The Energy-Based Control Frame and its Limitation for Half-Bridge MMC

Energy-based control (EBC) for the half-bridge modular multilevel converter (MMC) is emerging as a promising control scheme in decoupling the AC and DC dynamics and enhancing the small-signal stability. The basic principle of EBC is to introduce new control freedom for regulating the DC component of the arm output voltage. This paper proposes a general control frame for EBC, considering multiple control objectives and structures. The advantage of EBC is highlighted by a comparison analysis of the eigenvalues with the conventional vector-based control (VBC) scheme. The limitation of EBC on the feasible operation zone is revealed by analyzing the positivity condition for the arm modulation signal. The limited capability of providing capacitive reactive power is validated by electromagnetic simulation.