1. Relay Placement Problem in Smart Grid Deployment Wei-Lun Wang and Quincy Wu Department of Computer Science and Information Engineering, National Chi Nan University, Puli, Nantou, Taiwan

2. 2 Outline Power Grid V.S. Smart Grid System Architecture of National Science Council (NSC) Program in Taiwan Importance of the Intelligent Relay Placement Module Mathematical Facts about Relay Placement Conclusions & Future Works

3. 3 Power Grid [http://www.ferc.gov/industries/electric/indus-act/blackout/09-06-final-report.pdf]http://www.ferc.gov/industries/electric/indus-act/blackout/09-06-final-report.pdf The power grid is an interconnected network for delivering electricity from suppliers to consumers. In this kind of traditional power grid, some energy issues are needed to be noticed.

4. 4 Some Energy Issues Reliability (unexpected blackout) Economy (cost $25 to $180 billion annually) Efficiency (Pareto principle, 80-20 rule) Affordability (electricity price goes up and up) Environmental Impacts (greenhouse gas) Therefore, to improve the energy utilization efficiency, a better power grid is desired. That is why the smart grid was proposed for efficiently utilizing the limited resources.

5. 5 Smart Grid [http://www.ngpowereu.com/news/smart-grid-revolution]http://www.ngpowereu.com/news/smart-grid-revolution Like the power grid, the smart grid also delivers electricity from suppliers to consumers. However, it uses two–way digital technology to support communication between consumers and suppliers. It combines power systems, telecommunications, smart energy devices, information technology, and digital control.

6. 6 Characteristics Sensing and Measurement (suspicious behaviors) Integrated Communication (Critical Peak Pricing, CPP) Improved Interfaces and Decisions Support (credit points) Advanced Components (storage facilities) Advanced Control Methods (handle the whole system) To build a smart grid system, an advanced metering infrastructure (AMI) is required to actively measure, collect, and analyze energy consumption data.

7. 7 AMI (Advanced Metering Infrastructure) Generally, an AMI system consists of four components – the smart meter, the energy display and controller, the communication network, and the meter data management application (MDMA).

8. 8 National Science Council Program in Taiwan Four subprojects  Smart Power–saving Outlets  Small–scale Energy Storage System  Network and Communication Technology  Smart Energy Management Application Service Platform

9. 9 Interactive Relevance within Subprojects No matter how intelligent and wonderful the smart grid is, the cost of deployment and maintenance will be a key factor which will determine whether this new technology will be successful and widely adopted.

10. 10 Factors that Affect Deployment Cost [http://www.topology.com.tw/tri] (Topology Research Institute)http://www.topology.com.tw/tri

11. 11 Relay Placement Problem (RPP) To find positions of minimum number of relays in a smart grid system.

12. 12 Relay Placement Problem (RPP) Problem Definition  Input On an Euclidean plane, given a set of N sensors, which have the effective communication range 1, and a fixed number R ≥ 1, which is the effective communication range of a relay.  Output To place a minimum number of relays so that between every pair of sensors there is a path through sensors and/or relays such that the consecutive vertices of the path are within distance R if both vertices are relays and within distance 1 otherwise. We then use two different methods to deploy relays and compare their results.

13. 13 A Bad Deployment of Relays 1 < D ≦ 2

14. 14 A Wise Deployment of Relays 1 < D ≦ 2

15. 15 Mathematical Facts about Relay Placement Comparison of the amount of used relays BAD : WISE : Assume N=1000, D=2, and R=4. The required number of relays for the first approach is approximately 80919; however, the second approach only needs 1080 relays. That is to say, people who adopt the first approach to deploy relays must spend nearly 75 times higher cost than those who choose the second approach.

16. 16 Approximation Algorithms and Variations of RPP NP-hard Since Minimum Geometric Disk Cover (MGDC) problem is a special case of RPP, and MGDC is known to be NP–complete [9], RPP is an NP–hard problem. Variations  Form a connected network  Form a 2-connected network (higher reliability) Approximation Ratio Comparisons

17. 17 [THS2006]’s 8-approximation Algorithm for RPP Given a set of 25 sensors whose effective communication range is s = 1, and R = 2 is the effective communication range of a relay. Sensor Relay Sensor Relay

18. 18 [THS2006]’s 8-approximation Algorithm for RPP (cont.) Step 1a. Divide the region into cells with side length D = 2s = 2. For each cell, find all P-positions for relays. D = 2

19. 19 [THS2006]’s 8-approximation Algorithm for RPP (cont.) Step 1b. Apply a shrink operation. Step 2. Inside each cell C i, find a smallest subset of P-positions H i which can cover all sensors in the cell.

20. 20 Step 3. For each cell C i, if either H i and H i (Right) are not connected or H i and H i (Bottom) are not connected, add a relay at the right bottom corner of C i (add a relay at the right top corner of C i if C i is in the bottom row). [THS2006]’s 8-approximation Algorithm for RPP (cont.) Sensor Relay Sensor Relay (added in Step 2) RelayRelay (added in Step 3)

21. 21 Conclusions & Future Works The deployment cost of a smart grid system is crucial to its success. This paper illustrated the Relay Placement Problem, which significantly affects the cost of an AMI system when ZigBee is adopted in its communication network. To solve the Relay Placement Problem, we demonstrated a decision supporting system in our NSC project, which adopted intelligent algorithms to minimize the number of relays in question. When deploying larger networks, where significant amount of relays are needed, an efficient RPP algorithm would be very important to control the deployment cost. Thank you ~