Interconnection Topology Research Articles

Dissipativity-Guaranteed Distributed Model Predictive Controller for Reconfigurable Large-Scale System

This paper presents a distributed model predictive control strategy for reconfigurable large-scale systems to maintain global stability when there are subsystems joining in or leaving the system during closed-loop operation, which is also called the plug-and-play control. Dissipativity is an input–output property, and the overall dissipativity property of a large-scale system can be described by the ‘linear’ combination of the dissipativity properties of its subsystems based on their interconnection topology. The capacity of capturing interaction effects among subsystems on overall stability makes dissipative system theory a useful tool to design control system for reconfigurable large-scale system. The redesign is restricted to subsystems whose input–output property will be directly influenced by the topology change in order to allow quick operation. The overall stability condition can still be guaranteed if the dissipativity property of the redesigned subsystems does not spoil the overall dissipativity condition. Simulation results of a power network system with subsystems joining in and leaving the network show the effectiveness of the proposed strategy.

Consensus Tracking by Iterative Learning Control for Linear Heterogeneous Multiagent Systems Based on Fractional-Power Error Signals

This paper deals with the consensus tracking problem of heterogeneous linear multiagent systems under the repeatable operation environment, and adopts a proportional differential (PD)-type iterative learning control (ILC) algorithm based on the fractional-power tracking error. According to graph theory and operator theory, convergence condition is obtained for the systems under the interconnection topology that contains a spanning tree rooted at the reference trajectory named as the leader. Our algorithm based on fractional-power tracking error achieves a faster convergence rate than the usual PD-type ILC algorithm based on the integer-order tracking error. Simulation examples illustrate the correctness of our proposed algorithm.

Distributed Multiagent Convex Optimization Over Random Digraphs

This paper considers an unconstrained collaborative optimization of a sum of convex functions, where agents make decisions using local information in the presence of random interconnection topologies. We recast the problem as minimization of the sum of convex functions over a constraint set defined as the set of fixed-value points of a random operator derived from weighted matrices of random graphs. We show that the derived random operator has nonexpansivity property; therefore, this formulation does not need the distribution of random communication topologies. Hence, it includes random networks with/without asynchronous protocols. As an extension of the problem, we define a novel optimization problem, namely minimization of a convex function over the fixed-value point set of a nonexpansive random operator. We propose a discrete-time algorithm using diminishing step size for converging almost surely and in mean square to the global solution of the optimization problem under suitable assumptions. Consequently, as a special case, it reduces to a totally asynchronous algorithm for the distributed optimization problem. We show that fixed-value point is a bridge from deterministic analysis to random analysis of the algorithm. Finally, a numerical example illustrates the convergence of the proposed algorithm.

A New Cost Effective and Reliable Interconnection Topology for Parallel Computing Systems

Topology of the of interconnection network is one of the most important considerations in the design of parallel systems as it is the backbone network over which the different components of the computer communicate with each other. The properties of the topology such as connectivity, reliability, cost, fault tolerance, diameter and bisection width determine the flawless-less data transmission between the source and the sink nodes. In this paper, we propose a new hybrid interconnection network topology called TOR-CUBE (TC) which is a product of two classical popular interconnection topologies namely hypercube and torus. Further, we show the construction and characteristics of the proposed interconnection topology. We also presented some basic important properties and formulated two routing algorithms for TC. Our results show that the proposed interconnection topology has high connectivity, lesser diameter, low cost, fault tolerant, scalable and low average distance. The different reliability measures of TC are computed and found to be better as compared with its counterpart topologies and the parent topologies.

Cu,N-Codoped Carbon Nanodisks with Biomimic Stomata-Like Interconnected Hierarchical Porous Topology as Efficient Electrocatalyst for Oxygen Reduction Reaction.

Metal,N-codoped carbon (M-N-C) nanostructures are promising electrocatalysts toward oxygen reduction reaction (ORR) or other gas-involved energy electrocatalysis. Further creating pores into M-N-C nanostructures can increase their surface area, fully expose the active sites, and improve mass transfer and electrocatalytic efficiency. Nonetheless, it remains a challenge to fabricate M-N-C nanomaterials with both well-defined morphology and hierarchical porous structures. Herein, high-quality 2D Cu-N-C nanodisks (NDs) with biomimic stomata-like interconnected hierarchical porous topology are synthesized via carbonization of Cu-tetrapyridylporphyrin (TPyP)-metal-organic frameworks (MOFs) precursors and followed by etching the carbonization product (Cu@Cu-N-C) along with re-annealing treatment. Such hierarchical porous Cu-N-C NDs possess high specific surface area (293 m2 g-1 ) and more exposed Cu single-atom sites, different from their counterparts (Cu@Cu-N-C) and pure N-C control catalysts. Electrochemical tests in alkaline media reveal that they can efficiently catalyze ORR with a half-wave potential of 0.85 V (vs reversible hydrogen electrode), comparable to Pt/C and outperforming Cu@Cu-N-C, N-C, Cu-TPyP-MOFs, and most other reported M-N-C catalysts. Moreover, their stability and methanol-tolerant capability exceed Pt/C. This work may shed some light on optimizing 2D M-N-C nanostructures through bio-inspired pore structure engineering, and accelerate their applications in fuel cells, artificial photosynthesis, or other advanced technological fields.

Controllability and observability of multi-agent systems with general linear dynamics under switching topologies

This paper investigates controllability and observability of multi-agent systems, in which all the agents adopt identical general linear dynamics and the interconnection topologies are switching. For controllability, criteria are established by virtue of the switching sequence and the constructed subspace sequence, respectively. Furthermore, controllability is considered from the viewpoint of graph theory, and distance partition and almost equitable partition are introduced into switching topologies to quantitatively analyse the controllable state set of the system. For observability, sufficient and/or necessary conditions are presented in terms of the system matrices and the associated invariant subspace. Finally, some numerical simulations are worked out to illustrate the theoretical results.

From Dissipativity Theory to Compositional Abstractions of Interconnected Stochastic Hybrid Systems

In this paper, we derive conditions under which compositional abstractions of networks of stochastic hybrid systems can be constructed using the interconnection topology and joint dissipativity-type properties of subsystems and their abstractions. In the proposed framework, the abstraction, itself a stochastic hybrid system (possibly with a lower dimension), can be used as a substitute of the original system in the controller design process. Moreover, we derive conditions for the construction of abstractions for a class of stochastic hybrid systems involving nonlinearities satisfying an incremental quadratic inequality. In this paper, unlike existing results, the stochastic noises and jumps in the concrete subsystem and its abstraction need not be the same. We provide examples with numerical simulations to illustrate the effectiveness of the proposed dissipativity-type compositional reasoning for interconnected stochastic hybrid systems.

Formation control with obstacle avoidance of second-order multi-agent systems under directed communication topology

This paper addresses the obstacle avoidance problem of formation control for the multi-agent systems modeled by double integrator dynamics under a directed interconnection topology. The control task is finished by a leader-follower formation scheme combined with an artificial potential field (APF) method. The leader-follower scheme is carried out by taking the desired trajectory with the desired velocity as virtual leader, while the APF method is carried out by dealing with the obstacles as the high potential points. When the obstacle avoidance tasks are finished, the artificial potential forces degrade the formation performance, so their undesired effects are treated as disturbances, which is analyzed by the robust ${{H}_{\infty~}}$ performance. Based on Lyapunov stability theory, it is proved that the proposed formation approach can realize the control objective. The result is also extended to the switching multi-agent formation. The effectiveness of the proposed formation scheme is further confirmed by simulation studies.

Controllability of Switching Signed Networks

This brief investigates the controllability of switching signed networks, in which the interconnection topologies are directed, weighted, and switched. First, we study the controllability from the union digraph perspective and derive a graph-theoretic sufficient condition. It is shown that a switching signed network can be controllable even if each of its subnetworks is uncontrollable. Second, we consider the controllability of simultaneously structurally balanced signed networks. It is found that the controllability of simultaneously structurally balanced networks is equivalent to the controllability of their corresponding unsigned networks. Finally, several numerical examples are given to illustrate the effectiveness of the theoretical results.

Edge-bipancyclicity in conditional edge-faulty k-ary n-cubes

The class of k-ary n-cubes represents the most commonly used interconnection topology for parallel and distributed computing systems. In this paper, we consider the faulty k-ary n-cube with even k ≥ 4 and n ≥ 2 such that each vertex of the k-ary n-cube is incident with at least two healthy edges. Based on this requirement, we investigate the fault-tolerant capabilities of the k-ary n-cube with respect to the edge-bipancyclicity. We prove that in the k-ary n-cube Qnk, every healthy edge is contained in fault-free cycles of even lengths from 6 to |V(Qnk)|, even if the Qnk has up to 4n − 5 edge faults and our result is optimal with respect to the number of edge faults tolerated.

Photonic-integrated circuits with non-planar topologies realized by 3D-printed waveguide overpasses.

Complex photonic-integrated circuits (PIC) may have strongly non-planar topologies that require waveguide crossings (WGX) when realized in single-layer integration platforms. The number of WGX increases rapidly with the complexity of the circuit, in particular when it comes to highly interconnected optical switch topologies. Here, we present a concept for WGX-free PIC that relies on 3D-printed freeform waveguide overpasses (WOP). We experimentally demonstrate the viability of our approach using the example of a 4 × 4 switch-and-select (SAS) circuit realized on the silicon photonic platform. We further present a comprehensive graph-theoretical analysis of different n × n SAS circuit topologies. We find that for increasing port counts n of the SAS circuit, the number of WGX increases with n4, whereas the number of WOP increases only in proportion to n2.

Multi‐layer distributed protocols for robust cooperative tracking in interconnected nonlinear multiagent systems

SummaryWe develop a mixed graph and optimal control theoretic formulation to design a robust cooperative control protocol for a large‐scale multiagent system with partially known interconnected first‐, second‐, or mixed first‐ and second‐order dynamics. In each case, we transform the control protocol design task to a robust communication graph design problem, which, from a cyber‐physical perspective, is interpreted as the control layer design problem for an interconnected system with unknown agent layer dynamics. According to this viewpoint, each state variable has its own control layer communication topology separate from the other state variable's communication topology and the unknown agent layer interconnection topologies. We prove that all cooperative, decentralized, and centralized tracking protocols can be treated as a single design problem and, by deriving closed‐form solutions for the robust control layer topologies, we further provide a simpler design procedure, which is only based on the matrix manipulations. Aside from the linear implementation of the protocol and the connection of the proposed formulation to the well known rules‐of‐thumb in optimal control theory, this creates a higher potential to transfer ideas to industry. Modeling uncertainties tolerable by a given control layer topology is analyzed, and a preliminary performance‐oriented analysis and design approach for large‐scale interconnected systems is discussed. We show that exactly the same steps can be followed to design appropriate control layers for both tracking and stabilization.

Analysis of Dissipative Losses in Modular Reconfigurable Energy Storage Systems Using SystemC TLM and SystemC-AMS

Battery storage systems are becoming more popular in the automotive industry as well as in stationary applications. To fulfill the requirements in terms of power and energy, the literature is increasingly discussing electrically reconfigurable interconnection topologies. However, these topologies use switching elements on the cell and module level that exhibit an electric resistance due to their design and hence generate undesirable dissipative losses. In this article, we propose a new analysis and optimization framework to examine and minimize the losses in such topologies. For this purpose, we develop a SystemC model to investigate static and dynamic load scenarios, e.g., from the automotive domain. The model uses SystemC TLM for the digital subsystem, SystemC-AMS for the mixed-signal subsystem, and host-compiled simulation for the microcontroller executing the embedded software. Here, we analyze the impact of the dissipative losses on the system efficiency that depend on the modularization level, implying the number of serial and parallel switching elements. Our analysis clearly shows that in reconfigurable topologies, the modularization level has a significant influence on the losses, which in our automotive example covers several orders of magnitude. For the topologies we have investigated, the highest efficiency can be reached when a parallel-only modularization is aspired and the number of serial switching elements is minimized. It is also shown that the losses of the state-of-the-art topology with one battery pack protection switch are almost as high as in a smart cell approach in which each energy storage cell has its own switching element. However, due to the high number of switching elements, this results in a reduction of energy density and increases the system costs, showing that this is a multi-criteria optimization problem.

Ultra-Low Cost High-Density Two-Dimensional Visible-Light Optical Interconnects

Visible light communications have attracted considerable interest in recent years owing to the ability of low-cost light emitting diodes (LEDs) to act both as illumination sources and data transmitters with moderate data transmission rates. In this paper, we propose the formation of ultra-low cost visible-light integrated optical links by interfacing dense micro-pixelated LED arrays with matching multi-layered multimode polymer waveguide arrays. The combination of these two optical technologies can offer relatively high aggregate data densities ≥ 0.5 Tb/s/mm2 using very low cost components that can be directly interfaced with CMOS electronics and integrated onto standard printed circuit boards. Here, we present the basic system design and report the first proof-of-principle demonstration of such a visible light system employing 4×4 μLED arrays on a pitch matching four-layered waveguide array samples. Different interconnection topologies and light coupling schemes are investigated and their performance in terms of loss and crosstalk is compared. Data transmission of 2.5 Gb/s with a bit error rate within the forward-error correction threshold of 3.8×10−3 is achieved over a single μLED-waveguide channel using PAM-4 modulation and equalization. The results presented here demonstrate the potential of such ultra-low cost visible-light optical interconnects.

The effect of yeast supplementation on equine fecal microbial population dynamics following abrupt dietary changes

In this paper, we propose a compositional approach for the construction of finite abstractions (a.k.a. finite Markov decision processes (MDPs)) for networks of discrete-time stochastic control subsystems that are not necessarily stabilizable. The proposed approach leverages the interconnection topology and a notion of finite-step stochastic storage functions, that describes joint dissipativity-type properties of subsystems and their abstractions, and establishes a finite-step stochastic simulation function as a relation between the network and its abstraction. To this end, we first develop a new type of compositionality conditions which is less conservative than the existing ones. In particular, using a relaxation via a finite-step stochastic simulation function, it is possible to construct finite abstractions such that stabilizability of each subsystem is not necessarily required. We then propose an approach to construct finite MDPs together with their corresponding finite-step storage functions for general discrete-time stochastic control systems satisfying an incremental passivability property. We also construct finite MDPs for a particular class of nonlinear stochastic control systems. To demonstrate the effectiveness of the proposed results, we first apply our approach to an interconnected system composed of 4 subsystems such that 2 of them are not stabilizable. We then consider a road traffic network in a circular cascade ring composed of 50 cells, and construct compositionally a finite MDP of the network. We employ the constructed finite abstractions as substitutes to compositionally synthesize policies keeping the density of the traffic lower than 20 vehicles per cell. Finally, we apply our proposed technique to a fully interconnected network of 500 nonlinear subsystems and construct their finite MDPs with guaranteed error bounds on the probabilistic distance between their output trajectories.

(Gordon E. Moore Medal for Outstanding Achievement in Solid State Science and Technology Award Address) Towards Silicon-Based Photonic Integrated Circuits: The Quest for Compatible Light Sources

Optoelectronics and photonics are playing an essential role in many aspects of daily life, including information and communication technologies, environmental and green technologies, mechanical and chemical sensing, consumer electronics, and biomedicine. So far, the use of optical components in communication systems has been mainly limited to direct replacement of electrical cables by optical cables. With the continual increase in link bit rates, optical cables are now replacing electrical cables for shorter and shorter interconnect lengths. Optoelectronic and photonic technologies are becoming less costly and more integrated, and there is currently an opportunity for optics to move “inside the box” and change the interconnect topology at all levels. Optical interconnects are required these days for on-chip technology as an alternative to metal wires, because of data transmission bottlenecks introduced by their unavoidable delay times, significant signal degradation, problems with power dissipation, and electromagnetic interference. Such optical interconnects will help in extending the life of Moore’s Law [1]. Currently, most optoelectronic devices are fabricated as discrete components. This approach is based on serial (e.g., step-by-step) fabrication and packaging, and it makes optoelectronic technology drastically different compared to microelectronics, where the domination of parallel fabrication made possible ultra large scale integration. Also, discrete assembly reduces the optoelectronic system reliability and decreases the manufacturing yield. Additional complications arise due to materials issues: in microelectronics the major material is elemental silicon, while traditional semiconductor materials for optoelectronics are III-V compound alloys with much more complex technological requirements. Finally, optical waveguides and waveguide based devices are very bulky compared to electron devices; thus, the densities of electron devices in integrated circuits are many orders of magnitude greater compared to that in integrated optoelectronic systems. Silicon photonics, where photonics devices are fabricated by using silicon or silicon compatible materials and where the manufacturing is based on the available microelectronics infrastructure, is emerging as the technology that can face all these challenges [2]. Silicon photonics is booming and growing at an incredible pace with many breakthroughs appearing day by day [3,4]. Speed, integration density, active components, logic, nonlinear optics, etc., are all surpassed frontiers, which silicon photonics has continuously moved apart. Many devices enabled by silicon photonics are already on the market and new ones are emerging continually [5]. Despite these advances, the major deficiency in such optoelectronic and photonic devices remains the lack of suitable silicon-based light emitters and especially lasers, which would enable a fully integrated silicon platform. In order to be commercially viable, these light emitters need to be efficient, fast, operational at room temperature, and, perhaps most importantly, be compatible with mainstream CMOS technology. Another important requirement is in the emission wavelength, which should match the optical waveguide low-loss spectral region of 1.3–1.6 μm. The main problem in utilizing silicon as a light emitter is its indirect electronic band gap that results in inefficient carrier recombination and a long radiative lifetime. Many quite different approaches to alleviating the miserable light emission in bulk silicon (~10-4 quantum efficiency at 300 K) have been proposed and are actively being explored [6]. Some, such as Si1-xGex quantum well or Si/SiO2 superlattice structures, rely on band structure engineering, while others rely on quantum confinement effects in lower dimensional structures, as typified by silicon quantum dots or porous silicon. Still another approach is impurity-mediated luminescence from, for example, isoelectronic substitution or by the addition of rare earth or transition metal ions to silicon. In this presentation, the use of the quantum confinement approach we have employed to producing efficient light emission in silicon and germanium will be reviewed. Nanostructured systems that will be covered include porous silicon, silicon quantum wells and wires, super unit cells, and arrays of silicon-germanium quantum dots. https://en.wikipedia.org/wiki/Moore%27s_lawL. Pavesi and D.J. Lockwood, Silicon Photonics (Springer, Berlin, 2004).Special issue on Silicon Photonics, Proc. IEEE 97(7), July (2009).D.J. Lockwood and L. Pavesi, Silicon Photonics II: Components and Integration (Springer, Berlin, 2011).L. Pavesi and D.J. Lockwood, Silicon Photonics III: Systems and Applications (Springer, Berlin, 2016).D.J. Lockwood, Light Emission in Silicon (Academic, New York, 1998).

Distributed economic and environmental dispatch in two kinds of CCHP microgrid clusters

Interconnected microgrids can enable mutual power support among microgrids (MGs) and improves the utilization of renewable energy sources, especially for CCHP-based (Combined Cooling, Heating, and Power) Microgrid Cluster (MGC). To preserve information privacy and achieve scheduling independence of microgrids, the problem of multi-area economic and environmental dispatch in CCHP plus MGC can be computed by distributed algorithm framework, i.e., generalized benders decomposition (GBD), optimal condition decomposition (OCD) and auxiliary problem principle (APP), respectively for interconnected topology and bus topology. Moreover, chance constrained programming (CCP) is added to address the uncertainty factors of renewable energy, cooling, heating, and electrical loads. A consensus-based distributed fair cost allocation algorithm is proposed to make a comparison with the condition of adding selfish constraints and independent operation, so that guaranteeing the stability of economic coalition of MGC. A case study with four networked CCHP microgrids in two kinds of topology is tested to demonstrate the effectiveness of the proposed approach in summer scenario. In conclusion, distributed algorithms will have a prospective application on MGC as the result of the necessity from different entities in the future.

Power and mismatch losses mitigation by a fixed electrical reconfiguration technique for partially shaded photovoltaic arrays

Abstract Partial shading is the most commonly occurring scenario among the modules of the photovoltaic arrays invoking power and mismatch losses. To attenuate these losses, various interconnection topologies for partial shading mitigation have been proposed in the literatures. This paper proposes a fixed electrical reconfiguration technique for the modules that facilitates distribution of the effect of shading in the entire array thereby reducing the losses caused by partial shading. The technique proceeds with renumbering of the modules according to the proposed algorithm followed by electrical rewiring. The entire study has been accomplished by using MATLAB/Simulink environment and field experiment for the arrays of different sizes. The validity of the proposed technique has been critically evaluated using various artificially created shadings and compared with the hitherto known conventional and hybrid topologies. The response of the array having various topologies for every shade condition has been analysed using the characteristics curves and various performance parameters. From the study, it has been found that the proposed technique excels in performance in terms of reducing the number of peaks in the characteristics curves and maximizing power generation during all shade scenarios as compared to other topologies.

Event-triggered communication and control of networked systems for multi-agent consensus

This article provides an introduction to event-triggered coordination for multi-agent average consensus. We provide a comprehensive account of the motivations behind the use of event-triggered strategies for consensus, the methods for algorithm synthesis, the technical challenges involved in establishing desirable properties of the resulting implementations, and their applications in distributed control. We pay special attention to the assumptions on the capabilities of the network agents and the resulting features of the algorithm execution, including the interconnection topology, the evaluation of triggers, and the role of imperfect information. The issues raised in our discussion transcend the specific consensus problem and are indeed characteristic of cooperative algorithms for networked systems that solve other coordination tasks. As our discussion progresses, we make these connections clear, highlighting general challenges and tools to address them widespread in the event-triggered control of networked systems.

Balanced truncation of networked linear passive systems

This paper studies model order reduction of multi-agent systems consisting of identical linear passive subsystems, where the interconnection topology is characterized by an undirected weighted graph. Balanced truncation based on a pair of specifically selected generalized Gramians is implemented on the asymptotically stable part of the full-order network model, which leads to a reduced-order system preserving the passivity of each subsystem. Moreover, it is proven that there exists a coordinate transformation to convert the resulting reduced-order model to a state–spacemodel of Laplacian dynamics. Thus, the proposed method simultaneously reduces the complexity of the network structure and individual agent dynamics, and it preserves the passivity of the subsystems and the synchronization of the network. Moreover, it allows for the a priori computation of a bound on the approximation error. Finally, the feasibility of the method is demonstrated by an example.