Research On Large Signal Stability Of Charging Station Based On DC Microgrid Structure

The traditional automobile industry has brought people’s convenience to life while also bringing about environmental pollution caused by excessive use of fossil energy.With the increasing population and car ownership,traditional fossil fuels are gradually decreasing.How to use renewable energy and develop new energy vehicles is urgently needed,and electric vehicles and charging stations are rapidly developing.The charging station can efficiently supply power to multiple electric vehicles,and there are also other problems.In particular,the fast charging and charging mode with higher charging power will cause greater disturbance to the entire charging system,which in turn will generate a large disturbing the transient stability problem and even crashing the entire charging system.Therefore,it is necessary to study the large disturbance transient stability of electric vehicle charging stations.In this paper,the different ways and characteristics of electric vehicle battery charging are given firstly,and the electric vehicle battery is regarded as a kind of constant power load in the charging process.This paper gives two types of topology.The main differences between the two topologies is the AC/DC converter and whether containing distributed power supply.The influence of the negative impedance characteristic of the constant power load on the system operation is analyzed,and the negative impedance characteristic which has the positive feedback process is more difficult to stabilize when subjected to large signal disturbances than resistive loads.Then,the large-signal stability of the distributed power supply charging station is studied.The mathematical model of the Buck converter is analyzed and the large-signal model of the Buck converter is obtained.The theory of mixed potential function and its stability theorem are introduced.The theory is used to analyze the large signal stability of the distributed power supply charging station.According to the third theorem of stability,the large signal stability criterion of the system is obtained.According to the criterion,the large signal stability of the system is mainly related to the source converter’s voltage loop proportional coefficient and the total load power.There is conservative domain in the theoretical and simulation boundaries.The new stable stability boundary is obtained by the improved large signal stability analysis method.The effectiveness of the proposed method is verified by simulation and experiment.Finally,the large signal stability of distributed power supply charging station is studied.The large signal model of voltage three-phase bridge PWM rectifier is given.The stability criterion of the system is obtained by the theory of mixed potential function and the third theorem of stability.According to the criterion,the large signal stability of the system is related to the PWM rectifier voltage loop proportional coefficient,the current loop proportional coefficient,the AC side filter inductor,the AC side resistor and the DC side storage capacitor.The large signal stability analysis method obtains a new stability criterion.It can be verified by simulation that the method can reduce the conservative domain for the PWM rectifier.The stability of the large signal of the charging station after adding the photovoltaic system is analyzed.It is known that the addition of a photovoltaic system can increase the large signal stability domain of the system,and the added stability domain is the same as the output power of the photovoltaic system.However,changes in light intensity and temperature change the output power of the photovoltaic system,which in turn affects the large signal stability boundary.