Local-measurement-based protection elements are essential for the safety and stability of the VSC-MTDC. However, when a DC line fault occurs, the resistive coverage for each side of a protection ...element is not always identical. As a result, a certain side of the protection element may not be sufficiently sensitive to trip the fault, especially in scenarios of communication failure. To solve this problem, a mutual-speed-up protection strategy is proposed to identify dead-zone grounding faults. First, the time domain characteristics and frequency domain characteristics of the fault-induced primary traveling wave and those of the second traveling wave caused by the opening operation of the DC CB are analyzed. Then, based on the above-mentioned difference, a time difference criterion (TDC) and zero-crossing criterion (ZCC) are proposed, working in conjunction to discriminate the remote-end dead-zone fault and the external fault at the head of the adjacent DC line. Simulation results indicate that the proposed strategy works without communication and is sufficiently fast to operate before the blocking of the converter, thus making it a powerful supplemental strategy for existing main protection elements.
In this paper, a traveling wave based fault location method is proposed for distribution networks. Before fault occurs, an intrinsic distance difference matrix (IDDM) is established based on the ...characteristics of traveling wave propagation and the topology of distribution network. After the fault, the initial fault traveling wave signals are decomposed into several intrinsic mode function (IMF) signals by variational mode decomposition (VMD), and the first IMF signal is analyzed by teager energy operator (TEO) to determine the arriving time of initial fault traveling waves. According to the double-ended traveling wave method and the arrival time of traveling wave at all recorders, a fault distance difference matrix (FDDM) is built. By comparing the difference between IDDM and FDDM, a fault branch determination matrix (FBDM) and the lateral index Q are used to locate the fault. The effectiveness of the proposed method is verified via EMTP/ATP simulations. Results show that the proposed method has a high fault location accuracy, and does not need that all terminals of lines are installed traveling wave recorders.
With the advent of e-commerce and its fast-delivery expectations, efficiently routing pickers in warehouses and distribution centers has received renewed interest. The processes and the resulting ...routing problems in this environment are diverse. For instance, not only human pickers have to be routed but also autonomous picking robots or mobile robots that accompany human pickers. Traditional picker routing, in which a single picker has to visit a given set of picking positions in a picker-to-parts process, can be modeled as the classical Traveling Salesman Problem (TSP). The more involved processes of e-commerce fulfillment, however, require solving more complex TSP variants, such as the clustered, generalized, or prize-collecting TSP. In this context, our paper provides two main contributions: We systematically survey the large number of TSP variants that are known in the routing literature and check whether meaningful applications in warehouses exist that correspond to the respective TSP variant. If they do, we survey the existing research and investigate the computational complexity of the TSP variant in the warehousing context. Previous research has shown that the classical TSP is efficiently solvable in the parallel-aisle structure of warehouses. Consequently, some TSP variants also turn out to be efficiently solvable in the warehousing context, whereas others remain NP-hard. We survey existing complexity results, provide new ones, and identify future research needs.
•This paper surveys routing problems in warehouses.•We focus on variants of the TSP in warehouses.•New and old complexity results for the parallel-aisle structure are provided.•We elaborate warehouse use cases and future research needs.
Increasing the interaction current capacity and the interaction impedance is crucial to achieving high output power for traveling wave tubes (TWTs) in Formula Omitted-band and terahertz (THz)-band. ...With the increased distance between the upper and lower metal walls of folded waveguide (FW), the slow wave structure (SWS) named dual-tunnel FW (DTFW) is formed. Benefiting from such a rational design, the electric field in the noninteracting region decreased and naturally formed dual electron beam tunnels. Meanwhile, the operating mode is cutoff at the beam tunnel, the electromagnetic wave in DTFW can be propagated along the path similar to FW and operate in the fundamental mode. Furthermore, compared with FW, due to its larger size, the DTFW has the same structural complexity and less manufacturing difficulty, which is significant for Formula Omitted-band and THz-band. In this article, through the analysis of the high-frequency characteristics of the SWS using FW and DTFW, the physical mechanism of bandwidth and interaction impedance improvement of DTFW-SWS are revealed. Moreover, the particle-in-cell (PIC) simulation results reveal that, compared with a TWT using unprecedentedly excellent FW-SWS, the performance of TWT using DTFW-SWS has been significantly further improved in the aspects of saturated power, gain, and electron efficiency. Therefore, DTFW-SWS is a promising SWS for high-power and wide-bandwidth TWT in Formula Omitted-band and THz-band.
In this paper, we investigate the impact of the high-power amplifier non-linear distortion on multiple relay systems by introducing the soft envelope limiter, traveling wave tube amplifier, and ...solid-state power amplifier to the relays. The system employs amplify-and-forward either fixed or variable gain relaying and uses the opportunistic relay selection with outdated channel state information to select the best relay. The results show that the performance loss is small at low rates; however, it is significant for high rates. In particular, the outage probability and the bit error rate are saturated by an irreducible floor at high rates. The same analysis is pursued for the capacity and shows that it is saturated by a detrimental ceiling as the average signal-to-noise ratio becomes higher. This result contrasts the case of the ideal hardware where the capacity grows indefinitely. Moreover, the results show that the capacity ceiling is proportional to the impairment's parameter and for some special cases the impaired systems practically operate in acceptable conditions. Closed-forms and high SNR asymptotes of the outage probability, the bit error rate, and the capacity are derived. Finally, analytical expressions are validated by the Monte Carlo simulation.
This article reports a slow-wave structure (SWS) working at 1 THz which can be fabricated through nano-computer numerical control (nano-CNC) technology for the first time. First, a 1 THz deformed ...quasi sine waveguide (D-QSWG) SWS has been designed and simulated in this article. To reduce the metal loss of input and output waveguide, a coupler which transit the waveguide to over mode rectangular waveguide has been designed. The simulation result shows that input and output waveguides with this coupler have lower metal loss than that of WR1 rectangular waveguide. To fabricate the designed D-QSWG SWS, tungsten steel endmills have been used. The fabricated SWS has the surface roughness around 58-74 nm, the corresponding effective conductivity is around <inline-formula> <tex-math notation="LaTeX">2\times 10^{{7}} </tex-math></inline-formula>-1.85 <inline-formula> <tex-math notation="LaTeX">\times 10^{{7}} </tex-math></inline-formula> S/m. And the cold test results show that the insertion loss of the fabricated model is less than 30 dB while the reflection loss is less than −15 dB in the frequency range of 0.998-1.016 THz, which has a good consistency with the simulated results. The beam-wave interaction simulation results based on the cold test results show that the designed D-QSWG traveling wave tube (TWT) has the output power of 300 mW, and the 3 dB bandwidth is around 3 GHz.
In this paper, we study minimum-time motion planning and routing problems for the Dubins vehicle, i.e., a nonholonomic vehicle that is constrained to move along planar paths of bounded curvature, ...without reversing direction. Motivated by autonomous aerial vehicle applications, we consider the traveling salesperson problem for the Dubins vehicle (DTSP): given n points on a plane, what is the shortest Dubins tour through these points, and what is its length? First, we show that the worst-case length of such a tour grows linearly with n and we propose a novel algorithm with performance within a constant factor of the optimum for the worst-case point sets. In doing this, we also obtain an upper bound on the optimal length in the classical point-to-point problem. Second, we study a stochastic version of the DTSP where the n targets are randomly and independently sampled from a uniform distribution. We show that the expected length of such a tour is of order at least n 2/3 and we propose a novel algorithm yielding a solution with length of order n 2/3 with probability one. Third and finally, we study a dynamic version of the DTSP: given a stochastic process that generates target points, is there a policy that guarantees that the number of unvisited points does not diverge over time? If such stable policies exist, what is the minimum expected time that a newly generated target waits before being visited by the vehicle? We propose a novel stabilizing algorithm such that the expected wait time is provably within a constant factor from the optimum.
Turbines, as power sources for power generation, ships, etc. are capable of absorbing energy from high-temperature and high-pressure gas, converting thermal energy into mechanical energy. We propose ...a built-in variable wavelength traveling wave turbine that establishes a traveling wave mechanism in the rectangular flow channel. This device has the same function as a conventional turbine, extracting energy from incoming high-pressure gas, but it operates in a completely different way from axial flow and centripetal types. Numerical simulation is adopted to investigate the energy absorption characteristics and flow mechanism of the variable wavelength traveling wave turbine of two wave numbers. The traveling wave turbine is simplified to a two-dimensional traveling wave plate with analytical functions to control the motion parameters. The results show that influenced by variable wavelength, the motion waveform forms expansion type, equal wavelength type and contraction type. The curve of energy absorption rate of traveling wave turbine shows first increase and then decrease with the highest efficiency reaching 89.71%. The mass flow coefficients under two wave numbers correspond to the efficiency curves with approximately the same trend. There is the obvious distinction between pressure regions divided by the moving traveling wave plate, indicating that fluid energy is mainly transferred to traveling wave plate. The velocity varies prominently in X direction near the leading edge and trailing edge of the plate. Interestingly, as the variable wavelength changes, the vortex direction alters where the first formed vortex sheet shed the trailing part of the traveling wave plate. The area of vortex sheet varies significantly.
The explosive eruption of the Hunga-Tonga volcano in the southwest Pacific at 0415UT on 15 January 2022 triggered gigantic atmospheric disturbances with surface air pressure waves propagating around ...the globe in Lamb mode. In space, concentric traveling ionosphere disturbances (CTIDs) are also observed as a manifestation of air pressure waves in New Zealand ∼0500UT and Australia ∼0630UT. As soon as the air pressure waves reached central Australia ∼0800UT, conjugate CTIDs appeared almost simultaneously in the northern hemispheres through interhemispheric coupling, much earlier than the arrival of the surface air pressure waves to Japan after 1100UT. Combining observations over Australia and Japan between 0800 and 1000UT, both direct and conjugate CTIDs show similar horizontal phase velocities of 320–390 m/s, matching with the dispersion relation of Lamb mode. The arrival of atmospheric Lamb wave to Japan later created in situ CTIDs showing the same Lamb mode characteristics as the earlier conjugate CTIDs.
•The results demonstrate the efficacy of the proposed algorithm considering different values of fault resistances, different fault locations and all fault types. At the same time, in practice, the ...fault location performance of this method is better.•This method only uses the current traveling wave, and its anti-interference and noise ability is better than the existing traveling wave method, which greatly improves the accuracy of the second fault traveling wave identification.
This paper proposed a novel one-terminal traveling -wave-based fault-location method for transmission lines. Traveling waves (TWs) are induced in transmission lines by the occurrence of a fault. Different are formed by the superposition of forward and backward TWs when a fault occurs. The proposed fault-location method used a fault-location function to determine the location of faults from corresponding TW change-points. The proposed fault-location method was evaluated through modeling and simulating a three-phase 500 kV/50 Hz transmission system using PSCAD/EMTDC. The performance of the proposed fault-location method was evaluated for using different angles of fault inception, fault impedances, sampling rates, and noise. The fault-location method proposed in this paper was verified using real-world testing, which involved taking measurements from a TW-based fault-location device.
PDF
