The high penetration of power electronic converters into DC microgrids may cause the constant power load stability issues, which could lead to large voltage oscillations or even system collapse. On the other hand, dynamic performance should be satisfied in the control of power electronic converter systems with small overshoot, less oscillations and smooth transient performance. This paper proposes an offset-free model predictive controller for a DC/DC buck converter feeding constant power loads with guaranteed dynamic performance and stability. First, a receding horizon optimization problem is formulated for optimal voltage tracking. To deal with the unknown load variation and system uncertainties, a higher-order sliding mode observer (HOSMO) is designed and integrated into the optimization problem. Then an explicit closed-loop solution is obtained by solving the receding horizon optimization problem offline. A rigorous stability analysis is performed to ensure the system large signal stability. The proposed controller achieves optimized transient dynamics and accurate tracking with simple implementation. The effectiveness of the proposed controller is validated by simulation and experimental results.
This paper investigates an alternative non-recursive finite-time trajectory tracking control methodology for a class of nonlinear systems in the presence of general mismatched disturbances. By integrating a finite-time disturbance feedforward decoupling process via higher-order sliding modes (HOSMs), it is shown that, a novel non-recursive design framework resulting a simpler controller expression and easier gain tuning mechanism is presented. A new feature is that a quasi-linear inherent nonsmooth control law could be constructed straightforwardly from the system information, which is essentially detached from the determination of a series of virtual controllers. Moreover, by proposing a less ambitious semi-global tracking control objective, the synthesis procedure can be achieved without restrictive nonlinear growth constraints. Explicit stability analysis is given to ensure the theoretical justification. A numerical example and an application to the speed regulation of Permanent Magnet Synchronous Motor (PMSM) are provided to illustrate the simplicity and effectiveness of the proposed non-recursive control design approach.
This article presents a novel path-following algorithm for fixed-wing unmanned aerial vehicles by virtue of a nonlinear optimal control approach and wind disturbance observers. Different from some exiting algorithms, the proposed algorithm formulates the path-following problem into a control problem by introducing auxiliary dynamics for the path parameter. The proposed controller is designed in an optimal and systematic manner where the control action is generated according to a well-defined cost function. This framework does not require any complex geometric coordinate transformation and can be easily tuned to accommodate curved reference paths, making it straightforward to deploy in different flight missions. Moreover, the wind influences on the path-following performance is explicitly compensated by the proposed algorithm based on the wind estimates provided by nonlinear disturbance observers. The closed-loop stability, including the auxiliary dynamics for path parameter and observer dynamics for wind estimation, is also analyzed. The feasibility and effectiveness of the proposed algorithm have been thoroughly validated in simulation studies and realistic flight tests. Index Terms-Disturbance observer, optimal control, path following, unmanned aerial vehicle (UAV).
I. INTRODUCTIONR ECENT years have witnessed many successful applications of unmanned aerial vehicles (UAVs) in different domains, ranging from environmental monitoring, search, and rescue to surveillance and reconnaissance. Most of the common UAV tasks require to cruise along a predefined geometric path [1], [2]. This function also forms the basis
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