Electric power conversion systems – Frequency conversion without intermediate conversion to d.c. – By semiconductor converter
Reexamination Certificate
2000-02-17
2001-04-17
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Frequency conversion without intermediate conversion to d.c.
By semiconductor converter
Reexamination Certificate
active
06219268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power unit which generates single-phase AC power having a commercial frequency or a like frequency, and more particularly to a power unit of this kind which uses a cycloconverter comprised of thyristors and which has a small-sized generator having a relatively low output voltage, at an input side thereof, with means for preventing overvoltage from being applied to the thyristors due to characteristics of a load connected to the power unit.
2. Prior Art
Conventionally, a so-called cycloconverter is known, which directly converts AC power with a fixed frequency to AC power with another frequency.
Such a conventional cycloconverter is normally used for converting power supplied from a commercial frequency power line or power generated by a high power generator (see Japanese Patent Publication (Kokoku) No. 60-9429, for instance), and it is generally used for driving an AC electric motor.
Further, when a small-sized generator which generates several hundred to several thousand watts is connected to the output side of such a conventional cycloconverter, a large output voltage drop can occur when a heavy load is connected to the power unit, due to the limited power-generating capacity of the generator. The output voltage drop is particularly large when a magneto generator is employed as the generator. To cope with this, thyristors having a high withstanding voltage have to be used.
To eliminate this inconvenience, the present assignee has already proposed by Japanese Laid-Open Patent Publication (Kokai) No. 10-52045 and corresponding U.S. Pat. No. 5,886,893 a power unit which is comprised of a cycloconverter formed of positive and negative converters each constituted by a two-layered structure of two half-wave converters, and which thereby reduces the voltage applied to each of thyristors of the cycloconverter to a small value.
In the proposed power unit, however, the voltage applied to each thyristor (i.e. the output voltage of the power unit) occasionally undergoes a temporary sharp rise in a peak value thereof which occurs when the power unit is in a transient operating condition, e.g. when a load connected to the power unit is turned on or off, or occurring due to deformation of the output voltage waveform when a reactor load is connected to the power unit, or the like.
To cope with this problem, countermeasures have also to be taken.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power unit which is capable of restraining a rise in voltage applied to each of thyristors constituting a cycloconverter of the power unit even when the output voltage of the power unit undergoes a temporary sharp rise due to characteristics of a load connected thereto.
To attain the above object, the present invention provides a power unit comprising:
a generator having three-phase output windings;
a pair of variable control bridge circuits connected to the three-phase output windings of the generator and connected in an antiparallel manner to each other to form a cycloconverter for generating a single-phase alternating current output to be supplied to a load, the cycloconverter having a pair of output lines via which the single-phase alternating current output is delivered;
a bridge drive circuit for causing the variable control bridge circuits to be alternately switched to operate every half a repetition period of the single-phase alternating current output, to thereby cause the cycloconverter to generate the single-phase alternating current output;
a bridge rectifier connected between the pair of output lines, and having an output for delivering rectified output; and
an electric energy-storing capacitor circuit connected to the output of the bridge rectifier, for storing the rectified output therein.
According to this power unit, the bridge rectifier and the electronic energy-storing capacitor circuit operate to restrain a sharp rise in the peak value of the single-phase alternating current output, whereby a rise in voltage applied to the variable control bridge circuits can be prevented even when the output voltage of the power unit undergoes a temporary sharp rise due to characteristics of the load connected thereto.
Preferably, the power unit includes monitor means for monitoring a peak value of the single-phase alternating current output, and control means for controlling the variable control bridge circuits such that the operation of the variable control bridge circuits is stopped when the peak value monitored by the monitor means exceeds a predetermined value.
According to this preferred embodiment, while a sharp rise in the peak value of the single-phase alternating current output is prevented by the bridge rectifier and the electronic energy-storing capacitor circuit, the peak value of the single-phase alternating current output is monitored, and when the monitored peak value exceeds the predetermined value, the operation of the variable control bridge circuits is stopped. As a result, a temporary sharp rise in the voltage can be prevented and at the same time overvoltage can be easily detected, thereby enabling the power unit to perform its protective function of stopping the generation of electricity.
Preferably, the three-phase output windings have a neutral point, the output lines of the cycloconverter have a neutral point formed therebetween with respect to the single-phase alternating current output, the variable control bridge circuits each have a two-layered structure of two half-wave converters, and the neutral point formed between the output lines of the cycloconverter being connected to the neutral point of the three-phase output windings such that the variable control bridge circuits operate as a voltage doubler rectifier.
As a result, it is possible to use small-sized thyristors which are not high in withstanding voltage, and even if a sharp temporary rise in voltage occurs due to characteristics of the load, the small-sized thyristors can be used directly as they are.
Preferably, the generator is a magneto generator having a rotor formed of permanent magnets.
Preferably, the electric energy-storing capacitor circuit comprises a capacitor and a resistor.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3624472 (1971-11-01), Graham
patent: 3889167 (1975-06-01), Tanaka et al.
patent: 4570214 (1986-02-01), Tanaka
patent: 5285365 (1994-02-01), Yamato et al.
patent: 5886893 (1999-03-01), Asai
patent: 60-9429 (1985-03-01), None
patent: 10-52045 (1998-02-01), None
Asai Koichi
Eguchi Hiroyuki
Shimizu Motohiro
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Honda Giken Kogyo Kabushiki Kaisha
Nguyen Matthew
LandOfFree
Power unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467216