Virtual Input Research Articles

Adaptive fuzzy global fast terminal sliding mode control of an over-actuated flying robot

In this paper, the issue of full control (both position and orientation controls) of an over-actuated unmanned flying robot is addressed using an adaptive fuzzy global fast terminal sliding mode control (AF-GFTSMC) scheme in the presence of external disturbances and parametric uncertainties. At the first step, full dynamic equations of motion of a novel over-actuated flying robot are developed taking into account the rotational kinematics. Using the Lyapunov stability theorem, an AF-GFTSMC is designed to suppress the errors between desired references and actual responses of the robot in finite time. Since the number of actuators is more than control forces and torques, considering some constraints on actual control inputs, a control allocation strategy based on the reflective Newton algorithm is employed and formulated in order to compute the actual control inputs according to virtual control inputs. Finally, some simulations are performed in the presence of external disturbances and parametric uncertainties, utilizing different designed control strategies, classical and AF-GFTSMC methods. It is also clearly verified that the designed control approaches are effective and robust through tracking some predefined trajectory in 3D space as well as attenuation of chattering phenomena.

Wave energy localization near the rough surfaces of piezoelectric waveguide. Near-surface inhomogeneities as a resonator or filter

Propagation of high-frequency electro-elastic normal wave signal in a composite waveguide is investigated. The roughnesses on a two surfaces of the piezoelectric waveguide are filled with an ideal conductor and ideal dielectric respectively. The both of the influence of surface roughness and the influence non-homogeneity of materials near the surfaces on the process of high frequency electro-elastic normal wave signal propagation, is discussed. The behaviors the frequency characteristics of wave in the composite waveguide at the propagation of normal wave signals numerically are investigated. The problem by the method of virtual cross sections and input of Magneto Elastic Layered System (MELS) hypotheses is solved. It is shown that in a case of not filled roughness of the piezoelectric layer surfaces, only two short wave modes are arise. The filling of the surface roughness with a dielectric or a conductor respectively, leads to the appearance of up to four such wave modes, depending at the wave signal length. The dispersion dependencies for all possible characteristic modes of shear electroelastic waves are given. It is shown that in a case of the propagation of slow waves, on certain wave lengths the silence frequency zones are arise.

Practical control implementation of tri-tiltRotor flying wing unmanned aerial vehicles based upon active disturbance rejection control

Tilt rotor unmanned aerial vehicles exhibit their effectiveness via a novel and convenient structure. However, the flight control system is a critical problem in need of a robust solution. Focusing on its flight features, which display strong nonlinear and varying dynamics, caused by complexity in the aerodynamic layout and tilting structure, a practical control scheme is proposed to meet such technical issues. This paper first develops the nonlinear model, consisting of the interference between rotors and the wing body, relying on wind tunnel technology. A simplified linear model that decomposes the longitudinal and lateral components is used in order to facilitate controller design. Then, a time-scale separation decoupling control scheme based upon active disturbance rejection control is proposed to cope with control challenges. Introducing the concept of virtual control input, an effective control allocation is obtained by choosing the appropriate bandwidth in the frequency domain. The extended state observer is applied to estimate and compensate for unknown total disturbances and model uncertainties. Finally, robustness verification, successful test-bench experiments, and practical flight tests that show the fast tracking and disturbance rejection of the active disturbance rejection control controller are discussed. The proposed practical coupling rejection control design demonstrates its capability to employ a single input single output method to control a tri-tiltRotor flying wing unmanned aerial vehicle relying on active disturbance rejection control.

Control of MIMO mechanical systems interacting with actuators through viscoelastic linkages

This paper proposes a new method for control of nonlinear multi input – multi output (MIMO) mechanical systems that incorporate viscoelastic dampers (VED) for reducing undesired vibrations of actuators. To this end, a control algorithm is proposed based on considering various characteristics of the described dynamical systems (namely mechanical dynamics, viscoelasticity and actuator dynamics) in generation of control inputs guaranteeing convergence of system response to desired reference signals. This procedure features three consecutive parts within the control loop which are conducted iteratively at each control sample. At each sample, initially necessary forces and moments exerted to mechanical system are calculated as virtual control inputs generated based on a MIMO discrete-time sliding mode control (DSMC) algorithm. As the aim of control model is obtaining a closed-loop system without resulting in notable vibrational effects, undesired chattering effects should be eliminated from inputs generated by DSMC. This objective is attained by calculation of appropriate input bounds. Next, an additional virtual input is assigned corresponding to viscoelastic strain such that virtual mechanical input from previous part of the control loop is generated. To this end, Maxwell model for viscoelastic material is considered. Finally, actual controller input is generated such that all virtual control objectives are satisfied. The effectiveness of control procedure is numerically illustrated for a 3-PRR manipulator.

Fast Adaptive Robust Differentiator Based Robust-Adaptive Control of Grid-Tied Inverters with a New L Filter Design Method

In this research, a new nonlinear and adaptive state feedback controller with a fast-adaptive robust differentiator is presented for grid-tied inverters. All parameters and external disturbances are taken as uncertain in the design of the proposed controller without the disadvantages of singularity and over-parameterization. A robust differentiator based on the second order sliding mode is also developed with a fast-adaptive structure to be able to consider the time derivative of the virtual control input. Unlike the conventional backstepping, the proposed differentiator overcomes the problem of explosion of complexity. In the closed-loop control system, the three phase source currents and direct current (DC) bus voltage are assumed to be available for feedback. Using the Lyapunov stability theory, it is proven that the overall control system has the global asymptotic stability. In addition, a new simple L filter design method based on the total harmonic distortion approach is also proposed. Simulations and experimental results show that the proposed controller assurances drive the tracking errors to zero with better performance, and it is robust against all uncertainties. Moreover, the proposed L filter design method matches the total harmonic distortion (THD) aim in the design with the experimental result.

Synthesize identification and control for smart structures with time‐varying parameters under unknown earthquake excitation

The synthesis of structural identification with vibration control is cost-effective and beneficial for developing smart building structures. In the past several decades, techniques have been put forward for the combination of structural identification and vibration control. However, it is still a challenging task to synthesize identification and vibration control of time-varying structures under unknown earthquake excitation. First, structural dynamic responses collected by a structural health monitoring (SHM) system are absolute responses under unknown earthquake excitation, so existing identification approaches for unknown external excitations are not applicable for this situation. Moreover, it is essential to have an efficient algorithm for accurately tracking the various scenarios of time-varying structural physical parameters with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, an algorithm is put forward to tackle this challenging problem. It is proposed to treat structural time-varying effect as “virtual unknown inputs” to the corresponding time-invariant structure. A generalized extended Kalman filtering with unknown input (GEKF-UI) is proposed to circumvent the limitations of the existing EKF-UI approaches. The proposed GEKF-UI can simultaneously identify structural system, unknown earthquake excitation, and the “virtual unknown inputs” using only partially measured structural absolute responses. Then, the identified structural state is synthesized in real time with the instantaneous optimal control strategy for optimal semiactive control provided by magnetorheological dampers. Therefore, the proposed algorithm can track various structural time-varying with much less computation, which is more suitable for synthesis with structural control compared with other existing approaches. Some numerical cases of synthesizing identification and vibration control of various type time-varying structures under unknown earthquake motion are adopted to investigate the feasibilities of the proposed algorithm.

Integration of identification and vibration control of time-varying structures subject to unknown seismic ground excitation

The synthesis of structural health monitoring and vibration control is important in order to provide facilities for constructing smart structures. In recent years, some techniques have been developed to integrate structural identification and optimal vibration control. However, it is still challenging to integrate the identification and vibration control of time-varying structures subject to unknown earthquake excitation. The main difficulties are that structural dynamic responses collected by a simple harmonic motion system are absolute responses under unknown earthquake ground motion while previous identification approaches for unknown external excitation are not applicable for this situation and the need of an efficient algorithm to accurately track the various scenarios of time-varying structures with inexpensive computation to ensure the real-time performance requested by structural vibration control. In this paper, a novel algorithm is presented, in which structural time-varying parameters are treated as ‘virtual unknown inputs’ to the underlying time-invariant structure, a generalized Kalman filter with unknown inputs is proposed for joint identification of joint structural state, unknown earthquake excitation and ‘virtual unknown inputs’ with only partially measured structural absolute responses, and the identification results are integrated in real-time with the instantaneous optimal control scheme to reach the goal of optimal semi-active control provided by magneto-rheological dampers. Some numerical examples of integrated identification and vibration control of various time-varying structures subject to unknown earthquake excitation are used to demonstrate the performances of the proposed algorithm.

Dynamical analysis of the fractional-order centrifugal flywheel governor system and its accelerated adaptive stabilization with the optimality

This paper investigates the issues of dynamical analysis and accelerated adaptive stabilization of the fractional-order (FO) centrifugal flywheel governor system with optimality. The dynamic behavior of the centrifugal flywheel governor system is revealed and its local stability is discussed in the fractional calculus (FC). A speed function is introduced to accelerate convergence rate within a pre-given time and a hierarchical type-2 fuzzy neural network (HT2FNN) is employed to play an approximating role for unknown nonlinear items. An extended state tracking differentiator which overcomes repetitive differentiation problem is used to approximate the derivative of virtual control input. Then, a stabilization controller is designed by integrating with the speed function, neural network and tracking differentiator in the framework of backstepping. It is proved that the proposed scheme guarantees the boundedness of all signals of the closed-loop system by using the frequency distributed model and makes the predefined cost function smallest. Finally, simulation results verify the effectiveness of the presented scheme.

A Back-Stepping Control Method for Modular Multilevel Converters

In this article, a back-stepping method (BSM) in a–b–c reference is presented to establish the stable operating conditions for modular multilevel converter (MMC). The designed BSM utilizes arm currents, sum of submodule capacitors voltages and MMC input energy as the main variables to form the energy functions. The proposed BSM is designed by well-known dynamic MMC equations to be applicable for both single- and three-phase ones while the control of variables is also guaranteed by BSM. A virtual control input containing input energy error and its dynamics is defined in the second energy function to further enhance the appropriate transient responses of the MMC. The proposed BSM has inherent feature of the circulating current suppression control loops which helps avoiding additional control loops. Moreover, several assessments are presented to show how BSM coefficients contribute to the noticeable decrement in control variables errors of the MMC system. Experimental and simulation results prove an excellent capability of BSM for controlling MMCs compared to the conventional PI linear controller. Moreover, the BSM robustness against the variations of the MMC circuit parameters is validated.

Geometrical accuracy evaluation of an affordable 3D printing technology for spine physical models

ObjectiveThe aim of the study is to develop a workflow to establish geometrical quality criteria for 3D printed anatomical models as a guidance for selecting the most suitable 3D printing technologies available in a clinical environment. MethodsWe defined the 3D geometry of a 25-year-old male patient’s L4 vertebra and the geometry was then printed using two technologies, which differ in printing resolution and affordability: Fused Deposition Modelling (FDM) and Digital Light Processing (DLP). In order to measure geometrical accuracy, the 3D scans of two physical models were compared to the virtual input model. To compare surface qualities of these printing technologies we determined surface roughness for two regions of interest. Finally, we present our experience in the clinical application of a physical model in a congenital deformity case. ResultsThe analysis of the distribution of the modified Hausdorff distance values along the vertebral surface meshes (99% of values <1 mm) of the 3D printed models provides evidence for high printing accuracy in both printing techniques. Our results demonstrate that the surface qualities, measured by roughness are adequate (~99% of values <0.1 mm) for both physical models. Finally, we implemented the FDM physical model for surgical planning. ConclusionWe present a workflow capable of determining the quality of 3D printed models and the application of a high quality and affordable 3D printed spine physical model in the pre operative planning. As a result of the visual guidance provided by the physical model, we were able to define the optimal trajectory of the screw insertion during surgery.

Statistical accuracy analysis for virtual reference feedback tuning with two degrees of freedom controllers*

Virtual reference feedback tuning is one of data-driven control method, as only input–output data are used to design two degrees of freedom controller directly, i.e. feed-forward and feedback controller. Given two desired closed-loop transfer functions, virtual input and virtual disturbance are constructed, respectively to obtain one cost function, whose decision variables correspond to the two unknown controller parameters. Then after formulating the cost function as a linear regression form, the classical least squares algorithm is applied to identify the unknown parameter estimators. To quantify the quality or approximation error of the parameter estimators, statistical accuracy analysis is studied for virtual reference feedback tuning control. The detailed computational process about the asymptotic variance matrix is given by using some knowledge from probability theory and matrix theory. Based on our obtained asymptotic variance matrix, two applications of optimal input design and model structure validation are used to illustrate how to use the obtained asymptotic variance matrix. Finally, one simulation example has been performed to demonstrate the effectiveness of the theories proposed in this paper.

Almost global attitude stabilisation of a 3-D pendulum by means of two control torques

We investigate the problem of stabilising the attitude of a 3-D axially symmetric pendulum. The system is assumed to be actuated by two torques acting on a plane orthogonal to the symmetry axis. We develop a smooth control law to stabilise the pendulum to the upright position with a given orientation starting from almost all initial conditions. Our approach consists in two steps: first, stabilising the kinematic subsystem by using the angular velocity as a virtual input; second, exploiting the actual inputs to force the angular velocity to follow the reference designed in the previous step.

Adaptive NN Backstepping With Considering Integral of Tracking Error

In order to simplify the design procedure of traditional neural network backstepping and improve the robustness and precision of control, an improved scheme is studied for a class of nonlinear systems. To avoid reconstructing virtual control inputs in each recursive step, RBF neural networks are utilized as approximators to estimate the desired feedback control of the whole system only. Meanwhile, the integral action of tracking error is introduced into the backstepping design procedure, which not only participates in updating the neural network weight, but also serves as a component part of the control input. This design may benefit the parameter tuning and make controller perform better sometimes. Based on the Lyapunov synthesis approach, theoretical analysis and simulation results are provided to show the feasibility of the improved scheme.

Super Twisting Disturbance Observer-Based Fixed-Time Sliding Mode Backstepping Control for Air-Breathing Hypersonic Vehicle

This paper investigates the velocity and altitude tracking control problem for air-breathing hypersonic vehicle (AHV) under external disturbances and uncertainties. An improved smooth super-twisting based disturbance observer (SSTDOB) is proposed to estimate the unknown external disturbances. With the assistance of SSTDOB, an effective fixed-time sliding mode backstepping control (FSMBC) is designed to guarantee the tracking errors converge to a small neighbor of the origin. Meanwhile, a fixed-time tracking differentiator (FTD) is employed to estimate the virtual control inputs, which can eliminate the differential explosion problem. The overall stability of the closed-loop system is analyzed by utilizing Lyapunov stability theory. Simulation results demonstrate the effectiveness of the composite method.

Design of the controller module of mobile carrier radioactive source

A control module for mobile carrier radioactive source has been designed. Mobile carrier radioactive source is a tool used to carry out testing for radiation characteristics both statically and dynamically and to conduct calibration on the Radiation Portal Monitor according to the requirements of SNI IEC 62244-2016. The control module is designed to meet the that requirements, it can set a carrier speed of at least 8 km/h, it can adjust the height of the radioactive source between 1 m and 2.5 m, it has automatic forward and backward direction mode. Furthermore, the mobile carrier can be controlled remotely for personnel tester safety. The control module can stop the mobile carrier suddenly when an emergency occurs. The mobile carrier uses a portable power supply so that it can move freely and easily shifted. To meet these requirements, the driving power of the carrier a motor of 24-volt dc with 250 watts. The radioactive source uses a driving power of 12-volt dc motor with a minimum lift power of 5 kg. The control module designed uses a microcontroller with an android application-based interface that is connected by wireless. In the android application there are virtual numbers and input buttons to give commands to the control module. The application can also receive carrier speed information and the height of the radioactive source. To break the power of driving motor of carrier and the driving power of the lifter of the radioactive source, the mobile carrier uses two-level relays, namely low current conductivity relays and relays with high current conductivity. Next in order to move forward and backward automatically, at each end of the carrier is equipped with a limit switch. The button and top position barriers on the radioactive source lifter use a limit switch.

A Nonlinear Control Design Strategy for Piloting Fixed Wing Aircrafts

Abstract This paper proposes a novel nonlinear feedback control strategy for velocity and attitude control of fixed wing aircrafts. The key feature of the control design strategy is the introduction of a virtual control input in order to deal with the underactuation property of such vehicles and to indirectly control the orientaion of the aircraft. As such, the proposed strategy consists of three control loops each realising a specific task. Simulation results on Jetstream-3102 aircraft show very good performance in terms of convergence towards the desired reference trajectories and in terms of robustness with respect to modeling uncertainties.

Ecological Network-based Input-output Model for Virtual Water Analysis in China

In this study, an ecological network-based input-output model (ENIOM) is developed for assessing the virtual water in China. Direct/indirect water consumption efficiency and virtual water flow directions among different sectors are quantified by input-out model, and the relationship (e.g., exploitation, competition and mutualism) among different sectors are identified by network utility analysis. Based on China’s input-output table in 2017, results show that (i) agriculture sector has the highest direct water consumption coefficient, and manufacturing sector has the highest indirect water consumption coefficient; (ii) manufacturing sector is the largest virtual water input and output sector, with a total net input of 93.6×109 m3 from the remaining seven sectors; and (iii) exploitation is the main relationship existed in the water network system. These findings suggest that more attentions should be paid on agricultural and manufacturing sectors in terms of water resources management.

Universal Adaptive Fault-Tolerant Control of a Multicopter UAV

Abstract This paper presents a universal adaptive fault-tolerant control (FTC) design for multicopter unmanned aerial vehicles (UAVs). The proposed architecture consists of a two-loop control structure: a fault-tolerant controller generates normalized virtual control inputs to track the desired trajectory subject to actuator faults, and an adaptive augmentation controller deals with system uncertainties and also balances the design requirements for specific platform. The FTC approach is based on gain-scheduling control in the framework of structured H∞ synthesis. In order to implement the overall control system on most types of multicopter UAVs, an adaptive mapping algorithm is proposed. High fidelity simulations and experimental results, performed on various multicopters with different payload and configuration, show the effectiveness and robustness of the proposed approach in accommodating different levels of actuator degradation including total failures of the rotors as well as unknown mass and inertia, all using a single controller with fixed coefficients.

A globally fixed-time solution of distributed formation control for multiple hypersonic gliding vehicles

This paper investigates the distributed formation control problem for multiple hypersonic gliding vehicles (HGVs) under direct communication topology. Based on a formation flight framework of multiple HGVs, a globally fixed-time formation control scheme is proposed by using the fixed-time stability and the hierarchical control theory. Firstly, a fixed-time consensus law is addressed in the three-dimensional formation flight dynamics to generate the virtual control inputs. In order to design appropriate actual control inputs to track the virtual control commands rapidly and accurately, a composite fixed-time feedback control law is then put forward, where a new fixed-time tracking differentiator is designed to obtain the information on the time derivatives of virtual control inputs. Following, the problem of “explosion of complexity” can be resolved effectively. Finally, the globally fixed-time convergence is achieved in spite of the initial conditions of HGV's states, where the upper bound of the settling time can be estimated in advance by only using the control parameters and the direct communication topology. The desired formation configuration can be established within a prescribed convergence time. Extensive numerical simulations are performed to demonstrate the effectiveness and superiority of the proposed formation control strategy.

Adaptive Backstepping Nonsingular Fast Terminal Sliding Mode Control for Hydro-Turbine Governor Design

To investigate a typical large-scale nonlinear hydropower system (HS) with a stochastic water flow, a novel nonlinear adaptive control scheme, which is created by the combination of a backstepping strategy, nonsingular fast terminal sliding mode surface and command filter, is proposed for the hydro-turbine governor design of a HS to not only improve the transient stability of the HS but also increase the energy conversion efficiency and improve the reliability and availability of the electricity supply. In contrast to previous research based on ideal hydro-turbine models with accurate parameters, an adaptive backstepping nonsingular fast terminal sliding mode control (ABNFTSMC) with command filtered (CF) is proposed in which virtual control inputs and error compensations are applied to overcome distribution characteristics resulting from energy losses, while guaranteeing finite-time convergence. In addition, to avoid the requirement of analytic differentiation in Lyapunov stability, a command filter method is used to generate certain compensating signals and their derivatives. In this paper, the Nazi Gorge hydropower station in China is used as our verification model of a hydropower plant with monitored data, where energy losses and random water flow disturbances are considered. Simulation results illustrate that the proposed control strategy for a hydro-turbine governor can significantly increase the stability, reliability, and system performance of a HS even in the presence of uncertainties.