Search

Model-based fault diagnosis serves as a powerful technique for addressing fault detection and isolation issues in control systems. However, diagnosing faults in closed-loop control systems is more challenging due to their inherent robustness. This paper aims to detect and isolate actuator and sensor faults in the cascade electro-hydraulic control system of a turbofan engine. Based on the fault characteristics, we design a robust unknown perturbation decoupling residual generator and an optimal fault observer specifically for the inner and outer control loops to detect potential faults. To locate the faults, we analyze the steady-state propagation laws of actuator and sensor faults within the loops using the final value theorem. Based on this, we establish the minimal-dimensional fault influence distribution matrix specific to the cascade turbofan engine control system. Subsequently, we construct the normalized residual vectors and monitor its vector angles against each row of the fault influence distribution matrix to isolate faults. Experiments conducted on an electro-hydraulic test bench demonstrate that our proposed method can accurately locate four typical faults of actuators and sensors within the cascade electro-hydraulic control system. This study enriches the existing fault isolation methods for complex dynamic systems and lays the foundation for guiding component repair and maintenance. [ABSTRACT FROM AUTHOR]

A novel cascade visual control scheme is proposed to tailor for electrically driven robotic manipulators that operate under kinematic and dynamic uncertainties, utilizing an uncalibrated stationary camera. The proposed control approach incorporates adaptive weight radial basis function neural networks (RBFNNs) to learn the behaviors of the uncertain dynamics of the robot and the joint actuators. The controllers are designed to nullify the approximation error and mitigate unknown disturbances through an integrated robust adaptive mechanism. A major advantage of the proposed approach is that prior knowledge of the dynamics of the robotic manipulator and its actuator is no longer required. The controller autonomously assimilates the robot and actuator dynamics online, thereby obviating the need for fussy regression matrix derivation and advance dynamic measurement to establish the adaptive dynamic parameter update algorithm. The proposed scheme ensures closed-loop system stability, bounded system states, and the convergence of tracking errors to zero. Simulation results, employing a PUMA manipulator as a testbed, substantiate the viability of the proposed control policy. [ABSTRACT FROM AUTHOR]

This paper addressed the robust distributed fixed-time cooperative hunting problem of multiple quadrotors subject to disturbances in obstacles environment. To handle the underactuated issue inherent in quadrotor dynamics, an inner–outer (attitude-position) loop cascade control configuration is proposed to achieve the cooperative flight control of quadrotors. For position subsystem, as the information of target cannot be accessible to all quadrotors, a distributed fixed-time observer is devised to estimate the target's information. To improve the system's robustness, a fixed-time extended state observer is designed to reject disturbances actively. Based on two observers, the sliding mode position encirclement control protocol with repulsive force is presented to avoid obstacles and encircle the target within a fixed time. For attitude subsystem, a sliding mode attitude tracking control protocol is proposed such that tracking errors can converge to zero even under disturbances. The stability analysis is performed to show the stabilization of the whole closed-loop system with fixed-time convergence. Finally, two sets of comparison simulation are provided to show the superiority of the developed control strategy. • A distributed fixed-time observer is designed to estimate the target's information. • Two fixed-time extended state observers are presented to compensate the effects of disturbances. • The sliding mode position controller and attitude tracking controller are developed to avoid obstacles and encircle the target. [ABSTRACT FROM AUTHOR]

This paper investigates the robustness of output feedback control to the input delay mismatch for a wave-ODE cascaded system with the time-varying input and output delays. Firstly, we convert the output delay into a transport equation, resulting in a wave-ODE-transport coupled system. Secondly, we design an output feedback control for the coupled system without input delay mismatch, and prove the well-posedness and exponential stability of the closed-loop system. Then, the key point is that we prove that this control still works when there exists an input delay mismatch. Finally, some numerical simulations are given, which illustrate the effectiveness and robustness of the proposed control. [ABSTRACT FROM AUTHOR]

In this paper, the global stabilization problem of control systems with input saturation and multiple input delays is studied, and a new method is proposed to design nonlinear stabilization control laws. First, based on Luenberger's canonical decomposition, the multiple-input delay system is transformed into a series of linear time-delay systems with single inputs and input saturation. However, for the converted system, each subsystem is coupled to the others. Therefore, the idea of recursion is adopted to construct a special state transformation with time delay for each subsystem and convert it into a linear system with time delay for both state variables and input variables. For the conversion system, a nonlinear controller with cascade saturation control is designed, and the controller includes some free parameters. The control performance of the controller is improved by adjusting the free parameters online. At the same time, a less conservative stability condition is established to ensure the dynamic performance of the closed-loop system. Finally, the effectiveness and superiority of the proposed method are verified by numerical simulation and practical applications in a spacecraft rendezvous system. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a non‐fragile control approach for a non‐isolated two‐switch buck‐boost converter used as an on‐board charger for electric vehicles. The control scheme is based on a cascaded two‐loop configuration with non‐fragile Proportional Integral controllers in the inner current and the outer voltage loop. The control approach is based on designing a control law that can stabilize the closed‐loop system subject to uncertainties in the controller parameters while satisfying the H∞ norm bound constraint on disturbance attenuation. The proposed control technique helps to deal with inevitable uncertainties during the implementation of any control scheme. The proposed control technique is compared with the conventional approach and validated through experimental results. The experimental results are obtained from a 1‐kW laboratory prototype of a TSBB converter with an output voltage range of 150–400 V. The results demonstrate that the proposed approach effectively achieves good robustness against controller parameter variations and disturbances under various operating conditions. [ABSTRACT FROM AUTHOR]

Quadcopters are a type of unmanned aerial vehicles (UAV) that are kept aloft by four rotors. They are gaining increasing popularity for a variety of applications. However, quadcopters can be difficult to control and are susceptible to disturbances such as wind gusts. In this paper, we present a method for modelling, controlling, and simulating a quadcopter. The complete mathematical dynamics of quadcopter motion is obtained using Newton-Euler formalism. Stabilisation and trajectory tracking of the quadcopter are achieved by designing a cascade control scheme with nonlinear PID controllers and linear PD controllers. The nonlinear PID controllers in the inner loop stabilise the attitude of the quadcopter, while the linear PD controllers in the outer loop produce the desired references of the inner loop. The nonlinear PID controllers use error scaling in the integral action to improve the stability and performance of the closed-loop system. Based on the nonlinear model and control laws derived in this work, a graphical user interface (GUI) simulator is developed in terms of combining visualisation with animation features. Then, the effectiveness of the proposed method is evaluated through a set of simulation works on the nonlinear mathematical model. The results show that the quadrotor reaches the desired position within 4 s and effectively stabilises at the appropriate time. The proposed simulator will help engineers and researchers to tune controller parameters or test the performance of the quadcopter. [ABSTRACT FROM AUTHOR]

This paper investigates an optimal model-free control design for a synchronous reluctance motor (Syn-RM) with unknown nonlinear dynamic functions, parameter variations, and disturbances. The idea is to combine a predictive control with a time-delay estimation technique (TDE) in order to successfully deal with the system's uncertainties and make the Syn-RM control scheme easy to implement in real-time. This model-free control strategy comprises two cascade control loops namely outer and inner loops. The outer loop is designed for the mechanical part of Syn-RM to ensure the convergence of the speed dynamics by using a proportional-integral controller while the inner loop is developed to control the uncertain dynamics of currents via an optimal robust controller. In the proposed current loop, the predictive control is enhanced by the inclusion of ultra-local model theory where dynamic functions and disturbances are estimated by instantaneous input-output measurements of the Syn-RM using the TDE approach. Moreover, a particle swarm optimization (PSO) algorithm is also proposed to find the optimal design parameters to improve the dynamic performances of the closed-loop control system. Numerical validation tests of the proposed TDE-based model-free predictive current control (TDE-MFPCC) method are performed in the simulation environment of the Syn-RM system, and the results show the robustness and the effectiveness of the proposed TDE-MFPCC compared to the conventional model-based PCC. [ABSTRACT FROM AUTHOR]

In this study, we propose a data-driven design method for a cascade control system with inner and outer control loops. First, the input–output response of a controlled plant, which varies with the controller parameters of a fixed-structure inner-outer control law, is estimated directly from open-loop input–output data. Next, based on the estimated response, the controller parameters are optimized to minimize the difference between a reference model with a controlled closed-loop system. In the proposed method, the response of a fictitious reference input, which varies with the controller parameters, is estimated, and then the closed-loop response is estimated. Therefore, a closed-loop input–output data is not required, and the controller parameters are determined directly from an open-loop input–output data. Furthermore, the time constant of a reference model is also optimized so as to reduce the control error. The proposed method is compared with both conventional single-loop and cascade data-driven methods by means of numerical examples. • A data-driven cascade control system with inner and outer control loops is proposed. • Input-output response which varies with controller parameters is estimated. • The controller parameters that minimize a model reference problem are obtained. • The time constant of a reference model is also optimized. • The proposed method is compared with conventional single-loop and cascade methods. [ABSTRACT FROM AUTHOR]

This paper is concerned with the finite‐time boundedness (FTB) problem of a class of cascade switched affine nonlinear systems. In order to avoid unnecessary waste of network communication and Zeno behavior, a dynamical event‐triggered scheme is proposed, which is more general than some existing event‐triggered schemes with a common parameter matrix. By using the average dwell time method and multiple Lyapunov function technologies, sufficient conditions for the existence of controller gains are first proposed such that the closed‐loop system is finite‐time bounded with a finite‐time disturbance attenuation performance. It is also proved that the Zeno phenomenon is excluded. Finally, a numerical example is given to illustrate the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes an optimization‐based approach to selecting the sampling periods for classes of linear time‐invariant (LTI) regulators in a cascaded multi‐rate control structure, to account for practical implementation on numeric systems. Starting from the Shannon‐Nyquist sampling theorem, which proposes the minimum required sampling frequency for completely recovering the original analog signal from its discrete samples, the scope of the sampling process, viewed from a control perspective, is to ensure asymptotic stability of the closed‐loop system, with the smallest possible degradation of the initially‐proposed performance indices as possible according to a set of well‐picked criteria. As such, a configurable optimization‐based approach is proposed, solved with the mixed‐integer artificial bee colony (MI‐ABC) algorithm, for selecting the sampling periods by specifying the emphasis between closed‐loop fidelity and ease of implementation, with an intuitive visualization method. The proposed solution is illustrated on two case studies, with emphasis on the construction of the proposed functionals and their practical implications. [ABSTRACT FROM AUTHOR]

Every closed-loop system holds a level of fault tolerance, which could be increased by using a fault tolerant control (FTC) scheme. In this paper, an efficient FTC scheme for a class of nonlinear systems (Euler–Lagrange ones) is proposed, which guarantees high performance and stability in a faulty system. This scheme was designed on the basis of a cascade control structure in which the inner loop is the closed-loop system and the external loop is the FTC, a generalized proportional integral (GPI) observer-based controller, which manages the fault tolerance level increment. An important issue of the proposed scheme is that the GPI observer-based controller jointly estimates disturbances and faults, providing information about the state of health of the system, and then compensates their effect. The scheme is efficient because only the inertia matrix is required for the controller design, it is able to preserve the nominal control law unchanged and can operate properly without explicit information about system faults (fault diagnostic module). Simulation results, on a pendulum model, show the effectiveness of the proposed scheme for tracking control. [ABSTRACT FROM AUTHOR]

This article presents a nonlinear passivity-based control for a grid-connected cascaded H-bridge (CHB) photovoltaic (PV) system. The proposed control system is based on a port-controlled Hamiltonian model extracted from the synchronous reference frame system. Grid current dynamics is included in this model. Compared to existing solutions, the proposed control method has a robust performance and enhances the stability of the CHB-based PV system in the case of disturbances such as unequal irradiance over distinct PV arrays or a sudden sag or swell in the grid voltage. This controller also provides the independent control of each dc-link voltage. Therefore, the individual maximum power point tracking algorithms can be realized in each PV array, and the harvested energy can be maximized. Finally, simulation results and experimental investigations are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This work reveals an Internal Model Control (IMC)-based series cascade control for the non-minimum phase and time delay process. The combination of a higher-order fractional IMC filter and inverse response compensator for designing the outer loop controller illustrates the uniqueness of this work. For the time delay term, a higher-order approximation is considered. The standard IMC-PID structure adopts for the inner loop controller design. While the higher-order fractional filter coupled with inverse response compensator takes for the design of the outer loop controller. The suggested scheme demonstrates enhanced exhibition for setpoint tracking and disturbance rejection. Moreover, the sensitivity analysis is also accomplished to determine the robustness of the closed-loop system under process parameter variations. [ABSTRACT FROM AUTHOR]

A high-performance electrical drive with a permanent magnet synchronous motor (PMSM) should ensure superior dynamic properties, reasonable load torque compensation, and robustness against parameter variations. The performance investigation related to the dynamic properties is usually made using the step response indicators and integral performance indexes. The robustness evaluation is more complex than performance analysis since there are no simple tools for this purpose, especially if it is done experimentally to consider nonlinearities and unmodeled dynamics of the plant. In this article, sensitivity functions suitable for investigating the closed-loop control systems in the time and the frequency domain are proposed, explained, and experimentally verified. Three control schemes designed for the speed control of PMSM are analyzed: a cascade control structure, robust two-degrees-of freedom speed controller, and a cascade-free constrained state feedback controller. Studies are conducted for experimental responses of the drive in the time and the frequency domain to investigate the sensitivity of the PMSM drive against the moment of inertia and load variations. Analysis of nonlinearities influence on the developed sensitivity functions is also presented. [ABSTRACT FROM AUTHOR]

The current journal paper proposes an end-to-end analysis for the numerical implementation of a two-degrees-of-freedom (2DOF) control structure, starting from the sampling rate selection mechanism via a quasi-optimal manner, along with the estimation of the worst-case execution time (WCET) for the specified controller. For the sampling rate selection, the classical Shannon–Nyquist sampling theorem is replaced by an optimization problem that encompasses the trade-off between the fidelity of the controllers' representation, along with the fidelity of the resulting closed-loop systems, and the implementation difficulty of the controllers. Additionally, the WCET analysis can be seen as a verification step before automatic code generation, a computational model being provided. The proposed computational model encompasses infinite-impulse response (IIR) and finite-impulse response (FIR) filter models for the controller implementation, along with additional relevant phenomena being discussed, such as saturation, signal scaling and anti-windup techniques. All proposed results will be illustrated on a DC motor benchmark control problem. [ABSTRACT FROM AUTHOR]

In this paper, a cascade control structure with the modified Smith delay compensator for controlling nonsquare MIMO process is proposed. The proposed structure is designed with two disturbance estimators and a setpoint tracking controller. The estimators reject the disturbances in the forward path. These estimators also take part in delay compensation. The design of setpoint tracking controllers and disturbance estimators uses simple mathematical calculations as compared to the conventional IMC-based controllers. In the proposed design, Grey wolf optimization technique has been used to optimize the predictor. The closed-loop system produces the desired servo and regulatory response. The internal stability and robustness of the proposed MIMO cascade control structure have been analyzed. An example of a physical process has been included to illustrate the novelty of the proposed control strategy over multivariable PID controllers in terms of the time-domain performance and delay compensation. query Please check the edit made in the article title. [ABSTRACT FROM AUTHOR]

Limited-angle torque motor (LATM) is a critical component to precisely drive the valve angle of an engine's fuel metering apparatus and accurately measure the fuel flow, and research on it is of great significance. Thus, the LATM of a certain kind is regarded as the research object in this paper. Firstly, a Simscape-based LATM integrated physical modeling method is proposed, which can better demonstrate the real operational characteristics of a motor, compared with the current mathematical model. Secondly, a Proportional-Integral-Derivative (PID) parameter self-tuning method based on a constriction factor particle swarm optimization (CPSO) algorithm is broached since it is difficult to tune due to a large number of multi-loop cascade PID control parameters. Simulation and experimental results showed that the control performance increases by 40% in the triple closed-loop PID control system with a stronger disturbance rejection, simpler design, and quickly responds when compared with the previous empirical tuning method. The triple closed-loop PID control system comprises an angle loop + angle velocity loop + current loop and technically supports the engineering application design of motors. [ABSTRACT FROM AUTHOR]

Artificial intelligence can bring convenience to human life. In the field of sports rehabilitation, the application of artificial intelligence is becoming more and more in-depth. This paper is aimed at studying the prevention and detection of sports rehabilitation in the context of artificial intelligence and proposing a compliance control method for lower limb rehabilitation robots based on artificial neural networks. In this paper, a double closed-loop control system is designed: the outer loop is an adaptive impedance control model based on sEMG feedback, and the purpose is to adjust the predicted desired joint trajectories. In the inner loop, a sliding mode iterative learning controller is designed to suppress periodic disturbance and abnormal jitter and achieve stable tracking of the target trajectory. Finally, the control method is simulated and verified by matlab/simulink, and a statistical experiment is done on the patient's recovery. The experimental results show that the use of artificial intelligence technology can effectively increase the sensitivity of the control system and improve the recovery rate of patients. Compared with the traditional sports rehabilitation control system, the sensitivity is increased by 22.7%, and the patient recovery rate is increased by 10.4%, which is of great significance in the field of sports rehabilitation. [ABSTRACT FROM AUTHOR]

This paper focus on passivity and passive control for a cascade nonlinear system consisting of two switched systems. The asymptotic stability criterion for the cascade system is developed without requiring passivity of subsystem in the whole state interval. Passivity and stabilisation of the closed-loop system are achieved by co-designing an output feedback control law and a state-dependent switching signal if the full output information is measurable. While the output information of the first switched system are not available, the sampled integral stabilisation (SIS) technique which only adopts the output information and common energy function of the second one, is exploited to achieve passive control of two switched systems connected in a cascade way. Then, a particular case of cascade system where only one passive switched system exists is stabilised via SIS technique. Finally, the validity of the developed results is demonstrated via a plane articulation arm example. [ABSTRACT FROM AUTHOR]

In order to take advantage of the capabilities of a shunt active power filter (SAPF), the design of an adequate control scheme must be developed; generally, the SAPF control scheme corresponds to a cascade control composed of an inner loop and an outer loop. This article approaches the design of an inner loop control based on linear matrix inequalities (LMIs) for a SAPF with LCL coupling filter. The control design begins with the system rewriting in exact Takagi‐Sugeno (TS) models, in the sequel, through the use of a quadratic energy function, and considering the closed‐loop system, the Lyapunov direct method to establish LMI conditions is used. This proposal of inner loop control is called TSLMI, and in conjunction with a PI control, a PI‐TSLMI cascade control scheme is configured. The SAPF objectives are the reduction of the total harmonic distortion (THD) in the mains current, the power factor (PF) correction, and facing load changes. The results show a correct performance of the proposed PI‐TSLMI for both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an iterative learning control (ILC) scheme augmented with the feedback control for solving the nonlinear stabilisation and tracking control problem of ball on plate system, which is a class of under-actuated visual servo system. To enhance the trajectory tracking performance and deal with the real-time challenges of ball on plate system including the nonlinearity, inter-axis coupling and uncertain dynamics, we present a feed-forward learning control scheme, which iteratively updates the control input from one trial to the next, integrated with the cascade control. The ILC update law is synthesised based on the current iteration tracking error (CITE), and the uniform convergence of the input control sequence is presented using the contraction mapping technique. From image processing standpoint, for detecting the foreground objects from a video stream, a background subtraction algorithm using frame difference technique is employed. The efficacy of the proposed scheme is tested on a laboratory scale ball on plate system using hardware-in-the-loop (HIL) testing. Experimental results substantiate that augmenting the learning control with the feedback control not only reduces the tracking error significantly but also enhances the robustness of the closed loop system against the poor lighting conditions. [ABSTRACT FROM AUTHOR]

This paper investigates an observer-based deadbeat predictive speed controller (DBPSC) for a prototype surface-mounted permanent magnet synchronous motor (SPMSM) drive system. Unlike the conventional deadbeat controllers which are mainly used for deadbeat current control in the inner loop in a cascaded control structure, the proposed deadbeat controller is designed by incorporating a speed controller with a load torque disturbance observer. Specifically the proposed deadbeat speed control law consists of a deadbeat stabilizing feedback control term and a compensation control term. The stability of the proposed closed-loop system is assured based on the former term by forcing all poles of the dynamic error vector toward the origin within a short transient time, which guarantees a fast transient response of the control system by using the solution of an optimal control problem. The latter term is proposed based on the predicted q -axis current to compensate for the model nonlinearities and parameter uncertainties. Next, the deadbeat load torque observer (DBLTO) is proposed to provide a precisely estimated load torque with a high estimation rate for the predicted q -axis current in the latter term, which helps the proposed scheme in obtaining a small steady-state error (SSE), a low total harmonic distortion (THD), and robustness against the parameter variations. In addition, the proposed scheme possesses a simple structure, so it reduces the computational burden for digital implementation. The Lyapunov theory is utilized in the stability proof process of the proposed observer-based method. Finally, the comparative studies between the proposed DBPSC and a conventional deadbeat speed controller (DBSC) are performed under the sudden changes of speed and load torque through simulations on MATLAB/Simulink and experiments on a prototype SPMSM drive using a TI TMS320F28335 DSP platform. [Display omitted] • An observer-based deadbeat predictive speed controller for SPMSM is proposed. • All poles of the dynamic error vector are forced toward the origin in a short time. • Parameter uncertainties are compensated based on the predicted q -axis current. • The improved robustness is proven via the root locus in z -plane. • The load torque is precisely estimated via the deadbeat load torque observer. [ABSTRACT FROM AUTHOR]

In this study, a DC micro-grid consisting of multiple paralleled energy resources interfaced by both bidirectional AC/DC and DC/DC boost converters and loaded by a constant power load (CPL) is investigated. By considering the generic dq transformation of the AC/DC converters' dynamics and the accurate nonlinear model of the DC/DC converters, two novel control schemes are presented for each converter-interfaced unit to guarantee load voltage regulation, power sharing and closed-loop system stability. This novel framework incorporates the widely adopted droop control and using input-to-state stability theory, it is proven that each converter guarantees a desired current limitation without the need for cascaded control and saturation blocks. Sufficient conditions to ensure closed-loop system stability are analytically obtained and tested for different operation scenarios. The system stability is further analysed from a graphical perspective, providing valuable insights of the CPL's influence onto the system performance and stability. The proposed control performance and the theoretical analysis are first validated by simulating a three-phase AC/DC converter in parallel with a bidirectional DC/DC boost converter feeding a CPL in comparison with the cascaded PI control technique. Finally, experimental results are also provided to demonstrate the effectiveness of the proposed control approach on a real testbed.

Virtual reference feedback tuning (VRFT) is a data‐driven control method that optimises the response of a closed‐loop system to reference tracking at the expense of a not optimised response to disturbance rejection. This work presents the application of VRFT to two cascade control structures usually considered in the control literature to improve the overall closed‐loop performance for single‐input systems. For both structures, the authors derive the optimal and practical filter formulation to cope with the case where the controller to be designed is underparameterised. Also, in the case where the internal controller is at the feedback path, they derive a new approach that uses data from a single experiment and considers a unique reference model. Simulation examples illustrate the importance of using the VRFT filter, along with the performance improvements obtained from both cascade loops in terms of reference tracking and disturbance rejection. [ABSTRACT FROM AUTHOR]

For a class of nonlinear multivariable dual-rate systems with strong couplings and uncertainties, a dual-rate adaptive decoupling controller with nonlinear feedforward compensation is proposed. First, a dual-rate model consisting of a linear model and a nonlinear term is derived by using the polynomial transformation technique. The unknown parameter matrices in the linear model are identified by using a proposed recursive least square algorithm and available dual-rate data, while the unknown nonlinear term is compensated by using the identification error. Based on the dual-rate model, the adaptive decoupling controller is then designed. The stability of the closed-loop system is presented. Finally, experiments are conducted on a dual-tank flow-level cascade control system. The results illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, the authors propose a backstepping‐based, distributed formation control method that is stable independent of time delays in communication among multiple unmanned aerial vehicles (UAVs). Centralised formation control of UAVs requires each agent to maintain a separation distance from other agents, which burdens the communication network of the UAVs. To overcome this problem, the authors consider a distributed control scheme wherein each agent updates its attitude and position based on the state information gathered through its neighbours. Instead of directly controlling the thrust generated by the propellers, they partition the mathematical model of the UAV into two subsystems, a linear attitude control loop and a non‐linear position control loop. A backstepping‐based outer position controller is then designed that interfaces seamlessly with the inner attitude controller of the cascaded control system. The closed‐loop stability is established using a rigorous Lyapunov–Krasovskii analysis under the influence of distributed network time delays. Using the directed graph topology and a distributed backstepping structure, it is shown that the stability criterion is delay‐independent. The proposed control algorithms are verified in simulation and then implemented in hardware, and actual flight test experiments prove the validity of these algorithms. [ABSTRACT FROM AUTHOR]

The cascade control is widely used in chemical industries for disturbance attenuation as an alternative to a single feedback loop. This article presents an internal model control (IMC)-based series cascade control system for different time delay process models. The novelty of the work lies in the use of fractional order IMC filter of the first order and higher order for designing controller in the outer loop based on specific maximum sensitivity. The design also considers different approximations for the time delay term. The controller designed for the inner loop assumes the standard PID controller structure and the outer loop controller takes a fractional filter PID structure. The proposed method gives improved performance for set point tracking and disturbance rejection. Further, the proposed method gives robust performance for noise in the measured signal. Also, the robustness analysis is performed to know the insensitivity of the closed-loop system for process parameter variations. The fragility of the controller is investigated for perturbations in the controller parameters. [ABSTRACT FROM AUTHOR]

In this paper, we consider the uniform stabilization of some high-dimensional wave equations with partial Dirichlet delayed control. Herein we design a parameterization feedback controller to stabilize the system. This is a new approach of controller design which overcomes the difficulty in stability analysis of the closed-loop system. The detailed procedure is as follows: At first we rewrite the system with partial Dirichlet delayed control into an equivalence cascaded system of a transport equation and a wave equation, and then we construct an exponentially stable target system; Further, we give the form of the parameterization feedback controller. To stabilize the system under consideration, we choose some appropriate kernel functions and define a bounded inverse linear transformation such that the closed-loop system is equivalent to the target system. Finally, we obtain the stability of closed-loop system by the stability of target system. [ABSTRACT FROM AUTHOR]

Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Control system is the vital integrant in proportional–integral–derivative (PID) controller. The controllers are also planted in many special-purpose control systems. PID controller is often combined with logic, sequential functions, selectors, and simple function blocks to build the complicated automation systems used for energy production, transportation, and manufacturing. In the existing process, PID controller controls water level, speed, temperature, etc. Some of the issues arise while using PID controller can be easily solved by integrating fuzzy or with some other soft computing techniques. The major difficulty in PID controller is feedback system, with constant parameters and no direct knowledge of the process. Our proposed methodology has been introduced to control the speed of highly nonlinear hybrid electric vehicles (HEVs) having an electronic throttle control system in the cascade control loop. In recent PID controllers, no such specific tuning methods are applicable. The proposed method uses fractional order fuzzy PID nonlinear controller that is used in the cascade control loop. Aging leader and challenger-aided multi-objective dragonfly algorithm is considered for controller optimization in closed loop. It is employed to enhance the gain of the controller for the reduction of integral absolute error, maximum overshoot, settling time elimination of disturbance, uncertainty model, and control HEVs. [ABSTRACT FROM AUTHOR]

In this paper, an optimized dual-loop current controller for current balancing of a Zeta converter is presented and analysed in continuous current mode. The proposed strategy has an inner loop which is defined based on the input inductor current control. The reference signal of the sliding manifold is changed through an outer loop which works to regulate the output current. The stability analysis of the two-loop controllers is established by means of Routh–Hurwitz criterion and the equivalent control method. Then, the gains of the outer loop compensator are optimized using the integral gain maximization method to guarantee the robustness and disturbance rejection of the closed loop system in the presence of model uncertainties. The controller performance is investigated in depth taking into account the parametric variations associated with the converter operation in various equilibrium points. Moreover, a laboratory set-up of the suggested controller has been implemented by using analogue component devices. The experimental results demonstrate the effective performance of the controller. [ABSTRACT FROM AUTHOR]

Wind energy technology is developing more and more from recent decades in many countries. Therefore, addressing the latest wind turbine research issues, this study develops a dynamic model of a permanent magnet synchronous generator and an active rectifier—as part of a unified dynamic model of a wind turbine generator in MATLAB/Simulink. In addition, a novel technique for the verification of the open-loop and the closed-loop transfer functions in the frequency domain is presented. The technique develops by analysing the frequency responses of the transfer function at various frequencies. Furthermore, the cascaded control loops of the developed model are designed and the stability of the designed controllers is tested in response to step changes in reference values.

Under the single-loop structure, the problem of overcurrent protection for permanent magnet synchronous motor (PMSM) is investigated in this paper. Due to the combination of speed loop and current loop, the q-axis current become a state of PMSM control system, instead of the output of current loop in the cascade control. As a consequence, the conventional controllers can not restrict the q-axis current into a safe zone. But an oversize transient current may lead to damage of hardwares and property loss. To this end, a new current-constrained controller is proposed to deal with the issue of over-current protection. Different from previous methods of state constraints, the effects of disturbance is taken into account of controller design. A reduced-order generalized proportional integral observer (RGPIO) is adopted to estimate the uncertainties and disturbances. Our method can be considered as a composition of current-constrained control plus feed-forward compensation based on RGPIO. A rigorous stability analysis for the closed-loop system is presented. Compared with the conventional PID controller, the proposed method not only limits q-axis current to a safe range, but also has a good anti-disturbance ability. The feasibility and efficiency of the proposed method is validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a hierarchical Lyapunov-based adaptive cascade control scheme for a lower-limb exoskeleton with control saturation. The proposed approach is composed by two control levels with cascade structure. At the higher layer of the structure, a Lyapunov-based back-stepping regulator including adaptive estimation of uncertain parameters and friction force is designed for the leg dynamics, to minimize the deviation of the joint position and its reference value. At the lower layer, a Lyapunov-based neural network adaptive controller is in charge of computing control action for the hydraulic servo system, to follow the force reference computed at the high level, also to compensate for model uncertainty, nonlinearity, and control saturation. The proposed approach shows to be capable in minimizing the interaction torque between machine and human, and suitable for possible imprecise models. The robustness of the closed-loop system is discussed under input constraint. Simulation experiments are reported, which shows that the proposed scheme is effective in imposing smaller interaction torque with respect to PD controller, and in control of models with uncertainty and nonlinearity. [ABSTRACT FROM AUTHOR]

This study suggests a non-linear output voltage tracking controller for DC/DC boost converters in the form of a classical cascade control structure. Non-linearities in the converter dynamics as well as parameter uncertainties and load variations are considered. The first contribution of this study is the design of an auto-tuner, which automatically adjusts the control gain according to the output voltage error to enhance transient performance. The second contribution involves proving that the closed-loop system ensures the performance recovery without any steady-state errors in the presence of parameter and load variations. The effectiveness of the proposed algorithm was verified through experimental investigations using a 5 kW prototype DC/DC boost converter. [ABSTRACT FROM AUTHOR]

A cascade control structure for the simultaneous position and stiffness control of antagonistic tendon-driven variable stiffness actuators (VSAs) implemented in a laboratory setup is presented in the paper. Cascade control has the ability to accelerate, additionally stabilize, and reduce oscillations, which are all extremely important in systems such as a tendon-driven compliant actuators with elastic transmission. Inner-loop controllers are closed in terms of motor positions, and outer-loop controllers in terms of actuator position and estimated stiffness. The dominant dynamics of the system (position and stiffness), composed of the mechanical part and inner loops, are identified by a closed-loop auto-regressive with exogenous input (ARX) model. The outer-loop controllers are tuned on the basis of experimentally identified transfer functions of the system in several nominal operating points for different stiffness values. After the system is identified, a controller bank is generated in which a pair of actuator position and stiffness controllers correspond to a nominal operating point and covers the area surrounding the nominal point for which it is designed. The controllers used are integral-proportional differential (I-PD) and integral-proportional (I-P) controllers, which are a variation of the PID and PI controllers with dislocated proportional and derivative gains from a direct to feedback branch that result to no overshoot for even fast reference changes (i.e., step signal), which is essential for preventing tendon slackening (meeting the pulling constraint). Analytical formulas for controller tuning based on only one parameter, λ, are also presented. Since position and stiffness loops are decoupled, it is possible to change λ for both loops independently and adjust their performance separately according to the needs. Also, the controller structure secures the smooth response without overshooting step reference or step disturbance signal, which make practical implementation possible. After all the controllers were designed, the cascade control structure for simultaneous position and stiffness control was successfully evaluated in a laboratory setup. Thus, the presented control approach is simple to implement, but with a performance that ensures a pulling constraint for tendon-driven actuators as a foundation for bioinspired antagonistic VSAs. [ABSTRACT FROM AUTHOR]

In this paper the stability of a closed-loop cascade control system in the trajectory track- ing task is addressed. The considered plant consists of underlying second-order fully actuated perturbed dynamics and the first order system which describes dynamics of the input. The main theoretical result establishes the conditions for Lyapunov stability formulated for the perturbed cascade control structure taking advantage of the active rejection disturbance approach. In par- ticular, limitations imposed on a feasible set of an observer bandwidth are discussed. In order to illustrate characteristics of the closed-loop control system simulation results are presented. Furthermore, the particular implementation of the cascade control algorithm is verified exper- imentally using a two-axis telescope mount. The obtained results confirm that the considered control strategy can be efficiently applied for a class of mechanical systems when a high position tracking precision is required. [ABSTRACT FROM AUTHOR]

This brief investigates the optimal control design for a multimotor driving system (MDS). Since the dynamic characteristic of MDS is multivariable, high order, strong coupling, and nonlinear, it is difficult to design an appropriate control framework to simultaneously achieve the load tracking and multimotor synchronization. By dividing the MDS into a load subsystem and a multimotor subsystem, a novel cascade optimal control framework including outer and inner loops is proposed. In this framework, the optimal-tracking controller (OTC) and the optimal synchronization controller (OSC) can be designed individually by decomposing a comprehensive performance index. In order to construct the OTC, the backstepping approach is incorporated into the optimal control to make the load track a reference command; then, the OSC is developed via the mean deviation coupling control strategy to guarantee that all the motors’ states can converge their average value. In addition, the state and extended disturbance observers are combined with OTC and OSC to deal with the immeasurable states and the system uncertainties. The proposed control framework not only addresses the optimal control problems of the load tracking and multimotor synchronization but also has a strong robustness to the system uncertainties. The Lyapunov theory proves that all signals in the closed-loop system are ultimately uniformly bounded. Practical experiments based on a four-motor driving system are conducted to validate the efficiency of the proposed control framework. [ABSTRACT FROM AUTHOR]

Summary: The adaptive robust control problem for the speed and tension system of reversible cold strip rolling mill is studied based on the Hamilton theory in this paper. First, the dissipative Hamilton model of the rolling mill system's speed and tension outside loop is built through pre‐feedback control, and then, dissipative Hamilton controllers are designed by utilizing the interconnection and damping assignment and the energy shaping method. Second, in order to realize tensiometer‐free control and adaptive robust control for the perturbation parameters and load disturbance, full‐order state observers and adaptive robust controllers are designed for the rolling mill system's speed and tension outside loop by using the "extended system + feedback" method. Third, robust controllers for the rolling mill system's current inside loop are designed based on the cascade control thought, so as to realize the tracking control for the speed and tension of reversible cold strip rolling mill. Theoretical analyses show that the resulting closed‐loop system is stable. Finally, simulation research is carried out on the speed and tension system of a 1422‐mm reversible cold strip rolling mill, and simulation results verify the validity of the proposed control strategy in comparison with the decentralized overlapping control strategy. [ABSTRACT FROM AUTHOR]

• A hybrid cascade control scheme with continuous and discrete measurements is proposed. • The inner loop uses on-line continuous measurements to regulate a key variable. • The outer loop updates the inner loop reference at each sampling period. • The scheme has a reset observer to update the state vector at intersampling periods. The regulation of nonlinear dynamical systems with both continuous and discrete measurements is addressed by a robust control structure that considers the compromise between safety, productivity and quality. This structure is a hybrid cascade control scheme composed of an inner loop which uses on-line or fast enough measurements to regulate a key variable and updates its reference at each sampling period according to the available discrete information of the outer loop. The cascade control scheme includes a reset observer to update the state vector at the intersampling periods, enhancing the robustness of the closed-loop in the face of parametric uncertainty and load changes. A bifurcation study was also carried out to determine the state and control bounds that guarantee the operation of the nonlinear system under safe and attainable conditions, making the saturation limits an instrumental part of the cascade control design to guarantee closed loop stability for systems with multiple stable and/or unstable open loop equilibrium. The performance of the proposed cascade control scheme is illustrated via numerical simulations in two extreme study cases: an open loop unstable chemical reactor and a highly sensitive bioprocesses used in high yield wastewater treatment. [ABSTRACT FROM AUTHOR]

In this study, the authors consider the input-to-state stability of an ordinary differential equation (ODE)-heat cascade system with Dirichlet interconnection where the boundary control input is located at the right end of the heat equation and the disturbance is appeared as a non-homogeneous term in the ODE. Based on two backstepping transformations, they design a state feedback control law that guarantees the input-to-state stability of the closed-loop system. The well-posedness of the closed-loop system is presented by using the semi-group approach. Moreover, they design an output feedback control law by constructing an exponentially convergent observer. With the output feedback control, the input-to-state stability of the resulting closed-loop system is proven. [ABSTRACT FROM AUTHOR]

This study presents a non‐linear tip speed ratio (TSR) cascade controller for high power wind turbines (WTs) considering the effects of the large rotor inertia and torsional behaviour of the shafts. A model‐based non‐linear rotor speed controller is proposed for the inner loop. The required speed reference is provided by an outer loop. A design procedure for cascade control of WTs is based on a backstepping design. It is shown that the above two‐loop control schemes lead to a nice cascade structure for the closed‐loop systems. Stability result adapted for analysis of this particular kind of systems is developed. The effectiveness of the proposed control approach is evaluated on a WT by comparing with typical control strategies such as non‐linear TSR control, optimal torque control, and sliding mode control. Simulation results show that the proposed two‐loop controller exhibits better performance than the above typical control strategies. [ABSTRACT FROM AUTHOR]

This paper deals with the H ∞ control design for the networked cascade control systems (NCCSs) subject to periodic denial-of-service (DoS) attack. The controller structure is based on the state-feedback controller for the both control loops. The communication network of the primary loop is equipped with an event-triggered mechanism while the network is under periodic DoS attack. For stability analysis and controller design, the mathematical model of the closed-loop system is formulated based on the switching systems approach. By using the piecewise Lyapunov-functional-based approach and average dwell time techniques, some stability and stabilization criteria are derived and presented in the form of linear matrix inequalities (LMIs). Finally, an steam temperature cascade control system is utilized as a practical example to demonstrate the effectiveness of the proposed method. • The mathematical model of the proposed NCCS under DoS attack is formulated as a switching system. • Stability and stabilization of the closed-loop system is analysed by using the piecewise Lyapunov-functional-based approach. • A MDADT technique is employed to derive some new stability criteria for the proposed NCCS. • The proposed method have been applied for an steam temperature cascade control system as a practical example. [ABSTRACT FROM AUTHOR]

Aiming at the model uncertainty in design process of longitudinal motion control system of supercavitating vehicle, a backstepping controller is designed by combining with Radial Basis Function neural network (RBFNN). Considering that the environment of the supercavitating vehicle is complex during its traversal, it is not possible to measure all states directly. The calculation of planing force with nonlinear characteristics is related to vertical velocity, therefore, the accuracy of vertical velocity has impact on the value of planing force directly. A state observer is designed to estimate vertical velocity. In this paper, based on the backstepping method, the uncertain part of matrix coefficient in cascade control model of supercavitating vehicle is approximated by RBFNN. The output of the observer approximates the state variables, then, a depth tracking control law of the vehicle is obtained according to the observed values and the weight of neural network is calculated by Lyapunov function. Finally, it is proved that the control law can ensure the uniform ultimate boundedness of the closed-loop system. • Solve the model uncertainty in the design process of longitudinal motion control system of supercavitating vehicle. • Design state observer to estimate vertical velocity. • Approximate the uncertain part of matrix coefficient in the cascade control model of supercavitating vehicle by RBF neural network. • Calculate the weight of neural network by Lyapunov function. [ABSTRACT FROM AUTHOR]

This paper presents a level control problem of a coupled two tank single input single output (SISO) system. A cascade control strategy is adopted having a fractional order proportional integral (FOPI) controller and fractional order proportional derivative (FOPD) controller in the outer and the inner loops, respectively. Cascaded integer order proportional integral (IOPI) and integer order proportional derivative (IOPD) controllers are also designed to compare the performances. A frequency domain approach is followed to design all the controllers. It is mathematically shown that the FOPI and FOPD controllers can achieve less steady state error and consume less energy than that of the IOPI and IOPD controllers while meeting the same phase margin and gain crossover frequency. All propositions are validated on an experimental setup. [ABSTRACT FROM AUTHOR]

In this study, a new distributed fast terminal sliding mode exactly tracking control method is proposed for a class of non‐integral cascade high‐order uncertain non‐linear systems. Based on the concept of hierarchical design, a series of decentralised sliding mode surfaces are first developed in the authors' design scheme. Every sliding mode surface is independent of each other, besides, on this designed sliding mode surface, finite‐time convergence characteristic can be guaranteed. By using backstepping technology and dynamic surface control method, a finite‐time exact tracking controller is finally developed. Based on Lyapunov stability theory, the stability of system has been theoretically proved, and in finite time, all the closed‐loop system signals ultimately converge to the origin. Simulation results verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]