Direct current control for grid connected multilevel inverters

Control schemes for inverters of different topologies and various numbers of voltage levels are of great interest for many standard as well as special applications. This thesis describes a novel, robust and high-dynamic direct current control scheme for multilevel voltage source inverters. lt is highly independent from load parameters and universally applicable. The new control method is examined and validated with real measurements . The aim of the thesis is to establish and prove a new concept of a direct current control algorithm for multilevel inverter topologies for grid connected systems. This application is characterized by unknown grid conditions including failure modes and other distortions, complex inverter topologies and a large variety and complexity of current control algorithms for multilevel inverters. Therefore the complexity of the system needs to be reduced. Additionally , the advantages of multilevel inverters and the dynamic performance and robustness of direct current control techniques shall be combined. Starting from a detailed literature study on inverter topologies and direct as well as indirect current control methods, the thesis includes three chapters containing relevant contributions to the achievement of the objectives. A method reducing the control-complexity of multilevel converters has been developed. The simplification method is based on a transformation that converts any three-phase voltage (or current) into a non-orthogonal coordinate system. This choice minimizes the complexity and effort to determine the location of those discrete voltage space vectors directly surrounding the required reference voltage vector. A further improvement is achieved by scaling all coordinates to integer values. This is advantageous for further calculations on microprocessors or FPGA based control systems. The main contribution of this thesis is a new direct current control method minimizing the disadvantages of existing direct methods. At the same time advantages of other control algorithms shall be applied. The new method is based on a simple mathematical equation, that is, the solution of a scalar product, to always select the one inverter output voltage vector best reducing the actual current error. This results in the designation "Scalar Hysteresis Control - SHC". An advanced seeking algorithm ensures robust current control capability even in case of unknown, unsymmetrical or changing loads, in case of rapid set-point changes or in cases of unknown phase voltages . The new method therefore shows excellent properties in terms of simplicity , robustness, dynamics and independence from the inverter level count and the hardware topology . The properties of the control method are verified by means of simulations and real measurements on two-, three- and five-level inverters over the complete voltage operating range. Finally, all contributions are collected together and assessed with regard to the objectives. From the proposed control method new opportunities for future work, further developments and extensions are evolving for continuing scientific researchEls sistemes de control d'inversors de diferents topologies i diferent varis nivells de tensió són de gran interès per moltes aplicacions estàndard i també per aplicacions especials. Aquesta tesi investiga sobre un mètode de control directe de corrent per convertidors multinivell en font de tensió que es mostra robust i presenta una elevada dinàmica en el control de corrent. El mètode és molt robust davant de canvies als paràmetres de la càrrega i aplicable a qualsevol tipus de convertidor. En aquesta tesi s'analitza el mètode i es valida mitjançant resultats experimentals. L'objectiu d'aquesta tesi és establir i demostrar un nou de mètode i algorisme de control directe de corrent aplicat especialment a inversors connectats a la xarxa. L'aplicació es caracteritza per la desconeixença dels paràmetres de la xarxa, incloent diferents modes de falla i distorsions en la seva tensió i una varietat de tipologies de convertidors multinivell. El mètode de control busca simplificar l'algorisme i que pugui ser aplicat en aquest entorn de forma robusta, de forma que es pugui estendre l'ús dels convertidors multinivell sense afegir més complexitat als algorismes de control i modulació. La tesi aborda el problema iniciant amb un anàlisi de la literatura existent en aquest tipus de mètodes de control directe i indirecte del corrent i els convertidors multinivell, per continuar amb l'anàlisi del mètode proposat i la seva demostració mitjançant resultats de simulacions i experimentals. El mètode de simplificació està basat en una transformació que transforma qualsevol sistema trifàsic a un sistema de coordenades no-ortogonal. Escollir aquest sistema de coordenades redueix la complexitat i l'esforç per determinar la ubicació d'aquells vectors espacials que directament envolten el vector de referencia. A més, totes les coordenades s'escalen a valors enters, que permet la programació de l'algorisme en sistemes de control basats en microprocessadors o FPGAs. La principal contribució d'aquesta tesi és un nou mètode de control de corrent que intenta minimitzar els desavantatges dels mètodes indirectes existents a l'actualitat, al mateix moment que s'intenta incorporar els avantatges dels mètodes indirectes. El mètode proposat es basa en una equació matemàtica simple, la solució d'un producte escalar, per trobar el vector de tensió espacial que minimitza l'error de corrent, en el que s'anomena "Scalar Hysteresis Control" o SHC. L'algorisme assegura un control robust del corrent sense la necessitat de conèixer la tensió de fase, o les càrregues, tant si són desequilibrades o canviants. També presenta una dinàmica molt elevada en cas de canvies en la referència. El nou mètode mostra unes propietats excel·lents en termes de simplicitat, robustesa, dinàmica i independència de la tipologia del convertidor i, en el cas de convertidors multinivell, del nombre de nivells. Les propietats del mètode de control són verificades mitjançant simulacions i resultats experimentals en convertidors de dos, tres i fins a cinc nivells de tensió en tot el rang d'operació, fins i tot en la zona de sobremodulació. A partir del mètode de control proposat, s'estan desenvolupant noves aplicacions i extensions, continuant també la contribució a la recerca científica.Postprint (published version

Direct current control for grid connected multilevel inverters

Control schemes for inverters of different topologies and various numbers of voltage levels are of great interest for many standard as well as special applications. This thesis describes a novel, robust and high-dynamic direct current control scheme for multilevel voltage source inverters. lt is highly independent from load parameters and universally applicable. The new control method is examined and validated with real measurements . The aim of the thesis is to establish and prove a new concept of a direct current control algorithm for multilevel inverter topologies for grid connected systems. This application is characterized by unknown grid conditions including failure modes and other distortions, complex inverter topologies and a large variety and complexity of current control algorithms for multilevel inverters. Therefore the complexity of the system needs to be reduced. Additionally , the advantages of multilevel inverters and the dynamic performance and robustness of direct current control techniques shall be combined. Starting from a detailed literature study on inverter topologies and direct as well as indirect current control methods, the thesis includes three chapters containing relevant contributions to the achievement of the objectives. A method reducing the control-complexity of multilevel converters has been developed. The simplification method is based on a transformation that converts any three-phase voltage (or current) into a non-orthogonal coordinate system. This choice minimizes the complexity and effort to determine the location of those discrete voltage space vectors directly surrounding the required reference voltage vector. A further improvement is achieved by scaling all coordinates to integer values. This is advantageous for further calculations on microprocessors or FPGA based control systems. The main contribution of this thesis is a new direct current control method minimizing the disadvantages of existing direct methods. At the same time advantages of other control algorithms shall be applied. The new method is based on a simple mathematical equation, that is, the solution of a scalar product, to always select the one inverter output voltage vector best reducing the actual current error. This results in the designation "Scalar Hysteresis Control - SHC". An advanced seeking algorithm ensures robust current control capability even in case of unknown, unsymmetrical or changing loads, in case of rapid set-point changes or in cases of unknown phase voltages . The new method therefore shows excellent properties in terms of simplicity , robustness, dynamics and independence from the inverter level count and the hardware topology . The properties of the control method are verified by means of simulations and real measurements on two-, three- and five-level inverters over the complete voltage operating range. Finally, all contributions are collected together and assessed with regard to the objectives. From the proposed control method new opportunities for future work, further developments and extensions are evolving for continuing scientific researchEls sistemes de control d'inversors de diferents topologies i diferent varis nivells de tensió són de gran interès per moltes aplicacions estàndard i també per aplicacions especials. Aquesta tesi investiga sobre un mètode de control directe de corrent per convertidors multinivell en font de tensió que es mostra robust i presenta una elevada dinàmica en el control de corrent. El mètode és molt robust davant de canvies als paràmetres de la càrrega i aplicable a qualsevol tipus de convertidor. En aquesta tesi s'analitza el mètode i es valida mitjançant resultats experimentals. L'objectiu d'aquesta tesi és establir i demostrar un nou de mètode i algorisme de control directe de corrent aplicat especialment a inversors connectats a la xarxa. L'aplicació es caracteritza per la desconeixença dels paràmetres de la xarxa, incloent diferents modes de falla i distorsions en la seva tensió i una varietat de tipologies de convertidors multinivell. El mètode de control busca simplificar l'algorisme i que pugui ser aplicat en aquest entorn de forma robusta, de forma que es pugui estendre l'ús dels convertidors multinivell sense afegir més complexitat als algorismes de control i modulació. La tesi aborda el problema iniciant amb un anàlisi de la literatura existent en aquest tipus de mètodes de control directe i indirecte del corrent i els convertidors multinivell, per continuar amb l'anàlisi del mètode proposat i la seva demostració mitjançant resultats de simulacions i experimentals. El mètode de simplificació està basat en una transformació que transforma qualsevol sistema trifàsic a un sistema de coordenades no-ortogonal. Escollir aquest sistema de coordenades redueix la complexitat i l'esforç per determinar la ubicació d'aquells vectors espacials que directament envolten el vector de referencia. A més, totes les coordenades s'escalen a valors enters, que permet la programació de l'algorisme en sistemes de control basats en microprocessadors o FPGAs. La principal contribució d'aquesta tesi és un nou mètode de control de corrent que intenta minimitzar els desavantatges dels mètodes indirectes existents a l'actualitat, al mateix moment que s'intenta incorporar els avantatges dels mètodes indirectes. El mètode proposat es basa en una equació matemàtica simple, la solució d'un producte escalar, per trobar el vector de tensió espacial que minimitza l'error de corrent, en el que s'anomena "Scalar Hysteresis Control" o SHC. L'algorisme assegura un control robust del corrent sense la necessitat de conèixer la tensió de fase, o les càrregues, tant si són desequilibrades o canviants. També presenta una dinàmica molt elevada en cas de canvies en la referència. El nou mètode mostra unes propietats excel·lents en termes de simplicitat, robustesa, dinàmica i independència de la tipologia del convertidor i, en el cas de convertidors multinivell, del nombre de nivells. Les propietats del mètode de control són verificades mitjançant simulacions i resultats experimentals en convertidors de dos, tres i fins a cinc nivells de tensió en tot el rang d'operació, fins i tot en la zona de sobremodulació. A partir del mètode de control proposat, s'estan desenvolupant noves aplicacions i extensions, continuant també la contribució a la recerca científica

Center Phase Transition from Fundamentally Charged Matter Propagators

The center phase transition at non-vanishing temperatures is investigated in Landau gauge Quantum Chromodynamics (QCD) and scalar QCD. For each theory novel order parameters for the transition are introduced. The matter-gluon vertex which occurs in the Dyson-Schwinger equations of the propagators has to be modeled in contemporary studies. It is found that the nature of the phase transition depends strongly on the detailed structure of this vertex. Our investigation motivates a precise determination of the matter-gluon vertex at non-vanishing temperatures.Comment: 8 pages, Confinement X proceeding

Metrics for measuring distances in configuration spaces

In order to characterize molecular structures we introduce configurational fingerprint vectors which are counterparts of quantities used experimentally to identify structures. The Euclidean distance between the configurational fingerprint vectors satisfies the properties of a metric and can therefore safely be used to measure dissimilarities between configurations in the high dimensional configuration space. We show that these metrics correlate well with the RMSD between two configurations if this RMSD is obtained from a global minimization over all translations, rotations and permutations of atomic indices. We introduce a Monte Carlo approach to obtain this global minimum of the RMSD between configurations

Mutual interference between memory encoding and motor skills: the influence of motor expertise

In cognitive–motor dual-task situations, the extent of performance decrements is influenced by the attentional requirements of each task. Well-learned motor skills should be automatized, leading to less interference. This study presents two studies combining an episodic memory encoding task with well-practiced motor tasks in athletes. Study 1 asked 40 rowers (early teenagers to middle adulthood) to row on ergometers at slow or fast speeds. In study 2, Taekwondo athletes (n  =  37) of different skill levels performed a well-practiced sequence of martial arts movements. Performing the motor task during encoding led to pronounced performance reductions in memory in both studies, with costs of up to 80%. Cognitive costs were even larger when rowing with the fast compared to the slow speed in study 1. Both studies also revealed decrements in motor performances under dual-task conditions: Rowing became slower and more irregular (study 1), and the quality of the Taekwondo performance was reduced. Although higherlevel athletes outperformed others in motor skills under single-task conditions, proportional dual-task costs were similar across skill levels for most domains. This indicates that even well-practiced motor tasks require cognitive resources

Soluble Intracellular Adhesion Molecule-1 in Patients with Unipolar or Bipolar Affective Disorders

Background: Immunological and vascular markers may play a role in the pathophysiology of mood disorders and mood changes. Aim: To test whether the cell adhesion molecule soluble intracellular adhesion molecule-1 (sICAM-1) may serve as a biomarker for patients with unipolar or bipolar affective disorders when compared to a healthy control group, and whether sICAM-1 blood levels change during different mood states. Methods: sICAM-1 serum concentrations were compared between 20 healthy controls and 48 patients with affective disorders (unipolar, bipolar II and bipolar I disorder) during different mood states (euthymic mood state, depression or mania). Results: When compared to healthy controls, patients with affective disorders had significantly higher sICAM-1 levels during the euthymic state (p = 0.015). Differences became more pronounced during depression (p = 0.013). When unipolar and bipolar patients were analyzed separately, unipolar patients significantly differed from controls during the euthymic and depressive mood state, while bipolar II patients showed a trend towards higher sICAM-1 levels during depression. Patients with bipolar I disorders had significantly higher sICAM-1 levels during manic states when compared to controls (p = 0.007). Conclusions: sICAM-1 elevation in unipolar and bipolar patients, independent of mood changes, might support the hypothesis of chronic immune activation and endothelial dysfunction in patients with affective disorders. (C) 2016 S. Karger AG, Base