報告書番号

R11018

タイトル（和文）

半導体直流遮断器により直流線路事故を除去可能とした自励式電圧形変換器による直流送電システム

タイトル（英文）

A Self-Commutated Voltage-Source-Converter Based HVDC Transmission System being Capable of Clearing DC Line Faults by a Solid-State DC Circuit Breaker

概要 （図表や脚注は「報告書全文」に掲載しております）

従来の自励式変換器を用いた直流送電システムは，直流線路の地絡および短絡事故の発生時に，変換器による事故電流の抑制が困難である。そのため，交流遮断器を用いて事故を除去する必要があり，送電再開までに要する時間が長い。そこで本研究では，半導体スイッチを用いた高速な直流遮断器に適用できる，高耐圧化とサージ電圧抑制が可能な回路方式を提案し，交流遮断器の操作を伴わずに直流線路の地絡および短絡事故を除去し，他励式変換器と同等の時間で送電再開を可能とする自励式直流送電システムを開発した。提案法は，事故区間のみを切り離しできるため，直流多端子系統への適用に有効である。さらに，直流事故期間中にも変換器の運転を継続し，交流電圧維持のための無効電力制御を継続できる。

概要 （英文）

High voltage dc (HVDC) transmission systems are widely applied to large capacity and long distance power delivery in recent power systems. Conventional HVDC systems adopt line-commutated current-source converters (CSCs). In recent years, a system adopting self-commutated voltage-source converters (VSCs) is also applied to many projects because it has advantage in control characteristics and volume decrease. However, the VSCs have a drawback that the converters lose their current control capability when a short circuit fault occurs in their dc transmission line. In order to recover from the faults in the VSC HVDC systems, various dc circuit breakers have been studied and solid-state circuit breakers are a promising option in a system rated at several hundred kV. However, further developments are necessary to increase their blocking voltage and to suppress the surge voltage arising from current interruption.
This report focuses on a VSC HVDC system which can clear dc line faults by a solid-state dc circuit breaker. This report proposes a circuit topology for solid-state dc circuit breakers rated at several hundred kV. A snubber circuit was applied to the solid-state dc circuit breaker to connect multiple power semiconductor devices in series for increasing its blocking voltage. The surge voltage across the valve devices is reduced by using a freewheeling diode, making it possible to decrease the number of series connected semiconductor devices. Conduction loss of the proposed dc breaker is estimated at 0.045% of the rated power in a system rated at 300 MVA in power and 250 kV in dc voltage. It can rapidly interrupt the fault current in dc transmission lines and realize continuous operation of the VSCs. A downscaled HVDC system rated at dc 360 V and 10 kVA was built and a series of verification tests was executed to verify the operating performance of the proposed system.

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