Recent trends in shipboard power distribution network design, such as the transition from AC to DC result in new challenges on the issue of distribution network protection. Devices such as a solid state bus tie switch provide a first line of defence against propagation of low impedance faults across the distribution system by quickly separating the faulty portion of the network and preventing additional energy to be fed into the fault. This paper proposes a new topology of solid state bustie switch for shipboard power distribution networks. The topology is thoroughly described considering its operating principles, and a small scale prototype has been used to verify its operational performances. Current interruption capabilities are demonstrated, both in open loop and closed loop operation, with fault detection and decision algorithms implemented on a standalone controller.

This paper presents demonstration of a protection scheme integrated into marine DC power distribution networks to investigate the coordination between each protection action. The integrated protection scheme is based on three different time-frame protection actions: fast action -bus separation by a solid-state bus-tie switch, medium action -feeder protection by high-speed fuses, and slow action -power supply protection by generator deexcitation. As the backup protection of the power supply protection, AC fuses are installed between generators and rectifiers. To coordinate each protection action, the influences of the inductance in the bus-tie switch and the DC-link capacitance are investigated by DC short-circuit tests with the different inductance and capacitance values. The protection scheme, coordinated by the above investigation, is verified by system-level short-circuit tests for bus and feeder faults. To validate the protection scheme for various fault conditions, low-and high-impedance fault currents are analytically calculated for the bus faults and simulated for the feeder faults. Time-current curve analyses show that the coordinated protection scheme can effectively protect marine two-bus DC power distribution networks with correct operations of the protection measures and enough time margins between the different actions.

The need to increase efficiency and reduce operating cost of shipboard DC power distribution networks results in a desire to increase the operating voltage of such installations to the medium voltage levels. Devices such as solid state bus-tie switches are an essential component of such systems, as they allow for system reconfigurations and prevent fault propagation across different sections of the system. This paper presents a scalable solid state bus-tie switch topology designed initially for low voltage power distribution networks, but easily scalable in terms of voltage and current. The use of a single active device greatly increases simplicity and reliability of the solution. The ability to extend the current and voltage ratings has been verified on the prototypes through extensive experimental tests in parallel and series connection, respectively. Several methods for fault detection are discussed and further verified experimentally.

Series connected IGCTs find application in hard-switched commercial power converters at the MW power levels. Expanding the application of these devices to medium voltage dc-dc resonant converters is of great interest due to the IGCT's low conduction losses. This requires a deeper understanding of the device's behaviour in series connection and under switching conditions different than those in hard switched converters. In particular, the voltage sharing between series connected IGCTs must be achieved with significantly reduced turn-off currents, typical for resonant converters. Relying on a versatile IGCT test setup, this paper explores the operational performances of series connected IGCT operation at very low turn-off current and with snubber capacitance in the range of a few tens of nF. The results presented in the paper are obtained from commercially available 4.5 kV 68 mm reverse conducting IGCTs (with standard irradiation), as well as two customized engineering samples (high irradiated variants), optimized on their technology curve for high switching frequencies. The IGCTs are successfully operated in series connection at 5 kHz, with device voltage being effectively shared in resonant converter operation.