• Journal of Power Electronics
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• v.14 no.2
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• pp.324-340
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• 2014

Recent developments in power electronics technology have spurred interest in the use of renewable energy sources as distributed generation (DG) generators. The key component in DG generators is a grid-connected inverter that serves as an effective interface between the renewable energy source and the utility grid. The multifunctional inverter (MFI) is special type of grid-connected inverter that has elicited much attention in recent years. MFIs not only generate power for DGs but also provide increased functionality through improved power quality and voltage and reactive power support; thus, the capability of the auxiliary service for the utility grid is improved. This paper presents a comprehensive review of the various MFI system configurations for single-phase (two-wire) and three-phase (three- or four-wire) systems and control strategies for the compensation of different power quality problems. The advances in practical applications and recent research on MFIs are presented through a review of nearly 200 papers.

• Journal of Electrical Engineering and Technology
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• v.9 no.4
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• pp.1188-1195
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• 2014

This paper presents an analytical technique for reliability evaluation of electrical distribution network (EDN) containing distributed generation (DG). Based on hierarchical levels of circuit breaker controlling zones and feeder sections, a directed-relation-graph (DRG) for an END is formed to describe the hierarchical structure of the EDN. The reliability indices of EDN and load points can be evaluated directly using the formed DRG, and the reliability evaluation of an EDN containing DGs can also be done without re-forming the DRG. The proposed technique incorporates multi-state models of photovoltaic and diesel generations, as well as weather factors. The IEEE-RBTS Bus 6 EDN is used to validate the proposed technique; and a practical campus EDN containing DG was also analyzed using the proposed technique.

• Journal of Power Electronics
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• v.13 no.3
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• pp.409-418
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• 2013

This paper presents an enhanced control strategy which consists of a proportional-integral controller and a repetitive controller (RC) for improving the voltage performance of distributed generation (DG) under nonlinear load conditions. The proposed voltage controller is able to maintain a sinusoidal voltage at the point of common coupling (PCC) of the DG regardless of the harmonic voltage drop in the system impedance due to nonlinear load currents. In addition, by employing the delay time of the RC at one-sixth of the fundamental period, the proposed RC can overcome the slow response drawback of the traditional PI-RC. The proposed control strategy is analyzed and the design of the RC is presented in detail. The feasibility of the proposed control strategy is verified through simulation and experimental results.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.70-71
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• 2017

This paper presents a new cascaded boost multilevel converter topology for distributed generation (DG) systems. Most of DG systems, such as photovoltaic (PV), wind turbine and fuel cells, normally require the complex structure power converters, which makes the system expensive, complex and hard to control. However, the proposed converter topology can generate a much higher output voltage just by using the standard low-voltage switch devices and low voltage DC-sources in a simplified structure, also enhancing the reliability of the switch devices. Simulation and experimental results with a 1.2kW system are presented to validate the proposed topology and control method.

• Journal of Power Electronics
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• v.13 no.6
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• pp.1070-1079
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• 2013

This paper develops an enhanced harmonic voltage compensator which is implemented with the aid of two repetitive controllers (RCs) in order to improve the output voltage performance of stand-alone distributed generation (DG) systems. The proposed harmonic voltage compensator is able to maintain the DG output voltage sinusoidal regardless of the use of nonlinear and/or unbalanced loads in the load side. In addition, it can offer good steady-state performance under various types of loads and a very fast dynamic response under load variations to overcome the slow dynamic response issue of the traditional RC. The feasibility of the proposed control strategy is verified through simulations and experiments.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.137_138
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• 2009

The increasing of fault current by introducing of the distributed generation(DG) in distribution system disrupts the protective coordination. Therefore, this paper applies the superconducting fault current limiter(SFCL) to solve this problem. The distribution system with DG and SFCL is modeled by EMTP. According to various size of the DG, the fault is simulated and the operating time of overcurrent relay is investigated accoring to the resistance of SFCL.

• Journal of Electrical Engineering and Technology
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• v.8 no.6
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• pp.1352-1364
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• 2013

This paper describes a novel structure for single phase Unified Power Quality Conditioner-Distributed Generation (UPQC-DG) with direct grid connected DC-AC converter for low DC output DG systems which can be used not only for compensation of power quality problems but also for supplying of load power partly. This converter has been composed of one full-bridge inverter, one three winding high frequency transformer with galvanic isolation and two cycloconverters. Proper control based on Input Output feedback Linearization is used to tracking the reference signals. The simulation and experimental results are presented to confirm the validity of the proposed approach.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.450-452
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• 2005

Distributed generation (DG) plays an important role in the power system nowadays. Over-current relay, widely used in the DG protection, causes a wide outage section and long time delay. This paper proposes a DG protection technique to minimize the outage section. The proposed method uses three directional over-current relays with time delay, which are connected to the point of common coupling. The method can minimize the outage section.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1407-1418
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• 2018

Novel mechanism of customized adequacy formulation is proposed in order to enhance micro grids system reliability. The mechanism accounts for 2-levles of load curtailment, and is mainly based on probabilistic load profile and hybrid Distributed Generation (DG) units modeling. The two load curtailments are needed in order to ensure adequate technical constraints at steady state condition during islanding mode of operation. The effectiveness of the proposed formulation has been verified using system independent analytical expressions for the evaluation of both reliability and Expected Energy Not Served (EENS) indices. The evaluation has examined the impact of different penetration levels of Hybrid DG Units in case study islands. Results show the enhancement of the overall distribution system reliability and the recommended conditions for successful islanding mode of operation.

• Journal of Electrical Engineering and Technology
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• v.8 no.4
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• pp.737-743
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• 2013

The small-scaled onsite generators such as photovoltaic power, wind power, biomass and fuel cell belong to decarbonization techniques. In general, these generators tend to be connected to utility systems, and they are called distributed generations (DGs) compared with conventional centralized power plants. However, DGs may impact on stabilization of utility systems, which gets utility into trouble. In order to reduce utility's burdens (e.g., investment for facilities reinforcement) and accelerate DG introduction, the advanced operation algorithms under the existing utility systems are urgently needed. This paper presents the advanced voltage regulation method in power systems since the sending voltage of voltage regulators has been played a decisive role restricting maximum installable DG capacity (MaxC_DG). For the proposed voltage regulation method, the difference from existing voltage regulation method is explained and the detailed concept is introduced in this paper. MaxC_DG estimation through case studies based on Korean model network verifies the superiority of the proposed method.