A Dual-Level Optimal Control Strategy for Offshore Microgrid Considering Efficiency and Operation Cost in Wide Load Range

Both efficiency and operation cost are the key to offshore microgrids operation. At the same time, due to the lack of external energy support, the paralleled converters in offshore microgrids often needs to handle the operation in a wide load range. In that case, this article proposes a dual-level optimal control framework to improve overall operation performance of offshore microgrid with paralleled converters within a wide load range. First, a normalized nonlinear relationship between power loss and operation cost of paralleled converters is established. Based on it, a multiobjective optimal function is established. Then, the optimal operation condition is derived by Lagrange multiply method with the established converter performance index. Furthermore, optimal power sharing considering both efficiency and operation cost is proposed at first level. Then, second level control is proposed to improve system performance in a wide load range. The proposed decentralized dispatch strategy is realized by a consensus protocol mechanism with the mealy machine based on the established performance index. Experiment results in a scaled-down prototype are given to validate the effectiveness of the proposed dual-level control strategy. The proposed strategy is able to optimize performance of paralleled converters under different power profiles.