Symmetric Topology Research Articles

Comparative analysis of various multilevel inverter symmetrical topologies with minimum number of components

Multilevel inverters (MLI) are frequently used in different fields like, oil and gas sectors, installations of power supply, high power and medium voltage applications and in FACTS (flexible AC transmission system) devices to improve power quality. Lot of topologies has been developed in the literature regarding multilevel inverters such as diode clamped type, flying capacitor type and cascaded H-bridge type multilevel inverters. However, several challenges are being faced while implementing these topologies like more number of switches, more losses and cost. The optimized construction of multilevel inverter is to get more number of levels with less number of switches and low total harmonic distortion. In this paper, three different existing multilevel inverter topologies have been considered and analyzed for five level output voltage. A comparison table is given for number of switches, extra diodes and voltage sources. The total work is carried by using Matlab/simulink software and results are presented.

A Simulated Annealing-based optimization approach for minimizing the THD in asymmetric cascaded multilevel inverter

Objectives: This paper focuses on the reduction of harmonic content in the voltage output waveform of a 31 level asymmetric monophasic cascaded multilevel inverter using the Simulated Annealing Optimization (SAO) algorithm. Method: The SAO algorithm was used to find the appropriate switching angles for the stages of the converter using MATLAB. First, the technique employed was simulated and evaluated; then, a prototype of the multilevel inverter was developed for validating the results obtained in simulation. Findings: The output waveform, the harmonic profile graphic, and THD evolution were obtained both the simulation and the prototype. The SAO algorithm allowed to calculate the appropriate switching angles for the asymmetric multilevel inverter, permitting to obtain a low THD (less than 5%), using a relatively low number of semiconductors compared with the symmetric topology. The SAO algorithm also allowed finding the solution of transcendental equations system through a heuristic approach, avoiding the local minima problem presented in traditional methods. Novelty /Improvement: The proposed method (SAO) avoids the potential issues with local minima present in traditional methods for the switching angles computation in cascaded multilevel inverters. Keywords: Multilevel Inverter, Simulated Annealing, THD

Design of high‐performance bidirectional DC/DC converter applied for more electric aircraft

Bidirectional DC/DC converter is an important part of the more electric aircraft (MEA). A high-performance bidirectional DC/DC converter with high efficiency and power density reduces the both volume and power loss of the converter. There are mainly two kinds of basic topologies applied to bidirectional DC/DC converter. One is a dual active bridge (DAB) and the other is symmetrical CLLC resonant topology. Both topologies can realise zero-voltage switch (ZVS). The DAB has been widely researched and applied to many fields including the MEA as DAB is easy to design and control. However the ZVS region of the DAB is limited. What is worse, the DAB always switches when the current is at the peak. Symmetrical CLLC resonant topology has also been widely researched in recent years. Compared with the DAB, the symmetrical CLLC resonant converter can reach ZVS in a wider region. In this study both the topologies are discussed and the design of the better one is demonstrated. A 3 kW symmetrical CLLC resonant converter is designed to verify the conclusion.

Avoiding Collisions in Cucker--Smale Flocking Models under Group-Hierarchical Multileadership

The Cucker--Smale (C-S) flocking model can be applied to design several mobile autonomous agent systems such as unmanned aerial vehicles and robot systems. In these applications, the problem of collision is usually a nonnegligible issue that should be addressed. In the literature, extra bonding/repulsive forces are added to solve the problem of collision. However, all the known results are limited to the symmetric coupling topology. In this paper, we address this problem under a group-hierarchical multileadership consisting of symmetric coupling topologies and the hierarchical leadership. We obtain the following three main results. First, we show that the augmented C-S model achieves asymptotic flocking provided, roughly, that the ratio between the rate of bounding force and communication rate is sufficiently large. Second, we prove that, for a given augmented C-S model, there exists a set of initial states, which can be explicitly described, such that their corresponding solutions maintain some minimum distance between them. Finally, we show that, for a given set of initial states, we can control the system so that its corresponding solution is collision free by suitably choosing bounding forces, which are independent of given initial states. This in turn suggests that the corresponding system can be collision free by having tolerance for error in their initial states.

Implementation and Comparison of Symmetric and Asymmetric Multilevel Inverters for Dynamic Loads

This paper implements and compares a symmetric hybridized cascaded multilevel inverter and an asymmetric multilevel inverter utilizing a switched capacitor unit for 17 level inverters. The symmetric hybridized multilevel inverter topology consists of a modified H-bridge inverter, which results in an increase in the output voltage to five level from the three level by using a bi-directional switch at the midpoint of a dual-input dc source. In the proposed asymmetric multilevel inverter, dc sources are replaced with the switched capacitor unit, which in turn boosts the output voltage and produces twice the voltage levels at the loads. The proposed topology with the staircase modulation technique has been verified using MATLAB–SIMULINK, and the results are experimentally executed with prototype models, which are interfaced with dSPACE RTI 1104. The results of the proposed topologies are experimentally obtained for steady state, and the performance of the same is tested under different resistive and inductive load disturbance conditions. The results substantiate that these multilevel inverter topologies are better stabilized during load disturbance conditions with low total harmonic distortion, a lesser number of switches, and increased output voltage levels, and these topologies well suit for renewable energy applications.

Consensus of Fractional-Order Multiagent Systems with Nonuniform Time Delays

Due to the complex external environment, many multiagent systems cannot be precisely described or even cannot be described by an integer-order dynamical model and can only be described by a fractional-order dynamical model. In this paper, consensus problems are investigated for two types of fractional-order multiagent systems (FOMASs) with nonuniform time delays: FOMAS with symmetric time delays and undirected topology and FOMAS with asymmetric time delays and directed topology. Employing the Laplace transform and the frequency-domain theory, two delay margins are obtained to guarantee the consensus for the two types of FOMAS, respectively. These results are also suitable for the integer-order dynamical model. Finally, simulation results are provided to illustrate the effectiveness of our theoretical results.

A refractory metamaterial absorber for ultra-broadband, omnidirectional and polarization-independent absorption in the UV-NIR spectrum.

In this paper, efficient ultra-broadband absorption from ultraviolet (UV) to near infrared (NIR) is achieved using a metamaterial perfect absorber (MPA) with refractory constituents. Both simulated and experimental results indicate that this proposed MPA exhibits an average absorption over 95% at wavelengths ranging from 200 nm to 900 nm. Besides, owing to the ultrathin thickness and symmetrical topology of this device, it exhibits great angular tolerance up to 60° independent of the incident polarizations. Excellent thermal stability is also demonstrated at high operation temperatures. The physical origin of the ultra-broadband characteristics is mainly based on diffraction/interference engineering at short wavelengths and the anti-reflection effect at long wavelengths. We believe that such a device may find potential applications ranging from photodetection and photothermal energy conversion to ultraviolet protection and thermophotovoltaics.

A Simple Congestion-Aware Algorithm for Load Balancing in Datacenter Networks

We study the problem of load balancing in datacenter networks, namely, assigning the end-to-end data flows among the available paths in order to efficiently balance the load in the network. The solutions used today rely typically on an equal-cost multi path (ECMP) mechanism, which essentially attempts to balance the load in the network by hashing the flows to the available shortest paths. However, it is well-known that the ECMP performs poorly when there is asymmetry either in the network topology or the flow sizes, and thus, there has been much interest recently in alternative mechanisms to address these shortcomings. In this paper, we consider a general network topology where each link has a cost, which is a convex function of the link congestions. Flows among the various source–destination pairs are generated dynamically over time, each with a size (bandwidth requirement) and a duration. Once a flow is assigned to a path in the network, it consumes bandwidth equal to its size from all the links along its path for its duration. We consider low-complexity congestion-aware algorithms that assign the flows to the available paths in an online fashion and without splitting . Specifically, we propose a myopic algorithm that assigns every arriving flow to an available path with the minimum marginal cost (i.e., the path which yields the minimum increase in the network cost after assignment) and prove that it asymptotically minimizes the total network cost. Extensive simulation results are presented to verify the performance of the myopic algorithm under a wide range of traffic conditions and under different datacenter architectures. Furthermore, we propose randomized versions of our myopic algorithm, which have much lower complexity and empirically show that they can still perform very well in symmetric network topologies.

Analysis and Design of a Millimeter-Wave Cavity-Backed Circularly Polarized Radiator Based on Fundamental Theory of Multi-Port Oscillators

This paper presents the design and implementation of a millimeter-wave fundamental frequency circularly polarized radiator, which employs a multi-port cavity as the core of a high- $Q$ resonator, a power combiner, and an antenna. A general theory of multi-port oscillators—and in particular, the widely used circularly symmetric oscillator topologies—is presented, which quantitatively investigates and predicts all possible oscillation states, their associated modes of operation, and the oscillation stability. The outcomes of this theory are utilized to design a power-optimized eight-port rotationally symmetric radiator, excited at the oscillation state with a 45 phase difference between the adjacent ports, which, in turn, enables a high-efficiency circularly polarized radiation. Fabricated in 0.13- $\mu \text{m}$ BiCMOS process, this cavity-backed circularly polarized radiator operates at the frequency of 114 GHz and achieves 14.2-dBm equivalent-isotropic-radiated power (EIRP), 5.2% dc-to-EIRP conversion efficiency, 8.2 dBm radiated power, 1.3% dc-to-radiation efficiency, and −99.3 dBc/Hz phase noise at 1-MHz offset, without using silicon lens.

Grid-Interactive Cascaded H-Bridge Multilevel Converter PQ Plane Operating Region Analysis

Cascaded H-bridge (CHB) multilevel converters are being considered as a promising option for interfacing renewable energy resources with the grid due to their modularity, scalability, and increased efficiency when compared with traditionally used two-level inverters. When used as grid interfaces, CHB converters should be capable of controlling the injected active and reactive power while also satisfying operating criteria such as grid standards, e.g., IEEE 519. This paper aims to identify $PQ$ plane operating points available when using symmetric and asymmetric grid-interactive CHB converter topologies, and to determine the factors that prevent utilization of other converter output points. Notably, for asymmetric CHB converters, a technique is proposed to identify discordant output points where power is transferred between cells within a leg, e.g., one cell has a net regenerative power flow while the overall CHB leg does not. This work ( i ) provides distribution engineers with information regarding the active and reactive power that can feasibly be generated by grid-interactive CHB converter topologies, ( ii ) creates a framework for assessing operating point trajectories when altering the steady-state operation of grid-tied CHB converters, ( iii ) provides a basis for selecting and modifying steady-state pulse-width modulation generation techniques in order to meet desired performance criteria, and ( iv ) presents analytical techniques that can be built upon to facilitate analysis of grid-interactive CHB under conditions such as grid imbalance or during continued operation after CHB cell faults.

On weak completeness of products and direct sums in locally convex cones

We discuss the weak completeness of product and direct sum cones in the lower, upper and symmetric topologies. For the weak lower, upper and symmetric topology of a direct sum cone, there correspond bases of upper, respectively lower and symmetric, closed members in a coarser topology which leads us to investigate the weak completeness of direct sum cones.

Battery Internal Short Circuit Detection

Internal short circuit (ISCr) is one of the major obstacles that impede the improvement of the battery safety. In this work, a new ISCr detection method based on the symmetrical loop circuit topology (SLCT) for the battery pack is introduced. The SLCT ensures every battery has the same weight in the circuit and every battery will contribute the same amount of short circuit current to the ISCr once the ISCr happens. The ISCr battery could be identified by using the combination of the ratio and the sign of the short circuit currents. The battery pack based on individual DP (dual polarization) battery models is established to verify the ISCr detection method. The proposed ISCr detection method shows excellent effectiveness and efficiency on the identification of ISCr battery in the early stage, and hence provides sufficient time margin and safety margin to take countermeasures.

Third-Order Frequency-Agile Substrate-Integrated Waveguide Filter With a Pair of Transmission Zeros

In this letter, we present a third-order frequency-agile substrate-integrated waveguide (SIW) filter with a pair of transmission zeros. In addition, a relationship between the symmetric and asymmetric topologies for having same frequency responses is derived in this letter so that the coupling values of the asymmetric filter topology can be directly obtained from those of the symmetric one. For practical implementation, we also present a new methodology for physical implementation of a source-to-multiresonator coupling for frequency-tunable SIW resonator structure. The filter has been fabricated and measured for verifying the presented filter topology.

A Novel Symmetrical Cascade H-Bridge Multi-Level Inverter Topology with Reduced Switching Devices

A Novel Symmetrical Cascade H-Bridge Multi-Level Inverter Topology with Reduced Switching Devices

Phase Desynchronization: A New Approach and Theory Using Pulse-Based Interaction

In this paper, we present a novel approach for achieving phase desynchronization in a pulse-coupled oscillator network. Ensuring phase desynchronization is a difficult problem, and existing results are constrained to a completely interconnected network and a fixed number of nodes. Our approach is more robust than previous approaches, removing the constraint of a fixed number of nodes. The removal of this constraint is significant because it allows the network to receive and drop nodes freely without any change to the phase update strategy. Also, to our knowledge, our approach is the first to prove the convergence to the desynchronized state for a topology that is more general than the all-to-all topology. More specifically, our approach is applicable to any circulant, symmetric network topology, including the circulant symmetric ring topology. Rigorous mathematical proofs are provided to support the result that any circulant, symmetric network with ordered phases under our proposed algorithm will converge to uniform phase desynchronization. Simulation results are also presented to demonstrate the algorithm's performance.

Creative Structure of Symmetric and Asymmetric Multilevel Converter Topology Using Single-Double Source Unit

Creative Structure of Symmetric and Asymmetric Multilevel Converter Topology Using Single-Double Source Unit

Finite dimensional locally convex cones

We study the locally convex cones which have finite dimension. We introduce the Euclidean convex quasiuniform structure on a finite dimensional cone. In special case of finite dimensional locally convex topological vector spaces, the symmetric topology induced by the Euclidean convex quasiuniform structure reduces to the known concept of Euclidean topology. We prove that the dual of a finite dimensional cone endowed with the Euclidean convex quasiuniform structure is identical with it?s algebraic dual.

On the Wiener Polarity Index of Lattice Networks.

Network structures are everywhere, including but not limited to applications in biological, physical and social sciences, information technology, and optimization. Network robustness is of crucial importance in all such applications. Research on this topic relies on finding a suitable measure and use this measure to quantify network robustness. A number of distance-based graph invariants, also known as topological indices, have recently been incorporated as descriptors of complex networks. Among them the Wiener type indices are the most well known and commonly used such descriptors. As one of the fundamental variants of the original Wiener index, the Wiener polarity index has been introduced for a long time and known to be related to the cluster coefficient of networks. In this paper, we consider the value of the Wiener polarity index of lattice networks, a common network structure known for its simplicity and symmetric structure. We first present a simple general formula for computing the Wiener polarity index of any graph. Using this formula, together with the symmetric and recursive topology of lattice networks, we provide explicit formulas of the Wiener polarity index of the square lattices, the hexagonal lattices, the triangular lattices, and the 33 ⋅ 42 lattices. We also comment on potential future research topics.

A Level Dependent Source Concoction Multilevel Inverter Topology with a Reduced Number of Power Switches

Multilevel inverters (MLIs) have been preferred over conventional two-level inverters due to their inherent properties such as reduced harmonic distortion, lower electromagnetic interference, minimal common mode voltage, ability to synthesize medium/high voltage from low voltage sources, etc. On the other hand, they suffer from an increased number of switching devices, complex gate pulse generation, etc. This paper develops an ingenious symmetrical MLI topology, which consumes lesser component count. The proposed level dependent sources concoction multilevel inverter (LDSCMLI) is basically a multilevel dc link MLI (MLDCMLI), which first synthesizes a stepped dc link voltage using a sources concoction module and then realizes the ac waveform through a conventional H-bridge. Seven level and eleven level versions of the proposed topology are simulated in MATLAB r2010b and prototypes are constructed to validate the performance. The proposed topology requires lesser components compared to recent component reduced MLI topologies and the classical topologies. In addition, it requires fewer carrier signals and gate driver circuits.

Highly Porous Zirconium Metal-Organic Frameworks with β-UH3-like Topology Based on Elongated Tetrahedral Linkers.

Two non-interpenetrated zirconium metal-organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr6 and Zr8 clusters. They represent the first examples of MOFs to have the β-UH3-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m(2) g(-1)) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)3](2+) for heterogeneous photo-oxidation of thioanisole.