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In this article, on the basis of an existing dual layer nested (DLN) adaptive sliding-mode control (ASMC) strategy, an observer-based sliding-mode control strategy with an improved DLN adaptive tuning mechanism (IDLN-ASMC) is proposed for a three-level neutral-point-clamped converter. The proposed controller not only ensures good system performance but also mitigates two problems of the existing DLN-ASMC strategy. Meanwhile, three objectives are achieved. First, an adaptive supertwisting algorithm is utilized in the power tracking loop to converge power tracking errors to bounded regions in finite time. Next, a disturbance observer-based IDLN-ASMC strategy is proposed in the dc-link voltage regulation loop to regulate the dc-link voltage to its reference value. Finally, a simple proportional-integral controller is used in the dc-link voltage-balancing loop to reduce the voltage difference between the two dc-link capacitors. The results of simulation and experiment demonstrate the effectiveness and superiority of the proposed strategy.

Both the proportional-integral (PI) controller and the super-twisting algorithm (STA) are attractive alternatives to effectively govern power converters. The PI controller is smooth but is less robust to disturbances, while the STA exhibits good robustness with respect to disturbances but suffers from the negative effect of chattering when some high control gains are required in actual applications. To combine the advantages of both controllers, this article explores a novel observer-based varying exponent gain STA control scheme for the three-level neutral-point-clamped converter. By introducing a time-varying exponent gain into the STA, the proposed novel varying exponent gain STA combines the attractive traits of the PI controller (smooth control input) and the STA (robustness and fast dynamic response) simultaneously. In this sense, the controller exhibits a high performance in steady state as well as transient and provides strong robustness with respect to disturbances. In addition to the new controller, a higher order sliding-mode observer is integrated into the control scheme to compensate the disturbances and further enhance the disturbances rejection ability of the system. Finally, the effectiveness of the proposed control method is confirmed by comparing its results with the PI controller and the STA based on a set of experiments.

In this article, an observer-based prescribed performance speed control method is proposed for permanent magnet synchronous motors. A transformed speed error is introduced and a suitable controller is designed to make it converge to zero, while guaranteeing the original speed error evolves strictly within a prescribed region. The controller is designed based on a backstepping approach. A linear extended state observer is applied to estimate and feed forward the external constant load disturbance to improve robustness. A data-driven radial-basis function neural network is proposed to approximate the nonlinear dynamic caused by parameter uncertainties and periodic-changing disturbance by deploying real-time and historical data. The stability analysis is based on Lyapunov's control theory. Experimental results verify the effectiveness and advantages of the proposed control scheme.

The dc–dc converter is a crucial component in energy conversion system. However, designing an advanced controller for the dc–dc converter to maintain satisfactory control performance is challenging due to its inherent nonlinearity, internal uncertainty, and external disturbance. Although active disturbance rejection control (ADRC) method is a promising solution, its control ability still needs enhancement due to the limitation of the linear extended state observer (LESO). Therefore, this article tries to propose an adaptive ADRC by introducing an additional regulation law of ${{\bm{b}}}_0$, which is a coefficient of the conventional ADRC. When compared to the conventional ADRC, the proposed adaptive ADRC can effectively eliminate the system steady-state error caused by time-varying disturbances, improving the static performance of the closed-loop system. Besides, the estimation burden of LESO can be greatly reduced, leading to improved dynamic performance of the closed-loop system. The proposed adaptive ADRC method is validated on a dc–dc floating interleaved boost converter, and both simulation and experimental results demonstrate that it outperforms the conventional ADRC method and other adaptive ADRC method in terms of steady-state and dynamic performance.

The powerful control ability of the active disturbance rejection control (ADRC) method has attracted much attention from both the academic and industrial communities. This method successfully inherits the advantages of the conventional proportional integration (PI) control method, such as error-driven way, simple structure, and low design complexity. In addition, it also absorbs the observer technique from modern control theory. All these factors make the ADRC method show a big potential to be widely adopted in practical industrial applications. To facilitate this development trend, in this work, some advancements of ADRC are discussed in detail, and three typical applications in the power electronics field are briefly introduced, such that the engineers can have a more intuitive understanding of this method and the academics could recognize some topics that still need to be further researched.

In this article, an adaptive antisaturation fixed-time control method with a faster convergence rate is studied for uncertain robotic systems. First, a new segmental sliding variable is constructed to solve the singularity problem brought by the terminal sliding mode control (TSMC) and achieve a faster convergence rate. Second, to approximate and compensate for the model uncertainty and the viscous friction parameter, an adaptive neural network (ANN) is employed. Then, a novel auxiliary system is constructed to mitigate the effects of input saturation. Based on this, a novel nonsingular TSMC algorithm integrated with the ANN and the auxiliary system is designed, so that the trajectory tracking errors of the robotic system can converge within a faster fixed time with actuator saturation. Finally, the superiority and practicability of the present method are verified by comparative experiments.

This article aims to solve a hierarchical multi-UAV Dubins traveling salesman problem (HMDTSP). Optimal hierarchical coverage and multi-UAV collaboration are achieved by the proposed approaches in a 3-D complex obstacle environment. A multi-UAV multilayer projection clustering (MMPC) algorithm is presented to reduce the cumulative distance from multilayer targets to corresponding cluster centers. A straight-line flight judgment (SFJ) was developed to reduce the calculation of obstacle avoidance. An improved adaptive window probabilistic roadmap (AWPRM) algorithm is addressed to plan obstacle-avoidance paths. The AWPRM improves the feasibility of finding the optimal sequence based on the proposed SFJ compared with a traditional probabilistic roadmap. To solve the solution to TSP with obstacles constraints, the proposed sequencing–bundling–bridging (SBB) framework combines the bundling ant colony system (BACS) and homotopic AWPRM. An obstacle-avoidance optimal curved path is constructed with a turning radius constraint based on the Dubins method and followed up by solving the TSP sequence. The results of simulation experiments indicated that the proposed strategies can provide a set of feasible solutions for HMDTSPs in a complex obstacle environment.

This brief investigates the stabilization of second-order systems subject to mismatched uncertainties. We present prescribed-instant stability, a unique form of prescribed-time stability, where the uncertain second-order system is driven to the origin exactly at the prescribed time instant $T_{p}$ . A strict Lyapunov method proof is presented on two sides, i.e., the system converges to and reaches zero not after nor before $T_{p}$ . The former is very common in existing articles about prescribed-time stability. The latter is usually ignored, but it is very important to obtain the prescribed-instant stability in this brief. We present the controllers in two cases based on different mismatched uncertainties. Simulations validate the effectiveness of the proposed method.

This letter presents a prescribed-instant stabilization approach to high-order integrator systems by the Lyapunov method. Under the presented controller, the settling time of controlled systems is independent of the initial conditions and equals the prescribed time instant. With this method, the prescribed-instant stabilization method can be easily proved and extended. To be more specific, two differential inequalities of Lyapunov functions are presented to clamp/constrain the settling time to the prescribed time instant from both the left and right sides. This thought serves as an example to present a general framework to verify the designed stabilization property. Actually, the prescribed-time stability (PSTS) [1] can not prescribe the exact settling time. It can only prescribe the upper bound of the settling time and is different with this work. The detailed argumentation will be presented after a brief review of the existing important research.

The rapid development of high-speed railway bridges in China has brought enormous challenges to the ballast bed stability on the bridge. With the increase in the bridge span, the bridge deformation under the temperature load increases gradually, as well as the stability difference of ballast bed between different regions. Moreover, the track vibration response under high-speed driving conditions is larger, which can easily cause differential settlement, flying ballast, and deterioration of the ballast bed, thereby affecting the bearing capacity and stability of the ballast bed. In view of this, this article summarizes relevant research work on a ballast bed on the bridge from the perspectives of the resistance, deformation, and acceleration response of the ballast bed. In addition, this study discusses the existing measures for improving the ballast bed stability on the bridge, including the optimization of the sleeper and ballast bed structures. Finally, the main issues that need to be addressed to improve the ballast bed stability on the bridge are pointed out, and ideas for future research on ballast beds on bridges with different spans and structures are proposed.