15325000802322012.pdf

8/22/2019 15325000802322012.pdf

1/19

This article was downloaded by: [Indian Institute of Technology - Delhi]On: 23 May 2013, At: 06:59Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House37-41 Mortimer Street, London W1T 3JH, UK

Electric Power Components and SystemsPublication details, including instructions for authors and subscription information:

http://www.tandfonline.com/loi/uemp20

Hybrid Solar Photovoltaic/Wind Turbine Energy

Generation System with Voltage-based Maximum PowePoint TrackingNabil A. Ahmed

a, Masafumi Miyatake

b& A. K. Al-Othman

a

aElectrical Engineering Department, College of Technological Studies, Alrawda, Kuwait

bElectrical Engineering Department, Sophia University, Tokyo, Japan

Published online: 11 Dec 2008.

To cite this article: Nabil A. Ahmed , Masafumi Miyatake & A. K. Al-Othman (2008): Hybrid Solar Photovoltaic/Wind TurbineEnergy Generation System with Voltage-based Maximum Power Point Tracking, Electric Power Components and Systems, 37

43-60

To link to this article: http://dx.doi.org/10.1080/15325000802322012

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to

anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.
http://dx.doi.org/10.1080/15325000802322012http://www.tandfonline.com/page/terms-and-conditionshttp://dx.doi.org/10.1080/15325000802322012http://www.tandfonline.com/loi/uemp20

8/22/2019 15325000802322012.pdf

2/19

Electric Power Componen ts an d S ystems, 37:4360, 2009Copyright Taylor & Francis Group, LLCISSN: 1532-5008 print/1532-5016 onlineDOI: 10.1080/15325000802322012

Hybrid Solar Photovoltaic/Wind Turbine EnergyGeneration System with Voltage-based

Maximum Power Point Tracking

NABIL A. AHMED,1 MASAFUMI MIYATAKE,2 andA. K. AL-OTHMAN1

1Electrical Engineering Department, College of Technological Studies,Alrawda, Kuwait

2Electrical Engineering Department, Sophia University, Tokyo, Japan

Abstract This article proposes a hybrid energy system combining solar photovoltaicand wind turbine as a small-scale alternative source of electrical energy whereconventional generation is not practical. A simple and cost-effective control techniquehas been proposed for maximum power point tracking from the photovoltaic arrayand wind turbine under varying climatic conditions without measuring the irradianceof the photovoltaic or the wind speed. The proposed system is attractive because ofits simplicity, ease of control, and low cost. A complete description of the proposedhybrid system, along with detailed simulation results that ascertain its feasibility, aregiven to demonstrate the availability of the proposed system in this article. Simulation

of the hybrid system under investigation was carried out using PSIM software.

Keywords hybrid energy system, solar photovoltaic, wind turbine, permanent mag-net generator, stand-alone applications, boost DCDC converter, maximum power

point tracking

1. Introduction

Renewable energy from wind turbines (WTs) and solar photovoltaics (PVs) is the mostenvironment-friendly type of energy to use. They have come of age and are a globalphenomenonthe worlds fastest-growing energy resources and a clean and effectivemodern technology that provides a beacon of hope for a future based on sustainable,pollution-free technology. Todays WTs are state-of-the-art modern technologymodularand very quick to install. The importance of utilizing renewable energy systems, includingsolar PV and WT generation systems, has become apparent because electricity demand israpidly growing all over the world. Therefore, there is an urgent need for renewable energyresources, and it has formulated as a national strategy for the development of renewable

energy applications and energy conservation measures. For this purpose, continuousefforts to develop more attractive systems with lower cost, higher performance, and

Received 11 January 2008; accepted 5 June 2008.Address correspondence to A. K. Al-Othman, Electrical Engineering Department, College

of Technological Studies, P.O. Box 33198, Alrawda, 73452, Kuwait. E-mail: [email protected]

43

8/22/2019 15325000802322012.pdf

3/19

44 N. A. Ahmed et al.

multiple functions are required. Sensor-less approaches and combined generators, asexplained in this article, are examples.

Small-scale stand-alone power generation systems are an important alternative sourceof electrical energy because they can be applied in locations where conventional gener-

ation is not practical. Consider, for example, remote villages in developing countries orranches located far away from main power lines. It has been shown that a remote loadonly has to be a few miles away from a main power line for a stand-alone wind generatorto be cost-effective [13].

The certainty of load demands at all times is greatly enhanced by hybrid generationsystems, which use more than one power source. It is possible to achieve much highergenerating capacity factors by combining WT and PV generators with storage technologyto overcome the fluctuations in plant output. An efficient energy storage system is requiredto get constant power, and the electrical energy delivered by the WT and PV has to beeasily converted into storage energy. This conversion might be realized by a batterybank or energy capacitor system (ECS). The battery bank or ECS meets the daily loadfluctuations [4, 5].

In this article a hybrid energy system combining a variable-speed WT and PV arraygenerating system is presented to supply continuous power to the stand-alone load. Thewind and PV are used as main energy sources, while the battery is used as a back-upenergy source. Two individual DCDC boost converters are used to control the powerflow to the load. A simple and cost effective control with a DCDC converter is used formaximum power point tracking (MPPT) and, hence, maximum power extracting fromthe WT and the PV array.

2. Proposed Hybrid Energy System

Figure 1 depicts the topology of a hybrid energy system consisting of a variable-speedWT coupled to a permanent magnet generator (PMG) and PV array. The two energy

Figure 1. Equivalent circuit of proposed hybrid energy system.

8/22/2019 15325000802322012.pdf

4/19

Hybrid Solar Photovoltaic/Wind Turbine Generation 45

sources are connected in parallel to a common DC bus line through their individualDCDC converters. The load may be DC-connected to the DC bus line or may includea pulse width modulated (PWM) voltage source inverter to convert the DC power intoAC at 50 or 60 Hz. The load configuration is beyond the scope of this article.

Each source has its individual control. The diodes, D1 and D2, allow only unidi-rectional current flow from the source to the DC bus line, thus keeping each source fromacting as a load on each other or on the battery. Therefore, in the event of malfunctioningof any of the energy sources, the respective diode will automatically disconnect that sourcefrom the system.

The output of the hybrid generating system goes to the DC bus line to feed theisolating DC load or to the inverter, which converts the DC into AC. A battery chargeris used to keep the battery fully charged at a constant DC bus line voltage. When theoutput of the system is not available, the battery powers the DC load or discharges tothe inverter to power AC loads through a discharge diode, Db. The battery dischargediode Db prevents the battery from being charged when the charger is opened after afull charge. A dump load may be required, if excessive power is still available after fullycharging the battery. As depicted in the system configuration represented in Figure 1,Vdc is set to a fixed DC bus line voltage, and the output DC voltage from each source iscontrolled independently for both generation systems to get MPPT.

3. Solar PV System

The European PV Industry Association reported that the total global PV cell productionworld wide in 2002 was over 560 MW and has been growing about 30% annually inrecent years [6, 7].

The physics of the PV cell is very similar to that of the classical diode with a pnjunction formed by semiconductor material. When the junction absorbs light, the energyof absorbed photon is transferred to the electronproton system of the material, creatingcharge carriers that are separated at the junction. The charge carriers in the junction

region create a potential gradient, get accelerated under the electric field, and circulate ascurrent through an external circuit. The solar cell is the basic building of the PV powersystem, and it produces about 1 W of power. To obtain high power, numerous suchcells are connected in series and parallel circuits on a panel (module). The solar arrayor panel is a group of several modules that are electrically connected in series-parallelcombination to generate the required current and voltage. The electrical characteristicsof the PV module are generally represented by the current versus voltage (I-V) and thepower versus voltage (P-V) curves.

Using the equivalent circuit of the solar cells shown in Figure 2 the radiation-dependent voltage versus current (V-I) characteristic of ns series cell and np parallelmodules can be represented by

V

Dns AkT

q lnnpIsc IC npID

npId

ns

np

IRs ; (1)

where

Isc is the short-circuit current per cell (A),ID is the diode saturation current (A),q is the electron charge (1:6e19 C),k is the Boltzmann constant (1:38e23 J/K),

8/22/2019 15325000802322012.pdf

5/19


Figure 2. Equivalent circuit of PV module.

A is the pn junction material factor,T is the temperature (K), andRs is the series resistance.

For an ELR615 160Z, 750-W, Fuji electric solar panel (Fuji Electric Co. Ltd., Japan)(ns D 3, np D 5), which is used in this work, and neglecting the series and shuntresistances, Eq. (1) can be written as

V D 30:482

ln

5 3:281 IC 3 8:66e5

5 8:66e5: (2)

Figures 3 and 4 show the I-V and P-V characteristics of the used PV module atdifferent solar illumination intensities and the strong non-linearity of the I-V and P-Vcharacteristics of the used solar PV at different insolation levels. The I-V characteristic

Figure 3. I-V characteristics of PV module.

8/22/2019 15325000802322012.pdf

6/19


Figure 4. P-V characteristics of PV module.

of the solar PV decreases gradually as the voltage increases; when the voltage is low, thecurrent is almost constant. The power output of the panel is the product of the voltageand current outputs. The PV module must operate electrically at a certain voltage thatcorresponds to the peak power point under a given operation conditions.

Various techniques of maximum power tracking have been considered in PV powerapplications. Among these, the perturbation and observation (P&O) method, which moves

the operation point toward the maximum power point by periodically increasing ordecreasing the array voltage, is often used in many PV systems. The advantage ofthis method is that it works well when the irradiation does not vary quickly withtime; however, the P&O method fails to quickly track the maximum power points [8].The incremental conductance (IncCond) method is also often used in PV systems. TheIncCond method tracks the maximum power points by comparing the incremental andinstantaneous conductance of the PV array. The IncCond method offers good performanceunder rapidly changing atmospheric conditions [9]. However, the conductance methodhas two divisions, and the structure is similar to the P&O algorithm because the condition,dP=dVD 0, rarely happens.

For most PV modules, the ratio of the voltage at the maximum power point fordifferent insolation levels to the open-circuit voltage (Vmp=Voc ) is approximately constant.Also, the ratio of the current at the maximum power point for different insolation levels

to the short-circuit current (Imp=Isc ) is constant [10, 11]. Figures 5 and 6 indicate thelinear relation Vmp D 0:77 Voc and Imp D 0:89Isc with the computed (almost linear)dependency, shown by signs. Therefore, if an unloaded cell is installed on the arrayand kept in the same environment as the power-producing cells, its open-circuit voltageor short-circuit current are periodically measured. The operating voltage or the currentof the power-producing array are then set to the required values, which correspond tomaximum power as shown in Figures 5 and 6. The MPPT technique proposed in this work

8/22/2019 15325000802322012.pdf

7/19


Figure 5. Vmp and Voc of PV module.

makes use of a predetermined relationship between the operating voltage or current andthe open-circuit voltage/short-circuit current to obtain MPPT at any operating conditions.

Simulation of the PV system under investigation was carried out using PSIM soft-ware [12]. The simulation results of the dynamic performance, which validates theefficient MPPT of PV generation system when the irradiance changes dramatically, arepresented. Figure 7 shows the irradiation, the power and maximum power, PV voltage

Figure 6. Imp and Isc of PV module.

8/22/2019 15325000802322012.pdf

8/19


Figure 7. PV generation system characteristics under MPPT: (a) irradiation, (b) PV-generatedpower and maximum power, (c) PV voltage and reference voltage, and (d) duty cycle.

8/22/2019 15325000802322012.pdf

9/19


and reference voltage, and the PV DCDC boost converter duty cycle, respectively, of thevoltage-based MPPT technique when the irradiation changes dramatically from 1 kW/m2

to 0.25 kW/m2 and again to 1 kW/m2 at a step of 0.25 kW/m2 and at a time stepof 1 sec. The proposed simple MPPT is efficiently able to capture the maximum power

corresponding to each irradiance. The PV-generated power is not constant, and it dependson the irradiance conditions.

4. Wind Energy System

Because wind energy has become the least expensive source of new renewable energy thatis also compatible with environment preservation programs, many countries promote windpower technology by means of national programs and market incentives. The WT capturesthe winds kinetic energy in a rotor consisting of two or more blades mechanically coupledto an electrical generator.

The fundamental equation governing the mechanical power capture of the WT rotorblades, which drives the electrical generator, is given by

P D 12ACpV

3; (3)

where

is the air density (kg/m3),A is the area swept by the rotor blades,V is the velocity of air (m/sec), andCp is the power coefficient of the WT.

The theoretical maximum value of power coefficient Cp is 0.59, and it is oftenexpressed as a function of the rotor tip-speed to wind-speed ratio (TSR). TSR is definedas the linear speed of the rotor to the wind speed,

TSR D !mRV

; (4)

where R and !m are the turbine radius and the angular speed, respectively. In practicaldesigns, the maximum achievable Cp ranges between 0.4 to 0.5 for modern high-speedturbines and between 0.2 to 0.4 for slow-speed turbines. Attaining Cp above 0.4 isconsidered good. Whatever maximum value is attainable with a given WT, it must bemaintained constantly at that value for the efficient capture of maximum wind power. Arelatively small deviation on either side of the TSR will result in a significant reductionof the power available for conversion to electrical energy. Figure 8 exhibits the poor Cpperformance at a different TSR for various types of WTs [13]. Figure 9 illustrates thetypical power coefficient Cp curve for a 503 Series WINDSEEKER (Southwest Wind

Power, USA), which is used for the analysis and simulations discussed in this article.Figure 9 shows that Cp has its maximum value (Cp max) at a certain optimum valueof TSR, called TSRopt. For this case, it is clear that the maximum power captured bythe WT will occur when TSR is approximately 9. The maximum power for differentwind speeds is generated at different rotor speeds. Therefore, the turbine speed shouldbe controlled to follow the ideal TSR with an optimal operating point that is different forevery wind speed. This is achieved by incorporating a speed control in the system design

8/22/2019 15325000802322012.pdf

10/19


Figure 8.Cp vs. TSR for various types of WTs.

to run the rotor at high speed in high wind and at low speed in low wind. Employingcontrol of the rotational speed of the turbine allows the TSR to be controlled and thecoefficient of performance to be maximized. Thus, in turn, the generated electrical energymay be maximized. Unfortunately, accurate wind speed measurement in the rotor of theturbine is difficult and requires the use of a relatively expensive anemometer if it is tobe used for system control. Based on Eq. (4), the optimum speed of the rotor can beestimated as

!opt D TSRoptVR

: (5)

Figure 9. Typical Cp curve used for the analysis and simulation.

8/22/2019 15325000802322012.pdf

11/19


Combining Eqs. (3) and (5), the output torque of the turbine corresponding tomaximum power can be written as

T D1

2

ACp max

!opt R!opt

TSRopt 3: (6)

A typical small-scale stand-alone wind electric system is composed of a variable-speed WT, a PMG, and a diode bridge rectifier. In many small-scale systems, the DCsystem is set at a constant DC voltage and is usually comprised of a battery bankthat allows energy storage, a controller to keep the batteries from overcharging, and aload. The load may be DC or may include an inverter to an AC system. Connectinga wind generator to a constant DC voltage has significant problems due to the poorimpedance matching between the generator and the constant DC voltage (battery), whichwill limit power transfer to the DC system. In response to these problems, researchershave investigated incorporating a DCDC converter in the DC link [14, 15]. Adjustingthe voltage on the DC rectifier will change the generator terminal voltage, therebyproviding control over the current flowing out of the generator. Since the current isproportional to torque, the DCDC converter will provide control over the speed of theturbine. Control of the DCDC converter can be achieved by means of a predeterminedrelationship between rotor speed and rectifier DC voltage to achieve MPPT, or by meansof a predetermined relationship between generator electrical frequency and rectified DCvoltage [16].

4.1. Permanent Magnet Synchronous Generator

An analytical model of a small permanent magnet synchronous machine (PMSM) is usedto investigate the effect of controlling the DC-link voltage on the capture of maximumpower. The model relates the DC-link voltage of the machine to its rotor speed. Itneglects magnetic saturation. The effective air gap in a PMSM with magnets mounted

on the rotor surface can be considered constant and relatively large. This is due to therelative permeability of the permanent magnet material being close to unity. The d- andq-axis synchronous reactances are consequently identical. The generator armature currentcan be related to the torque and induced voltage as follows:

T D KtIa; (7)

E D Ke!m: (8)

Control over the rotor speed can be achieved simply by varying the generator terminalvoltage. The steady-state terminal voltage of the generator can be determined for amachine with negligible saliency and can be expressed as

Va DpE2 .IaXs cos C IaRa sin/2 C IaXs sin IaRa cos: (9)It is assumed that the generator is connected to a diode rectifier and that the phase

voltage and fundamental component of the armature current of the generator are inphase. Then Eq. (9) may be written as

Va DpE2 .Ia!Ls/2 IaRa: (10)

8/22/2019 15325000802322012.pdf

12/19


The rectified DC voltage may be obtained using the standard equations for a three-phase full-bridge diode rectifier and taking the effect of commutation overlap into accountas [17]

Vdc D 3p6Va 2Vdiode 3p

6!LsIa : (11)

Substituting Eqs. (6)(10) into Eq. (11), it is possible to obtain a prediction forrectified DC voltage as a function of the rotor speed (or electrical generated frequency)and TSR. Using the manufacturer-supplied machine constants, the theoretical ideal rela-tionship between DC-link voltage and rotor electrical angular frequency or rotor speed fordifferent wind speeds is obtained and is plotted in Figure 10 for the capture of maximumpower when the generator operates at the peak power coefficient Cp and TSRopt.

It should be mentioned that this is the optimum relationship for this machine togetherwith a turbine having a Cp characteristic similar to that of Figure 9. For different machineand turbine parameters, a similar plot could be obtained. One can see from Figure 10that the optimum rectified DC voltage profile can be simplified by a straight line.

The control relationship between frequency and DC voltage is obtained using simplecalculations without the need for detailed wind speed measurements. System control canbe considered together with Figure 1. The system should measure the frequency of thegenerated voltage (rotor speed) and use that value to control the duty cycle of a DCDCboost converter. The output voltage of the DCDC converter is fixed at a predeterminedvalue; therefore, adjusting the duty cycle will set an optimum value to the rectified DCvoltage based on Figure 10.

In order to better understand the system response to a rapid change in wind speed,consider Eqs. (4)(6) and Figure 10 and the case where the system is operating atTSRopt. A sudden increase in wind speed will decrease both TSR and Cp . According toEq. (6), an increase in the wind speed will result in an increase in the torque transmittedfrom the turbine to the generator. Also, the turbine will try to accelerate in response toan increase in wind speed. An acceleration of the turbine will result in an increase in

rotor speed of the generator, which will, in turn, produce an increase in the commanded

Figure 10. Optimum DC voltage vs. rotor speed characteristic.

8/22/2019 15325000802322012.pdf

13/19


rectified DC voltage, given by the control of Figure 10. (i.e., commanded rectified DCvoltage will increase in response to an increase in wind speed). Increasing the rectifiedDC voltage decreases the difference between the generated voltage and the rectified DCvoltage. Thus, the armature current decreases, which decreases the braking torque. This

will continue until the rotor speed is increased such that torque is balanced. When thewind speed falls rapidly, a sudden decrease in wind speed will result in a high TSR andCp will decrease, decreasing the torque. With low applied torque to the generator, theinductance and inertia of the system will result in a braking torque being applied, slowingthe generator and turbine. The reduction in speed will, of course, lower the commandrectified DC voltage. As the DC voltage falls, the difference between generated voltageand rectified DC voltage will be high, maintaining current flow and applied brakingtorque. This process will continue until the speed is reduced such that the TSR is lowenough that the turbine Cp increases and torque is balanced.

In order to evaluate the dynamic performance of the wind generation system, anexample wind speed variation was developed and is defined as

vw

D9

C j6 sin.4t/

C0:6 sin.36t/

j: (12)

The choice of Eq. (12) allows the investigation of the system response to a fast andcontinuous change in wind speed. The development of the control relationship is basedon the ideal steady-state relationship of the wind speed and rotational (turbine) speedgiven by Eq. (4). In the case where the wind speed is continuously changing, the systeminertia will introduce a time lag between a change in wind speed and a noticeable changein rotational speed. This time lag is neglected in this study.

5. System Control

As shown in Figure 1, the DCDC boost converter divides the system voltage into twolevelsvariable voltage at the output terminal of the energy source, Vi , and fixed DCvoltage at the DC-link, Vo.

The state equations of the DCDC boost converter can be given by Eq. (13), whereS is the switch state that takes the value 1 or 0, Vi is the input voltage to the DCDCconverter (output from each energy source), and Vo is the DC-link output voltage:2

664dvo

dt

diL

dt

3775 D

26641 SC

1RC

01 SL

3775"Vo

iL

#C24 01

L

35 Vi : (13)

In PV and WT systems, the terminal voltage is controlled based on the voltageerror signal. For the PV system, the PV voltage and current are sensed to determinethe reference voltage at which MPPT occurs. The error signal, which is the differencebetween the reference voltage and the actual voltage, of the PV is fed to the voltage

controller to control the duty cycle of the PV boost converter. For the WT, the errorsignal is the difference between the reference rectified voltage of the PMG for MPPTand measured rectified voltage. This error signal is fed to the voltage controller, whichcontrols the duty cycle of the WT boost converter.

Figure 11 shows the configuration of the control topology of the two individual DCDC converters. Since this system cannot allow reverse power flow and because of theconfiguration of DC boost converter, many generating units can be connected in parallel.

8/22/2019 15325000802322012.pdf

14/19


Figure 11. Control principles of DCDC boost converters: (a) MPPT of PV system and (b) MPPTof WT system.

Figure 12 depicts the simulation results of the dynamic performance, which validatesthe efficient MPPT of the WT generation system when the wind speed changes rapidlyand continuously, which illustrates the variation in wind speed, power coefficient Cp,tip-to-speed ratio TSR, rectified DC-link voltage, wind power, wind extracted power, andturbine speed and DCDC converter duty cycle. By controlling the DC-link link voltageaccording to Figure 10, the TSR can be kept closer to the ideal value of 9 and the powercoefficient is almost constant at its maximum value of 0.42. Therefore, the WT-generatedpower increases with wind speed, and the output power from the wind system is notconstant and varies with wind speed.

Simulation of the hybrid system under investigation was carried out using PSIMsoftware, where Figure 13 illustrates the total simulated system. The simulation results ofthe dynamic performance, which validates the efficient MPPT of PV and WT generationsystems when the irradiance and wind speed change dramatically, are presented.

Figure 14 illustrates the total generated power of the hybrid system. The output powerof the hybrid system is mostly fluctuating, and the fluctuation has an effect on systemfrequency. From Figure 14, it is clear that the power fluctuation of the hybrid system isless dependent on the irradiance conditions and wind speed variations as compared to thepower generated of the individual PV and WG systems shown in Figures 7(b) and 12(e).However, this fluctuation must be suppressed. One existing method to solve these issuesis to install batteries that absorb power from the system, as shown in Figure 1. Theother method is to install a dump load, which dissipates fluctuating power. Using thesemethods, the PV/WT hybrid generation system can supply almost good quality power, as

shown in Figure 15, where a battery is used as a storage device. To simplify the analysis,the system ignores the charge and discharge interface for the storage devices, which isnecessary to keep the normal charge or discharge cycle between the storage unit andthe DC-link voltage bus. This means that the storage system is considered as a constantvoltage.

Figure 16 shows the power supplied by the battery. As mentioned above, the chargeand discharge interface for the storage devices are not taken into account. During the

8/22/2019 15325000802322012.pdf

15/19


Figure 12. Wind generation system characteristics under MPPT: (a) irradiation, (b) tip-speed-ratio,(c) power coefficient, (d) DC voltage and reference voltage, (e) wind power and extracted power,(f) turbine speed, and (g) duty cycle. (continued)

8/22/2019 15325000802322012.pdf

16/19


Figure 12. (Continued)

availability of sun and wind, electricity can be supplied to the load and the charger (bi-directional DCDC converter) and regulates the DC-link voltage bus by allowing transferof power in either direction. When sun and wind are not available, the storage systemis fully discharged or discharged to the desired limit, and no power will be delivered

to the load. However, these methods have disadvantagesthey require a storage systemsuch as a battery, which is costly and bulky, and the installation of a dump load isnot an efficient method to dissipate fluctuating power. Moreover, they cannot guaranteecertainty of load demands at all times, especially during poor environmental conditionswhen there is no power from the PV and WG systems. In future work, a new hybridgeneration system will be suggested, which will combine solar PV, WG, and fuel cellgeneration systems.

8/22/2019 15325000802322012.pdf

17/19


Figure 13. Proposed hybrid system simulated model under MPPT control.

Figure 14. Generated power of hybrid system.

8/22/2019 15325000802322012.pdf

18/19


Figure 15. Load power.

Figure 16. Power supplied by battery.

6. Conclusions

This article describes a renewable energy hybrid generation system that combines solarPV and a variable-speed WT. A simple and cost effective MPPT technique is proposedfor the PV and WT without measuring the environmental conditions. This is based oncontrolling the PV terminal voltage or current according to the open-circuit voltage orshort-circuit current, and the control relationship between the turbine speed and therectified DC voltage is obtained using simple calculations. More expensive and complex

control algorithms are not required. A complete description of the hybrid system hasbeen presented along with its detailed simulation results that ascertain its feasibility. Thepower fluctuation of the hybrid system is less dependent on the environmental conditionscompared to the power generated by individual PV and WG systems. In this work, thispower fluctuation has been suppressed using a battery, and it will be the subject offuture work.

8/22/2019 15325000802322012.pdf

19/19


References

1. Kellogg, W. D., Nehrir, M. H., Venkataramanan, G., and Gerez, V., Generation unit sizing andcost analysis for stand-alone wind, photovoltaic, and hybrid wind/PV systems, IEEE Trans.

Energy Convers., Vol. 13, No. 1, pp. 7075, March 1998.2. Valenciaga, F., and Puleston, P. F., Supervisor control for a stand-alone hybrid generation

system using wind and photovoltaic energy, IEEE Trans. Energy Convers., Vol. 20, No. 2,pp. 398405, June 2005.

3. Senjyu, T., Nakaji, T., Uezato, K., and Funabashi, T., A hybrid system using alternative energyfacilities in isolated island, IEEE Trans. Energy Convers., Vol. 20, No. 2, pp. 406414, June2005.

4. Chianng, S. J., Chang, K. T., and Yen, C. Y., Residental photovoltaic energy storage system,Trans. Ind. Elect., Vol. 45, No. 3, pp. 385394, June 1998.

5. Hua, C. C., and Ku, P. K., Implementation of a stand-alone photovoltaic lighting system withMPPT, battery charger and high brightness LEDS, Proceedings of the IEEE Sixth InternationalConference on Power Electronics and Drive Systems, Kuala Lumpur, Malaysia, 28 November1 December 2005.

6. European Photovoltaic Industry Association (EPIA), available at: www.epia.org.7. Jger-Waldau, A., Huld, T. A., ri, M., Cebecauer, T., Dunlop, E. D., and Ossenbrink, H.,

Challenges to realise 1% electricity from photovoltaic solar systems in the European Unionby 2020, 4th World Conference on Photovoltaic Energy Conversion, Waikoloa, HI, 712 May2006.

8. Hua, C., Lin, J., and Shen, C., Implementation of a DSP controlled photovoltaic system withpeak power tracking, IEEE Trans. Ind. Elec., Vol. 45, No. 1, pp. 99107, February 1998.

9. Hussion, K. H., and Zhao, G., Maximum photovoltaic power tracking: An algorithm forrapidly changing atmospheric conditions, Proc. IEE, Vol. 142, No. 1, pp. 5964, 1995.

10. Maoum, M. A. S., Badejani, S. M. M., and Fuchs, E. F., Microprocessor-controlled newclass of optimal battery chargers for photovoltaic applications, IEEE Trans. Energy Convers.,Vol. 19, No. 3, pp. 599606, September 2004.

11. Maoum, M. A. S., Dehbone, H., and Fuchs, E. F., Theoretical and experimental analysesof photovoltaic systems with voltage- and current-bases power-point tracking, IEEE Trans.

Energy Convers., Vol. 17, No. 4, pp. 514522, December 2002.

12. Powersim Technologies, PSIM Version 7.1 for Power Electronics Simulations, User Manual ,Vancouver, Canada: Author, available at: http://www.powersimtech.com.13. Patel, M. R., Wind and Solar Power Systems, Design, Analysis and Operation, 2nd ed., New

York: Taylor & Francis, 2006.14. Yamamura, N., Ishida, M., and Hori, T., A simple wind power generating system with

permanent magnet type synchronous generator, Proc. IEEE Int. Conf. Power Max. Electron.Drive Syst., Vol. 2, pp. 849854, 1999.

15. De Broe, A. M., Drouilhet, S., and Gevorgian, V., A peak power tracker for small wind turbinesin battery charging applications, IEEE Trans. Energy Convers., Vol. 14, No. 4, pp. 16301635,December 1999.

16. Knight, A. M., and Peters, G. E., Simple wind energy controller for an expanded operatingrange, IEEE Trans. Energy Convers., Vol. 20, No. 2, pp. 459466, June 2005.

17. Mohan, N., Undeland, T. M., and Robbins, W. P., Power Electronics, Converts, Applicationsand Design, 2nd ed., New York: Wiley, 1995.

15325000802322012.pdf

Documents