Distributed feedback optimisation based optimal power flow control in fully inverter based islanded AC microgrids

A novel distributed feedback optimisation (FO) based control method is proposed to control grid-forming inverters (GFMIs) in fully inverter-based islanded AC microgrids (MGs). The proposed controller has two control layers. The upper layer uses FO to calculate the frequency and voltage setpoints of GFMIs, whereas the lower layer makes GFMIs track these setpoints. The proposed control method takes advantage of the flexibility of voltage control to regulate the system frequency, maintain both active power and reactive power sharing accuracies, keep bus voltage within allowable range and meanwhile preserves the optimality of the closed-loop system in term of optimal power flow. The gradient descent method is used to solve the proposed FO problem based on the real-time measurements in the MGs, which is implemented in a distributed way, and thus eliminates the need for a central controller. Case studies show the effectiveness of the proposed method. The authors use distributed feedback optimisation to continuously drive microgrids to their optimal states in optimal power flow problem in real-time. The time-scale of optimisation is shorter than the existing hierarchical control used in microgrids. Therefore, microgrids can track the optimal operating point of optimal power flow more quickly.image