Transient suppression in hybrid electric ship power systems

The requirements for power quality in ship power systems have been increasing over the years. This is an essential consequence of improving the efficiency of the onboard power network and reduce emissions in the long term. The connection of sophisticated navigation and measuring instruments into the grid has also necessitated a higher quality of power to ensure optimal operating conditions for all the loads and avoid malfunction of equipment onboard a ship. The most significant challenge to maintain power quality for the shipboard power system is to mitigate the transient conditions that arise due to the widely varying load conditions imposed by varying sea conditions as well as fluctuating onboard power demands. This work has attempted to illustrate the extent of the transient phenomena due to load changes in the case of vessels with hybrid mechanical and electrical propulsion. Subsequently, control solutions to limit and reduce such transient conditions and their propagation that include energy storage devices such as the capacitor and battery have been developed. A shipboard power system with hybrid propulsion has been modeled and the transient responses to various types of load changes during the course of different modes of operation possible for the hybrid system have been analyzed. An active damping strategy has been developed to reduce the torsional vibrations at the drive shaft of the thruster due to extreme load conditions while avoiding overdesign of the shaft itself. The strategy has been extended further to incorporate a capacitor clamped inverter to reduce the electrical transients that are caused by propagation of these transients from the mechanical portion of the hybrid propulsion system into the electrical system. A Model Predictive Control (MPC) strategy has also been developed for a Battery Energy Storage System (BESS) to mitigate the electrical transients arising as a result of propulsion and service load transients while keeping the main engine in the optimum operating range. The MPC power converter control allows for the battery to smoothen the electrical frequency profile during different types of extreme load change conditions and allows for charging and discharging the battery repeatedly. The findings of this research work have significant implications in defining the extent of transient conditions in hybrid power systems. In addition, the efficacy of integrating an energy storage system into the hybrid electric propulsion power network in order to reduce the transients has also been proven