Small-Signal Stability Analysis of a VSC-MTDC System for Investigating DC Voltage Oscillation

In this study, the DC voltage oscillation mechanism is investigated based on the linearized models of a voltage-source converter (VSC)-based multiple terminal DC (MTDC) system. First, the mechanism of DC voltage oscillation generation is revealed. DC voltage or DC voltage droop-controlled VSCs are identified as the DC voltage oscillation sources when master–slave or DC voltage droop control is separately applied to the VSC-MTDC system. Meanwhile, the active power-controlled VSC is equally regarded as a constant power source that does not provide any oscillation to the VSC-MTDC system. Subsequently, the impact of the dynamics of VSCs and MTDC network on the DC voltage oscillation is separately investigated. It is theoretically verified that the negative eigenvalues of the MTDC network conductance matrix can reduce the stability of the DC voltage oscillation. The constant power load is identified as the physical mechanism of a problematic scenario that induces DC voltage oscillation in the generalized VSC-MTDC system. Moreover, it is demonstrated for the first time that the steady-state power flow may cause DC voltage oscillations when the power flow is reversed. Finally, two VSC-MTDC systems, which individually adopt master–slave and DC voltage droop control, are presented to validate the findings using the standard MATLAB SIMULINK model.