Co-optimal Placement in Wide Area Measurement Systems

Xiaoxia Zhangx79zhang@bbcr.uwaterloo.ca

[1] M. Shahraeini, M.S. Ghazizadeh, and M.H. Javidi. Co-optimal placement of measurement devices and their related communication infrastructure in wide area measurement systems. Smart Grid, IEEE Transactions on, (99):1-8, 2012.[2] M. Shahraeini, M.H. Javidi, and M.S. Ghazizadeh. Comparison between communication infrastructures of centralized and decentralized wide area measurement systems. Smart Grid, IEEE Transactions on, 2(1):206-211, 2011.

Outline

• Introduction• Problem Formulation• Simulation Results• Conclusions

Introduction

Wide Area Measurement System

• Wide area measurement system (WAMS) is a measurement system include digital metering devices and communication system designed to monitor, operate and control in wide geographical area.

• WAMS process features three functions:Data acquisitionData transmittingData processing

Data Acquisition

• Performed by measuring devices• Devices are responsible for providing raw data

for different applications• Examples of devices:

Phasor measurement unit (PMU) Supervisory control and data acquisition (SCADA) Remote terminal unit (RTU) Digital protective relay (DPR) Digital fault recorder (DFR)

Data transmitting

• A communication infrastructure (CI) should be established

Data processing

• Performed by software packages in energy management systems (EMS)

• EMS applications has functions of operation, control and optimization in power systems based on the acquired dara.

• EMS functions include:Online state estimation (SE)Load flow (LF)Optimal power flow (OPF)Load forecast (LF) Online low-frequency oscillation (LFO) analyses

State Estimation

• Data acquired by measuring devices are raw data• Cannot be used by EMS applications directly• Online state estimation (SE) extracts creditable

data from raw data • Creditable data can be used by applications• SE is the basis of EMS applications

Phasor Measurement Unit (PMU)

• A data resource commonly used• Measures voltage and current phasors• Lead to a simplified linear state estimator• Sample rate is very high (30-60 samples per

second)• High data rate transmission is required• Focus of this work

Research issues

• Measurement placement study:

Observability: A system is observable if #of measured var. >= # of var. that should be estimated

• EMS application design:Fast and efficient algorithms for EMS applications

Research issues

• Communication infrastructure (CI) design and planningDependent media (parts of power network elements):

power line communication (PLC), all-dielectric self supporting (ADSS), and optical power ground wire (OPGW).

Independent media: wireless and satellite communication.

• Dependent media can be co-optimally designed in conjunction with power system planning problems.

Problem Formulation

Problem Formulation

• Objective: co-optimize the meter placement and its CI for state estimation problem.

• Measurement device: PMU• Transmission media: OPGW• Optimization tool: genetic algorithm (GA) due

to its accurate solution where high complexity is not a major concern

Subproblem 1:PMU placement opt.

• A PMU on a bus can observe this bus and all its incident buses.

• PMU placement: find minimum set of PMUs such that the entire system can be observed.Cost for one PMU Indicates whether there

is a PMU on bus i

n-dimentional arrays

Subproblem 1 Cont’d

• Define adjacency matrix

• Observability:• Add up the columns i of adjacency matrix if

PMUi=1. If the array of summation vector are equal or bigger than 1.

Subproblem 1 Cont’d

• Define adjacency matrix

• Observability:• Add up the columns i of adjacency matrix if

PMUi=1. If the array of summation vector are equal or bigger than 1.

Subproblem 1 Cont’d

• Gene (objective+constraint):

• Optimal case: fitness<1

Total # of PMUs Total # of zero arrays in OBS vector

Subproblem 2: Communication Links optimization

• OPGW cables perform both grounding and communication.

• Objective: find a minimal OPGW plan which covers all PMU enabled buses.

Cost per km cable Length of ith linkTotal # of OPGW links

Subproblem 2 Cont’d

• penalty:PMU enabled bus with maximum conjunction is found as

starting nodeThe path from starting node to all other PMU enabled bus is

examinedIf a path does not exist, increase the penalty function by 1

• Optimal case: fitness<1

Total length of transmission lines

Co-optimal Placement of PMUs and Links

• Objective: find the optimal set of PMUs and its required communication links simultaneously.

• Can be solved by multiobjective genetic algorithm (MOGA)

Simulation Results

• Comparison of two methods of placement:Independent

Find the optimum placement of PMUs, then determine the communication links

SimultaneousDetermine the placement of PMUs and links

together

Simulation Results

• IEEE 30, 57, 118-bus test networks

Simulation Results

CI Nodes: the number of nodes in their corresponding CIsOPGW Coverage: the length percentage of transmission lines which should be equipped by OPGW cable. Total Cost: the total cost of PMU sites and their corresponding CI.

Conclusions

• Optimal placement of PMUs and their required communication infrastructure of power systems are co-optimally designed for state estimation problem.

• Although the number of measurement devices, for full observability of the system, may be increased by proposed approach, the considerable reduction in communication media decreases the total cost of WAMS implementation.

Questions and Discussion?

Thank you!

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