Online Optimal Dual Harmonic Injection Strategy for MMC-SESS under Wind Power Fluctuations

A modular multilevel converter with an integrated supercapacitor-based energy storage system (MMC-SESS) is a promising solution to renewable energy integrations. However, the capacitor voltage ripple reduction of the MMC modules is significantly correlated to its lightweight design and operational performance. In this paper, an online optimal dual harmonic injection strategy is proposed for MMC-SESS to reduce its capacitor voltage ripples under wind power fluctuations. Firstly, the mathematical model of instantaneous arm power is established, considering dual harmonic injection and its parameter constraints. Based on this, online optimization of the instantaneous arm power model is conducted via particle swarm optimization (PSO) algorithm. Finally, simulations on PSCAD/EMTDC have shown that the proposed strategy can effectively suppress the capacitor voltage ripples and improve the efficiency of parameter optimization, enabling dual harmonic parameters to be optimized online under wind power fluctuations.