| Vessel integrated power system is a revolutionary technology for ships.Electricity is utilized as the only energy form to realize the comprehensive allocation and unified utilization of the energy of the entire ship.In 1998,the research team of Naval University of Engineering of China took the lead in putting forward the technical route of developing medium voltage DC shipboard integrated power system in the world.Compared with the traditional medium voltage AC system,the medium voltage DC system uses the high-speed integrated rectifier generator to replace the traditional line-frequency AC synchronous generator,which reduces the volume and weight of the device.The medium voltage DC distribution network is adopted to unlock the speed constraint of prime mover and improve the operation efficiency of the system.The introduction of energy storage elements greatly enhances the flexibility and reliability of ship power system.The use of intelligent energy management system strengthens the ability of information acquisition and processing,improves the power supply quality of ship power system,and speeds up the response of the system to sudden accidents.With the rapid development of vessel integrated power system,the types of shipboard energy ports,such as energy storage components,higher voltage buses,pulsed power sources or loads,are increasing,and the port characteristics of them are becoming more and more complex.In this regard,the traditional power distribution scheme based on two-port power conversion cannot meet the requirements of the second generation of integrated power system due to its shortcomings such as the large number of power conversion stages,long energy transmission paths,poor dynamic performance,and low operating efficiency.In contrast,shipboard power distribution scheme based on multi-port electric energy conversion uses multi-port power electronic converters to connect multiple energy ports,shorten the energy flow path and improv e the dynamic response performance of the system.However,there is still a lack of proper multiport power electronic converters that can satisfy the requirements of the second generation of vessel integrated power system.Therefore,the research of multi-port power electronic converters is of great significance to the development of shipboard power transformation and distribution systems.Among the various multi-port power electronic converter topologies,the switched capacitor based multi-port converter topology family is very suitable for the shipboard applications due to its high power density,high operating efficiency,good fault-tolerant operation capability and unbalanced operation capability.According to the tasks of the power distribution subsystem in the second generation of ship power system,eight typical operating modes are designed for the converter.The operating mode selection method under different working conditions is proposed,the modulation strategy is designed,and the small-signal mathematical model is established.Then,this article discusses three scientific problems of the proposed converter in depth.The specific content of each scientific problem is presented as follows.(1)Reliability analysis and multi-objective optimization parameter design.This paper deeply analyzes the fault operation characteristics of the converter and discusses the fault-tolerant operation characteristics of it.A three-stage quantitative reliability model based on Markov process and improved k/n voting model is established,and the fault protection strategies of the proposed converter and that of AC modular multilevel converter are compared.On the other hand,a multi-objective optimization parameter design scheme considering the reliability,operation efficiency and power density of the converter based on the fast non-dominated sorting genetic algorithm is proposed.The Pareto optimal frontier is calculated and pictured to provide users with optimal parameter choices for different application scenarios.(2)Closed-loop control strategy and cascade stability analysis.The closed-loop characteristics of modular triple-port DC-DC converter cascaded system are studied.On that basis,the control strategies of the converter under different operating modes is proposed.Especially for the working conditions when DC multi-port modular multilevel sub-converter controls the intermediate bus voltage,a triple-loop decoupling control strategy is proposed,which solves the problems of serious control loop coupling,uncontrolled medium voltage side current and low-frequency oscillation in the traditional strategy.Then,on the basis of the proposed control strategies,the port impedance models of the sub-converters are established.Finally,aiming at the problem that the traditional cascaded stability criterion fails to consider the cross coupling effect among the port impedance of the multi-port sub-converters,the small signal model of the whole cascaded system is established,and a set of new cascaded stability criterion suitable for modular three port DC converter is proposed.(3)Unbalanced operation principle considering SOC balancing of energy storage elements.In the shipboard power system,unbalanced SOC of the distributed energy storage elements is commonly seen.In order to balance the SOC,modular triple-port DC-DC converter is supposed to operate under unbalanced branch power.This dissertation first analyzes the unbalanced operation principle of the converter,and proposes the unbalanced operation boundary.On the basis of this boundary,the SOC fast balancing control strategy is proposed.The unbalanced branch power operation of the modular triple-port DC-DC converter will increase the DC current ripple on the medium voltage side and endanger the operation.Therefore,this paper analyzes the medium-voltage side DC current ripple characteristics under unbalanced operation,and proposes an optimal phase-shift modulation strategy,which significantly reduces the mediumvoltage side current ripple.Finally,a 20 k W principle prototype of the proposed modular triple-port DC-DC converter is designed and manufactured.The mechanical structure and control system of the prototype both adopt modular design,which is convenient for production,manufacturing and maintenance,and features good scalability.The master-slave ring network control architecture is employed.In this paper,with the help of the principle prototype experimental platform,the dynamic and static experiments of the proposed control strategy,the imbalance boundary verfication experiment,the SOC fast balancing control strategy experiment and the optimal phase-shifted modulation strategy experiment are carried out to validate the correctness of the theoretical research. |
PDF Full Text Request