DC fault current can be interrupted within several milliseconds by employing hybrid HVDC circuit breaker. However, this scheme is not cost effective, especially in meshed HVDC grid. In this paper, a novel integrated HVDC circuit breaker by sharing components is proposed to overcome these drawbacks. Supposing that a converter in a meshed HVDC grid is connected to m DC lines. The integrated HVDC circuit breaker consists of ${m+1}$ ultra-fast disconnectors (UFDs), ${m+1}$ load commutation switches (LCSs), m+1 mechanical disconnectors (DSs), and only one main breaker (MB) and surge arrester (SA). The behavior of the proposed integrated HVDC circuit breaker is similar to that of the conventional hybrid HVDC circuit breaker. These two kinds of breakers have the same operating time, which means the integrated HVDC circuit breaker is fast enough to clear DC faults. Besides, the IGBT modules in the MB and LCSs of the proposed integrated HVDC circuit breaker are connected in one direction, and the m DC lines share a single MB. Therefore, this scheme is more cost effective compared to conventional hybrid HVDC circuit breaker. Simulation results on a three-terminal HVDC grid are presented to verify the effectiveness and feasibility of the proposed scheme.

Microgrids have a strong ability to generate local power and consume renewable energy, which can solve the problems of power supply shortages and greenhouse gas emissions created in the process of social development. The honeycombed active distribution network (HADN) can flexibly, independently, and interconnectedly operate microgrids through power exchange stations, so appropriate HADN dispatch can produce increased low-carbon benefits than general microgrids. In this study, we first designed a model for optimizing HADN with the lowest carbon emission as the target, then we introduced the concept of carbon emission flow into the optimization process to determine the carbon emission level of each element. Finally, we illustrated and verified the proposed model by a HADN composed of three microgrids. The optimization results of the case study showed that by scheduling the DGs within the microgrids, the total carbon emissions of the system were reduced from 123,328.1 to 117,688 kg CO${}_2$; the system with a HADN structure was able to produce only 110,958 kg CO${}_2$ and effectively reduce carbon emissions by 10%, which proved that HADN can be scheduled with high flexibility and provides increased low-carbon performance through the proposed optimization dispatch method.

In order to reduce the cost of energy devices for IGBT drive circuits of the hybrid HVDC breaker, a self‐energy device for the HVDC breaker is proposed here, which connects to DC lines and takes power from DC lines directly. The device consists of three operating modes: the start‐up charging mode, the steady‐state charging mode, and the maintenance restart charging mode. In view of these modes, corresponding control strategies are proposed to ensure the stability of power supply to drive circuits, and the simulation model is built and studied. For multi‐terminal HVDC systems or HVDC grids, several self‐energy devices in different lines can be connected through a certain combination, which can get the DC current flow regulation function.