Research On Small-signal Stability Of DC Distribution System Under Voltage Droop Control

With the development of power electronic technology and the access of distributed power supply, domestic and foreign scholars pay close attention to the construction of DC network. Compared with high voltage direct current power grid, the construction of the dc distribution network has relatively mature technology and better technical economy, timely theory study of dc power distributed network is of great significance. Stability is an important content in the research of dc power distribution network, the small signal stability of DC distributed network refers to the ability to keep stable operation state after small disturbance, namely the voltage level can to return to the initial value or turns to a new stable value.At first, the small signal model of a DC distributed network under voltage drop control was proposed in mis paper, and the model of key devices in DC network, namely the DC/DC converter, AC/DC converter, DC lines and loads, was built one by one, and the power filter, flagging external characteristic, PI control method, filtering, and many other details are well considered to make the small signal model more accurate. Second, a time domain simulation model was built in this paper with the help of PSCAD software, which can verify the availability of the small signal model by comparing the point step response of the two models. Finally, according to eigenvalue theory of small signal stability analysis, the eigenvalues of the small signal model were calculated,which can reflect the system stability. Also, by changing the model parameters such as constant power load, droop coefficient and line resistance, the impact of these factors on the small signal stability can be analyzed according to the change trend of eigenvalues, which can be verified by the time-domain simulation results. The results show that with the increase of the constant power load and droop control coefficient, the small signal stability of the dc power distribution network becomes worse. Line resistance increases can als reduces the small signal stability of the dc distribution network, but the influence degree is much smaller than the first two factors.