• Proceedings of the KSR Conference
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• 1998.05a
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• pp.280-286
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• 1998

In recent years, the interest in noise increases gradually and the low noise level becomes one of the important performances in electrical equipment for railway vehicle. In the auxiliary power supply, most of the noise is made by the current ripple of alternating current reactor(ACL) which filters the output voltage. And this current ripple results from the voltage harmonics across the ACL. So the noise can be reduced by eliminating the voltage harmonics across the ACL. This paper shows harmonic eliminating technique which is making gating signals of upper and lower inverter have a phase difference in the 12-step inverter type auxiliary power supply. This technique was proved by testing on the developed 180KVA auxiliary power supply using IGBT.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1122-1130
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• 2016

This paper presents a novel approach for achieving both a tight DC voltage regulation and a power factor control by applying the Reaching Law Sliding Mode Control (RL-SMC) and the conventional Sliding Mode Control (SMC). Applying these strategies on a matrix rectifier (MR) can achieve a unity grid side power factor when the DC load changes widely and it can provide a ripple-free output voltage that is easily affected by distortions of the three-phase ac voltage supply. Furthermore, by employing the reaching law on the SMC can solve the chatting problem of the sliding motion. Comparative Matlab simulations and experimental verifications for these strategies have been presented and discussed in this paper. The results show that by applying the SMC and RL-SMC on a MR can achieve a unity grid side power factor and a regulated ripple-free DC output.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.290-298
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• 2010

This paper proposes an adaptive carrier-based pulse width modulation (PWM) method for a four-switch three-phase (4S3P) inverter under dc-link voltage ripple conditions. The proposed method guarantees balanced output currents despite of the existence of the voltage oscillations across two dc-link capacitors. And also, this new approach achieves a linear over-modulation with calculation time reduction. Simulation and experimental results are given to validate the feasibility of the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.6
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• pp.535-542
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• 2017

This paper proposes a simple 3-level interleaved charger-discharger for the uninterruptible power supply (UPS) with various combinations of battery cells. The proposed converter not only improves charging and discharging efficiency, but also reduces the physical volume and the cost. Furthermore, the converter also offers the capability of the neutral point voltage, so that more stable operation can be obtained. In addition, the proposed converter significantly reduces the ripple current of the battery inductor, thereby providing an expected life extension of the battery. Experimental results for a 300kVA UPS prototype verify the validity of the proposed converter. The proposed charger-discharger is suitable for UPSs and energy storage systems (ESSs) with wide input battery voltage ranges.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.150-151
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• 2017

This paper deals with the suppression of subharmonic current oscillation of V/F controlled high speed induction motor drive in turbo blower applications. High speed induction motor has a relatively low stator impedance for high speed operation and therefore the dc link voltage ripple may result in subharmonic current oscillation at the steady state in high speed operation. This paper shows that the subharmonic oscillation is caused by the dc link voltage ripple and also proposes the suppression method, which generates the compensation voltage through the proportional current controller to reduce the subharmonic current oscillation. The simulation and experimental results show that the proposed suppression method reduces the subharmonic current oscillation to the acceptable low level in turbo blower applications.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.22-24
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• 2001

This paper presents the characteristics of current harmonics and torque ripple of Brushless DC motor, which is developed the fan blower of vehicles, according to input voltage waveform. To investigate the torque ripple and the phase current harmonics, these characteristics is analysed and compared the experimental results. In the process of analysis, FEM is introduced and computed a transient state torque of BLDC with a sinusoidal and a PWM wave voltage.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1035-1046
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• 2015

This study presents a practical implementation of a multi-mode two-phase interleaved boost converter for fuel cell electric vehicle application. The main operating modes, which include two continuous conducting modes and four discontinuous conducting modes, are discussed. The boundaries and transitions among these modes are analyzed with consideration of the inductor parasitic resistance. The safe operational area is analyzed through a comparison of the different operating modes. The output voltage and power characteristics with open-loop or closed-loop operation are also discussed. Key performance parameters, including the DC voltage gain, input ripple current, output ripple voltage, and switch stresses, are presented and supported by simulation and experimental results.

• Journal of Power Electronics
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• v.16 no.6
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• pp.1991-2004
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• 2016

An LC filter is required to reduce the output current ripple in the auxiliary resonant snubber inverter (ARSI) for high-performance applications. However, if the traditional control method is used in the ARSI with LC filter, then unnecessary current flows in the auxiliary circuit. In addressing this problem, a novel load-adaptive control that fully uses the filter inductor current ripple to realize the soft-switching of the main switches is proposed. Compared with the traditional control implemented in the ARSI with LC filter, the proposed control can reduce the required auxiliary current, contributing to higher efficiency and DC-link voltage utilization. In this study, the detailed circuit operation in the light load mode (LLM) and the heavy load mode (HLM) considering the inductor current ripple is described. The characteristics of the improved ARSI are expressed mathematically. A prototype with 200 kHz switching frequency, 80 V DC voltage, and 8 A maximum output current was developed to verify the effectiveness of the improved ARSI. The proposed ARSI was found to successfully operate in the LLM and HLM, achieving zero-voltage switching (ZVS) of the main switches and zero-current switching (ZCS) of the auxiliary switches from zero load to full load. The DC-link voltage utilization of the proposed control is 0.758, which is 0.022 higher than that of the traditional control. The peak efficiency is 91.75% at 8 A output current for the proposed control, higher than 89.73% for the traditional control. Meanwhile, the carrier harmonics is reduced from -44 dB to -66 dB through the addition of the LC filter.

• Journal of Electrical Engineering and Technology
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• v.6 no.6
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• pp.842-848
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• 2011

The current study proposes the design of a hybrid series-parallel resonant converter (SPRC) and a three-stage Cockcroft-Walton voltage multiplier for precisely adjusting the power generated by a continuous wave (CW) $CO_2$ laser. The design of a hybrid SPRC, called LCC resonant converter, is described, and the fundamental approximation of a high-voltage and high-frequency (HVHF) transformer with a resonant tank is discussed. The results of the current study show that the voltage drop and ripple of a three-stage Cockcroft-Walton voltage multiplier depend on frequency. The power generated by a CW $CO_2$ laser can be precisely adjusted by a variable-frequency controller using a DSP (TMS320F2812) microprocessor. The proposed LCC converter could be used to obtain a maximum laser output power of 23 W. Moreover, it could precisely adjust the laser output power within 4.3 to 23 W at an operating frequency range of 187.5 to 370 kHz. The maximum efficiency of the $CO_2$ laser system is approximately 16.5%, and the minimum ripple of output voltage is about 1.62%.

• Journal of Electrical Engineering and Technology
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• v.10 no.2
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• pp.574-585
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• 2015

This paper aims to improve the performance of conventional direct torque control (DTC) drives proposed by Takahashi by extending the idea for 5-level inverter. Hybrid cascaded H-bridge topology is used to achieve inverter voltage vector composed of 5-level of voltage. Although DTC is very popular for its simplicity but it suffers from some disadvantages like- high torque ripple and uncontrollable switching frequency. To compensate these shortcomings conventional DTC strategy is modified for five levels voltage source inverter (VSI). Multilevel hysteresis controller for both flux and torque is used. Optimal voltage vector selection from precise lookup table utilizing 12 sector, 9 torque level and 4 flux level is proposed to improve DTC performance. These voltage references are produced utilizing a hybrid cascaded H-bridge multilevel inverter, where inverter each phase can be realized using multiple dc source. Fuel cells, car batteries or ultra-capacitor are normally the choice of required dc source. Simulation results shows that the DTC drive performance is considerably improved in terms of lower torque and flux ripple and less THD. These have been experimentally evaluated and compared with the basic DTC developed by Takahashi.