  This paper proposes a distributed design method of controllers having a
glocal (global/local) information structure for large-scale network systems.
Distributed design, independent design of all subcontrollers that constitute a
structured controller, facilitates scalable controller synthesis. While
existing distributed design methods confine attention to the decentralized or
distributed information structures, this study addresses distributed design of
glocal-structured controllers. Glocal control exploits the nature that network
system's behavior can typically be represented as a superposition of spatially
local fluctuations and global interarea oscillations by incorporating a global
coordinating subcontroller with local decentralized subcontrollers. The key
idea to distributed design of glocal controllers is to represent the original
network system as a hierarchical cascaded system composed of reduced-order
models representing the global and local dynamics, referred to as hierarchical
model decomposition. Distributed design is achieved by independently designing
and implementing subcontrollers for the reduced-order models while preserving
the cascade structure. This paper provides a condition for existence of the
hierarchical model decomposition, a specific representation of the hierarchical
system, a clustering method appropriate for the proposed approach, and a robust
extension. Numerical examples of a power grid evidence the practical relevance
of the proposed method.
