Disturbance-Tailored Super-Twisting Control for NPC Converters Under Unbalanced Grid Conditions

This article presents a high-performance control scheme for three-level neutral-point-clamped converters under unbalanced grid conditions. In the current tracking loop, a reset adaptive positive/negative sequence observer is developed for effective grid voltage synchronization, ensuring accurate reference current calculation and flexible objective adjustment of active/reactive power. For the voltage regulation loop, an adaptive-gain disturbance-tailored super-twisting controller is proposed to effectively address various forms of uncertainties, while maintaining a balance between dynamic response and steady-state control performance. In addition, a low-power peaking-free dead-zone high-gain observer is introduced to enhance voltage tracking robustness by minimizing overshoot and mitigating the impact of noise. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {L}_{2}$</tex-math></inline-formula> gain stability of the reset adaptive grid-voltage observer in handling noise is established, and the finite-time convergence of the adaptive-gain disturbance-tailored super-twisting controller is rigorously proven. Finally, experimental validation demonstrates the effectiveness and superiority of the proposed control scheme.