system consist renewable energy sources as photovoltaic(PV) system and micro hydro power system with an assumption that the power generated from hydro ...
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
Dynamic modeling and control of a Renewable Hybrid Power System with Fuel Cell System Swati Rawat Department of Electrical and Electronics Engineering DBGI,Saharanpur, India
Shailendra Singh Research Scholar, IIT BHU, Varanasi ,India
Abstract— This paper proposes the frequency control scheme for a hybrid isolated power system with energy storage system which can be used to fulfill load demand at remote areas. This hybrid system consist renewable energy sources as photovoltaic(PV) system and micro hydro power system with an assumption that the power generated from hydro system does not affected from weather conditions. The model of fuel cell system is introduced as energy storing element to improve frequency deviation due to mismatch between power generation and load demand. The proposed system is implemented in MATLAB and tested for various load conditions. Keywords-Fuel cells(FC), electrolyzer, micro hydro plant, Photovoltiac (PV), hydrogen storage. I. INTRODUCTION Energy generation schemes from renewable energy sources such as photovoltaic (PV), micro hydro plants, wind, bio-fuels etc are in trend and popular because of many advantages for example low transmission losses, environment friendly nature and cost effectiveness. For various applications, in the electric power system they are gradually replacing nonrenewable energy sources [1]. The integrated renewable energy system which consist PV, micro hydro and fuel cell system as energy storage system is considered a promising alternative to overcome the intermittent of the RE sources [2].
65
Praval Joshi Department of Electrical and Electronics Engineering GEU,Dehradun,India
Peerzada Ridwan Ul Zaman Department of Electrical and Electronics Engineering GEU,Dehradun,India
Hydrogen is an attractive fuel because it is plentiful and clean [3]. Like in battery storage a fuel cell also have a pair of electrodes and electrolyte. Hydrogen is suitable for seasonal storage application in compare of battery storage which is because of its inherent high mass energy density leakage from storage tank is insignificant. It is easy to install anywhere [4]. The new generation of fuel cells have applications in CHP (combined heat and power) units.[5] Photovoltaic system is the best solution for rural area power supply. Solar light directly converted into electricity using photovoltaic system [6]. The possibility of using an isolated power system including hydro solar/micro hydro power for low-priced electricity production which can satisfy load demand of rural area is discussed in [7]. The research work presents a electric energy efficient operation and management scheme for hydrogen and island electricity generation, with fuel cell and a micro hydro power in [8]. The installation, design and practical operation of the earliest micro hydro power system in Taiwan by researchers [9].The dynamic performance of a Photovoltaic (PV) system with micro hydro power system presented in [10]. The necessary function of an electrical power system is to meet the energy demand of consumers. The main reason of energy crisis in power sector is load mismatch. As variation in load demand there is variation in frequency. Energy storage system provides transient stability during load variation [11-12].
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
Therefore we proposed a hybrid renewable power system with FC (Fuel cell system) which is useful to control frequency deviation with respect to change in load. Hydrogen produced from electrolyzer used as fuel for fuel cell. This process is according to operational strategy of monitoring system.PEM (photon exchange membrane) fuel cell is used as energy storage system. II. FUEL CELL SYSTEM Basic concept of fuel cell is based on energy conversion principle that is energy can be converted one form to another form. Following that principle a fuel cell is an electrochemical device that converts chemical energy into electrical energy. Like in battery storage a fuel cell also have a pair of electrodes and electrolyte. As in case of battery, there is a need to recharge the battery. In case of fuel cell, the species consumed during the electrochemical reactions are continuously replenished so that there is never a need to recharge the cell. The basic requirement of a fuel cell is anode channel, cathode channel, electrolyte, fuel oxidant. Usually air is used as oxidant and hydrogen as a fuel. Working procedure of fuel cell having as fuel is supplied to fuel cell anode where fuel is oxidized that reaction producing electrons. These electrons travel through external circuit. At the cathode, the oxidant is reduced due to consuming the electrons, which are coming from external circuit. Ions travel through the electrolyte to balance the flow of electrons through the external circuit. The anode and cathode reactions and the composition and direction flow of the mobile ion vary with type of fuel cell. A single fuel cell will produce less than one volt of electrical potential. To produce higher voltages, fuel cells are stacked on top of each other and connected in series. A. Application of Fuel Cell System: 1. Portable power- Power for camping and recreational vehicles, electronic devices such as
66
computers and cellular phones, and power for soldiers deployed in the field. Fuel cells based on DMFC technology or PEMFC technology are well suited for many of these applications. 2. Transportation - The major driving force behind recent interest in fuel cell technology is the potential for using fuel cells in transportation applications including personal vehicles. 3. Stationary power- on site power generations, distributed generations, also used in grid connected system. 4. Thermal energy–-Thermal energy for water heating and for supplementing a heat pump. B. Mathematical Modeling Of Fuel Cell System: ΔP ηE × E HHV S ΔP 1 ΔVFC = × FC HHVη FC S ΔVE =
VH =VH(initial) +ΔVE -ΔVFC
Power generated by fuel cell
Power consumed by electrolyzer ELECTROLYZER
FUEL CELL
ΔVE
HYDROGEN STORAGE ΔVFC
Figure1.Operation of fuel cell system connected to hybrid power system Where ∆VE=Net change in H2 volume due to processing of electrolyzer, ∆VFC=Change in H2 volume due to process of fuel cell, ∆PFC= Change in fuel cell power ∆PE= Change in power consumption by electrolyzer, VH= Net H2 volume stored in tank, ηE= Efficiency of electrolyzer, ηFC =Efficiency of fuel cell, HHV=Higher heating value of H2. C. Electrolyzer:
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
The function of electrolyzer is splitting water into H2 and O2 by supply of direct current to its electrodes. A small fraction of the H2 production comes from the electrolysis. Now a day it is significantly cheaper to produce H2 from hydrocarbons. Net reaction for splitting of water is: H2+1/2O2=H2O (4) When alkaline electrodes are used in electrolyzer, that is called alkaline electrolyzer. Conventionally alkaline electrolyzers are used for constant H2 production rates. For variable rate of H2 production proton exchange membrane (PEM) electrolyzer is uses. PEM electrolyzer have simpler process layout. There is no circulating liquid electrolyte. That’s why this electrolyzer is easier to operate and providing quick start up. Its power density is high. The efficiency of PEM electrolyzers have less than other electrolyzers. PEM fuel cell is now their low operating life span systems which is main drawback of such type of energy storage system. D .Hydrogen Storage System: Hydrogen is stored as compressed gas, in solids (metal hydrides, carbon materials) which is produced by electrolyzer for wide area stationary storage; compressed air storage is suitable method which is obtained by the use of piston compressors or centrifugal compressors. III. MICRO HYDRO POWER SYSTEM Flowing and falling water have potential energy. Hydropower comes from converting energy in flowing water by means of a water wheel or through a turbine into useful mechanical power. This power is converted into electricity using an electric generator or is used directly to run milling machines. A micro-hydropower system is generally classified as having a generating capacity of less than 100 kW. Systems that have an installation capacity of between 100 kW and 1000 kW (1.0 MW) are referred to as minihydro.
67
Micro-hydro power is the small-scale harnessing of energy from falling water; for example, harnessing enough water from a local river to power a small factory or village. A. Application of Micro Hydro Power System: Micro hydro plants in remote hilly are being installed to supply power to remote villages. 1. It provide electricity for lighting and appliances (fan, radio, TV, computer, etc), in homes and public buildings such as schools and clinics. 2. Electrical or mechanical power for local service and cottage industries provided by micro hydro system 3. Electrical or mechanical power supplied for agricultural value-adding industries and labor saving activities 4. Electricity for lighting and general uses in public places and for events supplied by it. The electricity provided is in the form of 415/240-volt AC line connections to users, with 11 kV sub transmission, if required. B. Modeling of Micro Hydro Plant: TABLE.1 PARAMETERS AND RATINGS MICRO HYDRO POWER SYSTEM Turbine Francis Selected design Head
28 m.
Rated Capacity
40-110%
Rated Power
100Kw
FOR
PR =QR 9.8HηT ηG
(5) Where PR=Rated power of Generator (KW), QR=Rated capacity in % (discharge), ηT= % Efficiency of Turbine, ηG =% Efficiency of generator.
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
IV. PV SYSTEM A photovoltaic system makes use of one or more solar panel. It consists of various components which include the photovoltaic modules, mechanical and electrical connections and mountings and means of regulating and/or modifying the electrical output. A. Solar Cell The basic ingredients of PV cells are semiconductor materials, such as silicon. For solar cells, a thin semiconductor wafer creates an electric field, on one side positive and negative on the other. When light energy hits the solar cell, electrons are knocked loose from the atoms in the semiconductor material. When electrical conductors are connected to the positive and negative sides an electrical circuit is formed and electrons are captured in the form of an electric current that is, electricity. This electricity is used to power a load. A PV cell can either be circular or square in construction.
𝐼𝑅 = 𝐼𝑅,𝑟𝑒𝑓 1
𝑇 𝑇 𝑟𝑒𝑓
𝑇 /𝑘𝐴
3 𝐴
exp qEg 1 𝑇 − 𝑟𝑒𝑓 (8)
𝐼𝑅,𝑟𝑒𝑓 = 𝐼𝑠𝑐 ,𝑟𝑒𝑓
𝑉𝑜𝑐 ,𝑟𝑒𝑓
𝑒𝑥𝑝
𝐴𝑉𝑖 − 1
(9)
Where: ―Voc, ref ‖ is solar cell open circuit voltage at reference condition; ― Eg ‖ is bandgap energy in the solar cell, (1.12-1.15eV). Modified voltage-current characteristic equation of solar cell is given as: 𝑉+𝐼𝑅𝑆𝑒 𝑉+𝐼𝑅𝑆𝑒 𝐼 = 𝐼𝐿 − 𝐼𝑅 exp – 1 − (10) 𝐴𝑉 𝑅 𝑖
𝑆ℎ
Figure 2.Equivalent circuit diagram of PV model
C.Module B. Modeling of Solar Cell Because of the low voltage generation in a PV Current source in parallel with a diode is the cell (around 0.5V), several PV cells are simplest equivalent circuit of a solar cell. The connected in series (for high voltage) and in output of the current source depends to the light parallel (for high current) to form a PV module falling on the cell. The diode determines the Ifor desired output. Usually there are of 36 or 72 V characteristics of the cell. cells in general PV modules. Equation of ideal solar cell (6) which represents Current-voltage characteristic equation of the ideal solar cell model is: equivalent circuit for a PV module arranged in 𝑉 𝐼 = 𝐼𝐿 − 𝐼𝑅 exp 𝐴𝑉 – 1 (6) series N and parallel N can be described as: s p 𝑖 𝑉 𝑀 𝑁𝑠 + 𝐼 𝑀 𝑁𝑠 Where: 𝑀 𝐼 = 𝑁𝑝 𝐼𝐿 − 𝑁𝑝 𝐼𝑅 exp − 𝐴𝑉 𝑖 ―IL ‖ is photocurrent (A); ―IR ‖ is reverse 𝑁𝑝 𝑁𝑠 𝑉 𝑀 + 𝐼 𝑀 𝑅𝑆𝑒 saturation current(A); (11) 𝑅𝑆ℎ ―V” is diode voltage (V); “Vi” is thermal ― Np ‖ is cells parallel number; ― Ns ‖ is cells voltage, ―A‖ is diode ideality factor. series number. The photocurrent (IL) in (7) depends on solar 10 irradiance intensity and temperature which is 8 described as: 𝜆 6 𝐼𝐿 = 𝜆 𝐼𝑠𝑐 ,𝑟𝑒𝑓 + 𝜇𝐼𝑠𝑐 𝑇 − 𝑇𝑟𝑒𝑓 (7) 𝑟𝑒𝑓
Where: ―Isc,ref‖ is solar cell short –circuit current at reference condition. ―μIsc‖ is the solar cell short-circuit temperature coefficient. On the other hand, the cell’s reverse saturation current is described as:
68
PV module current (A)
1 KW / m2
.75 KW / m 2
.5 KW / m 2
.25 KW / m 2
4 2 0 0
5
10
15 20 25 PV module voltage (V)
30
35
40
Figure 3.VI characteristics of solar module
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
250
PV module Power (W)
1 KW / m 2
200
.75 KW / m 2 .5
150
KW / m 2
.25 KW / m 2
100 50 0 0
10
20 PV module voltage (V)
30
40
Figure 4.PV characteristics of solar module V. SYSTEM MODEL Consider a plant (fig 5), which has connected to a remote area power system. Plant having Micro hydro, PV power, fuel cell system, electrolyzer and a hydrogen storage facility has connected to power system which is connected to a variable loads. Plant output is mainly energy source for electricity and heat, as well as for spitting water into hydrogen and oxygen in the electrolyzer. H2 stored in hydrogen storage system, which consists of all equipment, which converts the hydrogen in volume format to, stored in storage tank. H2 has used as input to fuel cell system. In electrolyzer dc supply is required as input which supplied by power system by using ac-dc converter. There is another byproduct is produced by electrolyzer that is oxygen which stored in oxygen storage system. Fuel cell system, which consist fuel cell and dc-ac converter converts fuel cell dc output to ac power, which has supplied to power system. Fuel cell is producing heat energy, this has supplied to heat load. PV Generator
Micro Hydro Power Plant
6. A block diagram describes the modeling of the hybrid power system containing PV, MHP, FC, AE and hydrogen storage system. Power converters are properly operated at their suitable locations. Block diagram presents the mathematical analysis of each block separately. Change in total generated power can be determined as∆PT = ∆PV + ∆PFC + ∆PMHP − ∆PE
(12)
Where ∆PV, ∆PFC, ∆PMHP, ∆PE are the change in- PV generation, fuel cell power, micro hydro power generation and power consumption by the electrolyzer in per units Control strategy has determined by the difference between power demand ∆PD and change in total generation ∆PT. ∆PS = ∆PT − ∆PD (13) Where ∆PS is net change in power.
Figure 6.Mathematical block diagram of model
Remote area power supply UTILITY POINT
The system frequency variation calculated by𝐾 ∆𝐹 = 1+𝑇𝑃𝑆 ∆𝑃𝑆
∆F
is
𝑃𝑆
FUEL CELL
ELECTROLYZER
OXYGEN STORAGE SYSTEM
HEAT LOAD
HYDROGEN STORAGE SYSTEM
Figure5.Schematic diagram of a hybrid model A. Mathematical Model
A mathematical model of hybrid power generation system has been presented in figure
69
(14)
There is an inbuilt time delay between system frequencies .The transfer function for system frequency deviation to per unit power deviation can be represented as: 1 ΔF = D+sM . Δ𝑃𝑆 (15) D=
1
K PS
, M=
T PS
K PS
Where M and D are, the equivalent inertia constant and a damping constant in per unit of
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
the hybrid power system.1 MW power TABLE 2 generation has been considered as base value PARAMETER AND RATING OF THE for the whole system. HYBRID POWER SYSTEM a) Transfer Function Equation of Fuel KFC= 0.1, and Fuel cells power =10 KW, MHP CellsTFC = 0.03s Power = 100KW, The transfer function for system frequency PVPower=200KW,Electrolyzer variation to per unit fuel cell power is Power= 10KW expressed by KE=0.1,andTE H2 max. volume = 5000Nm3, H2 K FC min. volume = 600 Nm3, Intial ∆PFC = 1+sT . ∆F (16) = 0.05s FC H2 vol.= 3000Nm3 b) Transfer Function Equation of M = 0.2, and ηE = 85%, ηFC = 50% , HHV ElectrolyzerD = 0.04 =3.509 Kwh/Nm3 A part of the generated power is sent to the electrolyzer to produce available hydrogen for the fuel cell. The transfer function of the electrolyzer is expressed byKE ∆PE = 1+sT . ∆F E
Start
PV POWER
)
Change in load demand
MICRO HYDRO POWER
Power system ΔF YES
VI.OPERATION STRATEGY
If ΔF>0 NO
Operation of plant model can be represented by a flow diagram shown in fig 7.Frequency of power system is reciprocal to load demand. For stability of system, frequency variation should be zero. In order to obtain constant grid frequency, there should be no mismatch between load demand and power supply. The operation of plant is based on this principle. Fuel cell system supplies power to power system when frequency variation is negative. Fuel cell compares its hydrogen volume of tank before operating. If it is less than its maximum volume, then electrolyzer will run and produce H2 and O2 that is stored in their tanks. This H2 is used in fuel cell. It produces power only of volume of hydrogen present in it exceeds minimum volume limit. Fuel cell does not supply the power and thereby the total generated power reduces, when frequency variation is positive. Before running the electrolyzer, hydrogen volume of tank has compared to its maximum hydrogen volume and then excess power will supply to electrolyzer. If hydrogen volume is at maximum level in electrolyzer it will not work.
70
YES YES
NO
If ΔF=0
Vh < Vh max
NO Vh > Vh min
YES NO
STANDSTILL CONDITION
ELECTROLYZER
YES FUEL CELL SYSTEM
HYDROGEN STORAGE SYSTEM
Figure 7 .Illustration of the operation strategy VII.SIMULATION RESULTS & ANALYSIS Simulation of system models has been carried out in two cases as without fuel cell and with fuel cell for real time 24 hour simulation of the system model with random variation in load demand. In time, domain simulation both topologies are analyzed System model simulated using MATLAB / Simulink software. In this case, system model has simulated for 24 hours with variable load demand in this section time domain, simulation has done and the results have to analyze. For the purpose of calculation, all input and output quantities in the plots have considered in per unit (p.u.), responses of the hybrid system shown by time simulation are in per unit.
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
A. Simulation Results of Micro Hydro Power System Model 0.09 0.08 0.07 0.06 0.05
0.01
0.04 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (Hrs)
Figure8 .Variation in Micro Hydro Power 40
Temperature ( 0C)
38 36 34
Variation in fuel cell power(p.u.)
Variation in Micro Hydro Power (p.u)
0.1
supply should be increase to balance the frequency variation. Micro hydro system and PV system supplying energy to power system. Due to decrease in system frequency, fuel cell power can be increase to supply power to the hybrid system, up to its rated capacity and increase the production power. 0.008
0.006
0.004
0.002
32 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
30
Time (Hrs)
28
Figure12.Variation in fuel cell power
26 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hour)
Variation in PV power (p.u)
0.05
0.04
0.03
0.02
0.01
0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (Hours)
Figure10 .Variation in PV power Simulation results may observe in two cases. In first case when load demand increases, fuel cell is used to supply power to the hybrid system to control frequency fluctuation .In second case load demand decreases, electrolyzer works to avoid frequency variation. 0.15
Variation in Load Demand (p.u)
0.14 0.13
C.CASE 2 Decrease in Load Demand As changes in load decreases change in frequency increases, so production of supply power should be, decrease to maintain the frequency variation. Due to increase in frequency Micro hydro power has decreased, to reduce the generation power. Due to variation infrequency, net change in Micro hydro power shown in Figure 8. 51
With FC system Without FCsystem
Variation in Frequency(Hz)
Figure 9 .Variation of temperature
50.5
50
49.5
49
48.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
0.12
Time (Hrs)
0.11
Figure13 .Variation in frequency The frequency dip is much more without using fuel cell system at peak load demand as shown in figure 13.
0.1 0.09 0.08 0.07 0.06 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (Hrs)
Figure11 .Variation in load demand B.CASE 1 Increase in Load Demand As change in load demand increases change in frequency decreases so production of power
71
VIII.CONCLUSION The system frequency deviation can also be properly controlled to be within a very small range. Impact of Fuel cell system with PV, Micro hydro on power system has been
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
International Journal of Electronics, Electrical and Computational System IJEECS ISSN 2348-117X Volume 4, Special Issue February 2015
presented. Result of simulation indicates that a combination of fuel cells, PV, micro hydro gives better response in controlling frequency deviation in comparison to only PV and micro hydro system. Additionally, the operation of electrolyzer results in the considerable fuel saving of hydrogen as the volume of hydrogen is replenished in the storage tank. At the same time, frequency raised due fall in demand is also controlled by the operation of the electrolyzer. This flexible model of operation of fuel cell along with electrolyzer would be extremely useful for hybrid systems having micro hydro and solar component.
[1]
[2]
[3]
[4]
[5]
[6]
REFERENCES C.j. Hatziadoniu, A. A. Lobo, F. Pourboghrat, M. Daneshdoost, ―A Simplified Dynamic model of GridConnected Fuel-Cell Generators‖, IEEE Transactions On Power Delivery, vol.17, no.2, pp. 467-473, April 2002. Chen Qi, Zhu Ming, ―Photovoltaic Module Simulink Model for a Stand-alone PVSystem‖, Science Direct International Conference on Applied Physics and Industrial Engineering, Physics Procdia 29, pp. 94-100, 2012. Dong-Jing Lee and Li Wang, ―Small-signal stability analysis of an autonomous hybrid renewable energy power generation/energy storage system‖, Part I: Time-domain Simulations‖, IEEE Transactions On. Energy Conversion, vol.32, no.1, pp. 311– 320, 2008. http:// www.solarelectricsupply.com /pdf/sharp/SESG-216U1F.pdf. I.J. Nagrath, D.P. Kothari, Power system engineering, Tata McGraw-Hill, 2008. M. A. Langhton, ―fuel cells”, IET Journal and magazine, vol. 11, pp. 7-16, February2002.
72
[7]
[8]
[9]
[10]
[11]
[12]
Michael W. Ellis, Michael R. Von Spakovsky, and Douglas J.Nelson, ―Fuel Cell Systems: Efficient, Flexible Energy Conversion for the 21st Century‖, Proceedings of the IEEE, Vol. 8, No.12, pp.1808-08, December 2001. NishadMendis, kashem M. Muttaqi. Saad Sayeef, Sarath Perera, ―Hybrid Operation of Wind- diesel-Fuel Cell Remote Area Power Supply System‖, IEEE ICSET 2010, Kandy Shri Lanka, 6-9 December 2010. Singh, S.; Singh, A.K.; Chanana, S., "Operation and control of a hybrid photovoltaic-diesel-fuel cell system connected to micro-grid," Power India Conference, 2012 IEEE Fifth , vol., no., pp.1,6, 19-22 Dec. 2012 Ray, P.K.; Mohanty, S.R.; Kishor, N., "Dynamic modeling and control of renewable energy based hybrid system for large band wind speed variation," Innovative Smart Grid Technologies Conference Europe (ISGT Europe), 2010 IEEE PES , vol., no., pp.1,6, 11-13 Oct. 2010. P.K.Ray, S.R. Mohanty,NandKishor, ―Frequency Regulation of hybrid renewable Energy System for large Band Wind Speed Variation‖, Third IEEE International Conference on Power Systems, Kharagpur, INDIA December 27-29, 2009. Wandhare, R.G.; Thale, S.; Agarwal, V., "Reconfigurable hierarchical control of a microgrid developed with PV, wind, microhydro, fuel cell and ultracapacitor," Applied Power Electronics Conference and Exposition (APEC), 2013 Twenty-Eighth Annual IEEE , vol., no., pp.2799,2806, 17-21 March 2013.
Swati Rawat, Shailendra Singh, Praval Joshi, Peerzada Ridwan Ul Zaman
