Reducing power transients in diesel-electric dynamically positioned ships using re-positioning

Abstract

Abstract-A thrust allocation method with a functionality to assist power management systems by using the hull of the ship as a store of potential energy in the field of environmental forces has been recently proposed and demonstrated to work in simulation. This functionality allows the thrust allocation algorithm to decrease the power consumption in the thrusters when a sharp increase in power consumption is demanded elsewhere on the ship. This way, the high-frequency part of the load variations on the power plant can be reduced, at the expense of minor (typically less than 1 meter) variations in the position of the vessel. The advantages from reduced variations in load include reduced wear-and-tear of the power plant, more stable frequency on the electric grid, reduced risk of blackout due to underfrequency, and more reliable synchronization when connecting additional generators or connecting bus segments. In the present work, this functionality is improved further by continuously monitoring the environmental forces and modifying the setpoint of the dynamic positioning algorithm to place the vessel a short distance (e.g. 20 cm) in the direction of steepest increase of the environmental force potential, thus maximizing the available potential energy. The increased potential energy creates additional capacity for assisting the power plant, which is shown in simulation to be significant.

Review of Dynamic Positioning Control in Maritime Microgrid Systems

“…The research in this area proposes that the high-level positioning controller can be applied to predict the required forces in the 6 degrees of movement. Moreover, the thrust distribution system (TDS) which estimates the corresponding thrust power to command the direction of each thrusting motors has proposed in [40][41][42]. Furthermore, the effect of minimum control level of thrusting in calm to rough sea environments is emphasized in [50] to prevent the corrosion of mechanical parts, avoid the shutdown, and harmonic distortion in power delivery, respectively.…”

“…Furthermore, cost-effective and energy efficiency solutions for investing in tools, conservation, harmful gas emission, and fuel consumption because of generators running hours are significantly demanded. For instance, the doubts in electrical power demand of drilling, shuttle tankers, cable, and pipe laying where the importance of DPS for transferring energy from offshore wind farm by cable laying, oil resources by tankers in operational condition are made disturbances for the PMS to provide thrusting power [36][37][38][39][40][41]. In addition, the PMS be able to control the optimum power flow be sure of DP demand in the future operational condition.…”

“…Especially, in advanced vessels such as cable laying and shuttle tankers, more sophisticated energy management systems are applied to predict the power demand, route scheduling, and thrust allocation to keep the position of the vessel by using the DP control technique. On the other hand, the power management system (PMS) which was applied in [36][37][38][39][40][41][42][43][44][45][46][47][48] for controlling of power generators, blackout prevention, power limitation, load sharing, and load shedding. Without a doubt, the DP control is issued according to the information about available power from the PMS to set the desired pitch/rpm load demand to allocate power for thrusters systems.…”

Real-Time Marine Vessel and Power Plant Simulation

“…Thruster induced load fluctuations A known problem for vessels in DP operation is large fluctuations of the power consumption by the thrusters, due to wave-induced variations of the advance velocity of the propeller. This gives excessive wear and tear of the generator sets and frequency variations, and it should be avoided by better control of the propeller [20,21].…”