PV and battery hybrid

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)

Energy management of wind/PV and battery hybrid system M. F. Almi a,b, M. Arroufb, H.Belmilia, S. Bouloumaa, B. Bendiba a

Unité de Développement des Equipements Solaires. UDES/Centre de Développement des Energies Renouvelables, CDER, Bou Ismail, 42415, W. Tipaza, Algérie b Department 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.

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

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

Figure 1. The studied hybrid system configuration

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

3 WIND MODELING

Mechanical drive train : Tme  Tem  f .  j

3.1 Wind Speed

d dt

(13)

Tme : Mechanic torque

The wind speed is modeled as a deterministic, non-stationary signal given as the sum of sinusoids as follows [1]: Vv t   10  0.2 sin 0.1047t   2 sin 0.2665t    sin 1.293t   0.2 sin 3.6645t 



f . : Friction torque j : Moment of inertia.

f : Viscous Coefficient friction.

3.4 MPPT Control Strategy For Wind Turbine System

3.2 Wind Turbine The mechanical power PWind of the wind turbine is given by: 1 2

 Pwind  ..St .C p ( ,  ).V 3  The wind turbine used corresponds to the one with the numerical approximation developed in [2].  151   C p  0.73  0.58  0.002 2.14  13.2 e  i 

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]: 1 Pwind  . .St .C p ( ,  ).V 3 2 C p max  C p (max )

18.4

i

1 1 0.003  3   0.02   1  R  Vw

i 

Tem : Electromagnetic torque

(3)

(14)

Popt  K opt.3ref

(15) 5

1 R . . .C p max . 3 2  V .max  ref  R

(4)

K opt 

(5)

(16) (17)

3.3 Permanent Magnet Synchronous Generator

4 PHOTOVOLTAIC GENERATOR MODEL

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

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

Vsd   Rs I sd  Lsd Vsq   Rs I sq  Lsq

dIsd  Lsq I sq dt dI sq dt

 Lsd I sd   f

3 p( sd I sq  sq I sd ) 2  sd  Lsd I sd  f

Tem 

 sq  Lsq I sq Tem   f I sq  p( Lsd  Lsq ) I sd I sq Tem   f I sq

RS IPanel Io

(6)

ILight

RSH

RL

VPanel

(7) (8) (9) (10) (11) (12)

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 31

50%


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:

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

 VPanel  I Panel RS   I Panel RS   V a I Panel  I Light  I 0  e  1  Panel RSH    

For the battery bank modeling, Thevenin’s equivalent circuit of the battery has been used [9, 10].

(18)

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

a

N s . .K .Tc q

 I SC  I 0  e 

 V  1  OC  RSH

  K .TC   I SC  1 VOC    ln   q   I0 

(20)

(21)

I0 and ILight depend on irradiance and temperature.

I Light  I Light, STC S  

3

 q . E G   1 1     TC  C   Tref

  K .T  e  

   I SC   

     C 

1 1  Tref T

Cb

Vb

Figure 3. Thevenin’s equivalent circuit of the battery

The equivalent capacitance Cb is given by, Cb 

KWh  36001000



0.5 Voc2 max  Voc2 min



(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]. P  3.V .I  VDC .I DC VDC 

(23)

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.

(26)



(22)

4.1 Maximum Power Point Tracking

I dP d VI  I dI    V dV VdV V dV

Ib

Voc

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

T I 0  I 0, STC  C  Tref

Rb Rin

(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]. q .VOC K .TC

5 MODELING OF THE BATTERY

3



6

 .d

V

(27)

LL max . cos



6

VDC 

3

VDC 

3

(28) V  LL max VLL max  2.VLL (29) 3 VDC  2 .VLL (30)  From this, the relationship between VDC and phase voltage V is (31)

6 .V

 Then the relation between IDC and I is  I DC  I 6

(32)

(24)

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]. 1 Vi 1 I o  1   I i

Vo 

(33) (34)

6.3 DC/DC Buck Converter The average output voltage of the buck converter is given by: (35) Vo   .Vi 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: VA  1  1  1 a  V   VDC  1 1 .b      B 2

(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.

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: V s  1 (38) FT s   c  V s  LCs2  1 (39) s  j V  j  1 (40) FT  j   c  V  j  LC j 2  1 1 (41) FT  j   1  LC 2 In order that the filter operates without diminution of output signal magnitude, it must be that: FT  j   1 (42)

1  LC 2 c  2. . fc (43) Where: fc is the cut-off frequency (resonance) of LC filter. 1 (44) L 2 4. . f c2 .C 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 Figure 4. Equivalent circuit of LC filter

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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.

Vmin threshold  Vanest  Vmax threshold Vthreshold  220  33V

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.

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

Figure 6. Block Diagram of Frequency and voltage monitoring

8 PROPOSED CONTROL STRATEGY

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 f est  1%Hz . This frequency must lie between:

f min threshold  fest  f max threshold fthreshold  50  0.5Hz

Figure 7. Wind control

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 Vanest  15%V . Figure 8. GPV control

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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) 1000 900 800

Irradiation E(W/m2)

700 600 500 400 300 200 100 0

0

0.5

Figure 9. DC/DC Boost control

1

1.5 Time t(s)

2

2.5

3

Figure 13. Solar irradiation 70

60

rotational Speed W(rd/s)

50

40

30

20

10

0

0

0.5

Figure 10. DC/AC Inverter control

1

1.5 Time t(s)

2

2.5

3

Figure 14. Rotational speed of PMSG 3500

9 SIMULATION RESULTS 3000

Power Ppv(W)

2500

2000

1500

1000

500

0

0

0.5

Figure 11. Configuration used for the vérification off system protection

1

1.5 Time t(s)

2

2.5

3

Figure 15. Power of GPV

12 11.8

60 Vdc* Vdc

11.6

50

11.2

40

Voltage Vdc(V)

Wind speed Vw(m/s)

11.4

11 10.8 10.6

30

20

10.4 10.2

10 10

0

0.5

1

1.5 Time t(s)

2

Figure 12. Wind speed

2.5

3

0

0

0.5

1

1.5 Time t(s)

2

2.5

Figure 16. Voltage of DC bus 35

3






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.

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. 400 300

Voltage Van(V)

200 100 0 -100 -200 -300 -400

(a)

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.6

0.7

0.8

0.6

0.7

0.8

0.9

1

(a)

400 30

300 20

10

100

Curent I(A)

Voltage Van(V)

200

0

0

-100 -10

-200 -20

-300

-400

-30

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.6

0.7

0.8

0.9

1

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.9

1

(b)

(b)

Figure 18. (a, b): System application on an overvoltage from the network. (a) Network voltage; (b) Network current

20 15



10 5 0 -5 -10 -15 -20

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.6

0.7

0.8

0.9

1

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.

(c)

Figure 17. (a, b, c): System application with frequency variation. (a) Network frequency ;(b) Network current; (d)

Network voltages 36

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) 5

400

I V

4

Current I(A) and Voltage Van(pu)

300

Voltage Van(V)

200 100

0 -100 -200

3 2 1 0 -1 -2 -3 -4

-300

-5 -400

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.6

0.7

0.8

0.9

0

0.01

0.02

1

0.03 Time t(s)

0.04

0.05

0.06

Figure 21. Voltage and current of AC load

(a)

10 CONCLUSION

40 30 20

Curent I(A)

10 0 -10 -20 -30 -40

0

0.1

0.2

0.3

0.4

0.5 Time t(s)

0.6

0.7

0.8

0.9

1

(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

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 monophase 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.

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Appendix Shell 150-PC array Characteristics

I sc  4.8A; I mp  4.4 A;Vso  43.4V ;Vmp  34V Rs  0.529;  2mA / C 0 ;   152mV

N s  10; N p  2

PMSG parameters Pn  1.12KW ; Rs  8.39; Ls  0.08483H V  230V ; N  500rpm; P  3 Turbine parameters Pn  1.32KW ; R  1.26m; max  6.597; C p max  0.48 j  1.5Kg.m2 ;   1.14Kg / m3 ;V  240V ;VDC  400V

Boost parameters L  210.54H C  1.8mF Buck parameters L  450H C  0.26mF Batterie OPzS Solar 190

38