Accuracy Of Current Estimates Research Articles

A High-Bandwidth Current Estimator With Self Tunning for Digital Buck Controller

In order to solve the low-cost problem of high-speed current sampling in digital buck controllers, a current estimation method based on the direct current resistance (DCR) current detection principle is proposed in this paper. The inductor current including direct current (DC) and alternating current (AC) is obtained by performing high-frequency digital filtering on the voltage across the inductor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_L</i> ). Quantitative analysis of various factors affecting the accuracy of current estimation is carried out. For improving the estimated current accuracy, the multi-phase interleaved clock sampling technique and the algorithm of the average duty cycle in the filter cycle are proposed to improve the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_L</i> accuracy in each filter cycle. Meanwhile, considering the completeness of the current estimation algorithm, a calibration mechanism with a known current sink to adjust filter parameters online is adopted for the change of the inductance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> ) and its equivalent impedance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_L</i> ) due to process and aging. The proposed algorithm is verified in a buck prototyping board. Experimental results are presented to show that the proposed method is effective in both fixed frequency and variable frequency control modes. The DC and AC accuracy of estimated current reach 5% and 2%, respectively. The estimated inductor current delay is within 100 ns.

A Staggered Grid Based Water Current Aided SINS/DVL Integration Solution for Mid Water Navigation

Layer based water current aided strapdown inertial navigation system (SINS)/ Doppler velocity logs (DVL) integration system has provided continuously navigation solution for the underwater vehicles’ diving and rising periods in deep water areas. However, as the water current varies both vertically and horizontally, difficulty arises when the vehicle travels with large horizontal range. Thus, in this work, a novel staggered grid based water current aided SINS/DVL mechanization is proposed, which can be commonly employed using direct DVL velocity outputs. First, the staggered grid partition scheme is presented, based on which the continuous navigation mechanism in mid water area with large horizontal motion can be built. Then, the corresponding SINS/DVL integration method is illustrated, along with the construction of the observation vectors under the staggered grid division. Finally, the water current estimation algorithm is explored. Simulations are conducted to evaluate the effectiveness of the proposed solution, where both navigation results and water current estimation accuracy are discussed. The results indicate that the proposed solution outperforms the layer based solution as it fits better to the water current variation characteristic. Besides, the recursive least squares (RLS) based water current estimation algorithm shows better performance than bin average estimation method.

The state of health estimation of lithium-ion batteries based on data-driven and model fusion method

State of health (SOH) estimation of lithium-ion batteries is widely concerned. Currently, electric vehicles are rarely complete discharging in practical application, which remains lots of electricity and reduces constant current charging time. Therefore, this phenomenon hinders the applications of many traditional methods that require a complete constant current charging process. In this paper, we put forward a data-driven and model fusion method for SOH estimation based on constant voltage charging process (CVCP). Firstly, an improved equivalent circuit model (IECM) is established based on the current-time data of the CVCP. Secondly, Pearson correlation coefficient describes the strong mapping relationship between model parameters and SOH, so the model parameters are used as health indicators. Then, SOH prediction model is established by back propagation neural network whose model parameters are optimized by improved particle swarm optimization algorithm. Thirdly, considering time-consuming problem, a new scheme based on the incomplete CVCP that combine time constants prediction model and SOH prediction model is adopted. Finally, comparative results show that proposed IECM has the higher current estimation accuracy than traditional equivalent circuit models for different batteries. The SOH maximum errors of proposed method in different temperatures and data lengths are both within 2%.

Allometric biomass equations for young trees of four broadleaved species in Albania

Background: Biomass assessment of young forest stands is important because of their role in the carbon cycling. The aim of this study was to develop biomass equations for young broadleaved species growing in natural conditions in Albania. Methods: Five forest stands were investigated using circular sample plots. Diameter at breast height (DBH) and height (H) from 58 sampled trees ranging in age from 4 to 34 years old of Turkey oak (Quercus cerris L.), sweet chestnut (Castanea sativa Mill.), European hornbeam (Carpinus betulus L.) and manna ash (Fraxinus ornus L.) were measured in situ. Logarithmic regression equations were used and tested for their performance to estimate aboveground and tree-components biomass for each species using DBH, H and their combination DBH2 x H as predictors. Results: We found that DBH was a reliable predictor for estimation of aboveground and components biomass for young trees but the inclusion of height in biomass allometry did not improve the biomass estimation. We observed differences in scale (?0) and exponent (?1) coefficients of biomass models, not only between broadleaved species, but also among tree-components within species. Both coefficients were strongly species-specific and their values reflect differences in biomass stocking rate due to different growth strategies of each species in early development phases. Conclusions: Allometric equations to estimate aboveground and tree-component biomass appeared to be species-specific, meaning that such models are applicable for species growing at sites with similar ecological conditions. From the tree variables used, DBH was the most reliable predictor of aboveground and individual components biomass, whereas height proved to be a promising predictor for stand biomass. These allometric equations developed for young trees will improve the accuracy of current estimates of forest carbon stock in Albania.

Analysis of Field-Aligned Currents in the High-Altitude Nightside Auroral Region: Cluster Observation

In this paper we present analysis of current density when the Cluster spacecraft pass the nightside auroral region at about 4-5 RE from the center of Earth. The analysis is made when the inter-spacecraft separation is within 200 km, which allows all four spacecraft to be situated inside the same current sheet. On 22 February 2002, two field-aligned current (FAC) events were observed in both the southern and the northern hemispheres. The FACs were calculated with magnetic field data obtained by the four spacecraft using the Curlometer method. The scales of the FACs along the spacecraft trajectory and the magnitudes were hundreds of kilometers and tens of nA/m2, respectively, and both events were mapped to the auroral region in the ionosphere. We also examined reliability of the results with some parameters, and found that our results are adequately comparable with other studies. Nevertheless, some limitations that decrease the accuracy of current estimation exist.

Sensorless predictive current control with a charge balance current estimator for boost converters based on discrete‐time model considering current ripple

The performance of a sensorless predictive current controlled boost converter is usually susceptible to the accuracy of the employed converter and current estimator models. Since the accuracy of conventional current estimator would be degraded due to parasitic parameter variations, a charge balance current estimator (CBCE) is proposed to overcome this issue. Its estimation of peak inductor current is based on the charge balance principle of output capacitor and characteristics of inductor current ripple. Only one parasitic parameter - capacitor equivalent series resistance (ESR) is used in CBCE. Furthermore, the capacitor ESR is also estimated together with output load by a proposed equivalent load estimation scheme which can improve the current estimation accuracy. Besides, to achieve a high dynamic performance digital control, a discrete-time model considering current ripple is developed, in which the ripple is taken into account rather than treats inductor current as a constant in each switching cycle. It can achieve a higher accuracy than conventional averaged model, especially in the high-frequency region. Finally, its effectiveness is verified by simulation and experiment results.

Biomass and root attributes of eight of New Zealand\u2019s most common indigenous evergreen conifer and broadleaved forest species during the first 5\xa0years of establishment

BackgroundTree allometric equations are critical tools for determining tree volume, biomass and carbon stocks. However, there is a lack of species-specific biomass equations for juvenile trees of many of New Zealand’s indigenous species. The aim of this study was to provide allometric equations for total above- and below-ground biomass and total root biomass and length for eight common evergreen conifer and broadleaved species.MethodsIn a plot-based field trial, growth metrics of conifers Prumnopitys taxifolia (matai), Agathis australis (kauri), Prumnopitys ferruginea (miro), Podocarpus totara (totara), Dacrycarpus dacrydioides (kahikatea) and Dacrydium cupressinum (rimu) and broadleaved species Alectryon excelsus (titoki) and Vitex lucens (puriri) were measured annually. These species were selected based on their potential role as a long-term solution for mitigating erosion in areas of marginal land proposed for new afforestation/reforestation and as an important carbon (C) sink.ResultsRoot collar diameter (RCD) provided the best fit for tree height, total above-ground biomass (AGB) and total below-ground biomass (BGB), and all regressions were highly significant (P = 0.001). Most species showed significant increases in annual growth and, by year 5, the BGB ranged between 21 and 42% of total biomass and decreased with increasing plant age. Of the conifers, Podocarpus totara had the greatest mean maximum root spread (2.2 m) exceeded only by the broadleaved Vitex lucens (2.5 m). For all species, and in each year of the trial, 100% of the BGB remained confined to within 0.5 m of the ground surface. With the exception of Vitex lucens and Podocarpus totara, > 90% of the total root length remained within a 0.5-m radius of the root bole. The species-specific mean tree biomass of 5-year-old plants ranged from 0.32 to 4.28 kg plant−1. A mixed-species forest established at 1000 stems per hectare (spha), consisting of 200 of each of the best performed of the trialled species, would amass ~ 2.3 t ha−1 of biomass and a forest carbon stock of 3.8 t CO2 ha−1 within 5 years.ConclusionsInter-species differences in the allocation of BGB and AGB appeared to be age dependent. The root-growth metrics of these common indigenous forest species, as candidates for erosion control, have improved our understanding of their potential usefulness for stabilising marginal land. Whole-plant biomass of juvenile trees will greatly improve the accuracy of current estimates of forest carbon stocks for proposed new areas of indigenous afforestation/reforestation.

Online Inductor Parameters Identification by Small-Signal Injection for Sensorless Predictive Current Controlled Boost Converter

In a sensorless predictive current controlled boost converter, parameterizing the inductor plays an important role in controller performance. In this paper, a solution for inductor parameters online identification is investigated. A small-signal injection strategy is proposed to create a transient state, and convergence problem of inductance identification in steady state can be avoided. Then, a charge balance current observer (CBCO), derived from capacitor current charging balance concept, is adopted to estimate the inductor current for inductance identification. Since inductance is not used in CBCO, current estimation is not affected by inductance identification error. Because of rank-deficient problem, instead of identifying inductor parasitic resistance solely, the inductor equivalent parasitic resistance is derived. By applying it into the conventional current observer for current control loop, the accuracy of current estimation can still be guaranteed since more parasitic effects are included. To improve the accuracy of inductance identification, a load identification method is investigated. Furthermore, the effect of the equivalent series resistance of output capacitor on the proposed algorithm is analyzed. Finally, its effectiveness is verified by experimental results.

Battery State of Health Monitoring by Estimation of Side Reaction Current Density Via Retrospective-Cost Subsystem Identification

This paper introduces a new method to monitor battery state of health (SOH). In particular, the side reaction current density is estimated as a direct SOH indicator for the first time and its estimation is formulated as an inaccessible subsystem identification problem, where the battery health subsystem is treated as an inaccessible subsystem with the side reaction current density as the output. Inaccessibility in this context refers to the fact that the inputs and outputs of the subsystem are not measurable in situ. This subsystem is identified using retrospective-cost subsystem identification (RCSI) algorithm, and the output of the identified battery health subsystem provides an estimate for the side reaction current density. Using an example parameter set for a LiFePO4 battery, simulations are performed to obtain estimates under various current profiles. These simulations show promising results in identifying the battery health subsystem and estimating the side reaction current density with RCSI under ideal conditions. Robustness of the algorithm under nonideal conditions is analyzed. Estimation of the side reaction current density using RCSI is shown to be sensitive to nonideal conditions that cause errors in the measurement or estimation of the battery voltage. A method for quantitatively assessing the impact of nonideal conditions on the side reaction current estimation accuracy is provided. The proposed estimation technique, including the method for estimating the side reaction current density using RCSI and the framework analyzing its robustness, can also be applied to other parameter sets and other battery chemistries to monitor the SOH change resulting from any electrochemical-based degradation mechanism that consumes cyclable Li-ions.

Sensorless Predictive Peak Current Control for Boost Converter Using Comprehensive Compensation Strategy

For a sensorless predictive-peak-current-controlled boost converter, the output voltage steady-state error cannot be eliminated by voltage loop PI controller. The basic cause for this is investigated through analysis and theoretical approaches. To eliminate the voltage steady-state error and achieve high-accuracy current estimation, a comprehensive compensation strategy is proposed. First, a compensation algorithm for output voltage sampling is introduced. It can not only effectively eliminate the output voltage steady-state error but also guarantee current observer convergence. The compensation schemes for component parasitic parameter effects and switching delay are also investigated. With this comprehensive compensation strategy, both the system transient response and current estimation accuracy are greatly improved. Finally, the effectiveness of the proposed algorithm is verified by experimental results.

Digitally Controlled Current Sensorless Photovoltaic Micro-Converter for DC Distribution

In this paper, a digitally controlled photovoltaic (PV) micro-converter for dc distribution with sensing no current is presented. Current information for maximum power point tracking (MPPT) is estimated from system parameters, which leads to reducing power losses caused in sensing current and the number of components. Operation analysis of boundary conduction, quasiresonant, and discontinuous conduction modes is presented for its implementation. The high current estimation accuracy not only allows adaptive operation mode changes for efficiency optimization, but also guarantees achievement of high MPPT efficiency. Loss analysis of each operation mode is also presented to determine optimal transition points for mode change. A prototype PV micro-converter for a 120-W PV module is implemented by utilizing a digital signal processor. Experimental results verify that the proposed method is stable in both static and dynamic operations. European efficiency and MPPT efficiency are measured higher than 97.5% and 99.5%, respectively.

Interplate coupling along the Nankai Trough, southwest Japan, inferred from inversion analyses of GPS data: Effects of subducting plate geometry and spacing of hypothetical ocean-bottom GPS stations

Abstract We estimated the slip-deficit rate distribution on the plate boundary between the subducting Philippine Sea plate and the continental Amurian plate along the Nankai Trough, southwest Japan. Horizontal and vertical displacement rates were calculated from land-based Global Positioning System (GPS) data during the 5-year period from 1 January 2005 to 31 December 2009. We employed an inversion analysis of geodetic data using Akaike's Bayesian information criterion (ABIC), including an indirect prior constraint that slip distribution is smooth to some extent and a direct prior constraint that slip is mainly oriented in the plate-convergent direction. The results show that a large slip deficit exists at depths ranging from 15 to 20 km on the plate boundary in a belt-like form. The maximum slip-deficit rate was identified off Shikoku and reached 6 cm/year. The slip-deficit rate differed by as much as 1 cm/year when using a different geometric model of the subducting plate. On the basis of the spatial distribution of estimation errors and the resolution of the obtained slip-deficit rate on the plate boundary, we also found that the offshore slip-deficit rate cannot be estimated with sufficient accuracy using only land-based GPS data. Therefore, we tested the improvement in results when introducing hypothetical ocean-bottom GPS stations. The stations were arranged in four along-arc and across-arc spacings of 80 km and 40 km. The ocean-bottom data improved the estimation errors and resolutions, and successful results were obtained for a checkerboard with each square 75 km × 76 km. Our results indicate that 40-km along-arc and across-arc two-dimensional spacing of ocean-bottom GPS stations is required to obtain reliable slip-deficit distributions near the trough axis, assuming the current estimation accuracy for ocean-bottom horizontal displacement rates.

Net flux of carbon dioxide from tropical forests in 1980

Deforestation in the tropics is responsible for an annual net release of carbon to the atmosphere, estimated for 1980 at between 0.5 and 4.2 × 1015 g (refs 1–6). By comparison, the release of carbon from combustion of fossil fuels was 5.2 × 1015 g in 1980. The wide range of estimates for the tropical biota and soils has been due primarily to different estimates of the rate of deforestation2,7. A recent assessment of the world's tropical forests by the Food and Agriculture Organization/UN Environment Program8,9 provides a comprehensive, country-by-country survey of deforestation in the late 1970s as well as estimates of the volumes of wood in tropical forests. The assessment thus provides an independent data base, perhaps the most reliable to date, from which terrestrial releases of carbon to the atmosphere can be calculated. Here we compare the FAO/UNEP survey with other sources of data on rates of deforestation and stocks of carbon in the tropics; then we present the calculated net flux of carbon between tropical forests and the atmosphere based on these different data; and, finally, we consider the accuracy of current estimates of the net biotic flux.