Heterogeneous system stability analysis method based on nonlinear dynamic simplified model

Abstract

The invention provides a heterogeneous system stability analysis method based on a nonlinear dynamics simplified model, which comprises the following steps: establishing a simplified model topological structure based on a heterogeneous system and obtaining a phase angle difference which is the difference between the phase angle of a first node and the phase angle of a second node; based on the simplified model topological structure, obtaining a nonlinear dynamic simplified model according to the heterogeneous system and the phase angle difference; solving the nonlinear dynamic model by adopting an average method to obtain an analytic solution, wherein the analytic solution is an expression of the square of the system amplitude; performing time derivation on the analytical solution to obtain a third first-order derivative; when the third first-order derivative is zero, obtaining a stability criterion; and judging the stability of the heterogeneous system according to the stability criterion. The heterogeneous system stability analysis method based on the nonlinear dynamics simplified model is simple and efficient, the model order is low, the nonlinear characteristic of the system is reserved, analysis solution is performed based on the generalized average method, system stability criteria are provided, and stability analysis is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of smart grid control technology, and in particular to a heterogeneous system stability analysis method based on a simplified nonlinear dynamics model. Background Art

[0002] In recent years, the development of new energy has been rapid. With the continuous advancement of technology, the penetration of new energy in the power grid has increased day by day. At present, the grid-connected new energy is mainly achieved by using a grid-following converter to collect the voltage of the common connection point through a phase-locked loop for control, but sub- and super-synchronous oscillations are prone to occur under weak power grids. Grid-connected converters widely use droop control, most of which have power synchronization characteristics and can actively provide support for the voltage and frequency of the power grid. The use of the two converters has become a new trend, forming a heterogeneous new energy system. Therefore, it is of great practical significance to conduct research on the nonlinear dynamic behavior of heterogeneous new energy systems and analyze their transient stability. However, the commonly used transient simulation methods have long simulation operation time and low efficiency when analyzing system stability, which makes it difficult to meet the needs of rapid analysis and evaluation of system stability. The existing research also lacks stability analysis of heterogeneous systems. In this case, how to efficiently and accurately obtain the nonlinear dynamic behavior of heterogeneous systems and obtain their stability criteria for stability analysis has become a key issue. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a heterogeneous system stability analysis method based on a simplified nonlinear dynamics model, which reduces the model order while retaining the nonlinear characteristics of the system to the greatest extent, and can quickly obtain the system stability criterion while retaining the system nonlinearity, so as to facilitate stability analysis and reduce the difficulty of analysis.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: a method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model, comprising the following steps:

[0005] A simplified model topology structure is established based on a heterogeneous system; the simplified model topology structure includes a first control module, a second control module, a line module, a first node and a second node, one end of the line module is connected to the first control module through the first node, and the other end of the line module is connected to the second control module through the second node; the first control module is obtained based on a grid-forming converter, and the second control module is obtained based on a grid-following converter;

[0006] Based on the simplified model topology, a first phase angle and a second phase angle are obtained according to the heterogeneous system, wherein the first phase angle is a phase angle of the first node, and the second phase angle is a phase angle of the second node;

[0007] Obtaining a phase angle difference according to the first phase angle and the second phase angle, wherein the phase angle difference is a difference between a phase angle of the first node and a phase angle of the second node;

[0008] Based on the simplified model topology, a first first-order derivative, a first second-order derivative, a second first-order derivative, and a second second-order derivative are respectively obtained according to the heterogeneous system and the phase angle difference, wherein the first first-order derivative is the first-order derivative of the first phase angle with respect to time, the first second-order derivative is the second-order derivative of the first phase angle with respect to time, the second first-order derivative is the first-order derivative of the second phase angle with respect to time, and the second second-order derivative is the second-order derivative of the second phase angle with respect to time;

[0009] Based on the first first-order derivative, the second first-order derivative and the phase angle difference, a nonlinear dynamics simplified model is obtained by subtracting the second second-order derivative from the first second-order derivative;

[0010] The nonlinear dynamic model is solved by an average method to obtain an analytical solution, wherein the analytical solution is an expression of the square of the system amplitude;

[0011] Deriving the analytical solution with respect to time to obtain a third first-order derivative;

[0012] A stability criterion is obtained when the third first-order derivative is zero;

[0013] The stability of the heterogeneous system is judged according to the stability criterion.

[0014] Further, the step of obtaining the first first-order derivative is:

[0015] Based on the simplified model topology, a common angular frequency, a first electric quantity variable and a first control parameter of the power grid are obtained according to the heterogeneous system; the first electric quantity variable is the electric quantity variable at the first node, and the first control parameter is the control parameter of the grid-connected converter;

[0016] Obtaining a first expression according to the first electric quantity variable, where the first expression is an initial expression of the active power of the first node;

[0017] Obtaining the first node active power according to the first expression and the phase angle difference;

[0018] The first first-order derivative is obtained according to the common angular frequency of the power grid, the first control parameter and the first node active power.

[0019] Further, the step of obtaining the first second-order derivative is:

[0020] Deriving the first first-order derivative with respect to time to obtain a second expression, where the second expression is an initial expression of the first second-order derivative;

[0021] Deriving the active power of the first node with respect to time to obtain a third first-order derivative;

[0022] Substituting the third first-order derivative into the second expression obtains the first second-order derivative.

[0023] Further, the step of obtaining the second second-order derivative is:

[0024] Based on the simplified model topology, a common angular frequency, a first electric quantity variable, a second electric quantity variable, a line parameter, and a second control parameter of the power grid are obtained according to the heterogeneous system; the first electric quantity variable is the electric quantity variable at the first node, the line parameter is the circuit parameter of the line module, the second electric quantity variable is the electric quantity variable at the second node, and the second control parameter is the control parameter of the grid-type converter;

[0025] Obtaining the second first-order derivative according to the common angular frequency of the power grid, the second control parameter and the second electric quantity variable;

[0026] Deriving the second first-order derivative with respect to time to obtain a third expression, wherein the third expression is an initial expression of the second second-order derivative;

[0027] Obtaining a q-axis voltage of a second node according to the first electrical quantity variable, the line parameter and the phase angle difference;

[0028] Derivative the q-axis voltage of the second node with respect to time to obtain a fourth first-order derivative;

[0029] Substituting the fourth first-order derivative into the third expression obtains the second second-order derivative.

[0030] Furthermore, the nonlinear dynamics simplified model is:

[0031] in,

[0032]

[0033] Where x is the phase angle difference, is the first-order derivative of the phase angle difference with respect to time, is the second-order derivative of the phase angle difference with respect to time, a1 is the first intermediate expression, a2 is the second intermediate expression, a3 is the third intermediate expression, a4 is the fourth intermediate expression, a5 is the second intermediate expression, a6 is the sixth intermediate expression, k p is the proportional parameter of the grid-type converter PLL, k i is the integral parameter of the grid-type converter PLL, V a is the first node voltage, L abis the line inductance between the first node and the second node, I ad is the d-axis component of the current injected into the first node, D p is the droop coefficient of the grid-connected converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value of droop control of grid-connected converter.

[0034] Furthermore, the steps of using the average method to solve the nonlinear dynamic model to obtain the analytical solution are:

[0035] The nonlinear dynamics simplified model is subjected to Taylor expansion to obtain a process expression, which is:

[0036]

[0037] In the formula, f is a nonlinear function;

[0038] Based on the simplified model topology, the relationship between the system amplitude, the initial phase angle and the system frequency is obtained according to the heterogeneous system;

[0039] Based on the relationship, a fourth expression is obtained according to the process expression, and the fourth expression is an initial expression of the analytical solution; the fourth expression is:

[0040]

[0041]

[0042] In the formula, A is the system amplitude, θ is the initial phase angle, and t is the time;

[0043] Substituting the fourth expression into the nonlinear function obtains a fifth expression, which is:

[0044] in,

[0045]

[0046] Wherein, b1 is the seventh intermediate expression, b2 is the eighth intermediate expression, b3 is the ninth intermediate expression, b4 is the tenth intermediate expression, b5 is the eleventh intermediate expression, is the twelfth intermediate expression.

[0047] Substituting the fourth expression into the process expression, the averaged equation of the heterogeneous system is obtained, and the averaged equation is:

[0048]

[0049] In the formula, is the first-order derivative of the system amplitude with respect to time, is the first-order derivative of the initial phase angle with respect to time.

[0050] Substituting the fifth expression into the averaging equation obtains the analytical solution.

[0051] Furthermore, the analytical solution is:

[0052]

[0053] Where C is the integration constant.

[0054] Furthermore, the method for judging the stability of the heterogeneous system according to the stability criterion is:

[0055] When the stability criterion is less than zero, the heterogeneous system is stable;

[0056] When the stability criterion is equal to zero, the heterogeneous system is on the stability boundary;

[0057] When the stability criterion is greater than zero, the heterogeneous system is unstable.

[0058] A nonlinear dynamics simplified model is used for the heterogeneous system stability analysis method based on the nonlinear dynamics simplified model. The nonlinear dynamics simplified model is constructed based on the simplified model topology structure.

[0059] A storage medium includes a stored program, and when the program is run, the device where the storage medium is located is controlled to execute the heterogeneous system stability analysis method based on a simplified nonlinear dynamics model.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] The present invention simplifies the heterogeneous system to obtain a simplified nonlinear dynamics model, and uses the average method to analyze the model to obtain the system analytical solution amplitude, and then obtains the stability criterion, which reduces the steps of using traditional methods to establish a state equation model of the heterogeneous system, while reducing the model order and retaining the nonlinear characteristics of the system to the greatest extent. The system stability criterion can be quickly obtained while retaining the system nonlinearity, so as to facilitate stability analysis and reduce the difficulty of analysis.

[0062] The present invention obtains a simplified second-order nonlinear dynamics model of a heterogeneous system and performs an analytical solution based on a generalized average method, analyzes the amplitude of the system analytical solution, and proposes a system stability criterion.

[0063] The present invention solves the problems of the traditional heterogeneous system model being complex, inefficient and not having prominent nonlinear characteristics, and combines the nonlinear vibration theory to achieve further analysis of the system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 A schematic diagram of a simplified model topology structure in an embodiment of the present invention;

[0065] Figure 2 The present invention is a flow chart of a method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model. DETAILED DESCRIPTION

[0066] The grid-following converter is mainly controlled by a phase-locked loop (PLL). From the perspective of the external power grid, it can be equivalent to a current source. The amplitude of the current source is given by the current reference of the controller, and the phase is determined by the phase angle output by the PLL.

[0067] Grid-connected converters mostly use droop control. Since they do not require the support of an external grid and have voltage support capabilities, they can be equivalent to a voltage source from the perspective of the external grid. This voltage source does not consider reactive loop control, the voltage amplitude is constant, and the phase angle is affected by droop control.

[0068] A heterogeneous system is formed by using grid-type converters and grid-connected converters together. Regarding heterogeneous systems, most of the existing research is based on small signal state space models, but ignores nonlinear links and is difficult to reflect nonlinear characteristics.

[0069] See also Figure 1-2 The embodiment of the present invention provides a method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model, comprising the following steps:

[0070] A simplified model topology is established based on the heterogeneous system; the simplified model topology includes a first control module, a second control module, a line module, a first node and a second node, one end of the line module is connected to the first control module through the first node, and the other end of the line module is connected to the second control module through the second node; the first control module is obtained based on the grid-forming converter, and the second control module is obtained based on the grid-following converter; the grid-forming converter is equivalent to a voltage source, and the grid-following converter is equivalent to a current source. The first control module is referred to Figure 1 Control block diagram on the left, Figure 1 The lower dotted line frame is the control link of the first control module, and the second control module is shown in FIG. Figure 1 The control block diagram on the right side, Figure 1 The upper dotted box is the control link of the second control module. Figure 1 Point a is the first node, and point b is the second node;

[0071] Based on the simplified model topology, the first phase angle θ is obtained according to the heterogeneous system a and the second phase angle θ b, the first phase angle is the phase angle of the first node, and the second phase angle is the phase angle of the second node;

[0072] The phase angle difference x is obtained according to the first phase angle and the second phase angle, and the phase angle difference is the difference between the phase angle of the first node and the phase angle of the second node; that is, x = θ a -θ b ;

[0073] Based on the simplified model topology, the first-order derivatives are obtained according to the heterogeneous system and phase angle difference. First and second order derivatives Second first-order derivative and the second second derivative The first first-order derivative is the first-order derivative of the first phase angle with respect to time, the first second-order derivative is the second-order derivative of the first phase angle with respect to time, the second first-order derivative is the first-order derivative of the second phase angle with respect to time, and the second second-order derivative is the second-order derivative of the second phase angle with respect to time;

[0074] Preferably, the step of obtaining the first first-order derivative is:

[0075] Based on the simplified model topology, a common angular frequency, a first electric quantity variable and a first control parameter of the power grid are obtained according to the heterogeneous system; the first electric quantity variable is the electric quantity variable at the first node, and the first control parameter is the control parameter of the grid-forming converter;

[0076] A first expression is obtained according to the first electric quantity variable, and the first expression is an initial expression of the active power of the first node; the first expression is:

[0077]

[0078] Where P a is the active power of the first node, V ad is the first node d-axis voltage, V aq is the q-axis voltage of the first node, I ad is the d-axis component of the current injected into the first node, I aq A q-axis component of the current injected into the first node;

[0079] Usually, the q-axis component of the reference current of the grid-following converter is set to 0, that is, I aq =I bq =0, the first node active power is obtained according to the first expression and the phase angle difference; the first node active power is:

[0080]

[0081] The first first-order derivative is obtained according to the common angular frequency of the power grid, the first control parameter and the first node active power. The first first-order derivative is:

[0082]

[0083] The steps to obtain the first and second order derivatives are:

[0084] The second expression is obtained by differentiating the first first-order derivative with respect to time. The second expression is the initial expression of the first second-order derivative. The second expression is:

[0085]

[0086] The third first-order derivative is obtained by taking the derivative of the active power of the first node with respect to time. The third first-order derivative is:

[0087]

[0088] Substituting the third first-order derivative into the second expression, we obtain the first second-order derivative, which is:

[0089]

[0090] The steps to obtain the second second-order derivative are:

[0091] Based on the simplified model topology, the common angular frequency, the first electrical quantity variable, the second electrical quantity variable, the line parameter and the second control parameter of the power grid are obtained according to the heterogeneous system; the first electrical quantity variable is the electrical quantity variable at the first node, the line parameter is the circuit parameter of the line module, the second electrical quantity variable is the electrical quantity variable at the second node, and the second control parameter is the control parameter of the grid-forming converter;

[0092] The second first-order derivative is obtained according to the common angular frequency of the power grid, the second control parameter and the second electric quantity variable. The second first-order derivative is:

[0093]

[0094] The third expression is obtained by differentiating the second first-order derivative with respect to time. The third expression is the initial expression of the second second-order derivative. The third expression is:

[0095]

[0096] The q-axis voltage of the second node is obtained according to the first electrical quantity variable, the line parameters and the phase angle difference; the q-axis voltage of the second node can be written as:

[0097]

[0098] Where V bq is the q-axis voltage of the second node, ω b is the angular frequency of the second node, is the first derivative of the q-axis component of the current injected into the first node with respect to time, R abis the line resistance between the first node and the second node;

[0099] Similarly, since the q-axis component of the reference current of the grid-following converter is usually set to 0, that is, I aq =I bq =0, so the q-axis voltage of the second node is:

[0100] V bq =V a sin(θ a -θ b )-ω b L ab I ad ;

[0101] The fourth first-order derivative is obtained by derivation of the q-axis voltage of the second node with respect to time. The fourth first-order derivative is:

[0102]

[0103] Substituting the fourth first-order derivative into the third expression yields the second second-order derivative, which is:

[0104]

[0105] Based on the first first-order derivative, the second first-order derivative and the phase angle difference, the nonlinear dynamics simplified model is obtained by subtracting the second second-order derivative from the first second-order derivative; the nonlinear dynamics simplified model is:

[0106] in,

[0107]

[0108] Where x is the phase angle difference, is the first-order derivative of the phase angle difference with respect to time, is the second-order derivative of the phase angle difference with respect to time, a1 is the first intermediate expression, a2 is the second intermediate expression, a3 is the third intermediate expression, a4 is the fourth intermediate expression, a5 is the second intermediate expression, a6 is the sixth intermediate expression, k p is the proportional parameter of the grid-type converter PLL, k i is the integral parameter of the grid-type converter PLL, V a is the first node voltage, L ab is the line inductance between the first node and the second node, I ad is the d-axis component of the current injected into the first node, D p is the droop coefficient of the grid-connected converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value of droop control of grid-connected converter.

[0109] The average method is used to solve the nonlinear dynamic model to obtain the analytical solution, which is the expression of the square of the system amplitude; the average method is the average method of the single-degree-of-freedom self-consistent system;

[0110] The steps to obtain the analytical solution of the nonlinear dynamic model using the average method are as follows:

[0111] The simplified nonlinear dynamics model is Taylor expanded to obtain the process expression, which is:

[0112]

[0113] In the formula, f is a nonlinear function;

[0114] Based on the simplified model topology, the relationship between the system amplitude, initial phase angle and system frequency is obtained according to the heterogeneous system. The relationship is that the changes of the system amplitude and initial phase angle are much slower than the system frequency.

[0115] Based on the relationship, the fourth expression is obtained according to the process expression, and the fourth expression is the initial expression of the analytical solution; the fourth expression is:

[0116] in,

[0117]

[0118] In the formula, A is the system amplitude, θ is the initial phase angle, and t is the time;

[0119] Substituting the fourth expression into the nonlinear function, the fifth expression is obtained:

[0120] in,

[0121]

[0122] Wherein, b1 is the seventh intermediate expression, b2 is the eighth intermediate expression, b3 is the ninth intermediate expression, b4 is the tenth intermediate expression, b5 is the eleventh intermediate expression, is the twelfth intermediate expression.

[0123] Substituting the fourth expression into the process expression, we can obtain the average equation of the heterogeneous system, which is:

[0124]

[0125] In the formula, is the first-order derivative of the system amplitude with respect to time, is the first-order derivative of the initial phase angle with respect to time.

[0126] Substituting the fifth expression into the averaged equation, we obtain the analytical solution, which is:

[0127]

[0128] Where C is the integration constant.

[0129] Differentiate the analytical solution with respect to time to obtain the third first-order derivative;

[0130] The stability criterion is obtained when the third first-order derivative is zero;

[0131] The stability of heterogeneous systems is determined based on stability criteria.

[0132] Preferably, the method for determining the stability of a heterogeneous system according to a stability criterion is:

[0133] When the stability criterion is less than zero, the heterogeneous system is stable;

[0134] When the stability criterion is equal to zero, the heterogeneous system is on the stability boundary;

[0135] When the stability criterion is greater than zero, the heterogeneous system becomes unstable.

[0136] An embodiment of the present invention further provides a simplified nonlinear dynamics model for use in a stable analytical method for heterogeneous systems based on the simplified nonlinear dynamics model. The simplified nonlinear dynamics model is constructed based on a simplified model topology structure.

[0137] An embodiment of the present invention further provides a storage medium, comprising a stored program, which controls a device where the storage medium is located to execute a heterogeneous system stability analysis method based on a simplified nonlinear dynamics model when the program is running.

[0138] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model, characterized by: The following steps are involved: A simplified model topology structure is established based on the heterogeneous system; the simplified model topology structure includes a first control module, a second control module, a line module, a first node and a second node, one end of the line module is connected to the first control module through the first node, and the other end of the line module is connected to the second control module through the second node; The first control module is obtained based on the grid-forming converter, and the second control module is obtained based on the grid-following converter; Based on the simplified model topology, a first phase angle and a second phase angle are obtained according to the heterogeneous system, wherein the first phase angle is a phase angle of the first node, and the second phase angle is a phase angle of the second node; Obtaining a phase angle difference according to the first phase angle and the second phase angle, wherein the phase angle difference is a difference between a phase angle of the first node and a phase angle of the second node; Based on the simplified model topology, a first first-order derivative, a first second-order derivative, a second first-order derivative, and a second second-order derivative are respectively obtained according to the heterogeneous system and the phase angle difference, wherein the first first-order derivative is the first-order derivative of the first phase angle with respect to time, the first second-order derivative is the second-order derivative of the first phase angle with respect to time, the second first-order derivative is the first-order derivative of the second phase angle with respect to time, and the second second-order derivative is the second-order derivative of the second phase angle with respect to time; Based on the first first-order derivative, the second first-order derivative and the phase angle difference, a nonlinear dynamics simplified model is obtained by subtracting the second second-order derivative from the first second-order derivative; The nonlinear dynamic model is solved by an average method to obtain an analytical solution, wherein the analytical solution is an expression of the square of the system amplitude; Deriving the analytical solution with respect to time to obtain a third first-order derivative; A stability criterion is obtained when the third first-order derivative is zero; The stability of the heterogeneous system is judged according to the stability criterion.

2. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 1, characterized in that: The steps to obtain the first first-order derivative are: Based on the simplified model topology, a common angular frequency, a first electric quantity variable and a first control parameter of the power grid are obtained according to the heterogeneous system; the first electric quantity variable is the electric quantity variable at the first node, and the first control parameter is the control parameter of the grid-connected converter; Obtaining a first expression according to the first electric quantity variable, where the first expression is an initial expression of the active power of the first node; Obtaining the first node active power according to the first expression and the phase angle difference; The first first-order derivative is obtained according to the common angular frequency of the power grid, the first control parameter and the first node active power.

3. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 2 is characterized by: The steps to obtain the first second-order derivative are: Deriving the first first-order derivative with respect to time to obtain a second expression, where the second expression is an initial expression of the first second-order derivative; Deriving the active power of the first node with respect to time to obtain a third first-order derivative; Substituting the third first-order derivative into the second expression obtains the first second-order derivative.

4. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 1, characterized in that: The steps to obtain the second second-order derivative are: Based on the simplified model topology, a common angular frequency, a first electric quantity variable, a second electric quantity variable, a line parameter, and a second control parameter of the power grid are obtained according to the heterogeneous system; the first electric quantity variable is the electric quantity variable at the first node, the line parameter is the circuit parameter of the line module, the second electric quantity variable is the electric quantity variable at the second node, and the second control parameter is the control parameter of the grid-type converter; Obtaining the second first-order derivative according to the common angular frequency of the power grid, the second control parameter and the second electric quantity variable; Deriving the second first-order derivative with respect to time to obtain a third expression, wherein the third expression is an initial expression of the second second-order derivative; Obtaining a q-axis voltage of a second node according to the first electrical quantity variable, the line parameter and the phase angle difference; Derivative the q-axis voltage of the second node with respect to time to obtain a fourth first-order derivative; Substituting the fourth first-order derivative into the third expression obtains the second second-order derivative.

5. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 1, characterized in that: The nonlinear dynamics simplified model is: in, Where x is the phase angle difference, is the first-order derivative of the phase angle difference with respect to time, is the second-order derivative of the phase angle difference with respect to time, a1 is the first intermediate expression, a2 is the second intermediate expression, a3 is the third intermediate expression, a4 is the fourth intermediate expression, a5 is the second intermediate expression, a6 is the sixth intermediate expression, k p is the proportional parameter of the grid-type converter PLL, k i is the integral parameter of the grid-type converter PLL, V a is the first node voltage, L ab is the line inductance between the first node and the second node, I ad is the d-axis component of the current injected into the first node, D p is the droop coefficient of the grid-connected converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value of droop control of grid-connected converter.

6. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 5 is characterized by: The steps of using the average method to solve the nonlinear dynamic model to obtain the analytical solution are: The nonlinear dynamics simplified model is subjected to Taylor expansion to obtain a process expression, which is: In the formula, f is a nonlinear function; Based on the simplified model topology, the relationship between the system amplitude, the initial phase angle and the system frequency is obtained according to the heterogeneous system; Based on the relationship, a fourth expression is obtained according to the process expression, and the fourth expression is an initial expression of the analytical solution; the fourth expression is: In the formula, A is the system amplitude, θ is the initial phase angle, and t is the time; Substituting the fourth expression into the nonlinear function obtains a fifth expression, which is: in, Wherein, b1 is the seventh intermediate expression, b2 is the eighth intermediate expression, b3 is the ninth intermediate expression, b4 is the tenth intermediate expression, b5 is the eleventh intermediate expression, is the twelfth intermediate expression; Substituting the fourth expression into the process expression, the averaged equation of the heterogeneous system is obtained, and the averaged equation is: In the formula, is the first-order derivative of the system amplitude with respect to time, is the first-order derivative of the initial phase angle with respect to time; Substituting the fifth expression into the averaging equation obtains the analytical solution.

7. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 6, characterized in that: The analytical solution is: Where C is the integration constant.

8. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 1, characterized in that: Features: The method for judging the stability of the heterogeneous system according to the stability criterion is: When the stability criterion is less than zero, the heterogeneous system is stable; When the stability criterion is equal to zero, the heterogeneous system is on the stability boundary; When the stability criterion is greater than zero, the heterogeneous system is unstable.

9. A simplified nonlinear dynamics model, used to implement the heterogeneous system stability analysis method based on the simplified nonlinear dynamics model according to any one of claims 1 to 8, characterized in that: The nonlinear dynamics simplified model is constructed based on the simplified model topology structure.

10. A storage medium, characterized in that: It includes a stored program, which, when running, controls the device where the storage medium is located to execute the heterogeneous system stability analysis method based on the nonlinear dynamic simplified model as described in any one of claims 1 to 8.

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