Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Patent
1994-02-03
1995-11-14
Wong, Peter S.
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
363 98, H02M 75387
Patent
active
054672627
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improvement in an electric power converting apparatus for converting DC into AC and vice versa. More specifically, the present invention is related to control of an output voltage from an electric power converting apparatus.
BACKGROUND ART
A 3-level inverter produces a 3-level voltage, e.g., a high voltage, a medium voltage, and a lower voltage, by subdividing a DC power voltage (stringing voltage) into two DC voltages by way of series-connected capacitors, and selectively conducts these three leveled voltages to an inverter output terminal by turning ON/OFF the switching elements of the major circuit. The 3-level inverter has the following features.
That is, since the step number of the output voltage pulse is increased, the virtual switching frequency is increased and then an output with less distortion is obtained. Since the voltage applied to the element is reduced to approximately 1/2, as compared with that of the 2-level inverter, the switching elements with relatively low-withstanding voltages may be utilized. Since the voltages applied to the switching elements are lowered, loss occurring in the switching elements may be reduced.
As the generating/controlling method for the output voltage pulse of the above-described 3-level inverter, the following methods have been proposed: page 412. In FIG. 1, there are shown a so-called "dipolar modulation" (the output voltage is produced by alternately outputting the positive
egative pulses via the zero voltage within a half period of the output voltage), a so-termed "unipolar modulation" (the output voltage is produced by outputting the pulse with a single polarity within a half period of the output voltage), and also a method for switching the above-described dipolar modulation and unipolar modulation. Method" (IEEE Transaction on Industrial Electronics and Control Instrumentation, vol. IECI-28, No. 4, November 1981), page 316. In FIG. 2(b), such a modulation method (will be referred to "overmodulation") has been proposed. That is, a half period of the output voltage is constructed of a plurality of pulses each having a single polarity, and the output voltage is produced by reducing the number of pulses in such a manner that slits among the pulses are filled up from the center portion of this half period. 1991), page 411. In FIG. 16, the output voltage pulse generating/controlling method has been proposed for covering the output voltage from 0 to 100%.
DISCLOSURE OF INVENTION
When a 3-level inverter is employed in such usage as a railroad vehicle, various demands are made. That is, in order to realize a speed control over a wide range, a fundamental wave of an output voltage of an inverter can be continuously controlled, and also a harmonic wave of an output voltage of this inverter can be smoothly controlled from zero voltage up to a maximum voltage at which a voltage utilization factor reaches 100% (namely, a voltage region where only a single pulse is present within a half period of an output voltage, which will be referred to as a "1 pulse").
Then, in accordance with the above-described prior art (1), since a selection is made of the dipolar modulation capable of controlling a very small voltage containing a zero, the unipolar modulation means for covering the medium speed region (medium voltage), and the so-called "1 pulse" for covering the maximum voltage, the voltages from zero voltage to the maximum voltage can be outputted. The continuity of the fundamental wave can be maintained. The discontinuity happens to occur in the harmonic wave of the output voltage when the unipolar modulation is changed into the "1 pulse". Thus, there is such a problem that noises are produced due to sudden and great changes in the frequency.
In the technical idea described in the above-described prior art (2), there is another problem that the voltages from zero voltage to the maximum voltage cannot be reproduced.
On the other hand, in the above explained prior art (1), the control becomes complex in order to con
REFERENCES:
patent: 4270163 (1981-05-01), Baker
patent: 4443841 (1984-04-01), Mikami et al.
patent: 4635177 (1987-01-01), Shekhawat et al.
patent: 4723201 (1988-02-01), Tanamachi et al.
patent: 4855893 (1989-08-01), Kratz
patent: 5060129 (1991-10-01), Maruyama
patent: 5155675 (1992-10-01), Maruyama et al.
patent: 5321599 (1994-06-01), Tanamachi et al.
patent: 5361196 (1994-11-01), Tanamachi et al.
patent: 5375050 (1994-12-01), Nakata et al.
"A Novel Approach to the Generation and Optimization of Three-Level PWM Wave Forms", B. Velaerts, et al, PESC '88 Record, Apr. 1988, pp. 1255-1262.
"New Developments of 3-Level PWM Strategies", EPE'89 Record, 1989, pp. 411-416.
"PWM Systems In Power Converters: An Extension of the Subharmonic Method", IEEE Trans. on Industrial Electronics and Control Instrumentation, vol. IECI-28, No. 4, Nov. 1981, pp. 315-322.
"Study of 2 and 3-Level Precalculated Modulations", EPE' 91, Record, 1991.
JP-A-51-47848.
JP-A-56-74088.
JP-A-55-43998.
JP-A-50-44425.
JP-A-52-154020.
JP-A-61-251477.
Nakamura Kiyoshi
Nakata Kiyoshi
Suzuki Masato
Tanamachi Tokunosuke
Terunuma Mutsuhiro
Hitachi , Ltd.
Riley Shawn
Wong Peter S.
LandOfFree
Electric power converting apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric power converting apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric power converting apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1225395