This paper attempts to shed light on potential stability issues in MMC-based HVDC systems. In particular, the focus is given to the influence of converter control parameters on the small-signal stability of an HVDC system equipped with large fault current limiting DC reactors. Those DC reactors are often required to reduce the rate-of-rise in fault currents and thus to limit the currents below the maximum interruption capability of DC Circuit Breakers (DCCBs). However, the introduction of large DC reactors can degrade the system stability. The small-signal stability analysis of an MMC-based HVDC system model, including control loops, DC reactors, and frequency-dependent HVDC cables, corroborates the unstable behavior of the system in the presence of large DC reactors. Furthermore, the influences of the bandwidth of the closed-loop power controller and the DC voltage droop parameter on the stability margin of the system are investigated. The obtained results suggest that special attention should be paid to the design and parameter of the controller in each control mode when MMC-based HVDC systems are equipped with large DC reactors.
Kosei Shinoda, Abdelkrim BENCHAIB, Jing DAI
Presented at EPE’20 ECCE Europe