**Decentralized Plug-and-Play Protection Scheme for Low Voltage DC Grids**

**Nils H. van der Blij 1,\*, Pavel Purgat 1, Thiago B. Soeiro 1, Laura M. Ramirez-Elizondo 1, Matthijs T. J. Spaan 2 and Pavol Bauer 1**

1 Department of Electrical Sustainable Energy, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands; P.Purgat@tudelft.nl (P.P.); T.BatistaSoeiro@tudelft.nl (T.B.S.); L.M.RamirezElizondo@tudelft.nl(L.M.R.-E.);P.Bauer@tudelft.nl(P.B.)


Received: 22 April 2020; Accepted: 9 June 2020; Published: 18 June 2020

**Abstract:** Since the voltages and currents in dc grids do not have a natural zero-crossing, the protection of these grids is more challenging than the protection of conventional ac grids. Literature presents several unit and non-unit protection schemes that rely on communication, or knowledge about the system's topology and parameters in order to achieve selective protection in these grids. However, communication complicates fast fault detection and interruption, and a system's parameters are subject to uncertainty and change. This paper demonstrates that, in low voltage dc grids, faults propagate fast through the grid and interrupted inductive currents commutate to non-faulted sections of the grid, which both can cause circuit breakers in non-faulted sections to trip. A decentralized plug-and-play protection scheme is proposed that ensures selectivity via an augmented solid-state circuit breaker topology and by utilizing the proposed time-current characteristic. It is experimentally shown that the proposed scheme provides secure and selective fault interruption for radial and meshed low voltage dc grids under various conditions.

**Keywords:** decentralized protection scheme; fault analysis; low voltage direct current grids; plug-and-play systems; solid-state circuit breakers
