U.S. patent number 3,612,894 [Application Number 05/054,547] was granted by the patent office on 1971-10-12 for ac supply system.
This patent grant is currently assigned to Licentia Patent-Verwaltungs-G.m.b.H.. Invention is credited to Jurgen Schmidt.
United States Patent |
3,612,894 |
Schmidt |
October 12, 1971 |
AC SUPPLY SYSTEM
Abstract
The voltage stability of an AC supply system having a plurality
of AC current supply assemblies connected in parallel to a common
load is improved when a malfunction is detected in one of the
current supply assemblies by first connecting the load to a standby
AC main with which the current supply assemblies are synchronized,
disconnecting the malfunctioning current supply assembly from the
load, and, after adjusting the properly functioning current supply
assemblies to supply the total power output prior to the
malfunction, disconnecting the load from the standby AC main.
Inventors: |
Schmidt; Jurgen (Belecke,
DT) |
Assignee: |
Licentia
Patent-Verwaltungs-G.m.b.H. (Frankfurt am Main,
DT)
|
Family
ID: |
5739495 |
Appl.
No.: |
05/054,547 |
Filed: |
July 13, 1970 |
Foreign Application Priority Data
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|
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|
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Jul 11, 1969 [DT] |
|
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P 19 35 206.8 |
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Current U.S.
Class: |
307/30;
307/64 |
Current CPC
Class: |
H02J
9/062 (20130101); Y02B 70/30 (20130101); Y04S
20/20 (20130101) |
Current International
Class: |
H02J
9/06 (20060101); H02j 009/06 () |
Field of
Search: |
;307/64,60,80 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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3500166 |
March 1970 |
Mesenhimer et al. |
3351770 |
November 1967 |
O'Sullivan et al. |
|
Primary Examiner: Truhe; J. V.
Assistant Examiner: Smith; J. G.
Claims
I claim:
1. A method of improving the voltage stability of an AC supply
system including a plurality of current supply assemblies which are
synchronized with an AC main and which are connected in parallel
via individual energy storage devices to a common load upon the
malfunction of one of said current supply assemblies comprising the
steps of:
connecting said load to said standby AC main upon the detection of
a malfunction of one of said current supply assemblies;
disconnecting said malfunctioning current supply assembly from said
load;
adjusting the properly functioning current supply assemblies to
provide the total power output supplied by said system prior to the
malfunction; and
disconnecting said load from said standby AC main.
2. An AC current supply system comprising, in combination:
a plurality of current supply assemblies connected in parallel via
individual energy storage devices to a common load;
means for synchronizing said current supply assemblies with a
standby AC main;
first normally closed switch means for individually connecting said
current supply assemblies to said load;
second normally open switch means for connecting said load to said
standby AC main; and
control means responsive to the malfunctionings of one of said
current supply assemblies for: load to said standby AC main;
b. disconnecting said malfunctioning current supply assembly from
said load by opening the respective one of said first switch
means;
c. adjusting the properly functioning current supply assemblies to
provide the total power output supplied by said system prior to the
malfunction; and then
d. disconnecting said load from said standby AC main by opening
said second switch means, whereby said AC supply system then again
supplies the entire power required by said load and the voltage
stability of the system is maintained during the time required to
remove the malfunctioning assembly from the system.
3. The AC supply system as defined in claim 2 wherein said second
switch means comprises a plurality of individual switches, one for
each of said current supply means, each of which is connected
between the common output to said current supply assemblies and
said standby AC main.
4. The AC supply system as defined in claim 2 wherein said control
means responds to internal malfunctions of said current supply
assemblies.
5. The AC supply system as defined in claim 2 wherein said control
means responds to voltage drops and/or excess voltages at the
inputs of said current supply assemblies.
6. The AC supply system as defined in claim 2 wherein said current
supply assemblies are single phase static inverters containing
thyristors, bipolar thyristors or transistors.
7. The AC supply system as defined in claim 2 wherein said current
supply assemblies are three phase static inverters containing
thyristors, bipolar thyristors or transistors.
8. The AC supply system as defined in claim 2 wherein said current
supply assemblies are static inverters, and wherein said
synchronizing means synchronizes said current supply assemblies
with the said AC main via the control device for said static
inverters.
9. The AC supply system as defined in claim 8 wherein all of said
static inverters are controlled by a central control device.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved AC supply system of the type
including a plurality of individual current supply assemblies
connected in parallel to a common load. More particularly, this
invention relates to a method and apparatus for improving voltage
stability of such a system when one of the current supply
assemblies is malfunctioning.
In AC supply systems it is quite common to provide a standby AC
main with which the individual current supply assemblies or sets of
the system are synchronized and to which the load is switched or
connected in case of a malfunction in the system in order that the
power supplied to the load continue without interruption. Various
schemes for connecting the current supply assemblies to the load
and for switching or connecting them to the standby AC main are
known.
In one known type of AC supply system providing for the switching
of a load from a current supply assembly to a standby AC main or to
a substitute current supply assembly without interruption in the
event of a malfunction in the current supply assembly, at least two
current supply assemblies are provided which, when the system is
operating normally, individually feed identical partial loads which
are separated from one another but which together form the total
load. The two current supply assemblies are also designed to be
able to individually supply the current for the total load.
Whenever a malfunction is detected in one of the current supply
assemblies, the respective partial load is automatically switched
without interruptions in the current supply, by means of an
electronic switching device, directly to the output of the properly
functioning current supply assembly. If the latter current supply
assembly should then also malfunction, so that both assemblies are
then inoperative, the entire load is switched automatically and
without interruption to the standby AC main.
In another known type of AC supply system, a single current supply
assembly feeds the load under normal conditions and a substitute
assembly and a standby AC main are available for emergencies. When
the current supply assembly malfunctions, the substitute assembly
is automatically put into operation and the load is switched by
means of electronic switching devices, and in particular an
electronic switch common to both assemblies and a switch connected
to the standby AC main which are switched with overlapping closing
times, first temporarily to the standby AC main and then to the
substitute assembly.
It is also known to provide an AC supply system having a plurality
of current supply assemblies, e.g. thyristor inverters, which
operate in parallel for a single load in order to increase the
output or dependability of the system. In such a system, if a
malfunction occurs in one of the current supply assemblies, the
load voltage may deviate greatly from the rated or desired value
due to the influence exerted on the parallelly operating current
supply assemblies, depending on the type of malfunction, until the
malfunction assembly is separated or disconnected from the load.
This large voltage deviation is produced due to the fact that the
malfunctioning assembly represents a short circuit type load for
the properly operating assembly or assemblies. For some loads, for
example data processing systems, a continuously constant supply
voltage is an absolute must and accordingly, this type of supply
system can not normally be used for such loads.
SUMMARY OF THE INVENTION
It is accordingly the object of this invention to provide a
solution for the above-mentioned problem with AC supply systems
having a plurality of current supply assemblies connected in
parallel to a single load and requiring a minimum number of
switching devices. According to the invention, this object is
achieved in that whenever a malfunction of one of the current
supply assemblies is detected, the common output of the current
supply assemblies and hence the load is switched to the standby AC
main, with which the assemblies are synchronized, through the aid
of an electronic switch and, after separation of the malfunctioning
assembly from the system by opening the associated switching device
connected in the respective output line of the assembly, and after
stabilization of the remaining assemblies not affected by the
malfunction to the total power output provided by the system prior
to the malfunction, the remaining properly functioning current
supply assemblies are again disconnected from the standby AC
main.
According to a feature of the invention, energy storage devices,
e.g. chokes and capacitors of filter circuits, are disposed in the
outputs of the current supply assemblies. These energy storage
devices ensure that the load voltage will not suddenly change when
an internal malfunction of one of the current supply assemblies
occurs, but rather remains almost constant until the malfunction is
detected and the electronic switching triggered. Due to the
synchronism between the AC supply assemblies and the standby AC
main, switching can occur at any moment.
According to a further feature of the present invention, the
current supply assemblies are monitored for the occurrence of
internal malfunctions as well as for undue deviations in the load
voltage so that switching to the standby AC main without
interruptions is performed upon the malfunctioning of one of the
current supply assemblies as well as when there is an undue
deviation in the voltage, caused, e.g., by an external short
circuit.
In order to simplify the monitoring of malfunctions in a current
supply system, according to a further embodiment of the present
invention, a plurality of electronic switches which are
individually associated with the current supply assemblies and
which are disposed between the standby AC main and the common
output of the system are utilized. In this embodiment, the
individual current supply assemblies can each be separately
monitored by a monitoring member and the monitoring thus becomes
simpler than with central monitoring of the entire system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of one embodiment of an AC supply system
according to the invention utilizing a central monitoring and
control device.
FIG. 2 is a block diagram of a further embodiment of an AC supply
system according to the invention utilizing separate monitoring and
control devices for each of the current supply assemblies.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a block circuit diagram of
an AC supply system having two AC current supply or inverter
assemblies 1, 2 whose outputs are connected in parallel to a common
load 3. In a manner well known in the art, the inverters 1 and 2
which may, for example, be static single phase or three phase
inverter circuits containing thyristors, bipolar thyristors or
transistors, are controlled by a common control unit 4 which is
synchronized with a standby AC main N by means of a synchronizing
device 5, thus also synchronizing the inverter assemblies 1 and 2
with the standby AC main N. Connected in the output line of each of
the current supply assemblies 1 and 2 in a known manner, is an
energy store El or E2, respectively, which may, for example, be the
capacitors or inductances of a filter, and a switch S1 or S2,
respectively. Although the switches S1 and S2 are indicated as
mechanical switches, it is to be understood that they can also be
electronic switches. In order to monitor the operation of the
system, a central monitoring and control member 6 is provided
having, for this purpose, signalling lines a1, a2 leading from the
current supply assemblies 1 and 2, respectively, and a further
signalling line leading from the control unit 4. It should be noted
that the control lines a1 and a2 are schematic in nature and may in
fact contain a plurality of separate lines which monitor not only
the input and output voltages of the current supply assemblies, but
also internal operations of the assemblies, for malfunctions.
A thyristor-type converter having an energy store (filter) is
disclosed in an article by J. Schmidt, entitled "Gesicherte
unterbrechungsfreie Stromversorgungsanlagen mit
Thyristorwechselrichtern" ETZ-B, vol. 29 (1969), No. 16, pages
387-392.
In addition to the switches S1 and S2, according to the invention,
the system is further provided with a switch 8, preferably
electronic, which is connected between the common output line 9 of
the system and the standby AC main N. Closure of this switch in the
event of a malfunction will thus have the effect of connecting the
common output line 9 and hence the load to the AC main N. To
control the operation of the various switches and adjust the system
upon the occurrence of a malfunction, the monitoring and control
member 6 is provided with control lines d1 and d2 for the switches
S1 and S2, respectively, c for the switch 8, and e1 and e2 for the
inverters 1 and 2, respectively. These latter control lines e1 and
e2 are utilized to adjust the output of the functioning inverter
when a malfunction in the system is discovered.
Turning now to the operation of the system, it should first be
noted that all of the switches are shown in their positions for
normal operation of the system. If now during operation of the
supply system a malfunction occurs, for example, at inverter 1 so
that it ceases to function and as a consequence the power fed to
the load decreases, whereby, due to the increased load on the still
functioning inverter 2 from inverter 1, the supply voltage may
decrease accordingly, this malfunction of inverter 1 is signalled
through the signalling line a1 to the monitoring and control
circuit 6. Circuit 6 then immediately transmits an actuation or
control signal to the switch 8, via signalling line c, which sets
this switch into its closed position. The common inverter output
line 9 and the load 3 are thus connected to the standby AC main N
which replaces the missing power for the load 3. The switch 8
remains temporarily closed until the malfunctioning inverter 1 has
been separated or disconnected from the load 3 by opening its
switch S1 and the inverter 2 has been adjusted to produce the total
supply power. These latter functions are carried out by means of
two actuating signals which are produced by the circuit 6 almost
simultaneously with the actuation signal to the switch 8, and are
transmitted via signalling lines d1 and e2 to the switch S1 and the
inverter 2, respectively. After opening contactor S1 and adjusting
the inverter 2, the monitoring and control circuit 6 transmits a
further actuating signal via signalling lines c to the switch 8
which causes it to return to the open position, thus disconnecting
the load 3 from the AC main N.
If inverter 2 now also ceases to function properly due to a
malfunction, this malfunction is signalled to the monitoring and
control circuit 6 via signalling line a2 and a new closing signal
is then transmitted through signalling line c to the switch 8 and
an opening signal is transmitted through line d2 to the switch S2.
Since in this condition the standby AC main N feeds the load 3 by
itself, the switch 8 remains closed and the load 3 remains
connected to the standby AC main N. After repair of one or more of
the inverters, the load 3 can be switched back to the current
supply assemblies according to known methods which need not be
discussed here in detail. Of course, in the event of a malfunction
in the control circuit 4, indicating that the entire system is
malfunctioning, the signal transmitted to the circuit 6 via line b
will also cause the switch 8 to be closed and connect the load 3 to
the AC main N.
Referring now to FIG. 2, there is shown another embodiment of the
invention wherein in place of a single malfunction control switch 8
and a central monitoring and control circuit 6, separate
malfunction switches and monitoring and control circuits are
provided for each current supply assembly or inverter in the
system. As shown in the figure, in addition to the switch 8, a
second switch 8' is provided which is disposed, as is the switch 8,
between the standby AC main N and the common assembly output line 9
having the load 3 connected thereto. With two available switches 8,
8', one of them, for example switch 8, as indicated, is associated
as to its function with inverter 2 and the other, switch 8', is
associated with inverter 1. This is intended to mean that when
inverter 2 experiences a malfunction, the load 3 is temporarily
connected to the standby AC main N by means of switch 8 and when
inverter 1 is malfunctioning such a switching is accomplished by
means of switch 8'.
In addition to the monitoring and control circuit 6, a second
control circuit 6' is provided so that the circuits 6 and 6' are
associated with the inverters 2 and 1, respectively. In this
embodiment, however, each of the monitoring and control circuits
6'. 6 need only monitor one of the inverters 1 or 2, respectively,
and accordingly, they are connected to their associated inverters
by means of monitoring or input signal lines a'1 and a2,
respectively. The circuits 6 and 6' are also provided with
monitoring signal lines b and b', respectively, for monitoring the
control circuit 4.
In order to provide the required control functions according to the
invention, each of the circuits 6, 6' is provided with a respective
control line c or c' for controlling the switches 8 and 8',
respectively, a control line d2 or d'1, respectively, for
controlling the respective switches S2 and S1 associated with the
associated inverter being monitored, and a control line e1 or e'2
for adjusting the power output of the other inverter in the
circuit. The operation of this embodiment in the event of a
malfunction of one or more of the inverters is the same as that for
the embodiment of FIG. 1.
Independent of whether one operates with one or two switches 8, 8',
i.e., the embodiments of FIGS. 1 or 2, the respective switches 8
and 8' can be bridged in a known manner by means of an emergency
contactor S8 or S8', respectively, and the synchronizing device 5
monitored by a separate monitoring device 5'. When the
synchronizing device 5 is malfunctioning, the monitoring member 5'
initiates a signal via a signalling line f, f' which causes the
switches 8, 8' to be blocked and a relay SN in the standby AC main
to be opened. Switches 8 and 8' can then no longer be closed when
one of the inverters 1 or 2 malfunctions. Instead, in this case the
monitoring member 6 or 6' initiates a signal over lines d2 or d'1,
respectively, and sends it to the associated switch S8 or S8'
causing it to close, so that the load 3 can be connected to the
standby AC main N at least with an interruption in its supply
voltage.
Several possibilities for controlling the current supply assemblies
are known. As shown in the above embodiments, all of the current
supply assemblies may be controlled by a common control unit 4
which may be synchronized by means of a synchronizing oscillator 5
with the standby AC main N. Alternatively, each assembly can be
controlled by a separate control unit which can be synchronized
with the standby AC main by means of a common synchronizing
oscillator 5. The separate control units should be so designed that
they have a limited influence on each other as concerns their
frequencies. It will be understood that the above description of
the present invention is susceptible to various modifications,
changes and adaptations and the same are intended to be
comprehended within the meaning and range of equivalents of the
appended claims.
* * * * *