717 publications from this institution
This paper describes voltage balancing of all the four split dc capacitors for a five-level diode-clamped PWM inverter intended for a transformerless mediumvoltage motor drive with a three-phase diode rectifier used as the front end. A dc-voltage-balancing circuit is installed on the dc link, and introduces a new midpoint-voltage-balancing method based on phase-shift control. As a result, the dc mean voltages of the four split dc capacitors can be balanced, independent of the inverter control. Experimental results obtained from the 200-V 5.5-kW downscale model verify that the dc mean voltage of the four split capacitors are balanced well under all the operating conditions.
This paper describes a next-generation 6.6-kV motor drive employing a bi-directional isolated dc/dc converter instead of a line-frequency transformer. It consists of cascaded six "converter cells" in each phase. Each converter cell includes a bi-directional isolated dc/dc converter and two single-phase PWM converters. On the focus is dc voltage control by the bidirectional isolated dc/dc converter, together with the implementation of the dc/dc converter. Small-signal analysis reveals that the control system can be described as a second-order system. The control scheme is confirmed by both computer simulation and experiment based on a dc/dc converter rated at 360 V, 10 kW, and 20 kHz. Simulation and experimental results verify effectiveness of the control method in both steady-state and transient characteristics.
An optimum control scheme for current-source inverters using static induction thyristors in various high-frequency induction heating applications is described. The optimum control scheme implies an optimal control of the firing angle and extinction angle relative to the output voltage in order to minimize the surge voltage and the switching loss during the commutation interval. The tailing current problems of the SI thyristors which significantly influence the optimum firing angle and extinction angle are discussed theoretically. The validity of the optimum control scheme is verified by experiments with a 78 kHz, 17.4 kW (290 V, 60 A) inverter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper presents a fully-digital-controlled shunt hybrid filter for damping of harmonic propagation in power distribution systems. The harmonic propagation is caused by resonance between line inductances and power capacitors installed for power factor correction. A possible solution to damping out harmonic propagation is based on installation of a shunt pure active filter at the end of a feeder. This paper proposes a shunt hybrid active filter characterized by series connection of a seventh-tuned LC filter per phase and a small-rated three-phase active filter. Like the pure filter, the hybrid filter is connected to the end bus of a feeder. The capacitor of the LC filter imposes a high impedance to the fundamental frequency, so that the fundamental voltage appears across the capacitor. This unique feature allows us to directly connect the hybrid filter to the 6.6-kV power line without step-down transformers. Furthermore, the capacitor used in this hybrid filter is lighter, cheaper and smaller than the transformer used in the pure filter. Theoretical analysis, along with experimental results obtained from a 200-V, 20-kW laboratory system, verifies the viability and effectiveness of the proposed hybrid filter.
This paper presents a new method of harmonic power detection based on the instantaneous active power in three-phase circuits, and its applications to search for dominant harmonic sources in power systems. The proposed method requires only band elimination filters and a three-phase active power meter to detect the harmonic active power, and it is able to deal with harmonic power flow more easily and precisely than a conventional meter which is based on Fourier series of single-phase circuits. In addition, measurement errors of the harmonic power are discussed theoretically. The validity of the proposed method is demonstrated by digital simulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper provides a comprehensive discussion on the topology and terminology of the family of modular multilevel cascade converters, including their chronological review. It is followed by answering the following question: "What motivated the author to apply phase-shifted-carrier PWM to the multilevel converters?" The PWM is achievable from integrating inter-cluster balancing or inter-arm balancing control into the middle layer of a hierarchical control system consisting of three layers. This integration makes it easy to expand the phase-shifted-carrier PWM to any bridge-cell or chopper-cell count per cluster or arm.
This paper deals with a curious phenomenon referred to as the "whack-a-mole" that may occur in a long-distance distribution feeder having many capacitors for power factor correction. The whack-a-mole is that installation of an active or passive filter on the feeder makes voltage harmonics increase on some buses whereas it makes voltage harmonics decrease on other busses, especially at the point of installation. The distributed-constant circuit theory is applied to a simplified feeder in order to perform analysis of the whack-a-mole, thus reaching such an effective way as to avoid the whack-a-mole. Moreover, both theory and experiment clarify that installation of the active filter acting as a harmonic terminator on the end bus of the feeder can damp out harmonic propagation throughout the feeder without causing any whack-a-mole.
This paper presents dynamic control and performance of a unified power flow controller (UPFC) intended for installation on a transmission system consisting of two sets of three-phase transmission lines in parallel. When no UPFC is installed, interruption of either three-phase line due to a fault reduces an active power flow to half, because the line impedance becomes double before the interruption. Installing the UPFC makes it possible to control an amount of active power flowing through the transmission system. The validity of the theoretical analysis developed in this paper is verified by experiments using a 10-kVA laboratory setup, as well as a computer simulation.
This paper proposes a new inverter-fed induction motor drive system with a slip-frequency estimation circuit, in which the slip-frequency can be accurately estimated even under transient state without any speed sensor. The authors clarify the definition of "the instantaneous slip-frequency under transient state", and show some experimental results attained by the instantaneous slip-frequency estimation circuit.
This paper deals with a series active filter for harmonic-current compensation of a large-capacity diode rectifier with a capacitive load. Flux satulation may occur in a series matching transformer for connecting the series active filter to the ac side of the diode rectifier. This paper develops an analog controller of a dc magnetizing current flowing in the matching transformer, along with a model for the controller, to avoid the flux satulation. Operating characteristics of the controller are theoretically and exprimentally discussed, taking into account both an offset voltage in the controller and an error in a current sensor. Finally, this paper discusses a relation between magnetizing characteristics of the matching transformer and the amplitude of the magnetizing current.
This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cells (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, "interzigzag" inductors for the TSBC converter. Since each leg of the individual inductor has two windings, the three inductors have 18 windings in total. The wire leads are zigzagged among the three inductors. This unique structure of the "interzigzag" windings leads to the following feature: Both three-phase supply and motor currents produce no magnetic flux in each of the nine legs. This feature makes each inductor smaller in size and lighter in weight. A specially-designed downscaled motor-drive system rated at 400 V and 15 kW is constructed and tested to confirm the validity of a design of the proposed inductors, as well as to verify transient motor-drive performance during four-quadrant operation.
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No abstract is provided for this article.
