Switching as a function of a position setpoint in a pressure control mode

Abstract

The invention provides a method for improving the operating behavior of fluid-operated processes, in particular in gas turbines and steam turbines with closed-loop control installations.SOLUTION: For this purpose, the invention makes use of the steps of specifying a predetermined position setpoint value or a position setpoint value range and switching the drive from the position holding mode to the force holding mode after the position setpoint value or the position setpoint value range or the digital signal has been specified, without taking into account the actual position value. In an alternative embodiment, the steps of defining a threshold value from a measurable value for a position, a pressure, a current, a torque or a force at the valve in the fluid-operated process and operating the valve drive in a closed-loop control alternating between two or more manipulated variables from the manipulated variables determined in the preceding steps are used, wherein preferably the smallest value from the determined manipulated variables is used. The invention further provides an apparatus for carrying out at least one of these methods.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Technical Field The present disclosure relates to fluid-based processes, particularly in gas or steam turbines. The present disclosure particularly relates to limit stop behavior of shutoff and closed-loop control equipment in such processes, which limit stop behavior takes into account compression of sealing elements in the shutoff and closed-loop control equipment or prevents damage or destruction of the shutoff and closed-loop control equipment due to overload. Furthermore, the present disclosure relates to devices, particularly closed-loop control equipment, for implementing these processes. [Background technology]

[0002] Japanese Patent Publication No. 6577314 discloses a valve drive and valves for a steam turbine. The speed and power of the steam turbine are controlled in a closed loop by controlling the steam flow through the turbine. For this purpose, several different valves are used. In the event of a malfunction, these different valves are closed as quickly as possible to prevent steam leakage, accidents in the system, or other damage as much as possible. The valves used are typically hydraulically driven, based on the large forces and pressures generated. The possibility of such hydraulic control is provided by an electromechanical drive with hydrostatic transmission ("EMAH"), as also proposed for an embodiment in the same publication. In this case, according to one embodiment of the same publication, each valve drive includes its own dedicated hydraulic pump, and the valve position is controlled by operating the hydraulic pump.

[0003] Currently, this problem in power plant technology is solved by utilizing such pressure-compensated valves with a bypass stroke mechanism. To control the turbine, the corresponding valve is driven by an electric motor until a position transmitter reports the desired valve position, and optionally, in the case of a stop position (e.g., closed at machine standstill or open at full load), until a limit switch abuts the desired position, in particular the fully open or closed position. This limit stop is detected via an actual force or pressure threshold (i.e., a force or pressure increase in the hydraulic system) that occurs when or after exceeding the actual position threshold at the stop. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 6577314 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have found that in such a procedure, the limit stop must always be recognized before switching to force-holding operation. However, if the limit stop is not recognized or is recognized too late, for example, the disconnection equipment and closed-loop control equipment connected to the driven side may be damaged. In particular, if repeated runs to the stop are performed, this can initially cause damage, which can lead to non-tightness in the subsequent process. [Means for solving the problem]

[0006] To solve this problem and thus improve the operating behavior, the closed-loop control system according to the present invention operates in so-called force-holding mode when a predetermined position target value or position target value range, such as 100%, is set. Instead of a set position target value, other signals, such as digital switching signals, can also be used as setpoints. In this force-holding mode, closed-loop control of the pressure on the hydraulic pressure supply side of the EMAH, the current for the drive motor, the torque on the pump shaft, or closed-loop force control (closed-loop control of the force exerted by the hydraulic cylinder) to a required target value is implemented. Unlike the prior art, the switchover to force-holding mode is implemented independently of the current position of the system components that are closed-loop controlled in the process according to the present invention, i.e., independently of the current position of the cylinder piston for displacing a valve, for example.

[0007] The force-holding operation is a method for improving the operating behavior of fluid-operated processes, particularly gas and steam turbines with closed-loop control systems, that includes the steps of setting a predetermined position target value or position target range for a valve in the fluid-operated process or evaluating a digital signal as a setpoint, and switching the drive from position-holding operation to force-holding operation after the position target value or position target range or digital signal has been set, without taking into account the actual position, force, or pressure values. Thus, unlike the prior art, for example, according to JP 6577314 A, a target value or target range is set and then force-holding operation is immediately performed to achieve this target value, rather than when an actual position, force, or pressure value is detected. Thus, unlike the prior art, switching to force-holding operation can be performed independently of the position, and therefore does not require detecting the position or actual force or pressure values.

[0008] In this case, during "normal" operation, preferably, closed-loop control of the position of the cylinder piston is implemented as known from the prior art. However, at a predetermined position target value or target value range, in particular at a value or range of 100% (fully open valve), or alternatively, when a digital signal is input, i.e., for example, in the simplest form, when a switch is toggled, a force hold operation is initiated, whereby the system is held open with the required force. Such a force-closed-loop controlled operation avoids the above-mentioned problems when the valve opens, because only a predetermined force is applied to components located on the driven side, such as, for example, a seal or other valve components.

[0009] In a preferred embodiment, the force maintenance operation implements closed-loop control of the pressure on the fluid pumping side, the current for the drive motor, the torque on the pump shaft, or closed-loop control of the force to a required target value. In conventional systems, these values ​​are interdependent. To increase the pressure, the current for the drive motor is typically increased, which results in an increase in the torque on the pump shaft. Furthermore, the force generated depends on the pressure in the hydraulic system. Therefore, depending on the system, an appropriate quantity, preferably one of the quantities listed above, can be used as the controlled and / or manipulated variable.

[0010] More preferably, alternate closed loop control switching between two or more values ​​from position, pressure, current, torque or force may alternatively be implemented.

[0011] The "alternating closed-loop control" checks a number of different values, for example from the pressure, torque, and drive current values ​​already mentioned above. Each value is then compared with a target value, and an appropriate compensation is performed for the value with the smallest deviation. Furthermore, the actual position value or the deviation between the actual position value and the target position value is used for the position closed-loop control, and the other values ​​mentioned above are used for the closed-loop control of the force holding operation. In this case, the displacement is determined from the results of the position closed-loop control and the force holding operation, taking into account the desired direction of travel, using the respective smallest displacement value.

[0012] More preferably, the closed-loop control target value of the closed-loop control of pressure, current, or torque is adjustable. In particular, the closed-loop control target value or the maximum operating value of the closed-loop control can be set either fixedly or dynamically. If the closed-loop control target value can be set fixedly, for example, a gentler limit stop can be achieved by improving the drive control of the stop position. If the closed-loop control target value can be set dynamically, a force holding operation can be performed even when the cylinder piston is in an intermediate position. In this way, the closed-loop control is performed via force instead of position, which can make it possible to achieve more advantageous closed-loop control characteristics, for example, when the pressure and amount of the fluid (e.g., steam) to be closed-loop controlled are fluctuating.

[0013] Furthermore, it is preferred that the force-holding operation be switched back to the position-holding operation if the fed-back position value or position target value or digital signal (no longer) corresponds to the switch-over criterion for the force-holding operation. Preferably, the operation according to the invention is terminated again if the conditions for this are no longer fulfilled.

[0014] Alternatively, the method for improving the operating behavior of a fluid-operated process may be operated in an alternating closed-loop control based on essentially position and pressure, or current, torque, or force. In this case, too, thresholds must be set from measurable values, particularly for position, pressure, current, torque, or force, of a valve in the fluid-operated process. Subsequently, the valve driver is controlled or closed-loop-controlled in an alternating closed-loop control between two or more manipulated variables from the manipulated variables measured in the first step. In this alternative, the switching between the assumed closed-loop control parameters is performed, for example, in a time-controlled manner. Usually, the closed-loop control parameters are required to correspond (approximately) to each other. Thus, in a hypothetical installation, a steam pressure of 10 MPa may correspond to a valve stem position 1 mm short of the stop position and a predetermined current (e.g., 10 A) in the electric motor for maintaining this valve position with hydraulic fluid pumped from a pump operated with a predetermined torque of the electric motor. This predetermined current generates a torque.

[0015] More preferably, several of the values ​​are measured, and the valve drive is alternately operated depending on the several values, particularly based on the minimum deviation. In this way, it is possible to easily check if one of the closed-loop control parameters causes a behavior that deviates from the other closed-loop control parameters, which may lead to the assumption that a fault may occur. Thus, if one of the detected values ​​deviates from a target value, a system error can be reported. Then, further checks can be made to determine whether a fault exists when measuring the corresponding parameter, when adjusting the operating value that influences this parameter, or elsewhere. This allows a high level of safety to be guaranteed by circuit-technical measures.

[0016] In particular, the method according to the invention allows for closed-loop control of the pressure on the hydraulic pressure supply side, the hydraulic force for moving a valve, or the current to a hydraulic pump for generating a corresponding force, to a defined value at the start-up of the installation, as soon as the corresponding reaction force is registered in the system.

[0017] Finally, the present invention also includes an apparatus for carrying out the method. [Brief explanation of the drawings]

[0018] [Figure 1] 1A and 1B are diagrams illustrating switching between force holding operation and position closed-loop control according to a first embodiment of the present invention. [Figure 2] 10A and 10B are diagrams illustrating switching between force holding operation and position closed-loop control according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Description of the Examples Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0020] First Example FIG. 1 illustrates a switchover between force-holding operation and position closed-loop control according to a first embodiment of the present invention. First, the actual position value and a (external or predefined) position target value are fed into the position closed-loop control of an electromagnetic drive with hydrostatic transmission (EMAH). Simultaneously, target values ​​for current, force, torque, and / or pressure are fed into the closed-loop control for force-holding operation. In the normal case where the position target value is not within a predefined range (e.g., it is not required that the valve be fully open), a control signal is supplied via the position closed-loop control to a motor, which in turn hydraulically operates a piston in a cylinder that operates a valve (or equivalent component, not shown) to be closed-loop controlled. The actual values ​​of position, current, force, torque, and pressure, which are affected by changes in motor and cylinder position, are also fed back to the closed-loop control circuit, as is common in the prior art.

[0021] However, if it is determined based on the position target value that closed-loop control with force holding is desired for the reasons explained above, for example because the position target value is set to 100% (or another value from a predefined position target range) or if a corresponding signal logic triggers a switchover (not shown), then in this embodiment, especially if the digital signal is switched over, the "Digital Signal" block in FIG. 1 is activated. This block triggers a switchover from position closed-loop control to force holding. Thus, the motor and cylinder are no longer controlled depending on the valve position, but instead depending on the current, force, torque, or pressure actual values ​​(selectively or in combination). This means that possible displacements of the motor and cylinder again affect these actual values, thereby closing the closed-loop control circuit.

[0022] In a currently preferred embodiment, this control is based on the applied force (which, as mentioned above, depends on the motor torque, pressure, motor current, etc.), and is therefore referred to as "force holding operation." That is, in force holding operation, the motor and cylinder are controlled in a closed loop based on the parameters of the electric motor current, force, or torque, regardless of the valve position (opening). Thus, without detecting a limit stop, the valve can be held in the maximally open position, for example, to prevent the aforementioned damage to the driven component. Furthermore, in this case, the actual position value is no longer used while force holding operation is being performed.

[0023] 2 shows the switching between force holding operation and position closed-loop control according to a second embodiment of the invention. In the second embodiment, both the ("traditional") position closed-loop control and the force holding operation are performed in the same way as in the first embodiment. The crucial difference with respect to the first embodiment lies in the decision to "switch" between position closed-loop control and closed-loop control during force holding operation, more precisely, between closed-loop control based not "only" on the position target value, but also on the target values ​​of current, force, torque and / or pressure. In principle, it is also possible to take into account further values ​​as the basis for the alternating closed-loop control; for example, a value of the closed-loop controlled process can be used directly as the target value and correspondingly adjusted to one of the values ​​listed above.

[0024] Instead of being based on a change in the position setpoint to satisfy a "switching condition" as in the first embodiment, or on a "digital signal," in the "alternating closed-loop control" of the second embodiment, a minimum value is formed from the position closed-loop control signal and the "other" (i.e., current, force, torque, and / or pressure) closed-loop control signals. This minimum value drives the motor of the EMAH, and thus the cylinder, thereby influencing the position value and the "other" values ​​in the closed-loop control circuit.

[0025] In this case, the advantages of the second embodiment are the same as those of the first embodiment. Furthermore, the flexible use of different measured values ​​allows for emergency operation, for example, in the event of a sensor failure. Furthermore, closed-loop control can be used to periodically use different sensors. In this case, operation can be maintained even if one of the sensors fails or if another equivalent fault occurs.

[0026] Of course, the system of the present invention can also be selectively switched between alternating closed-loop control and "controlled" closed-loop control. In such a case, a system like that of Figure 1 is used, but when alternating closed-loop control is implemented, no digital signals are used. This allows for flexible use of the system.

Claims

1. 1. A method for improving the operating behavior of fluid-operated processes, in particular in gas and steam turbines with closed-loop control facilities, comprising: The method comprises: - setting a predetermined position target or range of position targets for a portion of a valve in the fluid-operated process, or evaluating a digital signal as a set point; after the position target value or the position target value range or the digital signal has been set, switching the drive from position-holding operation to force-holding operation without taking into account the actual position value; A method comprising:

2. The force maintenance operation performs closed-loop control of the pressure on the fluid pumping side, the current for the drive motor, the torque on the pump shaft, or closed-loop control of the force to a required target value. The method of claim 1.

3. Alternatively, switching to alternate closed-loop control between two or more values ​​from position, pressure, current, torque or force is implemented; 3. The method according to claim 1 or 2.

4. The closed-loop control target value of the closed-loop control of pressure, current or torque is adjustable as the position target value; 4. The method according to any one of claims 1 to 3.

5. The closed-loop control target value can be set either fixedly or dynamically. The method of claim 4.

6. switching back from the force-holding operation to the position-holding operation when the fed-back position value or the position target value or the digital signal no longer corresponds to a switching criterion.

6. The method according to any one of claims 1 to 5.

7. 1. A method for improving the operating behavior of fluid-operated processes, in particular in gas and steam turbines with closed-loop control facilities, comprising: The method comprises: - defining thresholds from measurable values, in particular related to position, pressure, current, torque or force at a valve in said fluid-operated process; - operating the valve drive in an alternating closed-loop control alternating between two or more manipulated variables from the manipulated variables measured in the preceding step; A method comprising:

8. a plurality of said values ​​are measured; Depending on the values, the valve drive is alternately operated, in particular based on the minimum deviation value. The method of claim 7.

9. If one of the detected values ​​deviates from the target value, a system error is signaled.

9. The method according to claim 7 or 8.

10. Apparatus for carrying out the method according to any one or more of the preceding claims.

Images