Stability Of Low Voltage DC Power Distribution System

In recent years, with the rapid development of distributed power and power electronics, power and load in grid has obvious changes, more DC devices have been used. Compared with traditional AC grid, low voltage DC power distribution system has many significant advantages, such as easy to control, low loss, high power quality, and does not require tracking the frequency and the phase of voltage. Therefore DC power distribution system has greater controllability and reliability that is possible more suitable for distributed power and load access. Currently, droop control strategy is studied widely in DC power distribution system which has good scalability and redundancy. In this paper, aiming at the problem of stability of low-voltage DC power distribution system, the research includes the following main content:1) The general structure of DC microgrid and the principle of droop control are described. Simulation model are built and parameters are selected for the converters of low voltage DC power distribution system, including AC/DC rectifier and DC chopper. AC/DC rectifier used SVPWM control strategy, and DC/DC converter used voltage and current double loop control strategy. The time-domain simulation of converters is completed by Matlab/Simulink.2) According to the structure and control strategy of DC microgrid, the state space equations of system is written and the small signal stability of DC microgrid is analyzed to obtain the eigenvalues of system when different droop factor is taken. Numerical results show that DC micro-grid which sets reasonable controller parameters and filter parameters remains stable when takes a larger droop factor. To further verify the validity of analytical methods, the timedomain simulation test based on DC micro-grid was implemented to demonstrate the correctness of the small signal stability analysis.3) For the problem of power sharing of low voltage DC power distribution system, the impact of the line resistance on power sharing among distributed generators is analyzed and the reason why the line resistance cannot be ignored is pointed out. An improved droop control method based on public bus feedback signal is proposed to achieve load power sharing at the same loading rate among distributed generators. The simulation test based on MATLAB/Simulink was implemented to demonstrate the proposed approach.