Harmonic Constraints Research Articles

Equilibrium and Nonequilibrium Effects in the Collapse of a Model Polypeptide

We present results of molecular simulations of a model polypeptide whose hydrophobic collapse proceeds as a cascade of downhill transitions between distinct intermediate states. Different intermediates are stabilized by means of appropriate harmonic constraints, allowing explicit calculation of the equilibrium free energy landscape. Nonequilibrium collapse trajectories are simulated independently and compared to diffusion on the calculated free energy surface. We find that collapse generally adheres to this surface, but quantitative agreement is complicated by nonequilibrium effects and by dependence of the diffusion coefficient on position on the surface.

Down-State Model of the KvAP Voltage-Sensing Domain

Voltage-gated potassium (Kv) channels play a crucial role in the generation and propagation of electrical impulses in excitable cells by controlling the flow of K+ ions into the cell membrane in response to changes in transmembrane potential. The voltage-sensing domains (VSD) of these channels have at least two distinct conformations, the so-called up- and down-states, corresponding to the open and resting/closed states of the channel. To date, structures of three different Kv channels have revealed the up-state of the VSD; in the down-state, there is a great deal of functional data, but no crystal structures have been reported. We report here a model of the KvAP VSD in a down-state. The model was generated by molecular dynamics simulations (MD) of the VSD in a lipid bilayer in excess water using harmonic constraints to steer an equilibrated up-state sensor into a configuration that is consistent with the biotin-tethered avidin accessibility measurements of Ruta et al. (2005, Cell 123: 463). We have run a MD simulation of the system for 30 ns in the absence of constraints. The system is stable in the new configuration, and is consistent with newly reported avidin accessibility measurements (Banerjee and MacKinnon, 2008, JMB 381: 569) that were not used to generate the model. In addition, we have estimated the gating charge transfer between the up- and down-state configurations. Compared to the Kv1.2 model by Pathak et al. (2007, Neuron 56: 124), we see slightly larger transmembrane displacements for the S3 and S4 helices with significant differences in their orientation.

Passive Harmonic Filter Planning in a Power System With Considering Probabilistic Constraints

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new method for planning single-tuned passive harmonic filters to control harmonic voltage distortion throughout a power system. In the problem, the probabilistic characteristics of the harmonic source currents and network harmonic impedances in the filter planning are taken into account. The objective is to minimize the total filter installation cost, while the harmonic voltage limits and filter component constraints are satisfied with predetermined confidence levels. To obtain the optimal size of each filter component of the planning problem, the proposed procedure is first to find the candidate filter buses based on the sensitivity analysis. Next, the formulated probability-constrained problem is transformed into a deterministic nonlinear programming problem and is solved by a genetic-algorithm-based optimizer. The proposed solution procedure is tested with an actual distribution network and is verified by the conventional deterministic approach and by the Monte Carlo simulation. Numerical experiences show that the proposed method yields favorable results compared with the other two approaches. </para>

High dynamics control under voltage/current and harmonic constraints: SM-PMSM application for AC railways

The main objective of the proposed work is to perform stator flux and torque high dynamics response related to specific railway requirements such as anti-slid re-adhesion control. Moreover, this type of application takes into account DC bus voltage and current limitations. In addition, systems controlled by pulse width modulation (PWM) line side converters, injects harmonic current into the feeding overhead line. Therefore, it is necessary to consider an additional harmonic constraint (harmonic shape) as an entire part of the global control system in order not to interfere with signaling systems. Consequently, the high dynamics control objectives must be considered together with the PWM constraint and voltage/current limitations, as a single control task. Real-time simulation as well as experimental results for a specific railway test bench will be presented to highlight the performances of such control algorithm.

Integrated feasible direction method and genetic algorithm for optimal planning of harmonic filters with uncertainty conditions

This paper presents an integrated approach of feasible direction method and genetic algorithm (FDM + GA) to optimize the planning of large-scale passive harmonic filters (PHF). The objective is to minimize the total demand distortion of harmonic currents, total harmonic distortion of load bus voltages, filters loss and the cost of total installation of LC tuned filters. Reactive power compensation and constraints of individual harmonics have been considered in the design process, and the constraints of harmonics with orders lower than the filter tuned-points have been set stricter to avoid amplifying non-characteristic harmonics as well. In order to determine a set of weights of objective function representing the relative importance of each term, the simplest and most efficient form of triangular membership functions have been employed. The designed FDM + GA heuristic is applied to the harmonic problems in a chemical plant with three 6-pulse rectifiers. Three design schemes are compared to demonstrate the performance of the FDM + GA heuristic. Finally, expectations and standard deviations of objective values are used to present the effects of filter parameter detuning, loading uncertainty, and changing of system impedance.

Extended Nonnegative Tensor Factorisation Models for Musical Sound Source Separation

Recently, shift-invariant tensor factorisation algorithms have been proposed for the purposes of sound source separation of pitched musical instruments. However, in practice, existing algorithms require the use of log-frequency spectrograms to allow shift invariance in frequency which causes problems when attempting to resynthesise the separated sources. Further, it is difficult to impose harmonicity constraints on the recovered basis functions. This paper proposes a new additive synthesis-based approach which allows the use of linear-frequency spectrograms as well as imposing strict harmonic constraints, resulting in an improved model. Further, these additional constraints allow the addition of a source filter model to the factorisation framework, and an extended model which is capable of separating mixtures of pitched and percussive instruments simultaneously.

Advances in Nonnegative Matrix and Tensor Factorization

Advances in Nonnegative Matrix and Tensor Factorization

Optimal Design of Discrete-Value Passive Harmonic Filters Using Sequential Neural-Network Approximation and Orthogonal Array

This paper presents a method for combining sequential neural-network approximation and orthogonal arrays (SNAOA) in the planning of large-scale passive harmonic filters. An orthogonal array is first conducted to obtain the initial solution set. The set is then treated as the initial training sample. Next, a back-propagation sequential neural network is trained to simulate the feasible domain for seeking the optimal filter design. The size of the training sample is greatly reduced due to the use of the orthogonal array. In addition, a restart strategy is also incorporated into the SNAOA so that the searching process may have a better opportunity to reach a near global optimum. To illustrate the performance of the SNAOA, a practical harmonic mitigation problem in a chemical plant is studied. The results show that the SNAOA performs better than the original scheme and satisfies the harmonic limitations with respect to the objective of minimizing the total demand distortion of harmonic currents and total harmonic distortion of voltages. Filter loss, reactive power compensation, and the constraints of individual harmonics are also considered. Additional results related to SNAOA are also reported and discussed as well.

Biochemical and structural comparative study between bird and mammal pancreatic colipases

Three colipases were purified from pancreas of two birds (ostrich and turkey) and one mammal (dromedary). After acidic and/or heat treatment and precipitation by sulfate ammonium and then ethanol, cofactors were purified by Sephadex G-50 gel filtration followed by ion-exchange chromatography first on Mono S and then on Mono Q. One molecular form was obtained from each species with a molecular mass of approximately 10 kDa. Cofactors were not glycosylated. The N-terminal sequences of the three purified cofactors showed high sequence homology. A 90 amino acid sequence of the ostrich cofactor was established based on peptide sequences from four different digests of the denaturated protein using trypsin, chymotrypsin, thermolysin, or staphylococcal protease. This sequence exhibited a high degree of homology with chicken and mammal cofactors. Bile salt-inhibited pancreatic lipases from five species were activated to variable extents by colipases from bird and mammal origins. The bird pancreatic lipase-colipase system appears to be functionally similar to homologous lipolytic systems from higher mammals. Our comparative study showed that mammal colipase presents a lower activation level toward bird lipases than the bird counterpart. Three-dimensional modeling of ostrich colipase suggested a structural explanation of this fact.

Nonlinear (4,8,4) multiplet of N=8, d=1 supersymmetry

Abstract We construct a nonlinear version of the d = 1 off-shell N = 8 multiplet ( 4 , 8 , 4 ) , proceeding from a nonlinear realization of the superconformal group OSp ( 4 ⋆ | 4 ) in the N = 8 , d = 1 analytic bi-harmonic superspace. The new multiplet is described by a double-charged analytic Goldstone superfield q 1 , 1 subjected to some nonlinear OSp ( 4 ⋆ | 4 ) covariant harmonic constraints. We construct the most general N = 8 supersymmetric actions of q 1 , 1 and find the general expression for the bosonic target metric in terms of the original analytic Lagrangian superfield density which is thus the target geometry prepotential. It also completely specifies the scalar potential. The metric is conformally flat and, in the SO ( 4 ) invariant case, is a deformation of the metric of S 4 .

Meeting IEEE-519 Current Harmonics and Power Factor Constraints With a Three-Phase Three-Wire Active Power Filter Under Distorted Source Voltages

An efficient steady-state compensation method and a conceptual design for sizing the three-phase three-wire shunt active power filter (APF) under nonsinusoidal source voltages are presented in this paper. Conventionally, the compensation currents injected by the APF are determined to eliminate harmonic currents of the nonlinear load as well as to compensate reactive power and maintain the sinusoidal source currents. However, the subject related to the optimal control of the APF to meet the IEEE-519 harmonic current limits and other constraints, such as minimum load power factor requirement after compensation with an optimal kilovolt-ampere rating, are rarely investigated. In this paper, an optimization-based solution algorithm is proposed to determine the three-phase three-wire APF current injections to meet different constraints with an optimal filter size, where the voltage compensation-based control strategy is formulated as a nonlinear programming problem and is solved to find the optimal compensator gains and APF current injections. Results obtained by simulations with Matlab/Simulink show that the proposed approach is very flexible and effective for compensating harmonic currents generated by the nonlinear load with an optimal size of the APF.

A New Approach for Optimal Shunt Active Power Filter Control Considering Alternative Performance Indices

A new steady-state approach for determining the optimal shunt active power filter (APF) reference compensation current injections to control harmonic currents generated by the nonlinear load and for reactive power compensation under ideal or nonideal supply voltages are presented in the paper. Conventionally, the compensation currents injected by the shunt APF are determined to eliminate harmonic currents of the load. However, when considering different APF performance indices such as minimizing source current distortion and maximizing compensated load power factor, the issues related to sizing the APF to meet IEEE-519 harmonic current limits and other constraints such as current imbalance limits and minimum load power factor requirement are rarely investigated. In the paper, a new theory of APF control in the a-b-c reference frame is proposed to determine the APF current injections to meet different constraints with an optimal APF size, where the filter control strategy is formulated as a nonlinear programming problem and is solved to find the optimal current injections. Results obtained by simulations with Matlab/Simulink show that the proposed approach is more flexible and effective than the conventional approaches on compensating reactive power and harmonic currents of the load.

Structural Basis of Cellulosome Efficiency Explored by Small Angle X-ray Scattering

Cellulose, the main structural component of plant cell walls, is the most abundant carbohydrate polymer in nature. To break down plant cell walls, anaerobic microorganisms have evolved a large extracellular enzyme complex termed cellulosome. This megadalton catalytic machinery organizes an enzymatic assembly, tenaciously bound to a scaffolding protein via specialized intermodular "cohesin-dockerin" interactions that serve to enhance synergistic activity among the different catalytic subunits. Here, we report the solution structure properties of cellulosome-like assemblies analyzed by small angle x-ray scattering and molecular dynamics. The atomic models, generated by our strategy for the free chimeric scaffoldin and for binary and ternary complexes, reveal the existence of various conformations due to intrinsic structural flexibility with no, or only coincidental, inter-cohesin interactions. These results provide primary evidence concerning the mechanisms by which these protein assemblies attain their remarkable synergy. The data suggest that the motional freedom of the scaffoldin allows precise positioning of the complexed enzymes according to the topography of the substrate, whereas short-scale motions permitted by residual flexibility of the enzyme linkers allow "fine-tuning" of individual catalytic domains.

Identification of Determinants of Ligand Binding Affinity and Selectivity in the Prostaglandin D2 Receptor CRTH2

The chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) is a G protein-coupled receptor that mediates the pro-inflammatory effects of prostaglandin D(2) (PGD(2)) generated in allergic inflammation. The CRTH2 receptor shares greatest sequence similarity with chemoattractant receptors compared with prostanoid receptors. To investigate the structural determinants of CRTH2 ligand binding, we performed site-directed mutagenesis of putative mCRTH2 ligand-binding residues, and we evaluated mutant receptor ligand binding and functional properties. Substitution of alanine at each of three residues in the transmembrane (TM) helical domains (His-106, TM III; Lys-209, TM V; and Glu-268, TM VI) and one in extracellular loop II (Arg-178) decreased PGD(2) binding affinity, suggesting that these residues play a role in binding PGD(2). In contrast, the H106A and E268A mutants bound indomethacin, a nonsteroidal anti-inflammatory drug, with an affinity similar to the wild-type receptor. HEK293 cells expressing the H106A, K209A, and E268A mutants displayed reduced inhibition of intracellular cAMP and chemotaxis in response to PGD(2), whereas the H106A and E268A mutants had functional responses to indomethacin similar to the wild-type receptor. Binding of PGE(2) by the E268A mutant was enhanced compared with the wild-type receptor, suggesting that Glu-268 plays a role in determining prostanoid ligand selectivity. Replacement of Tyr-261 with phenylalanine did not affect PGD(2) binding but decreased the binding affinity for indomethacin. These results provided the first details of the ligand binding pocket of an eicosanoid-binding chemoattractant receptor.

Application of combined feasible-direction method and genetic algorithm to optimal planning of harmonic filters considering uncertainty conditions

The paper presents an approach of combining a feasible-direction method and a genetic algorithm (FDM+GA) to investigate the planning of large-scale passive harmonic filters. The optimal filter scheme can be obtained for a system under abundant harmonic-current sources where harmonic-amplification problems should be avoided. The design is to minimise the total demand distortion of harmonic currents and total harmonic distortion of load bus voltages. Filter loss, reactive-power compensation and constraints of individual harmonics can be considered in the design procedures. The constraints of harmonics with orders lower than the filter tuned points have been set stricter to avoid amplification of noncharacteristic harmonics. The search for the global optimal solution is applied to the harmonic problems in a steel plant, where both AC and DC are furnaces are used and a static Var compensator (SVC) is installed. Three design schemes are compared to demonstrate the performance of the proposed method. Finally, expectations and standard deviations of objective functions are used to present effects of filter-parameter detuning, loading uncertainty and changes of system impedance.

Optimal multiobjective planning of large-scale passive harmonic filters using hybrid differential evolution method considering parameter and loading uncertainty

This paper is used to investigate the optimal multiobjective planning of large-scale passive harmonic filters for a multibus system under abundant harmonic current sources using the hybrid differential evolution (HDE) method. The migrant and accelerating operations embedded in HDE are used to overcome traps of local optimal solutions and problems of time consumption. The design purposes are to minimize the total demand distortion of harmonic currents and total harmonic distortion of voltages at each bus. Filters loss, fundamental reactive power compensation, and constraints of individual harmonics are also considered. The search for the global optimal solution is applied to the harmonic problems in a steel plant, where both ac and dc arc furnaces are used and a static var compensator is installed. Three design schemes are compared to demonstrate the performance of HDE. Finally, expectations of objective function are used to present the effects of filter parameter detuning and furnace loading uncertainty.

Optimisation-based strategy for shunt active power filter control under non-ideal supply voltages

A new theory and a conceptual design for the three-phase shunt active power filter (APF) control strategy under imbalanced and distorted supply voltages are presented. Conventionally, the compensation currents injected by the APF are determined according to reference frame transformation-based approaches, where the load instantaneous real and reactive powers are calculated in the new reference frame. The APF injection currents are then computed to maintain the balanced and sinusoidal source currents, as well as the least active power consumption by the APF. However, if current harmonics set by harmonic standards or other constraints are considered, the load harmonic currents after APF compensation can be controlled to meet the requirements. Therefore, the APF may have an adjustable performance. An optimal algorithm for the APF control in steady state is proposed, in which the individual and total harmonic current distortion limits, the minimum load power factor, levels of current imbalance and the size of the APF can be taken into account. The planned APF does not consume or produce active power and only the passive energy-storage elements are required in the new APF design. Results obtained by simulations with Matlab and Simulink show that the proposed approach is more flexible than conventional approaches for compensating reactive power and harmonic/neutral currents of the load, even if the source voltages are severely distorted and imbalanced. The new control strategy is very suitable for planning the APF when several alternative objective functions and constraints are under considerations.

A Controllable Reactor of Transformer Type

This paper clarifies the operating principles of a controllable reactor of transformer type (CRT). In nature, a CRT is equivalent to a multi-winding transformer for which the low-voltage windings (control windings) operate at short-circuited states in turn. This kind of reactor possesses such advantages as smooth power regulation, low current harmonic content, and fast response. Taking account of the coupling of the control windings, this paper examined the current harmonic content for the work winding by Fourier series decomposition, and thus derived the current harmonic coefficients. Based on the solution of the branch current equation of a multi-winding transformer, and introduction of the concept of equivalent winding impedance, a polygon-type equivalent circuit is proposed for a multi-winding transformer. Subsequently, formulae for the branch impedances of the equivalent circuit are presented. According to the harmonic content constraints, the number of control steps is determined. Then, by combining the MMF and branch current equations, an expanded equation about the winding currents and current-limiting reactances is obtained. According to the feature that the control windings are short-circuited in turn, the current-limiting reactances are calculated for each control winding step by step. At last, based on the proposed equivalent circuit for a multi-winding transformer, a simulation model for a CRT is fabricated with MATLAB/SIMULINK/PSB. The simulation results confirmed the presented work, which underpins the further analysis and design of a CRT.

Optimal planning of harmonic filters on distribution systems by chance constrained programming

Considering the random nature of harmonic sources in distribution systems, a chance constrained programming model for optimal planning of harmonic filters is presented in this paper. The locations and parameters of active and passive harmonic filters are determined simultaneously to minimize the total investment costs, while the harmonic voltage distortion limits and filter capacity constraints are satisfied with predetermined confidence levels. A stochastic simulation based genetic algorithm is used for solving this model. Test results on an 18-bus distribution system show that the proposed approach is more practical, efficient and economical than the conventional methods.

Goal-attainment method for optimal multi-objective harmonic filter planning in industrial distribution systems

A formulation of multi-objective optimisation for single-tuned harmonic filter planning in industrial distribution systems is presented. The objectives are total harmonic current distortion at the point of common coupling, total harmonic voltage distortion and harmonic filter investment cost. The minimisation of all the objectives is required in harmonic filter planning. The reactive power compensation constraints, the harmonic distortion constraints, the power source variation constraints and the filter de-tuning constraints are all taken into consideration. The goal-attainment method based on the simulated annealing approach is applied to solving general multi-objective harmonic filter planning problems by assuming that the decision-maker has goals for each of the objective functions. A desirable, global optimal solution generated is guaranteed by the solution methodology. Results of application of the proposed method to general multi-objective harmonic filter planning are also presented.