Sliding Mode Robust Control Based Active-Power Modulation of Multi-Terminal HVDC Transmissions

This paper presents a sliding mode robust control based active-power modulation (SMAPM) for voltage source converter based multi-terminal HVDC (VSC-MTDC) systems, which could enhance the stability of the onshore power system subjected to disturbances by fast changing transmitted power of onshore VSCs. The development of the SMAPM includes three steps. First, the onshore disturbed ac system could be divided into two areas with generators sharing different swing modes. The center of the inertia (COI) reference frame is utilized to be the representative of the area's behavior. Secondly, an index called sensitive index is proposed to quantify the sensitivity of generator angular speed to the active-power change of an onshore VSC. A strategy is developed to determine the modulation direction and intensity of each onshore converter. Thirdly, the final control law is derived based on sliding mode variable structure control method. Simulation verifications are run in a four-machine ac system and a modified New England 39-bus system.