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계통 연계형 그리드 포밍 컨버터의 Soft Start-up 기법
맹준열,최성휘 전력전자학회 2024 전력전자학회 논문지 Vol.29 No.2
Inverter-based resources connected to the power system have increased rapidly in recent years. However, this trend weakens grid strength, which is maintained by the inertia of synchronous generators. Therefore, grid-forming converters have attracted much attention owing to their ability to maintain stable connections with weak grids compared with conventional grid-following converters. Various control methods have been proposed for configuring virtual synchronous generators to control grid-forming converters. However, the stable grid integration and initial operation for each of these methods require further research. In this paper, the start-up characteristics of grid-forming converters were examined. The proposed method implements a soft start-up method in a synchronous power control-based grid-forming converter. The validity of the proposed method was verified with 250 kW simulation and hardware-in-the-loop simulation.
지그재그 변압기를 이용한 스타 결선 멀티레벨 전력변환 시스템의 클러스터 에너지 균형제어
김영웅,최성휘,정재정 전력전자학회 2024 전력전자학회 논문지 Vol.29 No.2
STATCOM systems are increasingly being integrated into the grid to enhance grid stability and power quality. Star-connected CHB converters are preferred for medium- and high-voltage STATCOM applications. One limitation of CHB converters is their inability to automatically balance three-phase unbalanced active power due to their distributed DC capacitors. Zero-sequence voltage injection is commonly employed to address this limitation. However, with increasing negative-sequence currents, the zero-sequence voltage can escalate to a point where it surpasses the maximum permissible output voltage, consequently restricting the system capacity for negative-sequence current compensation. In this paper, a cluster balancing control approach for the star-connected CHB converter was introduced to circumvent this challenge by utilizing a zigzag transformer to inject zero-sequence current. The effectiveness of the proposed method was verified through simulations and experimental results.
켈빈 소스를 포함하는 SiC MOSFET의 가전용 전력변환시스템 적용을 위한 부트스트랩 회로 설계
함지선,최성휘 전력전자학회 2024 전력전자학회 논문지 Vol.29 No.2
Research on wide bandgap(WBG) devices, such as silicon carbide metal oxide semiconductor field effect transistor(SiC MOSFET) and gallium nitride high-electron mobility transistor, has been recently conducted. The use of WBG devices in power conversion systems for home appliances has been increasingly reconsidered. Most home appliance systems use bootstrap circuits and shunt resistors to reduce costs. The bootstrap circuit with shunt resistors cannot be applied to a SiC MOSFET driving circuit in which a Kelvin source exists. In this paper, a bootstrap circuit design method for SiC MOSFET driving in the presence of shunt resistors and Kelvin sources was proposed. The validity of the proposed method was verified by a 7 kW grid-connected converter.
그리드포밍 인버터의 계통 주파수 안정도 기여 향상을 위한 새로운 가상동기발전기 기반 전력제어 방법
김기현,스티븐,최성휘,정재정 전력전자학회 2024 전력전자학회 논문지 Vol.29 No.4
As the penetration of renewable energy sources increases and the inertia of the power system decreases, frequency instability in the grid is a possibility. Furthermore, power electronic converters can induce various resonance instabilities in the power grid. Recently, research on grid-forming inverters, which emulate the dynamic characteristics of synchronous generators and provide inertia and damping to the power system, is actively being conducted. This paper conducts modeling of a grid-forming inverter for resonance stability analysis and controller design and proposes a novel control strategy that not only emulates the characteristics of synchronous generators but also improves the frequency nadir through faster primary frequency response compared with conventional grid-forming inverters by combining PI and IP controller.
가변 스위칭 주파수를 활용한 단상 PFC의전류 THD 최소화 PWM 기법
이재근,황인휘,최성휘 전력전자학회 2024 전력전자학회 논문지 Vol.29 No.1
The current total harmonic distortion(THD) in grid-connected converters must be lowered to improve efficiency and meet grid connection standards. In this study, closed-loop current control was performed by applying variable switching frequency, which minimizes THD at the same average number of switching times per fundamental period for full-bridge PFC. To achieve this, the switching frequency maintaining a constant current ripple size was calculated. Then, the pulse width of the PWM carrier wave changes in time to implement variable switching frequency. The results of the offline simulation and hardware-in-the-loop simulation showed that, compared with the fixed frequency method, THD was reduced by applying the proposed variable switching frequency.