Optimized Hybrid Modulation Strategy for AC Bypass Transformerless Single-Phase Photovoltaic Inverters

Shuhao Deng,Yao Sun,Jian Yang,Qi Zhu,Mei Su 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

Optimized Hybrid Modulation Strategy for AC Bypass Transformerless Single-Phase Photovoltaic Inverters

Deng, Shuhao,Sun, Yao,Yang, Jian,Zhu, Qi,Su, Mei The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

Seismic performance of beam-to- SST column connection with external diaphragm

Bin Rong,Shuhao Yin,Ruoyu Zhang,Lei Wang,Ziheng Yang,Hongtao Li,Wenyu Wan 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.37 No.6

This paper aims to study the seismic performance of external diaphragm connection between SST (square steel tube) column and H-shaped beam through experimental and analytical study involving finite element (FE) method and theoretical analysis. In the experimental study, three external diaphragm connection specimens with weak panel zone were tested under axial pressure on the top of the column and antisymmetric cyclic loads at the beam end to investigate the seismic performance of the panel zone. The hysteretic behavior, failure mode, stiffness and ductility of the specimens were discussed. Key point to be explored was the influence of the thickness of the steel tube flange on the shear capacity of the specimens. In the analytical study, three simplified FE models were developed to simulate the seismic behavior of the specimens for further analysis on the influence of steel tube flange. Finally, four existing calculation formulas for the shear capacity of the external diaphragm connection were evaluated through comparisons with the results of experiments and FE analysis, and application suggestions were put forward.

Modeling and Analysis for Output Impedance of Buck Converters

Xiaolong Yue,Shuhao Yang,Yin Chen,Fang Zhuo,Yunqing Pei 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

In distributed power systems, the impedance model of power modules is very important because of the close relationship between impedance and stability. For buck converters with a sinusoidal current perturbation at the output terminal, the output voltage will contain multiple components in frequency domain. The output impedance characteristics of power converters are actually single input multiple output (SIMO). However, traditional models and modeling methods only take the perturbation frequency into account and ignore the other components. The obtained impedance models, with single input single output (SISO) forms, are actually simplifications of the real impedance. In this paper, the output impedance of buck converters with SIMO characteristics is modeled by a matrix based method. Detailed analysis shows that it is reasonable to only consider the perturbation frequency itself in low frequency regions, but in high frequency regions, especially those around the switching frequency and its multiples, the corresponding low frequency component is also very significant and should be taken into account. Simulation and experimental results validate the accuracy and effectiveness of the proposed modeling method and conclusions.

Chatbot Design Method Using Hybrid Word Vector Expression Model Based on Real Telemarketing Data

( Jie Zhang ),( Jianing Zhang ),( Shuhao Ma ),( Jie Yang ),( Guan Gui ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.4

In the development of commercial promotion, chatbot is known as one of significant skill by application of natural language processing (NLP). Conventional design methods are using bag-of-words model (BOW) alone based on Google database and other online corpus. For one thing, in the bag-of-words model, the vectors are Irrelevant to one another. Even though this method is friendly to discrete features, it is not conducive to the machine to understand continuous statements due to the loss of the connection between words in the encoded word vector. For other thing, existing methods are used to test in state-of-the-art online corpus but it is hard to apply in real applications such as telemarketing data. In this paper, we propose an improved chatbot design way using hybrid bag-of-words model and skip-gram model based on the real telemarketing data. Specifically, we first collect the real data in the telemarketing field and perform data cleaning and data classification on the constructed corpus. Second, the word representation is adopted hybrid bag-of-words model and skip-gram model. The skip-gram model maps synonyms in the vicinity of vector space. The correlation between words is expressed, so the amount of information contained in the word vector is increased, making up for the shortcomings caused by using bag-of-words model alone. Third, we use the term frequency-inverse document frequency (TF-IDF) weighting method to improve the weight of key words, then output the final word expression. At last, the answer is produced using hybrid retrieval model and generate model. The retrieval model can accurately answer questions in the field. The generate model can supplement the question of answering the open domain, in which the answer to the final reply is completed by long-short term memory (LSTM) training and prediction. Experimental results show which the hybrid word vector expression model can improve the accuracy of the response and the whole system can communicate with humans.

Two-dimensional lamellar phosphogypsum/polyethylene glycol composite PCM: Fabrication and characterization

Jinfen Lou,Kai Zhang,Shuhao Qin,Yang Lei,Yufei Liu,Min He,Jie Yu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.113 No.-

In this work, a nanocomposite phase change material (PCM) has been designed by combining twodimensionallamellar anhydrous calcium sulfate with polyethylene glycol (PEG). We report a facile strategyto controllably fabricate two-dimensional lamellar anhydrous calcium sulfate (LAH) with the averagethickness of 28.63 nm from phosphogypsum (PG) through ethylenediamine tetraacetic acid disodium(Na2EDTA) induction in glycerol and ethylene glycol solutions at 98 C. The obtained 2D lamellarCaSO4 was a slit-type mesoporous material stacked by the nanosheet of calcium sulfate. It has a specificsurface area of 70.02 m2/g, which is 10 times larger than phosphogypsum. Na2EDTA acts as a crystalhabit-directing agent to regulate crystal morphology through nonclassical nanoparticle-mediated crystallizationprocesses, resulting in the crystalline morphology tending to be lamellar. Lamellar anhydrouscalcium sulfate phase change composites (LAHPCMs) were prepared with 2D lamellar anhydrous nano-CaSO4 and polyethylene glycol (PEG). The LAHPCMs had a high latent heat storage capacity (92.99 J/g). Lamellar anhydrous calcium sulfate phase change composites have good thermal stability and durability,structure stability, and good liquid leakage resistance. These results provide the possibility for phosphogypsumto be used for energy storage and thermal insulation.