Research Of Power Management System Control Strategy Of Electric Propulsion Ship

The interconnecting point for all the installed power equipment is the powerdistribution system. By starting and inrush transients, load variations, and networkdisturbances from harmonic effects, the load and generators are interacting andinfluencing each other. Optimum operation and control of the power system isessential for safe operation with a minimum of fuel consumption. The PowerManagement System (PMS) is a crucial part of the automation and power systems onmarine vessels, and in particular for ships with electric propulsion and station keepingthrusters. The PMS controls the power system in order to maximize the blackoutprevention capabilities and minimize the fuel consumption. It also serves to decreasethe maintenance costs through protecting the equipment against faults andmalfunctions. Through interaction between the PMS and other control systems, theperformance of the vessel can be maximized.This thesis deals mainly from generator allocation control, load limiting controland fast laod reduction control.The important aim of this thesis is to make a littlecontribution towards ensuring adequate and reliable power supply to the variousconsumers and to decrease operational costs of the marine vessel, increase the level ofautomatic control in the marine power plant.The thesis mainly includes four aspects:Firstly, the structural features, modules and modeling specications of the PMS arepresented in this thesis.In order to assure the simulation’s real-time and accuracy ofthe power system, one diesel model which can respond to a sudden load increase havebeen proposed. Due to relatively slow responses of the prime mover, compared to thegenerator, static model be used for generator and complex vector model for all powersystem.Analysis generator allocation control，load depended start/stop of generatingsets and computation of available power.Secondly, propulsion load limiting control and propeller loads dynamic arepresented and modelling.The propeller load loss caused by external environment andoperational mode. The power fluctuations on the network will increase with thirdpotential of the propeller nominal speed, so it is possible to improve the steady power supply and limit the propeller load. Load limiting controller based on the thrusteracceleration are presented.Thirdly, modern functionality of PMS is extended to reduce the load in situationsor fault scenarios than may initiate large frequency and voltage drop on the generatorand cause the consequent generator trip.Four main FLR algorithms have beenpresented and compared:Available power-based load shedding, Frequency-based loadshedding, Event-based FLR and Frequency sensitive phased back system.Withrespect to the quantity of the reduced load, two strategy may be used and optimized.Fourthly, a new strategy to completely attenuate the frequency and voltagefluctuations on the network is presented.The control is called the power redistributioncontrol,which based on the dynamic performance of diesel engine and the control ofthruster load limiting. These strategies aim to limit the bad performance thrustersfrom injecting fluctuating loads to network due to excessive propeller shaft torquefluctuations.