2,524 research outputs found
Practical second order sliding modes in single-loop networked control of nonlinear systems
Full text linkThis paper presents a novel Second Order Sliding Mode (SOSM) control algorithm for a class of nonlinear systems subject to matched uncertainties. By virtue of its Event-Triggered nature, it can be used as a basis to construct robust networked control schemes. The algorithm objective is to reduce as much as possible the number of data transmissions over the network, in order not to incur in problems typically due to the network congestion such as packet loss, jitter and delays, while guaranteeing satisfactory performance in terms of stability and robustness. The proposed Event-Triggered SOSM control strategy is theoretically analysed in the paper, showing its capability of enforcing the robust ultimately boundedness of the sliding variable and its first time derivative. As a consequence, it is also possible to prove the practical stability of the considered system, in spite of the reduction of transmissions with respect to a conventional SOSM control approach. Moreover, in order to guarantee the avoidance of the notorious Zeno behaviour, a lower bound for the time elapsed between two consecutive triggering events is provided. (C) 2017 Elsevier Ltd. All rights reserved
Design of robust higher order sliding mode control for microgrids
Full text linkThis paper deals with the design of advanced control strategies of sliding mode type for microgrids. Each distributed generation unit (DGu), constituting the considered microgrid, can work in both grid-connected operation mode (GCOM) and islanded operation mode (IOM). The DGu is affected by load variations, nonlinearities and unavoidable modelling uncertainties. This makes sliding mode control particularly suitable as a solution methodology for the considered problem. In particular, a second order sliding mode (SOSM) control algorithm, belonging to the class of Suboptimal SOSM control, is proposed for both GCOM and IOM, while a third-order sliding mode (3-SM) algorithm is designed only for IOM, in order to achieve, also in this case, satisfactory chattering alleviation. The microgrid system controlled via the proposed sliding mode control laws exhibits appreciable stability properties, which are formally analyzed in the paper. Simulation results also confirm that the obtained closed-loop performances comply with the IEEE recommendations for power systems
Event-Triggered Sliding Mode Control Strategies for a Class of Nonlinear Uncertain Systems
No full textThis chapter presents novel Sliding Mode Control (SMC) strategies of Event-Triggered (ET) type for a class of nonlinear systems affected by uncertainties and external disturbances. By virtue of its ET nature, the proposed control strategies are particularly appropriate for Networked Control Systems (NCSs), i.e., feedback systems including communication networks. The objective of the proposed control schemes is indeed to reduce the number of data transmissions over the communication network, in order to avoid problems typically due to the network congestion such as jitter and packet loss. In particular, an ET-SMC scheme and an ET Second Order SMC (ET-SOSMC) scheme are designed for a class of nonlinear uncertain NCSs, guaranteeing satisfactory performance of the controlled system even in presence of delayed transmissions. The proposed control schemes are theoretically analyzed in this chapter, showing their capability of enforcing the robust ultimate boundedness of the sliding variable associated with the controlled system, and also of its first time derivative in case of ET-SOSMC. Moreover, in order to guarantee the avoidance of the notorious Zeno behaviour, the existence of a lower bound for the time elapsed between consecutive triggering events is proven
Adaptive suboptimal second-order sliding mode control for microgrids
Full text linkThis paper deals with the design of adaptive suboptimal second-order sliding mode (ASSOSM) control laws for grid-connected microgrids. Due to the presence of the inverter, of unpredicted load changes, of switching among different renewable energy sources, and of electrical parameters variations, the microgrid model is usually affected by uncertain terms which are bounded, but with unknown upper bounds. To theoretically frame the control problem, the class of second-order systems in Brunovsky canonical form, characterised by the presence of matched uncertain terms with unknown bounds, is first considered. Four adaptive strategies are designed, analysed and compared to select the most effective ones to be applied to the microgrid case study. In the first two strategies, the control amplitude is continuously adjusted, so as to arrive at dominating the effect of the uncertainty on the controlled system. When a suitable control amplitude is attained, the origin of the state space of the auxiliary system becomes attractive. In the other two strategies, a suitable blend between two components, one mainly working during the reaching phase, the other being the predominant one in a vicinity of the sliding manifold, is generated, so as to reduce the control amplitude in steady state. The microgrid system in a grid-connected operation mode, controlled via the selected ASSOSM control strategies, exhibits appreciable stability properties, as proved theoretically and shown in simulation
Second order sliding mode control for nonlinear affine systems with quantized uncertainty
Full text linkThis paper deals with the design of a Second-Order Sliding Mode (SOSM) control algorithm able to enhance the closed-loop performance depending on the current working conditions. The novelty of the proposed approach is the design of a nonsmooth switching line, based on the quantization of the uncertainties affecting the system. The quantized uncertainty levels allow one to define nested box sets in the auxiliary state space, i.e., the space of the sliding variable and its first time derivative, and select suitable control amplitudes for each set, in order to guarantee the convergence of the sliding variable to the sliding manifold in a finite time. The proposed algorithm is theoretically analyzed, proving the existence of an upperbound of the reaching time to the origin through the considered quantization levels
Third order sliding mode voltage control in microgrids
Full text linkIn this paper, we propose a robust voltage control scheme for microgrids based on a suitable designed third-order sliding mode (3-SM) controller. The use of 3-SM allows to reject matched disturbances and unmodeled dynamics, due to the presence of a voltage-sourced-converter (VSC) as interface with the main grid. The motivation for using a 3-SM control approach, apart from its property of providing robustness to the scheme in front of a significant class of uncertainties, is also given by its capability of enforcing sliding modes of the controlled system with chattering alleviation. The microgrid system controlled via the proposed 3-SM approach proves to exhibit appreciable stability properties. Specifically, the voltage error with respect to the required reference is steered to zero in a finite time. The comparison with respect to second order sliding mode (SOSM) and PI controllers shows the beneficial effects of the proposed strategy, and simulation results confirm that our control law provides closed-loop performance complying with the IEEE recommendations for power systems
Event-triggered sliding mode control algorithms for a class of uncertain nonlinear systems: experimental assessment
Full text linkAn experimental assessment of the recently introduced event-triggered sliding mode control approach is presented in this paper. The major design requirement, in this approach, is to reduce the number of transmissions over the network, while guaranteeing that the sliding mode control is stabilizing with appropriate robustness in front of matched uncertainties. In the present paper a novel Event-Triggered Sliding Mode Control algorithm is first introduced and discussed and then it is compared with two different Model-Based Event-Triggered Sliding Mode Control algorithms. Finally, their experimental assessment is reported, obtaining satisfactory performance consistent with the theoretical treatment and fulfilling all the design requirements
Sliding mode observers for a network of thermal and hydroelectric power plants
Full text linkThis paper deals with the design of a novel sliding mode observer-based scheme to estimate and reconstruct the unmeasured state variables in power networks including hydroelectric power plants and thermal power plants. The proposed approach reveals to be flexible to topological changes to power networks and can be easily updated only where changes occur. The discussed numerical simulations validate the effectiveness of the proposed estimation scheme. (C) 2018 Elsevier Ltd. All rights reserved
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