Regular Sampling Method Research Articles

Sideband Harmonic Model Considering Sampling Delay Effect in the PMSM Drives With Regular Sampled SVPWM Technique under the Low Carrier Frequency Ratio

Regular sampled space vector pulse-width modulation (SVPWM) is a widely implemented technique in permanent magnet synchronous machine (PMSM) drives with the voltage-source inverter (VSI). The modulation technique would generate the sideband harmonics and increase electromagnetic loss, vibration, and acoustic noise. Therefore, a fast and accurate evaluation of sideband harmonics is particularly important. However, the carrier frequency ratio could be relatively low in some applications, which means it would cause sampling delay and influence the sideband harmonics. This paper analyzes the sampling delay effect in PMSM drives, and proposes a modified sideband harmonic model using Lagrange expansion and complex coordinate transformation for both symmetric and asymmetric regular sampling methods. Furthermore, the amplitudes and phases of whole sideband harmonic components are derived. Experiment results are carried out to validate the accuracy improvement of the modified model, which reveals that it could give a superior estimation of the sideband harmonics in the PMSM drives under the low carrier frequency ratio.

A regular sampling method based on the immediate mode for improving the stability of inverters

The shadow mode-based regular sampling methods are usually used in the digital control of power inverters, which introduce a control delay of one and a half sampling periods. The control delay affects the closed loop bandwidth and the stability of dc–ac inverters. Recently, regular sampling methods based on the immediate mode is emerging and helpful for reducing the digital control delay. When employing the immediate mode, the induced vertical crossings may arouse the duty-cycle loss and dead-band effect during the modulation process, which deteriorate the normal operation of the inverters. Although the duty-cycle loss can be avoided by forcing the PWM signal to flip at the occurrence of vertical crossings, the introduced dead bands still exist. Thus, this paper investigates the phenomenon of vertical crossings and proposes a control algorithm composed of predicting the occurrence of vertical crossings and compensating the dead-band effect for regular sampling methods based on the immediate mode. Finally, experimental results on a single-phase dc–ac inverter prototype are provided to compare the efficacy of different approaches.

Comparison of the Effectiveness of Cerebral Exercise and Play therapy Therapy on Empathy and Parent Relations in Students of Learning Disorders in Tehran

Background and Aim: Learning disorder in children is a neuro-developmental disorder that affects the effective processing of verbal or non-verbal information. The present study was conducted with the aim of comparing the effectiveness of brain exercise exercises and filial play therapy on empathy and parent-child relationships in students with learning disabilities in Tehran. Methods: It was quasi-experimental research with a pre-test, post-test design with a control group. The research community includes all students with specific learning disabilities in the elementary school of Tehran. Regular multi-stage random sampling method was selected and randomly divided into three groups (two experimental groups and one control group). In all three groups, children's cognitive and emotional empathy scale questionnaires: parent rating form (Dodds et al., 2008) and Pianta overall positive parent-child interaction questionnaire, brain exercise therapeutic exercises (8 sessions) and the second experimental group, Filial play therapy (10 sessions) and no intervention was done for the control group. Statistical analysis was performed using multivariate, univariate analysis of covariance and Bonferroni’s post hoc test and SPSS23 software. Results: The findings of the research have shown that brain exercise exercises and filial play therapy on emotion management skills (F=4.880 and P<0.01), social competence (F=200.64 and P<0.01), empathy (F=231.23 and P<0.01) and parent-child relationships (F=29.97 and P<0.01) were effective. Also, there is no significant difference between the group of brain exercise exercises and the filial play therapy group on the improvement of empathy and parent-child relationships. Conclusion: It can be concluded that these two types of educational techniques can be used to help and educate children with learning disabilities.

Design of Control Circuit and Control Strategy of Permanent Magnet Synchronous Motor Based On HT32

This article uses the HT32F1765 single-chip microcomputer introduced by Taiwan’s Holtek company as the control core of the system to explore the design of the control circuit and control strategy of the permanent magnet synchronous motor. The main circuit part is the AC-DC-AC frequency conversion main circuit composed of rectification, filtering, inverter, etc., and the control part adopts the regular sampling method to generate spwm waves for control. Finally, the HT32F1765 is used to realize the frequency conversion speed control of the permanent magnet synchronous circuit.

An Improved Active Damping Method Based on Single-Loop Inverter Current Control for LCL Resonance in Grid-Connected Inverters

This paper investigates active damping of LCL filter resonance in grid-connected inverters with only inverter current feedback control, since it only needs to sample one current to realize both current control and inverter protection. The traditional single-loop inverter current control (SLICC) can damp the LCL filter resonance actively. However, if the control delay is considered in digital control, the system stability will depend on the ratio of the LCL resonance frequency f res to the sampling frequency f s , and the valid damping region is only up to f s / 6 . Considering that the design region of the LCL resonance frequency f res is up to f s / 2 , the system can easily become unstable due to the LCL resonance frequency shifting. Thus, this paper proposes an improved active damping method based on SLICC, including the asymmetric regular sampling method and delay compensation method. The improved sampling method minimizes the control delay without introducing a switching ripple, and the delay compensation method further compensates for the delay effect. With a proper parameter design, the upper limit of the valid damping region is extended up to f s / 2 , which can cover all the possible resonance frequencies, and it has inherent robustness against grid-impedance variation. Finally, a few simulations in MATLAB/SIMULINK and experiments based on a 6 kW prototype are performed to verify the theoretical analysis.

An Evaluation of Paddy Field Consolidation Project with a Sustainable Livelihood Approach to Rural Households (Case Study: Choobar Rural District, Shaft County)

Purpose- Among the most important challenges in the agricultural sector are lack of optimal use of production factors, multiplicity of parcels and dispersion of agricultural lands. Land consolidation is one of the effective solutions which can change the size of fields and organize them to increase production, especially in paddy fields, which facilities agricultural development and ultimately achieves a sustainable livelihood in rural areas. The purpose of this study is to evaluate the success rate of paddy field consolidation project through the study of a group of farmers who are included in the land consolidation project. Design/Method/Approach- The population of the study consisted of 285 farmers from 11 villages of Choobar rural district in Shaft County who have been selected by regular sampling method. To collect the data, library and survey methods (observation and questionnaires) have been used. Cronbach's alpha was used to measure the reliability of the research tools, and in the analytical part, single-sample t-test was used to evaluate the success rate of the project in Choobar rural district; To investigate the relationship between land consolidation project and improvement in economic indicators of rural households, initially Spearman correlation coefficient was used, then simple regression test and coefficient of determination R2 were used to measure the effectiveness of the project on economic indicators. Finding- The research findings on the level of economic and social dimensions and the assessment of the success rate of the project in Choobar rural district showed the project was moderately to highly successful in the study area. The effects of the project in improving the socio-economic indicators of rural households in Choobar rural district are such that the highest correlations were found between the project and economic indicators in the use of machinery, land infrastructure, productivity, household employment, ease of access to machinery and manpower, income, and investment; At the level of social indicators the highest correlations were respectively found in interpersonal and generalized trust, objective participation, sense of physical security, insurance services, formal participation, conflict reduction and institutional trust. From farmers’ perspective, among the socio-economic indicators, the infrastructure indicator which is created by the government and the use of machinery after the implementation of the project, and the ease of access to machinery and manpower, interpersonal and generalized trust have had the greatest impact on the implementation of the project.

Asymmetric regular sampling SPWM method based on tangent approximation algorithm

Objectives In order to improve the quality of sinusoidal waveform output by the ship's high-frequency inverter charging device and reduce the CPU occupancy rate, an asymmetric regular sampling sinusoidal pulse width modulation (SPWM) method based on tangent approximation is proposed. Methods According to the basic principle and calculation method of the asymmetric regular sampling SPWM method based on tangent approximation, a Matlab/Simulink simulation model is built, and then the software algorithm flow that can be used in the high-frequency inverter charging device is designed together with the actual output of the tangent approximation method. The effects are then compared and verified by experiments. Results The simulation results show that under pure resistive load and resistive inductive load, the total harmonic distortion (THD) of the load-end waveform based on tangent approximation method is 2.12% and 2.08%, respectively, and its waveform quality is better than symmetric regular sampling. The experimental results show that the THD of load-end waveform based on the tangent approximation method is significantly lower than the symmetric regular sampling method. When the effective value of the input line voltage is 580 V (the modulation ratio is 0.8), the quality of the output waveform is relatively optimal. Conclusions The asymmetric regular sampling SPWM method based on tangent approximation overcomes the shortcomings of the traditional symmetric regular sampling method, such as the low quality of the output waveform and the traditional asymmetric regular sampling method's high sampling frequency and high CPU occupancy rate. The research results can provide reference for the design of ship's high frequency inverter charging devices.

A METHOD FOR EXTRACTING SUBSTATION EQUIPMENT BASED ON UAV LASER SCANNING POINT CLOUDS

Abstract. Smart grid construction puts higher demands on the construction of 3D models of substations. However, duo to the complex and diverse structures of substation facilities, it is still a challenge to extract the fine three-dimensional structure of the substation facilities from the massive laser point clouds. To solve this problem, this paper proposes a method for extracting substation equipment from laser scanning point clouds. Firstly, in order to improve the processing efficiency and reduce the noises, the regular voxel grid sampling method is used to down-sample the input point cloud. Furthermore, the multi-scale morphological filtering algorithm is used to segment the point cloud into ground points and non-ground points. Based on the non-ground point cloud data, the substation region is extracted using plane detection in point clouds. Then, for the filtered substation point cloud data, a three-dimensional polygon prism segmentation algorithm based on point dimension feature is proposed to extract the substation equipment. Finally, the substation LiDAR point cloud data collected by the UAV laser scanning system is used to verify the algorithm, and the qualitative and quantitative comparison analysis between the detected results and the manually extracted results are carried out. The experimental results show that the proposed method can accurately extract the substation equipment structure from the laser point cloud data. The results are consistent with the manually extracted results, which demonstrate the great potential of the proposed method in substation extraction and power system 3D modelling applications.

Passivity‐based output admittance shaping of the converter‐side current‐controlled grid‐tied inverter to improve the robustness to the grid impedance

In the LCL-filtered grid-tied inverter, the classical low-cost control strategy which is composed of the single converter-side current control and the unit grid voltage feedforward compensation, is commonly employed to inject the sinusoidal current into the utility. However, the inverter output admittance features the non-passive behaviour, which indicates that the harmonic currents may be amplified under the disturbances of the grid voltage and the grid impedance. Therefore, two dedicated current loops based on only the converter-side current feedback are proposed, which consist of the low-pass filter-based current regulation and the high-pass filter-based active damping (HFAD). The mixed asymmetrical regular sampling method is further used to reduce the control delay of the HFAD. Moreover, the low-pass filter-based feedforward is developed to make a compromise between the disturbance rejection and the stability. Fair comparisons with other typical control strategies are made through analysing the virtual resistor in parallel with the filter capacitor, which reveals that the positive virtual resistance at the frequency lower than half of the switching frequency is maintained. With the elaborated control parameters, the exhaustive experimental results finally verify the effectiveness of the proposed method in passivating the inverter output admittance.

Using jittered sampling in designing geometry and imaging in shallow 3D seismic surveys

ABSTRACTWhen the depth of the shallow three‐dimensional seismic exploration is less than 100 m, one often encounters very low velocities for the target and high frequencies in the data. Following Nyquist–Shannon sampling theorem, the permissible maximum receiver interval can be smaller in this case compared to relatively deeper seismic exploration. This suggests that there are still issues to be addressed in the design of geometry and in data processing in shallow three‐dimensional seismic exploration. This paper addresses these problems by applying the theory of compressed sensing for signal processing to shallow‐seismic geometry designing and data processing. Theoretical research shows that random sampling of data can better reconstruct the wavefield than undersampled data. Random sampled data can transform the coherent aliasing to non‐coherent noise, which turns the seismic data interpretation problem into a data denoising problem. The jittered random sampling method avoids the situation when the spatial data points of a randomly sampled dataset are too concentrated or too sparse. Our proposed approach was tested on simulated and real seismic data. The results show that if the jittered random undersampling method is used in shallow three‐dimensional seismic data acquisition, then a wider range of observation with fewer receivers in the layout is possible. This greatly improves the data collection efficiency in the field. In addition, the random sampling method has more flexibility in the field environment. When using the regular sampling method, an open survey area without large obstacles is needed. However, the random sampling method can be adapted to rugged terrains. When obstacles are encountered, the receiver spacing can be increased appropriately. In open areas, the receiver spacing can be decreased to compensate for the reduced data.

Real-Time Calculation Method for Single-Phase Cascaded H-Bridge Inverters Based on Phase-Shifted Carrier Pulsewidth Modulation

The time delay caused by the digital computation and the update of the duty cycle tend to worsen the dynamic performance of digitally controlled power converters. This paper proposes a real-time calculation method for single-phase cascaded H-bridge (CHB) inverters with the phase-shifted carrier pulsewidth modulation (PSC-PWM) to eliminate the time delay caused by the digital computation in the control loop without the loss of duty cycle. In the approach, a sampling method for the PSC-PWM applied in a single-phase CHB inverter is introduced, which samples the current and voltage at points of the intersection for triangular carriers of legs in all adjacent H-bridge cells. The sampling method is used alternately with the conventional regular sampling method by following a selection rule in order to avoid the loss of duty cycle. Experimental results verify that the proposed method effectively improves the transient performance of the current control loop and suppresses the effect of the distortion of the grid voltage on the line current.

Research and Implementation of Natural Sampling SPWM Digital Method for Three-Level Inverter of Photovoltaic Power Generation System Based on FPGA

The digital method of natural sampling sinusoidal pulse width modulation (SPWM) is studied based on the characteristics of neutral point clamped three-level inverters of Photovoltaic power generation system. Based on field programmable gate array (FPGA), A three-level natural sampling SPWM digital framework is constructed. The digital implementation methods of triangular carrier generation, sinusoidal modulation waveform generation, switching state combination configuration and dead-zone setting are studied. A ultra-realtime comparison calculation method of switching time based on FPGA technology is proposed in this paper. This method avoids complex calculation such as Taylor series expansion and convergence judgment in natural sampling SPWM. Under the same conditions, the harmonic content of the SPWM output waveform using this method is smaller than that of the symmetrical regular sampling method. And the harmonic content is equivalent to that of natural sampling. The digital natural sampling method can further improve the quality of output waveform and the stability of DC bus voltage of three-level inverters. The theoretical research is realized by VHDL (Very High Speed Integrated Circuit Hardware Description Language) and FPGA chip. The experimental results prove the correctness and feasibility of the digital method.

Four-Dimensional Space Vector PWM Strategy for Five-Phase Voltage Source Inverter

For a five-phase motor with non-sinusoidal windings arrangement, the electromagnetic torque can be enhanced by injecting third harmonic current. This paper studies the driving system and the fundamental and third harmonic spaces of the five-phase motor with non-sinusoidal windings, proposing a four-dimensional space vector PWM strategy based on modulation function method. According to the relationship of duty circle and modulation function of the periodic midpoint, for a symmetric regular sampling method, the phase modulation function can be obtained. It greatly simplifies the computational complexity and the occupied storage space. To deal with saturation, it only needs to limit the duty cycle or the amplitude of modulation function, which eliminates the complex division operation. To verify the correctness of the proposed method, the simulation and experiment are conducted on MATLAB/Simulink and hardware-in-the-loop simulation platform of RT-LAB/dSPACE, respectively. Finally, the phase current of the motor is analyzed with Fast Fourier Transform (FFT), showing the third harmonic content is basically the same as the set value.

Rainfall monitoring network design using conditioned Latin hypercube sampling and satellite precipitation estimates: An application in the ungauged Ecuadorian Amazon

Rain gauge networks are crucial for enhancing the spatio‐temporal characterization of precipitation. In tropical regions, scarcity of rain gauge data, climatic variability, and variable spatial accessibility make conventional approaches to design rain gauge networks inadequate and impractical. In this study, we propose the use of conditioned Latin hypercube sampling (cLHS) method with multi‐temporal layers of remotely sensed precipitation measurements for capturing the spatio‐temporal precipitation patterns in ungauged areas. The study was conducted in the Amazon region of Ecuador, for which monthly precipitation averages were derived based on a 16‐year period of Tropical Rainfall Measuring Mission (TRMM 3B43 V7) data which were used as prior information to select representative sampling points through cLHS. Two scenarios for the sampling design were considered and evaluated, one without and one with restrictions on accessible sites according to the proximity to roads and settlements. Results showed that both optimized networks captured the variability of precipitation according to the TRMM climatology. Furthermore, evaluation against an independent satellite precipitation data set showed that the optimized networks support mapping precipitation based on ordinary kriging (OK). Comparison with regular and random sampling methods showed that particularly when a practical scenario is considered, the optimized network provided more reliable results over time, highlighting the suitability of the network to capture temporal changes and map precipitation with high accuracy. The proposed approach could be easily adopted in other ungauged and poorly accessible regions for rain gauge network design as well as to the design of multi‐objective monitoring networks.

Effect of Preconception Care Education by Health Volunteers on Knowledge and Attitudes of Women: Application of the Health Belief Model

Preconception care identifies and modifies the risk factors for pregnancy and childbirth. The present study aimed to determine the effects a preconception care education program, which was based on the Health Belief Model (HBM) and implemented by health volunteers, on knowledge and attitudes of women. A semi-experimental study was conducted using 22 health volunteers and 110 women aged 15-49 years selected from two comprehensive health centers of Mashhad, Iran, in 2016. The convenience sampling method was employed for selecting the volunteers and the regular random sampling method for choosing the women. For data collection, we applied a researcher-made tool with verified validity and reliability. HBM-based education was implemented by the volunteers during three sessions. Data analysis was performed in SPSS using Mann-Whitney test, Friedman, and Spearman's rank correlation coefficient; repeated measures data analysis was carried out at the significance level of 0.05. The mean age of the women was 30.6±6.6 years in the intervention group and 31.6±6.5 years in the control group. The mean levels of knowledge and attitude increased significantly after the intervention (P<0.001). We suggest using the current educational intervention based on the HBM to promote women's knowledge and attitudes towards preconception care.

Hybrid Trajectory Planning for Autonomous Driving in Highly Constrained Environments

In this paper, we introduce a novel and efficient hybrid trajectory planning method for autonomous driving in highly constrained environments. The contributions of this paper are fourfold. First, we present a trajectory planning framework that is able to handle geometry constraints, nonholonomic constraints, and dynamics constraints of cars in a humanlike and layered fashion and generate curvature-continuous, kinodynamically feasible, smooth, and collision-free trajectories in real time. Second, we present a derivative-free global path modification algorithm to extract high-order state information in free space for state sampling. Third, we extend the regular state-space sampling method widely used in on-road autonomous driving systems to a multi-phase deterministic state-space sampling method that is able to approximate complex maneuvers. Fourth, we improve collision checking accuracy and efficiency by using a different car footprint approximation strategy and a two-phase collision checking routine. A range of challenging simulation experiments show that the proposed method returns high-quality trajectories in real time and outperforms existing planners, such as hybrid A* and conjugate-gradient descent path smoother in terms of path quality, efficiency, and computation resources used.

A Method for the Realization of an Interruption Generator Based on Voltage Source Converters

In this paper we described the structure and working principle of an interruption generator based on voltage source converters (VSCs). The main circuit parameters of the VSCs are determined according to the target of power transfer capability, harmonic suppression, and dynamic response capability. A state feedback linearization method in nonlinear differential geometry theory was used for dq axis current decoupling, based on the mathematical model used in the dq coordinate system of VSCs. The direct current control strategy was adopted to achieve the independent regulation of active power and reactive power. The proportional integral (PI) link was used to optimize the dynamic performance of the controller, and PI parameters were adjusted. Disturbance voltage waves were generated by the regular sampling method. PSCAD/EMTDC simulation results and physical prototype experiments showed that the device could generate various disturbance voltage waveforms steadily, and had good dynamic and steady-state performance.

Некоторые методические проблемы водолазных гидробиологических учетных съемок и пути их разрешения

Methods of SCUBA hydrobiological surveys are discussed on the base of the author’s 18-year experience in the western Tatar Strait (Japan Sea) and in the Okhotsk Sea. Typical errors of the assessments are analyzed. So far as the methods of underwater researches develop actively, there are no universal one in this field. Regular sampling and uniform assessment methods do not guarantee to avoid the errors but usually cause excessive volume of samples and man-hours. Optimal planning of the sampling should be based on statistical analysis of preliminary information about distribution of the assessed objects in the area of survey. Planned number and location of the sections, stations and samples should be adjusted on the spot, if necessary, following the principle of sufficiency for obtaining representative data. The sections should be performed taking into account types of the coast, the stations - in accordance with natural biotic stratification. Sampling tools and methods should be chosen in dependence on nature, size, density, and distribution patterns of the assessed objects and specific conditions of survey. Modern technical means of underwater video surveillance, echolocation and satellite navigation must be involved into practice of SCUBA surveys. Some original sampling tools developed by the author are presented. Their use can significantly reduce the SCUBA man-hours, and in some cases allows to manage without diving. Rational planning and competent conducting multiply effectiveness of SCUBA survey, allowing to reduce its labor and time costs.

Flexible binding simulation by a novel and improved version of virtual-system coupled adaptive umbrella sampling

Virtual-system coupled adaptive umbrella sampling (VAUS) enhances sampling along a reaction coordinate by using a virtual degree of freedom. However, VAUS and regular adaptive umbrella sampling (AUS) methods are yet computationally expensive. To decrease the computational burden further, improvements of VAUS for all-atom explicit solvent simulation are presented here. The improvements include probability distribution calculation by a Markov approximation; parameterization of biasing forces by iterative polynomial fitting; and force scaling. These when applied to study Ala-pentapeptide dimerization in explicit solvent showed advantage over regular AUS. By using improved VAUS larger biological systems are amenable.

Relationship between SVPWM and carrier‐based PWM of eight‐switch three‐phase inverter

Space-vector pulse-width modulation (SVPWM) and carrier-based PWM (CBPWM) of eight-switch three-phase inverters (ESTPIs) which are the post-fault reconfigured topologies for the three-level neutral-point-clamped inverter with an open-circuit fault in a leg are introduced. On the basis of the PWM regular sampling method, the modulating functions of CBPWM which are equivalent to SVPWM of ESTPIs are derived, therefore the relationship between SVPWM and CBPWM of ESTPIs is revealed. The validity of the theoretical analysis is verified by experimental results.