Solid-State Protection of Low Voltage DC Distribution Grids

Abstract

With the increasing introduction of DER in the everyday energy landscape, it becomes essential that a partial transition from AC to DC within the whole range of voltage levels has to be re-considered especially in practical cases where DC system performance seems outstanding compared to AC based counterparts. On that note, LVDC microgrids have become an attractive option for efficient integration and distribution of high-quality power to commercial, residential and data center facilities as well as in propulsion and automotive power systems. However, the lack of standards, guidelines and practical experience are among the main reasons for holding the large scale integration of DC at the low-voltage distribution level back. The main challenge to be tackled in order for low-voltage DC grids to emerge from small DC nano- and micro-grids to a full scale DC distribution grid is the development of economically feasible, safe and reliable protection equipment and techniques. In the context of this thesis a fault detection and location method for ultra-fast fault selective current interruption is being proposed without the need of any additional control and/or communication requirements. In order to experimentally validate the proposed fault selective protection (FSP) algorithm a bi-directional 400V/20A solid-state circuit breaker prototype has been developed and tested utilizing a full short-circuit protection scheme with additional inrush-current limiting control functionality for grid start-up.