Multithreaded State Controller for Grid-Connected Converter With Imposed Limits

This article proposes an innovative approach to control a grid-connected converter. The method combines the versatility and high-quality control offered by the state-feedback controllers for linear plants with the ease of imposing limits on the controlled variables offered by the cascaded control systems. The method is groundbreaking in its ability to bridge the gap between the elegance of the full-state-feedback control structure and its lack of popularity among power electronics engineers and possibly also other groups of practitioners. A multithreaded state controller is proposed in the form of three state controllers: one to control grid currents and dc-link voltage if limits of the currents are not reached, and two state controllers that are put into the closed loop if one of the current limits is reached. A complete design procedure is proposed, including the selection of all gains present in the three state-feedback controllers using the pole placement method. An algorithm of soft switching between the three control signals is also developed. Sharing the desired dynamics between the threads is fulfilled thanks to the eigenstructure assignment introduced to overcome the problem of multiple solutions by choosing the most orthogonal eigenvectors. The proposed control system is then verified in a simulation, and its high practicality is demonstrated experimentally.