• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2047-2049
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• 1997

Computers and automatic equipment are very sensitive to the disturbances such as voltage transients, voltage sag, and harmonics. These disturbances cause them to have a malfunction or fault which brings about damages and losses. UPS (uninterruptible power supply) and SPS(stand-by power supply) have been used to provide the required voltage in a critical load without disturbances. However, UPS has appreciable losses due to the operation of the inverter in full rated power at all times. SPS, although whose inverter losses are smaller than those of UPS, transfers disturbances with a short duration to the load, due to the limited reaction time. In this research, a dynamic voltage compensator, which can make up for the weakness of UPS and SPS, is proposed. The operation of the proposed system was verified by a computer simulation. A hardware scaled-model was fabricated and tested to conform the feasibility of the actual system development.

• Proceedings of the KAIS Fall Conference
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• 2004.06a
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• pp.193-197
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• 2004

The four-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. In this paper a novel line interactive Uninterruptible Power Supply(UPS) using the two four-leg VSCs is proposed. One VSC is in parallel with the ac link reactor of the power source side, and the other is in series with the load. The parallel four-leg voltage source inverter controls the three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series four-leg voltage source inverter compensates the line voltage and allows it to be balanced and harmonic-free. Both of the parallel and series four-leg voltage source inverters always act as independently controllable voltage sources, so that the three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulations results.

• Journal of Power Electronics
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• v.15 no.3
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• pp.695-701
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• 2015

Uninterruptible Power Supplies (UPSs) can be largely divided into the passive-standby, line-interactive and double-conversion methods. This paper proposes a double-conversion UPS with a low cost and high performance. This single phase UPS uses a single-loop robust voltage controller and 1-switch voltage doubler strategy PFC. The proposed UPS is composed of a single phase PFC, a half-bridge inverter, a battery charger and a battery discharger. Finally, the validity of proposed UPS was verified by various experimental tests.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.77-81
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• 2004

In this paper a novel line interactive UPS (Uninterruptible Power Supply) using the two 4-leg VSCs and AC line reactor is proposed. The 4-leg Voltage Source Converter(VSC) can use the DC link voltage effectively by the 3-D SVPWM method. Hence the DC battery voltage can be reduced by $15\%$ in comparison to that of the conventional line-interactive UPS system. One VSC is in parallel with the AC line reactor of the power source side, and the other is in series with the load. The parallel 4-leg voltage source inverter controls three-phase line voltage independently in order to control the line reactor current indirectly. It eliminates the neutral line current and the active ripple power of the source side using the pqr theory so that unity power factor and the sinusoidal source current can be achieved even though both the source and the load voltages have zero sequence components. The series 4-leg voltage source inverter compensates the line voltage and allows the load voltage to be balanced and harmonic-free. Both of parallel and series 4-leg voltage source inverters always act as independently controllable voltage sources, so that three-phase output voltage shows a seamless transition to the backup mode. The feasibility of the proposed UPS system has been investigated and verified through computer simulation results.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.1
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• pp.1-11
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• 2007

In this paper, a new fully digital control method for UPS inverter, which is based on the double control loop such as the outer voltage control loop and inner current control loop, is proposed. In the proposed control system, overshoots and oscillations due to the computation time-delay are compensated by explicit incorporation of the time-delay in the current control loop transfer function. The inner current control loop is adopted by an internal model controller. The internal model controller is designed to a second order deadbeat reference-to-output response which means that its response reaches the reference in two sampling time including computational time-delays. The outer voltage control loop employing P-Resonance controller is proposed. The resonance controller has an infinite gain at resonant frequency, and the resonant frequency is set to the fundamental frequency of the reference voltage in this paper. Thus the outer voltage control loop causes no steady state error as regard to both magnitude and phase. The effectiveness of the proposed control system has been verified by the simulation and experimental results respectively.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.293-296
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• 2007

본 논문에서는 UPS 기능을 갖는 단상 태양광 발전 시스템을 제안하였다. 제안하는 시스템은 태양광 어레이 (photovoltaic array)에서 최대전력을 얻기 위해 MPPT (maximum power point tracking)를 수행하는 컨버터, 계통전원 상태나 태양광 발전량에 상관없이 부하에 정현파 전압을 공급하는 인버터, 태양광 어레이에서 발전된 잉여전력을 계통으로 전달하거나 부하에 필요한 전력을 dc bus로 공급하는 인버터, 정전시 dc bus에 전력을 공급하는 양방향 컨버터 (bidirectional converter)로 구성된다. 제안하는 시스템은 발전된 전력을 계통으로 전달할 뿐만 아니라, UPS (uninterruptible power supply)기능도 수행하는 시스템으로 계통전압이 불안정하거나 정전시에도 부하에 안정적이고 깨끗한 전압을 항상 공급할 수 있다. 각각의 인버터, 컨버터, 및 양방향 컨버터는 dc bus를 공유하며, dc bus의 전압에 따라 동작상태가 결정이 된다. dc bus중심의 제어는 dc bus전압을 안정적으로 유지시키며, 부하에 걸리는 전압의 변동을 최소로 하고 시스템의 디자인 및 제어를 단순화한다. 모든 알고리즘과 제어기를 하나의 마이크로 컨트롤러로 구현하였고 제안된 시스템의 우수성을 실험을 통해 검증하였다.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.486-487
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• 2014

본 논문은 멀티레벨 인버터를 이용한 무정전 전원장치 시스템 (UPS; Uninterruptible Power Supply)의 신뢰성 향상을 위한 중성점 전압 불평형 제어 기법을 제안한다. 무정전 전원장치 시스템 (UPS)은 불평형 부하조건 시 직류단에 전압 불평형이 발생되며 이는 출력 전류의 왜곡을 일으켜, 민감한 부하에 손상을 입힐 수 있다. 제안한 제어기는 커패시터 전압 측정을 통해 시간오프셋을 추정한 후 공간 벡터 변조 방식의 변형 없이 중성점 전압 불평형을 제어하여, 직류단의 전압을 평형상태로 유지한다. 또한, 100kW급 UPS 시스템 시뮬레이션 검증을 통해 제어기의 타당성을 입증하였다.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.3
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• pp.209-215
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• 2006

Now, in this paper, going to present you with an Idea related to a new inverter of multi-step voltage source, that Is, the double-connected 12-step inverter with an auxiliary circuit. It possibly can be 24-step inverter with 3-phase voltage source which will enable us make full application even to medium and high power-level Motor drive, UPS, STATCOM, SVC, etc. in which the PWM method could not be employed. 24-step operation can be obtained from the link between the existing 12-step inverter and the additional auxiliary circuit in which the transformer of auxiliary circuit generates ripple voltage delivered to the inverter. Through a lot of experiments and simulations, (from which the validity of this scheme is confirmed,) we came to the conclusion that the increase of the primary winding number on transformer by 2N(N=1,2,3....) leads to the 12M-step(M=2,3,4...) inverter. The validity of the proposed scheme is confirmed by the simulated and experimental results.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.312-317
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• 1996

This paper compares the output voltage control strategies of three-phase PWM inverter for uninterruptible power supply. The feedforward control, feedforward/feedback control, and decoupled feedback control in both the synchronous reference frame and the stationary reference frame are examined. In particular, it is shown that the response of the decoupled feedback controller in the synchronous reference frame can be improved by pole-zero cancellation method. It is also shown that the pole-zero cancellation method reduces to the deadbeat control, when it is implemented with digital controller.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.50 no.7
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• pp.347-355
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• 2001

The conventional output filter design methods of a voltage source inverter includes two main problems: the performance is not sure to satisfy the specification under the nonlinear load; the designed filter must be occasionally modified when the controller is designed. In this paper, we analyze the relation between both linear and nonlinear loads, the output voltage magnitude, LC lowpass filter parameters, and the control response time. Upon the basis, both filter and controller are simultaneously designed for the performance to satisfy the specification under the nonlinear load as well as linear load. The proposed method sharply enhances the reliability of the performance. P.U is used for the method to be applied to all the quantities of the system. The simulation and the experiment of the proposed method carried out respectively to verify the validity.