Received: April 1, Revised: May 5, 2

Impact of Large-Scale Wind Power Penetration on Dynamic Voltage Stability of

Interconnected Power System: An Indonesia Case Study

Awan Uji Krismanto1 Irrine Budi Sulistiawati1 F Yudi Limpraptono1 Ardyono Priyadi2
Herlambang Setiadi3* Muhammad Abdillah4

1
Department of Electrical Engineering, Faculty of Industrial Technology,
Institut Teknologi Nasional Malang, Indonesia
2
Department of Electrical Engineering, Faculty of Intelligent Electrical and Informatics Technology,
Institut Teknologi Sepuluh Nopember, Indonesia
3
Faculty of Advanced Technology and Multidicipline, Universitas Airlangga, Surabaya, Indonesia
4
Department of Electrical Engineering, Universitas Pertamina, Indonesia
* Corresponding author’s Email: h.setiadi@stmm.unair.ac.id

Abstract: The increasing penetration of wind power plant introduces a various effect on power system stability,
operation and control. Unpredictable, uncertain and fluctuating circumstances can significantly affect the
performance of power system. Moreover, employment of novel technologies in wind power plant significantly alter
the control characteristic and operation procedure of power system to deal with load variations and fast changing of
generated power from wind-based power plant. One of the main focus in integrating large scale wind power plant is
how to maintain voltage stability under transient and steady state scenarios. In this paper, effects of large-scale wind
power plants on voltage stability of power system is investigated. Practical test system of South-West Sulawesi,
Indonesia with integration of two large scale wind power plants are considered. Hence the novelty of this paper is to
introduce new and practical test system for power system stability study considering renewable energy integration.
The simulation results suggest that the additional power injection from wind power plant introduces beneficial
effects on power system voltage stability performance. It was monitored that the increasing power injection from
wind power plant enhanced the voltage profile (0.96 pu to 0.975 pu), voltage margin and load-ability (200 MW to
215 MW) of the system. Furthermore, it was also observed that additional power injection from wind power plant
significantly improved the dynamic voltage stability performance of the power system, ensuring stable operation
under transition stages when the power system was subjected to disturbances.
Keywords: Renewable energy, Wind power, Voltage stability.

the capacity of power generation must meet the

1. Introduction power demand, quality of delivered power should be
The power system grows significantly in maintained in allowable circumstances to ensure
proportion with the significant increase of electric normal operation of power system.
power consumption. The increase of power In conventional power system network, the power
consumptions is followed by the expansion of generation is dominated by fossil fuel-based power
coverage area of power system. The transmission generations. The main problems with fossil fuel are
and distribution lines need to be extended and the decreasing deposits due to continuous and
planned carefully to ensure reliability of electricity increasing consumption. With massive consumption
supply and to reach the user in urban dan remote of fossil fuel, it is extremely difficult to forecast and
areas. The significant growth of power demand determine the availability and sustainability of fossil
requires a sufficient power generation to ensure a fuel. A safe assessment suggests that there are
balance condition between generation and demand. sufficient fossil fuel deposits to provide energy for
Beside 30

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
years [1]. As main energy resources, fossil fuel such power network as a contribution to reduce pollution
as coal, petroleum and gas have become important and global warming mitigation.
commodities in the world which potentially triggers
conflict or even war among countries. Moreover,
from environmental point of view, the increasing
consumption of fossil fuel introduces some
drawbacks. The fossil fuel conversion process
produces pollutant and gas emission which
deteriorates the environment in terms of climate
change, global warming and green house effects.
Therefore, it is very important to find alternative
energy resources to fulfil the demand and more
environmentally friendly. With all the possible
disadvantages of fossil fuel, energy security has
become a major concern worldwide. Implementation
of novel energy resources based on renewable
energy are mandatory to ensure energy supply for
the customers. The integration of renewable energy-
based power generation on the other hand, would
gradually decrease the dependency to fossil fuel,
reducing economic cost and providing beneficial
effects on environment.
Integration of renewable power generation on
electricity grid has been increasing significantly due
to some benefits of abundant sources and
environmental issues. Moreover, the development of
energy conversion and material technologies
encourages integration of renewable energy
resources-based power plants on power system
network. Despites the advantages of integrating
novel power plant technologies, the increasing
penetration
of renewable power plant introduces some
challenges on power system operation. Integration of
large-scale renewable energy-based power plant
significantly
affects power flow and stability of interconnected
power system network. The increase of
intermittency
and uncertainty in power system as a consequence of
integrating renewable energy would affect the
equilibrium point of power system operations. The
balance conditions dynamically change due to
unpredictable power contribution from renewable
energy based power generation [2].
Among renewable energy resources, wind power
plant and photovoltaic based power generations are
the most renewable energy-based power plants
which
have been connected to power system network. By
2020, 650.758 GW capacity of wind power plants
have been installed throughout the world [3]. The
development of large-scale wind power plant in
Indonesia has been increasing continuously. The
installation of 150 MW wind power plant at
Sulawesi network encourages the increasing of
clean-energy energy implementation in Indonesia

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
Various effects of integrating large scale
renewable power plant, especially wind power plant
have been thoroughly studied. In general, basic
configuration of wind power plant can be classified
into two types according to the type of generator and
energy conversion devices used to deliver power.
The first type is fix speed wind turbine which
utilizing squirrel cage induction generator and
permanent magnet synchronous generator without
power electronic devices. The second types is
variable speed wind turbine which can be operated
in different wind speed level due to implementation
of power electronic devices as energy conversion
and control devices [4-6].
As the size of wind turbine and capacity of wind
power plant is increasing, it is preferable to used
variable speed than fixed speed wind turbine. The
main reason is the ability of the variable wind
turbine to operate in different wind speed and
additional isolation provided by power electronic
device which can separate the mechanical and
electrical side of the wind power plant. Hence, the
fluctuating condition in mechanical side of wind
power would not affect the electrical side or grid
side. Variable speed wind power plant such as
double fed induction generator and fully rated
converter types provides an additional reactive
power to the system. The ancillary services of wind
power plant in providing reactive power injection
to the system might enhance the system voltage
profiles which consequently improves load- ability
of the system [7, 8]. Even though the additional
power injection from wind power plant can help to
fulfil the load demand and enhanced the voltage
profiles, uncertain power injections from wind
power plant and features of wind power generation
technologies potentially introduce novel stability
concerns in power system operation and control [9,
10]. One of the main concerns of integrating wind
power plant is maintaining voltage stability of the
power system [11]. Effect of wind power on a small
test power system is studied in [12]. It was
monitored that in power system with dominant wind
power, the system load-ability decreased with the
increase of wind power penetration. Moreover, at
high wind power situation more oscillatory
condition was observed when power system is
subjected to disturbances.
Fast change power injection from wind power
plant under fluctuating condition of wind speed
might
influence dynamic/ transient voltage stability. Wind
power plant usually situated in coastal or off-shore
area. This requires a long transmission network to
deliver power for the load. The existence of long
transmission might bring a weak power system
operation especially when power system operated
International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:
 Received: April 1, Revised: May 5, 2
under heavy loading scenarios. Hence, voltage Pw[pu,W]
instability risk increases as an consequence of those
weak transmission lines [13]. Integration of wind
power plant introduced a novel challenge on system
stability due to interaction between control system of
wind power plant and conventional power plant [14],
[15]. Furthermore, as a portion of generated power
from conventional power plant is replaced by
injected power from wind power plant, it potentially
reduces
Vci Vr Vco Wind
performance. Speed[m/s]
The massive development of power conversion
technologies in wind power plant introduces a Figure. 1 Wind power curve
challenge in power network operation and control.
The utilization of power electronic devices as energy influenced by mechanical characteristic of wind
conversion and power conditioning devices may
turbine, power output curve and actual wind speed
either enhance wind power injection or deteriorate
stability of power system due to less inertia values. For a specific wind turbine, a typical power
characteristic of such device configuration. curve of a wind-based power generator is depicted in
Moreover, implementation of asynchronous Fig.1. Wind turbine normally operates between cut-
generator requires a certain amount of reactive power in (Vci) and cut-off speed (Vco). The generated power
from the network. Hence, it potentially influences the increases proportionally as wind speed increased
reactive power flow and voltage stability. Therefore, between those limits, and reach the nominal values
a robust control algorithm is required in wind power
when the wind speed is equal to rated speed (Vr).
plant to ensure continuity of electricity service and
maintain voltage stability of the power system with However, beyond those limits the wind turbine is not
high penetration of wind power plant. Hence, operated due to efficiency and safety reasons
dynamic and static voltage stabilities can be respectively [17].
maintained under fluctuated power injection from Using the presented wind power curve, the
wind power plant [16]. generated power from wind power plant can be
With the possible advantages and drawbacks of formulated as given by the following equation [18],
having a such large-scale wind power plant in power [19].
system, it is necessary to provides a comprehensive
analysis of those impacts. However, most of the 0 ��𝑜𝑟 𝑣 < ���𝑖 𝑜𝑟 𝑣 > ����
previous research only presents the investigation of
wind power impact on test power system. So far, less �� (� ��� ��𝑜𝑟 (1)
paper provides investigation of �� −
�� ) { ��𝑖 ���𝑖 ≤ 𝑣 ≤
���
wind power effects on practical power system. ��� ��𝑜𝑟 ��� < 𝑣 < ����
Therefore, this paper addresses a comprehensive
analysis of impacts of integrating wind power plant Where Pw and Pwr represent a power output at a
on dynamic and static voltage stability of a practical particular wind speed and the equivalent rated power
power system in Indonesia. It is expected that the output of wind power plant. In this research, power
obtained results can be used as consideration and injection from wind power plant is increasing
recommendation for planning the renewable energy proportionally to investigate impacts of increasing
integration. The remainder of the paper is organised wind power penetration on power system voltage
as follows. Wind power plant model is presented in stability.
Section II. The simulation results are presented and As mentioned previously, fluctuating conditions
discussed in Section III. Eventually, conclusions and of wind speed result in fluctuating power injection
contributions of this paper are highlighted in Section from wind power plant. Hence, a variable speed
IV. operation capability of wind power plant is required
to ensure stabile operation and reliability of
2. Wind power plant dynamic model electricity services. In this research, a fully rated
wind power generation is considered. Those direct
Generated power from wind power plant is driven
International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:
 Received: April 1, Revised: May 5, 2
wind power plant technology provides a full service
and flexible operations of back to back inverter
system for controlling and maintaining a stable

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2

Local
Bus
DC/AC
AC/DC
Inverter
I Converter + Cdc
module
Rf iiB Lf Rc iLB Lc
f
module C
- Vdc based
vo io
w vge n based PWM
PWM

mqgen mqgrid mdgrid

d abc to dq mdgen vgrid

abc to
transform d Synchronization

Control
P

dq
I

PI
Controller
P
I

P
I

iqgen ioq
idgen
iod
iqgen_ref idgen_re iqgrid_ref
f idgrid_ref
Control

PI
PI

vdgen + vqgen
2 2
P

P
I

I
ler

vge n vod
P voq
vref Vdc p=vod iod +vo
q ioq
ref Q q=vodioq -voq iod iod
Qref ioq
MPPT
Pref
Figure. 2 Dynamic model of wind power generation

generated power under fast change of wind speed.

vqref
The dynamic model fully rated wind power
wref
generator is comprising of current model of vqgrid
1/s
d
KpP LL+KiPLL/s
induction generator and a detailed model of back to vgrid
abc to
back inverter system as presented in [20, 21]. In this dq
trans
vdgrid Qref
research, it is assumed that the wind power plant is form K
pP LL
+K
iPLL

operated at a constant pitch angle. Hence, only

vdref
controllers of back to back inverter system is
considered in the dynamic wind generation model. Figure. 3 PLL controller
A block diagram of dynamic model of fully rated
wind generation is depicted in Fig. 2. Control system stable operation of power system in different
of fully rated wind power generation consists of two power injection level from wind power plant.
major parts; generator and grid side controllers. The The synchronisation controller determines
generator-side controller allows variable speed reference angle, frequency and voltage values. A
operation capability under fluctuating condition of synchronized operation between wind power plant
wind speed. Control signal for generator-side and synchronous machine-based power plants is
converter is obtained from reference values of maintained using phase lock loop (PLL) controller as
generator and DC link voltages. Hence, the stable depicted in Fig. 3.
operation of fully rated wind power plant can be well Dynamic behaviour of the PLL controller is
maintained. Grid-side controller is responsible for represented by a set of auxiliary state variables
providing a stable output power by controlling the (���𝑃𝐿�� , ��������� ) as given by the
active and reactive power flow to the grid [22]. following equation.
Moreover, it also enhances the power quality by � 𝜑 � 𝑃𝐿 𝐿 � 𝜑 � 𝑃𝐿 𝐿
reducing total harmonic distortion due to high �𝑡 = 𝑣���−
�𝑣
�𝑡 = 𝑣���−
�
������ ������
frequency switching operation of the inverter
system. (2)
In grid connected mode of wind power plant,
synchronisation procedure is important to ensure

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
The calculated reference reactive power and ��� � �� ���𝑛
���𝑛 −𝑖 , =𝑖 −
= 𝑖 ����_ �� ����_
angular frequency from PLL controller are given by �𝑡
��� ��
�
���
the following equations. 𝑖�� 𝑡
�� (8)
The algebraic equations of modulation indices
���� = ���������� ���𝑃��𝐿 + reference signal for generator side converter are
��������� (������ − �������� ) given by.
(3)

𝜔��� = ��������𝐿 �������𝐿 +

��������� (������ − �������� )
(4)
∗
=𝐾 � + 𝐾�4 𝑣����_ − 𝐾�41𝑖
The obtained reactive power and angular frequency 𝑚�� � ��
reference values from synchronization controller are �� �4 �� 1 ��� ����
then applied to the local controller of wind power
1 (9)
plant which comprising of generator and grid-side ∗
� = 𝐾�
𝑚�� +𝐾 𝑣 −𝐾 𝑖
converter control algorithms. �� �3 ����_ �31 ����
The generator-side converter control is �� �3 �� 1 ��� (10)
1
responsible for maintaining a stable condition of
terminal generator and DC link voltage, allowing Similar to the generator-side control, the grid-side
variable speed operation of the induction generator. inverter control in fully rated converter-based wind
Measured terminal generator and DC link voltage power plant is consisting of slow response outer and
are compared to their reference values. The fast response inner control loops. In the outer control
determined errors are then controlled using
loop, the calculated active and reactive power
conventional PI
reference values are compared to the measured
control method to derive reference values of direct
active and reactive output power. The obtained error
and quadrature currents. By considering �����
is then regulated by PI controller, yielding the
and reference values for the inner current control loop.
����� as auxiliary state variables of outer
By considering ������� and ������� as
control
auxiliary state variables of the outer control
loop of generator side converter, state equations of loop of grid-side
the controller can be stated as.
� ��
� �� converter, state equations of the controller can be
���𝑛
=𝑣 −𝑣 ���𝑛 −𝑣 (5)
, = 𝑣���_
� �� �� �� stated in the following equations.
𝑡 �� ��� �
�𝑡

The reference currents of generator side converter � �� ��� ��� � �� ��� ���
are given by. = =
� �
��𝑡 − �, ��𝑡 − � (11)
𝑖����_��� = ����21 ����� +
���21 ������ − ���21 ���� (6)
reference values and compared to the actual values of
generator currents (𝑖���� , 𝑖���� ).
𝑖����_��� = ����11 ����� + A similar algorithm is implemented to the current
���11 �����_��� − ���11 𝑣��� control loop to determine the modulation indices
(7)

Output variables from the outer control loop are

then applied to inner current control loop as

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
The reference currents of grid-side converter are
calculated as follows. 𝑖������_��� = ����12 ������� +

𝑖������_��� = ����22 ������� + ���12 ���� − ���12 � (13) By

���22 ���� − ���22 �
(12)
comparing and regulating the difference
between reference (𝑖������_��� ,
𝑖������_��� ) and measured output current
(𝑖�� , 𝑖�� ), the modulation
∗ ∗
(𝑚
���� , �� ) for the generator-side converter. ∗
�� indices references (𝑚������
the grid-side ,∗𝑚������ ) for
These modulation indices are afterward employed as inverter are determined. These modulation indices
control variables of PWM switching scheme for the
are afterward employed as control signal of PWM
converter. Auxiliary state variables of ����� switching scheme for the inverter. Auxiliary state
and variables of ������� and ������� are
����� are required to provide state equation of
required to provide state equations of the current
the controller loop as given by
current controller as given by

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
and stopped when the voltage collapse point or nose
� � � ��� ��� of the PV curve is reached [24].
��� −𝑖 ��� ��� −𝑖
� =𝑖 ����� 0�, = 𝑖����� 0
𝑡
�_���
�𝑡
�_��� � Reactive power is key to voltage stability. Even
though reactive power is easier to generate compared
(14)
The algebraic equations of modulation indices to active power, it is more difficult to transmit. At
reference signal for grid-side inverter are given by. higher loading conditions, transmission lines are
unable to deliver reactive power. It was also been
∗ observed that the greater distance of the reactive
� = 𝐾�
𝑚��� �� + 𝐾�3 𝑣����� − 𝐾�32𝑖
power source from the reactive power demand, the
�3 �� 2 �_��� ��
��� greater required amount of reactive power
2 �� (15)
compensation and more difficult to control the
∗ voltage level. Therefore, the unbalance or deficit of
� = 𝐾�
𝑚��� ��� + 𝐾�4 𝑣����� − 𝐾�42𝑖
�4 ��� 2 �_��� �� reactive power either locally or globally leads to
���
2 poor voltage profiles. Under fluctuating power
(16) generation and increasing in loading conditions, it
potentially led
3. Voltage stability analysis to voltage collapse. As depicted in Fig. 1, reactive
power margin which indicates how much further the
3.1 Static voltage stability loading on a particular bus can be increased before
voltage collapse is reached, is measured as a distance
Voltage stability analysis in power system can be
between lowest reactive power point in QV curve
classified according to the type of disturbance, or the and
time frame over which the instability may occur the voltage axis [25]. By investigating PV and QV
[23]. Due to the type of disturbance, large voltage curves, voltage stability margin and loading
instability can be defined as the ability of power maximum can be determined to ensure stable
system to maintain voltage after suffered a large operation of power system.
disturbance such as faults, loss of generator or
V (pu)
contingencies. While, the ability of power system to V (p Load Margin
maintain voltage after being subjected to small u)
Load Margin
disturbance such as incremental or small load change
is defined as small disturbance instability. Regarding Criti al Point
the time span, voltage instability concerns are Critical
Voltage
Critical Point
c
Critical Stable Region
classified into long term stability (few minutes to Voltage Stable Region
hour), mid-term stability (10 seconds to few
Unstable
minutes) and short term or transient voltage stability UnRsetgaibo
(0-10 minutes). Transient or short-term voltage lnRegion
e
Collapse
stability considers fast dynamic response of the CoMllapg
system voltage under change of operating point. Msien rgin
While, long- term voltage stability involves slower- a P
acting of the (MP
Po Pm W)
equipment in responding the disturbances. (MW)
Pm
Most of the incidences of voltage instability can a.
PVPCourve
be observed as slow phenomenon of voltage a. PV Curve
(a)
Q
variations over a certain time-span followed by rapid (MVar)
change of voltage magnitude when it approaches Q (MVar)
near to the instability. This phenomenon can be
analysed as “static phenomenon” and classified into
static voltage stability. To assess the static stability 0
concerns, two curves that have been popularly used 0
r
are P-V and Q-V curves. The typical P-V and Q-V Reactive
curves is depicted in Fig. 4. The P-V curve shows Powe Voltag
ReactMivaerP e
the system voltage under different values of real
goinwer VCooltll
power Margin aagpes
V (pu)
and fixed load power factor. The P-V curve is e
applied ColPlao

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, V (pu) 2
to determine the maximum real power loading b. QV Curve
margin which also known as static voltage stability b. QV Curve
margin. The power system load is gradually (b)
increased
Figure. 4 Typical: (a) PV and (b) QV Curve

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2

Bus 6 Bus 1
Bus 7 Bus 21 Bus 20 Bus 5 Bus 3 Bus 2 Bus 17
Load

Gen 7 Load 7 Load 6 Bus 30 Load 3 Load Load 1

Bus 22 Gen 6 20 Gen 5 Load 5 Gen 3 Gen 2 Load 2 Gen 1
Bus 4 17
Bus 32 Bus 19
Bus 35 Bus 34 Bus 31
Bus 18
Load
Bus 37 32 Load Load
31 Gen 4 18 Load
Bus 36 Bus 16
Bus 28 19
Bus 23 Bus 14 Bus 15
Bus 33 Gen 14
Load
Load 23 Gen 16 Load 16 28
Load 33 Load Gen 15 Load
15
14
Bus 12
Bus 29
Gen 12 Load Load
Load Gen 13
12 13
29

Bus 24 Bus 8 Bus 25 Bus 26 Bus 9 Bus 10 Bus 11 Bus 27

Gen 11
Load 24 Gen 9
Gen 8 Load 8 Load 9 Gen 10 Load 10 Load 11 Load 27
Load 25

Figure. 5 South-west Sulawesi 150 kV network

3.2 Dynamic voltage stability wind power technology provides a better variable
speed operation capability due to independent
Under fluctuating conditions or after being control capability of generator and grid side inverter.
subjected to a disturbance, an oscillatory condition is The discussions were focused on impact of
monitored. When power system is able to maintain increasing wind power penetrations on voltage
stability, the oscillation would decrease and profiles and dynamic responses of bus voltage when
eventually diminish after a new equilibrium point is the system was subjected to small and large
reached. On the other hand, an increasing magnitude disturbances. Voltage profiles and static voltage
of oscillation reflects unstable situations. With the stability margin would be evaluated to determine the
increase of uncertainties in power generation maximum loading capability of the investigated
andload demand, oscillatory circumstances are system under different power injection from wind
frequently observed. Therefore, static stability power plant. Moreover, the system dynamic
analysis is not sufficient to capture the performance performance would be evaluated to capture the risk
of power system. of instability under different wind power penetration
The dynamic response should be carefully when fault and fast changing loading circumstances
observed to provide a complete picture of system are experienced.
dynamic behaviour. This involves time-domain Additional power injection from large-scale wind
simulations. The power system component are power plants altered the direction of power flow and
represented by a set of not-linear equations which is hence influenced the losses of the system. As power
solved using time integration methods [26]. The injection from wind power plant may change the
dynamic analysis is also required to determine the power flow direction of the interconnected power
maximum allowable critical clearing time to ensure system, it also influences the transmission line
stable operation of power system [27, 28]. congestion. Consequently, integration of a such
power source potentially either enhances or
4. Results and Discussions deteriorates voltage profiles at feeder endings
depending on its capacity and location. Impact of
An interconnected power system network
different wind power penetration on steady state
comprising of 16 synchronous generators was
system performance, in particular system losses is
considered. The investigated network was South
depicted in Fig. 6. It was clearly monitored that the
West Sulawesi 150 kV system, with two 150 MW
increasing wind power penetration introduces a
wind power plants in Sidrap (bus 28) and Jeneponto
beneficial effect on system losses. With wind power
(bus 9) as depicted in Fig. 5 [29]. Fully rated wind
penetration, the real power losses decrease around
power conversion system technology as described in
20% from 26.82 MW in base case scenario to 21.23
the previous section is considered. The implemented

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2
80
under sudden change of generated power from
base case
available generators and fluctuating load
60 80 MW w ind
140 MW w ind
circumstances. In a weak grid with marginal values
of voltage profiles, the sudden increase of load
Power Losses

40
demand and loss of power generation potentially
deteriorates stability of power system. In this
20 condition, further increase of load demand
potentially lead to the risk of voltage collapse which
0 result to partially or even entire black-out.
MW Losses MVAr Losses
System Losses The voltage stability analysis involves a
Figure. 6 Power losses capability transfer of real power from one area to
1.04
another area in power system and its effects to the
base case
system voltage. The voltage profiles of the
1.02 80 MW Wind interconnected power system network are mainly
140 MW
Wind
influenced by power balance between generation and
1 demand, power flow direction and transmission
Voltage

network congestion management. As wind power

0.98
plant inject a certain amount of power to the grid, it
low
er
voltage m it
li potentially influences voltage margin and maximum
0.96
loading condition of power system. Maximum
0.94
loading condition can be assessed using PV curve
5 10 15
35
20 25 30
which indicates the voltage
Bus
Figure. 7 Voltage profiles 1

base case
0.98
60 MW w ind
MW and 20.07 MW with 80 MW and 140 MW wind 0.96
120 MW w ind

power penetrations respectively. Moreover, the

Voltage

significant decrease was observed in reactive power 0.94

losses as indicating by 25% decrement from 76.75 0.92

criticalvoltage limit
MVAr in base scenario to 54.20 MVAr and 53.02 0.9
MVAr in 80 MW and 140 MW wind power
penetrations respectively. As power injection from 0.88
50 100 150 200 250 300
wind power increases, the power losses decrease Real Pow er (MW)

proportionally. With the decrease of system losses, it (a)

would provide an enhancement of system voltage 1
profiles.
Impact of large-scale wind power penetrations on 0.9
critical
voltage profiles is depicted in Fig. 7. Two different voltage
Voltage

0.8

level of power injections from wind power plants are limit

considered. In general, it was monitored that at 0.7

higher power injection from wind power 0.6

base
60 MW
casew ind
plant, the 140 MW w ind
0.5
improvements of voltage profile of the buses are 50 100 150 200 250 300

observed. Significant enhancements of voltage Real Pow er (MW)

profiles were monitored at bus 19 and bus 31. In (b)

base case scenario without wind power penetration, 1 base case

the voltage profiles at bus 19 and 31 were 0.96 pu 60 MW w ind

0.98
and 140 MW w ind

0.948 pu respectively. As wind power was gradually 0.96

Voltage

increased, the voltage profiles at those buses

0.94
improved to 0.972 and 0.952 respectively.
Especially for bus 31, the wind power penetration 0.92 critcal
contributes for removing under voltage concern. voltage limit

Voltage profile is an important indicator to 0.9

50 100 150 200 250 300

determine the allowable load demand which can be Real Pow er (MW)

connected to the system. Capability to maintain (c)

voltage profiles under different loading conditions is
International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:
 Received: April 1, Revised: May 5, 2
important to ensure stable operation of power system Figure. 8 PV Curves of bus: (a) 19, (b) 31 and (c) 32

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2

base case base case

100 100 60 MW w ind 100
60 MW w ind
B 140 MW w
B base case B
50 140 MW w 50 50
ind 60 MW w ind
0 0 0
140 MW w

Reactive Power
Votl ge gin e Margin

Reactive Power
Reactive Power

ind
-50 -50 -50
-150 Votlag Margn -150 a Mar -150
e i
-200 -200 -200 Votlag
-250 -250 -250

-300 -300 -300

A
-350 A -350 A
-350

-400 -400 -400

0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1
Voltage (pu) Voltage (pu) Voltage (pu)

Point A Point A Point A

-344
-346 -347

-347
-346 -348
Reactive Power

Reactive Power

Reactive Power
-348
-349
-348 -349

-350 -350
-350
-351 -351

-352 -352
-352
0.44 0.46 0.48 0.5 0.52 0.54 0.44 0.46 0.48 0.5 0.52 0.54 0.56 0.44 0.46 0.48 0.5 0.52 0.54
0.56 0.58 0.56
Voltage Voltage Voltage (pu)
(pu) (pu)

Point B Point B Point B

4
4
5
2 2
Reactive Power

Reactive Power
Reactive Power

0
0
0
-2
-4
-5 -4
-6

1.004 1.006 1.008 1.01 1.012 1.003 1.004 1.005 1.006 1.007 1.008 1.009 1.005 1.006 1.007 1.008
Voltage (pu) Voltage (pu) Voltage (pu)

(a) (b) (c)

Figure. 9 QV curve of bus: (a) 19, (b) 31, and (c) 32
variation at a particular bus in different loading system to maintain voltage profiles in higher
scenarios. maximum loading condition increased, voltage
Impacts of different wind power penetration on stability margin also increased proportionally. The
load-ability and voltage margin of the selected bus is enhancement of voltage stability margin reflects
depicted in Fig. 8. As depicted in Fig.8, higher more robust condition of the system static voltage
power injection from wind power plant contributes stability.
to improve bus voltage. The improvements of The critical feature of wind power plant involves
voltage profiles are followed by the higher load unpredictable and fluctuating change of generated
demand which can be supplied without causing power according to wind conditions. Therefore,
under voltage or even voltage collapse. It was power conditioning is required to ensure stable
clearly monitored that maximum loading points of power
the selected buses slightly shifted to the right side injection from such renewable energy-based power
with the increased of wind power penetrations. At plant. Most wind power generation is comprising of
bus 19, under base case scenario without wind asynchronous generator and power converter as
power, the critical voltage limit was reached at 200 interfacing devices. This configuration is required to
MW loading condition. The loading limit increased facilitate flexible operation capability under different
to 210 MW and 215 MW with wind speed circumstances. On the other hand, the
80 MW and 140 MW wind power penetration utilization of asynchronous generator technology in
respectively. Similar trends were observed at bus 31 wind power plant requires a certain amount of
and 32, indicating by slight increase of loading limit reactive power from the grid for facilitating energy
under higher power injection from wind power conversion. As absorption of reactive power of wind
plants. power generation depend on generated active power
The increase of loading limit indicated the increase from wind turbine, it may affect the flow of reactive
of voltage stability margin and load-ability of those power and eventually bus voltages. Deficit of
buses. As the capability of the investigated power reactive

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:

 Received: April 1, Revised: May 5, 2

0.99
0.98
0.97 base case 0.98
base case
0.96 100 MW w
ind 0.97 100 MW w
0.96 ind

Voltage

Voltage
0.94 0.96
0.95
0.92 0.95
Voltage

0.94 0.94
base case 0.9
100 MW w
0.93
ind 0.93
100 101 102 103 104 105 106 107 108 100 101 102 103 104 105 106 107 108 100 101 102 103 104 105 106 107 108
Time (s) time (s) Time (s)

(a) 1 Bus 19 under fault (a) 2 Bus 31 under fault (a) 3 Bus 32 under fault
0.951 0.951
base case base case
0.9544
0.950 100 MW w 0.950 100 MW w
8 ind 8 ind

0.9506 Voltage 0.9506 0.9542

Voltage

0.9504 0.950 0.954

Voltage
4

0.9502 0.9502 0.9538

base case
0.95 0.95 0.9536 100 MW w ind

0.9498 0.9498
100 105 110 115 120 125 100 105 110 115 120 125 0.9534
130 130 100 105 115 120 125 130
110 Time (s)
Time Time (s)
(s)

(b) 1 Bus 19 under load change (b) 2 Bus 31 under load change (b) 3 Bus 32 under fault
Figure. 10 Dynamic voltage response under: (a) fault and (b) load change conditions
power with the increasing of loading condition may contributing factors. Dynamic analysis, on the other
lead to unstable condition or even local or globally hand, is useful for a detailed study of the risk of
interruption due to poor voltage profiles. Similar to voltage fluctuation and collapse situations. The
PV curve analysis, voltage stability condition can dynamic analysis is required to capture the system
also be assessed by analysing how the fluctuation of dynamic performance in particular response of
reactive power influence the bus voltages. The system voltage under transient conditions.
influence of reactive power variation injection and In this paper, two scenarios of transient
absorption on bus voltage can be monitored through phenomenon in power system is considered to
QV curve. investigate dynamic voltage stability performance of
Fig. 9 represents QV curve of the selected bus in power system involving the effect of power injection
base case scenario and with different wind power from wind power plant. The dynamic voltage
penetrations. It was monitored that wind power stability under faulty and load changes conditions in
penetration introduces a positive impact on electrical base-case and with 100 MW wind power penetration
power network operation. The voltage margin of the is depicted in Fig. 10. It was monitored that
selected bus slightly increased with the increased of additional wind power injection enhanced
wind power penetration. Thus, improving voltage dynamic voltage
stability of the system. From PV and QV curve stability performances. After being subjected to a
analysis, it was monitored that additional power fault, more oscillatory condition of bus voltage was
injection from wind power plant enhanced voltage experienced when there is no power injection from
profiles and loadability as indicated by the increase wind power plant. In base case scenario, longer
of system abilility to maintain voltage profile at oscillatory conditions are also monitored, indicated
higher maximum loading conditions and reactive longer time to reach steady state values eventhough
power demand. The increase of system loadability the power sytsem has reached the new equilibrium
point. With additional 100 MW power injection from
highly correlated with higher flexibility of power
wind power plant, more damped response was
system in maintaining voltage profiles under
observed, reflected by lower oscillatory amplitude
different loading conditions. More flexibility of and faster settling time.
power system in maintaining voltage profiles In second scenario, effect of wind power plant
reflects enhancement of static voltage stability integration on dynamic voltage stability performance
performance. was investigated when the real power of the entire
The static voltage stability performance of power connected load was suddently increased by 5%.
system as analysed using PVand QV curves, allows Similarly, improvement of dynamic voltage stability
examination of voltage stability in a wide range of was monitored when system was subjected to load
system condition of power system and provides change. Under transition stage, more fluctuating
much
insight of the nature of the problem and various
International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI:
 Received: April 1, Revised: May 5, 2
condition was observed in base-case scenario fast control action of power electronic devices
without wind power injection as indicated by lower provides a faster response to regain an equilibrium
undershoot and longer settling time. Furhtermore, point or reach a novel stable operating point after
integration of wind power plant enhances system being subjected to disturbance. The enhancement of
dynamic response, indicated by smaller undershoot dynamic voltage performance of power system is
and faster settling time. As a result, novel reflected by more damped voltage response and
equilibrium point can be reached faster and hence faster settling time to reach a stable steady state
dynamic voltage stability can be maintained. The voltage condition.
enhancement of dynamic voltage stability response
under load change scenario was mainly caused by Conflicts of interest
the contribution of wind power plant in replacing a “The authors declare no conflict of interest.”
certain amount of the generated power from
conventional synchronus generator based power Author contributions
plant. As the wind power plant implement power “Conceptualization, Awan Uji Krismanto, Irrine
electronic devices as interface devices, the control Budi Sulistiawati and F Yudi Limpraptono;
action of those devices provides faster response than methodology, Awan Uji Krismanto, Ardyono Priyadi
a conventional power plant fueled by fossil fuel and Herlambang Setiadi; Awan Uji Krismanto, F
such. Therefore, when an equilibrium operating Yudi Limprapto and Muhammad Abdillah;
point changes due to disturbance, faster response validation, Awan Uji Krismanto, Irrine Budi
from wind power plant can significantly help the Sulistiawati and F Yudi Limpraptono; formal
power system to regain the equilibrium point or analysis, Awan Uji Krismanto, Ardyono Priyadi and
reach the novel a stable operating point. Herlambang Setiadi; investigation, Awan Uji
Eventhough, faster response is the advantages of Krismanto and Muhammad Abdillah; resources,
having a such wind power plant, replacing a certain Awan Uji Krismanto; writing original draft
amount of generated power from synchronous preparation, Awan Uji Krismanto; writing review
generator based power plant may have either
and editing, Irrine Budi Sulistiawati, Ardyono
decrimental or beneficial effects. The decrimental
Priyadi and F Yudi Limpraptono; visualization,
effect corelates to the decrease of sytem inertia.
Lack of system inertia would reduce damping of the Awan Uji Krismanto, Muhammad Abdillah, and
system Herlambang Setiadi. All authors have read and
which may lead to more oscillaory condition when agreed to the published version of the manuscript”.
the large disturbance occurred. On the other hand,
having more wind power plant would reduce References
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Appendix
Table 1: List of notations used in this paper
Symbol Meaning
Vci Cut in wind turbine speed
Vco Cut off wind turbine speed
Vr Rated speed
Pw Power output at a particular wind speed

Pwr Equivalent rated power output of wind power plant

𝜑�𝑃𝐿𝐿 Auxiliary state variable in D

axis
𝜑�����𝐿 Auxiliary state variable in Q
axis
����� Auxiliary state variable of outer control loop of generator side converter in
D axis

����� Auxiliary state variable of outer control loop of generator side converter in
Q axis

𝑖���� Generator actual current in D

axis
𝑖���� Generator actual current in Q
axis
∗ Modulation index for
��
����
generator-side conveter in D
axis
∗ Modulation index for
��
����
generator-side conveter in Q
axis
������� Auxiliary state variable of outer control loop of grid side converter in D
axis

������� Auxiliary state variable of outer control loop of grid side converter in Q
axis

𝑖������_��� Grid side current reference in D

axis
𝑖������_��� Grid side current reference in Q
axis
𝑖�� Actual current output in D axis
𝑖�� Actual current output in D axis
∗
�������� Modulation index for grid-side inverter in D axis

International Journal of Intelligent Engineering and Systems, Vol.14, No.4, DOI: