In this article, we propose an attack-resilient control structure for a cyber-physical system (CPS) to enhance the CPS security against stealthy system integrity attacks that manipulate the state of ...the physical plant while undetected. With the help of nonlinear encoding/decoding components, the proposed structure can detect stealthy attacks and preserve the nominal performance without considering attacks. Meanwhile, for avoiding the eavesdropping of transmitted signals used to synchronize encoding/decoding components between the physical and cyber layers, the chaotic oscillators are employed for the secure communication. The resilience against the malicious attacks and the robustness under the time delay and nonlinear components of the proposed CPS structure are investigated in view of input-to-state stable framework. Simulations for quadruple-tank process are performed to validate the performance of the proposed method.
•Bayesian forecasting is adopted to develop probabilistic solar power forecasts.•Copulas are derived to model the dependencies between solar power and temperature.•The method is comprehensively ...examined by various models, locations, and times.•Bayesian forecasting outperforms benchmarks in 55 out of total 64 testing cases.•The accuracy improvement is 3.72
With increased penetration of solar energy sources, solar power forecasting has become more crucial and challenging. This paper proposes a copula-based Bayesian approach to improve probabilistic solar power forecasting by capturing the joint distribution between solar power and ambient temperature. A prior forecast distribution is first obtained using different underlying point forecasting models. Parametric and empirical copulas of solar power and temperature are then developed to update the prior distribution to the posterior forecast distribution. A public solar power database is used to demonstrate effectiveness of the proposed method. Numerical results show that the copula-based Bayesian method outperforms the forecasting method that directly uses temperature as a feature. The Bayesian method is also compared with persistent models and show improved performance. This article includes supplementary material (data and code) for reproducibility.
In this paper, a cooperative control analysis and design method is investigated for heterogeneous dynamical systems that may be of arbitrary relative degree or nonminimum-phase or both. To achieve ...consensus or cooperative stability, a negative value of input-feedforward passivity index is used to accommodate and analyze such systems, and the magnitude of the index value is also used as the impact coefficient to quantify the impacts of heterogeneous dynamics of these systems on their networked operations. Physical-system-level designs are explicitly carried out to make individual linear and nonlinear systems (which are either feedback linearizable or nonminimum phase of certain form) become passivity-short and to embed one pure integrator into their input–output dynamics. The network-level distributed control can simply be chosen without any knowledge of the heterogeneous dynamics but with only information of an upper bound on their impact coefficients. It is shown, using the impact equivalence principle, that these controls separately designed but implemented together always ensure either local or global consensus and that a global non-trivial consensus emerges if and only if the information network has at least one globally reachable node or is varying but cumulatively connected. The proposed methodology of fully modularized designs unravels complexity of analyzing and designing cyber–physical systems and enables their plug-and-play into networked operations.
Accurate calculation of time to go until impact is an essential component in coordinating multiple precision-guided munitions for a simultaneous strike. Conventional means for calculating time to go ...contain potential errors, due in part to the trajectory curvatures, and may fall short on the accuracy required to achieve a desired impact time, especially if velocity changes rapidly due to atmospheric drag and gravity. A closed-loop guidance law will be presented in which an optimized, piecewise continuous, and smooth family of polynomial trajectories is parameterized in terms of downrange distance and has a closed-form solution of arc length for improved calculation of time to go.
A linear-quadratic N-pursuer single-evader differential game is considered. The evader can observe all the pursuers but pursuers have limited observations of themselves and the evader. The evader ...implements the conventional feedback Nash strategy and the pursuers implement Nash strategies based on a novel concept of best achievable performance indices. This problem has potential applications in situations where a well-equipped unmanned vehicle is evading several weakly equipped pursuing vehicles. An illustrative example is solved, and several scenarios are presented.
Islanding detection is important to ensure the reliability and safety of distributed generation (DG). In this paper, a new active islanding detection method (IDM) is proposed, and it depends on ...individually estimating an overall transient stiffness measure for any multi-DG system to establish a clear separation between prior- and post-islanding stiffness. For the multi-DG system to avoid spectrum overlapping, each of its DGs is required to perturb at distinct frequencies. By using this concept of perturbation separation, the proposed technique can be applied to multi-DG systems without requiring any communication among the DGs. Simulation results show that the proposed technique is scalable and robust against different loading conditions and variations of grid stiffness levels as well as with respect to the number of connected DGs and different types of DG controllers. It is also shown that the proposed technique can successfully distinguish islanding conditions from other disturbances that may occur in power system networks.
To date, multicopters have mainly been used in the entertainment and information‐gathering fields, but can potentially be used to transport payloads. Specifically, multicopters are more suited for ...manoeuvring tough terrains and delivering payloads to areas unaccessible by other means. The authors propose a control method to achieve cooperative transport with a plural multicopter system and address the problem of delivering a payload being suspended via cables from multicopters. In cooperative transport using a multicopter system, disturbance (weight, wind, and inertia force) may cause destabilization. A consensus algorithm is used to coordinate flight of helicopters in a formation and to ensure that the payload follows a virtual leader. Disturbances (such as wind and cable tension) are primary causes of destabilization and, in the multicopter setting, they are suppressed by an adaptive robust control, Robust Integral of Sign of the Error control. It is shown that the proposed control design can achieve not only convergence under the ideal setting but also robust operation under significant disturbances. In addition, additional control objectives such as cable tension, payload attitude, and collision avoidance can be integrated and achieved. As an auxiliary method, cable tension control, maintaining a horizontal payload attitude, and collision avoidance are considered. The usefulness of the proposed method was verified by simulations and laboratory flight testing demonstrations.
The presence of distributed generators (DGs) such as photovoltaic systems (PVs) is increasing significantly in distribution networks, and in order to accommodate a higher penetration of DGs, ...technical issues arising from fluctuation and unpredictability of their power output must be addressed. It is beneficial if DGs of high penetration can be dispatched when necessary. To this end, a distributed control and generation estimation approach is developed to dispatch multiple DGs, each of which consists of a PV and a controllable load. A strongly connected digraph with a row stochastic adjacency matrix is a sufficient requirement for the communication topology. A distributed weights adjustment algorithm adaptively makes the adjacency matrix doubly stochastic so that the aggregated power generation capacity can be estimated. Then, the expected consensus operational point of the DGs is calculated by those DGs that can obtain power dispatch command from the supervisory control and data acquisition system and is propagated to the rest of the DGs with a consensus algorithm. With this method, all the DGs operate at the same ratio of available power, while their aggregated power meets the power dispatch command. Simulations in the IEEE standard 34-bus distribution network verify the effectiveness of the proposed approach.
A novel, unified control design is proposed for software-defined inverters (SDIs) to operate in either grid-forming (GFM) or grid-following (GFL) mode in AC grids/microgrids and to switch between the ...two modes seamlessly. The proposed GFM and GFL controls are systematically developed and analytically synthesized based on the dynamic state space models of the inverter, its output filters, and its terminal voltage and current at the AC grid/microgrid. The proposed GFM and GFL controls have, a) a nonlinear nominal output tracking control as the seed design, and b) a constraint-enforcing control. The GFM nominal control tracks frequency, voltage-magnitude, and angle, while the GFL nominal control tracks frequency as well as real and reactive power references. Tracking of either GFM or GFL output vector is ensured under the recursive Lyapunov design paradigm, naturally resulting in consistent current and voltage control laws. This paradigm allows the implementation of constraint-enforcing control that ensures that the frequency, voltage, power, and current injections dynamically satisfy their operational constraints in the presence of load variations and intermittent renewable power sources. Stability and convergence of the proposed GFM and GFL controls, and constraint enforcement are concluded analytically, and their effectiveness is demonstrated through simulations.
With the rising number of applications for sensor networks comes a need for more accurate cooperative fusion algorithms. In this paper, a distributed and optimal state estimator is presented for ...implementation through a dynamically switching, yet strongly connected, directed communication network to cooperatively estimate the state of a dynamic system. The Kalman-Consensus filter approach is used to incorporate a consensus protocol of neighboring state estimates into the traditional Kalman filter. It has been known that the main difficulty associated with implementing such an optimal solution is its fully coupled covariance matrix. Presented is a distributed computation of the covariance matrix at every node achieved by taking advantage of its independence from state estimates. Reductions to the distributed covariance computations are achieved through shared processing made available by the strongly connected digraph. Should the digraph change over time, a distributed topology estimation algorithm is included to facilitate the implementation of the proposed Kalman-Consensus filters. Together, these advances render a distributed and optimal solution to the consensus-based cooperative Kalman filter design problem. Convergence and stability of the proposed algorithms are analyzed and analytically concluded with performance verified through simulation of an illustrative example.
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