Due to its high conversion efficiency and high power density, interleaved critical-mode converter is widely employed by modern power converters. This topology is utilized in ac-dc, dc-dc, and dc-ac converters. Because of the variable switching-frequency operation, phase-shift control is a challenge in the design of critical-mode power converters. This paper presents a triangle phase-shift control strategy for interleaved critical-mode power converters. Based on circuit parameters of the topology and current information of the master phase, a control ramp is derived to control the current phase of slave phase. Based on the proposed control ramp, triangle phase-shift control is proposed. The proposed control strategy is experimentally verified on a dual-phase interleaved dc-dc converter.
In modular photovoltaic conditioning system (PCS), microinverter is the important device to convert solar energy to grid electricity. A hybrid resonant microconverter served as front-end converter in a two-stage microinverter with two different modes was proposed previously [1]. The topology with two operating modes can achieve wide-input regulation and maintain high-efficiency over a wide input range. This paper derives the linearized models and control-to-input transfer functions of two operating modes for this high-efficiency hybrid resonant microconverter. Voltage controllers and a smooth transition are designed based on proposed models. The derived linearized models matched well with simulations. Experimental results with a 300 W prototype verify the performance of voltage controllers and transition.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
With the emergence of high-dimensional data and a deeper research in complex network, scholars began to analyze the features of multi-dimensional network, such as the high-dimension community structure. Especially in the temporal network, many researchers have already proposed community discovery algorithms based on tensor decomposition. However, there are still some deficiencies in current research, which is the disconnection between traditional community detecting theory and the algorithm based on tensor decomposition. To solve this problem, this paper proof that there is a relationship between the modularity in the community discovery and the optimization goal of tensor decomposition. Based on the proof, a new community discovery algorithm based on modularity tensor in temporal network is proposed. Experiments in simulated dataset and real PSTN dataset have proved that our proposed algorithm can find a better community division than the traditional algorithm.
An inductance model-based sensorless control strategy with torque ripple and acoustic noise minimization for switched reluctance machines is proposed. In order to simultaneously reduce the torque ripple and acoustic noise, a specific-shaped current waveform that is needed and obtained from a torque-sharing function (TSF) is used in this paper. With the inductance model-based sensorless control strategy and the specific-shaped current modulation, the any rotor position within the entire electrical angle can be calculated by the bisection algorithm so that a specific current profiling can be obtained and therefore torque ripple and acoustic noise minimization can be achieved. The traditional trapezoid-shaped current modulation is compared with the specific current profiling in term of torque ripple. A 2 kW 12/8 SRM sensorless drive is modelled using the PSIM software. The simulated results indicate that the new sensorless control strategy is effective in reducing torque ripple. A hardware prototype of 2 kW converter with TMS320F28335 is also constructed and tested. The experimental results indicate that the new sensorless control strategy is effective in rotor position estimation.
The strong corrosion behavior at the Al current collector restricts the application range of lithium bis (trifluoromethanesulfonylimide) (LiTFSI), despite its high stability against water and thermal. The adding LiODFB into LiTFSI-based electrolytes as a co-salt can successfully suppress the Al corrosion. However, the mechanism of the synergistic effect is still not clear, electrochemical performance at high-temperature and is also not clear. In this work, electrochemical tests and physical characterization of mixed lithium salts in different proportions were carried out at a high temperature of 45oC, and it was concluded that LiODFB0.2-LiTFSI0.8-based electrolyte had the best electrochemical performance at 45oC. The capacity retention rate of the battery after 200 cycles is 95%, that’s due to the good film-forming property of LiODFB and the high thermal stability of LiTFSI. This work provides a universal electrolyte design strategy for designing stable and safe high-temperature electrolytes for the LiCoO2 cathode.
The paper proposes a new power electronic transformer (PET), for the application in the distribution system, which is composed of the three-stage power circuits. The input stage uses three-phase three-level PWM rectifier to reduce the voltage stress rating of components, where the reactive power and high-voltage dc-link voltage closed-loop controls provide the ability to adjust the reactive power and stabilize the dc-link voltage in the high-voltage side. The isolation stage employs the low-voltage dc-link voltage closed-loop control with a high-frequency step-down transformer to maintain the constant low dc voltage and isolate the low-voltage side from the high-voltage side. In the third-stage, three-phase two-level inverter outputs the desired voltage and power to the load through the output voltage closed-loop control. With the three-stage control strategy, the PET's input currents and the output voltages have quality sinusoidal waveforms, and the input power factor is controllable. The PET model is established on MATLAB/SIMULINK, and this system is also implemented in laboratory based on DSP TMS320F2812. The simulation results and experimental results verify the proposed PET system.
In this paper, the ac small signal modeling technique for both pulse-width-modulation (PWM) current and speed controller of SRM drive system is presented. With the small signal modeling for linearization of the SRM, the output transfer function in both PWM current loop and speed loop can be obtained. Both PI current controller and PI speed controller can be also designed with sufficient stability margin by using the small signal model. A criterion for selection of proportional and integral (PI) controller for an SRM is also proposed. In order to simultaneously reduce acoustic noise and torque ripple, a specific current profile was applied to SRM drives with proposed current and speed controller. A hardware prototype of 12/8, three-phase 2kW SRM with TMS320F28335 was constructed and tested. The criteria for selection of PI controller is applied to the SRM Drive system. Torque ripple and acoustic noise in both cases of traditional square current waveform and the modified current profile are compared. The experimental results indicate that the proposed method for derivation of optimized gains can lead to reduced acoustic noise and improve the dynamic performances of the SRM drive system.
Sunflower broomrape (Orobanche cumana Wallr.) is a holoparasitic plant species which mainly parasitizes a few species of the Asteraceae in the wild and is exclusively found growing on sunflower in agricultural fields (Fernández-Martínez et al. 2015). O. cumana is a serious threat to sunflower production in Xinjiang and Inner Mongolia (Shi et al. 2015). Karelinia caspia (Pall.) Less. (Asteraceae) is an ecologically important plant species occurring across the desert ecosystems of Russia, Central Asia, and northwest China. It plays an important role in reducing wind erosion and desertification (Xu et al. 2018). During the 2018 and 2019 growing seasons, sunflower broomrape was observed parasitizing K. caspia in non-cultivated areas adjacent to sunflower fields near Beitun city (87°51'E, 47°15'N) in Xinjiang, China. Sunflower broomrape plants were identified morphologically as O. cumana according to Pujadas-Salvà and Velasco (2000). The host plants were identified morphologically as K. caspia according to Lin et al (1979). The ribosomal DNA internal transcribed spacer (ITS) and the trnL-F region of the parasite were amplified by PCR using primer pairs ITS1/ITS4 and trnL-FF/trnL-FR, respectively (Taberlet et al. 1991; Anderson et al. 2004). The ITS sequence of the parasite (Accession No. MT795725.1) showed 100% identity (675bp out of 689bp) to that of O. cernua var. cumana (KC811228.1). The trnl-F sequence of the parasite (Accession No. ON843707) showed 98% identity (675 of 689 bp) to O.cernua var. cumana (KT387722.1). Multi-locus phylogenetic analysis of the two sequences showed clustering with sunflower broomrape. The ITS region of the parasite and host was were amplified by PCR using the primer pair ITS1F/ITS4R (Taberlet et al.1991), and the ITS sequences of the host (Accession No. MT791995.1) showed 99.86% identity (728bp of 802bp) to that of K. caspia (LN607483.1). Rhizotron and pot experiments were carried out to assess the parasitic relationship between O. cumana and K. caspia. In the rhizotron experiment, 2-week-old seedlings of K. caspia were inoculated with sterilized 400 O. cumana seeds in a 15-cm petri dish filled with a sponge overlaid with glass fiber filter paper. The parasitic state of O. cumana was observed 9 days after inoculation. In another trial, seeds of K. caspia were sowed in 2-L and 4-L pots containing sand-vermiculite-compost (1:1:1 v:v:v). These pots were artificially inoculated with 50 mg of O. cumana seeds per 1 kg of substrate. After 20 and 70 days, corresponding to the early parasitic and flowering stages, respectively, of O. cumana, K. caspia plants were uprooted from the media and washed carefully. The parasitic relationship was confirmed by the attachment position of the broomrape to the K. caspia root. To our knowledge, this is the first report of O. cumana parasitizing K. caspia in Xinjiang, China. This phenomenon means that sunflower broomrape can raise up seed on a newly recognized host. Weed eradication in and near sunflower fields is a key measure to control sunflower broomrape.
Since the railway bridge has many spans and long distance, it is complicated and time-consuming to model and analyze the random earthquake response of the structure with the finite element software. The dynamic frequency response equation of longitudinal vibration of simply supported girder bridge is established with the unit impulse as the input excitation, based on the motion equation of the MDF system and he transfer matrix principle. Finally, Taking seven cross-simply supported girder bridge as an example, the frequency response of the vertical displacement and axial force are computed with the Rayleigh damping. The result of the vertical displacement and axial force shows that: the mid-span displacement of spans in the middle of the bridge is slightly larger than that of the side spans while the difference between each value is small, but the mid-span axial force of spans in the ends of the bridge is significantly larger than that of the middle spans. And the corresponding Fourier amplitude spectrums under pulse loads are given. With this method, it is convenient to program and calculate the dynamic frequency response of the simply supported girder bridge by mathematical software, and it is available to provide a reference for the random seismic design of the structure.
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