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This article proposes a capacitor voltage ripple reduction method used for a modular multilevel cascade converter (MMCC) with single delta bridge cells (SDBC), by applying a third harmonic zero-sequence current. A practical case study on an 80 MVar/33 kV MMCC-SDBC-based STATCOM is used to demonstrate the method. The impact of the third harmonic zero-sequence current level of the capacitor ripple reduction and the electrothermal stresses on insulated gate bipolar transistor modules are analyzed. An optimal parameter of the current level is obtained by compromising the above-mentioned performance factors. The obtained result shows that the required capacitance, as well as the capacitor bank volume, is reduced by 20% without increasing the total power semiconductor losses by using the proposed method. [ABSTRACT FROM AUTHOR]

We report on a measurement of the size of charge clouds produced by X-ray photons in X-ray Silicon-on-insulator (SOI) pixel sensor named XRPIX. We carry out a beam scanning experiment of XRPIX using a monochromatic X-ray beam at 5.0 keV collimated to $\sim 10{\mathrm{ ~\mu m}}$ with a 4- ${\mathrm{ \mu m\phi }}$ pinhole and obtain the spatial distribution of single-pixel events at a subpixel scale. The standard deviation of charge clouds of 5.0-keV X-ray is estimated to be $\sigma _{\mathrm{ cloud}}=4.30\pm 0.07{\mathrm{ \,\,\mu m}}$. Compared to the detector response simulation, the estimated charge cloud size is well explained by a combination of photoelectron range, thermal diffusion, and Coulomb repulsion. Moreover, by analyzing the fraction of multi-pixel events in various energies, we find that the energy dependence of the charge cloud size is also consistent with the simulation. [ABSTRACT FROM AUTHOR]

Modular multilevel cascade converters (MMCCs) are becoming attractive solutions as high-voltage Static Synchronous Compensators (STATCOMs) for power plants in renewable energy generation, in order to satisfy the strict grid codes under both normal and grid fault conditions. This paper investigates the performances of four potentially used configurations of the MMCC family for the STATCOM in large-scale offshore wind power plants, with special focus on asymmetrical low-voltage ride through capability under grid faults. The specifications and the sizing of components of each type of practical 80-MVar/33-kV-scaled MMCC-STATCOM are carefully designed and compared. The total cost and volume are compared based on the total power semiconductor chip area and the total energy stored in the passive components. Asymmetrical reactive power delivering operation of the MMCC family considering the dc-link capacitor voltage-balancing method is solved mathematically in order to quantitatively understand the performance limitations and behaviors. The electrothermal stress of the power modules used in each type of the MMCC for a practical 80-MVar/33-kV-scaled STATCOM is analyzed. The asymmetrical reactive power capability of the MMCC solutions is compared under different scenarios of grid faults, while considering the device temperature limits as well as voltage saturation. It is found that the MMCC configuration with double-star bridge cells becomes the most attractive circuit configuration for the STATCOM application based on the obtained results. [ABSTRACT FROM AUTHOR]

In order to operate an ‘improved’ Fourier synthesis imager at higher photon energies than are accessible with solid-state detectors, we developed a new one-dimensional γ-ray position sensor consisting of inorganic scintillators whose light is read out by a silicon strip detector (SSD). The SSD is read out through stripped p-electrodes (DC-coupled, 32 channels at 400 μm pitch). The n-side of the SSD does not have a metallic surface, and has a relatively good optical transparancy. A stack of optically isolated thin CsI(TI) scintillator plates (10 mm × 10 mm in area and 0.3 mm thick) is attached, edge-on, to the n-side of the SSD. When a γ-ray photon hits the stacked scintillator, the generated scintillation light is detected by the SSD, with the signal pulse-height largest in the p-electrode which is just beneath the CsI plate hit by the γ-ray. The 32-channel outputs from the SSD are acquired simultaneously for each event with a low-noise analog ASIC. The γ-ray position can be calculated as a weighted mean of pulse heights. Using this system, we have obtained a position resolution significantly finer than 1 mm for γ-rays with energies greater than ∼500 keV up to ∼1300 keV. [ABSTRACT FROM AUTHOR]

We are developing a Compton camera based on Si and CdTe semiconductor imaging devices with high energy resolution. In this paper, results from the most recent prototype are re- ported. The Compton camera consists of six layered double-sided Si Strip detectors and CdTe pixel detectors, which are read out with low noise analog ASICs, VA32TAs. We obtained Compton reconstructed images and spectra of line gamma-rays from 122 keV to 662 keV. The energy resolution is 9.1 keV and 14 keV at 356 keV and 511 keV, respectively. [ABSTRACT FROM AUTHOR]

Employing Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the ∼ 10 keV to ∼ 200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 μm pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional "modulation collimator" grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 mm with harmonic ratios. Combining the CdTe strip detector and the grids, we have verified hard X-ray 241Am imaging performance of this system. Using an Am source, we have successfully obtained an image in the 10-70 keV range with a spatial resolution of 0.5 mm. [ABSTRACT FROM AUTHOR]

A Compton camera is the most promising approach for gamma-ray detection in the energy region from several hundred kiloelectronvolts to megaelectronvolts, especially for application in high energy astrophysics. In order to obtain good angular resolution, semiconductor detectors such as silicon, germanium and cadmium telluride (CdTe) have several advantages over scientillation detectors, which have been used so far. Based on the recent advances of high resolution CdTe and silicon imaging detectors, we are working on a SI/CdTe Compton camera. We have developed 64-pixel CdTe detectors with a pixel size of 2 mm ×2 mm and double-sided Si strip detectors (DSSDs) with a position resolution of 800 μm. As a prototype Si/CdTe Compton camera, we use a DSSD as a scatterer and two CdTe pixel detectors as an absorber. In order to verify its performance, we irradiate the camera with 100% linearly polarized 170 keV γ-rays and demonstrate the system works properly as a Compton camera. The resolution of the reconstructed scattering angle is 22 ° (full-width at half-maximum). Measurement of polarization is also reported. The polarimetric modulation factor is obtained to be 43%, which is consistent with the predcition of Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Recent results from the Schottky CdTe diode detectors employing a guard-ring (GR) electrode are reported. A cathode electrode, made of platinum, was separated into an active electrode(s) and a surrounding GR. Typical leakage current of a device with active area of 2 × 2 mm² and 0.5 mm thickness surrounded by a GR, is 7 and 20 pA at a bias of 100 and 500 V, respectively, operated at 20 ° Spectral resolution of this device is 0.93 and 1.2 keV (FWHM) at 59.5 and 122 keY, respectively, operated at 20 °C with a bias of 800 V. Detailed study of the characteristics of these devices working as a gamma-ray detector is presented. [ABSTRACT FROM AUTHOR]