Ratatoskr: Wide-area Actuator RPC over GridStat with Timeliness, Redundancy, and Safety
The development of the communication infrastructure for the north-American electrical power grid has failed to fully incorporate important developments in the field of computer science, affecting the stability and efficiency of the power grid as a whole. The current power-grid communication standard, SCADA, utilizes protocols specialized for centralized communication, hampering communication between field sites key for envisioned improvements of power grid safety and efficiency. Further, a number of different proprietary communication protocols are in use, making communication between power utility companies very difficult.
GridStat is a communication infrastructure designed for a power grid environment that solves many of the problems with the current situation. GridStat uses a specialization of the publish-subscribe middleware paradigm, status dissemination, that takes advantage of the semantics of status data to provide flexible acquisition of power-grid data with multiple dimensions of QoS semantics. The middleware approach enables communication between utilities independent of proprietary network protocols, and allows enhanced network features such as forwarding data through multiple redundant paths. While GridStat provides excellent support for data acquisition, the publish-subscribe architecture supports only one-way communication and provides syntax and semantics unsuitable for control communications.
This thesis presents Ratatoskr, a novel scheme for control of actuators using GridStat communication. It constructs a two-way communication channel on top of GridStat publish/subscribe paths, and utilizes the QoS semantics and middleware properties GridStat
provides. For control communication Ratatoskr uses remote procedure call (RPC), providing programmer friendliness and familiarity. The QoS semantics of GridStat are drawn upon to provide the timeliness required for power-grid operation. Reliability concerns are addressed by ing three redundancy schemes, ACK/resend, transmitting multiple copies of a single packet, and spatial redundancy through GridStat’s redundant routing paths feature. Additionally, pre- and post-condition expressions over GridStat status variables are built into call semantics. The architecture and design of Ratatoskr is presented, along with results from an evaluation of a
prototype implementation.
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