Coordination of MMCs With Hybrid DC Circuit Breakers for HVDC Grid Protection

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.

A Multi-Function Integrated Circuit Breaker for DC Grid Applications

“…), the maximum current exhibited by LCSs and UFDs at different bypass branches would be different. According to (19), the larger ( + ) is, the smaller , would be and, hence, an LCS and an UFD with a smaller current rating could be selected. Conversely, for a smaller value of ( + ) , both the LCS and the UFD would require a higher current rating.…”

“…An alternative is the implementation of an H-bridge-based HCB with additional bypass branches but fewer IGBTs [18]. The number of IGBTs within an HCB can be also reduced by coordinating the protection strategy between converters and HCBs to suppress fault currents [19].…”

Bridge-Type Integrated Hybrid DC Circuit Breakers

“…If 45.8 < k < 79.5, BT-ICBtyp1 is the cheapest; however, when k > 79. 5 Inter-DCCB becomes the most economic as it has less UFDs than BT-ICBtyp1 (see Table II). Only if k rises to 89.8 and 105.8, respectively, the cost of BT-ICBtyp2 and BT-ICBtyp1 will be higher than when conventional HCBs are used.…”

Review of technologies for DC grids – power conversion, flow control and protection

“…The mechanical UFD must be designed to support the prospective dc voltage when opened. When the dc fault is detected in the type '1' DCCB, the LCS is turned off to initiate commutation of the dc fault current from the principle conduction path to the main circuit breaker (MCB), which is a typical high-voltage semiconductor switch, capable of carrying high current for short period (<10ms) [86,87]. After the entire dc fault current is commutated to the MCB, the mechanical UFD is opened at near zero current and voltage, and during this period the fault current continues to flow in the MCB, and then, the MCB is opened to interrupt the dc fault current.…”