A method for evaluating primary frequency regulation capability of thermal power units in dynamic processes

Abstract

The present invention discloses a method for evaluating the primary frequency regulation capability of a thermal power unit in a dynamic process. First, a single decoupling model of a steam turbine is established, and its parameters are identified based on historical data. Then, the overall heat storage of the boiler is calculated based on the heat storage of the cold fluid working medium at the boiler outlet and the heat storage of the boiler metal, and a dynamic response process equation for the primary frequency regulation performance of the steam turbine is obtained. Finally, the heat storage increment is combined with the steam turbine model to obtain a prediction of the primary frequency regulation capability.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal power generation, and in particular relates to a method for evaluating the primary frequency regulation capability of a dynamic process thermal power unit. Background Art

[0002] Currently, under the dual carbon development goals and with the increasing proportion of renewable energy, the frequency stability of the power system is facing significant pressure and challenges. Providing primary frequency regulation will become one of the most important tasks of future thermal power plants. However, existing technologies do not fully understand the primary frequency regulation capabilities of thermal power units, making it difficult for dispatchers to arrange optimal operation, resulting in frequency security issues.

[0003] Current thermal power unit modeling approaches can be broadly divided into two categories. One approach involves identifying key state variables and then fitting external characteristics using dynamic operating data or test data. The other approach uses mechanism analysis to establish module models using mass conservation, momentum conservation, and energy conservation equations. Power system dynamic simulation software provides models with corresponding boiler modules, but these have rarely been used in previous frequency simulations. Simplified boiler models ignore the transient characteristics of the thermal system. Experiments have shown that pressure-controlled fuel combustion dynamics can compensate for steady-state differences, validating the model's accuracy over long timescales. However, the short timescale of primary frequency modulation does not allow fuel combustion dynamics to respond quickly. Boiler dynamics are related to the spontaneous physical properties of pressure, temperature, and flow. Models that ignore transient characteristics will introduce certain errors.

[0004] Existing thermal power unit models are mostly targeted at operational control and energy optimization. Simplified, general-purpose boiler models are suitable for medium- and long-term simulations, but they cannot meet the requirements of primary frequency regulation simulation for thermal power units. Furthermore, because the frequency regulation capability of a unit is dependent on its operating conditions, model parameters under different loads are not constant. Therefore, determining these model parameters for different operating conditions is challenging.

[0005] Purpose of the Invention

[0006] The purpose of the present invention is to solve the problems faced in the prior art. Starting from the key factors affecting the primary frequency regulation capability of thermal power units, by analyzing the thermal system characteristics of thermal power units, a dynamic process thermal power unit primary frequency regulation capability evaluation method is provided. Summary of the Invention

[0007] The present invention provides a method for evaluating the primary frequency regulation capability of a dynamic process thermal power unit, the method comprising the following steps:

[0008] Step 1: Establish a single decoupling model of the steam turbine and perform parameter identification on it based on historical data. The single decoupling model of the steam turbine is derived as shown in formula (1):

[0009]

[0010] In formula (1), ΔP g is the integrated valve position command increment, ΔP t Represents the mechanical power increment, F HP is the high pressure cylinder power coefficient, T RH is the reheater steam capacity coefficient, T SC is the volume coefficient of the high-pressure steam chamber, λ is the natural overshoot coefficient of the high-pressure cylinder power;

[0011] According to the gas continuity equation and the relationship between liquid water and gas water, the steam flow rate variation equation of the steam turbine single decoupling model is expressed as shown in formula (2):

[0012]

[0013] In formula (2), M is the total mass of steam in the steam chamber, V is the total volume of the steam chamber, ρ is the steam density, and m in and m out is the steam flow rate at the inlet and outlet, P is the steam pressure, and T represents the steam temperature in Kelvin;

[0014] Performing Laplace transform on equation (2) yields equation (3):

[0015]

[0016] In formula (3), T sv is the time constant of the steam chamber;

[0017] The power proportions of the high-pressure, medium-pressure, and low-pressure cylinders are estimated by approximating the decreasing enthalpy. The other undetermined coefficients are the power proportions of each part, expressed as shown in formula (4):

[0018]

[0019] In formula (4), m H 、m I 、m L Respectively represent the flow rate of high, medium and low pressure cylinders; h Hi 、h Ii 、h Li Represents the inlet steam enthalpy of high, medium and low pressure cylinders; h Ho 、h Io 、h Lo Represents the outlet steam enthalpy of high, medium and low pressure cylinders;

[0020] Where λ is calculated by formula (5):

[0021]

[0022] Where ε represents the intake and exhaust pressure ratio, and k is the adiabatic index of the process;

[0023] Step 2: Calculate the overall heat storage of the boiler based on the heat storage of the cold fluid at the outlet of the steam turbine boiler and the heat storage of the boiler metal. The working fluid in the superheater and reheater is a single-phase segment, and the medium volume increases with the increase of the primary frequency modulation dynamic response. The energy conversion value of the entire thermal change process is expressed as shown in formula (6):

[0024]

[0025] In formula (6), m0 and h0 represent the mass flow rate and enthalpy of the steam at the superheater inlet, Q1, Q2 and Q3 represent the heat exchange of the primary superheater, platen superheater and final superheater respectively;

[0026] According to the principle of mass conservation, the volume of the medium increment is expressed as shown in formula (7):

[0027]

[0028] In formula (7), m i 、v i represent the mass flow rate and specific volume of the i-th segment respectively;

[0029] The energy added by the working fluid expansion is expressed as shown in formula (8):

[0030]

[0031] In formula (8), Q4, Q5 and Q6 represent the metal heat storage of the primary superheater, platen superheater and final superheater respectively, ΔQ represents the input increment on the turbine side due to valve operation, ξ represents the thermal-electric conversion efficiency of the turbine, and N represents the current load of the thermal power unit;

[0032] The dynamic response process of the primary frequency regulation performance of the steam turbine is expressed as shown in formula (9):

[0033]

[0034] Where ΔE is the power increment during a frequency modulation process;

[0035] Step 3: Combine the heat storage increment with the steam turbine model to obtain a prediction of the primary frequency regulation capability. Specifically, ΔE is used as the steam turbine input, and the primary frequency regulation output curve of the steam turbine is obtained through the steam turbine single decoupling model.

[0036] Preferably, the speed control system of the thermal power unit consists of a controller, an actuator and a controlled object, and the controlled object is a steam turbine; the speed control system of the thermal power unit sends the measured speed deviation signal through a valve position action amplification circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a single decoupling model of a steam turbine constructed in a specific embodiment of the present invention.

[0038] Figure 2 It is the estimated primary frequency regulation capability under various working conditions. DETAILED DESCRIPTION

[0039] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0040] The present invention provides a method for evaluating the primary frequency regulation capability of a dynamic process thermal power unit, comprising the following steps:

[0041] Step 1: Establish a single decoupling model of the steam turbine and perform parameter identification based on historical data, as follows:

[0042] Field tests are an effective way to obtain relevant parameters of steam turbines. However, due to the complexity of field test conditions, the collected data will inevitably be inaccurate, causing the model to deviate from the actual situation, especially PFC data. The parameter calculation method based on mechanism analysis can effectively avoid this defect.

[0043] The speed control system of a thermal power unit mainly consists of a controller, an actuator, and a controlled object, the controlled object being the steam turbine. The speed control system of a thermal power unit sends the measured speed deviation signal through a valve position amplification circuit. Currently, the model of the speed control system is undisputed and can be expressed as 1 / (1+T g ), where T g is the inertia time constant of the actuator. The operating conditions of the thermal power unit have little effect on the speed control system and can be regarded as a constant model, but the time scale of the secondary frequency regulation is larger than that of the primary frequency regulation. Therefore, the response accuracy of the turbine is not of concern at the beginning of the dynamic response process. However, the primary frequency regulation is a short response process, and most of the time duration is usually less than 60 seconds. In the prior art, the response process characterization of the non-decoupled steam turbine model is not accurate at first. In an embodiment of the present invention, a natural overshoot coefficient of increasing λ at the high-pressure cylinder is used to increase the accuracy of the model. Figure 1 This is the single decoupling model of the steam turbine constructed in the specific implementation of the present invention. Figure 1 As shown in the single decoupling model of the steam turbine, the steam flow parameters at the connection between the intermediate pressure cylinder and the low pressure cylinder can be ignored. Therefore, the single decoupling model of the steam turbine is derived as shown in formula (1):

[0044]

[0045] Where, ΔP gis the integrated valve position command increment, ΔP t Represents the mechanical power increment, F HP is the high pressure cylinder power coefficient, T RH is the reheater steam capacity coefficient, T SC is the volume coefficient of the high-pressure steam chamber, and λ is the natural overshoot coefficient of the high-pressure cylinder power.

[0046] According to the gas continuity equation and the relationship between liquid water and gas water, the steam flow rate variation equation of the steam turbine single decoupling model is expressed as shown in formula (2):

[0047]

[0048] Where M is the total mass of steam in the steam chamber, V is the total volume of the steam chamber, ρ is the steam density, m in and m out is the steam flow rate at the inlet and outlet, P is the steam pressure, and T represents the steam temperature in Kelvin;

[0049] Performing Laplace transform on equation (2) yields equation (3):

[0050]

[0051] Where, T sv is the time constant of the steam chamber;

[0052] The power proportions of the high-pressure, medium-pressure, and low-pressure cylinders are estimated by approximating the decreasing enthalpy. The other undetermined coefficients are the power proportions of each part, expressed as shown in formula (4):

[0053]

[0054] Where m H 、m I 、m L Respectively represent the flow rate of high, medium and low pressure cylinders; h Hi 、h Ii 、h Li Represents the inlet steam enthalpy of high, medium and low pressure cylinders; h Ho 、h Io 、h Lo Represents the outlet steam enthalpy of high, medium and low pressure cylinders;

[0055] Where λ is calculated by formula (5):

[0056]

[0057] Where ε represents the intake and exhaust pressure ratio, and k is the adiabatic index of the process.

[0058] Step 2: Calculate the overall heat storage of the boiler based on the heat storage of the cold fluid at the boiler outlet and the heat storage of the boiler metal;

[0059] During the primary frequency response, the main steam pressure drops, and when the control valve opens, the flow rate into the turbine suddenly increases. Therefore, the entire thermal change is considered during the primary frequency response. The working fluid expands in volume, absorbing heat from metal bodies (such as superheater and reheater piping) when the valve opens. The increase in working fluid volume and the metal heat transferred to the fluid are considered the primary energy of the primary frequency response.

[0060] The working fluid in the superheater and reheater is a single-phase segment. The medium volume increases with the increase of the primary frequency modulation dynamic response. The energy conversion value of the entire thermal change process is expressed as shown in formula (6):

[0061]

[0062] Where m0 and h0 represent the mass flow rate and enthalpy of the steam at the superheater inlet; Q1, Q2 and Q3 represent the heat exchange rates of the primary superheater, platen superheater and final superheater respectively.

[0063] According to the principle of mass conservation, the volume of the medium increment is expressed as shown in formula (7):

[0064]

[0065] Where m i 、v i represent the mass flow rate and specific volume of the i-th segment respectively;

[0066] The energy added by the working fluid expansion is expressed as shown in formula (8):

[0067]

[0068] Where Q4, Q5, and Q6 represent the metal heat storage of the primary superheater, platen superheater, and final superheater, respectively; ΔQ represents the input increment on the turbine side due to valve operation; ξ represents the turbine thermal-electric conversion efficiency; and N represents the current load of the thermal power unit.

[0069] In addition, due to the slight changes in nominal load and main steam pressure during the primary frequency regulation response process, the changes in flue gas energy and unit efficiency are ignored.

[0070] Therefore, the dynamic response of the primary frequency regulation performance of the steam turbine is expressed as shown in formula (9):

[0071]

[0072] Where ΔE is the power increment during a frequency modulation process.

[0073] Step 3: Combine the heat storage increment with the steam turbine model to obtain the primary frequency regulation capability prediction. Specifically, ΔE is used as the steam turbine input, and the corresponding primary frequency regulation output curve is obtained through the above single decoupling model.

[0074] Figure 2 This diagram shows the estimated primary frequency regulation capabilities under various operating conditions, using the method described in this invention. As shown, the primary frequency regulation method described in this invention covers the primary frequency regulation capabilities under various operating conditions, which is of great significance for estimating frequency regulation capabilities under current conditions of wide-load operation and deep peak regulation of thermal power units.

Claims

1. A method for evaluating the primary frequency regulation capability of a dynamic process thermal power unit, characterized in that: The following steps are involved: Step 1: Establish a single decoupling model of the steam turbine and perform parameter identification on it based on historical data. The single decoupling model of the steam turbine is derived as shown in formula (1): In formula (1), ΔP g is the integrated valve position command increment, ΔP t Represents the mechanical power increment, F HP is the high pressure cylinder power coefficient, T RH is the reheater steam capacity coefficient, T SC is the volume coefficient of the high-pressure steam chamber, λ is the natural overshoot coefficient of the high-pressure cylinder power; According to the gas continuity equation and the relationship between liquid water and gas water, the steam flow rate variation equation of the steam turbine single decoupling model is expressed as shown in formula (2): In formula (2), M is the total mass of steam in the steam chamber, V is the total volume of the steam chamber, ρ is the steam density, and m in and m out is the steam flow rate at the inlet and outlet, P is the steam pressure, and T represents the steam temperature in Kelvin; Performing Laplace transform on equation (2) yields equation (3): In formula (3), T sv is the time constant of the steam chamber; The power proportions of the high-pressure, medium-pressure, and low-pressure cylinders are estimated by approximating the decreasing enthalpy. The other undetermined coefficients are the power proportions of each part, expressed as shown in formula (4): In formula (4), m H 、m I 、m L Respectively represent the flow rate of high, medium and low pressure cylinders; h Hi 、h Ii 、h Li Represents the inlet steam enthalpy of high, medium and low pressure cylinders; h Ho 、h Io 、h Lo Represents the outlet steam enthalpy of high, medium and low pressure cylinders; Where λ is calculated by formula (5): Where ε represents the intake and exhaust pressure ratio, and k is the adiabatic index of the process; Step 2: Calculate the overall heat storage of the boiler based on the heat storage of the cold fluid at the boiler outlet and the heat storage of the boiler metal. The working fluid in the superheater and reheater is a single-phase segment, and the medium volume increases with the increase of the primary frequency modulation dynamic response. The energy conversion value of the entire thermal change process is expressed as shown in formula (6): In formula (6), m0 and h0 represent the mass flow rate and enthalpy of the steam at the superheater inlet, Q1, Q2 and Q3 represent the heat exchange of the primary superheater, platen superheater and final superheater respectively; According to the principle of mass conservation, the volume of the medium increment is expressed as shown in formula (7): In formula (7), m i 、v i represent the mass flow rate and specific volume of the i-th segment respectively; The energy added by the working fluid expansion is expressed as shown in formula (8): In formula (8), Q4, Q5 and Q6 represent the metal heat storage of the primary superheater, platen superheater and final superheater respectively, ΔQ represents the input increment on the turbine side due to valve operation, ξ represents the thermal-electric conversion efficiency of the turbine, and N represents the current load of the thermal power unit; The dynamic response process of the primary frequency regulation performance of the steam turbine is expressed as shown in formula (9): Where ΔE is the power increment during a frequency modulation process; Step 3: Combine the heat storage increment with the steam turbine model to obtain a prediction of the primary frequency regulation capability. Specifically, ΔE is used as the steam turbine input, and the primary frequency regulation output curve of the steam turbine is obtained through the steam turbine single decoupling model.

2. The method for evaluating the primary frequency regulation capability of a dynamic process thermal power unit according to claim 1, characterized in that: The speed control system of the thermal power unit consists of a controller, an actuator and a controlled object, wherein the controlled object is a steam turbine; the speed control system of the thermal power unit sends the measured speed deviation signal through a valve position action amplification circuit.

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