U.S. patent number 3,891,344 [Application Number 05/298,081] was granted by the patent office on 1975-06-24 for steam turbine system with digital computer position control having improved automatic-manual interaction.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Andrew S. Braytenbah.
United States Patent |
3,891,344 |
Braytenbah |
June 24, 1975 |
Steam turbine system with digital computer position control having
improved automatic-manual interaction
Abstract
An improvement in the operation of an electric power plant
utilizing a steam turbine controlled, in an automatic mode, by
means of a digital computer, is accomplished by simplifying the
interaction between the programmed automatic process control and
the manual backup control. The position setpoint for each of a
plurality of valves in the system to be controlled is established
as a direct digital holding function in a respective bistable relay
register. In addition, a single valve control holding register is
provided which is coupled to all of the valve position controls in
parallel. Automatic operation is then possible in either single
valve or programmed sequential valve modes, and the programmed
interaction to accomplish switching from manual to automatic
control is simplified by updating the automatic control status
until the single valve holding register has a setting equal to the
manual control representation before consummating the manual to
automatic switching. The direct digital holding registers also
improve total system operation in eliminating drift with respect to
the valve positions represented so as to extend the period of
reliable operation in the manual mode, and also make it possible to
retain the last valid position setpoints held in the respective
registers prior to a computer power failure.
Inventors: |
Braytenbah; Andrew S.
(Pennsauken, NJ) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
26763832 |
Appl.
No.: |
05/298,081 |
Filed: |
October 16, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
80710 |
Oct 14, 1972 |
3741246 |
|
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|
Current U.S.
Class: |
415/1;
415/17 |
Current CPC
Class: |
F01D
17/24 (20130101) |
Current International
Class: |
F01D
17/24 (20060101); F01D 17/00 (20060101); F01d
017/00 () |
Field of
Search: |
;415/1,17 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Husar; C. J.
Attorney, Agent or Firm: Patterson; H. W.
Parent Case Text
This is a division, of application Ser. No. 80,710 filed Oct. 14,
1972, now U.S. Pat. No. 3,741,246.
Claims
I claim:
1. A method for operating a steam turbine system for controlling
power output to a generator connected to said turbine as a function
of the position of the series of governor valves said method
comprising: establishing individual governor valve setpoints for
each respective valve during a sequential mode of operation;
establishing a single valve setpoint applied in parallel to all of
said governor valve controls during a single valve control;
applying a single common manual control signal to all of said
valves in parallel during a manual mode of operation, said single
valve control signal and said manual control signal being
switchably combined through an automatic-manual control; and
summing the switchably combined automatic and manual control signal
with the individual sequential governor valve control signal to
form a composite governor valve control signal suitable for
application to respective governor valve actuators.
2. A method for controlling the valves of a turbine to improve
automatic-manual interaction, said method comprising: providing
individual valve setpoints of digital words during a sequental
valve control operation; providing a single valve setpoint during a
single valve setpoint operation and applying said single valve
setpoint in parallel to all valves; summing said parallel-applied
single valve setpoint individually with each respective separate
valve setpoint; and switchably introducing a single valve control
during manual operation to a point common with said point of
application of said single valve setpoint.
3. An improved method for automatic turbine valve control
comprising: separately producing a governor valve series of
setpoint control signals, a single valve setpoint signal, and a
manual control signal; selectively switching either said single
valve control signal or said manual control signal to a common
control point; and summing the signal output of said common control
point with individual separate valve control signals to form a
plurality of valve actuator signals.
Description
CROSS REFERENCE TO RELATED APPLICATION
1. System and Method For Operating a Steam Turbine and An Electric
Power Generating Plant by T. C. Giras and M. E. Birnbaum, Ser. No.
722,779, filed Apr. 19, 1968, and assigned to the same assignee as
the present invention.
2. Improved Computer Positioning Control System With Manual Backup
Control by T. C. Giras and W. W. Barnes, Ser. No. 815,882 filed
Apr. 14, 1969, now U.S. Pat. No. 3,552,872 assigned to the present
assignee.
BACKGROUND OF THE INVENTION
The present invention relates to computer process control systems
and more particularly to electric power plant steam turbines and
digital computer control systems arranged to operate such
turbines.
The flow of steam through a steam turbine is determined by
positioning the turbine admission valves in order to control the
turbine speed and/or load. Turbine valve positioning may
additionally be directed to throttle pressure control where such
control is required for the steam generating system.
In the aforementioned Birnbaum and Giras copending patent
application, there is presented a survey of the prior steam turbine
control art. Generally, automatic steam turbine valve control has
developed from essentially mechanical and mechanical-hydraulic type
control systems to essentially electrohydraulic type control
systems. The Birnbaum and Giras application (reference 1 above)
discloses a further advanced automatic digital electrohydraulic
turbine control system which employs a programmed digital computer
in its preferred form. A paper entitled Digital Control For Large
Steam Turbine-Generators presented to the American Power Conference
during Apr. 23-25, 1968 by M. Birnbaum and T. Giras describes a
similar computer type turbine control system.
In addition to automatic control, safety and reliability in steam
turbine operation usually makes it desirable to employ manual
backup control. To interface the manual control with the automatic
control and the steam turbine, it is necessary to provide suitable
conditions for bumpless or other appropriate transfer from
automatic to manual control and from manual to automatic control.
In turn, the character of the automatic valve positioning control
as well as the character of the interfacing arrangement itself
enter into determining the efficiency and economy with which
automatic/manual steam turbine control is provided. This is
particularly so in relation to large steam and other turbine
control systems which involve positioning control over a plurality
of steam turbine admission valves.
Prior art electrohydraulic control systems typically might provide
for manual backup control but such schemes are limited to analog
type systems. The Giras and Barnes application (reference 2 above)
is directed to a digital positioning control system and
particularly a steam turbine valve positioning control system in
which a digital computer provides a relatively fast and accurate
positioning operation and with which a manual backup positioning
control is interfaced.
The Giras and Barnes application (reference 2 above) describes a
digital computer system wherein time series turbine valve position
setpoint control words are converted to analog values and
multiplexed for application to track and hold circuits associated
with respective electrohydraulic turbine valve position control
loops. During manual operation, a manual control applies a setpoint
control signal to all of the track and hold circuits in parallel. A
read multiplexer keeps the computer updated on valve positions
during manual control.
While the Giras and Barnes system provides the first interface
between the automatic operation of the digital computer and a
manual backup positioning control it has certain limitations.
During automatic operation the computer must generate a relatively
large number of setpoint control words and further the system must
provide for the conversion of these control words into analog
values before they become effective to establish the desired
setpoint control. During manual operation the read multiplexing
operation requires a comparable number of inputs in order to keep
the computer updated with respect to the manual control.
Accordingly, while the Giras and Barnes system is relatively fast
with respect to the prior art and provides an important improvement
with respect to the interfacing of automatic and manual controls it
is limited with respect to the speed of input and output because of
the number of control words which must be transmitted or received
in order to operate.
A further limitation in the operation of the system of the
copending application is in the period during which manual control
may be effective. Since the system of the copending application
relies upon track and hold circuits, periods in excess of a week of
operation cannot be reliably maintained due to the relative drift
which will occur among the various setpoint signals.
SUMMARY OF THE INVENTION
In accordance with the broad principles of the present invention, a
digital computer positioning control system has improved
performance through the introduction of a simplified interaction
between the programmed automatic process control and the manual
backup control. The position setpoint for each of the plurality of
valves in the system to be controlled is established as a direct
digital holding function in a respective bistable relay register.
In addition, a single valve control holding register is provided
which is coupled to all of the valve position controls in parallel.
The hybrid or combined analog-digital control part of the system
then provides for the digital to analog conversion of the setpoint
value in a control register with the converted value of the
setpoint in the single valve holding register during automatic
operation or that value provided by the manual control during
manual operation.
Automatic operation becomes possible then in either a single valve
or programmed sequential valve mode, and the programmed interaction
required to accomplish switching from manual to automatic control
is simplified with respect to the technique of the copending
application by updating the automatic control status until the
single valve holding register has a setting equal to the manual
control representation before consummating the manual to automatic
switch.
The direct digital holding registers also improve total system
operation in eliminating drift with respect to valve positions
which are represented so as to extend the period of reliable
operation in the manual mode, permitting a virtually unlimited
period of manual operation. The use of bistable relays is also
important as a specific improvement of the invention since these
make it possible to retain the last valid position setpoint held in
a respective register prior to a computer power failure. The manual
backup control operation is presumed, in order to gain full
advantage of this feature to have an independent power supply. In
the preferred embodiment of the invention, an improvement in the
specific operation of the manual control itself is accomplished
through the use of a digital up/down counter which is responsive to
RAISE and LOWER input signals and provides control signals which
are summed with any of the then remaining setpoint signals
developed during the terminated automatic operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic diagram of a large steam turbine system,
the valves of which are controlled according to the present
invention;
FIG. 2 shows a schematic diagram of a digital computer control
system operable with the steam turbine system of FIG. 1, such
computer control system being utilized to provide the digital
setpoint signals employed in the control system of the present
invention;
FIG. 3 is a schematic diagram showing how the system of the present
invention is interconnected with the computer control system of
FIG. 2 to provide the improved functioning of the invention;
FIGS. 4A and 4B show two types of manual control circuits, one
utilizing a digital up/down counter and the other using an analog
track and hold amplifier; and
FIG. 5 is a schematic diagram of a suitable form of output and
multiplexing system for use in the system of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 are similar to those described in the aforementioned
copending patent applications constituting references (1) and (2)
above and therefore will be just briefly reviewed herein.
Reference is made to FIG. 1 where steam from a suitable generating
system 26 is shown as passing through throttle valves TV1-TV4 to
governor valves GV1-GV8 providing steam input to a high pressure
turbine section 20 forming part of a turbine-generator system 10.
The positions of the valves are controlled by respective control
systems, the throttle valves being controlled through position
controls 50 and actuators 42 and the governor valves being
controlled through controls 52 and actuators 44. Various setpoint
signals are shown as being applied to the controls, representing
digital output words, as will be discussed in further detail with
respect to FIGS. 3 and 5 herein.
Although consideration herein will be directed primarily to the
control of governor valves GV1 through GV8 it will be understood
that the principles herein developed are applicable as well to
throttle valve control or to the control of other valves such as
intercept and stop valves shown following reheater 28 in FIG.
1.
In FIG. 2 the relationship between central processor 62 and various
means utilized according to the present invention is shown in block
diagram form. It will be noted that the processor 62 provides
certain output signals applied to contact closure output system 86
which direct computer words to the valve position control output
system 90. Control output system 90 also receives an input from
manual control 92, a specific form of which is provided by the
present invention. It will be noted that processor 62 receives
certain input signals through an analog input system 72 including
signal AMSV (auto-manual single valve) from a point 140 shown in
FIG. 3. Signal AMSV will be discussed in connection with FIG. 3 as
being a feedback signal referencing the position of the manual or
single valve automatic control to facilitate the "bumpless"
transfer between automatic and manual modes of operation.
Reference is now made to FIG. 3 where it will be noted that
setpoint control words provided by processor 62 are passed through
output system 86 to digital multiplexers 102 and 104. The function
of the multiplexers will be considered in detail with reference to
FIG. 5. Multiplexer 102 is coupled to a series of registers
referenced as GVR1...GVR8 corresponding to governor valves GV1
through GV8, and is also coupled to a register SVR providing the
holding means for single valve control. Multiplexer 104 is coupled
to a similar control network (not shown) for throttle valve control
coupled to each setpoint storage register, is a digital-to-analog
converter referenced, in the case of the governor valves, as:
DAC-G1. . .DAC-G8 and, in the case of the single valve control, as:
DAC-SV.
Converter DAC-SV is also referenced as 100 to show that it
corresponds to the "means for converting set point representations
from digital to analog form at a control point", specified also as
means 100 in reference (2) above.
It will be noted that wherever the means employed according to the
present invention are the same as those of reference (2) the same
reference number is used. Relay contact 136 in FIG. 3, corresponds
to the contact of the same number in the copending application, and
is used to switch from manual control to automatic. It is shown in
a position making contact with point 136M, corresponding to the
manual mode of operation. During automatic operation, the contact
is transferred to make contact with point 136A, at which time the
setpoint value of register SVR is effective through converter
DAC-SV to provide a single valve control signal.
Point 140 in FIG. 3 is the common control point for either
automatic or manual and is applied to a series of summing
impedances which may be resistors referenced as 134-1 to 134-8
corresponding to eight governor valve controls. It will be
understood, of course, that as governor valves are grouped for
control, the number of control functions is thereby reduced. For
example, in a typical operation utilizing the invention, governor
valves GV1 to GV4 may be controlled together so that setpoint
register GVR1 is then utilized to provide a single position
setpoint for valve GV1-GV4. In this case register GVR1 could be
renamed as: GVR1-4. If the remaining governor valves are controlled
individually then registers GVR5, GVR6, GVR7 and GVR8 would be
employed. The invention may be utilized in any combination to
provide the desired control.
The signal at point 140 is also fed back to analog input system 72
as signal AMSV for computer programmed tracking of the manual
control signal prior to the switching back to automatic. The actual
transfer of switch 136 from manual to automatic is a complex
computer control function.
The governor valve setpoints stored in registers GVR1-GVR8 are
converted through their respective digital to analog converters
DAC-G1 through DAC-G8 to output signals which are applied through
resistors 124-1 . . . 124-8 to summing junctions 125-1 . . . 125-8
connected to respective servo amplifiers SA1 . . . SA8 Also
connected to summing junctions 125 are feedback position signals
PDG1 . . . PDG8, applied through summing resistors 126-1 . . .
126-8, respectively. For example, signal PDG1 is fed back through
resistor 126-1 to summing point 125-1 connected to servo amplifier
SA1.
It will be noted that a system similar to that just described with
respect to controlling the governor valve actuators may also be
provided for throttle valve control. This is indicated by the
showing of multiplexer 104 having an output connected to various
throttle valve controls.
Switching power through appropriate means 145 is applied through
contacts 116-1 . . . 116-8 to respective governor valve registers
during automatic operation. Contacts 116 are opened during the
manual control mode and registers GVR1-GVR8 then hold the last
setpoint established by the computer. It is important therefore
that registers GVR be bistable relays as shown in FIG. 5 which do
not require power to hold their states. Since manual control may
have been entered into due to a computer malfunction, the automatic
removal of switching power from the set point storing registers
provides an effective means of preventing an inadvertent change in
these values. Once manual control begins through means 92, the
signal developed by manual control is applied to point 140 and then
modifies the position or signal input to the actuators in parallel
by applying such modifying signal through resistors 134.
Reference is now made to FIG. 4A where one form of manual control
provided by the invention is shown. In FIG. 4A an analog comparator
921 receives the output signal of DAC-SV and also that of converter
927 (DAC-M). During automatic operation output signals references
as INC and DEC produced by comparator 921 are utilized to develop
UP (INC) and DOWN (DEC) control signals for a counter 925 by means
of logic 923. This will be discussed in detail below. During manual
operation, the UP and DOWN control signals for counter 925 are
derived through logic 923 as a function of input signals: RAISE and
LOWER. Comparator 921 and counter 925 are conventional devices well
known in the art and will not be described in detail herein.
During manual control each time a RAISE signal is applied through
logic 923, counter 925 is incremented at a predetermined rate in an
UP direction and the output of counter 925 is converted into an
analog signal through converter 927. This analog signal passes
through relay switch 136 to point 140 and thence to impedances 134
shown in FIG. 3. A similar operation occurs when a LOWER signal is
applied through logic 924 to counter 925, causing it to be reduced
in value and the analog equivalent of counter 925 is supplied
through point 140 to resistors 134. In this manner, digital
tracking of the manual control is continuously updated through
counter 925 which provides a stable manual control reference
suitable for long time period utilization without drift.
Furthermore, when the system is in the automatic mode of operation,
the counter 925 is caused to continuously follow the setpoint value
entered into register SVR so that when switchover occurs from
automatic to manual, there is a "bumpless" transfer with respect to
the signal at point 140.
The logic for means 923 may be expressed in a generalized and
simplified form as follows:
UP = (INC.A + RAISE.M).R'
DOWN = (DEC.A + LOWER.M) + R,
Where A represents automatic control, M represents manual control,
R represents runback, R' represents the not-runback case, INC, DEC,
RAISE and LOWER are previously defined. The dot (.) is the logical
"and" and the plus (+) is the logical "or". The prime (') is used
to represent the complement.
According to this logic the UP control to counter 925, causing
counting up at a predetermined rate, is provided in response to
signal INC for automatic control and in response to signal RAISE
for manual control, the UP control being disabled by the condition
R' during runback.
The DOWN control for counter 925 is provided by the logic of
decrease (DEC) for automatic, or lower (LOWER) for manual, or
during runback control R.
The system may be switched from automatic to manual without any
discontinuity in control since all values in registers GVR1-GVR8
remain undisturbed once switching power is removed and the value of
the signal at point 140 is taken over by the manual control.
The transition from manual to automatic involves computer tracking
control in order to insure that the setting of register SVR
conforms to signal AMSV feedback through input system 72.
If the long term drift stability of counter 925 is not required and
the advantage of certain simplicity is desired, the alternative
embodiment of FIG. 4B may be employed. In this embodiment, the
comparator function provided by circuit 921 is effectively
accomplished through resistors 922 and 924 when contact 931 is in
its upper position 931A for the automatic operation. In this case,
amplifier 928 acts as a tracking amplifier and continuously charges
a capacitor 926 to cause it to follow the value of the setpoint
entered into register SVR. When switching to manual is made,
whereby contact 136 assumes position 136M, and contact 931 assumes
position 931M, track and hold amplifier 928 provides the "bumpless"
transfer whereby the signal applied to point 140 and resistors 134
are not disturbed. After the transfer to manual control the value
of the output signal of amplifier 928 may be adjusted by control
signals RAISE and LOWER by applying suitable negative and positive
voltage through resistor 930 and switch 931 to the amplifier.
It will be understood that although relay switching has been
specified herein, the broad concept of the invention is not so
limited. The term "switch" therefore as utilized herein is intended
to be a generic term covering any means accomplishing the desired
end result.
In the above discussion it has been assumed that the means
providing digital word communication between the central processor
and the various setpoint storage registers is a multiplexer such as
that referenced as means 102 in FIG. 3. In the broad context of the
invention, however, any means suitable for directing setpoint
control words to the appropriate register will serve this function.
To illustrate a suitable control technique FIG. 5 is provided where
the central processor 62 is assumed to include means for providing
an input output-control instruction referenced as CON including an
operation code IOA specifying input or output from the accumulator,
a control bit representing I/O where a 1 represents input and a 0
represents output and a channel address code for selecting an
appropriate receiving register in the case illustrated. In
addition, the processor includes an accumulator ACC which is filled
with the setpoint to be routed to the addressed register. The
output system 86 then is controlled by the channel address to
select, through appropriate digital output gating, which of the
registers is to receive the setpoint.
It is assumed in the illustrative case of FIG. 5 that there are a
plurality (M) of bistable relay registers and a corresponding
plurality of digital to analog converters coupled thereto. Each
register is referred to as a contact output register and the
references COR1 . . . CORM are provided to represent the plurality
of registers and associated control functions. Only the specific
details of COR1 will be considered since the control functions may
be identical in all registers. Considering specifically the control
for set and reset armatures SR11 and RR11, it will be noted that a
transfer contact TC11 may assume either of two possible bistable
states under the control of the set and reset armatures. Sufficient
magnetism remains in each armature to hold contact TCC1 in whatever
position it is placed without power so that if switch 116 is
opened, as previously discussed, and power is removed from the
system contact TC11 and other similar contacts will remain in
whatever state they have been placed prior to power removal. Reset
armature RR11 is controlled through a timing circuit TC110 and set
armature SR11 is controlled through a timing circuit TC111 each of
which receives a signal to an appropriate gate G11 receiving its
signal through the digital output gating. The function of gate G11
is to operate timing TC110 when the input bit is a zero and to
operate timing circuit TC111 when the input bit is a one. The
purpose of the timing circuits is to hold a control signal on the
appropriate relay armature for a minimum period of five
milliseconds after the digital output gating has terminated so as
to permit the processor to continue its operating functions while
providing a sufficient current actuation time for the relatively
slow acting relay.
Corresponding to contact output relay control COR11 there are a
total of N similar or identical circuits within contact output
register control COR1 only the first and the nth in this series are
shown and specific details of the bistable relay are shown only in
COR11. Corresponding to the number of setpoint register controls
required there are M circuits like COR1 and within each of these
are a number (N) of relay control circuits that have been described
corresponding to the number of binary bits in the control words
which is utilized to specify the setpoint in the system.
During the automatic computer operation the so-called multiplexing
is accomplished by program control and setting up the appropriate
setpoint value in the accumulator ACC and establishing the
corresponding channel address and input output control as noted
above. If the program is made to automatically sequence setpoint
entry for all registers it may then be considered to be
multiplexing program, but the invention may be operated to control
only a single register during a particular program subroutine such
as may be utilized for tracking the manual operation just prior to
the switching to automatic control.
From the foregoing description it should now be apparent that the
present invention provides an important improvement in means for
improving the operation of an electric power plant with particular
emphasis upon an automatic-manual control technique whereby the
valves of a steam turbine may be positioned either automatically
through a computer program or by means of a manual backup control
system. The invention simplifies the tracking which is required for
either manual to automatic or automatic to manual switching and
eliminates drift with respect to valve position so as to extend the
period of reliable operation in the manual mode. The specific use
of the bistable relay control provides a further improvement in
that computer power failure will not cause the loss of the last
setpoint position and the invention makes it further possible to
take over manual control from the last setpoint position and to
increase or decrease the position signals then existing.
* * * * *