This paper presents a five-level diode-clamped pulse width-modulated (PWM) inverter intended for a medium-voltage motor drive with a constant-torque load but no regenerative braking. It is applicable to drilling rigs, extruders, and rubber mixers. The power conversion system consists of a three-phase six-pulse diode rectifier, a five-level diode-clamped PWM inverter, and a dc- voltage-balancing circuit including a single coupled inductor. The five-level inverter is characterized by injecting a common ninth-harmonic zero-sequence voltage on each of the three-phase reference voltages in a low-modulation-index region. This injection contributes not only to mitigating magnetic-flux fluctuation of the coupled inductor but also to making uniform the power losses produced by eight insulated-gate bipolar transistor modules per leg. In addition, the dc-voltage-balancing circuit introduces a control method capable of reducing an amplitude of magnetic flux of the coupled inductor. The combination of this control method and the ninth-harmonic zero-sequence voltage injection keeps the peak value of the magnetic flux within its designed value.
This paper describes the design, construction, and testing of a 750-V 100-kW 20-kHz bidirectional isolated dual-active-bridge dc-dc converter using four 1.2-kV 400-A SiC-MOSFET/SBD dual modules. The maximum conversion efficiency from the dc-input to the dc-output terminals is accurately measured to be as high as 98.7% at 42-kW operation. The overall power loss at the rated-power (100 kW) operation, excluding the gate-drive and control circuit losses, is divided into the conduction and switching losses produced by the SiC modules, the iron and copper losses due to magnetic devices, and the other unknown loss. The power-loss breakdown concludes that the sum of the conduction and switching losses is about 60% of the overall power loss and that the conduction loss is nearly equal to the switching loss at the 100-kW and 20-kHz operation.
This paper discusses a 6.6-kV transformerless STATCOM intended for installation on industrial and utility distribution systems in the near future. In addition, this paper provides experimental results obtained from a laboratory model rated at 200V and 10kVA. The authors propose such a control method as to superimpose a 6th-harmonic zero-sequence component on each of three-phase voltage references. This helps to stabilize the voltage of the inner midpoint in the dc link. As a result, the laboratory model installs two bi-directional buck-boost choppers on the dc link for the porpose of stabilizing the voltages of two outer midpoints. Experimental results obtained from the laboratory model verify the validity of the system design, giving promise of the viability of the 6.6-kV transformerless STATCOM.
This paper proposes a drive system for a three-phase hybrid stepping motor, combining sensorless closed-loop control with conventional open-loop control. It is characterized by sophisticated control providing both prevention of pulling out from synchronism and suppression of natural rotor oscillation, without any position sensor attached to the motor shaft. A switching technique in chopper control which can enlarge the speed range controllable in the sensorless closed-loop control is described. Starting and stopping sequences are developed to reduce mechanical natural oscillation produced in the transient state. Finally, the proposed drive system is compared experimentally with a conventional constant-current open-loop drive system. It is shown that the proposed drive system can perform the switchover from starting to sensorless closed-loop operation within 20 ms, and can reduce the natural oscillation caused just after positioning. © 2000 Scripta Technica, Electr Eng Jpn, 131(3): 80–90, 2000
This paper proposes a practical approach to suppressing both shaft voltage and leakage current in an ac motor driven by a voltage-source PWM inverter. This approach is characterized by using a neutral line of the ac motor. A common-mode inductor is connected between the inverter and the motor. Moreover, a resistor and a capacitor are connected in series between the motor neutral point and the inverter negative dc bus. This unique circuit configuration makes the common-mode inductor effective in reducing the common-mode voltage appearing at the motor terminals. As a result, both shaft voltage and ground current are significantly suppressed with low cost. Over-voltages at the end of a cable can be suppressed by a normal-mode inductor and a resistor which are connected in parallel. The validity and effectiveness of the new approach are verified by experimental results from a 5-kVA laboratory system.
This paper provides an experimental discussion on a real-time real-power emulator for a medium-voltage, high-power, high-speed motor drive. This emulator is characterized by integrating mechanical dynamics of both motor and load into it. The power-electronic circuit of the emulator consists of a three-phase modular multilevel double-star chopper-cell (DSCC) rectifier, three inductors, and a single two-winding common-mode inductor. This paper designs, builds, and tests a 400-Vdc 10-kW downscaled test bench in which a three-phase DSCC inverter under test is connected in front-to-front (FTF) with the emulator. The DSCC inverter is the same in circuit configuration as the DSCC rectifier. Experimental waveforms obtained from the downscaled test bench lead to the following conclusion: The emulator can reproduce both electrical and mechanical dynamics of a three-phase 200-V, 10-kW, four-pole, 9 000-r/min induction motor coupled with a centrifugal compressor.
No abstract is provided for this article.
This paper presents a dynamic voltage restorer (DVR) that is characterized by the use of a high-frequency unidirectional isolated dc-dc converter. A traditional DVR has a large and bulky series transformer even for low-voltage (200 or 400 V) applications because the transformer operates at the line frequency (50 or 60 Hz). The emergence of the state-of-the-art semiconductor devices and magnetic cores has driven power electronics engineers to develop compact high-frequency isolated dc-dc converters. This paper discusses control and performance of a DVR including a high-frequency isolated dc-dc converter intended for 200 or 400-V applications. The high-frequency (20 kHz) transformer in the dc-dc converter is much smaller, say one-hundredth, in volume than the line-frequency transformer. Moreover, connecting the shunt converter to the load side brings a significant reduction in energy-storage capacity to the DVR. Experimental results obtained from a 200-V 5-kW laboratory system confirm the viability and effectiveness of the system configuration.
This paper presents theoretical and experimental relationships in between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source PWM inverter. A method of reducing both the currents is proposed, based on an equivalent model taking parasitic stray capacitors inside an induction motor into account. Electromagnetic interference (EMI) radiated by a 3.7 kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3m]. Experimental results verify that the combination of the already proposed common-mode transformer and the normal-mode filters being proposed in this paper is a practically viable and effective way to reduce the EMI resulting from both the common-mode and normal-mode currents.
This paper describes position-sensorless control of an interior permanent magnet synchronous motor (IPM motor), which is characterized by real-time position estimation based on magnetic saliency. The real-time estimation algorithm proposed in this paper determines the inductance matrix including rotor position information from current harmonics produced by switching operations of an inverter driving the IPM motor, and then estimates the rotor position every period of pulse-width modulation (PWM). Position estimation without any special signal injection is achieved with a satisfactory response and accuracy even at a standstill and at low speed. An experimental system consisting of an IPM motor and a voltage-source PWM inverter has been implemented and tested to confirm the effectiveness and versatility of the approach. Some experimental results show that the experimental system has the function of electrically locking the loaded motor, along with a position response of 20 rad/s and a settling time of 300 ms. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 68–79, 2000
We describe a boy with a deletion of the short arm of chromosome 3; (46, XY, del (3) (p25-pter) who presented several minor craniofacial anomalies at birth. Only 34 cases of small distal 3p deletion have been described in the literature, seven of them showed hearing loss and four of the 34 cases had brain anomalies. But in none of the 34 cases the middle and internal ear were radiographically examined. Despite the severe hearing loss detected by auditory brainstem evoked responses (ABR), computerized tomographic scanning (CT-scan) of the ear showed a normal anatomy in this patient. The head CT-scan and magnetic resonance imaging (MRI) disclosed a hypoplastic corpus callosum and an enlargement of the lateral ventricles.
This paper describes a hybrid active filter intended for mitigating the line-side harmonic currents of a three-phase 12-pulse diode rectifier used as the front end of a medium-voltage high-power motor drive. This hybrid filter is characterized by series connection of a simple LC filter and a small-rated active filter. This circuit configuration brings low cost, small size, and light weight to the hybrid filter. A three-phase experimental system rated at 400 V and 15 kW is designed, constructed, and tested, which is a downscaled model of the medium-voltage motor drive system. In this experiment, the LC filter is tuned to the 11th-harmonic frequency, and the active filter is based on a three-level neutral-point-clamped pulsewidth modulation converter (NPC PWM) with a dc capacitor voltage as low as 28 V. This hybrid filter is connected on either first or fourth winding of a line-frequency transformer with a first Δ-winding voltage of 400 V in the primary, and a second Δ-winding voltage of 220 V, a third Y-winding voltage of 220 V, and a fourth Δ-winding voltage of 400 V in the secondary. Experimental results show that the hybrid filter performs satisfactory filtering in a range from no-load to full-load conditions.
In this article, a simple and effective method for reducing the supply current harmonics has been proposed for a parallel connected 12-pulse thyristor converter with an interphase reactor. The proposed method requires only an interphase reactor with an optimal inductance value being much smaller than conventional inductance values, without any additional devices or components. The supply current waveform of the 12-pulse thyristor converter with the optimal interphase reactor is more sinusoidal than that of a 36-pulse thyristor converter. The proposed design concept of the interphase reactor has been discussed, and confirmed by using digital computer simulation. An experimental system has been constructed and tested, and the experimental results have verified the practicability and effectiveness. The authors conclude that the proposed concept provides a clean power utility interface for various industrial/utility applications including superconducting energy storage systems (SMES).
No abstract is provided for this article.
Ameloblastoma originates from the dental tissue and is generally regarded as a benign tumor although it often recurs and sometimes becomes malignant. The choice of treatment is very impor-tant in this disease. The incidence of relapse in patients treated surgically has been reported to be fewer than that in patients treated by conservative methods. Even when this tumor had been removed radically however, the possibility of recurrence remains.In this paper, a 56-year-old male with recurrent ameloblastoma is reported. The patient under-went hemimandibulectomy and an ameloblastoma was resected in 1971. The postoperative course was good.In 1995, however, he complained of swelling in the left gingiva and was referred to our hospital. On physical examination, a hard, reddish tumor located on the lateral side of the left gingiva was revealed. CT and MRI showed that the tumor was located in the left inf ratemporal f ossa, and that it grew from the bone remaining after the previous surgery. The tumor was regarded as a recurrent ameloblastoma and was removed surgically by means of Weber's incision. Histological examination confirmed a diagnosis of ameloblastoma of the follicular type. There has been no sign of recurrence 10 months after surgery.
