Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2001-10-22
2002-08-20
Patel, Rajinikant B. (Department: 2832)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S132000, C363S098000
Reexamination Certificate
active
06437998
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a rectifying circuit for converting an N-phase (N being a natural number equal to or greater than 2) AC voltage into a DC voltage, as well as a control method therefor.
FIG. 14
shows a conventional rectifying circuit for converting a three-phase AC voltage into a DC voltage. This conventional technique is substantially described in Japanese Patent Publication (KOKAI) No. 9-182441. In
FIG. 14
, R, S and T denote AC input terminals; P and N denote DC output terminals; L
1
, L
2
and L
3
denote reactors; D
1
to D
18
denote diodes; S
1
to S
3
denote switching devices of corresponding phases; and C
1
and C
2
denote capacitors.
Next, the operation of this circuit will be described. In the following, names of elements may be omitted, with only their reference numerals shown. For example, when the switching devices S
1
and S
2
are turned on, current flows through a path R→L
1
→D
1
→S
1
→D
8
→D
9
→S
2
→D
4
→L
2
→S→R to accumulate energy in the reactors L
1
and L
2
. Furthermore, when S
1
is turned off with S
2
on, the energy from the reactors L
1
and L
2
is charged to the capacitor C
1
through the path R→L
1
→D
1
→D
13
→C
1
→D
9
→S
2
→D
4
→L
2
→S→R. On the other hand, when S
2
is turned off with S
1
on, current flows through a path R→L
1
→D
1
→S
1
→D
8
→C
2
→D
16
→D
4
→L
2
→S→R to charge the energy from the reactors L
1
and L
2
to the capacitor C
2
.
Further, when both S
1
and S
2
are turned off, current flows through a path R→L
1
→D
1
→D
13
→C
1
→C
2
→D
16
→D
4
→L
2
→S→R to charge the energy from the reactors L
1
and L
2
to both capacitors C
1
and C
2
. Repetition of such switching operations enables an AC voltage to be converted into a DC voltage while the input current is controlled at a high power factor. Further, the voltages of the two capacitors C
1
and C
2
can be individually regulated by adjusting the on-time of the switching devices S
1
to S
3
.
In the conventional three-phase input technique shown in
FIG. 14
, the number of semiconductor devices (switching devices and diodes) through which current passes is six for storage of energy in the reactors, five for individual charging of the capacitor C
1
or C
2
, and four for the simultaneous charging of both capacitors C
1
and C
2
. Thus, current passes through a large number of devices, thus increasing energy loss in the semiconductor devices. Further, the cooling parts for reducing heat generated by the energy loss must be large, thereby increasing the size and price of the apparatus. Additionally, a main circuit includes a large number of semiconductor devices, specifically
21
.
It is thus an object of the present invention to provide a rectifying circuit and control method therefor for reducing the number of semiconductor devices through which current passes as compared to the prior art, thereby reducing energy loss, and for reducing number of semiconductor device parts, making it possible to reduce the size, weight, and price of the apparatus.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To attain the above object, the first aspect of the present invention is a rectifying circuit for converting an N-phase (N being a natural number equal to or greater than 2) AC voltage into a DC voltage. In the rectifying circuit, a series circuit of two switching devices having the same conductive direction and a series circuit of two diodes having the same conductive direction are connected together in parallel to constitute a bi-directional switch circuit for one phase. N bi-directional switch circuits are provided, and a junction between the switching devices of each bi-directional circuit is connected to an AC input terminal of a corresponding phase via a reactor. A cathode of the diode series circuit of each bi-directional switch circuit is connected to a positive DC output terminal via a diode, and an anode of the diode series circuits of each bi-directional switch circuit is connected to a negative DC output terminal via a diode. Two capacitors are connected in series between the positive and negative DC output terminals. The junction between the diodes of each bi-directional switch circuit is connected to a junction between the two capacitors.
In the second aspect of the present invention, two series circuits each comprising a diode and a switching device having different conductive directions are formed, and the first and second series circuits are connected together in parallel so that the cathodes of the diodes are connected together to constitute a bi-directional switch circuit for one phase. N bi-directional switch circuits are provided, and an internal junction of the first series circuit of each of the bi-directional switch circuits is connected to an AC input terminal of a corresponding phase via a reactor. The cathodes of the diodes of each bi-directional switch circuit are connected to a positive DC output terminal via a diode, and a junction between the switching devices of each bi-directional switch circuit is connected to a negative DC output terminal via a diode. Two capacitors are connected together in series between the positive and negative DC output terminals. All internal junctions of the second series circuits of the bi-directional switch circuits are connected to a junction between the two capacitors.
In the third aspect of the present invention, two series circuits each comprising a diode and a switching device having different conductive directions are formed, and the first and second series circuits are connected together in parallel so that the anodes of the diodes are connected together to constitute a bi-directional switch circuit for one phase. N bi-directional switch circuits are provided, and an internal junction of the first series circuit of each of the bi-directional switch circuits is connected to an AC input terminal of a corresponding phase via a reactor. A junction between the switching devices of each bi-directional switch circuit is connected to a positive DC output terminal via a diode, and the anodes of the diodes of each bi-directional switch circuit are connected to a negative DC output terminal via a diode. Two capacitors are connected together in series between the positive and negative DC output terminals via a diode. All internal junctions of the second series circuits of the bi-directional switch circuits are connected to a junction between the two capacitors.
In the fourth aspect of the present invention, a series circuit of two diodes having the same conductive direction and a series circuit of two switching devices having the same conductive direction are connected together in parallel to constitute a bi-directional switch circuit for one phase. N bi-directional switch circuits are provided, and a junction between the diodes of each bi-directional switch circuit is connected to an AC input terminal of corresponding phase via a reactor. A cathode of the diode series circuit of each bi-directional switch circuit is connected to a positive DC output terminal via a diode, and an anode of the diode series circuits of each bi-directional switch circuit is connected to a negative DC output terminal via a diode. Two capacitors are connected in series between the positive and negative DC output terminals, and a junction between the switching devices of each bi-directional switch circuit is connected to a junction between the two capacitors.
In the fifth aspect of the present invention, according to any of the second to fourth aspects, one of the two diodes constituting each bi-directional switch circuit is replaced with a thyrister and, when the interphase power is low, the thyrister is turned on to restrain a rush current to the capacitor when the power supply is turned on.
In the si
Kuroki Kazuo
Mino Kazuaki
Fuji Electric & Co., Ltd.
Kanesaka & Takeuchi
Patel Rajinikant B.
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