  Inter-area oscillations in bulk power systems are typically poorly
controllable by means of local decentralized control. Recent research efforts
have been aimed at developing wide- area control strategies that involve
communication of remote signals. In conventional wide-area control, the control
structure is fixed a priori typically based on modal criteria. In contrast,
here we employ the recently-introduced paradigm of sparsity- promoting optimal
control to simultaneously identify the optimal control structure and optimize
the closed-loop performance. To induce a sparse control architecture, we
regularize the standard quadratic performance index with an l1-penalty on the
feedback matrix. The quadratic objective functions are inspired by the classic
slow coherency theory and are aimed at imitating homogeneous networks without
inter-area oscillations. We use the New England power grid model to demonstrate
that the proposed combination of the sparsity-promoting control design with the
slow coherency objectives performs almost as well as the optimal centralized
control while only making use of a single wide-area communication link. In
addition to this nominal performance, we also demonstrate that our control
strategy yields favorable robustness margins and that it can be used to
identify a sparse control architecture for control design via alternative
means.
