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Micro grid test bed design with renewable energy sources

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Microgrid test-bed design with renewable energy sources
Article · December 2014
DOI: 10.1109/EPEPEMC.2014.6980622
3 authors:
Ersan Kabalcı
Eklas Hossain
Nevşehir Hacı Bektaş Veli University
Oregon Institute of Technology
R. Bayindir
Gazi University
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16th International Power Electronics and Motion Control Conference and Exposition
Antalya, Turkey 21-24 Sept 2014
Microgrid Test-bed Design with Renewable Energy
Ersan Kabalci1 Eklas Hossain2 Ramazan Bayindir3
[email protected]; [email protected]; [email protected]
Nevsehir University, Faculty of Engineering, Department of Electrical & Electronics Engineering, Nevsehir-Turkey
University of Wisconsin-Milwaukee, Department of Mechanical Engineering, Milwaukee, WI-53211, USA
Gazi University, Faculty of Engineering, Department of Electrical & Electronics Engineering, 06500, Ankara-Turkey
Abstract—This paper is dedicated to microgrid design by using
several renewable energy sources (RES) together. The generator
side contains the most widely used three types of RESs that are
wind energy, solar energy, and fuel cells. The wind turbine is
designed according to parameters of a 6.5kW commercial
permanent magnet synchronous generator (PMSG). The solar
plant that has 15kW rated power is constituted with string
connection of 96 solar panels that has 170Wp rated power for
each. The last generator of system is modelled according to
parameters of a fuel cell that generates 10.5kW peak power. All
the generation units are coupled over dc bus-bar by adjusting the
voltages to 48Vdc. The dc loads are directly connected to bus-bar
while the ac loads are supplied by ac bus-bar that is built by a
three-phase 48V/380V-50Hz inverter. An RLC load with
10kW/250VA/250VAR power is connected to the output of
inverter. The proposed test-bed can be improved by adding
several generator and load types, and additional controllers,
breakers, and contactors. In its current state, the proposed testbed is considered as a preliminary design.
Keywords-wind turbine, solar panel, fuel cell, microgrid,
renewable energy.
The renewable energy sources (RES) are one of the most
extensively studied area among power electronics and energy
engineering. Since the limited reserves of fossil based fuels and
increased costs, the researchers and scientists are focused on
alternative energy sources that may tackle the cost and
sustainability problems [1-3]. The distributed generation (DG)
concept enables service providers and consumers to eliminate
the dependency to a uniformed energy generation met in
centralized systems. The DG plants are intended to generate the
energy where it is located at near-site/on-site to consuming
sites. A microgrid consists of several on-site DG sources
together [4-6]. The thermal energy sources can also be
integrated to electrical sources in these improvements. The
actual microgrid studies cover DG planning, power flow
controls, power sharing issues, and grid integration criteria.
There are numerous methods developed to manage the load
sharing, and related communication methods [6]. The control
methods of microgrid are classified as centralized, namely
hierarchical and decentralized regarding to requirements itself.
The decentralized control promotes the distributed control
mechanisms and allows managing the complex infrastructures
by providing autonomous systems. However, it involves
significant coordination among related parts of the entire
system [7]. On the other hand, the hierarchical control is based
on a master-controller that tracks the generating and consuming
parts in terms of real and reactive power flows. The reactive
power of voltage and real power of frequency yields the
required real and reactive power of microgrid. Therefore, the
master controller manages the droop characteristics of
frequency or voltage in order to control the power flow [7,8].
The study proposed in this paper covers a microgrid
improvement with centralized control features for each
generator where the microgrid model consists of a wind
turbine, solar plants, and a fuel cell stack. The powers
generated by the sources are used to form a dc coupling that is
interfaced with a unique inverter instead of configuring ac
coupling. The wind turbine is modeled by using the parameters
of a 6.5kW PMSG in Simulink. The solar plants that provide
15kW total power are configured with serial and parallel
connection of 96 separate solar panels that each generates
170W peak power itself. The wind energy conversion system
(WECS) consists of uncontrolled rectifier and buck converter
to transfer the generated power to dc bus. The solar plants and
fuel cell are connected to dc bus over dc-dc converters since
they do not contain any ac waveform. All the converters are
controlled with PI loops, and maximum power point tracking
(MPPT) algorithm in solar system. The details of entire
microgrid designed are introduced in the following sections
such as the proposed design of microgrid testbed along with the
mathematical model of DGs has illustrated in section II; in
section III, the verification and analyses of designed on-site
generation section will be found and finally this research paper
will be concluded future direction of work in section IV.
The microgrid configurations are based on numerous
sources generating energy that enables to enhancing the energy
efficiency and improving the total yield. The microgrid has a
robust structure depending on the “plug and play”
characteristic of energy sources. This definition stands for the
facility of any source integrated to existing DG system without
requiring any configuration. There are many ways to integrate
different renewable energy generation sources to form a hybrid
system that are dc-coupling, ac-coupling, and hybrid coupling
[1, 9]. The proposed design is based on dc-coupling integration
as shown in Fig.1. The parameters of the generators are given
in Table 1 where the modelling studies of each generation unit
978-1-4799-2060-0/14/$31.00 ©2014 IEEE
PEMC 2014
16th International Power Electronics and Motion Control Conference and Exposition
Antalya, Turkey 21-24 Sept 2014
v= Velocity of wind (m/s)
The efficiency of rotor Cp varies with the tip-speed ratio
(TSR) which defines as follows for a given wind speed,
R= rotor radius,
Ȧ= angular speed (rad/s)
Fig. 1. Schematic diagram of the modelled dc-coupled microgrid.
are introduced in this section. The cut-in speed of wind turbine
is 3m/s while the cut-off speed is 20m/s. The rated power
output is obtained at 9m/s where the rotational speed is around
100 rpm.
Wind Turbine
Generator Type
Nominal Voltage
Nominal Speed
Rated Power
Stator phase resistance
Phase inductance
230 rpm
Solar Panel
Rated Power
Open Circuit Voltage (Voc)
Maximum Power Voltage (Vpm)
Short Circuit Current (Isc)
Maximum Power Current (Ipm)
Number of Series Panel
Number of Parallel Panel
Fuel Cell Stack
DC Voltage at 135A
Cell Count
Maximum Current
Nominal stack efficiency (%)
Fuel composition
blend • 80% H2
A. Wind Turbine and Power System
The output power of wind turbine vary depending on
mechanical parameters as wind speed, air pressure, pitch angle
and coefficient.The mechanical power of wind turbine is
determined using (1);
C p (O , E ) ˜ U ˜ A ˜ v 3
Pm= mechanical output power of wind turbine,
Cp= Coefficient of performance (the rotor efficiency),
Ȝ= Pitch angle (degree),
ȕ= Peak velocity ratio,
ȡ= Air density (kg/m3),
A= Rotor swept area (m2),
PEMC 2014
The PMSG are widely used in small-scale wind turbines
for variable speed configurations [10]. The efficiency that is
one of the most important features of PMSG is provided by its
self-excitation property. It does not require any external
excitation source and the maintenance cost is reduced since
the brushes, slip rings, and rotor windings are removed. The
technical details and equations of PMSG can be found in
textbooks [17]. Therefore, they will not be repeated in this
section. The output current and voltage waveforms supplied
by wind turbine at 6 m/s are shown in Fig.2. The generator
voltage is measured at 116V while the current is around 10A.
B. Solar Panel and Power System
The solar panel model is built in Simulink by using the
analytical equation of a photovoltaic (PV) cell that is shown in
§V I R
I L I Rs ¨ «exp ¨ O o s
· º VO I O RS
¸ 1» Rsh
¹ ¼
in where;
Io: output current of panel,
IL: current generated by irradiation value,
IRs: current of output resistor,
VT: thermal voltage,
Vo: output voltage,
ȘI : diode ideality factor
The electrical power obtained from a PV cell depends on
the short-circuit current (Isc), the ideality factor of diode (ȘI),
the shunt resistance (Rsh), and the series resistance (RS)
parameters [1]. The solar panel module is constituted with
series and parallel connection of PV cells in the required
Fig. 2. Current and voltage waveforms of wind turbine.
16th International Power Electronics and Motion Control Conference and Exposition
Fig. 3. I-V and P characteristics of modelled PV module under various
irradiation conditions, (a) I-V characteristic when irradiation increases from
200 W/m2 to 1000 W/m2, (b) Power characteristic under same conditions.
number where the similar connection of panels are also
performed to design the solar plants that yield 15kW rated
power to microgrid. The verification of a solar panel model is
done by visualizing the current-voltage (I-V) and power
curves according to various irradiation values. The curves has
shown in Fig.3 are obtained by applying irradiation from 200
W/m2 to 1000 W/m2 to solar panel models. The MPPT
algorithm of the solar plant is implemented adding PI control to
conventional perturb&observe algorithm where the response
time is decreased. The MPPT algorithm provides dynamic gate
triggering signal to switch of buck converter that stabilizes the
output voltage to 48V.
C. Fuel Cell Stack and Power System
The fuel cell stack model is designed regarding to
commercial features of a polymer electrolyte membrane
(PEM) fuel cell that has 10.5kW rated power. Differing from
other designs, the fuel cell model is provided by Simulink
libraries where it can be configured according to demanded
parameters. The stack design is modelled with the parameters
shown in Table 1. A PEM fuel cell converts the chemical
energy to electrical energy during an electrochemical reaction
of hydrogen and oxygen. The reaction of anode, cathode, and
total electrical energy generated by a cell are calculated as
shown in (4)-(6) respectively [11-13].
H 2 o 2H 2e ? E 0
2 H 2e o H 2O ? E 0 1.229V
H2 O2
o H 2O ? E 0 1.229V
The configured stack generates 77.6V nominal output
while supplying 135A to the load. The maximum output
values are 100V and 160A for the transient peak times. The
voltage, current, and efficiency curves of the stack are shown
in Fig.4, respectively. The output voltage is applied to a buck
converter that adjusts the dc line voltage owing to its PI
feedback controller.
PEMC 2014
Antalya, Turkey 21-24 Sept 2014
Fig. 4. Waveforms of fuel cell stack.
D. DC-DC Converter and Inverter
The converters utilized in each generating unit are modeled
in buck converter topology that is well established in power
electronics area. The switching signals are updated in each
cycle of feedback comparison and are separately generated at
30 kHz for each converter. The feedback control scheme is
illustrated in Fig.5. The reference voltage of dc line V*dc is set
to 48V and the instant output voltage of Vdc is measured to
compare and minimize the error.
Fig. 5. Basic feedback control scheme of buck converter
The inverter is modelled in full-bridge topology of 3-phase
configuration with MOSFET switches. The modulator is
improved regarding to sinusoidal pulse width modulation
(SPWM) where the detailed information can be found in [3].
The input voltage of inverter is supplied at 48Vdc by dccoupled busbar, and the rms value of output voltage is
obtained around 40Vac. A line transformer that increases the
line voltage to 380Vac at 50Hz line frequency drives the
output of inverter [14-16].
The verification of the modeled microgrid system is
performed by analyzing the generated power and related
waveforms. The output voltages of each generation unit are
shown in Fig.6 respectively to fuel cell stack, solar plants, and
wind turbine where the last [Fig. 4] curve illustrates the
coupled dc busbar voltage. The voltages generated by fuel cell
and solar plants are adjusted to desired dc bus voltage instantly
since they do not involve any mechanical and moving parts
means the response time and time constant of entire system is
tiny. However, the PI controller of wind turbine acts slower
according to others because of mechanic response of wind
turbine retards the PI controller. The busbar voltage that
couples of each generator tolerates the spikes in power level
fluctuations and harmonic noise seen in wind turbine
waveforms in section II, and drives the dc bar of inverter as
most of the resources is intermitting nature.
16th International Power Electronics and Motion Control Conference and Exposition
The switching frequency of inverter is set to 5kHZ by the
SPWM signals that are generated with 0.8 modulation index.
The prescribed operating conditions of inverter converts dc
Antalya, Turkey 21-24 Sept 2014
busbar voltage to 3-phase 40Vac (Fig.7) that is later amplified
to 380V/50Hz sinusoidal voltages. The phase voltages of
inverter are shown in Fig. 8 at 220V.
Fig. 6. Voltage waveforms of each generator and dc busbar.
Fig. 7. Output phase voltages of inverter
Fig. 8. Output phase voltages of line transformer with respect to time in second
PEMC 2014
16th International Power Electronics and Motion Control Conference and Exposition
This study introduces a microgrid testbed design consisting
wind turbine, solar plants, and fuel cell stack. The modeling
and analyses operations are performed in Simulink focusing on
coupling various generators on a dc busbar. Therefore, this
paper is considered to analyze point of common coupling
(PCC) control. There are several points of the design can be
examined in detail according to different aspects of microgrid
requirements. The implemented microgrid testbed will allow to
prospective studies containing communication, voltage and
frequency control, load sharing, and power flow issues.
KabalcÕ E., KabalcÕ Y, “Multi-channel power line communication
system design for hybrid renewables”, 4th International Conference on
Power Engineering, Energy and Electrical Drives, 13-17 May 2013,
Istanbul, Turkey, pp. 563-568.
Colak I., KabalcÕ E., Bal G., “Parallel DC-AC conversion system based
on separate solar farms with MPPT control”, IEEE 8th International
Conference on Power Electronics, May 30-June 3 2011, Jeju Korea, pp.
KabalcÕ E., “Design and analysis of a hybrid renewable energy plant
with solar and wind power”, Energy Conversion and Management, vol.
72, pp. 51–59, August 2013.
Changhee Cho; Jin-Hong Jeon; Jong-Yul Kim; Soonman Kwon;
Kyongyop Park; Sungshin Kim, "Active synchronizing control of a
microgrid," Power Electronics, IEEE Transactions on , vol.26, no.12,
pp.3707,3719, Dec. 2011
Emna Mahersi, Adel Khedher, M.Faouzi Mimouni, “The wind energy
conversion system using PMSG controlled by vector control and SMC
strategies”, International Journal of Renewable Energy Research, Vol.3,
No.1, pp.41-50, 2013.
Majumder, R.; Ghosh, A.; Ledwich, G.; Zare, F., "Power management
and power flow control with back-to-back converters in a utility
connected microgrid," IEEE Transactions on Power Systems, vol.25,
no.2, pp.821,834, May 2010
PEMC 2014
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Antalya, Turkey 21-24 Sept 2014
Khodayar, M.E.; Barati, M.; Shahidehpour, M., "Integration of high
reliability distribution system in microgrid operation," IEEE
Transactions on Smart Grid, vol.3, no.4, pp.1997,2006, Dec. 2012
Poh Chiang Loh; Ding Li; Yi Kang Chai; Blaabjerg, F., "Autonomous
control of interlinking converter with energy storage in hybrid AC–DC
microgrid," IEEE Transactions on Industry Applications, vol.49, no.3,
pp.1374,1382, May-June 2013
Kasem Alaboudy.A.H.; Zeineldin, H.H.; Kirtley, J., "Simple control
strategy for inverter-based distributed generator to enhance microgrid
stability in the presence of induction motor loads," IET Generation,
Transmission & Distribution, vol.7, no.10, pp.1155,1162, October 2013
Carrillo, C.; Diaz-Dorado, E.; Silva-Ucha, M.; Perez-Sabín, F., "Effects
of WECS settings and PMSG parameters in the performance of a small
wind energy generator," Power Electronics Electrical Drives
Automation and Motion (SPEEDAM), 2010 International Symposium on
, vol., no., pp.766,771, 14-16 June 2010
Palma, L.; Enjeti, P.N., "A modular fuel cell, modular DC–DC converter
concept for high performance and enhanced reliability," IEEE
Transactions on Power Electronics, vol.24, no.6, pp.1437,1443, June
Lee, J.-G.; Choe, S.-Y.; Ahn, J.-W.; Baek, S.-H., "Modelling and
simulation of a polymer electrolyte membrane fuel cell system with a
PWM DC/DC converter for stationary applications," IET Power
Electronics, vol.1, no.3, pp.305,317, September 2008.
Song-YulChoe; Jong-Woo Ahn; Jung-Gi Lee; Soo-Hyun Baek,
"Dynamic simulator for a PEM fuel cell system with a PWM DC/DC
converter," IEEE Transactions on Energy Conversion, vol.23, no.2,
pp.669,680, June 2008.
Maity, I.; Rao, S., "Simulation and pricing mechanism analysis of a
solar-powered electrical microgrid," IEEE Systems Journal, vol.4, no.3,
pp.275,284, Sept. 2010
Majumder, R., "A hybrid microgrid with DC connection at back to back
converters," IEEE Transactions on Smart Grid, , vol.5, no.1,
pp.251,259, Jan. 2014
Chen, Chien-Liang; Yubin Wang; Jih-Sheng Lai; Yuang-Shung Lee;
Martin, D., "Design of parallel inverters for smooth mode transfer
microgrid applications," IEEE Transactions on Power Electronics,
vol.25, no.1, pp.6,15, Jan. 2010
von Meier, Alexandra (2006). Electric Power Systems: A Conceptual
Introduction. Hoboken, New Jersey: John Wiley & Sons, Inc. pp. 96–97.
ISBN 978-0-471-17859-0.