A secondary reheat main steam temperature cascade control system and control method

Abstract

A secondary reheat main steam temperature cascade control system relates to the technical field of thermal power generation, and solves the problem of how to improve the control quality of a three-stage superheater when water spraying is used to reduce the temperature to control the main steam temperature. The system comprises a main loop control system, a secondary loop control system, a secondary superheater, a secondary desuperheater, a third superheater, a PID controller, and a desuperheating water regulating valve; the secondary superheater, the secondary desuperheater, and the third superheater are connected in series in sequence by sealed pipes; the desuperheating water regulating valve is connected between the secondary superheater and the secondary desuperheater through a three-way sealed pipe; the secondary loop control system is used to control the opening of the desuperheating water regulating valve to roughly adjust the main steam temperature at the outlet of the third superheater; the main loop control system is used to control the opening of the desuperheating water regulating valve to finely adjust the main steam temperature at the outlet of the third superheater, and the system has fast response speed and good control quality; the control method adopts a particle swarm algorithm, so that the PID cascade control setting method is concise and has strong adaptability to operating conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal power generation, and relates to a secondary reheat main steam temperature cascade control system and a control method. Background Art

[0002] With the increasing economic development and the improvement of people's living standards, the energy resource consumption and carbon dioxide emissions caused by factory electricity and household electricity consumption have increased sharply. Reheating refers to the reheating of steam that has done part of the work in the turbine, and then leading it back to the turbine to continue to do work. Through reasonable reheating, the exhaust humidity can be reduced and the thermal cycle efficiency can be improved. Under the same parameters, the ultra-supercritical unit using the secondary reheating technology can reduce the emission of carbon dioxide, nitrogen oxides, etc. while improving the overall efficiency of the unit. It is an important development direction for my country's thermal power units in the future. Compared with the single reheating unit of the same capacity, the secondary reheating thermal power unit has a large difference in process structure. For example, a first-stage reheating system is added to the boiler side, and the steam-water flow is increased; the heating surface layout is more complicated, and the flue gas recirculation is used to reduce the heat absorption of the furnace and increase the heat absorption of the convection heating surface, etc., which makes the dynamic and static characteristics of the unit change greatly. Therefore, the configuration of the steam turbine, boiler and its related systems, especially the control of the main steam temperature, of the secondary reheating unit is much more complicated than that of the single reheating unit.

[0003] The main steam temperature system is a multi-input single-output object. The main steam temperature is mainly affected by three factors: steam flow, flue gas heat and cooling water flow. The main steam temperature is controlled by changing the cooling water flow. This regulation method is sensitive and precise. When the three-stage superheater uses water spray cooling to control the main steam temperature, due to the large delay and inertia of the object control channel and the requirement for a small steam temperature control deviation during operation, a single-loop control system often cannot achieve good control quality.

[0004] The Chinese invention patent application with application publication number CN110687778A, "Cascade control method for electric heating system and PID parameter tuning method for main regulator Cascade control method for electric heating system and PID parameter tuning method for main regulator", discloses a main regulator self-tuning method: initializing parameters and particle swarm, each particle position contains 3 variables, if the particle meets the mutation condition, the particle is mutated and the position of the particle is updated, if the mutation condition is not met, the particle weight, speed, position and fitness value are updated and iterated; if the mutation condition is met, if the fitness value of each particle is better than the fitness value of the optimal position Pi experienced by the particle, it is used as the current Pi; for each particle, its fitness value is compared with the fitness value of the optimal position Pg experienced by the entire particle swarm, if its fitness value is better than the fitness value of the optimal position Pg experienced by the entire particle swarm, it is used as the current Pg; using the optimal position Pg of the current particle swarm as the initial search point, calling the Rosenbrock algorithm for local search, updating Pi and Pg, and outputting the three variables of the particle.

[0005] Although the above invention patent application can improve the system response speed, it does not solve the problems of large inertia delay of the superheated steam temperature control channel, slow response of the controlled variable, and poor control quality of the single-loop control system when the three-stage superheater uses water spray to reduce the temperature to control the main steam temperature. Summary of the invention

[0006] The technical problem to be solved by the present invention is how to improve the control quality of a three-stage superheater when the main steam temperature is controlled by water spraying and cooling.

[0007] The present invention solves the above technical problems through the following technical solutions.

[0008] A secondary reheat main steam temperature cascade control system comprises a main loop control system, a secondary loop control system, a secondary superheater (1), a secondary desuperheater (2), a tertiary superheater (4), a PID controller (9), and a desuperheating water regulating valve (10); the secondary superheater (1), the secondary desuperheater (2), and the tertiary superheater (4) are sequentially connected in series by using sealed pipes; the desuperheating water regulating valve (10) is connected between the secondary superheater (1) and the secondary desuperheater (2) through a three-way sealed pipe; the input end of the secondary loop control system is connected to the secondary desuperheater (2) and the tertiary superheater (4); ... The output end of the secondary loop control system is connected to the PID controller (9) and is used to control the opening of the cooling water regulating valve (10) to roughly adjust the main steam temperature at the outlet of the tertiary superheater (4); the input end of the main loop control system is connected to the outlet of the tertiary superheater (4) and is used to collect the main steam temperature at the outlet of the tertiary superheater (4); the output end of the main loop control system is connected to the PID controller (9) and is used to control the opening of the cooling water regulating valve (10) to finely adjust the main steam temperature at the outlet of the tertiary superheater (4).

[0009] The changing trends of the steam temperature at the inlet of the tertiary superheater are consistent with the outlet main steam temperature, while the response speed of the steam temperature at the inlet of the tertiary superheater is significantly faster than that of the outlet main steam temperature. The steam temperature at the inlet of the tertiary superheater is added to the control channel of the control object as a parameter of the sub-loop control system of the main steam temperature cascade control system, which is used to control the opening of the desuperheating water regulating valve to roughly adjust the outlet main steam temperature of the tertiary superheater, thereby improving the response speed of the control system and the control quality of the control system.

[0010] As a further improvement of the technical solution of the present invention, the secondary loop control system comprises a first thermocouple temperature sensor (3) and a first temperature transmitter (6); the main loop control system comprises a second thermocouple temperature sensor (5), a second temperature transmitter (7), and a particle swarm intelligent computing unit (8); the first thermocouple temperature sensor (3) is installed at the output end of the secondary desuperheater (2); the first thermocouple temperature sensor (3) is electrically connected to the first temperature transmitter (6), and the output end of the first temperature transmitter (6) is electrically connected to a PID controller (9); the second thermocouple temperature sensor (5) is installed at the output end of the tertiary superheater (4); the second thermocouple temperature sensor (5) is electrically connected to the second temperature transmitter (7); the output end of the second temperature transmitter (7) is electrically connected to the particle swarm intelligent computing unit (8); the output end of the particle swarm intelligent computing unit (8) is electrically connected to the PID controller (9); the output end of the PID controller (9) is electrically connected to the control end of the desuperheating water regulating valve (10).

[0011] As a further improvement of the technical solution of the present invention, the first thermocouple temperature sensor (3) collects the temperature at the output end of the secondary desuperheater (2), sends the temperature signal to the first temperature transmitter (6), and the first temperature transmitter (6) converts the temperature signal into a standard electrical signal that is linearly related to the temperature and sends it to the PID controller (9); at the same time, the second thermocouple temperature sensor (5) collects the temperature at the output end of the tertiary superheater (4), sends the temperature signal to the second temperature transmitter (7), and the second temperature transmitter (7) converts the temperature signal into an electromotive force signal and sends it to the particle swarm intelligent operator (8), and the particle swarm intelligent operator (8) calculates the input standard electrical signal and sends it to the PID controller (9); the PID controller (9) controls the opening of the desuperheating water regulating valve (10) according to the input signal.

[0012] As a further improvement of the technical solution of the present invention, when the temperature at the first thermocouple temperature sensor (3) changes, the main steam temperature at the outlet of the tertiary superheater (4) is first roughly adjusted; the rough adjustment specifically includes: after the temperature signal is directly calculated by the PID controller (9), the opening of the cooling water regulating valve (10) is changed to change the flow rate of cooling water, the steam temperature at the inlet of the tertiary superheater (4) is initially maintained, and the main steam temperature at the outlet of the tertiary superheater (4) is roughly adjusted; then the main steam temperature at the outlet of the tertiary superheater (4) is finely adjusted; the fine adjustment specifically includes: the fine adjustment of the main steam temperature at the outlet of the tertiary superheater (4) is controlled by the particle swarm intelligent operator (8), as long as the outlet steam temperature of the tertiary superheater (4) does not reach the main steam temperature set value, the output of the particle swarm intelligent operator (8) continuously changes, so that the PID controller (9) continuously adjusts the opening of the cooling water regulating valve (10) to change the flow rate of cooling water until the main steam temperature returns to the main steam temperature set value.

[0013] As a further improvement of the technical solution of the present invention, the thermocouple temperature sensor adopts the high-temperature K-type thermocouple of Omega Company. The K-type thermocouple can directly measure the liquid vapor temperature in the range of 0°C to 1300°C, and the model is KQXL-14E-18.

[0014] As a further improvement of the technical solution of the present invention, the cooling water regulating valve (10) adopts a pneumatic valve of Vatak Company. The pneumatic cooling water regulating valve is characterized in that it automatically adjusts the flow of the system according to the input signal to realize automatic control during the operation of the unit.

[0015] A control method for a secondary reheat main steam temperature cascade control system, comprising the following steps:

[0016] Step 1: Difference between the main steam temperature set value r(t) and the system output value y(t) to obtain the error value e(t). The calculation formula is:

[0017] (1)

[0018] Among them, r(t) is the main steam temperature set value, y(t) is the system output value, and e(t) is the error value.

[0019] Step 2: Send the error value e(t) to the particle swarm intelligent operator (8) for calculation to obtain the proportional coefficient K p , integral coefficient K i , differential coefficient K d ; Set the proportionality factor K p , integral coefficient K i , differential coefficient K d The controller output value u(t) is input into the PID controller (9) to obtain the controller output value u(t). The calculation formula of the controller output value u(t) is:

[0020] (2)

[0021] Among them, Kp, Ki and Kd are proportional, integral and differential coefficients respectively, u(t) is the controller output value, t is the independent variable, and τ is the integral intermediate variable;

[0022] Step three, the controller output value u(t) and the secondary loop disturbance are input together into the control object transfer function device to output the system output value y(t), which is used to control the opening of the cooling water regulating valve (10).

[0023] As a further improvement of the technical solution of the present invention, the method of performing calculation in the particle swarm intelligent operator (8) in step 2 is:

[0024] 1) Initialize the particle swarm, randomly generate the position and velocity of particles, and determine the optimal position of the particles and the optimal position of the entire particle swarm;

[0025] 2) Compare the fitness value of each particle with the optimal position it has experienced, and update the optimal position;

[0026] 3) Compare the fitness value of each particle with the optimal position experienced by the entire particle swarm, and update the optimal position of the entire particle swarm;

[0027] 4) Update the particle's velocity and position according to formula (3) and formula (4);

[0028] 5) If the number of iterations and the absolute error time integral meet the requirements, exit the algorithm and obtain the optimal solution, otherwise return to step 2).

[0029] As a further improvement of the technical solution of the present invention, the formula for updating the speed and position of the particle in step 4) is:

[0030] (3)

[0031] (4)

[0032] Among them, vt and vt+1 represent the speed of the particle before and after the update respectively; xt and xt+1 represent the position of the particle before and after the update respectively; c1 and c2 are acceleration constants; r1 and r2 are generated random numbers; and are the individual optimal position and global optimal position of the particle respectively, and w is the inertia factor.

[0033] As a further improvement of the technical solution of the present invention, the absolute error time integral value in step 5) is used as a performance evaluation index of the particle swarm intelligent operator, and the smaller the value, the better the performance of the system; the calculation formula of the absolute error time integral is:

[0034] (5)

[0035] Among them, J min is the time integral value of the absolute error, e(t) is the error between the output and the input, and t is the time;

[0036] The number of iterations and the absolute error time integral satisfying the requirements means that the number of iterations reaches a set value of 600, and the absolute error time integral value is less than a set value of 0.1.

[0037] The advantages of the present invention are:

[0038] (1) The present invention aims at the fact that the changing trends of the steam temperature at the inlet of the tertiary superheater and the outlet main steam temperature are consistent, and the response speed of the steam temperature at the inlet of the tertiary superheater is significantly faster than that of the outlet main steam temperature. The steam temperature at the inlet of the tertiary superheater is added from the control channel of the control object as a parameter of the sub-loop control system of the superheater main steam temperature cascade control system, which is used to control the opening of the desuperheating water regulating valve to roughly adjust the outlet main steam temperature of the tertiary superheater, thereby improving the response speed of the control system and the control quality of the control system.

[0039] (2) The main steam temperature cascade control system of the present invention adopts a particle swarm algorithm, which not only has the characteristics of fast response speed of the cascade system, but also combines the intelligent calculation of the particle swarm algorithm to automatically adjust the main loop PID parameters, making the PID cascade control adjustment method simple and highly adaptable to operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural diagram of a secondary reheat main steam temperature cascade control system according to an embodiment of the present invention;

[0041] Figure 2It is a control block diagram of a secondary reheat main steam temperature cascade control system according to an embodiment of the present invention;

[0042] Figure 3 is a flow chart of a control method of a secondary reheat main steam temperature cascade control system according to an embodiment of the present invention;

[0043] Figure 4 It is a simulation model diagram of a secondary reheat main steam temperature cascade control system according to an embodiment of the present invention;

[0044] Figure 5 It is a simulation result diagram of the secondary reheat main steam temperature cascade control system of an embodiment of the present invention. DETAILED DESCRIPTION

[0045] 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 combination with 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.

[0046] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0047] Embodiment 1

[0048] like Figure 1 As shown, a secondary reheat main steam temperature cascade control system includes a main loop control system, a secondary loop control system, a secondary superheater 1, a secondary desuperheater 2, a tertiary superheater 4, a PID controller 9, and a desuperheating water regulating valve 10; the secondary superheater 1, the secondary desuperheater 2, and the tertiary superheater 4 are sequentially connected in series by sealed pipes; the desuperheating water regulating valve 10 is connected between the secondary superheater 1 and the secondary desuperheater 2 through a three-way sealed pipe; the input end of the secondary loop control system is connected to the secondary desuperheater 2 and the tertiary superheater 4, for collecting the steam temperature at the inlet of the tertiary superheater 4; the output end of the secondary loop control system is connected to the PID controller 9, for controlling the opening of the desuperheating water regulating valve 10 to roughly adjust the main steam temperature at the outlet of the tertiary superheater 4; the input end of the main loop control system is connected to the outlet of the tertiary superheater 4, for collecting the main steam temperature at the outlet of the tertiary superheater 4, and the output end of the main loop control system is connected to the PID controller 9, for controlling the opening of the desuperheating water regulating valve 10 to finely adjust the main steam temperature at the outlet of the tertiary superheater 4.

[0049] The changing trends of the steam temperature at the inlet of the tertiary superheater are consistent with the outlet main steam temperature, while the response speed of the steam temperature at the inlet of the tertiary superheater is significantly faster than that of the outlet main steam temperature. The steam temperature at the inlet of the tertiary superheater is added to the control channel of the control object as a parameter of the sub-loop control system of the main steam temperature cascade control system, which is used to control the opening of the desuperheating water regulating valve to roughly adjust the outlet main steam temperature of the tertiary superheater, thereby improving the response speed of the control system and the control quality of the control system.

[0050] The secondary loop control system includes a first thermocouple temperature sensor 3 and a first temperature transmitter 6; the main loop control system includes a second thermocouple temperature sensor 5, a second temperature transmitter 7, and a particle swarm intelligent operator 8; the first thermocouple temperature sensor 3 is installed at the output end of the secondary desuperheater 2; the first thermocouple temperature sensor 3 is electrically connected to the first temperature transmitter 6, and the output end of the first temperature transmitter 6 is electrically connected to the PID controller 9; the second thermocouple temperature sensor 5 is installed at the output end of the tertiary superheater 4; the second thermocouple temperature sensor 5 is electrically connected to the second temperature transmitter 7; the output end of the second temperature transmitter 7 is electrically connected to the particle swarm intelligent operator 8; the output end of the particle swarm intelligent operator 8 is electrically connected to the PID controller 9; the output end of the PID controller 9 is electrically connected to the control end of the desuperheating water regulating valve 10.

[0051] The first thermocouple temperature sensor 3 collects the temperature at the output end of the secondary desuperheater 2, and sends the temperature signal to the first temperature transmitter 6. The first temperature transmitter 6 converts the temperature signal into a standard electrical signal that is linearly related to the temperature and sends it to the PID controller 9; at the same time, the second thermocouple temperature sensor 5 collects the temperature at the output end of the tertiary superheater 4, and sends the temperature signal to the second temperature transmitter 7. The second temperature transmitter 7 converts the temperature signal into an electromotive force signal and sends it to the particle swarm intelligent operator 8. The particle swarm intelligent operator 8 calculates the input standard electrical signal and sends it to the PID controller 9; the PID controller 9 controls the opening of the desuperheating water regulating valve 10 according to the input signal.

[0052] When the temperature at the first thermocouple temperature sensor 3 changes, the outlet main steam temperature of the tertiary superheater 4 is first roughly adjusted; the rough adjustment is specifically: after the temperature signal is directly calculated by the PID controller 9, the opening of the cooling water regulating valve 10 is changed to change the flow of cooling water, the steam temperature at the inlet of the tertiary superheater 4 is initially maintained, and the outlet main steam temperature of the tertiary superheater 4 is roughly adjusted; then the outlet main steam temperature of the tertiary superheater 4 is finely adjusted; the fine adjustment is specifically: the fine adjustment of the outlet main steam temperature of the tertiary superheater 4 is controlled by the particle swarm intelligent operator 8, as long as the outlet steam temperature of the tertiary superheater 4 does not reach the main steam temperature set value, the output of the particle swarm intelligent operator 8 is constantly changing, so that the PID controller 9 continuously adjusts the opening of the cooling water regulating valve 10 to change the flow of cooling water until the main steam temperature returns to the main steam temperature set value.

[0053] The thermocouple temperature sensor adopts the high temperature K-type thermocouple of Omega Company. The K-type thermocouple can directly measure the liquid vapor temperature in the range of 0°C to 1300°C. The model is KQXL-14E-18.

[0054] The desuperheating water regulating valve 10 is a pneumatic valve from Vatak. The pneumatic desuperheating water regulating valve is characterized in that it automatically adjusts the flow of the system according to an input signal, thereby realizing automatic control during the operation of the unit.

[0055] The particle swarm intelligent operator 8 calculates the input standard electrical signal and sends it to the PID controller 9; the PID controller 9 controls the opening of the cooling water regulating valve 10 according to the input signal.

[0056] like Figure 2 As shown, the method in which the particle swarm intelligent operator 8 calculates the input standard electrical signal and sends it to the PID controller 9 comprises the following steps:

[0057] Step 1: Difference between the main steam temperature set value r(t) and the system output value y(t) to obtain the error value e(t). The calculation formula is:

[0058] (1)

[0059] Among them, r(t) is the main steam temperature set value, y(t) is the system output value, and e(t) is the error value.

[0060] Step 2: Send the error value e(t) to the particle swarm intelligent operator 8 for calculation to obtain the proportional coefficient K p , integral coefficient K i , differential coefficient K d ; Set the proportionality factor K p , integral coefficient K i , differential coefficient K dInput into the PID controller 9 to obtain the controller output value u(t), the calculation formula of the controller output value u(t) is:

[0061] (2)

[0062] Among them, Kp, Ki and Kd are proportional, integral and differential coefficients respectively, u(t) is the controller output value, t is the independent variable, and τ is the integral intermediate variable;

[0063] Step three, the controller output value u(t) and the secondary loop disturbance are input together into the control object transfer function device to output the system output value y(t), which is used to control the opening of the cooling water regulating valve 10.

[0064] like Figure 3 As shown, the method of performing calculation in the particle swarm intelligent operator 8 in step 2 is:

[0065] 1) Initialize the particle swarm, randomly generate the position and velocity of particles, and determine the optimal position of the particles and the optimal position of the entire particle swarm;

[0066] 2) Compare the fitness value of each particle with the optimal position it has experienced, and update the optimal position;

[0067] 3) Compare the fitness value of each particle with the optimal position experienced by the entire particle swarm, and update the optimal position of the entire particle swarm;

[0068] 4) Update the particle's velocity and position according to formula (3) and formula (4);

[0069] The formula for updating the speed and position of particles is:

[0070] (3)

[0071] (4)

[0072] Among them, vt and vt+1 represent the speed of the particle before and after the update respectively; xt and xt+1 represent the position of the particle before and after the update respectively; c1 and c2 are acceleration constants; r1 and r2 are generated random numbers; and are the individual optimal position and global optimal position of the particle respectively, and w is the inertia factor.

[0073] 5) If the number of iterations and the absolute error time integral meet the requirements, exit the algorithm and obtain the optimal solution, otherwise return to step 2).

[0074] The absolute error time integral value is used as a performance evaluation index of the particle swarm intelligent operator. The smaller the value, the better the system performance. The calculation formula of the absolute error time integral is:

[0075] (5)

[0076] Among them, J min is the time integral value of the absolute error, e(t) is the error between the output and the input, and t is the time.

[0077] The number of iterations and the absolute error time integral in step 5 satisfying the requirements means that the number of iterations reaches the set value of 600, and the absolute error time integral value is less than the set value of 0.1.

[0078] like Figure 4 As shown, the control method is tested through simulation experiments, the PSO algorithm program is written on the simulation analysis Matlab, and the PID model file is built in the Simulink system;

[0079] Enter the Simulink modeling interface to build the model. The initial parameters of the standard particle swarm algorithm are set as follows: the number of particles pop is 40; the maximum number of iterations is 100; K p , K i , K d The position search range of the three parameters is [0, 100], and the speed range is [-1, 1]; the learning factor c1=c2=1.49; the inertia weight decreases linearly from 0.9 to 0.3; according to the control characteristics of the main steam temperature in the industrial field, the simulation time is set to 500s; the particle swarm optimization algorithm is used for PID tuning, and the following is obtained:

[0080] Kp=22.5632, Ki=0.1704, Kd=98.4566;

[0081] like Figure 5 As shown in the figure, the simulation results show that after the particle swarm algorithm optimization, the system output decreases immediately and tends to be stable after the first oscillation occurs, the stabilization time is 60s, and the control performance of the main regulation loop is significantly improved.

[0082] Embodiment 2

[0083] like Figure 3 As shown, a control method applied to the secondary reheat main steam temperature cascade control system comprises the following steps:

[0084] Step 1: Difference between the main steam temperature set value r(t) and the system output value y(t) to obtain the error value e(t). The calculation formula is:

[0085] (1)

[0086] Among them, r(t) is the main steam temperature setting value, y(t) is the system output value, and e(t) is the error value;

[0087] Step 2: Send the error value e(t) to the particle swarm intelligent operator 8 for calculation to obtain the proportional coefficient K p , integral coefficient K i , differential coefficient K d ; Set the proportionality factor K p , integral coefficient K i , differential coefficient K d Input into the PID controller 9 to obtain the controller output value u(t), the calculation formula of the controller output value u(t) is:

[0088] (2)

[0089] Among them, Kp, Ki and Kd are proportional, integral and differential coefficients respectively, u(t) is the controller output value, t is the independent variable, and τ is the integral intermediate variable;

[0090] According to formula (2), the transfer function formula is:

[0091] (3)

[0092] Among them, T i is the integration time constant, T d is the differential time constant;

[0093] The method of performing calculation in the particle swarm intelligent operator 8 in step 2 is:

[0094] 1) Initialize the particle swarm, randomly generate the position and velocity of particles, and determine the optimal position of the particles and the optimal position of the entire particle swarm;

[0095] 2) Compare the fitness value of each particle with the optimal position it has experienced, and update the optimal position;

[0096] 3) Compare the fitness value of each particle with the optimal position experienced by the entire particle swarm, and update the optimal position of the entire particle swarm;

[0097] 4) Update the particle's velocity and position according to formula (3) and formula (4);

[0098] The formula for updating the speed and position of the particle in step 4) is:

[0099] (3)

[0100] (4)

[0101] Among them, vt and vt+1 represent the speed of the particle before and after the update respectively; xt and xt+1 represent the position of the particle before and after the update respectively; c1 and c2 are acceleration constants; r1 and r2 are generated random numbers; and are the individual optimal position and global optimal position of the particle respectively, and w is the inertia factor.

[0102] 5) If the number of iterations and the absolute error time integral meet the requirements, exit the algorithm and obtain the optimal solution, otherwise return to step 2).

[0103] The absolute error time integral value in step 5) is used as a performance evaluation index of the particle swarm intelligent operator. The smaller the value, the better the system performance. The calculation formula of the absolute error time integral is:

[0104] (5)

[0105] Among them, J min is the time integral value of the absolute error, e(t) is the error between the output and the input, and t is the time;

[0106] The number of iterations and the absolute error time integral satisfying the requirements means that the number of iterations reaches a set value of 600, and the absolute error time integral value is less than a set value of 0.1.

[0107] Step three, the controller output value u(t) and the secondary loop disturbance are input together into the control object transfer function device to output the system output value y(t), which is used to control the opening of the cooling water regulating valve (10).

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A secondary reheat main steam temperature cascade control system, characterized in that: The invention comprises a main loop control system, a secondary loop control system, a secondary superheater (1), a secondary desuperheater (2), a tertiary superheater (4), a PID controller (9), and a desuperheating water regulating valve (10); the secondary superheater (1), the secondary desuperheater (2), and the tertiary superheater (4) are connected in series in sequence by means of sealed pipes; the desuperheating water regulating valve (10) is connected between the secondary superheater (1) and the secondary desuperheater (2) through a three-way sealed pipe; the input end of the secondary loop control system is connected between the secondary desuperheater (2) and the tertiary superheater (4) for controlling the temperature of the secondary superheater (1) and the tertiary superheater (4) The steam temperature at the inlet of the tertiary superheater (4) is collected; the output end of the secondary loop control system is connected to the PID controller (9) and is used to control the opening of the cooling water regulating valve (10) to roughly adjust the main steam temperature at the outlet of the tertiary superheater (4); the input end of the main loop control system is connected to the outlet of the tertiary superheater (4) and is used to collect the main steam temperature at the outlet of the tertiary superheater (4); the output end of the main loop control system is connected to the PID controller (9) and is used to control the opening of the cooling water regulating valve (10) to finely adjust the main steam temperature at the outlet of the tertiary superheater (4); The secondary loop control system comprises a first thermocouple temperature sensor (3) and a first temperature transmitter (6); the primary loop control system comprises a second thermocouple temperature sensor (5), a second temperature transmitter (7), and a particle swarm intelligent computing unit (8); the first thermocouple temperature sensor (3) is installed at the output end of the secondary desuperheater (2); the first thermocouple temperature sensor (3) is electrically connected to the first temperature transmitter (6), and the output end of the first temperature transmitter (6) is electrically connected to a PID controller (9); the second thermocouple temperature sensor (5) is installed at the output end of the tertiary superheater (4); the second thermocouple temperature sensor (5) is electrically connected to the second temperature transmitter (7); the output end of the second temperature transmitter (7) is electrically connected to the particle swarm intelligent computing unit (8); the output end of the particle swarm intelligent computing unit (8) is electrically connected to the PID controller (9); the output end of the PID controller (9) is electrically connected to the control end of the desuperheating water regulating valve (10); The first thermocouple temperature sensor (3) collects the temperature at the output end of the secondary desuperheater (2) and sends the temperature signal to the first temperature transmitter (6). The first temperature transmitter (6) converts the temperature signal into a standard electrical signal that is linearly related to the temperature and sends it to the PID controller (9). At the same time, the second thermocouple temperature sensor (5) collects the temperature at the output end of the tertiary superheater (4) and sends the temperature signal to the second temperature transmitter (7). The second temperature transmitter (7) converts the temperature signal into an electromotive force signal and sends it to the particle swarm intelligent operator (8). The particle swarm intelligent operator (8) calculates the input standard electrical signal and sends it to the PID controller (9). The PID controller (9) controls the opening of the desuperheating water regulating valve (10) according to the input signal. When the temperature at the first thermocouple temperature sensor (3) changes, the outlet main steam temperature of the tertiary superheater (4) is first roughly adjusted. The rough adjustment specifically includes: after the temperature signal is directly calculated by the PID controller (9), the opening of the cooling water regulating valve (10) is changed to change the flow rate of cooling water, and the steam temperature at the inlet of the tertiary superheater (4) is initially maintained, and the outlet main steam temperature of the tertiary superheater (4) is roughly adjusted; then the outlet main steam temperature of the tertiary superheater (4) is finely adjusted. The fine adjustment specifically includes: the fine adjustment of the outlet main steam temperature of the tertiary superheater (4) is controlled by the particle swarm intelligent operator (8). As long as the outlet steam temperature of the tertiary superheater (4) does not reach the main steam temperature set value, the output of the particle swarm intelligent operator (8) is continuously changed, so that the PID controller (9) continuously adjusts the opening of the cooling water regulating valve (10) to change the flow rate of cooling water until the main steam temperature returns to the main steam temperature set value.

2. A secondary reheat main steam temperature cascade control system according to claim 1, characterized in that: The thermocouple temperature sensor adopts the high temperature K-type thermocouple of Omega Company, model KQXL-14E-18.

3. A secondary reheat main steam temperature cascade control system according to claim 1, characterized in that: The desuperheating water regulating valve (10) is a pneumatic valve from Vatak.

4. A control method for the secondary reheat main steam temperature cascade control system according to any one of claims 1 to 3, comprising the following steps: Step 1: Difference between the main steam temperature set value r(t) and the system output value y(t) to obtain the error value e(t). The calculation formula is: （1） Among them, r(t) is the main steam temperature setting value, y(t) is the system output value, and e(t) is the error value; Step 2: Send the error value e(t) to the particle swarm intelligent operator (8) for calculation to obtain the proportional coefficient K p , integral coefficient K i , differential coefficient K d ; Set the proportionality factor K p , integral coefficient K i , differential coefficient K d The controller output value u(t) is input into the PID controller (9) to obtain the controller output value u(t). The calculation formula of the controller output value u(t) is: （2） Among them, Kp, Ki and Kd are proportional, integral and differential coefficients respectively, u(t) is the controller output value, t is the independent variable, and τ is the integral intermediate variable; Step three, the controller output value u(t) and the secondary loop disturbance are input together into the control object transfer function device to output the system output value y(t), which is used to control the opening of the cooling water regulating valve (10).

5. The control method of a secondary reheat main steam temperature cascade control system according to claim 4, characterized in that: The method of performing calculation in the particle swarm intelligent operator (8) in step 2 is: 1) Initialize the particle swarm, randomly generate the position and velocity of particles, and determine the optimal position of the particles and the optimal position of the entire particle swarm; 2) Compare the fitness value of each particle with the optimal position it has experienced, and update the optimal position; 3) Compare the fitness value of each particle with the optimal position experienced by the entire particle swarm, and update the optimal position of the entire particle swarm; 4) Update the particle's velocity and position according to formula (3) and formula (4); 5) If the number of iterations and the absolute error time integral meet the requirements, exit the algorithm and obtain the optimal solution, otherwise return to step 2).

6. The control method of a secondary reheat main steam temperature cascade control system according to claim 5, characterized in that: The formula for updating the speed and position of the particle in step 4) is: （3） （4） Among them, vt and vt+1 represent the speed of the particle before and after the update respectively; xt and xt+1 represent the position of the particle before and after the update respectively; c1 and c2 are acceleration constants; r1 and r2 are generated random numbers; and are the individual optimal position and global optimal position of the particle respectively, and w is the inertia factor.

7. The control method of a secondary reheat main steam temperature cascade control system according to claim 6, characterized in that: The absolute error time integral value in step 5) is used as a performance evaluation index of the particle swarm intelligent operator. The smaller the value, the better the system performance. The calculation formula of the absolute error time integral is: （5） Among them, J min is the time integral value of the absolute error, e(t) is the error between the output and the input, and t is the time; The number of iterations and the absolute error time integral satisfying the requirements means that the number of iterations reaches a set value of 600, and the absolute error time integral value is less than a set value of 0.1.

Images