LVDC-Redefining Electricity
LVDC-Redefining Electricity
First International Conference on Low Voltage Direct Current
New Delhi, India,
26 & 27 October 2015
International
Electrotechnical
Commission
Bureau of
Indian Standards
The Development of LVDC
Distribution System in KOREA
Jintae Cho
KEPRI (KEPCO Research Institute) jintaecho@kepco.co.kr
South Korea
Contents
1 Introduction of KEPRI
2 Research activities in Korea
3 Background of KEPCO LVDC system
4 LVDC current study status by KEPRI
5 Future Plan & Conclusion
Introduction
Introduction
R&D Vision
Strategy
Structure
Research activities
IDC (Internet Data Center)
• 48V, 380V DC distribution system
• 13% Efficiency increase
• Elimination of AC UPS, STS (20% Cost down)
• Improvement of power reliability
KT Mok-Dong IDC, Seoul
Research activities
DC Home
• DC distribution and appliances
• DC-based power sources and energy storage
- PV, Wind , Fuel cell and Li-ion Battery
• 1.5 ~ 3% efficiency increase
Wind Power
PV Power
DC Appliances
Electric
Vehicle
EMS
Smart Meter
Li-ion Battery Zero Energy House (Samsung C&T)
Research activities
DC Home
• DC Home test-bed (KETI)
- Max. 6% with PV, 279kWh in a year
• Environment-friendly house with DC (SNU)
DC home test-bed (KETI) Green IT DC distribution test-bed (SNU)
Research activities
DC building (K-MEG)
• Energy saving of building using DC system
• Equipment for DC : ELCB, CB, Panel, LED, Meter
• DC load : DC OA equipment, Inverter for OA
• Bi-directional AC/DC Inverter
• Adoption of BIPV, Roof-top PV, Energy storage
• Monitoring & Control
• Field test in Campus building(SNU)
• Cooperation with VTT
- Field test of BEMS in VTT building
K-MEG Test-site (SNU)
Research activities
Others
• Factory , Railway, Ship, etc.
• Most activities are related to the customer side (IDC, home, building, etc.)
- To improve energy efficiency and to reduce costs related to energy
Electric Utility needs the DC distribution System ?
Background
Demand increase of DC and high quality power
• 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%)
Growth of renewable energy
• Increase of DC output power distributed generation (PV, Fuel cell, Battery, etc.)
- By 2035, provide 11% of total primary energy supply with NRE
• Needs of MicroGrid energy efficiency improvement
Background
Advantages of LVDC system for Utility
• Increase of transmission capacity in LV system
• Extension of transmission distance in LV system
• Reduction of system construction expenses for low-density customer
• Improvement of power supply reliability
• Enhancement of power quality for customer
• Easy connection between power system and DG, Battery
What is the business model in current system
• Needs to prove feasibility of LVDC system through the case study
Structure & Voltage
Mono-Pole vs Bi-Pole
• 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
Line voltage 1,500V(±750V) and Customer 380V
• 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
Economical 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
Economical Analysis
MVAC system LVDC system
Economical Analysis
Distribution system for PV area
• Analysis of distribution line for 32 homes have own PV
• Calculation of system loss from converter efficiency
• Evaluation between AC installation/loss costs and DC’s
• DC distribution is more effective when the DC load is over 44%
Grounding
IT grounding system
• Serious electrical corrosion by DC current
• Maximum 120Vdc touch voltage by IEC 606364
• Grounding makes high touch voltage despite of low earth resistance
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
Converter
Rectifier
• Bi-directional 150kW 3-Level NPC AC/DC converter
• Input : AC 380V, Output : DC ± 750V
• Unbalanced voltage compensation and short-circuit protection
Software
Voltage Balancing
V o1
Voltage
[200V/div] I o1
Current Limit
V o2
Voltage
[200V/div]
I o2
Current Limit
I o2
Current I o1
Current
[10A/div] [10A/div]
10s/div
I o1,
I o2
Current Limit
Hardware
Voltage Balancing
Converter
DC/DC Converter
• Bi-directional high efficient 10kW DC/DC converter
• Input : DC ± 750V, Output : DC ± 380V
110.00%
100.00%
90.00%
80.00%
70.00%
60.00%
50.00%
0.5kW
1kW 2kW 3kW 4kW 5kW
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
Fig: Simulation results of Bus voltage control
1.05
1
0.95
0.9
1
Without control ac/dc control
G8 injection
G8+G7 injection
2 3 4
Number of Bus
5 6 7 8
Voltage control
Voltage control of LVDC distribution system
• Application of distributed control using P-gate
• Hybrid control using communication and Droop
Demonstration
Test-lab
• ± 750/ ± 380 and mono-pole/bi-pole selection
• Monitoring of voltage and current
• Control of each component by serial comm.
Demonstration
Gochang Power Testing Center
Demonstration
Pilot system
• Demonstration for actual field application using LVDC system
• 1km overhead lines, rectifier, converters, loads, and monitoring system
Future Plan
Field test infrastructure(Gochang power test center)
• Integrated LVDC distribution network with simulators of PV, WT, Battery, etc.
• Performance test facility for power conversion system
Application of LVDC distribution network at Island
• Construction of diesel, PV,WT, storage and dc customers
• LVDC distribution management system( based MG management system)
Distribution Equipment for the future
• 13.2kV SST, high efficiency AC/DC converter, DC customer switchgear
• High performance CB and fault detection device for IT grounding
MVDC (Medium Voltage Direct Current)
• Application possibility, economic analysis, etc.
Conclusion
Most research activities about DC home, DC building and IDC
Advantage : Energy efficiency and cost down
DC distribution research of Utility is at the early stage
Rapid growth of Digital loads and Renewable energies
Needs to prepare the demand from DC customer
Needs to find new obvious business model like MG
Needs of joint action with government, company, and Utility
