• The Transactions of the Korean Institute of Electrical Engineers P
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• v.62 no.4
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• pp.210-215
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• 2013

This paper analyze the bus voltage sags in the power distribution system with a small scale cogeneration system when the superconducting fault current limiter was introduced. Among the solutions to decrease the short-circuit current considering the locations of the small scale cogeneration system, the superconducting fault current limiter (SFCL) has been announced as one of the promising methods to reduce the fault current because the installation of the small scale cogeneration system which increases the short-circuit current. According to the application locations of the small scale cogeneration system in a power distribution system, it has caused the variations of voltage sag and duration which depends on the change of the short-circuit current, which can make the operation of the protective device deviate from its original set value when the fault occurs. To investigate the voltage sag when a SFCL was applied into a power distribution system where the small scale cogeneration system was introduced into various locations, the SFCL, small scale cogeneration system, and power system are modeled using PSCAD/EMTDC. In this paper, the effects on voltage sags are assessed when the SFCL is installed in power distribution system with various locations of the small scale cogeneration system.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.5
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• pp.82-91
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• 2014

The combined generator system by integrating several renewable energy sources can share the electrical infrastructure and therefore have the advantage of constructing not only the transmission system but also the power conversion system. Among the various combined renewable system, the wind power and wave power has a high possibility of future growth due to the economic feasibility in offshore environment. This kind of large-scale combined systems might be follow the determination by the transmission system operator's directions and control the output profile by focusing at PCC. However, both renewable energies are depend on the unpredictable environmental variation; it is needed to do the compensation devices. In this paper, the ESS compensation plan is proposed to do output determination of the combined generator system by paying attention to active power of utility grid with the analysis of the controllable elements of the wind and wave power generator. The improvement of the new application technique of the combined system is confirmed through using the PSCAD/EMTDC. The entire simulation process was designed by adopting the active power control according to the reference signal of TSO.

• Journal of Power Electronics
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• v.10 no.6
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• pp.762-768
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• 2010

This paper describes the development of a new islanding detection method for inverter-based distributed generation systems, which uses a signal cross-correlation scheme between the injected reactive current and the power frequency deviation. The proposed method injects 1% of the reactive current to the rated current which brings about a negligible degradation of the power quality. It discriminates the islanding state, when the calculated cross-correlation index is larger than 0.5. The operational feasibility was verified through computer simulations with PSCAD/EMTDC software and experimental research with a hardware prototype. The proposed method can detect the islanding state without degrading the power quality at the point of common connection. Further study is required to overcome the cancellation of the injected reactive current from multiple distributed generation units interconnected with the utility grid.

• Journal of Power Electronics
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• v.17 no.3
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• pp.744-755
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• 2017

With the high penetration of various sustainable energy sources, the control and protection of Microgrids has become a challenging problem considering the inherent current limitation feature of inverter-based Distributed Generators (DGs) and the bidirectional power flow in Microgrids. In this paper, a hybrid control and protection scheme is proposed, which combines the traditional inverse-time overcurrent protection with the biased differential protection for different feeders with different kinds of loads. It naturally accommodates various control strategies such as P-Q control and V-f control. The parameter settings of the protection scheme are analyzed and calculated through a fast Fourier transform algorithm, and the stability of the control strategy is discussed by building a small signal model in MATLAB. Different operation modes such as the grid-connected mode, the islanding mode, and the transitions between these two modes are ensured. A Microgrid model is established in PSCAD and the analysis results show that a Microgrid system can be effectively protected against different faults such as the single phase to ground and the three phase faults in both the grid-connected and islanded operation modes.

• Journal of Power Electronics
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• v.18 no.1
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• pp.204-211
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• 2018

At present, one of two LCC-HVDC systems is responsible for controlling the grid frequency of the Jeju Island Power System (JIPS). The grid voltage is regulated by using STATCOMs. However, these two objectives can be achieved in one device that is called by a modular multilevel converter-high voltage direct current (MMC-HVDC) system. Therefore, this paper proposes frequency and voltage control strategies for the JIPS based on a MMC-HVDC system. In this case, the ancillary frequency and voltage controllers are implemented into the MMC-HVDC system. The modelling of the JIPS is done based on the parameters and measured data from the real JIPS. The simulation results obtained from the PSCAD/EMTDC simulation program are confirmed by comparing them to measured data from the real JIPS. Then, the effect of the MMC-HVDC system on the JIPS will be tested in many cases of operation when the JIPS operates with and without STATCOMs. The objective is to demonstrate the effectiveness of the proposed control strategy.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.51-52
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• 2014

전력계통은 전력수요의 지속적인 성장에 따라서 전력설비의 추가를 지속적으로 추진하고 있지만, 심해지는 환경문제 등으로 인해 용지 확보에 어려움이 있다. 이로 인해 송전선로 장거리화, 용량부족량 등 전력계통에 여러 가지 복잡한 문제가 야기되는데, 이것은 곧 전력계통의 안정도와 직결된다. 이러한 문제를 효과적이면서 경제적인 해결방법으로 FACT(Flexible AC Transmission System)기술이 주목 받고 있다. FACTS 기기 중 SVC(Static Var Compensator)는 상용운전 중이며, 기존 동기조상기에 비해 저렴하고, 신속 정확한 전압제어를 하는 장점이 있다. SVC는 TCR(Thyristor Controlled Reactor)과 TSC(Thyristor Switched Capacitor), FC(Fixed Capacitor)등 여러 종류의 구성을 가질 수 있다. TCR과 TSC는 실제 운전에 앞서 여러 가지 방법으로 검증이 필요하다. 합성 시험회로 설비(Synthetic Test Circuit)는 TCR과 TSC 안에 존재하는 Thyristor Valve의 동작을 실제 동작 조건으로 동작시켜, 동작의 신뢰성을 검증하는 설비이다. 본 논문에서는 TCR의 Operational Test를 위한 STC를 기술하고 있다. 설계된 STC는 PSCAD를 사용하여 검증하였다.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.461-462
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• 2015

The government on Jeju Special Self-governing Province has a policy named 'Carbon Free Island Jeju by 2030'. The main purpose in this policy is to install wind power system with the total capacity of 1.35 GW by 2020. When the demand load on Jeju Island power system is lower than entire output power, a lot of dump power will be produced from the large-scale wind farms. It will be able to cause the wind power limit on Jeju Island. Consequently, the additional power facility must be installed to ensure stable power system operation in Jeju Island and increase wind power limit. From this point, this paper proposes the installation of MMC-HVDC, which can supply power in real time in the desired direction. The effectiveness of MMC-HVDC based on measured data of Jeju Island power system will be verified by using PSCAD/EMTDC simulation program.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.22-27
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• 2012

Correct and fast detection of a micro-grid (MG) islanding is essential to the MG since operation, control and protection of the MG depend on an operating mode i.e., an interconnected mode or an islanding mode. When islanding occurs, the frequency of the point of common coupling (PCC) is not the nominal frequency during the transient state owing to the frequency rise or drop of generators in the MG. Thus, the active and reactive power calculated by the frequency domain based method such as Fourier Transform might contain some errors. This paper proposes an islanding detection algorithm for the MG based on the instantaneous active and reactive powers delivered to the dedicated line in the time domain. During the islanding mode, the instantaneous active and reactive powers delivered to the dedicated line are constants, which depend on the voltage of the PCC and the impedance of the dedicated line. In this paper, the instantaneous active and reactive powers are calculated in the time domain and used to detect islanding. The performance of the proposed algorithm is verified under various scenarios including islanding conditions, fault conditions and load variation using the PSCAD/EMTDC simulator. The results indicate that the algorithm successfully detects islanding for the MG.

• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.921-930
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• 2016

This paper proposes a design and control method for a high-voltage direction current modular multilevel converter (HVDC-MMC) considering the capacitor voltage ripple of the submodule (SM). The capacitor voltage ripple consists of the line frequency and double-line-frequency components. The double line- frequency component does not fluctuate according to the active power, whereas the line-frequency component is highly influenced by the grid-side voltage and current. If the grid voltage drops, a conventional converter increases the current to maintain the active power. A grid voltage drops, current increment, or both occur with a capacitor voltage ripple higher than the limit value. In order to reliably control an MMC within a limit value, the SM capacitor should be designed on the basis of the capacitor voltage ripple. In this paper, the capacitor voltage ripple according to the grid voltage and current are analyzed, and the proposed control method includes a current limitation method considering the capacitor voltage ripple. The proposed design and control method are verified through simulation using PSCAD/EMTDC.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.121-124
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• 2006

In the newly developed control method, the current flowing into SPE cell is the only one considerable factor. So, the structure of control circuit becomes simple and the manufacturing cost of the control device decreases. In conventional power comparison MPPT control method however, a voltage and current coming out from PV cell should be feedbacked to chase maximum power point at every moment. Then, the structure of control circuit becomes so complex and the risk of control failure is much higher than the novel MPPT control method. Therefore, PV generation system by a novel MPPT control method is especially operated much more safely in case of a huge system, because the voltage coming out from PV-cell is not needed to be feedbacked. In this paper, the PV-SPR system was actually manufactured based on the simulation model of PSCAD/EMTDC program and the results tested were shown. Authors are sure that it is the most useful method to maximize power from PV to SPE with only a feedback of SPE input current.