Robust Control and Stable Performance of a Grid-Tied Dumbbell-Type Multilevel Converter Interfaced DG Unit Using Differential Flatness Theory

Abstract

This paper proposes a robust control technique based on Differential Flatness Theory (DFT) for a grid-tied Distributed Generation (DG) to mitigate several uncertainties while controlling the DG for its main functions. A recently introduced structure named Dumbbell Type (D-type) Switched-Capacitor Multilevel Converter (SC-MLC) with a single DC source, utilizing only ten switches with no further series diodes, is employed as an interfacing converter. The DFT enriched by the Lyapunov criterion is developed for the SC-MLC to guarantee both the stable performance of the proposed DG-based supply system and the robustness feature against any unwanted uncertainties. The control inputs of the D-type converter are initially shaped using the reactive and active power-based flat outputs without the observance of stability issues. To attain the proposed robust control inputs, a Lyapunov function is properly defined and engaged in providing the global asymptotic stability for the grid-tied multilevel converter by means of the proportional and integral errors of the flat outputs under the model uncertainties and parameter change. Lyapunov coefficients are subsequently assessed through their related active and reactive power errors. Both simulation and experimental results are employed to verify the ability of the proposed generation system in robust performance against parameter alternations, transient stability during contingency events at the grid side, and dynamic and steady state stability under different scenarios of power sharing with direct active and reactive power flows control.

Keywords

• Multilevel converter
• grid-tied distributed generation (DG)
• D-type switched capacitor multilevel converter (SC-MLC)
• differential flatness theory (DFT)
• Lyapunov stability
• robust controller