Presentation

1,019 views

Published on

On-line Method for Identifying Harmonic Sources in Power Systems

1 Comment
0 Likes
Statistics
Notes
  • Be the first to like this

No Downloads
Views
Total views
1,019
On SlideShare
0
From Embeds
0
Number of Embeds
17
Actions
Shares
0
Downloads
36
Comments
1
Likes
0
Embeds 0
No embeds

No notes for slide
  • Hello My name is Prayag Parikh. I am a Master’s student at University of North Carolina at charlotte. Topic of my today’s presentation is diagnostics and prognostics for multiple induction machines using a single set of current transducers. It is a part of my thesis. During this project I was helped by Rebecca, Arun and Jason. My work in this project was guided by my adviser Dr. Robert Cox.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Induction machines are the work horses of modern commercial and industrial applications. Induction machines are everywhere, in commercial-industrial buildings, power plants ,shipboards and air-plane. Failure of critical induction machine can cost millions of dollars in terms of cost of maintenance and lost of revenue. In some cases failure of induction machine can also jeopardize the safety of personals working on the floor.
  • Figure shows the block diagram of standard NILM. Typical installation location includes switchboards and motor control centers. From the block diagram it can be seen that NILM measures line voltages and aggregate current going to a bank of loads. Here data acquisition module converts analog data in to digital form with the help of 12bit A-to-D converter. Preprocessor uses these raw current and voltage data to get the active and reactive component of current. Event classifier uses preprocessed data to disaggregate individual load from the aggregate current data. Diagnostic and systems manangement module produces useful statistics for the operator, which can be used to analyze the health of different loads. Further slides will describe each block of NILM in detail.
  • Currently NILM is monitoring aggregate power flowing to loads of US Navy’s DDG-51 Land based engineering site. This site is a mock-up of no. 2 main engine room aboard a DDG-51 class destroyer. This site includes Low pressure air compressors for pneumatic valve actuation and tool operations. Figure shows the power drawn at one of the switchboards serving the DDG-51 Land based Engineering site. The beginning of each LPAC load interval has been shown with a circle. In this system compressor is running continuously, whenever receiver tank needs to be pressurized compressor is loaded and it consumes more power. Once the tank is properly pressurized compressor is unloaded and it consumes less power. Currently NILM logging load and unload intervals.
  • Presentation

    1. 1. On-line Method for Identifying Harmonic Sources in Power Systems Himanshu Jain Advised by Prof. Robert Cox University of North Carolina, Charlotte
    2. 2. Problem Description <ul><li>Non-linear power electronic loads introduce harmonic currents into power systems </li></ul><ul><li>These currents can have detrimental effects </li></ul>
    3. 3. Problem Description <ul><li>Harmful effects include: </li></ul><ul><ul><li>Overloading of neutrals </li></ul></ul><ul><ul><li>Overheating of transformers </li></ul></ul><ul><ul><li>Nuisance tripping of circuit breakers </li></ul></ul><ul><ul><li>Over-stressing of power factor correction capacitors </li></ul></ul><ul><ul><li>Unbalanced voltages </li></ul></ul><ul><li>Utilities would like an effective way to charge customers for creating these harmonics </li></ul>
    4. 4. Outline <ul><li>Discussion of harmonic sources </li></ul><ul><ul><li>Linear vs. non-linear loads </li></ul></ul><ul><ul><li>The difficulty of identify harmonic sources </li></ul></ul><ul><li>Proposed measurement approach </li></ul><ul><li>Experimental results </li></ul>
    5. 5. Harmonic Sources <ul><li>Non-linear loads are very common </li></ul><ul><ul><li>Most common example: Rectifier </li></ul></ul><ul><li>Load current contains many harmonics, typically odd harmonics </li></ul>
    6. 6. Quantifying Harmonics <ul><li>Total harmonic distortion </li></ul><ul><li>Each harmonic as a percentage of the total RMS value </li></ul><ul><li>Could customers be charged for their THD? </li></ul>
    7. 7. Coupling <ul><li>Generally, linear loads do not draw harmonics </li></ul><ul><li>Problem: Harmonic currents from non-linear loads produce a distorted voltage waveforms because of line impedances </li></ul>
    8. 8. Example <ul><li>Problem: Heater will also distort the PCC voltage because the PCC is distorted </li></ul><ul><ul><li>This masks the effects of the rectifier </li></ul></ul><ul><ul><li>But, the heater would not have drawn such currents, however, without the rectifier </li></ul></ul>Current harmonics for heater Current harmonics for rectifer Harmonic Number Current w/ Rectifier in Parallel (A RMS) Current w/o Rectifier in Parallel (A RMS) 1 st 6.6 6.7 3 rd 0.1 0 5 th 0.1 0 7 th 0.1 0 Harmonic Number Current w/ Heater in Parallel (A RMS) Current w/o Heater in Parallel (A RMS) 1 st 1.1 1.3 3 rd 0.9 1.2 5 th 0.6 0.9 7 th 0.3 0.6
    9. 9. Potential Solutions <ul><li>It is difficult to charge customers for harmonics because harmonic voltages in the PCC affect the harmonics that are drawn </li></ul><ul><li>Several methods have been considered: </li></ul><ul><ul><li>Power direction method </li></ul></ul><ul><ul><ul><li>Xu et al. 2003 proved that this method is flawed </li></ul></ul></ul><ul><ul><li>Neural network method </li></ul></ul><ul><ul><ul><li>Mazumdar et al. 2007 created a NN mapping between PCC voltage and current – no physical meaning </li></ul></ul></ul><ul><li>Here we present a different approach </li></ul>
    10. 10. Proposed Approach <ul><li>One potential method would be to </li></ul><ul><ul><li>Detect operation of non-linear loads </li></ul></ul><ul><ul><li>Determine their harmonic content given “ideal” conditions </li></ul></ul><ul><li>Requires: </li></ul><ul><ul><li>Load model </li></ul></ul><ul><ul><li>Knowledge of source impedance </li></ul></ul>
    11. 11. Smart Meters <ul><li>As a part of Smart Grid efforts, utilities are deploying Smart meters throughout the country </li></ul><ul><li>Smart meters could perform necessary measurements with software changes </li></ul>
    12. 12. NILM Overview
    13. 13. Transient-Based Identification <ul><li>Transient electrical behavior is strongly influenced by the physical task performed by the load </li></ul>
    14. 14. Load Identification <ul><li>Templates are matched to power data </li></ul>
    15. 15. Proposed Approach <ul><li>First step: A Smart Meter with NILM software must identify the operation of a non-linear load such as a motor drive </li></ul><ul><li>Example templates for VSD: </li></ul>
    16. 16. Impedance Estimation <ul><li>Line impedance is the major cause of distortion in the PCC </li></ul><ul><li>Line impedance is small and time-varying </li></ul><ul><li>Typical measurement method: </li></ul><ul><ul><li>Inject large currents at the PCC </li></ul></ul><ul><ul><li>Requires additional expensive hardware </li></ul></ul><ul><li>Currents are normally injected very close, but not at, 60Hz </li></ul>If ω inj ≠ ω s
    17. 17. Our Approach <ul><li>Loads such as motors and power electronics naturally inject currents into the line that are close to the line frequency. </li></ul><ul><li>Example: 4-pole induction motor current spectrum </li></ul><ul><li>Injected signals are much smaller, so the measurement problem is more difficult, but it is far cheaper and more convenient solution </li></ul>
    18. 18. Our Approach and Results <ul><li>Traditional frequency domain approaches (FFT) are limited because of the small signal </li></ul><ul><li>Approach is based on communications theory, i.e. detection of small sinusoidal signals in the presence of noise </li></ul><ul><li>Maximum likelihood estimation scheme is used to estimate the amplitude, frequency, and phase of the “injected” signal </li></ul>
    19. 19. Model Identification <ul><li>The problem: When simulating the isolated rectifier with a pure sinusoidal source, how should it be modeled? </li></ul><ul><li>Consideration: Typically, the rectifier is loaded by a constant power load (i.e. a regulator or an inverter driving a motor) </li></ul><ul><li>Our assumption: </li></ul><ul><ul><li>When the converter is isolated in simulation, the power demand on the output side is the same as when the rectifier is connected in the system with the non-ideal source </li></ul></ul>
    20. 20. Model Identification of Non-linear load <ul><li>Research has shown that a reasonable rectifier model with a constant power load (i.e. regulator) is the following: </li></ul><ul><li>Question: How do you measure output power?? </li></ul><ul><li>Output power can be measured: </li></ul><ul><ul><li>In most large power-electronic drives, the DC link voltage is known </li></ul></ul><ul><ul><li>The DC current can be measured from the AC-side current </li></ul></ul><ul><li>The diodes are assumed to be ideal </li></ul><ul><li>The nameplate value for the capacitor is used </li></ul>
    21. 21. Simulation <ul><li>An ideal source is connected to an isolated rectifier and a simulation is performed in Simulink </li></ul><ul><li>DC current is adjusted until output power matches on-line value </li></ul>
    22. 22. Simulation <ul><li>FFT of current is used to determine the contribution of desired harmonics </li></ul>
    23. 23. Experimental Setup <ul><li>Resistively-loaded rectifier connected in parallel with 900W heating element </li></ul><ul><li>Loads are connected to single-phase test source through 1.5 Ohms and 0.3mH </li></ul><ul><li>Both NILM and a Fluke power meter are used for measurement </li></ul>
    24. 24. Current Plots Heater Current Total Current Rectifier Current
    25. 25. Model Validation <ul><li>To test the validity of the method, several tests were performed with the rectifier only and the results were compared to the simulation </li></ul><ul><ul><li>Test 1: Pure sinusoidal excitation </li></ul></ul><ul><ul><li>Test 2: Excitation with 10% third harmonic added </li></ul></ul>Test 1 Test 2 Harmonic Number Simulated Current (A rms) Measured Current (A rms) 1 st 1.3 1.3 3 rd 1.2 1.2 5 th 1.0 0.9 7 th 0.7 0.6 Harmonic Number Simulated Current (A rms) Measured Current (A rms) 1 st 1.2 1.2 3 rd 1.0 1.0 5 th 0.6 0.6 7 th 0.3 0.3
    26. 26. Experimental Measurements <ul><li>Current drawn by rectifier with and without the heating element turned on: </li></ul>Harmonic Number Current w/o Heater (A rms) Current w/ Heater (A rms) 1 st 1.3 1.1 3 rd 1.2 0.9 5 th 0.9 0.6 7 th 0.6 0.3
    27. 27. Experimental Measurements <ul><li>Measured and simulated rectifier currents: </li></ul><ul><li>Simulated current similar to measured current when heater was not connected </li></ul><ul><li>Differences between simulation and measurement are expected – simulated results indicate what should be the case w/o the heater . </li></ul><ul><li>The heater’s harmonics (which are not it’s fault) partially mask the effects of the rectifier </li></ul>Harmonic Number Simulated Current (A rms) Measured Current (A rms) 1 st 1.3 1.1 3 rd 1.2 0.9 5 th 1.0 0.6 7 th 0.7 0.3
    28. 28. Conclusion and Future Work <ul><li>Utilities could potentially bill large customers based on “true” distortion </li></ul><ul><li>The harmonic source detection method has worked well in the lab, field tests may be performed in Fretwell </li></ul><ul><li>This approach could be coupled into Smart Meters </li></ul>
    29. 29. Thank You!
    30. 30. Linear load v/s Non Linear load <ul><li>Linear Load </li></ul><ul><li>Impedance remains constant throughout its operation </li></ul><ul><li>Load current does not contains harmonics </li></ul><ul><li>Zero neutral current if loads are equally balanced </li></ul><ul><li>May not demand high inrush currents while starting </li></ul><ul><li>Linear load is usually resistive, can have small inductance and capacitance. </li></ul><ul><li>Follows Ohm’s law </li></ul><ul><li>Non Linear Load </li></ul><ul><li>Impedance changes with applied voltage </li></ul><ul><li>Load current contains all odd harmonics </li></ul><ul><li>Neutral current could be 2.7 times the line current even if loads are equally balanced </li></ul><ul><li>Essentially very high inrush current (20 time of I Normal) is drawn while starting </li></ul><ul><li>Usually an equipment with Diode and Capacitor and can’t be categorize as leading or lagging load </li></ul><ul><li>Ohm’s law is not applicable </li></ul>

    ×