• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.120-121
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• 2017

This paper proposes an enhanced distributed generation (DG) unit with an adaptive virtual impedance control approach in order to address the inaccurate reactive power sharing problem. The proposed method can adaptively regulate the DG virtual impedance, and the effect of the mismatch in feeder impedances is compensated to share the reactive power accurately. The proposed control strategy is fully distributed and the need for the microgrid central controller is eliminated. Furthermore, the proposed method can be directly implemented without requirement of pre-knowledge of the feeder impedances. Simulations are performed to validate the effectiveness of the proposed control approach.

• Proceedings of the KIPE Conference
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• 2019.07a
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• pp.115-117
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• 2019

In this paper, an intelligent control scheme based on Fuzzy PID controller is proposed for accurate power sharing in DC Microgrid. The proposed Fuzzy PID controller is designed with the aid of a closed loop control based on per unit power of each distributed generator (DG), and accurate power sharing is successfully realized in proportional to each DG's power rating regardless of the line resistance difference or the load change. Thanks to Fuzzy PID controller, the dynamic response becomes faster and the stability of the microgrid system are improved in comparison to conventional PID controller. The superiority of the proposed method is analyzed and verified by simulation in Matlab and Simulink.

• Journal of the Korean Solar Energy Society
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• v.35 no.6
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• pp.9-15
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• 2015

In this paper, a parallel operating technique for the stand alone photovoltaic (PV) power conditioning system (PCS) is proposed. The proposed parallel operating technique can increase the power rating of the system easily. Also, it provide three-phase connection function. The proposed technique does not separated master and slave system. Also, it does not use the separated synchronization line. Therefore, the PCS can supply continuous power even if one of the PCS breaks down. This technique is composed of a phase locked loop (PLL) control, droop control, current limit control and etc. Experimental result obtained on 2-kW prototype to verify the proposed technique.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1575-1581
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• 2019

Due to the mismatched line impedance among distributed generation units (DGs) and uncontrolled harmonic current, the droop controller has a number of problems such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To solve these problems, this paper proposes a resistive-capacitive virtual impedance control method. The proposed control method modifies the DG output impedance at the fundamental and harmonic frequencies to compensate the mismatched line impedance among DGs and to regulate the harmonic current. Finally, reactive power sharing is accurately achieved, and the PCC voltage distortion is compensated. In addition, adaptively controlling the virtual impedance guarantees compensation performance in spite of load changes. The effectiveness of the proposed control method was verified by experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.3
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• pp.191-200
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• 2019

This study proposes a hardware-in-the-loop simulation (HILS) system based on National Instruments' PXI platform to test power management and operation strategies for DC microgrids (MGs). The HILS system is developed based on the controller HIL prototype, which involves testing the controller board in hardware with a real-time simulation model of the plant in a real-time digital simulator. The system provides an economical and effective testing function for research on MG systems. The decentralized power management strategy based on the DC bus signaling method for DC MGs has been developed and implemented on the HILS platform. HILS results are determined to be similar to those of the off-line simulation in PSIM software.

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.79-87
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• 2008

This paper proposes the design and implementation of a direct torque controlled induction motor drive system. The method is based on control of decoupling between amplitude and angle of reference stator flux for determining reference stator voltage vector in generating PWM output voltage for induction motors. The objective is to reduce electromagnetic torque ripple and stator flux droop which result in a decrease in current distortion in steady state condition. In addition, the proposed technique provides simplicity of a control system. The direct torque control is based on the relationship between instantaneous slip angular frequency and rotor angular frequency in adjustment of the reference stator flux angle. The amplitude of the reference stator flux is always kept constant at rated value. Experimental results are illustrated in this paper confirming the capability of the proposed system in regards to such issues as torque and stator flux response, stator phase current distortion both in dynamic and steady state with load variation, and low speed operation.

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.367-375
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• 2022

Generally, a proportional-resonant controller is used to eliminate steady-state errors during the voltage-current control of a double-conversion uninterruptible power supply (UPS) in a stationary reference frame. Additionally, the feed-forward control compensating for the load current, which can be considered a disturbance of the voltage controller, can be used to improve the disturbance rejection performance. However, during the parallel operation of UPSs, circulating current can occur between UPS modules when performing both feed-forward control and droop control because feed-forward control reduces the circulating current impedance. This study proposes a feed-forward compensation technique that considers the impedance of circulating current. An additional feed-forward compensation technique is developed to enhance the disturbance rejection performance. The validity of the proposed feed-forward compensation technique is verified by the experiment results of the parallel operation of a 500 W double-conversion UPS module.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.143-145
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• 2005

There has been increasing interest in the renewable energies. Wind energy is worldwide number one renewable energy from the installed capacity viewpoint. Most of the power systems utilizing wind energy are connected to other large systems. In such integrated systems, frequency control is not big issue. Rut the situation is different in isolated systems like Korean power system. It is important to assess appropriate capacity of wind power for our system, as it affects the system operation and control strategy. In this paper we made it clear the relationship among generator inertias, governor droop, system damping and wind energy capacity.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.14-15
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• 2013

본 논문에서는 컨버터의 병렬운전을 하는데 있어 제안한 드룹제어를 사용하여 전력을 분담한다. 제안한 방법을 이용하면 직류배전에서 병렬시스템의 용량증설을 용이하게 할 수 있다. 기존의 교류전원에서 사용하는 드룹 제어 방법을 새롭게 개선하여 직류전원에서 드룹 제어가 적용되도록 드룹 제어기를 설계한다. 그리고 제안한 드룹 제어기의 제어방법을 상세히 설명한다. 본 논문에서는 제안한 제어방법을 50[kW] 직류배전 시스템에 적용하여 시뮬레이션을 통하여 제안된 기법의 타당성을 검증한다.

• 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.