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Abstract

This article proposes an algorithm based on load priorities to ensure survivability in shipboard zonal secondary DC-grids. The transition to alternative fuels introduces new opportunities and new challenges. Using inherent DC power electronics for integrating energy storage systems (ESSs) and renewable energy sources (RESs) demands novel control mechanisms for dealing with power converter overload conditions. In that sense, the power management system (PMS) has to incorporate active load management systems to ensure the continuous operation of essential loads when the ship is operating in critical missions or during abnormal power situations. This work employs the concept of a zonal DC secondary distribution network, which is based on the insertion of supercapacitors for voltage time constant enhancement. This grid concept is used to formulate the survivability objective as a DC-link voltage recovery function, with a minimum operation voltage that must not be exceeded whilst sustaining continuous operation whenever feasible. That is relevant for short-circuit currents and underestimated and unforeseen high peak loads. In these cases, the load demand may exceed the nominal ratings of the DC/DC converter that feeds the secondary zone load. Moreover, the power converter may suddenly become unavailable. Then, supercapacitors can provide the additional power, enabling the momentary survivability of the zonal secondary grid. However, in this process, the DC-link voltage value decreases while the ESS is discharged. The power imbalance can only be sustained for a limited period, determined by the supercapacitor's initial operation conditions. If the DC voltage limit is exceeded, load reduction is required to counterbalance the load mismatch and ensure voltage recoverability. A load priority approach is applied in this article to meet the load reduction objective, with essential and emergency loads having the highest priority. A study case is proposed using time-domain simulations in a Matlab-Simulink environment to demonstrate the load management functionality. The results show that supercapacitors and load management substantially increase the survivability of the zonal secondary load centre whenever one of the DC/DC converters fails during operation. Bart Wingelaar, Research & Development Dept., Royal IHC Kinderdijk, The Netherlands, b.wingelaar@royalihc.com Jacques Julien Deroualle, FD Engineering Dept., Royal IHC Kinderdijk, The Netherlands, jj.deroualle@royalihc.com

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