The wind power research at the division of Electricity at Uppsala University is aimed towards increased understanding of vertical axis wind turbines. The considered type of wind turbine is an H-rotor with a directly driven synchronous generator operating at variable speed. The experimental work presented in this thesis comprises investigation of three vertical axis wind turbines of different design and size. The electrical, control and measurement systems for the first 12 kW wind turbine have been designed and implemented. The second was a 10 kW wind turbine adapted to a telecom application. Both the 12 kW and the 10 kW were operated against dump loads. The third turbine was a 200 kW grid-connected wind turbine, where control and measurement systems have been implemented. Experimental results have shown that an all-electric control, substituting mechanical systems such as blade-pitch, is possible for this type of turbine. By controlling the rectified generator voltage, the rotational speed of the turbine is also controlled. An electrical start-up system has been built and verified. The power coefficient has been measured and the stall behaviour of this type of turbine has been examined. An optimum tip speed ratio control has been implemented and tested, with promising results. Use of the turbine to estimate the wind speed has been demonstrated. This has been used to get a faster regulation of the turbine compared to if an anemometer had been used.

Αυτή η διπλωματική εργασία εξετάζει θέματα που αφορούν την παρεχόμενη ποιότητα ισχύος στα σύγχρονα ηλεκτρικά συστήματα. Θα εξετάσουμε την απόδοση ενός στατικού σύγχρονου αντισταθμιστή STATCOM, που λειτουργεί ως ρυθμιστής τάσης, σε ένα σύστημα αυτοδιεγειρόμενης επαγωγικής γεννήτριας που τροφοδοτεί μη γραμμικά φορτία. Εκτός της θεωρητικής ανάλυσης των συνιστωσών του εξεταζόμενου συστήματος, θα πραγματοποιήσουμε προσομοίωσή του, με τη βοήθεια του λογισμικού PSCAD/EMTDC, με σκοπό την εξαγωγή χρήσιμων συμπερασμάτων από τα παραγόμενα αποτελέσματα. Ειδικό ενδιαφέρον θα δοθεί εκτός από την απόδοση στη ρύθμιση της τάσης και στη συνολική αρμονική παραμόρφωση της τάσης και την επίδραση των αρμονικών στην ποιότητα ισχύος. / This diploma thesis studies issues concerning the provided power quality in modern power systems. We will examine the performance of a STATCOM (Static synchronous Compensator) based voltage regulator in a, self excited induction generator (SEIG) feeding non-linear loads system. Besides the theoretical analysis of each component of the examined system, we will simulate it with the help of a software program called PSCAD/EMTDC in order to get useful conclusions through the provided results. Specific attention will be given, besides the efficiency in voltage regulation, in total harmonic distortion and the effect harmonics cause in power quality.

H αυξανόμενη ανάγκη για στροφή της παραγωγής ηλεκτρικής ενέργειας σε βιώσιμες και ανανεώσιμες πηγές έχει οδηγήσει στη ραγδαία ανάπτυξη της αιολικής ενέργειας και στη διείσδυσή της στην αγορά ενέργειας. Η παρούσα εργασία πραγματεύεται ένα αιολικό σύστημα παραγωγής ενέργειας βασισμένο σε σύγχρονη γεννήτρια μόνιμου μαγνήτη. Η συγκεκριμένη μηχανή αποτελεί τη νέα τάση στην αγορά εξ’ αιτίας των σημαντικών πλεονεκτημάτων που προσφέρει, ιδίως αυτό της δυνατότητας για απουσία κιβωτίου ταχυτήτων που οδηγεί το σύστημα σε αυξημένη απόδοση. Στην εργασία αυτή, θα γίνει μια παρουσίαση των χαρακτηριστικών των σύγχρονων αιολικών συστημάτων, θα γίνει η μοντελοποίηση της σύγχρονης γεννήτριας μόνιμου μαγνήτη και θα αναλυθεί η λογική του ελέγχου που ακολουθείται και στηρίζεται στο διανυσματικό έλεγχο προσανατολισμού σε πεδίο. Τέλος, θα γίνει η παρουσίαση και ο σχολιασμός των αποτελεσμάτων του μοντέλου, που αναπτύχθηκε σε περιβάλλον Matlab/Simulink, με την παράλληλη εξαγωγή συμπερασμάτων για την απόκρισή του. / The ongoing increase in electric power demand and the need for sustainable and renewable energy has led wind energy into high rates of growth and penetration to the energy markets. This thesis deals with a permanent magnet synchronous generator based wind power system. This type of machine has become a trend for the markets, due to its specific benefits and, especially, for the absence of gearbox that leads the whole system to higher efficiency. In this thesis, we will discuss the characteristics of a modern wind power system, then, the permanent magnet synchronous generator will be modelled, and the field oriented vector control strategy will be analyzed. Finally, we will present and discuss the outcome of the model that was built in the Matlab/Simulink programme, and we will come into certain conclusions about its response.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this study a new type of gearless, direct-drive wind generator, which can be connected directly to the grid, is proposed. The working characteristics of this generator are based upon the principles of the permanent magnet induction generator (PMIG). By omitting the need for a gearbox and power electronic converter this generator type has several advantages regarding cost and reliability. Although the PMIG is proposed in previous studies as favourable for wind power generation, the mechanical complexity and difficult construction associated with these types of generators, seems to be the main reason why these generator systems are not used. The design methods presented in this study are intended to alleviate these constructional issues by proposing the split-PMIG (S-PMIG), where the stator winding and the induction cage-rotor windings are electromagnetically separated. The machine is basically split into two permanent magnet (PM) machines, a grid connected synchronous generator (SG) unit and a turbine connected induction generator (IG) unit. These two units are mechanically linked by a common PM-rotor. To evaluate this concept a finite element (FE) design analysis is done independently for both machine components. The emphasis of the design optimisation is the minimisation of the cogging torque, while still having a decent performing, easily constructible generator. This generator should also have low load ripple content. Cogging torque can result in the failure of the turbine to start up, especially at low wind speeds. As this is a directly grid connected generator, torque ripple transferred to the common PM-rotor can destabilise the generator. Based upon the FE designs a preliminary S-PMIG system is constructed and practically evaluated. Due to the modular nature of the design it is possible to implement the synchronous generator part of the S-PMIG in conjunction with a grid-connected solid state converter (SSC). This allows for a useful comparison with the S-PMIG system. Promising results are obtained from initial tests of the S-PMIG directly connected to the grid. It is shown that the operation of this generator is stable under a wide range of wind load conditions. However, some important machine design issues are identified from these practical results, which could prove vital in the implementation of future S-PMIG designs. / AFRIKAANSE OPSOMMING: In hierdie studie word 'n nuwe ratkaslose direk-aangedrewe wind generator voorgestel, wat direk aan die krag netwerk gekoppel kan word. Hierdie generator is gebaseer op die beginsels waarop permanente magneet induksie generators (PMIG’s) werk. Deur die ratkas en drywings-elektroniese omsetter uit te laat, het hierdie generator verskeie voordele rakende koste en betroubaarheid. Alhoewel vorige studies hierdie generator voorstel as 'n belowende opsie vir gebruik in wind-energie-stelsels, lyk dit of die meganiese kompleksiteit en moeilike konstruksie die hoof rede is hoekom hierdie generator stelsels tans nie gebruik word nie. Die ontwerpsmetodes wat in hierdie studie voorgestel word poog om die genoemde konstruksie probleme op te los deur die gesplete-PMIG (S-PMIG), waar die stator wikkelings en die induksie masjien kou-rotor wikkelings elektromagneties ontkoppel is, voor te stel. Hierdie masjien is basies verdeel in twee permanente magneet (PM) masjiene, 'n netwerk gekoppelde sinchroongenerator (SG) eenheid en 'n turbine gekoppelde induksie generator (IG) eenheid. Hierdie twee eenhede word gekoppel deur 'n gemeenskaplike PM-rotor. Om hierdie konsep te evalueer word eindige element analise onafhanklik vir beide masjiene gedoen. Die fokus van die ontwerp optimering is die minimalisering van die vertandingsdraaimoment, terwyl die generator steeds goed presteer en maklik is om te vervaardig. Vertandingsdraaimoment kan tot die gevolg hê dat die turbine versuim om te begin draai, veral by lae windsnelhede. Dit is ook belangrik dat die generator 'n lae rimpel inhoud onder las bevat. Omrede hierdie generator direk aan die netwerk gekoppel is, kan draaimoment pulsasies, oorgedra aan die gemeenskaplike PM-rotor, die masjien destabiliseer. Gebaseer op die eindige element ontwerpe, is 'n voorlopige gesplete-PMIG gebou en prakties geëvalueer. As gevolg van die modulêre struktuur van die ontwerp, is dit moontlik om die SG gedeelte van die gesplete- PMIG saam met 'n drywings-elektroniese omsetter te implementeer. Dit laat toe vir 'n nuttige vergelyk tussen die twee stelsels. Belowende eerste toets resultate is verkry van die gesplete-PMIG direk gekoppel aan die netwerk. Daar word gewys dat hierdie generator stabiel oor 'n wye operasionele gebied kan funksioneer. Verskeie belangrike masjien ontwerpsfaktore word ook uitgelig met die praktiese evaluering van die gesplete-PMIG. Hierdie faktore kan uiters belangrik wees in die ontwerp en implementering van toekomstige gesplete-PMIG stelsels. / Sponsored by the Centre for Renewable and Sustainable Energy Studies

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The slip synchronous permanent magnet generator (SSG) is a direct-driven direct-grid connected generator developed to alleviate the need for expensive gearboxes and solid-state power converters on wind turbine generators. This study identifies certain key areas where the current wind turbine generator (WTG) system does not comply with the grid code for wind energy facilities (WEF) as specified by the National Energy Regulator of South Africa. The current WTG system does not have a reactive power compensation device. The main focus in this study is the development of an on-load tap changer (OLTC) transformer to control the terminal voltage of the generator. By controlling the terminal voltage of the generator the excitation-mode of the SSG can be changed allowing for control over the reactive power output of the SSG. An OLTC transformer utilising a solid-state assisted mechanical diverter circuit is built and tested to determine the viability of using an OLTC as a reactive power control device. Practical test results show that the OLTC can successfully control the terminal voltage of the SSG without interrupting the load current. The required accuracy regarding power factor control capability was not met due to the large change in reactive power output per tap change operation. A method of using small shunt capacitor banks to provide additional reactive power in between consecutive tap changes is evaluated in simulation. Simulation results show that the addition of these small shunt capacitor banks dramatically improves the reactive power control accuracy. Additionally the grid code specifies that a WEF must have the ability to curtail the active power output during frequency disturbances. The effects of frequency disturbances on the SSG output is simulated and it was found that the SSG will comply with the minimum connection requirements as specified in the grid code. A method of using an IGBT switched DC load to limit the active power output of the WEF is developed and simulated. From the simulation results it was found that the proposed active power curtailment device will meet the minimum power curtailment response time requirements as specified in the grid code. / AFRIKAANSE OPSOMMING: Die glip sinchroon permanente magneet generator (SSG) is ʼn direkte dryf, direkte netwerk gekoppelde wind generator wat ontwikkel is om behoefte aan duur ratkaste en drywing elektroniese omsetters te verlig. Hierdie studie identifiseer sekere sleutel areas waar die huidige wind generator opstelling nie aan die netwerk kode spesifikasie soos uiteengesit deur die Nasionale Energie Reguleerder van Suid-Afrika voldoen nie. Die wind turbine generator stelsel beskik nie oor ʼn reaktiewe drywing beheer meganisme nie. Die belangrikste fokus in hierdie studie is die ontwikkeling van ʼn transformator tap wisselaar wat gebruik sal word om die generator se terminale spanning te beheer. Deur die terminaal spanning te beheer kan die opwekking modus van die generator verander word om dan die uittree reaktiewe drywing te beheer. ʼn Tap wisselaar wat gebruik maak van ʼn drywingelektronies gesteunde meganiese skakelaar is ontwikkel en getoets om die lewensvatbaarheid van die tegniek te ondersoek. Praktiese toets resultate toon dat die tap wisselaar suksesvol beheer oor die generator se terminaal spanning kon uitvoer, sonder om die las-stroom te onderbreuk. Ongelukkig is die vereiste akkuraatheid ten opsigte van die reaktiewe drywing beheer nie gehaal nie. Die rede hiervoor is dat die verandering in uittree reaktiewe drywing baie groot is vir opeenvolgende tap verstellings. ʼn Metode waar twee klein kapasitor banke geskakel word om reaktiewe drywing te lewer, tussen opeenvolgende tap veranderinge, is deur middel van simulasie ondersoek. Die simulasie resultate toon aan dat die toevoeging van die kapasitors ʼn drastiese verbetering in die beheerbaarheid van die uittree reaktiewe drywing het. Verder spesifiseer die netwerk kode ook dat ʼn wind plaas oor die vermoë moet beskik om die aktiewe drywing te verminder tydens ʼn netwerk frekwensie versteuring. Die effek wat ʼn frekwensie versteuring op die SSG het, is deur middel van simulasie ondersoek en daar is gevind dat die SSG aan die netwerk verbinding spesifikasie sal voldoen. ʼn Metode waarby ʼn IGBT geskakelde GS las gebruik word om die aktiewe drywing van die wind generator te beperk is ondersoek en gesimuleer. Vanaf die simulasie resultate is daar gevind dat die drywing beperkings toestel aan die minimum drywing en reaksie tyd spesifikasies soos vereis sal voldoen.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work in this study covers a powerful technique to derive propagation and scattering information in an expedient fashion. Expedient because time-domain (TD) data gathers a broad spectrum in a single transmitted pulse. TD has been criticised because of a lack of dynamic range, which has now been overcome by the direct sampling system, RATTY and RTA. This study focuses on the investigation of a TD metrology system, to assist with the characterisation of MeerKAT systems. The elementary components of the system include a fast-rising impulse generator that was coupled with an impulse radiating antenna (IRA). The system was calibrated and tested before practical measurements and preliminary testing in the Karoo were done. For TDmetrology a larger bandwidth accelerates measurements without the loss of accuracy. The pulse generator’s (PG’s) fundamental components are an avalanche transistor and a step recovery diode (SRD), to sharpen the leading edge of the pulse. Improving the rise-time of a pulse increases its bandwidth in the spectrum. The external circuitry around these components is pivotal and it determines the shape, amplitude and rise-time of the pulse. In the course of the investigation, the general circuitry around the PG was improved to obtain the best possible pulse for measurements inside a reverberation chamber (RC) and for measurements in the Karoo. In light of this, a second and third PG source were obtained. For measurements in the Karoo, a larger amplitude pulse was required to increase the spectral content and this is essential for propagation measurements over distance and the shielding effectiveness (SE) of structures. Stacking avalanche transistors allow larger amplitude pulses and it improves the dynamic range of the spectrum. A PG incorporating stacked avalanche transistors, was designed, built and measured to assist with RC and small-scale field measurements in the Karoo. The third PG was bought for the practical measurements in the Karoo. The PG produces kilovolt pulses with pico-second rise-times that extend the spectral range of the current PGs at our disposal. With these PGs, an antenna is required for the radiation of impulse-like transients. The IRA is a high-gain large-bandwidth antenna. The IRA consists of a parabolic reflector, conical-plate transmission lines that are terminated through resistors onto the dish, and a feeding balun. The IRA design was thoroughly discussed and a first model for metrology was designed, measured and optimised. The IRA was also simulated with computation software code, FEKO. Before deployment of theTDsystem, calibration and characterisation measurements are required. The measuring devices used within this study were sampling oscilloscopes and direct sampling systems. The limitations of each device were explored and are discussed. The final measurements that were conducted contribute to work related to the SKA. This incorporated antenna pattern calibration, propagation over distance and the SE of a berm built from Karoo soil. The system investigated the propagation attenuation over the Karoo soil and vegetation, with great promise. A broad spectrum was measured over a few kilometres and compared to free-space loss. The SE of the berm covered the same spectral bandwidth. In this measurement, scattering effects and knife-edge diffraction were observed. / AFRIKAANSE OPSOMMING: Die werk in hierdie studie dek ’n kragtige tegniek wat gebruik kan word om die voortplanting en die verstrooiingsinligting van elektromagnetiese golwe op ’n voordelige manier af te lei. Dit is voordelig, want tydgebieddata versamel ’n wye spektrum in ’n enkele oordraagbare puls. Tydgebied is in die verlede baie gekritiseer omdat dit ’n dinamiese reikwydte kortkom en dit is nou oorwin deur die direkte steekproefnemingstelsel, RATTY en RTA. Hierdie studie fokus op die ondersoek van ’n tydgebiedmetingssisteem en dit help met die karakterisering van MeerKAT sisteme. Die elementêre komponente van die sisteem bestaan uit ’n vinnig-stygende impulsgenerator wat gekoppel is aan ’n impulsuitstralende-antenna (IRA). Die sisteem is gekalibreer en getoets voordat praktiese metings en toetse in die Karoo uitgevoer kon word. Vir tydgebiedmetings versnel ’n groter bandwydte die metings sonder om die akkuraatheid daarvan te beïnvloed. Die pulsgenerator se fundamentele komponente is ’n stortvloedtransistor en ’n stap-herstel diode (SRD) wat die voorpunt van die puls verskerp. Die eskterne stroombaan rondom hierdie komponente is noodsaaklik en dit bepaal die vorm, amplitude en die stygtyd van die puls. Deur die loop van hierdie ondersoek is die algemene stroombaan rondom die puls verbeter, om die beste moontlike puls vir metings binne in die weerkaatsingskamer en vir metings in die Karoo, te verkry. Na aanleiding van dit is ’n tweede en derde pulsgenerator bron verkry. Vir die metings in die Karoo is ’n puls met ’n groter amplitude vereis om die spektrale inhoud te vermeerder. Dit is noodsaaklik vir elektromagnetiese golf voortplantingsmetings oor afstand asook die beskermings effektiwiteit (SE) van die strukture. Stapel-stortvloed transistors skep pulse met groter amplitudes en dit verbeter die dinamiese reikwydte van die spektrum. ’n Pulsgenerator wat gestapelde stortvloedtransistors insluit is ontwerp, gebou en gemeet om te help met metings in die weerkaatsingskamer en kleinskaal veldmetings in die Karoo. Die derde pulsgenerator is gekoop vir praktiese metings in die Karoo. Die pulsgenerator vervaardig kilovolt pulse met pikosekond stygtye, wat die reikwydte van die spektrum van ons huidige puls uitbrei. Hierdie pulsgenerators vereis ’n antenna vir die uistraling van impulsagtige seine. Die IRA is ’n hoë-wins, groot-bandwydte antenna. Die IRA bestaan uit ’n paraboliese weerkaatser, konieseplaat transmissielyne wat deur weerstande op die skottel getermineer word, asook ’n voedings "balun". Die IRA ontwerp is deeglik bespreek en ’n model is ontwerp, gemeet en verbeter. Die IRA is ook gesimuleer met behulp van ’n rekenaarsagtewareprogram, FEKO. Voordat die tydgebiedsisteem benut kan word, moet dit gekalibreer word en karakteriseringsmetings moet ook daarmee uitgevoer word. Die meetinstrumente wat in hierdie studie gebruik is, is steekproefneming-ossilloskope en direkte steekproefneming-sisteme. Die tekortkominge van elke instrument is ondersoek en bespreek. Die finale meting wat uitgevoer is, dra by tot die werk wat geassosieer word met die SKA. Dit behels antennapatroonkalibrasie, voortplanting van elektromagnetiese golwe oor afstand en die SE van ’n "berm"wat gebou is uit Karoo-grond. Hierdie sisteem is gebruik om die voortplantings-verswakking oor die Karoo-grond en plantegroei te ondersoek en dit lyk baie belowend. ’nWye spektrumis oor ’n paar kilometer gemeet en dit is met wrywinglose ruimte vergelyk. Die SE van die "berm"het dieselfde spektrale bandwydte gedek. In hierdie meting is verstrooiingseffekte en mespunt-diffraksie waargeneem.

This research investigates existing relationships between the three apparently unrelated subjects: Markov process, Semigroups and Partial difierential equations. Markov processes define semigroups through their transition functions. Conversely particular semigroups determine transition functions and can be regarded as Markov processes. We have exploited these relationships to study some Markov chains. The infnitesimal generator of a Feller semigroup on the closure of a bounded domain of Rn; (n ^ 2), is an integro-diferential operator in the interior of the domain and verifes a boundary condition. The existence of a Feller semigroup defined by a diferential operator and a boundary condition is due to the existence of solution of a bounded value problem. From this result other existence suficient conditions on the existence of Feller semigroups have been obtained and we have applied some of them to construct Feller semigroups on the unity disk of R2. / Decision Sciences / M. Sc. (Operations Research)

La première partie de cette thèse présente une revue historique sur les méthodes d'enregistrements d'activité neuronale, suivie par une étude sur une nouvelle technique d'imagerie pour le poisson zèbre : la microscopie par nappe laser 2 photon. En combinant, les avantages de la microscopie 2 photon et l'imagerie par nappe de lumière, le microscope par nappe laser 2 photon garantie des enregistrements à haute vitesse avec un faible taux de lésions photoniques et permet d'éviter l'une des principales limitations du microscope à nappe laser 1 photon: la perturbation du système visuel. La deuxième partie de cette thèse traite de la navigation dirigée. Après une revue exhaustive sur la chemotaxis, la phototaxis et la thermotaxis, nous présentons des résultats qui révèlent les bases neuronales de la phototaxis chez le poisson zèbre. Grace à des expériences de comportement en réalité-virtuelle, des enregistrements d'activité neuronale, des méthodes optogénétiques et des approches théoriques, ce travail montre qu'une population auto-oscillante située dans le rhombencéphale appelée l'oscillateur du cerveau postérieur (HBO) fonctionne comme un pacemaker des saccades oculaires et contrôle l'orientation des mouvements de nage du poisson zèbre. Ce HBO répond à la lumière en fonction du contexte moteur, biaisant ainsi la trajectoire du poisson zèbre vers les zones les plus lumineuses de son environnement (phototaxis). La troisième partie propose une discussion sur les bases neuronales des saccades oculaires chez les vertébrés. Nous concluons ce manuscrit avec des résultats préliminaires suggérant que chez le poisson zèbre, le même HBO est impliqué dans les processus de thermotaxis. / The first part of this thesis presents an historical overview of neural recording techniques, followed by a study on the development of a new imaging method for zebrafish neural recording: two-photon light sheet microscopy. Combining the advantages of two-photon point scanning microscopy and light sheet techniques, the two-photon light sheet microscope warrants a high acquisition speed with low photodamage and allows to circumvent the main limitation of one-photon light sheet microscopy: the disturbance of the visual system. The second part of the thesis is focused on goal-directed navigation in zebrafish larvae. After an exhaustive review on chemotaxis, phototaxis and thermotaxis in various animal models, we report a study that reveals the neural computation underlying phototaxis in zebrafish. Combining virtual-reality behavioral assays, volumetric calcium recordings, optogenetic stimulation, and circuit modeling, this work shows that a self-oscillating hindbrain population called the hindbrain oscillator (HBO) acts as a pacemaker for ocular saccades, controls the orientation of successive swim-bouts during zebrafish larva navigation, and is responsive to light in a state-dependent manner such that its response to visual inputs varies with the motor context. This peculiar response to visual inputs biases the fish trajectory towards brighter regions (phototaxis). The third part provides a discussion on the neural basis of ocular saccades in vertebrates. We conclude with some recent preliminary results on heat perception in zebrafish suggesting that the same hindbrain circuit may be at play in thermotaxis as well.

The author focuses on the possibility of using wood chips as fuel for tractors and machinery in agriculture and related fields, in order to increase self-sufficiency and achieving carbon neutrality. The work compares wood and conventional motor fuels in the real operation. Part of this thesis is to design a functional device with an output of 5-10 kW.

Made available in DSpace on 2015-03-26T12:30:59Z (GMT). No. of bitstreams: 1 texto completo.pdf: 959343 bytes, checksum: d150e2e757e58574596f5386c116d0ad (MD5) Previous issue date: 2007-10-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work aimed to analyze cherry coffee drying after wet removal of skin and mucilage in an intermittent concurrent flow batch dryer using a heat pump to condition the drying air. To evaluate the technical viability and operational cost of this system, a comparative study was carried out using a fixed-bed dryer, using a gas heat generator, liquefied gas of petroleum (LGP), as heat source for the drying air. Drying air temperature was 40 °C in the intermittent concurrent flow batch dryer and during predrying in the fixedbed dryer. For complete drying in the fixed-bed dryer, drying air temperature was 50 °C. Three tests were carried out for each drying system studied. Coffee (Coffea arabica L.) was the product used. As control, an elevated patio under the sun was used with one drying being conducted for each assay until the coffee reached a final moisture content of 11.0 ± 0.5% w.b., to compare the quality of the final product. To evaluate the drying energy efficiency of the systems, fuel and electric energy consumptions were determined. Based on the results obtained, it was possible to observe a lower energy specific consumption in the intermittent concurrent flow batch dryer in all tests, compared to the fixed-bed dryer. Performance coeficient (PCO ) of the heat pump presented 2.3; 2.4 and 2.5 for tests 1, 2 and 3, respectively. The operational cost of the complementary drying per 60 kg bag of processed coffee was R$ 16.00, R$ 15.89 and R$ 18.48 for tests 1, 2 and 3, respectively, for the intermittent concurrent flow batch dryer; and R$ 7.66, R$ 6.44 and R$ 5.57, for tests 1, 2 and 3, respectively, for the fixed-bed dryer. The final quality of the product was not compromised when drying under the two systems was compared with their respective control samples. / Objetivou-se com este trabalho analisar a secagem de café cereja descascado e desmucilado em secador de café em lotes intermitentes de fluxos concorrentes, utilizando uma bomba de calor para condicionar o ar de secagem. Na avaliação da viabilidade técnica e do custo operacional deste sistema, fez-se um estudo comparativo com o sistema de secagem para café em secador de leito fixo em leiras, utilizando, como fonte de aquecimento do ar de secagem, um gerador de calor a gás, tendo sido utilizado neste trabalho o gás liqüefeito de petróleo (GLP). A temperatura do ar de secagem foi de 40 °C no secador de café em lotes intermitentes de fluxos concorrentes e durante a pré- secagem no secador de leito fixo em leiras. Na secagem completa no secador de leito fixo em leiras, a temperatura do ar de secagem foi de e 50 °C. Foram realizados três testes para cada um dos sistemas de secagem estudados. Utilizou- se como produto o café (Coffea arabica L.). Como amostra testemunha, fez-se, em terreiro suspenso, ao sol, uma secagem para cada ensaio até que o café atingisse o teor final de umidade de 11,0 ± 0,5% b.u., visando à comparação de qualidade final do produto. Para a avaliação da eficiência energética de secagem dos sistemas, determinaram-se o consumo de combustível e o consumo de energia elétrica. Com base nos resultados obtidos, foi possível observar menor consumo específico de energia no secador de café em lotes intermitentes de fluxos concorrentes em todos os testes, quando comparados com o secador de leito fixo em leiras. O coeficiente de desempenho (COP ) da bomba de calor apresentou valores de 2,3; 2,4 e 2,5 para os testes 1, 2 e 3, respectivamente. O custo operacional da secagem complementar, por saca de 60 kg de café beneficiado, foi de R$ 16,00, R$ 15,89 e R$ 18,48 para os testes 1, 2 e 3, respectivamente, para a secagem no secador de café em lotes intermitente de fluxos concorrentes; e de R$ 7,66, R$6,44 e R$ 5,57, para os testes 1, 2 e 3, respectivamente, para a secagem no secador de leito fixo em leiras. A qualidade final do produto não foi comprometida quando comparada com as secagens nos dois sistemas estudados com suas respectivas amostras testemunhas.