Electricity: single generator systems – Automatic control of generator or driving means – Current output
Reexamination Certificate
2000-02-17
2001-11-20
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Current output
C363S161000
Reexamination Certificate
active
06320356
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power unit which generates a 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 having an input side thereof connected to a generator generating relatively small power and is constructed such that electric current to be supplied to a load connected to the power unit is limited when the power unit is in an excessively loaded state or the load is in a nearly short-circuited state.
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.
In a conventional power unit using the cycloconverter described above, the cycloconverter is not provided with means for storing energy. Therefore, when the cycloconverter is used to obtain single-phase sinusoidal alternating current, the energy input to the cycloconverter also sinusoidally changes.
Therefore, when a small-sized generator which generates small power e.g. of several hundreds to several thousands kW is connected to the input side of the cycloconverter to generate a single-phase sinusoidal wave, only peak portions of the input sinusoidal waves can be utilized as input energy, so that the utilization efficiency is very low, resulting in only a very small output power being taken out as single-phase alternating current.
To overcome this inconvenience, a power unit has been proposed by the present assignee in Japanese Laid-Open Patent Publication (Kokai) No. 10-52047, in which as the load applied to the power unit increases, a desired waveform of a drive signal for driving the cycloconverter is changed from a sinusoidal waveform to a rectangular waveform which has maximum amplitude thereof limited by the output voltage of the power unit, to thereby keep the cycloconverter operating without difficulty even if an excessive load is applied to the power unit.
However, the conventional power unit is adapted to supply electric current to a load connected thereto under any excessive load condition according to the degree of the applied excessive load, so that even when there is no need to supply electric current to the load, judging from the load condition, the power unit continues to supply the electric current to the load. The load condition under which there is no need to supply electric current to the load includes, for example, an excessive load condition close to a short circuit of the load (including a short-circuited state). When the load is in such a condition, it is not necessary to continue supplying a sufficient amount of electric current to the load.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power unit which is capable of controlling electric current to be supplied to a load connected to the power unit, in a flexible manner in dependence on a condition of the load.
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 single-phase alternating current to be supplied to a load;
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, to thereby cause the cycloconverter to generate the single-phase alternating current;
desired wave-forming means for forming a desired waveform of a drive signal input to the bridge drive circuit, for causing the drive bridge circuit to drive the variable control bridge circuits, such that the single-phase alternating current has a desired alternating current waveform;
waveform-changing means for changing a shape of the desired waveform in dependence on variation in the load so as to stabilize an output voltage of the cycloconverter; and
amplitude-limiting means for limiting amplitude of the desired waveform to a smaller value when the output voltage of the cycloconverter becomes equal to or lower than a predetermined value.
According to the power unit of the invention, it is possible to change the shape of the desired wave when the power unit is temporarily excessively loaded, whereby the output from the power unit can be automatically increased to a value close to the upper limit of the whole input energy from the generator, and further under a further excessive load condition of the power unit, the amplitude of the desired waveform is limited to an even smaller value, so that it is possible to flexibly control the electric current to be supplied to the load, according to the load condition of the power unit.
Preferably, the power unit includes comparison means for comparing between the output voltage of the cycloconverter and a desired output voltage, and the waveform-changing means changes the shape of the desired waveform from a sinusoidal one to a rectangular one when the load increases, based on results of comparison by the comparison means.
More preferably, the waveform-changing means changes the shape of the desired waveform from the sinusoidal one to the rectangular one to an increasing degree as the load increases.
More preferably, the amplitude of the desired waveform the amplitude-limiting means limits to an even smaller value when the load becomes nearly short-circuited.
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: 5585708 (1996-12-01), Richardson et al.
patent: 5886893 (1999-03-01), Asai et al.
patent: 5943221 (1999-08-01), Asai et al.
patent: 6018200 (2000-01-01), Anderson et al.
patent: 6111390 (2000-08-01), Inaba et al.
patent: 6219268 (2001-04-01), Asai et al.
patent: 60-9429 (1985-03-01), None
patent: 10-52047 (1998-02-01), None
Asai Koichi
Eguchi Hiroyuki
Shimizu Motohiro
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Honda Giken Kogyo Kabushiki Kaisha
Ponomarenko Nicholas
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