A modeling method for active grid control of high-proportion renewable energy systems

Abstract

The present invention provides an active grid control modeling method for a high-proportion renewable energy system, which belongs to the field of energy, including: constructing a converter active power output variation model under small disturbances, thereby establishing a linear relationship between the converter active power output and the load power variation and the converter phase angle difference variation; constructing a VSG control model, and establishing a mathematical model of the converter control link; VSG represents a virtual synchronous generator; constructing an active frequency response model of multiple VSGs running in parallel; and constructing a prediction and correction link model to accurately reflect the actual dynamic behavior of the system. The present invention provides theoretical support for the optimization of active grid control performance.

Description

Technical Field

[0001] The invention belongs to the field of energy, and in particular relates to an active grid control modeling method for a high-proportion renewable energy system. Background Art

[0002] In recent years, high-proportion renewable energy sources such as wind power and photovoltaics have been connected to the power grid on a large scale, and grid control technology has been widely used to provide the necessary voltage and frequency support for the system. Among them, virtual synchronous generator (VSG) technology is the current mainstream grid control method. VSG simulates the dynamic characteristics of synchronous generators to provide virtual inertia and damping for the system. However, when a high-proportion renewable energy system is in island operation mode and multiple VSGs are running in parallel, active power oscillation problems will occur due to system parameter mismatch. At present, in a high-proportion renewable energy system, the active-frequency response model parameters of multiple VSGs running in parallel are complex and difficult to obtain accurately, which directly affects the design and actual performance of the grid control strategy. Therefore, there is an urgent need for an active grid control modeling method that is suitable for a high-proportion renewable energy system. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an active grid control modeling method for a high-proportion renewable energy system, which fully considers the influence of line parameters on the dynamic response of the system, constructs a multi-VSG active-frequency response model covering line impedance parameters, and provides theoretical support for the optimization of active grid control performance.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] An active grid control modeling method for a high-proportion renewable energy system includes the following steps:

[0006] Step 1: construct a model of the change in active power output of the converter under small disturbance, so as to establish a linear relationship between the active power output of the converter and the change in load power and the change in phase angle difference of the converter;

[0007] Step 2: construct a VSG control model and establish a mathematical model of the converter control link; VSG stands for virtual synchronous generator;

[0008] Step 3: Based on the linear relationship in step 1 and the VSG control model in step 2, an active-frequency response model of multiple VSGs in parallel operation is constructed to realize rapid modeling of active network control of multiple VSGs in parallel operation;

[0009] Step 4: Based on the active power-frequency response model of multiple VSGs running in parallel constructed in step 3, a prediction and correction link model is constructed to accurately reflect the actual dynamic behavior of the system.

[0010] Beneficial effects:

[0011] The present invention establishes an active-frequency response model of multiple VSGs in parallel operation through complete mathematical derivation. The model includes line parameters and VSG control parameters. The number of parameters is small and easy to obtain, which can realize the rapid modeling of active network control of multiple VSGs in parallel operation. At the same time, the present invention adds model prediction and correction links to ensure that the model can accurately reflect the actual dynamic behavior of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1a Schematic diagram of electrical wiring for multiple VSGs running in parallel;

[0013] Figure 1b It is a schematic diagram of the equivalent impedance network of multiple VSGs running in parallel;

[0014] Figure 1c It is a schematic diagram of the system admittance model of multiple VSGs running in parallel;

[0015] Figure 2 The active control loop response block diagram of VSG active networking;

[0016] Figure 3 The present invention is a flowchart of an active grid control modeling method for a high-proportion renewable energy system. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0018] like Figure 3 As shown, an active grid control modeling method for a high-proportion renewable energy system of the present invention comprises the following steps:

[0019] Step 1: construct a model of the change in active power output of the converter under small disturbance, so as to establish a linear relationship between the active power output of the converter and the change in load power and the change in phase angle difference of the converter;

[0020] Step 2: construct a VSG control model and establish a mathematical model of the converter control link;

[0021] Step 3: Based on the linear relationship in step 1 and the VSG control model in step 2, an active-frequency response model of multiple VSGs in parallel operation is constructed to achieve rapid modeling of active networking control of multiple VSGs in parallel operation.

[0022] The active power-frequency response model of multiple VSGs operating in parallel includes line parameters and VSG control parameters, and the number of parameters is small and easy to obtain.

[0023] Step 4: Based on the active power-frequency response model of multiple VSGs running in parallel constructed in step 3, a prediction and correction link model is constructed to accurately reflect the actual dynamic behavior of the system.

[0024] Specifically, the step 1 includes:

[0025] like Figure 1a As shown in the figure, VSG1, VSG2, and VSG3 represent three virtual synchronous generators running in parallel. VSG1, VSG2, and VSG3 are all connected to the grid through RLC filters. f1 , L f1 , C f1 , R1, L1 are the filter resistance, filter inductance, filter capacitor, line resistance, and line inductance on the first line, R f2 , L f2 , C f2 , R2, L2 are the filter resistance, filter inductance, filter capacitor, line resistance, and line inductance on the second line, R f3 , L f3 , C f3 , R3, L3 are the filter resistor, filter inductor, filter capacitor, line resistor, and line inductor on the third line. VSG1, VSG2, and VSG3 are all connected to the load through the PCC point, where the load includes different first loads, second loads, to nth loads. Assuming that the high proportion of renewable energy system operates normally, the load active power at the PCC point is P L , the load reactive power is Q L , the load voltage amplitude is U L Since the present invention aims to discuss the relationship between active power and frequency, the load reactive power Q L Set to 0.

[0026] like Figure 1b As shown, the equivalent load adopts a constant impedance model, so Z L Indicates the load of a system with multiple VSGs running in parallel. f With filter capacitor C f Much smaller than the filter inductance L f , the line resistance R is much smaller than the line inductance L, so the filter resistance R is ignored in the equivalent impedance network of multiple VSGs running in parallel. f With filter capacitor C fAssume that there are three VSGs, and the internal electromotive force of each VSG is E1∠δ1, E2∠δ2, E3∠δ3, E1, E2 and E3 are the internal electromotive force amplitudes of VSG1, VSG2 and VSG3, ∠δ1, ∠δ2 and ∠δ3 are the internal electromotive force phases of VSG1, VSG2 and VSG3, respectively. The following can be obtained: Figure 1c The system admittance model of multiple VSGs running in parallel is shown.

[0027] like Figure 1c As shown, each VSG is equivalent to a voltage source, and the output voltages of the three voltage sources are E1∠δ1, E2∠δ2, and E3∠δ3, respectively. 12 is the admittance between VSG1 and VSG2, y 13 is the admittance between VSG1 and VSG3, y 23 is the admittance between VSG2 and VSG3, y 10 is the admittance between VSG1 and the grounding point, y 20 is the admittance between VSG2 and the grounding point, y 30 is the admittance between VSG2 and the grounding point.

[0028] Assume that after the load is connected, the steady-state voltage of the load node is U L0 , then the derivation process of equivalent admittance is as follows:

[0029] (1)

[0030] (2)

[0031] (3)

[0032] Where ω is the system angular frequency, L i , L fi is the line inductance and filter inductance on the i-th line, P L is the active power of the load, x i ,y i is the impedance and admittance of the line where the i-th VSG is located, y0 represents the equivalent admittance of the load in the system admittance model, y i is the line admittance of the jth VSG, y ij For Figure 1c The admittance on each line in the system admittance model. .

[0033] based on Figure 1c The system admittance model in the system, the self-admittance and mutual admittance in the system with multiple VSGs running in parallel are:

[0034] (4)

[0035] Among them, Y 11 , Y 22 and Y 22 are the self-admittances of VSG1, VSG2 and VSG3 respectively, and Y 12 , Y 21 represents the mutual admittance between VSG1 and VSG2, Y 13 , Y 31 represents the mutual admittance between VSG1 and VSG3, Y 23 , Y 32 represents the mutual admittance between VSG2 and VSG3, G 11 , G 22 and are the self-conductances of VSG1, VSG2 and VSG3, respectively. 12 , G 21 represents the mutual conductance between VSG1 and VSG2, G 13 , G 31 represents the mutual conductance between VSG1 and VSG3, G 23 , G 32 represents the mutual conductance between VSG2 and VSG3; B 11 , B 22 and B 22 are the self-susceptance of VSG1, VSG2 and VSG3 respectively, and B 12 , B 21 Indicates the mutual susceptance between VSG1 and VSG2, B 13 , B 31 Indicates the mutual susceptance between VSG1 and VSG3, B 23 , B 32 represents the mutual susceptance between VSG2 and VSG3; m represents the imaginary unit.

[0036] It can be seen from formula (2) that active power is introduced when deriving the admittance parameters, so the parameters in formula (4) can be regarded as functions of active power.

[0037] In a system where multiple VSGs are running in parallel, the active power output by the first VSG, the second VSG, and the third VSG (i.e., VSG1, VSG2, and VSG3 mentioned above) meets the following requirements:

[0038] (5)

[0039] Among them, P E1 , P E2 , P E3 are the active powers output by the first, second and third VSGs, respectively. E1, E2 and E3 are the electromotive forces of the first, second and third VSGs, respectively. 12Indicates the power angle difference between the first VSG and the second VSG, δ 13 Indicates the power angle difference between the first VSG and the third VSG, δ 23 Indicates the power angle difference between the second VSG and the third VSG.

[0040] The self-admittance, mutual-admittance and sinusoidal quantity of the system with multiple VSGs running in parallel are linearized at the rated power P0. The active power output of the i-th VSG is for:

[0041] (6)

[0042] in, is the initial value of the active power output by the i-th VSG, K ii is the active linear coefficient of the ith VSG, is the load active power change, K ij is the linear coefficient of the phase angle between the i-th VSG and the j-th VSG, represents the change in the power angle difference between the i-th VSG and the j-th VSG, that is, the change in the power angle difference between each VSG. ; , the expressions are:

[0043] (7)

[0044] Among them, B ij(0) M is the susceptance value when the power is equal to the rated power P0, ij is the conductivity G ij The linear coefficient of the load power change ΔP.

[0045] According to equations (6) and (7), the change in active power output by the three VSGs under small disturbance is derived as:

[0046] (8)

[0047] Among them, ΔP E1 , ΔP E2 , ΔP E3 Indicates the change in active power output of the first, second, and third VSGs, K 11 , K 22 , K 33 are the active linear coefficients of the first, second and third VSGs, respectively, K 12 is the phase angle linear coefficient between the first VSG and the second VSG, K 13 is the phase angle linear coefficient between the first VSG and the third VSG, K 23is the phase angle linear coefficient between the second VSG and the third VSG. Indicates the change in the power angle difference between the first VSG and the second VSG. Indicates the change in the power angle difference between the first VSG and the third VSG. Indicates the change in the power angle difference between the second VSG and the third VSG.

[0048] Formula (8) is the model of the change in active power output of the converter under small disturbance.

[0049] Substituting formula (1), formula (2), formula (3) and formula (4) into formula (7), we can obtain the following by simplifying:

[0050] (9)

[0051] Among them, x1, x2, and x3 are the reactances of the lines where the first VSG, the second VSG, and the third VSG are located, respectively. is the phase angle linear coefficient between the second VSG and the first VSG, is the phase angle linear coefficient between the third VSG and the first VSG, is the phase angle linear coefficient between the 3rd VSG and the 2nd VSG. is the steady-state voltage at the load node.

[0052] Specifically, the step 2 includes:

[0053] Figure 2 The input-output relationship of the active power control loop of the VSG active network is described, and the transfer function of the active power control loop is:

[0054] (10)

[0055] Where s is the Laplace operator, Δω v is the change in VSG output frequency signal, ΔP E K is the change in VSG output active power, J is the inertia coefficient, K D is the primary frequency modulation coefficient.

[0056] Figure 2 In the equation, ΔP represents the input power, ω N Indicates the input frequency.

[0057] In a system where multiple VSGs are running in parallel, the power angle difference between the VSGs can be obtained by the following formula:

[0058] (11)

[0059] Among them, Δω viand Δω vj are the output frequency signal changes of the i-th VSG and the j-th VSG respectively; .

[0060] Equation (10) and Equation (11) are the VSG control models.

[0061] Specifically, the step 3 includes:

[0062] By integrating the converter active power output variation model under small disturbance with the VSG control model, the active power-frequency response model of multiple VSGs running in parallel can be obtained as follows:

[0063] (12)

[0064] Among them, K Ji , K Di are the inertia coefficient and primary frequency modulation coefficient of the i-th VSG, .

[0065] Specifically, step 4 includes:

[0066] Based on formula (12) in step 3, for each time t, the active-frequency response model of multiple VSGs in parallel operation and the phase angle difference parameter δ of each VSG obtained in step 3 are used. ij (t) Predict the active power output at the next moment , that is, the model prediction output, as the model prediction output, the expression is as follows:

[0067] (13)

[0068] Where g is a function describing the dynamic behavior of the VSG, and u is the control input vector, including the power set point and other control signals; Represents the power angle difference between the VSGs at time t;

[0069] Actual active power output P(t+1) and model predicted output The difference between t+1 It can be expressed as:

[0070] (14)

[0071] The gradient descent method is further used to update the parameters, and its expression is as follows:

[0072] (15)

[0073] in, represents the change in the power angle difference between the VSGs at time t, η is the learning rate, which determines the amplitude of parameter adjustment of the active power-response model of the system with multiple VSGs in parallel operation at each update, is the loss function J relative to the phase angle difference parameter δ of each VSG ij The gradient of (t), the loss function J is defined as a function of the error:

[0074] (16)

[0075] So the gradient It can be written as:

[0076] (17)

[0077] in, is the Jacobian matrix of the predicted output with respect to the parameters, which describes how changes in the parameters affect the predicted output.

[0078] Formula (15) is the prediction and correction model.

[0079] The entire step 4 first calculates the error between the actual active power and the model predicted value, and uses the gradient descent method as the optimization algorithm. By calculating the gradient of the error relative to the model parameters, the direction and step size of the parameter adjustment are determined, thereby optimizing the model parameters to ensure that the model can accurately reflect the actual dynamic behavior of the system.

Claims

1. An active grid control modeling method for a high proportion of renewable energy systems, characterized in that: The steps include: Step 1: construct a model of the change in active power output of the converter under small disturbance, so as to establish a linear relationship between the active power output of the converter and the change in load power and the change in phase angle difference of the converter, including: Assume that after the load is connected, the steady-state voltage of the load node is U L0 , then the equivalent admittance formula is: （1） （2） （3） Where ω is the system angular frequency, L i , L fi is the line inductance and filter inductance on the ith line, P L is the active power of the load, x i ,y i is the impedance and admittance of the line where the i-th VSG is located, y0 represents the equivalent admittance of the load in the admittance model, y i is the line admittance of the jth VSG, y ij is the admittance of each line in the system admittance model, ; Step 2: construct a VSG control model and establish a mathematical model of the converter control link; VSG stands for virtual synchronous generator; Step 3: Based on the linear relationship in step 1 and the VSG control model in step 2, an active-frequency response model of multiple VSGs in parallel operation is constructed to realize rapid modeling of active network control of multiple VSGs in parallel operation, including: The converter active power output variation model under small disturbance is integrated with the VSG control model to obtain the active power-frequency response model of multiple VSGs running in parallel as follows: （12） Among them, Δω vi and Δω vj are the output frequency signal changes of the i-th VSG and the j-th VSG, respectively, and K Ji , K Di are the inertia coefficient and primary frequency modulation coefficient of the i-th VSG, K ii is the active linear coefficient of the ith VSG, is the load active power change, K ij is the linear coefficient of the phase angle between the i-th VSG and the j-th VSG; δ ij represents the power angle difference between the i-th VSG and the j-th VSG, represents the change in the power angle difference between the i-th VSG and the j-th VSG, ; Step 4: Based on the active power-frequency response model of multiple VSGs in parallel operation constructed in step 3, a prediction and correction link model is constructed to accurately reflect the actual dynamic behavior of the high-proportion renewable energy system, including: Based on formula (12) in step 3, for each time t, using the active power-frequency response model of multiple VSGs running in parallel obtained in step 3, the phase angle difference parameter δ of each VSG is ij (t) Predict the active power output at the next moment , as the model prediction output, the expression is as follows: （13） Where g is a function describing the dynamic behavior of the VSG, and u is the control input vector, including the power set point and other control signals; Represents the power angle difference between the VSGs at time t.

2. The active grid control modeling method for a high-proportion renewable energy system according to claim 1 is characterized in that: The step 1 also includes: The admittance model of a system with multiple VSGs running in parallel is established, and based on the admittance model, the self-admittance and mutual-admittance in the system with multiple VSGs running in parallel are obtained as follows: （4） Among them, Y 11 , Y 22 and Y 22 are the self-admittances of VSG1, VSG2 and VSG3 respectively, and Y 12 , Y 21 represents the mutual admittance between VSG1 and VSG2, Y 13 , Y 31 represents the mutual admittance between VSG1 and VSG3, Y 23 , Y 32 represents the mutual admittance between VSG2 and VSG3, G 11 , G 22 and are the self-conductances of VSG1, VSG2 and VSG3, respectively. 12 , G 21 represents the mutual conductance between VSG1 and VSG2, G 13 , G 31 represents the mutual conductance between VSG1 and VSG3, G 23 , G 32 represents the mutual conductance between VSG2 and VSG3; B 11 , B 22 and B 22 are the self-susceptance of VSG1, VSG2 and VSG3 respectively, and B 12 , B 21 Indicates the mutual susceptance between VSG1 and VSG2, B 13 , B 31 Indicates the mutual susceptance between VSG1 and VSG3, B 23 , B 32 represents the mutual admittance between VSG2 and VSG3; VSG1, VSG2 and VSG3 represent the first VSG, the second VSG and the third VSG respectively; y ij is the admittance of each line in the system admittance model, ; m represents the imaginary unit.

3. The active grid control modeling method for a high-proportion renewable energy system according to claim 2 is characterized in that: The step 1 also includes: The change in active power output by the first, second, and third VSGs under small disturbances is derived as follows: （8） Among them, ΔP E1 , ΔP E2 , ΔP E3 Indicates the change in active power output of the first, second, and third VSGs, K 11 , K 22 , K 33 are the active linear coefficients of the first, second and third VSGs, respectively, K 12 is the phase angle linear coefficient between the first VSG and the second VSG, K 13 is the phase angle linear coefficient between the first VSG and the third VSG, K 23 is the phase angle linear coefficient between the second VSG and the third VSG; Indicates the change in active power of the load; Indicates the change in the power angle difference between the first VSG and the second VSG. Indicates the change in the power angle difference between the first VSG and the third VSG. Indicates the change in the power angle difference between the second VSG and the third VSG.

4. The active grid control modeling method for a high-proportion renewable energy system according to claim 3 is characterized in that: The step 1 also includes: The calculated active linear coefficients and phase angle linear coefficients are: （9） Among them, x1, x2, and x2 are the reactances of the lines where the first VSG, the second VSG, and the third VSG are located respectively; is the phase angle linear coefficient between the second VSG and the first VSG, is the phase angle linear coefficient between the third VSG and the first VSG, is the phase angle linear coefficient between the third VSG and the second VSG; E1, E2, and E3 represent the electromotive force of the first VSG, the second VSG, and the third VSG respectively; is the steady-state voltage at the load node.

5. The active grid control modeling method for a high-proportion renewable energy system according to claim 4 is characterized in that: Calculate the actual active power output P(t+1) and the model predicted output The difference between them is e t+1 , and further use the gradient descent method to update the parameters, the expression is as follows: （15） in, represents the change in the power angle difference between the VSGs at time t, η is the learning rate, which determines the amplitude of parameter adjustment of the active power-response model of the system with multiple VSGs in parallel operation at each update, is the loss function J relative to the phase angle difference parameter δ of each VSG ij The gradient of (t); the loss function J is the function of the error; So the gradient Written as: （17） in, is the Jacobian matrix of the predicted output with respect to the parameters; Formula (15) is the prediction and correction model.

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