Small-Signal Stability Analysis of Different Outer-Loop Control Combinations under AC/DC Decoupled Control Frame for Hybrid MMC

The AC/DC decoupled control is applicable for improving the DC fault-ride-through performance of the hybrid modular multilevel converters. There exist multiple possible control combinations for the outer loops of the decoupled control frame. This paper analyzes the impact of several outer-loop control combinations on the small-signal stability characteristics. The unstable modes and corresponding participation factors are compared via time-domain eigen-value studies. The propagation of oscillation between AC and DC network, and the maximum transferable active power are also analyzed and validated by electromagnetic simulation.