Visualization of high‐speed phenomena using an acousto‐optic laser deflector

An acousto‐optic laser deflector was used for visualization of high‐speed phenomena, such as shock waves and density perturbations accompanying an impulse discharge, or shock waves generated by laser‐induced breakdown in air. Using a continuous wave laser as the light source, shadowgraphs of shock waves and density perturbations were obtained at shutter speeds down to 1µs. Results showed that shock waves propagated at a speed of 417 m/s in the case of an impulse discharge, and 485 m/s in the case of laser‐induced breakdown. Prebreakdown phenomena such as leaders progressing from the high‐voltage electrode were also visualized. Compared to conventional high‐speed imaging techniques, this method is useful when using a laser light source, since the acousto‐optic crystal can accommodate high‐intensity laser light. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 9–15, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20279     

Novel current‐source multilevel inverter driven by single gate drive power supply

This paper proposes a novel current‐source multilevel inverter, which is based on a current‐source half‐bridge topology. Multilevel inverters are effective for reducing harmonic distortion in the output voltage and the output current. However, the multilevel inverters require many gate drive power supplies to drive switching devices. The gate drive circuits using a bootstrap circuit and a pulse transformer can reduce the number of the gate drive power supplies, but the pulse width of the output PWM waveform is limited. Furthermore, high‐speed power switching devices are indispensable to create a high‐frequency power converter, but various problems, such as high‐frequency noise, arise due to the high dv/dt rate, especially in high‐side switching devices. The proposed current‐source multilevel inverter is composed of a common emitter topology for all switching devices. Therefore, it is possible to operate it with a single power supply for the gate drive circuit, which allows stabilizing the potential level of all the drive circuits. In this paper, the effectiveness of the proposed circuit is verified through experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 88–95, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20475     

Design of A Soft X‐ray Source with Periodic Microstructure Using Resonance Transition Radiation for Tabletop Synchrotron

A soft X‐ray source with a periodic aluminum multilayer structure with vacuum layers in between for tabletop synchrotrons with low‐energy electrons was designed, and the dependence of radiation performance on structural parameters was clarified using a theoretical calculation of the resonance transition radiation. A photon density of 1 keV pr incident electron was calculated by optimizing the thickness of the aluminum and vacuum layers. Furthermore, the designed structure was fabricated by a microfabrication technique. The effects of dimensional error on the photon density are discussed on the basis of the calculated results and the prototype structure of a 6‐MeV synchrotron. It is clarified that dimensional errors of 1.5% in Al layers and of plus or minus a few dozen nanometers in the vacuum layers are negligible in obtaining a photon density of more than 90% of the maximum value. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Current‐fed isolated PFC pre‐regulator for multiple LED lamps with extended lifetime

To emit high‐quality LED light, one or a bin of LED lamp(s) is normally driven by a PWM‐controlled constant current source to minimize device variation and achieve accurate brightness control. Powered from offline AC mains, the front‐end power converters should provide a relatively low DC voltage bus for the inputs of post‐end LED current regulators. To match the long lifetime of LEDs, the whole LED driver (ballast) should work as durably as the LEDs. However, the lifetime of the driver is usually limited by the high‐voltage electrolytic charge storage capacitors used in conventional PFC pre‐regulators. In this paper, our previously proposed resonant current‐fed isolated PFC pre‐regulator is extended to operate in discontinuous conduction mode (DCM). It allows the use of the low‐voltage storage capacitors on the transformer secondary, and therefore extends the overall lifetime of the LED lighting system. A detailed procedure for finding the expected lifetime of the low‐voltage electrolytic capacitor is given. As before, the high‐voltage stress on the main switches, which is typical in current‐fed isolated converters, is reduced substantially by taking advantage of the transformer leakage inductance necessary for resonance. Additionally, high efficiency is ensured by the use of dual non‐cascading structures. Steady‐state state‐space averaging analysis is performed for designing the converter in DCM operation. A prototype converter is built to verify performance of the proposed PFC LED pre‐regulator. Copyright © 2011 John Wiley & Sons, Ltd.     

Carrier‐envelope phase‐stabilized chirped‐pulse amplification system

We demonstrated a carrier‐envelope phase (CEP) stabilized chirped‐pulse amplifier system. This amplifier system is composed of grating based pulse‐stretcher and compressor, a regenerative amplifier and a multi‐pass amplifier. We employed a new pulse‐pick‐up method to select CEP stabilized seed pulses. This pulse selection method is different from established practice which is based on pulse train timing, but is based on CEP of seed pulse. We measured amplitude‐to‐phase noise conversion coefficient of microstructure fiber and evaluated the additional out‐of‐loop error of carrier‐envelope offset (CEO) control. We also investigated the effect of beam pointing of the measured fringe shift in self‐referencing spectral interference method. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 35–42, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20334 Copyright © 2006 Wiley Periodicals, Inc.     

Electron‐beam‐pumped light sources using graphite nanoneedle field emitters and Si electron‐transparent films

Sputter‐induced carbon nanoneedle field emitters and Si electron‐transparent films have been developed for electron‐beam‐pumped light sources. The sputter‐induced carbon nanoneedle field emitters exhibited a stable electron emission of 0.1 mA at an average field of 13 V/µm. The 1.5‐µm thick Si electron‐transparent films achieved an electron transmittance of about 60% at an acceleration voltage of 27 kV. An electron‐beam‐pumped light source was demonstrated from the excitation of N₂ gas, and a N₂ gas spectrum was clearly observed. The increase of the beam current is important for increasing the light intensity. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A 0.008‐mm2, 35‐μW, 8.87‐ps‐resolution CMOS time‐to‐digital converter using dual‐slope architecture

This paper presents a high resolution time‐to‐digital converter (TDC) for low‐area applications. To achieve both high resolution and low circuit area, we propose a dual‐slope voltage‐domain TDC, which is composed of a time‐to‐voltage converter (TVC) and an analog‐to‐digital converter (ADC). In the TVC, a current source and a capacitor are used to make the circuit as simple as possible. For the same reason, a single‐slope ADC, which is commonly used for compact area ADC applications, is adapted and optimized. Because the main non‐linearity occurs in the current source of the TVC and the ramp generator of the ADC, a double gain‐boosting current source is applied to overcome the low output impedance of the current source in the sub‐100‐nm CMOS process. The prototype TDC is implemented using a 65‐nm CMOS process, and occupies only 0.008 mm². The measurement result shows a dynamic range with an 8‐bit 8.86‐ps resolution and an integrated non‐linearity of ±1.25 LSB. Copyright © 2016 John Wiley & Sons, Ltd.     

High‐repetition‐frequency short pulses in a VHF discharge‐excited slab‐type carbon dioxide laser using an ultrasonic vibrator

We propose a novel method for producing high‐repetition‐frequency short pulses with a halved confocal configuration consisting of an unstable concave–convex resonator in a very high frequency (VHF) discharge‐excited slab‐type carbon dioxide laser. This method utilizes a fully reflective concave mirror with variable curvature which can be controlled by a piezoelectric device. In general, slab lasers are modulated directly by varying the pulse voltage. However, because plasma fluctuation occurs at the pulse transitions, the repetition frequency is less than 10 kHz and the minimum pulse width is 1 µs. On the other hand, in our method there is no disturbance of the plasma, because the power source is not modulated. There is also little mechanical constraint, because we use a piezoelectric device. As a result, pulse shortening with a high repetition rate is possible. The pulse shape is well reproduced by a three‐level rate equation. The mechanism of the method involves changes in ejection efficiency with periodic variation of the radius of curvature of the mirror. Good agreement between observations and calculations was also obtained for the peak power and the pulse width. In this paper we compare measurements with calculations. The possibility of achieving high repetition rate oscillation and pulse shortening by this method is examined. The results confirm the possibility of achieving a repetition frequency between 1.4 kHz and 170 kHz. The shortest pulse width that can be achieved is 160 nanoseconds. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 1–7, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10127     

Newly proposed hybrid resonant commutation bridge‐leg link snubber‐assisted three‐phase ZVZCS‐PWM soft‐switching inverter

This paper presents the newly proposed hybrid resonant commutation bridge‐leg link (HRCB) snubber circuit which can achieve zero voltage and zero current soft‐switching commutation for single‐phase and three‐phase voltage source‐type inverter, along with its unique features and operation principle. The circuit parameter design approach for the HRCB snubber circuit and the determination estimating scheme of the gate pulse timing processing which is more suitable and acceptable for single‐phase and space voltage vector modulated three‐phase voltage source inverter using the HRCB snubber circuit are described in this paper. In particular, the three‐phase voltage source soft‐switching inverter associated with the proposed HRCB circuits are evaluated and discussed from simulation and experimental viewpoints. The practical effectiveness of the HRCB snubber‐assisted three‐phase voltage source soft‐switching inverter using IGBT power modules which is based on the instantaneous space voltage vector modulation is clarified on the output voltage waveform, actual efficiency of electromagnetic noise in comparison with three‐phase voltage source‐type conventional hard‐switching inverter. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 75–84, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20111     

Space vector pulse‐width modulation for single‐phase full‐bridge Z‐source inverter

The space vector pulse‐width‐modulation technique is extensively applied in the three‐phase power electronics circuits because of its easy digital implementation and wide linear modulation range features. However, the attempt of this technique for the single‐phase Z‐source inverter has seldom been reported because of its unique topology and operational characteristics. In this paper, based on an in‐depth mathematical derivation and theoretical explanation, the space vector pulse‐width‐modulation principles have been discussed in detail. Various implementation schemes are demonstrated, and a comparison study for selected switching patterns is conducted. In addition, the theoretical analysis is validated by both the simulation and experimental results. This work will be helpful for understanding the space vector pulse‐width‐modulation concept and modulation techniques of the single‐phase full‐bridge Z‐source inverters. Copyright © 2013 John Wiley & Sons, Ltd.     

A three‐phase constant‐current source using an immittance converter

The term immittance converter refers to an impedance–admittance converter. The immittance converter has an input impedance that is proportional to the admittance of the load connected across output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant‐voltage source into a constant‐current source and a constant‐current source into a constant‐voltage source. It is well known that the quarter wavelength transmission line shows immittance conversion characteristics. However, it has a very long line length for the switching frequency, and is not suitable for power electronics applications. We thus proposed immittance converters that consist of lumped elements L, C and show improved immittance conversion characteristics at a resonant frequency. A three‐phase constant‐current source is proposed in this paper. It is possible to realize this by a simple circuit using an immittance converter. In this paper, circuit operation, characteristic equations, and results of simulation are described. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 47–54, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20078     

A study of decoupling with skeleton matrix in two‐degree‐of‐freedom generalized minimum variance control

There are many multi‐input multi‐output (MIMO) systems in chemical plants, and they have multiple time delays of different length in each input and output pair. This paper explains a two‐degree‐of‐freedom (2DOF) control system based on generalized minimum variance control (GMVC) for MIMO systems. It can improve the tracking performance with respect to the reference signals and the response properties for the disturbance. The states between the sampling period can be expressed by using the modified z transform to take account of multiple time delays. Additionally, a tracking controller is designed to decouple the plant. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 28–36, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21046     

Steady‐state solutions of a voltage source converter with dq‐frame controllers by means of the time‐domain method

A voltage source converter (VSC) is one of the most widely used power converters in a power system. In this paper, a time‐domain‐based accelerated steady‐state method is proposed to solve for a closed‐loop pulse‐width modulated (PWM) VSC with dq‐frame controllers, which is able to account for the harmonic interactions between the converter and the rest of the power network, between the AC and DC sides of a VSC, and between the converter and its controllers. The proposed time‐domain method is based on the modified time‐domain shooting method, where the Jacobian matrix is updated by the quasi‐Newtons method. This will drastically increase the computation efficiency as it avoids re‐evaluating and inverting the Jacobian matrix, whose size is usually very large for a PWM‐VSC due to high number of times of switching. All the results are shown to be consistent with those obtained by a PSCAD/EMTDC model, which has been validated with the experiment in a previous publication. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A three‐phase voltage‐source PWM inverter system characterized by sinusoidal output voltage with neither common‐mode voltage nor normal‐mode voltage

This paper deals with an inverter system integrating a small‐rated passive EMI filter with a three‐phase voltage‐source PWM inverter. The purpose of the EMI filter is to eliminate both common‐mode and normal‐mode voltages from the output voltage of the inverter. The motivation of this research is based on the well‐known fact that the higher the carrier or switching frequency, the smaller and the more effective the EMI filter. An experimental system consisting of a 5‐kVA inverter, a 3.7‐kW induction motor, and a specially designed passive EMI filter was constructed to verify the viability and effectiveness of the EMI filter. As a result, it is shown experimentally that both three‐phase line‐to‐line and line‐to‐neutral output voltages look purely sinusoidal as if the inverter system were an ideal variable‐voltage, variable‐frequency power supply when viewed from the motor terminals. This results in complete solution of serious issues related to common‐mode and normal‐mode voltages produced by the inverter. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 88–96, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10206     

A novel robust current control approach using adaptive line enhancer for three‐phase current‐source active power filter

An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014     

Automated X‐ray inspection method for fillet‐less mounted chip components

Chip components mounted on the printed circuit board are rapidly being miniaturized. Furthermore, the fillet‐less chip soldering technique, which does not use a solder fillet, is widely used in portable products such as mobile phones. However, there is no method to inspect the soldering of fillet‐less chip mounting. In this paper, we propose an automated X‐ray inspection technique for fillet‐less chip mounting. It extracts three inspection parameters from the X‐ray image. In the experiments, we evaluate the repeatability and inspecting ability of the technique and confirm that sufficient information for failure detection is obtained. An automated X‐ray inspection system using this technique is now in operation at some factories, so in conclusion our automated method would be useful in practice. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Development of a high‐speed laser interferometer using an acousto‐optic deflector

An acousto‐optic laser deflector was used as a shutter for high‐speed imaging of laser interference fringes using an ordinary CCD camera. The exposure duration was set by the pulse width of the high‐frequency signal applied to the acousto‐optic deflector. Changes in laser interference fringes due to an impulse discharge in air were obtained at an exposure duration of 4 µs. By applying a sequence of high‐frequency signals with different frequency, the beam was deflected to four different angles at different times, allowing four interference images to be captured on a single video frame. This was used for time‐resolved imaging of the interference fringe pattern. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 76–83, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20011     

Photoemission study on natural oxidation of Cu3Au with synchrotron radiation

We report the results of a study of the natural oxidation of Cu₃Au(110) with high‐resolution X‐ray photoemission spectroscopy in conjunction with synchrotron radiation. The clean surface of Cu₃Au(110) is terminated with 50% Au and 50% Cu atoms. After natural oxidation in the air, Cu atoms segregate on the surface and produce Cu‐oxide. As a result, Au atoms move into the bulk. Au atoms below the oxide reduce the diffusion of O atoms farther into bulk and limit the oxide thickness. The face dependence of natural oxidation indicates that the diffusion of Cu atoms also contributes to oxide formation. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(4): 43–47, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21149     

A novel quasi‐Z‐source indirect matrix converter

A new type of three‐phase quasi‐Z‐source indirect matrix converter (QZS‐IMC) is proposed in this paper. It uses a unique impedance network for achieving voltage‐boost capability and making the input current in continuous conduction mode (CCM) to eliminate the input filter. The complete modulation strategy is proposed to operate the QZS‐IMC. Meanwhile, a closed‐loop DC‐link peak voltage control strategy is proposed, and the DC‐link peak voltage is estimated by measuring both the input and capacitor voltages. With this proposed technique, a high‐performance output voltage control can be achieved with an excellent transient performance even if there are input voltage and load current variations. The controller is designed by using the small‐signal model. Vector control scheme of the induction motor is combined with the QZS‐IMC to achieve the motor drive. A QZS‐IMC prototype is built in laboratory, and experimental results verify the operating principle and theoretical analysis of the proposed converter. The simulation tests of QZS‐IMC based inductor motor drive are carried out to validate the proposed converter's application in motor drive. Copyright © 2013 John Wiley & Sons, Ltd.     

Noise removal for medical X‐ray images in wavelet domain

Many important problems in engineering and science are well‐modeled by Poisson noise, and the noise of medical X‐ray images is Poisson noise. In this paper, we propose a method for noise removal for degraded medical X‐ray images using improved preprocessing and an improved BayesShrink (IBS) method in the wavelet domain. First, we preprocess the medical X‐ray image. Second, we apply the Daubechies (db) wavelet transform to medical X‐ray images to acquire scaling and wavelet coefficients. Third, we apply the proposed IBS method to process wavelet coefficients. Finally, we compute the inverse wavelet transform for the threshold coefficients. Experimental results show that the proposed method always outperforms traditional methods. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 37– 46, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20486