Research on dynamic current sharing method of parallel connected IGBT modules for NPC three level converters

The parallel connection of IGBTs has been being applied in high power neutral point clamped (NPC) three level converters. This paper investigates the impact of gate parameters (gate resistor and capacitance) on dynamic current imbalance of parallel connected IGBT for NPC three level converter. A gate parameters calculation method is proposed in the paper, and the delay time and collector current difference can be analysed quantitatively. Experimental results have shown the effectiveness of the method.

An Accurate Doppler Parameters Calculation Method of Geosynchronous SAR Considering Real-Time Zero-Doppler Centroid Control

The zero-Doppler centroid control in geosynchronous synthetic aperture radar (GEO SAR) is beneficial to reduce the imaging complexity (reduces range-azimuth coupling in received data), which can be realized by adjusting the radar line of sight (RLS). In order to maintain the zero-Doppler centroid throughout the whole orbit of the GEO SAR satellite, the RLS needs to be adjusted in real-time. Due to the ultra-long synthetic aperture time of GEO SAR, the RLS variation during the synthetic aperture time cannot be neglected. However, in the previous related papers, the real-time variation of RLS during the synthetic aperture time was not taken into account in the calculation of Doppler parameters, which are closely related to the RLS, resulting in inaccurate calculation of Doppler parameters. Considering this issue, an accurate Doppler model (the model of relative motion between satellite and ground target) of GEO SAR is proposed in this paper for the accurate calculation of Doppler parameters (Doppler centroid and Doppler bandwidth and other parameters). Finally, simulation experiments are designed to confirm the effectiveness and necessity of the proposed model. The results indicate that the RLS variation during the synthetic aperture time has a considerable effect on Doppler parameters performance of the GEO SAR, and refers to a more stable azimuth resolution performance (the resolution is kept near a relatively stable value at most positions of the elliptical orbit) compared with the case that does not consider the real-time zero-Doppler centroid control.

A new flowchart for parameters calculation of Hybrid Active Power Filter with Injection Circuit

This paper presents a new flowchart for parameters calculation of Hybrid Active Power Filter with Injection Circuit (IHAPF). The first is the necessity to use the IHAPF model and the parameters of the IHAPF needed to search have been shown. Next, the constraints of the parameters to be searched and the objective function to be reached are given. Since then a flowchart is designed to look for parameters of IHAPF using the Jaya optimization algorithm. The Jaya algorithm has the advantage of simplicity, few parameters, and good performance. Therefore it reduces search time. Compared to the flowchart using the firefly algorithm, particle swarm optimization algorithm, and simulated annealing algorithm, the simulation results performed on an IHAPF 10kV-50Hz model have proven that: the proposed flowchart gives better results in minimizing the compensation errors, minimum phase shift angle between supply current, and source voltage, minimum total harmonic distortion of supply current.

Physical modeling of a skip pneumatic winder

Introduction. The analytical phase of research on mine skip pneumatic winders has been passed, so the theoretical provisions have to be tested by the methods of physical modeling which is aimed at confirming the mathematical model adequacy and assessing the effectiveness of different types of sealing devices. Research methods. Physical modeling phases have been formulated, including modeling by geometric and aerodynamic similarity criteria, constructing aerodynamic characteristics of the installation, carrying out experiments with non-contacting and combined seals, and calculating the values of the installation volumetric efficiency based on the experimental data obtained. Research results. The lifting time of the skip model with different masses of material and seal types has been determined. The installation working points in the “flow rate–pressure” coordinate system have been identified, and the values of the volumetric efficiency have been calculated for each working point. Analysis of the results. A satisfactory convergence of calculated and experimental parameters of the physical model has been established. The model's volumetric efficiency has reached a technically acceptable level. The expected value of the experimental model’s volumetric efficiency has been calculated according to the similarity constants. Conclusions. The model's study revealed the convergence of the experimentally obtained volumetric efficiency of the model with its calculated values and proved the applicability of the mathematical model to experimental sample parameters calculation. The volumetric efficiency of the installation with both non-contacting and combined seals is quite high allowing to recommend the studied sealing devices for mine pneumatic winders.

Mathematical Parameters Calculation of Double Exponential Function by a New Numerical Method

Background: Lightning electromagnetic pulse (LEMP) and high-altitude electromagnetic pulse (HEMP) are widely described by three physical parameters (rise time tr, full-width at half-maximum pulse width tw, and maximum electric field strength E0). These pulse shapes are often given by a double exponential form concerning four mathematical parameters, namely α, β, k and Ep. Objective: The transformation from physical parameters into mathematical parameters is necessary in waveform simulation and is traditionally accomplished by linear fit functions regarding the two groups of parameters. However, traditional methods commonly rely on data analysis and calculation. In order to obtain more concise and clear mathematical parameters. Methods: In this paper, a numerical method to calculate the mathematical parameters by solving nonlinear equations with three key constraints is proposed. Firstly, we establish the nonlinear system of equations regarding four variables, namely t1, t2, α and β. Then, three constraints are given to converge the solutions of the equations. Lastly, selecting the minimal value of the convergent solution of each equation. Results: Results: Comparing the solutions obtained by our proposed method to the iterated ones, the overall relative error is less than 2×10-8. Conclusion: The results show that our proposed method not only simplifies the transformation from physical parameters to mathematical parameters, but also keeps the solutions highly accurate.

A Novel Approach of Dynamic Parameter Calculation in Real Time While Managed Pressure Cementing and its application in Ultra-Deep Well

Tremendous amounts of oil and gas reservoir are located in ultra-deep formations, such as Shunnan block in Tarim basin of China, some reservoirs buried deeper than 8000m and which are major exploration areas of SINOPEC. The formation geological conditions are complicated, multiple pressure systems co-exist in the same borehole, narrow pressure-margin problems, all above may cause down-hole troublesome conditions while cementing, such as leaking, fracturing formations and so on. And the managed pressure cementing (MPC) was selected for solving the above problems. But the key for a successful MPC depend on accurate, real-time knowledge of dynamic parameters calculation. Therefore, a real time dynamic parameters calculation for MPC is very important. Firstly, a comprehensive real-time hydraulic calculation method for cementing replacement process was established, in which the difference of density, rheological properties, location and length of different fluids were taken into account. In order to improve the calculation precision, the flow channel both in pipe and annuli was divided into several sections, through which the different diameters of the channels were considered. Secondly, according to the density contrast of operating fluids, a vacuum (U-Tube effect) will appear at the inlet in the cementing replacement process, an integrated U-Tube effect analytical model was established based on the Euler equation, in which the influence of well deviation was taken into account too, and though which the height and volume of vacuum, the down-hole operating fluids acceleration, the out flow rate variation et al. all can be accurately calculated and simulated. Moreover, a series of system calculation software were developed to predict cementing fluids position, fluids acceleration, flow pressure drop, BHP, expected WHP and the related control parameters for MPC. The proposed model has been applied in HPHT ultra-deep well MPC operation of SINOPEC Northwest oil filed in Traim basin, there is an excellent match between the calculated and measured data. Furthermore, this simulation software has been used for designing the MPC parameters, and it runs smoothly with convenient operation. Therefore it can be seen this system can be applied to provide more convenient fast and precise dynamic parameters monitoring for MPC. This study proposed a novel model of Cementing dynamic parameters calculating and developed a comprehensive real-time monitoring system for MPC. Through the application of the monitoring, we can adjust the cementing parameters in real time while MPC, and this real-time monitoring has been applied in several wells very well. Therefore, this study is novel and can afford an effective approach to improve cement quality.

Recommendations for parameters calculation of pressureless channels with arbitrary cross section for rainwater disposal

Based on the analysis of geometric and hydraulic characteristics of pressureless water channels cross sections, recommendations for parameters calculation of these systems with an arbitrary shape of their cross section were elaborated in this article. Elements of hydraulic modeling and analogy were used in the preparation of the presented material. The considered pressureless channels are widely used in rainwater disposal systems designing and can also be used in the designing of other special water disposal networks. Well-known theoretical and empirical hydraulic dependences, relevant reference data, in particular, discharge and velocity characteristics, local resistance coefficients were used in this article. Necessary information on selection of water disposal wells is given. The proposed method of calculation the parameters of water disposal channels can be used in different fluid flow modes: both pressureless and pressure, steady and unsteady. It is recommended for use in the water disposal networks designing, regardless of the pipelines material.

“OKVision® SMARTFIT™” Customizable Mini-Scleral Lenses Fitting Guide

As of today, scleral lenses are the only optical rehabilitation method that provides high visual quality of vision for patients with irregular cornea. This fitting guide is aimed at helping ophthalmologists acquire professional knowledge in the field of fitting scleral lenses and suggest tactics for managing patients with irregular corneas.The workshop outlines indications for prescribing scleral lenses, describes the basic principles of lens parameters calculation and fitting, taking into account the patientspecific parameters of the eyes. In addition, guidelines for acquiring skills in assessing and changing the position of scleral lenses on the patient’s eye, using customization options, daily care, manipulations for inserting on and removing lenses, and further dispensary observation are given.Mastering the basic skills of calculation and fitting customized scleral lenses helps practitioners expand their areas of practice, enhance professional competitiveness and provide patients with high quality vision, even in the most difficult clinical cases.