717 publications from this institution
Solving a short mileage and a long charging time is indispensable to putting electrical vehicles (EVs) on the full-scale market. A moving wireless power transfer (WPT) system is one of the effective solutions, because it can feed electric power to moving EVs. This paper proposes a moving WPT system consisting of several stationary ground-side (primary) coils and a moving vehicle-side (secondary) coil. This system is characterized by the use of the common vehicle-side coil to both moving and stationary WPT situations. Theoretical analysis concludes that the moving WPT system resulting from a stationary WPT system is the same in equivalent circuit as the stationary system. The moving WPT system employs solenoid coils that are superior to circular coils in terms of misalignment and flux-distribution performance. A downscaled moving WPT system rated at 3 kW is designed, constructed, and tested to verify the principles of operation, and the capability of continuous power transfer.
For the treatment of nasopharyngeal carcinomas, radiotherapy with or without adjunctive chemotherapy has been generally accepted as the first choice. However, recent advances in skull base surgery and imaging diagnosis have extended the indications for surgical intervention in the treatment of recurrent or residual carcinomas.Although there are several approaches to nasopharyngeal surgery, such as the transpalatal, transmaxillary, transpterygoid, transmandibular-transcervical and infratemporal fossa approaches, Mann et al recently developed the anterolateral transfacial approach.We operated on a 57-year-old male with recurrent nasopharyngeal carcinoma using this approach. This approach is characterized by temporary removal of the malar complex and resection of the coronoid process and pterygoid plates to achieve an excellent view of the nasopharynx and retromaxillary f ossa. This approach has the cosmetic advantage of preserving facial contouring by using the malar complex as a free bone graft, as well as the functional advantage of maintaining mouth opening by rehabilitation of mandibular movement. This approach is thought to be a valuable procedure for resection of nasopharyngeal carcinomas.
This paper focuses on fault-tolerant control for a battery-energy-storage system based on a multilevel cascade pulsewidth-modulation (PWM) converter with star configuration. During the occurrence of a single-converter-cell or single-battery-unit fault, the fault-tolerant control enables continuous operation and maintains state-of-charge balancing of the remaining healthy battery units. This enhances both system reliability and availability. A 200-V, 10-kW, 3.6-kW·h laboratory system combining a three-phase cascade PWM converter with nine nickel-metal-hydride battery units is designed, constructed, and tested to verify the validity and effectiveness of the proposed fault-tolerant control.
This paper describes a 6.6-kV adjustable-speed motor drive for pumps and blowers without transformer. The power conversion system consists of a front-end diode rectifier, a five-level diode-clamped PWM inverter with a voltage-balancing circuit, and a hybrid active filer for harmonic-current mitigation of the diode rectifier. A 200-V 5.5-kW downscale model is designed, constructed and tested with focus on the five-level PWM inverter. Experimental results obtained from the 200-V downscale model verify the viability and effectiveness of the 6.6-kV adjustable- speed motor drive, showing that the four split dc capacitors are well balanced in all the operating conditions with improvements of operating performance at low inverter modulation indices.
This paper presents a modular push-pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium- or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms based on a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, focusing on voltage balancing of all the floating dc capacitors. Moreover, a comparison is made between the MPC and a modular multilevel converter (MMC), under an assumption that both are used as the same battery energy storage system. The validity of the operating performance and control method is confirmed by both computer simulation using the "PSCAD/EMTDC" software package and experiment using a three-phase, 200-V, 5-kW downscaled model.
No abstract is provided for this article.
This paper describes the study results of the inverters running in parallel. In the consideration of the operation algorithm, it is important to reveal output impedance characteristics of the inverters. First, simulation results demonstrate that the output impedance depends on the control scheme of the output voltage and characteristics of the circulating current that flows through the inverter differs. Next, as examples, two control schemes and their experimental results are demonstrated. The two schemes are: “PQ droop method” based control and “common current distribution method” based control. In the both case, since the output impedance is resistive, the phase of the output voltage is adjusted by using the reactive component of the circulating current. The amplitude of the output voltage is not manipulated. In the latter control system, quantity of the output-current feedback changes with the output impedance. This characteristic clarifies that the output impedance among the inverters becomes higher and the output impedance of the loads gets smaller. Moreover, suppression of the circulating current and excellent output voltage characteristics can be maintained.
Harmonic interference problems generated by bulk semiconductor power converters become more serious in power systems with their wide use 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. To install the passive or active filters, it is necessary to find exactly 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 a problem in that it is difficult to discuss exactly 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 are revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation.
The conventional reactive power in single-phase or three- phase circuits has been defined on the basis of the average value concept for sinusoidal voltage and current waveforms in steady states. The instantaneous reactive power in three-phase circuits is defined on the basis of the instantaneous value concept for arbitrary voltage and current waveforms, including transient states. A new instantaneous reactive power compensator comprising switching devices is proposed which requires practically no energy storage components.
This article presents an advanced method for power-loss breakdown of a high-power bidirectional isolated dual-active-bridge (DAB) dc-to-dc converter using SiC-<small>mosfet</small>/SBD H-bridge modules. This method is so simple and practical as to extract a switching loss from accurately measured overall losses. A test bench designed and built in this article is characterized by cascading the two identical 750-V 100-kW 16-kHz DAB converters equipped with the two identical unity-turns-ratio transformers. The test bench allows power-loss breakdown at buck and boost operation. When a dc-input voltage of 750 V is different from a dc-output voltage of 850 V at 100 kW and 16 kHz, “hybrid” phase-shift control makes the overall power loss lower by 158 W than “pure” phase-shift control.
No abstract is provided for this article.
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.
No abstract is provided for this article.
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 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.
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.
