A novel transient rotor current control scheme of a doubly-fed induction generator equipped with superconducting magnetic energy storage for voltage and frequency support

A novel transient rotor current control scheme is proposed in this paper for a doubly-fed induction generator（DFIG）equipped with a superconducting magnetic energy storage（SMES） device to enhance its transient voltage and frequency support capacity during grid faults. The SMES connected to the DC-link capacitor of the DFIG is controlled to regulate the transient dc-link voltage so that the whole capacity of the grid side converter（GSC） is dedicated to injecting reactive power to the grid for the transient voltage support. However, the rotor-side converter（RSC） has different control tasks for different periods of the grid fault. Firstly, for Period I, the RSC injects the demagnetizing current to ensure the controllability of the rotor voltage. Then, since the dc stator flux degenerates rapidly in Period II, the required demagnetizing current is low in Period II and the RSC uses the spare capacity to additionally generate the reactive（priority） and active current so that the transient voltage capability is corroborated and the DFIG also positively responds to the system frequency dynamic at the earliest time. Finally, a small amount of demagnetizing current is provided after the fault clearance. Most of the RSC capacity is used to inject the active current to further support the frequency recovery of the system. Simulations are carried out on a simple power system with a wind farm. Comparisons with other commonly used control methods are performed to validate the proposed control method.

Study of 3G/4G Network Convergence Planning Scheme in High-Speed Railway

This paper mainly introduces some related problems about special mobile communication signal based on TD-LTE and TD-SCDMA in high-speed railway, summaries the main difficulty of TD-LTE coverage in high-speed railway and analyses TD & LTE wireless network coverage characteristics and key technologies under the environment of high-speed railway. First, we make a contrast of the coverage range of TD<E uplink and downlink in ordinary and special situations. Then we consider effective cover radius, the distance and grazing angle between stations and railway in 2G/3G/4G networks, calculate different distance between stations. Last, we did capacity planning for TD & LTE as telephone traffic throughput required in high-speed railway. The result shows that distance between stations is limited by LTE on sharing station address. Using single RRH with two antennas, the antenna height is 30m, and the speed of the train is 250 KM/h, the RRH distance among different cells can be 1177 m, and the RRH distance among same cells can be 1311 m. In the tunnel scene, the leakage cable cover is used and the station space distance of TD & LTE is 0.5 km. Tunnel station should move the switch belt to outdoors as much as possible without switching. This paper finished the link budget, protection distance measurement of cells and study of coverage method in the tunnel scene. The result helps guiding in planning, designing and optimizing for high-speed railway network in reality.

Nonlinear restructuring of patterned thin films by residual stress engineering into out-of-plane wavy-shaped electrostatic microactuators for high-performance radio-frequency switches

Electrostatic microelectromechanical (MEMS) switches are the basic building blocks for various radio-frequency (RF) transceivers. However, conventional cantilever-based designs of MEMS switches require a large actuation voltage, exhibit limited RF performance, and suffer from many performance tradeoffs due to their flat geometries restricted in two dimensions (2D). Here, by leveraging the residual stress in thin films, we report a novel development of three-dimensional (3D) wavy microstructures, which offer the potential to serve as high-performance RF switches. Relying on standard IC-compatible metallic materials, we devise a simple fabrication process to repeatedly manufacture out-of-plane wavy beams with controllable bending profiles and yields reaching 100%. We then demonstrate the utility of such metallic wavy beams as RF switches achieving both extremely low actuation voltage and improved RF performance owing to their unique geometry, which is tunable in three dimensions and exceeds the capabilities of current state-of-the-art flat-cantilever switches with 2D-restricted topology. As such, the wavy cantilever switch presented in this work actuates at voltages as low as 24 V while simultaneously exhibiting RF isolation and insertion loss of 20 dB and 0.75 dB, respectively, for frequencies up to 40 GHz. Wavy switch designs with 3D geometries break through the design limits set by traditional flat cantilevers and provide an additional degree of freedom or control knob in the switch design process, which could enable further optimization of switching networks used in current 5G and upcoming 6G communication scenarios.

An embedded packet train and adaptive FEC scheme for effective video adaptation over wireless broadband networks

With the rapid growth of wireless broadband technologies, such as WLAN and WiMAX, quality streaming video contents are available through portable devices anytime, anywhere. The layered multicast system using scalable video codecs has been proposed as an efficient architecture for video dissemination taking account of user and link diversities. However, in the wired/wireless combined best-effort based heterogeneous IP networks which provide more fluctuation in available bandwidth and end-to-end delay, the performance of streaming systems has been greatly degraded due to frequent packet loss, resulting from either wired congestion or wireless fading/shadowing. In this paper, we present a real-time embedded packet train probing scheme for estimating end-to-end available bandwidth so as to accomplish effective congestion and error control. This is facilitated by effective classification of packet loss sources, delay trend detection algorithm and flexible transmission rate of packets. Under the proper wireless channel modelling and estimation, our layered structure can allow appropriate subscription of video layers and adaptively insert necessary amount of forward error correction (FEC) packets so as to achieve QoS optimized system for scalable video multicasting.

A network condition classification scheme for supporting video delivery over wireless Internet*

Real-time video transport over wireless Internet faces many challenges due to the heterogeneous environment including wireline and wireless networks. A robust network condition classification algorithm using multiple end-to-end metrics and Support Vector Machine (SVM) is proposed to classify different network events and model the transition pattern of network conditions. End-to-end Quality-of-Service (QoS) mechanisms like congestion control, error control, and power control can benefit from the network condition information and react to different network situations appropriately. The proposed network condition classifica- tion algorithm uses SVM as a classifier to cluster different end-to-end metrics such as end-to-end delay, delay jitter, throughput and packet loss-rate for the UDP traffic with TCP-friendly Rate Control (TFRC), which is used for video transport. The algorithm is also flexible for classifying different numbers of states representing different levels of network events such as wireline congestion and wireless channel loss. Simulation results using network simulator 2 (ns2) showed the effectiveness of the proposed scheme.

Reusing Test Cases Based on the Function Point

Reusing test cases from existing test case library is quite common in the software testing field. Testing practice tells us that there is a strong relationship between the granularity of a function unit under testing and that of the test case. A function unit with small granularity usually results in the test cases with the same small granularity. Therefore a test case defined as the function point,i. e.,the smallest size function unit,was provided for the first time.Though test cases with smaller granularity usually have better reusability,the cost of accurately reusing and integrating such test cases is also higher. In order to balance the test case reusability and the cost of test case reuse,a novel test case reuse model based on the function point was proposed in this paper. In this model,a reusable test case for specification-based testing was defined and some reuse strategies and three formal reuse methods were given. Finally,the complete automatic software process was realized by a reusing generation tool. The new method has improved reuse accuracy,while greatly enhances the software productivity.

Transfer Function Relating Compressive Pressure to Interfacial Stress Sensor for Biomedical Applications

To help comfort for an amputee, it is important to understand the load distribution between the residual limb and the prosthetic socket for a prosthetic socket system. An interfacial stress sensor was presented which was capable of measuring compressive pressure and shear stress simultaneously. A mathematical model was built and an experiment was conducted to obtain the transfer function of interfacial stress sensor to compressive pressure. The results show that the sensor is capable of measuring a range of 30-217 kPa compressive pressure with a relative error of 32.15% in lower range and 6.22% in upper range.

Mirrorless MEMS imaging:a nonlinear vibrational approach utilizing aerosol-jetted PZT-actuated fiber MEMS scanner for microscale illumination

This study introduces a novel image capture and lighting techniques using a cutting-edge hybrid MEMS scanner system designed for compact microscopic imaging.The scanner comprises a tapered optical fiber waveguide and innovative aerosol-jet printed PZT(lead zirconate titanate)bimorph push-pull actuators on a stainless-steel substrate,effectively addressing issues that are commonly associated with PZT on silicon substrates such as fracture and layer separation.By leveraging nonlinear vibration,the scanner achieves a spiral scan pattern from a single signal input,in addition to the expected two-dimensional scanning and target illumination from two phase-shifted inputs.This capability is further enhanced by a novel process to taper the optical fiber,which reduces illumination scattering and tunes the fiber to the resonant frequencies of the scanner.The precisely tapered tip enables large fields of view while maintaining independent 2-axis scanning through one-degree-of-freedom actuation.Experimental validation showcases the successful generation of a spiral scan pattern with a 60μm diameter scan area and a 10 Hz frame rate,effectively reconstructing scanned images of 5μm lines,cross patterns(15μm in length with a 5μm gap),and structures of a Psychodidae wing.

Nanostructured fibers as a versatile photonic platform: radiative cooling and waveguiding through transverse Anderson localization

Broadband high reflectance in nature is often the result of randomly,three-dimensionally structured materials.This study explores unique optical properties associated with one-dimensional nanostructures discovered in silk cocoon fibers of the comet moth,Argema mittrei.The fibers are populated with a high density of air voids randomly distributed across the fiber cross-section but are invariant along the fiber.These filamentary air voids strongly scatter light in the solar spectrum.A single silk fiber measuring~50μm thick can reflect 66%of incoming solar radiation,and this,together with the fibers’high emissivity of 0.88 in the mid-infrared range,allows the cocoon to act as an efficient radiative-cooling device.Drawing inspiration from these natural radiative-cooling fibers,biomimetic nanostructured fibers based on both regenerated silk fibroin and polyvinylidene difluoride are fabricated through wet spinning.Optical characterization shows that these fibers exhibit exceptional optical properties for radiative-cooling applications:nanostructured regenerated silk fibers provide a solar reflectivity of 0.73 and a thermal emissivity of 0.90,and nanostructured polyvinylidene difluoride fibers provide a solar reflectivity of 0.93 and a thermal emissivity of 0.91.The filamentary air voids lead to highly directional scattering,giving the fibers a highly reflective sheen,but more interestingly,they enable guided optical modes to propagate along the fibers through transverse Anderson localization.This discovery opens up the possibility of using wild silkmoth fibers as a biocompatible and bioresorbable material for optical signal and image transport.

Transporting droplets through surface anisotropy

This review article examines digital microfluidic systems that manipulate droplets through surface anisotropy.These systems are categorized as surface tension driven or contact line driven.Surface tension driven systems include electrowetting on dielectric,Marangoni flow on microheater arrays,and chemical gradient surfaces,whereas contact line driven systems include anisotropic ratchet conveyors,nanostructured Parylene ratchets,and tilted pillar arrays.This article describes the operating principles and outlines the fabrication procedures for each system.We also present new equations that unify several previous models of contact line driven systems.The strengths and weaknesses of each system are compared,with a focus on their ability to perform the generation,switching,fusion,and fission of droplets.Finally,we discuss current and potential future applications of these systems.