IEEE Electrification Magazine - September 2014 - 8

influence at the network frequency. Thus, in terms of fundamental RMS values and relationships of input and
output (1) and (2), the structures behave as variable impedances controlled by the duty cycle a. The expressions for
input impedance for step-down and step-up configurations are given by (3) and (4), respectively.

i1

i2
ac

v1

Z
V
Z in . I in . out
,
in
a2

(3)

V
Z in . I in . Z out a 2 .
in

(4)

For example, if impedance Z out is capacitive at the grid
frequency, then the converters act as variable capacitors.
Thus, a reactive power compensator can be implemented
using the controlled impedance concept. The supplied
reactive power can be expressed as (5) for step-down
mode and (6) for step-up mode

v2
ac

V 2
Q = Z in a 2,
out

(5)

Vin2
.
a 2 Z out

(6)

Q=

α
Figure 1. The principle of direct ac/ac conversion.

Application of the Controlled Impedance
Concept to reactive power Compensation
Currently, most of the main-line traffic is from locomotives
equipped with thyristor rectifiers. That is why (as traffic and
load increase) reactive power compensation is required to
reduce reactive power and to keep the voltage from sagging.
Basic power-factor correction is realized by fixed capacitors.
The problem of such configurations is that when the overhead lines operate at no load, the voltage will rise but may
not exceed the 29-kV standard limit. If an increase of compensation is required, then a variable reactive power compensator must be added to the fixed-capacitor banks.
Today, French National Railways [Société Nationale des
Chemins de fer Français (SNCF)] use some lines equipped

v1
i1
v2
i2
Figure 2. The typical ac chopper current and voltage waveforms for
duty cycle a = 0.5.

iin

i2 = iout

i1

Ln

ac

ic
Vin = V1

V2

Vn

LF
VL

Zout

Vout

CF
ac
Load
α

Network

iout

(a)
i1
ic

Zout

i2 = iin

LF

Ln

ac
V2

Vout = V1

VL

Vin

Vn

ac
Load
α
(b)

Network

Figure 3. The CCI with buck or boost ac/ac converter: (a) the step-down configuration and (b) the step-up configuration.

8

I E E E E l e c t r i f i c ati o n M agaz ine / september 2014



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2014

IEEE Electrification Magazine - September 2014 - Cover1
IEEE Electrification Magazine - September 2014 - Cover2
IEEE Electrification Magazine - September 2014 - 1
IEEE Electrification Magazine - September 2014 - 2
IEEE Electrification Magazine - September 2014 - 3
IEEE Electrification Magazine - September 2014 - 4
IEEE Electrification Magazine - September 2014 - 5
IEEE Electrification Magazine - September 2014 - 6
IEEE Electrification Magazine - September 2014 - 7
IEEE Electrification Magazine - September 2014 - 8
IEEE Electrification Magazine - September 2014 - 9
IEEE Electrification Magazine - September 2014 - 10
IEEE Electrification Magazine - September 2014 - 11
IEEE Electrification Magazine - September 2014 - 12
IEEE Electrification Magazine - September 2014 - 13
IEEE Electrification Magazine - September 2014 - 14
IEEE Electrification Magazine - September 2014 - 15
IEEE Electrification Magazine - September 2014 - 16
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IEEE Electrification Magazine - September 2014 - 18
IEEE Electrification Magazine - September 2014 - 19
IEEE Electrification Magazine - September 2014 - 20
IEEE Electrification Magazine - September 2014 - 21
IEEE Electrification Magazine - September 2014 - 22
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IEEE Electrification Magazine - September 2014 - 26
IEEE Electrification Magazine - September 2014 - 27
IEEE Electrification Magazine - September 2014 - 28
IEEE Electrification Magazine - September 2014 - 29
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IEEE Electrification Magazine - September 2014 - 31
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IEEE Electrification Magazine - September 2014 - 33
IEEE Electrification Magazine - September 2014 - 34
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IEEE Electrification Magazine - September 2014 - 36
IEEE Electrification Magazine - September 2014 - 37
IEEE Electrification Magazine - September 2014 - 38
IEEE Electrification Magazine - September 2014 - 39
IEEE Electrification Magazine - September 2014 - 40
IEEE Electrification Magazine - September 2014 - 41
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IEEE Electrification Magazine - September 2014 - 49
IEEE Electrification Magazine - September 2014 - 50
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IEEE Electrification Magazine - September 2014 - 56
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IEEE Electrification Magazine - September 2014 - 60
IEEE Electrification Magazine - September 2014 - 61
IEEE Electrification Magazine - September 2014 - 62
IEEE Electrification Magazine - September 2014 - 63
IEEE Electrification Magazine - September 2014 - 64
IEEE Electrification Magazine - September 2014 - Cover3
IEEE Electrification Magazine - September 2014 - Cover4
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https://www.nxtbook.com/nxtbooks/pes/electrification_september2022
https://www.nxtbook.com/nxtbooks/pes/electrification_june2022
https://www.nxtbook.com/nxtbooks/pes/electrification_march2022
https://www.nxtbook.com/nxtbooks/pes/electrification_december2021
https://www.nxtbook.com/nxtbooks/pes/electrification_september2021
https://www.nxtbook.com/nxtbooks/pes/electrification_june2021
https://www.nxtbook.com/nxtbooks/pes/electrification_march2021
https://www.nxtbook.com/nxtbooks/pes/electrification_december2020
https://www.nxtbook.com/nxtbooks/pes/electrification_september2020
https://www.nxtbook.com/nxtbooks/pes/electrification_june2020
https://www.nxtbook.com/nxtbooks/pes/electrification_march2020
https://www.nxtbook.com/nxtbooks/pes/electrification_december2019
https://www.nxtbook.com/nxtbooks/pes/electrification_september2019
https://www.nxtbook.com/nxtbooks/pes/electrification_june2019
https://www.nxtbook.com/nxtbooks/pes/electrification_march2019
https://www.nxtbook.com/nxtbooks/pes/electrification_december2018
https://www.nxtbook.com/nxtbooks/pes/electrification_september2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2018
https://www.nxtbook.com/nxtbooks/pes/electrification_december2017
https://www.nxtbook.com/nxtbooks/pes/electrification_september2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2017
https://www.nxtbook.com/nxtbooks/pes/electrification_june2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2016
https://www.nxtbook.com/nxtbooks/pes/electrification_september2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2016
https://www.nxtbook.com/nxtbooks/pes/electrification_march2015
https://www.nxtbook.com/nxtbooks/pes/electrification_june2015
https://www.nxtbook.com/nxtbooks/pes/electrification_september2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2014
https://www.nxtbook.com/nxtbooks/pes/electrification_june2014
https://www.nxtbook.com/nxtbooks/pes/electrification_september2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2014
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