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Plants with integrators possess control-relevant modeling requirements that are typically ignored in the literature. Desired closed-loop speeds of response for such systems can differ significantly from their open-loop dynamics, causing conventional system identification guidelines to fail or be inaccurate. One such issue relates to experimental design. This paper presents guidelines for the design of excitation signals for system identification of plants with integrators, with application to the modeling and control of a microalgae raceway reactor. The concept is to excite the system through optimized test signals with control-relevant shaping of their power spectra. This facilitates a shift in emphasis of the identification objective from estimating a model with good open-loop performance to having a model possessing desired closed-loop characteristics. Such a consideration is particularly important when generating informative databases for estimating predictive models for closed-loop control. An illustration for this experimental design procedure is accomplished in this paper through the estimation of ARX-based models and, subsequently, model predictive control of the pH dynamics of an experimental raceway photobioreactor facility hosting sustainable microalgae production.

The aim of this paper is to emphasize the importance of PID control for our society in general and for the control engineering community in particular. To this end, we first equate the relevance of PID controllers with other inventions in history to remark how PID control has contributed to revolutionizing our world as the main ambassador of the automatic control field. Afterwards, the PID control resilience is provided by showing a brief historical evolution to realize its timely adaptation, and how nowadays it is much more than just the three terms; P, I, and D. Moreover, it is summarized how PID control has been demonstrated to be equivalent to other optimal control solutions and how the recurrent comparison with Model Predictive Control (MPC) is not necessary at all, as both control algorithms should be considered as complementary approaches. Finally, encouragements and suggestions are summarized to continue working on PID control topics.

Greenhouses provide controlled environments for cultivating crops. This work explores the design of PID-based greenhouse climate control techniques using natural ventilation, considering both measurable disturbances and operational constraints. A nonlinear model was developed to relate natural ventilation (the primary climate actuator) with interior temperature in greenhouses, the critical factor being the relationship between air flow rate and vent aperture, which is a source of uncertainty in the related literature. Novel calibration issues are included for this term. The nonlinear model is used to devise control strategies combining PI control and feedback linearization. The resulting simulations and robustness analysis, which accounts for uncertainties in the relevant parameters, demonstrate that the combination of PID and feedback linearization techniques is a suitable control approach. In summary, practical tradeoffs can be achieved between setpoint tracking, disturbance rejection, control effort, and robustness.

Inrecent years there has been a revolution in the development of interactive applications for teaching control theory. In parallel, much work has been done on the development of experimental and virtual control laboratories. In this work, different interactive tools are presented that aim to link both worlds with the aim of promoting the link between theory and practice, using the most common equipment that can be found in automatic control laboratories.

AbstractNon-esterified fatty acids (NEFAs) and Insulin-like growth factor-I (IGF-1) concentrations are modified after the induction of a "male effect". The present study examined the effect of the introduction of males into a group of females that were previously isolated from males, during different phases of the sexual cycle, to determine the changes to the NEFAs and IGF-1 concentrations. Sixty-four does were divided into six groups. The males were introduced with the females at different points after sponge removal. Introduction was carried out 48 h (n = 10, Group 48H), 72 h (n = 12, Group 72H), 4 days (n = 10, Group 4 D), 13 days (n = 10, Group 13 D) or 18 days after sponge removal (n = 10, Group 18 D), and a control group was implemented that had no contact with males (n = 12, Control Group). Plasma samples were taken every day to determine daily progesterone (P4) and NEFAs concentrations, and every second day for IGF-1 determination. No effects from the experimental groups were observed on the mean NEFAs or IGF-1 concentrations (p > .05). No differences between the time before male introduction and after male introduction were observed on the NEFAs concentrations (p > .05) or IGF-1 concentrations (p > .05). On the whole, only differences were observed in the NEFAs concentrations between the follicular and the luteal phases (9.48 ± 0.38 vs 8.15 ± 0.15 mg/dL for follicular and luteal phases, respectively, p < .01). The results of the present experiment demonstrated that the introduction of sexually active males at different moments of the oestrous cycle does not modify the NEFAs or the IGF-1 concentrations.HighlightsResults shows that NEFAs or IGF-1 concentrations did not vary after the introduction of males.Results shows that NEFAs concentrations increases during the follicular phase.Results shows that IGF-1 concentrations did not vary during the oestrous cycle.

The viability of conventional goat farms, such as the native Payoya dairy goat, could be improved by switching to organic production, but product quality needs to be ensured. The present work assesses the carcass and meat quality of Payoya kids raised under conventional and organic grazing-based systems. Twenty-four kids (12 males, 12 females) were selected from each system (n = 48). The slaughter live weight (8.52 vs. 8.28 kg), cold carcass weight (4.44 vs. 4.29 kg) and farm dressing percentage (51.7 vs. 50%) of the conventionally raised kids were significantly higher than those of the organic kids. The shoulder (first category) (21.7 vs. 22.3%) and long leg (32 vs. 32.9%) percentages were lower in the conventional than in the organic kids. The percentage contribution of the intermuscular fat (10.70 vs. 8.11%) to the shoulder weight was greater in the conventional kids, while the percentages of muscle (59.7 vs. 57.2%) and bone (24.7 vs. 22.8%) were higher in the organic kids. For the chemical composition, there were only differences between the two sexes in the percentage of fat (6.64 and 7.99% on dry matter, for male and female, respectively). For rheological variables, only differences were found in the water holding capacity (% water expelled), the meat of the organic females had a higher value (17%) than that of the conventional females (14%). For the meat colour, the conventional male kids returned the highest values for C*and Hº(14.32 and 64.34, respectively). Farms following conventional grazing-based management could easily switch to organic production. Most of the meat and carcass quality variables studied were very similar across the systems.

This paper proposes a new method for the analysis of continuous and periodic event-based state-feedback plus static feed-forward controllers that regulate linear time invariant systems with time delays. Measurable disturbances are used in both the control law and triggering condition to provide better disturbance attenuation. Asymptotic stability and L2-gain disturbance rejection problems are addressed by means of Lyapunov–Krasovskii functionals, leading to performance conditions that are expressed in terms of linear matrix inequalities. The proposed controller offers better disturbance rejection and a reduction in the number of transmissions with respect to other robust event-triggered controllers in the literature.

This paper presents a simple and effective control solution to regulate temperature and humidity inside a greenhouse, which are the main climatic variables affecting crop growth and health. A multivariable control strategy with inverted decoupling is proposed in two schemes. The nighttime control scheme uses heating and dehumidification, and the daytime control scheme uses natural ventilation, dehumidification, and humidification. A system identification methodology is used to obtain low-order linear models from data measured in a greenhouse. This simplifies the design of proportional-integral (PI) controllers and allows the use of well-known control techniques. For instance, anti-windup is used to deal with the saturation of the actuators and for a bumpless transfer mechanism to switch between the nighttime and the daytime control schemes. Setpoint weighting is used for the humidity controllers to attenuate undesired effects on the temperature control loop when the humidity setpoint is changed. Furthermore, split range control is used for the first time to control humidity by combining a heat-pump dehumidifier and a fogging system. The control solution presented in this work allows the integral absolute error to be reduced, on average, by 88.5% for the interactions affecting the temperature control loop, and by 85.6% for the humidity control loop, compared to decentralized PI control. The control schemes have been tested in simulation with real disturbance data from a Mediterranean greenhouse and in preliminary form in a real facility to conclude that the proposed multivariable control strategy could be effective in decoupling the temperature and the humidity control loops.

AbstractThe number of organic farms is growing, but switching from conventional to organic production requires farms continue to produce high quality products. This study compares the carcase and meat quality of Blanca Andaluza goat suckling kids raised under organic and conventional grazing-based stock raising production systems. Twenty-four twin kids (12 males, 12 females) were selected from representative farms of each system. Body weight, dressing percentage, carcase linear measurements, non-carcase components, primary carcase and minor cuts, tissue composition, chemical composition and rheological variables, pH and colorimetric variables, were examined. No significant differences were seen between the production systems or sex with respect to most of the variables studied. However, some non-carcase components and colorimetric variables were affected, with the organic kids' meat returning lower values for lightness, yellow index, chroma and Hue angle. Indeed, some of the meat colour variables examined easily discriminated between the animals raised under the different production systems. These results show that conventional grazing–based farms raising these goats could easily turn to organic production without carcase or meat quality being affected.HighlightsOrganic farms are growing in number.The transformation to organic kid-raising is easy, with meat quality unaffected.These results are of interest with respect to the viability of conventional goat farms.

ABSTRACTThis study examines the reproductive response and reproductive performance of does subjected to the male effect at different male:female ratios when photostimulated males are used. One hundred and thirty does were distributed homogeneously into six groups with male:female ratios of either 1:30 (two repetitions of 30 females with one male each), 1:20 (20 females with one male), 1:15 (15 females with one male), 1:10 (20 females with two males), or 1:5 (15 females with three males). After the introduction of the males (all made sexually active by keeping them for three months under long days), oestrous activity was recorded daily by direct visual observation of the marks left by marking harnesses worn by the males. Ovulation was confirmed via the plasma progesterone concentration. Fecundity, fertility, prolificacy and productivity values were also determined. The 1:30 group returned the lowest percentage of does that ovulated and that showed oestrous activity; it also returned the lowest fecundity and fertility values. The highest values for all these variables were recorded for the 1:5–1:20 groups (with no significant difference between them). These results show that, under Mediterranean latitudes, the reproductive response, fecundity and fertility are diminished when the photostimulated male:female ratio is very low (1:30). The optimum ratio would appear to be around 1:20.

This paper treats development and research at the regulatory control layer in process control. It is noticed that very little attention is payed to this subject, with the exception PID controller tuning. The reason for this is discussed. Two examples of recent advances in the field treating feedforward control and ratio control, respectively, are presented. A goal of the paper is to point out the need for further research in the area. One reason for this is the great industrial impact such research may have, since the functions appearing in this layer are used at so many places in so many industries. A second reason is the need for well functioning regulatory control layers to form solid foundations for the advanced process control layers.

This paper presents the methodology followed to evaluate students ability to face the challenge of controlling a refrigeration system based on vapour compression proposed as a benchmark for PID control design in the PID18 Conference. This benchmark has been also proposed as test-bed plant for the design of controllers in the subject Industrial Control Techniques at the University of Almería, Spain. The solutions proposed by the students range from simple SISO PID control loops (including anti-windup effect) to MIMO ones, including decoupling, filters and feedforward action to reject disturbances. All these solutions rely on models obtained from the reaction curve method. The selection of adequate specifications is encouraged, although students creativity has led them to exploit very aggressive specifications taking into account the different system restrictions, and obtaining very good values of the proposed evaluation indexes. © Copyright IFAC 2018.

This paper presents the modification of the well-known pole placement method for first-order systems and PI control for the tracking problem. The main drawback of the original method is the presence of a zero in the closed-loop transfer function, which has a negative influence in the desired closed-loop response. Typically, this effect is cancelled by using a reference filter within a two-degree-of-freedom control scheme. However, in this work we present a simple modification of the original method that allows us to consider the zero effect in advance. First, the effect of a zero term in the response of second-order systems is analyzed to see how the time response parameters (overshoot, peak time, rise time and settling time) are affected. Afterwards, this analysis and the resulting equations are combined with the pole placement method to propose the new solution. Finally, simulation results are presented to demonstrate the advantages of the proposed method, where it is shown that faster responses than by using a reference filter are obtained.

This paper presents a multivariable TITO (two inputs two ouputs) controller aimed to improve the start-up procedure of a Solar Membrane Distillation (SMD) facility, located at Plataforma Solar de Almería (PSA). The control structure includes PID controllers and decouplers, as well as a reference governor based on a real time optimizer. The filtered Smith Predictor (SP) control structure has been used for controlling one of the output variables, whereas a cascade control scheme is employed to control the other one. The proposed approach has been tested in simulation on a nonlinear model of the SMD facility, showing promising results.

Feedforward control schemes to compensate for disturbances are very well known in process control. In those control approaches, PID controllers are usually considered in the feedback loop, where nominal design for both feedback and feedforward controllers are commonly performed. This paper presents a robustness analysis to study how uncertainties can affect the classical feedforward control scheme. Afterwards, a robust PI controller is designed by using Quantitative Feedback Theory to account for these uncertainties and to fulfill robust specifications for the regulation control problem. Results based on frequency and time domains are presented.

This paper presents ongoing project to develop new interactive books for control education. The novelty of the proposed idea is to merge web-based solutions with LaTex text into a epub format. In such a way, classical interactive tools for control education are combined with static text and thus interactive books are created, being compatible with standard e-book readers. A book chapter about the teaching of second-order processes is presented as example to show the different steps and the results of the proposed idea

Uno de los campos de aplicación más significativos de la robótica móvil consiste en robots capaces de operar en condiciones exteriores sobre terrenos no preparados (robots planetarios, robots en agricultura, robot en operaciones de búsqueda y rescate, robots militares, etc.). Sin embargo, conseguir que los robots se muevan de forma eficiente y precisa en este tipo de entornos no es una tarea sencilla. Un primer aspecto crítico es el sistema de locomoción. En este caso, las orugas constituyen una alternativa sólida a otro tipo de sistemas y desde principios del siglo XX han demostrado sus bondades en vehículos tripulados. En este artículo se motiva y se demuestra mediante pruebas reales la idoneidad de este tipo de locomoción para robots móviles en terrenos no preparados. Es importante remarcar que este artículo pretende ser un resumen extendido del libro recientemente publicado por los autores “Autonomous Tracked Robots in Planar Off-Road Conditions” (González et al., 2014), y, por lo tanto, no pretende ser una contribución original. Inicialmente se presenta una perspectiva histórica de los vehículos y los robots con orugas. Posteriormente se discuten los aspectos de modelado con especial mención al fenomeno del deslizamiento. A continuación, se analizan varias estrategias de localización, en particular, la odometria visual. También se analiza el aspecto del control de navegación, para ello se analizan varias estrategias con compensación del deslizamiento. Finalmente se expresan las conclusiones del trabajo en base a la experiencia de los autores en este campo.

This paper presents the idea about how to combine a set of software and hardware resources available in literature to be used as support to control engineering education. The available tools allow to mix topics related to programming, communications, operating systems, and control theory. The well-known Raspberry Pi board is used as platform to exploit the di_erent proposed concepts. SciPy, Matplotlib, and NumPy libraries, which are Python-based open-source libraries for scienti_c computing and graphical representation, are used to perform Matlab-like simulations and to implement classical control loops. On the other hand, virtual processes developed in Easy Java Simulations are adapted to be controlled through the network from a controller implemented on the Raspberry Pi with Python. This option is very useful from a teaching point of view since time-based, networked-based, or event-based control approaches can be easily introduced on this proposed architecture. Furthermore, once students know how to implement control loops on the Raspberry Pi using Python, external real processes can be easily controlled by using the GPIO interface available in the this electronic board. Then, a project based on these tools and ideas is motivated and presented in this paper to control a two-tank level process © Copyright IFAC 2015.

This paper deals with a symmetric send-on-delta PI control strategy for controlling the internal temperature of a greenhouse. It is shown that, by properly designing the control system, the disturbances represented by the soil temperature, the solar radiation, the wind velocity, and the outside temperature can be effectively compensated with a limited number of events. The role of the design parameters is outlined and simulation results demonstrate the efficacy of the methodology by comparing it with previously proposed techniques.

This study examined which neural mechanism (opioid, dopaminergic, or serotonergic system) is involved in the regulation of luteinizing hormone (LH) secretion, with and without nutritional modulation, at different times of the photoperiodic cycle. Goats were randomly distributed into two experimental groups that received either 1.1 (high group; n = 18) or 0.7 (low group; n = 18) times the nutritional maintenance requirements. The goats were exposed to alternations of 3 mo of long days and 3 mo of short days. Plasma LH concentrations were measured twice a week. The effects of intravenous injections of naloxone (endogenous opioid receptor antagonist), pimozide (dopaminergic2receptor antagonist), and cyproheptadine (serotonin 5-hydroxytryptamine2receptor antagonist) on LH secretion were assessed during challenges in three different photoperiodic situations: the onset of LH stimulation by short days (OnsetSD), the onset of LH inhibition by long days (OnsetLD), and during the LH inhibition by long days (LateLD). The role of the different neural systems was clearly modified by the level of nutrition. In the low-nutrition group, only naloxone increased LH concentrations during onsetLD (P< 0.05). However, in the high-nutrition group, naloxone increased the concentration and pulsatility of LH (P< 0.05) in onsetSD and onsetLD. Pimozide increased LH concentration and pulsatility (P< 0.05) in onsetLD and LH concentration in lateLD (P< 0.001). Finally, cyproheptadine significantly increased LH concentration at all three times (P< 0.001). These results provide evidence that all three systems are involved in the inhibition of LH release in onsetLD, and that the opioid and serotonin mechanisms are involved during the onsetSD that were enhanced by a high plane of nutrition.