| Increasing concerns on environmental issues and fuel economy have forced the maritime industry to pursue the solutions of low emission and fuel efficiency.The International Maritime Organization(IMO)and many countries with seaports have established relevant regulations to control ship emissions and require a substantial reduction in ship exhaust emissions.The shipboard power system is the basis of vessel.Advanced shipboard power system can greatly promote the development of China's ship and maritime industry.The electric propulsion ship,which usually operates under complex conditions,and its load power has large or continuously change.For example,a platform supply vessel(PSV)is employed with a bow thruster,and the bow thruster load characteristic is similar to pulse load.Therefore,it is very important to improve operation stability,improve energy efficiency and reduce costs of shipboard power system.The main work of this thesis is aimed at improving the stability,energy efficiency and operation cost of electric propulsion ships under complex conditions.A scheme that hybrid energy storages are connected to the DC bus of the bow thruster driver in an electric propulsion ship is proposed.And a hierarchical coordinated control strategy is presented to improve the energy efficiency of shipboard power system and to make the system stable.Firstly,for electric propulsion ship with small capacity,this thesis proposes to insert the power batteries in the DC bus of the back-to-back converter of the bow thruster,which can take into account both energy and required power.Compared with the connection of ultra-capacitors,power batteries can have volume and price advantages.The batteries are connected to DC bus through three-phase interleaved parallel DC/DC converter.The voltage adaptive PI controller of DC/DC converter is designed,and the influence of controller parameters on the system operation stability and response speed is analyzed.This scheme can improve the dynamic response speed of the converter,and restrain the load power fluctuations of the bow thruster.Therefore,the output power from the diesel generator sets to the bow thruster is constant,and the capacity of the diesel generator sets is effectively reduced.Secondly,for electric propulsion ship with large capacity and in complex operation conditions,a scheme for hybrid energy storage device with power batteries and ultra-capacitors connected to the DC bus of back-to-back frequency converter of bow thruster is designed.Implement the following scenarios:(1)The diesel generator can provide the average power required by the bow thruster.(2)The power batteries can be responsible for low-frequency fluctuations in the active power of the bow thrusters.(3)The ultra-capacitors can be responsible for providing the high-frequency and spike fluctuations of pulsed active power.A hierarchical coordinated control scheme is designed for DC/DC converters with hybrid energy storage.In the bottom layer control,the DC/DC controller adopts high/low-pass filter and V-I droop control to realize the load power sharing of the batteries and ultra-capacitors at different frequencies.The upper power controller can keep the output active power of the diesel generator sets to the bow thruster stable after rectification.The impedance analysis method and eigenvalue method are used to analyze the stability of the bidirectional DC/DC converter and its controller,and the influence law and stability range of system parameters and controller parameters on system stability are obtained.The scheme can effectively suppress the load power fluctuation of the bow thruster.When the bow thruster operates quickly,the hybrid energy storage can replace the braking resistance to absorb the braking energy.Finally,based on the Matlab/Simulink simulation platform,this thesis builds a simulation model of hybrid energy storage electric propulsion ship.The estimated simulation results show that the proposed control strategy is correct and effective. |
PDF Full Text Request