315 research outputs found
New MMC capacitor voltage balancing using sorting-less strategy in nearest level control
No full textThis paper proposes a new strategy for balancing the Capacitor Voltages (CVs) for Modular Multilevel Converters (MMCs). The balancing is one of the main challenges in MMC applications and it is usually solved by adopting a global arm control approach. For performing such an approach, a sorted list of the SubModules (SMs) according to their capacitor voltages is required. A common way to accomplish this task is to implement a sorting algorithm in the same controller used for the modulation technique. However, the execution time and the computational efforts of these kinds of algorithms increase very rapidly when the number of SMs grows. A novel idea is presented in this paper by using a mapping strategy that directly stores in a ranked list the SMs according to the measured CVs. Avoiding the use of sorting algorithms leads to a considerable reduction of the execution time as well as the computational efforts
FPGA-based implementation of sorting networks in MMC applications
No full textIn this paper an implementation technique for Field Programmable Gate Array (FPGA) devices of two Sorting Networks (SNs) used for control of Modular Multilevel Converter (MMC) is presented. In such applications, the classical sorting algorithms are based on repetitive/recursive loops, and they are usually implemented in microcontrollers or DSPs. However, they are not convenient for hardware implementation due to their inherent sequential operation. Instead, the proposed SNs, are suitable for FPGA devices thanks to their fixed parallel structure that allows improving the timing performance of the capacitor voltage balancing algorithm. The advantages and the main challenges of the Bitonic SN and Even-Odd SN in MMC applications are discussed. Moreover, in order to pre-evaluate the required resources and the execution time, equations are derived for both the proposed SNs and then a comparison is performed between them. The proposed equations are validated by comparing the real required resources with the estimated ones by using the Xilinx Vivado Design Suite tool. Finally, the operation of the proposed Bitonic SN is also tested in Vivado Simulator, achieving the sorted list of 8 elements in 18 clock cycles as expected
System-on-chip implementation of embedded real-Time simulator for modular multilevel converters
No full textThe aim of this paper is to present the implementation of an Embedded Real-Time Simulator (ERTS) for Modular Multilevel Converters (MMCs), using low-cost System-on-Chip (SoC) platform. In order to achieve new functionalities such as sensor-less control, monitoring, diagnostic and fault detection, the MMC plant model can be implemented along with the controller. In MMC applications, the implementation of the RTS is particularly challenging due to the complex structure of the MMC and its stringent timing constraints, especially when the number of Sub-Modules (SMs) increases. In addition to the previous requirements, in case of ERTS, the hardware resources are also limited in order to keep low the cost of the entire controller. Moreover, the chosen device must also provide enough modulators for driving all the SMs and sufficient ADC interfaces for acquiring the capacitor voltages. For these reasons, a Xilinx Zynq SoC platform is adopted; this device provides two hard-processors along with the programmable gate array. In this work, the MMC plant model and the MMC controller are implemented in the two available microcontrollers, whereas, all the modulators and interfaces can be implemented in the programmable gate array. The achieved implementation is evaluated in terms of execution time and maximum allowable number of SMs. In order to validate the proposed implementation, HIL results for a single-phase MMC simulator are also provided
The negotiated revolution in Hungary
No full textPublished online: 20 January 2012The paper is an updated version of a piece that I wrote about the Hungarian regime change of 1989 with some cautious parallels to the North African regime changes. It analyses the strategies of the opponents and the defendants of the regime, the way they have adjusted their strategies to perceived changes in geopolitical constellations and the frames they have used to mobilize support for changing or conserving the regime. [BRUSZT, Laszlo (Author), HORVATH, George K. (Translator), The Negotiated Revolution in Hungary, Social Research, 1990, 57, 2, 365-387, 0037-783X
Performance comparison of the modulators with balancing capability used in MMC applications
No full textSeveral modulation methods with balancing capability have been proposed to control Modular Multilevel Converters (MMC). Due to the complexity of the system it is difficult to decide which modulator ensures better performance. In this paper, the performance of the carrier and carrier-less modulation techniques are discussed separately from their balancing capability. By using different simulation models the key performance parameters, such as: number of switching, circulating current, balancing, are compared for Nearest Level Control (NLC), Phase Shifted Carrier (PSC) and Level Shifted Carrier (LSC) methods. Both cases are discussed when low and when high number of submodules are employed in the MMC.</p
Recommended from our members
Laszlo Varga: Pedagogy, history, and legacy
No full textThe purpose of this essay is to provide a detailed exploration of the personal history, teaching techniques, and professional achievements of Laszlo Varga, a famous and important Hungarian cellist living in America.Varga is considered one of the greatest living cellists and pedagogues in America today. He now resides in Sarasota, Florida, where he teaches and writes cello ensemble arrangements. He also performs and lectures throughout the world. Very little has been written about this cello virtuoso and master teacher who grew up in Hungary and worked with such artists as Casals and Starker.Varga agreed to spend several hours with the author answering questions and discussing his own history, teaching techniques, and current projects. The author met with Varga in his Sarasota, Florida home and conducted two taped interviews with him. Subjects covered in the interview included Varga's interest in performing on a five-string cello, the main issues he covers in a student's lesson, the scale system, etudes and methods he employs, and the repertoire he favors. In addition, an important part of the interview addressed Varga's impressions and stories about the many extraordinary musicians that he has met during his career.</p
FPGA-Based Implementation of MMC Control Based on Sorting Networks
No full textIn Modular Multilevel Converter (MMC) applications, the balancing of the capacitor voltages is one of the most important issues for achieving the proper behavior of the MMC. The Capacitor Voltage Balancing (CVB) control is usually based on classical sorting algorithms which consist of repetitive/recursive loops. This leads to an increase of the execution time when many Sub-Modules (SMs) are employed. When the execution time of the balancing is longer than the sampling period, the proper operation of the MMC cannot be ensured. Moreover, due to their inherent sequential operation, sorting algorithms are suitable for software implementation (microcontrollers or DSPs), but they are not appropriate for a hardware implementation. Instead, in this paper, Sorting Networks (SNs) are proposed due to their convenience for implementation in FPGA devices. The advantages and the main challenges of the Bitonic SN in MMC applications are discussed and different FPGA implementations are presented. Simulation results are provided in normal and faulty conditions. Moreover, a comparison with the widely used bubble sorting algorithm and max/min approach is made in terms of execution time and performance. Finally, hardware-in-the-loop results are shown to prove the effectiveness of the implemented SN
Nouvel environnement européen et stabilité de l'Europe centrale
No full textThe New European Environment and the Stability of Central Europe, by Laszlo Valki
According to the author after the withdrawal of the Soviet troops front Hungary, Czechoslovakia, the former GDR, and most probably from Poland and after the dissolution of the Warsaw Pact no power vacuum will emerge in Central Europe. There is no immediate danger of any armed conflict in the region, even not in consequence of ethnical controversies. Much more threatening are the grave economie troubles, inherited from the post-Stalinist regimes. The author is very much afraid that many tasks simply cannot be solved simultaneously, e.g. decreasing enormous debts, accomplishing privatization, creating real market conditions, ensuring energy-supply, coping with the dissolution of Comecon, in other words, to start and bring to the end the system transformation. If these historical tasks will not be solved in the next couple of years, the world has to face with serious destabilization of domestic political orders, which might lead to destabilization of international relations in Central Europe, too.Selon l'auteur, après le retrait des troupes soviétiques de Hongrie, de Tchécoslovaquie, de l'ancienne RDA, et très vraisemblablement de Pologne, et après la dissolution du pacte de Varsovie, il n'y aura pas de vide du pouvoir en Europe centrale. Il n'y a aucun danger immédiat de conflit armé dans la région, même si l'on prend en compte les querelles ethniques. Les graves problèmes économiques hérités des régimes poststaliniens représentent un danger beaucoup plus grand. La grande crainte de l'auteur est que de nombreux impératifs ne puissent tout simplement pas être respectés simultanément comme, par exemple, réduire les énormes dettes, réussir la privatisation, créer une véritable économie de marché, assurer l'approvisionnement en énergie, s'adapter à la dissolution du Come-con ; autrement dit, commencer puis mener à terme la transformation du système. Si ces impératifs d'ordre historique ne sont pas respectés au cours des quelques années à venir, le monde devra faire face à une grave déstabilisation des régimes politiques intérieurs, ce qui pourrait aussi avoir comme conséquence une déstabilisation des relations internationales en Europe centrale.Valki Laszlo. Nouvel environnement européen et stabilité de l'Europe centrale. In: Politique étrangère, n°1 - 1991 - 56ᵉannée. pp. 157-164
Provenance-based trust for grid computing: Position Paper
No full textCurrent evolutions of Internet technology such as Web Services, ebXML, peer-to-peer and Grid computing all point to the development of large-scale open networks of diverse computing systems interacting with one another to perform tasks. Grid systems (and Web Services) are exemplary in this respect and are perhaps some of the first large-scale open computing systems to see widespread use - making them an important testing ground for problems in trust management which are likely to arise. From this perspective, today's grid architectures suffer from limitations, such as lack of a mechanism to trace results and lack of infrastructure to build up trust networks. These are important concerns in open grids, in which "community resources" are owned and managed by multiple stakeholders, and are dynamically organised in virtual organisations. Provenance enables users to trace how a particular result has been arrived at by identifying the individual services and the aggregation of services that produced such a particular output. Against this background, we present a research agenda to design, conceive and implement an industrial-strength open provenance architecture for grid systems. We motivate its use with three complex grid applications, namely aerospace engineering, organ transplant management and bioinformatics. Industrial-strength provenance support includes a scalable and secure architecture, an open proposal for standardising the protocols and data structures, a set of tools for configuring and using the provenance architecture, an open source reference implementation, and a deployment and validation in industrial context. The provision of such facilities will enrich grid capabilities by including new functionalities required for solving complex problems such as provenance data to provide complete audit trails of process execution and third-party analysis and auditing. As a result, we anticipate that a larger uptake of grid technology is likely to occur, since unprecedented possibilities will be offered to users and will give them a competitive edge
- …
