Study On Dynamic Power Balance Of Microgrid Based On Network Graph Theory

A microgrid is a low-voltage grid that combines various small distributed power sources to provide electrical energy to local loads.The microgrid has two modes of grid connection and islanding.The seamless switching between microgrid grid-connected and island operation mode is an important factor to ensure its safe and stable operation.However,the microgrid has a large system power difference from the unplanned switching of the grid to the island.,the topological structure and the drastic changes of the system parameters make the whole system in a transient unstable state.In order to make the microgrid recover to normal operation after unplanned switching,the dynamic power balance of the microgrid system needs to be studied.The network graph theory can not only solve the problem of micro-grid topology change,but also convert the time-domain equation to the S-domain,and then study the system.Therefore,this paper takes a microgrid as the research object,and proposes a dynamic power balance method based on network graph theory.Firstly,this paper introduces the grid-connected principle of distributed power supply with inverter interface,and analyzes the general model of inverter based on this,by establishing the relationship between distributed generation output power and inverter output voltage,the expression of the output voltage of the inverter in the time domain and finally establishes the equivalent model of the distributed inverter in the S-domain.Secondly,in view of the microgrid from interconnection mode into an island,after system power difference is very big,in the microgrid resistance and reactance difference is not obvious,and the microgrid nerwork topology and changeable problem,was proposed based on network grah theory method of microgrid power dynamic balance method.The method transforms the components in the microgrid into the S-domain for analysis,and uses the network graph theory to establish the dynamic model of the microgrid in the S-domain.Based on this,the microgrid is designed in the S-domain.The dynamic power balance analysis algorithm,and by changing the frequency-dependent Laplacian operator,can find the dynamic power balance relationship between the voltage and power of each load branch.Finally,this paper applies the dynamic power balance method based on network graph theory to the microgrid load shedding,and finds the relationship between voltage and power according to the dynamic power balance method based on network graph theory,and calculates the power value required to be cut of the system according to the voltage change value at the moment of grid-to-island conversion.Comparing the load shedding strategy considering the dynamic power balance relationship with the traditional low frequency load shedding strategy,the effectiveness and rapidity of the load shedding strategy considering the dynamic power balance relationship in the microgrid load shedding are verified.