| With the development of DC distributed generators(DG),energy storage systems(ESSs),as well as high penetration of modern DC loads,DC microgrid(MG)attracts increasing attentions and has become an indispensable part of smart grid.Due to its high efficiency and convenience.Nowadays,stand-alone DC MG plays an important role in some applications,such as smart building,new energy transportation systems,data centers and distant communication stations.As a clean and efficient renewable energy,fuel cell(FC)connected to DC microgrid is significant in improving the power supply reliability and power quality.However,multiple heterogeneity renewable energy sources connected to DC microgrid bring a new challenge on energy management technology,limiting its application in the special fields.Focusing on the FC-based DC microgrid,this dissertation aims at solving a series of key problems in the energy management of fuel cell stand-alone DC microgrid and the coordinative control of DC microgrid cluster.On this basis,the energy management technology of FC-based DC microgrid of hybrid tram is also researched thoroughly.The research contents and achievements are mainly manifest in the following aspects:(1)A FC-based DC microgrid system structure is designed,and a FC-based DC microgrid experimental system is established.The dissertation gives a detailed introduction on DC microgrid system structure consisting of PV array,hydrogen generation system(including fuel cell,electrolyzer and hydrogen storage),battery pack and DC load(building load,electric vehicles,and so on).The detailed models and operating characteristics of the main subsystems(PV,battery,fuel cell,electrolyzer,hydrogen storage,and so on)are further researched,and a PV/hydrogen/battery DC microgrid real-time simulation system is built.Furthermore,the hardware system,including PV generation system,battery pack system,fuel cell generation system,electrolyzer system are established,and an energy management system based on RT-LAB real-time simulation machine is developed.Then the PV/fuel cell/battery DC microgrid and PV/hydrogen/battery DC microgrid experimental platforms are established respectively.(2)This dissertation proposes a hierarchical energy management method including equipment control layer and system management layer for the system structure and control objectives of PV/fuel cell/battery DC microgrid,to realize stable operation and reasonable power distribution.In the equipment control layer,the subsystems with various output characteristics are controlled by the different control methods.In the system management layer,PI control,state machine control and equivalent consumption minimum strategy(ECMS)are adopted for varies control objectives,to drive the equipment control layer for power coordination distribution.The PV/fuel cell/battery DC microgrid experimental platform is used for verifying the control performance of the above hierarchical energy management methods.The experiment result shows that: the hierarchical energy management methods can realize the stable operation of PV/fuel cell/battery DC microgrid,and the different power distribution strategies show different control performance on SoC control ability,system efficiency and equivalent hydrogen consumption.(3)This dissertation proposes a decentralized energy management method based on a mode-triggered droop scheme for the system structure and control objectives of PV/hydrogen/battery DC microgrid.In the mode division step,this DC microgrid is divided autonomously into eight operating modes based on the system local information such as bus voltage levels and the state of charge(SoC)states.In the droop control step,the system operating modes drive the distributed generation units to adjust their droop characteristics for stable operation and power distribution of DC microgrid.This decentralized energy management method is verified in the PV/hydrogen/battery DC microgrid experimental platform,and the results show that without communication of PV output power and load consumption,this method is effective to control the microgrid under various operating conditions based on less local information.(4)A distributed cooperative control method with virtual inertia is presented for the DC microgrid cluster.In the DC microgrid cluster,a large number of power electronic equipment will cause the problems,such as low system inertia,and the power fluctuation of RESs and DC load,which will affect the system stability.In order to solve the above problems,a droop control loop based on virtual capacitor is added into the local energy management system.In this way,the disturbance resistance can be improved by adjusting the droop coefficient in real time during the transient process.For the coordinated control of DC microgrid cluster,a distributed cooperative control method based on the framework multi-agent system(MAS)is used for the secondary control of the local energy management system.The voltage secondary control loop is used for the bus voltage smooth control at the moment of microgrids interconnection,and the power control loop is applied for effective control of power flow between sub-microgrid,to realize the ESSs SoC converge uniformly in finite time.In addition,a DC microgrid cluster real-time simulation system is built to verify the control performance of the proposed control method on the smooth control of bus voltage,the SoC consistency control,load abrupt response and ‘plug and play'.(5)A multisource coordination energy management method based on adaptive droop is proposed for power coordinated control of fuel cell DC microgrid in the hybrid tram.In this vehicle-mounted DC microgrid,three operating modes are defined based on load power,ESS SoC,and so on.For the stable operation of DC microgrid and the SoC consistency of ESSs,the reference output power of fuel cell system is calculated in real-time based on various operating modes,and the automatic charging and discharging of battery pack and super-capacitor pack are controlled based on the adaptive droop method.In addition,this dissertation develops a RT-LAB real-time simulation system of stand-alone DC microgrid which consists of two fuel cell generation system,two lithium battery packs,two super-capacitor packs and related power electronic equipment.The test results under a real driving cycle show that the proposed energy management method can contribute to efficient and stable operation of multisource and SoC consensus control. |
PDF Full Text Request