PWM Inverter Using High-Gain Pulse-Triggered Power Transistors and a New PWM Control Method

Rugged PWM transistor inverters are expected to be put into practical use for providing high reliability under adverse operating conditions. The bipolar power transistors are more common compared with MOSFET's power transistors in balance between power-handling capability and switching speed. High over current capability, low switching loss, high-speed switching, and high-current gain are requisite functions in the PWM inverter employing bipolar power transistors. These functions are of great concern in the power electronics field. A new PWM transistor inverter which can meet these requirements is presented in this paper. For this purpose, a concept of high-gain pulse-triggered power transistor (PTPT) with amorphous saturable current transformer (CT) is introduced.     

New design for the high-performance drive system for DC brushless motor

The dc brushless motor, permanent magnet-type synchronous motor (PM motor), has been used widely in industrial robots, the machine tools for factory, and factory automations. Therefore, it is more desirable to improve the performance of the PM motor variable speed control system. Although only the torque component current is adjusted as the control method for the PM motor, so-called Vector Control, it is expected that the developed characteristics will be added to the PM motor. In this paper, new driving methods for the PM motor and a new design method for the variable speed control system are presented. The new motor driving methods which bring to the PM motor a new driving performance, e.g., a quick transient response or high-efficiency motor driving, can be implemented by controlling not only the torque component current, but also the magnetizing component current. A developed optimal control theory, i.e., the error system technique, is employed for designing the control system. The control law is endowed with a steady robustness against the variation of the system parameters and the ability of compensating the delay time due to the control processing. The effectiveness of the proposed method is confirmed by simulations and experiments.     

Requirements for intelligent network service operations

A service operation architecture and operation system platform are proposed that separate commonly used information from operations functions, and that use access control functions. This enables new applications to be developed more easily and increases operating efficiency. The operation system platform is related to several surrounding platforms, and requires standardized reference points such as CMIS/P and managed objects. A managed object methodology is a suitable approach for accessing the operation system platform, and managed object classes and methods are proposed for intelligent network service operations. This architecture and platform will allow telecommunication to meet the demands created by intelligent networks for enhanced customer services, more reliable operation systems, and lower development costs. On the basis of proposed platform, service surveillance prototype systems for free-phone services have already been developed, and the next versions of the service operations systems for virtual private networks services are being developed.     

Polymers for optoelectronics

This paper discusses polymers for optoelectronics, especially plastic optical fibers (POFs) for near-infrared (near-IR) use and polymeric nonlinear optical materials expected for use as switching devices. Near-IR transmissible plastic optical fibers are investigated using fluorination and deuteration for conventional polymers. Among them pentafluoro-trideutero-styrene polymer core POF has excellent transparency in the near-IR region even after water vapor absorption. Nonlinear optical polymeric materials with excellent processibilities are also investigated. The third-order nonlinear optical susceptibility of poly-aromatic vinylene thin film was measured and revealed to have a higher susceptibility than previously reported.     

High-temperature 1H n.m.r. study of oxidized coal

Two coking coals, a caking and a non-caking coal are examined in a Bruker pulsed ¹H n.m.r. spectrometer in the temperature range 293–730 K. One coking and the caking coal are oxidized in air at 383 K for 13 days. Temperatures of signal appearance and loss are noted as well as the temperatures of minimum signal half-peak width ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$). There occurs no change in the above three temperatures with oxidation of the coals. The variation of ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) with temperature of the coal is also measured. Changes in ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) are more pronounced for the caking coal. The softening and solidification temperatures are below and above, respectively, those reported using the Gieseler method. Values of ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) increase beyond the minimum value as the fluidity continues to increase. This may be caused by an increase in average molecular weight of constituent molecules and/or an increasing concentration of free radicals in the fluid phase. This experimental approach may afford a new method to characterize coals which are to be used in liquefaction processes.     

A procedure for estimating the mean activity coefficient of dye in fibre

A procedure for estimating values that are proportional to the mean activity coefficients of sodium 4′-dialkylaminoazobenzene-4-sulphonates in cellophane is presented. These values are derived from the mean activity coefficients of the dye in solution, and the dye concentrations in solution and in cellophane.     

Carbonization behaviour of pitch in the presence of inert material

The influence of silica gel (< 45 μm) as an inert additive on the carbonization reactions of A240 pitch was investigated by optical microscopy, measurements of transferable hydrogen, high-temperature e.s.r. and high-temperature ¹H n.m.r. Additions of silica gel have the effect of reducing the size of the optical texture of mesophase which appears in the early stages of carbonization. The higher the concentration of silica gel, the smaller is the amount of transferable hydrogen. The spin concentration of pitch increases with increasing silica gel content. Measured values of $\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, using high-temperature ¹H n.m.r., suggest that the molecular motions in the pitch become restricted on addition of silica gel. The effect of silica gel on the physical properties and chemical reactivity of carbonizing pitch is discussed.     

Influence of polarity of polymer on inorganic particle dispersion in dielectric particle/polymer composite systems

The influence of the polarity of polymers on the degree of dispersion of BaTiO₃ particles in BaTiO₃/polymer composite systems was investigated. The BaTiO₃ polymer composite systems were prepared from BaTiO₃ particles and low-density polyethylene (LDPE) or ethylene vinyl acetate copolymer (EVA) with 7 and 15 wt % vinyl acetate. Scanning electron microscopy observation showed that BaTiO₃ particles aggregated in the polymer matrices and dispersed more readily into the EVA matrix than into LDPE. The shift of the β-peak temperature by ca. +5°C in the temperature dispersion of the loss modulus was observed for EVA–BaTiO₃ composite systems in dynamic mechanical property measurement. On the other hand, the β-peak temperature of the polymers filled with graphite particles, which have hydrophobic surfaces, was almost constant in a volume fraction region of 0–0.3. The ellipsoidal axes' ratios given by comparison of experimental dielectric constant values and theoretical ones using the Maxwell equation were 4.2, 3.6, and 3.1 for LDPE/BaTiO₃, EVA(7%)/BaTiO₃, and EVA(15%)/BaTiO₃ composite systems, respectively. The axes' ratio decreased by the introduction of polar vinyl acetate groups into nonpolar LDPE. The results confirmed that the polarity of the polymers was one of the key factors governing the dispersibility of BaTiO₃ particles in the polymer matrix. © 1995 John Wiley & Sons, Inc.     

Graphitization behavior of hydrogenated ethylene tar pitch

The graphitization behavior of cokes prepared from ethylene tar pitch (ETP) hydrogenated at temperatures from 473 to 673 K has been studied by magnetoresistance measurements at liquid nitrogen temperature and by scanning electron microscopy. Graphitization heat treatment of the cokes was carried out at 3273 K. Hydrogenation temperatures of 473 and 523 K resulted in graphitized cokes with random layer plane textures and low degrees of graphitization. Hydrogenation at higher temperatures was effective in promoting development of flow-type textures during graphitization. The coke from ETP hydrogenated at 673 K showed the highest graphitizability, preferred orientation and flow-type texture developed by heat treatment.