 of 4 kW active power, 3.3143 kVAR
connected through breaker 2 at 0.6 second. So
from 0.4 second to 0.6 second the Load will be
7.5 kW, 5.0404 kVAR; from 0.6 second to 0.8
second the Load will be 11.5 kW, 8.3547
kVAR and from 0.8 second to 1 second the
Load will be 4 kW active power, 3.3143
kVAR. These local ac loads are connected to
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
230 V, 50 Hz Grid. The system is simulated
for 1 second. The results are as follows:
Case-II: Variable Generation &
Change in Load
In this case Hybrid Wind/PV
generation the input parameters are varied,
irradiance of PV is changed from 900 W/m2 to
600 W/m2 at 0.5 second, Similarly for WECS
the change in speed from 6m/s to 8m/s at 0.5
second. Change in Load is achieved by using 2
Breakers for connecting Loads. The Power
required by the Load is supplied by the Hybrid
system and remaining power is fed in to the
Grid.
DC Link Voltage case II
CONCLUSIONS AND SCOPE FOR
FUTURE WORK
Conclusions
Power of Hybrid System case II
Active Power Distribution case II
Load Current case II
Observations :
Case-I:Constant
Constant Load
Generation
&
In this case both Hybrid Wind/PV generation
as well as ac load is constant. Load of 7.5 kW
active power, 5.0404 kVAR is connected to ac
grid at 0.5 second by a breaker. The Power
required by the Load is supplied by the Hybrid
system and remaining power is fed in to the
Grid. So Hybrid Wind/PV active power
generation remains constant, wind reactive
power is maintained at zero as controller has
restricted the Hybrid model to generate it and
at common point of coupling inverter, grid and
load voltage remains at Peak voltage 325.26 V,
50Hz.
ISSN: 2231-5381
The modeling of hybrid Wind/PV for power
system
configuration
is
done
in
MATLAB/SIMULINK environment. The
present work mainly includes the grid tied
mode of operation of hybrid system. The
models are developed for all the converters to
maintain stable system under various loads and
resource conditions and also the control
mechanism are studied. The dynamic
performance of Hybrid Wind/photovoltaic
power systems are studied for different system
disturbances like load variation, wind speed
variation and different irradiation and
temperature inputs. The simulation results
shows that, using a VSI and PQ control
strategies, it is possible to have a good
response of grid-connected hybrid energy
system. The hybrid grid can provide a reliable,
high quality and more efficient power to
consumer. The hybrid grid may be feasible for
small isolated industrial plants with both PV
systems and wind turbine generator as the
major power supply.
Scope for future work
The control strategy which is implemented in
this work is grid-connected RES hybrid energy
system. Implementation of control strategy for
islanding operation of RES can be done to
operate hybrid energy system to supply local
loads during islanding. Also, connecting BSES
(Battery storage Energy system) across the DC
link can be modeled to increase the reliability
and efficiency during peak conditions.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 17 Number 1 – Nov 2014
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