Protection system is a crucial part of the power grid. It protects people, equipment and property. Reliability of such mission critical systems is of extreme importance. Protection systems have strict requirements to reliability including dependability, security and timeliness. Formal methods for verification provide such rigorous testing of the software and provide definitive proof of the system properties.
In this project the student was working towards verifying protection function for power distribution network. This project focused on the formal modeling of the protection functions in a closed loop with the model of the electrical distribution network. This approach hopes to gain advantages of the formal verification and closed loop validation.
The student developed closed loop model of the electrical network together with its protection system. Both controller and the distribution network have to be modeled in the discrete domain using IEC 61499. Then using automated tool convert the model of a closed loop system into formal model in SMV.
Modeling dynamic power system model without relying on differential equations has proven to be challenging. Consequently, the system was considered as a “black box” and modeled in terms of observable behavior using state space. State variables represent state of the whole distribution network. State variables were defined in terms of state of current transformers, since they reflect changes in the power flow in the system.
The model is validated via simulation and was compared with comprehensive model of the network in Matlab Simulink. In future work, the model will be used to formally verify reliability requirements of the protection system.