As the control systems and mechanical structures of wind turbines have become increasingly complex, it has simultaneously become more difficult to guarantee that a wind turbine structure is not damaged in any given situation. To avoid damage to the wind turbine a safety supervisor system, which can initialise an emergency shutdown, should be implemented. The purpose of a safety supervisor is to keep the components of the wind turbine from being damaged.

This project considers the design of a safety supervisor system which is able to guarantee the safety of complex wind turbine systems. In particular, multivariate safety supervisor systems are considered. This is done using the concept of safety envelopes, in which the system can be shut down without structural damage.

To construct safety envelopes, a model-based framework of barrier certificates, Positivstellensatz and sum of squares polynomial decomposition are considered. The framework enables an inclusion of a bounded stochastic wind disturbance and the emergency shutdown procedure in the safety envelope construction. To utilise this framework, a polynomial wind turbine model is developed. The model is developed such that structural safety critical components of the wind turbine are included. The resulting model is able to produce emergency shutdown trajectories of a typical 5-MW wind turbine.

The construction of safety envelopes is formulated as sum of squares programs (SOSP), with optimisation criteria related to the safety envelope size. The SOSP of the complete wind turbine system turns out to be computational complex. To reduce the complexity of the calculations, two different approaches are tested; safety envelope construction of separate subsystems and a compositional technique which includes the subsystem interconnections in the envelope construction. Both methods are implemented and tested on the fictitious NREL 5-MW wind turbine in the simulator FAST. The results indicate that multivariate safety supervisors, that guarantee the safety of complex wind turbines, can successfully be designed using this method.