IEEE Electrification Magazine - June 2015 - 54

v Reference

+
PID Regulator

-

Amplifier

Exciter

v

Generator

Synchronous Machine
Sensor

AVR
Figure 4. The voltage control cycle block scheme.

error levels in every AVR, caused only by sensors offsets
that are not perfectly compensated (which is an impossible goal to reach). To avoid that, the only solution is the
insertion of a decoupling element between the generators' terminals, where the voltage is sensed, and the
common connection point of the system (which is the
main switchboard in an IPS). This can be achieved in two
different ways: the first is the interposition of a transformer, whose internal reactance decouples the generators each other; the second is the adoption of the voltage
droop in the AVRs. In particular, the latter is the most
adopted solution since transformers are not essential in
shipboard power systems generators because of the voltage levels of the system (usually large ships' distribution
voltages up to 11 kV are easily managed directly by the
rotating electrical machines) and are space-consuming
devices. (Space in ships is limited and must be reserved
as much as possible for payload.)
The voltage droop technique implies the adoption of a
negative feedback on the voltage regulator's input,

depending on the reactive power generated by the alternator. By doing so, the steady-state voltage output lowers
as the reactive power generated increases (Figure 6), introducing an equivalent inductive reactance (totally virtual)
between the generator and the main switchboard. This
enables a stable parallel operation without adding losses
and weight, and without consuming space. Moreover, the
droop mode imposes the steady-state VAR sharing
between the paralleled alternators, allowing the change in
the reactive power sharing distribution by the simple variation of the droop's constants of the generators.

Inverter-Based Generators
The advancements in power electronics made in recent
years have unearthed the possibility to couple the alternators
with ICEs, which are not dedicated solely to the generation
purpose. In some cases, mostly in military ships, the propulsion is yet realized with ICEs, in particular, using gas turbines
(GTs). This is due to the high speed requirements of these
units, implying very high propulsion power requirements,

P
0.8

0.9

0.95

0.95

1.00

0.6

0.75
5
0.4

0.8

0.9

1

0.6

3

2
0.4

0.50

0.25

6

Q

4
1.00

0.75

0.50

0.25

0.00

0.25

0.50

0.75

Capability Chart
(1) Stator Thermal Limit
(4) Rotor Thermal Limit
(2) Nominal Working Point (5) Underexcitation Limit
(3) Turbine Limit
(6) Minimum Excitation Current
Figure 5. The region of admissible operating points.

54

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2015

1.00



Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2015

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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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