Low Carbon Economy, 2010, 1, 29-38
doi:10.4236/lce.2010.11005 Published Online September 2010 (http://www.SciRP.org/journal/lce)
1
Effect of Wind Generation System Rating on
Transient Dynamic Performance of the Micro-Grid
during Islanding Mode
Rashad M. Kamel, Aymen Chaouachi, Ken Nagasaka
Environmental Energy Engineering, Department of Electronics & Information Engineering, Tokyo University of Agriculture and
Technology, Tokyo, Japan.
Received August 3rd, 2010; revised October 8th, 2010; accepted October 11th, 2010.
ABSTRACT
Recently, several types of distributed generations (DGs) are connected together and form a small power system called
Micro Grid (MG). This paper developed a complete model which can simulate in details the transient dynamic per-
formance of the MG during and subsequent to islanding process. All MG’s components are modeled in detail. The de-
veloped model is used to investigate how the transient dynamic performance of the MG will affected by increasing the
rating of wind generation system installed in the MG. Two cases are studied; the first case investigates the dynamic
performance of the MG equipped with 10 kW fixed speed wind generation system. The second studied case indicates
how the dynamic performance of the MG will be affected if the wind generation system rating increases to 30 kW. The
results showed that increasing of wind generation rating on the MG causes more voltage drops and more frequency
fluctuations due to the fluctuation of wind speed. Increasing voltage drops because wind turbine generator is a squirrel
cage induction generator and absorbs more reactive power when the generated active power increases. The frequency
fluctuations due to power fluctuations of wind turbine as results of wind speed variations. The results proved that when
the MG equipped with large wind generation system, high amount of reactive power must be injected in the system to
keep its stability. The developed model was built in Matlab® Simulink® environment.
Keywords: MG, Distributed Generators, Wind Power Rating and Dynamic Performance
1. Introduction
Recent technological developments in micro generation
domain, necessity of reducing CO2 emissions in the elec-
tricity generation field, and electricity business restruct-
ing are the main factors responsible for the growing in-
terest in the use of micro generation [1,2]. In fact the
connection of small generation units—the micro sources
(MS), with power rating less than a few tens of kilowatts—
to low voltage (LV) networks potentially increases the
reliability to final consumers and brings additional bene-
fits for global system operation and planning, namely,
regarding investment reduction for future grid reinforce-
ment and expansion [3].
In this context, a MG can be defined as a LV network
(e.g. a small urban area, a shopping center, or an indus-
trial park) plus its loads and several small modular gen-
eration systems connected to it, providing both power
and heat to local loads [combined heat and power (CHP)]
[3]. The MG is intended to operate in the following two
different operating conditions:
 Normal Interconnected Mode: MG is connected to
a main grid (distribution network), either being supplied
by it or injecting some mount of power into the main sys-
tem.
 Emergency Mode: MG operates autonomously, in a
similar way to physical islands, when the disconnection
from the upstream distribution network occurs.
The development of MGs can contribute to the reduc-
tion of emissions and the mitigation of climate changes.
This is because available and currently developing tech-
nologies for distributed generation units are based on re-
newable sources and micro sources that are characterized
by very low emissions [4]. The new micro sources tech-
nologies (e.g. micro gas turbine, fuel cells, photovoltaic
panels and several kinds of wind turbines) used in MG
are not suitable for supplying energy to the MG directly

30 Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode
[3]. They have to be interfaced with the MG through an
inverter stage. Thus, the use of power electronic inter-
faces in the MG leads to a series of challenges in the de-
sign and operation of the MG [5]. Technical challenges
associated with the operation and control of MG are im-
mense. Ensuring stable operation during network distur-
bances, maintaining stability and power quality in the
islanding mode of operation requires the development of
sophisticated control strategies for MG’s inverters in or-
der to provide stable frequency and voltage in the pres-
ence of arbitrarily varying loads. This paper’s objective
is to demonstrate the transient dynamic performance of
the MG during and subsequent to islanding process and
how it will affected with increasing the wind power rat-
ing installed in the MG.
Reference [6] discusses MG autonomous operation du-
ring and subsequent to islanding process but the renew-
able micro sources not included, also, this reference used
PSCAD/EMTDC package for analysis. In references [7]
and [8] a control scheme based on droop concepts to op-
erate inverter feeding a standalone AC system is dis-
cussed. References [9] and [10] discuss the behavior of
distributed generators (DGs) connected to distribution
network, however, the dynamics of the primary energy
sources has not been considered, not allowing obtaining
the full picture of the MG long-term dynamic behavior,
which is largely influenced by the micro sources dynamic.
This paper developed a complete model to simulate
the dynamic performance of the MG. All MG’s compo-
nents are modeled in details. The developed model is a
general and can be used to study any disturbance which
may occur in the MG. Effect of increasing wind power
rating is investigated. Two cases are studied; the first ca-
se is studying the transient dynamic performance of the
MG equipped with 10 kW fixed speed wind generation
system. The second case is how the dynamic perform-
ance of the MG will affect when the wind generation sys-
tem is increased to 30 kW. The developed model was
built in Matlab® Simulink® environment.
To conduct the proposed studies, single line diagram
of the studied MG is presented in Section 2. Section 3
gives a brief description of all MG’s components devel-
oped models. Section 4 presents a description of the com-
plete model with the applied controls. Two studied cases
with results and discussions are explained in Section 5.
Conclusions are presented in Section 6.
2. Single Line Diagram of the Studied
Micro-Grid
Figure 1 shows single line diagram of the studied MG.
It consists of 7 buses. Flywheel is connected to bus # 1.
Wind generation system is connected to bus # 2. Two
Figure 1. Single line diagram of the studied MG.
photovoltaic panels with rating 10 kW and 3 kW are
connected to buses 4 and 5, respectively. Single shaft
micro turbine (SSMT) with rating 22 kW is connected to
bus # 6. Bus 7 is provided with 22 kW solid oxide fuel
cell (SOFC). The values loads and line parameters of the
MG are available in reference [11].
3. Description of Microgrid Individual
Components Models
3.1. Inverter Models
Inverters play a vital role in the system which interfaces
of the micro sources with the AC power system. Two
control models of the inverter which used to interface
micro sources to the MG are developed. The configura-
tion of the basic inverter interfaced micro sources is sho-
wn in Figure 2.
The inverter controls both the magnitude and phase
angle of its output voltage (V in Figure 2). The vector
relationship between the inverter voltage (V) and the lo-
cal MG voltage (E in Figure 2) along with the inductor’s
reactance determines the flow of active and reactive
powers from the micro source to the MG [12]. The cor-
responding mathematical relations for P (active power)
and Q (reactive power) magnitudes are given by the fol-
lowing equations:
sin ()
VE
VE
PL



 (1)
2
cos ()
VE
VVE
QLL



  (2)
From Equation (1) and Equation (2), the control of ac-

Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode31
V
V

 E
 E
Figure 2. Basic inverter interfaced micro source.
tive and reactive powers flow reduces to the control of
power angle and the inverter’s voltage level, respectively.
P is the active (real) power (Watts) generated by micro
sources (Flywheel, wind generator, fuel cell, micro tur-
bine and photovoltaic panels). Frequency control depends
on the amount of active power (P) in the Micro Grid. If P
generated by micro sources is higher than P consumed by
loads, frequency increase than its nominal value and vice
versa.
On the other hand, Q is the reactive power (its unit is
Volt Ampere Reactive VAR). The value of the reactive
power can be controlled by controlling inverters which
interface micro sources with the Micro Grid (MG). Vol-
tage is controlled by controlling amount of reactive power
generated in the MG.
3.1.1. Inverter Model with PQ Controller Scheme
The basic structure of inverter PQ controller is shown in
Figure 3 [8].
Active and reactive powers can be controlled indepen-
dently to a good extent, then as shown in Figure 3, two
Proportional Integral (PI) controllers would suffice to
control the flow of active and reactive powers by gener-
ating the proper values of voltage magnitude (V) and
phase angle (δV) based on the instantaneous values of
voltages and currents which are measured from local MG
voltage (Ebus). If the inverter switching details are ig-
nored, the control system will be simplified to the con-
figuration shown in Figure 4 [12].
Inverter PQ model is suitable for interfacing single
shaft micro turbine, solid oxide fuel cell and photovoltaic
panels. Figure 5 shows the terminal block diagram of the
PQ inverter developed model. The input terminals are
active and reactive powers produced by the micro source,
while the output terminals are the three phase terminals
connected to the MG.
3.1.2. Inverter Model with Vf Controller
In order to develop a model for voltage-frequency con-
trolled inverter, two control loops are needed. Frequency
controller is a proportional integral (PI) controller which
is driven by the frequency deviation. As shown in Figure
6(a), frequency of the system can be measured by a pha-
se locked loop (PLL), and in order to get a better perfor-
mance, a feed-forward controller can be implemented. To
V
V


E
E


Figure 3. Basic structure of the inverter PQ control scheme.
V
V


E
E  
Figure 4. Simplified inverter PQ control scheme.
Qout
Q
Pout
Pr e f
Qr e f
Pout
Qout
Va
Vb
Vc
PQ Inverter
P
A
B
C
a
b
c
Outp u t
of PQ
Figure 5. Inverter PQ control model.
regulate the voltage, the set point (reference voltage Eref)
is compared with the measured voltage (MG voltage E)
and a PI controller is responsible to generate the adequate
voltage magnitude V as shown in Figure 6(b) [12]. Vf
mode is the model which keep the voltage at constant
value and return the frequency to its nominal after dis-
turbance occurring by controlling the amount of the ac-
tive power injected in the MG. Vf inverter is used to in-
terface the flywheel to the MG and represents the refer-
ence bus (slack bus) of the MG during and subsequent to
islanding occurrence as shown in Figure 7.
3.2. Micro Sources Models
Detailed standalone models for micro turbine, fuel cell,
wind generation system and photovoltaic panels are de-
veloped. Those models are briefly described as follows:
E
∠
E
δ V∠V

V∠V

V∠V

E
E
δ∠

32 Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode
Figure 6. Inverter Vf control scheme.
50
f0
f
fo
Er e f
f
Vout
Va
Vb
Vc
Vf Inverter (VSI)
V
A
B
C
a
b
c
Output
of Vf
Vout
Figure 7. Vf controlled inverter.
3.2.1. Single Shaft Micro Turbine Model (SSMT)
References [13-16] describe in details the mathematical
model of single shaft and split-shaft micro turbine. The
mathematical model is simulated in Matlab® Simulink®
environment and the model is shown in Figure 8(a). In-
put terminal is Pref which represent the desired power.
The output terminal is Pe (electrical power output from
synchronous generator which coupled with micro turbine).
Pe is connected to P input terminal of the PQ inverter.
Load connected to the synchronous generator is a virtual
resistive load because in Matlab® Simulink® the syn-
chronous generator model must always connected to ex-
ternal load.
3.2.2. Solid Oxide Fuel Cell (SOFC) Model
Detailed mathematical model of solid oxide fuel cell (S-
OFC) is discussed by references [13,14,17]. This model
is simulated using Matlab® Simulink® and model block
diagram is shown in Figure 8(b). Input terminals are Pref
(desired power) and rated voltage of fuel cell (Vrated). Out-
put terminal is Pe which represents the electrical power
output from fuel cell. This terminal is applied to P input
terminal of the PQ inverter model.
3.2.3. Wind Generation System Model
Wind generator used in this paper is a squirrel-cage in-
duction generator that directly connected to the MG.
Wind turbine model is based on the steady state power
characteristic of the turbine. The stiffness of the drive
1
Pe
Go to
Inverter
-C-
Vrated
A B C
Virtual
Load
Pm
wm
Pe
Va
Vb
Vc
Synchrounous
Ge ne ra tor
( a )
Pref
P ref
wm
Pref
Pm
Microturbine
Vrated
Pr ef
Pout
Fuell cell model
( b )
Pe
Active
power
Generator
Figure 8. Micro turbine and fuel cell standalone developed
models.
train is infinite and the friction factor and the inertia of the
turbine must be combined with those of the generator cou-
pled to the turbine [14,18].
The output power of the turbine is given by the follow-
ing equation:
3
2
),( windPm v
A
CP

  (3)
where:
Pm: Mechanical output power of the turbine (W).
CP: Performance coefficient of the turbine.
ρ: Air density (kg/m3).
wind
v
: Wind speed (m/s).
λ: Tip speed ratio of the rotor blade tip speed to wind
speed.
β: Blade pitch angle (deg.) and
A: Turbine swept area (m2).
A generic equation is used to model CP (λ, β). This
equation, based on the modeling turbine characteristics
of reference [18], is:
5
2
134
(, )()i
c
P
i
c
cccce

6
c




  (4)
with: 3
11 0.035
0.08 1
i
  

 (5)
The coefficient C1 to C6 are: C1 = 0.5176, C2 = 116, C3
= 0.4, C4 = 5, C5 = 21 and C6 = 0.0068 [18].
For the induction generator, the well-known 4th order
dq model is used, expressed in the arbitrary reference
frame, rotating with an angular velocity

[19]:
..
s
dssd sq
uri p
sd


  (6)
..
s
qs sqsdsq
uri p
 

 (7)
0.( ).
rdr rdrrqrd
uri p




  (8)
0.( ).
rqr rqrrdrq
uri p




  (9)
Where
0
1d
pdt

, and 0

is the base electrical an-
gular frequency. Generator convention is used for the
stator currents. The zero sequence equation is omitted,
since the machine stator is connected. The stator and ro-

Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode33
.
tor fluxes are related to the currents by:
.
s
dssdmrd
X
iXi

  (10)
..
s
qssqmrq
X
iXi

  (11)
.
rdm sdr rd
.
X
iXi

  (12)
.
rqmsqr rq
.
X
iXi

 (13)
The electromagnetic torque is given by:
.
eqrdrdrq
Ti.
r
i

 (14)
The wind turbine implemented in this paper is a pitch
angle controlled and directly connected to the MG with
no power electronic interface. Developed wind genera-
tion system model is shown in Figure 9. The wind tur-
bine is coupled to a squirrel cage induction generator.
The input terminals of the wind turbine are wind speed
(m/sec.) and pitch angle of the turbine blades (degree).
The output terminal of the wind turbine is mechanical
torque (Tm) which applied to the shaft of the induction
generator. The terminals of the induction generator are
connected directly with the MG. In the two studied cases,
the wind speed changes continuously. The values of ac-
tual wind speed are available in reference [4].
3.2.4. Photovoltaic Panel Model.
The PV array is a grouping of PV modules in series
and/or in parallel, being a PV module a grouping of solar
cells in series and/or in parallel. In this study, Maximum
Power Point Tracker (MPPT) is used to assure that the
PV array generates the maximum power for all irradiance
and temperature values as shown in Figure 10. The whole
algorithm for the computation of the maximum power of
the PV under certain ambient Temperature (Ta) and Ir-
radiance (Ga) is summarized in the next steps:
 The required parameters are extracted from MG pa-
rameters data base (required voltage, current and power).
 The PV module’s power is computed based on its
dependency on Irradiance and cell Temperature as given
in Equation (15) [4,14].
,,
,
[(
Max
MM a
MaxMax oPMMo
ao
G
PP TT
G
 )] (15)
where:
max
M
P: PV module maximum power [W]
max,
M
o
P: PV module maximum power at standard condi-
tions [W]
,ao
G: Irradiance at standard conditions [W/m2]
M
ax
P

: Maximum power variation with module tem-
perature [W/℃]
M
T: Module temperature [℃]
,
M
o
T: Module temperature at standard conditions [℃]
 The working temperature of a PV module TM depends
exclusively on the Irradiance (Ga) and on the ambient
wind
speed m/s
0
pitch
angle
Generator speed (pu)
Pitch angle (deg)
Wind speed (m/s)
Tm (pu)
Wind Turbine
A
B
C
RLc
load
pm
Pm
Pe
Tm
wm
Pm
Pe
Va
Vb
Vc
Induction
Ge ne r at or
Figure 9. Wind generation system model.
Figure 10. Typical I-V characteristics for a PV array.
temperature (Ta), as shown in Equation (16) [4,14]:
20
.800
Maa
NOCT
TTG   (16)
where:
M
T
T
: Module temperature [℃]
a
G
: Ambient temperature [℃]
a
NOC
: Irradiance [W/m2]
T: Normal cell operating temperature [℃]
 Substituting Equation (16) in Equation (15) and
multiplying by the number of modules of the plant, we
obtain the maximum power output of the PV plant in
Equation (17).
,
20
[.(.
1000 800
Max
M a
MaxMax oPaa
GNOCT
PN PTG 

 25)]
(17)
This model is developed in Matlab® Simulink envi-
ronment and shown in Figure 11. Input terminals are
Irradiance Ga [W/m2] and ambient temperature Ta [Kel-
vin]. In the two studied cases the irradiance is assumed to
change continuously and the actual values of irradiance
are available in reference [4]. The output terminal is Pmax,
which represents the maximum output power developed
by photovoltaic panel. This terminal is applied to the in-
put terminal of the PQ inverter.
4. Complete Model Description
The operation of the MG with several PQ inverters and a
single Vf inverter is similar to operation of the MG with
synchronous machine as a reference bus (slack bus). Vf

34 Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode
1
Pma x
Temperature
(Ta)
Ga
Ta
Pm ax
PV Model
Irradiance
(Ga)
Figure 11. PV array developed model.
inverter provides the voltage reference for the operation
of the PQ inverters when the MG is isolated from the
main power system. Acting as a voltage source, the Vf in-
verter requires a significant amount of storage capability
in the DC link or a prime power source with a very fast
response in order to maintain the DC link voltage con-
stant. In other words, the power requested by a Vf inver-
ter needs to be available almost instantaneously in the
DC link. In fact, this type of behavior actually models the
action of the flywheel system. Flywheel was considered
to be existing at the DC bus of the Vf inverter to provide
the required instantaneous power. The Vf inverter is re-
sponsible for fast load-tracking during transients and for
voltage control. During normal operation conditions (sta-
ble frequency at nominal value), the output active power
of the Vf inverter is zero; only reactive power is injected
in the MG for voltage control.
4.1. Control of Active Power in Each Micro
Source
During islanded (autonomous) operation, when an im-
balance between load and local generation occurs, the
grid frequency drifts from its nominal value. Storage de-
vices (flywheel) would keep injecting power into the
network as long as the frequency differed from the no-
minal value. Micro turbine and fuel cell are controllable
sources which their output power can be controlled. A PI
controller (input of this controller is the frequency devia-
tion) acting directly in the primary machine (Pref of fuel
cell and micro turbine) allows frequency restoration. Af-
ter frequency restoration, storage devices will be operat-
ing again at the normal operating point (zero active po-
wer output). This controller can not apply to wind gene-
ration system and photovoltaic panels because those mi-
cro sources are uncontrollable sources and their output
power depends on weather conditions (wind speed, ir-
radiance and ambient temperature). Figure 12 shows the
PI controller block diagram used to control output power
of fuel cell and micro turbine.
4.2. Reactive Power-Voltage Control
Figure 13 describes the adopted voltage control strategy.
2
P
Active Power
Reference for
microsour ce
( Fuel Cell and
Microturbine )
50
f0 0.6
Pset
Kp
Proportional
gain
1
s
Integrator
KI
Inte gral
ga in
1
Gr id
freque ncy
Figure 12. Control of active power of SOFC and micro tur-
bine.
Figure 13. Droop control of the Vf inverter terminal voltage.
Knowing the network characteristics, it is possible to
define the maximum voltage droop. To maintain the vol-
tage between acceptable limits, Vf inverter connected to
the flywheel will adjust the reactive power in the network.
It will inject reactive power if the voltage falls under its
nominal value and will absorb reactive power if the vol-
tage rises over its nominal value.
4.3. Active Power-Frequency Control
The transition to islanded operation mode and the opera-
tion of the MG in islanded mode require micro genera-
tion sources to particulate in active power-frequency
control, so that the generation can match the load. During
this transient period, the participation of the storage de-
vices (flywheel) in system operation is very important,
since the system has very low inertia, and some micro
sources (micro turbine and fuel cell) have a very slow
response to the request of an increase in power genera-
tion. As already mentioned, the power necessary to pro-
vide appropriate load-following is obtained from storage
devices (flywheel). Knowing the network characteristics,
it becomes possible to define the maximum frequency
droop as shown in Figure 14. To maintain the frequency
between acceptable limits, Vf inverter connected to fly-
wheel will adjust the active power in the network. It will
inject active power if the frequency falls below its nomi-
nal value and will absorb active power if the frequency
rises over its nominal value.
4.4. Complete Model
All micro sources developed models, all inverters developed

Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode35
Figure 14. Frequency droop control Vf inverter.
models and the control strategies described in the previ-
ous sections are collected in one complete model. This
model is general and can be used to describe any distur-
bance may be occur in the MG.
5. Results and Discussions
In the simulation platform, the two PV panels, the SOFC
and the single shaft micro turbine are interfaced to MG
through PQ inverters. As the inverter control is quite fast
and precise, it is possible to neglect the DC link voltage
fluctuations; if losses are also neglected, the output active
power of a PQ inverter is equal to the output power of
the associated micro source. Flywheel is connected to Vf
inverter.
Case 1: MG Dynamic Performance Equipped with 10
kW Fixed Speed Wind Generation System.
In this case, amount of active power and reactive power
generated from micro sources are adjusted to force MG
imports 13 kW and 16 kVAr from the main grid. Dis-
connection of the upstream main grid was simulated at t
= 70 seconds. The simulation results were presented for
the main electrical quantities (frequency, voltages, active
and reactive powers).
From the previous figures (Figures 15-18), the sequence
of the events can be interpreted as follows:
 Before islanding occurrence, MG operates at its
steady state and imports active and reactive powers from
the main grid. Also, the frequency is at its nominal value
(50Hz).
 Islanding occurred at t = 70 seconds; the active power
provided by main grid is lost which led to decrease in the
MG frequency (49.78 Hz) as shown in Figure 15. Also,
losing of some reactive power which was supplied by
main grid forced the voltages to drop to about 97% of
their nominal values as shown in Figure 16.
 The difference between load powers (active and re-
active) and micro sources generated powers (active and
reactive) must be compensated by Vf inverter connected
to the flywheel as shown in Figure 17.
 Due to frequency deviation, PI controllers connected
to SOFC and SSMT increases the reference powers of
those micro sources. The output powers of SOFC and
SSMT begin to increase and help frequency restoration
65 70 7580 8590 95100105110115120
49.7
49.75
49.8
49.85
49.9
49.95
50
50.05
50.1
Ti me( sec.)
Frequency (Hz)
Figure 15. MG frequency before and subsequent islanding.
70 8090100 110 120
0. 95
1
time (sec)
Voltage ( pu )
Bus # 1 (Flywheel)
708090 100 110120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 2 (Wind generation system)
70 8090100 110 120
0. 95
1
time ( sec )
Voltage ( pu )
Bus # 4 ( PV2)
708090 100 110120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 5 (PV1)
70 8090100 110 120
0. 95
1
time ( sec )
Voltage ( pu )
Bus # 6 ( Micro turbine)
708090 100110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 7 (Fuel cell)
Figure 16. Voltages at all micro sources buses.
65 70 7580 8590 95100 105 110 115 120
-5
0
5
10
15
20
25
30
35
40
45
Time ( sec. )
Power
Active and reactive power injected by the flywheel (VSI)
Active power( KW )
Reactive power( KVAr )
Reactive Power ( KVAr )
Active Power ( KW )
Figure 17. Flywheel (Vf inverter) active and reactive powers.
as shown in Figure 18.
 Due to wind speed fluctuations, the power gener-
ated by wind generator (Squirrel cage induction genera-
tor) fluctuates which led to frequency fluctuations. Also,
the reactive power absorbed by wind generator (depends

36 Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode
65 707580 85 90 95 100 105110 115120
-2
0
2
4
6
8
10
12
14
16
18
20
Time ( sec. )
Active power ( KW )
Fuel Cell Active Power
Micro turbine Power
Power of PV2 at bus #4
Wind Generator Power
Power of PV1 at bus # 5
Figure 18. SOFC, SSMT, wind generator and photovoltaic
panels generated active powers.
on the amount of generated active power) fluctuates which
led to small flicker in voltage. The fluctuations on fre-
quency and voltages are small because the wind genera-
tion system has small rating. The variation of photo-
voltaic panels’ output powers is small, because the irradi-
ance and temperature variation is less than the fluctuation
of wind speed.
 Due to small rating of wind generation system,
amount of reactive power injected in the MG by flywheel
to keep the voltage with acceptable limits is small (less
than 25 kVAr).
 As shown in Figure 18, the response of SSMT is
faster than the response of SOFC, so that, SSMT is pre-
ferred for system needs fast dynamic response.
 After 30 seconds from islanding occurrence, amount
of power produced by micro sources nearly equal to
power consumed by the loads and flywheel injected
power is nearly equal to zero (only small reactive power
injected or absorbed by flywheel Vf inverter to compen-
sate renewable sources power fluctuations).
Case 2: Dynamic Performance of MG Equipped with
30 kW Fixed Speed Wind Generation System.
In this case, the MG has the same conditions of the
first case except the 10 kW fixed speed wind generation
system is replaced by 30 kW fixed speed wind generation
system. The disconnection of the upstream main grid was
simulated at t = 70 seconds, and the simulation results are
shown through the following figures.
From the previous figures (Figures 19-22), the follow-
ing points can be summarized:
 When MG was connected to the main grid, fre-
quency is at its nominal value (50Hz). Difference be-
tween loads consumed powers and micro sources genera-
ted powers are compensated by the main grid. Active
power injected by flywheel settles nearly at zero.
 When islanding occurred at t = 70 seconds, large
amount of active and reactive power was lost which led
to high drop in frequency (49.74 Hz) and voltage at all
buses (94%) as shown in Figures 19 and 20, respectively.
 To keep MG stability, flywheel Vf inverter must in-
ject high amount of active and reactive powers as shown
in Figure 21.
 Controllable micro sources (Fuel cell and micro tur-
bine) increase their generated powers to help frequency
restoration as shown in Figure 22.
 Due to high rating wind generation system, the fluc-
tuations of wind speed causes high fluctuations on output
power of the generator which led to high fluctuations on
the MG’s frequency as shown in Figure 19.
 Voltages dropped to about 94% compared with 97%
in the first case.
 Amount of reactive power which must be supplied
by the Vf inverter connected to flywheel is about 45
kVAr compared with 22 kVAr only in the first case.
65 707580 859095100105 110115120
49.7
49.75
49.8
49.85
49.9
49.95
50
50.05
50
.
1
Time
(
sec.
)
Frequency (Hz)
Figure 19. MG frequency.
70 80 90100 110 120
0.95
1
time (sec)
Voltage ( pu )
Bus # 1 (Flywheel)
70 80 90 100 110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 2 (Wind generation system)
70 80 90100 110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 4 ( PV2)
70 80 90 100 110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 5 (PV1)
70 80 90100 110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 6 ( Micro turbine)
70 80 90 100 110 120
0.95
1
time ( sec )
Voltage ( pu )
Bus # 7 (Fuel cell)
Figure 20. Voltages at all micro sources buses.
6. Conclusions
In this paper, the effect of increasing wind generation
system rating in transient dynamic performance of the

Effect of Wind Generation System Rating on Transient Dynamic Performance of the Micro-Grid during Islanding Mode37
65 70 7580 8590 95100105 110 115 120
-5
0
5
10
15
20
25
30
35
40
45
Time ( sec. )
Power
Active and reactive power injected by the flywheel (VSI)
Active power( KW )
Reactive power( KVAr )
Reactive Power ( KVAr)
Active Power ( KW)
Figure 21. Flywheel (Vf inverter) active and reactive powers.
65 70 75 80859095100105110 115 120
-2
0
2
4
6
8
10
12
14
16
18
20
Time ( sec. )
Active power ( KW )
Wind generator Power
Power of PV1 at bus # 5
Power of PV2 at bus # 4
Micro turbine power
Fuel cell power
Figure 22. SOFC, SSMT, wind generator and photovoltaic
panels generated active powers.
MG during and subsequent to islanding mode is investi-
gated in details. The paper developed a complete model
which can describe the dynamic performance of the MG
at any disturbance conditions. Two cases are studied, the
first case describes the transient dynamic performance of
the MG before and subsequent to islanding occurring
when the MG is equipped with 10 kW fixed speed wind
generation system. The second case describes how the
MG dynamic performance will affect if the rating of the
fixed speed wind generation system is increased to 30
kW. It is found that, increase the rating of wind genera-
tion system required more reactive power which causes
high voltage drops at all buses of the MG. Also, fluctua-
tion of wind speed causes more fluctuations in the micro
grid frequency in the second case, because the power
captured from the wind is proportional to the cube of the
wind speed. This paper provides MG’s designers with a
full picture of the effect of wind generation system rating
on dynamic performance of MG and recommends that to
prevent the voltage drops with high wind power rating
and keep the MG stability, MG should be equipped with
adjustable reactive power compensations devices likes
static VAR compensator (SVC) or static compensator
(STATCOM).
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