Observer Gain Research Articles

Observer‐based finite‐time congestion control for TCP/AQM network system with time‐varying delays and UDP flows

AbstractIn this paper, the problem of observer‐based finite‐time congestion control for transmission control protocol (TCP)/active queue management (AQM) network systems with time‐varying delay and nonresponsive flows such as UDP is studied. The congestion control problem of TCP/AQM network system with time delay and external disturbances observer‐based finite‐time control is solved for the first time, and a theorem proved by the Lyapunov function of TCP/AQM network systems finite‐time bounded is given to ensure that the closed‐loop system is finite‐time bounded. Finally, the control gain and observer gain are obtained by linear matrix inequality (LMI) technique. Simulation results show the effectiveness and superiority of the proposed method.

Boundary stabilization and state estimation of ODE-transport PDE with in-domain coupling

This paper deals with the exponential stabilization of first order ODE-transport PDE coupled at the boundary point. A state feedback boundary control law has been formulated with the help of the backstepping method. The main novelty of this paper is that the stabilization of the coupled system is discussed by Lyapunov theory and the appropriate observer gain is designed by using the linear matrix inequalities (LMIs). An anti-collocated observer design for the corresponding dual system is also presented. The state feedback boundary controller, observer design and the stabilization of the closed-loop system are discussed in detail with illustrative numerical examples.

An Intersection-Method-Based Current Controller for Switched Reluctance Machines With Robust Tracking Performance

Good current tracking is beneficial to the torque ripple suppression methods like current profiling techniques for the switched reluctance machines (SRMs). An intersection-method-based current controller for the SRM with robust tracking performance is proposed in this article. First, with the aid of the predicted current at the next sampling instant, the prestored reference current, and the flux-linkage information, the required duty cycle for the next control period under specific reference current is estimated through the intersection method. To compensate for the difference between the adopted flux-linkage model and the real ones inside the machine, a Lyapunov-based adaptive flux-linkage observer is presented. Hence, the heavy dependence issue on the accurate flux-linkage model for the current controller is resolved. With the above techniques, robust reference current tracking is achieved in a simple form and only one observer gain. Besides, a balanced switching scheme is presented to reduce the switching frequency requirement of the power transistors and evenly distribute the switching losses. Extensive experimental tests have been carried out on a four-phase 5.1-kW 8/6 SRM setup for the proposed method and conventional current control methods at different operation conditions. These testing results verified the effectiveness of the proposed method.

A Switching Observer for a Class of Nonuniformly Observable Systems via Singular Time-Rescaling

We present a switching observer for a class of nonuniformly observable systems that are affine in the unmeasured states and nonlinear in the measured output. Using a singular time-rescaling, the dynamics of the estimation error is transformed into that of a bimodal switched linear system. Sufficient conditions that guarantee the observer’s uniform asymptotic stability are provided; these are stated in terms of persistency of excitation and dwell-time of the (output-dependent) time-scaling function evaluated along the trajectories of the system. Unlike most results on switching observers, our approach does not rely on the solution of a set of linear matrix inequalities to compute the observer gain. In addition, we compare our scheme against the Kalman observer in a particular, but meaningful, case-study of observer-based control in automotive systems.

축소 차수 모델 기반 제어기와 결합한 PI 관측기 기반 제어 시스템의 안정성 해석

System model order reduction is a popular technique employed by control systems engineers due to its ability to reduce model complexity. However, control systems designed based on reduced-order model may cause closed-loop system instability when applied to the full-order model. In addition, conventional control system improvement methods such as increasing the controller gains or using robust control techniques in particular disturbance observers can further deteriorate system performance. In order to shade light on this phenomena, this paper presents an analytical study of the effects of high observer gain on the stability of observer compensated control systems whereby both the controller and the observer are designed using the reduced-order system model. The analysis is performed by carrying out stability analysis of the closed-loop system through root locus method and Routh-Hurwitz stability criterion. The paper also presents a comparative analysis between placing all the closed-loop poles of the controller at a single location or multiple locations using LQR technique for the aforementioned class of controller. The results obtained from the analysis have been validated through a DC motor position control system application.

Observer‐based finite‐time event‐triggered H∞ control for nonlinear switched systems with interval time‐varying delay

AbstractThe problem of observer‐based finite‐time event‐triggered H∞ control for nonlinear uncertain switched systems is investigated in this paper. An observer‐based event‐triggered controller is constructed using a state observer. The event‐triggering updating strategies for the control law are designed. The multiple Lyapunov–Krasovskii functional and average dwell time technique are utilized to derive some sufficient conditions that guarantee the switched system is observer‐based event‐triggered H∞ finite‐time stabilizable. We give the observer gain and controller gain. At the end of this paper is a numerical example that illustrates the effectiveness and advantages of the proposed approaches.

Robust Observer-based Leader-Following Consensus for Multi-agent Systems

This paper presents a robust observer-based leader-following consensus control for multi-agent systems subject to external disturbances. The stability and robustness to external disturbances are addressed through the Lyapunov approach and an optimal H criterion. It is shown that the design conditions for a correct convergence of the estimated states and consensus control can be expressed in a set of linear matrix inequalities whose solution allows computing the observer and controller gain matrices. In order to show the effectiveness of the proposed strategy, numerical examples are carried out to solve the formation control problem of a fleet of unmanned aerial vehicles (UAVs) under the effect of wind turbulence.

A non-linear disturbance observer-based cooperative adaptive cruise control for real traffic scenarios

Cooperative adaptive cruise control (CACC) has a strong potential to improvise highway traffic capacity and ease traffic disturbances. Extensive exploration is not carried out in the area of CACC for a cut-in maneuver. Contemporary control strategies proposed for CACC cannot regulate the peaking of control input and thus the acceleration/deceleration of following vehicles when applied for various real traffic scenarios. This paper aims to develop a non-linear disturbance observer-based sliding mode control to control a CACC system for various traffic scenarios. The proposed observer estimates the uncertainty present in the actuator dynamics and the preceding vehicle’s acceleration as the lumped disturbance at the same time, it adjusts the observer gain to alleviate the peaking of control input. The stability of individual vehicles and the string stability of vehicle platoon are derived The performance of the proposed scheme is validated with various traffic scenarios, that is, cut-in maneuver, cut-out maneuver, and non-zero initial conditions. The effectiveness of the proposed scheme is demonstrated by comparing it with a linear disturbance observer-based control.

Further results on the design of a class of discrete‐time set‐valued state estimators

AbstractIn this work, two improvements are proposed for a class of interval‐based state estimators applied to discrete‐time uncertain linear systems subject to additive bounded process and measurement uncertainties. First, we propose to compute the observer gain as a solution of an off‐line constrained nonlinear optimization problem, where the cost function depends on the estimation error width and the constraints ensure the invariance of the estimation error set. Second, to obtain tighter state enclosures, we propose to apply zonotope set computation instead of interval analysis to design a new set‐valued state estimation algorithm. Through simulations, we highlight the interest of the proposed technical improvements.

Adaptive output feedback tracking for time-delay nonlinear systems with unknown control coefficient and application to chemical reactors

In this paper, the problem of global adaptive output feedback tracking is considered for a class of highly nonlinear time-delay systems with unknown control coefficient and relaxed lower-triangular growth constraints. Based on the non-separation principle, a non-identifier-based adaptive output feedback controller is proposed by designing a novel update law of the dynamic gain in observer and controller. The novel gain can simultaneously compensate the uncertain parameters, the output-polynomial growth rate and the unknown time-varying delay. The proposed controller is well universal attributed to using the non-identification adaptive mechanism, and all design parameters are easy to get by simple calculation. With the help of Lyapunov–Krasovskii functionals and Barbalat’s lemma, it is shown that the solutions of the resulting closed-loop system are globally uniformly ultimately bounded by improving the backstepping design and dynamic high-gain scaling approach; the adaptive tracking is achieved under any small pre-given tracking error. Finally, the effectiveness of the proposed controller is illustrated by two examples.

Averting BER Floor with Iterative Source and Channel Decoding for Layered Steered Space-Time Codes.

The widespread development in wireless technologies and the advancements in multimedia communication have brought about a positive impact on the performance of wireless transceivers. We investigate the performance of our three-stage turbo detected system using state-of-the-art high efficiency video coding (HEVC), also known as the H.265 video standard. The system makes use of sphere packing (SP) modulation with the combinational gain technique of layered steered space-time code (LSSTC). The proposed three-stage system is simulated for the correlated Rayleigh fading channel and the bit-error rate (BER) curve obtained after simulation is free of any floor formation. The system employs low complexity source-bit coding (SBC) for protecting the H.265 coded stream. An intermediate recursive unity-rate code (URC) with an infinite impulse response is employed as an inner precoder. More specifically, the URC assists in the prevention of the BER floor by distributing the information across the decoders. There is an observable gain in the BER and peak signal-to-noise ratio (PSNR) performances with the increasing value of minimum Hamming distance () using the three-stage system. Convergence analysis of the proposed system is investigated through an extrinsic information transfer (EXIT) chart. Our proposed system demonstrates better performance of about 22 dB than the benchmarker utilizing LSSTC-SP for iterative source-channel detection, but without exploiting the optimized SBC schemes.

Robust Stabilization and Observer-Based Stabilization for a Class of Singularly Perturbed Bilinear Systems

An infinite-bound stabilization of a system modeled as singularly perturbed bilinear systems is examined. First, we present a Lyapunov equation approach for the stabilization of singularly perturbed bilinear systems for all ε∈(0, ∞). The method is based on the Lyapunov stability theorem. The state feedback constant gain can be determined from the admissible region of the convex polygon. Secondly, we extend this technique to study the observer and observer-based controller of singularly perturbed bilinear systems for all ε∈(0, ∞). Concerning this problem, there are two different methods to design the observer and observer-based controller: one is that the estimator gain can be calculated with known bounded input, the other is that the input gain can be calculated with known observer gain. The main advantage of this approach is that we can preserve the characteristic of the composite controller, i.e., the whole dimensional process can be separated into two subsystems. Moreover, the presented stabilization design ensures the stability for all ε∈(0, ∞). A numeral example is given to compare the new ε-bound with that of previous literature.

Fault detection for uncertain nonlinear systems via recursive observer and tight threshold

This paper presents an fault detection (FD) method for a class of uncertain nonlinear systems with unmatched nonlinear fault functions and disturbances. A recursive FD observer is designed with predetermined and small output estimation error. The nonlinear observer gain function is achieved by introducing predetermined output estimation accuracy-dependent nonnegative functions. Combining Lyapunov functions, it is shown that the absolute value of the residual signal is equal or lesser than tight threshold before fault occurrence. The FD scheme is proposed following fault detectability analysis, simulation example indicates the validity of the proposed method.

Resilient observer design of sensor fault estimation for discrete‐time multi‐agent systems: A distributed approach

AbstractIn this article, the issue of distributed sensor fault estimation with resilient property is studied for a class of multi‐agent systems. Based on the relative output information, a novel fault estimation design is presented to estimate sensor fault and state vectors simultaneously. Meanwhile, the variation of observer gain is considered to improve the robustness of fault estimation observer. Furthermore, robust performance is used to suppress the influence of external interference on sensor fault estimation error. Finally, simulations are provided to present effectiveness of the developed approach.

Emerging approaches for nonlinear parameter varying systems

Emerging approaches for nonlinear parameter varying systems

A new speed adaptive estimation method based on an improved flux sliding-mode observer for the sensorless control of PMSM drives

In this paper, an improved speed adaptive flux sliding-mode observer (FSMO) is presented for the sensorless control of surface-mounted permanent magnet synchronous motor (PMSM) drives. First, to suppress the chattering of the traditional FSMO, an algorithm for online adjusting the observer gain is designed. In this algorithm, a transition mode is introduced between the existing reaching and sliding modes, and an error criterion function with speed and current is constructed for the three motion modes. Second, to reduce the rotor speed estimation error, a new speed adaptive estimation method is presented instead of the traditional phase-locked loop (PLL). In this method, the adaptive law for estimating the speed is derived using Lyapunov stability and model reference adaptive theories. Meanwhile, the physical meaning of the speed adaptive law is illustrated. Finally, the proposed FSMO scheme is implemented on a TMS320F28335 digital signal processing (DSP) microcontroller-based surface-mounted PMSM sensorless control experimental bench. Test results demonstrate the excellent dynamic performance, robustness and stability of the proposed FSMO under various operating conditions.

Non-fragile mixed H ∞/passive-based asynchronous sliding mode control for nonlinear singular Markovian jump systems

In this paper, the problem of asynchronous sliding mode control (SMC) is addressed for discrete-time singular Markovian jump systems (DSMJSs) with external disturbances and randomly occurring nonlinearities. Moreover, the states of DSMJSs are unavailable for measurement, and the synchronisation between the controller and the system modes is not surely ensured. Our attention is mainly focused on solving the control problem by proposing an observer-based adaptive sliding mode controller for such a class of complex systems. First, a non-fragile observer is designed not only to estimate the system states but also to relax the multiplicative gain variations and to construct an appropriate mode-dependent sliding mode surface function. Then, by assuming that the bounds of nonlinear terms are unknown, an adaptive SMC control law is synthesised to drive the system trajectories onto the specified sliding surface and completely compensate for the influences of the external disturbances and fluctuations of the controller and observer gains. Sufficient conditions are established to ensure that the closed-loop system is stochastically admissible with a γ level of the mixed /passive performance, and to provide the observer and controller gain matrices. Finally, to numerically substantiate the efficacy of the proposed control scheme, two examples are given.

Robust Adaptive Current Control of a 1.2-MW Direct-Drive PMSM for Traction Drives Based on Internal Model Control With Disturbance Observer

In order to improve the efficiency of the electric locomotive, the MW-level direct-drive permanent magnet synchronous motor (DD-PMSM) is used to replace the original traction motor and gearbox in the electric locomotive. However, the DD-PMSM parameters will change with the operating conditions during the operation of the electric locomotive, and the absence of the gearbox in direct drives increases the sensitivity of the control performance to uncertainties in the drive system. In order to solve the problems, a novel robust adaptive (RA) current control of MW-level DD-PMSM for traction drives based on internal model control with disturbance observer (IMCDO) is proposed in this article. IMCDO is simply designed as the estimated uncertainty function, and simple control law is derived based on the Lyapunov function to guarantee the system stability and improve the antidisturbance performance. Then, in order to adjust the internal model disturbance observer properly, the observer gain selection criteria are given by using the stability analysis based on the discrete Lyapunov function. The proposed method in the article is verified on a 1.2-MW DD-PMSM, and the comparative experiments demonstrate the validity and effectiveness of the proposed method.

A non-fragile robust observer design for uncertain time-delay fractional Itô stochastic systems with input nonlinearity: An SMC approach

This article considers the problem of non-fragile observer design for uncertain fractional Itô stochastic systems. The design is based on a sliding surface whose reachability in finite time is guaranteed by introducing a novel sliding mode control law. Employing the fractional infinitesimal operator and the related lemmas, the stochastic stability of the overall closed-loop system is transformed to the problem of solving a set of linear matrix inequalities. Addressing the fragility issue, a norm-bounded term is added to the observer gain, which prevents failure of the estimation error system. The adverse effects of the input nonlinearity and time-varying delay are alleviated by the proposed approach. Furthermore, the present method is investigated for the fractional Itô stochastic systems with known states. A numerical example is presented to illustrate the effectiveness of the proposed method.

Research on coordinated control strategy based on hybrid multi-terminal HVDC transmission network

Most of the control strategies of hybrid multi-terminal HVDC transmission technology consider frequency support, voltage control and power control, which ignore the influence of external parameter disturbance and power change. Aiming at the deficiencies of the above control strategies, this paper proposes a coordinated control strategy that can resist the external parameters to be disturbed and suppress the bus voltage to be fluctuated caused by the power mutation. Firstly, the control law function with passive characteristics is derived by using the system topology, and the optimal injection damping parameters can be selected by the bode diagram of the transfer function of the state variable, which proves that the traditional passivity-based control (PBC) strategy has certain anti-parameter disturbance ability. Secondly, considering that the traditional PBC strategy does not eliminate the influence of sudden external power changes on the AC bus voltage, the nonlinear disturbance observer (NDO) is applied to the PBC strategy to realize real-time monitoring of disturbance variables. Meanwhile, the selection of appropriate observer gain can shorten the time of voltage fluctuation and improve its stability. Finally, simulation results based on Matlab/Simulink verify the practicability and effectiveness of the control method proposed in the hybrid multi-terminal HVDC grid.