Automatic control method for load shedding of BEST double-unit regenerative power plant converter

Abstract

The present application belongs to the field of automatic control technology of thermal power generating unit, and specifically discloses a BEST double-machine regenerative thermal power plant converter load rejection automatic control method, which comprises the following steps: determining the steam-driven feed water pump shaft power and the small generator shaft power; determining the pre-action opening of the BEST feed water pump turbine admission valve after the converter load rejection according to and; predicting the petro-flying speed of the BEST steam-driven feed water pump group according to and; starting the minimum flow recirculation valve control method of the steam-driven feed water pump and the BEST feed water pump turbine back pressure control method, and determining the speed control method of the BEST feed water pump turbine according to and. The present application shortens the speed fluctuation process of the BEST steam-driven feed water pump group, reduces the fluctuation amplitude of the boiler inlet feed water flow, and ensures the stability and safety of the whole unit after the converter load rejection.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology for thermal power generating units, and specifically relates to an automatic control method for load shedding of converters in BEST dual-unit regenerative thermal power plants. Background Technology

[0002] With the large-scale grid connection of new energy units in recent years, the role of thermal power plants as a ballast has become increasingly apparent. To achieve energy conservation and emission reduction, designing a BEST dual-unit regenerative thermal power plant is an effective approach. To reduce the throttling losses of the BEST feedwater pump turbine, the BEST dual-unit regenerative thermal power plant utilizes the remaining power of the BEST feedwater pump turbine and the BEST steam-driven feedwater pump unit when the valves are fully open by setting up a small generator. This achieves the goals of reducing plant power consumption, improving the efficiency of the BEST feedwater pump turbine, and enhancing the unit's economic efficiency.

[0003] During the operation of the BEST dual-unit regenerative unit, there is a special operating condition where the converter sheds load due to a fault, requiring automatic control to stabilize the relevant parameters of the unit. The conventional control method after the converter sheds load uses a certain threshold value for the small generator power. When the small generator power is greater than the threshold, the BEST feedwater pump turbine inlet steam regulating valve is fully closed, and then gradually opened under PID control of the BEST feedwater pump turbine speed. When the small generator power is less than the threshold, the BEST feedwater pump turbine inlet steam regulating valve is pre-closed to a fixed preset value, and then gradually opened under PID control of the BEST feedwater pump turbine speed. Under this control method, speed control lags and has poor matching with actual operating conditions, resulting in large fluctuations in feedwater flow and a long time required to restore stability. In engineering examples, incidents have occurred where large fluctuations in feedwater flow during converter load shedding led to unit load reduction, and excessive vibration of the steam-driven feedwater pump caused tripping and unit shutdown, affecting the safe and stable operation of the unit. The main reason for these issues is that the aforementioned feedwater pump turbine automatic control method suffers from incomplete control logic design, inaccurate parameter settings, and untimely actions. Summary of the Invention

[0004] The purpose of this invention is to provide an automatic control method for load shedding of converters in BEST dual-unit regenerative thermal power plants, in order to solve the technical problems of existing load shedding control methods for BEST dual-unit regenerative thermal power plants, such as lagging speed control and poor matching with actual operating conditions, resulting in large fluctuations in feedwater flow and long time required to restore stability.

[0005] This invention provides an automatic load shedding control method for converters in a BEST dual-unit regenerative thermal power plant. The BEST dual-unit regenerative thermal power plant includes a BEST steam-driven feedwater pump unit, which comprises a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. The automatic load shedding control method for the converters in the BEST dual-unit regenerative thermal power plant includes:

[0006] Step 1: Determine the shaft power of the steam-driven feedwater pump and small generator shaft power ;

[0007] Step 2, according to and After determining the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve after the converter load shedding... ;

[0008] Step 3, according to and Predicting the rapid speed increase of BEST steam-driven feedwater pump sets ;

[0009] Step 4: Start the minimum flow recirculation valve control method for the steam-driven feedwater pump and the BEST feedwater pump turbine back pressure control method, and according to... and Determine the speed control method for the BEST feedwater pump turbine.

[0010] Preferably, according to and The speed control method for the BEST feedwater pump turbine is determined as follows:

[0011] Determine a constant value And obtain the overspeed protection setting value of the BEST feedwater pump turbine. ;

[0012] when At that time, the BEST feedwater pump turbine inlet steam regulating valve command was set. When the speed of the BEST feedwater pump turbine begins to decrease and the opening of the steam inlet regulating valve is at... Then, the speed will be controlled by the conventional BEST feedwater pump turbine PID control method.

[0013] when When the BEST feedwater pump turbine inlet steam regulating valve command is set to zero, the command is reset when the BEST feedwater pump turbine speed begins to decrease. When the opening degree of the BEST feedwater pump turbine inlet steam regulating valve is at If the speed is controlled by the conventional BEST feedwater pump turbine PID control method, then the speed will be controlled again.

[0014] Preferably, a fixed value is determined. Specifically:

[0015] The delay time between the acquisition of the converter load shedding action signal and the start of closure of the BEST feedwater pump turbine inlet regulating valve. Net closing time after BEST feedwater pump turbine inlet steam regulating valve command is set to zero ;

[0016] according to and Determine the initial constant value ;

[0017] At the initial constant value When the unit load is 50%~75% THA, an actual converter load shedding test is conducted, and the actual speed rise of the BEST feedwater pump turbine during the speed rise to stability process is obtained. ;

[0018] according to , and Determine a constant value .

[0019] Preferably, according to , and Determine a constant value Specifically:

[0020] when At that time, Set to 0;

[0021] when and At that time, Set as ;

[0022] when hour, And determine whether it has been achieved. If not, then let until ,in It is the moment of inertia; This is the load torque of the small generator.

[0023] Preferably, the method for controlling the minimum flow recirculation valve of the steam-driven feedwater pump is as follows:

[0024] Boiler inlet feedwater flow rate when the converter load shedding action signal is triggered ;

[0025] During the rising speed phase of the steam-driven feedwater pump, when the inlet flow rate of the steam-driven feedwater pump... Compare When the preset flow rate is high, the minimum flow recirculation regulating valve of the steam-driven feedwater pump opens to a preset extent on the original opening degree, and then opens at a preset first speed uniformly; during the stage when the speed of the steam-driven feedwater pump decreases, the minimum flow recirculation regulating valve of the steam-driven feedwater pump closes at a preset second speed until the converter load shedding action signal is reset.

[0026] Preferably, the method for starting the BEST feedwater pump turbine back pressure control is as follows:

[0027] After the converter load shedding action signal is triggered, the back pressure of the BEST feedwater pump turbine is increased to the preset back pressure at the preset third rate. The preset back pressure is the minimum value between the upper limit of the exhaust pressure that satisfies the exhaust pressure ratio and the high exhaust pressure alarm value.

[0028] After the converter is reset due to load shedding, the automatic control target values ​​of the overflow valve and bypass valve of the BEST feedwater pump turbine are reduced to the normal exhaust pressure control range at a preset fourth rate.

[0029] Preferably, step 3 specifically includes:

[0030] Step 3.1, according to Determine the shaft torque of the steam-driven feedwater pump and according to Determine the load torque of the small generator ;

[0031] Step 3.2, according to and Determine the BEST feedwater pump turbine steam drive torque after eliminating all frictional resistance torques. ;

[0032] Step 3.3: Based on whether the BEST dual-unit regenerative thermal power plant has a smart power plant server and... , , Predicting the rapid speed increase of BEST steam-driven feedwater pump sets .

[0033] Preferably, step 3.3 specifically includes:

[0034] When the BEST dual-machine regenerative thermal power plant has a smart power plant server, it obtains... Zero and delay hour, exist The value decreases uniformly from the initial value to 0.9 times the initial value within a given time period. The highest speed of the BEST steam-driven feedwater pump unit during the process is denoted as the flyback speed. ;

[0035] The delayed closing time from the converter load shedding action signal triggering the BEST feedwater pump turbine inlet steam regulating valve to begin closing; This refers to the net closing time after the BEST feedwater pump turbine inlet steam regulating valve command is set to zero.

[0036] Preferably, step 3.3 specifically includes:

[0037] When there is no smart power plant server in the BEST dual-unit regenerative thermal power plant, the first formula is used to determine... The first formula is:

[0038] ;

[0039] In the formula, It is the moment of inertia; This is the initial speed of the BEST steam-driven feedwater pump set; The delayed closing time from the converter load shedding action signal triggering the BEST feedwater pump turbine inlet steam regulating valve to begin closing; This refers to the net closing time after the BEST feedwater pump turbine inlet steam regulating valve command is set to zero.

[0040] Preferably, step 2 specifically includes:

[0041] Determine the percentage of steam flow corresponding to the actual opening of the BEST feedwater pump turbine inlet regulating valve before the converter load shedding. ;

[0042] Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and the percentage of steam flow rate Determine the percentage of flow rate occupied by the steam-driven feedwater pump. ;

[0043] Based on the percentage of flow occupied by the steam-driven feedwater pump After determining the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve after converter load shedding .

[0044] The BEST dual-unit regenerative thermal power plant converter load shedding automatic control method of the present invention has the following advantages compared with the prior art:

[0045] This invention enables continuous and real-time judgment and control of the BEST feedwater pump turbine speed throughout the entire process after the BEST dual-unit regenerative thermal power plant converter sheds its load, thereby minimizing the significant interference caused by discontinuous control of equipment and systems.

[0046] The automatic control method of the present invention is equipped with reasonable valve preset opening calculation logic after converter load shedding, feedwater pump recirculation automatic control logic, BEST feedwater pump turbine speed control logic, and BEST feedwater pump turbine back pressure control logic. This shortens the speed fluctuation process of the BEST steam-driven feedwater pump group, reduces the fluctuation amplitude of boiler inlet feedwater flow, and ensures the stability and safety of the entire unit after converter load shedding.

[0047] The automatic control method of the present invention is equipped with two sets of converter load shedding speed rise prediction modules for smart power plants and conventional thermal power plants, which can be used as a reference for other dual-unit regenerative units. Attached Figure Description

[0048] Figure 1 This is an overall flowchart of the automatic load shedding control method for the BEST dual-machine regenerative thermal power plant converter and the reset of the load shedding action signal in an embodiment of the present invention. Detailed Implementation

[0049] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0050] Before implementing automatic load shedding control for the BEST dual-unit regenerative thermal power plant converter, the following automatic control conditions need to be confirmed in this embodiment of the invention:

[0051] (1) The BEST feedwater pump turbine MEH system has a basic BEST feedwater pump turbine speed control PID module, which can realize automatic speed control.

[0052] (2) The converter load shedding action signal can be transmitted from the converter device to the MEH system and DCS system.

[0053] (3) The automatic back pressure control module of BEST feedwater pump turbine is working normally and can dynamically adjust the exhaust pressure according to the changes in the inlet steam pressure and the final stage pressure ratio of BEST feedwater pump turbine.

[0054] (4) It can effectively and accurately obtain the following real-time data: small generator power ;BEST feedwater pump turbine speed The inlet and outlet feedwater parameters for the BEST steam-driven feedwater pump set, including the inlet feedwater temperature of the steam-driven feedwater pump. Import pressure Export pressure Pump inlet feedwater mass flow rate .

[0055] (5) The maximum efficiency of the BEST feedwater pump turbine has been obtained based on the information provided by the manufacturer. Minimum efficiency of small generator and converter sets .

[0056] (6) The flow characteristic curve of the BEST feedwater pump turbine inlet regulating valve has been obtained, and the correlation formula between the valve opening percentage and the valve flow rate percentage has been obtained.

[0057] (7) The actual measured delay time from the converter load shedding action signal triggering the BEST feedwater pump turbine inlet regulating valve to begin closing. Net closing time after BEST feedwater pump turbine inlet steam regulating valve command is set to zero .

[0058] (8) The moment of inertia of the steam-driven feedwater pump-BEST feedwater pump turbine-small generator shaft system has been obtained. .

[0059] (9) The overspeed protection setting value of the steam-driven feedwater pump-BEST feedwater pump turbine-small generator has been obtained. .

[0060] The BEST dual-unit regenerative thermal power plant of this embodiment includes a BEST steam-driven feedwater pump unit, which comprises a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. After the above confirmation, the BEST dual-unit regenerative thermal power plant converter automatic load shedding control method of this embodiment is as follows: Figure 1 As shown, it includes:

[0061] Step 1: Determine the shaft power of the steam-driven feedwater pump and small generator shaft power .

[0062] According to the embodiment of the present invention, the shaft power of the steam-driven feedwater pump is determined by formula (1). :

[0063] (1)

[0064] In the formula, This refers to the mass flow rate of the feedwater at the inlet of the steam-driven feedwater pump. This refers to the inlet pressure of the steam-driven feedwater pump. This refers to the outlet pressure of the steam-driven feedwater pump. The highest efficiency of the BEST feedwater pump turbine; The feedwater density inside the steam-driven feedwater pump is kg / m³. 3It is obtained from the inlet temperature and inlet pressure of the steam-driven feedwater pump.

[0065] The embodiment of the present invention determines the shaft power of the small generator according to formula (2). :

[0066] (2)

[0067] In the formula, For small generator power; This represents the minimum efficiency for small generators and converter units.

[0068] Because the highest efficiency of the BEST feedwater pump turbine was used when calculating the shaft power of the steam-driven feedwater pump, and the lowest efficiency of the small generator and converter group was used when calculating the shaft power of the small generator, the small generator shaft power accounts for a larger proportion when calculating the shaft power distribution on the steam-driven feedwater pump-BEST feedwater pump turbine-small generator shaft system. This helps to obtain a higher speed with a safety margin for the subsequent speed increase.

[0069] Step 2, according to and Determine the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve after the converter sheds load. Specifically:

[0070] Step 2.1: Determine the actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the converter sheds load. corresponding percentage of steam flow .

[0071] In this embodiment of the invention, the actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the converter load shedding is known to be... ,Will Substitution Calculate the percentage of steam flow corresponding to the opening degree. .

[0072] Step 2.2: Based on the shaft power of the steam-driven feedwater pump Small generator shaft power and percentage of steam flow Determine the percentage of flow rate occupied by the steam-driven feedwater pump. As shown in formula (3):

[0073] (3)

[0074] Step 2.3: Based on the percentage of flow occupied by the steam-driven feedwater pump After determining the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve after converter load shedding Specifically:

[0075] Step 2.3.1, in Multiply by 0.9 to obtain the percentage of flow rate corresponding to the pre-action of the BEST feedwater pump turbine inlet regulating valve after the converter load shedding. .

[0076] After the converter sheds load, there is a recovery process after the speed increases; the percentage of flow occupied by the steam-driven feedwater pump... The purpose of multiplying by 0.9 is twofold: firstly, to minimize the speed spike while reducing the recovery time of the BEST steam-driven feedwater pump unit's speed fluctuations; and secondly, to provide a basis for calculating the power change of the BEST feedwater pump turbine drive shaft in step 3.

[0077] Step 2.3.2, will Substitution The pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is calculated by reverse calculation. .

[0078] Step 3, according to and Predicting the speed jump of BEST steam-driven feedwater pump set using a shaft torque dynamic balance model. In this embodiment of the invention, since the steam-driven feedwater pump, the BEST feedwater pump turbine, and the small generator are connected on a single shaft, the speed increase of the BEST steam-driven feedwater pump unit is significant. This refers to the rapid speed increase of the steam-driven feedwater pump, the BEST feedwater pump turbine, and the small generator. .

[0079] The formula for the dynamic balance model of the shaft torque is as follows:

[0080] (4)

[0081] In the formula, It is the rotor rotational angular velocity (rad / s); It is the moment of inertia of the rotor (kg·m) 2 ); The torque of the steam-driven feedwater pump shaft (N·m); The load torque of the small generator is (N·m). The BEST feedwater pump turbine steam drive torque (N·m) after eliminating all frictional resistance torque is given. and sum.

[0082] The relationship between shaft power and torque satisfies:

[0083] (5)

[0084] BEST steam-driven feedwater pump set speed With rotational angular velocity Relationship:

[0085] (6)

[0086] Steam-driven feedwater pump shaft torque Simultaneously satisfy:

[0087] (7)

[0088] Based on the above dynamic balance model of shaft torque, the runaway speed of the BEST steam-driven feedwater pump set is predicted. Specifically:

[0089] Step 3.1, combining formula (5), according to Determine the shaft torque of the steam-driven feedwater pump and according to Determine the load torque of the small generator .

[0090] Step 3.2, according to and The sum determines the BEST feedwater pump turbine steam drive torque, which has already offset all frictional resistance torques. .

[0091] Step 3.3, according to , , And does the BEST dual-unit regenerative thermal power plant have a smart power plant server to predict the runaway speed of the BEST steam-driven feedwater pump unit? .

[0092] When the BEST dual-unit regenerative thermal power plant has a smart power plant server, the speed increase can be directly obtained through programming calculations on the smart power plant server. .

[0093] Specifically: in the initial state, the rotational speed is The shaft torque of the steam-driven feedwater pump set is The load torque of the small generator is The driving torque of the BEST feedwater pump turbine is .when Suddenly zero, delay , exist From the initial value within the time period Decrease at a constant speed to 0.9 times Find the highest speed of the BEST steam-driven feedwater pump unit during this process, and denote the highest speed as the fly-up speed. .in, The delayed closing time from the converter load shedding action signal triggering the BEST feedwater pump turbine inlet steam regulating valve to begin closing; This refers to the net closing time after the BEST feedwater pump turbine inlet steam regulating valve command is set to zero.

[0094] Regardless of the calculation model and components used in the smart power plant server, it is important to note that since the maximum speed increase time is within 2 seconds, the calculation step size of the prediction algorithm should be within 0.05 seconds to prevent the predicted speed increase value from being too large due to an excessively long step size.

[0095] It should be noted that this invention considers the valve opening to pre-action to... hour, Depend on exist It decreased at a constant speed of 0.9 times within a given time period. That is, when the converter sheds load, the BEST feedwater pump turbine inlet steam regulating valve is pre-activated to... It is precisely for the purpose of from Reduced to 0.9 times To maintain a certain safety margin.

[0096] use Instead As The time for uniform speed change is also derived from the characteristic that the control valve closes quickly at first and then slowly under the action of the servo valve. This method is also used to predict the rapid increase in the speed of the turbine generator unit when it is shearing load; the specific principle will not be elaborated here.

[0097] Meanwhile, due to the simulation of rapid speed increase, The time corresponding to the temperature dropping to 0 (i.e., the BEST feedwater pump turbine inlet valve nonlinearly fully closed) is In this invention, the valve is not fully closed; therefore, it is used in simulation prediction. This will result in a higher, more conservative speed increase.

[0098] When the BEST dual-unit regenerative thermal power plant lacks a smart plant server and is merely a conventional thermal power plant, the increased load torque of the steam-driven feedwater pump due to rising speed has a suppressive effect on the rapid speed increase. Initially, the speed is... The shaft torque of the steam-driven feedwater pump is The load torque of the small generator is The driving torque of the BEST feedwater pump turbine is .when Suddenly zero, delay , exist Within a time period Nonlinearity reduced to Referring to the formula for the speed increase after the turbine of a steam turbine generator set sheds load, the speed increase is... satisfy:

[0099] (8)

[0100] In the formula, It is the moment of inertia; This is the initial speed of the BEST steam-driven feedwater pump set; The delayed closing time from the converter load shedding action signal triggering the BEST feedwater pump turbine inlet steam regulating valve to begin closing; This refers to the net closing time after the BEST feedwater pump turbine inlet steam regulating valve command is set to zero.

[0101] Step 4: Start the minimum flow recirculation valve control method for the steam-driven feedwater pump and the BEST feedwater pump turbine back pressure control method, and according to... and Determine the speed control method for the BEST feedwater pump turbine.

[0102] In this embodiment of the invention, after the converter load shedding action is triggered, the data is synchronously transmitted to the MEH system and the DCS system, and the following three control logics are activated at the same time: the minimum flow recirculation valve control logic of the steam-driven feedwater pump, the speed control logic of the BEST feedwater pump turbine, and the back pressure control logic of the BEST feedwater pump turbine.

[0103] (1) Control method for minimum flow recirculation valve of steam-driven feedwater pump (steam pump recirculation valve control)

[0104] Based on the actual characteristics of the boiler steam-water system, the boiler inlet feedwater flow rate is locked when the converter load shedding action signal is triggered. During the rising speed phase of the steam-driven feedwater pump, when the inlet flow rate of the steam-driven feedwater pump... Compare When the flow rate is 50t / h, the minimum flow recirculation regulating valve of the steam-driven feedwater pump is opened by 10% from its original opening, and then opened at a preset first speed. During the stage when the speed of the steam-driven feedwater pump decreases, the minimum flow recirculation regulating valve of the steam-driven feedwater pump is closed at a preset second speed until the converter load shedding action signal is reset.

[0105] The opening and closing rates of the recirculation system are related to the design and equipment configuration of the feedwater system in a dual-unit regenerative thermal power plant, and need to be determined based on the design flow rate of the recirculation control valve and its flow characteristic curve. The valve opening rate is set at opening the feedwater pump recirculation control valve within 10 seconds until its flow rate reaches 40%; the valve closing rate is half the opening rate, i.e., the second rate is half the first rate. This serves two purposes: first, to reduce the sudden increase in boiler inlet feedwater flow caused by a rapid increase in the speed of the BEST steam-driven feedwater pump unit; and second, to increase the shaft power of the BEST steam-driven feedwater pump unit, suppressing the rapid speed increase and allowing the system to stabilize more quickly.

[0106] (2) Method for controlling back pressure (exhaust pressure) of BEST feedwater pump turbine.

[0107] Based on the characteristics of the BEST feedwater pump turbine exhaust piping system, the back pressure control of the BEST feedwater pump turbine is generally achieved through a combination of overflow regulating valves, bypass regulating valves on its exhaust header, and extraction steam piping valves leading to the corresponding low-pressure heater. Under normal circumstances, the extraction steam piping valves remain fully open, and the back pressure of the BEST feedwater pump turbine is controlled by automatically adjusting the opening degrees of the overflow valves and bypass valves.

[0108] After the converter load shedding action signal is triggered, the back pressure of the BEST feedwater pump turbine is increased to the preset back pressure at a third rate. The preset back pressure is the minimum value between the upper limit of the exhaust pressure to meet the exhaust pressure ratio and the high exhaust pressure alarm value. That is, the automatic control target values ​​of the relief valve and bypass valve are increased to the target values ​​at the third rate until the exhaust pressure reaches the set value or the relief valve and bypass valve are fully closed. In this embodiment of the invention, the third rate is 0.1 MPa / s.

[0109] After the converter is reset due to load shedding, the automatic control target values ​​of the overflow valve and bypass valve of the BEST feedwater pump turbine are reduced to the normal exhaust pressure control range at a fourth rate. In this embodiment of the invention, the fourth rate is 0.05 MPa / s.

[0110] The purpose of increasing the back pressure in this invention is to suppress the magnitude of the speed increase and shorten the time of speed fluctuation; at the same time, changing the set value at a constant speed is also to stabilize the control process.

[0111] (3) The speed control method of the BEST feedwater pump turbine is specifically based on... and The speed control method for the BEST feedwater pump turbine is determined as follows:

[0112] Determine a constant value And obtain the overspeed protection setting value of the BEST feedwater pump turbine. ;

[0113] when When the converter load shedding action signal is triggered, the BEST feedwater pump turbine inlet steam regulating valve command is set. When the speed of the BEST feedwater pump turbine begins to decrease and the opening of the steam inlet regulating valve is at... If the speed is controlled by the conventional BEST feedwater pump turbine PID control method, then the speed will be controlled again.

[0114] when When the converter load shedding action signal is triggered, the BEST feedwater pump turbine inlet steam regulating valve command is set to zero; when the speed of the BEST feedwater pump turbine begins to decrease, the BEST feedwater pump turbine inlet steam regulating valve command is set to zero. When the opening degree of the BEST feedwater pump turbine inlet steam regulating valve is at If the speed is controlled by the conventional BEST feedwater pump turbine PID control method, then the speed will be controlled again.

[0115] The main factor affecting the speed increase is the torque change of the BEST steam-driven feedwater pump unit, which includes the loss of torque from the small generator, the increase in load torque of the steam-driven feedwater pump after the speed increases, and the change in steam drive torque caused by the opening and closing of the BEST feedwater pump turbine inlet regulating valve. The steam torque change process mainly consists of three parts: the work done during the valve closing delay after the converter sheds load, the work done during the valve closing process, and the continued work done by the steam in the turbine chamber. When predicting the speed increase, the first two factors have been considered, but the steam work capacity in the turbine chamber (generally expressed as a volumetric time constant) has not been taken into account. (Characteristics). Because the BEST feedwater pump turbine differs from the generator turbine, its back pressure varies significantly under different unit loads, and the back pressure also changes with the inlet steam pressure, making it impossible to accurately estimate and calculate its volumetric time constant. Furthermore, the effects of factors such as the deviation between the actual and designed shaft rotational inertia, the suppression of rotational speed after the steam-driven feedwater pump recirculation is activated, the accuracy of feedwater flow measurement points, and the deviation between the equipment's operating efficiency and its design efficiency are all difficult to assess. Therefore, this invention addresses this by setting a set value... This is used to characterize the combined effect of these factors.

[0116] The above determined value The specific process is as follows:

[0117] The delay time between the acquisition of the converter load shedding action signal and the start of closure of the BEST feedwater pump turbine inlet regulating valve. Net closing time after BEST feedwater pump turbine inlet steam regulating valve command is set to zero .

[0118] according to and Determine the initial constant value Specifically, this involves setting the time constant. The initial setpoint is determined by the influence of the time constant on the lift speed. This refers to the maximum generator load torque under the design operating conditions of the BEST dual-unit regenerative unit. When it disappears, in The rotational speed at which the aircraft ascends at a constant speed within a given time period. satisfy:

[0119] (9)

[0120] exist The calculated value is rounded up to 10 digits and used as the initial value.

[0121] At the initial constant value In this case, when selecting a unit load of 50%~75% THA (the small generator load torque in this load range) Under conditions of high speed and sufficient safety margin for the pump speed to exceed the overspeed setpoint, an actual converter load shedding test was conducted, and the changes in exhaust pressure of the BEST feedwater pump turbine, the actual overspeed, and the predicted overspeed were obtained during the process of speed surge to stability. The difference between them. And the final result is obtained according to the following three cases. :

[0122] when At that time, Set it to 0.

[0123] when and At that time, Set as .

[0124] when At that time, The speed spike is caused by adding a 0.1-second volumetric time constant to the actual speed exceeding the predicted speed plus a safety margin. That is:

[0125] (10)

[0126] in Z =0.1, then determine whether it has been reached. If not, then let until ,in It is the moment of inertia; This is the load torque of the small generator.

[0127] It should be noted that the actual moment of inertia of the unit is often greater than the design value, the pump torque increases significantly after the steam-driven feedwater pump recirculation is turned on, and the steam inlet regulating valve of most BEST feedwater pump turbines acts quickly. The speed rise prediction value calculated according to the method of this invention is generally greater than the actual rise value. Except for the first working condition, the other working conditions generally will not occur. As long as the predicted speed is not greater than the overspeed speed, the safety of the equipment can be guaranteed.

[0128] Step 5: When the deviation between the BEST feedwater pump turbine speed command and the actual speed is less than 20 rpm, the converter load shedding action signal is reset, and the BEST steam-driven feedwater pump group maintains the normal BEST feedwater pump turbine control speed mode.

[0129] The automatic control method of the present invention will be described in detail below with more specific embodiments.

[0130] This invention takes a 1000MW dual-unit regenerative power plant in Anhui Province as an example. The feedwater pump system of the BEST dual-unit regenerative power plant is composed of a steam-driven feedwater pump, a BEST feedwater pump turbine, and a small generator. The automatic load shedding control method for the converter in a BEST dual-unit regenerative thermal power plant is explained using the unit's operating parameters at 75% THA.

[0131] An automatic load shedding control method for a BEST dual-unit regenerative thermal power plant converter includes the following: reasonable backup conditions for the automatic control method and the automatic load shedding control method for a BEST dual-unit regenerative thermal power plant converter.

[0132] The specific prerequisites are as follows:

[0133] (1) The BEST feedwater pump turbine MEH system has a basic BEST feedwater pump turbine speed control PID module, which can realize automatic speed control.

[0134] (2) The converter load shedding action signal can be transmitted from the converter unit to the MEH system and DCS system.

[0135] (3) The automatic back pressure control module of the BEST feedwater pump turbine is functioning normally and can dynamically adjust the exhaust pressure according to the changes in the inlet steam pressure and the final stage pressure ratio of the BEST feedwater pump turbine. The unit controls the exhaust pressure of the feedwater pump turbine by automatically controlling the opening of the overflow valve and the bypass valve.

[0136] (4) It can effectively and accurately obtain the following real-time data: the power output of the small generator when the unit is in 75% THA condition. =18741kW, BEST feedwater pump turbine speed =3843rpm, BEST steam-driven feedwater pump set inlet and outlet feedwater parameters, including steam-driven feedwater pump inlet temperature =190℃, inlet and outlet pressure =3.32MPa / =30.53MPa, pump inlet feed water mass flow rate =1972.8t / h.

[0137] (5) The maximum efficiency of the BEST feedwater pump turbine has been obtained based on the information provided by the manufacturer. =86%, minimum efficiency of small generators and converter sets =97.5%.

[0138] (6) The flow characteristic curve of the BEST feedwater pump turbine inlet regulating valve has been obtained, and the correlation formula between valve opening and valve flow rate has been derived. The conditions in Table 1 are met.

[0139] Table 1 Relationship between valve opening degree and valve flow rate

[0140]

[0141] (7) The actual measured delay time from the converter's load shedding action to the BEST feedwater pump turbine inlet regulating valve's closing action has been measured. =0.1s and net shutdown time for zeroing instruction =0.6s.

[0142] (8) The moment of inertia of the steam-driven feedwater pump-BEST feedwater pump turbine-small generator shaft system has been obtained. =711kg·m 2 Moment of inertia of various parts: 400 kg·m for small generator 2 Small steam turbine 288.7 kg·m 2 Water pump 22.3 kg·m 2 .

[0143] (9) The overspeed protection setting value of the steam-driven feedwater pump-BEST feedwater pump turbine-small generator has been obtained. =5300rpm.

[0144] The BEST dual-unit regenerative thermal power plant converter load shedding automatic control method according to this embodiment of the invention is as follows:

[0145] Step 1: Determine the shaft power of the steam-driven feedwater pump and small generator shaft power .

[0146] Based on real-time operating data of the BEST steam-driven feedwater pump set and the maximum efficiency of the BEST feedwater pump turbine Calculate the shaft power of the water pump set. Based on the small generator's electrical power and the minimum efficiency of the small generator and converter unit. Calculate the shaft power of the converter and small generator. .

[0147] The shaft power of the water pump set meets the following requirements:

[0148] ;

[0149] In the formula, The density of the feed water in the feed pump is kg / m³. 3 It is obtained from the inlet temperature and inlet pressure of the water pump.

[0150] The shaft power of the small generator satisfies:

[0151] ;

[0152] Step 2, according to and Determine the pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve after the converter sheds load. .

[0153] The actual opening degree of the BEST feedwater pump turbine inlet regulating valve before the converter load shedding is known. ,Will Substitution

[0154] Based on the power distribution of the feedwater pump set shafts before the converter sheds load, calculate the percentage of flow occupied by the steam-driven feedwater pump. , satisfy:

[0155] ;

[0156] exist Multiply by 0.9 to obtain the percentage of flow rate corresponding to the pre-action of the BEST feedwater pump turbine inlet regulating valve after the converter load shedding. .

[0157] Will Substitution The pre-action opening degree of the BEST feedwater pump turbine inlet regulating valve is calculated by reverse calculation. .

[0158] Step 3, according to and Predicting the speed jump of BEST steam-driven feedwater pump set using a shaft torque dynamic balance model. .

[0159] Power of the steam-driven feedwater pump shaft Converter and small generator shaft power The speed of the BEST steam-driven feedwater pump set Moment of inertia of the steam-driven feedwater pump - BEST feedwater pump turbine - small generator shaft system BEST feedwater pump turbine inlet steam regulating valve delayed closing time and net closing time Substitute the values ​​into the lift speed prediction calculation module to obtain the lift speed prediction value. .

[0160] The predicted speed of ascent was obtained through the following model and simulation calculations:

[0161] BEST Steam Pump Generator Set Rotor Rotation Balance Equation:

[0162] ;

[0163] in, It is the rotor rotational angular velocity (rad / s).

[0164] It is the rotor's moment of inertia (kg·m) 2 ).

[0165] For the shaft torque of the steam-driven feedwater pump ( N · m ).

[0166] For the load torque of the small generator ( N · m ).

[0167] The BEST feedwater pump turbine steam drive torque after eliminating all frictional resistance torque ( N · m ),for and sum.

[0168] (1) The relationship between shaft power and torque satisfies:

[0169] ;

[0170] (2) Speed ​​of BEST steam-driven water pump set With rotational angular velocity Relationship:

[0171] ;

[0172] (3) Torque of steam-driven feedwater pump shaft Simultaneously satisfy:

[0173] ;

[0174] Given the above model, the ascent speed is obtained through two methods. :

[0175] Method 1: For thermal power plants equipped with smart power plant servers, the data can be obtained directly through programming calculations on the smart power plant server.

[0176] At a unit load of 750MW, the speed is The shaft torque of the water pump set is =44685 N·m, the load torque of the small generator is =47761 N·m, the driving torque of the BEST feedwater pump turbine is =92446 N·m. When Suddenly zero, delay =0.1s, exist / 2=0.3s time from (92446 N·m) Decreases at a constant speed to 0.9 times. (40216.5 N·m). The highest rotational speed during this process is the predicted lift-off speed. .

[0177] By using the open-source libraries "nummy" and "scipy" in Python to predict the engine speed increase, the result obtained was 4007.6 rpm.

[0178] Method 2: For conventional thermal power plants, the following methods can be used to obtain the information.

[0179] Ignoring the effect of the increased load torque of the steam-driven feedwater pump on suppressing the speed rise in the above model, in the initial state, the speed is... The shaft torque of the steam-driven feedwater pump is The load torque of the small generator is The driving torque of the BEST feedwater pump turbine is .when Suddenly zero, delay , exist Within a time period Nonlinearity reduced to Referring to the formula for the speed increase after the turbine of a steam turbine generator set experiences load shedding, the predicted speed increase is... satisfy:

[0180] ;

[0181] Step 4: After the BEST dual-unit regenerative thermal power plant converter load shedding action is triggered, three control logics are activated simultaneously: the steam-driven feedwater pump minimum flow recirculation valve control logic, the BEST feedwater pump turbine speed control logic, and the BEST feedwater pump turbine back pressure control logic.

[0182] After the converter load shedding signal is triggered, it is synchronously transmitted to the MEH system and DCS system; at the same time, the following three automatic control modules are activated:

[0183] A. Minimum Flow Recirculation Valve Control Module for Steam-Driven Feedwater Pump

[0184] Boiler inlet feedwater flow rate when the converter load shedding action signal is triggered During the rising speed phase of the steam-driven feedwater pump, when the inlet flow rate of the steam-driven feedwater pump... When the flow rate is greater than 2022.8 t / h, the minimum flow recirculation regulating valve of the steam-driven feedwater pump is directly opened by 10% from its original opening, and then opened at a rate of 2% / s; during the stage when the speed of the steam-driven feedwater pump decreases, the minimum flow recirculation regulating valve of the steam-driven feedwater pump is closed at a rate of 1% / s; until the converter load shedding action signal is reset.

[0185] B. BEST Feedwater Pump Turbine Back Pressure Control Module

[0186] The high exhaust pressure alarm value for this unit is 1.05 MPa.

[0187] The pressure ratio of the last stage of the BEST feedwater pump turbine in this project is equal to the extraction pressure of 6 / the exhaust pressure of the BEST feedwater pump turbine (7 extraction). The pressure ratio of the last stage is controlled to be no less than the value in Table 2.

[0188] Table 2. Correspondence between pressure ratio and speed of feedwater pump turbine

[0189]

[0190] When the unit load is 750MW, the extraction pressure of the 6th stage is 1.32MPa; when the BEST feedwater pump turbine speed is 3843rpm, the pressure ratio of the last stage group is 1.158; therefore, the maximum exhaust pressure is 1.32MPa÷1.158=1.14MPa>1.05MPa. Therefore, after the converter load shedding is triggered, the setpoints of the relief valve and bypass valve increase to 1.05MPa in increments of 0.1MPa / s.

[0191] After the converter is reset by load shedding, the automatic control target values ​​of the relief valve and bypass valve are reduced to the normal exhaust pressure control range at a rate of 0.05 MPa / s.

[0192] Table 3 Normal Range of Exhaust Steam Pressure for This Unit

[0193]

[0194] C. BEST feedwater pump turbine speed control module

[0195] Predicting the speed of ascent With BEST feedwater pump turbine overspeed protection setting value Relative size, if Then, the following scheme A will be used for the speed control of the BEST feedwater pump turbine; if If so, the following scheme B will be used to control the speed of the BEST feedwater pump turbine.

[0196] Option A: After the converter load shedding action signal is triggered, the BEST feedwater pump turbine inlet steam regulating valve command is set. When the speed of the BEST feedwater pump turbine begins to decrease and the regulating valve opening is at... Then, the speed will be restored to the normal PID control speed of the small steam turbine.

[0197] Option B: After the converter load shedding action signal is triggered, the BEST feedwater pump turbine inlet steam control valve command is set to 0; when the turbine speed begins to decrease, the BEST feedwater pump turbine inlet steam control valve command is set to... When the BEST feedwater pump turbine regulating valve opening is at Then, the speed will be restored to the normal PID control speed of the small steam turbine.

[0198] Preset initial value The calculation sets the time constant. =0.25s, satisfy:

[0199] ;

[0200] exist The calculated value is rounded up to 10 digits and used as the initial value to distinguish between schemes A and B. =170rpm.

[0201] According to the configuration of a smart power plant, the deviation between the overspeed setpoint and the predicted value for this project is:

[0202] ;

[0203] Option A: After the converter load shedding action signal is triggered, the BEST feedwater pump turbine inlet steam regulating valve command is set. When the speed of the BEST feedwater pump turbine begins to decrease and the regulating valve opening is at... Then, the speed will be restored to the normal PID control speed of the small steam turbine.

[0204] Step 5: When the deviation between the BEST feedwater pump turbine speed command and the actual speed is <20 rpm, the converter load shedding action signal is reset; the BEST steam-driven feedwater pump group maintains the normal BEST feedwater pump turbine control speed mode.

[0205] This invention enables continuous and real-time judgment and control of the BEST feedwater pump turbine speed throughout the entire process after the BEST dual-unit regenerative thermal power plant converter sheds its load, thereby minimizing the significant interference caused by discontinuous control of equipment and systems.

[0206] The automatic control method of the present invention is equipped with reasonable valve preset opening calculation logic after converter load shedding, BEST feedwater pump recirculation automatic control logic, BEST feedwater pump turbine speed control logic, and feedwater pump turbine back pressure control logic. This shortens the speed fluctuation process of the BEST steam-driven feedwater pump group, reduces the fluctuation amplitude of boiler inlet feedwater flow, ensures the stability and safety of the entire unit after converter load shedding, and makes the automatic control after converter load shedding practically operable.

[0207] The automatic control method of the present invention is equipped with two sets of converter load shedding speed rise prediction modules for smart power plants and conventional thermal power plants, which can be used as a reference for other dual-unit regenerative units.

[0208] The above descriptions are merely a few embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for automatic control of load rejection of a BEST double-unit regenerative power plant converter, characterized in that, The BEST double-machine regenerative thermal power plant includes a BEST steam-driven feed water pump set, the BEST steam-driven feed water pump set including a steam-driven feed water pump, a BEST feed water pump steam turbine and a small generator, a BEST double-machine regenerative thermal power plant converter load rejection automatic control method, comprising: Step 1, Determine steam-driven feedwater pump shaft power and small generator shaft power ; Step 2, determine the pre-action opening of the BEST feedwater pump turbine admission valve after the load rejection of the converter and ;​ Step 3, according to and Predicting the best speed of a motor-driven feedwater pump group ; Step 4, start the minimum flow recirculation valve control method of the steam feed water pump and the BEST feed water pump turbine back pressure control method, and determine the rotation speed control method of the BEST feed water pump turbine according to and the rotation speed of the BEST feed water pump turbine. According to and The application discloses a method for determining the rotating speed control of a BEST water supply pump turbine. determining a constant value And get the overspeed protection setting value of the BEST feedwater pump turbine ; When the BEST feedwater pump turbine admission valve command is ; when the speed of the BEST feedwater pump turbine begins to decrease and the admission valve opening is , the normal BEST feedwater pump turbine speed PID control method is resumed to control the speed. When the BEST feedwater pump turbine admission valve command is zero; when the speed of the BEST feedwater pump turbine begins to decrease, the BEST feedwater pump turbine admission valve command is ; when the BEST feedwater pump turbine admission valve opening is , the normal BEST feedwater pump turbine speed PID control method is restored to control the speed. determining a constant value in particular: The delay closing time from the acquisition of the converter load rejection action signal trigger to the start of the closing of the BEST feedwater pump turbine admission valve The net closing time after the BEST feedwater pump turbine admission valve command is zeroed ; According to and determining initial values ; At the initial setting And when the unit load is 50%~75%THA, the actual inverter load rejection test is carried out, and the actual fly-up speed of the BEST feed water pump turbine during the fly-up to stable process is obtained ; According to , and determining a constant value ; According to , and determining a constant value , in particular: when At that time, Set to 0; When and , set to ; When , , and determine whether to reach , if not, then , until , wherein is the moment of inertia; is the small generator load torque.

2. The BEST double-unit regenerative power plant converter load rejection automatic control method according to claim 1, characterized by, A start-up steam-driven feed water pump minimum flow recirculation valve control method, specifically: Locking the inverter load dump action signal trigger when the boiler inlet feed water flow ; In the speed rising stage of the steam-driven feed water pump, when the steam-driven feed water pump inlet flow Compared with the preset flow value, the steam-driven feed water pump minimum flow recirculation regulating valve is opened by a preset amplitude at the original opening degree, and then is opened at a preset first rate; in the speed descending stage of the steam-driven feed water pump, the steam-driven feed water pump minimum flow recirculation regulating valve is closed at a preset second rate until the variable transformer load shedding action signal resets.

3. The BEST double-unit regenerative power plant converter load rejection automatic control method according to claim 1, characterized by, A start-up BEST feed water pump steam turbine back pressure control method, specifically: After a converter load rejection action signal is triggered, a preset third rate is used to increase the back pressure of the BEST feed water pump steam turbine to a preset back pressure, the preset back pressure being the minimum value of an upper limit value of exhaust pressure satisfying an exhaust pressure ratio and an exhaust pressure high alarm value; After a converter load rejection reset, a preset fourth rate is used to decrease the automatic control target values of the overflow valve and the bypass valve of the BEST feed water pump steam turbine to a normal exhaust pressure control range.

4. The BEST dual-unit regenerative power plant converter load shedding automatic control method of claim 1, wherein, Step 3 specifically is: Step 3.1, according to determining steam-driven feedwater pump shaft torque , and according to determining small generator load torque ; Step 3.2, according to and Determination of the steam driving moment of the BEST feedwater pump turbine with all friction torques removed ; Step 3.3, according to , , and whether there is a smart power plant server in the BEST double-exchange-heat thermal power plant, to predict the BEST steam-driven feed water pump set's flying speed .

5. The BEST double-unit regenerative power plant converter load rejection automatic control method according to claim 4, characterized by, Step 3.3 specifically is: When there is a smart power plant server in the BEST double-machine regenerative thermal power plant, obtaining is zero and is delayed , In time from the initial value to 0.9 times the initial speed of the highest speed of the BEST steam-driven feed water pump set during the process, and the highest speed is recorded as the femtosecond speed ; The delay closing time for the converter load rejection action signal trigger to start closing the BEST feedwater pump turbine admission valve; The net closing time after the BEST feedwater pump turbine admission valve command is zeroed.

6. The BEST dual-unit regenerative power plant converter load shedding automatic control method of claim 4, wherein, Step 3.3 specifically is: When there is no intelligent power plant server in the BEST double-machine regenerative thermal power plant, the first formula is used to determine , the first formula is: ； wherein is the moment of inertia; is the initial rotational speed of the BEST steam-driven feedwater pump set; is the delay closing time from the variable frequency converter load rejection action signal trigger to the start of the closing of the BEST feedwater pump turbine admission control valve; is the net closing time after the BEST feedwater pump turbine admission control valve command is set to zero.

7. The BEST dual-unit regenerative power plant converter load shedding automatic control method of claim 1, wherein, Step 2 specifically is: Determine the steam flow percentage corresponding to the actual opening of the BEST feedwater pump turbine admission valve before the load rejection of the converter ; determining the steam flow percentage occupied by the steam driven feed water pump , the small generator shaft power and the steam flow percentage , determining the steam flow percentage occupied by the steam driven feed water pump ; According to the percentage of the flow occupied by the steam-driven feed water pump Determine the pre-action opening of the BEST feed water pump turbine admission valve after the load rejection of the converter .

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