Loop Scheme Research Articles

Minimising current ripple in electric vehicle batteries by proper pulse width modulation techniques

Batteries are one of the key components of electric vehicles (EVs). Batteries supply energy to output in normal working mode by converting internal chemical energy to electric energy (discharging), and they restore energy in regenerative working mode as opposed to discharging (charging). During each mode, battery current contains ripple which influences battery lifetime negatively. Simulations which include ideal models for battery and DC bus capacitors do not give realistic results in terms of battery ripple current. This paper presents comparative investigations and evaluations with regard to battery current waveform, battery current harmonic spectrum and the ratio of battery current harmonic components to battery average current. Various modulation methods and operating conditions (i.e., a different modulation index and load power factor for an open loop scheme, and a different speed and torque for a closed loop scheme) are considered with high-frequency models of battery and DC bus capacitors.

Fuzzy-Sliding Mode Force Control Research on Robotic Machining

The low stiffness has limited the applications of robot to machining process. In this paper, a fuzzy-sliding mode control scheme is proposed to manage the oscillation and chatter appearing in machining operation by adjusting the feed rate. The robotic machining dynamics is first analyzed to identify the parameters with focus on the system stiffness and the behavior during machining process. A controller consisting of a fuzzy estimation enginery which can determine the control gain coefficients according to system status and a sliding mode controller which is used to guarantee convergence and global stability of the system is then proposed. Simulations and experiments results show that, in comparison with open loop and fuzzy-PID control scheme, the fuzzy-sliding mode control scheme can reduce the amplitude and period of oscillation.

Isogeometric shape optimisation of shell structures using multiresolution subdivision surfaces

We introduce the isogeometric shape optimisation of thin shell structures using subdivision surfaces. Both triangular Loop and quadrilateral Catmull-Clark subdivision schemes are considered for geometry modelling and finite element analysis. A gradient-based shape optimisation technique is implemented to minimise compliance, i.e. to maximise stiffness. Different control meshes describing the same surface are used for geometry representation, optimisation and finite element analysis. The finite element analysis is performed with subdivision basis functions corresponding to a sufficiently fine control mesh. During iterative shape optimisation the geometry is updated starting from the coarsest control mesh and proceeding to increasingly finer control meshes. The proposed approach is applied to three optimisation examples, namely a catenary, a roof over a rectangular domain, and free-form architectural shell roof. The influence of the geometry description and the used subdivision scheme on the obtained optimised curved geometries are investigated in detail.

Type $\widehat{\mathrm C}$ Brauer loop schemes and loop model with boundaries

In this paper we study the Brauer loop model on a strip and the associated quantum Knizhnik–Zamolodchikov (qKZ) equation. We show that the minimal degree solution of the Brauer qKZ equation with one of four dierent possible boundary conditions, gives the multidegrees of the irreducible components of generalizations of the Brauer loop scheme of [16, Knutson–Zinn-Justin ’07] with one of four kinds of symplectic-type symmetry. This is accomplished by studying these irreducible components, which are indexed by link patterns, and describing the geometric action of Brauer generators on them. We also provide recurrence relations for the multidegrees and compute the sum rules (multidegrees of the whole schemes).

Perception as a closed-loop convergence process.

Perception of external objects involves sensory acquisition via the relevant sensory organs. A widely-accepted assumption is that the sensory organ is the first station in a serial chain of processing circuits leading to an internal circuit in which a percept emerges. This open-loop scheme, in which the interaction between the sensory organ and the environment is not affected by its concurrent downstream neuronal processing, is strongly challenged by behavioral and anatomical data. We present here a hypothesis in which the perception of external objects is a closed-loop dynamical process encompassing loops that integrate the organism and its environment and converging towards organism-environment steady-states. We discuss the consistency of closed-loop perception (CLP) with empirical data and show that it can be synthesized in a robotic setup. Testable predictions are proposed for empirical distinction between open and closed loop schemes of perception.

Intelligence Based Soft Starting Scheme for the Three Phase Squirrel Cage Induction Motor with Extinction Angle AC Voltage Controller

Whenever a squirrel cage induction motor is started, notable electromechanical torque and current pulsations occur. The adverse effects of starting torque pulsations and high inrush current in induction motor are eliminated using digital power electronic soft starting schemes that guarantee higher degrees of compliance of the requirements of an ideal soft starter for the induction motor. Soft starters are cheap, simple, reliable and occupy less volume. In this paper, an experimental setup of soft starting technique with extinction angle AC voltage controller and a speed and stator current based closed loop scheme is demonstrated using Artificial Neural Network (ANN) and Fuzzy Logic Control (FLC) by the way of MATLAB/SIMULINK based simulation. The ANN based soft starting scheme produces best results in terms of smooth starting torque and least inrush current. The results thus obtained were satisfactory and promising.

Jitter Reduced Self Biased PLLs—A Systematic Simulation Study

The self biased Phase Locked Loop (PLL) has become a default choice for clock generation in many microprocessors. In today’s scenario, the processor cores are made to operate at rapidly varying combinations of clock frequencies and very low supply voltages. Though the traditional self biased PLL is still being widely used with hardly any modification, it is becoming imperative to take a relook at the design aspects of these PLLs with respect to their jitter performance. This paper presents a systematic simulation study of designing the self biased PLL with the goal of reducing jitter. It further shows that if the self biased PLL is adapted into a dual loop scheme in a systematic manner, a significant jitter improvement can be obtained. Detailed simulations carried out in 0.18 μm CMOS technology indicate a reduction of 56% or more in jitter for the systematically designed dual loop scheme in comparison to the jitter reduced traditional self biased PLL.

DDS-Based Signal-Generation Architecture Comparison for an Imaging Radar at 300 GHz

Submillimeter-wave imaging radars for standoff detection require broadband and fast-switch signal-generation architectures in order to achieve a high-range-resolution and near-video-rate imaging system. The signal generation has a strong influence on the radar image quality, primarily due to the transmitted phase noise. Two direct digital synthesis-based architectures for continuous-wave linear-frequency-modulated signal generation have been fabricated and tested for a high-range-resolution imaging radar at 300 GHz for standoff sensing of person-borne concealed threats. In order to select the signal-generation architecture that ensures the proper operation of the imaging radar with a cost-saving objective, three figures of merit have been used: 1) radar image quality; 2) power consumption; and 3) cost. The impact of the signal-generation architectures on the imaging radar indicates that both architectures present a similar radar performance in terms of radar image quality, although the narrowband direct-digital-synthesis/phase-locked loop scheme is a cost-effective solution compared with the broadband direct-digital-synthesis scheme in order to develop an affordable and energy-efficient high-performance preindustrial radar prototype.

Closed loop identification using a modified Hansen scheme

It is often not feasible or even impossible to identify a plant in open loop. This might be because the plant contains unstable poles, or it is simply too expensive to remove the plant from its intended operation, among other possibilities. There are several methods for identifying a plant in closed loop [4], and one such method is the Hansen scheme [1]. Standard identification using Hansen scheme demands generating the identification signals indirectly. In this paper it is instead proposed to use the relationship between the Youla factorization of a plant and its stabilizing controller to directly measure the signals used for identification. A simulation example and identification of a gas bearing is given to show the method in action. Rotors supported by controllable gas bearings are open loop stable systems. However as the rotational speed is increased feedback control is necessary in order to keep the system stable. Furthermore because the dynamics of such a system depends on the rotational speed it is needed to conduct an identification while the system is part of a closed loop scheme. The authors believe the paper able to contribute towards a simpler and more direct way of identifying closed loop plants using Hansen scheme.

Streamflow data assimilation in SWAT model using Extended Kalman Filter

Summary The Extended Kalman Filter (EKF) is coupled with the Soil and Water Assessment Tools (SWAT) model in the streamflow assimilation of the upstream Senegal River in West Africa. Given the large number of distributed variables in SWAT, only the average watershed scale variables are included in the state vector and the Hydrological Response Unit (HRU) scale variables are updated with the a posteriori / a priori ratio of their watershed scale counterparts. The Jacobian matrix is calculated numerically by perturbing the state variables. Both the soil moisture and CN2 are significantly updated in the wet season, yet they have opposite update patterns. A case study for a large flood forecast shows that for up to seven days, the streamflow forecast is moderately improved using the EKF-subsequent open loop scheme but significantly improved with a newly designed quasi-error update scheme. The former has better performances in the flood rising period while the latter has better performances in the recession period. For both schemes, the streamflow forecast is improved more significantly when the lead time is shorter.

On the difficulty to optimally implement the Ensemble Kalman filter: An experiment based on many hydrological models and catchments

Summary Forecast reliability and accuracy is a prerequisite for successful hydrological applications. This aim may be attained by using data assimilation techniques such as the popular Ensemble Kalman filter (EnKF). Despite its recognized capacity to enhance forecasting by creating a new set of initial conditions, implementation tests have been mostly carried out with a single model and few catchments leading to case specific conclusions. This paper performs an extensive testing to assess ensemble bias and reliability on 20 conceptual lumped models and 38 catchments in the Province of Quebec with perfect meteorological forecast forcing. The study confirms that EnKF is a powerful tool for short range forecasting but also that it requires a more subtle setting than it is frequently recommended. The success of the updating procedure depends to a great extent on the specification of the hyper-parameters. In the implementation of the EnKF, the identification of the hyper-parameters is very unintuitive if the model error is not explicitly accounted for and best estimates of forcing and observation error lead to overconfident forecasts. It is shown that performance are also related to the choice of updated state variables and that all states variables should not systematically be updated. Additionally, the improvement over the open loop scheme depends on the watershed and hydrological model structure, as some models exhibit a poor compatibility with EnKF updating. Thus, it is not possible to conclude in detail on a single ideal manner to identify an optimal implementation; conclusions drawn from a unique event, catchment, or model are likely to be misleading since transferring hyper-parameters from a case to another may be hazardous. Finally, achieving reliability and bias jointly is a daunting challenge as the optimization of one score is done at the cost of the other.

An optoelectronic oscillator‐based strain sensor with extended measurement range

ABSTRACTAn optoelectronic oscillator (OEO)‐based strain sensor with extended measurement range is proposed and demonstrated. The OEO is embedded with an electrical phase shifter (EPS) to cancel out the strain‐induced phase shift real‐timely via a phase‐locked loop scheme. Theoretically, the control voltage of the EPS is linear to the strain applied on the sensing fiber, leading to a simple and straightforward frequency demodulation. Thanks to the real‐time close‐loop interrogation, the mode‐hopping‐free frequency shift range can exceed one free spectrum range, thus, the measurement range of the sensor is extended. The obtained strain measurement range is up to 2762 με. The achieved strain resolution is 0.86 με. The root‐mean‐square deviation of more than 2‐h test for a fixed strain is 1.1 με. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2336–2339, 2015

SampleLite

We consider the link adaptation problem in 802.11n wireless LANs that involves adapting MIMO mode, channel bonding, modulation and coding scheme, and frame aggregation level with varying channel conditions. Through measurement-based analysis, we find that adapting all available 802.11n features results in higher goodput than adapting only a subset of features, thereby showing that holistic link adaptation is crucial to achieve best performance. We then design a novel hybrid link adaptation scheme termed SampleLite that adapts all 802.11n features while being efficient compared to sampling-based open-loop schemes and practical relative to closed loop schemes. SampleLite uses sender-side RSSI measurements to significantly lower the sampling overhead, by exploiting the monotonic relationship between best settings for each feature and the RSSI. Through analysis and experimentation in a testbed environment, we show that our proposed approach can reduce the sampling overhead by over 70% on average compared to the widely used Minstrel HT scheme. We also experimentally evaluate the goodput performance of SampleLite in a wide range of controlled and real-world interference scenarios. Our results show that SampleLite, while performing close to the ideal, delivers goodput that is 35-100% better than with existing schemes.

Self-healing hierarchical architecture for ZigBee network in smart grid application

In this paper, by analysing the characteristics of node assignments, network structures and the data transmission in the smart grid, we propose and evaluate a self-healing hierarchical architecture SHA for the ZigBee networks in the smart grid application. The SHA could maintain the network structure based on the link quality indication LQI and the modified neighbour table information to optimise the parent child relationship from the viewpoint of overall network. A backup loop scheme is also introduced to enhance the robustness. A backup link is calculated for each node based on the network address information. The simulation results show that the SHA achieves better performance by obtaining lower average hops, lower transmitter power and less bit error rates. For the backup loop scheme, the result shows it has a greater packet delivery ratio when network topology is damaged.

Quadrature demultiplexing using a degenerate vector parametric amplifier.

We report on quadrature demultiplexing of a quadrature phase-shift keying (QPSK) signal into two cross-polarized binary phase-shift keying (BPSK) signals with negligible penalty at bit-error rate (BER) equal to 10(-9). The all-optical quadrature demultiplexing is achieved using a degenerate vector parametric amplifier operating in phase-insensitive mode. We also propose and demonstrate the use of a novel and simple phase-locked loop (PLL) scheme based on detecting the envelope of one of the signals after demultiplexing in order to achieve stable quadrature decomposition.

Improving Low Voltage Ride Through Capability of Wind Generators Using Dynamic Voltage Restorer

Abstract The increasing wind power integration with power grid has forced the situation to improve the reliability of wind generators for stable operation. One important problem with induction generator based wind farm is its low ride through capability to the grid voltage disturbance. Any disturbance such as voltage dip may cause wind farm outages. Since wind power contribution is in predominant percentage, such outages may lead to stability problem. The proposed strategy is to use dynamic voltage controller (DVR) to compensate the voltage disturbance. The DVR provides the wind generator the ability to remain connected in grid and improve the reliability. The voltage dips due to symmetrical and unsymmetrical faults are considered for analysis. The vector control scheme is employed for fault compensation which uses software phase locked loop scheme and park dq0 transformation technique. Extensive simulation results are included to illustrate the control and operation of DVR.

A prediction model based on neural networks for the energy consumption of a bioclimatic building

Energy in buildings is a topic that is being widely studied due to its high impact on global energy demand. This problem involves the performance of an adequate management of the energy demand, combining both convectional and renewable sources. To this end, the use of control strategies is an important tool. These control strategies can take advantage of knowledge of variables that act as disturbances in the closed loop scheme. Thus, it is of great importance the development of predictions of such variables. The main objective of this paper is to develop and assess a short-term predictive neural network model of the electricity demand for the CIESOL bioclimatic building, located in the southeast of Spain. The performed experiments show a quick prediction with acceptable final results for real data with a short-term prediction horizon equal to 60min and with a mean error of 11.48%. One-step ahead predictions and dynamic modeling simulations have also been evaluated.

A new on-line bandwidth tuning approach for biquad OTA-C filters

A new and general bandwidth (BW) tuning strategy for biquad OTA-C filters is presented. We have taken benefit of the advantages of the classical Phase-Locked Loop (PLL) scheme to on-line tune the central frequency fo and we have applied it to tune also the bandwidth BW of biquad filters. The proposed design procedure uses only two different sizes of OTAs. This methodology has been applied to five biquad band-pass OTA-C filters, allowing fo-tuning and BW-tuning in an independent way. Furthermore, the influence of OTA non-idealities is discussed by including compact and general expressions for fo and BW for all these filters. Simulation results validate our proposal with excellent BW-tuning accuracies: an rms error of 0.73% with respect to the bandwidth desired.

Advanced SOGI-FLL Scheme Based on Fuzzy Logic for Single-Phase Grid-Connected Converters

This paper proposes a frequency-locked loop (FLL) scheme for a single-phase grid-connected converter. A second-order generalized integrator (SOGI) based on fuzzy logic (FL) is applied to this converter to achieve precise phase angle detection. The use of this method enables the compensation of the nonlinear characteristic of the frequency error, which is defined in the SOGI scheme as the variation of the central frequency through the self-tuning gain. With the proposed scheme, the performance of the SOGI-FLL is further improved at the grid disturbances, which results in the stable operation of the grid converter under grid voltage sags or frequency variation. The PSIM simulation and experimental results are shown to verify the effectiveness of the proposed method.

Method for digital measurement of phase-frequency characteristics for a fixed-length ultrasonic spectrometer

One of the most accurate methods for measuring the compressibility of liquids is resonance measurement of sound velocity in a fixed-length interferometer. This method combines high sensitivity, accuracy, and small sample volume of the test liquid. The measuring principle is to study the resonance properties of a composite resonator that contains a test liquid sample. Ealier, the phase-locked loop (PLL) scheme was used for this. In this paper, we propose an alternative measurement scheme based on digital analysis of harmonic signals, describe the implementation of this scheme using commercially available data acquisition modules, and give examples of test measurements with accuracy evaluations of the results.