A method for selecting logic configuration of dual LVDT feedback for steam turbine valve control

Abstract

The invention discloses a steam turbine valve dual LVDT feedback selection logic configuration method, which relates to the field of automatic control technology. When the steam turbine valve uses dual LVDT feedback, the control logic makes a difference between the real-time valve command and the two LVDT feedbacks, and then compares them. The LVDT feedback with a small deviation from the valve command is selected as the valve real feedback, which is used as the valve PID control servo valve command to control the valve opening. This prevents the valve command from being smaller than the valve feedback during the valve closing process when a single LVDT fails and the valve adjustment is uncontrolled and fully closed, causing a turbine operation failure.

Description

Technical Field

[0001] The invention relates to the field of automatic control technology, and in particular to a steam turbine regulating valve dual LVDT feedback selection logic configuration method. Background Art

[0002] Steam turbine valve control is crucial to the safe operation of steam turbines. The valve command is adjusted and controlled according to the unit load. The turbine valve feedback is generally selected by dual LVDT, and then the difference is made with the valve command. The difference is adjusted by the PID function block to adjust the servo valve command and control the valve opening. Therefore, how to select the two LVDT feedbacks has become a key research topic.

[0003] In the prior art ( Figure 1 ), because the conventional logic selects two LVDT feedbacks to participate in the control of the valve, when the fault of a single LVDT feedback remains unchanged, the valve command decreases during the process of closing the valve, and the normally operating LVDT feedback will decrease with the command, while the faulty LVDT feedback remains unchanged, so the control logic will select the unchanged, higher value, faulty LVDT feedback. At this time, the valve command is always less than the valve feedback after the high selection, and the control logic will continuously output the command to close the servo valve, causing the valve to continue to close until it is fully closed, causing the turbine valve to lose control, which brings great safety hazards to the operation of the turbine. Therefore, there is an urgent need for a logic configuration method that can correctly select LVDT feedback, which is of great significance to improving the safety of turbine operation. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide a steam turbine regulating valve dual LVDT feedback selection logic configuration method to solve the problem that the prior art cannot correctly select the regulating valve LVDT feedback, causing the regulating valve to lose control and threatening the safe operation of the steam turbine.

[0005] The technical solution adopted by the present invention to solve the above problem is: a steam turbine valve regulating dual LVDT feedback selection logic configuration method, which is characterized by obtaining the valve regulating command received by the steam turbine and two LVDT feedbacks;

[0006] According to the valve control command and the valve control LVDT feedback, the difference is calculated by the SUB-1 function block, the output value is calculated by the ABS-1 function block, and the absolute value is input to the LE function block X1;

[0007] The difference between the valve control command and the valve control LVDT feedback 2 is calculated by the SUB-2 function block, and the output value is calculated by the ABS-2 function block for absolute value, and then input into the LE function block X2;

[0008] According to the comparison between X1 and X2 in the LE function block: when X1≤X2, the LE function block outputs 1; when X1>X2, the LE function block outputs 0.

[0009] Further, the first and second LVDT feedbacks of the regulating valve are switched and selected according to the output signal of the LE function block;

[0010] According to the output value of the LE function block to the SFT function block, when the Z value of the SFT function block is 1 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X1; when the Z value of the SFT function block is 0 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X2;

[0011] According to the output Y of the SFT function block, it is sent to the PID function block FB and compared with the valve control command X. The servo valve command is adjusted through proportional, integral and differential effects. When X>FB, Y increases; when X<FB, Y decreases; when X=FB, Y remains unchanged.

[0012] Compared with the prior art, the present invention has the following advantages and effects: by selecting the LVDT feedback which is in normal operation and has a small deviation from the valve control command, it is prevented that when a single LVDT fails and remains unchanged, the valve control command is always smaller than the valve control feedback during the valve closing process, and the valve control is out of control and fully closed, causing the turbine operation failure, thereby improving the operation safety of the turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Select the logic diagram for the dual LVDT feedback of the existing steam turbine regulating valve.

[0014] Figure 2 This is a logic diagram for selecting the dual LVDT feedback of the steam turbine regulating valve in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and by way of examples. The following examples are intended to explain the present invention but the present invention is not limited to the following examples.

[0016] The present invention provides a steam turbine regulating valve dual LVDT feedback selection logic configuration method. When the steam turbine regulating valve adopts dual LVDT feedback, the control logic makes a difference between the real-time regulating valve command and two LVDT feedbacks, and compares them. The LVDT feedback with the smallest deviation from the regulating valve command is selected as the real feedback of the regulating valve, which is used as the regulating valve PID regulation servo valve command to control the regulating valve opening.

[0017] The method provided by the above scheme selects a normally operating LVDT feedback with a small deviation from the valve control command to prevent the valve control command from being always smaller than the valve control feedback during the valve control process when a single LVDT fails and the valve control adjustment is out of control and completely closed, causing a turbine operation failure, thereby improving the safety of turbine operation.

[0018] See also Figure 1 , Figure 2 It should be noted that HS is a high selection function block. When X1≥X2, Y=X1; when X1<X2, Y=X2. PID is a proportional integral differential control function block. It makes a difference between X and FB. After the difference is processed by proportional, integral and differential, the Y value is output. When X>FB, Y increases; when X<FB, Y decreases; when X=FB, Y remains unchanged. SUB is a subtraction function block, Y=X1-X2. ABS is an absolute value function block. LE is a comparison function block. When X1≤X2, D=1; when X1>X2, D=0. SFT is a switching function block. When Z=0 and the duration exceeds T, Y=X2; when Z=1 and the duration exceeds T, Y=X1; T is the time constant 1s. The circle is an analog signal and the rectangle is a time constant.

[0019] The method is specifically as follows:

[0020] Get the valve control command and two LVDT feedbacks received by the turbine;

[0021] According to the valve control command and the valve control LVDT feedback, the difference is calculated by the SUB-1 function block, the output value is calculated by the ABS-1 function block, and the absolute value is input to the LE function block X1;

[0022] The difference between the valve control command and the valve control LVDT feedback 2 is calculated by the SUB-2 function block, and the output value is calculated by the ABS-2 function block for absolute value, and then input into the LE function block X2;

[0023] According to the comparison between X1 and X2 in the LE function block: when X1≤X2, the LE function block outputs 1; when X1>X2, the LE function block outputs 0.

[0024] Switch and select the first and second LVDT feedbacks according to the output signal of the LE function block;

[0025] According to the output value of the LE function block to the SFT function block, when the Z value of the SFT function block is 1 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X1; when the Z value of the SFT function block is 0 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X2;

[0026] According to the output Y of the SFT function block, it is sent to the PID function block FB and compared with the valve control command X. The servo valve command is adjusted through proportional, integral and differential effects. When X>FB, Y increases; when X<FB, Y decreases; when X=FB, Y remains unchanged.

[0027] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0028] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the protection scope of the present invention. Any changes and modifications made by any technician familiar with the technology without departing from the concept and scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A steam turbine valve dual LVDT feedback selection logic configuration method, characterized in that: Get the valve control command and two LVDT feedbacks received by the turbine; According to the valve control command and the valve control LVDT feedback, the difference is calculated by the SUB-1 function block, the output value is calculated by the ABS-1 function block, and the absolute value is input to the LE function block X1; The difference between the valve control command and the valve control LVDT feedback 2 is calculated by the SUB-2 function block, and the output value is calculated by the ABS-2 function block for absolute value, and then input into the LE function block X2; According to the comparison between X1 and X2 in the LE function block: when X1≤X2, the LE function block outputs 1; when X1>X2, the LE function block outputs 0; Switch and select the first and second LVDT feedbacks according to the output signal of the LE function block; According to the output value of the LE function block to the SFT function block, when the Z value of the SFT function block is 1 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X1; when the Z value of the SFT function block is 0 and is maintained for more than 1 second, the output Y of the SFT function block is equal to its input X2; According to the output Y of the SFT function block, it is sent to the PID function block FB and compared with the valve control command X. The servo valve command is adjusted through proportional, integral and differential effects. When X>FB, Y increases; when X<FB, Y decreases; when X=FB, Y remains unchanged.

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