Pump-back Test Research Articles

High-Scalability Enhanced Gate Drivers for SiC MOSFET Modules With Transient Immunity Beyond 100 V/ns

Silicon-carbide (SiC) transistors with growing readiness for the power converter market have raised an emerging need for high-performance gate driver (GD) units to maximize their remarkable characteristics. In particular, the GD units for the SiC devices that experience extremely fast commutations at the medium-voltage level require powerful driving capability, effective short-circuit (SC) protection, and superb common-mode transient immunity. Thereby, this article presents a systematic enhanced GD (eGD) solution that incorporates three scalable features compatible with almost all the SiC mosfet modules. First, a BJT-based multicell current booster is proposed to attain balanced high driving current, low losses, gate-loop inductance less than 1 nH, and great cross-talk immunity. Second, a nonintrusive Rogowski switch-current sensor with high bandwidth and fair accuracy is developed, capable of detecting SC fault in 86 ns and softly turning off 5 kA SC current in 1 $\mu$ s. Third, two noise-free isolation architectures are proposed to mitigate common-mode noise-admittance by more than 100 dB. Fundamentals, analytical designs, experimental validations, and scalability discussions of the three techniques are elaborated, respectively. Finally, a 6-kV, 84-A, and 102-V/ns continuous pump-back test is demonstrated, for the first time, to verify the eGD's excellent performance.

Drift pump back test for residence time distribution in engineered treatment system

Tracer tests use conservative dyes to estimate hydraulic parameters of aquifers such as permeability and velocity. However, deionized water is rarely used in tracer tests. A novel permeable reactive barrier (PRB) designed and installed to collect and treat acidic water seeps from spoil heaps was investigated. In the present work, deionized water as a tracer was used to estimate the residence time and velocity distribution in reactive media placed in the PRB. Drift pump back tracer tests were carried out in multilevel boreholes in the reactive media using deionized water. Breakthrough curves of relative electrical conductivity were analyzed. The velocity and residence time differed horizontally and vertically at less than the optimum values predetermined in the design phase for effective treatment. The treatment efficiency is higher in the lower level than that at upper level inside the PRB. The quantity of deionized water used as a tracer should be big enough to force the tracer to move out of the well bore zone and travel significant distances into the reactive media. Consequently, representative breakthrough curves are obtained and better estimate the residence time and velocity. Using deionized water as a tracer has advantages over other tracer dyes such as fluorescein as it is inexpensive and requires no lab analysis for water samples and has less ionic strength and sorption. The disadvantage of using deionized water in reactive media is that it is recharged with high saline acidic water drainage from spoil. In drift tests the velocity is in direct proportion to permeability, drift time and time to recover half tracer mass. To overcome porosity reduction due to mineral fouling in the reactive media, the contaminated water should be forced to flow into several avenues in the reactive media in a direction parallel to PRB length instead of crossing the reactive media to increase the residence time inside the reactive media.

On the Switching Frequency of Hysteresis Control in a Silicon Carbide Converter Pump-Back Test

The pump-back test is widely adopted in the industry for characterizing and qualifying high-power converters. One popular pump-back test configuration is to tie the dc links of two converters together and circulate the current through the inductor connected between the ac terminals. In this configuration, one of the converters operates in the voltage mode to generate the virtual grid and the other converter regulates the circulating current, where hysteresis control could be applied. However, the switching characteristics of hysteresis control are unique due to the pulsewidth modulation type voltage being the virtual grid. This paper contributes to analyzing the switching frequency characteristics of the hysteresis control in this pump-back test configuration. The switching frequency tracking phenomenon is revealed and reported in this paper for the first time. Theoretical analysis, simulation validation, and experimental demonstration are provided to support the major conclusions.

A High-Frequency High-Power Test Bench for 11 MW/595 Hz Drives With 1.25 MW Grid Capability

This paper presents a pumpback test bench for high-frequency high-power variable-frequency drives (VFDs) with 11 MW power rating and up to 595 Hz load frequency. A voltage combiner concept is applied to allow a high-frequency output from the two three-level neutral-point-clamped integrated gate-commutated thyristor bridges with minimum switching losses. The accordingly developed pumpback test bench applies a dc power coupling concept combined with a virtual grid concept that can achieve 11 MW test capability with only a 1.25 MW facility transformer. By applying a virtual machine concept, the pumpback test can be conducted without the need of high-frequency machines, while the circulating power losses in the pumpback loop are minimized as well. The virtual grid including the concept tradeoff, filter parameters, and modulation schemes is presented in detail. Moreover, design and installation guidelines for high-frequency components, especially the cables, are presented. The high-frequency high-power VFD and its pumpback test bench are both successfully built and experimentally validated at their rated operation points.

Single Well Tracer Tests in Aquifer Characterization

AbstractWhen the purpose of aquifer testing is to yield data for modeling aqueous mass transport, pumping tests and gradient measurement can only partially satisfy characterization requirements. Effective porosity, ground water flow velocity, and the vertical distribution of hydraulic conductivity within the aquifer are left as unknowns. Single well tracer methods, when added to the testing program, can be used to estimate these parameters. A drift, and pumpback test yields porosity and velocity, and point‐dilution testing yields depth‐discrete hydraulic information, A single emplacement of tracer into a test well is sufficient to conduct both tests. The tracer tests are facilitated by a simple method for injecting and evenly distributing the tracer solution into a wellbore, and by new ion‐selective electrode instrumentation, specifically designed for submersible service, for monitoring the concentration of tracers such as bromide.

Stray-Load Losses of D-C Machines

This article describes a method of measuring strayload losses which is readily adaptable to the test departments of the manufacturers. Usually no additional test apparatus will be required beyond that already available. The same arrangement used for a pump-back heat-run test is used with only slight modification. Experimental data are given showing the effect of speed, load, and field strength upon these losses.