Energy management of wind/PV and battery hybrid system

Energy management of wind/PV and battery hybrid system

M. F. Almi a,b, M. Arroufb, H.Belmilia, S. Bouloumaa, B. Bendiba

aUnité de Développement des Equipements Solaires. UDES/Centre de Développement des Energies

Renouvelables, CDER, Bou Ismail, 42415, W. Tipaza, Algérie bDepartment of Electrical Engineering, University of Batna 05000, Algeria

[email protected]

ABSTRACT

This paper deals with power control of a wind and

solar hybrid generation system for interconnection

operation with electric distribution system. Power

control strategy is to extract the maximum energy

available from varying condition of wind speed and

solar irradiance while maintaining power quality at a

satisfactory level. In order to capture the maximum

power, variable speed control is employed for wind

turbine and maximum power point tracking is applied

for photovoltaic system. The grid interface inverter

transfers the energy drawn from the wind turbine and

PV array into the grid by keeping common dc voltage

constant. To ensure safety these inverters automatically

shut down in the event of : High/Low grid AC-voltage;

High/Low grid frequency; Grid Failure; or Inverter

malfunction. Modeling and simulation study on the

entire control scheme is carried out using a power

system transient analysis tool, Matlab Simulink.

The simulation results show the control performance

and dynamic behavior of the wind/PV system.

KEYWORDS

Wind; PV; Control; islanding; Protection.

1 INTRODUCTION

Advances in wind turbine and photovoltaic

generation technologies have brought opportunities for utilizing wind and solar resources for electric power generation. They have unpredictable random behaviors. However, some of them, like solar radiation and wind speed, have complementary profiles [1, 2].

The Wind/solar complementary power supply system is a reasonable power supply which makes good use of wind and solar energy. This system can not only provide a bargain of low cost and high

dependability for some region where power transmission is not convenient such as frontier defenses and sentry, relay stations of communication, a farming or pasturing area and so on, but also inaugurate a new area which resolve the crisis of energy sources and environment pollution.

It is very difficult to make use of the solar and wind energy all weather just through solar system or wind system individually, for the restriction of time and region. So a system that is based on renewable resources but at the same time reliable is necessary and wind/solar hybrid system with battery storage can meet this requirement.

2 HYBRID SYSTEM CONFIGURATION

A typical hybrid energy generation system is shown in Fig. 1

Figure 1. The studied hybrid system configuration

International Journal of New Computer Architectures and their Applications (IJNCAA) 4(1): 30-38 The Society of Digital Information and Wireless Communications, 2014 (ISSN: 2220-9085)

30

mailto:[email protected]

3 WIND MODELING

3.1 Wind Speed

The wind speed is modeled as a deterministic,

non-stationary signal given as the sum of sinusoids as follows [1]:

tt

tttVv

6645.3sin2.0293.1sin

2665.0sin21047.0sin2.010

3.2 Wind Turbine

The mechanical power WindP of the wind turbine

is given by:

3).,(...2

1VCSP ptwind

The wind turbine used corresponds to the one with the numerical approximation developed in [2].

ieCi

p

4.18

14.2 2.13002.058.0151

73.0

(3)

1

003.0

02.0

1

1

3

i (4)

wV

R (5)

3.3 Permanent Magnet Synchronous Generator

Permanent magnet synchronous generators

(PMSG’s) are typically used in small wind turbines for several reasons including high efficiency, gearless, simple control...etc. [3].

(6)

fsdsd

sq

sqsqssq ILdt

dILIRV (7)

)(2

3sdsqsqsdem IIpT (8)

fsdsdsd IL (9)

sqsqsq IL (10)

sqsdsqsdsqfem IILLpIT )( (11)

sqfem IT (12)

Mechanical drive train :

dt

djfTT emme

. (13)

meT : Mechanic torque

emT : Electromagnetic torque

.f : Friction torque

j : Moment of inertia.

f : Viscous Coefficient friction.

3.4 MPPT Control Strategy For Wind Turbine

System

According to the operation theory of wind

turbine, the maximum output power of wind generator depends on the optimal tip speed ratio

opt . In terms of this, the MPPT is controlled to

track the maximum power of the wind turbine and the battery charging voltage in such a way [4]:

3).,(...2

1VCSP ptwind (14)

)( maxmax pp CC

3. refoptopt KP (15)

3

5

max ....2

1

RCK popt (16)

R

Vref

max. (17)

4 PHOTOVOLTAIC GENERATOR MODEL

Generally, the PV panel can be modeled using the equivalent circuit shown in Fig. 2.

Io

ILight

RS

RSH RL 50%VPanel

IPanel

Figure 2. Equivalent circuit of the PV cell

This lumped circuit includes a current generator providing the short-circuit current (ILight), which is a function of the solar irradiation, a diode to account for the typical knee of the current–voltage curve through the reverse saturation current (I0), a

sqsqsd

sdsdssd ILdt

dILIRV


31

series resistor (RS), and a shunt resistor (RSH), emulating intrinsic losses depending on PV cell series and parallel connections. The PV module current at a given cell temperature and solar irradiance is given by:

SH

SPanelPanela

RIV

LightPanelR

RIVeIII

SPanelPanel

10 (18)

a: is the modified panel ideal factor defined by a is

the modified panel ideal factor defined by:

q

TKNa cs

... (19)

q is the electron charge, K is Boltzmann’s constant, γ is the usual PV single-cell ideal factor (typically ranging between 1 and 2), NS is the number of cells in series, and TC is the PV panel temperature [5, 6].

SH

OCTK

Vq

SCR

VeII C

OC

1

.

.

0 (20)

Since the ratio between VOC and RSH is typically negligible, VOC can be derived from the diode saturation current as

1ln

.

0I

I

q

TKV SCC

OC (21)

I0 and ILight depend on irradiance and temperature.

CrefC

G

TTTK

Eq

ref

C

STCe

T

TII

11

.

.3

,00 (22)

Cref

SCISTCLightLight

TTSII

11,

(23)

4.1 Maximum Power Point Tracking

Incremental conductance method has been

implemented in this study. If the array is operating at voltage V and current I, the power generation is P=VI, at the maximum power point, dP/dV should be zero and the sign of dP/dV may be identified by equation (24). Increase or decrease in the PV array voltage is determined by judging the sign of this equation.

dV

dI

V

I

VdV

VId

dV

dP

V

I (24)

The MPPT flow returns the desired PV array voltage for the dc/dc converter.

5 MODELING OF THE BATTERY

For the battery bank modeling, Thevenin’s

equivalent circuit of the battery has been used [9, 10].

Figure 3. Thevenin’s equivalent circuit of the battery

The equivalent capacitance Cb is given by,

2min

2max5.0

10003600

ococ

bVV

KWhC

(25)

6 MODELING OF POWER ELECTRONICS

6.1 Three-Phase Diode Bridge Rectifier

The diode rectifier is the most simple, cheap,

and rugged topology used in power electronic applications [11].

DCDC IVIVP ...3 (26)

dVV LLDC .cos.3

6

6

max

(27)

max

3LLDC VV

(28)

LLLL VV .2max (29)

LLDC VV .23

(30)

From this, the relationship between VDC and phase voltage V is

VVDC .63

(31)

Then the relation between IDC and I is

IIDC6

(32)

Voc

Rin

Vb

Ib

Cb

Rb


32

6.2 DC/DC Boost Converter

In this model, the boost converter has been

controlled to yield constant output DC voltage level, V0 by varying the duty ratio, in response to variations in Vi [12].

io VV

1

1 (33)

io II 1 (34)

6.3 DC/DC Buck Converter

The average output voltage of the buck

converter is given by:

io VV . (35)

Assuming negligible converter losses, the average output current is of the buck converter is

given by [13].

io

II (36)

6.4 Inverter Modeling

The output voltage of the inverter, Vop, is the

voltage between VA and VB, where VA and VB are the potentials at the points A and B with respect to the neutral potential (VN=0) [14, 15].

The voltage vector [VA VB]T can be expressed as:

b

aV

V

VDC

B

A.

11

11

2

1 (37)

6.5 LC Filter

A system with forced commutation like MLI or

other control techniques of voltage source inverter

generates chopping harmonics. In order to

eliminate these harmonics the insertion of a filter

between the converter and the load, in the majority

of the cases is a low passes band filter. This makes

it possible to carry out the objective.

Figure 4. Equivalent circuit of LC filter

a) Calculation of L and C low passes band

filter [16, 18]. At load less I2=0 if we neglect the internal

resistance of the inductor (R=0) The filter transfer function become:

1

12

LCssV

sVsF c

T (38)

)39( js

1

12

jLCjV

jVjF c

T (40)

21

1

LCjFT

(41)

In order that the filter operates without

diminution of output signal magnitude, it must be that:

1jFT (42)

21 LC

cc f..2 (43)

Where: fc is the cut-off frequency (resonance) of LC filter.

Cf

Lc ...4

122

(44)

6.6 Phase looked loop (PLL) The PLL can track the instantaneous network

fundamental voltage phase and find its frequency. Other methods were developed but the majority of them are used only if the voltage signal is purely sinusoidal [16].... The Phase Locked Loop (PLL) is by far the most

technique used to extract the direct fundamental

component voltage phase in the low voltage

electrical supply networks.

Figure 5. General structure of a single phase PLL


33

7 ELECTRICAL PERTURBATIONS

The electric power is provided in voltage form

constituting mono-phase sinusoidal system with the followings characteristic parameters:

frequency

Voltage magnitude

Wave form

The measurement of these parameters makes it

possible to judge the voltage quality. A

deterioration of the one of them or several at the

same time let’s suppose the presence of an

anomaly in the electrical supply network.

7.1 Protection of Decoupling

A device made up of a protection and a

decoupling body must be installed at the generator output [17]. This device must respond to the design and operation technical specifications for connection with a distribution public network of an electric generating station.

a) Frequency monitoring

The frequency monitoring is achieved using a

PLL, this allows the estimation of the angular frequency from the estimated voltage.This estimated pulsation makes it possible to have the estimated frequency by dividing it by 2 the frequency can be thus supervised. It is compared with two thresholds values corresponding to Hzfest %1 . This frequency must lie between:

thresholdestthreshold fff maxmin

Hzfthreshold 5.050

The monitoring system activates a temporization if a threshold is crossed during more than 0.1s. The inverter operation is stopped and isolated from the network thanks to the control switchgear envisaged for this purpose. If the frequency returns between these thresholds values temporization is given to zero.

b) RMS Voltage network monitoring

It is made in the same manner as that of

frequency. A minimum and maximum threshold is given VVanest %15 .

thresholdanestthreshold VVV maxmin

VVthreshold 33220

The two RMS voltages are measured. It is

necessary that both are below thresholds to start temporization. The same latency time is considered: 0.1 s. This monitoring is necessary for an overvoltage or an under voltage.

Figure 6. Block Diagram of Frequency and voltage

monitoring

8 PROPOSED CONTROL STRATEGY

Figure 7. Wind control

Figure 8. GPV control


34

Figure 9. DC/DC Boost control

Figure 10. DC/AC Inverter control

9 SIMULATION RESULTS

Figure 11. Configuration used for the vérification off system

protection

0 0.5 1 1.5 2 2.5 310

10.2

10.4

10.6

10.8

11

11.2

11.4

11.6

11.8

12

Time t(s)

Win

d s

peed V

w(m

/s)

Figure 12. Wind speed

0 0.5 1 1.5 2 2.5 30

100

200

300

400

500

600

700

800

900

1000

Time t(s)

Irrad

iatio

n E(

W/m

2)

Figure 13. Solar irradiation

0 0.5 1 1.5 2 2.5 30

10

20

30

40

50

60

70

Time t(s)

rota

tiona

l Spe

ed W

(rd/s

)

Figure 14. Rotational speed of PMSG

0 0.5 1 1.5 2 2.5 30

500

1000

1500

2000

2500

3000

3500

Time t(s)

Pow

er

Ppv(

W)

Figure 15. Power of GPV

0 0.5 1 1.5 2 2.5 30

10

20

30

40

50

60

Time t(s)

Vol

tage

Vdc

(V)

Vdc*

Vdc

Figure 16. Voltage of DC bus


35

Simulation of frequency variation The network frequency undergoes a variation of

(ramp) type. The aim of this simulation is to check the well operation of the block “frequency monitoring” of figure.6.

This variation starts at t = 0.42 s of 50 Hz and attain 50.5 Hz at t = 0.54s as shown in figure.18 (a). The currents and voltages follow the variations which appear insignificant.

After a second at t = 0.64 s, the system activate the switchgear and stops the inverter as shows in figures .18 (b, c). The network currents and voltages then became zero.

(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time t(s)

Vol

tage

Van

(V)

(b)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-20

-15

-10

-5

0

5

10

15

20

Time t(s) (c)

Figure 17. (a, b, c): System application with frequency

variation. (a) Network frequency ;(b) Network current;

(d) Network voltages

Over voltage simulation The aim of this simulation is to show that the

decoupling system detects overvoltage and isolate the inverter from the network. A progressive over voltage starts at t = 0.4s. The maximum threshold voltage is reached at 0.6s as shown in the figure .19 (a). The current reacts since the network voltage increases and thus the power should be transmitted on the network is constant. The networks currents I decrease as shown in the figure.19 (b). The system reacts 0.6 after the voltage maximum threshold was reached. The currents and voltages become null at 0.7s.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time t(s)

Voltage V

an(V

)

(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-30

-20

-10

0

10

20

30

Time t(s)

Cur

ent

I(A

)

(b)

Figure 18. (a, b): System application on an overvoltage from

the network. (a) Network voltage; (b) Network current

Under voltage simulation The network voltage decreases from t = 0.4 as

shown in figure.20(a). The minimal threshold value is reached at t = 0.6 s. The current increases up to its authorized maximum value as shown in figure .20(b) whereas the voltage decreased. The under voltage activates the whole system at nearly 0.7 s; this parameters became zero.


36

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time t(s)

Vol

tage

Van

(V)

(a)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-40

-30

-20

-10

0

10

20

30

40

Time t(s)

Cure

nt

I(A

)

(b)

Figure 19. (a, b): System application on under voltage from

the network (a) Network voltage; (b) Network current

In the two simulations cases, of overvoltage and under voltage, it would be desirable to have a faster cutoff time according to the importance of overvoltage or under voltage . This determination could possibly be done by a training algorithm using the techniques of neuro-fuzzy, genetic algorithms, neurons networks or other forms of artificial intelligences.

Figure 20. Configuration used for the vérification off system

islanding

0 0.01 0.02 0.03 0.04 0.05 0.06-5

-4

-3

-2

-1

0

1

2

3

4

5

Time t(s)

Cur

rent

I(A

) an

d V

olta

ge V

an(p

u)

I

V

Figure 21. Voltage and current of AC load

10 CONCLUSION

Solar power is well known to be an expensive

solution to remote electrification. This cost can be reduced by adding wind turbine generators to reduce the reliance on PV.

In this paper, We have focused on the study of photovoltaic wind production of electrical energy optimization as well as its transfer to the mono-phase electrical network supply through an inverter with minimum possible losses. The adopted approach was to improve the chain various parts point by point. a pv/wind system protection device is implemented i.e. This system is able to react to overvoltage, under voltages and frequency variations. It was subjected to an overvoltage, an under voltage and frequency variation. The system showed good results in each cited case.

The small price difference between the classic solution and the island grid solution is justified by the flexibility and extendibility offered by the SMA system, in particular the addition of additional generation equipment at a later date.

The type of connection of the different components to the system is just as important. The AC coupling with inverter allows we to connect nearly any type of electricity generator and any type of consumer to our system. This makes our system easily extendable on the consumer side as well as on the generator side. Finally, we see that the energy produced by the system remains constant, according to the load with a voltage of (220V/50Hz). This is due to the power stored in the batteries, which will be used to compensate energy lacks and the efficiency of the control strategy we have used.


37

11 REFERENCES

[1] A.Mirecki “Etude comparative de chaînes de conversion

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[2] R. Melício , V.M.F. Mendes , J.P.S. Catalão “ Comparative study of power converter topologies and control strategies for the harmonic performance of variable-speed wind turbine generator systems ” Energy 36 (2011) 520e529.

[3] F. Valenciaga and P. F. Puleston “Supervisor Control for a Stand-Alone Hybrid Generation System Using Wind and Photovoltaic Energy” ieee transactions on energy conversion, vol. 20, no. 2, june 2005.

[4] Z. Lubsony, Wind Turbine Operation in Electric Power Systems, Springer-Verlag, Germany, 2003.

[5] A. Hoque et K. A. Wahid « New mathematical model of a photovoltaic generator (PVG) » Journal of Electrical Engineering The Institute of Engineers, Bangladesh Vol. EE 28, No. 1, June 2000.

[6] Project group INTRO-712, “Residential Microgrid System”, Aalborg University, 2008.

[7] D. Sera,R.Teodorescu,T.kerekes « Teaching Maximum Power Point Trackers Using a Photovoltaic Array Model with Graphical User Interface » Photovoltaic Specialists Conference, 2000. Conference Record of the 28th IEEE 15-22 Sept. 2000 Pages:1699 – 1702.

[8] Mukund R. Patel, Wind and Solar Power Systems. CRC Press, USA, 1999.

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[10] Tamer H. Abdelhamid and Khaled El-Naggar, “Optimum estimation of single phase inverter’s switching angles using genetic based algorithm,” Alexandria Engineering Journal, Vol. 44, No.5, 751-759, 2005.

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[12] M. G. Molina, D. H. Pontoriero, P. E. Mercado. “An efficient maximumpower-point-tracking controller for grid-connected photo-voltaic energy conversion system”. Brazilian Journal of Power Electronics, vol.12, no.2, pp.147–154, 2007.

[13] L. Barote and C. Marinescu “Renewable Hybrid System with Battery Storage for Safe Loads Supply” Paper accepted for presentation at the 2011 IEEE Trondheim PowerTech.

[14] J.Martinez, A.Medina “A state space model for the dynamic operation representation of small-scale wind-photovoltaic hybrid systems” Renewable Energy 35 (2010) 1159–1168.

[15] N.A. Ahmed, A.K. Al-Othman, M.R. AlRashidi “Development of an efficient utility interactive combined wind/photovoltaic/fuel cell power system with MPPT and DC bus voltage regulation” Electric Power Systems Research 81 (2011) 1096–1106

[16] R.E.Best “phase locked loups design, simulation, and applications” Best engineering Oberwil,Switzerland 1987.

[17] M. F. Almi, M. Arrouf, H.Belmili, B. Bendib “Contributionto the Protection of PVG Connected to

Three Phase Electrical Network Supply” Energy Procedia 18 ( 2012 ) 954 – 965.

Appendix

Shell 150-PC array Characteristics

VVVVAIAI mpsompsc 34;4.43;4.4;8.4

mVCmARs 152;/2;529.0 0

2;10 ps NN

PMSG parameters

HLRKWP ssn 08483.0;39.8;12.1

3;500;230 PrpmNVV

Turbine parameters

48.0;597.6;26.1;32.1 maxmax pn CmRKWP

VVVVmKgmKgj DC 400;240;/14.1;.5.1 32 Boost parameters

HL 54.210

mFC 8.1

Buck parameters

HL 450

mFC 26.0

Batterie OPzS Solar 190


38

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Energy management of wind/PV and battery hybrid system

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