Fault protection for a modular multi-level converter (MMC)-based high voltage direct current (HVDC) grid with dc circuit breakers (DCCBs) is a great challenge, because faults need to be isolated fast to prevent the collapse of the grid and overcurrent damage to the equipment. Before clearing faults, faults must be detected as soon as possible. However, the fast rising speed of fault currents and the emerging fault between the DCCB and line reactor increase the difficulty of fault protection. A fast and reliable fault detection and protection method relying on bus-voltage change rate and fault component current is proposed in this paper. It requires the measurements with local sensors and makes use of a lower number of voltage sensors. The proposed algorithm is applied to a four-terminal MMCHVDC grid. Results show that the proposed method can identify the fault type and discriminate bus faults, line faults, and wall bushing faults. It can detect faults quickly and does not generate erroneous and unnecessary trip signals.

具有直流断路器 (DCCB) 的基于模块化多电平转换器 (MMC) 的高压直流 (HVDC) 电网的故障保护是一个巨大的挑战，因为需要快速隔离故障以防止电网崩溃和过流损坏设备。在清除故障之前，必须尽快检测到故障。但故障电流上升速度快，DCCB与线路电抗器之间出现故障，增加了故障保护的难度。本文提出了一种基于母线电压变化率和故障分量电流的快速可靠的故障检测和保护方法。它需要使用本地传感器进行测量并使用较少数量的电压传感器。所提出的算法应用于四端MMC高压直流电网。结果表明，所提出的方法可以识别故障类型并区分母线故障、线路故障和穿墙套管故障。它可以快速检测故障，不会产生错误和不必要的跳闸信号。