The single-phase photovoltaic (PV) inverter needs significant capacitance to buffer the double-line frequency power pulsation at ac port. The two-stage inverter allows the designer to choose the dc-link voltage and the capacitor size flexibly. With the reduced capacitance, the lifetime of the dc-link capacitor can be prolonged by replacing the electrolytic capacitors with film capacitors. However, the capacitance deduction results in high double-line frequency voltage ripple on dc-link, which increases a series of odd harmonics in the output current. This paper hence analyzes the harmonics caused by the voltage ripple in an inverter with feedback control. The inverter is modeled as a time-varying system by considering the dc-link voltage ripple. A closed-form solution is derived to calculate the amplitude of the ripple-caused harmonics. This analysis helps the designer to understand the effect of the dc-link voltage ripple on current harmonics, evaluate effectiveness of existing approaches, and stimulate new ideas and solutions. The study also derived the theoretical limit to select dc-link capacitance and sampling rate of current reference without violating the grid-tied regulations in power quality. The analysis is verified both by simulation and experimental evaluation.
High conversion gain of voltage is generally required to interface various renewable energy sources, such as PV modules. This paper focuses on the optimal analysis and design of non-isolated DC-DC converters to meet the high-step-up gain requirement and achieve high efficiency. The proposed topology utilizes the coupled inductor technique to achieve high step-up voltage conversion ratio. A power loss model is developed to identify losses in each component for efficiency enhancement. The switch has relatively low voltage stress since leakage energy is directly transferred to the output to avoid voltage spikes across it. In addition, the coupled inductor alleviated the reverse recovery issue of the diode. The circuit operation and steady-state analysis of the proposed converter are presented in detail. A prototype circuit is built and tested to prove the circuit analysis and optimal design.
This work deals with single-stage three-phase grid-connected Photovoltaic (PV) systems with a focus on developing an efficient Maximum Power Point Tracking (MPPT) technique under partial shading conditions. As partially shaded PV arrays exhibit a multi-modal behavior on their Power-Voltage (P-V) characteristics with a number of possible patterns, the MPPT strategy under such conditions is a complex and challenging task. An Extremum-Seeking Control (ESC) based method is proposed in this paper to track the global power peak under non-uniform irradiance conditions. It relies on the measurements of power and estimation of the power gradient to iteratively determine the segment of the P-V characteristics in which the global peak lies, without converging at the other local maxima. The proposed method is compared to the sequential ESC-based MPPT method presented in the literature. Different test scenarios of partial shading show that the proposed method can reach the global peak with a faster convergence rate and higher tracking efficiency than conventional approaches.
Conventional two-stage power factor correction (PFC) architecture based on a boost PFC front end and an isolated dc–dc back end is increasingly challenged by the recent trend toward higher power density and efficiency. One key reason for the challenge is the difficulty of increasing the operating frequency of the boost PFC stage. This article presents a new star PFC architecture that allows the boost PFC stage to operate efficiently at a higher frequency while maintaining the performance of the second dc–dc stage, leading to a high-power-density and high-efficiency ac–dc converter design across a universal input. The high performance of star architecture is enabled by realizing: 1) continuous-conduction-mode (CCM) operation of the boost PFC stage; and 2) full-range zero-voltage-switching (ZVS) of all active switches. In addition, the star architecture can: 1) operate at a constant frequency via a proper selection of the circuit topology and modulation method; and 2) be controlled based on simple and low-cost analog circuits. A 300-kHz, 240-W, 48-V-output, and universal-input prototype is built to verify the performance of the star architecture, showcasing high power factor, constant output voltage, 97.1 % full-load efficiency, 55.6 W/in $^{3}$ power density by box volume.
This paper provides a comparative study on the various parameter identification techniques for PV modeling under the Standard Test Condition (STC). The mathematical representation of Ideal Single Diode Models (ISDM) is first investigated using the enclosure methods of Bisection, Fixed-Point Iteration and Newton-Raphson to find the Diode ideality factor. The detailed derivation is given for exploring the parameter identification problems based on a simple case study, followed by further investigations on using the Simplified Single Diode Model (SSDM). The numerical solvers under study are then compared against the embedded functions of MATLAB for both ISDM and SSDM in terms of solvers' performance and speed to identify the efficient method for solving simple photovoltaic models. Finally, complexity of self-implemented algorithms have been shown non directly correlated to their efficiency, encouraging the avoidance of complicated solvers for large-scale power system simulation based on simplified PV models.
The aim of the present study was to determine the reliability and validity of the Chinese version of the Calgary Depression Scale for Schizophrenia (CDSS-C) in schizophrenia patients.One hundred and one inpatients from four mental health units who met DSM-IV criteria for schizophrenia were enrolled. The Positive and Negative Syndrome Scale (PANSS), Hamilton Depression Rating Scale (HDRS-24), Simpson-Augus Rating Scale (SAS), and Barnes Acathisia Rating Scale (BARS) were administered by the first rater, whereas the CDSS-C was assessed by a second independent rater.The internal consistency (Cronbach's alpha = 0.80) and the inter-rater reliability (kappa coefficient >0.79) were good. The test-retest reliability was high (r = 0.927). The scale had good construct validity, with statistically significant correlations with the HDRS-24, G6 item (depression) of PANSS, and significant weak correlations with the general psychopathology subscale of PANSS. The CDSS-C showed no correlation with the positive and negative subscale of PANSS, the SAS and the BARS.The Chinese version of CDSS is a valid and reliable instrument for the assessment of depression in schizophrenia.
Dual-rotor permanent-magnet synchronous motors (PMSMs) offer the merits of higher efficiency, higher torque density, and inherent electric differential (ED). This paper proposes a novel four-axis vector-controlled dual-rotor PMSM drive for driving plug-in electric vehicles (PEVs). A four-axis d-q model of the dual-rotor PMSM is developed with the proposed three-phase to four-phase transformation. This transformation separately resolves the stator variables to the d-q-axes of the inner and outer rotor. Instead of applying back electromotive forces and rotor power angles, the d-axis fluxes are used for computing the displacement between the two d-q-axes, which is essential for the transformation. The proposed four-axis vector control of dual-rotor PMSM allows for the independent control of stator quantities corresponding to the inner and outer rotors. This facilitates ED and better control under parametric differences, such as rotor inertia and permanent magnet flux for the inner and outer rotors. The comparison of the dual-rotor PMSM-based PEV operation with the proposed control and two earlier reported schemes reveals that the proposed scheme offers effective ED without the loss of vehicle control. Furthermore, the proposed configuration is validated with different drive cycles, including the loss modeling, sensitivity analysis, and efficiency mapping.
Provenance is a record that describes entities and processes involved in producing, delivering and influencing a resource. Provenance management and reuse can enable interesting applications for knowledge discovery and analytics. One crucial component of a provenance management system is the comparison between provenances. In the era of big data, provenance management systems are in need of a scalable algorithmic solution for efficient comparison. Existing solutions to the problem have large memory footprint and require overlong system response time. In this paper, we present a new solution to threshold-based provenance comparison.It models provenance directly as graphs, and proposes to measure their similarities using provenance edit distance. We first provide analytic results regarding the expected search space of the existing and the proposed solution. On top of the depth-first search paradigm, we design an algorithm PEDSim using an encoding technique specific to provenance graphs and quantifiable heuristics. Extensive experiments on real data demonstrate the superiority of our method to other alternatives.
With the increasing integration of photovoltaic power generation in the low-voltage distribution network, the grid voltage regulation becomes critical, which demands support from different resources. This study presents the feasibility study of home appliance to be applied for appliance to grid mode of operation. The analysis includes the amendments in topology and control to support the concept of supportive platform provided by smart home and smart grid. Home appliances are then proposed as new distributed reactive sources, which are utilised to resolve the issue of voltage regulation, as well as produce reactive power locally for voltage stability. This study discusses the technical transitions in current home appliance to accommodate auxiliary functionality of grid reactive power support (RPS) and how it can fit in the home energy management system architecture to provide the required RPS.
PDF HTML阅读 XML下载 导出引用 引用提醒 改进的多变元数据可视化方法 DOI: 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: Supported by the National Natural Science Foundation of China under Grant No.60172012 (国家自然科学基金) Improved Multivariate Data Visualization Method Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:针对传统多变元可视化方法——星形坐标法(star coordinates,简称SC)降维过程信息损失较为严重、可视化结果无法体现维度分布信息及手动配置维度轴十分繁杂的不足,提出一种改进的星形坐标法(advanced star coordinates,简称ASC),使用沿直径方向的向量作为维度轴,设计维度轴配置策略优化各维度轴之间的夹角及排列顺序,以减小多维信息对象在改进星形坐标系中与在多维坐标系中坐标差别为准则,使用最优化方法实现对用户有意义的降维运算,将多维信息映射到低维可视空间中.实验结果表明,ASC的可视化结果不仅易于理解,而且能够有效提供维度分布信息,有利于用户发掘隐性知识,基于相关度的维配置策略可以大大减轻用户操作负担,使其能够快速而准确地定位多维信息集合中的隐含特征,降维算法高效,适用于数据量较大、维数较高的信息集合. Abstract:Star coordinates (SC), a traditional multivariate data visualization technique, loses much information due to oversimple dimension reduction algorithm. And the SC visualization can’t offer the dimension distribution information. Moreover, the manual dimension axis configuration of SC is too complex. To address these problems, the paper proposes the advanced star coordinates (ASC), which uses the diameter instead of the radius as the dimension axis, designs the dimension configuration strategy to optimize the order and the angle of dimension axes, and projects the multi-dimensional object to low dimension visual space through the dimension reduction algorithm. And the dimension reduction process is meaningful to user and the algorithm uses the minimum of the object coordinates variation between the multi-dimensional coordinates and the advanced star coordinates as criterion. Experimental results show that the dimension reduction algorithm is highly efficient and suitable for the aggregation with a great amount of high-dimensional data. The dimension configuration strategy relieves the user’s operation burden greatly and helps them detect the connotative characteristics of the multidimensional information aggregation quickly and exactly. The visualization is easy to understand and can express the dimension distribution information effectively, which is helpful for user to view the multi-dimensional information and to discover the implicit information in knowledge discovery process. 参考文献 相似文献 引证文献
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