Multivariable Control of a Grid Forming System Based on Back-To-Back Topology

This paper presents steps of an unified modeling and controller design for a back-to-back converter applied to a grid forming system. The proposed procedure captures in a single state-space model a grid-interface converter with an output L filter, a grid-forming converter with an output LC filter and DC capacitor. This approach deals with a modern multivariable linear quadratic regulator control strategy for taking full advantage of the unified model. A full state-feedback controller has been designed for control the grid-interface converter input currents, grid-forming converter output voltages and DC-bus voltage behavior. Resonant controllers are also proposed to reject the current harmonic disturbance drawn by nonlinear loads. The controllers are designed and tested in PSIM, then simulation results are show to verify the proposed control strategy.