Small-signal Stability Assessment Method for DC Distribution System with Multiple Voltage Levels

With the rapid development of DC distribution technology, the DC distribution systems have gradually shown the remarkable characteristics of multiple voltage levels, multiple DC buses and multiple power electronic converter access, which leads to more complex impedance coupling relationship among converters and the increasingly prominent problem of system stability. In order to evaluate the small-signal stability of the DC distribution systems with multiple voltage levels, the small-signal equivalent model of the system is established, and then the unified transfer function from all system input disturbances to any bus voltage is derived according to the different control modes of the DC transformers between adjacent buses. On this basis, the system stability assessment method is proposed. Furthermore, a distribution system with two-voltage level DC buses is taken as an example to analyze the impedance factors affecting the system stability. At the same time, the stability criterion based on the system equivalent loop gain is proposed. Finally, two system cases are designed, and the correctness of the proposed stability assessment method of the DC distribution system with multiple voltage levels is verified based on MATLAB/Simulink simulation. © 2022 Automation of Electric Power Systems Press. All rights reserved.