Study on Clamping Type DC Circuit Breaker with Short Fault Isolation Time and Low Energy Dissipation

The development of DC grids faces challenges from DC fault protection.The conventional DC circuit breaker(DCCB)employs metal-oxide varistor(MOV)to isolate the faulted line,in which the fault isolation process is coupled with the energy dissipation process.In this study,a clamping type DCCB(CTCB)using internal capacitors to clamp the converter voltage is proposed.Thanks to the proposed configuration,fault isolation and energy dissipation are decoupled,resulting in a fast fault isolation and low energy dissipation compared to the conventional DCCB.The working principle of the proposed CTCB is presented and verified in a DC grid simulation model.A comparison is made with the traditional DCCB.The fault isolation time can be reduced by 34.5%.The dissipated energy can be reduced by 17.4%.The energy dissipation power can be reduced by 76.2%.

Optimal Planning of Hybrid AC/DC Low-voltage Distribution Networks Considering DC Conversion of Three-phase Four-wire Low-voltage AC Systems

The increasing integration of distributed household photovoltaics(PVs)and electric vehicles(EVs)may further ag gravate voltage violations and unbalance of low-voltage distribu tion networks(LVDNs).DC distribution networks can increase the accommodation of PVs and EVs and mitigate mutilple pow er quality problems by the flexible power regulation capability of voltage source converters.This paper proposes schemes to es tablish hybrid AC/DC LVDNs considering the conversion of the existing three-phase four-wire low-voltage AC systems to DC op eration.The characteristics and DC conversion constraints of typical LVDNs are analyzed.In addition,converter configura tions for typical LVDNs are proposed based on the three-phase four-wire characteristics and quantitative analysis of various DC configurations.Moreover,an optimal planning method of hybrid AC/DC LVDNs is proposed,which is modeled as a bi-level programming model considering the annual investments and three-phase unbalance.Simulations are conducted to verify the effectiveness of the proposed optimal planning method.Sim ulation results show that the proposed optimal planning method can increase the integration of PVs while simultaneously reduc ing issues related to voltage violation and unbalance.