Five-level selective harmonic elimination PWM strategies and multicarrier phase-shifted sinusoidal PWM: A comparison

The multicarrier phase-shifted sinusoidal pulse-width modulation (MPS-SPWM) technique is well-known for its important advantage of offering an increased overall bandwidth as the number of carriers multiplied with their equal frequency directly controls the location of the dominant harmonics. In this paper, a five-level (line-to-neutral) multilevel selective harmonic elimination PWM (MSHE-PWM) strategy based on an equal number of switching transitions when compared against the previously mentioned technique is proposed. It is assumed that the four triangular carriers of the MPS-SPWM method have nine per unit frequency resulting in seventeen switching transitions for every quarter period. Requesting the same number of transitions from the MSHE-PWM allows the control of sixteen non-triplen harmonics. It is confirmed that the proposed MSHE-PWM offers significantly higher converter bandwidth along with higher modulation operating range. Selected results are presented to confirm the effectiveness of the proposed technique

Generalized formulation of multilevel selective harmonic elimination PWM: Case I-Non-Equal DC Sources

The paper presents optimal solutions for eliminating harmonics from the output waveform of a multilevel staircase pulse-width modulation (PWM) method with non-equal dc sources. Therefore, the degrees of freedom for specifying the cost function increased without physical changes as compared to the conventional stepped waveform. The paper discusses an efficient hybrid real coded genetic algorithm (HRCGA) that reduces significantly the computational burden resulting in fast convergence. An objective function describing a measure of effectiveness of eliminating selected order of harmonics while controlling the fundamental for any number of levels and for any number of switching angels is derived. It is confirmed that multiple independent sets of solutions exist and the ones that offer better harmonic performance are identified. Different operating points including five- and seven-level inverters are investigated and simulated. Selected experimental results are reported to verify and validate the effectiveness of the proposed method

On abolishing symmetry requirements in the formulation of a five-level selective harmonic elimination pulse-width modulation technique

Selective harmonic elimination pulse width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It was shown recently that symmetry requirements can be relaxed as a constraint. This changes the way the problem is formulated, and different solutions can be found without a compromise. This letter reports solutions to the switching transitions of a five-level SHE-PWM when both the quarter- and half-wave symmetry are abolished. Only the region of high-modulation indices is reported since the low-modulation indices region requires a unipolar waveform to be realized. Selected simulation and experimental results are reported to show the effectiveness of the proposed method

A Seven-level defined selective harmonic elimination PWM strategy

Selective harmonic elimination pulse-width modulation (SHE-PWM) techniques offer an optimized control approach for a given converter and are therefore suitable for the low switching frequency high-power applications. Optimization techniques can be successfully used to obtain the solutions of the equations defining the SHE-PWM waveform. In this paper, a seven-level multilevel strategy (MSHE-PWM) defined on the line-to-neutral basis and based on a ratio of a variable number of angles distributed over three levels to be able to calculate the transition points is reported. The technique provides eighteen switching transitions for every quarter period in the standard modulation index range. In the overmodulation region, this can be changed in order to increase the gain of the modulator which in turn results in a compromised bandwidth. The switching angles as a function of the modulation index are reported for the standard as well as the overmodulation range. Selected simulation results are presented to verify the effectiveness and feasibility of the proposed method

Comparison of bipolar sub-modules for the alternate arm converter

© 2016 IEEE.Research on dc-fault tolerant multilevel converters has gained noticeable attention over recent years. The alternate arm converter (AAC) is one of such emerging multilevel converter topologies, and a hybrid topology of the two-level converter and the modular multilevel converter (MMC). Bipolar sub-modules (SMs) that can produce both positive and negative voltages are the building blocks of the AAC. This paper analyses the operation of an AAC with the full-bridge SM (FB-SM) and the cross-connected SM (CC-SM). The conduction and switching losses of the two SM configurations are evaluated and compared, in order to identify the suitability of CC-SM for AACs and its performance compared to the FB-SM. The CC-SM with identical semiconductor devices has reduced losses compared to the CC-SM with higher rated devices in the cross-connected path. It is concluded that the CC-SM does not offer advantages in the losses, construction, and application to the AAC, compared to FB-SM

Vom Palladion zur Nikephoros: Der Kult der Athena im Kontext der Herrschaftslegitimation im spätklassischen und hellenistischen Pergamon

Die politische Instrumentalisierung des Athena-Kultes durch die Führungsschichten Pergamons von seiner Gründung in der spätklassischen Zeit bis zum Ende der attalidischen Herrschaft steht im Mittelpunkt des Beitrags. Dabei werden die Zuschreibung der Initiation dieses Kultes an Barsine und Herakles relativiert, und gleichzeitig direkte Bezüge zu Alexander dem Großen konstatiert. Reflexionen des Kultbildes in der Münzprägung und Reliefkunst lassen als Vorbild das mythische Palladion Trojas, wie es in der Vasenmalerei, Kleinkunst und Plastik erscheint, fassen. Athena wird somit zum prägnanten Verknüpfungspunkt für die Gründer des Kultes der Göttin in Pergamon mit dem großen Argeaden. Einige ikonographische Elemente des Kultbildes sowie die räumliche Beziehung des Athena-Tempels zu weiteren Heiligtümern auf der Akropolis und in der Umgebung von Pergamon legen ferner eine intentionelle, enge Verbindung zu Meter nahe, durch die eine Akzeptanz des neu eingeführten Athena-Kultes durch die Einheimischen begünstigt wurde. Die religionspolitische Tätigkeit der pergamenischen Herrscher wird mit einem besonderen Augenmerk auf ihren Umgang mit Athena und Meter skizziert, und in Verbindung mit der Mythisierung der Stadtgeschichte betrachtet. Auch die Bezugnahme auf Athen im Zuge der Stilisierung Pergamons als Beschützerin von Recht und Ordnung, sowie als Hüterin der griechischen Kultur in der Nachfolge des klassischen Athen wird überprüft und relativiert. Athena- und Meter-Kult werden zu zentralen Mitteln der attalidischen Bemühungen um die Legitimierung ihrer Macht gegenüber der griechischen Welt und der einheimischen Bevölkerung.The article focuses on the political instrumentalization of the cult of Athena by the ruling classes of Pergamon from its foundation in late Classical times to the end of Attalid rule. Attribution of the initiation of the cult to Barsine and Herakles is qualified and direct connections with Alexander the Great are noted. Reflections of the cult image in coinage and relief art enable us to recognize what it was modelled on: the mythical palladium of Troy as it appears in vase painting, glyptic and small-format plastic art. Thus for the founders of the goddess’ cult at Pergamon, Athena becomes a substantial link with the great Argead. Furthermore, some iconographic elements of the cult image in addition to the spatial relationship of the Temple of Athena with other sanctuaries on the acropolis and in the vicinity of Pergamon suggest an intentional, close connection with Meter – which was conducive to the acceptance of the recently introduced Athena cult by the local population. The religious policy of the Pergamene rulers is sketched, with particular attention being paid to their approach to Athena and Meter, and is considered in connection with the mythification of the city’s history. Also reassessed and relativized is the reference to Athens in the course of the stylization of Pergamon as the defender of law and order and guardian of Greek culture, following on from classical Athens. The cults of Athena and Meter become key instruments in Attalid efforts to legitimize their rule with respect to the Greek world and to the local population.Pergamon’un yönetim kademeleri tarafından kurulduğu Geç Klasik dönemden Attalid hükümdarlığının sona erişine kadar Athena kültünün siyasi bir araç haline gelişi, bu makalenin odak noktasını oluşturmaktadır. Bunun yanı sıra bu kültün kökenini Barsine ve Herakles kültlerinde olduğu görüşü uyarlanmıştır; aynı zamanda Büyük İskender ile doğrudan ilişkilendirildiği saptanmıştır. Bu kültün sikke darbı ve rölyef sanatındaki yansımaları, vazo boyama, küçük sanatlar ve heykeltıraşide de olduğu gibi, mitolojik Truva Palladion’unun modeli olarak anlaşılabilir. Böylelikle Athena, Pergamon’daki tanrıça kültünün kurucuları için, büyük Argeadlar’la esaslı bağlantı noktası olmuştur. Kültün bazı ikonografik unsurları kadar Athena tapınağının Akropolis’teki ve Pergamon çevresindeki başka kutsal alanlarla olan mekânsal ilişkisi Meter’le bilinçli, sıkı bir bağlantı olasılığını güçlendirmektedir. Bu da, yöre halkı tarafından tercih edilen, yeni tanıtılan Athena kültünün kabul edilişinden anlaşılmaktadır. Pergamon krallarının dini-politik görevleri, Athena ve Meter’i kullanmalarına özel bir dikkat gösterilerek kısaca gösterilmiştir. Bu da kent tarihinin mitleştirilmesiyle birlikte ele alınmıştır. Düzenin ve hukukun koruyucusu olduğu gibi, Klasik Atina’nın ardılı Yunan kültürünün hamisi olarak Pergamon’un stilize edilmesi bağlamında Atina ile ilgili olarak da gözden geçirilmiş ve böylece daha geniş bir perspektif içinde değerlendirilmiştir. Athena ve Meter kültü, Attaloslar’ın güçlerini Yunan dünyasına ve yöre halkına karşı ispat etme çabalarının temel aracı olmuştur

Network topology independent multi-agent dynamic optimal power flow for microgrids with distributed energy storage systems

This paper proposes a multi-agent dynamic optimal power flow (DOPF) strategy for microgrids with distributed energy storage systems. The proposed control strategy uses a convex formulation of the ac DOPF problem developed from a d-q reference frame voltage-current model and linear power flow approximations. The convex DOPF problem is divided between autonomous agents and solved based on local information and neighbour-to-neighbour communication over a sparse communication network, using a distributed primal subgradient algorithm. Each agent is only required to solve convex quadratic sub-problems, for which robust and efficient solvers exist, making the control strategy suitable for receding horizon model predictive control. Also, the agent sub-problems require limited power network information and include only a subset of the centralised optimisation problem decision variables and constraints, providing scalability and data privacy. Unlike existing distributed optimal power flow methods, such as alternating direction method of multipliers, under the proposed control strategy the information required by each agent is independent of the communication network topology, providing increased flexibility and robustness. The performance of the proposed control strategy was verified for an ac microgrid with distributed lead-acid batteries and intermittent photovoltaic generation, using an RTDS Technologies real-time digital simulator