Control of grid side converters under constraints in unbalanced operating conditions. A Lyapunov framework

This work presents a Lyapunov-based control of a grid side converter of distributed energy systems. The analysis focuses on the constraints imposed by unbalanced operation and thermal limits. On one side, the proposal, which considers symmetrical components, allows controlling the converter in such a way that it is able to deliver constant real power to the grid in the presence of highly unbalanced voltages. On the other side, to solve the operation under thermal constraints, the references in control loops are adapted. Both issues, unbalanced operation but also thermal constraints, are considered in a sole Lyapunov function, formed by the union of a set of Lyapunov ones. This ensures the stability of the whole system by using simple PI controllers. Finally, different scenarios, strong disturbances and reaching current limits are explored in simulation results.