Transcript Dirk Audring DE Academic Village Barcelona 12

Barcelona 12-15 May 2003
Supplying micro-grids with
stationary fuel cell systems
Prof. Dr.-Ing. G. Balzer, Dipl.-Ing. D. Audring
Darmstadt University of Technology
Department of Electrical Power Systems
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Barcelona 12-15 May 2003
Structure
• Examined micro-grid
• Short-circuit performance
• Disconnection from power system
• Conclusions
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Barcelona 12-15 May 2003
Examined micro-grid
3PEN~50Hz 230/400V
SC 2
UBB
D
C
B
SC 1
M1
7 kW
Micro-grid
V1
5 kVA
cos j = 1,0
M
3~
5 kVA
cos j = 0,95
iM1
• Fuel cell sets voltage and
frequency of micro-grid
A
V2
FC
50 kVA
• Micro-grid is supplied by one
fuel cell
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• Induction motor and two loads
are connected to micro grid
• Network connection is
simulated for back-up power
supply using a disconnecting
switch
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Short-circuit performance
iA [kA]
Currents of feeder A:
• Fuel cell acts as a
voltage source with
limited current output
0.2
0.1
0
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
(t-TSC)[s]
iFC [kA]
Currents of fuel cell:
0.1
0
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
• This leads to low shortcircuit current at microgrid
• Selectivity with overcurrent protection is
difficult to achieve
(t-TSC)[s]
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Short-circuit performance
Main busbar of
Micro-grid
Short-circuit
u
=
i
Fuel cell stack
iFC,1
~
~
iFC,2
iFC,3
Inverter
• Short-circuit currents are limited by inverter
• Transformation ratio and vector group of invertertransformer influences short-circuits at micro-grid
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Short-circuit performance
Phase-to-phase short-circuit
clear of earth:
iSC [A] Single-phase short-circuit:
200
100
0
-100
-200
-0,05
0
0,05
0,1 -0,05
(t-TSC1) [s]
iSC [A]
Three-phase short-circuit:
100
0
-100
-200
-0,05
0
0,05
0,1 -0,05
(t-TSC1) [s]
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0
0,05
0,1
(t-TS C1 ) [s]
Two-phase-to-earth
short-circuit:
0
0,05
0,1
(t-TS C1 ) [s]
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Disconnection from power system
• Short-circuit at power system
leads to voltage drop at
connected micro-grid
uBB [kV]
Busbar voltage of microgrid:
0.3
0.2
0.1
0.0
-0.1
-0.2
-0.3
0
• Induction motor slows down
iIM[kA]
0.05
0.1
0.15
0.2
0.25
0.3
(t-TSC)[s]
Currents of induction motor:
0.1
• Induction motor must be reaccelerated after
disconnection from network
0.0
-0.1
-0.05
0
0.1
0.15
0.2
0.25
1.0
0.3
(t-TSC)[s]
Revolution of induction motor
Applied torque
[p.u.]
• Power quality is poor during
disconnection and not
acceptable for PC etc.
0.05
0.8
0.6
0.4
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
(t-TSC)[s]
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Conclusions
• Main characteristic of micro-grid supplied by fuel cell is low
short-circuit current
• Selectivity with over-current protection is difficult to achieve
• Transformation ratio and vector group of inverter-transformer
is to consider for calculation of short-circuit currents at
micro-grid
• Disconnection from power system due to short-circuit has to
carried out fast to reduce voltage disturbances at micro-grid
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