Subsystem Partitioning Research Articles

Research on the mechanism and transmission path of the oscillation in DFIG-connected flexible DC transmission system

Concerning the oscillations in DFIG (doubly-fed induction generator)-connected flexible DC transmission system caused by large disturbances, an analysis method based on subsystem partitioning and dynamic energy modeling is put forward. Firstly, the complex high-order system is partitioned into several low-order subsystems, and the dynamic energy model of each subsystem is built using the first integration method. Then, by analyzing the directions and variation patterns of the interaction energy flows between different subsystems in the oscillation process, the redistribution of the primary flow paths of the system’s oscillation energy after large disturbances occur is determined. And then, an oscillation tracing method based on the response characteristics of the oscillation energy links of the subsystems is proposed. In the oscillation process, the interaction energy links between different subsystems are categorized into 'oscillation gaining links', 'oscillation maintaining links' and 'oscillation damping links', according to the contribution of each interaction energy link to the system’s oscillation energy. By analyzing the ‘oscillation gaining links’ corresponding to the dominant interaction energy links of different subsystems, the transmission paths by which the dominant oscillation energy links keeps gaining can be obtained, and the energy source that induces oscillation can be located. Finally, hardware-in-loop tests are conducted on the RTLAB semi-physical simulation platform, the results of which verify the effectiveness of the proposed method. This research paper can provide theoretical support for suppressing the oscillation by adding compensation branches between the subsystems (i.e. damping control strategies based on supplementary compensation branches).

Iterative distributed moving horizon estimation of linear systems with penalties on both system disturbances and noise

In this paper, partition-based distributed state estimation of general linear systems is considered. A distributed moving horizon state estimation scheme is developed via decomposing the entire system model into subsystem models and partitioning the global objective function of centralized moving horizon estimation (MHE) into local objective functions. The subsystem estimators of the distributed scheme that are required to be executed iteratively within each sampling period are designed based on MHE. Two distributed MHE algorithms are proposed to handle the unconstrained case and the case when hard constraints on states and disturbances, respectively. Sufficient conditions on the convergence of the estimates and the stability of the estimation error dynamics for the entire system are derived for both cases. A benchmark reactor-separator process example is introduced to illustrate the proposed distributed state estimation approach.

Structure Preserving Uncertainty Modelling and Robustness Analysis for Spatially Distributed Dissipative Dynamical Systems

The paper deals with uncertainty modelling, robust stability and performance analysis of multi-input multi-output (MIMO) reduced order spatially distributed dissipative dynamical systems. While researching the topic of modern robust control of such systems, two key findings were discovered: (i) systematic modelling of the uncertainty and model order reduction (MOR) at the level of a subsystem gives both modelling freedom and the ability for obtaining less conservative uncertainties on the level of a subsystem; (ii) for a special class of interconnected dissipative dynamical systems, uncertainty conservatism at the subsystem level can be reduced—a novel, structure preserving algorithm employing subsystem partitioning and subsystem MOR by means of balanced truncation method (BTM) is used to obtain low-order robustly stable interconnected systems. Such systems are suitable for practical decentralized and distributed robust controller synthesis. Built upon a powerful framework of integral quadratic constraints (IQCs), this approach gives uncertainty modelling flexibility to perform robustness analysis of real world interconnected systems that are usually affected by multiple types of uncertainties at once. The proposed uncertainty modelling procedure and its practical application are presented on the numerical example. A spatially discretized vibration dynamical system comprised of a series of simply supported Euler beams mutually interconnected by springs and dampers is examined. Spatial discretization of the mathematical model is carried out using the finite element method (FEM).

Projector-Based Quantum Embedding for Molecular Systems: An Investigation of Three Partitioning Approaches.

Projector-based embedding is a relatively recent addition to the collection of methods that seek to utilize chemical locality to provide improved computational efficiency. This work considers the interactions between the different proposed procedures for this method and their effects on the accuracy of the results. The interplay between the embedded background, projector type, partitioning scheme, and level of atomic orbital (AO) truncation are investigated on a selection of reactions from the literature. The Huzinaga projection approach proves to be more reliable than the level-shift projection when paired with other procedural options. Active subsystem partitioning from the subsystem projected AO decomposition (SPADE) procedure proves slightly better than the combination of Pipek-Mezey localization and Mulliken population screening (PMM). Along with these two options, a new partitioning criteria is proposed based on subsystem von Neumann entropy and the related subsystem orbital occupancy. This new method overlaps with the previous PMM method, but the screening process is computationally simpler. Finally, AO truncation proves to be a robust option for the tested systems when paired with the Huzinaga projection, with satisfactory results being acquired at even the most severe truncation level.

Latent Symmetry Induced Degeneracies.

Degeneracies in the energy spectra of physical systems are commonly considered to be either of accidental character or induced by symmetries of the Hamiltonian. We develop an approach to explain degeneracies by tracing them back to symmetries of an isospectral effective Hamiltonian derived by subsystem partitioning. We provide an intuitive interpretation of such latent symmetries by relating them to corresponding local symmetries in the powers of the underlying Hamiltonian matrix. As an application, we relate the degeneracies induced by the rotation symmetry of a real Hamiltonian to a non-Abelian latent symmetry group. It is demonstrated that the rotational symmetries can be broken in a controlled manner while maintaining the underlying more fundamental latent symmetry. This opens up the perspective of investigating accidental degeneracies in terms of latent symmetries.

Orbital Alignment for Accurate Projection-Based Embedding Calculations along Reaction Paths

In projection-based embedding (PbE) the subsystem partitioning of a chemical system is based on localized orbitals. We demonstrate how the localization step can lead to inconsistent orbital spaces along reaction paths, with severe consequences for reaction barriers and energies. We propose an orbital alignment procedure that resolves this problem without manual input. The usefulness of this alignment is demonstrated for a reaction benchmark set in combination with a direct orbital selection approach to automatize PbE calculations of double hybrid-in-nonhybrid density functional theory (DFT) and wave-function-in-DFT type for reaction energies and barriers. We show how the embedded calculations are accelerated in comparison to the corresponding supersystem calculations for realistic example reactions, using a new implementation of domain-based local pair natural orbital coupled cluster with single, double, and perturbative triple excitations [DLPNO-CCSD(T0)]. The embedded calculations yield results within an error margin below 4 kJ mol-1 for the reaction barrier and energy when compared to the supersystem calculation. The calculations can be executed in a user-friendly, black-box-like fashion with minimal manual input.

Model predictive control of vinyl chloride monomer process by Aspen Plus Dynamics and MATLAB/Simulink co-simulation approach

Characteristics of a vinyl chloride monomer (VCM) process is complex and nonlinear due to interactions between units in a reaction-separation network, multiple process streams, and multiple control loops involved. A fluctuation of the thermal cracking unit could result in a difficulty in maintaining downstream units at the setpoints. In this work, an approach to develop a model predictive control (MPC) for the VCM process by deploying a co-simulation between MATLAB/Simulink and Aspen Plus Dynamics is presented. The co-simulation provides more capability and comfortability to design the MPC controller, and evaluate controllability. The VCM process consisting of thermal cracking, quench and distillation is modelled by Aspen Plus Dynamics. The MPC is developed by integrating the concept of plant-wide control and subsystem partitioning. To reduce the burden of mathematical modeling, the MATLAB system identification toolbox is used to develop a multivariable linear model for the MPC controller by reconciling dynamics data from the VCM plant model. Performances of the developed MPC is evaluated under the regulatory test of the EDC feed disturbance. By comparison with the multiple single-input-single-output proportional-integral controllers through the efficiency indexes—an integral squared error, an overshoot and a settling time. Simulation results supported that the MPC controller outperforms proportional-integral controllers.

Dynamic ecological system analysis: A holistic analysis of compartmental systems

This article develops a new mathematical method for holistic analysis of nonlinear dynamic compartmental systems in the context of ecology. The method is based on the novel dynamic system and subsystem partitioning methodologies through which compartmental systems are decomposed to the utmost level. The dynamic system and subsystem partitioning enable tracking the evolution of the initial stocks, environmental inputs, and intercompartmental system flows, as well as the associated storages derived from these stocks, inputs, and flows individually and separately within the system. Moreover, the transient and the dynamic direct, indirect, acyclic, cycling, and transfer (diact) flows and associated storages transmitted along a given flow path or from one compartment, directly or indirectly, to any other are analytically characterized, systematically classified, and mathematically formulated. Further, the article develops a dynamic technique based on the diact transactions for the quantitative classification of interspecific interactions and the determination of their strength within food webs. Major concepts and quantities of the current static network analyses are also extended to nonlinear dynamic settings and integrated with the proposed dynamic measures and indices within the proposed unifying mathematical framework. Therefore, the proposed methodology enables a holistic view and analysis of ecological systems. We consider that this methodology brings a novel complex system theory to the service of urgent and challenging environmental problems of the day and has the potential to lead the way to a more formalistic ecological science.

Static ecological system analysis

In this article, a new mathematical method for static analysis of compartmental systems is developed in the context of ecology. The method is based on the novel system and subsystem partitioning methodologies through which compartmental systems are decomposed to the utmost level. That is, the distribution of environmental inputs and intercompartmental system flows as well as the organization of the associated storages generated by these flows within the system is determined individually and separately. Moreover, the transient and the static direct, indirect, acyclic, cycling, and transfer (diact) flows and associated storages transmitted along a given flow path or from one compartment, directly or indirectly, to any other are analytically characterized, systematically classified, and mathematically formulated. A quantitative technique for the categorization of interspecific interactions and the determination of their strength within food webs is also developed based on the diact transactions. The proposed methodology allows for both input- and output-oriented analyses of static ecological networks. The input- and output-oriented analyses are introduced within the proposed mathematical framework and their duality is demonstrated. Major flow- and stock-related concepts and quantities of the current static network analyses are also integrated with the proposed measures and indices within this unifying framework. This comprehensive methodology enables a holistic view and analysis of ecological systems.

A new approach for FPGA-based real-time simulation of power electronic system with no simulation latency in subsystem partitioning

In real-time Hardware-in-the-Loop (HIL) test applications for power electronic systems, the main hurdle is to tackle with the mathematical models of variable topology of complex and high frequency driven converter. The most widespread solution is to separate the whole system into subsystems. However, partitioning method usually introduces simulation time step latency between different subsystems, which causes numeric instabilities especially when stiff situation occurs. In this paper, we propose a novel parallel simulation approach which has no time step latency in the whole system division, from which a numerically stable system modeling can be realized. Its numerical accuracy of the solution, the architecture design, and the issue pertaining to the parallel calculation are discussed in detail in this paper. The pertinence of the developed solution is also tested using a case study relating to a traction system power electronic application. For this case study, implementations are made both on a 3 GHz Xeon CPU of RT LAB real-time simulator with a 2 μs simulation step and a Field Programmable Gate Arrays (FPGA) Kintex-7 embedded in National Instruments FlexRIO PXIe-7975 enabling a simulation step below 50 ns. Besides, comparison with results obtained from Simpower system in Matlab allows to evaluate the accuracy of our proposed modeling approach.

A Fully-Decentralized Consensus-Based ADMM Approach for DC-OPF With Demand Response

This paper discusses a consensus-based alternating direction method of multipliers (ADMMs) approach for solving the dynamic dc optimal power flow (DC-OPF) problem with demand response in a distributed manner. In smart grid, emerging techniques together with distributed nature of data and information, significantly increase the complexity of power systems operation and stimulate the needs for distributed optimization. In this paper, the distributed DC-OPF approach solves local OPF problems of individual subsystems in parallel, which are coordinated via global consensus variables (i.e., phase angles on boundary buses of adjacent subsystems). Three distributed DC-OPF algorithms are discussed with different convergence performance and/or communication requirement. All three distributed algorithms can effectively handle prevailing constraints for the transmission network, generating units, and demand response in individual subsystems, while the global convergence can be guaranteed. In particular, based on the traditional distributed ADMM approach, a fully decentralized algorithm without the central controller is proposed in Algorithm 2 with a new communication strategy, in which only limited information on boundary buses are exchanged among adjacent subsystems. In addition, the accelerated ADMM is discussed in Algorithm 3 for improving the convergence performance. In recognizing distributed OPF approaches in literature, one major research focus on this paper is to quantify the impact of key parameters and subsystem partitioning strategies on the convergence performance and the data traffic via numerical case studies. A general guidance for subsystem partitioning is proposed and verified via large-scale power systems.

Embedded Mean-Field Theory with Block-Orthogonalized Partitioning.

Embedded mean-field theory (EMFT) provides a simple, flexible framework for describing subsystems at different levels of mean-field theory. Subsystems are defined by partitioning a one-particle basis set, with a natural choice being the atomic orbital (AO) basis. Although generally well behaved, EMFT with AO partitioning can exhibit unphysical collapse of the self-consistent solution. To avoid this issue, we introduce subsystem partitioning of a block-orthogonalized (BO) basis set; this eliminates the unphysical collapse without significantly increasing computational cost. We also investigate a non-self-consistent implementation of EMFT, in which the density matrix is obtained using BO partitioning and the final energy evaluated using AO partitioning; this density-corrected EMFT approach is found to yield more accurate energies than BO partitioning while also avoiding issues of the unphysical collapse. Using these refined implementations of EMFT, previously proposed descriptions of the exact-exchange coupling between subsystems are compared: although the EX1 coupling scheme is slightly more accurate than EX0, the small improvement does not merit its substantially greater computational cost.

Nonlinear decomposition principle and fundamental matrix solutions for dynamic compartmental systems

A decomposition principle for nonlinear dynamic compartmental systems is introduced in the present paper. This theory is based on the mutually exclusive and exhaustive, analytical and dynamic, novel system and subsystem partitioning methodologies. A deterministic mathematical method is developed for the dynamic analysis of nonlinear compartmental systems based on the proposed theory. The dynamic method enables tracking the evolution of all initial stocks, external inputs, and arbitrary intercompartmental flows as well as the associated storages derived from these stocks, inputs, and flows individually and separately within the system. The transient and the dynamic direct, indirect, acyclic, cycling, and transfer ($\texttt{diact}$) flows and associated storages transmitted along a particular flow path or from one compartment-directly or indirectly-to any other are then analytically characterized, systematically classified, and mathematically formulated. Thus, the dynamic influence of one compartment, in terms of flow and storage transfer, directly or indirectly on any other compartment is ascertained. Consequently, new mathematical system analysis tools are formulated as quantitative system indicators. The proposed mathematical method is then applied to various models from literature to demonstrate its efficiency and wide applicability.

Subsystem partitioning for power system black-start considering restoration reliability

Subsystem partitioning for power system black-start considering restoration reliability

Density functional theory embedding for correlated wavefunctions: Improved methods for open-shell systems and transition metal complexes

Density functional theory (DFT) embedding provides a formally exact framework for interfacing correlated wave-function theory (WFT) methods with lower-level descriptions of electronic structure. Here, we report techniques to improve the accuracy and stability of WFT-in-DFT embedding calculations. In particular, we develop spin-dependent embedding potentials in both restricted and unrestricted orbital formulations to enable WFT-in-DFT embedding for open-shell systems, and develop an orbital-occupation-freezing technique to improve the convergence of optimized effective potential calculations that arise in the evaluation of the embedding potential. The new techniques are demonstrated in applications to the van-der-Waals-bound ethylene-propylene dimer and to the hexa-aquairon(II) transition-metal cation. Calculation of the dissociation curve for the ethylene-propylene dimer reveals that WFT-in-DFT embedding reproduces full CCSD(T) energies to within 0.1 kcal/mol at all distances, eliminating errors in the dispersion interactions due to conventional exchange-correlation (XC) functionals while simultaneously avoiding errors due to subsystem partitioning across covalent bonds. Application of WFT-in-DFT embedding to the calculation of the low-spin/high-spin splitting energy in the hexaaquairon(II) cation reveals that the majority of the dependence on the DFT XC functional can be eliminated by treating only the single transition-metal atom at the WFT level; furthermore, these calculations demonstrate the substantial effects of open-shell contributions to the embedding potential, and they suggest that restricted open-shell WFT-in-DFT embedding provides better accuracy than unrestricted open-shell WFT-in-DFT embedding due to the removal of spin contamination.

Controller Design for a Large-Scale Ultrasupercritical Once-Through Boiler Power Plant

A large-scale once-through-type ultrasupercritical boiler power plant is investigated for the development of an analyzable model for use in developing an intelligent control system. Using data from the power plant, a model is realized using dynamically recurrent neural networks (NN). This requires the partitioning of multiple subsystems, which are each represented by an individual NN that when combined form the whole plant model. Modified predictive optimal control was used to drive the plant to desired states; however, due to the computational intensity of this approach, it could not be executed quickly enough to satisfy project requirements. As an alternative, a reference governor was implemented along with a PID feedback control system that utilizes intelligent gain tuning, which, while more complicated, satisfied the computational speed required for the controller to be realized.

An analytical calibration approach for microwave polarimetric radiometers

We present an analytical calibration approach for passive microwave polarimeters that is applicable where the instrument can be partitioned into distinct, functional radio-frequency blocks. The methodology is focused on polarimetric system characterization, not polarimetric measurements. It requires characterization of each major internal functional subsystem with a vector network analyzer to obtain a closed-form transfer function. The goals of this approach are to provide a transfer function describing the system in its entirety and to isolate the contribution of each subsystem to the uncertainty in the final modified Stokes parameters. Notably, the approach does not assume ideal polarization isolation in the radiometer system. A significant benefit of this approach is that the cascaded transfer functions serve as a realistic instrument simulator revealing where improvements in component performance would have greatest benefit for system performance over the dynamic range of the instrument. This systems-focused approach is applied to the National Aeronautics and Space Administration Goddard Space Flight Center polarimetric Airborne C-band Microwave Radiometer (ACMR), whose architecture allows the necessary subsystem partitioning. The characteristics of each subsystem were extensively measured, converted to a transfer function, and imported into the overall closed-form system model. Inversion of the system model and error analysis inherent to this calibration approach are illustrated by a full Stokes parameter retrieval for a senescent cornfield.

Packaging of bio-MEMS: strategies, technologies, and applications

Biomicroelectromechanical systems (bio-MEMS) are MEMS which are designed for medical or biological applications. As with other MEMS, bio-MEMS frequently, have to be packaged to provide an interface to the macroscale world of the user. Bio-MEMS can be roughly divided in two groups. Bio-MEMS can be pure technical systems applied in a biological environment or technical systems which integrate biological materials as one functional component of the system. In both cases, the materials which have intimate contact to biological matter have to be to avoid unintentional effects on the biological substances, which in case of medical implants, could harm the patient. In the case of biosensors, the use of nonbiocompatible materials could interfere with the biological subcomponents which would affect the sensor's performance. Bio-MEMS containing biological subcomponents require the use of biocompatible technologies for assembly and packaging; e.g., high temperatures occurring, for instance, during thermosonic wire bonding and other thermobonding processes would denature the bioaffinity layers on biosensor chips. This means that the use of selected or alternative packaging and assembly methods, or new strategies, is necessary for a wide range of bio-MEMS applications. This paper provides an overview of some of the strategies, technologies, and applications in the field of bio-MEMS packaging. It includes the following: strategies for the partitioning of subsystems within integrated microsystems for (bio)chemical analysis/synthesis; methods for microassembly of bio-MEMS; technologies for bonding of polymer bio-MEMS components; packaging of miniature medical devices; packaging of biosensors for in vitro applications; packaging of micropumps as a bio-MEMS component. The applications discussed are derived from different fields to demonstrate the plethora of bio-MEMS considerations. In commercial production, packaging is possibly the major cost factor of bio-MEMS-based products, and its development requires special attention.

Design Considerations For A Flexible High-Resolution Film Recording System

The High Resolution Film Recording System (HRFRS), recently delivered to NASA/Goddard Space Flight Center by RCA, is uniquely characterized by full flexibility in: resolution (1,000 to 20,000 pixels/scan), line rate (15-350' lines/sec), data rate (0.5 to 20 Mbit/sec), optical spot size (10 itaM to 200 pm), pixel aspect ratio (0.5 to 2.0), and frame aspect ratio (0.5 to 2.0). This flexibility is designed to accommodate the specific characteristics of all NASA's satellite, imaging sensors of the 1970s and 1980s. RCA renamed this system Operation Laser Beam Recorder (OLBR) to reflect the production environment in which this versatile, high performance image recorder must operate. Design tech niques and objectives are presented which meet the required flexibilities while maintaining simplicity of design, repeatability, quality of performance, and operability in an image production environment. Human factors, careful partitioning of subsystems, and innovative design techniques are successfully employed to yield a versatile film recording system with a minimum of operational complexity..

Shuttle Avionics System

The Space Shuttle flight vehicle is composed of a reusable Orbiter vehicle, an external tank containing ascent propellants used by the Orbiter main engines, and two reusable solid rocket boosters. The Shuttle system is being designed to provide frequent, economical access to space and return for scientific and applications satellites beginning in the early 1980 timeperiod. Payloads up to 65,000 pounds, 15 feet in diameter, and 60 feet in length can be accommodated by the Orbiter. Current technology is being applied to achieve the lowest cost for placing payloads into earth orbit. The Orbiter avionics system is a key element in the development of the Shuttle system.The Orbiter avionics system provides the command, control, and monitoring for the mated Shuttle vehicle. The avionics include functions for guidance and navigation, flight control, communications and tracking, rendezvous, instrumentation, displays and controls, data processing, payload verification, systems management, and electrical power distribution and control.The basic Orbiter avionics system employs five computers in a general-purpose computer complex which interfaces with the various Orbiter subsystems through 24 one-megabit data buses and remote multiplex/demultiplex units located at the subsystems. All primary guidance, navigation and control functions are performed by the computers, with manual override permitted. Special features of the avionics implementation include redundancy management, software partitioning, switch scan, and ground uplink command of Orbiter subsystems via computer update. In addition to each computer main memory size of 65,000, 32-bit words redundant mass memories provide for storage of 8.3-million words of Orbiter and pay-load software which may be updated in orbit from the ground.