Jozsef Bokor

Budapest University of Technology and Economics, Department of Control for Transportation and Vehicle Systems, Faculty Member

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Doing research in various field of dynamic systems and control

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Papers by Jozsef Bokor

The impact of suspension control on the controllability of the lateral vehicle dynamics

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Continuity of the maximal negative graph spaces

In the framework of LPV and qLPV controller design one often encounter the problem of finding a m... more In the framework of LPV and qLPV controller design one often encounter the problem of finding a maximal negative graph subspace of a parameter dependent non-singular indefinite matrix. For practical reason it is necessary that these subspaces depend continuously on the parameters. The paper provides an exhaustive condition for the existence of such a continuous solution.

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Inversion-based Approaches to Robust Fault Detection and Isolation with Applications in Linear Systems

ABSTRACT In this paper the idea of inversion-based direct input reconstruction for robust detecti... more ABSTRACT In this paper the idea of inversion-based direct input reconstruction for robust detection, separation and estimation of multiple simultaneous faults in the presence of persistent disturbances in linear dynamical systems is presented. In particular, it is shown how in a specific filtering structure a residual generator, relying on the inverse representation of the system, by means of estimation of the inverse dynamics can be designed providing robust fault decoupling. The development of the method and its applicability to earlier not solvable problems is demonstrated based on an aircraft monitoring application example.

Controller blending - a geometric approach

In order to design efficient algorithms that work on the set of controllers that fulfill a given ... more In order to design efficient algorithms that work on the set of controllers that fulfill a given property, e.g., stability or a norm bound, it is important to have an operation that preserves that property, i.e., a suitable blending method. While available approaches use the Youla parameters in order to define this operation for stability in a trivial way, they do not provide a general answer to the problem. This paper places the controller blending problem in a more general setting by pointing to the basic global geometric structures that are related to feedback stability or suboptimal ℋ∞ design. A detailed analysis is given for feedback stability: an operation is given under which well-posedness is a group while stability is a semigroup. Moreover, an operation is given that makes controllers with strongly stable property a group.

Data-driven linear parameter-varying modelling of the steering dynamics of an autonomous car

IFAC-PapersOnLine, 2021

Developing automatic driving solutions and driver support systems requires accurate vehicle speci... more Developing automatic driving solutions and driver support systems requires accurate vehicle specific models to describe and predict the associated motion dynamics of the vehicle. Despite of the mature understanding of ideal vehicle dynamics, which are inherently nonlinear, modern cars are equipped with a wide array of digital and mechatronic components that are difficult to model. Furthermore, due to manufacturing, each car has its personal motion characteristics which change over time. Hence, it is important to develop data-driven modelling methods that are capable to capture from data all relevant aspects of vehicle dynamics in a model that is directly utilisable for control. In this paper, we show how Linear Parameter-Varying (LPV) modelling and system identification can be applied to reliably capture personalised model of the steering system of an autonomous car based on measured data. Compared to other nonlinear identification techniques, the obtained LPV model is directly utilisable for powerful controller synthesis methods of the LPV framework.

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Dynamics and Control of Autonomous Vehicles: PLENARY TALK

Parametrization and Identification of Dynamic Systems

Realization of homogeneous multi-agent networks

A class of large-scale systems with decentralized information structures, such as multi-agent sys... more A class of large-scale systems with decentralized information structures, such as multi-agent systems, can be represented by a linear system with a generalized frequency variable. In these models agents are modelled through a strictly proper SISO state space model while the supervisory structure, representing the information exchange among the agents, is represented via a linear state-space model. The starting point of the paper is that the agent $h(s)$ and the overall system $\mathcal{G}(s)$ are known through their Markov parameters. Based on these data a condition is given that characterizes compatibility, i.e., the existence of a transfer function $G(s)$ that describes the network and leads to the relation $\displaystyle \mathcal{G}(s)=G \left(\frac{1}{h(s)} \right)$. If compatibility holds, the paper also presents an algorithm to compute the Markov parameters of the unknown transfer function $G(s)$. Then, a minimal state space representation of this transfer function can be computed through the Ho-Kalman algorithm.

On constrained input controllability of LTI and LPV systems

Identification of vehicle models and road roughness estimation

IFAC Proceedings Volumes, Jul 1, 2004

An identification method is presented for the parameters of a quasi linear parameter varying mode... more An identification method is presented for the parameters of a quasi linear parameter varying model (qLPV) of a quarter car suspension system. In this model nonlinear components of the suspension system are taken into consideration. Since not all the variables necessary for the identification are available, some numerical techniques need to be applied, e.g. the numerical integration of measured signals. It is also shown that the selection of the sampling time might be critical in this type of application. By using the result of this identification an algorithm is given for the road signal reconstruction. The road roughness estimation is based on this reconstructed signal for classification purposes by and an autoregressive-moving average model structure is used. Finally, demonstration examples show the results of the proposed approach.

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Robust control theory with automotive applications

Modeling of LPV Systems

Advances in industrial control, Nov 19, 2016

In general terms, control theory can be described as the study of how to design the process of in... more

Adaptive Cruise Control in Longitudinal Dynamics

Advances in industrial control, Nov 19, 2016

In the last decade, the longitudinal vehicle control based on the look-ahead approach has been in... more

Generalised system level approach

IFAC-PapersOnLine, 2021

Recently, system level approach has been proposed as a novel design tool for largescale cyber phy... more Recently, system level approach has been proposed as a novel design tool for largescale cyber physical systems in the discrete time LTI framework. The main idea of the new paradigm is a shift from constructing and parametrizing the desired optimal controller to the parametrization of the achievable closed loop behaviours (closed loop shape). Then, the controller is synthesised from the system level data in a way that keep the imposed structural constraints intact. In this paper we lift the main idea of the system level parametrization to a general level, that also includes the class of LPV systems. We also provide a general scheme for the realization related to different Möbius transforms which are formulated in terms of the original data and also keep intact the structural information.

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Development and performance evaluation of an infinite horizon LQ optimal tracker

European Journal of Control, 2018

The paper presents an infinite horizon LQ optimal tracking control solution (LQ tracker) for disc... more The paper presents an infinite horizon LQ optimal tracking control solution (LQ tracker) for discrete time linear time invariant systems. The reference preview need is reduced to only two steps irrespective of the type of reference signal making real-time implementation an achievable goal. A rigorous proof of optimality is provided for a set of infinite horizon reference commands which includes the linear combination of constant and exponentially bounded signals. Dissipativity, finite gain and l 1 performance of the controlled system are also evaluated. The behaviour of the proposed LQ tracker and its previously published sub-optimal version with one-step preview is demonstrated in conjunction with an application example. Their performances are compared to those of alternative solutions including set point control and model predictive control. Finally, it is concluded that the proposed rigorous solution of the infinite horizon tracking problem is real-time realizable and performs advantageously compared to other solutions.

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Monocular image parameter-based aircraft sense and avoid

This paper deals with the problem of monocular image parameter-based sense and avoid. It consider... more This paper deals with the problem of monocular image parameter-based sense and avoid. It considers image parameters as decision variables and selects decision thresholds related to collision and non-collision scenarios. The main contribution is non-heuristic threshold selection. Another contribution is the characterization of possible intruder threats with sizespeed curves given in closed form formulae. This makes it possible to avoid the use of lookup tables. The overall decision and avoidance concept is evaluated in a software-in-the-loop simulation campaign considering threats ranging from small UAV to large airliner. The miss detection rate of the method is zero which is an excellent result, however the false alarm rate is high. The causes of this are pointed out and targeted as further developments. Finally, promising results are presented executing the method for real camera images.

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Development and hardware-in-the-loop testing of an Extended Kalman Filter for attitude estimation

This paper describes the development and hardware-in-the-loop testing of an Extended Kalman Filte... more This paper describes the development and hardware-in-the-loop testing of an Extended Kalman Filter (EKF) for attitude estimation. After literature review, a multimode solution to the estimation problem is introduced. It uses the sensor measurements optimally relying on the magnetic and acceleration data on the ground, and magnetic and GPS data in the air. An emergency aerial mode dealing with lost GPS data is also developed. The quaternion dynamic equations are chosen to represent system dynamics. Their special structure makes it possible to perform continuous-discrete transformation with a closed form solution of the Heun scheme. This can improve the prediction performance of the EKF. The observability of the system was examined using gridding of the state space in every modes of the filter. The computing steps of the new filter are summarized before presenting issues of implementation and testing. This article presents hardware-in-the-loop test results with simulated GPS losses. Comparison to another filter is also presented. The estimator was tested in real flights and performed as expected.

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Loop Shifting and Non-Conservative qLPV Design

Acta Polytechnica Hungarica, Apr 25, 2014

As an extension of the robust theory, the time domain design based on linear matrix inequalities ... more As an extension of the robust theory, the time domain design based on linear matrix inequalities (LMI) is a conceptually simple and efficient framework to obtain qLPV controllers. However, the constructed scheduling variables are not always suitable for an efficient implementation. This paper investigates the possibility of constructing the scheduling block of a qLPV controller explicitly, i.e., in the form of a linear fractional transformation (LFT). It is shown here that if both the primary and dual multiplier LMI equations lead to maximal indefinite subspaces and a coupling condition holds, the problem can be solved and a constructive algorithm results to build the desired scheduling variables.

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Generalized piecewise linear feedback stabilizability of controlled linear switched systems

The paper consider the (closed-loop) stabilizability problem of controlled linear switched system... more The paper consider the (closed-loop) stabilizability problem of controlled linear switched systems. It is shown that if the switching system is completely controllable then it is stabilizable. Moreover, it is shown that for these systems it can be found a closed-loop (event driven) switching strategy with suitable linear feedbacks that (weakly) stabilizes the system, i.e. the switching system is stabilizable by a generalized piecewise linear feedback. These results holds for systems where the control inputs are sign constrained, too.

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Quadratic separators in the input-output setting

ABSTRACT The paper provides a formulation of the quadratic separator result in a fairly general i... more ABSTRACT The paper provides a formulation of the quadratic separator result in a fairly general input-output operator framework and it focuses on the specific points that are different compared to the usual finite dimensional formulations. The major contribution of the paper is to emphasize the role of the causality in obtaining the stability result having a quadratic separator and the fact that the plant and the boundedness constant in the formulation of the well-posedness condition determine the robust stability domain associated to the given plant, i.e., the set of those systems {K} that stabilizes the given plant and produce the given “disturbance rejection” level γ Concerning the causality issue the necessity of the homotopy argument in the IQC results is also explained and its relation with a general result concerning nest algebras is pointed out.

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