Modeling and Simulation of ICT Network Architecture for Cyber-Physical Wind Energy System

Conference Paper (PDF Available) · August 2015with 581 Reads
DOI: 10.1109/SEGE.2015.7324601
Conference: IEEE International Conference on Smart Energy Grid Engineering (SEGE), 2015
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Abstract
There are many challenges and concerns about the impact of integrating more and more wind power farms (WPFs) into the power grid. A WPF can be considered as a cyber-physical energy system (CP-ES) due to the coupling between the physical power system and the cyber communication network. While the information and communication technology (ICT) infrastructure is the key concept to support a reliable operation, real-time monitoring and control of large-scale wind farms, it has been less addressed and rarely discussed. This work aims to design the ICT network architecture for a cyber-physical wind energy system (CP-WES) which consists of wind turbines, meteorological masts, substation, and a local control center. We consider different applications: operation data (analogue measurements & status information) from wind turbines, meteorological data from the meteorological towers, and protection & control data from intelligent electronic devices (IEDs). A real wind farm project (Zafarana-1, Egypt) has been considered as a case study. The proposed ICT network architecture is modeled and evaluated using OPNET Modeler. Network topology, link capacity, and end-to-end delay are three critical parameters investigated in this work. Our network model is validated by analyzing the simulation results. Keywords—wind power farm (WPF); Cyber-physical wind energy system (CP-WES); information and communication technology (ICT).
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Modeling and Simulation of ICT Network
Architecture for Cyber-Physical Wind Energy System
Mohamed A. Ahmed1, Yong Cheol Kang1,2, Young-Chon Kim1,3,*
Dept. of Electrical Engineering2, Dept. of Computer Engineering3
WeGAT Research Center1, Smart Grid Research Center, Chonbuk National University
Jeonju, Korea
{mohamed, yckang}@jbnu.ac.kr, *Corresponding author: yckim@jbnu.ac.kr
Abstract—There are many challenges and concerns about the
impact of integrating more and more wind power farms (WPFs)
into the power grid. A WPF can be considered as a cyber-
physical energy system (CP-ES) due to the coupling between the
physical power system and the cyber communication network.
While the information and communication technology (ICT)
infrastructure is the key concept to support a reliable operation,
real-time monitoring and control of large-scale wind farms, it has
been less addressed and rarely discussed. This work aims to
design the ICT network architecture for a cyber-physical wind
energy system (CP-WES) which consists of wind turbines,
meteorological masts, substation, and a local control center. We
consider different applications: operation data (analogue
measurements & status information) from wind turbines,
meteorological data from the meteorological towers, and
protection & control data from intelligent electronic devices
(IEDs). A real wind farm project (Zafarana-1, Egypt) has been
considered as a case study. The proposed ICT network
architecture is modeled and evaluated using OPNET Modeler.
Network topology, link capacity, and end-to-end delay are three
critical parameters investigated in this work. Our network model
is validated by analyzing the simulation results.
Keywords—wind power farm (WPF); Cyber-physical wind
energy system (CP-WES); information and communication
technology (ICT).
I. INTRODUCTION
Nowadays, with the direction toward electricity generation
from renewable energy resources, many projects of large-scale
wind power farms (WPFs) are scheduled to be constructed in
the near future. This expected growth in WPFs will
significantly affect the monitoring, operation and control of
today electric power grid. In this direction, information and
communication technology (ICT) will play an important role to
support the real-time monitoring and protection of both electric
power system and wind turbines. Due to the coupling between
the physical power system and the cyber communications
network, WPFs are considered as a typical cyber-physical
energy systems (CP-ESs) [1]. In view of wind farm electric
power system, several research work and investigations have
been carried out to study the wind farm sub-systems (wind
turbine, collector system, substation, etc.) which have been
addressed and discussed in many publications. However, the
supervisory control and data acquisition (SCADA) systems and
the underlying communication network infrastructures are
relatively less addressed and rarely discussed [2-4]. A typical
WPF consists of wind turbines, meteorological system, local
wind turbine grid, collecting point, transformers, and
substation. Cables with different cross section areas are used to
connect among wind turbines which are connected to the utility
system through transformers and distribution lines [5]. From
the communication network point of view, the communication
network usually follows the electric topology configuration.
However, different electric/communication topologies may be
configured based on wind farm size. The main function of the
ICT infrastructure is to transmit measured information and
control signals between wind turbines and the control center
[6-9].
This work aims to design the ICT network architecture for
a cyber-physical wind energy system (CP-WES) where both
the electric power system and the underlying communication
network are interdependence and tightly connected. The
physical power system consists of wind turbines, local wind
turbine grid, transformers, and a substation, while the cyber
communication network consists of network components
(servers, switches, routers, network cables, etc.) and
measurement devices (sensors, intelligent electronic devices,
etc.). The communication network within WPF is regarded as a
local area network (LAN). A Real wind farm project
(Zafarana-1, Egypt) has been considered as a case study. Three
critical parameters: network topology, link capacity and end-
to-end (ETE) delay have been investigated and discussed.
This paper is organized as follows. Section 2 gives an
overview of the cyber-physical wind energy system, wind farm
electric topology, wind farm SCADA systems, and wind farm
communication infrastructure. Section 3 shows the proposed
ICT network architecture for a case study of a real project
(Zafarana-1 wind farm, Egypt) and the simulation results.
Finally, Section 4 concludes.
II. CYBER-PHYSICAL WIND ENERGY SYSTEM
A. Grid Integration of Wind Power Farms
A typical electric power system consists of power
generation, transmission, distribution and customers as shown
in Fig. 1. The future smart grid aims to enable the two-way
flow of electricity and information with the target to make the
IEEE International Conference on Smart Energy Grid Engineering (SEGE), 2015
17-19 Aug. 2015, Oshawa, ON, Canada
DOI: 10.1109/SEGE.2015.7324601
conventional electric grid more reliable, efficient and secure. In
this direction, the ICT will play an essential role in order to
bring the future smart grid into a reality [4]. In view of wind
energy, as more and more wind turbines are integrated into the
power grid, the monitoring scope has been expanded from
monitoring individual wind turbines to cover the whole wind
farm as well as the electric substation [6]. In such architectures,
the communications network are considered the essential part
that allow the exchange of measured information and control
signals between the wind turbines and the control center. With
the huge amount of monitoring data that need to be
communicated with the control center, the network
infrastructure will become a bottleneck.
B. Wind Farm Physical Power System
Generally, WPF is defined as a group of wind turbines
connected together and tied to the utility through a system of
transformers, transmission lines, and a substation. A wind
turbine generator consists of the wind turbine itself, circuit
breaker, and step-up transformer. The generation voltage of
each wind turbine is stepped up using the step-up transformer.
Wind turbines are divided into groups, and each group is
connected to collector bus through a circuit breaker. Multiple
collector feeders are connected to high voltage (HV)
transformer which steps up the voltage to transmission level
[10-11]. Figure 2 shows a single line diagram of a typical WPF.
The WPF is divided into different zones: wind turbine zone,
collector feeder zone, collector bus zone, high voltage
transformer zone and transmission line zone.
C. Wind Farm SCADA System
The wind farm main components are wind turbines,
meteorological system and electric system [12]. The SCADA
systems are used for data acquisition, remote monitoring, real-
time control, and data recording [13]. It remotely collects the
process information from wind farm components and based on
the collected information, the control center executes
appropriate actions. Each WPF has a dedicated connection to a
local control center for real-time monitoring and control.
However, one control center can remotely manage and control
one or more WPFs. There are multiple applications covered by
the SCADA systems in a WPF. The three main applications are
Turbine SCADA system, Wind Farm SCADA system and
Security SCADA system [2], [7].
Turbine SCADA system provides the connectivity
among wind turbines and enables the control center
operator to remotely monitor and control each wind
turbine and their associated sub-systems.
Wind Farm SCADA system provides the control
center operator with the status of all devices in a WPF
such as wind turbines, meteorological masts, electric
substation system, protection and control devices
(IEDs), etc. The main function is to connect all devices
from all wind turbines, as well as the electric
substation together.
Security SCADA system provides the IP telephony
services and video surveillance system for the WPF.
Fig. 1. Grid integration of a wind power farm.
Fig. 2. Single line diagram of typical wind power farm.
D. Wind Farm Cyber Communication Infrastructure
The SCADA communication network for WPF is based on
Switch-based architecture, which consist of Ethernet Switches
and communication links in every wind turbine [7]. The
communication infrastructure provides the connection among
wind farm elements, and is divided into two parts: turbine area
network (within a turbine) and farm area network (between
wind turbines and control center) [14-15]. Inside a wind
turbine, there are a number of propriety communication
protocols used such as field bus, industrial Ethernet protocols,
and control area network (CAN) [16]. For a wind farm, point-
to-point (P2P) communication and local area network (LAN)
based on Ethernet-based architecture can be used for network
configuration. In order to link the wind farm network with a
remote control center, different wide area network (WAN)
technologies wired/wireless could be configured such as
optical fiber cables, microwave, and satellite. Figure 3 shows
the wind farm SCADA communication infrastructure which
consists of three hierarchical levels: process level, bay level,
and station level.
Fig. 3. SCADA communication network architecture of a wind farm.
III. CASE STUDY: ZAFARANA WIND POWER FARM
The Zafarana wind farm project is located in Egypt,
approximately 190 Km Southeast of Cairo. The average annual
wind speed is about 9.5 m/s. There are many projects have
been constructed in different stages since 2001. The projects
are named Zafarana-1 (30 MW- 50 WTs- 600 KW), Zafarana-2
(33 MW- 55 WTs- 600 KW), Zafarana-3 (30 MW- 46 WTs-
660 KW), Zafarana-4 (47 MW- 71 WTs- 660 KW), Zafarana-5
(85 MW- 100 WTs- 850 KW) and Zafarana-6 (80 MW-
94WTs- 850 KW) as shown in Fig. 4. In 2010, the wind farm
total installed capacity was 545 MW, which includes 700 wind
turbines from different models (Nordex, Vestas, and Gamesa)
[11] [17-18]. The Zafarana-1 project has been considered as a
case study in this work.
Fig. 4. Zafarana wind power farm [11].
A. Proposed ICT Network Architecture for Zafarana-1
The Zafarana-1 project consists of 50 wind turbines
(Nordex N43). The wind turbines are arranged in two rows
with a total capacity of 30 MW, as shown in Fig. 5. We
assumed that the electric topology consists of three feeders,
one bus, and one transformer. The proposed ICT network
architecture has been constructed using Switch-based
architecture.
1) Modeling the process level. The process level includes
sensor nodes (SNs) and measurement devices (MDs) which
are the basic data sources. Both the SNs and MDs are
connected to different elements of WPF, where the main
function is only to report the measurements such as
temperature, speed, voltage, current and pressure [19]. The
condition monitoring system (CMS) at wind turbine is
continuously collecting a large volume of data signals in real
time. Then, wind turbine controller (WTC) performs the
control operation for the wind turbine based on data collected
from CMS, sensors, and other devices. Also, the data of the
weather condition such as wind speed, wind direction are
collected using meteorological towers. Table 1 lists the types
of wind farm traffic at the process level. For a wind turbine,
the total number of sensor nodes and measurement devices are
102 based on IEC 61400-25, as shown in Table 2 [14].
Fig. 5. Zafarana-1 wind farm project. Note: The distance is extracted from
Google Earth based on wind turbines location.
TABLE I. WIND FARM TRAFFIC AT THE PROCESS LEVEL.
Traffic Type Direction
Monitoring
Analogue Measurements
Status Information
Meteorological data
Uplink
Continuous
Protection Protection Information Uplink
Continuous
Control Control Instructions
Downlink
/On Demand
TABLE II. CONDITION MONITORING PARAMETERS FOR WIND TURBINE
Turbine
Subsystem
Number
of
Sensors
Number of Analogue
Measurement
Number of Status
Information
Rotor 14 9 5
Transmission 18 10 8
Generator 14 12 2
Converter 14 12 2
Transformer 12 9 3
Nacelle 12 8 4
Yaw 7 5 2
Tower 4 1 3
Meteorological 7 7 -
TOTAL 102 73 29
2) Modeling the bay level. The bay level includes the
protection and control intelligent electronic devices (P&C-
IEDs). The IEDs are located at different portions of the WPF.
Based on the IEDs function, there are five types of P&C
devices: circuit breaker (CB) IED, merging unit (MU) IED,
transformer (T) IED, feeder (F) IED, bus (B) IED and line (L)
IED [20-24]. Given the CB-IED as an example, it control the
breaker (open/close), monitors the status and condition of the
CB, and receive command (trip/close) from P&C-IEDs or
control center. If the breaker condition changed, it would send
a state change event to P&C-IED. The IEDs configuration of
Zafarana-1 project is given in Table 3.
We assumed that each wind turbine generator (WTG) has
a merging unit acquire current, voltage, and breaker signals
for substation automation. Data packets are transmitted over a
communication network to a central relaying unit (CRU) for
P&C functions of the whole wind farm [10]. For MU-IEDs,
we assumed that the sampling frequency of the voltage and
current data are 6400 Hz for a 50 Hz power system, and each
sampling data is represented by 2 bytes [25]. Considering 3-
phase voltage and current measurement, the MU-IEDs are
sending updated values of 76,800 bytes/s to the P&C server at
the local control center. Also, the CB-IED is sending a status
value of 16 bytes/s to P&C server [23]. The wind turbines,
feeders, and bus are modeled as a subnet consists of one CB-
IED, one MU-IED, one P&C-IED and one Ethernet Switch as
shown in Table 3. The configuration of data flow for different
IEDs are given in Table 4.
TABLE III. IED CONFIGURATION FOR ZAFARANA-1 PROJECT
Zone MU
IED
P&C
IED
CB
IED
Wind Generator (WTG) 1 1 1
Collector Feeder (F1, F2, F3) 1 1 1
Collector Buse (B1) 1 1 1
Substation Transformer (T1) 1 1 2
TABLE IV. TRAFFIC GENERATION OF IEDS
Parameter Type From To
Data
Generation
MU-IED Sampled value message
3-phase V, I MU Station
Server
76,800
bytes/s
CB-IED Send Breaker Status CB
Station
Server 16 bytes/s
3) Modeling the station level. The station level consists of
three servers: SCADA server, protection, and control server,
and meteorological mast server. Servers are used to store the
data received from different wind farm applications. The
control center executes appropriate actions based on the
received data.
B. Substation Automation Results
The OPNET Modeler is used for network modeling and
simulation of the proposed ICT network architecture. The
Zafarana-1 WPF consists of 50 WTs divided into three groups:
group 1 (17 WTs), group 2 (17 WTs) and group 3 (16 WTs) as
shown in Fig. 6. Figure 7 shows the OPNET model of ICT
network architecture for Zafarana-1. In this work, only group 1
with 17 WTs (17 MU-WTG and 17 CB-WTG) was considered.
The first task is to validate the network model by comparing
the generated amount of traffic from different IEDs with the
received traffic at the control center server. The CB-IEDs and
MU-IEDs were configured to send their messages (given in
Table 4) to the protection and control server at the local control
center. The Server FTP traffic received traffic is about 368
bytes/s (23 CB-IEDs*16 bytes/s) and 1,689,600 bytes/s
(22MU-IEDs*76,800 bytes/s) for CB-IEDs and MU-IEDs,
respectively. The simulation results shown in Fig. 8 agree with
our calculations discussed in the previous section.
Fig. 6. Proposed ICT network architecture of CP-WES for Zafarana-1.
Fig. 7. OPNET model of ICT network architecture for Zafarana-1.
Fig. 8. Traffic received at the protection and control server.
The second task focuses on the network performance by
measuring the end-to-end delay for different WPF applications.
It was observed that using 10Mbps for LAN speed is not
sufficient, where the amount of network traffic is much higher
than the channel capacity. The results obtained for the
minimum and maximum end-to-end delay for the protection
and control IEDs of the WTGs using LAN speed of 100Mbps
and 1Gbps are shown in Table 5. The maximum E2E delay
was about 12.99 ms for MU-IED and about 2.29 ms for CB-
IED. Table 6 shows the timing requirement for different
applications based on IEEE 1646 standard of electric
substation automation. Using 1Gbps for LAN speed satisfies
the timing requirement for protection information of wind
turbine generator as given in Table 5. The end-to-end delay of
MU-IEDs for feeder protection (F1, F2, and F3) is shown in
Fig.9.
TABLE V. ETE-DELAY OF WTG-IEDS
Wind Turbine Zone End-to-end Delay (ms)
LAN Speed (Mbps) Min Max
100 CB-IEDs
MU-IEDs
1.017
12.533
2.290
12.995
1000 CB-IEDs
MU-IEDs
0.152
1.254
0.329
1.296
TABLE VI. TIMING REQUIREMENTS FOR DIFFER ENT APP LICAT IONS
BASED ON IEEE 1646 STANDARD
Information Type Internal External
Monitoring and control 16 ms 1 s
Protection 4 ms 8-12 ms
Operation and maintenance 1 s 10 s
Fig. 9. ETE delay of MU-IEDs for feeder protection (BW:100Mbps).
C. Real-Time Monitoring Data Results
In this section, the design of the communication network
infrastructure for Zafarana-1 is drawn from real large-scale
projects such as the Horn Rev project in Denmark [8] and the
Greater Gabbard project in United Kingdom [7]. This section
shows the results obtained for the network modeling of
SCADA system for group 1 of Zafaran-1 WPF (17 wind
turbines and a meteorological tower). Table 7 shows the
assumptions for different SCADA applications [14]. The traffic
received at control center (SCADA server and MET Mast
server) is shown in Fig. 10. The traffic received for analogue
measurements, status information, and meteorological data are
3834248 bytes/s (225544*17), 986 bytes/s (58*17) and 1670
bytes/s, respectively. Figure 11 shows the ETE delay for real-
time monitoring data. In case of 100Mbps channel capacity, the
average ETE delay for SCADA and MET mast data was about
11ms and 1.4ms, respectively. In case of 1Gbps, the average
ETE delay for SCADA and MET mast data was about 1.1ms
and 0.46ms, respectively.
TABLE VII. WIND FARM MONITORING TRAFFIC
Type From To Data Generation
Analogue Measurements
Status Information
Wind
Turbine
SCADA
Server
225,544 bytes/s
58 bytes/s
Meteorological data MET
Tower
Station
Server 1,670 bytes/s
Fig. 10. Traffic received at the SCADA and MET Mast servers.
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