Switched capacitor converters:a new approach for high power applications

High-power, high-voltage and high voltage-conversion ratio DC-DC converters are an enabling technology for offshore DC grids of the future. These converters are required to interface between offshore wind farms and an offshore DC grid and a key design issue is the size and weight of the converter, which significantly impacts the cost of the associated off-shore platform. In addition to this application, some rural communities, particularly in Canada, Australia and South Africa,which are located far away from the electrical power generators, can take the advantages of this technology by tapping into existing HVDC transmission line using a high voltage-conversion ratio DC-DC converter. The work described in this thesis is an investigation as to how such DC-DC converters may be realised for these applications. First a review of existing DC-DC converters was carried out to assess their suitability for the target applications. A classification of DC-DC converters into Direct and Indirect converters was proposed in this work based on the manner in which the energy is transferred from the input to the output terminal of the converter. Direct DC-DC converters, particularly Switched Capacitor(SC) converters are more promising for high-voltage, high-power and high voltage-conversion ratio applications, since the converter can interface between the low-voltage and the high-voltage terminals using low-voltage and low-power power electronic modules. Existing SC topologies were examined to identify the most promising candidate circuits for the target applications. Four SC synthesis techniques were proposed in order to derive new SC circuits from existing topologies. A new 2-Leg Ladder, modular 2-Leg Ladder and bi-pole 2-Leg Ladder were devised, which had significant benefits in terms of size and weight when compared with existing circuits. A scaled power 1 kW converter was built in the laboratory in order to validate the analysis and compare the performance of the new 2-Leg ladder circuit against a conventional Ladder circuit, where it was shown that the new circuit had higher efficiency, smaller size and lower output voltage ripple than the Ladder converter

Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters

Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality.To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies.Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter.To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver

Coconut dehusker machine

Generally, coconut is dehusked manually using either a machete or a spike. These methods required skill labor and tiring to use. Attempts made so far in development of dehusking tools have been only partially successful and not effective in replacing manual methods. The reasons quoted for the failure of these tools include unsatisfactory and incomplete dehusking, breakage of the coconut shell while dehusking, spoilage of useful coir, greater effort needed than manual methods, etc

PERFORMANCE ANALYSIS OF FIVE LEVEL Z SOURCE NEUTRAL POINT CLAMPED MULTILEVEL INVERTER USING SPWM AND SVPWM

The scope of this paper is to reduce the harmonic content and to boost the output voltage by introducing an emerging technique termed as Z-Source multilevel inverter. The Z-Source inverter had overcome many drawbacks in traditional inverters (Voltage source & Current source Inverters).The main advantage of Z- Source inverter is the presence of a shoot through the period (Short circuit) which plays an important role in boosting the voltage. When the number of levels in the output voltage of multilevel inverter is increased then accordingly the harmonic content is also reduced. Normally for a multilevel inverter the output voltage is restricted to the summation of all the input voltage values.To enhance this feature Z-Source is introduced with a multilevel inverter to obtain boosted voltage along with low harmonic distortion.The proposed methodology analysis the Z-Source Neutral point clamped inverter using the Space vector modulation technique with MATLAB/Simulink model and the related parameters is analyzed

Modular multilevel inverter for renewable energy applications

This paper proposes a Multilevel Inverter (MLI) which focuses on two objective , minimal voltage sources and lesser switching component. The proposed Asymmetrical Cascaded Multilevel Inverter (ACMLI) is able to achieve the objective by selectively opting the voltage level of DC sources chosen and implementing the mathematical operation of addition and subtraction on the DC sources. This system also utilizes multiple carrier sinusoidal pulse width modulation technique (MCS-PWM) for operating the switches. It is found that the number of switches required for proposed modular bridge ACMLI and modified H bridge ACMLI was lesser than the traditional Cascaded H bridge Multilevel Inverter (CHB-MLI). It is also evident that the number of DC voltage sources and filter required for smoothing the output waveform is reduced compared to the traditional MLI. The Total Harmonic Distortion (THD) for the proposed circuit was simulated and analyzed in MATLAB Simulink environment and the results are found to be very less and satisfactory. The proposed circuit can find its application in integrating Renewable Energy Sources (RES) to the utility grid, Electrical Vehicle (EV) , harmonic reduction and so on. The simulation results of the proposed circuits are tabulated and compared with the traditional cascaded MLI

Design and Optimization of InterCell Transformers for Parallel MultiCell Converters

Les convertisseurs multicellulaires parallèles permettent de traiter des puissances importantes et de profiter d'une certaine standardisation des équipements. Ces dernières années, ces structures ont connu un regain d'intérêt lié notamment à la possibilité de couplage magnétique des inductances. Ce couplage aboutit à un composant magnétique aux propriétés très différentes appelé Transformateur Inter-Cellules (ICT) ; il ne modifie pas le courant de sortie, par contre il réduit l'ondulation de courant dans les bobines et l'ondulation de flux dans certaines parties du noyau. On peut montrer que ce couplage entraîne une réduction des pertes Joules dans les conducteurs et des pertes magnétiques dans le noyau. La réduction de l'ondulation de courant diminue également le courant efficace dans les semiconducteurs ce qui réduit les pertes par conduction, et la différence entre le courant à l'amorçage et au blocage des interrupteurs, ce qui permet la diminution des pertes dans les semiconducteurs lorsque les pertes au blocage sont supérieures aux pertes à l'amorçage. Le dimensionnement d'un ICT n'est pas fondamentalement différent de celui fait pour d'autres composants magnétiques en ce sens qu'il est basé sur le respect de certaines valeurs limites (induction, température) ce qui suppose une évaluation des différentes pertes et l'élaboration d'un modèle thermique. Par contre, la manière d'évaluer ces différentes grandeurs est tout à fait spécifique et n'a que quelques points communs avec les méthodes de calcul des inductances et des transformateurs Dans ce travail de thèse, on montre comment dimensionner ces ICTs en considérant plusieurs topologies et méthodes différentes, correspondant à différents niveaux de sophistication et de complexité. L'explication de ce dimensionnement est divisée en quatre parties : Pertes Cuivre, Pertes Fer, Densité de Flux de Saturation et Aspects Thermiques. L'évaluation des pertes cuivre liées aux composantes alternatives des ICTs constituent un point particulièrement délicat dans la mesure où elles résultent de la combinaison de deux facteurs eux-mêmes difficiles à évaluer ; l'inductance de fuite qui détermine l'amplitude des courants alternatifs mais dépend des flux principalement non canalisés et circulant dans l'air (volume d'étude important, effets 3D…), et la résistance équivalente des bobinages qui en haute fréquence est sujette à des phénomènes complexes comme les effets de peau et de proximité. En se basant sur l'utilisation d'un logiciel simple mais néanmoins robuste et fiable pour calculer précisément les résistances en haute fréquence et les inductances de fuite des ICTs, plusieurs astuces permettant de réduire les pertes cuivre non seulement des ICTs mais aussi des transformateurs et des inductances sont suggérées. Des tableaux simples sont développés pour aider le concepteur de transformateurs à identifier la meilleur configuration de conducteurs dans une fenêtre de bobinage en prenant en compte la forme d'onde du courant, le nombre de tours des enroulements, la fréquence des courants et les paramètres géométriques. Des formules analytiques et des outils de calcul adéquats ont ensuite été utilisés pour développer des routines d'optimisation ayant pour but la réduction de la masse, du volume, des pertes ou du coût des ICTs. Des interpolations multidimensionnelles des valeurs présimulées des résistances et inductances de fuite en haute fréquence sont utilisées afin de réduire le temps d'exécution de la routine d'optimisation. Plusieurs dimensionnements des ICTs ont été comparées vis-à-vis des matériaux du noyau et des conducteurs, du nombre de cellules de commutation et de la fréquence de découpage. Des comparaisons avec des selfs ont également été faites afin de montrer les avantages de ces ICTs. Des aspects de la commande des convertisseurs multi-niveaux triphasés ont également été étudiés vis-à- is du flux circulant dans les ICTs. Des homopolaires, spécifiques pour chaque stratégie MLI et chaque topologie convertisseur/charge, sont créées afin de minimiser le flux dans les ICTs et par conséquent de réduire davantage la masse et la taille de ces composants. Des comparaisons entre différentes méthodes de MLI sont effectuées et vérifiées expérimentalement. ABSTRACT : In recent years, the interest for parallel multicell converters has grown, which is partially due to the possibility of coupling the inductors used to connect the different commutation cells together. Coupling the inductors to form an InterCell Transformer (ICT) does not usually modify the output current, but it reduces the current ripple in the windings and the flux swing in some regions of the core. It can be shown that this brings a reduction of copper and core losses in the magnetic component. The reduction of the phase current ripple also reduces the difference between turn on and turn off current in the switches, which brings a reduction of switching losses for devices generating more losses at turn off than at turn on. The design of an ICT is not that different from any other magnetic component but it is very specific and inherent features must be taken into account. Taking full benefit of the potential advantages of ICTs requires the development of special tools and methods which are the focus of the study. We show how to design ICTs considering several topologies and different methods, from the most precise and time-consuming to the less accurate but more quickly calculated. The explanation of the ICT design is divided in four main parts: Copper Losses, Core Losses, Flux Density Saturation and Thermal Aspects. Further attention is given to high frequency copper losses since complex phenomena such as skin and proximity effects highly influence the ICT design. Based on Finite Element Method simulations, smart practices are suggested to reduce high and low frequency copper losses, not only in ICTs but also in inductors and transformers. Simple tables are developed to help transformer designers to identify the best configuration of conductors inside a given core window, depending on the current waveform and frequency, number of turns and geometrical parameters. Optimization routines to reduce the ICT total mass, volume, losses or cost are developed and multidimensional interpolation of pre-simulated values of AC resistance and leakage inductance is used to speed up the optimization routine. Comparison of ICT designs with regard to core and conductor material, number of cells and switching frequency is performed. Comparison with regular inductors is also made in order to verify the benefits of this kind of magnetic component. Multilevel converter control aspects applied to three- hase systems is also investigated in terms of the ICT flux. Zero sequence signals, specific for a PWM strategy and converter/load topology, are created in order to minimize the flux in ICTs and consequently reduce even further the mass and size of these components. Comparison between several PWM methods are performed and experimentally verified

Design, Optimization and Implementation of a High Frequency Link Multilevel Cascaded Inverter

This thesis presents a new concept of cascaded MLI (CMLI) device reduction by utilizing low and high frequency transformer link. Two CMLI topologies, symmetric and asymmetric are proposed. Compared with counterpart CMLI topologies available in the literatures, the proposed two inverter topologies in this thesis have the advantages of utilizing least number of electronic components without compromising overall performance particularly when a high number of levels is required in the output voltage waveform

Enforce transmission of unnatural power flow of series converter with clamped multi level Neutral point converter

In my paper, enforcing of the unnatural power flow in a transmission grid can be controlled by using Unified power flow control (UPFC) to sustain the maximizing power. In the UPFC the direct power is valuable control technique. The direct flow control can be used with any topology of voltage source converter. For series multi level converter non ideal transformers and load. While comparing other controllers we can obtain the better response under balanced and unbalanced conditions. Simulation and experimental results of a full three-phase model with non-ideal transformers, series multilevel converter, and load confirm minimal control delay, no overshoot, no cross coupling. In this paper, the direct power control is demonstrated in detail for a third-level neutral point clamped converter

Analysis and Design of a Hybrid Dickson Switched Capacitor Converter for Intermediate Bus Converter Applications

By 2020 it is predicted that 1/3 of all data will pass through the cloud. With society\u27s growing dependency on data, it is vital that data centers, the cloud\u27s physical house of content, operate with optimal energy performance to reduce operating costs.Unfortunately, today\u27s data centers are inefficient, both economically and environmentally. This has led to an increase in demand for energy-efficient servers. One opportunity for improved efficiency is in the power delivery architecture which delivers power from the grid to the motherboard. In this dissertation, the main focus is the intermediate bus converter (IBC), used for the intermediate conversion, typically 48-12V/5V, in server power supplies. The IBC requires compact design so that it can be placed as close to the load as possible to enable more space for computing power and high efficiency to reduce the need for external cooling. Most commonly used converter topologies today include expensive bulky magnetics hindering the converter\u27s power density. Furthermore, high output current of an IBC makes the efficiency very sensitive to any resistance, such as magnetic parasitic resistance or PCB trace resistance. In this work, analytical loss models are used to review the advantages and disadvantages of frequently used IBC topologies such as the phase-shifted full bridge and LLC. The Hybrid Dickson Switched Capacitor (HDSC) topology is also analyzed. The HDSC\u27s high step-down conversion ratio and low dependence on magnetics due to the reduced applied volt-seconds, provides a new opportunity for applications such as the intermediate bus converter. The HDSC designs the on-time of devices in order to achieve soft-charging between flying capacitors. Other advantages of the HDSC include low switch stress, small magnetics and adjustable duty cycle for voltage regulation. Challenges, such as minimizing parasitic inductance and resistance between flying capacitors, are addressed and recommendations for PCB layout are provided. In this paper, a 4:1 24-5V and 8:1 48-5V, 100W GaN-based HDSC is designed and tested. The influences of capacitor mismatch and limitations placed on soft-charging operation for the HDSC is also modeled. This analysis can be used as a tool for designers when selecting flying capacitors

Cascaded Converters For Integration And Management Of Grid Level Energy Storage Systems

ABSTRACT CASCADED CONVERTERS FOR INTEGRATION AND MANAGEMENT OF GRID-LEVEL ENERGY STORAGE SYSTEMS by ZUHAIR ALAAS December 2017 Advisor: Dr. Caisheng Wang Major: ELECTRICAL ENGINEERING Degree: Doctor of Philosophy This research work proposes two cascaded multilevel inverter structures for BESS. The gating and switching control of switching devices in both inverter typologies are done by using a phase-shifted PWM scheme. The first proposed isolated multilevel inverter is made up of three-phase six-switch inverter blocks with a reduced number of power components compared with traditional isolated CHB. The suggested isolated converter has only one battery string for three-phase system that can be used for high voltage and high power applications such as grid connected BESS and alternative energy systems. The isolated inverter enables dq frame based simple control and eliminates the issues of single-phase pulsating power, which can cause detrimental impacts on certain dc sources. Simulation studies have been carried out to compare the proposed isolated multi-level inverter with an H-bridge cascaded transformer inverter. The simulation results verified the performance of the isolated inverter. The second proposed topology is a Hierarchal Cascaded Multilevel Converter (HCMC) with phase to phase SOC balancing capability which also for high voltage and high power battery energy storage systems. The HCMC has a hybrid structure of half-bridge converters and H-bridge inverters and the voltage can be hierarchically cascaded to reach the desired value at the half-bridge and the H-bridge levels. The uniform SOC battery management is achieved by controlling the half-bridge converters that are connected to individual battery modules/cells. Simulation studies and experimental results have been carried on a large scale battery system under different operating conditions to verify the effectiveness of the proposed inverters. Moreover, this dissertation presents a new three-phase SOC equalizing circuit, called six-switch energy-level balancing circuit (SSBC), which can be used to realize uniform SOC operation for full utilization of the battery capacity in proposed HCMC or any CMI inverter while keeping balanced three-phase operation. A sinusoidal PWM modulation technique is used to control power transferring between phases. Simulation results have been carried out to verify the performance of the proposed SSBC circuit of uniform three-phase SOC balancing