Multi-Receiver GPS-based Direct Time Estimation for PMUs Sriramya - PowerPoint PPT Presentation

Multi-Receiver GPS-based Direct Time Estimation for PMUs Sriramya Bhamidipati, Yuting Ng and Grace Xingxin Gao University of Illinois at Urbana-Champaign University of Illinois at Urbana-Champaign CREDC All Hands Meeting | Oct 14 2016

Motivation • Supply and demand of electricity should be balanced to maintain power grid stability • Power grid vulnerable to External attacks Natural disasters Man-made errors University of Illinois at Urbana-Champaign 1

Massive power blackouts Northeast Brazil Java-Bali India USA 2009 2005 2012 2003 87 million 670 million 50 million 100 million people affected people affected people affected people affected University of Illinois at Urbana-Champaign 2

Goals of US power community • Synchronized phasor measurements • Reliable communication network • Real-time information monitoring • Automation of the power grid • Improving the security margins Development of reliable and robust Smart Power Grid University of Illinois at Urbana-Champaign 3

Goals of US power community • Synchronized phasor measurements In use currently Supervisory • Reliable communication network Control and Data Acquisition • Real-time information monitoring (SCADA) • Automation of the power grid • Improving the security margins University of Illinois at Urbana-Champaign 4

Goals of US power community • Synchronized phasor measurements In use currently Supervisory • Reliable communication network Control and Data Acquisition • Real-time information monitoring (SCADA) • Automation of the power grid • Improving the security margins Switching to Phasor Measurement Units (PMUs) University of Illinois at Urbana-Champaign 4

Phasor Measurement Unit (PMU) • Highly synchronized measurements • PMU measures current and voltage in power grid [NASPI] University of Illinois at Urbana-Champaign 5

GPS Timing for PMUs GPS used for time synchronization Power grid GPS GPS clock PMU Antenna Advantages Global coverage Freely available 𝜈𝑡 -level accurate time University of Illinois at Urbana-Champaign 6

GPS Conventional Approach • Inputs • Center: 3D satellite position • Radius: Pseudoranges • Unknowns to be estimated: • 3D position 𝐲, 𝐳, 𝒜 • Methodology Trilateration technique • Trilateration technique University of Illinois at Urbana-Champaign 7

GPS Conventional Approach • Inputs • Center: 3D satellite position • Radius: Pseudoranges • Unknowns to be estimated: • 3D position 𝐲, 𝐳, 𝒜 • Clock bias 𝒅𝜺𝒖 • Methodology Trilateration technique • Trilateration technique • Minimum 4 satellites required University of Illinois at Urbana-Champaign 7

GPS Timing for PMUs GPS used for time synchronization Power grid GPS GPS clock PMU Antenna Advantages Disadvantages Global coverage Unencrypted structure Freely available Low signal power 𝜈𝑡 -level accurate time Vulnerable to attacks University of Illinois at Urbana-Champaign 8

GPS Timing Attacks Authentic Authentic GPS signals GPS signals Power sub-station High-power Power noise signal sub-station Replay signal with high power Jamming: Makes timing Meaconing: Mislead PMU unavailable for PMUs with wrong time University of Illinois at Urbana-Champaign 9

Objectives Propose a robust GPS time transfer technique to: • Mitigate the effect of external timing attacks • Improve tolerance against noise and interference University of Illinois at Urbana-Champaign 10

Outline Motivation and Objectives GPS Conventional approach Multi-Receiver Direct Time Estimation (MRDTE) Experimental setup Results and Analysis Ongoing Work Summary University of Illinois at Urbana-Champaign 11

MRDTE: Approach Power substation, Sidney, IL University of Illinois at Urbana-Champaign 12

MRDTE: Approach • Multiple receivers Receiver • Geographical diversity Receiver Receiver Receiver Power substation, Sidney, IL University of Illinois at Urbana-Champaign 12

MRDTE: Approach • Multiple receivers Receiver • Geographical diversity Receiver • Position Aiding • Static receiver location Receiver Receiver Power substation, Sidney, IL University of Illinois at Urbana-Champaign 12

MRDTE: Approach • Multiple receivers Receiver • Geographical diversity Receiver • Position Aiding • Static receiver location • Direct Time Estimation (DTE) Receiver • Works with timing parameters • Receiver No intermediate pseudoranges Power substation, Sidney, IL University of Illinois at Urbana-Champaign 12

MRDTE: Approach • Multiple receivers Receiver • Geographical diversity Receiver • Position Aiding • Static receiver location • Direct Time Estimation (DTE) Receiver • Works with timing parameters • Receiver No intermediate pseudoranges • Triggered by common external Power substation, Sidney, IL clock Reduction in no. of unknowns from z, cδ t × # of receivers to 2 (cδt, cδ 8 x, y, z, cδt, x, y, t) University of Illinois at Urbana-Champaign 12

MRDTE: Architecture Raw GPS signals from multiple receivers 2 MRDTE 3 1 Direct Time Estimation 4 Output from PMU: Synchronized All receivers phasor triggered by a measurements common clock MRDTE Filter Time PMU University of Illinois at Urbana-Champaign 13

MRDTE: Architecture Raw GPS signals from multiple receivers 2 MRDTE 3 1 Direct Time Estimation 4 Output from PMU: Synchronized phasor All receivers measurements triggered by a common clock MRDTE Filter Time PMU University of Illinois at Urbana-Champaign 14

Direct Time Estimation Clock Bias Receiver All satellites 3D position 3D position Across the and velocity and velocity candidates in Clock Drift search space Combined satellite signal replica University of Illinois at Urbana-Champaign 15

Direct Time Estimation Clock Bias Receiver All satellites 3D position 3D position Across the and velocity and velocity candidates in search space Clock Drift Combined satellite signal replica Vector Correlation Incoming raw GPS signal University of Illinois at Urbana-Champaign 15

Direct Time Estimation Clock Bias Receiver All satellites 3D position 3D position Across the and velocity and velocity candidates in search space Clock Drift Combined satellite Maximum signal replica likelihood clock state Vector Correlation Incoming raw GPS signal University of Illinois at Urbana-Champaign 15

DTE: Vector Correlation Code phase depends Carrier frequency depends on clock bias on clock drift Code residual ( Δ𝜚 𝑑𝑝𝑒𝑓 ) , Carrier residual (Δ𝑔 𝑑𝑏𝑠𝑠 ) independently estimated in two parallel threads University of Illinois at Urbana-Champaign 16

DTE: Vector Correlation Continued Direct correlation involves non-coherent summation • Non-coherent summation across satellites to track code phase and carrier frequency. University of Illinois at Urbana-Champaign 17

DTE: Max Likelihood Estimation 𝑂 Maximum 𝑍 𝑗 𝑑𝜀𝑢 𝑘 , 𝑑𝜀 𝑑𝑝𝑠𝑠 𝑘 = 𝑑𝑝𝑠𝑠 𝑆, 𝑢 𝑘 likelihood clock state 𝑼 𝑵𝑴𝑭 𝑗=1 𝑈 𝑁𝑀𝐹 = 𝑛𝑏𝑦 𝑘=1,..,𝑄 𝑑𝑝𝑠𝑠 𝑘 = [𝑑𝜀𝑢 𝑁𝑀𝐹 , 𝑑𝜀 𝑢 𝑁𝑀𝐹 ] Where, 𝑄 = number of grid points 𝑆 = incoming raw GPS signal 𝑍 𝑗 = 𝑗 𝑢ℎ satellite signal replica University of Illinois at Urbana-Champaign 18

DTE: Robustness Strong signal environment Weak signal environment Direct Time Estimation Across the satellites ... ... Direct Time Estimation more robust than Scalar Tracking University of Illinois at Urbana-Champaign 19

MRDTE: Architecture Raw GPS signals from multiple receivers 2 MRDTE 3 1 Direct Time Estimation 4 Output from PMU: Synchronized phasor All receivers measurements triggered by a common clock MRDTE Time Filter PMU University of Illinois at Urbana-Champaign 20

MRDTE Filter: Kalman Filter • Prediction model: Overall Measurement Time error 𝑈 𝑢+1,𝑙 = 1 Δ𝑈 𝑈 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 𝑈 update 𝑓 𝑢.𝑙 0 1 𝑢+1,𝑙 State vector 𝑈 𝑢,𝑙 = 𝑑𝜀𝑢 𝑙 Measurement • 𝑑𝜀 𝑢 𝑙 update 𝑈 𝑢,𝑙 • Error covariance matrix is Overall calculated by processing measurement the last 19 measurement update 𝑈 errors 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 University of Illinois at Urbana-Champaign 21

MRDTE Filter: Overall Filter • Overall filter to obtain the Overall Measurement final corrected clock state Time error 𝑈 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 𝑈 update 𝑓 𝑢.𝑙 𝑢+1,𝑙 • Measurement error matrix Measurement 𝑢,1 − 𝑈 𝑈 update 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 : 𝑓 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 = 𝑈 𝑢,𝑙 − 𝑈 𝑈 𝑢,𝑙 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 𝑢,𝑀 − 𝑈 𝑈 Overall 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 measurement 𝑢,𝑙 = 𝑑𝜀𝑢 𝑙 update Where 𝑈 𝑙 = 1. . 𝑀 𝑑𝜀 𝑈 𝑢 𝑙 𝑢,𝑝𝑤𝑓𝑠𝑏𝑚𝑚 University of Illinois at Urbana-Champaign 22