Cooperation for aggregating complex electric power networks to ensure system observability

In this paper, we study the cooperative observability conditions for the local observers formulated on large-scale power systems. A complex large-scale power system model can be considered as a union of several low-dimensional sub-systems where local observers are to implemented. Even if the large-scale system is observable, local observers formulated on such sub-systems may be unstable if the resulting local sub-systems are un-observable. The aggregated effect of the sub-systems, although, may lead to observability. Under certain assumptions, we show that the un-observable local sub-systems can lead to observability by allowing appropriate cooperation among the local observers. In particular, the local error covariances of the local observers can be assimilated such that they preserve a certain (approximated) structure of the global error covariance. This results into stable local observers for un-observable, but, cooperating sub-systems. We provide simulations to assert the findings in the paper.