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Compared to the AC microgrids, the advantages of DC microgrids are notable. However, the development of DC microgrids is being constrained by the lack of mature protection schemes. For the foundation of designing protection schemes, the existing fault analysis focused on the fault characteristics of voltage source converters and ignored other generators. However, in DC microgrids with high permeability of photovoltaic (PV) powers, the effects of PV powers should be paid considerable attention. In this paper, the cable fault characteristics of the PV powers are analyzed in detail, and both the pole-to-ground fault and the pole-to-pole fault are considered. The fault processes are divided into several stages, and the fault circuits and main equations are described for each stage. All of the analyses are verified by the simulation model based on the PSCAD/EMTDC, and with the help of simulation results, the two main challenges the protection system confronted with are emphasized and the impacts of fault distance are analyzed. Finally, this paper proposes to employ a more reasonable converter structure and a transverse differential protection to overcome the main challenges; the effectiveness of the methods is verified by the simulation. [ABSTRACT FROM AUTHOR]

An improved system structure and a corresponding protection system are proposed in this paper, which aims at providing future DC microgrids with suitable protection ideas. At first, the ring-bus system is adjusted to balance the system control and protection and make the system more conventional for the equipment expansion. In addition, based on this structure, a protection system is established. It consists of two parts, which are local protection and pilot centralized protection. The local protection is designed for protecting the vulnerable power electronic components in converters and the pilot protection is mainly proposed for the fault isolation. The combination between two parts makes the whole system overcome the contradiction between protection speed and reliability and the method also takes the protection suitability into consideration. Finally, all the methods are verified by the simulation system based on the PSCAD /EMTDC. [ABSTRACT FROM AUTHOR]

Integrated Photonics Rare‐earth‐ion‐doped thin‐film LiNbO3 (RE:LNOI) meets the urgent demands for chip‐integrated laser sources, optical amplifiers, and quantum memories based on LNOI photonics. In article number 2200059, Yuechen Jia, Yuping Chen, Feng Chen, and colleagues provide a timely review on the development of RE:LNOI photonics in terms of ion‐doping techniques, chip‐integrated lasers and amplifiers, as well as low‐temperature optical characterizations for quantum photonics. And the RE:LNOI platform is expected to soon become a photonics game‐changer. [ABSTRACT FROM AUTHOR]