Papers by Julio Elias Normey-Rico
Renewable Energy, Aug 1, 2020
The high thermal energy consumption is one of the main drawbacks hampering the commercial impleme... more The high thermal energy consumption is one of the main drawbacks hampering the commercial implementation of Membrane Distillation (MD) technology. The development of adequate operating strategies can help to reduce these energy requirements. Accordingly, this paper focuses on the optimal management of the array of MD modules composing a commercial-scale MD plant, trying
Procedings do XV Simpósio Brasileiro de Automação Inteligente
Thermal solar power plants operating in a day-ahead market scheme aim to maximize the solar energ... more Thermal solar power plants operating in a day-ahead market scheme aim to maximize the solar energy captured in the solar collector fields and the electric energy revenue in the power block according to the energy tariff. Classic control strategies are not able to obtain good performance for this kind of framework because of the variability of the energy tariff profile over the days. In this context, this work presents the assessment of the potential of an optimal controller to increase the profitability of the plants. Simulation results with energy tariffs and meteorological data from Spain are presented in order to illustrate the performance of the methodology. Finally, a comparative study with a classic control strategy shows the improvements in the energy revenue produced in this scenario.
1999 European Control Conference (ECC)
This paper analyzes the global stability of a dead-time compensator when considering a saturation... more This paper analyzes the global stability of a dead-time compensator when considering a saturation in the control action and uncertainties in the estimation of the dead-time. The analysis is made using a first order plant with dead-time controlled by a Smith predictor plus a pi controller, that is, a scheme commonly used in the process industry. Using a frequency domain analysis the stability and the bifurcations of the system are analyzed when a saturation is included in the control system. The obtained results suggests the use of filters to avoid the undesirable effects produced by the error in the estimation of the dead-time and the saturation. The design of these filters is based on the stability analysis performed in this paper and gives less conservative results than the ones obtained using others approaches. In order to illustrate the results, some simulation examples are shown.
Revista Principia - Divulgação Científica e Tecnológica do IFPB
The power inspection of energy transmission networks is an effective way of mitigating risks, fai... more The power inspection of energy transmission networks is an effective way of mitigating risks, failures, and avoiding mistakes in the transmission system. However, the inspection market is highly competitive and has very difficulties in this process, mainly due to the high altitude of the lines. A standard solution for inspection of high-altitude power lines can be implemented using drones and aircraft, however, has a high cost for operation and poor logistics viability. In this scenario, "Prof. Raul Guenther Robotic Lab" developed a project of a robot that goes through low and medium-voltage wires to power inspection of transmission systems in urban networks. In this paper we propose the uses of a self-balancing robot, aiming to execute the inspection, using a 2D balance control to stabilize the balance on the cable. Moreover, we evaluate the viability and effectiveness of the proposed control strategy, highlighting its advantages and properties using numerical simulations considering a non-linear model, and expected disturbances. Moreover, we develop computational experiments with graphical results, simulating the model in different situations to find the limits of the controller, based on the maximum speed of the wind and the robot moving through the wires.
Procedings do XV Simpósio Brasileiro de Automação Inteligente, 2021
This works presents a technique for the distributed control of the AC grid in offshore wind farms... more This works presents a technique for the distributed control of the AC grid in offshore wind farms based on synchronous generators. This modular rectifier comprises one or more uncontrolled modules (such as diode rectifiers), and the proposed control technique allows the connection of the offshore wind farm to the grid onshore using a diode-based HVDC rectifier. Wind power supply systems receive a reactive power reference from an external central regulator to maintain the common frequency of the AC line. The proposed external control uses the control of commercial wind turbines. This method for controlling the voltage and frequency of the local offshore grid allows the operation of the HVDC link rectifiers. PSCAD® simulations are used to prove the technical feasibility of the control and the topology concept. Resumo: Este trabalho apresenta uma técnica para o controle distribuído da rede CA em parques eólicos offshore com base em geradores síncronos. Este retificador modular compreende um ou mais módulos não controlados (como retificadores de diodo), e a técnica de controle proposta permite a conexão do parque eólico offshore com a rede em terra usando um retificador HVDC baseado em diodo. Os sistemas de fornecimento de energia eólica recebem uma referência de potência reativa de um regulador central externo para manter a frequência comum da linha CA. O controle externo proposto utiliza o controle de turbinas eólicas comerciais. Este método para controlar a tensão e a frequência da rede offshore local permite a operação das diferentes extremidades dos retificadores do link HVDC. Simulações usando PSCAD® são utilizadas para comprovar a viabilidade técnica do controle e o conceito da topologia.
Anais do Congresso Brasileiro de Automática 2020, 2020
This paper deals with the trajectory tracking problem of a tilt-rotor unmanned aerial vehicle car... more This paper deals with the trajectory tracking problem of a tilt-rotor unmanned aerial vehicle carrying a suspended load. An explicit model predictive control (eMPC) based on multiparametric optimization is used to derive optimal control laws which could be implemented in an embedded system. The eMPC is designed based on the nominal linearized error model of the system, which is obtained around a generic trajectory. The optimal control problem (OCP) is solved taking into account input and state constraints. Additionally, a terminal cost is considered to guarantee stability. Euler-Lagrange formulation is used to derive the multibody non-linear dynamic model. Numerical experiments are performed to evaluate the proposed controller when the system is aected by constant disturbances at different instants of time and parametric uncertainties.
This work deals with a ruled-based control strategy to produce hydrogen from wind and wave energy... more This work deals with a ruled-based control strategy to produce hydrogen from wind and wave energy in an offshore platform. These renewable energies feed a set of alkaline electrolyzers that produce H2. The proposed control system allows regulating the operation of the electrolyzers, taking into account the energy available and optimizing the performance of the plant. Simulation results obtained are presented, showing correct operation of the platform under this proposed control.
ISA Transactions, 2020
The SARS-CoV-2 virus was first registered in Brazil by the end of February, 2020. Since then, the... more The SARS-CoV-2 virus was first registered in Brazil by the end of February, 2020. Since then, the country counts over 70000 deaths due to COVID-19, and profound social and economical backlashes are felt all over the country. The current situation is an ongoing health catastrophe, with the majority of hospital beds occupied with COVID-19 patients. In this paper, we formulate a Nonlinear Model Predictive Control (NMPC) to plan appropriate social distancing measures (and relaxations) in order to mitigate the pandemic effects, considering the contagion development in Brazil. The NMPC strategy is designed upon an adapted data-driven Susceptible-Infected-Recovered-Deceased (SIRD) contagion model, which takes into account the effects of social distancing. Furthermore, the adapted SIRD model includes time-varying auto-regressive contagion parameters, which dynamically converge according to the stage of the pandemic. This new model is identified through a three-layered procedures, with analytical regressions, Least-Squares optimization runs and auto-regressive model fits. The data-driven model is validated and shown to adequately describe the contagion curves over large forecast horizons. In this model, control input is defined as finitely parametrized values for social distancing guidelines, which directly affect the transmission and infection rates of the SARS-CoV-2 virus. The NMPC strategy generates piece-wise constant quarantine guidelines which can be relaxed/strengthen as each week passes. The implementation of the method is pursued through a search mechanism, since the control is finitely parametrized and, thus, there exist a finite number of possible control sequences. Simulation essays are shown to illustrate the results obtained with the proposed closedloop NMPC strategy, which is able to mitigate the number of infections and progressively loosen social distancing measures. With respect to an "open-loop"/no control condition, the number of deaths still could be reduced in up to 30 %. The forecast preview an infection peak to September 2nd, 2020, which could lead to over 1.5 million deaths if no coordinate health policy is enacted. The framework serves as guidelines for possible public health policies in Brazil.
2017 8th International Renewable Energy Congress (IREC), Mar 1, 2017
Coupling of a Long Term System (LTS) with a Short Term System (STS) of a hydrogen-based microgrid... more Coupling of a Long Term System (LTS) with a Short Term System (STS) of a hydrogen-based microgrid is considered here in this work to control the operation of a set of electrolyzers that produce hydrogen from renewable energies. Both systems are based on Model Predictive Control (MPC) ideas. The LTS manages the on/off conditions of the electrolyzers taking into account control and prediction horizons in terms of hours (high level control), regulating the operation point of the devices using meteorological predictions. The STS adapts in a low-level control the behavior of the electrolyzers with the rest of the components of the microgrid (battery and ultracapacitor). The plant is modeled in the Mixed Logic Dynamic (MLD) framework due to the presence of logical states such as the startup/shut down of the electrolyzers and charge/discharge states in the battery and ultracapacitor. These systems are validated in a simulation showing the adequate operation of the components of the microgrid.
Anais do 14º Simpósio Brasileiro de Automação Inteligente, 2019
Solar Energy, 2018
This paper outlines the development of models of a solar-assisted heat generation system for a Mu... more This paper outlines the development of models of a solar-assisted heat generation system for a Multi-Effect Desalination (MED) plant, to be used both for simulation and control purposes. Some of these models have been developed based on static and dynamic energy and mass balances, and some others are based on step response methods (experimental tests). The heat generation system comprises a solar flat-plate collector field, an air cooler, a heat exchanger and the corresponding pipelines and interconnections. The main purpose of the heat generation system is to feed the MED unit with hot water within a specific temperature range using two thermal storage tanks as input buffers to the MED system. The main achievement of this paper is that the developed model provides an adequate tradeoff between complexity and performance.
IFAC Proceedings Volumes, 2012
This paper presents a non-linear control scheme to deal with dead-time (DT) processes where small... more This paper presents a non-linear control scheme to deal with dead-time (DT) processes where small rise times are required. The control scheme is based on the combination of two strategies appeared in the literature to deal with DT processes, the Filtered Smith Predictor (FSP), which is a Smith Predictor (SP) including a filter to improve the robustness, and the PI+CI, a PI with a partial reset action on the control signal when the process output is equal to the reference input. In the proposed strategy, the reset action allows to achieve very small rise times with small overshoots, improving the results from FSP. On the other hand, the use of the robust predictor allows to deal with the dead time in a better and systematic way than the PI+CI with variable reset ratio and variable reset band does.
IFAC Proceedings Volumes, 2006
This paper presents a methodology to introduce the control of deadtime processes using a simple a... more This paper presents a methodology to introduce the control of deadtime processes using a simple and intuitive predictive approach. A trivial solution for the control of a process with a dead-time is first proposed. From this strategy the idea of the predictor based controller is derived. Open-loop predictors and closed-loop ones are then used to analyze the obtained solution. A simple tuning of the proposed structure for a first order plus dead-time process together with a polynomial approximation of the dead-time allows to derive a pid controller. Thus, the approach based on the idea of prediction can be used to interpret the use of a pid to control a dead-time process. It is illustrated how the performance of the pid controller is limited by the modelling error introduced in the approximation. The presented approach gives a measurement of the achievable performance. Several simulation examples illustrate the results. Copyright c IFAC Keywords: Dead-time compensators, control education, predictors, PID controllers. design of controllers for dead-time systems is more difficult (Palmor, 1996). As dead time processes are very common in real word the study of dead-time systems and the design of controllers for these processes is very important and must be included in a basic control course. Two of the most remarkable strategies that use simple concepts to control deadtime process are the Proportional + Integral + Derivative (pid) controllers and the Dead-Time Compensators (dtc). Also in industry these are the most used control algorithms in process control (Takatsu et al., 1998).
IFAC Proceedings Volumes, 2007
This paper presents a Model Predictive Control (MPC) Technique for Nonlinear Systems. The algorit... more This paper presents a Model Predictive Control (MPC) Technique for Nonlinear Systems. The algorithm is based on a new interpretation of the procedure used by traditional linear predictive controllers, like Dynamic Matrix Control (DMC) and Generalized Predictive Controller (GPC), to compute the predictions. The proposed technique requires no specific model structure, treating equally models based on neural networks, difference equations or ordinary difference equation systems. Comparisons to other techniques are presented in the paper applying the algorithm to nonlinear systems available in literature. The main advantages of the proposed approach are: (i) it makes no use of iterative algorithms, (ii) the control action can be obtained by the same methods used in linear MPCs and (iii) any type of nonlinear model can be used.
IFAC Proceedings Volumes, 2014
This paper presents a repetitive model predictive controller to reject periodic disturbances in i... more This paper presents a repetitive model predictive controller to reject periodic disturbances in industrial processes. The proposed technique uses a state-space model with embedded repetitive action to integrate most important characteristics from both repetitive and predictive controllers. Thus, the obtained control strategy combines best characteristics from both repetitive and model predictive control. A simulation case study is presented to discuss several aspects related to disturbance rejection performance, parameters tuning and constraints effects, and to compare this new control strategy with traditional repetitive and model predictive controllers.
IFAC Proceedings Volumes, 2007
This paper presents a new approach to solve the on line optimization problems associated to the s... more This paper presents a new approach to solve the on line optimization problems associated to the solution of mixed integer predictive control (MIPC). The MIPC is obtained using an hybrid Model Predictive Control (MPC) approach and a parametrization of the binary variables. Furthermore, the proposed formulation allows for a systematic controller design which can be also applied to nonlinear hybrid systems. A Buck Boost converter is used as case study to illustrate the difficulties associated to the control problem and the advantages of the proposed controller.
IFAC Proceedings Volumes, 2002
The relevance of the conceptual learning in control education is analyzed in this paper. It indic... more The relevance of the conceptual learning in control education is analyzed in this paper. It indicates a concepts-on view of control education. This approach, that already is the tacit model of classroom education, tries to complement recent control educational trends. In this context, it presents a recent project called "Virtual Control School" in development at the Federal University of Santa Catarina. This project tries to integrate pedagogical, computational and epistemological aspects in order to assist the control teaching and learning processes.
IFAC Proceedings Volumes, 2008
In autonomous vehicles control, there is a need to interconnect several electronic component unit... more In autonomous vehicles control, there is a need to interconnect several electronic component units (ECUs) in a proper manner to allow the embedded computational system to perform its control task in an efficient and reliable way. Therefore, this paper presents an objectbased communication architecture that provides an infrastructure to design such systems. The proposed architecture relies in the publisher/subscriber protocol, which is characterized by the uncoupling between its components, anonymous communication with content-based messages, and many-to-many communications. Our architecture is based in the concept of sentient-objects, which are reactive entities distributed across the network that normally represent elements from the problem-domain. This paper presents the architecture, as well as an application used for controlling an autonomous vehicle.
IFAC Proceedings Volumes, 2005
This paper presents a constrained horizon predictive controller based on a filtered Smith predict... more This paper presents a constrained horizon predictive controller based on a filtered Smith predictor structure (CHSPPC). The proposed algorithm is particulary appropriate to control dead time systems as it exhibits better robustness than others, specially when errors in the dead time estimation are considered. The tuning of the controller parameters includes a low pass filter that is easy defined to obtain a compromise between performance and robustness. Simulation results show that the proposed control strategy allows better results than other approaches.
Journal of Process Control, 2012
Computational simplicity is one of the most important aspects to take into account in robust mode... more Computational simplicity is one of the most important aspects to take into account in robust model predictive control (MPC). In dead-time processes, it is common to use an augmented state-space representation in order to apply robust MPC strategies but, this procedure may affect computational aspects. In this paper, explicit dead-time compensation will be used to avoid augmented representation. This technique will be analyzed in terms of robust stability and constraint satisfaction for discrete-time linear systems. The results of this discussion will be applied to a robust tube-based MPC strategy which is able to guarantee robust stability and constraint satisfaction of a dead-time system by considering a prediction model without dead-time. Moreover, taking advantage of the proposed scheme, the robust MPC will be particularized for first-order plus dead-time models which simplifies significantly controller synthesis. The proposed dead-time compensation method will be applied to different robust MPC strategies in two case studies: (i) a simulated quadruple-tank system, and (ii) an experimental scaled laboratory heater process.
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Papers by Julio Elias Normey-Rico