717 publications from this institution
The emergence of power semiconductor devices such as insulated-gate bipolar transistors (IGBTs) or injection-enhanced gate transistors (IEGTs) and gate-commutated turn-off (GCT) thyristors or integrated gate-commutated thyristors (IGCTs) enables power conversion systems to expand into utility, leading to FACTS controllers. This paper describes prospects and directions of power electronics in the 21st century, with much focus on silicon-carbide devices suitable for the next-generation FACTS controllers.
This paper describes an induction heating system of 1kW 450kHz which is developed for dental casting machines. This system consists of a single-phase diode rectifier, a voltage-source inverter using four power MOSFET's, and a series resonant circuit with a matching transformer of turn ratio 8:1. No capacitor is connected on the DC side of the rectifier except for a high frequency capacitor of 0.47 μ F. Thus, the DC voltage across the high frequency capacitor is fluctuating at 100Hz, that is, twice as high as the line frequency of 50Hz as if no capacitor were connected. Not only does the fluctuation have no effect on heating or melting but also the fluctuation plays an essential role in shaping the line current of the rectifier into sinusoid and unity power factor, because it is seen from the DC side of the rectifier that the inverter plus the resonant circuit acts as a pure resistance.The power control covering a wide range from 50W to 1kW is achieved by power factor control of the inverter which takes the place of DC voltage control of the rectifier.The system efficiency is estimated to be 76% by sophisticated measurement of the actual heating power, which is based on Lissajous's figures for voltage and charge.
These keynote speeches discuss the following: Power Electronics - Trends and Research Challenges; Stability Issue for Power Systems with Multiple Electronic Converters: What Is the Appropriate Analytical Approach?; Modular Multilevel Cascade Converters for Grid Connections and Motor Drives; Series Compensation of Open-Winding PM Machines.
The battery energy storage system is an essential enabling device of the smart grid, because it helps grid connection of massive renewable energy resources. This paper has a brief discussion on a battery energy storage system based on a multilevel cascade pulsewidth-modulated (PWM) converter for its practical use. The active-power control of individual converter cells is presented to make it possible to charge and discharge the battery units at different power levels while producing a three-phase balanced line-to-line voltage. This results in the maximum utilization of battery energy even when the power-handling capabilities of the battery units differ. Experimental results obtained from a 200-V, 10-kW, 3.6-kWh battery energy storage system verify the effectiveness of the presented active-power control.
No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
This paper presents the control and performance of a pulse-density-modulated (PDM) series-resonant voltage-source inverter developed for corona discharge processes. The PDM inverter produces either a square-wave AC-voltage state or a zero-voltage state at its AC terminals to control the average output voltage under constant DC voltage and operating frequency. This results in a wide range of power control from 0.5% to 100%, even in the corona discharge load with a strong nonlinear characteristic. A 30 kHz 6 kW surface treatment system consisting of a voltage-source PDM inverter, a step-up transformer, and a corona discharge treater shows the establishment of a stable corona discharge in an extremely wide range of power control and, therefore, succeeds in performing both strong and weak surface treatment processes for film.
This paper discusses a transformerless hybrid active filter integrated into a 6.6-kV, 1-MW adjustable-speed motor drive system. The hybrid filter consists of an active filter using a three-level diode-clamped PWM converter rated at 60 kVA and a 250-kVA passive filter tuned to the 7th-harmonic frequency both of which are directly connected in series. This circuit configuration enables to use 1.2-kV IGBTs because the DC voltage of the three-level converter is 1.32 kV (20% of 6.6 kV). Voltage-balancing control based on superimposing a 6th-harmonic voltage on the active-filter voltage reference is introduced to the three-level converter. Experimental waveforms obtained from a 400-V 15-kW down-scaled experimental system verify the viability and effectiveness of the proposed transformerless three-level shunt hybrid filter, keeping two DC-capacitor voltages balanced well.
Active power filters have been used in practice to suppress the harmonic interference in power systems. To compensate for harmonic currents of loads, active power filters usually are connected to power systems in parallel with the loads. These filters, which are called shunt active filters here, are very effective for loads that can be considered as current sources, such as thyristor rectifiers with large dc reactances. Many papers have covered the shunt active filters applied to these current‐source loads, however, none has discussed characteristics of the shunt active filters when they are applied to voltage‐source loads. On the other hand, since more and more diode rectifiers with capacitive dc filters have recently been used, harmonics generated by them have become an issue. The diode rectifier with capacitive dc filters behaves as a voltage source rather than a current source. When a shunt active filter is applied to such a diode rectifier, the current injected from the shunt active filter may flow into the diode rectifier. As a result, harmonics of the source current cannot be reduced effectively, and harmonic current flowing into the diode rectifier increases greatly. This paper presents the aforementioned problem of shunt active filters analytically and experimentally. Then a series active filter is proposed to suppress the harmonic current of the diode rectifiers. The features, operating conditions, and considerations of shunt active filters and series active filters are described analytically and demonstrated experimentally. Taking a diode rectifier with capacitive dc filter as a typical voltage‐source load, compensation characteristics of shunt active filters and series active filters are discussed by experiment and simulation. The validity of the series active filters is illustrated experimentally.
This paper discusses automatic gain adjustment in a fully-digital-controlled shunt active filter intended for installation on power distribution systems. This is the first step in cooperative control of multiple shunt active filters based on voltage detection for harmonic damping throughout power distribution systems. In general, an optimal control gain is equal to the characteristic impedance of a distribution line. However, it is difficult to know circuit parameters of a real distribution line, which depend strongly on feeder connections, shunt capacitors and loads. Therefore, the main purpose of the gain adjustment is to help the active filter to damp out harmonic propagation without considering the circuit parameters. Moreover, the gain adjustment can reduce the compensating current and losses in the active filter. The active filter having the function of automatic gain adjustment is experimentally compared to that with a constant gain. Experiment results verify the effectiveness of the active filter having the function of automatic gain adjustment.
Recently, attention has been paid to a voltage-sag compensator or the so-called dynamic voltage restorer (DVR), the power circuit of which consists of series and shunt converters. However, few discussions have been made on which is more practical for the DVR, a circuit configuration installing the shunt converter on the load side or that installing it on the supply side. This paper focuses on the circuit configuration installing the shunt converter on the load side, along with comparisons between the two configurations. As a result, the conventional configuration installing the shunt converter on the supply side requires a large-capacity energy storage device such as a dc link capacitor bank. On the other hand, the configuration characterized by installing it on the load side does not require any energy storage device in principle. Its operating characteristics and theoretical discussions are confirmed by computer simulation using the software package PSCAD/EMTDC.
Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. The bearingless switched reluctance motors are characterized by integration of switched reluctance motors and magnetic bearings. These motors have two kinds of stator windings composed of motor main windings and suspension windings in the same stator in order to produce suspension force that can realize rotor shaft suspension without mechanical contacts or lubrication. For successful stable operation, accurate theoretical formulae of instantaneous torque and suspension force are necessary to a rotational speed controller and a rotor radial position controller. This paper derives the theoretical formulae of the instantaneous torque and the suspension force from an assumption of simple permeance distribution. This derivation process makes an assumption that fringing fluxes are distributed on elliptical lines. It is shown with experimental results that the derived theoretical formulae are very accurate in terms of practical application.
This paper provides an experimental discussion on zero-voltage-ride-through (ZVRT) capability of a phase-shifted pulsewidth-modulation distribution static synchronous compensator (D-STATCOM) using the modular multilevel cascade converter based on single-star bridge cells (SSBC). The cluster-balancing control producing a significant effect on the ZVRT capability is modeled and analyzed with focus on either a low-pass filter (LPF) or a moving-average filter (MAF) to attenuate the 100-Hz (double the line frequency) component inherent in each dc capacitor voltage. The cluster-balancing control using the MAF is better in transient performance than that using the LPF. A three-phase downscaled SSBC-based D-STATCOM rated at 150 V and 10 kVA is designed, constructed, and tested to verify the ZVRT capability under the severest single-, two-, and three-phase voltage sags with a voltage depth of 100%. Experimental waveforms show that the STATCOM continues operating stably as if no voltage sag occurred.
