Study On Charateristics Of Short-circuit Current Of Micro Power Grid

In order to solve the control and high expenditure problems as distributed power connecting power grid, the concept of micro power grid is proposed and increasingly becomes a research focus. Micro grid can not only be applied to grid-connected operation, but also can run independently, having great flexibility and can improving the power supply reliability of distributed power. The connection of micro power grid to power grid can change the traditional distribution network structure, which converts the radial network with single power resource into two-way power supply network with more powers. Short-circuit fault current caused by micro power grid can also change the value and direction of current,effecting normal operation of original protection equipment. Study on short circuit current can provide data support for the protection strategy formulation, which is of great significance.After converting non power frequency ac or dc to power frequency ac power,distributed power can be connected to power grid through power electronic interface running in parallel operation. Power electronic devices have quick response, leaving short circuit characteristics of distributed power different with those of traditional generators. So inverter control method is needed to design when analyzing the fault characteristics.The paper briefly introduces the basic principle and main purpose of three different kinds of inverter control modes, which are the constant power(PQ) control,constant frequency control(V/f) and droop control.Secondly, coordinate transformation of the mathematical model of three-phase inverter is conducted. The design methods of the PQ control and V/f control inverter distributed powers are studied as well. Then the parameters of every control link are calculated. And through the frequency domain analysis, the performance and stability of each part is verified.Based on Matlab/Simulink simulation platform, the simulation models of PQ control and V/f control distributed powers are established, verifying the reliability of every link. Micro power grid model is established, and the simulation results show that the model is verified to be effective and reliable. Based on this micro grid, respectively running independently and connecting to power grid, the different short circuit faults are simulated, and characteristics of different short circuit current of short faults are compared and analyzed.