Decoupled Power Control for a Modular-Multilevel-Converter-Based Hybrid AC–DC Grid Integrated With Hybrid Energy Storage

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Abstract
This paper presents a decoupled power control strategy for a modular multilevel converter (MMC)-based hybrid ac-dc grid integrated with a hybrid energy storage system (HESS). This system can mitigate the active power fluctuation caused by intermittent renewable generation and also realize reactive power compensation as required by voltage regulation. The proposed hybrid ac-dc system is novel in that batteries and supercapacitors are distributed into the upper arm and lower arm of MMC, respectively. It is therefore possible to design fully decoupled power control and simultaneously optimize the performances of batteries and supercapacitors. Firstly, the system modeling and operational principles of MMC are briefly introduced in this paper. Based on these analyses, the power decoupling between upper arm and lower arm is presented to realize different control objectives. Moreover, battery state-of-charge (SOC) balancing control and supercapacitor voltage control are presented also, which are crucial for ensuring the normal operation of these energy storage components and the proposed MMC-based hybrid ac-dc grid. Finally, the proposed system and its control strategies are verified by laboratory experimental results.
Funding Information
  • Nanyang Technological University (NTU-SUG M4081608)

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