• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.830-835
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• 1998

This paper describes a new digital control method of 3-phase PWM inverter with LC filter for uninterruptible power supply(UPS). The overall control system is based on the dead beat control, which has the minor loop of current control within the voltage control major loop. In this paper, the full-order disturbance observer is proposed to compensate the disturbances generated due to a sudden change of load currents. The proposed disturbance observer is composed of dead beat observer which estimates state values within a finite time, and cancels the disturbances by adding feedforward compensation loop in the control system. In addition, on order to remove a defect of oscillation generated in output of conventional dead beat controller, a modified dead beat algorithm is proposed in this paper.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.1
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• pp.20-29
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• 2011

This paper proposes critical load following back-up system using MCFC stack. This system enables MCFC generation system to supply power to critical load without UPS and to generate rated power under grid fault state. This back-up system includes 'Load Leveler' that is connected with 3-phase inverter and is controlled by additional algorithm that includes critical load following. The proposed system and algorithm are verified by computer simulation based on 5kW system.

• Journal of IKEEE
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• v.23 no.2
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• pp.495-501
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• 2019

This paper proposes a variable passive harmonic filter for reduction and improvement of harmonics and power factor of single-phase uninterruptible power supply(UPS) with full bridge rectifier. Recently, UPSs have excellent harmonic and power factor operation characteristics by applying 2-level or more levels of power conversion methods. On the other hand, the single-phase UPS of the full bridge rectifier seriously causes the third, fifth, and seventh harmonics, and the power factor reduction on the grid side. Therefore, we present a variable passive harmonic filter for eliminating (2n+1) order harmonics and improving the power factor generated by the full bridge rectifier operation. In order to evaluate the performance of the proposed variable harmonic filter, the its validity is verified by various simulations and experiments.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.36T no.4
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• pp.53-59
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• 1999

In this paper, a bi-directional UPS with the performance of active power filter has been proposed. The operation of the proposed system can be divided into two modes, such as the active power filter mode and the battery back-up power mode. To improve the transient response for the effective compensation of harmonics and reactive power in active power filter mode, a novel closed-loop control strategy is used to calculate the reference current instantaneously. Finally, the performance of proposed UPS is verified by the simulation and experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.12
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• pp.108-115
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• 2014

Recently, Uninterruptible power supply(UPS) is spotlighted from concern about black out, due to reserve power problem caused by increased power consumption. When fault occurs on the grid, UPS system supplies power to loads instead of the grid. Also, it is an advantage of possible operation as Energy storage system(ESS). Bi-directional power control of AC/DC Pulse width modulation(PWM) converter is essential for grid-connected UPS system. And, mode transfer control has to be performed considering phase and dynamic characteristic under grid condition. In this paper, control of mode transfer and bi-directional power control of AC/DC PWM converter is proposed for UPS system. Also, it is verified by simulation and experimental results.

• 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.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.148-149
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• 2014

본 논문에서는 직렬 멀티 모듈형 무정전 전원 장치(UPS, Uninterruptible power supply) 시스템의 배터리 밸런싱 알고리즘을 제안하였다. 제안한 알고리즘은 배터리의 고유 특성에 의한 SOC(State of charge) 차이를 최소화시키기 위해 각 배터리의 출력전력 제어를 함으로써 배터리 가용 용량을 높인다. 직렬로 연결된 UPS 모듈의 배터리 전압을 이용하여 전력 지령을 계산하고 이를 바탕으로 각 UPS 모듈의 출력전력을 제어한다. 제안한 배터리 밸런싱 알고리즘의 타당성은 수학적 분석 및 시뮬레이션을 통해 검증하였다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.19-20
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• 2016

This study deals with the control method of the output impedance for the UPS(Uninterruptible Power Supply) system's wireless parallel opertaion. In order to avoid using any communication between modules, the P/Q droop method was applied. The experiment result based on NPC(Neutral Point Clamped) inverters is included.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.2
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• pp.163-169
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• 2014

Using the classical cascade voltage control strategy, this paper proposes an analytical solution to an MPC (Model Predictive Control) problem with a hexagonal input constraint set for the inner-loop to regulate the output voltage of the UPS (Uninterruptible Power Supply). Focus is placed on how to deal with the hexagonal input constraint set without any approximation. Following the conventional cascade voltage control strategy, the PI (Proportional-Integral) controller is used in the outer-loop in order to regulate the output voltage. The simulation results illustrate that the capacitor voltage rapidly goes to its reference in a satisfactory manner while keeping other state variables bounded under an unexpected load changes.