Power converter

Details Power converter Power converter

2002-11-05

2004-04-13

Han, Jessica (Department: 2838)

Electrical transmission or interconnection systems

Plural supply circuits or sources

Connecting or disconnecting

C307S082000, C363S065000

Reexamination Certificate

active

06720675

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a power conversion apparatus such as an uninterruptible power supply that is capable of supplying power to a load even if an abnormality, such as a power failure or a momentary voltage drop, occurs in a system power supply. More particularly, the present invention relates to an apparatus having a function of coping with unbalanced loads.
BACKGROUND ART
A conventional AC/DC conversion apparatus disclosed in JP Patent No. 2765372 is shown in FIG.
24
. In this drawing, reference numeral
100
denotes an AC power supply, numeral
101
a switch means, numeral
102
a reactor, numerals
103
and
104
transistors, numerals
105
and
106
diodes, numerals
107
and
108
capacitors, numerals
109
and
110
resistors functioning as DC loads, and numeral
111
a battery.
In the apparatus constructed in this manner, in the case where the AC power supply
100
operates normally, the switch means
101
is connected to a contact point A and the transistors
103
and
104
are alternately turned on/off. As a result, a current of the reactor
102
is controlled so that the power factor of a current flowing to the AC power supply
100
becomes one, and the capacitors
107
and
108
are charged. Also, the charged energy is supplied to each of the resistors
109
and
110
.
Also, in the case where an abnormality, such as a power failure, occurs in the AC power supply
100
, energy is supplied from the battery
111
to the resistors
109
and
110
. During this operation, in the case where the resistors
109
and
110
have the same resistance value, that is, in the case where these resistors consume the same amount of power, the amount of energy supplied from the capacitor
107
to the resistor
109
becomes the same as that supplied from the capacitor
108
to the resistor
110
. As a result, the voltages of the capacitors
107
and
108
become equal to each other at all times. That is, the voltage values of the capacitors
107
and
108
are balanced by the energy supplied from the battery
111
.
However, in the case of unbalanced loads where values of the resistors
107
and
108
differ from each other, for instance, voltages values of the capacitors
107
and
108
are unbalanced. This is because only the battery
111
charges the two capacitors
107
and
108
and it becomes impossible to control the potential at an interconnection point C between the capacitors
107
and
108
.
Even if the AC power supply operates normally, in the case of such unbalanced loads, an imbalance occurs. However, for instance, JP Laid-Open No. 2000-278954 discloses a technique of eliminating imbalance by changing the ratio between on/off times during the switching of the transistors
103
and
104
using an unillustrated control circuit.
By the way, if an abnormality like a power failure occurs in the AC power supply
100
and the voltages of the capacitors
107
and
108
are unbalanced, there occurs a problem that desired voltages are not applied to the loads
109
and
110
. That is, in the case of unbalanced loads where the value of the resistor
110
is smaller than the value of the resistor
109
, for instance, the voltage of the capacitor
108
ultimately becomes zero and the voltage of the capacitor
107
becomes VB.
In view of this problem, with the conventional technique disclosed in the above-mentioned publication, in the case where an abnormality like a power failure occurs in the AC power supply
100
, the switch means
101
is switched to a contact point B. Also, to stabilize the potential at the interconnection point C, the current of the reactor
102
is controlled by performing the switching of the transistors
103
and
104
using an unillustrated control circuit. As a result of this operation, the voltages of the two capacitors
107
and
108
become equal to each other at all times even in the case of the unbalanced loads. Also, power supply to the loads
109
and
110
is performed with stability.
By the way, in the case of a single-phase three-wire system AC power supply, conversion blocks
114
and
115
, each of which includes a reactor, a transistor, and a diode a in
FIG. 24
, are connected to AC power supplies
112
and
113
, as shown in FIG.
25
. In this drawing, reference numerals
116
and
117
denote capacitors, numerals
120
and
121
resistances, and numeral
124
a battery.
In the case of such a single-phase three-wire system, an attempt may be made to use the conventional technique disclosed in JP Patent No. 2765372 described above, which is also capable of coping with unbalanced loads when an abnormality occurs in an AC power supply. Then, there may be conceived a method with which control is performed so that the voltage values of the capacitors
116
and
117
are balanced by switching contact points of the switch means
125
and
126
as shown in FIG.
26
. However, with the construction shown in
FIG. 26
, the voltages VC
1
and VC
2
of the capacitors
116
and
117
are applied to the reactors within the conversion blocks
114
and
115
as they are, so that there occurs a problem that ripple currents flowing to the reactors become large. As a result, the efficiency of AC/DC conversion is lowered or noise from the reactors is increased.
Also, as shown in
FIG. 27
, there may be a case where a filter capacitor
130
is connected to remove a ripple current that occurs in the reactor
102
due to the switching of the transistors
103
and
104
. In this case, as shown in
FIG. 28
, when it is detected that an abnormality occurs in the AC power supply
100
(T(fault)) and the switch means
101
is switched from “A” to “B”, a voltage remains in the filter capacitor
130
. Consequently, a steep current that leads to the discharging of the voltage of the filter capacitor
130
is generated concurrently with the switching of the switch means
101
. Also, this steep current flows to the switch means
101
, so that there may occur a problem that the switch means
101
is damaged by an excess current. FIG.
28
(
a
) shows a voltage waveform of the AC power supply
100
, FIG.
28
(
b
) shows a voltage waveform of the filter capacitor
130
, and FIG.
28
(
c
) shows a current waveform of the filter capacitor
130
.
The present invention has been made to solve the problems described above, and a first object of the present invention is to provide a power conversion apparatus having a plurality of AC power supplies, wherein even if an abnormality occurs in at least one of the AC power supplies and loads that are respectively connected to two capacitors are not balanced, the power conversion apparatus is capable of balancing voltages of the two capacitors and is also capable of reducing losses and noises by decreasing a ripple current flowing to a reactor during the switching of the transistors
103
and
104
.
Also, in the case where a filter capacitor is connected, a second object of the present invention is to provide a power conversion apparatus that is capable of preventing a situation where a switch means is damaged because electric charges of the filter capacitor are discharged and a steep current flows to the switch means when the switch means is turned on.
Further, in the case where a filter capacitor is connected, a third object of the present invention is to provide a power conversion apparatus that is capable of reducing losses by suppressing unnecessary resonance that occurs between the filter capacitor and a reactor when a switch means is turned on.
DISCLOSURE OF THE INVENTION
According to the present invention, a first power conversion apparatus is provided with: a first AC/DC conversion means constructed by connecting a first AC power supply, a first reactor, and a series body of a first switching means in series; a second AC/DC conversion means constructed by connecting a second AC power supply, a second reactor, and a series body of a second switching means in series; two capacitors connected in series, an interconnection point of the two capacitors being connected to one end of each of the two AC power suppl

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