A NOVEL ON HYBRID WIND SOLAR ENERGY CONVERSION SYSTEM
TO IMPROVE THE POWER QUALITY USING CASCADED H-BRIDGE
MULTILEVEL INVERTER
MEKALA MANIKUMAR
[1] P.G SCHOLAR
DAVULURI SRIKANTH[2]
ASSISTANT PROFESSOR
P.PURNA CHANDRA RAO[3]
ASSOCIATE PROFESSOR & M.TECH (PH.D)
[1,2,3]DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
[1,2,3]CHALAPATHI INSTITUTE OF TECHNOLOGY, MOTHADAKA, GUNTUR, A.P.
ABSTRACT
This thesis presents an improved
cascaded H-Bridge multilevel inverter (CHBMLI)
based grid connected hybrid wind-solar energy
conversion system (HWSECS) with the mandate of
power quality. The wind energy conversion system
(WECS) and solar energy conversion system (SECS)
are connected individually to an isolated dc-links of
the CHBMLI through their respective DC/DC
converters based maximum power point tracking
(MPPT) system. The CHB topology when endorsed
as PWM rectifier sustain with the capacitor
unbalancing issues among the dc links feeding
distinct dc loads and the same arise when piloted in
regenerative operation with distinct sources popping
uneven power into each cell. The proposed HWSECS
system suffers the similar unbalance voltages as two
distinct sources (WECS and SECS) are augmented
among isolated dc-links. The author made efforts in
exploiting the advantages of topology concurrently
inscribed the solution to the hurdles during the
system operation and control. The features of the
proposed system and the control scheme impart
maximum power extraction from RES and injection
into grid along with other advantages. The simulation
studies has been carried out in MATLAB/Simulink.
I. INTRODUCTION
The hybrid renewable energy sources
(HRES) have been progressively researched and
invented to satisfy the increasing energy demand, and
gained broad attention in recent years as of their
prosperity of being ample and non-pollutant nature.
In diverse hybrid systems, two or more RES are
joined simultaneously for enhancing the power
supply reliability [1–4]. Among these different RES,
wind and solar energy sources have been mostly and
efficiently used together. Wind power is one such
most prominent RES as it is easily available and
collected by wind turbines with high power capacity.
Solar power is another auspicious green energy
source since it is most abundant and easily harnessed
by using PV modules. Actually, wind and solar
power complement each other since during the night
time and cloudy days when solar power is less
available but strong winds are mostly to occur
whereas weak winds usually occur in sunny days [5–
7]. Hence, irrespective of varying environmental
conditions a hybrid wind-solar energy conversion
system (HWSECS) can deliver continuous output
power supply than any other individual power
generation systems. With the remarkable fast growth
of power electronics devices and control techniques,
the use of grid-connected HWSECS has been
increased significantly [8].
For HWSECS, design and control of power
electronic converters are prime interest. In this type
of HRES, rectifiers, boost converters and inverters
used for the efficient power conversion. Separate
DC/DC converters for each power generating source
or single DC/DC converter for whole system can be
used [8–11]. In addition, the need of inventive and
futuristic DC/AC converter configuration and their
efficient control mechanism is required. Recently
multilevel inverters (MLI) topologies have been
become popular as they are more propitious; having
higher voltage handling capability, nearly sinusoidal
output voltage waveform with better harmonic
spectra, good electromagnetic compatibility and
lower voltage stress for the switches when compared
to a basic 2-level inverter [12]. Various conventional
symmetrical, asymmetrical and reduce device count
MLI topologies along with control mechanism and
modulation techniques were proposed for grid
integration of RES in [9,12,13]. Some power quality
problems like voltage variations, harmonic
generation, flickers and unbalanced dc-link capacitor
voltages are arises during working of HWSECS.
Unwanted harmonics produced due to the presence of
power converters. Due to the varying wind speed and
solar irradiation, flicker or voltage variation occurs in
output power supply. As a result, peak value of the
DC currents in the DC capacitor links becomes
different, which result in unbalanced dc-link
capacitor voltages. This in turn leads to unequal
voltage stress across the switching devices, making
the use of DC/AC converters unproductive. So the
dclink capacitor voltages and current need to be
controlled independently [14–16]. Various power
conditioning schemes to compensate these power
quality problems, maximum power extraction from
RES and many control strategies used for controlling
the dc-link voltages in grid integrated MLI topologies
is reported in literature [4,5–7,9,13–19]. A
proportional integral derivative supplementary
damping control is designed for stability
improvement of hybrid PV-wind system model in
[1]. In context of extracting maximum power from
integrated RES and to maintain power quality under
different condition, low cost controllers with a
control scheme in d-q reference frame are presented
in [4] however proposed system consists only single
DC/DC converter with common dc bus link and
controlled only by using PV array MPPT. A control
scheme for power flow management having a multi
input transformer coupled bidirectional DC/DC
converter for a HRES only for household applications
is given in [5] but power quality issues during grid
integration were not addressed. A P&O MPPT
algorithm is used for maximum power extraction and
the grid side control of MLI to extract the maximum
current from HRES with common dc-link proposed
in [6,7]. DC bus intermediate voltage balancing by
using space vector modulation (SVM) for grid
integrated three level voltage source inverter was
proposed in [16], but it is complicated as compared to
conventional PI controller based schemes and also
required filter designing in proper manner. In [17] a
control method and PWM scheme for modular
multilevel converters (MMC) to mitigate the
converter circulating current for a grid integrated
RES is presented, but for practical implementation
this is found more complicated in structure. In
[15,20] single phase MLI topology having self-
voltage balancing capability with reduce device count
and unity power factor (UPF) was proposed, they
maintained UPF requirements but only designed and
explained to work on low grid voltage. Among all
standard MLI topologies, “cascaded H-bridge
inverter (CHBI)” is predominantly used for grid-
connected HWSECS because of its modular design,
high resolution and the use of low voltage rated semi-
conductor switches for achieving medium or high
power levels [12,13,15,17,20,21].
The major advantage of adopted CHBMLI
topology possessing the isolated dc-links plays the
prominent role to legitimate in connecting two
distinct type of sources with unequivocal power at
any point of time. In addition, this MLI support to
adjoin two medium voltage sources from HWSECS
to feed the total power generated into the high
voltage grid without any transformers but at the same
time, the system achieves the better synchronization
along with calibrated and controlled power flow. It is
an important note to consider that either the CHB
topology used as an inverter or a rectifier the mandate
of possessing equal dc-link voltages is essential to
justify identical permissible voltage stress among all
switching devices in multilevel topologies at high
voltage applications. But, CHB topology when
endorsed as PWM rectifier sustain with the capacitor
unbalancing issues among the dc-links feeding
distinct dc loads. At the same time, when the PWM
rectifier piloted in regenerative operation the same
capacitor imbalance problems arise with distinct
sources popping uneven power into each cell. The
present proposed HWSECS system suffers the
similar unbalance voltages as two distinct sources
(WECS and SCES) are augmented among isolated dc
links. The various power conditioning schemes,
control strategies and inverter topologies proposed
above have advantages as such novel cascaded
topologies, reduction of switches and increase in
level, power flow management, and maintaining
unity power factor etc. for largescale HRES
applications. But power quality problem arises due to
dclink voltage imbalance in CHBMLI based
HWSECS not addressed in an efficient way. In this
study, efforts has made to bring a robust solution to
the grid connected HWSECS system. The proposed
control framework decouple the control of every H-
bridge cell (HBC) giving particular estimation of
reference voltages. Moreover, the sinusoidal phase
shifted multilevel pulse width modulation (SPWM)
scheme has been considered with the objective to
preserve the appropriate information of reference
voltages to acquire a multilevel waveform on ac side
to justify the equal voltage stress among the switches
in the MLI operation. Also, the control scheme
presented have the capability to investigate the
control aspect of bidirectional power flow and
potentially to accomplish totally separate control of
each HBC and an independent and flexible power
extraction capability of the dc links. Because of
which dc link capacitor balancing is practiced
regardless of RES power mismatching whatever the
environmental condition would be. Furthermore, the
low ripple sinusoidal current are provided to the
power grid with better power quality. The author has
made efforts in exploiting the advantages of topology
concurrently inscribing the solution to the hurdles
during the system operation and control.
Fig1: Grid connected HWSECS in conjunction with
MLI
II.LITERATURE SURVEY
Electrical energy becomes necessary for
human being. Generation of electrical energy mostly
depends on fossils fuel, they are limited in nature and
also responsible for environmental
pollution. Renewable energy resources provides a
better alternative for future,In comparison to
conventional energy resources economical aspect is a
major issue of renewable energy sources with the
feasibility and efficiency. These limitations are tried
to overcome by deployment hybrid renewable energy
resources. There are certain criteria to analyze and
implement the sized, optimized and cost efficient
system. This paper focus on hybrid energy systems
based on solar photovoltaic (PV) and wind resources.
This paper shed lights on various parameters
of economic feasibility, sizing strategies with logical
advancements to enhance their utilization, future
prospects, and their arrangement. Strategies to
develop an effective storage system is also presented
here.A brief review on developments in optimization
techniques, reliability index and cost analyzing
techniques for hybrid renewable energy systems are
also presented.
This paper presents the optimal hybrid
power system design including various
configurations of renewable energy generation. To
decide the optimal configuration of parameters a new
multi-objective function with six separate objectives
of hybrid renewable system is presented using GA,
PSO, BFPSO and TLBO optimization techniques.
The different parameters namely technical (LPSP,
Renewable factor), economical (COE, Penalty &
Fuel consumption) and social (Job creation, HDI &
PM) features are investigated as objectives
simultaneously for optimal design of hybrid system.
The design consideration of hybrid system using a
novel PM factor, human health impacts are directly
shown whereas pollutant emission is measured in the
hybrid system design. Based on the minimum value
of multi-objective function optimal values are
decided for objective indices. For optimal
configuration including various combinations of
wind, PV, diesel generator, biomass and battery bank,
separate cases from I to VI of hybrid system are
tested. Performance of TLBO is found to be better
than BFPSO, PSO and GA as per the analysis of
results for individual cases. Also the case I found to
be the most efficient solution among all cases.
III.PHOTOVOLTAIC INVERTER
Fig.2 Schematic diagram of PV system
1. PV unit : A PV unit consists of number of PV
cells that converts the energy of light
directly into electricity (DC) using
photovoltaic effect.
2. Inverter : Inverter is used to convert DC
output of PV unit to AC power.
3. Grid : The output power of inverter is
given to the nearby electrical grid for the
power generation.
4. MPPT : In order to utilize the maximum
power produced by the PV modules, the
power conversion equipment has to
be equipped with a maximum power
point tracker (MPPT). It is a device
which tracks the voltage at where
the maximum power is utilized at all
times.
Photovoltaic cell and array modeling
A PV cell is a simple p-n junction diode that
converts the irradiation into electricity. Fig.2
illustrates a simple equivalent circuit diagram of a PV
cell. This model consists of a current source which
represents the generated current from PV cell, a diode
in parallel with the current source, a shunt resistance,
and a series resistance.
Fig.3.Equivalent circuit diagram of the PV cell
IV.MULTI LEVEL INVERTER
An inverter is an electrical device that
converts direct current (DC) to alternating current
(AC) the converted AC can be at any required
voltage and frequency with the use of appropriate
transformers, switching, and control circuits. Static
inverters have no moving parts and are used in a wide
range of applications, from small switching power
supplies in computers, to large electric utility high
voltage direct current applications that transport bulk
power. Inverters are commonly used to supply AC
power from DC sources such as solar panels or
batteries. The electrical inverter is a high power
electronic oscillator. It is so named because early
mechanical AC to DC converters were made to work
in reverse, and thus were "inverted", to convert DC to
AC.
4.1 Cascaded H-Bridges inverter
A single phase structure of an m-level
cascaded inverter is illustrated in Figure 4.1. Each
separate DC source (SDCS) is connected to a single
phase full bridge, or H-bridge, inverter. Each inverter
level can generate three different voltage outputs,
+Vdc
, 0, and –Vdc
by connecting the DC source to the
ac output by different combinations of the four
switches, S1, S
2, S
3, and S
4. To obtain +V
dc, switches
S1
and S4
are turned on, whereas –Vdc
can be obtained
by turning on switches S2
and S3. By turning on S
1
and S2
or S3
and S4, the output voltage is 0. The AC
outputs of each of the different full bridge inverter
levels are connected in series such that the
synthesized voltage waveform is the sum of the
inverter outputs. The number of output phase voltage
levels m in a cascade inverter is defined by m = 2s+1,
where s is the number of separate DC sources. An
example phase voltage waveform for an 11 level
cascaded H-bridge inverter with 5 SDCSs and 5 full
bridges is shown in Figure 4.2. The phase voltage
+
…(4.1)
For a stepped waveform such as the one
depicted in Figure 4.2 with s steps, the Fourier
Transform for this waveform follows
( )
∑ [ ( ) ( )
( )] ( )
…(4.2)
Fig.4Single-phase structure of a multilevel cascaded
H-bridges inverter
Fig5. Output phase voltage waveform of an 11 level
cascade inverter with 5 separate dc sources.
V.WIND POWER
Wind is abundant almost in any part of the
world. Its existence in nature caused by uneven
heating on the surface of the earth as well as the
earth‟s rotation means that the wind resources will
always be available. The conventional ways of
generating electricity using non renewable resources
such as coal, natural gas, oil and so on, have great
impacts on the environment as it contributes vast
quantities of carbon dioxide to the earth‟s atmosphere
which in turn will cause the temperature of the
earth‟s surface to increase, known as the green house
effect. Hence, with the advances in science and
technology, ways of generating electricity using
renewable energy resources such as the wind are
developed. Nowadays, the cost of wind power that is
connected to the grid is as cheap as the cost of
generating electricity using coal and oil. Thus, the
increasing popularity of green electricity means the
demand of electricity produced by using non
renewable energy is also increased accordingly.
Fig6: Formation of wind due to differential heating
of land and sea
VI.PROPOSED SYSTEM AND CONTROL
DESIGN
6.1 System Description The block diagram for the proposed grid
connected HWSECS in conjunction with MLI is
shown in Fig. 6.2. The WECS and SECS are
connected individually to isolated dc-links of the
proposed 5-level CHBMLI through their respective
boost converters based MPPT.The dc voltages
„Vwind‟ and „VPV‟ are acquired from PMSG
rectified output voltage and PV array respectively.
By applying the P&O MPPT algorithm to the power
semiconductor switches, the boost converter can
extract maximum power from the wind turbine and
PV array individually. The dc-link voltages (VDC1
and VDC2) will be kept balanced by the use of
SPWM along with proposed control scheme. In
following subsections the general properties with
relevant mathematical modelling expressions of PV
system, wind system and design of boost converter is
given.
6.2 Dynamics of different components of PMSG
based WECS
WECS composed of a wind turbine (WT), a
PMSG that is used for converting mechanical energy
extracted by WT in to the electrical energy. Shaft of
turbine directly connected to the PMSG with the help
of the gearbox that provides rated torque to the
PMSG, and generated three-phase voltage and
current. Then the output power obtained from the
PMSG is delivered to AC–DC–AC converters so that
the output ac voltage (Vac) will be maintained at
required amplitude and frequency. The dc-link
voltage can be affected by the varying wind speed.
Therefore, by keeping dc-link voltage (VDC2)
constant at its reference value the amplitude of „Vac‟
can be controlled at the required grid voltage [14].
6.2.1 Wind turbine characteristics
WT extracted the wind kinetic energy and gives
the mechanical power output (Pm) that is calculated
by using Betz theory and expressed as in Eq.
Where „ρ‟ is the air density in kg/m3 , „vw‟ is
the wind velocity in m/s, „A‟ is the area swept by the
turbine blades and „CP (λ, β)‟ is the turbine power
coefficient, which is a function „λw‟ tip speed ratio
and „β‟ blade pitch angle and given as in Eq.
Where, „c1 – c7‟ are the turbine constant
coefficients. Hence optimised „CP‟ for used WT
found by accurate arrangement and precision of these
factors. Fig. 4 shows the output power and speed
characteristics of the WT for various wind speed
[25]. For a specific wind speed, WT parameters and
„ρ‟ are constant; so „Pm‟ only depends on the „CP‟
value, which successively depends on WT rotor
speed. Thus, WT can operate at MPP by at optimal
rotor speed „ϖopt‟ (in rad/s), which is expressed in
Eq.
Fig.6.1 . Mechanical power and speed characteristics
of selected wind turbine.
Here „λopt‟ is the optimal tip speed ratio in radians
and „R‟ is the turbine radius in meters. Furthermore,
the Fig.6.1 shows that for each wind speed a
particular turbine speed exists upon which obtained
power is maximum.
6.2.2 Permanent magnet synchronous generator
(PMSG)
PMSG has gained broad attention in wind
energy applications due to its high efficiency
operation, self-excitation capability and leading to a
high power factor. The mathematical d–q voltage
equations of a threephase PMSG connected to a WSC
is given as [6,27]:
where „vdg‟ and „vqg‟ are d–q terminal
voltages of PMSG, „Ldg‟ and „Lqg‟ are the d-q –axis
of PMSG filter inductance, „ ‟ and „ᴪpm‟ is the
angular frequency and the flux, „rg‟ is PMSG
equivalent resistance and „iqg‟ and „idg‟ represents
the stator winding current. Table 1 shows the
parameters of selected WTG used for simulation. The
essential dc-link voltage is approximately set by
using the following equation:
Where „Vm‟ is the peak value of the
generated PMSG output voltage at vw = 12 m/s
6.3 Mathematical modelling and description of
proposed grid connected CHBMLI topology The proposed CHBMLI having two HBC
modules with independent solar and wind systems
under inconsistent solar radiation and wind speed
respectively are connected to the two isolated dc-
links is shown in Fig. 6.3. As two HBC modules per
phase are used in proposed CHBMLI, five-levels are
obtained in the converter output ac side phase
voltage. Increase in number of HBC modules, results
in more levels in converter output voltages, thus
reducing the device stress in the HBC. This also
expunge the requirement of filters on ac side, and
number of RES can be increased [34,35]. The
maximum power recommended by the respective
MPPTs of WECS and SECS is variable in reference
to the available environmental conditions. Therefore,
the extractable currents from the sources are distinct
and further the capacitor voltages in the isolated dc-
links of the CHBMLI are not equal. Dynamical
properties of the system are expressed by using a
proposed mathematical analysis. Due to symmetrical
nature of three phases of bidirectional grid connected
CHBMLI, in this study mathematical analysis is
derived only for single-phase. For converter
operation analysis the switching function for each leg
of a HBC has been derived by using basic curve
fitting. The power switches are controlled in such a
way that two switches in a HBC leg should not be
ON at the same time [27,36,37]. If isolated RES
connected with respective dc-link of HBC in
proposed system is assumed identical then the two
capacitors of the respective cell equitably, share half
of the VDC. Desired converter output phase voltage
can be obtained by selecting proper switching
function. Table 2 shows the switching states and
corresponding voltage levels for identical isolated
RES or dc sources. Let „Sy‟ be the switching function
that defines the per unit value of the converter output
phase voltage. The used switching function „Sy‟ can
be represented mathematically as in Eq.. In this
equation, two generalized leg switching functions
„Spj‟ and „Snj‟ for each leg of HBC has been defined
as shown in Fig. 6, where „p‟ is for the first leg, „n‟
for second leg. Further, for upper HBC the value of j
= 1 and for lower HBC j = 2. The variation of
generalized leg switching function with respect to
switches activated in each HBC is defined as: if the
upper switch in the first leg is ON then „Spj‟ is taken
as +1 and if the lower switch in first leg is ON the
„Spj‟ is taken as -1. Similarly, for the second leg if
the upper switch is ON then „Snj‟ is taken as -1 and
for the lower switch is ON the „Snj‟ is taken as +1.
Fig6.2: Grid-connected CHBMLI.
Fig6.3: Equivalent circuit of 5-level grid connected
CHBMLI
As different kind of RES are used in actual
hybrid system model, therefore the dc-link voltage
for both HBC in a phase may be different. The
converter output phase voltage is the algebraic sum
of voltages obtained at the AC side of each HBC
[38]. Indirectly the output phase voltage is a function
of dc-link capacitor voltages and derived as in Eq.
6.4. Control scheme and switching strategy for
CHBMLI based grid connected HWSECS
The system has been designed to address the
problem of capacitor voltage unbalancing during the
HWSECS operation and control. Unequal power will
be generated from WECS and SECS in isolated DC
cells, which result in power quality problems like
harmonic generation and introduce unbalanced
current in the grid. For proper injection of power and
to resolve problems associated in the HRES, an
improved control technique with SPWM scheme is
proposed for CHBMLI. The block diagram of
proposed control scheme is given in Fig. 6.3. The
basic purposes of the used control scheme are given
as:
i DC-link capacitors balancing even with
two distinct RESs popping uneven power into each
cell of CHBMLI.
ii To attain UPF and sinusoidal current
injection into connected grid with better THD
[34,39].
iii Transformer less high voltage grid
integration.
iv Maximum power extraction from the RES and
injection into grid. The control scheme is divided into
two parts named as primary and secondary parts. The
primary part comprehends of individual MPPT
algorithm for both RES, voltage proportional integral
(PI) controller and one proportional (P) controller for
current. Initially, total DC voltage (VDC) is
compared with reference DC voltage (VDC* ) and
the obtained difference (ΔVDC) is fed to the voltage
controller.
Fig6.4: Proposed control scheme.
Where obtained voltage component is
divided by „VDC* ‟.
This gives the sum of modulation signals,
mx = mx1 + mx2. At the acme of this part, „VDC1‟ is
kept up to reference capacitor voltage, by subtracting
the sum of generated reference voltages in secondary
part (modulation signal „mx2‟) of the remaining
lower HBC from the generated reference voltage
(modulation signal „mx‟). Control of remaining (N-1)
HBC i.e. lower HBC is featured in the secondary part
of control technique, with each HBC controlled
individually and corresponding dc-link capacitor
voltages of all HBCs, is compared with their
reference values, and is controlled using a voltage
controller (PI).
VII.SIMULATION RESULTS
Fig7.1 : Proposed Diagram of Grid-connected
CHBMLI
The proposed CHBMLI having two HBC
modules with independent solar and wind systems
under inconsistent solar radiation and wind speed
respectively are connected to the two isolated dc-
links is shown in Fig. 7.1. As two HBC modules per
phase are used in proposed CHBMLI, five-levels are
obtained in the converter output ac side phase
voltage. Increase in number of HBC modules, results
in more levels in converter output voltages, thus
reducing the device stress in the HBC. This also
expunge the requirement of filters on ac side, and
number of RES can be increased [34,35]. The
maximum power recommended by the respective
MPPTs of WECS and SECS is variable in reference
to the available environmental conditions. Therefore,
the extractable currents from the sources are distinct
and further the capacitor voltages in the isolated dc-
links of the CHBMLI are not equal.
7.1 Simulation results for SECS and WECS at
varying irradiation and wind speed respectively:
Fig7.2 : PV array output current
The proposed HWSECS model is simulated
and its performance is tested under varying
environmental conditions to investigate the
performance of the proposed control scheme.
Fig7.3: PV array output power
Table 4 shows the values of parameters
employed in the simulation. Initially for a time of
„2.5 s‟ the values of the wind speed and solar
irradiation are set as vw1 = 12 m/s, λ1 = 200 W/m2 ,
and after „t = 2.5 s‟ the values are changed to vw2 =
10 m/s, λ2 = 300 W/m2 .
Fig7.4: wind system output current
Fig7.5: wind system output power
Corresponding to these conditions the
obtained currents (IPV and Iwind) and power (PPV
and Pwind) of PV array and WTG are shown in Fig
7.2, Fig 7.3, Fig7.4 & 7.5
After „t = 2.5 s‟ with increase in solar
irradiation, the PV extracted power gets affected and
is increased to a value of 3100 W from its initial
obtained value 2050 W. Similarly when the wind
speed decreases after t = 2.5 s the wind extracted
power is reduced to a value of 3600 W from its initial
value of 5200 W. As the WECS and SECS are
connected to individual isolated dclinks of CHBMLI,
these values are fed to corresponding individual
dclink respectively.
Fig7.6: dc-link currents corresponding to SECS and
WECS
The obtained two currents/power are distinct
in nature, which leads to different dc-link capacitor
currents as plotted in Fig. 7.6 And results in power
quality problems like dc-link capacitor imbalance and
introduce unbalanced grid current to the connected
grid, which is not desirable for proper operation of
HWSECS. Thus, the control technique is designed to
maintain dc-link capacitor voltages balancing even
under inconsistent environmental conditions and
inject current into the grid network with improved
power quality.
Fig7.7: dc-link capacitor voltages across CDC1 and
CDC2
Fig7.7 shows the dc-link capacitor voltages
VDC1 and VDC2 w.r.t time. Initially it is clearly
seen that in the proposed HWSECS, the dclink
voltages start oscillating but within very less time (t =
0.8 s) the used dc-link capacitors CDC1 and CDC2
achieve balanced nature. At „t = 2.5 s‟ when the wind
speed and solar irradiation changes to vw2 = 10 m/s,
λ2 = 300 W/m2 , by using the proposed control
technique the dc-link capacitors again balanced
within „0.3 s‟ That validate the feasibility of proposed
control scheme.
Fig7.8: grid current (Is) variation with change in
wind speed and irradiation.
VIII.CONCLUSION
In this THESIS, proposed grid-connected
five-level CHBMLI converts the power obtained
from HWSECS to ac power and feeds into the grid
system. This topology will help to improve the
utilisation of connected wind power sources and PV
array, which are connected individually to each dc-
link, with the independent MPPT algorithm. It is
clear from the above discussed simulation and
experimental studies that along with the input and
output performance parameters of the proposed
control scheme and system model extracts the
maximum power that can be enabled from each RES.
The mathematical modelling of single-phase grid
connected CHBMLI has been derived to find out the
relation of dclink capacitor voltages (VDC1 and
VDC2), CHBMLI output voltage (Vac), dc-link
currents (IDC1 and IDC2) and grid current (Is) in
terms of switching functions. Simulations are carried
on to justify that, in varying dc-link currents in
integrated wind and solar system the DC capacitor
balancing is achieved, and a grid current is injected
into the grid network which is sinusoidal in shape
having minimum THD and UPF. The simulation
results clearly support the simulation results obtained,
and thus the motive of this control technique is
accomplished. This developed grid connected
HWSECS converter topology with the applied
control technique thus helping to acquire the DC
capacitor balancing and high power quality.
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Author Profile:
MEKALA MANIKUMAR, PG STUDENT,
Chalapathi Institute of Technology, Mothadaka,
Guntur. MAIL:[email protected]
Davuluri Srikanth M.Tech, (Ph.d.), Assistant Professor
Chalapathi Institute of Technology, Mothadaka,
Guntur. Mail Id:[email protected]
P.PURNA CHANDRA RAO,
Associate Professor &
HOD, Dept of EEE, Chalapathi Institute of
Technology, A.R Nagar,Mothadaka,
Guntur,India. (E-mail: [email protected]
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