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WindTurbineWirelessCommunicationNetwork&HeadingMeasurementSystem(FeasibilityStudy)CONFERENCEPAPERNOVEMBER2010

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Wind Turbine Wireless Communication Network & Heading Measurement System (Feasibility Study)

Hakam Saffour and Prof. A. S. Omar Institute of Electronics, Signal Processing and Communications, Chair of Microwave and Communication Engineering

University of Magdeburg 39106 Magdeburg, Germany

Email: hakam.saffour@ovgu.de, a.omar@ieee.org

Abstract this paper reviews the technical possibilities and challenges of building a wireless communication network for wind turbines. Wireless network is utilized to transmit some measured environmental and physical parameters of and around the wind turbine to the main receiver station. The measured parameters are temperature, humidity, wind speed and heading angle of wind turbine. The purpose of measuring those parameters and transmitting them on wireless radio link is to monitor the wind turbine status and conditions for further optimization and controlling. Suitable radio protocols and topologies for such application are explored; also options for developing a heading measurement system to determine the direction of the wind turbine are highlighted.

Keywords: wind turbine, wireless sensor network, heading system.

I. INTRODUCTION Wind energy has great potential to provide clean and

renewable energy wherever wind is blowing. In 2050, 50% of electric power needed for Europe will be supplied by wind turbines [1]. With the importance of wind energy increasing, monitoring and optimization of wind turbines operation becomes more critical, and since wind turbines are expensive and complex devices they require continuous monitoring and frequent maintenance. Condition monitoring offers significant value to a wind farm operator as the cost of downtime is significant not only in terms of equipment repair but also in terms of lost revenue [2]. Wireless monitoring of wind turbines would provide an easy way to gather data related to wind turbine especially in remote locations such as mountains, hills and offshore wind farms.

II. OBJECTIVES & APPROACHES As mentioned previously, the purpose of this research

project is to build a wireless communication network for wind turbines. The wireless network will be utilized to transmit some measured parameters of and around the wind turbine to the main receiver station. The measured parameters are temperature, humidity, wind speed and heading angle. The purpose of measuring those parameters and transmitting them on wireless radio link is to monitor the wind turbine status and conditions for further optimization and controlling. For such

monitoring system, it is important to have a universal monitoring system that can be installed on any wind turbine regardless its model or manufacturing brand.

The objectives of this research project are: 1) To build a wireless communication network that will

be installed on the hub and blades of the wind turbines (see Figure 1). The wireless network will transmit the data measured from different weather sensors (the red points in Figure 1) to a transceiver station fixed on the hub.

2) To build a wireless communication network that will let each wind turbine pass its data to the next wind turbine in a wind farm until the data reached to the main receiver station (data collector) as shown in Figure 1 (the green dotted lines).

3) To develop heading measurement system to determine the direction of the wind turbine (Yaw angle) as shown in Figure 2.

Figure 1. Position of wireless sensors on the wind turbine and individual radio links. Red: radio link within the sensors; Blue: radio link for

transmitting the measured values to the transceiver station; Green: radio link for passing through the measured values to other wind turbines till the main

receiver station [3].

Sponsor: Federal ministry of education and research in Germany.

Figure 2. YAW angle in wind turbine [4].

The research is conducted based on looking for a communication system that meet the following requirements:

a) Wireless based. b) Cost effective: wireless system will be much cost

effective compared to the costly process of pulling wire inside and on the surface of the wind turbine.

c) Easy to install: wireless network allows for quick and relatively easy installation compared to wired network

d) Stand alone: power required for the sensors and wireless transceiver has to be generated independently by using long life battery and power harvesting techniques.

e) Reliable: data to be measured and transmitted has to be accurate and sustainable.

III. COMMUNICATION NETWORK In this section characteristics of some communication

networks are presented in order to find out the proper and efficient communication network for wind turbines. Firstly it is needed to have an idea about the dimensions of wind turbine in order to determine the maximum required coverage area for the wireless network, for this sake and as an example, one of the largest wind turbines in the market is considered. Figure 3 shows the dimensions of E126 wind turbine from Enercon [5].

Figure 3. Dimensions of Enercon E126 wind turbine, HH: hub height, RD: rotor diameter, TC: tip clearance, TH: tip height.

Two dimensions are in our concern, the hub height (HH) and the rotor diameter (RD), the hub height is needed to calculate using Pythagoras' theorem- the distance between transceiver station fixed on the hub and the main receiver station as shown in Figure 1, and the rotor diameter is needed to find the distance range between the wireless sensors which will be installed on the blades and the transceiver station fixed on the hub- which is in E126 example less than 63 meters.

Also it is important to consider the average distance between each wind turbine in a wind farm. Typical layout for a wind farm is shown in Figure 4, the figure shows that in a wind farm, the maximum distance between two wind turbines is the distance between two consecutive wind turbines in the wind direction which is five times the rotor diameter [6], considering the rotor diameter of Enercon E126 wind turbine shown in Figure 3 the distance will be 5x126=630 meter.

Figure 4. Typical layout of wind farm [6].

A. Wireless Sensor Network (WSN) The idea behind the wireless sensor network is based on

installing wireless sensors in different locations and let those wireless sensors communicate- via radio link- with each other to pass through the measured data till it reach the base station. Data are collected at the wireless node, compressed and transmitted to the gateway directly or, if required, uses other wireless sensor nodes to forward data to the base station, and then the data are transferred to the monitoring system for further analysis. See Figure 5.

Figure 5. Typical wireless sensor network architecture [7].

B. Network Topologies There are number of different topologies for

communication networks, two of them are in our concern, the star and mesh network topology. The star network topology will be implemented on the individual wind turbine communications; while the mesh network topology will be implemented for the communications between the wind turbines till the data reach the final destination. Refer to Figure 1 and Figure 6.

The reasons for choosing such network topologies for such structure are based on the advantages and disadvantages of each topology, the restrictions of the project requirements and nature of the wind turbine structure. In the following two sections, the reasons are explained in more details.

1) Reasons of choosing star network topology: A star network allows for a single base station to send and/or receive a message to/from a number of remote nodes. The remote nodes can only send or receive a message from the single base station. The advantages of star topology are the opportunity to have a simple wireless network and the minimum power consumption for remote nodes. In the other hand the disadvantages of star network topology are the dependency of a single node base station- to manage the network and the base station must be within radio range of all nodes. Taking into consideration the advantages and disadvantages of star network topology and the proposed idea of using such topology for the individual wind turbine communications, the following points are concluded:

a) Simple wireless network will be suitable and enough to let the few sensors installed on the wind turbine to send their data to the transceiver station. See Figure 1.

b) Since the sensors have to manage its own power by using one of energy harvesting techniques, having low power consumption for the wireless sensors is an important requirement, and star topology fit that purpose.

c) The condition of the base station being within the radio range of all nodes is not an issue for the discussed application, because the distribution of the wireless sensors and the transceiver station fixed on the hub guarantee that all wireless sensors will be in the radio range of the transceiver station (radio range will be discussed in section III part C).

d) The dependency of the network on a single node- base station- is an acceptable price to be paid for having low power consumption network.

Figure 6. Mesh and star network topology.

2) Reasons of choosing mesh network topology: A mesh network allows for any node in the network to transmit to any other node in the network that is within its radio transmission range. Mesh networks is self-healing, the network can still operate when one node breaks down or a connection goes bad. It allows for continuous connection and reconfiguration around broken or blocked paths by hopping from node to node until the final destination is reached. See Figure 7.

Figure 7. Mesh network structure. (a) all nodes operated. (b) broken connection. (c) reconfigured connection around broken one [8].

The advantages of mesh network topology are redundancy and scalability, the redundancy allows the remote node to communicate to any other node in its range, and scalability allows extending the range of network by just adding extra node to the network. Higher power consumption is the first disadvantage of mesh network topology due to the multi-hop communication technique, additionally, as the number of communication hops to the destination increase, the time to deliver the message also increase. Taking into consideration the advantages and disadvantages of mesh network topology and the proposed idea of using such topology for communication between the wind turbines, the following points are concluded:

a) Since the purpose of this research project is to monitor the wind turbine, it is crucial to have a redundant system that guarantee sustainable communication link.

b) The scalability of mesh network topology has a great advantage in the sense of extending the rage of the network by just adding the additional node to the existing network.

(a)

(b)

(c)

c) The higher power consumption is the price for the advantages mentioned previously.

d) The issue of getting longer time to deliver the message is not an issue in this specific application, because of the small size of data that has to be transmitted out from the wind turbine; where the measured data consist of simple information about temperature, wind speed and direction, heading angle, etc.

C. Radio Options for Wireless Sensor Network Four wireless standards are taken into consideration, the

WLAN (IEEE 802.11b/g), Bluetooth (IEEE 802.15.1), IEEE 802.15.4 and WiMax (IEEE 802.16). The four standards are examined to find the proper one for this research project requirement. The examination parameters are based on the requirements the communication system has to meet (targets are mentiond at the end of section II). TABLE I demonstrates the comparison between the four wireless communincation standards. Taking into consideration the requirements of the communication system listed in Section II, the distances between different sensors installed on the wind turbine and the distances between the wind turbines in a wind farm- as mentioned in section III, the following analysis is presented:

1) All listed standards are for wireless communication, which meet the first requirement.

2) Bluetooth standard is excluded from the selection due to the short coverage range and the limited number of nodes per network.

3) WLAN standard is also excluded from the selection because of relatively high transmission power compared to coverage range.

TABLE I. RADIO STANDARDS OPTIONS FOR WSN

WLAN IEEE

802.11b/g

Bluetooth IEEE

802.15.1 IEEE

802.15.4 WiMax

IEEE 802.16

Frequency (GHz) 2.4 2.4

2.4 (868MHz)

2-11 & 10-66

Data Rate (kb/s)

11000-54000 720 250 (20) 70000

Coverage Distance (m)

100 10 100-1500 1500 (for mobile station)

No. of nodes per network

Virtually unlimited

coordinates of the previous position [11] [12]. Direction =

(1)

It is important to highlight the fact that the GPS receiver calculates the direction based on the current position and the last saved position, so in order to have correct information about the direction, the GPS receiver should be in moving state. Stopping in a certain positioning and turning around without moving at least for 10 feet will not give the correct direction of the GPS receiver [13].

Considering the above explanation, it is found that using GPS to determine the heading direction of the wind turbine is not a feasible option for the following reasons:

1) Since two different locations is required to calculate the direction, determining the direction of not moving object wind turbine- is technically not possible.

2) Low accuracy of GPS receiver (in range of few meters).

3) Complicated data processing especially for the triangulation calculations.

4) High power consumption. B. Heading System using Inclinometer

An inclinometer (or tilt sensor) is an instrument for measuring angles of slope (tilt), or elevation of an object with respect to gravity [13], see Figure 8. Different technologies can be used within an inclinometer, these include electronic accelerometer, gas, and pendulum designs. Electronic inclinometer accuracy can typically range from 0.01 to 2. Since the inclinometer measures the angle with respect to the gravity, it cannot measure rotation around gravity vector [14] [15].

Figure 8. Function of inclinometer [15].

Considering the above explanation, it is found that using inclinometer to determine the heading direction of the wind turbine is technically not possible, because the inclinometer is not able to measure the angle around the gravity vector, and the Yaw angle in the wind turbine is around the gravity vector, as shown in Figure 2.

C. Heading System using Inertial Measurment Unit (IMU) IMU is an electronic device that measures velocity

orientation, and gravitational forces [16]. It consists of a combination of three axis accelerometer and three axis gyroscopes. The range of IMU is 360 and the accuracy can reach to 0.5. The IMU works by detecting the current rate of acceleration using one or more accelerometer, and detects changes in rotational attributes like pitch, roll and yaw using

one or more gyroscopes [17]. The incorporation of magnetometer allows the IMU to report an accurate yaw (heading) as well as pitch and roll [18].

Considering the above explanation, it is found that the IMU can be used to measure the heading angle of the wind turbine. Experimental studies have to be conducted to investigate its feasibility.

V. CONCLUSIONS In this paper the feasibility of building wireless sensor

network on wind turbine has been investigated. Also the options for installing a heading measurement system for wind turbine have been explored. The feasibility study conducted based on predefined targets. The paper shows that mesh network could be very reliable, as there is often more than one path between a source and a destination in the network. Also it is concluded that IEEE 802.15.4 is the most suitable communication standard for the wind turbine project taking into consideration its special conditions and requirements.

Using GPS or inclinometer to determine the heading angle of the wind turbine is technically not possible. However the inertial measurement unit is capable of determining the heading angle of the wind turbine.

VI. FUTURE STUDIES Further studies are needed to find the effect of

electromagnetic field produced by the wind turbine on both the wireless sensor network and the heading measurement system. Also it is needed to investigate the possibilities to power up the wireless sensor network by utilizing the already existing magnetic field around the wind turbine.

REFERENCES [1] Eddie OConnor, Chief Exceutive, Mainstream Renewable Power

2050 Challenge video interview on The European Wind Energy Association website, http://www.ewea.org/offshore/ [retrieved on 20.04.2010].

[2] Martcon, Wireless sensor networks & wind farms, 10 February 2010, The Vertoda Framework, http://www.vertoda.com/index.php/blog-menu/39-blogs-category/125-wireless-sensor-networks-a-wind-farms [retrieved on 21.04.2010].

[3] University of Magdeburg, Uni.ventus, wind farm monitoring and optimization, research project (phase 1) funded by ForMaT Unternehmen Region program of ministry of education and research in Germany.

[4] Steve Miller, Wind turbine model, 05 Nov 2009, Matlab Central, http://www.mathworks.co.jp/matlabcentral/fileexchange/25752-wind-turbine-model [retrieved on 26.04.2010].

[5] ENERCON, Windblatt, Enercon magazine for wind energy, issue 04, 2007, p.16.

[6] Allan Laursen Molbech, Pro/E & VR Administrator, Vestas Wind System A/S, Hannover Fair, April 2010 [verbal discussion], and V112-3.0MW One turbine for one world, Technical brochure, Vestas Wind System A/S, 8940 Randers SV, Denemark.

[7] Adi Mallikarjuna Reddy V, Wikipedia The Free Encyclopedia, Wireless sensor network, June 2007,ccccccccccccccccccccccccccccc http://en.wikipedia.org/wiki/Wireless_sensor_network [retrieved on 05.05.2010].

[8] Fdacosta, Wikipedia The Free Encyclopedia, Mesh networking, self-from self-heal, November 2007 http://en.wikipedia.org/wiki/File:Self-form-self-heal.gif [retrieved on 05.05.2010].

[9] GARMIN, What is GPS? Whats the signal, 1996-2010 Garmin Ltd. http://www8.garmin.com/aboutGPS/ [retrieved on 20.05.2010].

[10] Rare Niche Web Sites, How does a GPS receiver figure its distance from a GPS satellite?, How GPS Works, 2006-2008 Rare Niche Web Sites, http://www.how-gps-works.com/faq/q0111.shtml [retrieved on 20.05.2010].

[11] Rare Niche Web Sites, How does GPS triangulation work?, How GPS Works, 2006-2008 Rare Niche Web Sites, http://www.how-gps-works.com/faq/q0110.shtml [retrieved on 20.05.2010].

[12] Nel Samam, Global positioinig; technologies and performance, chapter 4, 2008 John Wiley & Sons, Inc.

[13] Gpsreview.net, What is an electronic compass?, 2005-2010 gpsreview.net, http://www.gpsreview.net/electronic-compass/ [retrieved on 20.05.2010].

[14] Jonathan, Bob, "How Does An Inclinometer Work?." How Does An Inclinometer Work?, August 2006, EzineArticles.com.ccccccccccccccc http://ezinearticles.com/?How-Does-An-Inclinometer--Work?&id=276738 [retrieved on 20.05.2010].

[15] Crossbow, CXTA tilt sensor datasheet, document part number: 6020-0013-01 Rev E, Crossbow Technology, Inc.ccccccccccccccccccccccccc http://www.xbow.com/Products/Product_pdf_files/Tilt_pdf/CXTA_Datasheet.pdf [retrieved on 20.05.2010].

[16] SignalQuest Precision Microsensors, SQ-SI2X-360DA solid state wide range MEMS inclinometer data sheet, September 2008, SignalQuest, Inc. 1999-2008, NH 03766 USA,cccccccccccccccccccccc http://www.signalquest.com/datasheets/SQ-SI2X 360DA_Wide%20Range%20MEMS%20Inclinometer%20Datasheet.pdf [retrieved on 20.05.2010].

[17] Wikipedia, Inertial measurment unit, Wikepedia the free encyclopedia, May 2010,cccccccccccccccccccccccccccccccccccccccccc http://en.wikipedia.org/wiki/Inertial_measurement_unit [retrieved on 20.05.2010].

[18] Microstrain, Inclinometer and orientation sensors, Microstrain Inc., http://www.microstrain.com/pdf/Shortform%20Orientation%20Ad.pdf [retrieved on 20.05.2010].

[19] Microstrain, 3DM-GX3-25 heading reference system data sheet, Microstrain Inc.,http://www.microstrain.com/product_datasheets/3DM-GX3-25_datasheet_version_1.04.pdf [retrieved on 20.05.2010].

Hakam B.E. Saffour is a PhD candidate in the field of communication engineering at Otto von Guericke University Magdeburg in Germany. He received his B.Sc. in Electronics Engineering from Princess Sumaya University of Applied Sciences in Jordan, and M.Sc. in Electronics Systems & Engineering Management from University of Bolton in UK and South Westphalia

University of Applied Sciences in Germany. His main topics of interests are wireless sensor network, WiMax, and heading measurment system.

Prof. A.S. Omar is a professor in the filed of high frequency technology, and the head of Institute of Electronics, Signal Processing and Communication of the Otto von Guericke University Magdeburg.