A modal decomposition approach to distributed observation and control for grid integration of renewable generation

To enable renewable generation to fully contribute to reliable grid operation with higher levels of penetration, it is important that such resources contribute to grid control, including faster time scale active power control that is valuable to small-signal electromechanical stability. However, given the small size and distributed nature of many renewables, it is unrealistic to assume that they will employ the type of centrally coordinated control schemes typical of large, central station synchronous generators. This paper proposes a distributed control design approach that allows each distributed renewable generator or energy storage device to be responsible for improving damping of a single oscillatory electromechanical mode. The consequence is that one may employ a static state feedback design (a classic LQ design is employed here) that requires information of state behavior only within a two-dimension invariant subspace associated with the mode of interest. Using a modal-focused Hautus matrix test of obervability, we develop simple tests to establish grid buses from which a desired mode may be most effectively observed from either local frequency measurement, or from a local measurement plus a single remote phasor measurement unit (PMU) signal. In this framework, the state information required may then be recovered by a Luenberger observer of as little as second order. That is, the local, distributed controller on a given renewable generator or energy storage device uses only one or two measurements, may be as simple as second order, and yet contributes to the system objective of improving modal damping.