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Summary: Data‐driven feedforward control for tracking of varying and non‐resetting point‐to‐point references requires continuous updating of feedforward parameters instead of task‐by‐task updating. The aim of this paper is to develop an adaptive feedforward controller for non‐resetting point‐to‐point motion tasks by a data‐driven feedforward controller. An approximate optimal instrumental variable (IV) estimator with real‐time bootstrapping is employed in a closed‐loop setting to update the feedforward parameters. A case study on a wafer‐stage and experimental validation on a benchmark motion system show the performance benefit. [ABSTRACT FROM AUTHOR]

Mobility using wheelchair is a crucial feature for disabled people. Between a manual wheelchair and an electric wheelchair, there is a very interesting and promising solution consisting of an electrical kit that converts a manual wheelchair to an electric wheelchair. Autonomad‐Mobility is a company selling such kits, where the wheels are equipped with a brushless motor. It presents new possibilities for mobility, especially for crossing obstacles and running on different types of soil. Several methods have been tested, from linear to nonlinear ones including the linear parameter‐varying control framework. Nevertheless, the most dangerous and critical issue is to be able to produce a so‐called safe and robust swing‐up: the transition from standard mode (four wheels on the ground) to gyroscopic mode (the wheelchair balancing on the rear push‐wheels). The gyroscopic mode is a unique feature improving mobility by providing a way to overcome obstacles that would normally be unsurpassable due to the caster wheels. Whereas some results exist, the solution must be compatible with any wheelchair and any disabled person whatever is her/his height and weight. Robustness of this unstable feature is therefore the key point of the work knowing that "exact" modeling is unrealistic. With the model in descriptor form and using the quasi‐linear parameter‐varying framework new stabilization conditions formulated as linear matrix inequality constraints are developed for attaining the goal. Simulations and real‐time experiments demonstrate the interest of this approach. [ABSTRACT FROM AUTHOR]

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]

Summary: This article deals with the model predictive control (MPC) of linear, time‐invariant discrete‐time polytopic (LTIDP) systems. The 2‐fold aim is to simplify the treatment of complex issues like stability and feasibility analysis of MPC in the presence of parametric uncertainty as well as to reduce the complexity of the relative optimization procedure. The new approach is based on a two degrees of freedom (2DOF) control scheme, where the output r(k) of the feedforward input estimator (IE) is used as input forcing the closed‐loop system ∑f. ∑f is the feedback connection of an LTIDP plant ∑p with an LTI feedback controller ∑g. Both cases of plants with measurable and unmeasurable state are considered. The task of ∑g is to guarantee the quadratic stability of ∑f, as well as the fulfillment of hard constraints on some physical variables for any input r(k) satisfying an "a priori" determined admissibility condition. The input r(k) is computed by the feedforward IE through the on‐line minimization of a worst‐case finite‐horizon quadratic cost functional and is applied to ∑f according to the usual receding horizon strategy. The on‐line constrained optimization problem is here simplified, reducing the number of the involved constraints and decision variables. This is obtained modeling r(k) as a B‐spline function, which is known to admit a parsimonious parametric representation. This allows us to reformulate the minimization of the worst‐case cost functional as a box‐constrained robust least squares estimation problem, which can be efficiently solved using second‐order cone programming. [ABSTRACT FROM AUTHOR]

The present study sheds new light on advanced control methods of photovoltaic (PV) emulators using finite set model predictive control (FS‐MPC). In the first part of the study, a predictive PV emulator (P‐PVE) based on a Buck converter is proposed and tested under hard climatic conditions and load variations. The high performance of the P‐PVE in terms of dynamic response, reference tracking, accuracy, simplicity, and efficiency is confirmed experimentally when compared with those of the commonly used one based PI controller. The second part of the study proposes an efficient cascaded predictive control (CPC) method applied[AQ ID=Q1] on two topologies of PV systems, namely the stand‐alone system and the grid‐connected system. In each topology, the P‐PVE is cascaded to a maximum power point tracking Boost converter in order to track efficiently the maximum power point. In addition to the high performance offered by the FS‐MPC, the proposed control strategy allows to control all cascaded converters at the same time in one stage instead of controlling them separately, thus providing more flexibility and simple controllability. Extensive experimental results are done confirming the correctness and the effectiveness of the proposed CPC under hard climatic conditions, even in the presence of distorted grid voltage. [ABSTRACT FROM AUTHOR]

Summary: This paper addresses the reference tracking problem for plants that can primarily be modeled as a linear time‐invariant (LTI) system preceded by a slope‐restricted hysteresis nonlinearity. This structure is particularly interesting due to its wide use in modeling smart actuator dynamics such as shape‐memory alloy and piezoelectric. The hysteresis nonlinearity is considered to be slope restricted; however, no specific modeling framework is exploited. Based on the slope bounds of the nonlinearity, conditions for asymptotic tracking are proposed in terms of linear matrix inequalities (LMIs) when constant reference is considered. By solving the LMIs, the controller parameters can be obtained, which eventually ensures asymptotic convergence of tracking error to zero. The proposed model‐free design technique is further reformulated considering parametric uncertainties in the LTI part. The resulting conditions in LMI framework facilitate solving the robust tracking problem for hysteretic systems. The results are applicable for multiple‐input–multiple‐output systems as well, with decoupled hysteresis nonlinearity. Additionally, with only integral control, the proposed results are specialized for the case of stable LTI part having positive definite symmetric part of the DC gain matrix. It is shown that there always exists such a tracking controller for the hysteretic system. Numerical examples are presented to illustrate the effectiveness of the proposed results. [ABSTRACT FROM AUTHOR]

A dual‐mode flyback inverter is proposed for photovoltaic power applications. The proposed dual‐mode flyback inverter makes use of both discontinuous conduction mode (DCM) and continuous conduction mode (CCM) operations for more than 200 W power applications. However, it suffers from output current control problems such as low system gain during DCM and right‐half‐plain zero problem during CCM. To achieve accurate reference tracking, the authors propose to adopt the repetitive control scheme that increases the system gain at the fundamental and its harmonic frequencies of the grid. To reduce the burden from the conventional proportional‐integral controller, the authors use the dual‐mode nominal duty that helps the dual‐mode flyback inverter generate the target output current while attenuating the effect of disturbances. To make the dual‐mode flyback inverter operate at the maximum power point (MPP), the authors use the incremental conductance method that offers smooth transition to the MPP. The experimental results show that the proposed flyback system implemented for 200 W dual‐mode flyback inverter prototype achieves high MPP tracking efficiency, low total harmonic distortion, high power conversion efficiency, and high power capacity. [ABSTRACT FROM AUTHOR]

Establishing and maintaining reference is a crucial part of discourse. In spoken languages, differential linguistic devices mark referents occurring in different referential contexts, that is, introduction, maintenance, and re-introduction contexts. Speakers using gestures as well as users of sign languages have also been shown to mark referents differentially depending on the referential context. This article investigates the modality-specific contribution of the visual modality in marking referential context by providing a direct comparison between sign language (German Sign Language; DGS) and co-speech gesture with speech (German) in elicited narratives. Across all forms of expression, we find that referents in subject position are referred to with more marking material in re-introduction contexts compared to maintenance contexts. Furthermore, we find that spatial modification is used as a modality-specific strategy in both DGS and German co-speech gesture, and that the configuration of referent locations in sign space and gesture space corresponds in an iconic and consistent way to the locations of referents in the narrated event. However, we find that spatial modification is used in different ways for marking re-introduction and maintenance contexts in DGS and German co-speech gesture. The findings are discussed in relation to the unique contribution of the visual modality to reference tracking in discourse when it is used in a unimodal system with full linguistic structure (i.e., as in sign) versus in a bimodal system that is a composite of speech and gesture. [ABSTRACT FROM AUTHOR]

Although the language we encounter is typically embedded in rich discourse contexts, many existing models of processing focus largely on phenomena that occur sentence-internally. Similarly, most work on children's language learning does not consider how information can accumulate as a discourse progresses. Research in pragmatics, however, points to ways in which each subsequent utterance provides new opportunities for listeners to infer speaker meaning. Such inferences allow the listener to build up a representation of the speakers' intended topic and more generally to identify relationships, structures, and messages that extend across multiple utterances. We address this issue by analyzing a video corpus of child-caregiver interactions. We use topic continuity as an index of discourse structure, examining how caregivers introduce and discuss objects across utterances. For the analysis, utterances are grouped into topical discourse sequences using three annotation strategies: raw annotations of speakers' referents, the output of a model that groups utterances based on those annotations, and the judgments of human coders. We analyze how the lexical, syntactic, and social properties of caregiver-child interaction change over the course of a sequence of topically related utterances. Our findings suggest that many cues used to signal topicality in adult discourse are also available in child-directed speech. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a new sporadic control approach to the tracking problem for MIMO closed-loop systems. An LTI sampled data plant with unmeasurable state affected by external unknown disturbances is considered. The plant is interconnected to an event-based digital dynamic output-feedback controller via a network. Both the external reference and the unknown disturbance are assumed to be generated as the free output response of unstable LTI systems. The main feature of the new event-driven communication logic (CL) is that it works without the strict requirement of a state vector available for measurement. The purpose of the CL is to reduce as much as possible the number of triggered messages along the feedback and feedforward paths with respect to periodic sampling, still preserving internal stability and without appreciably degrading the control system tracking capability. The proposed event-driven CL is composed of a sensor CL (SCL) and of a controller CL (CCL). The SCL is based on the computation of a quadratic functional of the tracking error and of a corresponding suitably computed time-varying threshold: a network message from the sensor to the controller is triggered only if the functional equals or exceeds the current value of the threshold. The CCL is directly driven by the SCL: the dynamic output controller sends a feedforward message to the plant only if it has received a message from the sensor at the previous sampled instant. Formulation of the controller in discrete-time form facilitates its implementation and provides a minimum inter-event time given by the sampling period. An example taken from the related literature shows the effectiveness of the new approach. The focus of this paper is on the stability and performance loss problems relative to the sporadic nature of the control law. Other topics such as network delay or packets dropout are not considered. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study addresses two major single‐input single‐output control problems involving both feedback and feedforward actions: (i) the model matching in reference tracking and (ii) the rejection of measurable disturbances. Its aim is to overcome the limitations of inversion‐based feedforward design methods when system uncertainty is considered, and to find a control engineering solution based on the quantitative feedback theory (QFT). The proposed methodology leads to minimum cost of feedback by limiting the feedback action to the strictly necessary amount that enables the use of a feedforward controller. Although the model matching problem had drawn some attention of the QFT community in the last few years, the measurable disturbance rejection problem remained unaddressed. This study provides a novel solution for both of them in which the need for feedback is linked to the existence of a common feedforward solution for all plants within the model uncertainty. This work also deals with the generation of the corresponding quadratic inequalities and new QFT bounds for the mentioned feedback demand. A practical and well‐known benchmark example illustrates the main details and advantages of the new methodology. [ABSTRACT FROM AUTHOR]