Advanced Phasor Measurement Units for the Real-Time Monitoring of Transmission and Distribution Networks Paolo Romano Distributed Electrical Systems Laboratory École Polytechnique Fédérale de Lausanne - EPFL Good morning everyboy, most of you know me already. My name is Paolo Romano and I am here for presenting my research plan proposal for my candidacy exam. As you can see form the title I am going to talk about PMU and I hope to do it in the most clear and easy way.

Outline Introduction PMU requirements Proposed synchrophasor estimation algorithm Algorithm implementation Experimental validation Conclusion

Introduction (1) Power networks new paradigms Evolution of distribution networks passive  active major changes in their operational procedures; need of advanced and smarter tools to manage the increasing complexity of the grid; main involved aspect is the network monitoring by means of Phasor Measurement Units (PMUs); PMU definition (as stated in IEEE Std.C37.118-2011): “A device that produces synchronized measurements of phasor (i.e. its amplitude and phase), frequency, ROCOF (Rate of Change Of Frequency) from voltage and/or current signals based on a common time source that typically is the one provided by the Global Positioning System UTC-GPS.”

Introduction (2) What is a Phasor Measurement Unit (PMU)? PMU timeline: 1988 1st PMU prototype 1992 1st commercial PMU 1995 Standard (IEEE 1344) 2005 New PMU (IEEE C37.118 -2005) 1893 Introduction of “Phasor” concept 1980s GPS technology 2011 Latest version of IEEE Std. C37.118-2011 2012 1st PMU prototype at EPFL PMU typical configuration:

Introduction (3) PMU applications within transmission networks

Introduction (4) PMU applications within active distrib. networks Phasor Data Concentrator - PDC RT Power System State Estimator Network in normal operation: Voltage sensitivities computation Power flows sensitivities computation V/P real time optimal control Real time congestion management Network in emergency conditions: Islanding detection Fault identification Fault location The main focus of this activity together with several other project from our lab is concentrated on the development of a new infrastructure where the protection and control functionalities are concentrated and unified in a single object Within this context the PMU plays a very relevant role since it’s the device the support the whole infrastructure. In particular… = Phasor Measurement Unit

PMU requirements (1) IEEE Std. C37.118-2011 - Definitions Synchrophasor definition:

PMU requirements (2) IEEE Std. C37.118-2011 – Measurement compliance Reporting rates: Performance classes: P-class: faster response time but less accurate M-class: slower response time but greater precision Measurement evaluation:

PMU requirements (3) Active Distribution Networks applications Peculiar characteristics of distribution networks: reduced line lengths; limited power flows values; high harmonic distortion levels; dynamic behaviors Improved accuracy of synchrophasors measurements

PMU requirements (4) Active Distribution Networks applications  synchrophasor #1  synchrophasor #2

4 Harmonic interference Proposed synchrophasor est. algorithm (1) State of the Art of DFT based algorithms Considered error sources: 4 Harmonic interference 3. Short range leakage 1. Aliasing 2. Long range leakage

4 Harmonic interference Proposed synchrophasor est. algorithm (2) State of the Art of DFT based algorithms Correction approaches: Iterative compensation of the self-interaction Use of appropriate windowing functions Introduction of adequate anti-aliasing filters Increasing of the sampling frequency 1. Aliasing 2. Long range leakage 3. Short range leakage 4 Harmonic interference Interpolated DFT methods

Proposed synchrophasor est Proposed synchrophasor est. algorithm (3) Structure of the proposed algorithm Signal acquisition (voltage/current), within a GPS-PPS tagged window T (e.g. 80 ms, i.e. 4 cycles at 50 Hz) with a sampling frequency in the order of 50-100 kHz. DFT analysis of the input signal, opportunely weighted with a proper window function. First estimate of the synchrophasor by means of an interpolated-DFT approach. Iterative correction of the self-interaction between the positive and negative image of the DFT main tone.

Proposed synchrophasor est. algorithm (4) Flow chart

Proposed synchrophasor est. algorithm (4) Flow chart 3-4 periods of the fundamental frequency tone

Proposed synchrophasor est. algorithm (4) Flow chart Hanning window:

Proposed synchrophasor est. algorithm (4) Flow chart

Proposed synchrophasor est. algorithm (4) Flow chart

Proposed synchrophasor est. algorithm (5) Flow chart

Proposed synchrophasor est. algorithm (5) Flow chart

Proposed synchrophasor est. algorithm (5) Flow chart

Proposed synchrophasor est. algorithm (5) Flow chart

Proposed synchrophasor est. algorithm (5) Flow chart

Algorithm implementation (1) FPGA-optimized software implementation

Algorithm implementation (2) FPGA-optimized software implementation Process 1 Process 2 Process 3 GPS-synchronization process: Time uncertainty of ± 100 ns Compensation of the FPGA clock drift Pipelined signal acquisition: 6 parallel channels (3 voltages 3 currents) Phase correction Synchrophasor estimation algorithm: Optimized DFT computation for power systems typical frequencies 32-bits fixed-point implementation

Algorithm implementation (3) Phase correction

Algorithm implementation (4) FPGA clock error compensation

Experimental validation (1) Compliance verification platforms HW - PXI based platform: SW - Desktop based platform: Generate the test signal in host according to each test item in IEEE C37.118, 2011 then run the FPGA algorithm in desktop. Control and synchronization of the other PXI boards Time-Sync accuracy ±100 ns with 13 ns standard deviation 18-bit resolution inputs at 500 kS/s, analog input accuracy 980 μV over ±10 V input range (accuracy of 0.01%)

Experimental validation (2) Static tests – Signal frequency range

Experimental validation (3) Static tests – Harmonic distortion

Experimental validation (4) Dynamic tests – Amplitude-phase modulation

Experimental validation (5) Dynamic tests – Frequency sweep

Experimental validation (6) Dynamic tests – Amplitude step

Conclusions (1) Future improvements Design of a iDFT algorithm satisfying both class P and M requirements: Sensitivity to algorithm parameters (Fs, N, w(n), interpolation scheme, no. of iteration) Out of band interference test compliance (signal pre-filtering) Adaptation of the algorithm to specific hardware platform: NI-9076 (SIL-nanotera) Zynq Integration of GPS-independent synchronization systems: Autonomous clocks (e.g. Rubidium-Oscilloquartz) External synchronization signals provided by telecom protocols (Alcatel)

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