IEEE Electrification Magazine - September 2014 - 13

xx
Input filter: To balance the substation even when it is
223

250
Power Losses (kW)

200
141

128.2

150

80.6

100

61.3
33.6

50
0
2-L VSI

NPC 3-L VSI

Active
Steinmetz

Scomp = 5.7 MVA (UF = 1.5% at SL = 10 MVA)
Scomp = 10 MVA (UF = 0% at SL = 10 MVA)
Figure 15. A comparison between voltage-balancer topologies in terms
of power losses.

400,000

250,000

50,000
0

Energy
Capacitor
VSI-2L

21,160

100,000

19,186
18,628

150,000

10,472

200,000

Energy
Inductors

VSI NPC-3L

200,302

340,200

300,000

181,116

On the basis of the design presented in the previous sections, Figure 15 summarizes the power losses for different
voltage-balancer topologies. Losses are referred to a
working condition for the compensators when the load
phase is z L = 0c. Comparing the two solutions based on
VSI converters, the three-level neutral point clamped
(NPC) solution is characterized by lower losses. In addition,
if the active Steinmetz compensator is compared with the
three-level NPC topology, a reduction in the power losses
of about 60% is achieved.
The energy stored in the reactive elements is used as a
qualitative index of the components space volume. The
peak values for current I| and voltage V| in the inductors

Energy (J)

Comparison of VSI Versus Active Steinmetz

358,828

350,000

31,631

not loaded, the already existing 2.7-Mvar reactive
power compensator was replaced with one that was
900 kvar, and the input filter capacitor of the CCI was
chosen to provide a reactive power Q F = 900 kvar. In
this way, when no trains are supplied by the substations, the circuit is seen from the three-phase network
as a balanced load. Moreover, L F1,2 is simply the leakage inductance of the 3.3-MVA transformer.
xx
Maximum ac chopper output current: The number of
modules in parallel (N 1 or N 2) was chosen according
to the thermal limits of the IGBTs (case temperature:
TC = 100 cC, and junction temperature: T J = 125 cC)
with a maximum RMS current I MAX of 735 A.
xx
Maximum power: Output impedance parameters
obtain 3.3 Mvar at the maximum duty cycle (0.9). Moreover, a 10% maximum current ripple at the switching
frequency was chosen to determine the output impedance of the capacitive ac choppers.
The reactive powers and peak input voltages (Vin1 and
Vin2) of the controlled impedances versus duty cycles a 1
and a 2 are shown in Figure 14.

Total
Active Steinmetz

Figure 16. A comparison in terms of energy stored in reactive elements
^S comp = 5.7MVAh .

iL

(A)

100
0

-100
1

1.02

(W) (var)

Pload

1.04

Qload

Time (s)
(a)

1.06

1.08

1.1

1.06

1.08

1.1

6,000 K
4,000 K
2,000 K
0K
1

1.02

1.04

Time (s)
(b)

Figure 17. (a) The substation current waveform and (b) active and reactive power.
	

IEEE Elec trific ation Magazine / s ep t em be r 2 0 1 4

13



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
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IEEE Electrification Magazine - September 2014 - Cover3
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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
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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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