Virtual synchronous generator model control of PV for improving transient stability and damping in a large‐scale power system

Because of the significant changes in environmental policies and electric power deregulation in the last decade, a lot of photovoltaic generations (PV) have been and will be installed into the power system in Japan and the ratio of PVs to other synchronous generators will be increased. As a countermeasure against the decrease in the rotational inertia in the whole power system, a virtual synchronous generator (VSG) model control of the PV has so far been proposed. However, the system stabilization effect of the VSG in large‐scale power systems has been unclear. In this paper, a virtual step‐out blocking method of VSG for improving the transient stability is proposed. In addition, the necessity of governor control of VSG in a large‐scale power system is discussed. Finally, the rated kw and kwh capacities of the battery required for realizing the VSG‐model control are evaluated.     

Degradation mechanisms of GaAs PHEMTs in high humidity conditions

We have studied the degradation mechanisms of AlGaAs/InGaAs pseudomorphic HEMTs (PHEMTs) under high humidity conditions (85 °C, 85% relative humidity). The degraded samples under high humidity conditions show a decrease in maximum drain current (I_max) and a positive shift in threshold voltage (V_th). Cross-sectional transmission electron microscopy (TEM) images from the deteriorated devices reveal an existence of damaged recess surface region and a peeling of a passivation film (SiN_x). The secondary ion mass spectrometry (SIMS) depth profile at the interface between the passivation film and AlGaAs surface also indicates the diffusion of gallium (Ga), arsenic (As) and aluminum (Al) into the passivation film. The degradation of PHEMTs arises from mainly two mechanisms: (1) the positive shift in V_th due to stress change under the gate caused by the peeling of passivation films, and (2) the decrease in I_max due to the net carrier concentration reduction of the AlGaAs carrier supply layer caused by the combination of surface degradation at the AlGaAs recess regions and diffusion of Ga, As and Al at the interface between the passivation film and AlGaAs surface. A special treatment just prior to the deposition of SiN_x films on the devices effectively suppresses the degradation of PHEMTs under high humidity conditions without degradation of the high frequency performance.     

Total elemental composition analysis of soil samples using the PIXE technique

The determination of major and trace element contents in soils was developed by acid digestion method combined with particle-induced X-ray emission spectrometry (PIXE). The digestion of soils was achieved by using nitric acid (HNO₃), hydrochloric acid HCl and hydrogen peroxide (H₂O₂) with repeated additions. A 20 μL aliquot from the digested samples was evaporated on the Nuclepore Track-Etch Membrane and irradiated by the 2.5 MeV proton beam from the single-end type Van de Graaff accelerator. The accuracy of this methodology was estimated based on series of measurements done for a reference material of soil CRM 023-050. The proposed experimental procedure was shown to have good reproducibility of the experimental results. The corresponding limits of detection (LODs) for Na, Mg, Al, P, S, Cl, K, Cr, Mn, Fe, Ni, Cu, Zn, As, Sr, Mo and Cd were estimated. Other soil characteristics such as total carbon (TC) and nitrogen (TN) content, pH and electrical conductivity (EC) were also measured.     

Development of a microchip-based bioassay system using cultured cells

We developed a novel bioassay system using a glass microchip and cultured cells. A microchamber for cell culture and microchannels for reactions and detection were fabricated on a Pyrex glass substrate by photolithography and wet etching techniques. Cell culture, chemical and enzymatic reactions, and detection were integrated into the microchip. To keep different temperatures locally in three areas of the microchip, we designed and fabricated a temperature control device. Nitric oxide released from macrophage-like cells stimulated by lipopolysaccharide was successfully monitored with the microchip, the temperature control device, and a thermal lens microscope. The total assay time was reduced from 24 to 4 h, and detection limit of NO was improved from 1 x 10(-6) to 7 x 10(-8) M compared with conventional methods. Moreover, the system could monitor a time course of the release, which is difficult to measure by conventional batch methods. We conclude that this system is promising for a rapid bioassay system with very small consumption of cells.     

A 0.5-W 64-kilobyte snoopy cache memory with pseudo two-portoperation

A 64-kbyte snoopy cache memory was developed. The modified double word-line architecture with word-line buffers resulted in a large-size memory and a time-multiplex snoop operation by the pseudo-two-port method with a single-port cell. The flexible expandability was achieved by cascading multiple cache memories. The device was successfully implemented with 1.0-μm double-polysilicon and double-metal CMOS technology. Low-power sense amplifiers and comparators limited power dissipation to 0.5 W at 40 MHz     

Effect of chemical structure of monoamide resins on adsorptivity to uranium(VI) in nitric acid media

For the development of resins with selectivity for uranium(VI) in nitric acid media, some silica-supported monoamide resins with different chemical structures have been newly synthesized and the adsorptivities to U(VI) in HNO₃ have been examined based on our previous results that the chemical structure of monoamide resins might largely affect their adsorptivities to U(VI). The resin consisting of N-vinyl-2-pyrrolidone was found to show relatively strong adsorptivity to U(VI) in the wide concentration range of HNO₃ and little dependence on them. On the other hand, the adsorptivity to U(VI) of the resin with methylacetamide showed dependence on HNO₃ concentrations such as dimethylacrylamide (DMAA) resins which were previously studied, whereas the affinity to U(VI) was smaller than those of DMAA resins. According to the probable adsorption mechanism of U(VI) onto monoamide resins that two oxygen atoms of the two amide groups coordinate to U(VI), the adsorption data suggest that the adsorptivity of monoamide resins is strongly affected by the ‘chelating effect’, namely there are some optimum numbers of the atoms participating in the chelating formation.