Surgical procedures to correct malformations of the external auditory canal are associated with the risk of facial nerve injury. We operated on a 6-year-old boy with a stenotic external auditory canal using a Viewing Wand (ISG Technologies Inc., Mississauga, Ontario, Canada) for improved visualization. We present our experience using this imaging system for aural surgery.
This paper presents the application of a modular multilevel cascade converter based on single-delta bridge cells (SDBCs) to a STATic synchronous COMpensator (STATCOM), particularly for negative-sequence reactive-power control. The SDBC is characterized by cascade connection of multiple single-phase H-bridge (or full bridge) converter cells per leg, thus facilitating flexible circuit design, low-voltage steps, and low-electromagnetic-interference emissions. This paper designs, constructs, and tests a 100-V 5-kVA pulsewidth-modulated STATCOM based on the SDBC, with focus on the operating principle and performance. Experimental results verify that it can control not only positive-sequence reactive power but also negative-sequence reactive power and low-frequency active power intended for flicker compensation of arc furnaces.
This paper presents theoretical and experimental discussions on low-voltage-ride-through (LVRT) operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. As the penetration of distributed generation from renewable energy sources connected to medium- and high-voltage grids increases, grid-tied inverters progressively need to abide to stricter grid codes, which demand measures to maintain reliability of the grid. The latest grid codes require inverters in generation systems to provide dynamic grid support in the event of grid faults by injection of a reactive current. This paper discusses two unique solutions for an SDBC inverter to enable dynamic grid support. One method is to inject a zero-sequence current through feedforward control within the inverter, and the other is by utilizing power from the distributed dc-dc converters. No negative-sequence current is injected into the grid in both cases. This paper also highlights the issue of voltage-sag transformation through delta-wye transformers and its effect on the LVRT capability of the SDBC inverter. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through symmetric and asymmetric voltage sags.
A self-commutated BTB(Back-To-Back) system for the purpose of achieving power flow control and/or frequency change in transmission systems has attractive features of reliable and continuous operations even under power fault conditions. However, an overvoltage appearing across the dc link during the fault conditions should be suppressed as small as possible because it does affect the voltage ratings of power devices.This paper proposes a new control method for effectively suppressing the overvoltage under power fault conditions. This method based on a combination of feedback and feedforward controls is characterized by compensation of power flow imbalance between two power converters. The validity of both the proposed method and the developed theory is confirmed by computer simulation.
This paper presents the system design, operation and enhanced switching strategy of a three-phase bidirectional isolated dc-dc converter (3P-BIDC). The paper discusses the operating modes of the 3P-BIDC using phase-shift modulation (PSM), with analysis on its soft-switching characteristics. The phase-shift modulation is the simplest modulation technique that can be applied to the 3P-BIDC. However, it comes with the consequences of low efficiency performance in the low-load conditions. Therefore, this paper investigates the improvement in efficiency of the 3P-BIDC during low-load condition using an enhanced switching strategy combining burst-mode switching and phase-shift modulation. The model of a 700-V, 100-kW, 20-kHz 3P-BIDC and the enhanced switching strategy are verified via simulation using PSCAD. The simulation results shows that the combination of burst-mode and phase-shift modulation technique improves the efficiency of the 3P-BIDC at low-load conditions.
This paper presents a 4 kW 400 kHz voltage source inverter for induction heating applications, which is characterized by power control based on PDM (pulse density modulation). The pulse density modulated inverter makes an induction heating system simple and compact, thus leading to higher efficiency. The modulation strategy is proposed to realize an induction heating system capable of operation at the frequency and power level of interest. Some experimental results are shown to verify the validity of the concept.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This article designs, builds, and tests the 850-V 100-kW 16-kHz bidirectional isolated dc-dc converter using the latest 1.2-kV 400-A SiC-MOSFET/SBD H-bridge modules, with focus on efficiency improvement. Here, SBD stands for Schottky barrier diode. It proposes intermittent operation with continuous-current mode (CCM), to reduce switching losses in partial loads. Experimental results verify that the conversion efficiency from the dc input to the dc output is as high as 99.3% at the rated power of 100 kW, and 99.2% at a partial load of 10 kW. These are measured and calculated, discarding auxiliary power losses of 82W in total, which are produced by the digital controller, gate-drive circuits, and cooling fans. Experimental transient waveforms show that no dc magnetic flux is included in the 850-V 100-kW 16-kHz transformer at intervals of switchover between the continuous operation and the CCM intermittent operation when power reversal from -100 to 100 kW is performed at an interval of 1 ms. Finally, this article presents an experimental and theoretical discussion on the voltage ripples appearing across the dc capacitor of each bridge.
The field-oriented control, or the vector control, has emerged as a powerful tool for controlling squirrel-cage induction motors. The dynamic performance, however, depends on the controllability of the stator currents.
Harmonic interference problems generated by bulk semiconductor power converters become more serious in power systems as they are widely used in industrial applications. Shunt passive filters consisting of LC tuned filters or shunt active filters using PWM inverters have been used to suppress harmonic currents in distribution systems. In order to install the passive or active filters, it is necessary to exactly find a dominant harmonic source in distribution feeders. A harmonic power on each phase and order at a receiving terminal has been investigated by using a digital power meter including an FFT analyzer. However, the conventional detection method has such a problem that it is difficult to exactly discuss harmonic power flow because the detected harmonic power is much smaller compared with a fundamental active power at the receiving terminal. In this paper, the harmonic power in three phases, which can be detected on real time, is defined by applying the pq theory. Next, it is verified by a digital simulation that the proposed method can discuss harmonic flows more easily than the conventional method. As a result, it is more simple and precise to find the harmonic source. Moreover, measurement errors of the harmonic power is revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation.
This paper deals with a dynamic voltage restorer (DVR), or a voltage-sag compensator, which consists of a set of series and shunt converters connected back-to-back, three series transformers, and a dc capacitor installed on the common dc link. The DVR is characterized by installing the series converter on the source side and the shunt converter on the load side. This system configuration allows the use of an extremely small dc capacitor intended for smoothing the common dc-link voltage. This paper provides a design procedure of the dc capacitor under a voltage-sag condition, and proposes a control method for the series converter, which is capable of reducing the voltage ratings of both the series converter and the series transformers. Experimental results obtained from a 200-V, 5-kW laboratory system are shown to confirm the validity of the design procedure, and the effectiveness of the control method.
This paper presents a transient analysis of a unified power flow controller (UPFC), and design of capacitance of the DC-link capacitor. Active power flowing out of the series device in transient states is theoretically discussed to derive what amount of electric energy the DC link capacitor absorbs or releases through the series device. As a result, it is clarified that the active power flowing out of the series device is stored in the line inductance as magnetic energy during transient states. Design of capacitance of the DC-link capacitor is also presented in this paper, based on the theoretical analysis. Experimental results obtained from a 10-kVA laboratory setup are shown to verify the analytical results.
With remarkable progress of switching devices, the switching frequency of a voltage-source PWM inverter has been higher and higher. A high frequency PWM inverter gives great benefits in reduction of current ripples and acoustic noises. However, high frequency hard switching causes the increase of switching losses and EMI to be solved.The authors propose a zero-current-switching based three-phase PWM inverter which has small resonant circuits on the ac side. The current flowing in a switching device is a sum of the resonant current and the load current. Since the switching device is turned on and off at zero current, the switching losses and electromagnetic noises are greatly reduced. This paper describes the principle of the zero current switching operation, the design of the resonant circuits and the control scheme for the new soft switching inverter. Moreover, it shows interesting experimental results obtained by the zero-current-switching PWM inverter which drives an induction motor of 2.2kW.
In most cases, nystagmus develops as a physiological or pathological reflex. However, cases of voluntary nystagmus have been reported.A 14-year-old boy complained of several attacks of dizziness with nausea. He could induce voluntary nystagmus and demonstrated this to us. Since 9 year of age he has been able to induce nystagmus in frontal gazing. His nystagmus was pendular jerky. Amplitude was 5-10 degree and the frequency was 6-7 Hz. Nystagmus could be sustained for more than 1 minute. The nystagmus did not diminish and was not limited by fatigue. We observed no nystagmus in gazing. Neither positional nystagmus nor positioning nystagmus was noted. Although the horizontal eye movement was slightly saccadic, the vertical eye movement was smooth. Optokinetic nystagmus was not well developed and showed partial inversion. Convergence was possible and latent nystagmus was not observed. Nystagmus as assessed by a caloric test was well developed. No abnormal neurological findings were indicated and MRI imaging revealed no lesion.Since William's first study was reported in 1865, many cases of voluntary nystagmus have been documented. Voluntary nystagmus is usually described as being of a high frequency and low amplitude. The duration is brief, less than 30 seconds, and limited by fatigue. In most cases, nystagmus is pendular and is sometimes jerky.We divide cases of voluntary nystagmus, which were examined by an optokinetic nystagmus (OKN) test, into two groups. One group showed a normal OKN pattern, which was described as typical voluntary nystagmus, and the other group showed an abnormal OKN pattern similar to congenital nystagmus. Our case was classified in the abnormal OKN group. In this case, nystagmus which is usually latent develops when the patient cannot control his eye movements or when he does so voluntarily.
This paper considers the transient performance and stability of a recurrent DFT-based control method for a series active filter integrated with a 12-pulse diode rectifier. The control method targets specific harmonics and/or the negative sequence fundamental component of the supply current and is intended for use with non-sinusoidal/unbalanced supply voltages. The proposed control method is based on DFTs instead of the dq-method and a simple approach is used to account small frequency variations found in practical power systems.
IgA nephropathy (IgAN) is the most common form of chronic glomerulonephritis with IgA deposits present mainly in the mesangial areas. We performed a 10-year retrospective case-control study of 71 patients with IgAN to evaluate the long-term effects and prognostic factors associated with tonsillectomy. Forty-one patients (19 males and 22 females) underwent tonsillectomy (Group A) and 30 patients (13 males and 17 females) did not (Group B). These patients were followed for more than 10 years after renal biopsy. The average age at initial renal biopsy was 29.78 years in Group A and 33.0 years in Group B. The average follow-up period was 13 years and 3 months in Group A, and 12 years and 7 months in Group B. Glomerular damage demonstrated on renal biopsy was more extensive in Group A than in Group B. Prognosis after 10 years of follow-up was compared between the two groups. The clinical remission rate was 24.4% in Group A and 13.3% in Group B, the stable renal function rate was 82.9% in Group A and 70.0% in Group B, and the renal survival rate was 95.1% in Group A and 73.3% in Group B. The renal survival rate in Group A was significantly higher than that in Group B (p <0.05). Although evaluation of renal pathology based on renal biopsy was useful in predicting the long-term effects of tonsillectomy in IgAN patients, the results of tonsillar provocation tests were not.
No abstract is provided for this article.
No abstract is provided for this article.
This paper describes a position sensorless brushless dc motor drive system, in which an interior permanent magnet (IPM) motor is used as a synchronous motor. It is characterized by the position-sensing technique based on current detection of the free wheeling diodes. A three-phase voltage-source inverter with the conducting interval of 120 degrees in each phase is employed in the drive system. Reluctance torque plays an important role in producing torque of the IPM motor, having q-axis inductance larger than d-axis inductance, so that the control of id=0 can not achieve the highest motor efficiency.The characteristic analyses of the position detection and the commutation overlapping angle are done, in which the saliency of the motor and harmonics of the back electromotive force are taken into consideration. It is shown that the detection angle and the commutation leading angle tend to lead with increase of the load torque, while the phase angle of the fundamental armature current lags by half of commutation overlapping angle. As the result, the total leading angle of the fundamental armature current exists near the optimal one which can attain the highest efficiency. The experimental results shows that higher efficiency is achieved at the rated speed without special phase angle control in relation to the load torque.
