JPS6158643B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for detecting the opening start point of a steam control valve.

(Prior Art) In general, a turbine speed-up control system includes a first control section that controls the steam control valve from the fully closed position to the point where the valve starts to open through which steam begins to pass, and a first control section that controls the operation of the turbine from the point where the valve starts to open. A second control section is provided that performs feedback control until the final target rotation speed is obtained,
These control devices are completely separate and are switched at the point at which the valve begins to open.

Therefore, since the opening start point is used as the operation switching point of the control device, its detection is extremely important for control.

This is because the steam control valve has characteristics as shown in FIG.

FIG. 2 is a graph illustrating the relationship between the opening degree of the steam control valve and the rotation angle of the drive motor that controls the opening and closing of the steam control valve. In turbine speed increase control, it is necessary to increase the speed at a predetermined acceleration rate due to its thermal stress and mechanical strength. Therefore, in order to control the acceleration rate, it is necessary to control the flow rate of steam flowing into the turbine by manipulating the opening degree of the steam control valve. In addition, the steam control valve must have a steam shutoff ability to stop the turbine, and therefore the opening degree of the steam control valve has to be adjusted to the rotation angle of the valve drive motor, so that the opening degree of the steam control valve is determined by the amount of free play shown in section A at the fully closed position. It has an interference margin to ensure reliable shutoff, and the opening degree and rotation angle are proportional from the valve opening starting point B to the fully open position C.

Conventionally, however, the opening point of the steam control valve has been detected by a pressure switch and by monitoring the differential value of the controlled variable, that is, the rate of change in the turbine rotational speed, and based on the degree of the change.

When the steam control valve starts to open, a load is applied to the control oil in the steam control valve oil cylinder to overcome the steam pressure, and the pressure switch uses this increase in control oil pressure.It is a switch that operates at a predetermined fluid pressure. Therefore, it is necessary to select a pressure switch that takes into account the control hydraulic pressure at the rated load.Since the steam pressure is low when the turbine is started, it is affected by the error in the operating point of the pressure switch, and the detection accuracy is low. It was hot.

One way to solve this problem is to detect the differential value of the controlled variable of the controlled object, that is, the acceleration rate of the turbine rotation speed, and compare it with a predetermined set value, and then calculate the change in the acceleration rate from the set value. A detection method has been adopted in which the opening point is considered to be the point when the opening occurs.

FIG. 3 is a block diagram showing the circuit configuration of a turbine speed increase control system for realizing such a detection method, and FIG. 4 is a flowchart of its operation.

In FIG. 3, the control device 1 includes a first control section 1a that performs open loop control of the steam control valve 3 from the fully closed position to the point where it starts to open.

The first control section 1a applies a constant valve opening operation signal to the drive motor 2 to open the control valve 3 from the start of the speed-up control until the pressure switch 10 for detecting the start of opening of the steam control valve operates.

Further, the control device 1 has a second control device that performs closed-loop acceleration control from the opening start point to the target rotation speed at a predetermined acceleration rate.
The controller 1b includes a controller 1b.

The second control unit 1b drives the motor 2 using a signal obtained by adding a PID (proportional, integral, differential) calculation operation to the difference between the commanded rotation speed and the actual rotation speed, controls the opening of the control valve 3, and controls the boiler. The flow rate of steam flowing into the turbine 4 from the turbine 8 is controlled, and the speed of the turbine 4 is increased.

The first sensor 5 detects the rotation angle of the valve drive motor 2, that is, the opening position signal of the steam control valve 3, and sends it back to the control device 1.

The second sensor 6 detects the actual rotational speed of the turbine 4 and sends it back to the second control unit 1b of the control device 1.

The third sensor 7 that detects the acceleration rate of the rotation speed of the turbine 4 feeds back the acceleration rate to the control device 1,
The point at which the valve begins to open is taken as the degree of change in the acceleration rate.

When the steam control valve 3 begins to open, the steam generated in the boiler 8 flows into the turbine 4 and expands adiabatically, converting thermal energy into kinetic energy.

The turbine 4 receives the kinetic energy and begins to rotate the generator (load) 9, but when the steam control valve 3 begins to open, the turbine rotational speed is increased so that its differential value, that is, the acceleration rate also increases.

Therefore, the acceleration rate is detected and compared with a predetermined set value that takes into account noise, etc., and when the acceleration rate exceeds the set value, it is detected as the acceleration start point, that is, the opening start point of the steam control valve 3.

When the steam control valve 3 is in the fully closed position, the acceleration rate≦0, and once the steam starts flowing, the acceleration rate becomes positive.

Therefore, we derive the point at which the acceleration rate becomes positive as the point at which acceleration has started, that is, the steam control valve 3 has started, and
Eliminates the inconveniences of the conventional pressure switch detection method.

(Problem to be solved by the invention) However, in the turbine speed-up process, above the opening point, the speed is not continuously increased to the target rotation speed, but the starting conditions at the time of starting the turbine (for example, mismatch Depending on the temperature, the turbine may be held at a certain rotational speed to reduce thermal stress on the turbine.

Further, there are cases where the turbine speed increase is interrupted due to vibration or the like during the turbine speed increase, and constant value control is performed to maintain the turbine rotation speed in a safe rotation speed range.

In these cases, when the rotation speed is controlled, if a malfunction occurs in the pressure switch using only the conventional detection method, the speed will be accelerated and the acceleration rate will be reduced, even though constant value control or rotation speed maintenance should be performed. There was a risk that the opening point could not be detected and the transition to closed-loop control could not occur until the value exceeded the set value.

Furthermore, if the pressure switch repeatedly turns on and off due to malfunction during turbine speed increase, the control system will be switched between the first control section that performs open-loop control and the second control section that performs closed-loop control. There was a risk that this would occur.

In other words, when the turbine is currently rotating at a constant speed due to manual operation by the operator, when constant value control using closed loop control is started in order to maintain the rotation speed using computer control, the actual contact input that begins to open fails. If the valve does not operate, the computer assumes that it is not the point where it begins to open, and opens the valve more and more with a constant pulse.

Therefore, the turbine speeds up, and by determining the acceleration rate, it can be determined that it is at the point where it begins to open, and it can move to a closed loop and start constant value control, but by that time the rotation speed has already increased to a certain degree. This means that constant value control at the originally desired rotation speed cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control valve opening start point detection method that overcomes the conventional drawbacks and allows smooth turbine speed increase control at all times.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a controlled object that is operated by the opening degree of a fluid flow control valve, and is controlled by a constant continuous valve opening operation signal from the fully closed position of the control valve to the opening start point. The first control section that performs open loop control and the control valve after the opening point
A second control unit that performs closed-loop control using a PID operation signal, detects a differential value of the controlled variable of the controlled object, monitors a change in the differential value, and detects when the differential value exceeds a first constant. In the control valve opening starting point detection method, the control valve opening starting point is detected as the opening starting point of the control valve, when the differential value does not exceed a first constant, the controlled variable of the controlled object and the differential value of the controlled variable are detected. A control valve opening starting point detection method of detecting the opening starting point of the control valve when the controlled amount is at least a certain value and the differential value of the controlled amount is at least a second constant smaller than the first constant. It is.

(Operation) In the present invention, when the controlled variable of the controlled object is above a certain value, the differential value of the controlled variable is first compared with a first constant, and if the differential value of the controlled variable is above the first constant, the differential value of the controlled variable is compared with the first constant. At some point, it is determined that the steam control valve has reached the opening point, and when the differential value of the controlled variable is smaller than the first constant, it is further compared with a second constant that is smaller than the first constant. . If the differential value of the control amount is greater than or equal to the second constant, it is determined that the steam control valve has reached the point where it begins to open, while if it is smaller than the second constant, the steam control valve is closed for the first time. It is determined that there is.

Therefore, if the controlled variable of the controlled object is, for example, the turbine rotational speed, and the turbine rotational speed is above a certain rotational speed, the acceleration rate of the turbine, which is the differential value of the controlled variable, becomes the first constant. Even if it is smaller than the second constant, it is determined that the steam control valve has reached the opening point when it is greater than or equal to the second constant, so it is possible to smoothly enter closed-loop control even when the turbine rotation speed is being controlled at a constant value. becomes possible.

(Example) The detection method in an example of the present invention is shown in a flowchart as shown in FIG.

The circuit configuration (hardware) for carrying out this control valve opening starting point detection method is shown in the block diagram of FIG.

The same reference numerals represent the same elements in all drawings.

Further, in the following embodiments, the rotation speed of a turbine will be explained as an example of the controlled variable of the controlled object. Therefore, the differential value of the controlled variable is the acceleration rate of the turbine.

Start with step 11, then step 12
It is determined whether the pressure switch 10 for detecting the start of opening has operated, and if the answer is yes, the process proceeds to step 13, where the control system is switched to PID control, and the process proceeds to branch jump A (boanch jump A) at step 22.

If the answer is negative in step 12, the process proceeds to step 14, and it is determined whether the change in acceleration rate a is large, that is, a>α when α is the first constant.If the answer is affirmative, the process proceeds to step 13, and if the answer is negative, the process proceeds to step 15.

Then, in step 15, it is determined whether the rotation speed is above a certain value, and if it is affirmative, the process proceeds to step 16, where it is judged whether the acceleration rate is above a certain value.
Proceed to.

That is, it is checked whether the rotational speed n of the turbine 4 is greater than or equal to a certain value (constant) v, and if n≧v, it is further checked whether the acceleration rate a is greater than or equal to the second constant β, and if a≧β. Proceed to step 13.

However, since step 16 is performed when a<α in step 14 and n≧v in step 15, the relationship between the first constant α and the second constant β is naturally α>β. .

On the other hand, if the answer is negative at step 15 or step 16, proceed to step 17 in either case.
Here, it is determined whether the specified time has been exceeded, and if the answer is yes, the process proceeds to step 18, where the control is stopped due to a driving operation failure and is switched to manual mode, and the process proceeds to step 19, branch jump B.

By the way, if the result in step 17 is negative, the process proceeds to step 20, and if a constant opening operation signal is output, the process proceeds to branch jump C in step 21.

Therefore, in the present invention, the second sensor 6 detects the rotation speed of the turbine 4, and the third sensor 7 detects the acceleration rate of the turbine 4.
The acceleration rates are each returned to the control device 1 at
The point at which the valve begins to open is determined as a combination of the rotational speed and acceleration rate.

Here, if it is determined in step 15 that the turbine speed n is equal to or higher than the constant value v, the acceleration rate a is compared with the second constant β without immediately entering closed loop control. This is to confirm that the steam control valve has reached the point where it begins to open.

That is, even if the turbine rotational speed n is equal to or higher than a certain value v, the steam control valve may be closed during a turbine trip. In other words, in order to confirm whether or not the steam control valve has reached the opening point, it is not sufficient to simply require that the turbine rotational speed n is greater than or equal to a certain value v; it is also necessary that the acceleration rate a is greater than or equal to the second constant β. Conditions are required.

Note that when the rotational speed n is equal to or higher than the constant value v, the steam control valve has almost always reached the opening point, so the acceleration rate a for checking this can be small, and therefore the second The constant β is smaller than the first constant α. Thereby, when the turbine is shifted from constant value control to closed loop control, the turbine can be smoothly shifted with almost no speed increase.

In other words, the present invention can be applied even if the pressure switch detector is not operating when the turbine speed increase control is started from a state where the rotation speed is maintained, and furthermore, when the pressure switch is repeatedly turned on and off due to malfunction. too,
This is a method that can detect the starting point of opening based on the above judgment.

Note that the detection method of the present invention can be applied to both analog control devices and digital control devices.

〔Effect of the invention〕

Thus, by using the detection method of the present invention, the control systems of the two control units 1a and 1b of the control device 1 can be switched more reliably and smoothly, thereby eliminating the inconvenience in detecting the opening start point that may occur conventionally. can be significantly reduced.

Further, the present invention can improve the reliability of opening start point detection without adding anything to conventional instrumentation or sensors.

Further, according to the present invention, since the reliability of the method for detecting the opening start point is improved, it can be expected that the reliability of the turbine speed increase control system as a whole can be improved.

[Brief explanation of the drawing]

Fig. 1 is a flowchart in one embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between the opening degree of the steam control valve and the rotation angle of the drive motor, and Fig. 3 is a conventional example to which the present invention is applied. A block diagram showing the circuit configuration, and FIG. 4 is a flowchart of a conventional example. 1...control device, 1a is open loop section, 1b is closed loop acceleration control section, 2...valve drive motor, 3...
Steam control valve, 4...Turbine, 5...Sensor for detecting valve opening position signal, 6...Sensor for detecting turbine rotation speed, 7...Sensor for detecting acceleration rate, 8...Boiler, 9...Load, 10...Detection pressure switch.

Claims (1)

[Scope of Claims] 1. A first control system that includes a controlled object operated by the opening degree of a fluid flow control valve and that is controlled in an open loop by a constant continuous valve opening operation signal from the fully closed position of the control valve to the opening start point. After the control section and control valve start opening point
A second control unit that performs closed-loop control using a PID operation signal, detects a differential value of the controlled variable of the controlled object, monitors the differential value, and determines that the differential value is the first one.
In the method for detecting the opening start point of the control valve, when the differential value exceeds a constant, it is detected as the opening start point of the control valve, when the differential value does not exceed the first constant, the controlled variable and the controlled variable of the controlled object A differential value of the control valve is detected, and when the controlled variable is greater than or equal to a certain value and the differential value of the controlled variable is greater than or equal to a second constant that is smaller than the first constant, the point at which the control valve starts to open is detected. Features a control valve opening start point detection method.