U.S. patent application number 12/420567 was filed with the patent office on 2009-09-10 for stable power supplying apparatus.
This patent application is currently assigned to KANSAI Electric Power Co., Inc.. Invention is credited to Yoshitaka Sugawara.
Application Number | 20090225573 12/420567 |
Document ID | / |
Family ID | 35599813 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090225573 |
Kind Code |
A1 |
Sugawara; Yoshitaka |
September 10, 2009 |
STABLE POWER SUPPLYING APPARATUS
Abstract
A stable power supply apparatus in accordance with the present
invention comprises a secondary battery, a bidirectional chopper
circuit and a bidirectional converter, wherein the secondary
battery, the chopper circuit and the converter are connected in
this order in the direction from the secondary battery side to a
system bus line side. The converter is formed of a wide-gap
semiconductor device, more particularly, a wide-gap bipolar
semiconductor device, and the instantaneous large-power operation
capability of the wide-gap bipolar semiconductor device and the
instantaneous large-power supplying capability of the secondary
battery are utilized. For a short time during which the influence
of an instantaneous drop is prevented, the converter is operated as
a converter having capability exceeding the instantaneous
large-power supplying capability of the secondary battery and
having power capacity several times or more the rating of the
converter.
Inventors: |
Sugawara; Yoshitaka;
(Osaka-shi, JP) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET, SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
KANSAI Electric Power Co.,
Inc.
Osaka
JP
|
Family ID: |
35599813 |
Appl. No.: |
12/420567 |
Filed: |
April 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10894328 |
Jul 19, 2004 |
7554220 |
|
|
12420567 |
|
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Current U.S.
Class: |
363/56.01 |
Current CPC
Class: |
H01M 10/42 20130101;
H02J 9/062 20130101; Y02E 60/10 20130101; H01M 10/425 20130101 |
Class at
Publication: |
363/56.01 |
International
Class: |
H02H 7/122 20060101
H02H007/122 |
Claims
1. A converter comprising a wide-gap bipolar semiconductor device
with positive temperature dependence of device resistance at over
several hundreds degrees centigrade as a switching device, and
having a first control status to be operated under a rated power
and a second control status to be operated under a power that is 3
to 30 times the rated power.
2. A converter comprising a wide-gap bipolar semiconductor device
as a switching device with positive temperature dependence of
device resistance at over several hundreds degrees centigrade, and
having a first control status to be operated under a rated power
and a second control status to be operated under a power that is
1.4 to 5 times the rated power.
Description
[0001] This application is a division of U.S. patent application
Ser. No. 10/894,328 filed Jul. 19, 2004, which is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a stable power supply
apparatus connected to a power system, and more particularly to a
stable power supply apparatus utilizing a secondary battery, such
as a redox flow battery, a sodium sulfur battery or a lead-acid
battery.
[0003] In recent years, electronic apparatuses which are sensitive
to fluctuations in a power supply voltage, such as personal
computers and precision electronic apparatuses equipped with
precision motors, have been used frequently. Hence, the need for
countermeasures against an instantaneous voltage drop (hereafter
simply referred to as an instantaneous drop), a phenomenon wherein
the power supply voltage lowers significantly for a short time, is
growing, and demand for stable power supply apparatuses serving as
demand for stable power supply apparatuses serving as instantaneous
voltage drop countermeasure apparatuses is increasing. In addition,
it is required to add an instantaneous voltage drop countermeasure
function to various kinds of stable power supply apparatuses having
been used conventionally, such as a load leveling apparatus, a peak
cut apparatus, a frequency fluctuation suppressive apparatus, a
voltage regulating apparatus and a flicker countermeasure
apparatus. The state wherein the above-mentioned load leveling
apparatus, peak cut apparatus, etc. are operating in accordance
with their ordinary functions, such as load leveling and peak
cutting, is hereafter referred to as "normal time."
[0004] FIG. 11 is a block diagram of a power supply system having a
conventional stable power supply apparatus 101 using a redox flow
battery as a secondary battery. In the figure, a system bus line
102 is connected to the power system 100 of a substation 130 via a
transformer 120. The stable power supply apparatus 101 is connected
to this system bus line 102 via a switch 103. To the system bus
line 102, important loads 104 and 105, for example, are connected
via switches 114 and 115, respectively. The important loads 104 and
105 are, for example, important facilities of bulk power customers
requiring particularly stable power supply, such as semiconductor
production plants and precision machining plants. A general load
110 is also connected to the system bus line 102 via switches 109
and 111. The stable power supply apparatus 101 comprises a
transformer 106 mainly serving as an interconnecting reactor, a
converter 107 for converting AC power to DC power or vice versa,
and a redox flow battery serving as a large-capacity secondary
battery 108. This stable power supply apparatus 101 functions as a
peak cut apparatus or a load leveling apparatus in normal time;
however, it also operates as an instantaneous voltage drop
countermeasure apparatus for preventing operation stop or the like
of the important loads 104 and 105 during an instantaneous drop
owing to the occurrence of a lightning accident or the like.
[0005] The function of the stable power supply apparatus 101 will
be described below in detail. In "stationary time," a state wherein
the supply and demand state of the power in the power supply system
connecting the substation 130 to the important loads 104, 105, and
the general load 110 is balanced, the AC power supplied from the
system bus line 102 to the stable power supply apparatus 101 via
the switch 103 and the transformer 106 is converted into DC power
by the converter 107 and charges the secondary battery 108. On the
other hand, in the case that the power consumption of the important
load 104 or 105 increases significantly and the power supplied to
the loads 104 and 105 transiently exceeds the capacity of the
substation 130, this state is detected by a detection circuit 8
having a voltage detector 10 and a current detector 11. The
detected output of the detection circuit 8 is fed to a control
circuit 9. The control circuit 9 controls the converter 107 to
convert the DC power discharged from the secondary battery 108 into
AC power with the converter 107 and supplies an active power
corresponding to the amount of the above-mentioned excess to the
system bus line 102, thereby stabilizing the supply and demand. The
power corresponding to the excess amount that should be supplied
from the system bus line 102 is supplied from the stable power
supply apparatus 101 instead, whereby the peak of power supplied
from the system bus line 102 can be cut; hence, this function is
referred to as "peak cut."
[0006] In the case that the capacity of the secondary battery 108
of the stable power supply apparatus 101 is made larger so that a
power capable of being supplied for a long time can be stored, the
apparatus can be used as a load leveling apparatus. In other words,
the secondary battery 108 is charged with constant power for a
constant time (about eight hours in a typical case) during a low
consumption time zone at night, and power is supplied from the
secondary battery 108 at constant power for a constant time (about
eight hours in a typical case) during a high consumption time zone
in the daytime. Hence, a power exceeding the servable power of the
substation 130 can be supplied during the high consumption time
zone. The stable power supply apparatus for this use levels the
large difference between the power demand in the daytime and that
at night; hence, the apparatus is referred to as a "load leveling
apparatus."
[0007] In the case when the power system 100 was struck by
lightning and an instantaneous drop occurred in the voltage of the
system, the voltage detector 10 detects the instantaneous drop. The
voltage of the system must be restored immediately to the voltage
before the instantaneous drop in order to prevent operation stop
and the like of the important loads 104 and 105 due to the
instantaneous drop. For this purpose, the stable power supply
apparatus 101 controls the converter 107 with the control circuit 9
and supplies reactive power and active power from the secondary
battery 108 to the important loads 104 and 105 via the converter
107 and the system bus line 102 so as to maintain the stable supply
of power. When the power supplied from the secondary battery 108 is
insufficient, the switch 109 is opened to disconnect the general
load 110 that is low in importance so as to supply desired power to
at least the important loads 104 and 105 and to prevent operation
stop of the important loads 104 and 105. Immediately after recovery
from the instantaneous drop, the converter 107 is recovered to its
normal operation state, and power is supplied.
[0008] In the conventional stable power supply apparatus, during
peak cut time and load leveling time, it is necessary to supply,
for example, a power of about 500 kW in the former case or a power
of about 2 MW in the latter case for a relatively long time (for
example, about one hour in the former case or about eight hours in
the latter case). When an instantaneous drop occurs owing to
lightning during peak cut or load leveling operation, it is
necessary to additionally supply a power of one to several MW for a
relatively short time (for example, two seconds) in order to
recover the lowered voltage.
[0009] Secondary batteries, such as a redox flow battery, a sodium
sulfur battery and a lead-acid battery, have "instantaneous
large-current supplying capability", whereby they can supply, for
several seconds to several minutes, a current about several times
the rated current thereof that can be supplied in normal time. By
utilizing this capability at the time of an instantaneous drop,
countermeasures against the instantaneous voltage drop can be taken
without increasing the rated capacity of the secondary battery. For
this reason, the conventional stable power supply apparatus was
equipped with the large converter 107 having a large power capacity
corresponding to the instantaneous large current supplying
capability of the secondary battery. It was necessary to set the
power capacity of the converter 107 to several times the power
capacity required in normal time, for example.
[0010] Such an instantaneous drop owing to lightning does not occur
very frequently, about 20 times at most in a year. In addition, the
duration of an instantaneous drop owing to lightning is several
seconds even in the case of multiple lightning. A short circuit or
a ground fault may occur in a rare case when a small animal, such
as a snake or a bird, is caught on power transmission lines or when
trees make contact with power transmission lines. In this case, an
"instantaneous drop" of a relatively long time, exceeding several
minutes, may occur. However, providing a large converter having
rated power several times the power supplied in normal time to take
countermeasures for an instantaneous drop or an instantaneous power
failure that does not occur frequently as described above causes
problems; that is, the stable power supply apparatus is made large
in size and heavy in weight, the power loss thereof increases, the
cost of the equipment rises, and the expenses during operation also
rise.
SUMMARY OF THE INVENTION
[0011] The present invention purposes to realize a stable power
supply apparatus capable of supplying power significantly exceeding
the power in normal time at the time of an instantaneous drop or an
instantaneous power failure by using a converter having a power
rating corresponding to the power required in normal time so that
the stable power supply apparatus is made compact in size, light in
weight, low in loss and low in cost.
[0012] A stable power supply apparatus in accordance with the
present invention comprises a secondary battery for charging and
discharging DC power, and a converter, connected between the
above-mentioned secondary battery and the system bus line of a
power transmission power supply and having a switching device
formed of a wide-gap bipolar semiconductor device, for converting
AC input from the above-mentioned system bus line into DC so as to
output to the above-mentioned secondary battery, and for converting
DC output from the above-mentioned secondary battery into AC so as
to output to the above-mentioned system bus line.
[0013] The wide-gap bipolar semiconductor device can control power
that is 3 to 30 times the rated power thereof for a short time of
several seconds. Furthermore, in the case that a high-performance
heatsink is used, the device can control power that is 1.4 to 5
times the rated power for several minutes. In the present
invention, a wide-gap semiconductor device is used as the switching
device of the converter, and its rated power is set at the value
obtained in "normal time." At the time of an instantaneous drop or
an instantaneous power failure during which large power is required
to be supplied in significantly exceeding the rated power; however,
the converter is not broken since the time during which the large
power is supplied is short.
[0014] A stable power supply apparatus in accordance with another
aspect of the present invention comprises a secondary battery for
charging and discharging DC power (Sic), and a bidirectional
chopper circuit, connected to the above-mentioned secondary
battery, for lowering the charge voltage of the secondary battery
and for raising the discharge voltage of the secondary battery.
Between the above-mentioned chopper circuit and the system bus line
of a power transmission power supply, a converter having a
switching device formed of a wide-gap bipolar semiconductor device
is connected to convert AC inputted from the above-mentioned system
bus line into DC so as to output to the chopper circuit, and to
convert DC inputted from the above-mentioned chopper circuit into
AC so as to output to the above-mentioned system bus line.
[0015] In the stable power supply apparatus in accordance with the
present invention, the charge voltage of the secondary battery is
lowered and the discharge voltage thereof is raised by the
bidirectional chopper circuit; hence, in addition to bidirectional
chopper circuit; hence, in addition to the above-mentioned effect,
the stable power supply apparatus can also be applied to the system
bus line having a voltage higher than the voltage of the secondary
battery.
[0016] A stable power supply apparatus in accordance with another
aspect of the present invention comprises a secondary battery for
charging and discharging DC power, and a bidirectional chopper
circuit, connected to the above-mentioned secondary battery, for
lowering the charge voltage of the secondary battery and for
raising the discharge voltage of the secondary battery. Between the
above-mentioned chopper circuit and the system bus line of a power
transmission power supply, a converter having a switching device
formed of a wide-gap bipolar semiconductor device is connected to
convert AC inputted from the above-mentioned system bus line into
DC so as to output to the chopper circuit, and to convert DC
inputted from the above-mentioned chopper circuit into AC so as to
output to the above-mentioned system bus line. The above-mentioned
stable power supply apparatus further comprises a detection
apparatus for detecting the voltage of the above-mentioned system
bus line and for detecting the supply and demand state of the power
on the basis of the detected voltage, and a control circuit for
controlling the above-mentioned converter on the basis of the
detected output of the above-mentioned detection apparatus so as to
charge the above-mentioned secondary battery when the supply and
demand state of the power between a load connected to the
above-mentioned system bus line and the power transmission power
supply is balanced and so as to discharge the above-mentioned
secondary battery and to supply power to the system bus line when
the demand becomes larger than the supply.
[0017] In accordance with the present invention, in addition to the
above-mentioned effect, by detecting the voltage of the system bus
line, the generation of an instantaneous drop is detected, whereby
the voltage of the system can be prevented from lowering at the
time of the instantaneous drop.
[0018] A stable power supply apparatus in accordance with another
aspect of the present invention comprises a secondary battery for
charging and discharging DC power, and a bidirectional chopper
circuit, connected to the above-mentioned secondary battery, for
lowering the charge voltage of the secondary battery and for
raising the discharge voltage of the secondary battery. Between the
above-mentioned chopper circuit and the system bus line of a power
transmission power supply, a converter having a switching device
formed of a wide-gap bipolar semiconductor device is connected to
convert AC inputted from the above-mentioned system bus line into
DC so as to output to the chopper circuit, and to convert DC
inputted from the above-mentioned chopper circuit into AC and so as
to output to the above-mentioned system bus line. The
above-mentioned stable power supply apparatus further comprises a
detection apparatus for detecting the voltage and current of the
above-mentioned system bus line and for detecting the supply and
demand of the power of the above-mentioned load on the basis of the
detected voltage and current, and a control circuit for controlling
the above-mentioned converter on the basis of the detected output
of the above-mentioned detection apparatus so as to charge the
above-mentioned secondary battery when the supply and demand of the
power between a load connected to the above-mentioned system bus
line and the power transmission power supply is balanced, and so as
to discharge the above-mentioned secondary battery and to supply
power to the system bus line when the demand becomes larger than
the supply.
[0019] In accordance with the present invention, in addition to the
above-mentioned effect, by detecting the voltage and current of the
system bus line, the supply and demand state of the power of the
system can be detected. Since the supply and demand state of the
power can be detected, the stable power supply apparatus in
accordance with the present invention can be used for load
leveling.
[0020] A stable power supply apparatus in accordance with another
aspect of the present invention outputs discharge power that is 2
to 12 times the rated discharge power of the above-mentioned
secondary battery from the above-mentioned secondary battery at the
time of an instantaneous voltage drop during which the voltage of
the above-mentioned system bus line lowers significantly for a
short time owing to the occurrence of a lightning accident or the
like. The above-mentioned converter is controlled by the
above-mentioned control circuit so as to convert the discharge
power of the above-mentioned secondary battery, corresponding to
that of 2 to 12 times the rated control power of the converter,
into AC and to output a predetermined reactive power and an active
power that is 2 to 12 times the rated power to the system bus
line.
[0021] At the time of instantaneous voltage drop during which the
voltage of the above-mentioned system bus line lowers significantly
for a short time owing to the occurrence of a lightning accident or
the like, discharge power that is 2 to 12 times the rated discharge
power of the above-mentioned secondary battery is output from the
above-mentioned secondary battery. The above-mentioned converter is
controlled by the above-mentioned control circuit to convert the
discharge power of the above-mentioned secondary battery,
corresponding to that of 2 to 12 times the rated control power of
the converter, into AC and to output predetermined reactive power
and active power that is 2 times or less the rated power to the
system bus line.
[0022] It is characterized in that a transformer having the
function of an interconnecting reactor is provided between the
above-mentioned system bus line and converter.
[0023] It is characterized in that an interconnecting reactor is
provided between the above-mentioned system bus line and
converter.
[0024] It is characterized in that a transformer is provided
between the above-mentioned system bus line and converter.
[0025] It is characterized in that the above-mentioned secondary
battery is a redox flow battery or a sodium sulfur battery.
[0026] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is a gate turn off thyristor (GTO)
wherein silicon carbide (SiC) is used as a basic material.
[0027] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is a semiconductor device wherein
gallium nitride is used as a basic material.
[0028] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is formed of at least one SiC-GTO
chip.
[0029] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is an insulated gate bipolar
transistor (IGBT) wherein silicon carbide (SiC) is used as a basic
material.
[0030] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is formed of at least one SiC-GTO chip
or a plurality of SiC-GTO chips connected in parallel.
[0031] It is characterized in that the above-mentioned wide-gap
bipolar semiconductor device is formed of at least one SiC-IGBT
chip or a plurality of SiC-IGBT chips connected in parallel.
[0032] A stable power supply apparatus in accordance with another
aspect of the present invention comprises a secondary battery for
charging and discharging DC power, and a bidirectional chopper
circuit for lowering the charge voltage of the above-mentioned
secondary battery and for raising the discharge voltage of the
above-mentioned secondary battery. Between the above-mentioned
chopper circuit and the system bus line of a power transmission
power supply, a converter having a wide-gap bipolar semiconductor
device serving as a switching device is connected to convert AC
inputted from the above-mentioned system bus line into DC so as to
output to the chopper circuit, and to convert DC inputted from the
above-mentioned chopper circuit into AC so as to output to the
above-mentioned system bus line. The above-mentioned stable power
supply apparatus further comprises a detection apparatus for
detecting the frequency of the above-mentioned system bus line and
for detecting the supply and demand state of the power on the basis
of the detected frequency, and a control circuit for controlling
the above-mentioned converter on the basis of the detected output
of the above-mentioned detection apparatus so as to charge the
above-mentioned secondary battery when the supply and demand state
of the power between a load connected to the above-mentioned system
bus line and the power transmission power supply is balanced, and
so as to discharge the above-mentioned secondary battery and to
supply power to the system bus line when the demand becomes larger
than the supply.
[0033] A stable power supply apparatus in accordance with another
aspect of the present invention comprises a secondary battery for
charging and discharging DC power, and a wide-gap bipolar
semiconductor device serving as a switching device and connected
between the above-mentioned secondary battery and a load connected
to the system bus line of a power transmission power supply. The
above-mentioned stable power supply apparatus further comprises a
converter for converting AC inputted from the above-mentioned
system bus line into DC so as to output to the above-mentioned
secondary battery, and for converting DC output from the
above-mentioned secondary battery into AC and so as to output to
the above-mentioned load.
[0034] This stable power supply apparatus further comprises a
detection apparatus for detecting the voltage and current of the
power supplied to a load connected to the above-mentioned system
bus line and for detecting the supply and demand state of the power
of the above-mentioned load on the basis of the detected voltage
and the current. The above-mentioned stable power supply apparatus
further comprises a control circuit for controlling the
above-mentioned converter on the basis of the detected output of
the above-mentioned detection apparatus so as to charge the
above-mentioned secondary battery when the supply and demand of the
power between the above-mentioned load and power transmission power
supply is balanced, and so as to discharge the above-mentioned
secondary battery and to supply power to the system bus line when
the demand becomes larger than the supply.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 is a block diagram showing a stable power supply
apparatus for peak cut in accordance with a first embodiment of the
present invention;
[0036] FIG. 2 (a) is a top view of the module configuration of a
SiC-GTO device for a converter in accordance with the first
embodiment;
[0037] FIG. 2 (b) is a sectional view taken on line b-b of FIG. 2
(a);
[0038] FIG. 3 is a cross-sectional view of a SiC-GTO chip;
[0039] FIG. 4 is a block diagram of a stable power supply apparatus
for load leveling in accordance with a second embodiment and a
sixth embodiment of the present invention;
[0040] FIG. 5 is a block diagram of a stable power supply apparatus
for frequency fluctuation prevention in accordance with a third
embodiment of the present invention;
[0041] FIG. 6 is a block diagram of a stable power supply apparatus
for peak cut in accordance with a fourth embodiment of the present
invention;
[0042] FIG. 7 is a block diagram of a stable power supply apparatus
in accordance with a fifth embodiment of the present invention;
[0043] FIG. 8 is a block diagram of the stable power supply
apparatus in accordance with the first embodiment of the present
invention in the case of dealing with an instantaneous drop;
[0044] FIG. 9 is a block diagram of the stable power supply
apparatus in accordance with the fourth embodiment of the present
invention in the case of dealing with an instantaneous drop;
[0045] FIG. 10 is a block diagram of the stable power supply
apparatus in accordance with the fifth embodiment of the present
invention in the case of dealing with an instantaneous drop;
and
[0046] FIG. 11 is the block diagram of the conventional stable
power supply apparatus for peak cut.
DETAILED DESCRIPTION OF THE INVENTION
[0047] Embodiments in accordance with the present invention will be
described below.
[0048] Wide-gap semiconductor devices in which SiC (silicon
carbide), GaN (gallium nitride), diamond, etc. are used as basic
materials are low in loss and have a physical property of being
capable of operating at high temperatures in comparison with
semiconductor devices in which Si (silicon) is used as a basic
material. With attention paid to this point, the maximum allowable
power in a short time, which was controlled by a wide-gap
semiconductor device was examined, and it was found that the
wide-gap semiconductor device was not broken for a short time of
about several seconds even when a current far beyond the rated
current thereof was passed therethrough. It was confirmed that a
wide-gap bipolar semiconductor device in particular had
"instantaneous large-power operation capability" that was able to
pass a large current beyond the "instantaneous large-current
supplying capability" of a secondary battery. A converter is formed
by using a wide-gap semiconductor device having this characteristic
as a switching device and is operated at a voltage and a current
within the rating of the wide-gap semiconductor device in normal
time. At the time of an instantaneous drop, discharged DC power
several times the value in normal time depending on the
instantaneous large power supplying capability of the secondary
battery is converted into AC power by the above-mentioned converter
and is supplied to a system bus line.
[0049] In normal time, after the DC output voltage obtained by the
discharge of the secondary battery is raised by a chopper circuit,
it is converted into AC power by the converter and is output to the
system bus line, whereby various power stabilizing functions are
carried out. The secondary battery is charged in "stationary time"
wherein the power stabilizing functions are not carried out. When
the secondary battery is charged, the AC power from the system bus
line is converted into DC power by the converter and lowered by the
chopper circuit and is charged into the secondary battery. The
power values charged and discharged in stationary time and in
normal time are within the rating of the converter.
[0050] At the time of an instantaneous drop or an instantaneous
power failure, a current several times the rating is supplied from
the secondary battery depending on the instantaneous large-current
supplying capability thereof while a voltage almost close to the
rated voltage of the battery is maintained. In other words, DC
power almost several times the rated power is supplied. After this
DC power is raised by the chopper circuit, it is converted into AC
power by the converter and is output to the system bus line,
whereby power supply is stabilized.
[0051] As the converter, a converter having a generally known
PWM-operation-type switching device is used to carry out pulse
width modulation. It is desired that the phase of the output
voltage of a pulse width modulation converter (hereafter referred
to as a PWM converter) should be advanced with respect to the phase
of the voltage of the system bus line, and the same power as that
obtained in normal time should be output to the system bus line,
and that active power for stable power supply should be output.
Since the voltage of the system bus line lowers at an instantaneous
drop in many cases, the converter is operated by enlarging the
pulse width in pulse width modulation, whereby a reactive power
several times the value obtained in normal time is output, and the
dropped voltage of the system bus line is recovered to the voltage
before the instantaneous drop.
[0052] In the case that the wide-gap semiconductor devices of the
converter are operated at the time of an instantaneous drop at
large power depending on the instantaneous large-current supplying
capability of the secondary battery, it was found by experiment
that the instantaneous large-power operation capability of a
unipolar semiconductor device, such as a wide-gap semiconductor
MOSFET, was about two times the rating thereof. On the other hand,
it was found by experiment that the instantaneous large-power
operation capability of a wide-gap bipolar semiconductor device,
such as a GTO (Gate turn off thyristor) or an IGBT (Insulated gate
bipolar transistor), was larger than that of the unipolar
semiconductor device, 3 to 30 times or more the rating. According
to the results of the above-mentioned experiments, the wide-gap
bipolar semiconductor device is more suitable for the semiconductor
device that is used for the switching device of the converter of
the stable power supply apparatus in accordance with the present
invention rather than the unipolar semiconductor device.
[0053] The converter can be formed using one wide-gap semiconductor
chip for controlling small power. For controlling large power, it
is difficult to produce a chip having a large area capable of
passing a large current such as a use in the present invention,
because numerous crystal defects are present in the SiC of the
basic material, of the wide-gap semiconductor device. If the
technology for reducing the crystal defects in SiC is improved, a
semiconductor device can be attained by using a single chip having
a large area, as in the case of Si; however, in the present state,
a method of connecting a plurality of chips in parallel is thought
to pass a large current. It is regarded that the parallel
connection of a plurality of chips, in the case of a Si
semiconductor device, is possible in a combination device such as
an IGBT in which unipolar operation and bipolar operation coexist;
however, it is regarded that the parallel connection is difficult
in the case of a semiconductor device such as a GTO in which only
the bipolar operation exists. The reason is described below. In the
combination device such as an IGBT in which unipolar operation and
bipolar operation coexist, the bipolar operation has a negative
temperature dependency, and the unipolar operation has a positive
temperature dependency. Therefore, even if a large current flows,
thermal runaway does not occur because of the canceling effect of
the positive and negative temperature dependencies. In other words,
in the case of the unipolar operation device, the resistance of
channel is the largest in the ON resistance of the device, and the
positive temperature dependency of this channel resistance is
mainly predominant.
[0054] On the other hand, in the case of the bipolar operation
device, when its temperature rises, its junction potential lowers
and carrier injection increases; however, because its life time is
prolonged, its current increases. Hence, the temperature of the
device rises further, the carrier injection and the increase of the
life time are accelerated, and the current increases further; the
device thus has a negative temperature dependency. Even if a large
current flows, thermal runaway does not occur in the IGBT because
of the canceling effect of the positive and negative temperature
dependencies. However, a pure bipolar device such as a GTO has only
a negative temperature dependency; hence, when a large current
flows, thermal runaway occurs, resulting in the breakage of the
device.
[0055] In the case of the SiC, the inventor found that the increase
of current by parallel connection was possible even in the case of
the GTO if the flowing time was not long; the stable power supply
apparatus in accordance with the present invention is attained by
applying this matter. Large current flowing can be obtained by the
matter that the resistance of the low-concentration base region
which is the electric field relaxation region of a SiC-GTO has a
positive temperature dependency. In other words, at a low
temperature, the negative temperature dependency in the bipolar
operation is larger than the positive temperature dependency of the
resistance of the low-concentration base region; hence, the SiC-GTO
has a negative temperature dependency. However, the inventor found
a phenomenon that the SiC-GTO had a positive (Sic) temperature
dependency because the positive temperature dependency of the
low-concentration base region canceled the negative temperature
dependency of the bipolar operation at several hundred degrees
centigrade or more, and conversely the positive (Sic) temperature
dependency became predominant.
[0056] Since the SiC has a wide bandgap, its property as a
semiconductor can be maintained at a high temperature of
1000.degree. C. or more, the present invention fully utilizes this
phenomenon. On the other hand, in the case of a Si semiconductor
device, the limit temperature at which its property as a
semiconductor is maintained is low. Since the semiconductor must
usually be used at a junction temperature of 200.degree. C. or
less, the above-mentioned phenomenon does not emerge, and its
utilization is difficult. The time period in which this phenomenon
can be utilized is the time period from the time when the internal
temperature of the device rises owing to the difference between the
amount of heat generated inside the device and the amount of heat
dissipated outside the device to the time when the internal
temperature of the device reaches the limit temperature at which
its property as a semiconductor cannot be maintained. This time
period is determined by the structure of the device, the density of
flowing current, the structure of the module, etc. The fact that
the SiC has low power loss and high thermal conductivity in
comparison with the Si is very advantageous in increasing the
instantaneous large-power operating capability when it is applied
to a converter. In addition, the switching time of a GTO using the
SiC is about 1 .mu.s, shorter by an order or more of magnitude than
that of a GTO using the Si. In this respect, in the case of GTOs
such as GTOs of the Si, having a long interrupting time at the
turn-off operation, a problem in which interrupting currents
concentrate in a few of the GTOs and the GTOs are apt to be broken
can be prevented, and parallel connection is made possible.
[0057] In addition, also in a SiC-IGBT, unlike a Si-IGBT, it was
found that the positive temperature dependency of the resistor in
the low-concentration drift region serving as the electric field
relaxation region gives a significant effect, and that the SiC-IGBT
exhibits a positive temperature dependency at several hundred
degrees centigrade or more. In other words, in the Si-IGBT, at a
temperature not more than the limit temperature at which Si can
firmly maintain its property as a semiconductor, the negative
temperature dependency of the bipolar operation is cancelled by the
positive temperature dependency of the unipolar operation, and
thermal runaway is prevented even if a large current flows;
however, at 200.degree. C. close to the limit temperature or more,
the bipolar operation becomes predominant abruptly. At around this
temperature, the positive temperature dependency in the
low-concentration drift region is still small and cannot cancel the
abruptly increased negative temperature dependency of the bipolar
operation, resulting in thermal runaway. However, in the case of
the SiC-IGBT, at several hundred degrees centigrade or more, the
positive temperature dependency of the low-concentration drift
region cancels the negative temperature dependency of the bipolar
operation, and the SiC-IGBT turns to have a positive temperature
dependency, because conversely the positive temperature dependency
becomes predominant. As a result, by connecting a plurality of
SiC-IGBTs in parallel, a current far larger than that in the case
of Si-IGBTs can be passed for a short time, and the reliability
thereof is improved.
[0058] A stable power supply apparatus having a conventional
converter using a GTO or IGBT of Si is required to have a converter
of a large capacity corresponding to the power several times the
power supplied from the secondary battery in normal time at the
time of an instantaneous drop.
[0059] On the other hand, the converter using a GTO or an IGBT of
SiC in the stable power supply apparatus of the present invention
can withstand an excessive current several times the rated current,
whereby the converter in which its rated current is set at a
current required in normal time can deal with the large current
flowing at the time of an instantaneous drop. Hence, various
components constituting the stable power supply apparatus, such as
a transformer serving as a reactor, heatsinks for semiconductor
devices and bus bars, can be made compact. In addition, since the
capacity is small, the absolute value of the loss is small even if
conversion efficiency is the same; hence, loss reduction is
realizable, and significant cost reduction can also be attained. A
large converter for power utility is required to have a high
withstand voltage and also a high reliability in comparison with a
small converter. Furthermore, since it is required to have many
protective functions, it is high in price. For example, in the case
of a use requiring a converter of 5 MW in the conventional stable
power supply apparatus, that of 1 MW is sufficient to the apparatus
in accordance with the present invention. Therefore, the cost is
about a fifth of that of the conventional apparatus, and
significant cost reduction can be attained. The effect of cost
reduction becomes large rather in the stable power supply apparatus
having a large power capacity. As described above, the stable power
supply apparatus in accordance with the present invention is made
significantly compact in size, light in weight, low in loss and low
in cost.
[0060] Preferred embodiments in accordance with the present
invention will be described below referring to FIGS. 1 to 7.
First Embodiment
[0061] FIG. 1 is a block diagram of a stable power supply apparatus
1 for peak cut in accordance with a first embodiment of the present
invention and a power supply system, to which the stable power
supply apparatus 1 is connected, from a substation 130 to important
loads 104 and 105 and an general load 110. "Peak cut" is defined as
supplying an excess amount from a power supply other than the
substation 130 when power consumption exceeds the power that can be
supplied from the substation 130, and the period in this state is
referred to as "peak cut time." In addition, the period in states
other than the state of the peak cut time is referred to as "normal
time." In the figure, a system bus line 102 is connected to the
power system 100 of the substation 130 via a transformer 120. To
the system bus line 102, particularly important loads 104 and 105
are connected via switches 114 and 115, respectively. Furthermore,
a general load 110, less important than the important loads 104 and
105, is also connected to the system bus line 102 via switches 109
and 111. When an abnormality occurs in the system bus line 102, the
switch 109 first disconnects the general load 110 so that power
supply to the important loads 104 and 105 is maintained
preferentially. To the system bus line 102, the stable power supply
apparatus 1 in accordance with the present invention is connected
via a switch 6. Since a control apparatus for operating the
switches 6, 109, 111, 114 and 115 is well known in this field, it
is not shown in the figure.
[0062] The stable power supply apparatus 1 comprises a secondary
battery 2 formed of a redox flow battery rated at 500 kW for
example, a bidirectional chopper circuit 3 for raising and lowering
the voltage thereof, a converter rated at 500 kW and a transformer
5 also serving as an interconnecting reactor, and is connected to
the system bus line 102 of 6.6 kV via the switch 6. The voltage and
current of the system bus line 102 are detected by a voltage
detector 10 and a current detector 11, respectively, and the supply
and demand state of the power is detected by a detection circuit 8
on the basis of the detected voltage and current. A potential
transformer (PT) or the like is used for the voltage detector 10.
The current detector 11 is a current transformer (CT) or the like
provided inside the substation 130 and detects the output current
of the substation 130. A control circuit 9 controls the output
power of the converter 4 depending on the detected output fed from
the detection circuit 8 and indicating the supply and demand state
of the power. The redox flow battery serving as a secondary battery
has a capacity capable of supplying a DC current of 625 A at a
voltage of 800 V for about one hour. The switching devices of the
chopper circuit 3 and the converter 4 are anode-gate-type GTOs made
of SiC (hereafter each referred to as a SiC-GTO), and their rated
voltage and current are 8 kV, 800 A and 8 kV, 400 A, respectively.
The power capacity of this apparatus is about 450 kW in
consideration of power losses occurring in the chopper circuit 3,
the converter 4 and the transformer 5. In the case when the power
consumption of the important loads 104 and 105 increases and
transiently exceeds the power capacity of the substation 130, the
voltage detector 10 and the current detector 11 detect the state,
and active power corresponding to the excess amount of power, up to
about 450 kW, can be supplied from the secondary battery 2 to the
system bus line 102. The secondary battery 2 is charged by the
power supplied from the system bus line 102 in "stationary time"
(the supply and demand state of the power is balanced between the
substation 130 and the loads, such as the important loads 104 and
105 and the general load 110).
[0063] Although the DC output voltage of the 800 V for example, at
the beginning of the period of use, it tends to lower from 800 V as
the period of use becomes longer. Hence, during the peak cut time,
the output voltage of the secondary battery 2 is raised by the
chopper circuit 3 of a constant-voltage-output-maintaining type,
and the voltage is made constant at all times and is supplied to
the converter 4. The converter 4 for converting DC power into AC
power uses a SiC-GTO as a switching device. The converter 4 is not
shown because it has a general and known circuit configuration.
Because of limitations due to defects inside the crystals of SiC,
it is difficult to increase the rated current of the SiC-GTO.
Therefore, it is desirable to obtain a desired power rate at a low
current rate and at a raised voltage rate. In this embodiment, the
output voltage of 800 V of the redox flow battery serving as the
secondary battery 2 is raised to 1600 V by the chopper circuit 3.
For example, the DC power of about 1600 V, 300 A is supplied to the
converter 4. The converter 4 converts this DC power to an AC power
of 736 V at 354 A and applies it to the transformer 5. The
transformer 5 raises the voltage of 736 V to 6.6 kV, outputs the
voltage to the system bus line 102 via the switch 6, and supplies
to the loads 104, 105 and 110.
[0064] During the peak cut time, while the stable power supply
apparatus 1 supplies the power of 450 kW in peak cut time, if a
lightning accident occurs in the power system 100 and if an
instantaneous voltage drop (hereafter referred to as an
instantaneous drop) occurs in the voltage of the system bus line
102 owing to the influence of the accident, serious trouble, such
as operation stop, may be caused in the important loads 104 and
105. To prevent this, the switch 109 is opened immediately to
disconnect the general load 110. At the same time, in the stable
power supply apparatus 1, the control circuit 9 controls the
converter 4 so that a DC power of 2.5 MW at the voltage of 800 V,
for example, corresponding to the instantaneous large-current
supplying capability is supplied from the secondary battery 2. The
chopper circuit 3 raises the DC voltage of 800 V to 3.2 kV and
supplies the voltage to the converter 4. The PWM pulse width for
driving the converter 4 is made larger than that in rated operation
time, and the converter 4 outputs an active power of 450 kW at 1.47
kV and a reactive power of 2.78 MVAR (the unit of reactive power)
at about 1.47 kV. The voltage of the active power and the reactive
power is raised to 6.6 kV by the transformer 5 and supplied to the
system bus line 102, whereby voltage drop is prevented. It is very
rare that the voltage drop at the system bus line 102 continues for
0.5 seconds or more owing to the influence of lightning. The
converter 4 of the stable power supply apparatus 1 in accordance
with this embodiment is designed so as to be able to supply an
active power of 450 kW and a reactive power of up to 2.78 MVAR for
about six seconds, therefore this is sufficient for a
countermeasure for an instantaneous drop owing to lightning. In the
above-mentioned example, the converter 4 can convert an
instantaneous large power about six times the rating for four
seconds.
[0065] In the case that the stable power supply apparatus in
accordance with this embodiment is used to deal with only
instantaneous drops, only the voltage detector 10 for voltage
detection should be provided as shown in FIG. 8; even if the
current detector 11 shown in FIG. 1 is not provided, it can be
dealt with by using the voltage data of the substation.
[0066] In the stable power supply apparatus 1 in accordance with
this embodiment, the converter 4 can be operated at power far
exceeding the rating because a SiC-GTO is used as a switching
device.
[0067] FIG. 2 (a) is a top view of an anode-gate-type SiC-GTO
device having a rated voltage of 8 kV and a rated current of 400 A,
which is used in this embodiment, and FIG. 2 (b) of is a sectional
view taken along the line b-b. This SiC-GTO device is obtained by
connecting in parallel five anode-gate-type SiC-GTO chips 131 to
135 having a rated current of 80 A so as to form a module. FIG. 2
(b), the five GTO chips 131, 132, 133, 134 and 135 having a nearly
square shape of 7 mm on one side, are held between an intermediate
lower electrode 16 provided on a cathode electrode 14 and an
intermediate upper electrode 17 provided on an anode electrode 15
and electrically connected in parallel. Spacers 18 are used to
determine the positions of the respective GTO chips 131 to 135 on
the cathode electrode 14. A ceramic package 19 is used to keep a
constant distance between the cathode electrode 14 and the anode
electrode 15 and to keep electrical insulation therebetween; its
diameter is about 10 cm. FIG. 3 shows a cross-section of the
anode-gate-type SiC-GTO chip 131. In this GTO chip 131, a p-type
base layer 51, an n-type base layer 52 and a p-type emitter layer
53 are laminated in this order on the upper face of a substrate 50
of n-type SiC functions as an emitter. A cathode electrode 54 is
provided on the lower face of the substrate 50, and an anode
electrode 55 is provided on the p-type emitter layer 53. An
anode-gate electrode 56 is provided on the n-type base layer
52.
[0068] The GTO chip 131 turns on when a drive current is passed
from the anode A to the anode-gate G. After turned on, the GTO chip
131 turns off when the current flowing between the cathode K and
the anode A is diverted around between the cathode K and anode-gate
G. The thicknesses of the respective layers constituting the GTO
chip 131 are as follows; the substrate 50 is about 400 .mu.m, the
p-type base layer 51 is about 80 .mu.m, the n-type base layer 52 is
about 3 .mu.m, and the p-type emitter layer 53 is about 5 .mu.m,
for example. In the currently available SiC, the minimum
resistivity of the p-type SiC is larger by an order or more of
magnitude than that of the n-type SiC. Hence, in the case that the
substrate 50 which is the thickest layer is formed by n-type SiC,
the resistance can be made lower than that in the case that the
substrate is formed by p-type SiC. This is advantageous in that
power loss during the on-state can be decreased significantly. In
this case, the gate turning-on current and the gate turning-off
current of a GTO thyristor can be made smaller significantly by
providing the anode-gate electrode 56 on the n-type base layer 52
as shown in FIG. 3 and by performing anode-gate driving than by
providing the anode-gate electrode 56 on the p-type base layer 51
and by performing cathode-gate driving. Hence, the output of a
drive circuit, not shown, requires only small power; therefore,
significant size and weight reduction is made possible, and loss
reduction can be made, whereby the object of the present invention
can be attained more effectively.
[0069] As mentioned above, since the bipolar operation of the
Si-GTO device has a negative temperature dependency; if a large
current flows and the internal temperature of the device rises, the
current increases further and the temperature rises more and more,
and thermal runaway eventually occurs, resulting in the breakage of
the device. In the case that a plurality of Si-GTO chips are
connected in parallel, if current concentration occurs once in an
Si-GTO chip, the currents of the other Si-GTO chips concentrate in
the chip, and this may result in thermal runaway in some cases.
Hence, it is difficult to connect numerous Si-GTO chips in
parallel. On the other hand, as mentioned above, the SiC-GTO chips
can be connected in parallel in the case that the time during which
a large current flows is a short time of 10 seconds or less. The
time duration in which the large current can flow is the time
duration elapsed in which the internal temperature of the device
rising owing to the difference between the amount of heat generated
inside the device and the amount of heat dissipated outside reaches
the limit temperature wherein the property of the device as a
semiconductor device can be maintained. This time duration is
determined depending on the structure of the device, the density of
the flowing current, the structure of the module; in the case of
the configuration shown in FIG. 2, it was confirmed by experiment
that no problem occurred for about eight seconds. A test was
carried out by generating an instantaneous drop of eight seconds
while a peak cut operation test was conducted for about 45 minutes
for example, and peak cut power was able to be supplied without
affecting the important loads 104 and 105.
[0070] In this embodiment, by utilizing the instantaneous
large-power operation capability of the SiC-GTO, the converter
using this SiC-GTO operates as a converter that converts power six
times the rating for 4.5 seconds to prevent the influence of an
instantaneous drop. Hence, unlike the case of the conventional
design, the capacity of the converter is not required to be the
large power required in consideration of an instantaneous drop, it
is sufficient to have a capability for supplying power required in
peak cut time, amounting to a fraction of power required at the
instantaneous drop. Therefore, the stable power supply apparatus
for peak cut can be made significantly compact in size, light in
weight, low in loss and low in cost.
Second Embodiment
[0071] FIG. 4 is a block diagram of a stable power supply apparatus
21 for load leveling in accordance with a second embodiment of the
present invention. The stable power supply apparatus 21 has a
secondary battery 22 formed of a sodium sulfur battery having a
rated voltage of 1.5 kV and a rated power of 1.5 MW, a
bidirectional chopper circuit 23, a converter 24 and a transformer
25, and is connected to a system bus line 102 of a voltage of 6.6
kV via a switch 6, like the stable power supply apparatus 1 shown
in the above-mentioned FIG. 1. The other configurations are the
same as those of the stable power supply apparatus 1.
[0072] "Load leveling" designates that power is stored during a low
power demand time zone and the power is discharged during a high
power demand time zone to deal with a phenomenon wherein power
demand becomes significantly different depending on the time zone
of the day. The switching device of the chopper circuit 23 is an
anode-gate-type SiC-GTO having a voltage of 10 kV and a current of
1400 A, and the switching device of the converter 24 is an
anode-gate-type SiC-GTO having a voltage of 10 kV and a current of
600 A. The secondary battery 22 is charged with constant power at
night during which power demand is small, for eight hours from 22
o'clock to 6 o'clock, for example. A power of about 1.35 MW is
supplied from the secondary battery 22 in the daytime during which
power demand is particularly large, for eight hours from 9 o'clock
to 17 o'clock, for example. The SiC-GTO device for the converter 22
in accordance with this embodiment is formed of six GTO chips,
having a rated current of 100 A, which are provided inside a
package similar to that shown in FIG. 2 and connected in parallel
so as to form a module.
[0073] By using a SiC-GTO having a relatively small rated current,
in order to increase the rated power by raising its voltage, the DC
output voltage of 1.5 kV of the secondary battery 22 (Sic) is
raised to 3 kV by the chopper circuit 23 while a power of 1.35 MW
is supplied in the daytime. As a result, a DC power of about 3 kV
at 480 A is supplied to the converter 24 (Sic). The converter 24
converts this DC power to an AC power of about 1.38 kV at 566 A and
supplies the power to the transformer 25. The transformer 25 raises
the voltage to 6.6 kV and supplies the voltage to the system bus
line 102 via the switch 6.
[0074] While the power of 1.35 MW is supplied, if an instantaneous
drop owing to a lightning accident occurs in the power system 100
(FIG. 1) and if the voltage of the system bus line 102 lowers
significantly owing to the influence thereof, the important loads
104 and 105 are liable to stop operation. To prevent this, the
output voltage of the secondary battery 22 is raised to 4.5 kV by
the chopper circuit 23 and supplied to the converter 24. In
addition, the PWM pulse width in switching control of the converter
24 is expanded. Consequently, an active power of about 1.35 MW of
the rated value, and a reactive power of about 6.44 MVAR at a
voltage of about 2.07 kV are output from the converter 24. The
output of the converter 24 is raised by the transformer 25 and
supplied to the system bus line 102, thereby preventing the voltage
of the system bus line 102 from lowering.
[0075] In this embodiment, by utilizing the instantaneous
large-power operation capability of the SIC-GTO, the converter
having a rated power of 1.5 MW operates as a converter having a
rated power about 4.7 times 1.5 MW for a predetermined time period
during which the influence of an instantaneous drop is prevented.
Therefore, the stable power supply apparatus for use in the load
leveling can be made significantly compact in size, light in
weight, low in loss and low in cost.
Third Embodiment
[0076] FIG. 5 is a block diagram of a stable power supply apparatus
31 for use in frequency fluctuation suppression in accordance with
a third embodiment of the present invention. The stable power
supply apparatus 31 has a secondary battery 32 using a redox flow
battery having a voltage of 800 V and a rated power of 700 kW, a
bidirectional chopper circuit 33, a converter 34 having a rated
power of 600 kW and a transformer 35, and is connected to the
system bus line 102 of a voltage of 6.6 kV via the switch 6 shown
in FIG. 1. The other configurations are the same as those shown in
FIG. 1.
[0077] "Frequency fluctuation suppression" designates to maintain
the frequency at a rated value by adjusting the power supply using
another power supply to prevent the frequency of AC of the power
system 100 from being deviated from the rated value (50 Hz or 60
Hz) due to abrupt change in power demand. The switching devices of
the chopper circuit 33 and the converter 34 are anode-gate-type
SiC-GTOs having a rated voltage of 8 kV and a rated current of 1000
A and having a rated voltage of 8 kV and a rated current of 500 A,
respectively. For example, when the supply and demand state of an
active power becomes unbalanced abruptly owing to load fluctuations
or a short circuit accident, etc., the frequency of the power
system 100 fluctuates and becomes unstable. A detector 10A measures
the frequency of the system bus line 102, and the measured output
is input to the detection circuit 8. The detected output of the
detection circuit 8 is applied to the control circuit 9. The
control circuit 9 controls the converter 34 on the basis of the
detected output; when the frequency lowers, active power is
additionally supplied from the secondary battery 32 to the system
bus line 102, and conversely, when the frequency rises, active
power is absorbed from the system bus line 102 to the secondary
battery 32, whereby the fluctuations of the frequency are
suppressed. The rated power of the stable power supply apparatus 31
in accordance with this embodiment is 540 kW, for example, and can
supply active power, up to the maximum output of about 540 kW, from
the secondary battery 32 of the redox flow battery depending on the
fluctuations of the frequency.
[0078] Also in this embodiment, in order to deal with a voltage
drop owing to the deterioration of the redox flow battery of the
secondary battery 32 with the passage of time, the output voltage
of 800 V of the secondary battery 32 is raised to 1600 V by the
chopper circuit 33 when a power of 540 kW is supplied from the
secondary battery 32. When the frequency lowers, a DC power of 160
V at 360 A is supplied from the secondary battery 32 to the
converter 34. The converter 34 converts this DC power into an AC
power of about 736 V at 425 A and applies the power to the
transformer 35. The transformer 35 raises the voltage of 736 V to
6.6 kV, and supplies an AC power of about kV at 47.4 A to the
system bus line 102 via the switch 6, thereby suppressing the
frequency from lowering.
[0079] When the stable power supply apparatus in accordance with
the present embodiment is in operation of the frequency fluctuation
suppression by supplying a power of 540 kW to the system bus line
102, in the case that a lightning accident occurs in the power
system 100 and an instantaneous drop occurs in the voltage of the
system bus line 102 owing to the influence thereof, the important
loads 104 and 105 are liable to stop operation. To prevent this, a
DC power of 3 MW corresponding to the instantaneous large-current
supplying capability is output immediately from the secondary
battery 32, and the voltage is raised to 3.2 kV by the chopper
circuit 33 and supplied to the converter 34. At the converter 34,
by the control of the control circuit 9, the PWM pulse width of the
switching operation is made larger than that during the rated
operation, and a reactive power of 3.72 MVAR having a voltage of
about 1.47 kV is output together with an active power of 540 kW
from the converter 34. The voltage of the converter 34 is raised by
the transformer 35 and supplied to the system bus line 102 via the
switch 6, thereby preventing the voltage of the system bus line 102
from lowering.
[0080] A voltage drop at the system bus line 102 owing to the
influence of lightning usually lasts 0.5 seconds or less, and a
voltage drop lasting longer than that is very rare. The stable
power supply apparatus 31 in accordance with the present embodiment
can supply a reactive power of up to 3.46 MVAR together with an
active power of 540 kW for 3.5 seconds. Therefore, this apparatus
can sufficiently deal with an ordinary instantaneous drop caused by
lightning. In this case, the converter 34 is operated at
instantaneous large power about 5.7 times the rated power for 3.5
seconds.
[0081] The SiC-GTO device which is used for the converter 34 in
accordance with this embodiment is formed of six SiC-GTO chips
having a rated current of 100 A, which are provided inside a
package similar to that shown in FIG. 2 and connected in parallel
so as to form a module. Even in the case when the control current
of the converter 34 significantly exceeds the rated current of the
SiC-GTO device, since the resistance of the low-concentration base
region serving as the electric field relaxation region (not shown)
of the SiC-GTO device has a positive temperature dependency, when
the time during which the large current flows is short; therefore,
in a temperature range of several hundred degrees centigrade or
more, this positive temperature dependency is canceled with the
negative temperature dependency of the bipolar operation, whereby
thermal runaway owing to current concentration can be
prevented.
[0082] In the present embodiment, by utilizing the instantaneous
large-power operation capability of the SiC-GTO, the converter 34
having a rated power of 700 kW can be operated as a converter
having rated power about 5.7 times the rated power for a short time
during which the influence of an instantaneous drop is prevented.
Therefore, the stable power supply apparatus for frequency
fluctuation suppression can be made significantly compact in size,
light in weight, low in loss and low in cost.
Fourth Embodiment
[0083] FIG. 6 is a block diagram of another example of a stable
power supply apparatus 41 for use of peak cut in accordance with a
fourth embodiment of the present invention. In this embodiment, a
sodium sulfur battery having a rated output of 500 kW at a voltage
of 800 V is used as a secondary battery 42. The switching device of
a converter 44 is a p-type gate-type SiC-IGBT having a rated
voltage of 7 kV and a rated current of 400 A. The other
configurations, operations, functions, etc. are substantially
similar to those of the first embodiment. While the stable power
supply apparatus 41 supplies a peak cut power of 450 kW for
example, when a lightning accident occurs in the power system 100
and the voltage of the system bus line 102 lowers owing to the
influence thereof, a reactive power of 2.78 MVAR at a voltage of
about 1.47 kV is output together with an active power of 460 kW
from the converter 44 to prevent the operation of the important
loads 104 and 105 from stopping. The output of the converter 44 is
raised by the transformer 45 and supplied to the system bus line
102, thereby preventing the voltage the system bus line 102 from
lowering. In this case, instantaneous large power about six times
the rated power is supplied from the converter 44 for about three
seconds.
[0084] The SiC-IGBT device in accordance with this embodiment is
obtained by connecting in parallel eight chips having a rated
current of 50 A so as to form a module. The operation of the
apparatus at a current significantly exceeding the rated current in
the present invention is made possible by the temperature
dependency that is unique to the SiC-IGBT. As described above
before, in the case of the SiC-IGBT, unlike the case of a Si-IGBT,
the positive temperature dependency of the resistance in the
low-concentration drift region serving as the electric field
relaxation region gives a significant effect. The SIC-IGBT exhibits
a positive (Sic) temperature dependency at several hundred degrees
centigrade or more.
[0085] Even in the case of the Si-IGBT, the negative temperature
dependency of the bipolar operation is cancelled by the positive
temperature dependency of the unipolar operation, and thermal
runaway can be prevented even if large current flows. However, this
is a case wherein the temperature of Si is lower than the limit
temperature at which the property of the semiconductor can be
maintained. At 200.degree. C. or more close to the limit
temperature, the bipolar operation becomes predominant abruptly;
hence, even the positive temperature dependency of the
low-concentration drift region cannot cancel the negative
temperature dependency, and thermal runaway occurs.
[0086] In the case of the SiC-IGBT, at several hundred degrees
centigrade or more, the positive temperature dependency of the
low-concentration drift region cancels the negative temperature
dependency of the bipolar operation, and conversely the positive
temperature dependency becomes predominant, consequently the
SiC-IGBT has positive temperature dependency. Hence, by connecting
a plurality of SiC-IGBTs in parallel, a current far larger than
that of the Si-IGBT can be passed for a short time. As mentioned
above, in the SiC-IGBT, in order to attain a large rated current
capacity, a plurality of chips can easily be connected in parallel
so as to form a module, and the reliability of the module is
high.
[0087] Unlike a thyristor device such as a GTO, an IGBT has a
function of controlling the current passing therethrough by
applying a control voltage to the gate. Hence, thermal runaway can
be prevented by detecting the current passing through a SiC-IGBT
device at high speed and by limiting the PWM pulse width of a
control signal so that a current larger than a predetermined
current does not flow; in this aspect, numerous IGBT chips can also
be used easily in parallel connection. If numerous chips having low
switching speed are connected in parallel, current concentrates in
a chip having low breaking speed in turn off time, and the chip is
apt to be broken. However, since the switching speed of the
SIC-IGBT is higher than that of the SiC-GTO by one digit or more,
this current concentration is avoided; in this respect, parallel
connection is made possible.
[0088] In the case that the stable power supply apparatus in
accordance with this embodiment is used to deal with only
instantaneous drops, only the voltage detector 10 for voltage
detection should be provided as shown in FIG. 9; even if the
current detector 11 shown in FIG. 6 is not provided, instantaneous
drops can be dealt with by using the voltage data of the
substation.
[0089] In this embodiment, by utilizing the instantaneous
large-power operation capability of the SiC-IGBT, the converter 44
having a rated power of 500 kW can be operated as a converter
having a rated power about six times the rated power for a short
time during which the influence of an instantaneous drop is
prevented. Therefore, the stable power supply apparatus 41 for peak
cut can be made significantly compact in size, light in weight, low
in loss and low in cost.
Fifth Embodiment
[0090] FIG. 7 is a block diagram of a stable power supply apparatus
61 for peak cut in accordance with a fifth embodiment of the
present invention. The stable power supply apparatus for peak cut
in accordance with this embodiment is an apparatus that carries out
peak cut for only the important load 104 that is particularly
important. The peak cut apparatus 61 comprises a redox flow battery
62 having a rated power of 350 kW, a bidirectional chopper circuit
63, a converter 64 having a rated power of 350 kW, a transformer 65
also serving as an interconnecting reactor, a voltage detector 66,
a current detector 69, a detection circuit 67 and a control circuit
68. This apparatus is connected to the connection point of the
important load 104 and the switch 114 via the switch 6, and further
connected to the system bus line 102 of 6.6 kV via the switch 114.
The redox flow battery 62 can supply power at a DC voltage of about
800 V for about 1.5 hours. The chopper circuit 63 and the converter
64 are formed of anode-gate-type SiC-GTOs rated at 8 kV, 1000 A and
rated at 8 kV, 300 A, respectively. The power capacity of this
apparatus is about 317 kW because power losses occur in the chopper
circuit 63, the converter 64 and the transformer 65; however, in
the case when fluctuations occur in the important load 104 and when
the power capacity transiently exceeds the predetermined power
capacity of the substation, an active power of up to about 317 kW
can be supplied from the redox flow battery 62 depending on the
load. The redox flow battery 62 has been charged via the system bus
line 102 during the time other than the peak cut time.
[0091] When a lightning accident occurs in an upstream system and
when the voltage of the system bus line lowers owing to the
influence thereof while a peak cut power of 317 kW is supplied, the
switch 114 is turned off instantaneously to prevent the operation
of the important load 104 from stopping. An active power of 3 MW is
supplied from the converter 64 to the important load 104 via the
transformer 65 (Sic), whereby the influence of the instantaneous
drop can be prevented. In this case, the converter 64 can be
operated at an instantaneous large power about 9.5 times the rating
within two seconds or less. When the voltage of the system bus line
102 returns within this period to the state before the
instantaneous drop, the switch 114 is turned on and the
predetermined power is supplied from the system bus line to the
important load. This instantaneous large power changes depending on
operation time, and operation is possible at an active power that
is 2 to 12 times the rated power. In practical design, it is
desirable that the active power should be 3 to 10 times the rated
power. The above-mentioned operation of the converter 64 at the
active power far exceeding the rating is made possible by using
SiC-GTOs, just as in the cases of the embodiments 1 and 2. The
SiC-GTO device in accordance with this embodiment is obtained by
connecting in parallel, for example six chips having a rated
current of 50 A so as to form a module.
[0092] In the case that the stable power supply apparatus in
accordance with this embodiment is used to deal with only
instantaneous drops, only the voltage detector 66 for voltage
detection should be provided as shown in FIG. 10; even if the
current detector 69 shown in FIG. 7 is not provided, instantaneous
drops can be dealt with by using the voltage data of the
substation.
[0093] In this embodiment, by utilizing the instantaneous
large-power operation capability of the SiC-GTO, the converter
having a rated power of 350 kW can be operated as a converter
having a rated power about 9.5 times the rated power for two
seconds or less during which the influence of an instantaneous drop
is prevented; therefore, the stable power supply apparatus for peak
cut can be made significantly compact in size, light in weight, low
in loss and low in cost.
Sixth Embodiment
[0094] A sixth embodiment of the present invention is a stable
power supply apparatus for load leveling, and this embodiment has a
configuration similar to that of the above-mentioned second
embodiment shown in FIG. 4. It will thus be described referring to
FIG. 4. Although the stable power supply apparatus 21 in accordance
with the above-mentioned second embodiment supplies active power
having the rated value in the stable power supply apparatus 21 in
accordance with the present embodiment, the control circuit 9
controls the converter 24 so as to supply an active power that is 2
to 12 times the rated value. For this purpose, the control circuit
9 carries out control so as to advance the phase of the output
voltage of the converter 24 with respect to the phase of the
voltage of the system bus line 102. The stable power supply
apparatus 21 in accordance with the present embodiment has a
secondary battery 22 formed of a sodium sulfur battery having a
rated power of 1.0 MW, a chopper circuit 23, a bidirectional
converter 24 having a rated power of 1.0 MW and a transformer 25,
and is connected to the system bus line 102 of 6.6 kV via the
switch 6. The switching devices of the chopper circuit 23 and the
converter 24 are formed of an anode-gate-type SiC-GTO having 8 kV
at 800 A. In the stable power supply apparatus 21 in accordance
with this embodiment, the secondary battery 22 is charged with
constant power for eight hours at night during which power demand
is small, and a power of 0.9 MW for example, is supplied from the
secondary battery 22 for eight hours in the daytime during which
power demand is large. The SiC-GTO device for the converter 24 in
accordance with this embodiment is obtained by connecting eight
chips having a rated current of 100 A in parallel so as to be
formed into a module.
[0095] Also in the present embodiment, like the above-mentioned
first embodiment, to deal with the relatively small rated current
of the SiC-GTO, the output DC voltage of the secondary battery 22
is raised to 3 kV by the chopper circuit 23 when a power of 0.9 MW
is supplied in the daytime. As a result, a DC current of about 320
A flows in the converter 24 (Sic). The converter 24 converts a DC
voltage of 3 kV to an AC voltage of about 1.2 kV and applies the
voltage to the transformer 25. The AC voltage is raised to 6.6 kV
by the transformer 25 and output to the system bus line 102 via the
switch 6 (Sic) and then supplied to the respective loads.
[0096] In the state that the power of 0.9 kW is supplied, when a
lightning accident occurs and the voltage of the system bus line
102 lowers owing to the influence thereof, a DC power of 4.8 MW is
supplied from the secondary battery 22 to the converter 24 via the
chopper circuit 23 in order to prevent the operation stop of the
important loads 104 and 105 owing to the voltage drop. From the
converter 24, an active power of about 4.5 MW and a reactive power
of about 3.38 MVAR at an output voltage of about 1.38 kV are
output. Active power that is up to 12 times the rating, about 12
MW, can be output for a very short time. The output voltage is
raised to 6.6 kV by the transformer 25 and supplied to the system
bus line 102. Hence, the voltage of the system bus line 102 is
prevented from lowering, and a part of the active power is supplied
to the important loads 104 and 105, whereby operation stop owing to
the instantaneous drop is prevented.
[0097] As described above, in the present embodiment, by utilizing
the instantaneous large-power operation capability of the SiC-GTO,
a DC power of about 5 MW that is about five times the rating is
output from the secondary battery 22 having a rated power of 1 MW
for a short time during which the influence of an instantaneous
drop is prevented, whereby the converter 24 having a rated power of
1 MW is operated at a power of about 6 MW that is about six times
the rating. In other words, by using the secondary battery 22 that
can discharge power two to several times the rating and the
converter 24 that can operate at power two to several times the
rating during the instantaneous drop, the stable power supply
apparatus for load leveling can be made significantly compact in
size, light in weight, low in loss and low in cost.
[0098] Although the present invention has been described in
accordance with the first to sixth embodiments, the present
invention is not limited to these embodiments, but is susceptible
of various modifications and applications.
[0099] For example, the switching devices of the converters 4, 24,
34 and 44 are not limited to GTOs or IGBTs; various wide-gap
bipolar semiconductor devices, such as electrostatic induction
thyristors, bipolar transistors, emitter switched thyristors (EST),
IEGT, SIAFET and SIJFET, can be used as the switching device. In
addition, the above-mentioned semiconductor devices using wide-gap
semiconductor materials other than SiC, that is, gallium nitride,
diamond, etc., can also be used similarly for the above-mentioned
respective converters.
[0100] Other than the redox flow battery and the sodium sulfur
battery, a lead-acid battery, a zinc chlorine battery, a zinc
bromine battery, a lithium ion battery, etc. may also be used as
the secondary batteries 2, 22, 32 and 42.
[0101] In the case of a stable power supply apparatus having a
small power capacity of 200 kW or less, its current capacity is
also small; hence, a wide-gap bipolar semiconductor device having a
small chip area is sufficiently adaptable. In this case, the
chopper circuit for raising voltage to obtain a predetermined power
at a small current is not necessarily required. In this case, the
voltage of the battery may be directly applied to the
converter.
[0102] Wide-gap bipolar semiconductor devices can easily be made
resistant against high voltage. By making the device resistant
against 20 kV or more for example, it can be connected directly to
the system bus line 102 of 6.6 kV; hence, only an interconnecting
reactor can be used without using the transformers 5, 25, 35 and
45.
[0103] In the above-mentioned respective embodiments, description
is made as to the power distribution system bus line of 6.6 kV as
an example; however, by making the respective elements constituting
the stable power supply apparatus resistant against high voltage
and large current, the elements can also be applied to a stable
power supply apparatus connected to a power system located further
upstream. In addition, the stable power supply apparatus in
accordance with the present invention can also be applied to an
"instantaneous power failure" lasting a relatively long time
exceeding several minutes in the case of a short circuit or a
ground fault caused by a small animal, such as a snake or a bird,
caught on power transmission lines or by trees which contact with
power transmission lines. Furthermore, in the case when one of a
plurality of generators of a power transmission power supply breaks
down or when a load (plant or the like) of a bulk power customer
suddenly stops operation, abrupt power fluctuations may occur, and
the supply and demand imbalance of power may continue for five or
more minutes. The stable power supply apparatus in accordance with
the present invention can also be applied to deal with the
fluctuations or the like in the frequency of the system owing to
the supply and demand imbalance of power for five minutes to one
hour, far longer than the duration (several seconds) of an
instantaneous drop owing to lightning, by increasing the capacity
of the secondary battery and by taking measures for maintaining the
temperatures of the switching devices at a predetermined
temperature or less, such as by cooling the switching devices. In
the case of this long time, the stable power supply apparatus in
accordance with the present invention can also be used as an
emergency power supply (Sic) since its power can be adjusted in the
range of about 1.5 to 3 times the rated output.
[0104] As described in detail in the respective embodiments,
according to the present invention, by utilizing the instantaneous
large-power operation capability of the wide-gap bipolar
semiconductor device, the converter having this wide-gap bipolar
semiconductor device is operated at a power several times or more
the rated power of the converter, exceeding the instantaneous
large-power supplying capability of the secondary battery, for a
short time during which the influence of an instantaneous drop is
prevented. Hence, an effect wherein the stable power supply
apparatus can be made significantly compact in size, light in
weight, low in loss and low in cost is obtained.
* * * * *