  Hybrid AC/DC networks are a key technology for future electrical power
systems, due to the increasing number of converter-based loads and distributed
energy resources. In this paper, we consider the design of control schemes for
hybrid AC/DC networks, focusing especially on the control of the interlinking
converters (ILC(s)). We present two control schemes: firstly for decentralized
primary control, and secondly, a distributed secondary controller. 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. Furthermore,
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 respectively. An optimal power allocation is also achieved at
steady-state. The applicability and effectiveness of the proposed algorithms
are verified by simulation on a test hybrid AC/DC network in MATLAB / Simscape
Power Systems.
