717 publications from this institution
This paper presents a transient analysis of a unified power flow controller (UPFC), and design of capacitance of the DC-link capacitor based on that analysis. 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.
This paper discusses the experimental verification of a virtual synchronous-motor drive test system. This test system consists of two identical modular multilevel double-star chopper-cell (DSCC) converters characterized by a front-to-front (FTF) connection. One converter acts as an inverter under test, while the other acts as a part of the virtual motor and load. The experimental waveforms obtained from the test system designed and constructed in this paper confirm satisfactory electrical and mechanical dynamics of the virtual three-phase 200-V, 10-kW, two-pole, 18,000-r/min synchronous motor with a virtual quadratic-torque-to-speed load an as a high-speed compressor. The driving performance of the test system shows that the DSCC inverter under test is applicable to high-speed synchronous motor drives.
The overall objective of this IEEE Power Electronics Society (PELS) Special Issue on high-frequency-link power-conversion systems is, therefore, to bring out the highlights of the ongoing world-wide activities in this area of advanced research to expose, analyze, and resolve the critical research and developmental challenges. The Special Issue received a total of 132 manuscripts for review considerations of which 35 manuscripts have been accepted for final publication. These publications encompass all four broad categories of high-frequency-link power-conversion systems (i.e., dc/ac, ac/dc, ac/ac, and dc/dc converters) with broad applicability in the following areas of application: photovoltaic energy, wind energy, electric vehicles, fuel-cell energy, energy storage, uninterruptible power systems, motor drives, high-frequency-ac power distribution systems, high-voltage direct- current transmission, active load emulator, smart/micro grid, solid-state transformers, induction heating, railway traction drive, pulsed power, plug-in hybrid-electric-vehicle, battery charging, inductive power transfer. The contributions of the articles compiled in this special issue are multifold encompassing topologies with plurality of stages and/or levels, modulation, loss-mitigating switching, high-frequency magnetics, control, modeling, switched-capacitor power conversion, power-factor correction, and broad overview of the Special-Issue subject area.
In recent years, attention has been paid to direct-drive for industrial robots which are essential to factory automation. Direct-drive robots, which are directly actuated with no gear reducer, have no backlash, low friction and good mechanical stiffness. This results in the excellent repeatability of positioning, that is, an order of magnitude better than that of gear-drive robots. It is, however, more prominent in the design of control system for direct-drive robots that the arm inertia variation depending on the arm configuration and the Coriolis and centrifugal torques are directly reflected to the motor axes due to the direct coupling.In this paper, a direct-drive robot with a two degree-of-freedom is developed for planer assembly tasks. The motion of the manipulator arm is constrained within a horizontal plane, so that this type of robot is referred to as a SCARA (Selective Compliance Assembly Robot Arm)-type robot. A balanced manipulator arm, the purpose of which is to cancel the inertia variation and nonlinear effects, is introduced to the direct-drive robot, thus leading to improved control performance as well as simple manipulator dynamics.In addition, the combination of feedforward compensation and a new approach to positioning control is proposed to perform stable and fast positioning without overshooting.
Direct connection of the synchrotron magnet power supply to the utilities causes the effect of pulsed reactive and active power in the AC line. Conventionally, Static Var Control system compensates the reactive power generated by the thyristor converter to reduce the flicker in the power line. However, it is necessary to control not only a reactive power but also an active power for the future large scale synchrotron magnet power supply in order to reduce the dissipation power and to realize the stabilization in the AC line. An adjustable-speed rotary condenser is capable of not only reactive power control but also active power control since it utilize a flywheel effect of the rotor. Research and development on these problems are now under going using a model system of 7.5 kW rotary condenser with flywheel (GD/sup 2/=3kg-m/sup 2/). Control and characteristic of an adjustable-speed rotary condenser and the experiment results will be presented.
The authors present a zero-current-switching (ZCS)-based three-phase PWM (pulse-width-modulated) inverter having small resonant circuits on the AC side, whose resonant frequency is 50 kHz. The ZCS inverter can greatly reduce the switching losses and electromagnetic noise. The principle of ZCS operation, the design of the resonant circuits, and the control sequence are described from theoretical and practical points of view. Experimental results obtained from a ZCS PWM inverter driving an induction motor of 2.2 kW are shown to verify the practicability of this device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper deals with a harmonic current-free AC/DC power conversion system which is characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The stability of the active filter based on feedback control is discussed theoretically, taking into account delay time in the control circuit. As a result, it is revealed that the delay time may produce a bad effect on stability, especially when the power conversion system is installed on a stiff power system with low system inductance. The authors propose a viable way of reducing the effect of delay time on the system stability. Analysis in the frequency domain enables us to know how much the system stability is improved in terms of gain and phase margins. A switching-ripple filter is designed to obtain good filtering performance without affecting the system stability. Experimental results obtained from a 20 kW laboratory system verify the validity of the developed theory, and confirm the viability and effectiveness of the proposed control circuit.
This paper deals with unified power quality conditioners (UPQCs), which aim at the integration of series-active and shunt-active power filters. The main purpose of a UPQC is to compensate for voltage flicker/imbalance, reactive power, negative-sequence current and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. This paper discusses the control strategy of the UPQC, with a focus on the how of instantaneous active and reactive powers inside the UPQC. Experimental results obtained from a laboratory model of 20 kVA, along with a theoretical analysis, are shown to verify the viability and effectiveness of the UPQC.
This paper describes the next-generation medium-voltage power conversion systems characterized by using bidirectional isolated dc/dc converters. A 350-V, 10-kW and 20-kHz dc/dc converter is designed, constructed and tested as a core circuit of the medium-voltage power conversion systems. It consists of two single-phase full-bridge converters with the latest trench-gate Si-IGBTs and a 20-kHz transformer with a nano-crystalline soft-magnetic material core and litz wires. The transformer plays an essential role in achieving galvanic isolation between the two full-bridge converters. The overall efficiency from the dc-input to dc-output terminals is accurately measured to be as high as 97%, excluding gate drive circuit and control circuit losses from the whole loss. Moreover, loss analysis clarifies that the use of SiC-based power devices may bring a significant reduction in conducting and switching losses to the dc/dc converter. As a result, the overall efficiency may reach 99% or higher
This paper discusses a transformerless hybrid active filter integrated into the 6.6-kV, 1-MW adjustable-speed motor drive having a three-phase diode rectifier at the front end. The hybrid filter consists of an active filter using a three-level diode-clamped pulsewidth modulator converter rated at 60 kVA, and a 250-kVA passive filter tuned to the seventh harmonic frequency. They are directly connected in series without a transformer. This circuit configuration enables one to use 1.2-kV insulated gate bipolar transistors because the dc voltage of the three-level converter is 1.32 kV (20% of 6.6 kV). Voltage balancing control characterized by superimposing a sixth harmonic zero-sequence voltage on the active filter voltage reference in each phase is introduced to the three-level converter with triangle carrier modulation. Experimental waveforms obtained from a 400-V, 15-kW downscaled system verify the viability and effectiveness of the proposed hybrid filter, keeping the two dc capacitor voltages well-balanced.
In recent years, attention has been paid to the concept of FACTS (Flexible AC Transmission Systems), along with significant progress in power electronic technology. A high speed phase shifter, which is one of the most promising devices in the FACTS concept, has the potential of power flow control and/or voltage stability in power transmission systems.In this paper, theory and experiment reveal that conventional high speed phase shifters may cause power swing in a transient state as a result of coupling between instantaneous active and reactive power control loops. Then, a couple of new control schemes for a high speed phase shifter are proposed to achieve both power flow control and power swing damping. The second proposed control scheme is based on the control scheme of an already proposed series active filter. Simulated and experimental results agree well with analytical results, not only in steady states but also in transient states.
This paper provides a theoretical discussion on energy-balancing control and capability of a modular multilevel cascade inverter (MMCI) based on single-delta bridge cells (SDBC). The SDBC inverter is intended for applications to utility-scale grid-tied photovoltaic (PV) systems involving asymmetric power generation. The distributed nature of electric power generated from individual power sources requires the inverter to be capable of operating under imbalanced conditions. As compared to a star-configured MMCI based on single-star bridge cells (SSBC), the SDBC inverter features a superior energy-balancing capability making it more suitable for these kinds of applications. This paper discusses the control, operational behavior, and limitations of a phase-shifted carrier pulsewidth modulated (PWM) SDBC inverter under imbalanced conditions among both bridge cells and clusters.
This paper focuses on precise conversion-efficiency measurement of a bidirectional isolated dc-dc converter using the 1.2-kV 400-A SiC-MOSFET/SBD H-bridge modules, along with a unity-turns-ration transformer. A specially-designed test bench for efficiency measurement is characterized by the cascade connection of the two identical 750-V 100-kW 16-kHz bidirectional isolated dc-dc converters. Although the test bench is equipped with two identical unity-turns-ratio transformers, both converters are capable of operating at different voltage ratios ranging from 0.87 to 1.13. Experimental results verify that the whole conversion efficiency from the dc input to the dc output is as high as 98.9% at the rated power of 100 kW with a voltage ratio of 1.13, and 98.6% at 100 kW with another voltage ratio of 0.87, excluding an auxiliary power loss of 82 W.
The superconducting magnetic levitation railway system (MAGLEV) under development in Japan uses a pulse-width-modulation (PWM) inverter for driving a linear synchronous motor (LSM). The inverter output voltage contains non-negligible harmonics which cause harmonic resonances in the LSM system, and therefore harmonics of the output voltage have been analyzed in order to control such harmonic resonances.This paper applies a third-harmonic injection method to the inverter for the purpose of enhancing the output voltage without changing the circuit configuration. It performs harmonic analysis of the output voltage of the inverter based on the third-harmonic injection. Validity of the harmonic analysis is verified by computer simulation.
This paper deals with the high-frequency leakage current caused by a voltage-source PWM inverter. A nonnegligible amount of leakage current would flow through stray capacitors between stator windings and a motor frame due to a, large step change of the common-mode voltage produced by the PWM inverter. An equivalent circuit for the leakage current is proposed, which is expressed by a series resonant circuit. The analysis applying the equivalent circuit gives us such a conclusion that the connection of a common-mode choke in series between the inverter and motor terminal is not effective to reduce the rms and average value of the leakage current, but effective to reduce the peak value. Furthermore, this paper shows that the modeling and analysis are valid in designing a previously proposed suppression method of the leakage current.
