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DC Microgrid Operational Method for Enhanced Service Reliability Using DC Bus Signaling
Hwang, Pyeong-Ik,Jang, Gilsoo,Pyo, Gi-Chan,Han, Byung-Moon,Moon, Seung-Il,Ahn, Seon-Ju The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.2
This paper proposes a DC microgrid operational strategy and control method for improved service reliability. The objective is to supply power to as many non-critical loads as possible, while providing an uninterrupted power supply to critical loads. The DC bus signaling method, in which DC voltage is an information carrier, is employed to implement the operational strategy in a decentralized manner. During grid-connected operation, a grid-tied converter balances the power of the microgrid by controlling the DC voltage. All loads are connected to the microgrid, and operate normally. During islanded operation, distributed generators (DGs), a backup generator, or an energy storage system balances the power. However, some non-critical loads may be disconnected from the microgrid to ensure the uninterrupted power supply to critical loads. For enhanced service reliability, disconnected loads can be automatically reconnected if certain conditions are satisfied. Control rules are proposed for all devices, and detailed microgrid operational modes and transition conditions are then discussed. Additionally, methods to determine control parameter settings are proposed. PSCAD/EMTDC simulation results demonstrate the performance and effectiveness of the proposed operational strategy and control method.
DC Microgrid Operational Method for Enhanced Service Reliability Using DC Bus Signaling
Pyeong-Ik Hwang,Gilsoo Jang,Gi-Chan Pyo,Byung-Moon Han,Seung-Il Moon,Seon-Ju Ahn 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.2
This paper proposes a DC microgrid operational strategy and control method for improved service reliability. The objective is to supply power to as many non-critical loads as possible, while providing an uninterrupted power supply to critical loads. The DC bus signaling method, in which DC voltage is an information carrier, is employed to implement the operational strategy in a decentralized manner. During grid-connected operation, a grid-tied converter balances the power of the microgrid by controlling the DC voltage. All loads are connected to the microgrid, and operate normally. During islanded operation, distributed generators (DGs), a backup generator, or an energy storage system balances the power. However, some non-critical loads may be disconnected from the microgrid to ensure the uninterrupted power supply to critical loads. For enhanced service reliability, disconnected loads can be automatically reconnected if certain conditions are satisfied. Control rules are proposed for all devices, and detailed microgrid operational modes and transition conditions are then discussed. Additionally, methods to determine control parameter settings are proposed. PSCAD/EMTDC simulation results demonstrate the performance and effectiveness of the proposed operational strategy and control method.
Pyeong-Ik Hwang,Gilsoo Jang,Seung-Il Moon,Seon-Ju Ahn IEEE 2016 IEEE transactions on smart grid Vol.7 No.3
<P>This paper proposes three-phase steady-state models for a distributed generator (DG) interfaced to a main system via a three-wire current-controlled voltage-source converter. In order to represent the DG in a realistic manner, the three major factors that determine the steady-state phase outputs under unbalanced operating conditions are considered: 1) the power control strategy; 2) output filter; and 3) voltage and current sensor positions. Based on these factors, the DGs are classified into various types. According to the position of the voltage sensor, two equivalent circuit models including an equivalent three-phase current source (ETCS) are proposed. For each type of DG, the output current of the ETCS is formulated as a function of the voltage of the ETCS-connected node, the filter impedances, and the active and reactive power references. To verify the accuracy of the proposed models, the results of the power flow incorporating them are compared with those obtained from the PSCAD simulation using detailed dynamic models of the DG.</P>
전압 및 배전 손실을 고려한 분산전원의 무효전력 제어 기법
황평익(Pyeong-Ik Hwang),윤용태(Yong-Tae Yoon),문승일(Seung-Il Moon),추철민(Cheol-Min Chu) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
본 논문에서는 배전계통의 전압을 적정 수준으로 유지하며 배전 손실을 최소화하기 위한 분산전원의 무효전력 제어 기법을 제안한다.
적응 간격 크기 셈법을 이용한 급전운영자 훈련 프로그램 용 전력계통 시뮬레이터 개발
황평익(Pyeong-Ik Hwang),안선주(Seon-Ju Ahn),문승일(Seung-Il Moon),윤용태(Yong-Tae Yoon),허성일(Seong-Il Hur) 대한전기학회 2010 전기학회논문지 Vol.59 No.3
Since it is almost impossible to train the dispatchers with real power system, the dispatcher training simulator(DTS) is used for the training. Among various components of the DTS, the power system model(PSM) emulates the dynamic behavior of the power system to calculate the frequency and voltage. The frequency is calculated from various parameters such as mechanical power of power plants, load, inertia, and the damping of the power system. In the PSM, the power plants are modeled as differential equations, so the mechanical power of the power plants are calculated by the numerical methods. Conventionally, the fixed step-size algorithm has been used in the PSM, however it has some drawbacks. This paper develops the prototype PSM using the Matlab, and analyzes the problems of the fixed step-size algorithm by comparing the results with those of PSCAD simulation. In order to overcome the limitations, this paper proposes a modified frequency calculation method using the adaptive step-size algorithm. From the simulation using the proposed method, it is verified that the accuracy of frequency calculation increases substantially while the simulation time is not greatly increased.
Kim, Young-Jin,Hwang, Pyeong-Ik,Moon, Seung-Il The Korean Institute of Electrical Engineers 2011 The Journal of International Council on Electrical Vol.1 No.1
Electric power quality in power transmission/distribution systems has deteriorated considerably with the increase in the number and the capacity of inverter-based distributed generators (DGs). This is caused by inverters, connecting DGs to conventional power grids, tend to generate harmonic currents and voltages due to the switching operations of their transistors and diodes. Therefore, this paper presents new methods to adopt harmonic filters to an inverter-based DG, considering a system consisting of both an inverter-based DG and harmonic filters. In order to prove that the system proposed in this paper can be used generally, this paper describes the simulation results obtained by using PSCAD/EMTDC: the relationship between the total harmonic distortion (THD) of the output current and the output power of a DG, and the harmonic mitigation ability of passive and active filters. Furthermore, the system is obliged to satisfy the regulations made by Korea Electric Power Corporation (KEPCO). In the regulations, DG power factor needs to be maintained between 0.9 and 1 in a grid-connected mode. Thus, this paper suggests two methods for the system to control its power factor. First, the power factor should be controlled by the DG inverter rather than an active filter because this brings a dramatic decrease in the capacity of the active filter. Second, the DG should absorb reactive power only in the low output power range in order to prevent a useless increase in the inverter capacity. This method is expected to result in a variable power factor of the system according to its output power. With these control methods, the proposed DG system can successfully operate in a grid-connected mode with an optimally-reduced capacity of active harmonic filters and DG inverters while satisfying the regulations in terms of voltage variation, power factor, and THD.
배전계통에서 PHEV 충전 시 충전 스케쥴링을 이용한 계통 손실 최소화
정호용(Ho-Yong Jeong),황평익(Pyeong-Ik Hwang),문승일(Seung-Il Moon) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
본 논문은 배전 손실을 최소화하는 PHEV의 충전 스케쥴링 기법을 제안한다. 이를 위해 선형 프로그래밍을 이용한 손실 최소화 알고리즘을 제시하고, 사례 연구를 통하여 본 논문에서 제시한 방법의 효과를 검증한다.
고조파 필터 및 인버터의 용량을 고려한 분산전원 시스템의 역률 제어에 관한 연구
김영진(Young-Jin Kim),황평익(Pyeong-Ik Hwang),문승일(Seung-Il Moon) 대한전기학회 2009 전기학회논문지 Vol.58 No.11
Electric power quality in power transmission/distribution systems has considerably been deteriorated with the increase in the capacity of distributed generators (DGs). It is because inverters, connecting DGs to conventional power grids, tend to generate harmonic current and voltage. For harmonic mitigation, a large amount of research has been done on passive and active filters, which have been operating successfully in many countries. This paper, therefore, presents how to adopt the filters to an inverter-based DG, with considering a system consisting of both inverter-based DG and harmonic filters. In particular, this paper describes the simulation results using the PSCAD/EMTDC: firstly, the relationship between total harmonic distortion(THD) of current and output power of DG: secondly, the harmonic mitigation ability of passive and active filters. The system, furthermore, is obliged to satisfy the regulations made by Korean Electric Power Corporation(KEPCO). In the regulations, power factor should be maintained between 0.9 and 1 in a grid-connected mode. Thus, this paper suggests two methods for the system to control its power factor. First, the inverter of DG should control power factor rather than an active filter because it brings dramatic decrease in the capacity of the active filter. Second, DG should absorb reactive power only in the range of low output power in order to prevent useless capacity increase of the inverter. This method is expected to result in the variable power factor of the system according to its output power.