Oil and gas pipeline long section cathode protection current target optimization method and system

Abstract

The invention discloses an oil and gas pipeline long-section cathode protection current target optimization method and system, and the method comprises the steps: outputting a proper cathode protection current through a bidirectional compensation cathode protection device, reducing the adverse impact on an oil and gas pipeline caused by the flowing of a stray current into and out of the oil and gas pipeline, enabling the potential distribution of the oil and gas pipeline to be uniform, and improving the stability of the oil and gas pipeline. And the cathode protection effect of the oil and gas pipeline in the whole section is optimal under the influence of stray current. According to the oil and gas pipeline long-section cathode protection current target optimization method, the magnitude of the output current I of the bidirectional compensation cathode protection device can be controlled, so that the pipe-to-ground potential of the vast majority of areas of the oil and gas pipeline is maintained within the cathode protection range, and the service life of the oil and gas pipeline is prolonged.

Description

Technical Field

[0001] The invention relates to the field of cathodic protection of oil and gas pipelines, and in particular to a method and system for optimizing a cathodic protection current target for a long section of an oil and gas pipeline. Background Art

[0002] Since the track and soil cannot be completely insulated, the traction current used to drive the subway will leak part of the current into the soil. This current is called stray current. The stray current will flow into and out of the oil and gas pipelines through the soil, causing severe electrochemical corrosion of the oil and gas pipelines, which will seriously threaten the safe operation of the energy transmission system.

[0003] In order to protect oil and gas pipelines from electrochemical corrosion, cathodic protection devices are often used to apply a cathodic protection current to suppress the potential deviation of the oil and gas pipelines to slow down the corrosion rate of the oil and gas pipelines. However, since the subway is always in motion, the stray current generated is also a dynamic stray current. The cathodic protection system cannot adjust the output current according to the change of the dynamic stray current, which will cause the problem of insufficient or over-protection of the oil and gas pipelines in sections. With the rapid development of pipeline network structure and urban rail transit, how to effectively control dynamic stray currents has become an important issue that needs to be solved in today's society.

[0004] The existing cathodic protection technology mainly relies on observing the pipe-to-ground potential value displayed in the monitoring system, artificially adjusting the cathodic protection device to output a larger cathodic protection current, and taking the monitoring point where the electrochemical corrosion is most serious as the benchmark, suppressing the pipe-to-ground potential value of this monitoring point within the cathodic protection range. However, this method will cause the overall negative deviation of the pipe-to-ground potential of the oil and gas pipeline in the section, and the possibility of hydrogen embrittlement risk in some areas of the oil and gas pipeline will increase significantly. The intelligence level of the cathodic protection system is low, and it is impossible to dynamically adjust the output current of the device to suppress the adverse effects of stray current on the oil and gas pipeline. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for optimizing the cathodic protection current target of a long section of an oil and gas pipeline in view of the shortcomings of the prior art. The method and system automatically adjust the output current of the bidirectional compensating cathodic protection device according to the pipe-to-ground potential of the section oil and gas pipeline collected in real time, so as to achieve the optimal cathodic protection effect of the section oil and gas pipeline under the interference of stray current.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for optimizing the target of negative current protection in a long section of an oil and gas pipeline, comprising the following steps:

[0007] S1, collect the pipe-to-ground potential u1(k)~u of monitoring points 1~n n (k);

[0008] S2. Calculate the difference between the pipe-to-ground potential at each monitoring point and the ideal target potential; assign a weight coefficient to each pipe-to-ground potential; wherein, the pipe-to-ground potential with a larger difference has a larger weight coefficient assigned thereto;

[0009] S3, the monitoring point ground potential u1(k)~u n (k) is inserted into the objective function M(k) after weight assignment, and the value of M(k) is calculated; represents the weight coefficient at time k, u i (k) represents the pipe-to-ground potential at the ith monitoring point at time k, u obj represents the ideal target potential, u up with u down Respectively represent the upper and lower limits of the protection potential;

[0010] S4, collecting the output current I(k) of the rear-stage bidirectional active full-bridge converter of the cathodic protection device at time k; respectively calculating the change ΔM(k) of the objective function value caused by the change in duty cycle from time k-1 to time k, the change ΔI(k) of the output current of the rear-stage bidirectional active full-bridge converter of the cathodic protection device caused by the change in duty cycle from time k-1 to time k, and the disturbance step Δd(k) at time k; using I(k), ΔM(k) and Δd(k) to calculate the duty cycle signal D(k) of the rear-stage bidirectional active full-bridge converter of the cathodic protection device of the oil and gas pipeline at time k;

[0011] S5, modulating the duty cycle signal D(k) by PWM to obtain a driving signal of the bidirectional active full-bridge converter, thereby changing the output current of the bidirectional active full-bridge converter;

[0012] S6. Repeat steps S1 to S5 until the objective function M(k) reaches a minimum value.

[0013] In the present invention, the calculation formula of the disturbance step length Δd(k) at time k is: Where Δd is the fixed perturbation step size.

[0014] The calculation process of the duty cycle signal D(k) at time k includes:

[0015] If M(k)-M(k-1)>0, I(k)-I(k-1)>0, then D(k+1)=D(k)-Δd(k);

[0016] If M(k)-M(k-1)>0, I(k)-I(k-1)<0, then D(k+1)=D(k)+Δd(k);

[0017] If M(k)-M(k-1)<0, I(k)-I(k-1)>0, then D(k+1)=D(k)+Δd(k);

[0018] If M(k)-M(k-1)<0, I(k)-I(k-1)<0, then D(k+1)=D(k)-Δd(k);

[0019] If M(k)-M(k-1)=0, then D(k+1)=D(k).

[0020] The duty cycle signal D(k) is initialized to D(0)=0.5.

[0021] As an inventive concept, the present invention also provides a target optimization system for cathodic protection current in a long section of an oil and gas pipeline, comprising a memory, a processor and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0022] Compared with the prior art, the present invention has the following beneficial effects: the present invention collects the pipe-to-ground potential values ​​monitored by the monitoring points of the oil and gas pipeline section, assigns weights to the pipe-to-ground potential values, and substitutes them into the constructed objective function. The controller automatically adjusts the output current of the bidirectional compensating cathodic protection device, so that the cathodic protection effect of the oil and gas pipeline section reaches the optimal state, thereby improving the service life of the oil and gas pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a long section bidirectional compensation management system for an oil and gas pipeline according to an embodiment of the present invention;

[0024] Figure 2 This is a flow chart of a method for optimizing the negative current target of a long section of an oil and gas pipeline according to an embodiment of the present invention;

[0025] Figure 3 It is a topological structure and control block diagram of a bidirectional compensation cathodic protection device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Figure 1 This is a schematic diagram of the structure of a long section bidirectional compensation treatment system for an oil and gas pipeline according to an embodiment of the present invention. The treatment system includes a bidirectional compensation cathodic protection device, a deep well anode, a target optimization controller, and reference electrodes No. 1 to No. n. The characteristics are as follows:

[0028] 1) The bidirectional compensation cathodic protection device is installed near the traction station, and the output positive electrode is connected to the deep well anode through a wire, and the output negative electrode is connected to the pipeline through a wire; the anode bed is installed about 80m underground, so as to realize the cathodic protection of the entire section of the oil and gas pipeline; reference electrodes 1 to n are all installed near the pipeline, and the potential difference between the reference electrode and the pipeline is the pipe-to-ground potential of the monitoring point; the target optimization controller collects the pipe-to-ground potential of each monitoring point of the oil and gas pipeline, processes these pipe-to-ground potential data, and adopts the proposed cathodic protection current target optimization method for the long section of the oil and gas pipeline to control the cathodic protection effect of the entire section of the oil and gas pipeline in the optimal state.

[0029] 2) The bidirectional compensating cathodic protection device includes a front-stage single-phase PWM rectifier, a rear-stage bidirectional active full-bridge converter and a target optimization controller; the input side of the bidirectional compensating cathodic protection device is connected to the mains, the positive pole of the output side is connected to the deep well anode, and the negative pole of the output side is connected to the pipeline; the target optimization controller is connected to the bidirectional compensating cathodic protection device to realize the target optimization method of the cathodic protection current in a long section of the oil and gas pipeline.

[0030] Figure 2 This is a flow chart of the cathodic protection target optimization method according to an embodiment of the present invention, and its implementation process is as follows:

[0031] 1) Construct an objective function for the purpose of uniform distribution of oil and gas pipeline protection potential. The sum of the squares of the difference between the pipe-to-ground potential at the oil and gas pipeline monitoring point and the ideal target potential is used as the objective function. The objective function is defined as in represents the weight coefficient, u i (k) represents the pipe-to-ground potential at the ith monitoring point at time k, u obj represents the ideal target potential, u up with u down Respectively represent the upper and lower limits of the protection potential, generally u obj Take -1V, u up Take -0.85V, u down Take -1.2V.

[0032] 2) Collect the pipe-to-ground potential u1(k)~u1(k) of monitoring points 1~n n (k);

[0033] 3) Calculate Δu i (k) = u i (k)-u obj The value of Δu i (k) A larger pipe-to-ground potential is assigned a larger weight coefficient, giving Δu i (k) A smaller pipe-to-ground potential is assigned a smaller weight coefficient;

[0034] 4) The ground potential of the monitoring point at time k is u1(k)~u n (k) is inserted into the objective function M(k) after weight assignment, and the value of M(k) is calculated;

[0035] 5) Collect the output current I(k) of the rear bidirectional active full-bridge converter of the cathodic protection device at time k;

[0036] 6) Calculate the change ΔM(k) of the objective function value due to the change in duty cycle from time k-1 to time k, the change ΔI(k) of the output current of the rear-stage dual active full-bridge converter of the cathodic protection device due to the change in duty cycle from time k-1 to time k, and the disturbance step length Δd(k) at time k;

[0037] 7) Calculate the duty cycle signal D(k) of the downstream dual active full-bridge converter of the oil and gas pipeline cathodic protection device at time k;

[0038] 8) The duty cycle signal D(k) described in step 7) is subjected to PWM modulation to obtain a driving signal of the dual active full-bridge converter, thereby changing the output current of the dual active full-bridge converter;

[0039] 9) Repeat steps 2) to 8) until the objective function M(k) reaches a minimum value;

[0040] Among them, the calculation formula of the perturbation step length Δd(k) is In order to avoid oscillation near the minimum value of the objective function, Δd is set to 0.1. The specific calculation process of the phase shift duty cycle D(k) includes:

[0041] If M(k)-M(k-1)>0, I(k)-I(k-1)>0, then D(k+1)=D(k)-Δd(k);

[0042] If M(k)-M(k-1)>0, I(k)-I(k-1)<0, then D(k+1)=D(k)+Δd(k);

[0043] If M(k)-M(k-1)<0, I(k)-I(k-1)>0, then D(k+1)=D(k)+Δd(k);

[0044] If M(k)-M(k-1)<0, I(k)-I(k-1)<0, then D(k+1)=D(k)-Δd(k);

[0045] If M(k)-M(k-1)=0, then D(k+1)=D(k).

[0046] Figure 3 It is a topological structure and control block diagram of a bidirectional compensation cathodic protection device according to an embodiment of the present invention. Figure 3In the method, the PWM rectifier is used as the front stage of the cathodic protection device, and the 220V AC voltage of the mains is converted into a 400V DC voltage through voltage closed-loop control. The output end of the front-stage PWM rectifier is connected to the output end of the rear-stage bidirectional active bridge converter to supply power to the rear-stage bidirectional active converter. The output current I of the rear-stage device is given by the target optimization method of the cathodic protection current in the long section of the oil and gas pipeline, and the rear-stage bidirectional active converter converts the 400V DC voltage into a given current through current closed-loop control and outputs it to the deep well anode and the oil and gas pipeline.

[0047] The front-stage PWM rectifier includes a filter inductor L1, a first switch tube S1, a second switch tube S2, a third switch tube S3, a fourth switch tube S4, and a voltage stabilizing capacitor C1. The input AC voltage is connected to the midpoints of the two bridge arms of the full bridge formed by the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 through the filter inductor L1, and the filter inductor L1 is used to filter out high-frequency noise in the power grid; the voltage stabilizing capacitor C1 is connected to the positive and negative electrodes of the output of the front-stage PWM rectifier respectively for voltage stabilization; the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 are used to convert the input AC voltage into a DC voltage, the first switch tube S1 and the third switch tube S3 are complementary to each other, the first switch tube S2 and the third switch tube S4 are complementary to each other, and u dc is the DC side output voltage of the previous PWM rectifier, and g1-g4 are the switching signals of the first switch tube S1, the second switch tube S2, the third switch tube S3, and the fourth switch tube S4 respectively.

[0048] The subsequent dual active bridge converter includes two DC side filter capacitors C2 and C3, a high frequency transformer T1, a resonant inductor L r , resonant capacitor C r , the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7, the eighth switch tube S8, the ninth switch tube S9, the tenth switch tube S 10 , Eleventh switch tube S 11 , the twelfth switch tube S 12 The fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7, and the eighth switch tube S8 constitute an input side full-bridge converter, and the ninth switch tube S9 and the tenth switch tube S 10 , Eleventh switch tube S 11 , the twelfth switch tube S 12 The output side of the full-bridge converter is formed; two DC side filter capacitors C2 and C3 are respectively connected to the input and output ends of the dual active bridge converter for voltage stabilization; the midpoints of the bridge arms of the two full bridges are respectively connected to the primary and secondary sides of the high-frequency transformer T1, and the high-frequency transformer T1 is used for isolation; the resonant inductor L r With the resonant capacitor C rConnected in series between the high-frequency transformer and the midpoint of the left full-bridge arm, the resonant inductor L r For transferring energy, the resonant capacitor C r At the same time, it acts as an isolation DC component to prevent the appearance of DC components on the high-frequency transformer. I is the output current of the subsequent bidirectional active full-bridge converter.

[0049] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0050] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for optimizing the target current of the long section of oil and gas pipeline. It is characterized in that The following steps are involved: S1, collect the pipe-to-ground potential u of monitoring points 1 to n 1 (k)~u n (k); S2. Calculate the difference between the pipe-to-ground potential at each monitoring point and the ideal target potential; assign a weight coefficient to each pipe-to-ground potential; wherein, the pipe-to-ground potential with a larger difference has a larger weight coefficient assigned thereto; S3, the monitoring point ground potential u at time k 1 (k)~u n (k) is inserted into the objective function M(k) after weight assignment, and the value of M(k) is calculated; represents the weight coefficient at time k, u i (k) represents the pipe-to-ground potential at the ith monitoring point at time k, u obj represents the ideal target potential, u up with u down Respectively represent the upper and lower limits of the protection potential; S4, collecting the output current I(k) of the rear-stage bidirectional active full-bridge converter of the cathodic protection device at time k; respectively calculating the change ΔM(k) of the objective function value caused by the change in duty cycle from time k-1 to time k, the change ΔI(k) of the output current of the rear-stage bidirectional active full-bridge converter of the cathodic protection device caused by the change in duty cycle from time k-1 to time k, and the disturbance step Δd(k) at time k; using I(k), ΔM(k) and Δd(k) to calculate the duty cycle signal D(k) of the rear-stage bidirectional active full-bridge converter of the cathodic protection device of the oil and gas pipeline at time k; S5, modulating the duty cycle signal D(k) by PWM to obtain a driving signal of the bidirectional active full-bridge converter, thereby changing the output current of the bidirectional active full-bridge converter; S6. Repeat steps S1 to S5 until the objective function M(k) reaches a minimum value.

2. The method for optimizing the target current of the long section of the oil and gas pipeline according to claim 1, It is characterized in that The calculation formula of the perturbation step length Δd(k) at time k is: Where Δd is the fixed perturbation step size.

3. The method for optimizing the target current of the long section of the oil and gas pipeline according to claim 1, It is characterized in that The calculation process of the duty cycle signal D(k) at time k includes: If M(k)-M(k-1)>0, I(k)-I(k-1)>0, then D(k+1)=D(k)-Δd(k); If M(k)-M(k-1)>0, I(k)-I(k-1)<0, then D(k+1)=D(k)+Δd(k); If M(k)-M(k-1)<0, I(k)-I(k-1)>0, then D(k+1)=D(k)+Δd(k); If M(k)-M(k-1)<0, I(k)-I(k-1)<0, then D(k+1)=D(k)-Δd(k); If M(k)-M(k-1)=0, then D(k+1)=D(k).

4. The method for optimizing the target cathode current of a long section of an oil and gas pipeline according to any one of claims 1 to 3, It is characterized in that The duty cycle signal D(k) is initialized to D(0)=0.

5.

5. A target optimization system for negative protection current in a long section of an oil and gas pipeline, comprising a memory, a processor and a computer program stored in the memory; It is characterized in that The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 4.

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