Optimal Operation of Flexible Devices for Bipolar DC Distribution Networks

The bipolar DC distribution network (Bi-DCDN) integrates a variety of flexible devices to control power flow, enhance operational levels, improve power quality, and integrate distributed energy resources. However, existing research on flexible devices mainly focuses on the primary and secondary control levels of Bi-DCDNs. The paper develops a general steady-state model for various flexible devices and utilizes it to optimize the operation of Bi-DCDNs at the tertiary level. Initially, the branch flow model of each flexible device, such as voltage balancer, DC transformer, DC power flow controller, and DC electric spring, is formulated separately. Subsequently, an optimization model is proposed to achieve the optimal operation of Bi-DCDNs, considering the variations in steady-state model parameters among different flexible devices and their distinct adjustable capacity. This model possesses favorable convexity properties, making it solvable in polynomial time. Finally, simulations are executed via a modified IEEE-33 node system. Numerical results show that the proposed model for coordinating multiple flexible devices can significantly improve the voltage quality of Bi-DCDNs, particularly reducing the voltage unbalance factor to approximately 8% in extreme asymmetric scenarios.