1. Power Electronics Research at Seoul National University
Bo-Hyung Cho
Department of Electrical Engineering & Computer Science
Seoul National University, Seoul, Korea
Presented at Nagasaki University

2. Outline Cho’s Lab Research Interest: - DC-DC Conversion
- AC-DC Conversion
- Distributed Power Systems
- Electrified Vehicles (EV) Systems
- Battery Management Systems

3. Cho’s Lab: DC-DC Conversion
DC-DC Conversion on EV Funded by
project outline
2.9 kW DC-DC converter development
power flow between high-voltage Li-ion battery to Pb battery
high efficiency: 94% with wide input/output voltage range
high power density: 550 W/Liter with 200 –A high current management
[ An Electric Vehicle Power and Drive System ]
[ Example of developed converter]

4. [ Prototype [145mm X 80mm X 6.3mm] ] [ Multi Layer PCB Windings ]
Cho’s Lab: AC-DC Conversion
labtop power adapter funded by
project outline
extremely low profile: 6.3mm
high mass-productivity using PCB winding
very high frequency switching: 1MHz
high efficiency: half load, full load
Multi Layer
[ Prototype [145mm X 80mm X 6.3mm] ]
[ Multi Layer PCB Windings ]

5. [ lamps and ballast circuit ]
Cho’s Lab: AC-DC Conversion
lamp ballast for street light system funded by
project outline
ballast circuit for metal halide lamp to substitute Hg-Na lamp
digital control with communication and diagnostics
robust to extreme operation conditions such as lightening, humidity, temperature
high efficiency: full load
[ circuit diagram ]
[ lamps and ballast circuit ]

6. Cho’s Lab: Distributed Power System
AC Distribution
inefficient interface as renewable sources are wide spread
Ineffective interface with storage (ac-dc)
efficiency and reliability issues
DC Distribution
streamlined conversion from renewable source to loads
effective interface with storage
improved efficiency and reliability expected
Issues
DC system design and operation strategy
Efficient interface of DC to AC grid
Interface for renewable energy sources and storage devices
Standards for DC system: STD voltage, regulation
Safety issues: Grounding, Isolation, Islanding
Protection strategies for subsystems and their cooperation

7. [ DC Distribution Green Building ]
Cho’s Lab: Distributed Power System
DC powered green building system funded by
project outline
renewable energy interface
high-efficiency power converters
system protections
smart meters with
wireless communications
plug-in hybrid vehicle charger
[ DC Distribution Green Building ]

8. [ system architecture] [ Building with PV panels ]
Cho’s Lab: Distributed Power System
building integrated photovoltaic (BIPV) panel funded by
project outline
power system for office building (testbed Seoul Nat’l Univ. Bld. #33)
36 kW roof-top PV and 20 kW BIPV
20 kW LED & various office loads
protection including arc detection and islanding
[ system architecture]
[ Building with PV panels ]

9. Cho’s Lab: Distributed Power System
PV interface power converter
project outline
high efficiency through ZVS and ZCS (higher than 98%)
electrolytic-cap-less design for reliability
Fujitsu DC relay applied for protection
arc fault protected Design
island detection guaranteed within 0.2s
Input Voltage (PV volt.)
0-145 V
Output Voltage (DC Line)
380 V
Maximum Power
120 W
Cdc
Film, 10 μF
Inductance, L
Core: RM14LP, 710 μH,
MOSFET, S
28NM50N, 500 V, 21A
Diode, D
SDT08S60, 600 V, 8A
[ system spec. ]
[ Prototype PV Converter ]
[ system architecture]
[ Anti-Islanding Algorithm ]

10. Cho’s Lab: Battery Management System
battery screening funded by
project outline
selecting battery cells to improve voltage/SOC balancing of battery pack
screening algorithm for multiple cells
[ capacity mismatch ]
[ State-of-charge mismatch ]
[ proposed algorithm for battery screening ]

11. Cho’s Lab: Battery Management System
battery management system funded by
project outline
implementation of battery management circuits connected to individual battery cells
estimation of state of charge (SOC) using
Extended Kalman Filters
[ cell SOC estimation ]
[ estimation algorithm for SOC estimation ]
[ experimental setup for BMS test ]
[ pack SOC estimation ]