Stability Analysis Of DC Microgrid With Constant Power Load And Boost DC/DC Networ

With the transformation of the energy system and the acceleration of the ’double carbon’ strategy,renewable energy has gradually become the main supply of electricity.Due to different resource distribution,energy is divided into centralized and distributed,and DC microgrid is widely used due to its advantages of easy acceptance of renewable distributed power sources and flexible power control.Due to the limited conditions of a single Boost DC/DC converter,the parallel structure of Boost DC/DC converter is widespread in the DC power supply system to improve the redundancy configuration,scalability and stability of the system.Load power sharing should be considered in multi-converter parallel system,and V-I and I-V droop are common control methods to realize this function.A class of load in DC power supply system is driven by power electronics,and its dynamic and steady-state operation reflects the characteristics of constant power load,with negative incremental impedance characteristics,which will weaken the system damping.This paper focuses on the stability of the parallel Boost DC/DC converter system and its capacity with constant power load,and systematically compares the stability law,advantages and disadvantages of the V-I and I-V droop control parallel Boost DC/DC converter system in practical application,in order to provide general design reference for engineering application or researchers.The main jobs of the paper are as following.Analysis of constant power load operation characteristics of converter interface.Firstly,the mathematical model of Buck DC/DC converter with constant voltage control is established,and the influence of controller parameters on the stability of Buck converter is analyzed.Then the operation characteristics of the input impedance model of Buck converter are analyzed.It is proved that the Buck converter with constant voltage control can indeed simulate the constant power load characteristics,and it is concluded that the increase of the voltage loop integral controller parameters will reduce the system damping.Finally,with the DC bus as the input port,the input impedance characteristics of the load subsystem including RLC are analyzed.The decrease of the bus voltage will cause potential resonance points in the load subsystem,which is not conducive to the stability of the subsystem.The stability analysis of source-end subsystem of multi-Boost DC/DC converter with V-I and I-V droop control is carried out.Firstly,two small-signal models of boost DC/DC converter with droop control are established,and the influence of controller parameters and droop coefficient(virtual impedance)on the stability of the converter is analyzed.Secondly,the output impedance model of source-end subsystem with V-I and I-V droop control is derived.It is found that the output impedance characteristics are affected by the main circuit parameters,voltage outer loop proportional controller and droop coefficient(virtual impedance).Then the state space model of source-end subsystem based on V-I and I-V droop control is established,and the characteristic value method is used to analyze the similarities and differences of parameter stability regions of two kinds of droop controllers when N parallel Boost DC/DC with resistive and inductive loads.When V-I or I-V droop control is adopted,the stability region of the controller parameters of each subsystem at the source does not change with the increase of the number of parallel units.When the V-I droop system decreases with the virtual impedance,or the I-V droop system increases with the virtual impedance,the system stability becomes worse.Finally,the accuracy of the results is verified by the time domain simulation method.Stability analysis of ’source-load’ system with constant power load cascade connection between parallel Boost DC/DC network with V-I and I-V droop control and converter interface.The impedance model of the ’source-load’ cascade system is established,and the capacity of different droop control methods for the ’source-load’cascade system with constant power load is analyzed by impedance method.The change of the load capacity of the two kinds of droop control Boost DC/DC systems is consistent with the stability direction.When the V-I droop system increases with the virtual impedance,or the I-V droop system decreases with the virtual impedance,the load capacity increases.Under the same virtual impedance,the load carrying capacity of multiple parallel V-I droop systems is greater than that of I-V droop systems,and the resonant frequency is higher than that of I-V droop systems.Under the same droop control method,with the increase of the number of parallel converters,the load capacity of the ’source-load’ cascade system decreases,but the resonant frequency increases.Finally,the loading capacity is verified by time domain simulation method.