Universal constrained power flow control for grid–tied power electronics converters

With the increasing amount of energy resources connected to the electric powered grid via power electronics converters, commonly referred to as inverted–based resources (IBR), the inertia and robustness of power systems have been greatly impacted. Grid–forming control arose as a solution to these issues by operating the IBRs as voltage sources. However, limiting the amplitude of the converter current became an issue. In this context, the concept of a constrained control strategy capable of limiting the amplitude of the system variables gained relevance. As a solution, this work proposes a nonlinear model predictive control strategy, that is categorized neither as grid–forming nor grid–following. It is capable of controlling the power flow through the converter to the grid, without a phase–locked–loop, allowing constraint satisfaction even in the condition of unknown grid impedance. The control strategy was tested through simulation of nominal operation and during symmetric and asymmetric faults. The results proved its effectiveness in achieving these objectives even in cases in which the grid behavior cannot be predicted.