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.

REFERENCES

[1] L. Wang, A.V. Prokhorov, Q. Son Vo, Stability

Improvement of a Multimachine Power System

Connected with a Large- Scale Hybrid Wind-

Photovoltaic Farm Using a Supercapacitor Quang-

Son Vo, IEEE Trans. Ind. Electron. 54 (2017) 1–9,

https:// doi.org/10.1109/TIA.2017.2751004.

[2] F.A. Khan, N. Pal, S.H. Saeed, Review of solar

photovoltaic and wind hybrid energy systems for

sizing strategies optimization techniques and cost

analysis methodologies, Renew. Sustain. Energy Rev.

92 (2018) 937–947, https://doi.org/10.1016/j.

rser.2018.04.107.

[3] Y. Sawle, S.C. Gupta, A.K. Bohre, Socio-techno-

economic design of hybrid renewable energy system

using optimization techniques, Renew. Energy. 119

(2018) 459–472,

https://doi.org/10.1016/j.renene.2017.11.058.

[4] M.M.R. Singaravel, S.A. Daniel, MPPT with

Single DC-DC Converter and Inverter for Grid-

Connected Hybrid Wind-Driven PMSG-PV System,

IEEE Trans. Ind. Electron. 62 (2015) 4849–4857,

https://doi.org/10.1109/TIE.2015.2399277.

[5] B. Mangu, S. Akshatha, D. Suryanarayana, B.G.

Fernandes, Grid-Connected PVWind-Battery-Based

Bidirectional DC-DC Converter for Household

Applications, IEEE J. Emerg. Sel. Top. Power

Electron. 4 (2016) 1086–1095, https://doi.org/10.

1109/JESTPE.2016.2544789.

[6] P. Shanthi, G. Uma, M.S. Keerthana, Effective

power transfer scheme for a grid connected hybrid

wind/photovoltaic system, IET Renew. Power Gener.

11 (2017) 1005–1017, https://doi.org/10.1049/iet-

rpg.2016.0592.

[7] Y. Chen, S. Member, Y. Liu, S. Hung, C. Cheng,

Multi-Input Inverter for GridConnected Hybrid PV /

Wind Power System, IEEE Trans. Power Electron.

22 (2007) 1070–1077,

https://doi.org/10.1109/TPEL.2007.897117.

[8] K. Basaran, N.S. Cetin, S. Borekci, Energy

management for on-grid and off-grid wind/PV and

battery hybrid systems, IET Renew. Power Gener. 11

(2017) 642–649, https://doi.org/10.1049/iet-

rpg.2016.0545.

[9] S. Debnath, J. Qin, B. Bahrani, M. Saeedifard, P.

Barbosa, Operation, Control, and Applications of the

Modular Multilevel Converter: A Review, IEEE

Trans. Power Electron. PP (2014),

https://doi.org/10.1109/TPEL.2014.2309937 1–1.

[10] H. sung Kim, J.H. Kim, B.D. Min, D.W. Yoo,

H.J. Kim, A highly efficient PV system using a series

connection of DC-DC converter output with a

photovoltaic panel, Renew. Energy. 34 (2009) 2432–

2436, https://doi.org/10.1016/j.renene.2009.01. 011.

Author Profile:

MEKALA MANIKUMAR, PG STUDENT,

Chalapathi Institute of Technology, Mothadaka,

Guntur. MAIL:manikumar865@gmail.com

Davuluri Srikanth M.Tech, (Ph.d.), Assistant Professor

Chalapathi Institute of Technology, Mothadaka,

Guntur. Mail Id:sreekanth02@gmail.com

P.PURNA CHANDRA RAO,

Associate Professor &

HOD, Dept of EEE, Chalapathi Institute of

Technology, A.R Nagar,Mothadaka,

Guntur,India. (E-mail: chandu.podila@gmail.com