Alberto Leva

• Professor (Associate) at Politecnico di Milano

Wireless systems are entering the arena of time-critical applications, including industrial controls. This makes clock synchronisation vital. A relevant source of synchronisation errors, especially in heavy-duty applications and harsh environments, is given by temperature variations that affect the quartz oscillators. This paper takes a control the...

To match the growing demand for biomethane production, anaerobic digestors need an optimal management of the input diet, and the said diet must not be constrained to a single substrate — that is, co-digestion is required. Co-digestion is far more complicated to govern than single substrate digestion, and constitutes a very hard challenge for the in...

The power density in modern Integrated Circuits (ICs) is tremendous. For example, Multi-Processor Systems-on-Chip (MPSoCs) nowadays undergo temperature swings of 40 degrees in 100 milliseconds or less, with rapidly emerging and vanishing sub-millimeter hot spots. As such, not only a simulation-based cooling assessment is vital, but one has to simul...

Within the Industry 4.0 context, different digital twins (DTs) are used to analyse manufacturing systems and assist decision-making processes throughout their entire life cycle. This means that many professionals, with various roles and cultures, build and use their own DTs; hence, methods and tools are required to ensure that the so taken decision...

This paper introduces MARCO, a research compiler aimed at the efficient generation of efficient simulation code from a large-scale Modelica model. MARCO’s design goals, requirements, and specifications are dis- cussed in the paper, as well as the software architec- ture, the current development status, and a future develop- ment roadmap. The result...

Digital Twins (DTs) are enablers for the fast optimisation processes required in the Industry 4.0 context. Declarative equation-based modelling languages, in turn, enable the creation of large-scale simulation-based DTs, as they relieve the analyst from creating the solution code. However, most industrial assets are Cyber-Physical Systems (CPSs), t...

Equation-based modelling is a powerful approach to tame the complexity of large-scale simulation problems. Equation-based tools automatically translate models into imperative languages. When confronted with nowadays’ problems, however, well assessed model translation techniques exhibit scalability issues, that are particularly severe when models co...

Equation-based modelling is a powerful approach to tame the complexity of large-scale simulation problems. Equation-based tools automatically translate models into imperative languages. When confronted with nowadays' problems, however, well assessed model translation techniques exhibit scalability issues, that are particularly severe when models co...

After designing and operating large laboratory classes in Automatic Control for 20 years, the pandemic brought us to rapidly set up replacements resorting entirely to the network. We here describe the solution we produced for basic courses, and that we offer to the community as free software. We also spend a very few words on (still preliminary) ev...

The paper presents a course on automation of energy systems, and a companion model library. Peculiar to the proposed didactic activity is to concentrate on the control layer that provides the individual units in the system with the capability of integrating into higher-level optimisation frameworks (a subject that probably deserves more attention t...

The DT-based design and control of modern production assets requires simulation models with different viewpoints, purposes, and nature. Most notably, component-level design and control require detailed physical models, while plant-level automation and production management mostly need DEVS-type ones. Inconsistencies among the said models can have s...

Digital Twins are of paramount relevance in the Industry 4.0 framework. However, the idea of Digital Twin has many different interpretations. These are tied to the intended use of a Digital Twin, thus to the viewpoint of the involved professionals (process designers, control specialists, managers, and so on). The said interpretations are often high...

We propose a periodic event-based control scheme in which, when the sensor triggers an event, also past and subsequent values of the controlled variable are transmitted. We employ this idea to obtain a stability condition independent of the used event-triggering mechanism. In turn, we exploit this independence to devise a methodology for extending...

The increasing power density in modern highperformance multi-processor system-on-chip (MPSoC) is fueling a revolution in thermal management. On the one hand, thermal phenomena are becoming a critical concern, making accurate and efficient simulation a necessity. On the other hand, a variety of physically heterogeneous solutions are coming into play...

Two established approaches to engineer adaptive systems are architecture-based adaptation that uses a Monitor-Analysis-Planning-Executing (MAPE) loop that reasons over architectural models (aka Knowledge) to make adaptation decisions, and control-based adaptation that relies on principles of control theory (CT) to realize adaptation. Recently, we a...

Digital Twins (DTs for short) are a powerful aid for creating, assessing and maintaining control strategies. This use of DTs however requires that the physical entities to control be described at different levels of detail. For example, simple I/O models are used to compute parameters of modulating controllers, more time-accurate ones may be requir...

We present the TDMH (Time Deterministc Multi-Hop) protocol, a complete stack for real-time wireless mesh networks. TDMH offers to applications a connection-oriented, bounded-latency communication model. Point-to-point data streams can be created and destroyed at any time. Path redundancy can be optionally introduced to improve reliability. TDMH exp...

The Industry 4.0 is pushing a fast evolution in all manufacturing operations under heterogeneous aspects. Maintenance, in all its numerous declinations along the life cycle of a production asset, is no exception. A myriad of decisions need taking—often on short time horizons, involving different physical and technological domains, and with limited...

In Smart Manufacturing, the Internet of Things technology brings about new possibilities as for the interaction of Cyber-Physical Systems with their virtual models—in Industry 4.0 jargon, Digital Twins. Besides traditional roles in engineering and control design, Digital Twins cab play innovative ones by evolving together with their cyber-physical...

To date, not that much. Improvements are possible, but some system-theoretically grounded re-design is necessary. We discuss the matter based on our experience, and as a consequence, we come to distilling some design clues and research directions.

Software obviously plays a relevant role in both control education and engineering. Methodology-centred tools help learning in the class and are also useful for high-level tasks in the profession. Engineering-centred ones are necessary for any realistically sized problem, and their comprehension helps designing efficient and well maintainable contr...

In process control, many PID loops are primarily devoted to rejecting load disturbances, and some of them are crucial for the quality of the overall plant operation. In such a scenario, automatic tuning is highly desired. However, load disturbance rejection calls for strong feedback up to quite high frequencies with respect to the dominant plant dy...

Current integrated circuits exhibit an impressive and increasing power density. In this scenario, thermal modelling plays a key role in the design of next generation cooling and thermal management solutions. However, extending existing thermal models, or designing new ones to account for new cooling solutions, requires parameter identification as w...

Big-data applications are batch applications that exploit dedicated frameworks to perform massively parallel computations across clusters of machines. The time needed to process the entirety of the inputs represents the application's response time, which can be subject to deadlines. Spark, probably the most famous incarnation of these frameworks to...

Terraneo [0000−0001−7475−6167] , Alberto Leva [0000−0003−2165−2078] , and William Fornaciari [0000−0001−8294−730X] DEIB, Abstract. Current integrated circuits exhibit an impressive and increasing component density, hence an alarming power density. Future devices will require breakthroughs in hardware power dissipation strategies and software active...

To define a reliable and simple model to be used to develop control strategies meeting specific biogas production goals by tuning the feeding pattern thus achieving a more flexible bio-energy production. The AMOCO model was extended to the co-digestion of corn silage, cattle manure and cheese whey. Model parameters identified with an LFT method and...

The problem addressed in this paper is the efficient operation of anaerobic digesters for biogas production. We improve the generality of a literature model (the AMOCO) to account for two hydrolysis steps. We introduce an LFTbased parameter identification technique, ans demonstrate the achievable match improvements by validating the model versus ex...

This paper proposes a first-principle model of GPS receivers, that allows us to exploit the trade-off between battery consumption and positioning accuracy. We present the model and propose a GPS sampling strategy that uses both the current positioning confidence, and information about the GPS status. We complement the GPS sensor with internal measu...

In computer engineering curricula, control is typically taught only to students willing to specialise in embedded systems, real-time, and the like. Nowadays, this is becoming a problem. Control-based techniques are gaining importance as a means to manage, optimise and also design computing systems. In such a scenario, a lack of control culture is c...

This chapter presents the proposed event-based thermal control solution at the HARPA-RT level, thus complementing the previous chapter which dealt with the same topic at the HARPA-OS level. A brief analysis of the thermal control problem is presented, evidencing as the main requirement the need for thermal control at the millisecond timescale, caus...

Computational sprinting was introduced to tackle the "dark silicon" problem, i.e., to allow a processor to transiently consume a power that could not be sustained indefinitely without thermal damage. However, the idea of sprinting has other potential applications, also tightly related to embedded systems. In this paper we evidence a few of these, a...

Supporting real-time communications over Wireless networks (WSNs) is a tough challenge, due to packet collisions and the non-determinism of common channel access schemes like CSMA/CA. Real-time WSN communication is even more problematic in the general case of multi-hop mesh networks. For this reason, many real-time WSN solutions are limited to simp...

Clock synchronization is a necessary component in modern distributed systems, especially Wirless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-...

Accurate and energy-efficient clock synchronization is an enabler for many applications of Wireless Sensor Networks. A fine-grained synchronization is beneficial both at the system level, for example to favor deterministic radio protocols, and at the application level, when network-wide event timestamping is required. However, there is a tradeoff b...

The development of distributed real-time systems often relies on clock synchronization. However, achieving precise synchronization in the field of Wireless Sensor Networks (WSNs) is hampered by competing design challenges, such as energy consumption and cost constraints, e.g., in Internet of Things applications. For these reasons many WSN hardware...

This paper addresses the important and well studied problem of synthesising PID controllers for load disturbance rejection. The tuning rationale, on which some general words are spent in connection to literature research, is to shape the disturbance-to-output frequency response, together with conveniently assigning the poles of the corresponding tr...

Many computer engineers either do not receive any control education, or are led to think that studying control is necessary only for those who want to specialise in embedded systems, real-time, and so forth. This causes a cultural gap that can have highly undesired consequences, since control-based techniques are gaining importance as a means to ma...

Applying controls to manage and optimise the behaviour of computers and networks is an important research field. In recent years, controllers have been gaining a role not only as add-ons to improve the efficiency of already functioning systems, but also as core components of those system themselves, and of their design. This paper provides a brief...

Accurate and energy-efficient clock synchronization is an enabler for many applications of Wireless Sensor Networks. A fine-grained synchronization is beneficial both at the system level, for example to favor deterministic radio protocols, and at the application level, when network-wide event timestamping is required. However, there is a tradeoff b...

Distributed real-time systems often rely on clock synchronization. However, the achievement of precise synchronization in Wireless Sensor Networks (WSNs) is hampered by competing design challenges, which finally causes many WSN hardware platforms to rely on low frequency clock crystal for local timebase provision. Although this solution is inexpens...

We present a model library conceived to design and assess critical components of big data frameworks, with a control-centric approach. The library adopts the object-oriented paradigm, using the Modelica language. Continuous-time and algorithmic models can be mixed, allowing to represent control code with high fidelity, and to reduce the simulation...

We present a control scheme combining a Model Predictive Control (MPC) layer and a hierarchically inferior one, in general not of the MPC type. The purpose is to avoid solving the MPC optimisation problem at each control step, thereby lightening the computational burden. The MPC controller can be designed within the classical receding horizon frame...

The design, control, and management of large-scale Smart Grids poses a number of challenging problems. Successfully addressing them requires high-level, flexible, efficient and scalable dynamic modelling and simulation frameworks. In this paper, the requirements for such frameworks are first stated. Then, it is shown how the equation-based, object-...

This paper accompanies a tutorial aimed at introducing the basics of system and control theory so as to foster their utilisation for the management, but most important for the design, of computing systems. The tutorial is divided into three parts. The first one introduces the fundamental concepts of dynamic system and feedback and gives an overview...

The density of modern microprocessors is so high, that operating all their units at full power would destroy them by thermal runaway. Hence, thermal control is vital, but at the same time has to integrate with power/performance management, to not unduly limit computational speed. In addition, the controller must be simple and computationally light,...

We study feedback control for discrete-time linear time-invariant systems in presence of quantization both in the control action and in the measurement of the controlled variable. While in some application the quantization effects can be neglected, when high-precision control is needed, quantization has to be explicitly accounted for in control des...

We study feedback control for discrete-time linear time-invariant systems in the presence of quantization both in the control action and in the measurement of the controlled variable. While in some application the quantization effects can be neglected, when high-precision control is needed, they have to be explicitly accounted for in control design...

This paper presents a didactic activity belonging to a long-term project, aimed at complementing the culture of computer engineering students with a solid knowledge of systems and control theory and methods. The use of control to govern and optimise the behaviour of computing systems is felt in the computer engineering community as a necessity. The...

A PID autotuning method is presented to exploit the knowledge of multiple frequency response points while employing simple and well assessed tuning rules (e.g. based on Internal Model Control). This is achieved by selecting, among the available frequency response points, the “best one” for indices that are compared based on also other points. Hence...

Modern Web applications exploit Cloud infrastructures to scale their resources and cope with sudden changes in the workload. While the state of practice is to focus on dynamically adding and removing virtual machines, we advocate that there are strong benefits in containerizing the applications and in scaling the containers. In this paper we presen...

Self-adaptive techniques have been introduced in the last few years to tackle the growing complexity of software/hardware systems, where a significant complexity factor leans on their dynamic nature that is subject to sudden (and sometime unpredictable) changes. Adaptation actions are aimed at satisfying system goals that are often related to non-f...

This paper is part of a long-term research on the application of event-based control to the thermal management of high-power, high-density microprocessors. Specifically, in this work we introduce and discuss a purpose-specific event-based realisation of a digital controller for thermal management, which integrates into a scheme that also takes care...

CellularAutomataLib is a library developed by the authors to facilitate the description of Cellular Automata (CA) models in Modelica. It supports the description of 1D and 2D CA and their combination with other Modelica models. Modelling versatility and scalability are the main focus in the design. The internal behaviour of CA models is programmed...

Computers and the network are widely used and studied as a means to provide control education. However, they also offer a wide variety of problems to teach control. This paper concentrates on the second aspect, presenting some didactic activities that are interesting for both control and computer science/engineering students. After motivating the p...

Clock synchronization is a necessary component in modern distributed systems, especially Wirless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-...

Time synchronization is crucial for wireless sensor networks (WSNs), where operations often rely on time ordering of events. WSNs are deployed in different scenarios, and therefore their timing requirements are often related to the peculiar characteristics of the specific environment they have to act in. Synchronization is anyway always an issue: t...

Disturbance rejection is a primary objective in many industrial control loops, thus a relevant goal for autotuning controllers. Nonetheless, autotuning has invariantly to cope with a reduced amount of process information. As a consequence, with the standard single-loop structure typically adopted in the addressed context, effective disturbance reje...

Resource reservation is a technique that allows isolating applications from interfering among each other. In the most classic setting, this method requires the periodic allocation of a given budget of resource over time. However, in reality, the actual budget allocation may deviate from its ideal value. Examples of causes of this deviation are: the...

The increasing computational density of modern processors, and the advent of 3D chip layouts, are making thermal control a requirement, often crucial for the life itself of the device. In demanding applications, traditional on/off control solutions - based e.g. on clock gating - cannot deliver the required regulation quality if not unacceptably red...

Self-adaptive techniques have been introduced in the last few years to tackle the growing complexity of software systems, where a major complexity factor leans on their dynamic nature subject to sudden and unpredictable changes that can heavily impact on the software architecture quality. Non-functional models, as generated from architectural descr...

Over the last years, several problems related to computing systems are being re-considered with a control-centric approach, leading to a system-theoretical component design and assessment, [2, 4]. Notable examples are thread scheduling [3], memory management [7], and time synchronisation [1]. When addressed as control ones, many of said problems re...

This paper presents and discusses a quite unusual application of the widely adopted relay-based identification technique for stable SISO processes. Besides providing a point on the process Nyquist diagram, the proposed method can obtain some quantitative information on its unit step response, namely a quite precise and highly noise-insensitive meas...

This work proposes a methodology to deal with model-based tuning of PI(D) regulators, and with the previous identification of the required process model, in a contextual way. The methodology can be applied to existing tuning rules, as done herein, leading to better control results, and also to process models capable of forecasting the closed-loop t...

This manuscript addresses the problem of tuning two-degree-of-freedom (2-dof) industrial controllers. Peculiar of the work is the idea of tuning the feedforward path of the regulator after the feedback path is synthesised, so as to allow the presented method to be used for complementing existing and well assessed tuning rules for 1-dof controllers....

In many industrial autotuning applications, the only available information is a nominal process model, of simple fixed structure, and parametrised based on experimental data. This manuscript proposes a way to select, based on that model and the control specifications, an appropriate model-based tuning method within a pre-specified set. After explai...

The vibration control of a turbomolecular vacuum pump presents several methodological and implementation peculiarities that make the design of an efficient controller difficult. In this manuscript the effects of system uncertainties and numerical implementation issues are discussed with reference to both feedback and feedforward active vibration co...

The anaerobic digestion model No.1 (ADM1) developed by the IWA Task Group for mathematical modelling of anaerobic digestion processes Batstone et al. [1] is a structural model which describes the main biochemical and physicochemical processes. For such purposes, other models have been proposed to describe anaerobic processes with a reduced set of p...

Cloud computing has recently received considerable attention, as a promising approach for delivering ICT services by improving the utilisation of data centre resources. On the other hand, the increased usage of ICT, jointly with the increased cost of energy, make designing and managing data centres with energy efficient strategies a crucial and str...

Time synchronisation is crucial for distributed systems, and particularly for Wireless Sensor Networks (WSNs), where each node is executing concurrent operations to achieve a real-time objective. However, synchronisation is quite difficult to achieve in WSNs, due to the unpredictable deployment conditions and to physical effects like thermal stress...

This manuscript proposes a novel viewpoint on computing systems’ modelling. The classical approach is to consider fully functional systems and model them, aiming at closing some external loops to optimize their behaviour. On the contrary, we only model strictly physical phenomena, and realize the rest of the system as a set of controllers. Such an...

Modelling and simulation nowadays permeate virtually any engineering activity, requiring tools capable of managing complex models efficiently. Nonetheless, whereas modern modelling languages and tools allow such models to be constructed even on lightweight platforms (e.g. a laptop), the same is not true when it comes to numerically integrating thos...

Desiccant wheels can improve the efficiency of air handling units, as their inherent heat recovery capabilities reduce the external energy needs. On the other hand, however, desiccant wheels introduce state variable interactions that are not present in traditional units. Hence, to actually yield the possible advantages, air handling units with desi...

This paper proposes a means to quantify the aptitude of a dynamic model to be partitioned into weakly coupled submodels. The proposal applies to both linear and nonlinear systems, is largely independent of their scale, and requires information that is easy to provide on the part of the analyst. The presented indices can be exploited in different ma...

Desiccant wheels can improve the efficiency of air handling units, as their inherent heat recovery capabilities reduce the external energy needs. On the other hand, however, desiccant wheels introduce state variable interactions that are not present in traditional units. Hence, to actually yield the possible advantages, air handling units with desi...