Decentralized Control Strategy for Hybrid Microgrid Cluster Bidirectional Interlinking Converters Based on Sub-Grid Priority Drive

With the increasing penetration of renewable energy, hybrid AC-DC microgrid clusters (HMG-Cluster) are gradually becoming resilient solutions for new power systems. As a key component for interconnecting and synergizing AC and DC microgrids, bidirectional interlinking converter (BIC) enables efficient power management and fault ride-through in HMG systems. However, how to control and optimize the power allocation scheme of BIC remains a fundamental challenge. To fill the gap in the existing research, a priority-driven BIC decentralized control strategy is proposed to ensure the optimization of the power exchange of the HMG-Cluster according to the different priorities and capacity requirements of the sub-grids in the system. First, the optimal power exchange model for HMG-Cluster is realized by taking the normalized AC frequency and DC voltage values as the state deviation factors of the sub-grids, and proposing a power exchange strategy with the objective of minimizing the total global deviation factor and considering the sub-grid priority and power supply capacity. Further, the optimal solution of the proposed optimization problem can be obtained by transforming the proposed power exchange model into a solvable mathematical problem and by constructing and solving the Lagrange function of the proposed optimization problem. Second, according to the optimal power exchange objective, A decentralized quasi-sag control strategy based on BICs is proposed. Since the BIC in this strategy only needs to detect the state deviation factor of the local AC frequency or DC voltage, the decentralized optimal power autonomous cooperative control can be achieved. In addition, since the main controller therein achieves accurate power tracking through dual voltage-current closed-loop, which in turn enables the HMG-Cluster energy to operate in the state of minimizing the overall deviation factor. Finally, the effectiveness of the proposed strategy is verified based on two simulation cases on a hardware-in-the-loop (HIL) system. Based on the simulation results under the two cases, the results show the control strategy proposed can be operated under sub-grid priority-driven, i.e., the state deviation coefficient ratios of the sub-grids are always consistent regardless of the system load surge or fault conditions, and the sub-grids with higher priority have higher voltage index and priority index compared to the global shared control strategy. In addition, in the case of insufficient system dispatchable power, the low-priority sub-grids will ensure that the loads with high priority are restored first by automatically dumping loads and increasing the deviation factor. Therefore, the optimization objective value of the control strategy proposed is smaller compared with the global shared control strategy. In summary, the following conclusions can be drawn: (1) The optimal power exchange model for HMG-Cluster with the objective of minimizing the global total deviation factor is constructed. The model is able to realize autonomous power interaction among sub-grids of the HMG-Cluster system based on the self-optimizing cooperative control of the BIC state deviation factor. (2) A decentralized quasi-sag control strategy for a BIC is proposed. Since the BIC in this strategy only needs to detect the local AC frequency and DC voltage signals, a decentralized quasi-sag control strategy based on BIC is proposed and used to realize power autonomous synergy in HMG-Cluster. (3) The decentralized control strategy based on priority driven HMG-Cluster system proposed in this article is a fundamental research that can achieve compatibility with any advanced control algorithm and achieve higher level control objectives in future research work. © 2024 China Machine Press. All rights reserved.