Abstract
A high-voltage direct-current (HVDC) grid protection strategy to suppress dc fault currents and prevent overcurrent in the arms of modular multilevel converters (MMCs) is proposed in this paper. The strategy is based on the coordination of half-bridge MMCs and hybrid dc circuit breakers (DCCBs). This is achieved by allowing MMC submodules to be temporarily bypassed prior to the opening of the DCCBs. Once the fault is isolated by the DCCBs, the MMCs will restore to normal operation. The performance of the proposed method is assessed and compared to when MMCs are blocked and when no corrective action is taken. To achieve this, an algorithm for fault detection and discrimination is used and its impact on MMC bypassing is discussed. To assess its effectiveness, the proposed algorithm is demonstrated in PSCAD/EMTDC using a four-terminal HVDC system. Simulation results show that the coordination of MMCs and DCCBs can significantly reduce dc fault current and the absorbed current energy by more than 70% and 90%, respectively, while keeping MMC arm currents small.
Highlights
V OLTAGE source converter (VSC) based high-voltage direct-current (HVDC) grids are expected to facilitate the large-scale integration of renewable energy generation into electricity grids and to enable cross-border energy trading [1]
Considering that future HVDC grids will likely employ dc circuit breakers (DCCBs), this paper proposes a new protection strategy to coordinate the operation of hybrid DCCBs and HB-modular multilevel converters (MMCs)
The method from [27] has the following main differences compared to the approach presented in this paper: (a) the method in [27] has been developed for point-topoint link protection, while this paper aims to provide a general solution for HVDC grid protection; (b) one MMC coordinates with multiple DCCBs in the study presented in this work; (c) the algorithm and duration for MMC bypassing is different in [27] compared to this work
Summary
V OLTAGE source converter (VSC) based high-voltage direct-current (HVDC) grids are expected to facilitate the large-scale integration of renewable energy generation into electricity grids and to enable cross-border energy trading [1]. Only two multi-terminal VSC-HVDC systems are in operation: the Nan’ao three-terminal HVDC system and the Zhou Shan five-terminal network [2]. Another four-terminal dc grid pilot project interconnecting Beijing and Zhangjiakou will be commissioned in 2018 [3]. Other notable VSC-based multi-terminal system projects include the Tres Amigas Superstation and the Atlantic Wind Connection, which are still under construction [6]. Date of publication April 27, 2018; date of current version January 22, 2019.
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