Reconfigurable of current-mode differentiator and integrator based-on current conveyor transconductance amplifiers

The reconfigurable of the differentiator and integrator based on current conveyor transconductance amplifiers (CCTAs) have been presented in this paper. The proposed configurations are provided with two CCTAs and grounded elements. The configurations can be operated in the differentiator and integrator by selecting external passive elements. The input and output currents have low and high impedances, respectively; therefore, the configurations can be cascaded without additional current buffer. The proposed configurations can be electronically tuned by external direct current (DC) bias currents, and it also has slight fluctuation with temperature. An application of universal filter is demonstrated to confirm the ability of the proposed configurations. The results of simulation with Pspice program are accordance with the theoretical analysis.

Research on power transformer vibration and noise under DC bias condition

In the process of Ultra high voltage direct current (UHVDC) transmission, the direct current (DC) bias of power transformer is easily induced, which makes the transformer exciting current distorted, the ferromagnetic material saturated and the magnetic leakage increased, and then leads to the increase of core vibration and noise. Aiming at this problem, taking a 240 MVA, 330 kV three-phase five-column power transformer as an example, the coupling of the electromagnetic field, structural force field and acoustic field is studied, and the influence of DC bias on vibration and noise of power transformer core is analyzed in this paper. According to the magnetic density and electric density of transformer core under different magnetic bias degree, the structural force field is solved, and the displacement and surface acceleration of core are obtained, which can be as the excitation of sound field to determine the noise distribution of transformer. In order to avoid the natural frequencies which easily cause resonance, the modal analysis is needed to obtain the natural frequencies and modal modes of the core. The transformer noise under no-load and DC bias conditions of the prototype is tested experimentally and compared with the theoretical calculation, the results prove the accuracy of the simulation calculation method in this paper.

Superposition of 2ω and Electrostatic Field Induced Terahertz Waveforms in DC-Biased Two-Color Filament

Increase in conversion efficiency from a femtosecond optical pump into broadband terahertz (THz) radiation is currently an essential issue since it boosts THz source performance for medicine and security applications. An air-plasma based THz radiation from a two-color femtosecond filament is the most efficient gas-based THz emitter, with a dipole local source having a maximum on the beam propagation axis. In this work, we show the novel advancement to THz yield increase with preservation of the forwardly directed dipole radiation. The two-color THz source can be enhanced if the filament plasma channel is placed into an external electrostatic field (DC bias), which is parallel to the second harmonic polarization direction. In the experiment, we produce a plasma channel from 800-nm, ∼50-fs, 2-mJ pulse with 200 μJ of 400-nm, ∼50-fs mixed with the pump, and allocate it between the electrodes carrying 7-kV/cm static field. Time-domain measurements and 3D+time simulations of THz waveforms from the two-color DC-biased filament show that the THz emission is the superposition of the THz waveforms generated in the 800+400-nm filament without a DC-bias and in the 800-nm (without 400-nm) plasma channel biased by 7-kV/cm static field. The additivity of the two local dipole THz sources is possible if the majority of free electrons are produced by the pump pulse.

Influence of HVDC Transmission on DC Bias of AC Grid and Its Treatment

With the rapid development of China’s electric power industry, the high-voltage and long-distance direct current (DC) transmission effectively solved the problem of uneven power distribution. When the high voltage direct current transmission is in unipolar operation or bipolar asymmetric operation, part of the DC current will flow into the transformer winding through the grounded neutral point, which will cause the DC bias problem. This article used CDEGS software for modeling, and introduced the process of CDEGS software for DC bias simulation modeling. In this paper, the DC bias model of regional power grid is first established, based on the Zhejiang power grid topology and the test soil resistivity date. Then the DC bias currents of the transformers are calculated, and finally the corresponding treatment measures are proposed. According to the governance measures, this article adjusted the simulation model. The calculation results show that the treatment measures have good effects, which can provide an important reference for the future treatment of transformer DC bias.