arXiv subjects

Konstantin Lastochkin

Publications and source records attributed to Konstantin Lastochkin.

26 records · Page 2Linked to original sources

arXiv2022

Exponentially Stable MRAC of MIMO Switched Systems with Matched Uncertainty and Completely Unknown Control Matrix

In this paper an attempt is made to extend the concept of the exponentially stable adaptive control to one class of multi-input-multi-output (MIMO) plants with matched nonlinearity and unknown piecewise constant parameters. Within the intervals between two consecutive parameter switches, the proposed adaptive control system ensures: 1) exponential convergence to zero of the parameter and reference model tracking errors, 2) the monotonicity of the control law adjustable parameters. Both properties are guaranteed in case the regressor is finitely exciting somewhere inside each of such intervals. Compared to the existing methods, the proposed one is applicable to systems with unknown switching signal function and completely unknown control matrix. The theoretical results are supported by the numerical experiments.

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arXiv2022

Unknown Piecewise Constant Parameters Identification with Exponential Rate of Convergence

The scope of this research is the identification of unknown piecewise constant parameters of linear regression equation under the finite excitation condition. Compared to the known methods, to make the computational burden lower, only one model to identify all switching states of the regression is used in the developed procedure with the following two-fold contribution. First of all, we propose a new truly online estimation algorithm based on a well-known DREM approach to detect switching time and preserve time alertness with adjustable detection delay. Secondly, despite the fact that a switching signal function is unknown, the adaptive law is derived that provides global exponential convergence of the regression parameters to their true values in case the regressor is finitely exciting somewhere inside the time interval between two consecutive parameters switches. The robustness of the proposed identification procedure to the influence of external disturbances is analytically proved. Its effectiveness is demonstrated via numerical experiments, in which both abstract regressions and a second-order plant model are used.

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arXiv2022

Exponentially Convergent Direct Adaptive Pole Placement Control of Plants with Unmatched Uncertainty under FE Condition

A new method of direct adaptive pole placement control (APPC) is developed for plants with unmatched uncertainty, which linearly depends on a state vector. It guarantees the exponential stability of a control system and exponential convergence of control law adjustable parameters to their true values when the regressor is finitely exciting. Considering the known classical APPC schemes and adaptive methods with exponential regulation, the advantages of the proposed one are that it does not require a priori information on a control input matrix and ensures the monotonic transient behavior of each adjustable parameter of the control law. The theoretical results are supported by the numerical experiments.

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arXiv2021

Robust Time-Varying Parameters Estimation Based on I-DREM Procedure

We consider a class of systems with time-varying parameters, which are written as linear regressions with bounded disturbances. The task is to estimate such parameters under the condition that the regressor is finitely exciting (FE). Considering such a problem statement, a new robust method is proposed to identify the time-varying parameters with bounded error, which could be reduced to the limit by the adjustment of such method parameters. For this purpose, the function of the system unknown parameters, which depends on time, is expanded into a Taylor series in order to turn the considered problem into the identification of the regression with piecewise-constant parameters. This results in the increase of the dimensionality of the problem to be solved. Then, the I-DREM procedure with exponential forgetting, resetting, and normalization of the regressor, which has been proposed earlier by the authors, is applied to the obtained regression. This allows one, in contrast to the known solutions, to get the dimensionality of the problem back to the initial one and provide the required exponential convergence of the parameter error to a bounded set with adjustable bound under the condition that the regressor is FE. In addition, this method guarantees that the parameter error is bounded beyond the regressor excitation interval. The above properties are proved analytically and shown via numerical simulations.

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arXiv2021

Exponential Convergence of Piecewise-Constant Parameters Identification under Finite Excitation Condition

A problem of identification of piecewise-constant unknown parameters of a linear regression equation (LRE) is considered. Such parameters change their values over the interval of the regressor finite (rather than persistent) excitation. To solve it, the previously proposed I-DREM procedure and the integral-based filtering method with the exponential forgetting and resetting are improved: the integral of the filter equations is taken over the finite time intervals, which belong to the finite excitation time range. This allows one to obtain an exponentially bounded identification error over the excitation interval, and, when the LRE parameters are constant outside such interval, to provide exponential convergence of the identification error to zero. In addition, the applied method of the regressor excitation normalization makes it possible to obtain the same rate of convergence of the parameter error for the regressors of various amplitudes. The stability and all the above-mentioned properties are proved for the derived identification method. The results of numerical experiments (including the case of the noise-contaminated regressor and output measurements) fully support the obtained theoretical results.

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arXiv2021

Normalization of regressor excitation as a part of dynamic regressor extension and mixing procedure

The method of excitation normalization of the regressor, which is used in the estimation loop to solve the plant identification problem, is proposed. It is based on the dynamic regressor extension and mixing procedure. Its application allows to obtain the same upper bound of the parameter identification error for the scalar regressors with different excitation level, using a constant value of the adaptation rate for all of them. This fact is a significant advantage from the practical point of view. Comparison of the developed method with the known one of the regressor amplitude normalization is conducted. It is shown that the classical approach does not have the above-stated property. To validate the theoretical conclusions made, the results of the comparative mathematical modeling of three loops are presented: 1) the classical gradient one, 2) the one with the normalization of the regressor amplitude, 3) the proposed one with the normalization of the regressor excitation.

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arXiv2021

I-DREM MRAC with Time-Varying Adaptation Rate & No A Priori Knowledge of Control Input Matrix Sign to Relax PE Condition

The known dynamic regressor extension and mixing method (DREM) is combined with the proposed filter of a new type, which uses the integration operation with forgetting, and the recursive least-squares method to develop the new I-DREM model reference adaptive control (MRAC) system. It does not require a priori knowledge of the sign or the elements values of the control input matrix of the plant. It also provides the exponential convergence of the adaptation process (with the automatically adjustable adaptation rate) without the regressor persistent excitation. Such control system allows to solve three actual problems of the adaptive control: 1) to provide the exponential convergence of the controller parameter error under the condition of the regressor initial excitation, 2) to make such convergence monotonic, 3) to calculate the adaptation rate online according to the current regressor value. Some numerical experiments are conducted to demonstrate the effectiveness of the proposed method.

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arXiv2020

Robust method to provide exponential convergence of model parameters solving LTI plant identification problem

The scope of this research is a problem of parameters identification of a linear time-invariant (LTI) plant, which 1) input signal is not frequency-rich, 2) is subjected to initial conditions and external disturbances. The memory regressor extension (MRE) scheme, in which a specially derived differential equation is used as a filter, is applied to solve the above-stated problem. Such a filter allows us to obtain a limited regressor value, for which a condition of the initial excitation (IE) is met. Using the MRE scheme, the recursive least-squares (RLS) method with the forgetting factor is used to derive an adaptation law. The following properties have been proved for the proposed approach. If the IE condition is met, then: 1) the parameter error of identification is a limited value and converges to zero exponentially (if there are no external disturbances) or to a bounded set (in the case of them) with an adjustable rate, 2) the parameters adaptation rate is a finite value. The above-mentioned properties are mathematically proved and demonstrated via simulation experiments.

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