Position tracking for a nonlinear underactuated hovercraft: controller design and experimental results

In this paper, two knowledge based controllers are proposed to overcome the difficulties of a computed torque nonlinear controller (NC) in perfect trajectory tracking of nonholonomic wheeled mobile robots (WMRs). First, the effects of different dynamic models developed in angular andCartesian coordinate systems are fully examined on the persistent excitation condition and consequently on the trajectory tracking performance of WMRs. Using the dynamic model coordinated in theCartesian frame as the base of theNCresults in perfect compensation of large position off‐tracks and unbiased estimation of the plant's unknown parameters. However, using theWMR's dynamic model with rotation angles of driving wheels as the base of nonlinear and fuzzy controllers leads to accurate orientation tracking. Through replacing the proportional and differential terms of theNCby fuzzy functions, a fuzzy nonlinear controller (FNC) is generated. Due to the complicated dynamics of the WMR in which the center of mass does not coincide with the center of rotation, the expert knowledge of fuzzy controllers is extracted considering the rotation angles and rates of driving wheels as input variables. Fuzzy tuning of theNCresults in a superior tracking performance against measurement noises, though the control torques are decreased and smoothed significantly. Second, a complete fuzzy controller (FC) is generated to make perfect tracking of theWMR's position and orientation. The local stability analysis of fuzzy controllers is examined considering the corresponding analytical structures as nonlinear controllers. The superior performances of the proposed fuzzy controllers compared to those of theNCs are evaluated through simulations.

This article proposed a nonlinear robust controller to achieve vehicle creep for dual-clutch transmission. The control problem is summarized as the tracking control, and linear quadratic approach is adopted to define the trajectory of the clutch slip before the controller design. The control scheme is derived from an error affine nonlinear system; meanwhile, by combining nonlinear H∞ method with the backstepping technique, the nonlinear controller is programmed to achieve the tracking of the clutch slip trajectory against the model uncertainties or disturbance. The designed controller is evaluated by simulation model including the dynamic powertrain and hydraulic actuator model, and the results show that the nonlinear controller is effective in clutch slip tracking control and has better control performance than that of the proportional–integral–derivative in terms of disturbance attenuation.

In response to the non-linear and underactuated characteristics of quadrotor UAV suspension transportation system, this paper proposes a novel control strategy aimed at achieving precise position control, attitude control, and anti-swing capabilities. Firstly, a dynamical model required for controller design is established through the Newton-Euler method. In the controller design process, the paper employs the energy method and barrier Lyapunov function to design a double-closed-loop nonlinear controller. This controller is capable of not only accurately controlling the position and attitude angles of the quadrotor UAV suspension transportation system but also effectively suppressing the swing of the payload. Building on this, considering the elastic deformation of the lifting cable, and by analyzing the forces in the Newton-Euler equations, this paper proposes an adaptive control design for the case where the length of the cable connecting the UAV and the payload is unknown. To validate the effectiveness of the proposed control scheme, comparative experiments were conducted in the MATLAB simulation environment, and the results indicate that the method proposed in this paper exhibits superior control performance compared to traditional controllers.

As a novel nonlinear control, backstepping is applied to the position tracking controller design of PMSM servo system. The design rule of backstepping makes the system global ultimate asymptotical stabilization(GUAS). The controller not only makes the system GUAS, but also has a quick and accurate position tracking performance. The position tracking can be greatly affected by the change of load torque. To efficiently reduce the effect of the change of load torque, the system design can estimate the load torque and regulate the controller with real time. The design can make the change of load torque have very little disturbance caused due to the position tracking error. At last, Matlab is used to simulate the whole system to prove the efficiency and feasibility of system design.

This paper is concerned with control design for a generalized discrete-time Takagi-Sugeno fuzzy system. The Takagi-Sugeno fuzzy system generally describes nonlinear systems by employing local linear system representations. It is a great tool to analyze a nonlinear system and to design a stabilizing controller for it. However, there is a case where a controller design for a nonlinear system based on the Takagi-Sugeno fuzzy system becomes difficult due to its representation. A generalized fuzzy system to be considered in this paper describes even a wider class of nonlinear systems by representing locally nonlinear systems, and gives a different representation from the standard Takagi-Sugeno fuzzy system, which leads to a rather easy controller design. For such a generalized system, a stabilizing controller design method is proposed by introducing a new class of nonlinear controllers. Then, the resulting closed-loop system becomes a fuzzy system with linear system structures locally, which makes the control design easier. Stabilizing controller design conditions are given in terms of a set of linear matrix inequalities(LMIs), which are easily numerically solvable. A relaxation method is used to reduce the conservatism of design conditions. Finally, numerical examples are given to illustrate our nonlinear control design and to show the effectiveness over other existing results.

A nonlinear position tracking controller with a disturbance observer (DOB) is proposed to track the desired position in the presence of the disturbance for electrohydraulic actuators (EHAs). The DOB is designed in the form of a second-order high-pass filter in order to estimate the disturbance. The nonlinear controller is designed for position tracking as a near input-output linearizing inner-loop load pressure controller and a backstepping outer-loop position controller. Variable structure control is implemented in order to compensate for the error in disturbance estimation. The desired load pressure is designed to generate the pressure using the differential flatness property of the EHA's mechanical subsystem. The disturbance within the bandwidth of the DOB can be cancelled by the proposed method. The performance of the proposed method is validated via simulations and experiments.

Dynamical systems are often nonlinear in nature. It motives people to explore various theoretical nonlinear analysis and control design tools, of which constructive nonlinear design methods are the most celebrated ones. However, applying a constructive tool faces up a big hurdle that the tool deals only with a certain dynamical structure, often not possessed by the natural dynamics. Nonlinear constructive control designs heavily relies on the identification of a particular structure via coordinate transformation and control transformation. To be realistic, these theoretical tools are not general to all of the nonlinear systems. Here, a challenging benchmark example–a four degrees of freedom inverted pendulum under the influence of a planar force–is considered that is nonlinear, multiple input and multiple output, underactuated and unstable. The benchmark is also of practical interests because it is an abstract of several applications. Three challenging control objectives are envisaged for the first time in the literature in order to how to apply various cuttingedge theoretical nonlinear control tools. In fact, the key step of all of the nonlinear designs is to identify spectral structures– certain “normal” forms. From this aspect, a sequence of preliminary designs will accompany the existing tools to construct nonlinear controllers, which is quite different from the linear control designs.

Electric power system is complex interconnected system that is subjected to rapid change in its structure. Addition of new equipment, operation close to stability limits and variation in load in summer and winter are some factors that make power system unstable and introduce electro-mechanical oscillations in the system.;Electro-mechanical oscillations of small magnitude often persist for long periods of time and restrict the power transfer capacity. These oscillations can further increase with the variation in load and system operating points. To stabilize the power system different control strategies are used to damp the oscillations. In the past, the dynamic stability of power system was modeled using linearized modeling of power system at operating points. Linear eigenvalue controllers damp the oscillation to some extent but are not robust for disturbance and variation in system operating points and therefore can render system unstable.;Non-linear controller design has found extensive application in robotics for stabilizing system. Synergetic Controller based on Synergetic Control Theory, is a non-linear controller that forces the system towards global stability and has extensively been used in power electronics.;In this research, a Single Machine Infinite Bus (SMIB) with HVDC link is considered for comparing the performance of linear and non-linear controllers. The test system has Static Var Compensator (SVC) connected on load bus. Reactive modulation is performed through SVC to damp oscillations in the system. The Synergetic Controller is designed for full transient model and the classical model of the synchronous machine.;The performance of both non-linear controller and linear controller is compared for different disturbance and variation in system parameters. Results show the robustness of non-linear controller which damps the oscillations effectively.

Guidance and control law design for missiles traveling at hypersonic speeds is an extremely difficult task due to the inherently coupled nonlinear nature of the system dynamics. The controller designs are further complicated by model uncertainty and unmodeled disturbances, which are inevitable in practical application. Beyond the challenges inherent in the system dynamics, additional complications arise in the design of hypersonic missile control laws, where terminal constraints are imposed in order to optimize target penetration. In this research, a robust nonlinear control technique is combined with an optimal control method to develop a control law for air-breathing hypersonic missiles in the presence of model uncertainty and unmodeled, nonlinear exogenous disturbances. The control law presented in this paper is designed to be computationally inexpensive, requiring no observers, online adaptive laws, or function approximators. One of the contributions of this research is detailed theoretical analysis of the performance characteristics of the proposed tracking control design. In addition, maximum target penetration is achieved by generating an optimal desired trajectory that incorporates terminal constraints in the cost function. Specifically, the trajectory optimization routine is designed to minimize angle of attack (AoA) and inertial angle of obliquity (AoO) at impact. A Lyapunov-based stability analysis is utilized to prove global asymptotic trajectory tracking, and high-fidelity numerical simulation results are provided to verify the practical performance of the proposed guidance law design.

ABSTRACTHeart rate can be used to define exercise intensity; feedback control systems for treadmills which automatically adjust speed to track arbitrary heart rate target profiles are therefore of interest. The aim of this study was to compare linear (L) and nonlinear (NL) controllers using quantitative performance measures. Sixteen healthy male subjects participated in the experimental L vs. NL comparison. The linear controller was calculated using a direct analytical design that employed an existing approximate plant model. The nonlinear controller had the same linear component, but it was augmented using static plant-nonlinearity compensation. At moderate-to-vigorous intensities, no significant differences were found between the linear and nonlinear controllers in mean RMS tracking error (2.34 vs. 2.25 bpm [L vs. NL], p=0.26) and average control signal power (51.7 vs. m2/s2, p=0.16), but dispersion of the latter was substantially higher for NL (range 45.2 to 56.8 vs. 30.7 to m2/s2, L vs. NL). At low speed, RMS tracking errors were similar, but average control signal power was substantially and significantly higher for NL (28.1 vs. m2/s2 [L vs. NL], p<0.001). The performance outcomes for linear and nonlinear control were not significantly different for moderate-to-vigorous intensities, but NL control was overly sensitive at low running speed. Accurate, stable and robust overall performance was achieved for all 16 subjects with the linear controller. This points to disturbance rejection of very-low-frequency heart rate variability as the overriding challenge for design of heart rate controllers.

Robust Nonlinear EGR and VGT Control with Integral Action for Diesel Engines

Output feedback nonlinear control for electro-hydraulic systems

To achieve more precise positioning of the electronic throttle plate, a nonlinear backstepping tracking control strategy is presented in this paper. In contrast to the existing control schemes for electronic throttles, the input saturation and unknown external disturbances are explicitly considered in the tracking control design. The difficulties in controlling an electronic throttle include the strong nonlinearity of the spring and friction as well as the unknown external disturbance. In particular, the valve plate angle is adjusted by the control input voltage of the driving motor, and the input voltage is limited to a certain range. Therefore, input saturation problems exist in the control system for an electronic throttle. To overcome the abovementioned difficulties, an auxiliary design system is presented to handle the input saturation, and its state is applied in the proposed control design. A sliding-mode control term is also utilized in the tracking controller to counteract the unknown external disturbance. The proof and analysis show that the satisfactory tracking performance of the valve plate angle can be achieved by using the designed control scheme for the electronic throttle system in the presence of input saturation and unknown external disturbances. Simulation studies and results are provided to illustrate the desired performance of the proposed nonlinear tracking controller.

This paper presents a new composite nonlinear bilateral control method based on the nonlinear disturbance observer &#x0028 NDOB &#x0029 for teleoperation systems with external disturbances. By introducing the estimations of NDOB and systems&#x02BC nominal nonlinear dynamics into controller design, a NDOB based composite nonlinear bilateral controller is constructed to attenuate the influence of disturbance and uncertain nonlinearities. As compared with the existing bilateral control methods which usually achieve force haptic &#x0028 i.e., contact force tracking &#x0029 through a passive way, the newly proposed method has two major merits: asymptotical convergence of both position and force tracking errors is guaranteed; disturbance influence on force tracking error dynamics is rejected through the direct feedforward compensation of disturbance estimation. Simulations on a nonlinear teleoperation system are carried out and the results validate the effectiveness of the proposed controller.

In this paper, we study the congestion control problem in TCP satellite networks, and present a new design for TCP network congestion control based on a nonlinear control and optimization framework. The proposed TCP/AQM control framework consists of two levels: the high-level generates the desired queue size for routers in the network by solving a network utility maximization problem using a distributed optimization scheme; the low-level provides a local nonlinear feedback control for the probability of packet mark/drop based on a typical fluid-flow model for TCP dynamical behaviors. The nonlinear control design is done using a backstepping method and its stability is proven by the Lyapunov direct method. Simulation results are included to show the effectiveness of the proposed new design.