Hammerstein system

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Identification scheme for fractional Hammerstein

Models with the delayed Haar Wavelet

Identification scheme for fractional Hammerstein Models with the delayed Haar Wavelet

In the literature, various techniques have been reported on nonlinear process identification using integer-order (classical) models. The Hammerstein process was estimated using the special test signal in [3] and further extended for Hammerstein- Wiener processes in [4], [5]. The separate block-oriented non- iterative relay feedback (SRF) method was illustrated in [6]. Mehta and Majhi [7] presented the non-iterative relay feedback (NRF) method to determine the structure prior to the parameters of the Hammerstein model. The Hammerstein system with time delay has been accurately identified using a recursive least squares method in [8]. Recently, a separate block-oriented parameter identification method for Hammerstein systems using least squares was described in [9]. Furthermore, another special input based identification of Hammerstein-Wiener nonlinear system with noise was discussed in [10]. Even though some efficient integer-order techniques have been developed so far, a fractional domain approach is yet to be fully explored for nonlinear process identification.
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Nonlinear equalization of Hammerstein OFDM systems

Nonlinear equalization of Hammerstein OFDM systems

A practical orthogonal frequency-division multiplexing (OFDM) system can generally be modelled by the Hammerstein system that includes the nonlinear distortion effects of the high power amplifier (HPA) at transmitter. In this contribution, we advocate a novel nonlinear equalisation scheme for OFDM Hammerstein systems. We model the nonlinear HPA, which represents the static nonlinearity of the OFDM Hammerstein channel, by a B-spline neural network, and we develop a highly effective alternating least squares algorithm for estimating the parameters of the OFDM Hammerstein channel, including channel impulse response (CIR) coefficients and the parameters of the B-spline model. Equalisation of the OFDM Hammerstein channel can then be accomplished by the usual one-tap linear equalisation as well as the inversion of the estimated B-spline neural network model. We propose to use an efficient Gauss-Newton algorithm for the latter inversion task. The effectiveness of our nonlinear equalisation scheme for OFDM Hammerstein channels is demonstrated by simulation results.
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Nonlinear System Identification Using Hammerstein-Wiener Neural Network and subspace algorithms

Nonlinear System Identification Using Hammerstein-Wiener Neural Network and subspace algorithms

There exists a lot of works on nonlinear system identification which use block-oriented models. For example estimating the formal information of neurons[27], using ARMA model for dynamic linear block and a multilayer feed forward neural network to model the static nonlinear[13], least square and SVD for Hammerstein model[11],[8], recursive identification for Hammerstein system with state space model[33], eigensystem realization algorithm(ERA) for accurate parameter estimation and the system order determination[23], over parameterization and iterative methods[22], iterative approaches[20][29], frequency-domain method[24], subspace method[17],[18][25],[26], stochastic algorithm[6], blind approaches[4], magnetosphere identification[3], constructing a model for ionospheric dynamics[16], using Genetic algorithm for H-W identification[14], initializing parameters and order determination by Lipchitz[1], fully automated recurrent neural network[31], using the spectral magnitude matching method[32], using a new maximum- likelihood based method[33].
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An Adaptive Nonlinear Filter for System Identification

An Adaptive Nonlinear Filter for System Identification

The primary difficulty in the identification of Hammerstein nonlinear systems (a static memoryless nonlinear system in series with a dynamic linear system) is that the output of the nonlinear system (input to the linear system) is unknown. By employing the theory of affine projection, we propose a gradient-based adaptive Hammerstein algorithm with variable step-size which estimates the Hammerstein nonlinear system parameters. The adaptive Hammerstein nonlinear system parameter estimation algorithm proposed is accomplished without linearizing the systems nonlinearity. To reduce the effects of eigenvalue spread as a result of the Hammerstein system nonlinearity, a new criterion that provides a measure of how close the Hammerstein filter is to optimum performance was used to update the step-size. Experimental results are presented to validate our proposed variable step-size adaptive Hammerstein algorithm given a real life system and a hypothetical case.
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A New Identification Approach of MIMO Hammerstein Model with Separate Nonlinearities

A New Identification Approach of MIMO Hammerstein Model with Separate Nonlinearities

have been proposed in [18]. The Least Squares Sup- port Vector Machines (LS-SVMs) have been presented in [19,20]. A generalized Hammerstein model con- sisting of a static polynomial function in series with time-varying linear model is developed in order to model the Hammerstein-like multivariable processes whose linear dynamics vary over the operating space in [21]. In this work, we propose a new coupled struc- ture identification of MIMO model with separate non- linearities. It is organized as follows: SISO Hammer- stein system is presented in part 1 of section 2. A new coupled structure for MIMO Hammerstein system is developed in part 2 of section 2. Simulation results of a quadruple-tank process is given in section 3. Finally, a conclusion is made.
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Adaptive Kernel Canonical Correlation Analysis Algorithms for Nonparametric Identification of Wiener and Hammerstein Systems

Adaptive Kernel Canonical Correlation Analysis Algorithms for Nonparametric Identification of Wiener and Hammerstein Systems

In recent years, a growing amount of research has been done on nonlinear system identification [1, 2]. Nonlinear dynami- cal system models generally have a high number of param- eters although many problems can be su ffi ciently well ap- proximated by simplified block-based models consisting of a linear dynamic subsystem and a static nonlinearity. The model consisting of a cascade of a linear dynamic system and a memoryless nonlinearity is known as the Wiener system, while the reversed model (a static nonlinearity followed by a linear filter) is called the Hammerstein system. These systems are illustrated in Figures 1 and 2, respectively. Wiener sys- tems are frequently used in contexts such as digital satellite communications [3], digital magnetic recording [4], chemi- cal processes, and biomedical engineering. Hammerstein sys- tems are, for instance, encountered in electrical drives [5] and heat exchangers.
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Existence and approximation of solution for a nonlinear second-order three-point boundary value problem

Existence and approximation of solution for a nonlinear second-order three-point boundary value problem

approximation of solutions. First, the integration method is proposed to transform the considered boundary value problems into Hammerstein integral equations. Second, the existence of solutions for the obtained Hammerstein integral equations is analyzed by using the Schauder fixed point theorem. The contraction mapping theorem in Banach spaces is further used to address the uniqueness of solutions. Third, the approximate solution of Hammerstein integral equations is constructed by using a new numerical method, and its convergence and error estimate are analyzed. Finally, some numerical examples are addressed to verify the given theorems and methods.
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IBFD Power Line Communication for Analog Interference Cancellation

IBFD Power Line Communication for Analog Interference Cancellation

be able to track channel variations simultaneously with data transmission. This problem is still not solved in this paper. However, when the symbol timing of the desired signal and the self-interference signal are synchronized, the problem does not arise because specific training symbols are unnecessary. Although this problem is very important, we treat it as a future work in this paper. The rest of this paper is organized as follows. In Section II, a detailed model of the self interference which includes nonlinearities of the IQ mixers and the power amplifier is provided. The proposed selection technique with the frequency domain Hammerstein self-interference canceller is presented in Section III. In Section IV, the performance of the proposed technique under different scenarios is analyzed with equivalent baseband signal simulations
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Model-based acceleration control of turbofan engines with a Hammerstein-Wiener representation

Model-based acceleration control of turbofan engines with a Hammerstein-Wiener representation

Abstract: Acceleration control of turbofan engines is conventionally designed through either schedule-based or acceleration-based approach. With the widespread acceptance of model-based design in aviation industry, it becomes necessary to investigate the issues associated with model-based design for acceleration control. In this paper, the challenges for implementing model-based acceleration control are explained; a novel Hammerstein-Wiener representation of engine models is introduced; based on the Hammerstein-Wiener model, a nonlinear generalized minimum variance type of optimal control law is derived; the feature of the proposed approach is that it does not require the inversion operation that usually upsets those nonlinear control techniques. The effectiveness of the proposed control design method is validated through a detailed numerical study.
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Hybrid Adaptive Fuzzy Neural Network Control for Grid-Connected SOFC System

Hybrid Adaptive Fuzzy Neural Network Control for Grid-Connected SOFC System

Abstract: The solid oxide fuel cell (SOFC) is widely acknowledged for clean distributed power generation use, but critical process problems frequently occur when the stand-alone fuel cell is directly linked with the electricity grid. To guarantee the optimal operation of the SOFC in a power system, it is essential, that its generation ramp rate and load following is fast enough to sustain power quality. In order to address these problems, a suitable and highly efficient control system will be required to control and track power load demands for complex SOFC power systems under grid connection. Therefore, novel nonlinear hybrid adaptive Fuzzy Neural Network (AFNN) is developed for control of grid connected SOFC. During peak power demand schedules from electric utility grid and large load perturbations, maintaining optimal power quality and load-following is a big challenge. Both the rapid power load following and safe SOFC operation requirement is taken into account in the design of the closed-loop control system. Simulation results showed that the proposed hybrid AFNN enhance the optimal power quality and load-following than conventional PI controller.
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A Note on Implicit Functions in Locally Convex Spaces

A Note on Implicit Functions in Locally Convex Spaces

The notion of osculating operators has been considered from different points of view see 2, 3. In this note we reformulate the definition of osculating operators. Our setting is a locally convex topological vector space. Moreover, we present a new implicit function theorem and, as an example of application, we study the solutions of an Hammerstein equation containing a parameter.

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Identification of Nonlinear Systems Structured by Wiener-Hammerstein Model

Identification of Nonlinear Systems Structured by Wiener-Hammerstein Model

Roughly, the iterative methods (e.g. [2]-[3]) necessitate a large amount of data; since computation time and memory usage drastically increase, and have local convergence properties which necessitates that a fairly accurate parameter estimates are available to initialize the search process. This prior knowledge is not required in stochastic methods but these are generally relied on specific assumption on the input signals (e.g. gaussianity, persistent excitation....) and on system model (e.g. MA linear subsystems, smooth nonlinearity). The frequency methods are generally applied to nonparametric systems under minimal assumptions and only require simple periodic excitations. But, they sometime necessitate several data generation experiments.
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Recursive Identification of Hammerstein Systems with Polynomial Function Approximation

Recursive Identification of Hammerstein Systems with Polynomial Function Approximation

be simple, accurate and general. This approximate description of the system can be constructed by system identification strategy, as the goal of system identification is to build a mathematical model of a dynamic system based on some initial information about the system and the measurement data collected from the system. According to [1], the process of system identification consists of designing and conducting the identification experiment in order to collect the measurement data, selecting the structure of the model and specifying the parameters to be identified and eventually fitting the model parameters to the obtained data [2]. Finally the quality of the obtained model is evaluated through model validation process. Generally system identification is an iterative process and if the quality of the obtained model is not satisfactory, some or all of the listed phases can be repeated in order to obtain one satisfied model.
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Development of Nonlinear Lattice-Hammerstein Filters for Gaussian Signals

Development of Nonlinear Lattice-Hammerstein Filters for Gaussian Signals

Using computer simulations, the properties of the lattice-Hammerstein filter derived in previous parts are inspected. The input is a colored Gaussian signal generated by an FIR filter defined by h=[0.9045 0.7 0.9045] whose input is zero-mean white Gaussian noise. The results are averaged over 100 independent trials. The number of input samples is 1000. In the first experiment, the noise variance is 0.0248, the degree of nonlinearity of Hammerstein is P=2, and the number of stages (memories) is M=10. To verify equations Eq. (31), Eq. (17), Eq. (18), and Eq. (19), power of forward and backward errors are depicted in Figs 4 (a), (b) and (c). In agreement with Eq. (19), Fig. 4 (a) shows that backward errors of different stages are orthogonal, and thus, nonzero at the same stages and zero elsewhere. Also, from Fig. 5 (b), it is seen that in accordance to Eq. (31), the power of forward and backward errors of similar stages are identical. Moreover, Fig. 5 (c) shows that forward/backward errors are orthogonal to the input signal as proved in Eq. (17) and Eq. (18).
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Iterative Solutions of Nonlinear Integral Equations of Hammerstein Type

Iterative Solutions of Nonlinear Integral Equations of Hammerstein Type

that the Hammerstein type equation u + KF u = 0 has a solution in H . It is our purpose in this paper to construct a new explicit iterative sequence and prove strong convergence of the sequence to a solution of the generalized Hammerstein type equation. The results obtained in this paper improve and extend known results in the literature.

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Numerical investigation of nonlinear volterra hammerstein integral equations via single term haar wavelet series

Numerical investigation of nonlinear volterra hammerstein integral equations via single term haar wavelet series

with the iterated collocation method. Guoqiang (1993) introduced and discussed the asymptotic error expansion of a collocation-type method for Volterra-Hammerstein integral equations. The methods in Kumar et al. (1987) and Guoqiang [1993] transform a given integral equation into a system of non-linear equations, which has to be solved with some kind of iterative method. In Kumar et al. (1987) the definite integrals involved in the solution may be evaluated analytically only in favorable cases, while in Guoqiang (1993) the integrals involved in the solution have to be evaluated at each time step of the iteration. Orthogonal functions, often used to represent arbitrary time functions, have received considerable attention in dealing with various problems of dynamic systems. The main characteristic of this technique is that it reduces these problems to those of solving a system of algebraic equations, thus greatly simplifying the problem. Orthogonal functions have also been proposed to solve linear integral equations. Runge –Kutta methods are being applied to determine numerical solutions for the problems, which are modeled as Initial Value Problems (IVP’s) involving differential equations that arise in the fields of Science and Engineering by Alexander and Coyle (1990), Murugesan et al. (1999; 2000; 2001; 2003), Shampine [1994] and Yaakub and Evans (1999). Runge-Kutta methods have both advantages and disadvantages. Runge-Kutta methods are stable and easy to adapt for variable stepsize and order. However, they have difficulties in achieving high accuracy at reasonable cost, which were discussed recently by Butcher (2003). Murugesan et al. (1999) have analyzed different second-order systems and multivariable linear systems via RK method based on centroidal mean. Park et al. (2004; 2005) have applied the RK- Butcher algorithm to optimal control of linear singular systems and observer design of singular systems (transistor circuits).Murugesan et al. (2004) and Sekar et al. (2004) applied the RK- Butcher algorithm to industrial robot arm control problem and second order IVP’s. In this paper, we are introducing here the STHW for finding the numerical solution of nonlinear Volterra-
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Numerical solution of nonlinear Hammerstein integral equations by using Legendre-Bernstein basis

Numerical solution of nonlinear Hammerstein integral equations by using Legendre-Bernstein basis

Abstract. In this study a numerical method is developed to solve the Hammerstein integral equations. To this end, the kernel has been approximated using the least-squares approximation schemes based on Legendre-Bernstein basis. The Legendre polynomials are orthogonal and this property improves the accuracy of the approx- imations. Also the nonlinear unknown function has been approxi- mated by using the Bernstein basis. The useful properties of Bern- stein polynomials help us to transform Hammerstein integral equa- tion to solve a system of nonlinear algebraic equations.

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Adaptive Control Schemes for a class of Hammerstein-Wiener nonlinear systems

Adaptive Control Schemes for a class of Hammerstein-Wiener nonlinear systems

This paper is organized as follows. In Section 2, the Bai's system for which we are developing the adaptive controler is presented. In Section 3 the proposed technique using the approximate inverse method is given. In Section 4 the proposed technique using the estimate of the plant noise is presented and Section 5 includes illustrative example and the simulation results for the developed technique.

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Taylor-Series Expansion Methods for Multivariate Hammerstein Integral Equations

Taylor-Series Expansion Methods for Multivariate Hammerstein Integral Equations

In this paper, we have extended the idea of the modified Taylor-series expansion method from one dimensional Ham- merstein equation to multivariate Hammerstein equation. Then we have applied it to find the numerical solution of multivariate Hammerstein equation. This new method finds an approximation of the solution pointwise and therefore lends itself to numerical computations which can be done in parallel. The method also computes the derivatives of the solution concurrently. The results of several numerical experiments have shown the efficiency and accuracy of this new method.

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A unified approach for the identification of SISO/MIMO Wiener and Hammerstein systems

A unified approach for the identification of SISO/MIMO Wiener and Hammerstein systems

Abstract: Hammerstein and Wiener models are nonlinear representations of systems composed by the coupling of a static nonlinearity N and a linear system L in the form N-L and L-N respectively. These models can represent real processes which made them popular in the last decades. The problem of identifying the static nonlinearity and linear system is not a trivial task, and has attracted a lot of research interest. It has been studied in the available literature either for Hammerstein or Wiener systems, and either in a discrete-time or continuous-time setting. The objective of this paper is to present a unified framework for the identification of these systems that is valid for SISO and MIMO systems, discrete and continuous-time setting, and with the only a priori knowledge that the system is either Wiener or Hammerstein. Keywords: Nonlinear system identification, Wiener systems, Hammerstein systems.
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