Title: Transient Response Improvement for Interconnected Linear Systems: Low-Dimensional Controller Retrofit Approach,
Abstract: In this paper, we propose a method of designing low-dimensional retrofit
controllers for interconnected linear systems. In the proposed method, by
retrofitting an additional low-dimensional controller to a preexisting control
system, we aim at improving transient responses caused by spatially local state
deflections, which can be regarded as a local fault occurring at a specific
subsystem. It is found that a type of state-space expansion, called
hierarchical state-space expansion, is the key to systematically designing a
low-dimensional retrofit controller, whose action is specialized to controlling
the corresponding subsystem. Furthermore, the state-space expansion enables
theoretical clarification of the fact that the performance index of the
transient response control is improved by appropriately tuning the retrofit
controller. The efficiency of the proposed method is shown through a motivating
example of power system control where we clarify the trade-off relation between
the dimension of a retrofit controller and its control performance.