Formalizing Performance Degradation Strategies as an Enabler for Selfhealing Smart Energy Systems

abstract

Smart behavior in reactive systems can be achieved when systems can react appropriately to environmental changes. These adjustments in behavior can be achieved through predefined strategies. In this work, we present a formal specification of performance degradation where the overall performance of the system is intentionally lowered in order to ensure high availability of the core services of the system in fault scenarios. We demonstrate the application of this strategy in the energy domain. Power outages can be foreseen as one of the big challenges in the smart grid functionality. In such a power outage situation, it is essential to support high priority services at all times. During such situations, to prolong support for high priority services , we propose an approach using constraint-based formal modeling by developing the degradation strategy. A service is selected or deactivated based on its priority, energy consumption and its performance contribution. As a consequence, when services have to be disabled due to insufficient available energy, the performance of the overall system degrades, but high priority services remain available. We validate our approach by using the Z3 SMT solver to identify a valid degradation strategy scheme for a fault scenario in the fortiss smart energy living lab demonstrator.