Small-Signal Stability Analysis of Multi-Terminal DC Grids

Abstract

This paper presents a detailed small-signal analysis and an improved dc power sharing scheme for a six terminal dc grid. The multi-terminal DC (MTDC) system is composed of (1) two voltage-source converters (VSCs) entities operating as rectification stations; (2) two VSCs operating as inverting stations; (3) two dc/dc conversion stations; and (4) an interconnected dc networking infrastructure. The small-signal state-space sub-models of the individual entities are developed and integrated to formulate the state-space model of the entire system. Using the modal analysis, it is shown that the most critical modes are associated with the power sharing droop coefficients of the rectification stations, which are constrained by the steady-state operational requirements. Therefore, a second degree-of-freedom compensation scheme is proposed to improve the dynamic response of the MTDC system without influencing the steady-state operation. Time domain simulation results are presented to validate the analysis and show the effectiveness of the proposed techniques.