A Study of the Commercial Frequency Component and Doubled Component on the dc Side of Three‐Phase Rectifiers and Their Influence on Electric Railways

This paper discusses nontheoretical harmonics on the dc‐side of a 12‐pulse rectifier in dc railway systems. These harmonics are the commercial frequency component and the doubled component. The causes of these harmonics are (a) diode forward voltage drop difference, (b) transformer secondary inductance difference, (c) voltage harmonics at the ac‐side of the rectifier, and (d) effects of the voltage induced by adjacent high‐voltage power transmission lines. We evaluated cases (a), (b), and (c), as case (d) has been previously studied 4 . The results of the evaluation were as follows: · The effects of both the transformer secondary inductance difference and the voltage harmonics inside the electric power system are not negligible in some cases in the discussion of the EMC problem among railway equipments. · If there are several traction circuits in parallel, each of which consists of an input filter, an inverter, and several traction motors, the harmonic reduction effect of the filters weakens significantly.     

SEVERAL NEW FACTORS INFLUENCING THE MEASUREMENT OF β-GLUCAN CONTENT USING CALCOFLUOR FLOW-INJECTION ANALYSIS METHOD

Factors such as temperature, calcofluor concentration, sample injection volume, void volume of the mixing tube and other factors have been reported to influence the calcofiuor flow-injection analysis (FIA) of β-glucan. In addition to these factors, we revealed the following factors and elucidated their effects on the FIA of β-glucans: the inside diameter and arrangement of the mixing tube, calibration method using peak area or peak height of the edition patterns, and the quality of the calcofluor reagent. An apparently lower value was obtained when (1) the mixing tube had a smaller inside diameter, (2) the mixing tube was looped in a ring of smaller diameter, or (3) the mixing tube was wound as double coils in a figure eight instead of a loop. Furthermore, it was indicated that the peak area calibration produced higher measures values than the peak height calibration. The reagent also affected the results; a calcofluor reagent from Sigma Chemical Co. gave a higher value than one from Polyscience Inc. It was concluded that these troublesome phenomena were derived from the difference between the test sample and the standard solution of β-glucan, that is, the molecular weight distribution of β-glucans and/or the sugar and ethanol in the sample solutions. Based on these findings, it is suggested that international standardization of the FIA method for β-glucan be made.     

A High‐Frequency Cycloconverter Based on a Phase‐Shift Control Method

This paper proposes a new control method for a high‐frequency cycloconverter consisting of two half‐bridge inverters and a series–resonant circuit. This cycloconverter acts as an ac‐to‐ac direct power conversion circuit without any dc stage. This circuit does not require a diode bridge rectifier, and thus, can be used to reduce forward voltage drops and power losses in the diodes. A new phase‐shift control method is proposed to regulate the capacitor voltage in each half‐bridge inverter and to achieve zero‐voltage switching. The proposed phase‐shift control is theoretically discussed and is also verified by an experimental circuit consisting of superjunction power MOSFETs. As a result, the proposed high‐frequency cycloconverter exhibits a good power conversion efficiency as high as 97.7% at the rated power of 1.3 kW.     

Electrical Conduction of Rare-Earth-Doped BaTiO3 Single Crystals

The effect of 0.2 to 0.8 at.% rare-earth ions on the conductivity of melt-grown BaTiO₃ crystals was studied by optical absorption, luminescence, Hall coefficient, and electrical conductivity measurements. The conductivity is proportional to the dopant concentration in these crystals; such is not the case in BaTiO₃ ceramics. A rare-earth ion substitutes on the Ba²⁺ site and yields a donor.