This work aimed to investigate the distribution characteristics of the low-frequency magnetic flux leakage (LF-MFL) field of defect on oil and gas pipelines in low-frequency electromagnetic detection technique (LFET). Taking four types of crack defects (rectangular, semicircular, trapezoidal, and V-shaped grooves) with equal lengths, widths and different bottom shapes into consideration, the specific mathematical model of the LF-MFL field was inferred and established on the basis of magnetic dipole theory. Experimental results demonstrated that the variation values of the tangential and normal component upper-lower envelope difference curves were linearly positively correlated with the defect cross-sectional area along the detection direction, which was strictly independent of bottom shape and excitation conditions (amplitude, frequency and lift-off).
Aiming at the problems of frequent overshoot and slow response time in space vector direct torque control system of permanent magnet synchronous motor, a control strategy based on a fast-super-twisting algorithm was proposed. Based on the traditional super-twisting algorithm, the fast terminal sliding mode reaching law (FTSMRL) is introduced in the strategy, which improves the algorithm’s robustness and convergence speed, suppresses the sliding mode chattering. The stability of the system is proved by using a quasi-quadratic Lyapunov function. Simulation results show that the proposed strategy can effectively improve the response speed and robustness of the system, and significantly reduce the system overshoot and sliding mode chattering.
We have experimentally demonstrated an observation method of broad band optical comb by retrieving from the fragments of spectra. The optical comb with 150 GHz bandwidth was divided into six fragments of spectra and they are individually detected by a coherent receiver with 18 GHz bandwidth. The fragments of spectra are unified based on the boundary condition where the highest frequency component of a fragment is equal to the lowest one in next fragment. The time domain waveform has been successfully retrieved from the fragments and agree well with that observed by 65 GHz sampling oscilloscope. To verify the validity of the method, 30 GHz optical comb was observed by both signal-shot and retrieving method. The results of amplitude and phase showed good agreement and revealed that the retrieving method is very effective to observe the complex amplitude of broadband optical comb.
Aiming at the high-efficiency charging application requirements of solar photovoltaic (PV) energy storage systems, a novel control system architecture for solar photovoltaic energy storage applications is presented. The system dynamically adjusts its working state according to the real-time power generation data of solar photovoltaic output, thus realizing the hierarchically combined operating mode and operation state changes when applying different Environmental parameters. In addition, the corresponding algorithm was proposed to achieve efficient control. Compared with the conventional control system architecture, the developed circuits can realize high-efficiency solar charging and multi-mode flexible applications. An experimental prototype is implemented and the test results are derived to verify the effectiveness and superiority of the proposed system, which provides the new ideas and references for the application of photovoltaic energy storage systems.
This paper presents a comparison of optical leaky-waveguide antennas, i.e., grating waveguide (GWG), waffle waveguide (WWG), and waffle-iron waveguide (WIWG), using both simulations and measurements. WIWG radiates a narrow beam that is tilted by sweeping the incident wavelength, and it possesses a higher antenna gain than GWG and WWG under the same fabrication condition. The reason is due to a slight difference in the effective index along the longitudinal sections, which provides a large aperture size for high antenna gain. We simulate the antenna characteristics and experimentally confirm the high antenna gain.
In this letter, a SIW (substrate integrated waveguide) linear coupling band-pass filter working in Ka-band is presented, it is designed to be a part of a Ka-band receiver front end. Due to the super heterodyne structure of the receiver, the system contains lots of chips, therefore stacked packaging structure is used. Considering the heat dissipation efficiency, process accuracy and cost, novel wafer-level silicon manufacturing process is adopted to fabricate the SIW filter. The design of the filter employs the coupling coefficients extraction method. Finally, a fourth-order band-pass filter was designed, manufactured and tested. The measured results are in good agreement with the simulation results, verifying the practicability of the silicon-based SIW filter in RF front end microsystem.