Quantitative analysis method and system for frequency static stability of power system

Abstract

The invention discloses a quantitative analysis method for frequency static stability of a power system. The quantitative analysis method comprises the following steps: acquiring data information of a target power system; performing refined modeling on the thermal power generating unit in the target power system; dynamically analyzing the change trend of the unit load, the water supply quantity and the fuel quantity of the target power system; obtaining a system static power frequency characteristic curve of the target power system when the frequency deviation is greater than a set range; and performing quantitative analysis of frequency static stability on the target power system. The invention also discloses a system for realizing the quantitative analysis method for static stability of the frequency of the power system. According to the method, through fine modeling, variation trend analysis, system static power frequency characteristic curve calculation and corresponding analysis of the thermal power generating unit, quantitative analysis of static stability of the frequency of the power system is realized on the basis of considering physical, control and protection processes of a boiler water supply system of the thermal power generating unit, and the reliability is higher; and the accuracy is better.

Description

Technical Field

[0001] The invention belongs to the field of electrical automation, and in particular relates to a quantitative analysis method and system for static frequency stability of an electric power system. Background Art

[0002] With the development of economy and technology and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and life, bringing endless convenience to people's production and life. Therefore, ensuring the stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] The power system frequency is one of the important parameters in the monitoring, analysis and operation of the power system, which reflects the balance between the active power of the generator and the load. Maintaining the frequency within the allowable range is an important task for the safe and stable operation of the power system. At present, the construction of a high proportion of renewable energy grid connection and large-capacity DC transmission has changed the form of the power grid: the inertia of the power system has decreased, the controllability of the unit power generation has deteriorated, and the active power disturbance has increased, which has brought great challenges to the safety and stability of the power grid frequency.

[0004] At present, the existing static stability analysis scheme of power system frequency ignores the impact of physical processes and system control and protection actions on system frequency stability during the analysis process, such as the physical, control and protection processes of the boiler feed water system of thermal power units. This processing method of the existing scheme can indeed meet the analysis needs of the power system under most normal operating conditions. However, with the development of the power system, the existing static stability analysis scheme can no longer meet the growing safe and stable operation requirements of the power system. Summary of the invention

[0005] One of the purposes of the present invention is to provide a quantitative analysis method for static frequency stability of a power system with high reliability and good accuracy.

[0006] A second object of the present invention is to provide a system for implementing the quantitative analysis method of the static stability of the power system frequency.

[0007] The quantitative analysis method of the static stability of the power system frequency provided by the present invention comprises the following steps:

[0008] S1. Obtain data information of the target power system;

[0009] S2. Based on the data information obtained in step S1, a refined modeling of the thermal power units in the target power system is performed;

[0010] S3. According to the modeling results of step S2, dynamic analysis is performed on the changing trends of the unit load, water supply and fuel quantity of the target power system;

[0011] S4. According to the analysis results obtained in step S3, a static power frequency characteristic curve of the target power system is obtained when the frequency offset is greater than the set range;

[0012] S5. According to the system static power frequency characteristic curve obtained in step S4, a quantitative analysis of the static frequency stability of the target power system is performed.

[0013] The step S2 of performing refined modeling of the thermal power units in the target power system according to the data information obtained in the step S1 includes the following steps:

[0014] Based on the output and load balance relationship of the generator set, the generator rotor motion process is modeled;

[0015] Based on the operation process of the steam turbine, the operation status of the steam turbine is modeled;

[0016] Based on the relationship between boiler main steam pressure and turbine valve opening and turbine input, the boiler dynamic process is modeled;

[0017] Based on the frequency deviation and the throttle opening, the speed regulator state process is modeled;

[0018] The process of converting fuel combustion into heat energy in the boiler furnace is converted into the dynamic links of the coal mill and the water-cooled wall, and the fuel combustion process is modeled;

[0019] Based on the operating characteristics of the water supply system, the water supply flow state is modeled;

[0020] Model the boiler main steam pressure deviation PI controller.

[0021] The step S2 specifically includes the following steps:

[0022] Based on the output and load balance relationship of the generator set, the generator rotor motion process is modeled; it is expressed as

[0023]

[0024] In the formula is the derivative of the angular frequency deviation; P m is the mechanical power of the steam turbine; P L is the unit load; D is the unit damping coefficient; H is the generator inertia time constant;

[0025] Based on the operation process of the steam turbine, the operation state of the steam turbine is modeled: the steam turbine converts steam into mechanical power, the input is the main steam flow, which is determined by the turbine valve opening and the main steam pressure before the turbine, and the output is the mechanical power. The state equation is expressed as

[0026] Pm =F HP x1+F IP x2+F LP x3

[0027]

[0028] D te =k6P t C V

[0029] Where P m is the mechanical power; F HP is the work ratio of the high-pressure cylinder; x1 is the state variable of the steam chamber; F IP is the work ratio of the intermediate pressure cylinder; x2 is the state variable of the primary reheater; F LP is the work ratio of the low-pressure cylinder, and F HP +F IP +F LP =1; x3 is the state variable of the connecting pipeline link; is the first-order derivative of x1; D te is the main steam flow rate output by the boiler; T CH is the steam chamber time constant; T R is the reheat time constant; T CO is the time constant of the connecting pipeline link; k6 is the internal third constant for simulating the balance between mass and energy; P t is the main steam pressure of the boiler; C V Adjust the valve opening for the steam turbine;

[0030] Based on the relationship between the boiler main steam pressure and the turbine throttle opening and the turbine input, the boiler dynamic process is modeled: the input of the boiler model is the turbine throttle opening and the effective heat absorption released by the boiler furnace combustion, and the output variable is the main steam flow entering the turbine. The state equation of the boiler dynamic model is expressed as

[0031]

[0032] In the formula P t The first derivative of; k2 is the second heat storage coefficient of the boiler drum and steam pipe; k3 is the equivalent heat storage time constant; P b is the boiler drum pressure; k5 is the second internal constant simulating the balance between mass and energy; P b The first derivative of; k1 is the first heat storage coefficient of the boiler drum and steam pipe; k4 is the first internal constant simulating the balance between mass and energy; D q The effective heat released by combustion in the boiler furnace;

[0033] Based on the frequency deviation and the throttle opening, the speed regulator state process is modeled; the speed regulator senses the frequency change, the input variables are the frequency deviation and the control system command, and the output variable is the throttle opening. The speed regulator state equation is expressed as

[0034] C V =x4

[0035]

[0036] ΔC V =K5ΔP t

[0037] Where C V is the valve opening; x4 is the speed regulator state variable; is the first derivative of x4; Δω is the frequency deviation; K3 is the proportional magnification factor; C V0 is the initial valve opening; ΔC V T is the control instruction for the change of the valve opening; SR is the time constant of the speed relay; K5 is the proportional coefficient; ΔP t Main steam pressure deviation;

[0038] The process of converting fuel combustion into heat energy in the boiler furnace is converted into the dynamic links of the coal mill and the water-cooled wall, and the fuel combustion process is modeled; it is expressed as

[0039]

[0040] Where D q is the effective heat released by the combustion in the boiler furnace; T2 is the inertia time constant of the dynamic link of the water-cooled wall; x6 is the state variable of the dynamic response link of the water-cooled wall; is the first derivative of x6; T1 is the inertia time constant of the dynamic link of the coal mill; x5 is the state variable of the dynamic response link of the coal mill; is the first derivative of x5; B0 is the initial fuel amount; ΔB is the fuel change;

[0041] Based on the operating characteristics of the water supply system, the water supply flow state is modeled: at the rated frequency, different water supply flows are adjusted by changing the water pipe resistance of the water supply system, which is expressed as

[0042]

[0043] Where Q is the water flow rate of the water supply system; K1 is the calculation coefficient determined by the unit structure and size; R is the water pipe resistance; ω is the system angular frequency; ω st is the critical angular frequency of the water supply system; f is the system frequency; f stis the critical frequency of the water supply system; after ω and f are normalized, there exists Δω*=Δf*, Δω* is the normalized value of the angular frequency deviation, and Δf* is the normalized value of the frequency deviation;

[0044] When the frequency deviation is greater than the set range, the water supply system output reaches the maximum value due to the power-frequency characteristic constraint; at this time, according to the mathematical relationship between the maximum water supply flow and the fuel amount, the state equation of x5 is converted to

[0045]

[0046] Where B m is the maximum value of auxiliary engine fuel output; a is the first fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; b is the second fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; Δf * is the frequency deviation;

[0047] The boiler main steam pressure deviation PI controller is modeled as follows:

[0048]

[0049] In the formula is the first derivative of the state variable x7 of the boiler main steam pressure PI controller; P t0 is the rated value of the boiler main steam pressure; K4 is the integral constant of the PI controller.

[0050] Step S3, based on the modeling result of step S2, dynamically analyzes the changing trends of the unit load, water supply and fuel quantity of the target power system, and specifically includes the following steps:

[0051] The auxiliary machine senses the frequency change and adjusts the feed water flow and fuel quantity to maintain the main steam pressure of the boiler. The actual fuel quantity is related to the unit active power instruction and the system frequency deviation. The calculated fuel quantity is used as the constraint condition for the input of the coal mill dynamic model. It is expressed as

[0052] B m =(a·Q m +b) / c

[0053] Where c is the nominal value of fuel quantity; Q m is the maximum water flow rate at the corresponding frequency, and the formula is Solved to get;

[0054] If the water supply system is equipped with a frequency converter, the maximum water supply flow rate Q at the corresponding frequency is m Represented as Q m =αQ+(1-α)Q0; α is the proportion of water supply system without inverter; Q0 is the rated water supply flow when the water supply system is equipped with inverter, and the formula is Solve at rated frequency.

[0055] The step S4, according to the analysis result obtained in step S3, obtains the system static power frequency characteristic curve of the target power system when the frequency deviation is greater than the set range, specifically including the following steps:

[0056] The unit output is subject to the maximum output of the auxiliary machine, expressed as

[0057] When the unit output is not constrained by the auxiliary machine output, the expression of unit output-frequency is:

[0058] P m =P0+K G Δf *

[0059] Where P0 is the initial load; K G is the power-frequency characteristic adjustment coefficient of the unit;

[0060] When the initial load P0 is greater than the set value, as the frequency decreases, the unit output reaches the maximum value; if the unit output is not restricted by the auxiliary machine output at this time, then P m =P0+K G Δf * P m =1, the unit output is not constrained by the auxiliary machine output and the unit output P m =1, the corresponding frequency value f1 is At this time, when the frequency is less than f1, the unit output is always maintained at the maximum value 1;

[0061] When the system static power frequency characteristic curve intersects the auxiliary machine output constraint curve at the right side of the inflection point, P m =1, and the frequency value f2 corresponding to the auxiliary machine output being 1 on the auxiliary machine output constraint curve is obtained as follows: α is the proportion of water supply systems not equipped with frequency converters;

[0062] When the system static power frequency characteristic curve intersects the auxiliary machine output constraint curve at the right side of the inflection point, and the unit output has not reached the maximum value 1, then the combined and P m =P0+K G Δf * , and we get the following formula:

[0063]

[0064] Where m1 is the first intermediate variable, and m1 = cP0-cK G -b-(1-α)Q0; m2 is the second intermediate variable, and m3 is the third intermediate variable, and m4 is the fourth intermediate variable, and

[0065] Formula By solving the problem, we can obtain the frequency f3 at the intersection of the unit output-frequency curve and the auxiliary machine output constraint curve when the unit output is not constrained by the auxiliary machine output.

[0066] The step S5 performs a quantitative analysis of the static frequency stability of the target power system according to the system static power frequency characteristic curve obtained in step S4, and specifically includes the following steps:

[0067] When f1≥f2, the unit output reaches the maximum value and is not restricted by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f2, and f2=f3; at this time, there is

[0068]

[0069] When f1<f2, the unit output has not reached the maximum value and is limited by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f3; at this time, there is

[0070]

[0071] The system frequency static stability margin index η is calculated using the following formula:

[0072]

[0073] Where f N is the rated frequency of the system; f R is the first frequency, and its value is f1; f G is the second frequency, and the value selection rule is: if f1≥f2, then f G =f2, if f1<f2 then f G =f3;

[0074] According to the obtained system frequency static stability margin index η, the frequency static stability analysis of the target power system is carried out:

[0075] If η≥0, the system frequency static stability is determined to be qualified;

[0076] If η<0, the system frequency static stability is judged to be unqualified.

[0077] The present invention also provides a system for implementing the quantitative analysis method of the static stability of the power system frequency, comprising a data acquisition module, a fine modeling module, a dynamic analysis module, a curve calculation module and a quantitative analysis module; the data acquisition module, the fine modeling module, the dynamic analysis module, the curve calculation module and the quantitative analysis module are connected in series in sequence; the data acquisition module is used to acquire data information of the target power system, and upload the data information to the fine modeling module; the fine modeling module is used to perform fine modeling of the thermal power units in the target power system according to the received data information and the acquired data information, and upload the data information to the dynamic analysis module; the dynamic analysis module is used to perform dynamic analysis on the changing trends of the unit load, water supply and fuel amount of the target power system according to the received data information and the modeling results, and upload the data information to the curve calculation module; the curve calculation module is used to obtain the system static power frequency characteristic curve of the target power system when the frequency offset is greater than the set range according to the received data information and the obtained analysis results, and upload the data information to the quantitative analysis module; the quantitative analysis module is used to perform quantitative analysis on the static stability of the frequency of the target power system according to the received data information and the obtained system static power frequency characteristic curve.

[0078] The quantitative analysis method and system for the static stability of the frequency of a power system provided by the present invention, through refined modeling of thermal power units, analysis of change trends, calculation and corresponding analysis of the static power frequency characteristic curve of the system, not only realizes the quantitative analysis of the static stability of the frequency of the power system on the basis of considering the physical, control and protection processes of the boiler feed water system of the thermal power units, but also has higher reliability and better accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 The figure is a schematic diagram of the method flow of the present invention.

[0080] Figure 2 It is a schematic diagram of the static power frequency characteristic curve of the system when the frequency is offset over a large range in the method of the present invention.

[0081] Figure 3 Schematic diagram of system static power frequency characteristic curves for two scenarios in the quantitative analysis of the method of the present invention.

[0082] Figure 4 Schematic diagram of the functional modules of the system of the present invention. DETAILED DESCRIPTION

[0083] like Figure 1 The method flow chart of the method of the present invention is shown as follows: The quantitative analysis method of the static stability of the frequency of the power system disclosed in the present invention comprises the following steps:

[0084] S1. Obtain data information of the target power system;

[0085] S2. Based on the data information obtained in step S1, a refined modeling of the thermal power units in the target power system is performed; the steps include:

[0086] Based on the output and load balance relationship of the generator set, the generator rotor motion process is modeled; it is expressed as

[0087]

[0088] In the formula is the derivative of the angular frequency deviation; P m is the mechanical power of the steam turbine; P L is the unit load; D is the unit damping coefficient; H is the generator inertia time constant;

[0089] Based on the operation process of the steam turbine, the operation state of the steam turbine is modeled: the steam turbine converts steam into mechanical power, the input is the main steam flow, which is determined by the turbine valve opening and the main steam pressure before the turbine, and the output is the mechanical power. The state equation is expressed as

[0090] P m =F HP x1+F IP x2+F LP x3

[0091]

[0092]

[0093] D te =k6P t C V

[0094] Where P m is the mechanical power; F HP is the work ratio of the high-pressure cylinder; x1 is the state variable of the steam chamber; F IP is the work ratio of the intermediate pressure cylinder; x2 is the state variable of the primary reheater; F LP is the work ratio of the low-pressure cylinder, and F HP +F IP +F LP =1; x3 is the state variable of the connecting pipeline link; is the first-order derivative of x1; D te is the main steam flow rate output by the boiler; T CH is the steam chamber time constant; T R is the reheat time constant; T CO is the time constant of the connecting pipeline link; k6 is the internal third constant for simulating the balance between mass and energy; P tis the main steam pressure of the boiler; C V Adjust the valve opening for the steam turbine;

[0095] Based on the relationship between the boiler main steam pressure and the turbine throttle opening and the turbine input, the boiler dynamic process is modeled: the input of the boiler model is the turbine throttle opening and the effective heat absorption released by the boiler furnace combustion, and the output variable is the main steam flow entering the turbine. The state equation of the boiler dynamic model is expressed as

[0096]

[0097] In the formula P t The first derivative of; k2 is the second heat storage coefficient of the boiler drum and steam pipe; k3 is the equivalent heat storage time constant; P b is the boiler drum pressure; k5 is the second internal constant simulating the balance between mass and energy; P b The first derivative of; k1 is the first heat storage coefficient of the boiler drum and steam pipe; k4 is the first internal constant simulating the balance between mass and energy; D q The effective heat released by combustion in the boiler furnace;

[0098] Based on the frequency deviation and the throttle opening, the speed regulator state process is modeled; the speed regulator senses the frequency change, the input variables are the frequency deviation and the control system command, and the output variable is the throttle opening. The speed regulator state equation is expressed as

[0099] C V =x4

[0100]

[0101] ΔC V =K5ΔP t

[0102] Where C V is the valve opening; x4 is the speed regulator state variable; is the first derivative of x4; Δω is the frequency deviation; K3 is the proportional magnification factor; C V0 is the initial valve opening; ΔC V T is the control instruction for the change of the valve opening; SR is the time constant of the speed relay; K5 is the proportional coefficient; ΔP t Main steam pressure deviation;

[0103] The process of converting fuel combustion into heat energy in the boiler furnace is converted into the dynamic links of the coal mill and the water-cooled wall, and the fuel combustion process is modeled; it is expressed as

[0104]

[0105] Where D q is the effective heat released by the combustion in the boiler furnace; T2 is the inertia time constant of the dynamic link of the water-cooled wall; x6 is the state variable of the dynamic response link of the water-cooled wall; is the first derivative of x6; T1 is the inertia time constant of the dynamic link of the coal mill; x5 is the state variable of the dynamic response link of the coal mill; is the first derivative of x5; B0 is the initial fuel amount; ΔB is the fuel change;

[0106] Based on the operating characteristics of the water supply system, the water supply flow state is modeled: at the rated frequency, different water supply flows are adjusted by changing the water pipe resistance of the water supply system, which is expressed as

[0107]

[0108] Where Q is the water flow rate of the water supply system; K1 is the calculation coefficient determined by the unit structure and size; R is the water pipe resistance; ω is the system angular frequency; ω st is the critical angular frequency of the water supply system; f is the system frequency; f st is the critical frequency of the water supply system; after ω and f are normalized, there exists Δω*=Δf*, Δω* is the normalized value of the angular frequency deviation, and Δf* is the normalized value of the frequency deviation;

[0109] When the frequency deviation is greater than the set range, the water supply system output reaches the maximum value due to the power-frequency characteristic constraint; at this time, according to the mathematical relationship between the maximum water supply flow and the fuel amount, the state equation of x5 is converted to

[0110]

[0111] Where B m is the maximum value of auxiliary engine fuel output; a is the first fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; b is the second fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; Δf * is the frequency deviation;

[0112] The boiler main steam pressure deviation PI controller is modeled as follows:

[0113]

[0114] In the formula is the first derivative of the state variable x7 of the boiler main steam pressure PI controller; P t0 is the rated value of the boiler main steam pressure; K4 is the integral constant of the PI controller

[0115] S3. According to the modeling results of step S2, a dynamic analysis is performed on the changing trends of the unit load, water supply and fuel quantity of the target power system; specifically, the steps include:

[0116] The auxiliary machine senses the frequency change and adjusts the feed water flow and fuel quantity to maintain the main steam pressure of the boiler. The actual fuel quantity is related to the unit active power instruction and the system frequency deviation. The calculated fuel quantity is used as the constraint condition for the input of the coal mill dynamic model. It is expressed as

[0117] B m =(a·Q m +b) / c

[0118] Where c is the nominal value of fuel quantity; Q m is the maximum water flow rate at the corresponding frequency, and the formula is Solved to get;

[0119] If the water supply system is equipped with a frequency converter, the maximum water supply flow rate Q at the corresponding frequency is m Represented as Q m =αQ+(1-α)Q0; α is the proportion of water supply system without inverter; Q0 is the rated water supply flow when the water supply system is equipped with inverter, and the formula is Solving at rated frequency yields:

[0120] S4. According to the analysis result obtained in step S3, a static power frequency characteristic curve of the target power system is obtained when the frequency deviation is greater than the set range; specifically comprising the following steps:

[0121] The analysis result obtained in step S3 is a system static power frequency characteristic curve of the target power system when the frequency deviation is greater than the set range, such as Figure 2 As shown;

[0122] The unit output is subject to the maximum output of the auxiliary machine, expressed as When it comes to specific implementation,

[0123] When the unit output is not constrained by the auxiliary machine output, the expression of unit output-frequency is:

[0124] P m =P0+K G Δf *

[0125] Where P0 is the initial load; K G is the power-frequency characteristic adjustment coefficient of the unit;

[0126] When the initial load P0 is greater than the set value, as the frequency decreases, the unit output reaches the maximum value; if the unit output is not restricted by the auxiliary machine output at this time, then P m=P0+K G Δf * P m =1, the unit output is not constrained by the auxiliary machine output and the unit output P m =1, the corresponding frequency value f1 is At this time, when the frequency is less than f1, the unit output is always maintained at the maximum value 1;

[0127] When the system static power frequency characteristic curve is at the inflection point ( Figure 2 When the right curve corresponding to point G intersects with the auxiliary machine output constraint curve, P m =1, and the frequency value f2 corresponding to the auxiliary machine output being 1 on the auxiliary machine output constraint curve is obtained as follows: α is the proportion of water supply systems not equipped with frequency converters;

[0128] When the system static power frequency characteristic curve intersects the auxiliary machine output constraint curve at the right side of the inflection point, and the unit output has not reached the maximum value 1, then the combined and P m =P0+K G Δf * , and we get the following formula:

[0129]

[0130] Where m1 is the first intermediate variable, and m1 = cP0-cK G -b-(1-α)Q0; m2 is the second intermediate variable, and m3 is the third intermediate variable, and m4 is the fourth intermediate variable, and

[0131] Formula Solve to obtain the frequency f3 at the intersection of the unit output-frequency curve and the auxiliary machine output constraint curve when the unit output is not constrained by the auxiliary machine output;

[0132] S5. According to the system static power frequency characteristic curve obtained in step S4, a quantitative analysis of the static frequency stability of the target power system is performed; specifically comprising the following steps:

[0133] like Figure 3 As shown:

[0134] When f1≥f2, the unit output reaches the maximum value and is not restricted by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f2, and f2=f3; at this time, there is

[0135]

[0136] When f1<f2, the unit output has not reached the maximum value and is limited by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f3; at this time, there is

[0137]

[0138] The system frequency static stability margin index η is calculated using the following formula:

[0139]

[0140] Where f N is the rated frequency of the system; f R is the first frequency, and its value is f1; f G is the second frequency, and the value selection rule is: if f1≥f2, then f G =f2, if f1<f2 then f G =f3;

[0141] According to the obtained system frequency static stability margin index η, the frequency static stability analysis of the target power system is carried out:

[0142] If η≥0, the system frequency static stability is judged to be qualified, indicating that the unit has a strong ability to increase output power and can better support the system transient frequency response process;

[0143] If η<0, the system frequency static stability is judged to be unqualified, indicating that the system frequency static stability is poor and the unit's ability to increase output power is weak.

[0144] In the solution of the present invention, the inflection point is defined as: the frequency value corresponding to the intersection of the static power-frequency characteristic curves of the unit output not constrained by the auxiliary machine output and the unit output constrained by the auxiliary machine output.

[0145] The method of the present invention is further described below in conjunction with an embodiment:

[0146] Considering a power system as a single-machine system, the typical parameters of the system are shown in Table 1:

[0147] Table 1 Typical system parameters

[0148] parameter Parameter Value parameter Parameter Value parameter Parameter Value <![CDATA[k1]]> 0.0111 H 4 <![CDATA[T SR ]]> 0.1 <![CDATA[k2]]> 3.5 <![CDATA[F HP ]]> 0.328 <![CDATA[T1]]> 5 <![CDATA[k3]]> 0.2 <![CDATA[T CH ]]> 0.297 <![CDATA[T2]]> 30 <![CDATA[k4]]> 4.167 <![CDATA[F IP ]]> 0.266 <![CDATA[K4]]> 1 / 2200 <![CDATA[k5]]> 0.2381 <![CDATA[T R ]]> 12.213 <![CDATA[K1 / R]]> 26.837 <![CDATA[k6]]> 0.0571 <![CDATA[F LP ]]> 0.406 a 0.1549 D 1 <![CDATA[T CO ]]> 0.0974 b 15.195 <![CDATA[P t0 ]]> 17.5 <![CDATA[K3]]> 25 c 150 α 0.2 <![CDATA[K G ]]> -20

[0149] Let the inflection frequency be f G The frequency at which the output value of the power-frequency characteristic curve reaches 1 on the right side of the inflection point is f R The static frequency stability characteristics of the system under different initial loads are shown in Table 2:

[0150] Table 2 Schematic diagram of static frequency stability evaluation results under different initial loads P0

[0151]

[0152] It can be seen from the results in Table 2 that when the initial load of the system is low, the static stability characteristics of the system are better, and the better the static stability characteristics are, the greater the disturbance the system can withstand during the transient process, that is, the better it can support the transient frequency response process of the system.

[0153] The present invention also provides a system for implementing the quantitative analysis method of the static stability of the power system frequency, comprising a data acquisition module, a fine modeling module, a dynamic analysis module, a curve calculation module and a quantitative analysis module; the data acquisition module, the fine modeling module, the dynamic analysis module, the curve calculation module and the quantitative analysis module are connected in series in sequence; the data acquisition module is used to acquire data information of the target power system, and upload the data information to the fine modeling module; the fine modeling module is used to perform fine modeling of the thermal power units in the target power system according to the received data information and the acquired data information, and upload the data information to the dynamic analysis module; the dynamic analysis module is used to perform dynamic analysis on the changing trends of the unit load, water supply and fuel amount of the target power system according to the received data information and the modeling results, and upload the data information to the curve calculation module; the curve calculation module is used to obtain the system static power frequency characteristic curve of the target power system when the frequency offset is greater than the set range according to the received data information and the obtained analysis results, and upload the data information to the quantitative analysis module; the quantitative analysis module is used to perform quantitative analysis on the static stability of the frequency of the target power system according to the received data information and the obtained system static power frequency characteristic curve.

[0154] The scheme of the present invention is based on the static power-frequency characteristics of the unit in a wide range of frequency offsets of the active-frequency response expansion model, takes into account the boiler thermal effect and the configuration of the frequency converter of the water supply system, and proposes a solution method for the correspondence between the power balance point and the inflection point of the characteristic curve of the static power-frequency characteristic curve of the unit / load in a wide range of frequency changes; then, the formulated static frequency stability quantitative margin index is used to give a quantitative analysis result of the frequency stability, which not only realizes the quantitative analysis of the static stability of the power system frequency on the basis of considering the physical, control and protection processes of the boiler water supply system of the thermal power unit, but also has higher reliability and better accuracy.

Claims

1. A quantitative analysis method for static frequency stability of a power system, comprising the following steps: S1. Obtain data information of the target power system; S2. Based on the data information obtained in step S1, a refined modeling of the thermal power units in the target power system is performed; S3. According to the modeling results of step S2, dynamic analysis is performed on the changing trends of the unit load, water supply and fuel quantity of the target power system; S4. According to the analysis results obtained in step S3, a static power frequency characteristic curve of the target power system is obtained when the frequency offset is greater than the set range; S5. According to the system static power frequency characteristic curve obtained in step S4, a quantitative analysis of the static frequency stability of the target power system is performed.

2. The quantitative analysis method for static frequency stability of a power system according to claim 1 is characterized in that The step S2 of performing refined modeling of the thermal power units in the target power system according to the data information obtained in the step S1 includes the following steps: Based on the output and load balance relationship of the generator set, the generator rotor motion process is modeled; Based on the operation process of the steam turbine, the operation status of the steam turbine is modeled; Based on the relationship between boiler main steam pressure and turbine valve opening and turbine input, the boiler dynamic process is modeled; Based on the frequency deviation and the throttle opening, the speed regulator state process is modeled; The process of converting fuel combustion into heat energy in the boiler furnace is converted into the dynamic links of the coal mill and the water-cooled wall, and the fuel combustion process is modeled; Based on the operating characteristics of the water supply system, the water supply flow state is modeled; Model the boiler main steam pressure deviation PI controller.

3. The quantitative analysis method for static frequency stability of a power system according to claim 2 is characterized in that The step S2 specifically includes the following steps: Based on the output and load balance relationship of the generator set, the generator rotor motion process is modeled; it is expressed as In the formula is the derivative of the angular frequency deviation; P m is the mechanical power of the steam turbine; P L is the unit load; D is the unit damping coefficient; H is the generator inertia time constant; Based on the operation process of the steam turbine, the operation state of the steam turbine is modeled: the steam turbine converts steam into mechanical power, the input is the main steam flow, which is determined by the turbine valve opening and the main steam pressure before the turbine, and the output is the mechanical power. The state equation is expressed as P m =F HP x1+F IP x2+F LP x3 D te =k6P t C V Where P m is the mechanical power; F HP is the work ratio of the high-pressure cylinder; x1 is the state variable of the steam chamber; F IP is the work ratio of the intermediate pressure cylinder; x2 is the state variable of the primary reheater; F LP is the work ratio of the low-pressure cylinder, and F HP +F IP +F LP =1; x3 is the state variable of the connecting pipeline link; is the first-order derivative of x1; D te is the main steam flow rate output by the boiler; T CH is the steam chamber time constant; T R is the reheat time constant; T CO is the time constant of the connecting pipeline link; k6 is the internal third constant for simulating the balance between mass and energy; P t is the main steam pressure of the boiler; C V Adjust the valve opening for the steam turbine; Based on the relationship between the boiler main steam pressure and the turbine throttle opening and the turbine input, the boiler dynamic process is modeled: the input of the boiler model is the turbine throttle opening and the effective heat absorption released by the boiler furnace combustion, and the output variable is the main steam flow entering the turbine. The state equation of the boiler dynamic model is expressed as In the formula P t The first derivative of; k2 is the second heat storage coefficient of the boiler drum and steam pipe; k3 is the equivalent heat storage time constant; P b is the boiler drum pressure; k5 is the second internal constant simulating the balance between mass and energy; P b The first derivative of; k1 is the first heat storage coefficient of the boiler drum and steam pipe; k4 is the first internal constant simulating the balance between mass and energy; D q The effective heat released by combustion in the boiler furnace; Based on the frequency deviation and the throttle opening, the speed regulator state process is modeled; the speed regulator senses the frequency change, the input variables are the frequency deviation and the control system command, and the output variable is the throttle opening. The speed regulator state equation is expressed as C V =x4 ΔC V =K5ΔP t Where C V is the valve opening; x4 is the speed regulator state variable; is the first derivative of x4; Δω is the frequency deviation; K3 is the proportional magnification factor; C V0 is the initial valve opening; ΔC V T is the control instruction for the change of the valve opening; SR is the time constant of the speed relay; K5 is the proportional coefficient; ΔP t Main steam pressure deviation; The process of converting fuel combustion into heat energy in the boiler furnace is converted into the dynamic links of the coal mill and the water-cooled wall, and the fuel combustion process is modeled; it is expressed as Where D q is the effective heat released by the combustion in the boiler furnace; T2 is the inertia time constant of the dynamic link of the water-cooled wall; x6 is the state variable of the dynamic response link of the water-cooled wall; is the first derivative of x6; T1 is the inertia time constant of the dynamic link of the coal mill; x5 is the state variable of the dynamic response link of the coal mill; is the first derivative of x5; B0 is the initial fuel amount; ΔB is the fuel change; Based on the operating characteristics of the water supply system, the water supply flow state is modeled: at the rated frequency, different water supply flows are adjusted by changing the water pipe resistance of the water supply system, which is expressed as Where Q is the water flow rate of the water supply system; K1 is the calculation coefficient determined by the unit structure and size; R is the water pipe resistance; ω is the system angular frequency; ω st is the critical angular frequency of the water supply system; f is the system frequency; f st is the critical frequency of the water supply system; after ω and f are normalized, there exists Δω*=Δf*, Δω* is the normalized value of the angular frequency deviation, and Δf* is the normalized value of the frequency deviation; When the frequency deviation is greater than the set range, the water supply system output reaches the maximum value due to the power-frequency characteristic constraint; at this time, according to the mathematical relationship between the maximum water supply flow and the fuel amount, the state equation of x5 is converted to Where B m is the maximum value of auxiliary engine fuel output; a is the first fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; b is the second fitting coefficient of the mathematical relationship between the actual feed water flow and the fuel amount; Δf * is the frequency deviation; The boiler main steam pressure deviation PI controller is modeled as follows: In the formula is the first derivative of the state variable x7 of the boiler main steam pressure PI controller; P t0 is the rated value of the boiler main steam pressure; K4 is the integral constant of the PI controller.

4. The quantitative analysis method for static frequency stability of a power system according to claim 3 is characterized in that Step S3, based on the modeling result of step S2, dynamically analyzes the changing trends of the unit load, water supply and fuel quantity of the target power system, and specifically includes the following steps: The auxiliary machine senses the frequency change and adjusts the feed water flow and fuel quantity to maintain the main steam pressure of the boiler. The actual fuel quantity is related to the unit active power instruction and the system frequency deviation. The calculated fuel quantity is used as the constraint condition for the input of the coal mill dynamic model. It is expressed as B m =(a·Q m +b) / c Where c is the nominal value of fuel quantity; Q m is the maximum water flow rate at the corresponding frequency, and the formula is Solved to get; If the water supply system is equipped with a frequency converter, the maximum water supply flow rate Q at the corresponding frequency is m Represented as Q m =αQ+(1-α)Q0; α is the proportion of water supply system without frequency converter; Q0 is the rated water flow rate when the water supply system is equipped with a frequency converter, and the formula is Solve at rated frequency.

5. The quantitative analysis method for static frequency stability of a power system according to claim 4 is characterized in that The step S4, according to the analysis result obtained in step S3, obtains the system static power frequency characteristic curve of the target power system when the frequency deviation is greater than the set range, specifically including the following steps: The unit output is subject to the maximum output of the auxiliary machine, expressed as When the unit output is not constrained by the auxiliary machine output, the expression of unit output-frequency is: P m =P0+K G Δf * Where P0 is the initial load; K G is the power-frequency characteristic adjustment coefficient of the unit; When the initial load P0 is greater than the set value, as the frequency decreases, the unit output reaches the maximum value; if the unit output is not restricted by the auxiliary machine output at this time, then P m =P0+K G Δf * P m =1, the unit output is not constrained by the auxiliary machine output and the unit output P m =1, the corresponding frequency value f1 is At this time, when the frequency is less than f1, the unit output is always maintained at the maximum value 1; When the system static power frequency characteristic curve intersects the auxiliary machine output constraint curve at the right side of the inflection point, P m =1, and the frequency value f2 corresponding to the auxiliary machine output being 1 on the auxiliary machine output constraint curve is obtained as follows: α is the proportion of water supply systems not equipped with frequency converters; When the system static power frequency characteristic curve intersects the auxiliary machine output constraint curve at the right side of the inflection point, and the unit output has not reached the maximum value 1, then the combined and P m =P0+K G Δf * , and we get the following formula: Where m1 is the first intermediate variable, and m1 = cP0-cK G -b-(1-α)Q0; m2 is the second intermediate variable, and m3 is the third intermediate variable, and m4 is the fourth intermediate variable, and Formula By solving the problem, we can obtain the frequency f3 at the intersection of the unit output-frequency curve and the auxiliary machine output constraint curve when the unit output is not constrained by the auxiliary machine output.

6. The quantitative analysis method for static frequency stability of a power system according to claim 5 is characterized in that The step S5 performs a quantitative analysis of the static frequency stability of the target power system according to the system static power frequency characteristic curve obtained in step S4, and specifically includes the following steps: When f1≥f2, the unit output reaches the maximum value and is not restricted by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f2, and f2=f3; at this time, there is When f1<f2, the unit output has not reached the maximum value and is limited by the auxiliary machine output. The frequency of the inflection point of the system static power frequency characteristic curve is f3; at this time, there is The system frequency static stability margin index η is calculated using the following formula: Where f N is the rated frequency of the system; f R is the first frequency, and its value is f1; f G is the second frequency, and the value selection rule is: if f1≥f2, then f G =f2, if f1<f2 then f G =f3; According to the obtained system frequency static stability margin index η, the frequency static stability analysis of the target power system is carried out: If η≥0, the system frequency static stability is determined to be qualified; If η<0, the system frequency static stability is judged to be unqualified.

7. A system for implementing the quantitative analysis method of the static frequency stability of a power system according to any one of claims 1 to 6, characterized in that It includes a data acquisition module, a fine modeling module, a dynamic analysis module, a curve calculation module and a quantitative analysis module; the data acquisition module, the fine modeling module, the dynamic analysis module, the curve calculation module and the quantitative analysis module are connected in series in sequence; the data acquisition module is used to acquire data information of the target power system and upload the data information to the fine modeling module; The fine modeling module is used to carry out fine modeling of the thermal power units in the target power system according to the received data information and upload the data information to the dynamic analysis module; The dynamic analysis module is used to dynamically analyze the changing trends of the unit load, water supply and fuel quantity of the target power system according to the received data information and the modeling results, and upload the data information to the curve calculation module; The curve calculation module is used to obtain the system static power frequency characteristic curve of the target power system when the frequency deviation is greater than the set range according to the received data information and the obtained analysis results, and upload the data information to the quantitative analysis module; The quantitative analysis module is used to perform a quantitative analysis of the static frequency stability of the target power system based on the received data information and the obtained system static power frequency characteristic curve.

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