Multiport hybrid dc circuit breakers (M-HCBs) have been recognized as suitable devices for protecting dc grids. Most M-HCB topologies include load current switch (LCS), leads to inevitable conduction losses as load current may flow through LCS under no-fault conditions. Only a few multiport current-injection HCB (M-C-HCB) topologies have been proposed in previous articles to remove LCS from load current branch, however, additional power supply or complex additional circuit for repetitive capacitor precharging is required, resulting in increased system cost and reduced reliability. To overcome the main shortcomings mentioned previously, this article proposes a novel M-C-HCB topology, only one capacitor configured with a simple bridge arm circuit is used to realize the fault current communication process from load current branch to main breaker branch, and external precharging solution is required for only once. The LCSs composed of semiconductor devices is removed from the load current branch to achieve minimizing the conduction losses. The working principle is introduced in detail and the parameter designs are discussed. A comparison with some traditional M-HCBs and other M-C-HCB solutions is presented to show the efficiency and economic advantage. Finally, the proposed topology is validated with three-terminal HVdc grid simulations and a scale-down experimental prototype.

The reliability of meshed DC grids mainly relies on their ability in DC fault protection and line power flow managing. Multiple DC circuit breakers (DCCB) and current flow controller (CFC) need to be installed, which significantly increases the system cost. A novel current flow controller integrated with hybrid dc circuit breaker (CFC-IHCB) is proposed to significantly reduce the loss and cost of the whole system. Only one unidirectional IGBT string based main breaker branch is needed for n lines, and the CFC function is integrated into the load communication switches (LCSs). The basic working principle of proposed topology is presented and analyzed. The functionality is verified and a comparison of the proposed solution and other DCCB/CFC solutions is given based on a multi-terminal HVDC system case study.

This paper proposes a local control strategy applied in the soft open point (SOP) to suppress voltage fluctuation when adding a renewable energy source into the system. The mathematic model of the grid connected to SOP is established based on the characteristics of a low-voltage distribution network. Combined with the mathematic model and local voltage information, the local control strategy is proposed to optimize the active and reactive power distribution and consume the minimum apparent power of the converter. The local control strategy can effectively suppress the voltage fluctuation caused by renewable energy access, which was testified by MATLAB/Simulink simulation. In addition, the local control strategy can deduce the communication resource and increase the response speed compared to global optimization. This paper is meaningful for renewable energy source distribution and voltage balance in low-voltage distribution systems.