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In this paper, an ambient power harvester with a single-diode device is proposed for simultaneously scavenging both radiofrequency (RF) and thermal energy in a mixed and cooperative manner. This cooperative harvesting process is theoretically examined through a proposed model of the diode and then validated by simulation and measurement. In the proposed cooperative power harvester, the harvested dc voltage from a thermal source is used to bias the diode for improving the diode's RF-to-dc power conversion efficiency (PCE). An accurate analytical model of the Schottky diode is developed for specifying the constraining parameters of RF-to-dc PCE and accurately predicting diode's performances in a low RF power range $({ \leq - \text{25}\;{\text{dBm}}})$ , respectively. The calculated results are found to be in a good agreement with the simulated ones obtained by the harmonic balance simulator in the advanced design system. For demonstration and validation, the proposed mixed cooperative power harvester is designed and prototyped on the basis of diode SMS7630. A total measured output dc power around 0.8 μW is obtained with an RF-to-dc PCE around 33.4%, when the two injecting power sources at the diode are both −30 dBm. In addition, rectennas with and without a matching network are both fabricated and tested. By eliminating the L matching network, the rectenna is found to offer a higher dc output power. The proposed mixed cooperative power harvester is hoped to find potential real-world applications in an ambient atmosphere with RF coverage and temperature gradient. It not only helps to produce a higher power but also provides a reliable way of improving the resilience of dc power production. [ABSTRACT FROM AUTHOR]

This paper is devoted to attitude tracking control of fractionated spacecraft with wireless communication. We consider the practical case that the spacecraft suffers from uncertain inertia parameters, external disturbances, and even unknown and time-varying actuator faults. Within the framework of the backstepping method, a novel event-triggered adaptive fault-tolerant control scheme is proposed. In our design, an event-triggering mechanism is introduced to determine the time instants for communication, which successfully avoids continuous communication and Zeno phenomenon. Then, with the aid of a bound estimation approach and a smooth function, the impacts of the actuator faults, as well as the network-induced error, are effectively compensated for. Moreover, by employing the prescribed performance control technique, it is shown that the attitude tracking errors can converge to predefined arbitrarily small residual sets with prescribed convergence rate and maximum overshoot, no matter if there exist unknown actuator faults. Compared with conventional adaptive attitude control schemes, the proposed scheme significantly reduces the communication burden, while providing high reliability and stable, rapid, and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear active disturbance rejection control (ADRC) scheme is designed to control the pneumatic muscle actuator system. To reflect the impact of the sampling period, a continuous-discrete extended state observer (CDESO) is employed to estimate the so-called total disturbance, which describes the unmodeled complexities. Then, a nonlinear composite controller is used, where the estimates provided by the CDESO act as the feedforward term. The sufficient conditions to guarantee the stability of the CDESO and the overall controlled system are provided, respectively. Finally, a number of practical experiments are conducted on a pneumatic motion platform in order to verify the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

The requirements for the control performances of space manipulators, especially for the stability and accuracy of the attitude control systems of the base spacecrafts, are ever increasing during the space target capturing tasks. However, the system uncertainties caused by parameter variations will degrade the system performances severely. This paper investigates the precise and fast trajectory tracking control problem for the free-flying space manipulator, after capturing a space target with uncertain mass. To compensate the system uncertainty with complex and uncertain dynamics, a novel adaptive sliding mode disturbance observer (ASMDO) is proposed. Then, a composite controller with prescribed transient and steady-state performances is developed. It is proved that the estimation error of ASMDO can be stabilized in finite-time, though the bound of the derivative of system uncertainty is unknown. Meanwhile, the trajectory tracking error can also be stabilized in finite-time and has preassigned maximum overshoot and steady-state error. Finally, numerical simulations and experimental studies are presented to demonstrate the effectiveness of proposed methods. [ABSTRACT FROM AUTHOR]

Although the flight control of quadrotor unmanned aerial vehicles have been widely studied, it is still very challenging to suppress multiple disturbances and efficiently utilize the inherent multi time-scale characteristics. As a well-known antidisturbance strategy, composite hierarchical antidisturbance control (CHADC) can compensate and attenuate disturbances simultaneously, thus enhancing the control performance of complex systems significantly. In the meantime, the singular perturbation theory (SPT) is employed to analyze the multi time-scale properties, and the original system is decomposed into the slow and fast subsystems. In this article, we present an antidisturbance control scheme based on the SPT and CHADC to enhance the capability of antidisturbance. A novel composite hierarchical antidisturbance (CHAD) predictor–corrector is proposed for the slow subsystem to integratively handle the disturbances from guidance and control perspective, and a CHAD ${{H}_{\infty }}$ controller is employed for the fast subsystem subject to external disturbances and inertial uncertainties. Meanwhile, the compensability of disturbance is explicitly analyzed. Finally, experiments are carried out to validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Focusing on a quadrotor unmanned aerial vehicle (UAV), the presence of unintended actuator faults and external disturbances increases the risk of a crash. Although plenty of efforts have been devoted, how to integrate capability analysis into safety control design is still an open issue. This article presents the design of a safety control system for quadrotor UAVs. Firstly, a system capability analysis method based on a differential flatness algorithm is developed, so that the derivatives (i.e., velocity, jerk, and snap) of flight trajectory can be formulated as flat variables. A tradeoff between system capability and permissible flight maneuverability is made to avoid actuator saturation. Secondly, dual-loop nonlinear disturbance observers are exploited to identify the actuator faults and disturbances, which can thereby be handled by a cascade control scheme. Moreover, the trajectory is regenerated online at the expense of degraded flight maneuverability or even emergency landing, in view of the remaining actuator control authority. When comparing to the existing methods, the gap among safety control, trajectory generation, and system capability analysis is bridged to ameliorate practical flight safety. Finally, flight tests are carried out to demonstrate the unique merits of the proposed system. [ABSTRACT FROM AUTHOR]

Multiple disturbances are the main constraints that hinder the high-performance velocity tracking of the gimbal servo system in control moment gyro. This article presents a non-cascade structured velocity-tracking controller based on a refined disturbance observer for handling multiple disturbances and improve the tracking performance. Specifically, a disturbance observer is designed to estimate the imbalance disturbance, which can be represented by an exogenous system. The disturbances that cannot be modeled a priori are treated as a lumped term and estimated via extended state observer. By resorting to disturbance estimation, a novel sliding mode controller based on the disturbance estimation values is developed to handle the mismatched problem and chattering issue. Finally, experimental tests are conducted to verify the effectiveness of the proposed anti-disturbance control scheme. [ABSTRACT FROM AUTHOR]

Disturbance-observer-based control (DOBC) and related methods have been researched and applied in various industrial sectors in the last four decades. This survey, at first time, gives a systematic and comprehensive tutorial and summary on the existing disturbance/uncertainty estimation and attenuation techniques, most notably, DOBC, active disturbance rejection control, disturbance accommodation control, and composite hierarchical antidisturbance control. In all of these methods, disturbance and uncertainty are, in general, lumped together, and an observation mechanism is employed to estimate the total disturbance. This paper first reviews a number of widely used linear and nonlinear disturbance/uncertainty estimation techniques and then discusses and compares various compensation techniques and the procedures of integrating disturbance/uncertainty compensation with a (predesigned) linear/nonlinear controller. It also provides concise tutorials of the main methods in this area with clear descriptions of their features. The application of this group of methods in various industrial sections is reviewed, with emphasis on the commercialization of some algorithms. The survey is ended with the discussion of future directions. [ABSTRACT FROM PUBLISHER]

The twenty-one papers in this special section focus on bringing the ideas of the worldwide research community working on various disturbance/uncertainty estimation and rejection methods in different engineering sectors into common platform and to present the latest advances and developments in design methods for disturbance/uncertainty estimation, design methods for disturbance/uncertainty attenuation, stability and performance analysis, practical implementation, and various case studies of the applications of these techniques. [ABSTRACT FROM PUBLISHER]

This paper explores a composite hierarchical antidisturbance control (CHADC) scheme for the resonance vibration suppression of a high-speed rotor system supported by active magnetic bearings (AMBs) in the magnetically suspended double-gimbal control moment gyroscope (MSDGCMG). The rotor dynamics with a fictitious integral term is introduced to meet the steady-state performance requirements. Resonance disturbances caused by harmonic drive transmission and gyroscopic torque disturbances caused by gimbal motions are also analyzed. The augmented composite AMB system with two types of disturbances and nonlinear electromagnetic dynamics is developed. Then, a disturbance observer is constructed and a stability analysis of the closed-loop system is performed using a Lyapunov approach. Simulation results show that the exogenous disturbance can be estimated and compensated with the appropriate control parameters. Rotor run-up experiments demonstrate that the proposed method has a good performance for disturbance rejection of harmonic drive resonance vibrations under the excitation of coupling torques. The gyroscopic torque disturbances with the bounded norm can also be attenuated effectively. [ABSTRACT FROM PUBLISHER]

Real-time thermal capacity estimation is not only part of prognostics and health management but also determines the dynamic loading capability of the traction transformer. The hot-spot temperature (HST) is the vital parameter for real-time thermal capacity estimation. In high-speed railway, the unbalanced loads of the two phases of the traction transformer cause unbalanced winding losses and therefore affect the top-oil temperature and further influence the HST in each phase. In order to explore the dynamic thermal performance of the transformer under unbalanced load (current), a thermal model for calculating the HST was proposed incorporating thermal interaction between two power supply phases. This model treats the winding loss of each phase independently, considering the temperature dependence of winding ohmic losses and eddy current losses. A thermal circuit topology is presented with independent phase windings sharing the same top-oil temperature, where an improved heat transfer correlation is used to account for the nonlinear thermal convection. The proposed model is verified by the factory temperature rise tests and field operation data for the same batch of transformers. [ABSTRACT FROM AUTHOR]

How to determine the absolute position of users, such as underwater autonomous vehicles, ships or other long-range vehicles, is a fascinating and challenging issue, especially in global navigation satellite system -denied environments. In this article, a bioinspired global autonomous positioning system based on polarized skylight is proposed. By comparing with the related literatures, the system is able to global positioning based on the degree of polarization pattern (DoP) pattern. To be more specific, in an attempt to use the DoP pattern for the geolocalization purposes, a bioinspired polarization compass is designed and in addition, an overall maximum DoP (MDoP) determination algorithm is presented. Moreover, on the basis of the MDoP value, the sun elevation angle can be ultimately measured by using the DoP pattern. The sun elevation angle difference algorithm is used to deduce the absolute position of users. Finally, the bioinspired global autonomous positioning system is developed and validated through experiments. The test results show that the location errors are in range of few kilometers, of which the latitude accuracy is 0.113° (1σ), and the longitude accuracy is 0.082° (1σ). [ABSTRACT FROM AUTHOR]

Oil-immersed transformer is one of the most important electrical equipment in power distribution and transmission systems. Dielectric response method is a well-recognized method to diagnose the insulation defect of oil-immersed transformers. However, the applicability of this method is restricted due to the long testing time. Under some special field conditions, the method is not even applicable. In this article, a novel testing method is proposed based on the following ideas: first, the low-frequency dielectric parameters are extracted by using mixing frequency excitation; then, parameters of the extended Debye equivalent circuit are determined based on cuckoo search optimization algorithm; finally, the specific parameters are used to the established simulation model and obtain the recovery voltage curve. Compared with the traditional method, the testing time of the proposed method has been greatly reduced. Besides, dielectric parameters in both frequency domain and time domain can be obtained simultaneously. The applicability of the proposed method is verified by the dielectric response measurements on a laboratory transformer and a real power transformer in a substation. [ABSTRACT FROM AUTHOR]

How to self-determine the attitude and heading of users is a challenging issue in unknown, global navigation satellite system (GNSS) denied, or magnetic disturbance environments. In this article, a bioinspired polarization-based attitude and heading reference system (PAHRS) aided by inertial sensors is presented. As compared with the existing studies, a polarization compass, which consists of three photoelectric-based polarization sensors is designed to cope with the three-dimensional polarization heading determination and distinguish issue. Hence, the real heading orientation can be determined without GNSS correction. To address the triaxis attitude and heading determination issue of PAHRS, the system measurement model tightly coupled the attitude and heading accumulate errors of inertial navigation system. Finally, the experimental platform is built and the results illustrate that the PAHRS is able to achieve satisfactory performance without the aid by GNSS and magnetic compass system. [ABSTRACT FROM AUTHOR]

In this paper, an active disturbance rejection control scheme with a nonlinear sampled-data extended state observer (NSESO) is proposed for a pneumatic muscle actuator (PMA) system. The phenomenon of the actuator saturation is taken into account in the design procedure. The NSESO is utilized to estimate the so-called total disturbance that reflects the aggregated impacts of unmodeled nonlinearities and disturbances. Then, an NSESO-based composite control strategy is designed, where the estimates provided by the designed NSESO serve as the compensation to eliminate the total disturbance. Finally, a number of practical experiments on the PMA systems are conducted to verify the validity and applicability of the proposed design method. [ABSTRACT FROM AUTHOR]

In this paper, an active disturbance rejection control (ADRC) method is investigated for the ranger neutral buoyancy vehicle (RNBV) via a delta operator approach. In order to eliminate unmodeled nonlinearities and exogenous disturbances for a neutral environment, a novel delta-domain ADRC method is put forward to achieve the tracking control performance of the RNBV. In the proposed ADRC method, an extended-state-observer (ESO) is designed in the delta domain to estimate the so-called total disturbance that reflects the aggregated impacts of the nonlinearities and disturbances. Then, by using the estimates provided by the ESO, a composite controller is developed such that the closed-loop system can be input-to-state stable. It is shown in practical experiments that the proposed delta-domain ADRC outperforms its discrete-domain counterpart in consideration of the finite-word-length effects. [ABSTRACT FROM AUTHOR]