J. Sheng

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (25)36.54 Total impact

  • IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-5. · 1.32 Impact Factor
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    ABSTRACT: This letter presents a new method of cross-range scaling in inverse synthetic aperture radar (ISAR) imaging. The effective rotational velocity (ERV), being the crucial factor for scaling, is generally unknown for noncooperative objects. By considering the degradation from target rotation, the proposed scheme estimates ERV based on image sharpness maximization. A range deviator induced by the center shift is also embedded in the estimation process. The cross-range scaling factor with an enhanced ISAR image can be obtained by an efficient Gauss–Newton method. The results acquired from both the simulations and real data experiments validate the effectiveness and robustness of the proposed method.
    IEEE Geoscience and Remote Sensing Letters 01/2015; 12(1):165-169. · 1.81 Impact Factor
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    ABSTRACT: Superconducting fault current limiter (SFCL) could reduce short circuit currents in electrical power system. One of the most important thing in developing SFCL is to find out the maximum permissible voltage of each limiting element. The maximum permissible voltage is defined as the maximum voltage per unit length at which the YBCO coated conductors (CC) do not suffer from critical current (Ic) degradation or burnout. In this research, the time of quenching process is changed and voltage is raised until the Ic degradation or burnout happens. YBCO coated conductors test in the experiment are from American Superconductor (AMSC) and Shanghai Jiao Tong University (SJTU). Along with the quenching duration increasing, the maximum permissible voltage of CC decreases. When quenching duration is 100 ms, the maximum permissible of SJTU CC, 12 mm AMSC CC and 4 mm AMSC CC are 0.72 V/cm, 0.52 V/cm and 1.2 V/cm respectively. Based on the results of samples, the whole length of CCs used in the design of a SFCL can be determined.
    Physica C Superconductivity 06/2014; · 1.11 Impact Factor
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    ABSTRACT: A dc resistive type superconducting fault current limiter (SFCL) is presented in this paper. This SFCL is designed for the HVDC system. Experiments are conducted to prove the current limiting ability of superconducting materials in dc system. Uniform current and voltage sharing among the SFCL modules can be observed through contact resistance tests, dc flow-through tests, and ac flow-through tests. Results of tests show that each limiting module has good uniformity in higher current system. Then, system simulation model based on these experimental data is built in PSCAD, and simulations are carried out to determine the value of shunt resistor. Results of simulation show that SFCL has fast responding time and good current limiting performance in dc network.
    IEEE Transactions on Applied Superconductivity 06/2014; 24(3):1-5. · 1.32 Impact Factor
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    ABSTRACT: In a resistive superconducting fault current limiter (SFCL), the electrodynamic force among the YBCO tapes is enormous when experiencing a high short circuit current, which may cause deformation of tapes and damage of their electrical characteristics. The purpose of this paper is to investigate how much electrodynamic force the YBCO tapes can bear. In this paper, an electrodynamic force simulation model is built to simulate the force, which the two parallel tapes experience and their deformation when short-circuit currents of different value flow through. Then we conducted experiments to observe the deformation of the tapes when they are experiencing a short-circuit current and see if the volt-ampere characteristic of the tapes has a noticeable change after that. Combining the results of the simulation and the experiments, we can obtain the electrodynamic force that tapes can bear. The result can guide us to design the layout of the tapes in the SFCL in accordance with the required fault current level.
    Journal of Superconductivity and Novel Magnetism 05/2014; 27(5). · 0.93 Impact Factor
  • J. Sheng, H. Sun, X. Liu, Z. Jin, Z. Hong
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    ABSTRACT: Over-current performance of YBa2Cu3O7-δ tapes under power frequency has been well-studied by previous researches. However, in power grid, superconducting apparatus will also experience lightning impulse current under special working conditions. In this paper, two kinds of lightning impulse current are applied to superconducting testing samples. Comparisons between superconducting characteristics before and after the testing are presented in this paper. Explanations of performance degradation are presented from both the perspectives of temperature and stress mathematic calculation. A maximum endurable value of lightning current which may not cause degradation is obtained from the testing results.
    Applied Physics Letters 03/2014; 104(11):112602-112602-4. · 3.52 Impact Factor
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    ABSTRACT: A novel autofocus method for synthetic aperture radar (SAR) image is studied. Based on a quadratic model for the phase error within each sub-area (narrow strip $times$ sub-aperture) after a wide range swath is subdivided into narrow range strips and long azimuth aperture into sub-apertures, an objective function for estimation of the error is derived through the principle of minimum entropy. There is only one unknown variable in the function. With the Chebyshev approximation, the function is approximated as a polynomial, and the unknown is then solved using the method of series reversion. Curve-fitting methods are applied to estimate phase error for an entire scene of the full-swath by full-aperture. Through simulations, the proposed method is applied to restore the defocused SAR imagery that is well focused. The restored and original images are almost identical qualitatively and quantitatively. Next, the method is implemented into an existing SAR data processor. Two sets of SAR raw data at X- and Ku-bands are processed and two images are formed. Well-focused and high-resolution images from plain and rugged terrain are obtained even without the use of ancillary attitude data of the airborne SAR platform. Thus, the studied method is verified.
    IEEE Transactions on Geoscience and Remote Sensing 03/2014; 52(3):1719-1728. · 2.93 Impact Factor
  • Y. Chen, S. Li, J. Sheng, Z. Jin, Z. Hong, J. Gu
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    ABSTRACT: Superconducting fault current limiter (SFCL) has become one of the most ideal current limiting devices to solve the problem of increasing short-circuit current in high-voltage power grid. This paper presents a resistive-type SFCL model developed using simulation software PSCAD/EMTDC. After being verified by finite-element model and experimental results, the model is used to study the impact of SFCLs on the power grid and the co-ordination between SFCL and relay protections in 10 kV distribution network. A series of simulations are carried out to find appropriate parameters of SFCL model to cooperate with relay protection devices. The final result in this paper could provide important quantitative basis of parameters for SFCL to be applied in a real power system.
    Journal of Superconductivity and Novel Magnetism 11/2013; · 0.93 Impact Factor
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    ABSTRACT: Because of the complexity of the electrical system, dc offset current and ac ripple current have generally existed. However, they are usually undesirable, and their influence to ac loss is also an important issue for superconducting devices built from YBaCuO-coated conductors. In this paper, ac loss of YBCO tapes with nonmagnetic substrate carrying dc or ac offset current have been both measured and calculated. Experiments based on “electrical method” composed of a high-performance amplifier and a wave recorder with filtering function has been carried out. To verify the measurement, a two-dimensional finite element method model based on finite element method and power law is applied to calculate the ac loss with current combined with ac and dc components. The results show that, a small value of dc offset current in a large ac component has minor effect to the ac loss. In addition, when the total current (combined with ac and dc components) approaches critical value, the ac loss would increase significantly.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5900704-5900704. · 1.32 Impact Factor
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    ABSTRACT: In superconducting power apparatus, electric insulation is one of the most important deciding factors on their performance. Bubbles produced during quench condition of superconducting tapes will degrade the insulation performance of liquid nitrogen and reduce the electrical breakdown voltage of the apparatus. This paper presents the bubble behavior and the influence on insulation properties of liquid nitrogen ( LN2) for superconducting power apparatus. The result will provide useful information for superconducting power devices in transmission voltage level, such as fault current limiter, transformers, and cables. Measurements are made to get the ac breakdown voltages in LN2 using spherical brass electrodes as quasi-uniform electric field. Different structures of HTS tapes are used as electrodes to simulate real working conditions. Bubbles are created by heaters, and their influences on the breakdown voltage are measured. How the breakdown strength would be affected by the bubbles is studied by changing the length of the gap of electrodes and the amount of bubbles. Breakdown voltage of G10 slice is also tested. Experiments show that the breakdown strength of LN2 is sensitive to the behavior of bubbles. Different structures of HTS tape have different breakdown properties under bubbling condition. G10 material is a good choice to provide insulation strength between HTS tapes.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5000205-5000205. · 1.32 Impact Factor
  • Z. Hong, J. Sheng, L. Yao, J. Gu, Z. Jin
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    ABSTRACT: This paper presents the design and performance test of a 10 kV, 200 A resistive type superconducting fault current limiter prototype. This is the continued study of the test towards an individual current limiting module, which was done and published in August 2011. The construction of the whole prototype including the cryostat has finished. A series of tests including short circuit test, recovery test, auto-reclosure test, and LN2 boiling test have been performed and the results are presented in this paper. This single phase superconducting fault current limiter is made from 15 current limiting modules. Several 1-m long YBCO coated conductors prepared by Shanghai Jiaotong University are used to build the current limiting module. Each module has 2 tapes connected in parallel to carry 200 A rated current (Ic of each tape is about 150 A) and 6 tapes connected in series to withstand 700 ~ 800 V voltage drop.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):5601304-5601304. · 1.32 Impact Factor
  • Jialian Sheng, Jia Duan, Mengdao Xing, Lei Zhang
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    ABSTRACT: The techniques of accurate cross-range scaling and motion compensation both play significant roles in inverse synthetic aperture radar (ISAR) imaging. This paper proposes a new method to estimate motion parameters for ISAR targets scaling as well as motion compensation. With a time-varying autoregressive (TVAR) model, the pole histories of dominant scatters can be obtained. According to the time-frequency relationship, motion parameters including the effective rotational velocity and the coefficients of phase error are extracted. Using these parameters, we can not only scale the image but also compensate phase error to focus the image. Simulation and real-data experiments illustrate its feasibility and robustness.
    Radar Conference 2013, IET International; 01/2013
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    ABSTRACT: To implement target detection, tracking and imaging in a multifunctional radar system, the wideband measurements for inverse synthetic aperture radar (ISAR) imaging are usually sparsely recorded. Considering the incoherence problem in such sparse-aperture ISAR (SA-ISAR) systems, we concentrate on the study of a coherent processing method in this work. Based on an all-pole model, the incoherence parameters between abutting sub-apertures can be effectively estimated. After coherence compensation, an optimization-based SAISAR imaging approach is provided from the view of statistics. Simulation and real data experiments validate the feasibility and effectiveness of the proposals.
    Sciece China. Information Sciences 08/2012; 55(8). · 0.70 Impact Factor
  • Gang Xu, JiaLian Sheng, Lei Zhang, MengDao Xing
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    ABSTRACT: There is always a compromise between unambiguous wide-swath imaging and high cross-range resolution owing to the constraint of minimum antenna area for conventional single-channel spaceborne synthetic aperture radar (SAR) imaging. To overcome the inherent systemic limitation, multi-channel SAR imaging has been developed. Nevertheless, this still suffers from various problems such as high system complexity. To simplify the system structure, a novel algorithm for high resolution multi-ship ScanSAR imaging based on sparse representation is proposed in this paper, where the SAR imaging model is established via maximum a posterior estimation by utilizing the sparsity prior of multi-ship targets. In the scheme, a wide swath is generated in the ScanSAR mode by continuously switching the radar footprint between subswaths. Meanwhile, high cross-range resolution is realized from sparse subapertures by exploiting the sparsity feature of multi-ship imaging. In particular, the SAR observation operator is constructed approximately as the inverse of conventional SAR imaging and then high resolution SAR imaging including range cell migration compensation is achieved by solving the optimization. Compared with multi-channel SAR imaging, the system complexity is effectively reduced in the ScanSAR mode. In addition, enhancement of the cross-range resolution is realized by incorporating the sparsity prior with sparse subapertures. As a result, the amount of data is effectively reduced. Experiments based on measured data have been carried out to confirm the effectiveness and validity of the proposed algorithm.
    Sciece China. Information Sciences 08/2012; 55(8). · 0.70 Impact Factor
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    ABSTRACT: Voltage tolerance during quench is one of the most important parameters for YBCO-coated conductors, especially for resistive type superconducting fault current limiter (SFCL) applications. How much voltage can be sustained per unit length of YBCO tape when experiencing fault current indicates the total required amount of the tapes to construct a resistive SFCL. In this paper, a step-down transformer is used to provide the short-current. As the voltage of the secondary side is not continuously variable, we change the voltage per unit length of the YBCO tape by varying the length of the tape. And the effect of the duration of short-current is also considered. A series of test have been performed to determine the maximum voltage drop that each YBCO tape can stand at fault current. The V-t curve has been measured after the tape experiencing successive quenches. Through a large number of experiments we will acquire the maximum endurable quenching voltage per unit length of YBCO tapes when experiencing short-current for different durations. The results presented in this paper would provide useful information for optimizing the design of a resistive SFCL.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):5602904-5602904. · 1.32 Impact Factor
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    ABSTRACT: Heat loss is one of the most important issues for resistive type superconducting fault current limiters (SFCL) built from YBaCuO-coated conductors. A newly designed 400 V SFCL module by Smart Grid Center, Shanghai Jiaotong University (SJTU) is tested and modeled in order to get a clear understanding of its characteristics of heat losses. Two main losses, including AC loss of superconducting tapes and the losses due to contact resistance inside the SFCL module are investigated. Experiments based on “electrical method” are set up to measure the AC loss at 77 K with lock-in amplifier conditions. Meanwhile, losses from the contact resistance are calculated by analyzing their V-I curve. To better understand the behavior of the AC loss in SFCL module and verify the accuracy of the experimental results, modeling analysis is performed by means of a 2-dimensional finite element modeling (FEM). Numerical results show that the results are very close to what we get from experimental method. Detailed results will be presented and the heat losses of 10 kV SFCL consisting of about 25 modules in series are going to be discussed.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):5602204-5602204. · 1.32 Impact Factor
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    ABSTRACT: This paper presents the design of a 10 kV, 200 A resistive type superconducting fault current limiter prototype. Several one-meter long YBCO coated conductors prepared by Shanghai Jiaotong University are used to build the current limiting module. Each module has 2 tapes connected in parallel to reach 400 A rated current ( of each tape is 150 A ~200 A) and 6 tapes connected in series to withstand 700~800 V voltage drop. A series of tests and measurements have been carried out to investigate the performance of the fault current limiting module. Short circuit test of the module has been performed on a specially designed transformer which is able to withstand large current on the secondary side. The power capacity of the lab allows performing the test up to 40 V and a few thousand Amperes. The whole process of a fault, including fault occurring, current limiting, circuit breaker opening and superconductors recovery, has been tested and the current and voltage of YBCO tapes are monitored. The current limiting module is tested with different shunt resistors to demonstrate its ability to vary its limited current.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):56005-. · 1.32 Impact Factor
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    ABSTRACT: A multi-physics finite element model of high temperature superconductors (HTS) is presented in this article. An electrical model based on a set of Maxwell's equations and E-J power law is used to solve the critical state of the superconductor. A heat transfer model is added to the electrical model to calculate the temperature distribution and therefore investigate the Jc (T) dependence of the superconductor. The model is used to study the quench behavior of YBCO-coated conductors for the application of resistive type fault current limiters. Some numerical techniques are applied and assumptions are made to simplify the calculation and improve convergence. An equivalent heat transfer coefficient which is much larger than the normal heat transfer coefficient is applied to the region surrounding the superconductors. This equivalent coefficient represents the drastic heat exchange during the boiling of the liquid nitrogen. The cross-section of YBCO tapes is divided into several sub-domains. The temperature is assumed to be uniform in each sub-domain. This simplification significantly improves the convergence of model and still is able to keep a reasonable level of accuracy. The model is then able to simulate the whole process of YBCO tapes quenching and recovering to superconducting state. The numerical results are compared with the fault current experiments and excellent agreement is obtained.
    IEEE Transactions on Applied Superconductivity 06/2012; 22(3):56020-. · 1.32 Impact Factor
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    ABSTRACT: Being capable of enhancing the flexibility and observing ability of synthetic aperture radar (SAR), squint mode is one of the most essential operating modes in SAR applications. However, processing of highly squinted SAR data is usually a challenging task attributed to the spatial-variant range cell migration over a long aperture. The Omega-k algorithm is generally accepted as an ideal solution to this problem. In this paper, we focus on using the wavenumber-domain approach for highly squinted unmanned aerial vehicle (UAV) SAR imagery. A squinted phase gradient autofocus (SPGA) algorithm is proposed to overcome the severe motion errors, including phase and nonsystematic errors. Herein, the inconsistence of phase error and range error in the squinted wavenumber-domain imaging is first presented, which reveals that even the motion error introduces very small phase error, it causes considerable range error due to the Stolt mapping. Based on this, two schemes of SPGA-based motion compensation are developed according to the severity of motion error. By adapting the advantages of weighted phase gradient autofocus and quality phase gradient autofocus, the robustness of SPGA is ensured. Real measured data sets are used to validate the proposed approach for highly squinted UAV-SAR imagery.
    IEEE Sensors Journal 01/2012; 12(5):1574-1588. · 1.85 Impact Factor
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    ABSTRACT: Spotlight synthetic aperture radar (SAR) is an effective way to obtain finer azimuth resolution than the achievement in strip-map mode with the same physical antenna. In general, for spotlight SAR imaging, high azimuth resolution requires long synthetic aperture length. However, in practical airborne applications, because of the inevitable atmospheric turbulence during the long flight trajectory, more complicated motion error is induced that severely degrades the focusing quality of the SAR image. It makes motion compensation (MOCO) for high-resolution spotlight (HR-Spotlight) SAR imagery more difficult than that for other SAR systems. To tackle the HR-Spotlight SAR data contaminated by the complicated motion error, a novel MOCO algorithm based on entropy minimisation is proposed, which is named by minimum entropy MOCO (ME-MOCO). In this approach, by fitting a polynomial to the motion error, the entropy of a focused image is utilised as the optimisation function of the polynomial coefficients. Attributed to damped Newton method, a modified strategy is designed, which results in that the data-driven ME-MOCO algorithm estimates high order polynomial parameters accurately and efficiently. Besides, the proposed algorithm is efficient for the capability of exploiting the fast Fourier transform through the processing chain. Real data experiments and comparisons demonstrate the effectiveness and superiority of the proposal.
    IET Radar Sonar ? Navigation 01/2012; 6(7):627-637. · 1.03 Impact Factor

Publication Stats

105 Citations
36.54 Total Impact Points

Institutions

  • 2012–2014
    • Shanghai Jiao Tong University
      • • School of Electronic, Information and Electrical Engineering
      • • Department of Electrical Engineering
      Shanghai, Shanghai Shi, China
  • 2010–2013
    • Xidian University
      Ch’ang-an, Shaanxi, China
  • 2011
    • Fudan University
      • Department of Oncology
      Shanghai, Shanghai Shi, China