717 publications from this institution
This paper describes electro-thermal co-simulation of two parallel-connected SiC-MOSFETs using a temperature-dependent compact model for a discrete SiC-MOSFET. The temperature-dependent compact model is constructed on the basis of the previous model with appropriate-modification of output characteristics and threshold voltage. This compact model also gives the accurate reproducibility of the transient waveforms in a high region of drain current. The current sharing simulation between the parallel-connected SiC-MOSFETs under thermally-imbalanced conditions is experimentally verified. Based on the above verification, the electro-thermal co-simulation in a boost chopper is conducted, which successfully shows the junction temperature distribution between the two SiC-MOSFETs.
This paper presents a new equivalent circuit of harmonic currents on the AC side of a rectifier and analyzes the power flow of the rectifier. In a conventional equivalent circuit, the rectifier has been considered as an ideal current source for harmonics. However, the theoretical derivation has not been reported. Some problems of the conventional equivalent circuit are pointed out, and a new equivalent circuit, which can solve the problems of the conventional one, is derived theoretically. Moreover, an interesting interpretation on the power flow of the rectifier is presented, attention being paid to the fundamental and harmonic frequencies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Since the late 1950s, power electronics has been developing by leaps and bounds without saturation into the key technology essential to modern society and human life, as well as to electrical engineering. This paper is focused on utility applications of power electronics technology in Japan, and on the state of the art of power semiconductor devices for high power applications. For instance, attention is paid to a /spl plusmn/500 kV, 2.8 GW high-voltage DC transmission system under construction, and to 8 kV, 3.5 kA light-triggered thyristors used for constituting its thyristor valves. This paper also presents future prospects and directions of power electronics technology in the 21st century, including the personal views and expectations of the author.
This paper discusses a 6.6-kV transformerless motor drive system based on the back-to-back connection of two five-level diode-clamped PWM converters. In addition, this paper designs, constructs and experimentally tests a down-scaled model rated at 200V and 5.5kW. This system consist of the two five-level converters, a common dc-link, and voltage-balancing circuits using two bi-directional buck-boost choppers. Experimental results obtained from the down-scaled model verify the validity of the system design, giving promise of the viability of the 6.6-kV transformerless motor drive system.
This paper presents a transformerless hybrid active filter that is integrated into medium-voltage adjustable-speed motor drives for fans, pumps, and compressors without regenerative braking. The authors have designed and constructed a three-phase experimental system rated at 400V and 15kW, which is a downscaled model from a feasible 6.6-kV 1-MW motor drive system. This system consists of the hybrid filter connecting a passive filter tuned to the 7th harmonic filter in series with an active filter that is based on a three-level diode-clamped PWM converter, as well as an adjustable-speed motor drive in which a diode rectifier is used as the front end. The hybrid filter is installed on the ac side of the diode rectifier with no line-frequency transformer. The downscaled system has been exclusively tested so as to confirm the overall compensating performance of the hybrid filter and the filtering performance of a switching-ripple filter for mitigating switching-ripple voltages produced by the active filter. Experimental results verify that the hybrid filter achieves harmonic compensation of the source current in all the operating regions from no-load to the rated-load conditions, and that the switching-ripple filter reduces the switching-ripple voltages as expected.
This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system that combines two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with DC power cables. Hereinafter, a single MMCC-DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simplicity. The HVDC transmission system is required to provide low-voltage-ride-through (LVRT) capability to enhance transmission system availability. This paper proposes a new LVRT method without any direct information exchange between the two DSCC converters. The validity of the method is verified, using simulated waveforms from the software package of “PSCAD/EMTDC” and experimental waveforms from a three-phase 200-V, 400-Vdc, 10-kW, 50-Hz downscaled HVDC system with a set of 300-meter-long DC power cables.
A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.
This paper presents a modular multilevel cascade converter based on double-star bridge-cells (MMCC-DSBC), which is characterized by a cascade connection of multiple single-phase full-bridge PWM converter cells per leg. It is suitable for a wind turbine generation system with a permanent magnet synchronous generator, the frequency band of which ranges typically from 5 to 20 Hz. This paper discusses a wind turbine generation system based on the DSBC, revealing that the DSBC can achieve a grid connection with an arbitrary dc-link voltage. Moreover, the operating principles and the control method are described in this paper. The validity of the system is verified experimentally by using a 200-V 10-kW downscaled model.
No abstract is provided for this article.
No abstract is provided for this article.
This paper deals with a leakage current flowing out of the heat sink of a voltage-source PWM inverter. The heat-sink leakage current is caused by a steep change in the common-mode voltage produced by the inverter. It flows through parasitic capacitors between the heat sink and power semiconductor devices when no EMI filter is connected. Experimental results reveal that the heat-sink leakage current flows not into the supply side, but into the motor side. These understandings succeed in describing an equivalent common-mode circuit taking the parasitic capacitors into account. The authors have proposed a passive EMI filter that is unique in access to the ungrounded motor neutral line. It is discussed from this equivalent circuit that the passive EMI filter is effective in preventing the leakage current from flowing. Moreover, installation of another small-sized common-mode inductor at the ac side of the diode rectifier prevents the leakage current from flowing into the supply side. Experimental results obtained from a 200-V, 3.7-kW laboratory system confirm the effectiveness and viability of the EMI filter.
This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in the 400-V, 15-kW induction motor driven by a voltage-source pulsewidth modulation (PWM) inverter. A shaft-to-frame voltage can be observed at either shaft end with respect to the grounded motor frame. A shaft end-to-end voltage can be observed as a voltage difference between the shaft-to-frame voltage at the drive end (DE) and that at the nondrive end (NDE). Experimental waveforms lead to the following interesting observations: motor internal coupling and parasitic capacitance, along with the high-frequency common-mode voltage generated by the PWM inverter, cause a shaft-to-frame voltage with a peak of 8 V at both DE and NDE. When the shaft-to-frame voltage at either DE or NDE exceeds a dielectric breakdown voltage of thin bearing lubricating grease films, a shaft end-to-end voltage with a peak of 2 V and a width of 30 ns occurs along the motor shaft. This paper makes experimental discussions on the shaft end-to-end voltage generation. Installing a differential-mode filter and/or a common-mode filter on the motor drive system gives a hint on the mechanisms of the occurrence of the shaft end-to-end voltage.
No abstract is provided for this article.
No abstract is provided for this article.
This paper deals with DC-flux deviations occurring in a doubly-fed flywheel generator with stator-current feedback control. An AC output voltage of the PWM inverter connected to the rotor produces the DC-flux deviations in the stator. It is difficult to detect the DC flux from the stator current and/or voltage, because the DC flux induces no electromotive force on the stator windings. This paper proposes a new control method for suppressing the DC flux deviations based on calculating the magnetizing current from the stator and rotor currents. Experimental results verify the viability of the proposed control method.
A combined system consisting of a passive filter and a small-rated active filter that are connected in series is discussed as a method of overcoming power system harmonic interferences caused by harmonic-producing loads such as diode or thyristor converters and cycloconverters. The system features filtering characteristics independent of the source impedance, parallel and series resonance between the source and the passive filter that is dumped by the active filter, and a required rating of the active filter which is much smaller than that of a conventional active filter. Experimental results obtained from a prototype model are shown to verify the developed theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
This paper describes a dc micro-grid system interconnecting distributed power generators. The system consists of five generation and control units; a solar-cell generation unit, a wind-turbine generation unit, a battery energy-storage unit, a flywheel power-leveling unit, and an ac grid-interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the dc grid voltage. This method brings high reliability, high-flexibility and maintenance-free operation to the system. The method pays attention to dc output voltage performance of each unit. Each of the power control unit and the energy-storage unit is controlled to act as a voltage source with imaginery impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power-leveling unit is controlled to act as a current source having the function of frequency selectivity like a high-pass filter. A 10-kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the dc-grid system.
