Glocal control for network systems via hierarchical state-space expansion

In this paper, we propose a glocal (global/local) control method for large-scale network systems. The objective of the glocal control here is to suppress global propagation of a disturbance injected at a local subsystem based on the integration of different types of controllers, called global and local controllers. For the design of global and local controllers, we construct an aggregated model and a truncated model that can, respectively, capture global average behavior and local subsystem behavior of the network system of interest. Based on state-space expansion, called hierarchical state-space expansion, we show that a cascade interconnection of the aggregated model and the truncated model can be seen as a low-dimensional approximate model of the original network system, which has good compatibility with independent design of the global and local controllers. Furthermore, we show that appropriate integration of the global and local controllers can improve control performance with respect to global propagation of local disturbance. Finally, the effectiveness of the proposed method is shown through a numerical example of a benchmark model representing the bulk power system in the eastern half of Japan.