Direct current power system stabilizers for HVDC grids: Current status

Abstract

A power system stabilizer (PSS) is a control system integrated into the control structure of specific generation units within AC grids. It monitors current, voltage, and machine shaft speed. Analysing these variables, the PSS generates appropriate control signals to the voltage regulator unit, aiming to damp system oscillations. With the advancement of high-voltage direct current (HVDC) overlaid high-voltage alternative current (HVAC) grids, it is anticipated that direct current power system stabilizers (DC-PSS) will be developed to perform a similar role as their AC counterparts. DC-PSS will be responsible for monitoring and controlling DC voltage levels, ensuring stable operations. This paper focuses on DC-PSS in HVDC grids, designed to ensure stable operation and mitigate voltage fluctuations. Unlike conventional AC power systems, HVDC includes only DC voltage and power. The input signal for DC-PSS is the variations in DC voltage, and the output signal is proportional to the power changes at the specific bus where the DC-PSS is installed, aiming to minimize DC voltage oscillations. These characteristics pose significant challenges in DC-PSS. The paper addresses the challenges and highlights issues such as inertia and low-frequency oscillations associated with DC-PSS. Various control methods are presented and a comparison is made among these methods.