Search

Fault-tolerant control allocation (FTCA) strategy is proposed for attitude stabilization of a flexible satellite with actuator redundancy. The control scheme is based on the infinite-dimensional model of a flexible satellite with no discretization, so the spillover instability is eliminated. This is one of the important benefits of the proposed control scheme over the previous FTCA schemes that have been used for the flexible satellite. The proposed scheme contains two modules. The first module provides a virtual control law to meet stabilization and vibration control objectives in the presence of uncertainties and external disturbances. There is no need to implement in-domain actuators on panels to stabilize their vibration. In this module, the virtual control is designed using adaptive integral sliding mode approach where the sliding surface includes angular velocities, internal reaction torques, and nominal control for healthy system. The second module, based on fault/failure information and using a control allocation scheme, provides redistribution of the virtual control law among the available actuators. Due to simultaneous actuator faults and control constraints, there is an error between the actual virtual control and the designed control that affects the overall system stability. To eliminate this error, gain of the virtual control signal is adjusted by an adaptive updating law. The closed-loop system stability is guaranteed for small changes in a neighborhood of the sliding surface with simultaneous vibration damping. A numerical example illustrates the effectiveness of the proposed control strategy.

Power outage, also known as blackout, is inevitable despite all operator efforts. Accordingly, an exhaustive restoration plan should be prepared beforehand. Considering all the static and dynamic constraints of power systems during system restoration leads to a comprehensive restoration plan which, in turn, results in the alleviation of its negative impacts. One of the challenges in developing the restoration plan is switching transients in energizing no-load or lightly loaded transformers and its effect on other power system equipment, arresters in particular. In this article, a restoration plan in the Iran power system is studied, focusing on switching transients. First, the flux–current curve is plotted applying three different methods, utilizing the real standard test data of a transformer; then, the thermal effect of switching transients on an arrester existing in Iran electric grid is studied. Results yielded that the arrester may be damaged in the absence of preventive actions; therefore, a proper countermeasure which takes into consideration the frequency and voltage constraints, as well as the asynchronous operation of circuit breaker contacts, is proposed. The simulation shows that the proposed countermeasure guarantees arrester safety.

This paper presents a distributed coverage control scheme based on receding horizon control for the coordination of multiple mobile robots to cover an event. The mission space is modeled using a probability density function representing the probability of occurrence of events. The distributed scheme is generated by the decomposition of a single optimal coverage problem into distributed receding horizon coverage control problems, each of them associated with one robot. The distributed coverage scheme is proven to optimally stabilize robots at a centroidal Voronoi configuration, which is an optimal configuration to cover an event. The control scheme is tested in three simulation environments to illustrate its good performance at environments with any probability density function of events, as well as its ability to generalize to much larger groups of mobile robots.