Propagation Channel Characterization and Modeling Outdoor Power Supply Grids

as Communication Channels

Prof. Dr.-Ing. habil.

Klaus Dostert

Institute of Industrial Information SystemsUNIVERSITY OF KARLSRUHE (TH)

2

Overview

Analysis of line and cable properties characteristic impedance branching & matching

Communication over outdoor electrical power supply lines

General aspects of channel modeling transfer function, impulse response, channel parameterization interference scenario

PLC channel simulation and emulation channel adapted system development

Network structures and their basic properties Access domain in Europe, ASIA, America

Conclusions and further work

3

History: Carrier Frequency Transmission since 1920 (on the high voltage level only)

no branching optimal „wave guiding“ by network conditioning

4

Current and Upcoming PLC Applications

High Speed Indoor Applications: 12 … 70MHz - PLC for digital entertainment systems (>100

Mbits/s)

Low Speed (10…100 kbits/s)- Office and home automation (intelligent appliances)- Energy information systems- Urban rail-based traffic systems

Broadband Services: 1…30 MHz (1…2 Mbits/s - „Last Mile“ and „Last Meter“ high-speed internet access,

voice over IP etc.

PLC in automobiles PLC for factory automation PLC for advanced safety systems in the mining industry

5

The European Power Supply Network Structure

high voltage level: 110..380 kV

medium voltage level10...30kV

low voltage distribution grid3 Phases: 230V, 400V

LV transformerstations

supply cells up to 350 households cable length 100...400m

transformerstation

400V 400V

400V

230V

230V

3-phase supplydetails

6

Typical Topology of European Power DistributionNetworks in Residential Areas

1 2

3 4 5

6

789

10 11 12 13 14

15

1617

19 20 2122

23

24

25262728

2930

3132

33

18

ServerTransformer Station

cabl

e le

ngth

: max

. 1 k

m

supply cable typeNAYY150SE

House connection cableNAYY50SE

NL1

L3L2

7

Some Details of “Last Mile” and “Last Meter” Environments

mediumvoltagenetwork

local transformerstation

cross-barsystem

ZL1 ZL2

points of mismatchhouse connection forming

a low impedance point - almost short circuit -

8

Power Supply Structures in Asia and Americahigh voltage level: 110..380 kV

1st medium voltage level10…30 kV

low voltage distribution gridsingle or split phase supply125V, 250V many LV transformers

transformerstation

2nd medium voltage distribution level 6 kV

125V 125V

250V

single andsplit-phase

small supply cells few households per transformer cable length 100m grounding of 3rd wire highly unsymmetrical

9

The Ideal Two-Wire System

X

compensation of exterior field

compensation of exterior field

10

Symmetry in Multi-Wire Structures

open wires

passive conductors

3-phase supply cable

X •X •

passive conductors

“earth” in case of a three-wire supply

11

Simplified Analysis of a Two-Wire System 650

100 150 200 250 300 350 400350

400

450

500

550

600

D in mm

ZL/ r =2mm

r =2mm

r =4mm

r =5mm

open wires: r=1

10 15 20 25 30

20

40

60

80

100

120

r =5mm

r =7mm

r =10mm

D in mm

ZL/

cable: r=3.5

0 5 10 15 20 25 30

-8

-6

-4

-2

0

f in MHz

A(f)/dB

l =5000m

l =2000m

l =1000m

l =500m

d=2r=5mm

attenuation at open wires due to Skin effect

D

r

2120

ln 12 2

L

r

Z D D

r r

2

'( )

2

'( )

L

R ff

Z

fR f

r

characteristic impedance

12

RF Properties of Typical Supply Cables

0' 2 r

rC

0 2L

r

02

fR

r

2 tanG f C

Lossy Line Parameters (low losses)

' '( ) ( ) ( )

2 2L

R GL

R G Zf f f

Z

'

'L

LZ

C

Attenuation CoefficientCharacteristic

Impedance

NL1r

L3L2ra

ri

L1

r

L2

L3

PEN

Access Cable Types

L1

N

L3

Model

10

0

1 2 5 10 20

A(f)[dB]

20

30

40

50

70

60

NAYY50SE

NAYY 150SE

40

30

50

20

10

01 2 5 10 20

ZL/

NAYY50SE

NAYY150SE

f /MHz

House Connection

Main Supply Cable

f /MHz

Characteristic Impedance Attenuation over 1km

13

ZL

ZLZL

ZL

ZL

mismatch: ZL/2

The problem of Branching and Possible Solutions

ZL

ZLZL

ZL

ZL

matched to ZL

ZL/3

ZL/3

L >> ZL

R=ZL/3

14

Some Ideas for Signal Coupling with Enhanced SymmetryImproving EMC

typical RF coupling devices Transformer Stationcross-bar system

cable: ZLC

L10µH

BALUN

MODEM

RF-shorts

impedancematching

decoupling

L > 10µH

RF-shorts

BALUN

House Connection

MODEM

powermeter

impedancematching

decoupling

cable: ZLC

Ferrite material is required for these decoupling coils, which carry high currents! Transformer: >150A House connection: >30A

15

Reflections Causing Echoes and Inter-Symbol Interference

direct echo

result

strong inter-symbol interference: Tbit

Tbit

1 1d / v

T

R2 2d / v

delay: =2-1

direct path echo path

wireless channel as example

t1 2

impulse response

simplified analysis of aline with 1 unmatched branch

T R1

2

in practice:multipleechoes

16

Approaches Toward Deterministic Network Modeling

bq

ri

a

bra

a

bS11 S12

S21 S22

a2

b2

a1

b1

source line element sink

a2

b2

a1

b1

a 3 b 3branch example

high computational effort requires detailed knowledge of network topology and device parameters not applicable in practice

17

1

N

E i ii

h t k t

impulse response

transfer function

j2

1

e i

Nf

E ii

H f k

0.5...11 2 0 1( )f c f c f a a f

skin-effect dielectric losses

Attenuation Coefficient:

The Echo-based Channel Modelconsidering only echoes : ki=const

( )( , ) e if di i ik k f d g

low-pass behavior

dependent on number, lengthand matching of branches

generally complex

s(t)

k1

r(t)

k2 k3 kN

vi

i

d

Fouri

er

transf

orm

j2

1

e ei

i

dN f f dvi

i

H f g

Result

18

T R200m 1

225m 2

FT

0 5 10 15 20 25 30-20

-15

-10

-5

0

f in MHz

dB

0 5 10 15 20 25 30

-40

-20

0

f in MHz

dB

path 2path 1

attenuation

1e ia f dig

H(f): single reflection, no losses

0 5 10 15 20 25 30

-40

-20

f in MHz

0

dB

single reflection, including losses

1 1.17 1.33 1.5 1.67 1.83 20

0.5

1

t in µs

path 1

path 2

h(t): impulse response

j2e ii

fg

19

0.52

0.347

0.26

0.208

0.173

0.149

0.46

0.627

0.71

0.76

0.793

0.817

Two-Path Channel without Losses butVarying Path Weights

Path 1

Path 2

20

path di/m gi

1 200 0.64

2 222.4 0.38

3 244.8 -0.15

4 267.5 0.05

j2

1

e ei

i

dN f f dvi

i

H f g

10 1 1

m7.8 10 f f

8 m

s1.5 10

r

cv

ZLG

30m

11m170m

0 5 10 15 20 25 30-50

-40

-30

-20

-10

0

frequency in MHz

dB |H(f)|

0 0.5 1 1.5 2 2.5 3 3.5

0

0.5

1

time in µs

h(t)

A First Realistic Example

0 5 10 15 20- 50

- 40

- 30

- 20

-10

0

f in MHz0 1 2 3 4 5

0

1

t in µs

0.5

calculationmeasurement

21

A Second Example(more complex)

path di/m gi

1 90 0.029

2 102 0.043

3 113 0.103

4 143 -0.058

5 148 -0.045

6 200 -0.040

7 260 0.038

8 322 -0.038

9 411 0.071

10 490 -0.035

11 567 0.065

12 740 -0.055

13 960 0.042

14 1130 -0.059

15 1250 0.049

10 1 1

m7.8 10 f f

8 m

s1.5 10

r

cv

0 5 10 15 20 25 30

-80

-60

-40

-20|H(f)|

dB

frequency in MHz

0 0.5 1 1.5 2 2.5 3 3.5-0.5

0

0.5

1

h(t)

time in µs

110m 15m

22

2 4 6 8 10 12 14 16 1880

70

60

50

40

30

20

10

0

Att

enua

tion

in d

B

Frequency in MHz

Transmission Characteristics According to Length Classes

150 m

200 m

300 m

380 m

23

A General Powerline Interference Model

tIAT

Am

plit

ude

time

tA

tB

A

A, tB and tA are random variables with exponential distributions

threat of burst errors

H(f) h(t)

Channel as a Linear Filter

narrowband-interference

backgroundnoise

Interference

+

periodic impulsive noiseasynchronouswith the mains

periodic impulsive noise synchronous with the mains

aperiodicasynchronous

impulsive noise

24

Idea of a Universal PLC-Channel Emulator

PLCModem

PLCModem

ConfigurationInterface

Host-PC

+

PGA

PGA DA

DA FIR

Filter

NoiseGenerator

DA

LPF

LPF LPF

FIRFilterLPF D

AD

A PGA +LPF

NoiseGenerator D

A PGALPF

25

FPGA8from

ADC

signal DACFIFO

channel emulation filtersdelay

5x7bitdelay

5x5bitcoeff.

32x8bitcoeff.

control

1420FIRNotch

FIRlowpass

32P_DATA

26

8 14

8-bit-circular memoryof length 500

periodic, synchronous, asynchronous impulsive noise & background noise

narrow band noise

control

+

P_ADDR

8x20bits load

500 x 8bitsload control

14

148

interference DAC

20bit shift register

8 m-sequences of length 220-1

control / load

Ampli-tude

Ampli-tude

14D

A

14D

A

Some Details Toward Emulator Realization

26

P LC M odem(Tran sm itte r)

P LC M odemL P

A D C

D A C

FPGA

EEPROM

D A C

S ign a l

N o ise

P G A

P G A

L P

ChannelEm ulator Hardware

PC

A First Powerline Channel Emulator Prototype

f in MHz

f in MHz

|H| in dB

|H| in dB

coeff. filter 1 coeff. filter 2reference channel modified filter structure

simulations,implementation

hardware

verificationmeasurements

27

FSK, GMSK

f1 f2 f3

ffN

not usable due to high attenuation

restricted e.g. for protection of broadcast services

OFDM sub-channel

Channel Transfer Function

Why OFDM for PLC?

28

Conclusions and Further Work

PLC or BPL offers a variety of valuable applications data rates exceeding many Mbits/s will enable numerous new servicesMature channel models are covering any channel of interest successful development of a new generation of ”channel adapted” PLC systems is possible no more pitfalls: sophisticated simulation and emulation

Further development and standardization of PLC or BPL goes on ETSI, CENELEC, CISPR EU Project OPERA (Open PLC European Research Alliance) HomePlug Alliance (USA) IEEE PHY/MAC Working Group

Building advanced and user-friendly simulation and emulationenvironments is now an important issue