Induction motor (IM) drives are employed in a wide range of industries due to low maintenance, improved efficiency and low emissions. Industrial installations of high-power IM drives rated up to 30 MW have been reported. The IM drives are also employed in ultra high-speed applications with shaft speeds as high as 500; 000 rpm. Certain applications of IM drives such as gas compressors demand high power at high speeds (e.g. 10 MW at 20; 000 rpm). In high-power voltage source inverter (VSI) fed induction motor drives, the semiconductor devices experience high switching energy losses during switching transitions. Hence, the switching frequency is kept low in such high-power drives. In high-speed drives, the maximum modulation frequency is quite high. Hence, at high speeds and/or high power levels, the ratio of switching frequency to fundamental frequency (i.e. pulse number, P ) of the motor drive is quite low. Induction motor drives, operating at low-pulse numbers, have significant low-order volt-age harmonics in the output. These low-order voltage harmonics are not filtered adequately by the motor inductance, leading to high total harmonic distortion (THD) in the line current as well as low-order harmonic torques. The low-order harmonic torques may lead to severe torsional vibrations which may eventually damage the motor shaft. This thesis addresses numerous issues related to low-pulse-number operation of VSI fed IM drives. In particular, optimal pulse width modulation (PWM) schemes for minimization of line current distortion and those for minimization of a set of low-order harmonic torques are proposed for two-level and three-level inverter fed IM drives. Analytical evaluation of current ripple and torque ripple is well established for the induction motor drives operating at high pulse numbers. However, certain important assumptions made in this regard are not valid when the pulse number is low. An analytical method is proposed here for evaluation of current ripple and torque ripple in low-pulse-number induction motor drives. The current and torque harmonic spectra can also be predicted using the proposed method. The analytical predictions of the proposed method are validated through simulations and experimental results on a 3:7-kW induction motor drive, operated at low pulse numbers. The waveform symmetries, namely, half-wave symmetry (HWS), quarter-wave symmetry (QWS) and three-phase symmetry (TPS), are usually maintained in induction motor drives, operating at low switching frequencies. Lack of HWS is well known to introduce even harmonics in the line current. Impact of three-phase symmetry on line current and torque harmonic spectra is analyzed in this thesis. When the TPS is preserved, there are no triplen frequency components in the line current and also no harmonic torques other than those of order 6, 12, 18 etc. While TPS ensures that the triplen harmonics in the three-phase pole voltages are in phase, these triplen frequency harmonics form balanced sets of three-phase voltages when TPS is not preserved. Hence, triplen frequency currents flow through the stator windings. These result in torque harmonics of order 2, 4, 6, 8, 10 etc., and not just integral multiples of 6. These findings are well supported by simulation and experimental results. One can see that two types of pole voltage waveforms are possible, when all waveform symmetries (i.e. HWS, TPS and QWS) are preserved in a two-level inverter, These are termed as type-A and type-B waveforms here. Also, QWS could be relaxed, while maintain-ing HWS and TPS, leading to yet another type of pole voltage waveform. Optimal switching angles to minimize line current THD are reported for all three types of pole voltage wave-forms. Theoretical and experimental results on a 3:7-kW IM drive show that optimal type-A PWM and optimal type-B PWM are better than each other in different ranges of modulation at any given low pulse number. In terms of current THD, the optimal PWM without QWS is found to be close to the better one between optimal type-A and optimal type-B at any modulation index for a given P . A combined optimal PWM to minimize THD is proposed, which utilizes the superior one between optimal type-A and optimal type-B at any given modulation index and pulse number. The performance of combined optimal PWM is shown to be better than those of synchronous sine-triangle (ST) PWM and selective harmonic elimination (SHE) PWM through simulations and experiments over a wide range of speed. A frequency domain (FD) based and another synchronous reference frame (SRF) based optimal PWM techniques are proposed to minimize low-order harmonic torques. The objective here is to minimize the combined value of low-order harmonic torques of order 6, 12, 18, ..., 6(N 1), where N is the number of switching angles per quarter cycle. The FD based optimal PWM is independent of load and machine parameters while the SRF based method considers both load and machine parameters. The offline calculations are much simpler in case of FD based optimal PWM than in case of SRF based optimal PWM. The performance of the two schemes are comparable and are much superior to those of synchronous ST PWM and SHE PWM in terms of low-order harmonic torques as shown by the simulation and experimental results presented over a wide range of fundamental frequency, The proposed optimal PWM methods for two level-inverter fed motor drives to minimize the line current distortion and low-order torque harmonics, are extended to neutral point clamped (NPC) three-level inverter fed drive. The proposed optimal PWM methods for the NPC inverter are compared with ST PWM and SHE PWM, having the same number of switching angles per quarter. Simulation and experimental results on a 3:7-kW induction motor drive demonstrate the superior performance of proposed optimal PWM schemes over ST PWM and SHE PWM schemes. The di_erent optimal PWM schemes proposed for two-level and three-level inverter fed drives, having di_erent objective functions and constraints, are all analyzed from a space vector perspective. The three-phase PWM waveforms are seen as a sequence of voltage vector applied in each case. The space vector analysis leads to determination of optimal vector sequences, fast o_ine calculation of optimal switching angles and e_cient digital implementation of the proposed optimal PWM schemes. A hybrid PWM scheme is proposed for two-level inverter fed IM drive, having a maximum switching frequency of 250 Hz. The proposed hybrid PWM utilizes ST PWM at a _xed frequency of 250 Hz at low speeds. This method employs the optimal vector sequence to minimize the current THD at any speed in the medium and high speed ranges. The proposed method is shown to reduce both THD as well as machine losses signi_cantly, over a wide range of speed, compared to ST PWM Position sensorless vector control of IM drive also becomes challenging when the ratio of inverter switching frequency to maximum modulation frequency is low. An improved procedure to design current controllers, and a closed-loop ux estimator are reviewed. These are utilized to design and implement successfully a position sensorless vector controlled IM drive, modulated with asynchronous third harmonic injected (THI) PWM at a constant switching frequency of 500 Hz. Sensorless vector control is also implemented successfully, when the inverter is modulated with synchronized THI PWM and the maximum switching frequency is limited to 500 Hz.

The use of insulated-gate bipolar transistor (IGBT)-based power converters is increasing exponentially. This is due to high performance of these devices in terms of efficiency and switching speed. However, due to the switching action, high frequency electromagnetic interference (EMI) noises are generated. Design of a power converter with reduced EMI noise level is one of the primary objectives of this research. The first part of the work focuses on designing common-mode (CM) filters, which can be integrated with differential-mode (DM) filters for three-phase pulse-width modulation (PWM) rectifier-based motor drives. This work explores the filter design based on the CM equivalent circuit of the drive system. Guidelines are provided for selection of the filter components. Different variants of the filter topology are evaluated to establish the effectiveness of the proposed topology. Analytical results based on Bode plot of the transfer functions are presented, which suggest effective EMI reduction. Experimental results based on EMI measurement on the grid side and CM current measurement on the motor side are presented. These results validate the effectiveness of the filter. In the second part of the work, it is shown that inclusion of CM filters into DM filters results in resonance oscillations in the CM circuit. An active damping strategy is proposed to damp the oscillations in both line-to-line and line-to-ground ac voltages and currents. An approach based on pole placement by state feedback is used to actively damp both the DM and CM filter oscillations. Analytical expressions for state-feedback controller gains are derived for both continuous-and discrete-time models of the filter. Trade-off in selection of the active damping gain on the lower-order grid current harmonics is analysed using a weighted admittance function method. In the third part of the work, single-phase grid-connected power converters are considered. An integrated CM filter with DM LCL filter is proposed. The work explores the suitability of PWM methods for single-phase and parallel single-phase grid-connected power converters. It is found that bipolar PWM and unipolar PWM with 180◦interleaving angle are suitable for single-phase and parallel single-phase power converters, respectively. The proposed configuration along with the PWM methods reduces the CM voltage, CM current, and EMI noise level effectively. It is also shown that the suggested circuit is insensitive to nonidealities of the power converter such as dead-time mismatch, mismatch in converter-side inductors, unequal turn on and turn off of the switches, and propagation delays. In the fourth part of the work, the inter-phase inductor in parallel interleaved power converters is integrated with LCL filter boost inductor. Different variant designs are presented and compared with the proposed structure. It is shown that the proposed structure makes use of standard core geometries and consumes lesser core material as well as copper wire. Hence, it reduces the overall size and cost of the power converter. In the present work, a 10kVA three-phase back-to-back connected with input LCL filter and output dv/dt filter, a 5kVA single-phase grid-connected power converter with LCL filter, and a 7.5kVA parallel single-phase grid-connected power converter with LCL filter are fabricated in the laboratory to evaluate and validate the proposed methods. The experimental results validate the proposed methods that result in significant EMI performance improvement of grid-connected power converters.

Voltage source inverter (VSI) fed induction motors are increasingly used in industrial and transportation applications as variable speed drives. However, VSIs generate non-sinusoidal voltages and hence result in harmonic distortion in motor current, motor heating, torque pulsations and increased acoustic noise. Most of these undesirable effects can be reduced by increasing the switching frequency of the inverter. This is not necessarily true for acoustic noise. Acoustic noise does not decrease monotonically with increase in switching frequency since the noise emitted depends on the proximity of harmonic frequencies to the motor resonant frequencies. Also there are practical limitations on the inverter switching frequency on account of device rating and losses. The switching frequency of many inverters often falls in the range 2 kHz - 6 kHz where the human ear is highly sensitive. Hence, the acoustic noise emission from the motor drive is of utmost important. Further, the acoustic noise emitted by the motor drive is known to depend on the waveform quality of the voltage applied. Hence, the acoustic performance varies with the pulse width modulation (PWM) technique used to modulate the inverter, even at the same modulation index. Therefore a comprehensive study on the acoustic noise aspects of induction motor drive is required. The acoustic noise study of the motor drive poses multifaceted challenges. A simple motor model is sufficient for calculation of total harmonic distortion (THD). A more detailed model is required for torque pulsation studies. But the motor acoustic noise is affected by many other factors such as stator winding distribution, space harmonics, geometry of stator and rotor slots, motor irregularities, structural issues controlling the resonant frequency and environmental factors. Hence an accurate model for acoustic noise would have to be very detailed and would span different domains such as electromagnetic fields, structural engineering, vibration and acoustics. Motor designers employ such detailed models along with details of the materials used and geometry to predict the acoustic noise that would be emitted by a motor and also to design a low-noise motor. However such detailed motor model for acoustic noise purposes and the necessary material and constructional details of the motor are usually not available to the user. Also, certain factors influencing the acoustic noise change due to wear and tear during the operational life of the motor. Hence this thesis takes up an experimental approach to study the acoustic noise performance of an inverter-fed induction motor at any stage of its operating life. A 10 kVA insulated gate bipolar transistor (IGBT) based inverter is built to feed the induction motor; a 6 kW and 2.3 kW induction motors are used as experimental motors. A low-cost acoustic noise measurement system is also developed as per relevant standards for measurement and spectral analysis of the acoustic noise emitted. For each PWM scheme, the current and acoustic noise measurements are carried out extensively at different carrier frequencies over a range of fundamental frequencies. The main cause of acoustic noise of electromagnetic origin is the stator core vibration, which is caused by the interaction of air-gap fluxes produced by fundamental current and harmonic currents. In this thesis, an experimental procedure is suggested for the acoustic noise characterization of an induction motor inclusive of determination of resonant frequencies. Further, based on current and acoustic noise measurements, a vibration model is proposed for the stator structure. This model is used to predict the acoustic noise pertaining to time harmonic currents with reasonable accuracy. Literature on motor acoustic noise mainly focuses on sinusoidal PWM (SPWM), conventional space vector PWM (CSVPWM) and random PWM (RPWM). In this thesis, acoustic noise pertaining to two bus-clamping PWM (BCPWM) schemes and an advanced bus-clamping PWM (ABCPWM) scheme is investigated. BCPWM schemes are mainly used to reduce the switching loss of the inverter by clamping any of the three phases to DC rail for 120◦ duration of the fundamental cycle. Experimental results show that these BCPWM schemes reduce the amplitude of the tonal component of noise at the carrier frequency, compared to CSVPWM. Experimental results with ABCPWM show that the overall acoustic noise produced by the motor drive is reduced at low and medium speeds if the switching frequency is above 3 kHz. Certain spread in the frequency spectrum of noise is also seen with both BCPWM and ABCPWM. To spread the acoustic noise spectrum further, many variable-frequency PWM schemes have been suggested by researchers. But these schemes, by and large, increase the current total harmonic distortion (THD) compared to CSVPWM. Thus, a novel variable-frequency PWM (VFPWM) method is proposed, which offers reduced current THD in addition to uniformly spread noise spectrum. Experimental results also show spread in the acoustic noise spectrum and reduction in the dominant noise components with the proposed VFPWM. Also, the current THD is reduced at high speeds of the motor drive with the proposed method.

L'évolution de l'électronique de puissance depuis ces dernières années est le résultat des enjeux énergétiques actuels qui exigent, entre autres, des architectures de conversion d'énergie capables de traiter des puissances de plus en plus importantes. Parmi les éléments les plus caractéristiques de cette évolution, l'avancement technologique des composants semi-conducteurs (nouveaux composants SiC ou GaN) ainsi que la conception de nouvelles architectures de convertisseurs statiques jouent un rôle important. Parmi ces architectures, différentes associations basées sur la connexion en série et en parallèle de cellules de commutation classiques ont été proposées. Ces associations permettent d'augmenter la puissance traitée par les convertisseurs sans accroitre les contraintes au niveau des interrupteurs. Elles permettent également l'obtention de signaux de sortie d'une meilleure qualité avec des fréquences apparentes de découpage plus importantes. Ces architectures utilisent des éléments de stockage d'énergie qui diminuent les contraintes au niveau des interrupteurs mais qui exigent, en revanche, une régulation précise des grandeurs de tension ou de courant propres à ces éléments. Pour l'association en série, les tensions des condensateurs doivent rester autour d'une fraction de la tension du bus d'entrée. Pour l'association en parallèle, le courant de sortie doit être réparti équitablement entre les différents bras afin d'éviter les phénomènes non linéaires propres aux éléments magnétiques utilisés dans les inductances (séparées ou magnétiquement couplées). Dans la première partie de cette thèse, nous présentons les généralités de l'association en série et parallèle des cellules de commutation. La modélisation des éléments magnétiques utilisés pour la mise en parallèle est également détaillée dans le but d'identifier de possibles sources de déséquilibre sur la répartition du courant de sortie. Une modélisation matricielle est appliquée pour simplifier la relation entre les variables propres à chaque association et les ordres de commande de toutes les cellules. Cette modélisation matricielle sera la base des stratégies de commande que nous avons développées dans la suite de nos travaux. Dans la deuxième partie de cette thèse, nous présentons les différentes stratégies de commande pouvant être appliquées sur ces convertisseurs. Les premières stratégies sont basées sur une approche classique utilisant un modulateur, un générateur d'ordres de commande et des régulateurs de type linéaire pour la régulation des variables internes et externes de chaque association. En termes de modulateurs, nous présentons principalement un modulateur de type PS (Phase Shifted), tandis que quelques applications et résultats sont présentés pour un modulateur de type PD (Phase Disposition). D'autres stratégies basées sur la commande prédictive sont également présentées. La première est la stratégie MPC qui utilise une fonction de coût pour choisir l'état optimal du convertisseur pour chaque période d'échantillonnage. Cette stratégie a été introduite récemment dans le domaine des convertisseurs statiques et présente des avantages liées à la facilité de sa mise en place ainsi qu'aux réponses du système lors des régimes transitoires. La deuxième stratégie, basée sur la commande prédictive, utilise des instants de commutation variables, une fonction de coût simplifiée et une machine d'état. Cette dernière permet de gérer les ordres de commande de toutes les cellules de commutation en fonction des variables à réguler. En plus des avantages liés à la stratégie MPC, sa mise en place est bien plus simple car elle fonctionne à une fréquence de découpage fixe et s'adapte facilement à différents points de fonctionnement. Dans la dernière partie de cette thèse, nous présentons l'implantation expérimentale de ces stratégies afin de valider leur performance sur les convertisseurs multicellulaires. / In the last years, the development in the power electronics field is the result of the current energy challenges. These challenges require power converters able to work with increasingly important powers. Among the most characteristic elements of this development, we can find the technological advancements of the semiconductor devices (based principally in SiC and GaN) and the conception of new power converters topologies. These new power converter topologies are principally based on the serial and parallel association of classical commutation cells. With these associations, the energy treated by the converter can be increased using the current semiconductor technology. The quality of the output signals can also be improved with higher apparent switching frequencies. These associations use elements for storing energy, such as inductors or capacitors. They equally allow the reduction of the constraints on the switches given the higher voltages and currents. However, the use of these elements requires a good control of the capacitors' voltage for the serial connection and a good distribution of the output current among the different phases for the parallel connection. In the parallel connection, when we use Inter Cells Transformers (ICT) instead of classical inductors, all the phase currents reduce their ripples while their frequency is reduced. Nevertheless, some differences between all the phases' currents can entail non-linear phenomena, producing perturbations and instabilities in the system. In the serial connection, the capacitor voltages must stay around a fraction of the input voltage in order to get an optimal multilevel output voltage. In the first part of this thesis, we present the generalities of the serial and parallel association of classical commutation cells. Different models of magnetic elements are used for getting a better representation of an ICT; these models are used for finding possible sources of currents imbalances. A matrix model is used to simplify the relationship between the control variables with the control of each commutation cell. In the second part of this thesis, some control strategies that can be applied with these converters are presented. The first strategy is based on a conventional approach that uses a modulator, a state machine for generating the commands of each cell and linear regulators for controlling the internal and external variables (output voltage and currents, capacitors in the serial association and the distribution of the current for the parallel connection). In terms of modulators, we present primarily a PS (Phase Shifted) modulator while some applications and results are presented for a PD (Phase Disposition) modulator. Other strategies based on predictive control are also presented. The first of these strategies is the classical MPC (model predictive control) strategy that uses a cost function to select the optimal state of the converter for each sampling period. This strategy has recently been introduced in the field of static converters and it has several advantages related to the facility of its implementation and the optimal transient responses. The second strategy uses variable switching instants, a simplified cost function and a state machine. The state machine is used to manage the capacitors' voltages and the differential currents (differences between the phase currents) while the cost function is used for controlling the output voltage and current. This strategy is simpler to be implemented, presents fast transient responses and works with a fixed switching frequency in different operating points. In the last part of this thesis, we present the experimental implementation of these strategies in order to validate their performance in the power converters based in the serial and parallel association of classical commutation cells.

No description available.

No description available.

Position weight matrices (PWMs) have become a tool of choice for the identification of transcription factor binding sites in DNA sequences. PWMs are compiled from experimentally verified and aligned binding sequences. PWMs are then used to computationally discover novel putative binding sites for a given protein. DNA-binding proteins often show degeneracy in their binding requirement, the overall binding specificity of many proteins is unknown and remains an active area of research. Although PWMs are more reliable predictors than consensus string matching, they generally result in a high number of false positive hits. A previous study introduced a novel method to PWM training based on the known motifs to sample additional putative binding sites from a proximal promoter area. The core idea was further developed, implemented and tested in this thesis with a large scale application. Improved mono- and dinucleotide PWMs were computed for Drosophila melanogaster. The Matthews correlation coefficient was used as an optimization criterion in the PWM refinement algorithm. New PWMs keep an account of non-uniform background nucleotide distributions on the promoters and consider a larger number of new binding sites during the refinement steps. The optimization included the PWM motif length, the position on the promoter, the threshold value and the binding site location. The obtained predictions were compared for mono- and dinucleotide PWM versions with initial matrices and with conventional tools. The optimized PWMs predicted new binding sites with better accuracy than conventional PWMs.

Depuis une bonne dizaine d'année, l'aéronautique a entamé sa mutation vers le "plus électrique".L'objectif étant de réduire la consommation de carburant, une des contraintes majeures de ces nouvelles solutions est de réduire la masse embarquée. Les filtres dimensionnés pour les convertisseurs statiques doivent donc être optimisés au mieux vis-à-vis de ce critère, ainsi que du volume. Il y a donc un fort besoin du côté des concepteurs d’avions de savoir quels choix parmi les différentes possibilités technologiques sont optimaux, et de connaître l'impact de ces choix sur le poids, le coût global et le volume de l'équipement. Le filtre CEM représente généralement environ 30% du coût et du volume d'un convertisseur électronique de puissance. Il va de soi que le volume et/ou la masse de ces filtres doit être optimisé. L'impact de la loi de commande du convertisseur, le choix des semi-conducteurs, du packaging, câbles (longueur et intégration dans l’avion), des machines électriques,...doivent être parfaitement connus pour atteindre un dimensionnement optimal.Dans cette perspective, les objectifs de ces travaux de thèse visent à fournir non seulement une démarche méthodologique pour la modélisation haute fréquence des variateurs de vitesse dédiés aux applications aéronautiques mais aussi une approche de dimensionnement par optimisation des filtres CEM. Pour cela, un outil logiciel évolutif d’aide à la génération rapide des modèles CEM est proposé. Une description modulaire et une mise en équation automatique du modèle fréquentiel complet ainsi que des gradients en facilitent l'utilisation en procédures d’optimisation sous contraintes. L’approche présentée dans ces travaux est relativement générique : la topologie du filtre, de la structure du convertisseur, du câblage et la loi de commande peuvent être facilement recalculées, grâce à cet environnement logiciel. / The More Electrical Aircraft concept is very promising regarding energy saves, but generates new problems, and especially the emergence of new power electronics loads on the electrical network. Keeping the same level of safety in the aircraft means developing these switching mode converters in accordance with the aircraft standards, as the DO160. This is not obvious since weights of equipments are especially constrained: indeed, the objective of weight and energy save needs to be balanced with the additional weight and volume of the required EMI filters. There is thus a strong need in helping the aircraft designers to choose among the various technological possibilities, and to know the impact of these choices on the global weight, cost and volume of the embedded equipments. The EMI filter usually represents roughly 30% of the cost and volume of a power electronics converter, and it is very important to optimize it. The impact of the converter control law, semiconductors choice, interconnects realization, harness selection and placement, electrical motors characteristics… should be perfectly known in order to reach a good system design. In this perspective, the objectives of this thesis are to provide not only an approach for modelling high frequency variable speed drives dedicated to aerospace applications but also a methodology to optimize the required EMI filters. For this purpose, new architecture software dedicated to the rapid generation of EMC models is proposed. A modular description and a complete automatic model generation facilitate the use by the designer in optimization procedures thanks to automatic gradient computation.The methodology presented in this work is not specifically developed for a given application. It is a very generic approach: the topology of the filter, the structure of the inverters, interconnects and the control law can be easily recalculated, using this software environment. Consequently, the impact of all these elements on the electromagnetic disturbances can be characterized, and the EMI filter optimized.

The objective of this master's thesis is new power converter design for bicycle with combustion engine and electric power transmission. The power converter is control by microprocessor and control algorithm is designed to achieve maximum efficiently of combustion engine. Converter and servomotor for controlling combustion engine throttle are located in metal box. Hardware, firmware and metal box are designed in the thesis.

Master thesis deals with design controllable switching power source. Device is supplied and controlled via USB bus of PC. The required output parameters are specified by user in a computer application. The teoretical part includes method of USB communication and introduction to switching power sources with focus on a Sepic topologii. The practical part describe individual circuit solution which contains of a complete device. Is analyzed in detail the proposal Sepic converter circuit and controling by microcontroller. The work also includes the design of microcontroller and computer applications. The result of this thesis is a functional device on which is the performed measurement.