Primary frequency modulation dynamic modeling method of photo-thermal power generation system based on heat flow method

Abstract

The invention relates to the technical field of primary frequency modulation of photo-thermal power generation, and discloses a primary frequency modulation dynamic modeling method of a photo-thermal power generation system based on a heat flow method, which is used for grid-connected operation of a photo-thermal power station. A primary frequency modulation model structure of the photo-thermal generator set is decomposed into a plurality of local models, including a speed regulator model, a steam generation system model and a steam turbine model, and according to a heat flow method, a steam generation system dynamic model is established; comprising the steps that dynamic models of the heat exchange process of two fluids of a steam-water working medium and high-temperature fused salt in all the sections and dynamic models of the steam-water working medium and the high-temperature fused salt in the flowing process are built for the preheating section, the overheating section and the evaporation section of a steam generation system correspondingly. According to the method, the primary frequency modulation dynamic model of the photo-thermal power generation system is constructed, the technical blank is filled, the model complexity is considered while the primary frequency modulation characteristics of the photo-thermal power generation system are represented, the simulation rapidity and the model accuracy can be well balanced, and the method has high adaptability in a dynamic simulation analysis scene of a power system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of primary frequency modulation of photo-thermal power generation, and particularly relates to a photo-thermal power generation system primary frequency modulation dynamic modeling method based on a heat flow method, which is applied to grid-connected operation of a photo-thermal power station. BACKGROUND

[0002] In the process of new power system construction and development, the proportion of wind power and photovoltaic power generation continues to increase, and the traditional alternating current system dominated by thermal synchronous generators is gradually changing into a power electronic AC / DC hybrid system dominated by wind and light, which means that the stable operation of the power system will face stronger vibration and impact. Frequency stability is one of the most critical requirements for the stable operation of the new power system, and power primary frequency modulation is a key means to ensure the frequency stability of the power system. However, in the new power system, wind and photovoltaic generators connected to power electronic devices do not have the rotational inertia and primary frequency modulation capability of traditional synchronous generators, and large-scale access leads to a decrease in the system's synchronous rotational inertia and primary frequency modulation capability, which reduces the system's resistance to power disturbance. In addition, a large-capacity DC fault will bring a huge power impact to the system, and the amount of power disturbance that the system safety needs to consider has increased, and the frequency response of the system has further deteriorated, and the frequency security problem has become increasingly prominent.

[0003] Solar photo-thermal power generation is a new renewable energy power generation technology that combines light-thermal conversion power generation, large-scale heat storage, and grid synchronous generator characteristics. Since it follows the steam turbine-synchronous generator technology, it can meet the inertia, voltage response, and other technical requirements of the existing alternating current synchronous power system. At the same time, the large-scale heat storage system can realize energy transfer in time, has good controllability and schedulability, and can meet the technical requirements of grid peak regulation, frequency regulation, and rotating reserve. Therefore, photo-thermal power generation is essentially a new energy form of traditional units with energy storage, which combines the advantages of new energy, energy storage, and conventional power sources, and is a grid-friendly new energy. In the future, photo-thermal power generation is expected to completely replace thermal power and become an important regulating power source to ensure and support the safe and stable operation of the new power system. Therefore, accurately grasping the true primary frequency modulation capability of photo-thermal generators is of great significance to the frequency security of the new power system.

[0004] However, the current research on dynamic models for grid-connected operation of photo-thermal power stations is still relatively scarce, especially the lack of dynamic mathematical models that can accurately reflect the primary frequency modulation process, which leads to uncertainty in the primary frequency modulation response characteristics and regulation capability of photo-thermal power stations under grid frequency disturbance, restricting their effective participation and optimal scheduling in power system stability control. SUMMARY

[0005] The application intends to provide a primary frequency modulation dynamic modeling method of a photo-thermal power generation system based on a heat flow method, construct a primary frequency modulation dynamic model of the photo-thermal power generation system, fill the model blank of the new technology at present, and balance the simulation rapidity and the model accuracy while the model represents the primary frequency modulation characteristics of the photo-thermal power generation system, so that the model has high adaptability in the dynamic simulation analysis scene of the power system.

[0006] The basic scheme provided by the application is a primary frequency modulation dynamic modeling method of a photo-thermal power generation system based on a heat flow method, which comprises the following steps: decomposing a primary frequency modulation model structure of a photo-thermal power generation unit into multiple local models, including a governor model, a steam generation system model and a steam turbine model. According to the heat flow method, the steam generation system dynamic model is established, including the dynamic models of the heat exchange processes of the two fluid flows of the steam-water working medium and the high-temperature molten salt in the preheating section, the superheating section and the evaporation section of the steam generation system, and the dynamic models of the steam-water working medium and the high-temperature molten salt in the flow processes, respectively.

[0007] The working principle and advantages of the application are as follows: Solar thermal power station integrates the advantages of new energy, energy storage and conventional power source. In the future, it is expected to completely replace thermal power in some areas of China and become an important frequency modulation power source to ensure the safe and stable operation of new power system. Primary frequency modulation of power source is the key means to ensure the stability of power system frequency. Therefore, it is crucial to build a primary frequency modulation model of solar thermal power generator set suitable for dynamic analysis of power system and accurately grasp the real primary frequency modulation capability of the unit. At present, researchers at home and abroad are basically in the initial exploration stage of the research on dynamic modeling of solar thermal power station for power system frequency modulation. The existing research on dynamic modeling of solar thermal power station mainly focuses on the research of its internal thermodynamic characteristics of components. The proposed model cannot fully represent the electrical characteristics of solar thermal power station, nor is it easy to combine with existing electrical component models. Solar thermal power station and traditional thermal power have some similarities in the structure of power module and the principle of thermal cycle. The methods and ideas of primary frequency modulation modeling of traditional thermal power lay a solid foundation for the construction of primary frequency modulation model of solar thermal power station. However, there are significant differences between solar thermal power station and traditional thermal power in energy supply mode, component structure parameters and control system. Specifically, in terms of energy supply mode, solar thermal power station uses high-temperature molten salt for heating. The randomness of solar radiation makes the temperature of high-temperature molten salt in the thermal storage system not constant, which leads to the additional influence of high-temperature molten salt temperature on the operating characteristics of solar thermal power station compared with thermal power. In terms of component structure, the storage device equipped in solar thermal power station enables the mass flow of high-temperature molten salt to be quickly adjusted, which makes it have more flexible power regulation capability than thermal power. In terms of control system, although solar thermal power station follows the hierarchical control structure of thermal power, there are still differences in specific control strategies such as molten salt flow control and main steam temperature control. Therefore, the primary frequency modulation model of traditional thermal power cannot accurately describe the primary frequency modulation dynamic characteristics of solar thermal power station, and it is necessary to study the dynamic model of solar thermal power station for power system primary frequency modulation.

[0008] The application considers the influence of the thermal dynamic characteristics of the steam generation system of the solar thermal power station on the frequency response characteristics of the unit on the basis of the traditional thermal power classic primary frequency modulation model, and proposes a solar thermal power unit primary frequency modulation model suitable for dynamic analysis of the power system. By analyzing the flow and heat exchange process of the high-temperature molten salt and the steam-water working fluid and the phase change characteristics of the steam-water working fluid, a dynamic model of the steam generation system is constructed based on the heat flow method; all the parameters of the designed steam generation system model can be calculated from the design manual of the power station and the monitoring data of the steady-state distributed control system, without the need for identification through disturbance test data or actual frequency modulation dynamic data, and the model parameters can be determined in real time when the disturbance has not occurred, helping the power grid to evaluate the real primary frequency modulation capacity of the unit; at the same time, the dynamic parameters of the steam generation system model change accordingly according to the change of the operating condition, which can reflect the difference in the dynamic characteristics and the primary frequency modulation capacity of the unit under different load conditions, and is more in line with the actual situation. On the basis of the established dynamic model of the steam generation system, a solar thermal power unit primary frequency modulation model is constructed, which comprehensively considers the dynamic coupling characteristics of the governor, the steam generation system and the steam turbine, and the influence of the main steam parameter dynamic characteristics on the primary frequency modulation performance of the unit is considered in detail, which can more accurately reflect (or simulate) the actual dynamic response characteristics of the key thermal state quantity and the unit frequency modulation power during the primary frequency modulation period and the characteristic difference of the output power of the solar thermal power unit under different operating conditions, has high adaptability in the simulation analysis scene of the large power system, and helps the power grid to master the real primary frequency modulation capacity of the solar thermal power unit, so as to accurately analyze the frequency safety.

[0009] In summary, the model provided by the application can characterize the primary frequency modulation characteristics of the solar thermal power system while considering the model complexity, can better balance the simulation speed and model accuracy, and has high adaptability in the dynamic simulation analysis scene of the power system. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The primary frequency modulation model structure of the solar thermal power unit provided by the embodiment of the application; Figure 2 The heat flow model of the dynamic characteristics of the existing heat exchange unit; Figure 3 The series structure schematic diagram of the heat exchange unit in the dynamic model of the steam generation system provided by the embodiment of the application; Figure 4 The heat exchange process schematic diagram of a single heat exchange unit provided by the embodiment of the application; Figure 5 The adjusting system model schematic diagram in the governor model provided by the embodiment of the application; Figure 6 The electro-hydraulic servo system model schematic diagram in the governor model provided by the embodiment of the application; Figure 7 A schematic diagram of a steam turbine model is provided for embodiments of the present application. DETAILED DESCRIPTION

[0011] The following is further described in detail through specific embodiments: Embodiments are substantially as shown in the accompanying drawings: Figure 1 A primary frequency modulation dynamic modeling method for a solar thermal power generation system based on a heat flow method, comprising: S1, decompose the primary frequency modulation model structure of the solar thermal power generating unit into multiple local models, including a speed regulator model, a steam generation system model, and a steam turbine model; Specifically, the primary frequency modulation model structure of the solar thermal power generating unit is as shown in Figure 1 , wherein represents the frequency difference, represents the main steam flow instruction change amount, represents the actual main steam flow, represents the mechanical power change amount.

[0012] S2, according to the heat flow method, establish a steam generation system dynamic model; Specifically, the heat flow method: combining the heat-electricity analogy theory, the temperature difference is analogous to the potential difference in electricity, the thermal resistance is analogous to the resistance, and the specific heat capacity of the heat exchanger wall is analogous to the capacitance in electricity. The heat flow model of the heat exchanger can be obtained as shown in Figure 2 The model contains two equivalent thermal resistances and one equivalent thermal capacity, respectively, representing the heat transfer, storage, and release processes in the unsteady state stage. Through the dynamic heat flow model, the heat transfer relationship in the dynamic heat transfer process of the heat exchanger is intuitively revealed, that is, part of the heat from the high-temperature molten salt is absorbed by the heat exchanger wall, and part of the heat is absorbed by the steam-water working medium.

[0013] For the preheating section and the superheating section of the steam generation system, the temperature and pressure of the steam-water working medium have distributed parameter characteristics in the process of heat exchange and flow. The temperature gradually increases along the flow direction, and the pressure gradually decreases along the flow direction. The changes in temperature and pressure will cause the property parameters of the steam-water working medium to change with the spatial position. In order to ensure the accuracy of the model, the idea of segmented modeling is adopted, and the preheating section and the superheating section are uniformly segmented along the flow direction of the working medium. When the area of each heat exchange unit is small enough, the property parameters of the steam-water working medium in the heat exchange unit can be considered to be equal everywhere in space. For the evaporation section, the temperature and pressure of the steam-water working medium are equal everywhere and do not change with the spatial position, and are equal to the saturation parameters of the steam-water working medium at that time. Therefore, no segmentation is performed.

[0014] The state of high-temperature molten salt is always uniquely determined in the preheating section (through the evaporation section) to the superheating section of the steam generation system, and is a single-phase working medium. During heat exchange and flow, the temperature and pressure of high-temperature molten salt have distributed parameter characteristics, and both gradually decrease along the flow direction. The changes in temperature and pressure will cause the property parameters of high-temperature molten salt to change with the spatial position. To ensure the accuracy of the model, the preheating section (through the evaporation section) to the superheating section is also uniformly segmented along the flow direction of high-temperature molten salt. When the area of each heat exchange unit is small enough, the property parameters of high-temperature molten salt in the heat exchange unit can be considered to be equal everywhere in space. The segmentation of the preheating section and the superheating section is consistent with the steam-water working medium.

[0015] Based on the above analysis, the schematic diagram of the series structure of the heat exchange unit of the two fluids (steam-water working medium and high-temperature molten salt) in the steam generation system is as follows Figure 3 , wherein Figure 3 (a) is the preheating section and the evaporation section, Figure 3 (b) is the heating section.

[0016] The total length of the preheating section and the evaporation section (the evaporation section is the phase change section) is uniformly divided into n sections, wherein n = m + P , and the length of each heat exchange unit is L 1. The numbering of the heat exchange units of the preheating section is i =1, 2, …, m . The first m +1 section enters the evaporation section (that is, the variable subscripts 1~m represent the thermodynamic parameters of the first 1~m heat exchange units of the preheating section, and the variable subscripts m+1~m+ P represent the thermodynamic parameters of the first 1~ P heat exchange units of the evaporation section). For the steam-water working medium, the heat exchange units of the evaporation section are analyzed as a whole, and for the high-temperature molten salt, the evaporation section is uniformly divided into P sections for analysis; the superheating section is uniformly divided into N sections, and the length of each heat exchange unit is L 2. The corresponding heat exchange unit numbering is i =1, 2, …, N . Figure 3 In the above, p h,i , p h,i , T h,in,i and respectively represent the density, pressure, inlet molten salt temperature and mass flow rate of high-temperature molten salt in the first i heat exchange unit of the steam generation system; Figure 3 In (a), pc,i , p c,i , T w,i , T c,in,i and These represent the first and second stages of the preheating process of the steam-water working medium. i The density, pressure, tube wall metal temperature, inlet temperature (which can also be understood as the working fluid temperature at the inlet), and mass flow rate of each heat exchange unit; p c,s , T c,s , T w,s and These represent the pressure of the steam-water working medium in the evaporation section, the corresponding saturation temperature at that pressure, the metal temperature of the pipe wall, and the mass flow rate of the saturated steam, respectively. Figure 3 (b) The variable subscript sh represents the thermodynamic parameters of the steam-water working fluid and the pipe wall metal in the superheated section. For details of the parameters, please refer to the corresponding explanation above.

[0017] In the preheating and superheating sections, both fluids are single-phase working media. When two independent thermodynamic parameters are known, the remaining physical properties can be obtained using CoolProp. When calculating the physical properties of the fluids in the heat exchange unit, the characteristic temperatures of the two fluids are defined as the arithmetic mean of the inlet and outlet temperatures of their respective heat exchange units. The physical properties of the fluids in each heat exchange unit, such as density and specific heat capacity at constant pressure, can be determined by calling the CoolProp property functions in MATLAB based on the characteristic temperature and pressure of that section of fluid. In the evaporation section, the steam-water working medium is a two-phase working medium. When the pressure value is known, the saturated physical properties at that pressure can be determined by calling the CoolProp property functions. The method for determining the physical properties of the high-temperature molten salt is the same as that for the preheating and superheating sections.

[0018] (1) Dynamic model of preheating section and superheating section In a solar thermal power plant, the heat transfer flow process of two fluids within each heat exchange unit of the preheating and superheating sections of the steam generation system is described using the same dynamic model. First, each heat exchange unit is considered as follows: Figure 4 The length shown is L i The heat exchanger is analyzed and modeled for each heat exchange unit, with the inlet temperature of the steam-water working fluid being... T c,in (Subscript c indicates the working fluid is steam-water mixture), the inlet temperature of the high-temperature molten salt is... T h,in (The subscript h indicates high-temperature molten salt).

[0019] Based on the law of conservation of energy, the heat balance differential equations for the steam-water working fluid, the tube wall metal, and the high-temperature molten salt in each heat exchange unit are written as follows: (1) In the formula, the subscript i This indicates the number of the heat exchange unit. L i Indicates the length of the heat exchange unit; Mc p This indicates the heat capacity of the pipe wall metal. G c , G h These represent the heat capacity flow of the steam-water working fluid and the high-temperature molten salt, respectively. k c , k h These represent the heat transfer coefficients between the steam-water working fluid and the pipe wall metal, and between the high-temperature molten salt and the pipe wall metal, respectively. A c , A h These represent the heat exchange areas between the steam / water working fluid and the tube wall metal, and between the high-temperature molten salt and the tube wall metal, respectively. k c A c (Right now( kA ) c ), k h A h (Right now( kA ) h The numbers () represent the thermal conductivities of the heat exchange units corresponding to the steam-water working fluid and the high-temperature molten salt, respectively. T c , T h and T w These represent the temperatures of the steam-water working fluid, the high-temperature molten salt, and the pipe wall metal, respectively. t and x They represent time and space, respectively.

[0020] Solve the differential equation of heat balance between the steam-water working medium and the high-temperature molten salt in formula (1) and take... x = L i The working fluids of the carbonated beverage and the high-temperature molten salt can be obtained in the first... i+ Inlet temperature of one heat exchange unit: (2) In the formula, , These represent the working fluids of the steam-water mixture and the high-temperature molten salt at the [number]th [year]. i The inlet working fluid temperature of each heat exchange unit; kA ) c,i 、( kA)h,i These represent the corresponding first and second working fluids of the steam-water mixture and the high-temperature molten salt, respectively. i Thermal conductivity of each heat exchange unit.

[0021] The heat exchanger wall temperature control equation in formula (1) is changed from 0 to... L i Integrating, we get: (3) In the formula, , These represent the working fluids of the steam-water mixture and the high-temperature molten salt at the [missing information - likely a specific point or time period]. i The average temperature within each heat exchange unit.

[0022] Change formula (2) from 0 to L i Integral and then divide by L i We can obtain: (4) In the formula, , .

[0023] Substituting equation (4) into equation (3), we get: (5) Based on the definition of thermal resistance in the heat flow method, formula (5) is transformed into: (6) In the formula, R c,i Indicates the first i The thermal resistance between the steam-water working fluid and the metal tube wall within each heat exchange unit; R h,i Indicates the first i The thermal resistance between the high-temperature molten salt and the metal tube wall within each heat exchange unit.

[0024] Change formula (6) from 0 to t Integrating, we can obtain the expression for the heat exchanger tube wall temperature as follows: (7) In the formula, Indicates the first i The time constant during the dynamic heat transfer process of each heat exchange unit.

[0025] According to the law of conservation of energy, the inlet temperatures of the steam-water working fluid and the high-temperature molten salt in two adjacent heat exchange units should satisfy the following: (8) In the formula, and These represent the volume of steam-water working fluid and high-temperature molten salt per unit length flowing through the first... i The time delay of each heat exchange unit; and Qh and Qw represent the heat transfer amount of high-temperature molten salt and steam-water working medium in the first heat exchange unit, respectively. i

[0026] Based on the above analysis, the dynamic model of the heat exchange process between the two fluids in the preheating section and the superheating section is: (9) (10) (11) According to the mass conservation and momentum conservation, the dynamic model of the steam-water working medium and the high-temperature molten salt during the flow process is: (12) (13) wherein, and represent the pipe cross-sectional area of the steam-water working medium and the high-temperature molten salt, respectively; and represent the pipe resistance coefficient of the steam-water working medium and the high-temperature molten salt, respectively.

[0027] Thus, the above formulas (9)-(13) constitute the dynamic model of the preheating section and the superheating section of the steam generation system of the solar-thermal power station.

[0028] (2) Dynamic model of the evaporation section (subscript s) The evaporation section steam-water working medium uses lumped parameters to describe its dynamic characteristics and ignores the pressure loss along the way. The evaporation section high-temperature molten salt uses distributed parameters to describe the dynamic characteristics of its heat exchange flow process.

[0029] 1) Dynamic model of the evaporation section steam-water working medium According to the volume conservation relationship of saturated water and saturated steam, we can get: (14) According to the mass conservation relationship of saturated water and saturated steam, we can get: (15) According to the energy relationship equation of saturated water and saturated steam, we can get: (16) wherein, , represent the volume of saturated water and saturated steam, respectively, , represent the density of saturated water and saturated steam, respectively, , represent the specific thermodynamic energy of saturated water and saturated steam, respectively,​h Indicates specific enthalpy. Indicates the effective metal coefficient, This indicates the specific heat capacity of the pipe wall metal. Indicates the mass of metal in the evaporation section. This indicates the effective metal heat capacity of the evaporation section. This indicates the temperature of the metal wall in the evaporation section, which is equal to the saturation temperature of the working fluid. This indicates the heat transfer from the pipe wall metal to the two-phase steam-water working fluid side.

[0030] The relationship between specific thermal energy and specific enthalpy Substituting into formula (16), we get: (17) In the formula, This represents the volume of the two-phase working fluid. This indicates the pressure of the carbonated beverage medium.

[0031] By processing the above basic equations and simultaneously solving formulas (14) and (15), we can obtain: (18) Combining formulas (15), (17), and (18), we obtain: (19) in,

[0032]

[0033]

[0034]

[0035] In the formula, During the first frequency regulation period, the pressure and the corresponding saturation temperature have an approximately linear relationship. Therefore, it is assumed that within the time scale of the first frequency regulation... k tp It is a constant. Furthermore, the densities of saturated water and saturated vapor are... , as well as , Follow It also approximates a linear relationship, therefore, we assume , , , It is also a constant. , These represent the mass flow rates of feedwater entering the steam drum from the preheater outlet and the saturated steam at the steam drum outlet, respectively. , respectively represent the specific enthalpy of the feed water entering the drum and the specific enthalpy of the saturated steam at the outlet of the drum.

[0036] The pressure and temperature of the vapor-liquid working medium in the evaporation section are equal everywhere and do not change with the spatial position, and are equal to the saturation pressure and the corresponding saturation temperature of the vapor-liquid working medium at this moment, i.e., (20) In the formula, represents the saturation temperature of the vapor-liquid working medium in the evaporation section.

[0037] The specific heat capacity of the vapor-liquid working medium in the evaporation section at constant pressure can be regarded as infinite, i.e., the heat capacity flow of the vapor-liquid working medium . Substituting into the heat transfer thermal resistance formula between the vapor-liquid working medium and the pipe wall metal can obtain: G c,s (21) In the formula, k c,s represents the heat transfer coefficient between the vapor-liquid working medium in the evaporation section and the pipe wall metal, A c,s represents the heat exchange area between the vapor-liquid working medium in the evaporation section and the pipe wall metal.

[0038] According to the definition of the heat transfer thermal resistance based on the inlet temperature difference, R c , s is the ratio of the heat transfer temperature difference between the pipe wall metal temperature in the evaporation section and the inlet working medium temperature (i.e., the saturation temperature) and the heat exchange amount, and therefore, the heat exchange amount between the vapor-liquid working medium in the evaporation section and the pipe wall metal is (22) According to the physical properties of the steam, the heat exchange amount between the vapor-liquid working medium in the evaporation section and the pipe wall metal is (23) In the formula, y represents the vaporization latent heat corresponding to the pressure of the vapor-liquid working medium in the evaporation section, and the calculation formula is (24) In the formula, and respectively represent the specific enthalpy of the saturated steam and the saturated water in the drum.

[0039] By combining formula (22) and (23), the mass flow rate of the saturated steam at the outlet of the drum in the evaporation section can be obtained: (25) In summary, formula (18)-(20) and (25) constitute the dynamic model of the vapor-liquid working medium in the evaporation section of the steam generation system of the solar thermal power station. ​

[0040] 2) Dynamic model of high-temperature molten salt in the evaporation section Extending the dynamic heat flow model of the preheating and superheating sections to the evaporation section, the dynamic model of the heat exchange process between the high-temperature molten salt and the tube wall metal in the evaporation section heat exchange unit is obtained as follows: (26) In the formula, This indicates the outlet temperature of the high-temperature molten salt in the evaporation section (which can be understood as the...). i The outlet temperature of the first heat exchange unit is the i+ (Inlet temperature of one heat exchange unit) This indicates the inlet temperature of the high-temperature molten salt in the evaporation section. This indicates the temperature of the tube wall in the evaporation section of the evaporator; This indicates the time delay of the high-temperature molten salt flowing through the evaporation section; This indicates the thermal resistance between the steam-water working fluid in the evaporation section and the metal of the pipe wall; This indicates the thermal resistance between the high-temperature molten salt in the evaporation section and the metal of the pipe wall; k h,s This represents the heat transfer coefficient between the high-temperature molten salt in the evaporation section and the metal of the pipe wall; A h,s This indicates the heat exchange area between the high-temperature molten salt in the evaporation section and the metal of the tube wall; G h,s This indicates the heat capacity flow of the high-temperature molten salt in the evaporation section.

[0041] The dynamic model of the heat exchange unit during the flow of high-temperature molten salt is the same as that of the preheating section and the superheating section, as shown in formula (13).

[0042] In summary, formulas (13) and (26) constitute a dynamic model of the high-temperature molten salt in the evaporation section of the steam generation system of a solar thermal power plant.

[0043] (3) Boundary conditions and constraints that the overall model of the steam generation system must satisfy; The boundary conditions and constraints that the overall model of the steam generation system must satisfy are shown in Equation (27).

[0044] (27) In the formula, , , and These represent the pressure, temperature, mass flow rate, and density of the main steam, respectively. According to the connection relationship of the superheater section model, the main steam pressure is the parameter value at the superheater outlet. , These represent the cross-sectional area and length of the main steam pipe, respectively. and These represent the specific enthalpy and mass flow rate of steam at the superheater outlet (which can be understood as the outlet of the N+1th unit being the superheater outlet); , and These represent the steam pressure in the first heat exchange unit of the superheated section model, and the steam temperature and mass flow rate at the inlet, respectively. , and These represent the pressure of the steam-water working fluid in the evaporation section, the corresponding saturation temperature, and the saturated steam density at that pressure, respectively. This represents the mass flow rate of saturated steam at the steam drum outlet; the variable subscript sh represents the thermodynamic parameters of the steam-water working fluid and the pipe wall metal in the superheated section; the variable subscripts m and m+1 represent the thermodynamic parameters of the m-th heat exchange unit in the preheating section and the thermodynamic parameters of the 1-th heat exchange unit in the steam section, respectively. N This indicates the total number of uniformly divided superheated sections; This represents the pipeline resistance coefficient of the steam-water working medium.

[0045] S3, Establish the speed governor model; The governor model reflects the unit's control characteristics. The governor model includes a regulation system model and an electro-hydraulic servo system model, and the specific mapping relationships are as follows: Figure 5 , 6 As shown.

[0046] Figure 5 In the middle, △ w Indicates the speed deviation. T 1 indicates the time constant of the rotational speed measurement process. This represents the complex frequency variable in the Laplace transform, used to describe the system's response characteristics to signals of different frequencies. K 1 represents the speed deviation amplification factor, which is the reciprocal of the droop coefficient. P CV This indicates a valve position command.

[0047] Figure 6 In this context, the hydraulic actuator is the actuating mechanism for the control valve. T o and T c These represent the opening and closing time constants of the hydraulic actuator, respectively. T 2 represents the time constant of the hydraulic motor stroke feedback loop. T This represents the pure delay time of the output signal for the main control valve opening. VEL open and VEL close These represent the overspeed opening and closing coefficients, respectively. K P , K I andK D Kp, Ki, Kd represent the proportional, integral, and derivative coefficients of the PID element, respectively, P MAX Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, P MIN Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, P GV Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, s represents the complex frequency variable in Laplace transform.

[0048] S4, establish a steam turbine model; The steam turbine model uses the standard model provided by IEEE, which is a single-reheater steam turbine model. The mapping relationship is shown in Figure 7 .

[0049] Figure 7 , d s Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, p 1 represents the pressure after the valve, p 2 represents the reheated steam pressure, p 3 represents the intermediate-low pressure connecting pipe steam pressure, P e Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, T CH , T RH Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, T CO Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, F HP , F IP Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, F LP Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, l Kmax, Kmin represent the maximum and minimum values of the total governing valve opening, respectively, s represents the complex frequency variable in Laplace transform.

[0050] This model contains three first-order inertia elements, which represent the volume effect of the high-pressure cylinder, the reheater, and the intermediate-low pressure connecting pipe, respectively. The mathematical model of each element is: (28) (29) (30) The output power of the steam turbine is: (31) The flow characteristics of the turbine governing valve are nonlinear. To achieve linear and accurate control of the speed and power, the distribution function converts the total valve position command received into the opening command of each valve to compensate for the nonlinearity of the flow characteristics. In the design of the controller, the main steam flow is proportional to the total valve position command and the main steam pressure. The relationship between the flow, the valve opening, and the main steam pressure can be expressed by the following equation: (32) wherein, c v and k v The values are different under different working conditions, p c , n P represents the main steam pressure, Q represents the main steam flow.

[0051] The embodiment provides a primary frequency modulation dynamic modeling method of a concentrated solar power system based on a heat flow method. On the basis of a traditional thermal power classic primary frequency modulation model, the influence of thermal dynamic characteristics of a steam generation system of a concentrated solar power station on frequency response characteristics of a unit is considered, and a primary frequency modulation model of a concentrated solar power unit suitable for dynamic analysis of a power system is provided. By analyzing a flow heat exchange process of two fluid flows of high-temperature molten salt and steam-water working medium and phase change characteristics of the steam-water working medium, a dynamic model of the steam generation system is constructed based on the heat flow method. On this basis, a primary frequency modulation model of the concentrated solar power unit is constructed, which comprehensively considers dynamic coupling characteristics of a speed regulator, the steam generation system, and a steam turbine. The model balances simulation rapidity and model accuracy while characterizing primary frequency modulation characteristics of the concentrated solar power system, and has high adaptability in a dynamic simulation analysis scene of the power system.

[0052] The above only describes the embodiments of the present application, and the common knowledge of specific structures and characteristics in the scheme is not described in detail. The ordinary skilled person in the art knows all the common technical knowledge in the field of the present application before the application date or the priority date, can know all the prior art in the field, and has the ability to apply conventional experimental means before the date. The ordinary skilled person in the art can improve and implement the present scheme based on the disclosure given in the present application, and some typical known structures or known methods should not be an obstacle for the ordinary skilled person in the art to implement the present application. It should be noted that, for the skilled person in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be regarded as the protection scope of the present application, and these will not affect the effect and practicality of the patent.

Claims

1. A dynamic modeling method for primary frequency regulation of a concentrated solar power (CSP) system based on the heat flow method, characterized in that, include: The primary frequency regulation model of the solar thermal power generator unit is decomposed into multiple local models, including the governor model, the steam generation system model, and the turbine model; Among them, a dynamic model of the steam generation system is established based on the heat flow method. This includes constructing dynamic models of the heat exchange process of the steam-water working fluid and the high-temperature molten salt in the preheating section, superheating section and evaporation section of the steam generation system, as well as dynamic models of the steam-water working fluid and the high-temperature molten salt in the flow process.

2. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, For the preheating and superheating sections of the steam generation system, the steam-water working fluid and the high-temperature molten salt are modeled separately. The dynamic models for the heat exchange processes of the steam-water working fluid and the high-temperature molten salt in the preheating and superheating sections are the same, which is... In the formula, the subscript i Indicates the number of the heat exchange unit; , These represent the working fluids of the steam-water mixture and the high-temperature molten salt at the [missing information - likely a specific point or time period]. i The inlet temperature of each heat exchange unit; Indicates the first i The metal temperature of the tube wall of each heat exchange unit; t Indicates time; Δ t c,i Δ t h,i These represent the volume of steam-water working fluid and high-temperature molten salt per unit length flowing through the first... i The time delay of each heat exchange unit; ( kA ) c,i , ( kA) h,i These represent the corresponding first and second working fluids of the steam-water mixture and the high-temperature molten salt, respectively. i Thermal conductivity of each heat exchange unit; G c,i , G h,i They represent the first i The heat capacity flow of the steam-water working fluid and high-temperature molten salt in each heat exchange unit; R c,i Indicates the first i The thermal resistance between the steam-water working fluid and the metal tube wall within each heat exchange unit; R h,i Indicates the first i The thermal resistance of heat transfer between the high-temperature molten salt and the metal tube wall in each heat exchange unit; Indicates the first i The time constant during the dynamic heat transfer process of each heat exchange unit.

3. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, The dynamic model of the steam-water working fluid during the flow process is the same in both the preheating and superheating sections, as follows: In the formula, the subscript i Indicates the number of the heat exchange unit; , and These represent the first and second stages of the preheating process of the steam-water working medium. i Density, pressure, and mass flow rate in each heat exchange unit; This represents the cross-sectional area of ​​the pipe containing the carbonated liquid. The pipe resistance coefficient representing the working fluid of steam and water; Indicates the first i The length of each heat exchange unit.

4. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, The dynamic model of the high-temperature molten salt during the flow process is the same in both the preheating and superheating sections, as follows: In the formula, the subscript i Indicates the number of the heat exchange unit; , and These represent the first and second stages of the high-temperature molten salt in the steam generation system. i Density, pressure, and mass flow rate in each heat exchange unit; The cross-sectional area of ​​the pipe representing high-temperature molten salt; The pipe resistance coefficient representing high-temperature molten salt; Indicates the first i The length of each heat exchange unit.

5. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, For the evaporation section of the steam generation system, the steam-water working fluid is not modeled in segments; its dynamic characteristics are described using lumped parameters, and pressure losses along the flow path are ignored. The dynamic model of the steam-water working fluid in the evaporation section includes: In the formula, and These represent the volumes of saturated water and saturated steam, respectively. and These represent the densities of saturated water and saturated vapor, respectively. This indicates the pressure of the working fluid in the evaporation section; This represents the mass flow rate of saturated steam corresponding to the working pressure of the steam-water working medium in the evaporation section. Indicates specific enthalpy; This indicates the heat transfer from the pipe wall metal to the two-phase steam-water working fluid side; , All represent coefficients; This indicates the mass flow rate of saturated steam at the steam drum outlet. Indicates the metal wall temperature of the evaporation section; This indicates the saturation temperature of the steam-water working fluid in the evaporation section; R c,s This represents the ratio of the heat transfer temperature difference between the metal temperature of the evaporator tube wall and the temperature of the working fluid at the evaporator inlet to the amount of heat exchanged. γ This represents the latent heat of vaporization corresponding to the pressure of the steam-water working medium in the evaporation section.

6. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, For the evaporation section of the steam generation system, the high-temperature molten salt is modeled in segments, and distributed parameters are used to describe the dynamic characteristics of its heat transfer flow process. The dynamic model of the high-temperature molten salt in the evaporation section includes the dynamic model of the heat transfer process between the high-temperature molten salt and the tube wall metal in the heat transfer unit of the evaporation section: The dynamic model of high-temperature molten salt in the evaporation section during the flow process is the same as that of high-temperature molten salt in the preheating and superheating sections during the flow process. The dynamic model of the heat transfer process in the tube wall metal is as follows: In the formula, This indicates the outlet temperature of the high-temperature molten salt in the evaporation section; This indicates the inlet temperature of the high-temperature molten salt in the evaporation section; This indicates the temperature of the tube wall in the evaporation section of the evaporator; t Indicates time; This indicates the time delay of the high-temperature molten salt flowing through the phase transition section; k h,s This represents the heat transfer coefficient between the high-temperature molten salt in the evaporation section and the metal of the pipe wall. A h,s This indicates the heat exchange area between the high-temperature molten salt in the evaporation section and the metal of the tube wall. G h,s This indicates the heat capacity flow of the high-temperature molten salt in the evaporation section.

7. The method for dynamic modeling of primary frequency regulation in a concentrated solar power (CSP) system based on heat flow as described in claim 1, characterized in that, The boundary conditions and constraints that the dynamic model of the steam generation system must satisfy are as follows: In the formula, , , , These represent the pressure, temperature, mass flow rate, and density of the main steam, respectively. , These represent the cross-sectional area and length of the main steam pipe, respectively. , These represent the specific enthalpy and mass flow rate of the steam at the superheater outlet, respectively. , and These represent the steam pressure in the first heat exchange unit of the superheated section, and the steam temperature and mass flow rate at the inlet, respectively. , and These represent the pressure of the steam-water working fluid in the evaporation section, the corresponding saturation temperature, and the saturated steam density at that pressure, respectively. This represents the mass flow rate of saturated steam at the steam drum outlet; the variable subscript sh represents the thermodynamic parameters of the steam-water working fluid and the pipe wall metal in the superheated section; the variable subscripts m and m+1 represent the thermodynamic parameters of the m-th heat exchange unit in the preheating section and the thermodynamic parameters of the 1-th heat exchange unit in the steam section, respectively. N This indicates the total number of uniformly divided superheated sections; This represents the pipeline resistance coefficient of the steam-water working medium.

8. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, The speed controller model includes a regulating system model and an electro-hydraulic servo system model; The regulation system model establishes a mapping relationship between speed deviation, time constant of speed measurement link, complex frequency variable, speed deviation amplification factor, reciprocal of adjustment coefficient, and valve position command; The electro-hydraulic servo system model constructs the actuator of the control valve and its opening and closing time constants, stroke feedback loop time constant, pure delay time of the main valve opening output signal, overspeed opening and closing coefficients, PID coefficients, maximum and minimum values ​​of the main valve opening, actual value of the main valve opening, and mapping relationships between complex frequency variables.

9. The method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 1, characterized in that, The turbine model adopts a single reheater turbine model, which includes three first-order inertial elements to represent the volumetric effects of steam in the high-pressure cylinder front chamber, reheater, and intermediate-low-pressure connecting pipe, respectively. Based on this, the main steam flow rate, the pressure after the regulating valve, the reheat steam pressure, the intermediate-low-pressure connecting pipe steam pressure, the mechanical power output of the turbine rotor, the steam volumetric time constants of the high-pressure cylinder, reheater, and intermediate-low-pressure connecting pipe, the power distribution coefficients of the high, medium, and low-pressure cylinders, and the mapping relationship between the complex frequency variable and the high-pressure cylinder power natural overshoot coefficient are constructed.

10. A method for dynamic modeling of primary frequency regulation in a solar thermal power generation system based on the heat flow method according to claim 9, characterized in that, Establish a mapping relationship between the flow rate, valve opening, and main steam pressure of the turbine regulating valve: In the formula, Indicates the main steam flow rate. c v and k v The value varies under different operating conditions. p c , n This indicates the main steam pressure.

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