• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.85-89
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• 1998

A switching power stage is a very nonlinear system because it has two or more operation modes in one switching cycle. To model a switching power stage, the state space averaging method has been developed. Though it allows a unified treatment of a large variety of switching power stages, the model it yields is always very nonlinear. So, it is required to linearize the averaged model. But it is well known that a controller for a nonlinear plant designed by the linearization frequently fails in showing satisfactory control performance. Hence it is very natural to try to design a nonlinear controller for a switching power stage. In design of a switching power system, nonlinear control approaches such as adaptive control and fuzzy control have been widely studied so far. In this research, a recently developed control method, time delay control is briefly studied and a design example for a ZVS PWM half bridge converter is given. The performance of the time delay controller is compared to its conventional counterpart, PI controller by computer simulations.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.120-124
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• 2001

A new technique for improving the efficiency of single-phase high-frequency boost converter is proposed. This converter includes an additional low-frequency boost converter which is connected to the main high-frequency switching device in parallel. The additional converter is controlled at lower frequency. Most of the current flows in the low-frequency switch and so, high-frequency switching loss is greatly reduced accordingly Both switching device are controlled by a simple method; each controller consists of a one-shot multivibrator, a comparator and an AND gate. The converter works cooperatively in high efficiency and acts as if it were a conventional high-frequency boost converter with one switching device. The proposed method is verified by simulation. This paper describes the converter configuration and design, and discusses the steady-state performance concerning the switching loss reduction and efficiency improvement.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.394-395
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• 2011

In order to increase the power conversion efficiency and improve the power factor, a modified forward converter is proposed, which adopts a capacitive output filter instead of the inductive output filter of the conventional forward converter. Therefore, the proposed converter has wide input voltage range in opposite to that of the conventional forward converters. Moreover, the proposed converter uses the critical conduction mode for automatic current shaping to improve the power factor. As a result, the proposed converter can achieve quasi-resonant zero-voltage-switching, which can minimize the switching loss of main MOSFET. In addition, the operational principle of the proposed converter is analyzed and the characteristic of the proposed converter is investigated in this paper. To validate the effectiveness of the proposed converter, a prototype of 13W is implemented and the experimental results are discussed in more detail.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.1
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• pp.66-69
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• 2019

This study proposes a high-efficiency phase-shifted full-bridge (PSFB) converter with a wide input voltage range. The conventional PSFB converter is a useful topology in high-power applications. This converter not only achieves the zero-voltage switching of the primary switches, but also has small RMS current in the primary side. However, because the conventional PSFB converter has large freewheeling current in the primary side when it is designed considering the hold-up time of the converter, such a converter has high conduction loss at the primary switches. To solve this problem, a new PSFB converter is proposed in this study. The experiment is implemented with an input voltage ranging from a 320 V-400 V and an output power specification of 715 W.

• Journal of Power Electronics
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• v.14 no.3
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• pp.507-518
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• 2014

This paper presents a new cascaded asymmetrical single phase multilevel converter with a lower number of power semiconductor switches and isolated DC sources. Therefore, the number of power electronic devices, converter losses, size, and cost are reduced. The proposed multilevel converter topology consists of two H-bridges connected in cascaded configuration. One H-bridge operates at a high frequency (high frequency inverter) and is capable of developing a two level output while the other H-bridge operates at the fundamental frequency (low frequency inverter) and is capable of developing a multilevel output. The addition of each power electronic switch to the low frequency inverter increases the number of levels by four. This paper also introduces a hybrid switching algorithm which uses very simple arithmetic and logical operations. The simplified hybrid switching algorithm is generalized for any number of levels. The proposed simplified switching algorithm is developed using a TMS320F2812 DSP board. The operation and performance of the proposed multilevel converter are verified by simulations using MATLAB/SIMULINK and experimental results.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.266-270
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• 2001

This paper presents a novel topological prototype of voltage source series quasi-resonant zero current soft-switching pulse frequency modulated dc-dc power converter circuit using IGBTs which incorporates a high-frequency flyback transformer link. Its steady-state operating principle is described on the basis of simulation analysis, along with the open loop controlled power regulation characteristics of the multi-functional coupled inductors linked dc-dc power converter operating under a principle of zero current soft switching commutation.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.464-470
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• 2022

A new type of soft-switching forward converter is proposed in this study. By adding only a few components, the inductor, diode, switch, and capacitor exhibit higher efficiency than the conventional forward converter. Therefore, the switching losses of the proposed forward converter are considerably reduced compared with those of the conventional forward converter. In addition, the reset winding is not used because of the capacitor employed in the auxiliary circuit. The auxiliary capacitor is adopted for zero-current-transition operation and for dissipating magnetization energy. The performance of the proposed forward converter is validated using experimental results from a 60 W, single-output, forward converter prototype, and design guidelines are presented.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1490-1499
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• 2017

The modular multilevel converter (MMC) is generally considered to be a promising topology for medium-voltage and high-voltage applications. However, in order to apply it to high-power applications, a huge number of switching devices is essential. The numerous switching devices lead to considerable switching losses, high cost and a larger heat sink for each of the switching device. In order to reduce the switching losses of a MMC, this paper analyzes the performance of the conventional discontinuous pulse-width modulation (DPWM) method and its efficiency. In addition, it proposes a modified novel DPWM method for advanced switching losses reduction. The novel DPWM scheme includes an additional rotation method for voltage-balancing and power distribution among sub modules (SMs). Simulation and experimental results verify the effectiveness and performance of the proposed modulation method in terms of its switching losses reduction capability.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.266-269
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• 2000

This paper presents a novel single-stage unity power factor converter which features the reduced switching losses by zero-voltage switching and zero-current switching (ZVZCS). Hence the turn-on and turn-off losses of switches are sufficiently reduced. And the reduced conduction losses are achieved by the elimination of one leg of front-end rectifier. And low on-resistance MOSFETs (Synchronous Rectifier) are used in the rectifier at the secondary side of high frequency transformer instead of diodes. Theoretical analysis simulated results of a AC to DC 150W(5V, 30A) converter are presented.

• Journal of Power Electronics
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• v.7 no.1
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• pp.13-20
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• 2007

LLC resonant converters display many advantages over the conventional LC series resonant converter such as narrow frequency variation over wide range of load and input variation and zero voltage switching even under no load conditions. This paper presents analysis and design consideration for the half bridge LLC resonant converter. Using the fundamental approximation, the gain equation is obtained, where the leakage inductance in the transformer secondary side is also considered. Based on the gain equation, the practical design procedure is investigated to optimize the resonant network for a given input/output specifications. The design procedure is verified through an experimental prototype of the 115W half-bridge LLC resonant converter.