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Changkyu Bai

Bio: Changkyu Bai is an academic researcher from Pohang University of Science and Technology. The author has contributed to research in topics: Capacitor & Control theory. The author has an hindex of 3, co-authored 10 publications receiving 50 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a bidirectional resonant dc/dc converter over a wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs) is presented.
Abstract: This article introduces a highly efficient bidirectional resonant dc/dc converter over wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs). It operates as a pulsewidth-modulation (PWM) full-bridge series-resonant converter in the forward direction and a half-bridge resonant boost converter in the backward direction. One advantage of the proposed converter is that it has a wide voltage gain range in the backward operation. Also, it requires only six active switches. To achieve high efficiency, SiC mosfet s are used for two bottom switches in the primary side, because only these switches suffer hard switching turn- off in both forward and backward directions. Since it operates with fixed-frequency and with PWM control, the magnetic components and passive filters can be optimally designed with respect to the volume and the loss. Thus, the proposed converter achieves low-cost, high-conversion ratio, and high efficiency over a wide range of battery voltages. Detailed analysis of the converter operation is presented along with the design procedure. A 3.3-kW/400-V prototype of the proposed converter has been built to operate for 250–415 V primary source voltages and tested to demonstrate its circuit design.

55 citations

Journal ArticleDOI
TL;DR: The proposed repetitive controller for a capacitor-less current-fed dual-half-bridge converter for a grid-connected fuel cell system can reduce the input current ripple significantly and suppress the dc-link voltage ripple within the predetermined range and thereby achieves ZVS.
Abstract: This paper proposes a repetitive controller (RC) for a capacitor-less current-fed dual-half-bridge (CF-DHB) converter for a grid-connected fuel cell system. The pulsating power caused by the ac grid makes the dc-link voltage and input current fluctuate with twice the grid frequency. To achieve zero-voltage-switching (ZVS) for the capacitor-less CF-DHB converter and to increase the lifetime of the fuel cell, we need to suppress the low-frequency dc-link voltage ripple and the low-frequency input current ripple. We first make use of the duty cycle to regulate the dc-link voltage, and of the phase-shift angle to regulate the input current. Because the transfer function from the duty cycle to the dc-link voltage has a right-half plane (RHP) zero, the conventional proportional-integral controller cannot achieve satisfactory performance at the dc-link voltage. To compensate for the phase lag due to the existence of the RHP zero, we propose to use an RC with phase-lead compensation for dc-link voltage control. Because the transfer function from the phase-shift angle to the input current has one left-half plane zero, the conventional RC is used to control the input current. In developing the proposed controller, we first derive the dynamic model of the CF-DHB converter in the grid-connected environment, and then use the model to design an RC. We also provide a detailed and practical design guideline to select the control parameters of the capacitor-less CF-DHB converter that can meet the desired performance. The proposed RC can reduce the input current ripple significantly and suppress the dc-link voltage ripple within the predetermined range and thereby achieves ZVS. Experimental results demonstrate that the proposed control scheme achieves desirable performance.

29 citations

Journal ArticleDOI
TL;DR: In this paper, a dual-half-bridge (CF-DHB) converter directly connected with a half-bridge inverter unit is proposed for residential photovoltaic power conversion systems.

10 citations

Journal ArticleDOI
TL;DR: A high step-up quasi-resonant converter that minimizes switching loss over a wide range of input voltages by employing a bidirectional switch and corresponding switching modulation achieves the main switch with almost zero voltage, and therefore incurs very little switching loss at all active switches.
Abstract: This article proposes a high step-up quasi-resonant converter that minimizes switching loss over a wide range of input voltages. By employing a bidirectional switch and corresponding switching modulation, the proposed converter achieves the main switch with almost zero voltage, and therefore incurs very little switching loss at all active switches. Moreover, no instantaneous reactive current flows through the circuit under wide variations of input voltages and loads. The duty cycle of primary-side switches is fixed to 0.5; then, the input and clamp capacitor voltages become identical, and thereby the following resonant capacitor voltages remain in balance. As a consequence, the proposed converter becomes compact and achieves high boost-ratio and high efficiency over a wide range of input voltages. The operating principle of the converter is presented along with its design procedure. 400-W/380-V prototype of the proposed converter has been implemented and tested at 40–60 V to verify its effectiveness.

6 citations

Journal ArticleDOI
TL;DR: The bridgeless triple-mode resonant ac–dc converter is introduced and its dynamic model and control technique is presented to demonstrate the validity of the proposed modeling and control approach.
Abstract: This paper introduces the bridgeless triple-mode resonant ac–dc converter and presents its dynamic model and control technique. The proposed converter operates in triple mode: discontinuous-conduction mode (DCM), continuous-conduction mode (CCM), and missing resonance mode (MRM). It has the advantages of small number of required components, medium power capacity, and high efficiency, but it is difficult to control because DCM, CCM, and MRM have their own dynamic characteristics. To solve this control problem, the mode boundaries are first identified and, corresponding to each mode, the dynamic model is developed to design the controller. In each mode, we propose to add a repetitive controller (RC) with a phase-lead compensator to the conventional duty ratio plus feedback controller. The RC is used to suppress the deterministic periodic disturbances and the phase-lead compensator is used to compensate for the incurred phase lag. A 1-kW digitally controlled converter prototype is built and used to demonstrate the validity of the proposed modeling and control approach.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: A comprehensive review of grid-connected fuel cell systems is presented to provide an extensive aspect on the status of fuel cell technologies to the researchers and scientists dealing with the grid connection.

106 citations

Journal ArticleDOI
TL;DR: The proposed topology not only reduces the voltage stress on the main switch but also maintains it steady for the entire duty cycle range, and the reverse recovery issue of the diodes is alleviated through the leakage inductance of the coupled inductor.
Abstract: In this paper, a new high voltage gain step-up dc–dc converter is proposed for interfacing renewable power generation. The configuration optimally integrates both the coupled-inductor and switched-capacitor techniques to achieve an ultra-high step-up gain of voltage conversion with low voltage stress and high efficiency. It consists of a voltage boost unit, a passive clamp circuit, and a symmetrical voltage multiplier network. The structure becomes modular and extendable without adding any extra winding for ultra-high step-up voltage gain. The proposed topology not only reduces the voltage stress on the main switch but also maintains it steady for the entire duty cycle range. Furthermore, the reverse recovery issue of the diodes is alleviated through the leakage inductance of the coupled inductor. The operation principle and steady-state analysis are presented in detail. Experimental evaluation validates the claimed advantages and demonstrates a well-distributed efficiency curve and the peak of 96.70%.

80 citations

Journal ArticleDOI
TL;DR: An extendable quadratic bidirectional dc–dc converter that has an improved voltage transfer ratio (VTR) with the capability of redundancy and modularity for electric vehicle applications is proposed.
Abstract: In this article, we propose an extendable quadratic bidirectional dc–dc converter that has an improved voltage transfer ratio (VTR) with the capability of redundancy and modularity for electric vehicle applications. As n modules are embedded, its VTR becomes n times higher for both directions of currents. Furthermore, the common electrical ground between the input and output is preserved. This is a simple structure with the lowest rating of semiconductors in the family of quadratic bidirectional converters leading to ease of control ability. The proposed converter performance is evaluated in both power flow direction using the deadbeat controller, which is a smooth, accurate, and fast response. Finally, the process of charging/discharging of a lithium-ion battery is controlled through the proposed converter. 500-W experimental results are provided in both power flow directions in a closed-loop system in the presence of the proposed controller. The obtained results verify the applicability of this structure.

56 citations

Journal ArticleDOI
TL;DR: In this article, a bidirectional resonant dc/dc converter over a wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs) is presented.
Abstract: This article introduces a highly efficient bidirectional resonant dc/dc converter over wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs). It operates as a pulsewidth-modulation (PWM) full-bridge series-resonant converter in the forward direction and a half-bridge resonant boost converter in the backward direction. One advantage of the proposed converter is that it has a wide voltage gain range in the backward operation. Also, it requires only six active switches. To achieve high efficiency, SiC mosfet s are used for two bottom switches in the primary side, because only these switches suffer hard switching turn- off in both forward and backward directions. Since it operates with fixed-frequency and with PWM control, the magnetic components and passive filters can be optimally designed with respect to the volume and the loss. Thus, the proposed converter achieves low-cost, high-conversion ratio, and high efficiency over a wide range of battery voltages. Detailed analysis of the converter operation is presented along with the design procedure. A 3.3-kW/400-V prototype of the proposed converter has been built to operate for 250–415 V primary source voltages and tested to demonstrate its circuit design.

55 citations

Journal ArticleDOI
15 Apr 2020-Energy
TL;DR: A new energy management method is developed to reduce electrical energy demand with the elimination of reactive energy consumption from the electrical grid and can not only supply active power to consumers but also provides smooth power factor between grid voltage and current.

53 citations