Voltage-Power Coordinated Control Of Dual-Bus DC Microgrid

Compared with alternating current(AC)microgrid,direct current(DC)microgrid has more advantages in absorbing distributed generation,energy storage,and DC load.For the DC microgrid,it is unnecessary to consider the frequency stability and reactive-power balance problems inherent to AC grids,but it is urgently needed for us to develop advanced control strategies to maintain the power balance and the DC-bus voltage stability of the DC microgrid.In this thesis,we study the voltagepower coordinated control strategy and the small-signal stability analysis method for the dual-bus DC microgrid.The main work of this thesis is summarized as follows:(1)Analyze the component characteristics of the dual-bus DC microgrid and establish the corresponding component model.Firstly,the topology and components of the dual-bus DC microgrid are briefly introduced.Secondly,the characteristics of the main components(such as PV units and energy storage units)are analyzed,and the corresponding mathematical models of these components are established.Finally,the operating modes of the components are determined according to the voltage-offset degree of the DC bus.(2)Propose a voltage-power coordinated control strategy for the dual-bus DC microgrid.First,considering the shortcomings of the traditional droop control in the voltage stability performance and power allocation accuracy,an adaptive coefficient based on the state of charge(SOC)power index is utilized to change the power allocation ratio dynamically for realizing accurate voltage and power control.Second,for the voltage-offset problems of the high-voltage(HV)and low-voltage(LV)DC buses due to power imbalance,a control strategy for the intermediate DC/DC converter is developed to realize mutual power support between the HV and LV buses.Finally,Matlab/Simulink software is used to build the dual-bus DC microgrid model,and the proposed control strategy is verified by the simulations.(3)Propose a small-signal stability analysis method for the DC microgrid with the voltage-power coordinated control strategy.At first,we establish the dynamic mathematical model of each component with its controller and the algebraic model of the DC network to formulate the differentialalgebraic model of the overall DC microgrid system.Then,we linearize the differential-algebraic model approximately at the equilibrium point and obtain the corresponding small-signal model.In the end,we analyze the effects of the adaptive coefficient,the DC load power,and the operating mode of the intermediate converter on the small-signal stability of the system by the eigenvalue-root trajectory method.In short,this paper proposes a voltage-power coordinated control strategy for the dual-bus DC microgrid,and analyzes the small-signal stability analysis method for the dual-bus DC microgrid.The simulation analysis and comparison of the results before and after improvement,the feasibility of the control strategy is verified.