Seok-Hyeong Ham
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Seok-Hyeong Ham has a total of 8 co-authors. Here are the top co-authors by number of shared publications:
- Bongkoo Kang
Department of Electrical Engineering, Pohang University of Science and Technology, Pohang 790-783, Korea
3 shared publications - Hyeon-Seok Lee
Department of Electrical Engineering, POSTECH, Pohang 37673, Korea
3 shared publications - Hyung-Jin Choe
Circuit Research Team, LG Display, Paju, Gyeonggi Korea, Republic of
2 shared publications - Ho-Young Yoon
Electrical Engineering, Pohang University of Science and Technology, 34995 Pohang Korea (the Republic of) 790-784
1 shared publication - Hyung-Jin Choe
Department of Electrical and Electrical Engineering, Tongmyong University, Busan, South Korea
1 shared publication - Sang-Won Lee
Department of Electrical, Electronics, and Control Engineering, Kongju National University, Cheonan, South Korea
1 shared publication
Latest Publications
- Open Access
High-efficiency Bidirectional Buck–Boost Converter for Residential Energy Storage System
This paper proposes a bidirectional dc–dc converter for residential micro-grid applications. The proposed converter can operate over an input voltage range that overlaps the output voltage range. This converter uses two snubber capacitors to reduce the switch turn-off losses, a dc-blocking capacitor to reduce the input/output filter size, and a 1:1 transformer to reduce core loss. The windings of the transformer are connected in parallel and in reverse-coupled configuration to suppress magnetic flux swing in the core. Zero-voltage turn-on of the switch is achieved by operating the converter in discontinuous conduction mode. The experimental converter was designed to operate at a switching frequency of 40–210 kHz, an input voltage of 48 V, an output voltage of 36–60 V, and an output power of 50–500 W. The power conversion efficiency for boost conversion to 60 V was ≥98.3% in the entire power range. The efficiency for buck conversion to 36 V was ≥98.4% in the entire power range. The output voltage ripple at full load was p.p for boost conversion (60 V) and 1.35 Vp.p for buck conversion (36 V) with the reduced input/output filter. The experimental results indicate that the proposed converter is well-suited to smart-grid energy storage systems that require high efficiency, small size, and overlapping input and output voltage ranges.
Open AccessHigh-efficiency Bidirectional Buck–Boost Converter for Residential Energy Storage System
This paper proposes a bidirectional dc–dc converter for residential micro-grid applications. The proposed converter can operate over an input voltage range that overlaps the output voltage range. This converter uses two snubber capacitors to reduce the switch turn-off losses, a dc-blocking capacitor to reduce the input/output filter size, and a 1:1 transformer to reduce core loss. The windings of the transformer are connected in parallel and in reverse-coupled configuration to suppress magnetic flux swing in the core. Zero-voltage turn-on of the switch is achieved by operating the converter in discontinuous conduction mode. The experimental converter was designed to operate at a switching frequency of 40–210 kHz, an input voltage of 48 V, an output voltage of 36–60 V, and an output power of 50–500 W. The power conversion efficiency for boost conversion to 60 V was ≥98.3% in the entire power range. The efficiency for buck conversion to 36 V was ≥98.4% in the entire power range. The output voltage ripple at full load was p.p for boost conversion (60 V) and 1.35 Vp.p for buck conversion (36 V) with the reduced input/output filter. The experimental results indicate that the proposed converter is well-suited to smart-grid energy storage systems that require high efficiency, small size, and overlapping input and output voltage ranges.
- Open Access
Miniature DC-DC Boost Converter for Driving Display Panel of Notebook Computer
This paper proposes a miniature DC-DC boost converter to drive the display panel of a notebook computer. To reduce the size of the circuit, the converter was designed to operate at a switching frequency of 1 MHz. The power conversion efficiency improved using a passive snubber circuit that consisted of one inductor, two capacitors, and two diodes; it reduced the switching losses by lowering the voltage stress of the switch and increased the voltage gain using charge pumping operations. An experimental converter was fabricated at 2.5 cm × 1 cm size using small components, and tested at input voltage 5 V ≤ VIN ≤ 17.5 V and output current 30 mA ≤ IO ≤ 150 mA. Compared to existing boost converters, the proposed converter had ~7.8% higher power conversion efficiency over the entire range of VIN and IO, only ~50% as much voltage stress of the switch and diodes, and a much lower switch temperature TSW = 49.5 °C. These results indicate that the proposed converter is a strong candidate for driving the display panel of a notebook computer.
Open AccessMiniature DC-DC Boost Converter for Driving Display Panel of Notebook Computer
This paper proposes a miniature DC-DC boost converter to drive the display panel of a notebook computer. To reduce the size of the circuit, the converter was designed to operate at a switching frequency of 1 MHz. The power conversion efficiency improved using a passive snubber circuit that consisted of one inductor, two capacitors, and two diodes; it reduced the switching losses by lowering the voltage stress of the switch and increased the voltage gain using charge pumping operations. An experimental converter was fabricated at 2.5 cm × 1 cm size using small components, and tested at input voltage 5 V ≤ VIN ≤ 17.5 V and output current 30 mA ≤ IO ≤ 150 mA. Compared to existing boost converters, the proposed converter had ~7.8% higher power conversion efficiency over the entire range of VIN and IO, only ~50% as much voltage stress of the switch and diodes, and a much lower switch temperature TSW = 49.5 °C. These results indicate that the proposed converter is a strong candidate for driving the display panel of a notebook computer.
- 17 November 2017
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Power Electronics
- Vol. 33 (10) , 8808-8817
Off-Time Control of LLC Resonant Half-Bridge Converter to Prevent Audible Noise Generation Under a Light-Load Condition
This paper presents a control method that can prevent audible noise generation in an LLC resonant half-bridge dc-dc converter at a light load condition, while achieving the same input voltage range and power conversion efficiency $\eta_e$ as the burst-control method that generates an audible noise. The proposed method reduces switching and conduction losses at light load by skipping several pairs of switch-control pulses, while varying the switching frequency less than the normal-control method does. This skip-control method enables the LLC resonant converter to have a large magnetizing inductance, and to have high $\eta_e$ over a wide range of load variation. At an input voltage of 385 V, an output voltage of 24 V, and a resonant frequency of 180 kHz, the proposed method achieved $\eta_e\geq 85.46\%$ for an output power range of $7.2 \sim 360 W$; the highest $\eta_e$ was 96.08% at $P_o= 336$ W.- 17 November 2017
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Power Electronics
- Vol. 33 (10) , 8808-8817
Off-Time Control of LLC Resonant Half-Bridge Converter to Prevent Audible Noise Generation Under a Light-Load Condition
This paper presents a control method that can prevent audible noise generation in an LLC resonant half-bridge dc-dc converter at a light load condition, while achieving the same input voltage range and power conversion efficiency $\eta_e$ as the burst-control method that generates an audible noise. The proposed method reduces switching and conduction losses at light load by skipping several pairs of switch-control pulses, while varying the switching frequency less than the normal-control method does. This skip-control method enables the LLC resonant converter to have a large magnetizing inductance, and to have high $\eta_e$ over a wide range of load variation. At an input voltage of 385 V, an output voltage of 24 V, and a resonant frequency of 180 kHz, the proposed method achieved $\eta_e\geq 85.46\%$ for an output power range of $7.2 \sim 360 W$; the highest $\eta_e$ was 96.08% at $P_o= 336$ W.- 13 October 2017
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Power Electronics
- Vol. 33 (8) , 6646-6655
Improvement of Power-Conversion Efficiency of AC–DC Boost Converter Using 1:1 Transformer
This paper proposes a circuit structure that can improve the power-conversion efficiency $\eta_e$ of an ac-dc boost converter. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, and a diode. The transformer forces the converter to operate in continuous conduction mode for input current, and thereby reduces input ripple. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn-ON of switch and reverse recovery of diode is minimized. The proposed converter has high $\eta_e$ over a wide range of ac input voltage $V_{ac}$: $\eta_e$ = 92.9% at $V_{ac}$ = 85 V and $\eta_e$ = 97.4% at $V_{ac}$ = 265 V, when the converter was operated at dc output voltage of 400 V and output power of 500 W. The temperature of the switch stabilized at ∼ 84 °C for $V_{ac}$ = 85 V, at ∼ 70 °C for $V_{ac}$ = 110 V, and at ∼ 42 °C for $V_{ac}$ = 220 V, whereas that in other ac-dc converters either failed or stabilized at much higher levels. The proposed converter is well suited to systems that require an input voltage range of 85 ~ 265 V in root-mean-square value.- 13 October 2017
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Transactions on Power Electronics
- Vol. 33 (8) , 6646-6655
Improvement of Power-Conversion Efficiency of AC–DC Boost Converter Using 1:1 Transformer
This paper proposes a circuit structure that can improve the power-conversion efficiency $\eta_e$ of an ac-dc boost converter. The circuit uses a 1:1 transformer and a voltage boost circuit composed of an inductor, a capacitor, and a diode. The transformer forces the converter to operate in continuous conduction mode for input current, and thereby reduces input ripple. The voltage boost circuit enables the switch to operate in critical conduction mode, so the power loss due to turn-ON of switch and reverse recovery of diode is minimized. The proposed converter has high $\eta_e$ over a wide range of ac input voltage $V_{ac}$: $\eta_e$ = 92.9% at $V_{ac}$ = 85 V and $\eta_e$ = 97.4% at $V_{ac}$ = 265 V, when the converter was operated at dc output voltage of 400 V and output power of 500 W. The temperature of the switch stabilized at ∼ 84 °C for $V_{ac}$ = 85 V, at ∼ 70 °C for $V_{ac}$ = 110 V, and at ∼ 42 °C for $V_{ac}$ = 220 V, whereas that in other ac-dc converters either failed or stabilized at much higher levels. The proposed converter is well suited to systems that require an input voltage range of 85 ~ 265 V in root-mean-square value.