Virtual Flux Research Articles

Seepage Control in a High Concrete Face-Rock Fill Dam Based on the Node Virtual Flow Method

The seepage control system of a high Concrete Face Rock-Fill Dam (CFRD) may have anti-seepage deficiencies during both construction and operation. In order to solve these, the three-dimensional Finite Element Method (FEM) model was built based on dam body filling, anti-seepage system, defect location and bedrock distribution. The seepage field simulation and computation were carried out using an improved node virtual flux method and the zero-thickness crack model theory. The water head distribution, seepage lines and dam leakage field were obtained by simulation under different conditions, and the seepage characteristics during construction and operation were analyzed systematically. Taking a high CFRD as an example, the results showed that during the flood-control construction period, the incomplete nature of the dam face slab can lead to seepage damage near the second seepage control line. Moreover, during operation period; the seepage control system was still effective when the dam face slab was incomplete.

Sensors fault diagnosis and fault tolerant control for grid connected PV system

This paper discusses a Sensors Fault Detection and Isolation (FDI) and Fault Tolerant Control (FTC) of three phase inverter for PV system application. All sensors used in the inverter control strategy are addressed in this work. The developed FDI algorithm focuses on residuals generation; it is defined by the different between measurement and reconstituted signal. So, estimators block are investigated, such as, two Models References Adaptive Systems (MRAS) are developed to reconstitute the information of three phase line currents and dc link voltage sensors. The reconstituted information is injected to the corresponding FDI algorithm. Grid voltage sensors FDI is presented in this contribution trough the use of scaled virtual flux estimator, based on Second Order Generalized Integrator and Frequency Looked Loop. When a fault detected, FTC is ensured by replacing the erroneous measurement by its corresponding estimator. Theoretical study and simulations results are presented to validate the effectiveness of the proposed method.

Study on Anti-Disturbance for MW Grade back-to-back Converter System Based on Small-signal Modelling

Dynamic performance of the front-end PWM rectifier is the basic guarantee of stable and reliable operating of a high power back-to-back converter system. Traditional double-loop PI regulator controlling may lead to DC-link voltage fluctuation and even more seriously overvoltage or under-voltage threatening the safe operation of the power switching device. In this paper, a small-signal model of high power virtual-oriented-flux is established to analyze the DC-link voltage fluctuation limitation of systems with conventional load current feed-forward control. A virtual line flux oriented control algorithm is also proposed based on the model mentioned above. Finally, a MATLAB simulation and practical test were carried out to certify the effectiveness and correction of the algorithm.

Quality improvement of shunt active power filter with direct instantaneous power estimator based on Virtual Flux

This paper presents a new control strategy which is based on a switching table applied for Virtual Flux Direct Power Control (VF-DPC) of voltage source inverter based shunt active power filter (SAPF). This control method is applied to eliminate harmonic pollution and compensate the reactive power in the presence of nonlinear loads and unbalanced sources. Its main goal is to select switching states of the SAPF converter appropriately based on a look-up table established by hysteresis controllers acting on the instantaneous error between the commanded and VF-estimated values of active and reactive power. Our method aims to improve the electrical quantity behavior in steady and dynamic states while reducing the installing cost of the filter through eliminating the AC line voltage sensors. Facing to disturbances affecting the electrical network, a phase locked loop (PLL) has been integrated.The control strategy proposed for the active filter has been tested in the Matlab/Simulink environment.

Predictive control of power flow between two islanded microgrids using nine-switch converter

Nine-switch converter has been recently known for its higher compactness with reduced switch count as compared to the back-to-back converter. The readily available dc-link capacitor made it an appropriate alternative for ac/dc/ac conversion in microgrids. Regardless of the complicated Pulse Width Modulation control scheme, this paper proposes a novel predictive power control for the nine-switch converter which is simple and allows concurrent control of real and reactive power flow between two islanded microgrids. The proposed control scheme adopts the virtual flux vectors and a newly defined reactive power to improve the power quality under the existence of grid voltage disturbances, i.e., voltage unbalance and voltage distortion. Simulation results of the proposed predictive power control guarantee decoupled active and reactive power controls, fast response, accurate power and dc-link voltage tracking, and sinusoidal current waveforms with low harmonic distortions under the various grid conditions.

Impacts of the representation of riverine freshwater input in the community earth system model

The impacts of the representation of riverine freshwater input on the simulated ocean state are investigated through comparison of a suite of experiments with the Community Earth System Model (CESM). The aspects of river and estuary processes investigated include lateral spreading of runoff, runoff contribution to the surface buoyancy flux within the K-Profile Parameterization (KPP), the use of a local salinity in the virtual salt flux (VSF) formulation, and the vertical redistribution of runoff. The horizontal runoff spreading distribution plays an important role in the regional salinity distribution and significantly changes the vertical stratification and mixing. When runoff is considered to be a contribution to the surface buoyancy flux, the calculation of turbulent length and velocity scales in the KPP can be significantly impacted near larger discharge rivers, resulting in local surface salinity changes of up to 12 ppt. Using the local surface salinity instead of a globally constant reference salinity in the conversion of riverine freshwater flux to VSF can reduce biases in the simulated salinity near river mouths but leads to drift in global mean salinity. This is remedied through a global correction approach. We also explore the sensitivity to the vertical redistribution of runoff, which partially mimics the impacts of vertical mixing process within estuaries and coastal river plumes. The impacts of the vertical redistribution of runoff are largest when the runoff effective mixing depth is comparable with the mixed layer depth, resulting from the enhanced vertical mixing and the increase of the available potential energy. The impacts in all sensitivity experiments are predominantly local, but the regional circulation can advect the influences downstream.

Optimal VF-PDPC of grid connected inverter under unbalanced and distorted grid voltages

In this article, an optimal virtual flux predictive direct power control (VF-PDPC) is proposed for three-phase grid connected voltage source inverter (VSI) operating under unbalanced and distorted grid supply voltage. The concept of virtual flux and extension pq theory is introduced in the conventional PDPC, where the former enhances its resilience toward distorted supply voltage while the latter enhances its resilience toward unbalanced supply voltage. The inherent advantages of the conventional PDPC scheme, such as simple implementation, fast dynamic responses, and no demand of modulators are retained. Getting rid of the complicated positive and negative sequence extraction of grid components, power compensation, or any tuning work, the proposed optimal VF-PDPC achieves excellent power tracking capability, and sinusoidal grid currents with low harmonics under various grid voltage conditions. Simulation results are presented to verify the effectiveness of the proposed control scheme when compared to the conventional PDPC, conventional VF-PDPC, and optimal PDPC.

A practical nonlinear controller for levitation system with magnetic flux feedback

This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedback are analyzed when compared with the current feedback. Then, a backstepping controller with magnetic flux feedback based on the mathematical model of levitation module is developed. To obtain magnetic flux signals for full-size maglev system, a physical method with induction coils installed to winding of the electromagnet is developed. Furthermore, to avoid its hardware addition, a novel conception of virtual magnetic flux feedback is proposed. To demonstrate the feasibility of the proposed controller, the nonlinear dynamic model of full-size maglev train with quintessential details is developed. Based on the nonlinear model, the numerical comparisons and related experimental validations are carried out. Finally, results illustrating closed-loop performance are provided.

Accurate Voltage Parameter Estimation for Grid Synchronization in Single-Phase Power Systems

This paper presents an adaptive observer-based approach to estimate voltage parameters, including frequency, amplitude, and phase angle, for single-phase power systems. In contrast to most existing estimation methods of grid voltage parameters, in this study, grid voltage is treated as a dynamic system related to an unknown grid frequency. Based on adaptive observer theory, a full-order adaptive observer is proposed to estimate voltage parameters. A Lyapunov function-based argument is employed to ensure that the proposed estimation method of voltage parameters has zero steady-state error, even when frequency varies or phase angle jumps significantly. Meanwhile, a reduced-order adaptive observer is designed as the simplified version of the proposed full-order observer. Compared with the frequency-adaptive virtual flux estimation, the proposed adaptive observers exhibit better dynamic response to track the actual grid voltage frequency, amplitude, and phase angle. Simulations and experiments have been conducted to validate the effectiveness of the proposed observers.

Voltage sensorless predictive direct power control of three‐phase PWM converters

This study develops a voltage sensorless predictive direct power control (PDPC) strategy for three-phase pulsewidth modulation (PWM) converters using accurate virtual flux (VF) estimation. This proposed PDPC can realise simultaneous control of the instantaneous active and reactive power, and achieve a constant switching frequency operation by adopting an on-line corrective space vector modulation modulator. AC voltage sensors are removed by using the following two techniques. One is that an accurate VF observer is employed to compensate the magnitude and phase errors introduced by the first-order low pass filter. The other is that grid voltages are estimated using the VF based estimation of instantaneous active and reactive power as intermediate variables. In addition, the time delay existing in a real system is taken into account in the proposed control model. Comparative results demonstrate the excellent performance of the proposed approach compared with the conventional look-up-table DPC and the conventional PDPC.

Virtual-Flux-Based Predictive Direct Power Control of Three-Phase PWM Rectifiers With Fast Dynamic Response

This paper proposes a power predictive control (PPC) method for three-phase pulse width modulated rectifiers without a proportional-integral controller. The proposed PPC method calculates the optimized voltage vector by analyzing the relationship between the virtual flux, active power, converter voltage, and filter parameters. Thus, an overshoot does not occur and the fast and accurate power control becomes possible. The predictive algorithm computes the power error that would be produced by applying each vector and selects the one that contributes the minimum error. The simulation and experimental results prove that the proposed method provides an excellent steady-state performance and quick dynamic response.

Virtual flux direct power control of the three-level NPC shunt active power filter based on backstepping control

In this paper, a novel control strategy of multilevel shunt active power filter is presented. The idea behind the proposed control scheme is to combine the backstepping control and direct power control with virtual flux concept into one controller able to improve the performance of active power filter. The choice of the multilevel topology leads to a clear enhancement in the compensation of the polluting load harmonics. To take full benefit of this choice, the task of balancing voltages of dc-link capacitors is assigned to the multilevel space vector modulation with balancing ability. For this reasons, the adopted multilevel active power filer is proposed to reduce harmonic currents flowing into the power system and to draw a nearly sinusoidal current with unity power factor. Complete simulation of the resultant active filtering system validates the efficiency of the proposed backstepping control law. Compared to the traditional control, the used of backstepping control allows to exhibit excellent transient response during large load variations.

Virtual Signal Injection Based Direct Flux Vector Control of IPMSM Drives

This paper describes a novel virtual signal injection-based direct flux vector control for the maximum torque per ampere (MTPA) operation of the interior permanent magnet synchronous motor (IPMSM) in the constant torque region. The proposed method virtually injects a small high-frequency current angle signal for tracking the optimal flux amplitude of the MTPA operation. This control scheme is not affected by the accuracy of the flux observer and is independent of machine parameters in tracking the MTPA points and will not cause additional iron loss, copper loss, and torque ripple as a result of real signal injection. Moreover, by employing a bandpass filter with a narrow frequency range the proposed control scheme is also robust to current and voltage harmonics, and load torque disturbances. The proposed method is verified by simulations and experiments under various operating conditions on a prototype IPMSM drive system.

The impact of the QNSE‐EDMF scheme and its modifications on boundary layer parameterization in WRF: modelling of CASES‐97

In recent years, many eddy‐diffusivity mass‐flux (EDMF) planetary boundary layer (PBL) parametrizations have been introduced. Yet most validations are based on idealized set‐ups and/or single‐column models. To address this gap, this article focuses on the effect the mass‐flux part has on the performance in the Quasi‐Normal Scale Elimination‐EDMF (QNSE‐EDMF) PBL scheme in the Weather Research and Forecasting (WRF) model by comparing the results to observations from the CASES‐97 field campaign. In addition, two refined versions, one introducing the parametrized clouds to the WRF radiation scheme, and the second adding a different entrainment formulation, have been evaluated.The introduction of mass flux reduced errors in the average moisture profile, but virtual temperature and wind speed profiles did not change as much. The modelled mixed‐layer depth, while still low compared to observations, was closer to observed values with the addition of mass flux. The major changes in the virtual potential temperature flux profiles were an increase in entrainment ratios and a slight decrease in surface values. Allowing for biases in the observed fluxes, modelled and observed flux profiles had a similar shape. However, the agreement among the modelled and between the modelled and observed water‐vapour flux profiles and vertical flux divergence was often poor, a likely result of the model's failure to capture the timing of the morning boundary‐layer water‐vapour maximum. Further, both virtual potential temperature and water‐vapour flux profiles display spurious spikes attributed to the way the non‐local and local terms interact in the model. Adding mass‐flux‐based clouds to the radiation calculation improved the time‐and space‐averaged modelled incoming short‐wave flux. The choice of the representation for entrainment/detrainment often affected the results to the same extent as adding mass flux.

P015 格子ボルツマン法と仮想流束法を用いた二次元羽ばたき飛行の数値解析(メカボケーション学生研究発表セッション)

P015 格子ボルツマン法と仮想流束法を用いた二次元羽ばたき飛行の数値解析(メカボケーション学生研究発表セッション)

P026 仮想流束法を用いた三次元胸部大動脈モデルにおける血液流れの数値解析(メカボケーション学生研究発表セッション)

P026 仮想流束法を用いた三次元胸部大動脈モデルにおける血液流れの数値解析(メカボケーション学生研究発表セッション)

P030 仮想流束法を用いた微粒子のろ過に関する数値シミュレーション(メカボケーション学生研究発表セッション)

P030 仮想流束法を用いた微粒子のろ過に関する数値シミュレーション(メカボケーション学生研究発表セッション)

Forward hadron production in ultra-peripheral proton–heavy-ion collisions at the LHC and RHIC

We discuss hadron production in the forward rapidity region in ultraperipheral proton-lead collisions at the LHC and proton-gold collisions at RHIC. Our discussion is based on the Monte Carlo simulations of the interactions of virtual photons emitted by a fast moving nucleus with a proton beam. We simulate the virtual photon flux with the STARLIGHT event generator and then particle production with the SOPHIA, DPMJET, and PYTHIA event generators. We show the rapidity distributions of charged and neutral particles, and the momentum distributions of neutral pions and neutrons at forward rapidities. According to the Monte Carlo simulations, we find large cross sections of ultraperipheral collisions for particle production especially in the very forward region, leading to substantial background contributions to investigations of collective nuclear effects and spin physics. Finally we can distinguish between proton-nucleus inelastic interactions and ultraperipheral collisions with additional requirements of either of the charged particles at midrapidity and a certain level of activities at negative forward rapidity.

Improved grid voltage sensorless control strategy for railway power conditioners

Rapid development of high-speed trains confronts the power grid with serious power quality problems. In this study, to compensate power quality, an improved grid voltage sensorless control method for the railway power conditioner (RPC) is proposed. The proposed control strategy utilises a moving average filter to better detect the compensating currents and a proportional-resonant controller to control the compensating currents. Moreover, a sensorless virtual flux method based on second order low-pass filters is presented to replace the AC voltage sensors. Using the proposed strategy, the dynamic and steady-state characteristic of the RPC is significantly enhanced. Through simulation tests, the effectiveness of the proposed methods is confirmed.

Development and application of a ray-tracing code integrating with 3D equilibrium mapping in LHD ECH experiments

The central electron temperature has successfully reached up to 7.5 keV in large helical device (LHD) plasmas with a central high-ion temperature of 5 keV and a central electron density of m−3. This result was obtained by heating with a newly-installed 154 GHz gyrotron and also the optimisation of injection geometry in electron cyclotron heating (ECH). The optimisation was carried out by using the ray-tracing code ‘LHDGauss’, which was upgraded to include the rapid post-processing three-dimensional (3D) equilibrium mapping obtained from experiments. For ray-tracing calculations, LHDGauss can automatically read the relevant data registered in the LHD database after a discharge, such as ECH injection settings (e.g. Gaussian beam parameters, target positions, polarisation and ECH power) and Thomson scattering diagnostic data along with the 3D equilibrium mapping data. The equilibrium map of the electron density and temperature profiles are then extrapolated into the region outside the last closed flux surface. Mode purity, or the ratio between the ordinary mode and the extraordinary mode, is obtained by calculating the 1D full-wave equation along the direction of the rays from the antenna to the absorption target point. Using the virtual magnetic flux surfaces, the effects of the modelled density profiles and the magnetic shear at the peripheral region with a given polarisation are taken into account. Power deposition profiles calculated for each Thomson scattering measurement timing are registered in the LHD database. The adjustment of the injection settings for the desired deposition profile from the feedback provided on a shot-by-shot basis resulted in an effective experimental procedure.