advantages and circuit configuration of a dc microgrid · load2 pfc 22kv/1.5kv ls rs cd pfc...
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Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
CanadaNatural ResourcesCanada
Advantages and Circuit Configuration of a DC Microgrid
Toshifumi ISE(Osaka University, JAPAN)
ise@eei.eng.osaka-u.ac.jp
PE&EESince 2002
2Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Problems on Microgrids
1)Synchronization of distributed generators
2)Inrush current
(transformers, Induction motors, Induction generators)
3) Three-Phase Unbalance
(single-phase loads, single-phase generators such as photovoltaic)
3Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Recent Trends
1) Introduction of many Inverter loads(AC/DC and DC/AC conversions are included)
2) Introduction of distributed generations with DC output (photovoltaic, fuel cell, variable speed type wind turbine, micro turbine, gas engine)
3) Needs for higher quality power
4Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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DC Loop Type Configuration
PFC
DCDC PV Cell
DCDC PV Cell
DCAC
Load
DCDC SMES
DCAC
G Wind Turbine
MT Micro Turbine
DCDC
FC Fuel Cell
DCDC
Secondary Battery
DCAC
Load
DCAC
Load
4kV
2kV
2kV
PFC Normal QualityLoop
High QualityLoop
22kV/1.2kV
22kV/1.5kV
Bi-directional Rectifier
Diode Rectifier
22kV/1.2kV
22kV/1.5kV
SFCL + Hybrid Switch
PFC
DCDC PV Cell
DCDC PV Cell
DCAC
Load
DCDC SMES
DCAC
GG Wind Turbine
MTMT Micro Turbine
DCDC
FCFC Fuel Cell
DCDC
Secondary Battery
DCAC
Load
DCAC
Load
4kV
2kV
2kV
PFC Normal QualityLoop
High QualityLoop
22kV/1.2kV
22kV/1.5kV
Bi-directional Rectifier
Diode Rectifier
22kV/1.2kV
22kV/1.5kV
SFCL + Hybrid Switch
5Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Circuits for Loss Comparison
DC Loop System
AC Radial System
2 k V
D CA C L o a d 1
1 k m
0 .5 k m
0 .5 k m
1 k m
1 k m
D CA C
D CA C L o a d 2
D CA C L o a d 3
2 k V
D CA C L o a d 1
1 k m
0 .5 k m
0 .5 k m
1 k m
1 k m
D CA C
D CA C L o a d 2
D CA C L o a d 3
1km
0.5km
0.5km
6.6kV
A C
D CA C L oad1
D CA C
D CA C L oad2
D C
D CA C L oad3
D CA C
1km
0.5km
0.5km
6.6kV
A C
D CA C L oad1
D CA C
D CA C L oad2
D C
D CA C L oad3
D CA C
A C
D CA C L oad1
D CA C
D CA C L oad2
D C
D CA C L oad3
D CA C
20MW
20MW
20MW
20MW
20MW
20MW
6Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Reduction of Rectifier Losses
0
2
4
6
8
10
12
0.95 0.96 0.97 0.98 0.99 1
Rectifier Efficiency of DC Loop Type Distribution System
Loss
[MW]
A C Type Distribution System DC Loop Type Distribution System
7Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Distance of Cable and Losses
0
2
4
6
8
10
12
14
16
0.5 1 1.5 2 2.5
D istance of C able [km ]
Loss
[MW]
A C Type D istribution System D C Loop Type D istribution System
8Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Loss Reduction due to Loop System
0
2
4
6
8
10
12
14
DC Loop Type DistributionSystem
DC Type Distribution System(W ithout Loop)
Loss [MW]
Losses of Inverters and Rectifier Losses of C able
9Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Loss Reduction by Feeding from Two AC Systems
0
2
4
6
8
10
12
0 10 20 30 40
Power of Load1 [M W ]
Loss [MW]
O ne AC System Two AC System s
10Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Control Method of Rectifiers Using Gain-Scheduling Method
Bi-directional Rectifier
dcV*
dcV
P
*i
Voltage Control
K
AC system
LPFP
K
Gain Scheduling
iP
V
P1K
2K
1 2K K>
K*i
dcV
*dcV +
−
Controlled Characteristics with Proportional Controller
11Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Effect of Gain Scheduling
V
P 1K
2K
1 2K K>
Voltage regulation
Power sharing
Large Gain KSmall Gain K
Gain Scheduling
Voltage Regulation Power SharingExcellent Fair
Fair ExcellentGoodGood
12Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Control of Multiple Rectifiers
AC system 1AC system 1
AC system 2AC system 2
Bi-directional Rectifier
1d cV*
d cV
1P
*i
Voltage Control
K
LPFP
K
1i1P
Gain Scheduling
2P
2d cV
*d cVK
2P*i2i
Communication line
13Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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10%Load 50%Load 100%LoadVoltage
Gain K0 2 4 6 8 10
0.88
0.86
0.9
0.92
0.94
0.96
0.98
1.0
Gain K
Load power
0
2
4
6
8
10
0 0.2 0.4 0.6 0.8 1.0
voltage variation 2%
voltage variation 6%
Gain K versus DC Voltage Characteristics
Gain K for Various Load Power with 2% Voltage Variation
14Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Simulation Circuit
sL sR
22 /1.2kV kV 400kW(Max) 300kW(Max)
300kW(Max)
3dcR 1dcR
2dcR
1km
1km
1km
0.5km 0.5km
Cd
1dcV
2dcV
+-
+-
Bi-directional
rectifier
Rectifier power1
Rectifier power2
AC system1
AC system2
15Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Simulation Results of Power Sharing
DC Voltage (kV)
+0.8+0.6+0.4+0.2+0
+1.8
+1.9+2
0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
8%
Power Sharing (MVA)10% 50% 100
%
Load PowerLoad Power100%
Time(s)
Load Power (MW)+0.4+0.3+0.2+0.1+0
+0.5
Load Power
0.3 0.5 0.7 0.9 1.1 1.3
Constant Gain
K=2
DC Voltage (kV)
Power Sharing (MVA)
Load Power (MW)
+0.8+0.6+0.4+0.2+0
+1.8
+1.9
+2
+0.4+0.3+0.2+0.1+0
+0.5
Time(s)0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
1%
Constant Gain
K=30
DC Voltage (kV)
Gain
Power Sharing (MW)
Common Gain
Time(s)
10% 50% 100%
Load Power (MW)
+0.8+0.6+0.4+0.2+0
+1.8
+1.9
+2
+0+10+20+30
+0.4+0.3+0.2+0.1+0
+0.5
0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
0.3 0.5 0.7 0.9 1.1 1.3
Load Power Load PowerLoad Power
2%
Gain-schedulingsystem1 system2 Load1 Load2 Load3
Power Ratio
54:46
Power Ratio
51:49
Power Ratio
57:43
16Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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DCAC
Load2
PFC
22kV/1.5kV
Ls Rs
Cd
PFC
22kV/1.5kV
Ls Rs
Cd
LCフィルタ
Cd2
Cd1 Load1
Cd3 Load3
1km
1km
1km
0.25km
0.5km
DCDC
Ldci
DCDC
Ldci
0.25km
短絡事故短絡事故
SFCL SFCL
SFCL SFCL太陽光発電太陽光発電
二次電池1二次電池1
二次電池2二次電池2
交流システム1交流システム1
交流システム2交流システム2
負荷1負荷1
負荷2負荷2
負荷3負荷3
HS11HS12
HS21HS22
IS1S2
IS1L1
IS2L3
IL1L2
IL2L3
ハイブリッドスイッチ1
ハイブリッドスイッチ1
ハイブリッドスイッチ2
ハイブリッドスイッチ2
DCAC
Load2
PFC
22kV/1.5kV
Ls Rs
Cd
PFC
22kV/1.5kV
Ls Rs
Cd
LC Filter
Cd2
Cd1 Load1
Cd3 Load3
1km
1km
1km
0.25km
0.5km
DCDC
Ldci
DCDC
Ldci
0.25km
短絡事故Fault Point
SFCL SFCL
SFCL SFCL太陽光発電Solar Battery
二次電池1Battery 1
二次電池2Battery 2
交流システム1AC System 1
交流システム2AC System 2
負荷1Load1
負荷2Load2
負荷3Load3
HS11HS12
HS21HS22
IS1S2
IS1L1
IS2L3
IL1L2
IL2L3
ハイブリッドスイッチ1
HybridSwitch 1
ハイブリッドスイッチ2
HybridSwitch 2
Simulation Circuit for Protecting Operation
17Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Current Through the Mechanical Switch
Current Through the Semiconductor Switch
Simulation of Protecting Operation
1ms 1ms
18Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Bulk Power system
Low Voltage Type DC Microgrid
DCDC
ACDC
G
Secondary Battery
Electric Double Layer Capacitor
Co-generator
DCDC
DCDC
Bi-directional Rectifier
Photovoltaic Cell
Communication Line
AC 200 V
AC100VDC 170 VDC 170 V
3φ AC200 V
1φ AC100 V
DC 100 V
Islanding Protector
DC
DC Fuel CellCenter Building
Rectifier
1φ AC100 V
1φ AC100 V
AC100V
AC100V
Power Exchange
Power Exchange
19Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Features of Low Voltage Type DC Microgrid
Distributed scheme of load side converters contributes to provide a super high quality power supplying. Various forms of electric power like single phase 100V, three phase 200V, DC 100V can be obtained without using transformers. If power consumption become more than a power production during a long term isolation, DC micro-grid can stop supplying power for some loads intentionally by load side converters in order to continue supplying power for more important loads.When a temporary overload occurs at one load, electric power can be shared by using additional electric power lines between load side converters.
20Montreal 2006 – Symposium on MicrogridsJune 23, 06 CanadaRessources naturelles
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Features of DC Microgrid
Synchronization of distributed generators are not necessary.
Fluctuation of generated power of distributed generators and load power can be compensated in the dc line by using energy storage devices.
Loads are not affected by voltage sag, voltage swell, three-phase voltage unbalance, and voltage harmonics.
Power quality is not affected by Inrush current, single-phase loads and single-phase generators.
Higher efficiency than AC microgrid is expected.
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