Method and system for controlling load frequency of interconnected power system under fan access

Abstract

The invention relates to the technical field of power systems, and particularly discloses an interconnected power system load frequency control method and system under fan access, and the method comprises the steps: integrating uncertain and time-varying disturbance terms, wind fluctuation and load disturbance into uncertain terms of a system; a fan is divided into a non-linear part and a linear part, the linear part provides inertia control to assist system frequency modulation, and the non-linear part is used for simulating wind fluctuation, so that the actual process of wind energy utilization is better met; a sliding mode control law is designed, an integral sliding mode surface is adopted as a sliding mode surface, an improved logarithmic power function reaching law is designed according to a sliding mode reaching law, and a self-adaptive law is designed for compensation for an integrated unknown uncertain item with an unknown upper bound. Compared with other control strategies, the multi-region interconnected power system applying the method has smaller overshoot, faster convergence speed and stronger robust performance when being influenced by multiple factors such as load disturbance and time lag.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power systems, and in particular to a method and system for controlling load frequency of an interconnected electric power system with wind turbines connected thereto. Background Art

[0002] With the continuous depletion of non-renewable resources and the deteriorating ecological environment, the penetration rate of renewable energy in the power system has increased year by year. Wind energy has become one of the most commercially promising power generation methods due to its clean and efficient characteristics. However, due to its inherent intermittent, volatile and random nature, wind power poses severe challenges to the stable operation of the power system. Therefore, it is particularly important to study the frequency stability of interconnected power systems under wind power access. In recent years, as the frequency stability problem has become more and more prominent, researchers have begun to consider the auxiliary participation of wind turbines in frequency regulation performance, but due to the limited frequency regulation capability of wind turbines in load frequency control, in order to achieve reliable control of the frequency of the interconnected power system, other control technologies are still needed to dominate the frequency regulation.

[0003] Sliding mode control is a control method that is insensitive to external disturbances. It has the advantages of simple structure, easy design, fast response speed and strong robustness. It can be well applied to load frequency control of interconnected power systems. However, when analyzing the frequency stability problem of interconnected power systems containing wind power, the influence of multiple factors such as parameter perturbations, communication delays, load disturbances, wind fluctuations, and nonlinear physical conditions are not considered at the same time, resulting in theoretical research deviating from reality to varying degrees. Summary of the invention

[0004] The present invention provides a method and system for controlling the load frequency of an interconnected power system under wind turbine access, and solves the technical problem of how to simultaneously consider the influence of multiple factors such as parameter perturbation, communication delay, load disturbance, wind power fluctuation, nonlinear physical condition constraints, etc., and perform high-performance control on the load frequency of the interconnected power system under wind turbine access.

[0005] In order to solve the above technical problems, the present invention provides a method for controlling the load frequency of an interconnected power system under wind turbine access, comprising the steps of:

[0006] Establish a system model of region i in the n-region interconnected power system with wind turbine access, n ≥ 2;

[0007] Considering parameter perturbation, communication delay, load disturbance and fan disturbance, a basic equation of sliding mode motion of the system corresponding to the system model is established;

[0008] The fan system in the basic equation of sliding mode motion of the system is divided into a nonlinear disturbance part not involved in frequency regulation and a linear disturbance part involved in frequency regulation, and inertial control is applied to the linear disturbance part through frequency;

[0009] Adding uncertain terms including matching disturbance terms and mismatching disturbance terms, we get the intermediate equation of sliding mode motion of the system with uncertain parameters.

[0010] Based on the mathematical model of the system state with uncertain parameters, the integral sliding surface is selected to obtain the equivalent control law;

[0011] The approaching law of logarithmic power function is improved and an adaptive mechanism is introduced to obtain the switching control law.

[0012] Combining the equivalent control law and the switching control law to obtain a sliding mode control law;

[0013] Substituting the designed sliding mode control law into the intermediate sliding mode motion equation of the system, an equivalent sliding mode motion equation of the system is obtained;

[0014] Based on the sliding mode motion equivalent equation of the system, the load frequency of the interconnected power system with wind turbine access is controlled.

[0015] Furthermore, the basic equation of sliding mode motion of the system is expressed as:

[0016]

[0017] Among them, x i (t) represents the state vector of region i, Represents x i The derivative of (t), u i (t) represents the sliding mode control law, d i (t) represents the time-varying lag function of the system, x i (td i (t)) represents the time-varying and delayed state vector of the system, ω i (t) represents the perturbation vector of region i, x j (t) represents the state vector of region j, A i ', B i '、A id '、 F i 'represents x respectively i (t),u i (t), x i (td i (t))、x j (t),ω i The perturbation parameter matrices of (t) are the system state matrix, system input matrix, system delay matrix, system correlation matrix and system disturbance matrix.

[0018] Furthermore, in the system model of region i, the fan frequency deviation △f according to the load i (t) Output power deviation △P participating in auxiliary frequency modulationW1i (t) That is, the linear disturbance part acts on the load, and the output power deviation △P that does not participate in frequency modulation W2i (t) That is, the nonlinear disturbance part acts on the load.

[0019] Furthermore, by applying inertial control to the frequency, the output power P of the fan participating in auxiliary frequency regulation W1i (t) is designed to change the constant control gain into a frequency change rate and frequency deviation △f i (t) Related variable functions.

[0020] Furthermore, the fan has a frequency deviation Δf according to the load i (t) Output power deviation △P participating in auxiliary frequency modulation W1i The specific process of (t) is:

[0021] Frequency deviation △f i (t) is input to the control gain module, and the control gain module calculates the control gain to obtain the deviation as the input signal to enter the fan pitch angle control module; the fan pitch angle control module outputs the adjustment value △X by controlling the information of the fan blade angle in the input signal ai (t) to the pitch control module; the pitch control module further optimizes the fan performance through the control strategy according to the fan blade angle in the input signal, and outputs the adjustment amount △X bi (t) to the hydraulic pitch actuator; the hydraulic pitch actuator performs hydraulic pitch operation and outputs the adjustment amount △X ci (t) to the data fitting response module; the data fitting response module performs data fitting prediction and outputs the adjustment amount △X di (t), and through the fan speed deviation △f Ti (t) is output; the fan speed deviation △f Ti (t) and system frequency deviation △f i (t) is subtracted to obtain the output power deviation △P involved in auxiliary frequency modulation W1i (t).

[0022] Furthermore, the state vector x of region i i (t) and frequency deviation △f i (t), turbine output power deviation △P gi (t), speed regulator regulation signal △P vi (t), power deviation △P on the inter-regional interconnection line tiei (t), according to the power deviation △P on the inter-regional interconnection line tiei (t) and frequency deviation △f i (t) Output frequency deviation integral control change △P ei(t), fan speed deviation △f Ti (t), output power deviation of wind turbine participating in auxiliary frequency regulation △P W1i (t) is related to the wind turbine state variables;

[0023] The perturbation vector ω of region i i (t) and load output power deviation △P Loadi (t) and the output power deviation of the fan not participating in frequency regulation △P W2i (t) relevant;

[0024] System state matrix A i ' and the damping coefficient D of the fan i and the inertia constant M i , the time constant T of the turbine chi , the time constant T of the speed regulator gi , the speed adjustment coefficient R of the speed regulator i , system control gain K i , Regional frequency offset factor B i , the power synchronization factor T of the tie line between regions i and j ij , fan coupling gain K Gi , fan feedback gain T ti , fan feedback time constant K Ti , fan pitch angle control time constant K ii , Parameter k for simulating primary frequency regulation of traditional fans pfi , parameter k for simulating the turbine inertia constant dfi , the pitch control gain K of the fan 1i , the hydraulic pitch actuator gain K of the fan 2i , the pitch response gain of the fan K 3i , fan constant gain K 4i , the pitch control time constant of the fan T 1i , the fan hydraulic pitch execution time constant T 2i , the pitch response time constant of the fan T 3i Related;

[0025] System input matrix B i ' and the time constant T of the speed regulator gi Related;

[0026] System delay matrix A id ' and the time constant T of the speed regulator gi Related;

[0027] System correlation matrix The power synchronization factor T of the tie line between regions i and j ij Related;

[0028] System disturbance matrix F i ' and the damping coefficient D of the fan i and the inertia constant M i Related.

[0029] Furthermore, in the intermediate equation of sliding mode motion of the system, the uncertainty term added is △A i , △B i , △A id , △E ij , △F i They respectively represent the uncertainties of the system state matrix, system input matrix, system delay matrix, system correlation matrix, and system disturbance matrix.

[0030] Furthermore, the equivalent control law is designed as follows:

[0031]

[0032] G i and L i represents different constant matrices, and G i Meet G i B' i is a non-singular matrix, L i Satisfy λ i (A' i -B' i L i )<0.

[0033] Furthermore, the sliding mode control law is designed as:

[0034]

[0035] Among them, sign(s i (t)) represents the sign function, s i (t) represents the selected sliding surface, represents the upper bound of system uncertainty α i (t), β i (t) and η i The estimated value of (t), α i (t), β i (t) and η i (t) is α i , β i and η i , α i , β i and η i Make holds, ||*|| represents the Euclidean norm, and the intermediate variable q i (t) is:

[0036]

[0037] Each coefficient, exponential parameter k 1i ,k 2i ,k 3i ,k 4i >0, 0<μ i <1, χ i ≥1,υ i ,ε i is a positive constant, s mi Defined as mi =|s i (t)|+σ i , σ i Is a positive number.

[0038] The present invention also provides a load frequency control system for an interconnected power system with wind turbine access. The system applies the load frequency control method for an interconnected power system with wind turbine access. The key lies in that the control system includes a system model building module, a system sliding mode motion equation processing module, a sliding mode control law generation module, and a load frequency control module;

[0039] The system model building module is used to build a system model of region i in an n-region interconnected power system with wind turbine access, where n≥2;

[0040] The system sliding mode motion equation processing module is used to establish the system sliding mode motion basic equation corresponding to the system model by considering parameter perturbation, communication delay, load disturbance, and fan disturbance; and divide the fan system in the system sliding mode motion basic equation into a nonlinear disturbance part that does not participate in frequency regulation and a linear disturbance part that participates in frequency regulation, and apply inertial control to the linear disturbance part through frequency; and add uncertain terms including matching disturbance terms and unmatching disturbance terms to obtain the system sliding mode motion intermediate equation with uncertain parameters;

[0041] The sliding mode control law generation module is used to select an integral sliding mode surface based on a mathematical model of a system state with uncertain parameters to obtain an equivalent control law; and to improve the approaching law of a logarithmic power function and introduce an adaptive mechanism to obtain a switching control law;

[0042] The system sliding mode motion equation processing module is also used to substitute the sliding mode control law designed by the sliding mode control law generation module into the system sliding mode motion intermediate equation to obtain the system sliding mode motion equivalent equation;

[0043] The load frequency control module is used to control the load frequency of the interconnected power system to which the wind turbine is connected based on the sliding mode motion equivalent equation of the system.

[0044] The load frequency control method and system of the interconnected power system under the access of wind turbines provided by the present invention integrate the uncertainty, time-varying disturbance term, wind power fluctuation and load disturbance in the model into the uncertainty term of the system in view of the uncertainties and disturbances of different properties contained in the actual power system; in view of the control strategy of the wind turbine participating in the auxiliary frequency regulation, the wind turbine is divided into a nonlinear part and a linear part, an inertial control auxiliary system frequency regulation is proposed for the linear part, and the nonlinear part is used to simulate wind power fluctuation, which is more in line with the actual process of wind energy utilization; a sliding mode control law is designed, in which the sliding mode surface adopts an integral sliding mode surface, and the sliding mode reaching law designs an improved logarithmic power function reaching law, and an adaptive law is designed to compensate for the uncertainty term with unknown upper bound of the integration.

[0045] Compared with other control strategies, the multi-region interconnected power system using the present invention has smaller overshoot, faster convergence speed and stronger robust performance when affected by multiple factors such as load disturbance and time delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of a method for controlling load frequency of an interconnected power system under wind turbine access provided by an embodiment of the present invention;

[0047] Figure 2 is a schematic diagram of a model of region i in a multi-region interconnected power system provided by an embodiment of the present invention;

[0048] Figure 3 is a schematic diagram of a linear part model of a wind turbine power generation system in region i provided by an embodiment of the present invention;

[0049] Figure 4 It is a frequency deviation curve diagram of the improved fan auxiliary frequency modulation control strategy and the traditional fan auxiliary frequency modulation control strategy (inertia control) provided by the embodiment of the present invention, and the fan not participating in the auxiliary frequency modulation strategy;

[0050] Figure 5 is a frequency deviation curve diagram corresponding to the application of five sliding mode convergence laws provided in an embodiment of the present invention;

[0051] Figure 6 It is a frequency deviation curve diagram obtained by changing system parameters within a certain range provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following specifically illustrates the implementation mode of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0053] The load frequency control method of the interconnected power system under the connection of wind turbines provided in the embodiment of the present invention is as follows: Figure 1 As shown in the flowchart, the steps include:

[0054] Establish a system model of region i in the n-region interconnected power system with wind turbine access, n ≥ 2;

[0055] Considering parameter perturbation, communication delay, load disturbance and fan disturbance, the basic equation of sliding mode motion of the system model is established;

[0056] The fan system in the basic equation of sliding mode motion of the system is divided into a nonlinear disturbance part that does not participate in frequency regulation and a linear disturbance part that participates in frequency regulation, and inertial control is applied to the linear disturbance part through frequency.

[0057] Adding uncertain terms including matching disturbance terms and mismatching disturbance terms, we get the intermediate equation of sliding mode motion of the system with uncertain parameters.

[0058] Based on the mathematical model of the system state with uncertain parameters, the integral sliding surface is selected to obtain the equivalent control law;

[0059] The approaching law of logarithmic power function is improved and an adaptive mechanism is introduced to obtain the switching control law.

[0060] The equivalent control law and the switching control law are combined to obtain the sliding mode control law;

[0061] Substitute the designed sliding mode control law into the intermediate equation of sliding mode motion of the system to obtain the equivalent equation of sliding mode motion of the system;

[0062] The load frequency of the interconnected power system with wind turbine access is controlled based on the system sliding mode motion equivalent equation.

[0063] Figure 2 This is a schematic diagram of the model of region i in the multi-region interconnected power system proposed in the present invention, which mainly includes a sliding mode controller, a speed regulator, a turbine, a generator-load and a fan starting system (referred to as a fan). For region i, when the speed regulator detects a frequency deviation △f caused by load fluctuations i (t), the speed adjustment coefficient R of the speed regulator i Send adjustment signal △P vi (t) to the turbine as a control signal for the turbine, by changing the valve opening and closing degree in the turbine, thereby changing the turbine output power deviation △P gi (t), and input it into the generator. The generator starts to move after receiving the signal from the prime mover, and adjusts the process according to the load in the system, and finally outputs a smaller frequency deviation △f i(t), so as to achieve the effect of frequency regulation. If there is still frequency deviation after the frequency regulation is stabilized, or when the load changes beyond the range of the frequency regulation, the load frequency control proposed by the present invention is performed, that is, according to the power deviation △P on the inter-regional interconnection line tiei (t) and frequency deviation △f i (t) Output frequency deviation integral control change △P ei (t), and then input the sliding mode control variable u generated by the sliding mode controller i (t) work together with the speed regulator to eliminate the frequency deviation. The wind turbine power generation system is based on the input frequency deviation △f i (t) Output power deviation △P participating in auxiliary frequency modulation W1i (t) acts on the load. Power deviation △P on the inter-regional interconnection line tiei (t) and system disturbance △P Di (t)(including load output power deviation △P Loadi (t) and the output power deviation of the fan not participating in frequency regulation △P W2i (t)) also acts on the load, and the power deviation △P on the inter-regional tie line tiei 、System disturbance △P Di (t), turbine output power deviation △P gi (t), output power deviation △P participating in auxiliary frequency modulation W1i (t) produces a frequency deviation △f i In this embodiment, a parameter with “(t)” indicates that the parameter changes with time t, and “(t)” may be omitted in some cases.

[0064] Figure 3 The schematic diagram of the linear part model of the wind turbine power generation system in region i proposed by the present invention, wherein the pitch angle control module outputs the adjustment value △X ai (t) is used to adjust the blade angle of the wind turbine, thereby controlling the output power of the wind turbine and ensuring its stable operation; the pitch control module outputs the adjustment amount △X bi (t) can maximize the use of wind energy and improve power generation efficiency; the hydraulic pitch actuator module output adjustment amount △X ci (t) Optimize wind energy capture and improve power generation efficiency by adjusting the angle of the wind turbine blades; the data fitting pitch response module outputs the adjustment value △X di (t) Accurately predict and adjust the response of wind turbines to changes in the external environment through data analysis and model fitting. ai , △X bi , △X ci , △X di is the fan state variable. Figure 3 △P WTimax(t) represents the maximum deviation of fan output. Figure 2 , Figure 3 The s in the transfer function represents a complex variable.

[0065] The fan frequency deviation △f according to the load i (t) Output power deviation △P participating in auxiliary frequency modulation W1i The specific process of (t) is:

[0066] Frequency deviation △f i (t) is input to the control gain module. After the control gain module calculates the control gain, the deviation is obtained as the input signal to enter the fan pitch angle control module to ensure that the output fan power changes with the system frequency deviation. The fan pitch angle control module optimizes the fan power performance by controlling the fan blade angle information in the input signal, and outputs the adjustment amount △X ai (t) to the pitch control module; the pitch control module further optimizes the fan performance through the control strategy according to the fan blade angle in the input signal, and outputs the adjustment amount △X bi (t) to the hydraulic pitch actuator; the hydraulic pitch actuator performs hydraulic pitch operation and outputs the adjustment amount △X ci (t) to the data fitting response module; the data fitting response module performs data fitting prediction and outputs the adjustment amount △X di (t), and through the fan speed deviation △f Ti (t) is output; the fan speed deviation △f Ti (t) and system frequency deviation △f i (t) is subtracted to obtain the output power deviation △P involved in auxiliary frequency modulation W1i (t).

[0067] Reference Figure 2 , Figure 3 , each state variable in the interconnected power system with wind turbine access is represented by a transfer function model, and each state variable is interrelated. Therefore, the basic sliding mode motion equation of the system in area i of the n-area interconnected power system with wind turbine access can be established according to the transfer function model:

[0068]

[0069] Among them, x i (t) represents the state vector of region i, Represents x i The derivative of (t), u i (t) represents the sliding mode control law, d i (t) represents the time-varying lag function of the system, x i (td i(t)) represents the time-varying and delayed state vector of the system, ω i (t) represents the perturbation vector of region i, x j (t) represents the state vector of region j, A i ', B i '、A id '、 F i 'represents x respectively i (t),u i (t), x i (td i (t))、x j (t),ω i The perturbation parameter matrices of (t) are the system state matrix, system input matrix, system delay matrix, system correlation matrix and system disturbance matrix.

[0070] x i (t) is expressed as:

[0071] x i (t) = [Δf i ΔP gi ΔP vi ΔP ei ΔP tiei Δf Ti ΔP W1i ΔX ai ΔX bi ΔX ci ΔX di ] T (2)

[0072] Among them, △f Ti (t) represents the fan speed deviation, and the superscript T represents the matrix transpose.

[0073] ω i (t) is expressed as:

[0074] ω i (t) = [ΔP Loadi (t)ΔP W2i (t)] T (3)

[0075] A i ′、B i ′、A id '、 F i ' respectively represent as follows:

[0076]

[0077]

[0078] Among them, D i 、M i Respectively represent the damping coefficient and inertia constant of the fan, T chi represents the time constant of the turbine, T gi Indicates the time constant of the speed regulator, R i Indicates the speed adjustment coefficient of the speed regulator, K i represents the system control gain, B i represents the regional frequency offset factor, T ij represents the power synchronization factor of the tie line between regions i and j, K Gi represents the coupling gain of the fan, T ti Indicates the feedback gain of the fan, K Ti Indicates the feedback time constant of the fan, φ i , κ i , τ i , ν i Represents different intermediate variables, The parameter representing the inertia constant of the simulated turbine (e is the natural base), K 1i represents the pitch control gain of the wind turbine, K 2i represents the hydraulic pitch actuator gain of the wind turbine, K 3i represents the pitch response gain of the wind turbine, K 4i represents the constant gain of the fan, T 1i represents the pitch control time constant of the wind turbine, T 2i Represents the hydraulic pitch execution time constant of the fan, T 3i Represents the pitch response time constant of the fan.

[0079] Intermediate variable φ i , κ i , τ i , ν i They are respectively expressed as follows:

[0080]

[0081] Among them, K ii represents the fan pitch angle control time constant, Indicates the parameters for simulating the primary frequency regulation of a traditional fan. is the parameter for simulating the inertia constant of the turbine, k pi and k 0i are different positive constants.

[0082] In order to consider the randomness and volatility of the fan itself while taking into account its participation in auxiliary frequency regulation, the fan system is divided into two parts: one is the nonlinear disturbance part that does not participate in frequency regulation, and the other is the linear part that participates in frequency regulation.

[0083] For the nonlinear model where the fan does not participate in frequency regulation, the output equation is as follows:

[0084]

[0085] Among them, P W2i represents the output power of the fan not involved in frequency modulation, ρ is the air density (kg / m 3 , kg per cubic meter), A is the area swept by the fan rotor blades (m 3 , cubic meters), A=πR 2 , R is the fan rotor radius (m, meter), V W is the average wind speed across surface A (m / s, meters per second), C p (λ,β) is the wind energy capture coefficient.

[0086] The linear part of the fan participating in frequency regulation has the ability to adjust the frequency by applying inertial control to the frequency. However, in traditional inertial control, a constant control gain is generally used, which will lead to the following two situations:

[0087] 1) When k dfi When k is too large, the frequency modulation potential of the fan will be limited and cannot be fully utilized. pfi If the fan is too small, it is easy for the fan to over-respond and eventually stall.

[0088] 2) When k dfi When k is too large, it will cause the fan rotor speed to drop excessively. pfi If the value is too small, the fan cannot provide effective inertia support.

[0089] Therefore, in order to overcome the above-mentioned shortcomings of the traditional inertial control, this embodiment proposes an improved inertial control, which changes the constant control gain into a variable function related to the frequency change rate and the frequency deviation, and the expression is as follows:

[0090]

[0091] P W1i Indicates the output power of the fan participating in auxiliary frequency regulation.

[0092] Compared with traditional inertial control, the improved control gain changes with the frequency change rate and frequency deviation, which can effectively avoid the problems faced by constant gain.

[0093] The mathematical model of the system considering parameter uncertainty can be described as:

[0094]

[0095] Among them, the aggregate uncertainty is:

[0096]

[0097] Among them, △A i , △B i , △A id , △E ij , △F i They respectively represent the uncertainties of the system state matrix, system input matrix, system delay matrix, system correlation matrix, and system disturbance matrix.

[0098] Generally speaking, the uncertainties of the system are divided into two types: matching and mismatching. In the actual power system, not all uncertainties can meet the matching condition. Therefore, this embodiment considers the matching disturbance term and the mismatching disturbance term in the system uncertainty at the same time, that is, the aggregated uncertainties include both the matching disturbance term and the mismatching disturbance term, which can be expressed as:

[0099] f i (x,t)=f im (x,t)+f imm (x,t) (14)

[0100] Among them, f im (x, t) is the matching disturbance term, f imm (x, t) is a mismatched perturbation term. Matched perturbations can be eliminated during the proof, but mismatched perturbations cannot.

[0101] For the above system, the following assumptions are made:

[0102] Assumption 1: System state matrix, system input matrix (A i ',B i ') is fully controllable and defines rank[B i ',fi(x,t)]≠rank[B i '], rank[K] represents the rank of matrix K;

[0103] Assumption 2: There exists a positive constant α i , β i , η i , making the uncertainty ||*|| is the Euclidean norm.

[0104] Therefore, the following integral sliding surface is selected:

[0105]

[0106] Among them, G i and L i represents different constant matrices, and G i Meet G iB' i is a non-singular matrix, L i Satisfy λ i (A' i -B' i L i )<0, thereby ensuring the stable performance of the closed-loop system.

[0107] When the system motion trajectory enters the selected sliding surface, s(t)=0 is satisfied. At the same time, combining assumptions 1-2 and equation (15), the equivalent sliding mode control law can be obtained:

[0108]

[0109] Substituting equation (16) into system equation (12), the equivalent equation of sliding mode motion of the system is obtained as follows:

[0110]

[0111] make:

[0112]

[0113] Then the sliding mode equation (17) can be written again as:

[0114]

[0115] Theorem 1: If there exists a constant ε i ,ξ i >0, positive definite matrix P i ,Q i , and a matrix N of appropriate dimension 1i 、N 2i If the following matrix inequality (20) is satisfied, then when the system state trajectory reaches the sliding surface, the sliding mode motion equivalent equation (19) is exponentially bounded and converges to

[0116]

[0117] The symbol * represents a symmetric term in the relevant symmetric matrix, and the remaining parameters are defined as follows:

[0118]

[0119] The design of the sliding mode approaching law can ensure that the system trajectory has good dynamic quality during the approaching process. This embodiment also designs an improved logarithmic power function approaching law, which can effectively solve the problem that the traditional approaching law converges too slowly when far away from the sliding mode stage, resulting in a long approaching time, and the speed is too fast when approaching the sliding mode stage, resulting in system chattering. The improved sliding mode approaching law is designed as follows:

[0120]

[0121] Among them, each coefficient, exponential parameter k 1i ,k 2i ,k 3i ,k 4i >0, 0<μ i <1, χ i ≥1,υ i ,ε i is a positive constant, s mi =|s i (t)|+σ i , σ i is a positive number, s i (t) represents the selected sliding surface.

[0122] The sliding mode reaching law of formula (22) consists of four parts. The first part This part plays a leading role when the sliding state is far away from the sliding surface. and the third part It plays a leading role when the sliding state approaches the sliding surface, and the third part avoids the discontinuity of the sliding state on the sliding surface, thereby effectively weakening the chattering phenomenon. This part aims to achieve faster convergence by adjusting parameters when the system is far away from the sliding surface.

[0123] In order to adapt to the unknown upper bound with uncertainty, based on the above improved reaching law, an adaptive mechanism is further introduced to ensure tracking control under uncertain factors. From Assumption 2, we can know that the upper bound of system uncertainty α i (t), β i (t) and η i (t) is unknown, let its estimated values ​​be Then we have:

[0124]

[0125] Finally, for the design of the sliding mode controller, according to the following formula:

[0126] u=u eq +u sw (twenty four)

[0127] Among them, u eq is the equivalent control law, u sw is the switching control law.

[0128] The control law of sliding mode motion is nonlinear, and its value changes continuously within the range of plus or minus 1. Since this nonlinear control quantity is difficult to analyze, a continuous linear control method can be used to approximate it, and the two are functionally equivalent. eq is the control law when there is no external disturbance and the system reaches the ideal sliding mode state, which can be solved by In addition, u sw Its role is to ensure that the stability of the system can be maintained even if the system state deviates from the sliding surface due to parameter changes or external disturbances.

[0129] Therefore, the final designed adaptive sliding mode control law is:

[0130]

[0131] sign(s i (t)) represents the sign function,

[0132] Among them, the intermediate variables are:

[0133]

[0134] The Lyapunov function can be selected to prove the stability of the above controller.

[0135] Finally, substitute equation (26) into equation (12) to obtain the equivalent equation of the sliding mode motion of the system.

[0136] In addition, the present invention also provides a load frequency control system for an interconnected power system under wind turbine access. The system applies the load frequency control method for an interconnected power system under wind turbine access. The control system includes a system model establishment module, a system sliding mode motion equation processing module, a sliding mode control law generation module, and a load frequency control module.

[0137] The system model building module is used to build the system model of region i in the n-region interconnected power system with wind turbine access, where n≥2;

[0138] The system sliding mode motion equation processing module is used to consider parameter perturbation, communication delay, load disturbance, and fan disturbance to establish the system sliding mode motion basic equation corresponding to the system model; and divide the fan system in the system sliding mode motion basic equation into a nonlinear disturbance part that does not participate in frequency regulation and a linear disturbance part that participates in frequency regulation, and apply inertial control to the linear disturbance part through frequency; and add uncertain terms including matching disturbance terms and unmatching disturbance terms to obtain the system sliding mode motion intermediate equation with uncertain parameters;

[0139] The sliding mode control law generation module is used to select the integral sliding mode surface based on the mathematical model of the system state with uncertain parameters to obtain the equivalent control law; and to improve the approaching law of the logarithmic power function and introduce an adaptive mechanism to obtain the switching control law;

[0140] The system sliding mode motion equation processing module is also used to substitute the sliding mode control law designed by the sliding mode control law generation module into the system sliding mode motion intermediate equation to obtain the system sliding mode motion equivalent equation;

[0141] The load frequency control module is used to control the load frequency of the interconnected power system under the access of wind turbines based on the system sliding mode motion equivalent equation.

[0142] The control system protects a physical entity (module) that can implement the above control method. The specific functions that the module can implement have been detailed in the above method and will not be repeated in the system.

[0143] Taking the two-region interconnected power system with wind power as the research object, Matlab / Simulink is used to build Figure 2 The models shown are used to verify the control effects of the method and system proposed in this embodiment.

[0144] Combination Figure 2 , the parameters of the dual-area interconnected power system under wind turbine access are given in Table 1.

[0145] Table 1

[0146]

[0147] In order to make the load frequency control in the interconnected power system more flexible and more effective, the present invention not only designs an adaptive sliding mode controller to control the load frequency, but also adds improved inertia control to the fan to participate in frequency modulation. The frequency deviation curves of the improved fan auxiliary frequency modulation control strategy provided by the present invention and the traditional fan auxiliary frequency modulation control strategy (inertia control) and the fan not participating in the auxiliary frequency modulation strategy are shown in Figure 2. Figure 4 As shown, Figure 4 (a) and (b) are the frequency deviation curves of regions 1 and 2, respectively. Figure 4 It can be clearly seen from sub-figure (a) and sub-figure (b) that, whether in terms of overshoot or fluctuation degree, the frequency deviation change of the system under the improved inertial control proposed in this embodiment is better than the frequency deviation effect under traditional inertial control and when the fan does not participate in auxiliary frequency regulation, thereby verifying the effectiveness and superiority of the improved inertial control proposed in this embodiment.

[0148] In order to verify the superiority of the adaptive sliding mode control law proposed in this embodiment, it is compared with the constant speed reaching law, exponential reaching law, fast power reaching law and double power reaching law. The above five sliding mode reaching laws are applied to the load frequency control of the interconnected power system respectively, and the obtained frequency deviation changes are as follows: Figure 5 As shown. Figure 5 (a) and (b) are the frequency deviation curves of regions 1 and 2, respectively. Figure 5 It can be seen from sub-figures (a) and (b) in that both the constant speed reaching law and the exponential reaching law show obvious chattering. Although the fast power reaching law and the double power reaching law do not have obvious chattering, they have larger overshoot and load frequency fluctuation compared with the improved reaching law proposed in this embodiment, which confirms the superiority of the adaptive sliding mode control law proposed in this embodiment.

[0149] In order to verify the effectiveness and robustness of the improved auxiliary frequency modulation control strategy of the fan proposed in this embodiment based on the adaptive sliding mode control law, consider changing the system parameter M within a certain range (+150%, -50%). i , D i 、T chi 、T gi , R i , B i 、T ti , the frequency deviation curve is as follows Figure 6 As shown. Figure 6 (a) and (b) are the frequency deviation curves of regions 1 and 2, respectively. Figure 6 It can be seen from sub-figures (a) and (b) in that changing the system parameters within a certain range will hardly change the load frequency response speed and overshoot of the system, thereby confirming that the improved control method and system proposed in this embodiment have good robust performance.

[0150] In summary, the load frequency control method and system for the interconnected power system with wind turbine access provided by the embodiment of the present invention integrates the uncertainty, time-varying disturbance terms, wind fluctuations and load disturbances in the model into the uncertainty of the system in view of the uncertainties and disturbances of different properties contained in the actual power system; with respect to the control strategy of the wind turbine participating in auxiliary frequency regulation, the wind turbine is divided into a nonlinear part and a linear part, and an inertial control auxiliary system frequency regulation is proposed for the linear part, and the nonlinear part is used to simulate wind fluctuations, which is more in line with the actual process of wind energy utilization; a sliding mode control law is designed, in which the sliding mode surface adopts an integral sliding mode surface, and the sliding mode reaching law designs an improved logarithmic power function reaching law, and with respect to the uncertainty terms with unknown upper bounds of the integration, an adaptive law is designed to compensate for them.

[0151] Compared with other control strategies, the multi-region interconnected power system using the present invention has smaller overshoot, faster convergence speed and stronger robust performance when affected by multiple factors such as load disturbance and time delay.

[0152] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for controlling load frequency of an interconnected power system with wind turbine access, characterized in that: Includes steps: Establish a system model of region i in the n-region interconnected power system with wind turbine access, n ≥ 2; Considering parameter perturbation, communication delay, load disturbance and fan disturbance, a basic equation of sliding mode motion of the system corresponding to the system model is established; The fan system in the basic equation of sliding mode motion of the system is divided into a nonlinear disturbance part not involved in frequency regulation and a linear disturbance part involved in frequency regulation, and inertial control is applied to the linear disturbance part through frequency; Adding uncertain terms including matching disturbance terms and mismatching disturbance terms, we get the intermediate equation of sliding mode motion of the system with uncertain parameters. Based on the mathematical model of the system state with uncertain parameters, the integral sliding surface is selected to obtain the equivalent control law; The approaching law of logarithmic power function is improved and adaptive mechanism is introduced to obtain the switching control law. Combining the equivalent control law and the switching control law to obtain a sliding mode control law; Substituting the designed sliding mode control law into the intermediate sliding mode motion equation of the system, an equivalent sliding mode motion equation of the system is obtained; Based on the sliding mode motion equivalent equation of the system, the load frequency of the interconnected power system with wind turbine access is controlled.

2. The method for controlling load frequency of an interconnected power system with wind turbine access according to claim 1, characterized in that: The basic equation of sliding mode motion of the system is expressed as: Among them, x i (t) represents the state vector of region i, Represents x i The derivative of (t), u i (t) represents the sliding mode control law, d i (t) represents the time-varying lag function of the system, x i (td i (t)) represents the time-varying and delayed state vector of the system, ω i (t) represents the perturbation vector of region i, x j (t) represents the state vector of region j, A i ', B i '、A id '、 F i 'represents x respectively i (t),u i (t), x i (td i (t))、x j (t),ω i The perturbation parameter matrices of (t) are the system state matrix, system input matrix, system delay matrix, system correlation matrix and system disturbance matrix.

3. The method for controlling load frequency of an interconnected power system with wind turbine access according to claim 2 is characterized in that: In the system model of region i, the fan frequency deviation △f according to the load i (t) Output power deviation △P participating in auxiliary frequency modulation W1i (t) That is, the linear disturbance part acts on the load, and the output power deviation △P that does not participate in frequency modulation W2i (t) That is, the nonlinear disturbance part acts on the load.

4. The method for controlling load frequency of an interconnected power system with wind turbine access according to claim 3 is characterized in that: By applying inertial control to the frequency, the output power P of the fan participating in auxiliary frequency regulation W1i (t) is designed to change the constant control gain into a frequency change rate and frequency deviation △f i (t) Related variable functions.

5. The method for controlling load frequency of interconnected power systems with wind turbine access according to claim 3 is characterized in that: The fan frequency deviation △f according to the load i (t) Output power deviation △P participating in auxiliary frequency modulation W1i The specific process of (t) is: Frequency deviation △f i (t) is input to the control gain module, and the control gain module calculates the control gain to obtain the deviation as the input signal to enter the fan pitch angle control module; the fan pitch angle control module outputs the adjustment value △X by controlling the information of the fan blade angle in the input signal ai (t) to the pitch control module; the pitch control module further optimizes the fan performance through the control strategy according to the fan blade angle in the input signal, and outputs the adjustment amount △X bi (t) to the hydraulic pitch actuator; the hydraulic pitch actuator performs hydraulic pitch operation and outputs the adjustment amount △X ci (t) to the data fitting response module; the data fitting response module performs data fitting prediction and outputs the adjustment amount △X di (t), and through the fan speed deviation △f Ti (t) Output the fan speed deviation △f Ti (t) and system frequency deviation △f i (t) is subtracted to obtain the output power deviation △P involved in auxiliary frequency modulation W1i (t).

6. The method for controlling load frequency of an interconnected power system with wind turbine access according to claim 5 is characterized in that: The state vector x of region i i (t) and frequency deviation △f i (t), turbine output power deviation △P gi (t), speed regulator regulation signal △P vi (t), power deviation △P on the inter-regional interconnection line tiei (t), according to the power deviation △P on the inter-regional interconnection line tiei (t) and frequency deviation △f i (t) Output frequency deviation integral control change △P ei (t), fan speed deviation △f Ti (t), output power deviation of wind turbine participating in auxiliary frequency regulation △P W1i (t) is related to the wind turbine state variables; The perturbation vector ω of region i i (t) and load output power deviation △P Loadi (t) and the output power deviation of the fan not participating in frequency regulation △P W2i (t) relevant; System state matrix A i ' and the damping coefficient D of the fan i and the inertia constant M i , the time constant T of the turbine chi , the time constant T of the speed regulator gi , the speed adjustment coefficient R of the speed regulator i , system control gain K i , Regional frequency offset factor B i , the power synchronization factor T of the tie line between regions i and j ij , fan coupling gain K Gi , fan feedback gain T ti , fan feedback time constant K Ti , fan pitch angle control time constant K ii , Parameter k for simulating primary frequency regulation of traditional fans pfi , parameter k for simulating the turbine inertia constant dfi , the pitch control gain K of the fan 1i , the hydraulic pitch actuator gain K of the fan 2i , the pitch response gain of the fan K 3i , fan constant gain K 4i , the pitch control time constant of the fan T 1i , the fan hydraulic pitch execution time constant T 2i , the pitch response time constant of the fan T 3i Related; System input matrix B i ' and the time constant T of the speed regulator gi Related; System delay matrix A id ' and the time constant T of the speed regulator gi Related; System correlation matrix The power synchronization factor T of the tie line between regions i and j ij Related; System disturbance matrix F i ' and the damping coefficient D of the fan i and the inertia constant M i Related.

7. The method for controlling load frequency of an interconnected power system with wind turbine access according to any one of claims 2 to 6, characterized in that: In the intermediate equation of sliding mode motion of the system, the uncertainty term added is A id , △E ij , △F i They respectively represent the uncertainties of the system state matrix, system input matrix, system delay matrix, system correlation matrix, and system disturbance matrix.

8. The method for controlling load frequency of interconnected power systems with wind turbine access according to claim 7, characterized in that: The equivalent control law is designed as: G i and L i represents different constant matrices, and G i Meet G i B′ i is a non-singular matrix, L i Satisfy λ i (A′ i -B′ i L i )<0.

9. The method for controlling load frequency of an interconnected power system with wind turbine access according to claim 8, characterized in that: The sliding mode control law is designed as: Among them, sign(s i (t)) represents the sign function, s i (t) represents the selected sliding surface, represents the upper bound of system uncertainty α i (t), β i (t) and η i The estimated value of (t), α i (t), β i (t) and η i (t) is α i , β i and η i , α i , β i and η i Make holds, ||*|| represents the Euclidean norm, and the intermediate variable q i (t) is: Each coefficient, exponential parameter k 1i ,k 2i ,k 3i ,k 4i >0, 0<μ i <1, χ i ≥1,υ i ,ε i is a positive constant, s mi Defined as mi =|s i (t)|+σ i , σ i Is a positive number.

10. A load frequency control system for an interconnected power system with wind turbines connected, the system applying a load frequency control method for an interconnected power system with wind turbines connected as claimed in any one of claims 1 to 9, characterized in that: The control system includes a system model building module, a system sliding mode motion equation processing module, a sliding mode control law generation module, and a load frequency control module; The system model building module is used to build a system model of region i in an n-region interconnected power system with wind turbine access, where n≥2; The system sliding mode motion equation processing module is used to establish the system sliding mode motion basic equation corresponding to the system model by considering parameter perturbation, communication delay, load disturbance, and fan disturbance; and divide the fan system in the system sliding mode motion basic equation into a nonlinear disturbance part that does not participate in frequency regulation and a linear disturbance part that participates in frequency regulation, and apply inertial control to the linear disturbance part through frequency; and add uncertain terms including matching disturbance terms and unmatching disturbance terms to obtain the system sliding mode motion intermediate equation with uncertain parameters; The sliding mode control law generation module is used to select an integral sliding mode surface based on a mathematical model of a system state with uncertain parameters to obtain an equivalent control law; and to improve the approaching law of a logarithmic power function and introduce an adaptive mechanism to obtain a switching control law; The system sliding mode motion equation processing module is also used to substitute the sliding mode control law designed by the sliding mode control law generation module into the system sliding mode motion intermediate equation to obtain the system sliding mode motion equivalent equation; The load frequency control module is used to control the load frequency of the interconnected power system to which the wind turbine is connected based on the sliding mode motion equivalent equation of the system.

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