Frequency and Voltage Regulation in Hybrid AC/DC Networks

Hybrid ac/dc networks are a key technology for sustainable electrical power systems, due to the increasing number of converter-based distributed energy resources such as solar or wind. In this article, we consider the design of control schemes for hybrid ac/dc networks, focusing especially on the control of the interlinking converters (ILCs). We present two control schemes: first for decentralized primary control and second a distributed controller to achieve secondary control objectives as well. In the primary case, the stability of the controlled system is proven in a general hybrid ac/dc network, which may include asynchronous ac subsystems. Furt hermore, it is demonstrated that power sharing across the ac/dc network is significantly improved compared to previously proposed dual-droop control. The proposed scheme for secondary control guarantees the convergence of the ac system frequencies and the average dc voltage of each dc subsystem to their nominal values. An optimal power allocation is also achieved at steady state. The applicability and effectiveness of the proposed algorithms are verified by advanced simulations on a test hybrid ac/dc network in Simscape Power Systems.