• 전력전자학회:학술대회논문집
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• 전력전자학회 2014년도 전력전자학술대회 논문집
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• pp.333-334
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• 2014

Converters employing IGCTs usually require di/dt snubber and Over Voltage Protection (OVP) circuit for the protection of IGCTs and fast diodes. In these IGCT-based converters, conventional di/dt snubber and OVP circuit dissipates a significant amount of power loss. To reduce this loss of conventional di/dt snubber and OVP circuit, this paper proposes a flyback type snubber circuit with di/dt limiting characteristic for IGCT-based converters in medium voltage wind turbines. This flyback type snubber circuit simply consists of a flyback type transformer and diode. The proposed circuit reduces loss and simplifies conventional di/dt snubber by adopting the flyback type transformer. Loss analysis of conventional di/dt snubber and OVP circuit is performed for the 3-level NPC type back-to-back VSC supplied from grid voltage of 6.9kV. The proposed flyback type snubber circuit can save the loss of conventional snubber circuit in the 3L-NPC type back-to-back VSC in multi-MW MV wind turbine. The proposed snubber circuit has a fewer number of components and improved efficiency leading to a reliable and efficient wind turbine systems.

• Journal of Power Electronics
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• 제18권6호
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• pp.1879-1888
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• 2018

With power level of grid-connected converters rising, the switching frequency of the switching devices is commonly greatly reduced to improve its power capacity. However, this results in serious couplings of the dq current components, which leads to degradation of the static and dynamic performances of grid-connected converters and fluctuations of the reactive power in dynamic processes. In this paper, complex vector models under low switching frequency are established for an L/LCL grid-connected converter, and the relationship between the switching frequency and the coupling degree is analyzed. In addition, a series decoupling current control strategy is put forward. It is shown that the proposed control strategy can eliminate the couplings, improve the performances and have good robustness to parameter variations through static and dynamic characteristics analyses and a sensitivity analysis. Experimental and simulation results also verify the correctness of the theoretical analyses and the superiority of the proposed control strategy.

• Journal of Power Electronics
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• 제17권4호
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• pp.1058-1070
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• 2017

This paper proposes a novel active damping scheme to suppress LCL-filter resonance with only grid-current feedback control in grid-connected voltage-source converters. The idea comes from the concept of the model reference adaptive control (MRAC). A detailed theoretical derivation is given, and the effectiveness of this method is explained based on its physical nature. According to the control structure of this method, the active damping compensator, which is essentially a second order resonant integrator (SORI) filter, provides an effective solution to damp LCL resonance and to eliminate the need for additional sensors. Compared with extra feedback methods, the cost and complexity are reduced. A straightforward tuning procedure for the active damping method has been presented. A stability analysis is illustrated in the discrete domain while considering a one-step delay. Finally, experimental results are presented to validate the analysis and to demonstrate the good performance of the proposed method.

• 한국전자통신학회논문지
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• 제11권2호
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• pp.179-184
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• 2016

본 연구를 통해 개발된 전기부하시험장치는 상용전원이 필요한 피시험장치(변압기, 정류기, 전압조정기, 인버터 등)와 상용전원이 불필요한 독립형 피시험장치(동력발전기, 풍력발전장치, 태양광발전장치, 하이브리드발전 장치, 배터리 등)에 대하여 정격용량시험이나 가변부하시험을 능동적으로 정밀하게 제어하면서도 시험 중에 사용되는 전기에너지를 소비하지 않고 전원변환장치를 통하여 계통선으로 전달하도록 설계되었다. 동기식 pwm 인버터회로를 상용전원과 연결시켜서 시험에 사용되는 전력을 계통선으로 귀환되도록 설계되었으며, 종전의 수동식 전기저항체를 사용한 전기부하시험장치에 비해 93.4% 정도의 전력을 소모하지 않고도 피시험체에 대한 시험이 가능하도록 하였다.

• 공학교육연구
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• 제13권3호
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• pp.11-17
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• 2010

우리나라는 전력망을 탄소 배출량 감소를 수월하게 하고, 발전설비 투자를 지연하여 수용가 부하를 담당함으로써 현존 인프라/자원을 좀 더 효율적으로 활용하고, 실시간 감시 및 제어를 통해 신재생에너지원을 지원할 목적으로 정보 및 운영 기술을 활용하는 지능형 전력망으로 대체하기 위한 세계 최초의 국가가 되고자 하는 계획을 세우고 있다. 이러한 상황에서 대학들은 오늘날의 전력망이 디지털 네트워크화 되어 감에 따라 최신식 기술을 다룰 수 있는 스마트 그리드 인력 양성을 최우선 과제로 추진할 필요가 있다. 본 논문에서는 2007년부터 시행되고 있는 전력IT 인력 양성 사업을 교훈삼아 스마트 그리드 인력 양성의 효과적인 추진 방안을 다방면으로 제안하여 전기공학 분야에 있어서의 전력 및 IT 전문가를 지속적으로 배출하는 것을 목표로 한다.

• 전기전자학회논문지
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• 제24권1호
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• pp.154-160
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• 2020

본 논문에서는 계통연계인버터용 정지좌표기반 전류제어알고리즘을 제안한다. PI 제어기는 계통 연결 인버터의 전류 제어기로 사용되고 있다. 정지좌표기반 PI 제어기를 사용할 경우, AC 신호 제어로 인하여 정상 상태 오류와 위상지연현상이 발생한다. 본 논문에서는 전향보상기를 추가하여 명령 추적 성능을 높이고 과도 응답을 개선하는 방법을 제안한다. 또한 계통 전압을 외란으로 사용하여 계통 오류 발생 시 시스템을 보호하기 위해 외란을 측정 및 제거하는 제어 방법을 제안한다. 제안된 제어 방법은 수학적으로 유도하고 전달 함수로 표현하였으며 시뮬레이션을 통하여 검증하였다.

• Journal of Power Electronics
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• 제17권6호
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• pp.1587-1599
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• 2017

This paper proposes a real-time implementation of an optimal operation of a double stage grid connected wind power system incorporating an active power filter (APF). The system is used to supply the nonlinear loads with harmonics and reactive power compensation. On the generator side, a new adaptive neuro fuzzy inference system (ANFIS) based maximum power point tracking (MPPT) control is proposed to track the maximum wind power point regardless of wind speed fluctuations. Whereas on the grid side, a modified predictive current control (PCC) algorithm is used to control the APF, and allow to ensure both compensating harmonic currents and injecting the generated power into the grid. Also a type 2 fuzzy logic controller is used to control the DC-link capacitor in order to improve the dynamic response of the APF, and to ensure a well-smoothed DC-Link capacitor voltage. The gained benefits from these proposed control algorithms are the main contribution in this work. The proposed control scheme is implemented on a small-scale wind energy conversion system (WECS) controlled by a dSPACE 1104 card. Experimental results show that the proposed T2FLC maintains the DC-Link capacitor voltage within the limit for injecting the power into the grid. In addition, the PCC of the APF guarantees a flexible settlement of real power exchanges from the WECS to the grid with a high power factor operation.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.959-968
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• 2017

Electrical safety monitoring System (ESMS) is a critical component in modern power systems, which is characterized by large-scale access points, massive users and versatile requirements. For convenience of the information integration and analysis, the software development, maintenance, and application in the system, the cloud platform based ESMS is established and assessed in this paper. Firstly the framework of the system is proposed, and then the assessment scheme with a set of evaluation indices are presented, by which the appropriate cloud product can be chosen to meet the requirements of a specific application. Moreover, to calculate the weights of the evaluation indices under uncertainty, an improved interval AHP method is adopted to take into consideration of the fuzziness of expert scoring, the qualitative consistency test, and the two normalizations in the process of eigenvectors. Case studies have been made to verify the feasibility of the assessment approach for ESMS.

• 전기학회논문지P
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• 제64권3호
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• pp.111-115
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• 2015

Recently, protection coordination issues can occur due to increased fault current in power system when power system being changed radial power system to grid system such as loop power system, micro grid and smart grid. This paper analyzed Recloser-Fuse coordination in loop power distribution system with Superconducting Fault Current Limiters(SFCLs) when single line ground fault occur in loop power distribution system with SFCLs. We analyzed Recloser-Fuse Coordination in radial power distribution system and changed coordination caused by increased Fault current because of loop system when single line ground fault occur in power distribution system. This paper simulated to improve changed coordination using SFCLs in loop power distribution system. Power distribution system, SFCLs and protective devices are modeled using PSCAD/EMTDC.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1709-1718
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• 2017

This paper presents a hybrid stochastic deterministic multi-timescale scheduling (SDMS) approach for generation scheduling of a power grid. SDMS considers flexible resource options including conventional generation flexibility in a chance-constrained day-ahead scheduling optimization (DASO). The prime objective of the DASO is the minimization of the daily production cost in power systems with high penetration scenarios of variable generation. Furthermore, energy storage is scheduled in an hourly-ahead deterministic real-time scheduling optimization (RTSO). DASO simulation results are used as the base starting-point values in the hour-ahead online rolling RTSO with a 15-minute time interval. RTSO considers energy storage as another source of grid flexibility, to balance out the deviation between predicted and actual net load demand values. Numerical simulations, on the IEEE RTS test system with high wind penetration levels, indicate the effectiveness of the proposed SDMS framework for managing the grid flexibility to meet the net load demand, in both day-ahead and real-time timescales. Results also highlight the adequacy of the framework to adjust the scheduling, in real-time, to cope with large prediction errors of wind forecasting.