Power transfer device

Details Power transfer device Power transfer device

2000-09-07

2002-10-15

Fleming, Fritz (Department: 2836)

Electrical transmission or interconnection systems

Plural supply circuits or sources

Diverse or unlike electrical characteristics

C307S070000, C307S087000

Reexamination Certificate

active

06465912

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power transfer device which is connected to AC power sources of different kinds, which normally supplies power from first AC power source to a load, and which, when an abnormality, such as a voltage drop, occurs in the power source, switches to another or second power AC power source so as to continuously supply power to the load.
2. Description of the Related Art
FIG. 12
is a diagram schematically showing the configuration of a conventional power transfer device which disclosed in, for example, U.S. Pat. No. 5,644,175, and
FIG. 13
is a flowchart showing a procedure of a transferring operation in the conventional power transfer device shown in FIG.
12
.
In
FIG. 12
,
1
a
denotes a first AC power source,
1
b
denotes a second AC power source, and
2
denotes a load which is connected to one of the AC power sources and requested to always operate.
The reference numerals
3
a
and
3
b
denote first and second current transfer switches (referred to also as current transferring section) which are connected between the first AC power source
1
a
and the load
2
, and the second AC power source
1
b
and the load
2
to select an AC power source which supplies a current to the load
2
, respectively.
The reference numerals
4
a
1
and
4
a
2
denote current directional semiconductor switches such as thyristors which constitute the first current transfer switch
3
a,
and which do not have self-arc extinguishing properties. The switches are connected in parallel so that their conduction directions are opposed to each other.
Similarly,
4
b
1
and
4
b
2
denote current directional semiconductor switches such as thyristors which constitute the second current transfer switch
3
b,
and which do not have self-arc extinguishing properties. The switches are connected in parallel so that their conduction directions are opposed to each other.
The reference numerals
5
a
1
and
5
a
2
denote gate drivers which supply gate signals to the semiconductor switches
4
a
1
and
4
a
2
constituting the first current transfer switch
3
a,
respectively, and
5
b
l and
5
b
2
denote gate drivers which supply gate signals to the semiconductor switches
4
b
1
and
4
b
2
constituting the second current transfer switch
3
b,
respectively.
The reference numerals
6
a
1
,
6
a
2
,
6
b
1
, and
6
b
2
denote signal switches for switching over an ON signal (conduction signal) and an OFF signal (non-conduction signal) that are to be supplied to the gate drivers
5
a
1
,
5
a
2
,
5
b
l, and
5
b
2
.
The reference numeral
7
denotes a voltage detector for detecting the voltage of the first AC power source
1
a,
8
denotes a power interruption detector for detecting a power interruption of the first AC power source
1
a
on the basis of the voltage of the AC power source
1
a
which is detected by the voltage detector
7
, and for outputting a power interruption signal,
9
denotes a current detector for detecting a current flowing from the first AC power source
1
a
to the load
2
, and
10
denotes a current direction detector for receiving the power interruption signal from the power interruption detector
8
, for detecting the current direction on the basis of the polarity of the current detected by the current detector
9
and flowing from the first AC power source
1
a
to the load
2
, and for causing the signal switches
6
b
1
and
6
b
2
to select the ON signal or the OFF signal in accordance with a result of the detection.
The power interruption detector
8
causes the signal switches
6
a
1
and
6
a
2
to select the ON signal until a power interruption is detected (i.e., during a period when the first AC power source normally operates in a correct manner), and, when a power interruption is detected, outputs the power interruption signal (i.e., a power transfer signal for transferring from the first AC power source to the second AC power source) to cause the signal switches
6
a
1
and
6
a
2
to select the OFF signal.
Next, the operation of the conventional power transfer device will be described.
Referring to
FIG. 12
showing the configuration of the conventional power transfer device, in a normal state, the signal switches
6
a
1
and
6
a
2
selects the ON signal, the gate drivers
5
a
1
and
5
a
2
supply the gate signal to the semiconductor switches
4
a
1
and
4
a
2
constituting the first current transfer switch
3
a,
the semiconductor switches
4
a
1
and
4
a
2
are therefore turned ON (enter the conduction state), and the first AC power source
1
a
is connected to the load
2
, so that the power is supplied to the load from the first AC power source
1
a.
When an abnormality such as a power interruption occurs in the first AC power source
1
a
and the voltage applied to the load
2
is lowered, the power interruption detector
8
detects the power interruption on the basis of the voltage drop of the first AC power source
1
a
which is detected by the voltage detector
7
, and generates the power interruption signal.
Upon reception of the power interruption signal output from the power interruption detector
8
, the signal switches
6
a
1
and
6
a
2
select the OFF signal to cancel the gate signals for the semiconductor switches
4
a
1
and
4
a
2
constituting the first current transfer switch
3
a.
At this time, since the semiconductor switches
4
a
1
and
4
a
2
constituting the first current transfer switch
3
a
cannot perform self-arc extinguishing, the semiconductor switches
4
a
1
and
4
a
2
cannot enter the OFF state (non-conduction state) until the currents of the semiconductor switches
4
a
1
and
4
a
2
are reduced to a predetermined current level or lower, and hence the load
2
cannot be disconnected from the power source
1
a.
To comply with this, in the conventional power transfer device disclosed in U.S. Pat. No. 5,644,175, the current flowing from the first AC power source
1
a
is cancelled by a current flowing from the second AC power source
1
b
which is the sound AC voltage source, whereby the current flowing through the semiconductor switch
4
a
1
or
4
a
2
is lowered to the predetermined current level or less which is required for attaining the OFF state, so as to hasten the interrupting operation of the first current transfer switch
3
a.
Furthermore, at the timing when the first current transfer switch
3
a
is interrupted, the second current transfer switch
3
b
has been already turned ON, and hence the time period when the voltage applied to the load
2
is low can be shortened.
The operation procedure of the conventional power transfer device will be described with reference to the flowchart of FIG.
13
.
In the following description, it is assumed that the direction of the current which is flowing from the first AC power source
1
a
to the load
2
at the occurrence of the power interruption coincides with that of the arrow shown above the current detector
9
in FIG.
12
.
When a power interruption occurs in the first AC power source
1
a
(step
1
of
FIG. 13
) and the voltage of the first AC power source
1
a
detected by the voltage detector
7
is lowered, the power interruption detector
8
detects the power interruption (step
2
of FIG.
13
), and then generates the power interruption signal.
In response to the power interruption signal generated by the power interruption detector
8
, the signal switches
6
a
1
and
6
a
2
switch over from the ON signal to the OFF signal, and the gate signals generated by the gate drivers
5
a
1
and
5
a
2
are cancelled (step
3
of FIG.
13
).
In response to the cancellation of the gate signals, the semiconductor switches
4
a
1
and
4
a
2
constituting the first current transfer switch
3
a
enter a state where the switches can be turned OFF at any time. Since the semiconductor switches
4
a
1
and
4
a
2
are semiconductor elements which cannot perform self-arc extinguishing, however, the semiconductor switch
4
a
1
through which the current is flowing continues to be in the ON state

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