**Contents**


## **About the Editors**

**Cristina I. Muresan** received a degree in control systems and a Ph.D. degree from the Technical University of Cluj- Napoca, Cluj-Napoca, Romania, in 2007 and 2011, respectively, where she is currently an Associate Professor in the Automation Department. She has published more than 150 papers and books. She is currently involved in several research grants, all dealing with multivariable, biomedical engineering and fractional order control. Her research interests include modern control strategies, such as predictive algorithms, robust non-linear control, fractional order control, time delay compensation methods, and multivariable systems.

**Eva H. Dulf** received her Ph.D. degree in Advanced Process Control, with applications in nuclear technologies, from the Technical University of Cluj-Napoca, Romania, in 2006, where she is currently a professor and leader of the Advanced Process Control Methods Group. She obtained her habilitation degree in 2015. Her research interests include advanced control strategies. More specifically, her research focuses on developing advanced control strategies for complex chemical and biochemical processes. She has published over 100 papers in journals and conferences and several books or book chapters. She has won 34 awards at international exhibitions of inventions. She has been an IEEE member since 2009.

## **Preface to "Control and Automation"**

Control and automation systems are at the heart of our everyday lives. This book is a collection of novel ideas and findings in these fields, published as part of the Special Issue on Control and Automation. The core focus of this issue was original ideas and potential contributions for both theory and practice. It received a total number of 21 submissions, out of which 7 were accepted. These published manuscripts tackle some novel approaches in control, including fractional order control systems, with applications in robotics, biomedical engineering, electrical engineering, vibratory systems, and wastewater treatment plants.

One of these papers presents a synchronous co-simulation of a six degree of freedom (6DOF) ball and plate platform, and its 3D computer model intended to simulate the actual dynamics of a rendezvous between a cargo vehicle, such as the Falcon 9 from SpaceX and the International Space Station (ISS). A supervisory action is required for initiating the docking mechanism. The novelty of the manuscript consists of an adaptive fractional order control solution. The tuning method is easy, and the control strategy is implemented and validated based on a laboratory benchmark. The results demonstrate that such an approach is suitable to meet the performance specifications, despite the large variability in the system dynamics. Vibratory systems and an efficient control for these processes are addressed in two of the published papers. One of these tackles the idea of using a fractional order differential equation to model such a process, based on its viscoelastic nature. Then, a fractional order linear quadratic regulator (LQR) is designed. To solve the Riccati equation of the LQR method, an iteration-based approach is proposed. Next, to estimate the states originating from the fractional-order derivative term, a fractional-order state observer is constructed. To demonstrate the efficiency of the proposed control algorithm, numerical simulations are presented, showing that vibrations are indeed suppressed. The second paper, which deals with vibratory systems, uses a smart beam to validate an experimental tuning approach for fractional order proportional–integral–derivative (PID) controllers. The tuning method is based on shaping the Bode magnitude plot to decrease the resonant peak. There is no need for a process model; only several experimental tests are required to obtain the necessary process information at different frequencies. Experimental results are provided to demonstrate the efficiency of the proposed approach. Both of the abovementioned algorithms use concepts from fractional calculus. To implement such fractional order controllers, digital realizations are often required, which use sample and hold (S&H) circuits to perform the conversion from analog to digital and vice versa. An excellent review of these S&H systems, as well as a new fractional order design of such systems, is presented in this issue. The proposed approach models these systems both in the time and Laplace domains and is a generalization of the classical devices, enabling a better understanding of the possibilities and limitations of S&H systems.

The field of biomedical engineering is currently receiving tremendous attention from the research community, especially regarding personalized and optimized medicine. Such a topic is addressed regarding carcinoma models and adequate chemotherapeutic treatment. The core problem in the delivery of a carcinoma model suitable for developing an optimized therapy consists of a limited number of measurable physiological signals—state variables—and the knowledge of model parameters. The proposed solution refers to the use of observers. A moving horizon estimation (MHE)-based observer is developed that uses a third-order tumor growth model. The performance of the observer is compared to that of an optimized extended Kalman filter (EKF). Results show that the proposed MHE is designed to be suitable for closed-loop applications and yields simultaneous state and parameter estimation.

Novel ideas in the field of optimal battery charging are also presented in this Special Issue. A battery model, designed for automotive battery managemen<sup>t</sup> systems applications, is used to design charging controllers in an optimal charging strategy. The standard model is altered to produce a non-linear electro-thermal battery aging model, which is linearized at several operating points. An optimal charging strategy is then designed for the simultaneous minimization of charging time and maximization of battery lifetime. An optimization problem that minimizes aging is solved to determine an appropriate charging trajectory. The CRONE methodology is then used to take into account the resulting linear model family. Several simulations are employed to show the efficiency of the resulting charge controller.

The Special Issue contains a seventh paper dealing with a weather-based prediction strategy inside the proactive historian with application in wastewater treatment plants. The authors propose a software reference architecture for the proactive historian, alongside a data dependency identification strategy and several applications for energy efficiency improvements in the water industry. However, complex research is required in order to offer a complete solution for real industrial processes. Part of this reference architecture that predicts the future evolution of the monitored system is developed in one of the papers of this Special Issue. The design is based on weather dependency and forecasting. In this way, the approach paves the way towards achieving a fully functional, real-world, tested, and validated proactive historian application, with potential to bring significant direct benefits to the water industry.

This Special Issue has gathered a selection of novel research results regarding control systems in several distinct research areas. We hope that these papers will evoke new ideas, concepts, and further developments in the field.

We wish to thank the authors for considering this Special Issue as a suitable way to disseminate their results. Additionally, we thank the reviewers for the extra effort put into reviewing the manuscripts. Finally, we thank the dedicated editorial team of *Applied Sciences*, especially assistant editor Wing Wang, the Special Issue Managing Editor, who provided help enormously with managing the papers.

> **Cristina I. Muresan, Eva H. Dulf** *Editors*

## *Editorial* **Special Issue: "Control and Automation"**

**Cristina-Ioana Muresan and Eva H. Dulf \***

> Department of Automation, Technical University of Cluj-Napoca, Memorandumului Street, No 28, 400114 Cluj-Napoca, Romania; Cristina.Muresan@aut.utcluj.ro **\***Correspondence:Eva.Dulf@aut.utcluj.ro

**1.Introduction**

A wide range of ongoing research in the areas of controller design and information engineering reveals that the pace of technological change in this domain seems to be accelerating. The primary focus is on futuristic segments ranging from robotics and genomics to chemical feedstock and electrical storage.

The main objective of this Special Issue was to provide a forum for researchers and practitioners to exchange their latest theoretical and technological achievements and to identify critical issues and challenges for future investigation on topics regarding advanced automation and control techniques based on information system technologies.

#### **2. Novel Ideas for Control**

The Special Issue focused on original ideas and potential contributions for theory and practice, at the same time. It received a total number of 21 submissions, among which 7 were accepted. These published manuscripts tackle some novel approaches in control, including fractional order control systems, with applications in robotics, biomedical engineering, electrical engineering, vibratory systems, waste water treatment plants.

One of these papers [1] presents a synchronous co-simulation of a 6DOF (six degrees of freedom) ball and plate platform and its 3D computer model intended to simulate the actual dynamics of a rendezvous between a cargo vehicle such as the Falcon 9 from SpaceX and the ISS (International Space Station). A supervisory action is required for initiating the docking mechanism. The novelty of the manuscript consists of an adaptive fractional order control solution. The tuning method is easy and the control strategy is implemented and validated on a laboratory benchmark. The results demonstrate that such an approach is suitable to meet the performance specifications despite the large variability in the system dynamics.

Vibratory systems and an efficient control for these processes are addressed in two of the published papers. One of these [2] tackles the idea of using a fractional order differential equation to model such a process, based on its viscoelastic nature. Then, a fractional order Linear Quadratic Regulator (LQR) is designed. To solve the Riccati equation of the LQR method, an iteration-based approach is proposed. Next, to estimate the states originating from the fractional-order derivative term, a fractional-order state observer is constructed. To demonstrate the efficiency of the proposed control algorithm, numerical simulations are presented showing that vibrations are indeed suppressed. The second paper that deals with vibratory systems uses a smart beam to validate an experimental tuning approach for fractional order proportional–integral–derivative (PID) controllers [3]. The tuning method is based on shaping the Bode magnitude plot, such that the resonant peak is decreased. There is no need for a process model, only several experimental tests are required to obtain the necessary process information at different frequencies. Experimental results are provided to demonstrate the efficiency of the proposed approach.

Both of the algorithms in [2,3] use concepts from fractional calculus. To implement such fractional order controllers, digital realizations are often required which use sample and hold (S&H) circuits to perform the conversion from analog to digital and vice versa.


**Citation:** Muresan, C.-I.; Dulf, E.H. Special Issue: "Control and Automation". *Appl. Sci.* **2021**, *11*, 5005. https://doi.org/10.3390/ app11115005

Received: 24 May 2021 Accepted: 25 May 2021 Published: 28 May 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

An excellent review of these S&H systems, as well as a new fractional order design of such systems, is presented in [4]. The proposed approach models these systems both in the time and Laplace domains and is a generalization of the classical devices, enabling a better understanding of the possibilities and limitations of S&H systems.

The field of biomedical engineering is currently receiving tremendous attention from the research community, especially regarding personalized and optimized medicine. In [5], such a topic is addressed regarding carcinoma models and adequate chemotherapeutic treatment. The core problem in delivering a carcinoma model suitable for developing an optimized therapy consists of the limited number of measurable physiological signals— state variables—and the knowledge of model parameters. The solution proposed in [5] refers to the use of observers. A moving horizon estimation (MHE)-based observer is developed that uses a third-order tumor growth model. The performance of the observer is compared to that of an optimized extended Kalman filter (EKF). Results show that proposed MHE is designed to be suitable for closed-loop applications and yields simultaneous state and parameter estimation.

Novel ideas in the field of optimal battery charging are presented in [6]. A battery model, designed for automotive battery managemen<sup>t</sup> systems applications, is used to design charging controllers in an optimal charging strategy. The standard model is altered to produce a nonlinear electro-thermal battery aging model, which is linearized in several operating points. An optimal charging strategy is then designed for simultaneous minimization of charging time and maximization of battery lifetime. An optimization problem that minimizes aging is solved to determine an appropriate charging trajectory. The CRONE methodology is then used to take into account the resulting linear model family. Several simulations are employed to show the efficiency of the resulting charge controller.

The Special Issue contains a seventh paper dealing with a weather-based prediction strategy inside the proactive historian with application in wastewater treatment plants [7]. The authors propose a software reference architecture for such a proactive Historian, along with a data dependency identification strategy and some obtained recipes for energy efficiency improvements in the water industry. However, complex research is required in order to offer a complete solution for real industrial processes. Part of this reference architecture that predicts the future evolution of the monitored system is developed in [7]. The design is based on weather dependency and forecast. In this way, the approach paves the way towards achieving a fully functional, real-world, tested and validated proactive Historian application, with potential to bring significant direct benefits to the water industry.

## **3. Conclusions**

This Special Issue has gathered a selection of novel research results regarding control systems in several distinct research areas. We hope that these papers will raise new ideas, concepts and further developments in the field.

We wish to thank the authors for considering this Special Issue as a proper way to disseminate their results. Additionally, we thank the reviewers for the extra effort put into reviewing the manuscripts. Last, but not least, we thank the dedicated editorial team of *Applied Sciences*, especially to assistant editor Wing Wang, the Special Issue Managing Editor who provided a lot of help with managing the papers.

**Author Contributions:** Conceptualization, C.-I.M. and E.H.D.; writing—review and editing, C.-I.M. and E.H.D. Both authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by gran<sup>t</sup> of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI–UEFISCDI, project number PN-III-P1-1.1-TE-2019-0745, within PNCDI III.

**Institutional Review Board Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
