Coordinated Control Method For Islanded Electric-Hydrogen AC/DC Hybrid Microgrid

With the development of science and technology and the acceleration of urbanization,more and more goods and services need to consume energy,which leads to the increasing energy demand all over the word.As burning of traditional fossil energy will bring increasingly serious environmental pollution and energy shortage caused by declining reserves,renewable energy power generation has become a promising way of power generation.However,the inherent uncertainty and intermittency of renewable energy power generation hinder its application.AC/DC hybrid microgrid is an effective solution which integrates renewable energy sources efficiently and reliably,while supplying both AC and DC loads.Energy storage system is an important guarantee for the safe and stable operation of islanded AC/DC hybrid microgrid.The combination of hydrogen energy storage system in long time scale and battery energy storage system in short time scale is considered to be a promising solution of energy storage system.In this thesis,a hardware in loop experiment platform of islanded electric-hydrogen AC/DC hybrid microgrid,which consists of DC subgrid,AC subgrid and bidirectional power converter is established.Aiming at the characteristics of energy storage systems in the studied system,which contains hydrogen energy storage system and battery energy storage system,the voltage stability control method of DC subgrid,power transmission control method between DC subgrid and AC subgrid,and the whole microgrid coordination control method are studied.The main research results of this thesis are as follows:(1)A semi-physical hardware-in-the-loop simulation platform of islanded electrichydrogen AC/DC hybrid microgrid is built based on RT-LAB real-time simulator,and the basic control strategy of studied system is verified.The platform is composed of RT-LAB realtime simulator,oscilloscope,DSP controller and simulation model based on Matlab/Simulink software of islanded electric-hydrogen AC/DC hybrid microgrid.The established simulation model includes two types of renewable energy sources,wind turbine and photovoltaic array,two types of energy storage systems,battery and hydrogen,and two types of load,AC load and DC load.(2)In terms of voltage stability control of DC bus,considering the limitations of line resistance to traditional droop control methods in power distribution accuracy and DC bus voltage deviation,a SOC-based consensus control method for multiple energy storage systems with no communication system is proposed.In this method,the droop coefficient is defined related to the line resistance and battery SOC.Besides,the distributed energy storage unit coordinated control method based on consensus algorithm for both SOC equalization and DC bus stability is also presented in this thesis.In this control method,a multi-agent system of distributed energy storage systems,and the weak communication network information interaction between the energy storage systems are built.Finally,the proposed two control methods are verified on RT-LAB real-time simulation platform.(3)Considering the importance of inertia in more power electronic converter system,this thesis proposes a flexible virtual inertial control method based on multi energy storage system.This method adopts SOC equalization algorithm when battery energy storage system is selected as working energy storage system,and uses the traditional droop control when hydrogen energy storage system operating.Besides,the reference power of energy storage system in AC subgrid and DC subgrid based on the coupling relationship between AC frequency and DC bus voltage is calculated to realize the global power support,and improve the dynamic response and inertia of the system.Finally,the proposed control method is verified on the hardware in the loop platform built in chapter 2.(4)Considering the economy during islanded operation of electric-hydrogen AC/DC hybrid microgrid,this thesis puts forwards a multi-time scale hierarchical coordinated control method,which can be divided into the upper layer of power allocation and local control layer.The upper layer of power allocation is assigned as the third-time scale power control according to the cycling cost function of battery energy storage system and hydrogen energy storage system.The local layer control includes the first-time scale power control composed of droop control in the AC and DC energy storage system converter and the second-time scale power control of flexible virtual inertial control in bidirectional power converter.Finally,the proposed control method is verified on the hardware in the loop platform built in chapter 2.