Multiphase induction motor drives - a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio

The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

Grid integration of renewable power generation

This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation.This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

A Comparative Analysis of Two Approaches in Envelope Tracking Power Supplies for Satellite Applications

In modern telecommunication systems, the requirements for amount of transmitted data are increasing. In order to transmit as much information as possible for a given spectral band, both amplitude and phase modulation are applied. The main power consumers in transmitters are power amplifiers(PA), placed in the output stage. During the last decade, a lot of efforts have been invested in optimization of the efficiency of RF power amplifiers. One of notable techniques is Kahn’s envelope and restoration (EER) principle, where highly efficient envelope tracker and non-linear RF amplifier (e.g. class E, F) are combined. In this paper, two different approaches in envelope tracking are presented. The first approach is based on an analog multiplexer and a linear regulator in series, while the second tracker consists of PWM controlled switches and the fourth order output filter. Both trackers are supplied with highly efficient (96%) switch-capacitor based multilevel power converter, which acts as a voltage divider. Additionally, the comparison between two prototypes of the first approach, with Si and GaN based transistors is presented. Experimental results show that peak efficiencies are 73% (Si) and 75% (GaN), in the case of a 5 MHz 64QAM reference signal, with 10 W average output power. For the second approach, different filter prototypes are analysed. Moreover, their impact on envelope signal processing is backed up with the simulation results and the experimental results for tracking of a 2 MHz 64QAM reference are presented, with 78% achieved efficiency (Si technology) and 9 W average output power

Digital Control of Power Converters and Drives for Hybrid Traction and Wireless Charging

In the last years environmental issues and constant increase of fuel and energy cost have been incentivizing the development of low emission and high efficiency systems, either in traction field or in distributed generation systems from renewable energy sources. In the automotive industry, alternative solutions to the standard internal combustion engine (ICE) adopted in the conventional vehicles have been developed, i.e. fuel cell electric vehicles (FCEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEV) or pure electric vehicles (EVs), also referred as battery powered electric vehicles (BEV). Both academic and industry researchers all over the world are still facing several technical development areas concerning HEV components, system topologies, power converters and control strategies. Efficiency, lifetime, stability and volume issues have moved the attention on a number of bidirectional conversion solutions, both for the energy transfer to/from the storage element and to/from the electric machine side. Moreover, along with the fast growing interest in EVs and PHEVs, wireless charging, as a new way of charging batteries, has drawn the attention of researchers, car manufacturers, and customers recently. Compared to conductive power transfer (usually plug-in), wireless power transfer (WPT) is more convenient, weather proof, and electric shock protected. However, there is still more research work needs to be done to optimize efficiency, cost, increase misalignment tolerance, and reduce size of the WPT chargers. The proposed dissertation describes the work from 2012 to 2014, during the PhD course at the Electric Drives Laboratory of the University of Udine and during my six months visiting scholarship at the University of Michigan in Dearborn. The topics studied are related to power conversion and digital control of converters and drives suitable for hybrid/electric traction, generation from renewable energy sources and wireless charging applications. From the theoretical point of view, multilevel and multiphase DC/AC and DC/DC converters are discussed here, focusing on design issues, optimization (especially from the efficiency point-of-view) and advantages. Some novel modulation algorithms for the neutral-point clamped three-level inverter are presented here as well as a new multiphase proposal for a three-level buck converter. In addition, a new active torque damping technique in order to reduce torque oscillations in internal combustion engines is proposed here. Mainly, two practical implementations are considered in this dissertation, i.e. an original two-stage bi-directional converter for mild hybrid traction and a wireless charger for electric vehicles fast charge

Advance control of multilevel converters for integration of distributed generation resources into ac grid

Premi extraordinari doctorat curs 2011-2012, àmbit d’Enginyeria IndustrialDistributed generation (DG) with a converter interface to the power grid is found in many of the green power resources applications. This dissertation describes a multi-objective control technique of voltage source converter (VSC) based on multilevel converter topologies, for integration of DG resources based on renewable energy (and non-renewable energy)to the power grid. The aims have been set to maintain a stable operation of the power grid, in case of di erent types of grid-connected loads. The proposed method provides compensation for active, reactive, and harmonic load current components. A proportional-integral (PI) control law is derived through linearization of the inherently non-linear DG system model, so that the tasks of current control dynamics and dc capacitor voltage dynamics become decoupled. This decoupling allows us to control the DG output currents and the dc bus voltage independently of each other, thereby providing either one of these decoupled subsystems a dynamic response that signi cantly slower than that of the other. To overcome the drawbacks of the conventional method, a computational control delay compensation method, which delaylessly and accurately generates the DG reference currents, is proposed. The rst step is to extract the DG reference currents from the sensed load currents by applying the stationary reference frame and then transferred into synchronous reference frame method, and then, the reference currents are modi ed, so that the delay will be compensated. The transformed variables are used in control of the multilevel voltage source converter as the heart of the interfacing system between DG resources and power grid. By setting appropriate compensation current references from the sensed load currents in control circuit loop of DG link, the active, reactive, and harmonic load current components will be compensated with fast dynamic response, thereby achieving sinusoidal grid currents in phase with load voltages while required power of loads is more than the maximum injected power of the DG resources. The converter, which is controlled by the described control strategy, guarantees maximum injection of active power to the grid continuously, unity displacement power factor of power grid, and reduced harmonic load currents in the common coupling point. In addition, high current overshoot does not exist during connection of DG link to the power grid, and the proposed integration strategy is insensitive to grid overload.La Generació Distribuïda (DG) injectada a la xarxa amb un convertidor estàtic és una solució molt freqüent en l'ús de molts dels recursos renovables. Aquesta tesis descriu una técnica de control multi-objectiu del convertidor en font de tensió (VSC), basat en les topologies de convertidor multinivell, per a la integració de les fonts distribuïdes basades en energies renovables i també de no renovables.Els objectius fixats van encaminats a mantenir un funcionament estable de la xarxa elèctrica en el cas de la connexió de diferents tipus de càrregues. El mètode de control proposat ofereix la possibilitat de compensació de les components actives i reactives de la potencia, i les components harmòniques del corrent consumit per les càrregues.La llei de control proporcional-Integral (PI) s’obté de la linearització del model inherentment no lineal del sistema, de forma que el problema de control del corrent injectat i de la tensió d’entrada del convertidor queden desacoblats. Aquest desacoblament permet el control dels corrents de sortida i la tensió del bus de forma independent, però amb un d’ells amb una dinàmica inferior.Per superar els inconvenients del mètode convencional, s’usa un retard computacional, que genera les senyals de referència de forma acurada i sense retard. El primer pas es calcular els corrents de referència a partir de les mesures de corrent. Aquest càlcul es fa primer transformant les mesures a la referència estacionaria per després transformar aquests valors a la referència síncrona. En aquest punt es on es poden compensar els retards.Les variables transformades son usades en els llaços de control del convertidor multinivell. Mitjançant aquests llaços de control i les referències adequades, el convertidor és capaç de compensar la potencia activa, reactiva i els corrents harmònics de la càrrega amb una elevada resposta dinàmica, obtenint uns corrents de la xarxa de forma completament sinusoïdal, i en fase amb les tensions.El convertidor, controlat amb el mètode descrit, garanteix la màxima injecció de la potencia activa, la injecció de la potencia reactiva per compensar el factor de potencia de la càrrega, i la reducció de les components harmòniques dels corrents consumits per la càrrega. A més, garanteix una connexió suau entre la font d’energia i la xarxa. El sistema proposat es insensible en front de la sobrecarrega de la xarxaAward-winningPostprint (published version

Minimum time control for multiphase buck converter: analysis and application

The combination of minimum time control and multiphase converter is a favorable option for dc-dc converters in applications where output voltage variation is required, such as RF amplifiers and dynamic voltage scaling in microprocessors, due to their advantage of fast dynamic response. In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented. Compared with the traditional method, the proposed control takes into account the phase delay and current ripple in each phase. Therefore, by investigating the behavior of multiphase converter during voltage transition, it resolves the problem of current unbalance after the transient, which can lead to long settling time of the output voltage. The restriction of this control is that the output voltage that the converter can provide is related to the number of the phases, because only the duty cycles at which the multiphase converter has total ripple cancellation are used in this approach. The model of the proposed control is introduced, and the design constraints of the buck converters filter for this control are discussed. In order to prove the concept, a four-phase buck converter is implemented and the experimental results that validate the proposed control method are presented. The application of this control to RF envelope tracking is also presented in this paper

Developing A Medium-Voltage Three-Phase Current Compensator Using Modular Switching Positions

The objective of this thesis is to present the context, application, theory, design, construction, and testing of a proposed solution to unbalanced current loading on three-phase four-wire systems. This solution, known as the Medium-Voltage Unbalanced Current Static Compensator or MV-UCSC, is designed to recirculate currents between the three phases of adistribution system. Through this redistribution of the currents negative- and zero-sequence current components are eliminated and a balanced load is seen upstream from the point of installation. The MV-UCSC as it operates in the distribution system is presented followed by its effect on traditional compensation equipment. The construction of the MV-UCSC as well as 13.8 kV simulations are then shown. Development of the switching positions required by the MVUCSC is then given followed by a variation on this switching position with the intent to reduce part count. Finally, the testing the 13.8 kV three-phase four-wire, neutral-point-clamped, elevenlevel, flying-capacitor-based MV-UCSC connected directly to the grid is presented

Convertisseurs modulaires multiniveaux pour le transport d'énergie électrique en courant continu haute tension

Les travaux présentés dans ce mémoire ont été réalisés dans le cadre d’une collaboration entre le LAboratoire PLAsma et Conversion d’Énergie (LAPLACE), Université de Toulouse, et la Seconde Université de Naples (SUN). Ce travail a reçu le soutien de la société Rongxin Power Electronics (Chine) et traite de l’utilisation des convertisseurs multi-niveaux pour le transport d’énergie électrique en courant continu Haute Tension (HVDC). Depuis plus d’un siècle, la génération, la transmission, la distribution et l’utilisation de l’énergie électrique sont principalement basées sur des systèmes alternatifs. Les systèmes HVDC ont été envisagés pour des raisons techniques et économiques dès les années 60. Aujourd’hui il est unanimement reconnu que ces systèmes de transport d’électricité sont plus appropriés pour les lignes aériennes au-delà de 800 km de long. Cette distance limite de rentabilité diminue à 50 km pour les liaisons enterrées ou sous-marines. Les liaisons HVDC constituent un élément clé du développement de l’énergie électrique verte pour le XXIème siècle. En raison des limitations en courant des semi-conducteurs et des câbles électriques, les applications à forte puissance nécessitent l’utilisation de convertisseurs haute tension (jusqu’à 500 kV). Grâce au développement de composants semi-conducteurs haute tension et aux architectures multicellulaires, il est désormais possible de réaliser des convertisseurs AC/DC d’une puissance allant jusqu’au GW. Les convertisseurs multi-niveaux permettent de travailler en haute tension tout en délivrant une tension quasi-sinusoïdale. Les topologies multi-niveaux classiques de type NPC ou « Flying Capacitor » ont été introduites dans les années 1990 et sont aujourd’hui couramment utilisées dans les applications de moyenne puissance comme les systèmes de traction. Dans le domaine des convertisseurs AC/DC haute tension, la topologie MMC (Modular Multilevel Converter), proposée par le professeur R. Marquardt (Université de Munich, Allemagne) il y a dix ans, semble particulièrement intéressante pour les liaisons HVDC. Sur le principe d’une architecture de type MMC, le travail de cette thèse propose différentes topologies de blocs élémentaires permettant de rendre le convertisseur AC/DC haute tension plus flexible du point de vue des réversibilités en courant et en tension. Ce document est organisé de la manière suivante. Les systèmes HVDC actuellement utilisés sont tout d’abord présentés. Les configurations conventionnelles des convertisseurs de type onduleur de tension (VSCs) ou de type onduleur de courant (CSCs) sont introduites et les topologies pour les systèmes VSC sont ensuite plus particulièrement analysées. Le principe de fonctionnement de la topologie MMC est ensuite présenté et le dimensionnement des éléments réactifs est développé en considérant une commande en boucle ouverte puis une commande en boucle fermée. Plusieurs topologies de cellules élémentaires sont proposées afin d’offrir différentes possibilités de réversibilité du courant ou de la tension du côté continu. Afin de comparer ces structures, une approche analytique de l’estimation des pertes est développée. Elle permet de réaliser un calcul rapide et direct du rendement du système. Une étude de cas est réalisée en considérant la connexion HVDC d’une plateforme éolienne off-shore. La puissance nominale du système étudié est de 100 MW avec une tension de bus continu égale à 160 kV. Les différentes topologies MMC sont évaluées en utilisant des IGBT ou des IGCT en boitier pressé. Les simulations réalisées valident l’approche analytique faite précédemment et permettent également d’analyser les modes de défaillance. L’étude est menée dans le cas d’une commande MLI classique avec entrelacement des porteuses. Enfin, un prototype triphasé de 10kW est mis en place afin de valider les résultats obtenus par simulation. Le système expérimental comporte 18 cellules de commutations et utilise une plate-forme DSP-FPGA pour l’implantation des algorithmes de commande. ABSTRACT : This work was performed in the frame of collaboration between the Laboratory on Plasma and Energy Conversion (LAPLACE), University of Toulouse, and the Second University of Naples (SUN). This work was supported by Rongxin Power Electronic Company (China) and concerns the use of multilevel converters in High Voltage Direct Current (HVDC) transmission. For more than one hundred years, the generation, the transmission, distribution and uses of electrical energy were principally based on AC systems. HVDC systems were considered some 50 years ago for technical and economic reasons. Nowadays, it is well known that HVDC is more convenient than AC for overhead transmission lines from 800 - 1000 km long. This break-even distance decreases up to 50 km for underground or submarine cables. Over the twenty-first century, HVDC transmissions will be a key point in green electric energy development. Due to the limitation in current capability of semiconductors and electrical cables, high power applications require high voltage converters. Thanks to the development of high voltage semiconductor devices, it is now possible to achieve high power converters for AC/DC conversion in the GW power range. For several years, multilevel voltage source converters allow working at high voltage level and draw a quasi-sinusoidal voltage waveform. Classical multilevel topologies such as NPC and Flying Capacitor VSIs were introduced twenty years ago and are nowadays widely used in Medium Power applications such as traction drives. In the scope of High Voltage AC/DC converters, the Modular Multilevel Converter (MMC), proposed ten years ago by Professor R. Marquardt from the University of Munich (Germany), appeared particularly interesting for HVDC transmissions. On the base of the MMC principle, this thesis considers different topologies of elementary cells which make the High Voltage AC/DC converter more flexible and easy suitable respect to different voltage and current levels. The document is organized as follow. Firstly, HVDC power systems are introduced. Conventional configurations of Current Source Converters (CSCs) and Voltage Source Converters (VSCs) are shown. The most attractive topologies for VSC-HVDC systems are analyzed. The operating principle of the MMC is presented and the sizing of reactive devices is developed by considering an open loop and a closed loop control. Different topologies of elementary cells offer various properties in current or voltage reversibility on the DC side. To compare the different topologies, an analytical approach on the power losses evaluation is achieved which made the calculation very fast and direct. A HVDC link to connect an off-shore wind farm platform is considered as a case study. The nominal power level is 100 MW with a DC voltage of 160 kV. The MMC is rated considering press-packed IGBT and IGCT devices. Simulations validate the calculations and also allow analyzing fault conditions. The study is carried out by considering a classical PWM control with an interleaving of the cells. In order to validate calculation and the simulation results, a 10kW three-phase prototype was built. It includes 18 commutation cells and its control system is based on a DSP-FGPA platform