• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1934-1944
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• 2017

As a key component of high-voltage power conversion system for electric vehicles (EVs), bidirectional DC/DC (Bi-DC/DC) is required to have high efficiency and light weight. Conventional design methods optimize the Bi-DC/DC at the maximum power dissipation point (MPDP). For EVs application, the work condition of the Bi-DC/DC is not strict as the MPDP, where the design method using MPDP may not be optimal during travel of EVs. This paper optimizes the Bi-DC/DC converter targeting efficiency and weight based on the driving cycle. By analyzing the two-phase interleaved Bi-DC/DC for hybrid energy storage systems (HESS) of EVs, its power dissipation is calculated, and an efficiency model is derived. On this basis, weight models of capacitor, inductor and heat sink are built, as well as a dynamic temperature model of heat sink. Based on these models, a method using New European Driving Cycle (NEDC) for optimal design of Bi-DC/DC which simultaneously considered efficiency and weight is proposed. The simulation result shows that compare with conventional optimization methods revealed that the optimization approach based on driving cycle allowed significant weight reduction while meeting the efficiency requirements.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.9
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• pp.1239-1248
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• 2018

This paper proposes a fault tolerant and high efficiency operation algorithm for a 4 LEG DC/DC converter for a battery energy storage system(BESS) forming a main power source in a standalone DC micro grid. The BESS for the main power supply in the stand-alone DC micro-grid is required to operate at high speed according to fault tolerant control and load by operating at all times. Fault-tolerance control changes the short-circuit fault to an open-circuit fault by using a fuse in case of leg fault in 4 legs, and operates stably through phase shift control. In addition, considering the loss of the power semiconductor, the number of LEG operation is adjusted to operate at high efficiency in the full load region. In this paper, fault tolerant control and high efficiency operation algorithm of DC/DC converter for BESS in standalone DC micro grid is presented and it is proved through simulation and experiment.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.9
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• pp.1674-1683
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• 2011

More than 80% of electric loads need DC electricity rather than AC at the moment. If DC power could be supplied directly to the terminal loads, power conversion stages including rectifiers, converters, and power adapters can be reduced or simplified. Therefore, DC microgrids may be able to improve energy efficiency of power distribution systems. In addition, DC microgrids can increase the penetration level of renewable energy resources because many renewable energy resources such as solar photovoltaic(PV) generators, fuel cells, and batteries generate electric power in the form of DC power. The integration of the DC generators to AC electric power systems requires the power conversion circuits that may cause additional energy loss. This paper discusses the capability and feasibility of DC microgrids with regard to energy efficiency analysis through detailed dynamic simulation of DC and AC microgrids. The dynamic simulation models of DC and AC microgrids based on the Microgrid Test System in KEPCO Research Institute are described in detail. Through simulation studies on various conditions, this paper compares the energy efficiency and advantages of DC and AC microgrids.

• Journal of Power Electronics
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• v.11 no.4
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• pp.561-567
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• 2011

This paper presents a high-efficiency power conditioning system (PCS) for grid-connected photovoltaic (PV) modules. The proposed PCS consists of a step-up DC-DC converter and a single-phase DC-AC inverter for the grid-connected PV modules. A soft-switching step-up DC-DC converter is proposed to generate a high DC-link voltage from the low PV module voltage with a high-efficiency. A DC-link voltage controller is presented for constant DC-link voltage regulation. A half-bridge inverter is used for the single-phase DC-AC inverter for grid connection. A grid current controller is suggested to supply PV electrical power to the power grid with a unity power factor. Experimental results are obtained from a 180 W grid-connected PV module system using the proposed PCS. The proposed PCS achieves a high power efficiency of 93.0 % with an unity power factor for a 60 Hz / 120 Vrms AC power grid.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.4
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• pp.61-72
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• 2007

This study proposed a high efficiency DC-DC converter with a new current doubler rectifier for fuel-cell systems for use with the Nexa(310-0027) PEMFC from the Ballard Co. The proposed high efficiency DC-DC converter for the fuel-cell system generated ZVS by applying partial resonance and using a phase shift PWM control method. Constantly switching frequency, loss of switching, peak current, and peak voltage were reduced by this system. In addition to this system, two inductors were attached to a rectifier circuit allowing it to be able to provide the direct current(DC) and DC voltage safely to a load with reduced ripple components. Also, by using the newly proposed current doubler rectifier, the high frequency DC-DC converter for the fuel cell system was capable of reaching a highest efficiency of 92[%] as compared to 88.3[%] efficiency in previous results, which means that efficiency increased 3.7[%]. The overall results were confirmed by a simulation and laboratory experiment.

• Journal of electromagnetic engineering and science
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• v.11 no.3
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• pp.161-165
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• 2011

In this paper, a high-efficiency DC-AC converter is used for wireless energy transmission. The DC-AC convertter is implemented by combining the oscillator and power amplifier. Given that the conversion efficiency of a DC-AC converter is strongly affected by the efficiency of the power amplifier, a high-efficiency power amplifier is implemented using a class-E amplifier structure. Also, because of the low output power of the oscillator connected to the input stage of the power amplifier, a high-gain two-stage power amplifier using a drive amplifier is used to realize a high-output power DC-AC converter. The high-efficiency DC-AC converter is realized by connecting the oscillator to the input stage of the high-gain high-efficiency two-stage class-E power amplifier. The output power and the conversion efficiency of the DC-AC converter are 40.83 dBm and 87.32 %, respectively, at an operation frequency of 13.56 MHz.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.54-62
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• 2013

This paper proposes a high-efficiency DC-DC converter with improved dynamic response characteristics for modular photovoltaic power conversion. High power efficiency is achieved by reducing switching power losses of the DC-DC converter. The voltage stress of power switches is reduced at primary side. Zero-current switching of output diodes is achieved at secondary side. A modified proportional and integral controller is suggested to improve the dynamic responses of the DC-DC converter. The performance of the proposed converter is verified based on a 200 [W] modular power conversion system including the grid-tied DC-AC inverter. The proposed DC-DC converter achieves the efficiency of 97.9 % at 60 [V] input voltage for a 200 [W] output power. The overall system including DC-DC converter and DC-AC inverter achieves the efficiency of 93.0 % when 200 [W] power is supplied into the grid.

• Journal of Industrial Technology
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• v.30 no.A
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• pp.69-73
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• 2010

In this paper, we designed the RF-DC converter used in wireless power transmission system and studied how to design the RF-DC converter of high conversion efficiency. The RF-DC converter operate at 2.45GHz and the diode is connected with series. The RF-DC converter uses shorted stub for DC loop and matching. We can divide the RF-DC converter circuit into four blocks. The reflection coefficients between the blocks were optimized for the maximum conversion efficiency at 0 dBm input power and $1300{\Omega}$ load impedance. The final design of the RF-DC converter has a 52 percent conversion efficiency.

• Journal of Korea Multimedia Society
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• v.19 no.2
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• pp.352-359
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• 2016

This paper presents high efficiency 5A synchronous DC-DC buck converter. The proposed DC-DC buck converter works from 4.5V to 18V input voltage range, and provides up to 5A of continuous output current and output voltage adjustable down to 0.8V. This chip is packaged MCP(multi-chip package) with control chip, top side P-CH switch, and bottom side N-CH switch. This chip is designed in a 25V high voltage CMOS 0.35um technology. It has a maximum power efficiency of up to 94% and internal 3msec soft start and fixed 500KHz PWM(Pulse Width Modulation) operations. It also includes cycle by cycle current limit function, short and thermal shutdown protection circuit at 150℃. This chip size is 2190um*1130um includes scribe lane 10um.

• Journal of Power Electronics
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• v.12 no.1
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• pp.157-163
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• 2012

Internet Data Centers (IDCs), which are essential facilities in the modern IT industry, typically have scores of MW of concentrated electric loads. The provision of an Uninterruptible Power Supply (UPS) is necessary for the power feed system of IDCs owing to the need for stable power. Thus, conventional IDC AC power feed systems have three cascaded power conversion stages, (AC-DC), (DC-AC), and (AC-DC), resulting in a very low conversion efficiency. In comparison, DC power feed systems require only a single power conversion stage (AC-DC) to supply AC main power to DC server loads, resulting in comparatively high conversion efficiency and reliability [4-11]. This paper compares the efficiencies of a 220V AC power feed system with those of a 300V DC power feed system under equal load conditions, as established by the Mok-Dong IDC of Korea Telecom Co. Ltd. (KT). Experimental results show that the total operation efficiency of the 300V DC power feed system is approximately 15% higher than that of the 220V AC power feed system.