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Current status of DC distribution system by KEPCO Jintae Cho Senior Researcher KEPCO Research Institute May 24, 2019
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Current status of DC distribution system by KEPCO
Jintae Cho
Senior Researcher
KEPCO Research Institute
May 24, 2019
1
Contents
Introduction of KEPRI 1
Background 2
Research activities of KEPCO 3
Future plan 4
Conclusion 5
2
Introduction of KEPRI
3
R&D Vision
Strategy
Structure
4
5
Demand increase of DC and high quality power
Growth of renewable energy
• By 2020, 50% of total will be digital loads(EPRI)
• Increasing high density DC loads (IDC)
• Energy efficiency improvement needs
- Dependence of Energy on Overseas (98%)
• AC/DC conversion energy lost is 10 ~ 25%
• Increase of DC output power distributed generation (PV, Fuel cell, Battery, etc.)
- By 2030, provide 20% of total primary energy supply with NRE
• DC market will grow to $241 billion in 2025(Navigant Research Report)
Background
6
IDC (Internet Data Center), DC home
Global trend
• ABB 380V DC Date Center • LBNL DC home
• Fraunhofer Power Electronics • India Solar DC home
7
Others
• NTT Hikari project • Benz DC automation
• DC Greenhouse • Siemens DC grid for offshore vessel
8
Domestic Trend
9
Benefit
• Transmission capacity
• Transmission distance
• Construction expenses
• Power supply reliability
• Power quality for customer
• Easy connected with DG
• Controllability
Advantage
[source : Delft University of Technology]
10
Grounding
Structure
Pro
tectio
n
DC
netw
ork an
alysis
Voltage Converter
LVDC distribution System
Research Activities
11
Economic Analysis
Method (NPV ; Net Present Value) • Total cost comparison with MVAC and LVDC
• Total cost = Investment + Loss + Fault + Maintenance + Outage
• System modeling and Loss analysis using Matlab/Simulink
• Case : MVAC distribution lines for small village and communication system
12
MVAC system LVDC system
13
Structure & Voltage
Mono-Pole vs Bi-Pole
Line voltage 1,500V(±750V) and Customer 380V
• Cost of Mono-pole is lower than Bi-pole
• Bi-pole, possible to supply power when one pole fault
• High cost, but high reliability for Electric Utility
• Mono-pole for small importance customers
• Standards
- Domestic : under DC 750V , IEC : under DC 1,500V
• Transmission capacity, distance and loss : line voltage 1,500V(±750V)
• Efficiency and global trend : customer voltage 380V
14
Grounding
IT grounding system • Serious electrical corrosion by DC current
• Maximum 120Vdc touch voltage by IEC 60364
• Grounding makes high touch voltage despite of low earth resistance
15
Protection
Protection system • Over-current protection by circuit breaker
• Over-voltage protection by surge arresters
• CB with Insulation Monitoring Device for ground fault
• Galvanic isolation between different grounding systems
16
Converter
Rectifier • Bi-directional 150kW 3-Level NPC AC/DC converter
• Input : AC 380V, Output : DC ±750V
• Unbalanced voltage compensation and short-circuit protection
Io2 Current Limit
Io1 Current Limit
Io2 Current
[10A/div]
Io1 Current
[10A/div]
Vo1 Voltage
[200V/div]
Vo2 Voltage
[200V/div]
Software
Voltage Balancing
Hardware
Voltage Balancing
Io1, Io2
Current Limit
10s/div
17
DC/DC Converter • Bi-directional high efficient 10kW DC/DC converter
• Input : DC ±750V, Output : DC ±380V
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%
110.00%
0.5kW 1kW 2kW 3kW 4kW 5kW
18
Voltage Control
Voltage control of LVDC distribution system • Considering loss, line voltage and feasible supply distance
• Cooperation between AC/DC and DERs
• Real time power flow analysis and voltage control
1 2 3 4 5 6 7 8
0.9
0.95
1
1.05
Fig: Simulation results of Bus voltage control
Number of Bus
Voltage am
plitude
Without control
ac/dc control
G8 injection
G8+G7 injection
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• Application of distributed control using P-gate
• Hybrid control using communication and Droop
Voltage control of LVDC distribution system
20
• ±750/±380 and mono-pole/bi-pole selection
• Monitoring of voltage and current
• Control of each component by serial comm.
Demonstration
Test-lab
21
Pilot system • Demonstration for actual field application using LVDC system
• 1.5km overhead lines, rectifier, converters, loads, and monitoring system
22
[Overall condition] [System status]
[Status of AC/DC converter] [Status of load container]
LVDC distribution line monitoring system
23
LVDC distribution system application(Gwangju)
24
LVDC distribution system application(Gwangju)
25
LVDC distribution system application(Gwangju)
• Operation from October, 2016
• Verification of power quality
• IMD 3-level alarm & block algorithm
26
DC Island
27
Design
Optimal DER capacity • NPV with installation and operating costs for 20 years by HOMER(NREL)
• Parameter : Solar radiation, Wind velocity, Load of the area and Investment
cost
[Economic analysis result]
[Solar radiation, Wind velocity]
[Seasonal load]
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• Existing AC system
- 3 Diesel Gens. , 2 D/L
• New DC distribution network
- DERs : ESS, PV, WT
- Gen. : Variable Speed Gen.
- Load : DC Streetlight,
Appliance, Vehicle
• Operation method
- DC isolated mode
- AC isolated mode
- DC-AC connected mode
DC network configuration
29
Construction
Components of DC system • LVDC distribution line, PV, WT, ESS and variable-speed Diesel Generator
• DC loads : AC/DC hybrid home, DC home, DC street light and DC V2G
±750Vdc
±190Vdc
750Vdc
750Vdc
±750Vdc
±190Vdc
30
DC EMS (Energy Management System)
31
DC EMS (Energy Management System)
32
Solid state Tr.(EPRI)
33
1s/div
Iac [20A/div]
Vdc_Stack[1] Vdc_Stack[2] Vdc_Stack[3] Vdc_Stack[4] Vdc_Stack[5]
[500V/div]
13.2kV Solid State Transformer • Input 13.2kV, output ±750, 150kW, Max. efficiency 96%
• H-bridge AC/DC rectifier + NPC type DAB converter
34
500kW AC/DC converter & DC smart switchgear
• 3-level NPC modular type, Input 380V, output ±750, Max. efficiency 98%
• Parallel operating algorithm for optimizing efficiency
• Switchgear consists of converter, ESS, PV and IED for DC customer with connected
and isolated modes
전력[kW]100 200 500400300
효율 최적효율 운전 방식
일괄제어 운전 방식
Parallel control
Serial control
Eff.
Power[kW]
35
High speed circuit breaker • Development of semiconductor and hybrid breaker for LVDC distribution system
• Operation with high speed and coordinative protection algorithm
36
Infrastructure
Testing infrastructure for DC distribution
• 6km testing distribution line can change to radial, closed-loop and mesh network
• DC distribution management system test with DER and DC load simulators
• Power converter performance evaluation system with real time simulator
37
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Future Plan
Source : Direct Current BV
KEPCO ↔ HYUNDAI ELECTRIC
[ Global Research Center of HYUNDAI HAEVY INDUSTRIES]
39
Conclusion
Source : Tony Seba, Clean Disruption
Power Electronics
