Performance Analysis of Wind - Fuel Cell

Hybrid System linked with BESS-VF Controller

Authored ByNarayan P. Gupta, Sushma Gupta, Anil Kumar

Presented ByNarayan P. Gupta

Department of Electrical EngineeringOriental Institute of Science & Technology, Bhopal, India

Contents

2

Introduction

Wind Turbine Systems

Vector Control Scheme of GSC and RSC

Solid Oxide Fuel Cell Energy Conversion System

Modeling of D-STATCOM

Simulation Results

Conclusion

Appendix

References

3

Wind energy is most promising renewable energy source & its share is increasing w.r.t. to installed capacity, worldwide. India has fifth largest installed capacity in the world.Due to the intermittent characteristics of wind resources, it has been a challenge to

generate a highly reliable power with wind turbines.To overcome this limitation, a solid oxide fuel cell (SOFC) is used in conjunction with

wind generating plant.A multi-source hybrid power system increases energy availability significantly, it

becomes advantageous for practical applications that need highly reliable power regardless of location

The DFIG based variable speed wind turbine (type C) is the most popular in the growing wind market. This system uses two back-to-back PWM voltage source converters in the rotor circuit designed as grid side converter (GSC) and rotor side converter (RSC). The vector control strategy is used for both converters

Introduction

4

These high frequency switching converters of DFIG will inject additional harmonics in the system, which are increasing with wind speed variations.Load unbalancing, Poor power factor, Harmonics, Voltage drop at PCC, Reactive Power are some of important power quality issues related with nonlinear load. D-STATCOM is used to mitigate the voltage dip, compensate the reactive power, flicker, harmonic mitigations, load balancing and neutral current compensation.

Contd…

POWER QUALITY POWER QUALITY

FLICKER FLICKER SYSTEM TRANSIENTS

SYSTEM HARMONICS

NOISE

ELECTROMAGNATCINTERFERANCE

VOLTAGE SAG & SWELL

LOWPOWER FACTOR

Electric Power Quality basically refers to maintaining a near sinusoidal power distribution bus voltage at rated magnitude and frequency.

Variation in voltage, current or frequency is generally termed as PQ problems

Good power quality meansConstant voltage levelLow harmonic distortionLess transient eventsGood power factor

Power Quality

6

Consequences Unexpected power supply failures Equipment overheating and failure Electro magnetic interferences and noise in power system Increase of system losses oversize installations to cope with additional electrical stress Malfunction of protective relaying and voltage sensitive devices Mains voltage flickering

Sources Of HarmonicsSources Of Harmonics

Modern (Power-Electronic) Types

Modern (Power-Electronic) Types

TransformersTransformers Rotating MachinesRotating Machines

Arc Furnaces

Arc Furnaces

Controlled Devices

Controlled Devices SMPSSMPS Fluorescent

LampsFluorescent

Lamps

RectifiersRectifiers InvertersInverters Cyclo-converterCyclo-

converterHVDC

TransmissionHVDC

Transmission

Traditional (Classical) Types Traditional (Classical) Types

Contributors Reactive power Harmonic pollution Load imbalance Fast voltage variations

Contd…

7

15 KW DFIG

Wind TurbineSOFC

BESS DSTATCOM

Non Linear Load

PCC

Grid SideConverter

Rotor Side Converter

Transformer33KV/440V

Controller

CHOKE

DSTATCOM Controller

Transformer

Grid

Breaker

A

B

C

a

b

c

Discrete,Ts = 5e-006 s. Wind

Wind Speed m/s

A

B

C

a

b

c

A

B

C

a

b

c

g

A

B

C

+

-

g

A

B

C

+

-

g

A

B

C

+

-

A

B

C

+

-

[output]

A B C

A B C

Cdc

A

B

C

a

b

c

A_SOFC

B_SOFC

C_SOFC

Pulses

Pulse_RSC

Pulse_GSC

A_grid

B_grid

C_grid

Tm m

A

B

C

a

b

c

Simulink Test System

Fig. Simulink configuration of test system

8

Vector control Scheme of Grid Side Converter

Fig. – Schematic diagram of GSC

Grid Side Converter is used to maintain the dc-link voltage constant The voltage oriented vector control technique is used to control the GSC The PWM converter is current regulated with the direct axis current is used to regulate the DC link

voltage where as 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

The voltage balance across the line is given by

Using the abc-to-dq transformation, the corresponding equation in the dq-reference frame rotating at ωe is

9

Contd…

Fig. – Vector Control Scheme of GSC

The control scheme utilizes current control loops for id and iq The id demand being derived from the dc-link voltage error, through a standard PI controllerThe iq demand determines the reactive power flow between the grid and grid side converterThe iq demand is set to zero to ensure unit power factor operation.

Vd D- axis grid voltage

Vq Q- axis grid voltage

Vd1 D- axis grid side converter voltage

Vq1 Q- axis grid side converter voltage

id D- axis grid side converter current

iq Q- axis grid side converter current

10

Vector control Scheme of Rotor Side Converter The main purpose of the machine side converter is to maintain the rotor speed constant irrespective

of the wind speed Vector control strategy has been implemented to control the active power and reactive power flow of

the machine using the rotor current components The active power flow is controlled through idr

The reactive power flow is controlled through iqr

To ensure unit power factor operation like grid side converter the reactive power demand is also set

to zero (Qref = 0)

The currents iq and id can be controlled using Vq and Vd respectively

The control scheme utilizes cascade control The inner current control loops are used for controlling the d-axis and q-axis rotor currents The outer power control loops are used to control the active and reactive power on the stator

11

Contd…The d-q axis rotor voltage equation is given by,

Vdr* and Vqr* equation is given by,

Where V'dr and V'qr are found from the current errors processing through standard PI controllers The q-axis reference current i*qr is found from the reactive power errors The reference current i*dr can be found either from the reference torque or form the speed errors (for the

purpose of speed control) through standard PI controllers

Where Te*=(Pmech-Ploss)/ωr

Ploss = Mechanical Losses + Electrical Losses

12Fig. – Vector Control Scheme of RSC

Contd…

Fuel Cell Energy Conversion System Fuel cell converts chemical energy of a reaction into electricity with byproduct of water and

heat . Fuel cell consists of an electrolyte layer in contact with two electrodes on either side. Hydrogen

fuel is fed to anode and oxygen from air is fed to cathode. At anode Hydrogen is decomposed into positive and negative ions Only positive ions flow from anode to cathode . Recombination of positive and negative ions with oxidant takes place at cathode to form

depleted oxidant (or pure water).Anode Reaction: Cathode Reaction:

Overall Reaction:

The dc Voltage across FC stack is given by nernest’s equation

WhereVfc – Operating dc voltage (V),E0 – Standard reversible cell potential (V), pi – Partial pressure of species i (Pa), r – Internal resistance of stack (S), I – Stack current (A), N0 – Number of cells in stack, R – Universal gas constant (J/ mol K), T – Stack temperature (K), F – Faraday’s constant (C/mol) 13

14

Contd…Proton exchange membrane fuel Cell (PEMFC) Alkaline Fuel cell (AFC)Phosphoric acid fuel cell (PAFC)Molten Carbonate fuel cell (MCDC)Solid oxide fuel cell (SOFC)Direct Methanol fuel cell (DMFC)

High-temperature operation of SOFC-1800oF removes the need for a precious-metal catalyst, thereby reducing the cost.

It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels (the input to the anode can be hydrogen, carbon monoxide or methane)and reduces the cost associated with adding a reformer to the system.

The electrolyte used is a ceramic oxide which increases the cost of SOFCs.At the cathode, electrochemical reduction takes place to obtain oxide ions. These ions pass through

the electrolyte layer to the anode where hydrogen is oxidized to obtain water.In case of carbon monoxide, it is oxidized to carbon dioxide.

P ref

V fc

r

N

currentequation

F low R ateequation

Partia l P ressureEquations

Voltage Equations

I

qH 2

qO 2

pH 2O pO 2 pH 2

Where qH2 – Fuel flow (mol/s), qO2 – Oxygen flow (mol/s),

KH2 – Valve molar constant for hydrogen (kmol/s atm),

KO2 – Valve molar constant for oxygen (kmol/s atm),

KH2O – Valve molar constant for water (kmol/s atm), τH2 –

Response time for hydrogen (s), τO2 – Response time for

oxygen (s), τH2O – Response time for water (s), τe –

Electrical response time (s), τf– Fuel response time (s),

Uopt – Optimum fuel utilization, rHO – Ratio of hydrogen to

oxygen, Kr – Constant (kmol/s A), Pref – Reference power

(kW)Fig. Block diagram for dynamic model of SOFC 15

16

Power conditioning for fuel cell connected to Grid

Fuel Cell Pow er P lant

DC

DC

DC

AC

LC Filter Utility Grid

ACBUS

Couplinginductor &

T ransm issionline

DC-DC ControllerVDCref

V DC

PQ

Q ref

IabcVabc

DC BUS

DC/DCConverter

DC/ACInverter

Contro lSignal

Contro lSignal

P Q

P ref

PI PI

Pulses

dq/abc

PIPI

Idref Iqref

IdrefIqref

abc/dq

PLL Iabc

angle

Id Iq

+- +-

+ -+-

Fig. Power conditioning for fuel cell connected to Grid

17

Performance of SOFCThe number of cells connected in series is taken as 450. Initially for a 50 kW of load the calculated SOFC

voltage is 403 volt.The output voltage of the DC/DC converter is maintained almost constant at 700V throughout the loading

conditions, by using a PI controller along with the DC/DC converter.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

300

350

400

450

Time

Fuel Cell Voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

100

200

300

400

500

600

700

800

900

1000

Time

Voltage (

V)

output voltage of DC-DC converter

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

50

100

150

200

250

300

350

400

450

Time

Fuel Cell Voltage

Fig. Output Voltage waveform of SOFC and DC-DC Converter waveform

18

Control Scheme of D-STATCOM

QuadratureCom ponent Refrence

current

AC VoltagePI

controller

In phasecom ponent

Refrence current

Com pensation ofam plitude of activepow er com ponent

of current

FrequencyPI controller

Frequencym easurem ent

+-

Ua Ub Uc

Unit VoltageTem plate G enerator

Quadrature VoltageTem plete G enerator

W a W b W c

+-

+_

Va Vb Vc

Vt

Isaq

Isbq

Iscq

Vrated Prated

Vtref

*

*

*

*

*

Ism q

Isad

Isb

d

Iscd** *

Ism d*

Iam d

Ig Vabc

Fref0

*

*

Isa Isb Isc* * *

Hysteresis Current contro ller

Isn*_

+

+

Ilc

Lf,Rf

Lf,Rf

Lf,Rf

Lf,Rf

S1

-

Vdc

S2

S5 S7

S6 S8

Cdc+

S3

S4

Battery

R1

Ro

+-Voc

IlaIlb

Iln

Isa

Isb

Isc

C battery

D-STATCOM is used to mitigate the voltage dip & compensate the reactive power.

It is also capable of flicker & harmonic mitigation’s, load balancing and neutral current compensation.

STATCOM consists of DC voltage source behind self commutated inverters using IGBT & coupling transformer. It is connected in shunt with distribution feeder.

It generates a current injection, which is added to non sinusoidal load current. Thus phase current taken from grid will be nearly sinusoidal

With voltage/frequency controller output voltage and frequency can be kept constant

19

Contd…

Prated = 15KW Vrated = 415 voltThe amplitude of active component of current is i*smd = igen(n) - ismd(n)

In phase component of reference source current are estimated as: i*sad = i*smd Ua, i*sbd = i*smd Ub , i*scd = i*smd Uc

Where Ua , Ub and Uc are in-phase unit current vectors , given by

Ua = Va / Vt , Ub = Vb / Vt , Uc = Vc / Vt

Where Vt is the amplitude of supply voltage Vt = 2/3(Va2 + Vb

2 + Vc2)1/2

instantaneous quadrature component of reference source current is estimated as i*saq = i*smqwa, i*sbq = i*smqwb , i*scq = i*smqwc

The unity amplitude template having instantaneous value in quadrature with instantaneous voltage Va, Vb, Vc are derived as

Wa = -Ua /√3 + Uc /√3

Wb= √3Ua/2 + ( Ub- Uc )/2√3

Wc= -√3 Ua/2+ (Ub-Uc)/2√3

20

The total reference source current is the sum of in-phase & quadrature component of reference source current.

i*sa = i*saq + i*sad

i*sb = i*sbq + i*sbd

i*sc = i*scq + i*scd

The reference source current (i*sa,i*sb,i*sc) are compared with measured source current .The error of

current are computed as: isa_error = isa - i*sa

isb_error = isb - i*sb

isc_error = isc - i*sc

These error signals are the drive of hysteresis current controller to generate six firing pulses for VSC

Design of BESS Controller

BESS consist of a CC-VSC with the battery at DC link. The terminal voltage of battery is given by Vbattery = (2√2/√3) VL; where VL is line rms

The equivalent capacitance can be determined from Cbattery = (kwh * 3600 * 103) / 0.5 (V2

ocmax – V2ocmin)

The parallel circuit of R1 & Cbattery is used to describe the energy & voltage during charging &

discharging

Contd…

21

Simulation for Unbalanced Reactive LoadThree single phase reactive load are applied between each phase and neutral at t=1.0 sec. At t=1.4sec

one phase is removed and another at t=1.5 sec making load unbalanced

1.3 1.4 1.5 1.6 1.7 1.8

-1

0

1

Vabc(p

u)

supply voltage

1.3 1.4 1.5 1.6 1.7 1.8

-20

0

20

Iabc

supply current

1.3 1.4 1.5 1.6 1.7 1.8-20

-10

0

10

20

Time

Icap

capacitor current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Ilabc

load current

1.3 1.4 1.5 1.6 1.7 1.8-40

-20

0

20

40

Icabc

controller current

1.3 1.4 1.5 1.6 1.7 1.8-20

-10

0

10

20

Time

Isn

source neutral current

1.3 1.4 1.5 1.6 1.7 1.8-20

0

20

Iln

load neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Icn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

dc link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

1.3 1.4 1.5 1.6 1.7 1.8-20

0

20

Iln

load neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Icn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

dc link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

22

Simulation for Unbalanced Non Linear Load A diode rectifier with resistive load and L-C filter at its DC side is considered. At t=1.0sec balanced

non linear load is inserted at t=1.4 sec one phase is removed and another at t=1.5 sec making load unbalanced.

It seems that controller current becomes nonlinear for eliminating the harmonic current.

1.3 1.4 1.5 1.6 1.7 1.8

-1

0

1

Vabc(p

u)

supply voltage

1.3 1.4 1.5 1.6 1.7 1.8

-20

0

20

Iabc(A

)

supply current

1.3 1.4 1.5 1.6 1.7 1.8-20

-10

0

10

20

Time

Icap(A

)

capacitor current

23

Contd…

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Ilabc

Load current

1.3 1.4 1.5 1.6 1.7 1.8

-20

0

20

Icab

c

controller current

1.3 1.4 1.5 1.6 1.7 1.8

-10

0

10

Time

Isn

Source neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Ilabc

Load current

1.3 1.4 1.5 1.6 1.7 1.8

-20

0

20

Icab

c

controller current

1.3 1.4 1.5 1.6 1.7 1.8

-10

0

10

Time

Isn

Source neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Iln

load neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Isn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.8400

600

800

1000

Vdc

DC link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Iln

load neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Isn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.8400

600

800

1000

Vdc

DC link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Iln

load neutral current

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Isn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.8400

600

800

1000

Vdc

DC link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

1.3 1.4 1.5 1.6 1.7 1.8-50

0

50

Iln

load neutral current

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-20

0

20

Icn

compensator neutral current

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

dc link voltage

1.3 1.4 1.5 1.6 1.7 1.80

20

40

60

Time

f

frequency

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

V

Vdc_V

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Te

Te

1.3 1.4 1.5 1.6 1.7 1.80

10

20

P(KW

)

P(KW)

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Time

Q(K

VAr)

Q(KVAr)

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

V

Vdc_V

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Te

Te

1.3 1.4 1.5 1.6 1.7 1.80

10

20

P(KW

)

P(KW)

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Time

Q(KV

Ar)

Q(KVAr)

1.3 1.4 1.5 1.6 1.7 1.80

500

1000

Vdc

V

Vdc_V

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Te

Te

1.3 1.4 1.5 1.6 1.7 1.80

10

20

P(KW

)

P(KW)

1.3 1.4 1.5 1.6 1.7 1.8-5

0

5

Time

Q(KV

Ar)

Q(KVAr)

24

Simulation for variable Wind SpeedThe wind speed is varied continuously throughout the simulation time (t = 5sec)During wind speed variation, The DFIG output voltage remains constant i.e. at 1pu by maintaining the DC

link voltage (Vdc) constant throughout.Though wind turbine torque (Tm) is fluctuating, the electromagnetic torque of DFIG (Tem) is constant

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 513

14

15

16

Ws

(m/s

)

Wind Speed (m/s)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

0

2

Vab

c (p

u)

Generator Voltage (volt)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.8

-0.6

Tm (p

u)

Mechanical Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

-1

0

1

Time

Tem

(pu

)

Electromagnetic Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 513

14

15

16

Ws

(m/s

)Wind Speed (m/s)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

0

2

Vab

c (p

u)

Generator Voltage (volt)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.8

-0.6

Tm (p

u)

Mechanical Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

-1

0

1

Time

Tem

(pu)

Electromagnetic Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 513

14

15

16

Ws (

m/s

)

Wind Speed (m/s)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

0

2

Vabc (

pu)

Generator Voltage (volt)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.8

-0.6

Tm

(pu)

Mechanical Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

-1

0

1

Time

Tem

(pu)

Electromagnetic Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 513

14

15

16

Ws (

m/s

)

Wind Speed (m/s)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

0

2

Vabc (

pu)

Generator Voltage (volt)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-1

-0.8

-0.6

Tm

(pu)

Mechanical Torque_pu

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-2

-1

0

1

Time

Tem

(pu)

Electromagnetic Torque_pu

25

Contd…

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5800

820

840

Vdc (

volt)

Vdc (V)_ GSC & RSC

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 51

1.2

1.4

Wr

(pu)

Wr (pu)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-20

0

20

P (

kw

)

P (KW)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-40

-20

0

20

Time

Q (

Kvar)

Q (Kvar)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5800

820

840

Vdc

(vo

lt)

Vdc (V)_ GSC & RSC

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 51

1.2

1.4

Wr

(pu)

Wr (pu)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-20

0

20

P (

kw)

P (KW)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-40

-20

0

20

Time

Q (

Kva

r)

Q (Kvar)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5800

820

840

Vdc

(vo

lt)

Vdc (V)_ GSC & RSC

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 51

1.2

1.4

Wr

(pu)

Wr (pu)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-20

0

20

P (

kw)

P (KW)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-40

-20

0

20

Time

Q (

Kva

r)

Q (Kvar)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5800

820

840

Vdc (

volt)

Vdc (V)_ GSC & RSC

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 51

1.2

1.4

Wr

(pu)

Wr (pu)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-20

0

20

P (

kw

)

P (KW)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-40

-20

0

20

Time

Q (

Kvar)

Q (Kvar)_DFIG

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 548

48.5

49

49.5

50

50.5

51

Sta

tor

Fre

quency

Stator Voltage Frequecy

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 549

49.5

50

50.5

51

Time

Roto

r F

requency

Rotor Voltage Frequecy

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 548

48.5

49

49.5

50

50.5

51

Sta

tor

Fre

quency

Stator Voltage Frequecy

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 549

49.5

50

50.5

51

Time

Roto

r F

requency

Rotor Voltage Frequecy

Power allocation between Grid, SOFC and Wind - DFIG

0

20

40

60

80

SO

FC P

ower

(KW

)

SOFC Power (KW)

0

50

100

Load

Pow

er (K

W)

Load Power (KW)

-100

-50

0

50

100

DFI

G P

ower

(KW

)

DFIG Power (KW)

-50

0

50

100

NLL

Pow

er (K

W)

NLL Power (KW)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-200

-100

0

100

200

Time

Grid

Pow

er (K

W)

Grid Power (KW)

27

Contd…

Sr no Type of Load % Total Harmonic Distortion

Va ia

1 Balanced Resistive load 0.33 3.23

2 Unbalanced Resistive load 0.33 3.23

3 Balanced reactive load 0.33 3.32

4 Unbalanced Reactive load 0.36 3.35

5 Balanced non linear load 0.34 3.53

6 Unbalanced nonlinear load 0.37 3.437 Balanced nonlinear load without

STATCOM5.45 49.74

Percentage THD of Supply voltage and Supply current under balanced / unbalanced linear, nonlinear load

28

ConclusionsBeing the wind energy is intermittent in nature; hybrid system constituting fuel cell; operated in

synchronism with wind generator and grid will be the feasible solution.

The interfacing of hybrid system with grid should comply the grid code requirements and power quality standards

Vector control scheme is very useful for controlling the grid side converter and rotor side converter; the system can work for any change in wind speed.

The dc link voltage of converters, rotor speed, and active power and reactive power exchange between machine and grid is almost constant during all operations.

The DFIG machine is perfectly synchronised with the SOFC -Grid and any sudden change in the load demand is met by sharing of power as per their rating.

With non linear load at PCC, the THD of supply current becomes more than IEEE-519-1992 limit (i.e. THD > 5%), hence D-STATCOM is used to restrict the total harmonic distortion caused by load.

Indirect current control scheme using hysteresis controller is useful for controlling of D-STATCOM . D-STATCOM improves the THD spectrum of source current and voltages; even in the case of any

sudden change in nonlinear load.D-STATCOM can be used as a solution to compensate reactive power, neutral current compensation,

load balancing and harmonic elimination.Power Factor correction has been done with help of D-STATCOM

29

Parameters of 15 KW, 440 V, 50Hz, DFIGRs = 0.023 pu, Rr = 0.016 pu, Ls = 0.018 pu, Lr = 0.16 pu, P = 6, J = 0.385 pu

Parameters of GSC and RSCVdc = 830 volt, Cdc = 9200 µF, Kp and Ki (GSC) = 0.83 and 5, Kp and Ki (RSC) = 0.6

and 8, Frequency of the grid-side and rotor-side PWM carrier = 2250 HZ and 1350 Hz

SOFC ParameterT = 1273K, Eo = 1.18 Volt, N= 450, Kr = .996*10-6Kmol/(s atm), Uopt = 0.85, KH2 =

8.43*10-4 Kmol/(s atm), KO2 = 2.81*10-4 Kmol/(s atm), KH2O = 2.52*10-3 Kmol/(s

atm), ), =26.1s, = 78.3 s, = 2.91 s, R = 0.16Ω, rHO = 1.145

Appendix

30

References

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2. Bhim singh, Shiv Aggrawal, Tara Chandra Kandpal (2010) “Performance of Wind Energy Conversion System using a Doubly Fed Induction Generator for Maximum Power Point Tracking” IEEE Industry App. Society Annual meeting, pp. 1-7.

3. Vishal Verma, Peeyush Pant, B. Suresh, Bhim Singh (2011) “Decoupled Indirect Current Control of DFIG for Wind Energy Applications” , IEEE Int. conf. on Power Electronics, pp. 1-6.

4. B. Singh and G. Kasal, (2008) “Voltage and Frequency Controller for a Three-Phase Four-Wire Autonomous Wind Energy Conversion System” IEEE Transactions on Energy Conversion, Vol 23, No. 2.pp-1170-1177.

5. Raul sarrias, Luis M Fernendez, Carlos A Garcia, Francisco Jurado (2012) “Coordinate operation of power sources in a doubly-fed induction generator wind turbine/battery hybrid power system ”Journal of Power Sources, Vol.205, 354–366.

6. Satish Choudhary, Kanungo Barada Mohanty, Birendra kumar Debta, (2011)“Investigation on Performance of Dou-bly-Fed Induction Generator Driven by wind turbine under Grid Voltage Fluctuation” IEEE Int. conf. on Environment and Electrical Engineering, pp.1-4.

7. N P Gupta, Preeti Gupta, Deepika Masand (2012) “Power Quality Improvement Using Hybrid Active Power Filter for A DFIG Based Wind Energy Conversion System” IEEE NUICONE, pp. 1-6.

8. E. Ribeiro, A. J. M. Cardoso, C. Boccaletti (2010) “Grid Interface for a Wind Turbine-Fuel Cell System” IEEE XIX In-ternational Conference on Electrical Machines - ICEM, pp. 1-6.

9. Nagasmitha Akkinapragada and Badrul H. Chowdhury (2006)“ SOFC-based Fuel cells for load following Stationary Applications” IEEE conference, pp. 553-560.

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