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Sewan Choi,Minsoo Jang Institute of Electrical and Electronics Engineers 2007 IEEE transactions on industrial electronics Vol.54 No.4
<P>This paper presents analysis and control of a hybrid filter that can suppress neutral harmonic currents in three-phase four-wire systems not only with harmonic voltage-source loads but also with harmonic current-source loads. The filter voltampere rating is significantly reduced compared to the conventional neutral-current-suppressing methods. The rectifier part of the neutral harmonic suppressor has been removed by controlling the dc capacitor voltage. The experimental results on a 50-kVA prototype validate the proposed control approach.</P>
Sewan Heo,Jinsoo Han,Wan-Ki Park Electronics and Telecommunications Research Instit 2023 ETRI Journal Vol.45 No.4
Renewable energy generation cannot be consistently predicted or controlled. Therefore, it is currently not widely used in the electricity market, which requires dependable production. In this study, reliability- and variance-based controls of energy storage strategies are proposed to utilize renewable energy as a steady contributor to the electricity market. For reliability-based control, photovoltaic (PV) generation is assumed to be registered in the power generation plan. PV generation yields a reliable output using energy storage units to compensate for PV prediction errors. We also propose a runtime state-ofcharge management method for sustainable operations. With variance-based controls, changes in rapid power generation are limited through ramp rate control. This study introduces new reliability and variance indices as indicators for evaluating these strategies. The reliability index quantifies the degree to which the actual generation realizes the plan, and the variance index quantifies the degree of power change. The two strategies are verified based on simulations and experiments. The reliability index improved by 3.1 times on average over 21 days at a real power plant.
Fabrication of drug delivery system with piezoelectric micropump for neural probe
Sewan Park,Yeonsu Jang,Hyeon Cheol Kim,Kukjin Chun 대한전자공학회 2008 ITC-CSCC :International Technical Conference on Ci Vol.2008 No.7
This paper describes a microelectromechanical systems (MEMS) micromachined drug delivery system with micropump and microchannel for neural probe capable of selectively delivering chemicals as well as electrically recording. The neural probe is developed to support research in neurophysiology. For the realization of chemical stimulating at controlled release rate, the micropump and fluidic microchannel are integrated. The micropump is a peristaltic type with diffuser/nozzle elements actuated by the piezoelectric force. The process for the neural probe are performed with one silicon wafer. The structure of neural probe, microchannel and chamber of micropump are defined by silicon deep etch process. The membrane of micropump and dielectric passivation layer is fabricated by polydimethylsiloxane (PDMS).
Harmonic Reduction of Parallel-Connected Thyristor Rectifiers with an Active Interphase Reactor
Sewan Choi,Junyong Oh,Kiyong Kim 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
This paper proposes a harmonic reduction technique of the parallel-connected twelve-pulse thyristor rectifiers. The proposed system is an improvement over the diode rectifier system with an active interphase reactor [2] In this scheme, a low kVA (0.15 Po (PU) ) active current source injects a triangular current into an interphase reactor of a twelve-pulse thyristor rectifier along the phase delay angle The current injection results in near sinusoidal input current with less than 1% THD Detailed analysis of the proposed scheme along with design equations is illustrated. Simulation results verify the concept.<br/>
Efficient Maximum Power Tracking of Energy Harvesting Using a μController for Power Savings
Sewan Heo,Yil Suk Yang,Jaewoo Lee,Sang Kyun Lee,Jongdae Kim 한국전자통신연구원 2011 ETRI Journal Vol.33 No.6
This letter describes an efficient technique for maximum power point tracking (MPPT) of an energy harvesting device. It is based on controlling the device voltage at the point of maximum power. Using a microcontroller with a power saving technique, the MPPT algorithm maintains the maximum power with low power consumption. An experiment shows that the algorithm maximizes the energy transfer power using an energy management IC fabricated in a 0.18-μm process. Compared to direct energy transfer to a battery, the proposed technique is more efficient for low-energy harvesting under variable conditions.
Sewan Choi,Prasad N.Enjeti,Honghee Lee 전력전자학회 1995 ICPE(ISPE)논문집 Vol.1995 No.10
In this paper, a new multi-pulse diode rectifier system is proposed for high power motor drives The proposed approach draws near sinusoidal currents from the utility line with 5th, 7th, 11th, 13th, 17th and 19th harmonics eliminated. A method to extend the conventional 12-pulse rectifier to a 24-pulse system is proposed.. With the addition of two controlled switches such as IGBT's, the pulse number is extended beyond 24 pulses. A generalized PWM technique is presented and an example 48-pulse system is demonstrated Simulation results verify the proposed concept and experimental results are provided from a 208V, 10kVA rectifier system.
Minimizing Leakage of Sequential Circuits through Flip-Flop Skewing and Technology Mapping
Sewan Heo,Youngsoo Shin 대한전자공학회 2007 Journal of semiconductor technology and science Vol.7 No.4
Leakage current of CMOS circuits has become a major factor in VLSI design these days. Although many circuit-level techniques have been developed, most of them require significant amount of designers’ effort and are not aligned well with traditional VLSI design process. In this paper, we focus on technology mapping, which is one of the steps of logic synthesis when gates are selected from a particular library to implement a circuit. We take a radical approach to push the limit of technology mapping in its capability of suppressing leakage current: we use a probabilistic leakage (together with delay) as a cost function that drives the mapping; we consider pin reordering as one of options in the mapping; we increase the library size by employing gates with larger gate length; we employ a new flipflop that is specifically designed for low-leakage through selective increase of gate length. When all techniques are applied to several benchmark circuits, leakage saving of 46% on average is achieved with 45-nm predictive model, compared to the conventional technology mapping.
Sewan Choi,Minsoo Jang 전력전자학회 2001 ICPE(ISPE)논문집 Vol.2001 No.10
Three-phase four-wire electrical distribution systems are widely employed in manufacturing plants, commercial and residential buildings Due to the nonlinear loads connected to the distribution system, the neutral conductor carries excessive harmonic currents even under balanced loading since the triplen harmonics in phase currents do not cancel each other. This may result in wiring failure of the neutral conductor and overloading of the distribution transformer In response to these concerns, a cost-effective neutral current harmonic suppressor system has been proposed [6].<br/> This paper proposes an improved control method for the harmonic suppressor system under unbalanced load conditions The proposed control method compensates for only the harmonic components in the neutral conductor, and the zero-sequence fundamental component due to unbalanced loading is prevented from flowing through the harmonic suppressor system This remedies overloading and power loss of the system The experimental results on a prototype validate the proposed control approach.