• Journal of Power Electronics
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• v.17 no.4
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• pp.860-873
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• 2017

The present article reports an analysis and investigation of a direct AC-AC quasi-resonant converter. A bidirectional power device, whose switching frequency is lower than the frequency of the current passing through the load, is used for its realization. The zero voltage switching mode is described when zero voltage on the power device is available by measuring it with the control system. The continuous current in the resonant inductance by switching the power device at zero voltage is considered, and it is characterized by two sub-modes. A mathematical analysis of the processes has been made and comparative results from the computer simulation and experimental study have been brought. The converter can be used in a wide areas of power electronics: induction heating, wireless power transfer, AC-DC converters, etc.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.1056-1061
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• 1998

In this paper, a novel zero current switching (ZCS) high frequency inverter for induction heating is proposed. The ZCS characteristics are investigated from both the numerical analysis and the experiment.

• Journal of Power Electronics
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• v.15 no.5
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• pp.1168-1177
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• 2015

This paper presents a scheme to improve the line current distortion of power factor corrector (PFC) topology at the zero crossing point using a predictive control algorithm in both the continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The line current in single-phase PFC topology is distorted at the zero crossing point of the input AC voltage because of the characteristic of the general proportional integral (PI) current controller. This distortion degrades the line current quality, such as the total harmonic distortion (THD) and the power factor (PF). Given the optimal duty cycle calculated by estimating the next state current in both the CCM and DCM, the proposed predictive control algorithm has a fast dynamic response and accuracy unlike the conventional PI current control method. These advantages of the proposed algorithm lower the line current distortion of PFC topology. The proposed method is verified through PSIM simulations and experimental results with 1.5 kW bridgeless PFC (BLPFC) topology.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.163-164
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• 2006

A current differential relay has been used for transmission line protection. The relay may maloperate in the case of a failure of the secondary circuit of a current transformer (CT) because the differential current is produced. This paper presents an algorithm to detect a failure of a CT using the zero-sequence current. If the magnitude of the zero-sequence current is the same as the magnitude of the current of the other healthy phases, a failure of a CT is detected and then the blocking signal is activated. The proposed algorithm prohibit the maloperation of a differential relay in the case of a CT failure and thus increase the security of the relay.

• Journal of Power Electronics
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• v.17 no.2
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• pp.323-333
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• 2017

This paper proposes a model-based optimal control algorithm for the clamp switch of a zero-voltage switching (ZVS) bidirectional DC-DC converter. The bidirectional DC-DC converter (BDC) can accomplish the ZVS operation using the clamp switch. The minimum current for the ZVS operation is maintained, and the inductor current is separated from the input and output voltages by the clamp switch in this topology. The clamp switch can decrease the inductor current ripple, switching loss, and conduction loss of the system. Therefore, the optimal control of the clamp switch is significant to improve the efficiency of the system. This paper proposes a model-based optimal control algorithm using phase shift in a micro-controller unit. The proposed control algorithm is demonstrated by the results of PSIM simulations and an experiment conducted in a 1-kW ZVS BDC system.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.251-255
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• 2001

This paper presents a new zero current switching (ZCS) inverter for grid-connected photovoltaic system. The proposed circuit provides zero current switching condition for all the switches, which reduces switching losses significantly. It is controlled to extract maximum power from the solar array and to provide sinusoidal current into the mains. Analysis, small signal modeling and design procedure are presented. The validity of the proposed system is verified by experimental results from the 1.2kW prototype inverter operating at 40kHz.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.953-955
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• 2001

This paper presents a new zero current switching (ZCS) inverter for grid-connected photovoltaic single phase inverter system. The auxiliaey circuit for the soft-switching consists of two resonant inductors and two resonant capacitors as well as two auxiliary switches rated at lower power. The proposed circuit provides zero current switching condition for all the switches, which reduces switching losses significantly. It is controlled to extract maximum power from the solar array and to provide sinusoidal current into the mains. The validity of the proposed system is verified by experimental results from the 1.2kW prototype inverter operating at 40kHz.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.663-666
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• 1999

This paper describes a three-phase converter with high power factor using a scheme of discontinuous current mode(DCM). The proposed system can replace the conventional diode bridge with step-up chopper which is used as a converter for adjustable speed drive. In this system, the current of reactor is zero at turn-on instance because of operation in DCM, while the switch turns off at the instance of maximum current. A soft-switching scheme with lossless snubber was proposed. Therefore, a zero-voltage switching at turn off can be achived by lossless snubber and zero-current switching at turn on can be obtained by operating under DCM. A theoretical analysis and computer simulations with PSpice were done to verify the operation of the proposed system. Also a prototype of hardware system was built and tested for verifying the feasibility of proposed system.

• Proceedings of the KIEE Conference
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• summer
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• pp.619-621
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• 2004

This paper presents the rapid and accurate algorithm for fault discrimination in transmission lines. When faults occur in transmission lines, fault discrimination is very important. If high impedance faults occur in transmission lines, it cannot be detected by overcurrent relays. The method using current and voltage cannot discriminate high impedance fault. Because of this reason this paper uses voltage and zero sequence current, and the proposed algorithm uses fuzzy logic method. This algorithm uses voltage and zero sequence current per period in case of faults. Single line ground fault and three-phase fault can be detective using voltage. Two-line ground fault and line to line fault and high impedance can be detected using zero sequence current. To prove the performance of the algorithm, it test algorithm with signal obtained from ATPDraw simulation.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.132-134
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• 1993

A new Zero-Current Switched(ZCS) High Power Factor Rectifier for the. power factor correction is proposed. The proposed single phase rectifier enables a zero-current switching operation of all the power devices allowing the circuit to operate at high switching frequencies and high power levels. A dynamic model and a predictive current control technique for the ZCS-High Power Factor Rectifier(HPFR) are proposed. With the proposed dynamic model, an analysis for the internal operational characteristics is explored. With the proposed control technique, the unity power factor.