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The digital controller of the grid-connected converter achieves closed-loop control by sampling key voltage and current signals. High-frequency switching of power electronic switches introduces high-frequency ripples into the signals, which may cause sampling aliasing. Severe distortion may happen in the output current of the converter because of the sampling aliasing. This paper explains how the aliasing problem arises by analyzing the spectrum of sampling-controlled signals. The explanation shows the severity of the aliasing problem and the necessity of adopting anti-aliasing methods. Next, this paper analyzes the impact of commonly used anti-aliasing low-pass filters on current control stability. From the conclusions, adopting a low-pass anti-aliasing filter reduces the stability margin of the current loop, which needs improvement. So this paper proposes a novel hybrid anti-aliasing filter based on the combination of the notch and low pass analog filters. An experiment on a 6kVA prototype verifies the proposed anti-aliasing method. This paper shows distortion and step-response oscillation of the output current when proposed and traditional anti-aliasing methods adopted. The comparison shows the advantages of the proposed anti-aliasing method.

The polymer film dielectric has been widely used in high voltage equipment for bulk insulation owing to the excellent insulation performance. Martin’s empirical formula for bulk breakdown is frequently used to predict the breakdown field strength of multilayer thin film with different electrode areas. In this article, based on the academic consensus that the cumulative breakdown probability of single-layer film obeys the Weibull distribution, the relationship between the cumulative breakdown probability of film dielectric under different electrode areas and the applied electrical field is deduced. Moreover, the relationship between the cumulative breakdown probability of film dielectric with various numbers of film layers and the applied electrical field is obtained and simplified. On these bases, combined with the experimental results of the average breakdown field of film dielectric with smaller electrode areas and fewer layers, a prediction model of the average breakdown field strength of film dielectric with different electrode areas and film layers is established. To obtain the solution of the prediction model concerning the number of film layer, an effective approximate solution method is proposed to solve the calculation problem with ultralarge and ultrasmall data, which significantly reduces the complexity of the solution process. A coaxial film capacitor is developed and tested to verify the prediction model with the “Chenguang” accelerator. The experimental breakdown field strength of 54 layers of 15 $\mu \text{m}$ biaxially oriented polypropylene (BOPP) film with an electrode area of 218.1 cm2 is 355.6 V/ $\mu \text{m}$ , which is comparable to the predicted result of 374 V/ $\mu \text{m}$. The prediction model presented in this article is of certain reference significance for the insulation design of film dielectrics. [ABSTRACT FROM AUTHOR]

Nowadays the phase controlled switching is a preferred method for capacitive switching. Thus the prestrike characteristic is an important issue for the control strategy. The objective of this paper is to understand the prestrike characteristics of vacuum interrupters (VIs) in the capacitive making operations of 40.5 kV vacuum circuit breakers (VCBs). In the experiment, three VIs with CuCr50 (50 wt% of Cr) contact material and three VIs with CuCr40 (40 wt% of Cr) contact material with contact diameter of 50 millimeters were prepared. The CuCr50 and CuCr40 contact materials are made by using infiltration and arc-melted technology, respectively. An L-C oscillating circuit generated an inrush current with a frequency of 207 Hz and with a peak of 6.48 kA, while the applied voltage was 46.3 kV which is equivalent to the peak voltage for a 35 kV three-phase network whose capacitive voltage factor is 1.4. The experimental results show that the complementary cumulative distribution function (CCDF) of the prestrike gaps dpre follows a 3-parameter Weibull distribution. The prestrike gap below which prestrike would always occur is similar for all six test VIs which is 2.4–3.1 mm. However, the average values of d\0, ¿50 and ¿90 for infiltration CuCr50 contact material are 57.5%, 45.3% and 28.9% higher than the ones in arc-melted CuCr40 contact material, respectively. During the inrush current flowing, at each zero-crossing of the inrush current the prestrike arc tries to extinguish with the occurrence of three types of contact gap breakdowns. Furthermore, if the contact gap breakdowns are withstood at the inrush current zero-crossing, inrush current interruption phenomenon happens, which proves a common phenomenon in capacitive making operation. The inrush current interruption phenomenon is mainly determined by the prestrike distance and not by the material quality. The experimental results imply that the field emission dominated breakdown and the micro-particle induced breakdown both take effect in the prestriking and contact gap breakdown process. [ABSTRACT FROM AUTHOR]