Pulse multiplication in autotransformer based AC-DC converters using a zigzag connection

This paper deals with pulse multiplication in zigzag connected autotransformer based 12-pulse AC-DC converters feeding vector controlled induction motor drives (VCIMD) for improving the power quality at the point of common coupling (PCC) without using a Zero-Sequence-Blocking-Transformer (ZSBT). The proposed 24-pulse AC-DC converter is based on the principle of DC ripple re-injection technique for pulse multiplication and harmonic mitigation. The design of the autotransformer is carried out for the proposed AC-DC converter and the effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC-DC converter. Test results from a laboratory developed prototype, along with simulated results, are presented to validate the design and model of the proposed 24-pulse AC-DC converter

Pulse Tripling Circuit and Twelve Pulse Rectifier Combination for Sinusoidal Input Current

In this paper, a novel pulse tripling circuit (PTC) is suggested, to upgrade a polygon autotransformer 12-pulse rectifier (12-PR) to a 36-pulse rectifier (36-PR) with a low power rating. The kVA rating of the proposed PTC is lower compared to the conventional one (about 1.57% of load power). Simulation and experimental test results show that the total harmonic distortion (THD) of the input current of the suggested 36-PR is less than 3%, which meets the IEEE 519 requirements. Also, it is shown that in comparison with other multi-pulse rectifiers (MPR), it is cost-effective, its power factor is near unity and its rating is about 24% of the load rating. Therefore, the proposed 36-PR can be considered as a practical solution for industrial applications

New methodology to calculate DC voltage signature in n-phases TRUs under supply voltage sags

A new methodology based on the shadow projection has been developed to study any multipulse rectifier's dynamic behavior under balanced and unbalanced conditions. The proposed methodology calculates the DC average voltage and instantaneous values under balanced and unbalanced supply voltage conditions for multiphase Transformer Rectifier Units (TRUs). The calculation of the developed algorithms is more practical than the classical methods and other approaches based on Fourier series or symmetrical components that are difficult to apply under unbalanced conditions. Furthermore, classical methods are not simple to determine the limits of the integrals and calculate them to obtain the average value, so a more friendly and practical methodology has been developed to analyze rectifiers operating under supply voltage sags. This new methodology has been validated by simulation for a 12-pulse TRU in series and parallel connections, and it has also been validated for a 36-pulse TRU in parallel connection using interphase inductors. The accuracy of the calculations is validated by the experimental results for 12-pulse TRUs, series, and parallel connection, and 18-pulse TRU in series connection.This work was supported by the research project ‘‘Estabilidad de redes MVDC integrando tecnologías de energías renovables, almacenamiento de energía y convertidores de fuente de impedancia,’’ by the Ministerio de Ciencia, Innovación y Universidades and European Union, under Grant RTI2018-095720-B-C33.Peer ReviewedPostprint (published version

Generic functional modelling of multi-pulse auto-transformer rectifier units for more-electric aircraft applications

The Auto-Transformer Rectifier Unit (ATRU) is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced kVA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future

Control of Harmonics in 6-Pulse Rectifiers

Harmonics are always present in electrical power systems. Harmonic distortion is harmless as long as its level is within the limit. However, with the recent rapid advancement of power electronics, i.e. non linear loads, the use of the variable speed drives are increasing day by day. Harmonics produced by non-linear loads are a potential risk if they are not evaluated, predicted, and controlled. The power electronic switching devices like thyristor used in the rectifier circuits inject harmonic distortion to the utility grid in different applications. The harmonic distortion causes different problems in the power system. To minimize the unwanted effects of harmonic distortion, IEEE Std 519-1992 recommends the amount of harmonics that is acceptable in the power system. IEEE Std 519-1992 suggests that an individual harmonic distortion to be under 3% and the total harmonic distortion, THD, to be under 5% of the fundamental component. Harmonic distortion can be mitigated using different methods. Based on the system configuration either active filters, passive filters, or phase shifting methods are used. In medium voltage high power applications, generally, phase shifting method is better suited. In addition to harmonic distortion in AC side, AC-DC converter produce ripple in DC side. DC ripple can be mitigated by the use of filter circuits. However, when phase shifting method is used in AC side for harmonic mitigation, a method called pulse multiplication can be used in DC side to mitigate DC ripple. Phase shifting and pulse multiplication methods are investigated in detail in this research. A three-phase 6-pulse rectifier is modeled in Alternative Transients Program (ATP). Voltage and Current waveforms are obtained and the amount of harmonic distortion produced is calculated. It was found that the harmonic distortion produced by an ideal three-phase 6-pulse rectifier to be 31.1% and not under IEEE 519-1992 recommendation. Therefore a 12-pulse rectifier has been investigated. The analysis shows that a 12-pulse rectifier produces 15.3% THD and provides a window opportunity to be used in certain areas where the grid is comparatively stronger. For a rectifier to be able to be used without ac side filter and dc side filter, and to mitigate the THD under the IEEE std 519-1992 recommendation and the dc ripple under the specified value, a higher pulse rectifier will be needed. Further investigation is needed using 18-pulse and 24-pulse phase shifting rectifiers

Polygon connected autotransformer based 24-pulse AC-DC converter for power quality improvement

This paper deals with a polygon connected autotransformer based 24-pulse AC-DC converter for power quality improvement in vector controlled induction motor drives (VCIMD's). A polygon connected autotransformer with multi windings per phase at different phase angles is used to realize the proposed 24-pulse AC-DC converter. The design of proposed autotransformer is presented along with the necessary modifications required for making it suitable for retrofit applications, where presently a 6-pulse diode bridge rectifier is used. The proposed 24-pulse AC-DC converter is able to eliminate upto 21st harmonics in the supply current along with the power factor improvement close to unity in the wide operating range of the drive. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC-DC converter. A set of power quality indices on input ac mains and on DC bus for a VCIMD fed from six-pulse and proposed AC-DC converter are presented to compare their performance

Contribucions a l'estudi de rectificadors no controlats m-fàsics en condicions no equilibrades per unitats TRUs o ATRUs multi polsos

Tesi amb diferents seccions retallades per drets de l'editorThis doctoral thesis has been developed to provide a new point of view and a new approach to the analysis and study of uncontrolled bridge rectifiers. The methodology developed has been generalized to extend the study to an m-phase system, applicable for both balanced and unbalanced systems. It is possible to quickly obtain an analytical formulation to calculate the average voltage for balanced systems. However, there are multiple formulations for unbalanced systems, and, in general, it is not easy to be applied. For this reason, an easy-to-apply formulation has been determined to calculate the average voltage, using the perimeter of the convex polygon defined by the ends of the phase voltages of the power supplies. As the convexity condition is necessary for its application, it has been determined that this approach is related to one of the formulas proposed by Cauchy. This formula determines the average width of a convex body, which has made it possible to relate the average width to the average voltage and the convex body to the convex polygon defined by the maximum stresses. The relationship with vision systems also has been observed. The projections and average widths in a rotation are used, for example, to determine the section of bones, veins, and muscles, which is the basis of the Computed Tomography (CT) scan. It is important to highlight the close relationship between the Couchy formula and the application to the CT scan. However, the proposed method has some differences from Cauchy's. While the Cauchy formulation applies to a body that must be derivable at all points, the proposed formulation applies to a convex polygon with no equal derivative at the vertices since the derivatives are different from the right than from the left vertex. This new method, called the Phasorial Convex Hull Method, has been published in the article "Average value of DC-link output voltage in multi-phase uncontrolled bridge rectifiers under supply voltage balance and unbalance conditions". In the demonstration of the developed method, it has been observed that the instantaneous voltage is obtained before calculating the average voltage of the DC bus. Therefore, the voltage signature at the rectifier's output allows detailed studies of behavior in the voltage sag, unbalance operation, faults, etc. This new methodology for obtaining instantaneous voltage has been titled "Shadow Projection", presented in the article "New Methodology to Calculate DC Voltage Signature in N-Phases TRUs Under Supply Voltage Sags". Because rectifiers are usually coupled to Transformers or Autotransformers, the Thesis was believed to be linked to Transformer Rectifier Units (TRUs) and Auto-Transformer Rectifier Units (ATRUs) and a patent study has been done to see how the industry has evolved, studying some configurations. Formulations have been proposed for solutions for series, parallel and / or coupling connections. The joint study of the rectifying units with the Transformer or the Autotransformer opens the study to determine the line currents on the AC side. Therefore, if the study of voltages goes from AC sources to DC load, the study of currents goes from DC side to AC side. Solutions have been proposed for the study of 12-pulse rectifiers in three-winding TRUs, and for Delta-polygonal ATRUs. This study, yet to be published, allows obtaining simple equivalent circuits for complex systems. The effect on DC voltage when there are fused diodes producing a lack of open circuit has also been studied, the proposed method allows to determine the diode or diodes that are missing and need to be replaced. In this case, the article entitled “Open-Circuit fault diagnosis and maintenance in multi-pulse parallel and series TRU topologies” has been published. The method is based on signing the DC voltage at the output of the rectifier, starting the period according to the hourly index of the transformer for 12-18 pulses.Aquesta Tesi doctoral ha estat elaborada amb l’objectiu d’aportar una nova visió i un nou enfocament a l’anàlisi i a l’estudi de rectificadors en pont no controlats. La metodologia desenvolupada s’ha generalitzat per tal d’estendre l’estudi a un sistema m-fàsic, essent aplicable tant per sistemes equilibrats com per sistemes no equilibrats. És possible obtenir de forma senzilla una formulació analítica pel càlcul de la tensió mitja per a sistemes equilibrats (igual mòdul i desfasament), però hi ha múltiples formulacions per als sistemes desequilibrats (diferent mòdul i/o desfasament), i en general d’aplicació complexa. És per aquest motiu que s’ha determinat una formulació de fàcil aplicació que permet determinar la tensió mitja amb el perímetre del polígon convex definit pels extrems de les tensions de fase de les fonts d’alimentació dividit pel número “pi”. Com per la seva aplicació, la condició de convexitat és necessària, s’ha determinat que aquest plantejament té relació amb una de les fórmules proposades per Cauchy. Aquesta formula determina l’amplada mitja d’un cos convex, i s’ha relacionat l’amplada mitja amb el voltatge mig, i el cos convex amb el polígon convex definit per les tensions màximes. També s’ha observat la relació que té amb els sistemes de visió, i com a partir de les projeccions i amplades mitges en una rotació es pot determinar per exemple la secció dels ossos, venes i muscles, que és la base del TAC. S’ha de destacar la relació estreta que hi ha amb la fòrmula de Couchy i l’aplicació al TAC. No obstant, el mètode plantejat presenta algunes diferències amb el de Cauchy. Mentre que la formulació de Cauchy s’aplica a un cos que ha de ser derivable en tots els punts, la formulació que s’ha desenvolupat s’aplica a un polígon convex que no té igual derivada en els vèrtex, ja que són diferents des de la dreta que des de l’esquerra del vèrtex. Aquest nou mètode que s’ha denominat “Phasorial Convex Hull Method” ha estat publicat a l’article titulat: “Average value of the DC-link output voltage in multi-phase uncontrolled bridge rectifiers under supply voltage balance and unbalance conditions”. En la demostració del mètode desenvolupat s’ha observat que en pas previ a obtenir la tensió mitja del bus de continua, s’obté la tensió instantània, i per tant la signatura de la tensió a la sortida del rectificador, el que obre les portes a estudis detallats del comportament davant de sots de tensió, desequilibris, faltes, etc. Aquesta nova metodologia per obtenir la tensió instantània s’ha titulat com “Shadow Projection”, que ha estat presentada en un article, amb el títol "New Methodology to Calculate DC Voltage Signature in NPhases TRUs Under Supply Voltage Sags". Els rectificadors acostumen a anar acoblats a transformadors (TRUs) o a autotransformadors (ATRUs), pel que s’ha fet un estudis de patents, analitzant com la indústria ha anat evolucionat amb l’aplicació de diferents configuracions. En aquesta Tesi s’han proposat formulacions per configuracions tant sèrie com paral·lel, i/o amb bobina d’acoblament. L’estudi conjunt de les unitats rectificadores amb el transformador o amb l’autotransformador permet determinar tant el corrent CC com els corrents de línia CA, i l’estudi de les tensions va des de les fonts de CA a la càrrega de CC. Com a exemple s’ha fet un estudi detallat de rectificadors de 12 polsos en TRUs de tres debanats, i també ATRUs Delta-poligonal. Aquest estudi, pendent de publicació, permet l’obtenció de circuits equivalents senzills per sistemes complexos. També s’ha estudiat l’efecte sobre la tensió de CC quant hi ha díodes fosos produint una falta de circuit obert, el mètode proposat permet determinar el díode o díodes que estan en falta i cal canviar-los. En aquest cas s’ha publicat l’article titulat “Open-Circuit fault diagnosis and maintenance in multi-pulse parallel and series TRU topologies”, en el que es mostra el mètode d’identificació de díodes en circuit obert, basat en la signatura de la tensió de CC a la sortida del rectificador, per a configuracions de 12 i 18 polsos. Aquest mètode d’identificació de faltes permetrà estudis més amples de manteniment amb Machine Learning.Postprint (published version

Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering

Advances and Technologies in High Voltage Power Systems Operation, Control, Protection and Security

The electrical demands in several countries around the world are increasing due to the huge energy requirements of prosperous economies and the human activities of modern life. In order to economically transfer electrical powers from the generation side to the demand side, these powers need to be transferred at high-voltage levels through suitable transmission systems and power substations. To this end, high-voltage transmission systems and power substations are in demand. Actually, they are at the heart of interconnected power systems, in which any faults might lead to unsuitable consequences, abnormal operation situations, security issues, and even power cuts and blackouts. In order to cope with the ever-increasing operation and control complexity and security in interconnected high-voltage power systems, new architectures, concepts, algorithms, and procedures are essential. This book aims to encourage researchers to address the technical issues and research gaps in high-voltage transmission systems and power substations in modern energy systems