Bob Nelson

1
Power Line Carrier Research Project

• Bob Nelson
• Yuxin Feng
• North Dakota State University
• Dept. of Electrical and Computer Eng.
• Fargo, ND

2
The work has been supported by Otter Tail Power
Company, and Has Three Major Aspects

• On-Line Testing of PLC Tuners
• PLC System Analysis and Simulations
• Self Tuner Project

3
What is Power Line Carrier (i.e. PLC)

• Use of the power transmission line as a high
  frequency transmission line to communicate
  between substations
• Substations communicate so that circuit breakers
  are opened at appropriate locations and times
• Has been used since 1930s.

4
(No Transcript)
5
What Does This Look Like in Real Life?
6
But The BIG Question is

• How Did Some EM (Electromagnetics) Folks Get
  Mixed Up in Power Line Research???

7
Its Dons Fault!!
8
On-Line Testing of PLC Tuners

• Periodic Testing/Maintenance needed to maintain
  optimum performance
• Typically based measurements of voltage and
  return loss
• Often taken at discrete frequencies
• Aids in making necessary Tuner Adjustments

9
Example of PLC Frequency Allocation
Sub. 3
97.00.5 93.00.5
97.00.5
93.00.5 101.50.5
101.50.5
Sub. 1
93.00.5
97.00.5 101.50.5
Sub. 2
10
Voltage Measurements at Discrete Frequencies
11
Return Loss Measurements at Discrete Frequencies
Or ...
12
Return Loss Measurements at Discrete Frequencies
13
Return Loss Measurements at Discrete Frequencies

• Very Accurate
• Quite Time-Consuming
• Important data points may be missed

14
Return Loss Measurements at Discrete Frequencies
Example of RL vs Freq.
15
Swept Frequency Voltage and Return Loss
Measurements

• Used Agilent (i.e., HP) 4395A, which is a
  combination
• Spectrum Analyzer
• Network Analyzer
• Impedance Analyzer
• Measurement results obtain much faster
• Allows us to see what is happening

16
Spectrum Analyzer Results
17
Network Analyzer Results
Before Tuner Adjustments
18
Network Analyzer Results
After Tuner Adjustments
19
PLC System Analysis SimulationsUsing MATLAB
20
Numerical Simulations

• Used numerical simulation to illustrate how
  various components of PLC system affected the
  return loss.
• The basic adjustments in line tuner are turns
  ratios used in impedance matching transformer,
  and the inductor/capacitor values for tuner.
• ABCD parameters for two-port networks are used to
  develop the simulation.

21
ABCD Parameters for Two-port Network

• The ABCD (or chain) parameters are defined as

22
Single-line Model PLC System

• The model includes
• 50 ? ? PLC transmitter connected to a short
  coaxial cable
• An impedance matching transformer
• A low-pass filter comprised of a series inductor
  and the coupling capacitor
• High-voltage power line (phase to ground),
  modeled as a transmission line (with given
  characteristic impedance) connecting the two
  substations
• Duplicate components at receive end.

23
ABCD Parameters of PLC System

• The overall ABCD matrix of the system can be
  written as the product of the individual ABCD
  matrices.
• Using this matrix, the return loss can be
  obtained.

24
RL for Very Short LineGood Impedance
Matching(12.76)
25
RL for Longer LineGood Impedance
Matching(12.76)
26
RL for Longer LineImpedance Matching Slightly
Off at Input End (12.0)
27
RL for Longer LineGood Impedance Matching Input
Series Inductor Slightly Off
28
Simulation Tool Can Presently Be Used For

• Plotting Return Loss at the Input
• Plotting the Voltage at the Load or Input
• Examine Lossless or Lossy Power Lines
• Use for Simple or more complex Tuners

29
Self Tuner Project
30
Line Tuner Coupling Capacitor
Line Tuner
Coupling Capacitor
Line Tuner
31
Schematic of Line Tuner
32
Frequency Response of LC Tuner

• Select the inductor to minimize the reflected PLC
  signal.

33

• Weather and temperature changes affect the
  characteristic impedance of the transmission
  line, thus affecting the tuning of the
  transmitter/receiver pair.

34

• A Self Tuner would be able to automatically
  adjust the settings of the impedance matching
  transformer and tuner inductors to provide the
  best possible return loss.

35
Self Tuner Project Description

• This project focuses on providing automatic
  tuning of the tuner inductor settings, assuming
  the impedance matching transformer is unchanged.
• This Self Tuner is designed for a tuner used
  for 46.1 kHz PLC signal.
• Measuring and minimizing the reflected power is
  the main idea in this project.

36
Diagram of Self Tuner
37
Directional Coupler

• The purpose of the directional coupler is to
  provide the reflected signal without effecting
  the communication on the transmission line.
• The sample signal has 20 dB attenuation, so a 20
  dB amplifier is used next.

(Reverse is selected)
Directional
Out
In
Coupler
Sample
20 dB
Automatic VLF power-SWR Meter
SIGNALCRAFTERS 70
38
Filter Design

• The spectrum of the transmission line and the
  measured return loss result determine the
  characteristic of band-pass filter.
• Sample Signal P46.1k Ptrsnsmit RL ? 6 dBm
• Sample Signal P44.1k Precieve ? 6 dBm
• The attenuation between 44.1 kHz and 46.1 kHz
  should be 15 dB at least.

39
Filter Implementation

• A 6-order MFB (Multiple Feedback Topology
  Band-pass) filter is used.
• The filter provides 16 dB attenuation between
  44.1 kHz and 46.1 kHz.

40
Rectifier Design

• The rectifier circuit converts the AC signal to
  DC signal.
• The DC value is proportional to the magnitude of
  the reflected signal.
• An adjustable amplifier is used to obtain a
  suitable signal magnitude.

41
Microprocessor

• The PIC16F876 microprocessor chip is used for
  control unit.

42
Relay Board

• The inductor board has four inductors (39 µH, 82
  µH, 160 µH and 330 µH), in series with the line
  tuner. The four-bit control signal facilitates
  selecting one of 16 add inductors range, from 0
  µH to 640 µH.
• EDR201A0500 relay chip is used for switch.

43
Flow Chart for PIC Controller
44
Test of Self Tuner

• One side PLC system was simulated in lab.
• Self tuner system was added and completed all the
  functions in design.

45
Test of Self Tuner

• Then the project was tested at substation in
  Forman, ND.
• A poor pick was made for the tuning inductor,
  and the self-tuner corrected the situation!

46
Conclusions

• PLC Research has been carried out for OTP, with
  focus on three areas
• New testing methods that facilitate ease of tuner
  adjustments
• The development of simulation tools for system
  analysis.
• Initial design of a self-tuner which can
  improve PLC performance.

47
Acknowledgements

• Special thanks goes to many individuals for
  significant help, including
• Don Stuehm
• Al Haman, Jon Wahlgren and Daryl Hanson
• Barry Adams, Roger Carlson, Floyd Kearns and Matt
  Tronnes.
• NDSU Senior Design Group Robert Frank, Chad
  Kunz, Paul Nordmeier and Paul Winter.

48
Questions???