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Due to the high-performance requirements of power converters in industrial applications, sliding-mode control has drawn extensive research attention for its insensitivity against external disturbances. In order to ensure this advantage while suppressing the chattering problem caused by discontinuous switching functions, in this article, a fuzzy sliding-mode control (FSMC) strategy consisting of three control loops is proposed for three-phase three-level neutral-point-clamped active front-end rectifiers. In the power tracking loop, an improved super-twisting algorithm is proposed to enforce the tracking errors of active power and reactive power to bounded regions in finite time and guarantee the transient performance. Next, in the dc-link voltage regulation loop, the regulation error of dc-link voltage converges to a bounded region with a super-twisting extended state observer-based FSMC strategy. A simple but efficient proportional-integral controller is employed in dc-link voltage balancing loop to reduce the voltage difference between two dc-link capacitors. The proposed controller is characterized by attenuated chattering phenomenon and improved the dc-link voltage regulation performance, disturbance rejection ability, and power tracking performance. Experimental results are provided to verify the effectiveness and superiority of the proposed strategy. [ABSTRACT FROM AUTHOR]

In this article, a nonlinear high-gain observer (NHGO)-based second-order sliding mode (SOSM) control strategy is proposed for the three-phase three-level neutral-point-clamped (NPC) converter. This controller applies the advanced SOSM algorithm both in the voltage regulation loop and in the power tracking loop, which provides a fast dynamic for the dc-link voltage, and also assures a good steady-state behavior for the NPC converter. Additionally, an NHGO technique is implemented in the voltage regulator combining with the SOSM algorithm. The conventional observer-based controllers suffer from the destructive effects of measurement noise, and it can only be addressed by diminishing the observer gain, which sacrifices the observer property. The NHGO technique adopts a time varying gain, that is, high gain in transient while low gain in steady state, which minimizes the adverse influence of measurement noise. The tuning method of the proposed NHGO-based SOSM controller is given to simplify the implementation process. Finally, the simulation and experimental results of the proposed control scheme for the NPC converter are given and compared with the conventional PI controller as well as the well-known linear extended state observer-based control method, which validates the feasibility and superiority of the proposed controller. [ABSTRACT FROM AUTHOR]