In Networked Control System (NCS), the absence of physical communication links in the loop leads to relevant issues, such as measurement delays and asynchronous execution of the control commands. In general, these issues may significantly compromise the performance of the NCS, possibly causing unstable behaviours. This paper presents an original approach to the design of a complete digital control unit for a system characterized by a varying sampling time and asynchronous command execution. The approach is based on the Embedded Model Control (EMC) methodology, whose key feature is the estimation of the disturbances, errors and nonlinearities affecting the plant to control and their online cancellation. In this way, measurement delays and execution asynchronicity are treated as errors and rejected up to a given frequency by the EMC unit. The effectiveness of the proposed approach is demonstrated in a real-world case-study, where the NCS consists of a differential-drive mobile robot (the plant) and a control unit, and the two subsystems communicate through the web without physical connection links. After a preliminary verification using a high-fidelity numerical simulator, the designed controller is validated in several experimental tests, carried out on a real-time embedded system incorporated in the robotic platform.

In Networked Control Systems (NCS), the absence of physical communication links in the loop leads to relevant issues, such as measurement delays and asynchronous execution of the control commands. These issues may lead to unwanted control behaviours. This ArXiv paper is intended to give additional results to the work presented in "Embedded Model Control of Networked Control Systems: an Experimental Case-study". The last one presents an original approach, based on the Embedded Model Control, to deal with experimental scenarios characterized by asynchronous control timing. The effectiveness of the proposed approach is demonstrated with a differential-drive robot, first with high-fidelity simulations and finally with several experimental tests. Specifically, the present work aims to study the stability analysis of the EMC experimental setup and to give further experimental results, to complement those presented in the main paper, "Embedded Model Control of Networked Control Systems: an Experimental Case-study".

Missions finalized at measuring the space-time variations of the Earth gravity field have become of high relevance in recent years. These missions are indeed of interest for scientific purposes and applications in several fields. Precise observations of the Earth gravity field can be accomplished by measuring the distance between two satellites flying in suitable orbits. Several mission concepts foresee an active formation control to maintain the distance variations between the two satellites within given bounds. In this paper, we first present an original constellation model, called the Triangle Dynamics (TD) model, which is particularly suitable to describe the orbital dynamics of satellite pairs. Open-loop simulations are performed, where the TD model is compared with a standard model, derived from the well-known Hill–Clohessy–Wiltshire (HCW) equations. The simulation results show that the TD model provides more accurate predictions than the HCW model. Then, we propose a formation control approach based on a new Model Predictive Control (MPC) algorithm. The core of this algorithm is the TD model, which is used in real-time to predict the behavior of the satellite pair, allowing the computation of an optimal formation control command. A case study concerned with the Next Generation Gravity Mission (NGGM) is presented to demonstrate the effectiveness of the proposed MPC-TD algorithm.

In the last few years, the observation of gravitational waves by means of LIGO and Virgo interferometers and the success of LISA Pathfinder, gave a significant boost to the development of space-based gravitational wave observatories. The European Space Agency confirmed LISA as the third large class mission of the Cosmic Vision program. The present work is part of the Drag Free and Attitude Control System (DFACS) preliminary prototyping study, which aims at the development of mathematical models and advanced controllers for the science phases of the LISA mission. Nonlinear modelling is a fundamental step for the derivation of linearized and decoupled models as well as for the development of suitable linear and nonlinear controllers. In this paper, an analytical nonlinear model is derived, which describes all the relevant dynamics of a LISA spacecraft, representing an effective compromise between accuracy and complexity. The model is extensively validated through linearization analysis and Monte Carlo simulations.

In this paper, a control system for unmanned aerial vehicles (UAVs) is designed, tested in simulation by means of a high-fidelity simulator, and then applied to a real quadrotor UAV. A novel approach is proposed for the control design, based on the combination of two methodologies: feedback linearization (FL) and embedded model control (EMC). FL allows us to properly transform the UAV dynamics into a form suitable for EMC; EMC is then used to control the transformed system. A key feature of EMC is that it encompasses a so-called extended state observer (ESO), which not only recovers the system state but also gives a real-time estimate of all the disturbances/uncertainties affecting the system. This estimate is used by the FL-EMC control law to reject the aforementioned disturbances/uncertainties, including those collected via the FL, allowing a robustness and performance enhancement. This approach allows us to combine FL and EMC strengths. Most notably, the entire process is made systematic and application oriented. To set-up a reliable UAV attitude observer, an effective attitude sensors fusion is proposed and also benchmarked with an enhanced complementary filter. Finally, to enhance the closed-loop performance, a complete tuning procedure, encompassing frequency requirements, is outlined, based on suitably defined stability and performance metrics.

This study presents an original approach to the design of a complete digital attitude control unit for a UAV quadrotor. The approach is developed within the framework of Active Disturbance Rejection Control (ADRC) and Embedded Model Control (EMC), two well-established control design methodologies, both based on the estimation of the disturbances/uncertainties affecting the plant to control, and on their online cancellation. The attitude control design carried out in this paper demonstrates the possibility of adopting a simple input–output model to control the UAV attitude, while relying on the disturbance rejector to bridge the gap between model and plant reality. The designed attitude control unit encompasses an attitude state predictor, a control law, and a model-based reference generator. A multi-step test strategy is proposed to assess the performance of this disturbance-rejection-based attitude controller. Consequently, the presented experimental results are obtained both using a high-fidelity numerical simulator and in several experimental tests, carried out either on a laboratory single-axial test-bench or in-flight. Finally, the control unit performance is benchmarked, in simulation, against a state-of-the-art high-performance UAV attitude controller.

The increasing use of electric vehicles connected to the power grid gives rise to challenges in the vehicle charging coordination, cost management, and provision of potential services to the grid. Scheduling of the power in an electric vehicle charging station is a quite challenging task, considering time-variant prices, customers with different charging time preferences, and the impact on the grid operations. The latter aspect can be addressed by exploiting the vehicle charging flexibility. In this article, a specific definition of flexibility to be used for an electric vehicle charging station is provided. Two optimal charging strategies are then proposed and evaluated, with the purpose of determining which strategy can offer spinning reserve services to the electrical grid, reducing at the same time the operation costs of the charging station. These strategies are based on a novel formulation of an economic model predictive control algorithm, aimed at minimising the charging station operation cost, and on a novel formulation of the flexibility capacity maximisation, while reducing the operation costs. These formulations incorporate the uncertainty in the arrival time and state of charge of the electric vehicles at their arrival. Both strategies lead to a considerable reduction of the costs with respect to a simple minimum time charging strategy, taken as the benchmark. In particular, the strategy that also accounts for flexibility maximisation emerges as a new tool for maintaining the grid balance giving cost savings to the charging stations.

In the paper "Control Design for UAV Quadrotors via Embedded Model Control" [1], the authors designed a complete control unit for a UAV Quadrotor, based on the Embedded Model Control (EMC) methodology, in combination with the Feedback Linearization (FL); when applied to non-linear systems. Specifically, [1] proposes to use the FL as a novel way to design the internal model for the EMC state and disturbance predictor. To support the treatise in [1], in this report the feedback-linearized model of the UAV quadrotor leveraged in [1] is step-by-step derived.

This study presents an estimation and control method for systems with asynchronous measurements with time-stamp. This approach is developed within the framework of Embedded Model Control (EMC), a control design methodology based on the estimation and the active rejection of the uncertainties affecting the plant to be controlled. The proposed control approach allows us to deal with control applications in which the measurement or the control law are characterized by a variable sampling time. Most notably, the proposed algorithm is capable to manage delays and package dropouts, potentially affecting networked control systems, by leveraging not only the sensors measurement information but also their time-stamp.

System and AOCS Challenges for the Design Consolidation of the Next Generation Gravity Mission / Dionisio, Sabrina; Anselmi, Alberto; Cesare, Stefano; Novara, Carlo; Colangelo, Luigi; Massotti, Luca; Silvestrin, Pierluigi. STAMPA. (2018). ((Intervento presentato al convegno AIAA SciTech Forum. Original System and AOCS Challenges for the Design Consolidation of the Next Generation Gravity Mission

The paper addresses the problem of reconciling the modern control paradigm developed by R. Kalman in the sixties of the past century, and the centenary error-based design of the proportional, integrative and derivative (PID) controllers. This is done with the help of the error loop whose stability is proved to be necessary and sufficient for the close-loop plant stability. The error loop is built by cascading the uncertain plant-to-model discrepancies (causal, parametric, initial state, neglected dynamics), which are driven by the design model output and by arbitrary bounded signals, with the control unit transfer functions. The embedded model control takes advantage of the error loop and its equations to design appropriate algorithms of the modern control theory (state predictor, control law, reference generator), which guarantee the error loop stability and performance. A simulated multivariate case study shows modeling and control design steps and the coherence of the predicted and simulated performance.

After the successful European gravity mission GOCE (Gravity field and steady-state Ocean Circulation Explorer), which provided an unprecedented high resolution static global map of the Earth’s gravity field, the European Space Agency has proposed several preparatory studies for a Next Generation Gravity Mission (NGGM). The NGGM mission objective aims at measuring the temporal variations of the Earth gravity field over a long time span with an unprecedented level of accuracy, both in spatial and temporal resolution. The GOCE technological heritage is leveraged as starting point while defining the NGGM future mission concept. Nonetheless, to accomplish its challenging scientific objective, the NGGM mission concept envisages a wide range of innovations, with respect to the past or flying missions, both on technological and automatic control side. Thus, this paper focuses on the guidance, navigation and control design evolution for the European gravity missions, from GOCE to NGGM. After recalling the GOCE GNC main design concepts, the paper will describe the most important innovation required by NGGM. Indeed, such a future concept will consist of a two-satellite long-distance loose formation, where each satellite is controlled independently to be drag-free, GOCE-like. The satellite-to-satellite distance variations, encoding gravity anomalies, will be then measured by laser heterodyne interferometry for inter-satellite ranging at 20 nm resolution, or better. Hence, an orbit and formation control is now required to counteract bias and drift of the residual drag-free accelerations, in order to reach a bounded orbit/formation long-term stability. Finally, GOCE control flight results as well as NGGM simulated results, via a high-fidelity simulator, will be provided. These results highlight the GOCE GNC in-flight achievements as well as the NGGM concept validity, showing that the expected control performances are in agreement with the consolidated mission requirements, all over the 10-year mission.

A Next Generation Gravity Mission (NGGM) concept for measuring the Earth's variable gravity field has been recently proposed by ESA. The mission objective consists in measuring the temporal variations of the Earth gravity field over a long-time span, with very high spatial and temporal resolutions. This paper focuses on the guidance, navigation and control (GNC) design for the science phase of the NGGM mission. NGGM will consist of a two-satellite long-distance formation like GRACE, where each satellite will be controlled to be drag-free like GOCE. Satellite-to-satellite distance variations, encoding gravity anomalies, will be measured by laser interferometry. The formation satellites, distant up to 200 km, will fly in a quasi-polar orbit at an Earth altitude between 300 and 450 km. Orbit and formation control counteract bias and drift of the residual drag-free accelerations, in order to reach orbit/formation long-term stability. Drag-free control allows the formation to fly counteracting the atmospheric drag, ideally subject only to gravity. Orbit and formation control, designed through the innovative Integrated Formation Control (IFC), have been integrated into a unique control system, aiming at stabilizing the formation triangle consisting of satellites and Earth Center of Masses. In addition, both spacecraft must align their control axis to the satellite-to-satellite line (SSL) with micro-radian accuracy. This is made possible by specific optical sensors and the inter-satellite laser interferometer, capable of materializing the SSL. Such sensors allow each satellite to pursue an autonomous alignment after a suitable acquisition procedure. Pointing control is severely constrained by the angular drag-free control, which must ideally zero the angular acceleration vector, in the science frequency band. The control unit has been designed according to the Embedded Model Control methodology and is organized in a hierarchical way, where the drag-free control plays the role of a wide-band inner loop, and orbit/formation and attitude/pointing controls are the narrow band outer loops. The relevant state equations were converted to discrete time providing the embedded model, a fundamental part of the control unit. The state predictor, control law and reference generator were built on and interfaced to the embedded model. Simulated results, via a high-fidelity simulator, prove the concept validity and show that the control performances are in agreement with the defined mission requirements. Indeed, the presented control strategy is shown to be capable of keeping the attitude and formation variables stable within the required boundaries, all over the 10-year mission, through a low-thrust authority in the order of a few milli-Newton.

This paper focuses on the orbit and formation control for the Next Generation Gravity Mission (NGGM), under study at the European Space Agency. In our past study an innovative integrated orbit/formation model (IFC) has been designed, introducing a novel set of Hill-type equations. The aim of this study is the refinement and the enhancement of the IFC architecture. The proposed solution is based on a modified state predictor plus an extended hierarchical and multi-rate structure of the control law, with respect to the preliminary design. Care was taken in the control design to reduce as much as possible the demanded extra-thrust effort. This improved control strategy has been shown to be far less sensitive to the initial formation perturbations as well as capable of keeping the formation variables stable within the required band, all over the 10-year mission, through a low-thrust authority in the order of few milli-newtons.

This study investigates the use of the feedback linearization approach as a novel way to design the internal model for Embedded Model Control (EMC). The feedback linearization allows to collect all the nonlinearities at command level. EMC, by means of a disturbance dynamics model, makes possible to estimate and then reject the non-linear terms through the control law. This idea is applied to the control of an Unmanned Aerial Vehicle: the Borea project quadrotor. Embedded Model Control methodology implies the design of an internal model (Embedded Model) coded into the control unit and running in parallel with the plant. The attitude reconstruction problem is faced by means of a state observer developed on purpose and fully integrated with the model. A two-modes control strategy is proposed in order to reject systematic sensor errors, thus enhancing the attitude estimation capability. Using a high-fidelity numerical simulator, the feasibility of the proposed control strategy was demonstrated. This indicates that a feedback linearization approach allows the extension of EMC techniques to non-linear systems control. What is more, the EMC was successfully applied to the control of the Borea quadrotor.

This paper is about the relationship between criminal victimization and people’s perception of safety. The study refers simultaneously to three indicators of fear of crime: feeling unsafe alone in the streets after dark, fear of sexual violence (her or her relatives), fear of crime affecting own habits - against sexual victimization and characteristics of the place of residence, controlling demographic and socio-economic attributes of Italian women. The main results show that a) the prior victimization and crime exposure shape perceived future risk; b) fear of crime partly reflects worries about one's degraded context; c) married women seem more affected by the fear of crime, especially the fear of suffering directly or indirectly any sexual violence. L’obiettivo di questo lavoro e studiare la relazione tra esperienza di vittimizzazione e senso di insicurezza delle donne. I risultati mostrano che oltre alle note caratteristiche socio-economiche e demografiche delle donne la paura del crimine sembra essere legata a fattori di contesto (degrado ambientale e sociale) in relazione alla residenza (Sud/Nord, grandi/piccole realta geografiche).

The paper presents experimental results related to attitude control of a quadrotor rotating about a single axis. The Embedded Model Control (EMC) methodology is used for control design. Indeed, this methodology can be very effective in applications involving relevant disturbances, modeling errors and unknown nonlinearities, since it allows a cancellation of all these sources of uncertainty. EMC control design is performed from a detailed quadrotor model, where the actuator dynamics is identified from experimental data. The designed EMC controller is compared with a standard proportional-integral-derivative (PID) controller in several tests, carried out on a laboratory testbench.

Feedback linearisation has been proved to be a powerful tool for making non-linear system dynamics fully or partially linear. This study investigates the use of the feedback linearisation approach as a novel way to design the internal model for Embedded Model Control, when applied to non-linear systems. This idea is applied to the control of an Unmanned Aerial Vehicle: the Borea project quadrotor. Embedded Model Control methodology implies the design of an internal model (Embedded Model) coded into the control unit and running in parallel with the plant. The difference between the internal model output and the plant output is used to estimate the unknown disturbances. These unknown disturbances include all the non-linearities that can be rejected by means of the control law. Using a numerical simulator, we demonstrate the feasibility of this methodology for accurate design of the internal model, starting from the non-linear system. This indicates that a feedback linearisation approach allows the extension of embedded model control techniques to non-linear systems control. What is more, the EMC is successfully applied to the control of the Borea quadrotor.

The paper presents the design and some simulated results of the attitude control of a satellite formation under study by the European Space Agency for the Next Generation Gravity Mission. The formation consists of two spacecrafts which fly more than 200km apart at an altitude from the Earth׳s ground of between 300 and 400km. The attitude control must keep the optical axes of the two spacecraft aligned with a microradian accuracy (pointing control). This is made possible by specific optical sensors accompanying the inter-satellite laser interferometer, which is the main payload of the mission. These sensors allow each spacecraft to actuate autonomous alignment after a suitable acquisition procedure. Pointing control is constrained by the angular drag-free control, which is imposed by mission science (Earth gravimetry at a low Earth orbit), and must zero the angular acceleration vector below 0.01μrad/s2 in the science frequency band. This is made possible by ultrafine accelerometers from the GOCE-class, whose measurements must be coordinated with attitude sensors to achieve drag-free and pointing requirements. Embedded Model Control shows how coordination can be implemented around the embedded models of the spacecraft attitude and of the formation frame quaternion. Evidence and discussion about some critical requirements are also included together with extensive simulated results of two different formation types.