Experimental Evaluation for an Extremum Seeking Control Strategy based on Input-output Correlation with a Mini-split Air Conditioning System

Extremum Seeking Control (ESC) has emerged as a model-free real-time optimization framework, typically based on dither-demodulation driven gradient estimation. However, such conventional ESC suffers from slow convergence. Salsbury et al. have recently proposed an input-output correlation based ESC (IOC-ESC) strategy anchored on a statistical analysis. The IOC-ESC algorithm is less sensitive to changes in its internal parameters because of the use of a normalized correlation coefficient in the feedback loop. The design goal of the algorithm is to have only two tunable parameters: (1) a time scale parameter that relates to the time open loop time constant of the system; and (2) the amplitude of the dither signal. A suitable set of generic internal parameters is still in the process of being identified as more test data become available from different system types. For the work reported here, the feedback gain (referred to as the tuning factor) with the IOC-ESC was also tuned for optimal performance. This study aims to conduct an experimental evaluation for the IOC-ESC strategy with a ductless mini-split air conditioning system, compared with conventional ESC (CON-ESC). The system features variable-capacity compressor operation and variable-speed operation for the evaporator and condenser fans. In this study, both single-input and two-input ESC scenarios are tested. The manipulated inputs include the evaporator and condenser fan speeds, while the total power consumption is used as feedback for all cases. The experimental setup is developed with a 9000 BTU variable-speed mini-split AC system serving a 4’x8’x6’ insulated chamber, and an electrical fan heater is used to provide an artificial heat load. The data acquisition and control algorithms are implemented on a National Instruments CompactRIO platform. Both IOC-ESC and CON-ESC are tested with the same setup. For single-input scenario, the manipulated input is the condenser fan speed. The testing results of five trials of IOC-ESC are used to evaluate the impact of the two tuning parameters, i.e. dither frequency and tuning factor, on the ESC performance. IOC-ESC#1, IOC-ESC#4 and IOC-ESC#5 have the same dither frequency but different tuning factors, while IOC-ESC#1, IOC-ESC#2 and IOC-ESC#3 have the same tuning factor but different dither frequencies. The testing results of two trials of CON-ESC are then compared with the IOC-ESC results. Both CON-ESC and IOC-ESC can effectively reduce the power consumption of the mini-split system without sacrificing zone temperature regulation. Moreover, the settling time of IOC-ESC ranges from 300 to 600 seconds, while the settling time of CON-ESC ranges from 900 to 1200 seconds. Overall, the IOC-ESC converges faster than the CON-ESC. For two-input scenario, the manipulated inputs are condenser fan speed and evaporator fan speed. The testing results of the two-input IOC-ESC are compared with the result of a two-input CON-ESC trial by Yan et al. with the same system. The settling times for CON-ESC and IOC-ESC are about 1800 and 1200 seconds, respectively. In summary, both CON-ESC and IOC-ESC can optimize the condenser fan speed and evaporator fan speed for energy efficient operation, while the IOC-ESC converges faster and has fewer tuning parameters

Probing Control : Analysis and Design with Application to Fed-Batch Bioreactors

In most control problems the objective is to control the output at a desired value in spite of disturbances. In some cases, the best setpoint is not known a priori and it should be found online to optimize the process performance. This thesis examines a probing strategy that can be applied for this class of problems. The focus is on the application of the technique to the control of feed supply in fed-batch fermentations of the bacterium Escherichia coli. The thesis is divided into three parts. In the first part, the convergence properties of the probing algorithm are examined. The analysis is limited to processes modeled by a linear time-invariant dynamic in series with a static nonlinearity. Stability and performance analysis taking into account the process dynamic is performed. Tuning guidelines that help the user for the design are also derived. The second part presents a novel cultivation technique based on the probing approach. The fermentation technique combines the advantages of probing control and temperature-limited fed-batch technique. The feeding strategy is well adapted for prolonged operation at the maximum oxygen transfer capacity of the reactor. The efficiency of the method is demonstrated by simulations and experimental results. The strategy leads to a high biomass and it limits the degradation of the recombinant protein activity in the late production phase. In the third part, the probing feeding strategy is evaluated in industrial-scale bioreactors. Based on experimental results the influence of scale and complex medium is discussed. It is shown that the flexibility and robustness of the technique makes it a useful tool for process development

Dither-less extremum seeking for hydrogen minimization in PEM fuel cells

This paper presents a nonsmooth adaptive extremum seeker that minimizes the hydrogen consumption in a fuel-cell system. The extremum seeker operates by estimating the gradient of the objective function but, unlike other seekers, it does not require a dither signal to produce such estimate. The absence of a dither signal simplifies the choice of parameter values for the seeker, and more importantly, it allows it to converge to the optimal value exactly, not only to a small neighborhood. The proper functioning of the proposed scheme is proved using nonsmooth Lyapunov analysis. The strategy is tested on the input-output map of a real polymer electrolyte fuel cell.The research of C. Kunusch has been supported by the Seventh Framework Programme of the European Community through the Marie Curie actions (GA: PCIG09-GA-2011-293876), the Puma-Mind project (GA: FCH-JU-2011-1-303419), the CICYT project DPI2011-25649 (MINECO-Spain), the CSIC MACPERCON project (201250E027) and the CSIC JAE-DOC Research Programme.Peer Reviewe

Ditherless extremum seeking for hydrogen minimization in PEM fuel cells

This paper presents a nonsmooth adaptive extremum seeker that minimizes the hydrogen consumption in a fuel-cell system. The extremum seeker operates by estimating the gradient of the objective function but, unlike other seekers, it does not require a dither signal to produce such estimate. The absence of a dither signal simplifies the choice of parameter values for the seeker, and more importantly, it allows it to converge to the optimal value exactly, not only to a small neighborhood. The proper functioning of the proposed scheme is proved using non-smooth Lyapunov analysis. The strategy is tested on the input–output map of a real polymer electrolyte fuel cells.Peer ReviewedPostprint (author’s final draft

Modélisation dynamique et commande optimale d'un système de réfrigération à base d'éjecteur

Recently, the ejector-based refrigeration system (ERS) has been widely used in the cooling industry as an appropriate alternative to the compressor-based cooling systems. However, the advantages of ERS such as the reliable operation and low operation and maintenance costs are overshadowed by its low efficiency and design complexity. In this context, this thesis presents the efforts to develop a control model enabling the ERS to operate in its optimal operational conditions. The extensive experimental studies of ERS revealed that at a fixed condenser inlet condition, there exists an optimal primary stream mass flow rate (generating pressure) that simultaneously maximizes the compression ratio (Cr) and exergy efficiency and minimizes the evaporating pressure. Then, the steady state models of the heat exchangers were developed and used to investigate the influence of the increase in generating pressure on the coefficient of performance (COP) of the system and it showed that increasing the generating pressure reduces the COP, linearly. In order to predict the choking regime of the ejector and explain the reasons of observed physical phenomenon, the 1D model of a fixed geometry ejector installed within an R245fa ERS was developed. The developed model demonstrated that the ejector operates in the subcritical mode when the generating pressure is below the Cr optimum point, while it operates in critical mode at or above the optimum generating pressure. Next, a dynamic model of the ERS was built to evaluate the ERS transient response to an increase in the primary stream mass flow rate. Since the ERS dynamics is mainly dominated by the thermal dynamics of the heat exchangers, the dynamic models of the heat exchangers were developed using the moving boundary approach and connected to the developed models of the ejector and steady state models of the pump and expansion valve to build a single dynamic model of the system. The built dynamic model of an ERS was used to estimate the time response of the system in the absence of accurate experimental data of the system’s dynamics. Finally, a control model was designed to drive an ERS towards its optimal operation condition. A self-optimizing, model-free control strategy known as Extremum seeking control (ESC) was adopted to minimize evaporating pressure in a fixed condenser thermal fluid inlet condition. The innovative ESC model named batch phasor ESC (BPESC) was proposed based on estimating the gradient by evaluating the phasor of the output, in batch time. The simulation results indicated that the designed BPESC model can seek and find the optimum evaporating pressure with good performance in terms of predicting the steady state optimal values and the convergence rates.Récemment, le système de réfrigération à éjecteur (SRE) a été largement utilisé dans l'industrie du refroidissement en tant que solution de remplacement appropriée aux systèmes de refroidissement à compresseur. Cependant, les avantages du SRE, tels que le fonctionnement fiable et les faibles couts d'exploitation et de maintenance, sont éclipsés par son faible rendement et sa complexité de conception. Dans ce contexte, ce projet de recherche de doctorat a détaillé les efforts déployés pour développer une stratégie de commande permettant au système de fonctionner dans ses conditions opérationnelles optimales. Les études expérimentales approfondies du SRE ont révélé que, dans une condition d'entrée de condensateur constante, il existe un débit massique optimal du flux primaire (générant une pression) qui maximise simultanément le taux de compression (Cr) et l'efficacité exergétique, et minimise la pression d’évaporation. Ensuite, les modèles à l’état d’équilibre des échangeurs de chaleur ont été développés et utilisés pour étudier l’influence de l’augmentation de la pression générée sur le coefficient de performance (COP) du système et il en ressort que l'augmentation de la pression génératrice réduit le COP de manière linéaire. Afin de prédire le régime d'étouffement de l'éjecteur et d'expliquer les raisons du phénomène physique observé, le modèle 1D d'un éjecteur à géométrie fixe installé dans un système SRE R245fa a été développé. Le modèle développé a démontré que l'éjecteur fonctionne en mode sous-critique lorsque la pression génératrice est inférieure au point optimal de Cr, alors qu'il fonctionne en mode critique à une pression égale ou supérieure à la pression génératrice optimale. Ensuite, un modèle dynamique du SRE a été développé pour étudier la réponse transitoire du SRE lors d’une augmentation du débit massique du flux primaire. Puisque la dynamique du SRE est principalement dominée par la dynamique thermique des échangeurs de chaleur, les modèles dynamiques des échangeurs de chaleur ont été développés à l'aide de l'approche des limites mobiles et connectés aux modèles développés de l'éjecteur et des modèles à l'état stationnaire de la pompe et de la vanne un seul modèle dynamique du système. En l’absence de données expérimentales précises sur la dynamique d’un système SRE, le modèle dynamique développé du SRE a été simulé numériquement pour étudier sa réponse temporelle. Enfin, une stratégie de commande extrêmale (ESC) a été élaboré pour régler automatiquement le SRE à ses conditions de fonctionnement optimales, c’est-à-dire pour trouver la vitesse de la pompe qui minimise la pression dans des conditions d'entrée de condenseur fixes. Afin de proposer une ESC implémentable en temps discret sur une installation réelle sujette à un bruit de mesure important et un traitement hors-ligne par trame, une nouvelle commande extrémale basée sur une approche par phaseur avec une procédure de traitement de signal par trame (BPESC) a été développée et simulée avec le modèle numérique. Les résultats de la simulation ont indiqué que le modèle BPESC peut trouver la vitesse optimale de la pompe avec de bonnes performances en termes de précision et de vitesse de convergence

Process Control of Crushing Circuits

Kivenmurskaus on keskeinen osaprosessi kiviaineksen, metallien ja sementin tuotannossa. Murskaamalla tuotetut raaka-aineet muodostavat nykyaikaisen infrastruktuurimme perustan. Huolimatta merkittävästä roolistaan, kivenmurskaus on yksi harvoista teollisista prosesseista, jonka prosessinohjaus toteutetaan edelleen kokemusperäisesti, ilman luotettavaa mittaustietoa suoritettujen ohjaustoimien vaikutuksista. Nykykäytäntö altistaa murskausprosessit prosessivaihteluille ja –häiriöille, ja johtaa viime kädessä tehottomaan tuotantoon ja kapasiteetin vajaakäyttöön. Pääsyinä nykytilaan voidaan pitää murskausprosessien puutteellista anturointia ja tutkimustiedon puutetta korkeamman automaatioasteen tuomista hyödyistä. Tässä väitöskirjassa pyrittiin ratkaisemaan edellä mainittu ongelma automaattisen prosessinohjauksen avulla. Päätavoitteena oli kehittää säätömenetelmät murskauspiirin suorituskyvyn saattamiseksi lähelle parasta saavutettavissa olevaa tasoa. Tämä tutkimus perustuu mallipohjaiseen säädönsuunnittelumenetelmään. Systemaattinen suunnitteluprosessi alkoi säätötavoitteiden määrittelystä ja dynaamisten prosessimallien kehittämisestä. Kehitettyjen prosessimallien avulla luotiin säätötavoitteet täyttävä säätöstrategia ja viritettiin strategian vaatimat prosessisäätimet. Lopuksi simulointimallien avulla kehitetty ja testattu säätöstrategia implementoitiin osaksi laitoksen automaatiojärjestelmää ja sen suorituskyky arvioitiin täyden mittakaavan prosessikokeiden avulla. Tämä väitöskirja on osoittanut, että murskauspiirin tehokas ja tarkoituksenmukainen toiminta vaatii eri kahden säätötavan toteuttamista: massataseen säätö ja hienonnusmäärän säätö. Massatasesäädön tavoitteena on varmistaa 100 % käyttöaste murskauspiirin pullonkaulassa. Hienonnusmäärän säätö varmistaa halutun murskaimen tuotemateriaalin partikkelikokojakauman. Kehitetyt hienonnusmäärän säätömenetelmät perustuvat itseoptimoituvaan säätötapaan, joka mahdollistaa likimain optimaalisen suorituskyvyn käyttämällä säätimessä vakio-asetusarvoa. Kun tämä asetusarvo valitaan optimaalisesti, mahdollistaa esitelty ohjausstrategia parhaan saavutettavissa olevan murskauspiirin suorituskyvyn. Työn merkittävä tunnuspiirre on erityisen kattava empiria. Kehitetyt menetelmät testattiin kattavasti useissa erilaisissa tuotantoskenaarioissa ja prosessikonfiguraatioissa. Täyden mittakaavan prosessikokeiden tulokset vastasivat hyvin lähelle simulaatioilla saatuja tuloksia. Tämä väitöskirja on merkittävä edistysaskel murskausprosessien säädössä. Työn tuloksena kehitetyt mittaus- ja säätötavat mahdollistavat tehokkaamman ja tarkoituksenmukaisemman raaka-ainetuotannon. Työn tuloksilla voidaan olettaa olevan merkittävä vaikutus siihen, miten ja millä tavoin murskausprosesseja ohjataan tulevaisuudessa. Työssä kehitetyn murskauspiirin automaattisen säätöstrategian voidaan olettaa toimivan perustana tulevaisuuden murskausprosessien prosessiautomaatio-toteutuksille.Crushing is an essential high-volume processing stage in the production of aggregates, metals and cement. Crushed products form the basis of our modern infrastructure and therefore play a major role in the economic growth and welfare. Despite its significant role in society, crushing is one of the few remaining industrial processes that is currently being operated using belief-based manual control without the possibility to quantify the consequences of performed control actions. This practice makes crushing processes vulnerable to process variation and exposes them to inefficient production and capacity underutilization. The aim of this thesis is to address this deficiency by bridging the gap between theoretically possible and realized crushing circuit performance, by means of automatic process control. This thesis covers the entire model-based control system design procedure – from the formulation of control objectives and development of dynamic process model(s), through the development of control strategy, to the control system implementation and performance evaluation – for crushing circuits. Research has led to significant advances within crushing process measurement and control. Developed methods have been rigorously tested in various production scenarios and circuit flowsheets, using both dynamic simulations and full-scale experiments. Experiments revealed expected behavior with a significant increase in performance. The results have shown that the efficient operation of a crushing circuit requires addressing two control tasks: mass balance control and size reduction control. The objective of mass balance control is to guarantee 100 percent circuit utilization, whereas size reduction control ensures the desired degree of size reduction. The ideal degree of size reduction is determined empirically to maximize the value of the used KPI. The developed control strategy delivers near-maximum circuit performance. This thesis represents a major leap forward in the area of process control of crushing circuits. It has opened entirely new possibilities by making it possible to quantify the instantaneous performance of crushing circuits and by introducing the ability to ensure consistent and efficient long-term production. These major breakthroughs can have a significant impact on how crushing plants will be operated in the future. Developed standard control practice can be expected to serve as a basis for future control system implementations of industrial crushing circuits