Analysis and Control of Multi-Mode Oscillations in Multi-Infeed MMC-HVDC Systems

In recent years, the phenomenon of wideband oscillation has emerged as a significant concern for small-signal stability in modular multilevel converter (MMC) based high-voltage direct current (MMC-HVDC) systems. Sub/super-synchronous oscillations (SSOs) and high-frequency oscillations (HFOs) have been frequently reported globally, prompting the implementation of numerous control strategies aimed at mitigating these oscillatory events. However, in more complex systems, such as multi-infeed MMC-HVDC systems, there exists the potential for multi-mode oscillations, which refers to the concurrent occurrence of multiple independent oscillation components at a single electrical node. This novel oscillation issue in multi-infeed MMC-HVDC systems is still lack of relevant research. To address this issue, an analytical approach using whole-system impedance analysis alongside a parameter sensitivity index is employed to investigate multi-mode oscillation phenomena in a multi-infeed MMC-HVDC system. Furthermore, an adaptive control strategy based on fast oscillation frequency detection is proposed, which demonstrates effectiveness across various operation conditions through case studies.