Analytical method for stability of heterogeneous systems based on simplified nonlinear dynamics model

Abstract

The present invention provides a method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model, comprising the following steps: establishing a simplified model topology based on the heterogeneous system and obtaining a phase angle difference, where the phase angle difference is the difference between the phase angle of a first node and the phase angle of a second node; obtaining a simplified nonlinear dynamics model based on the heterogeneous system and the phase angle difference based on the simplified model topology; solving the nonlinear dynamics model using an averaging method to obtain an analytical solution, where the analytical solution is an expression of the square of the system amplitude; differentiating the analytical solution with respect to time to obtain a third first-order derivative; obtaining a stability criterion when the third first-order derivative is zero; and determining the stability of the heterogeneous system based on the stability criterion. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model provided by the present invention is simple and efficient, has a low model order, retains the nonlinear characteristics of the system, performs an analytical solution based on a generalized averaging method, proposes a system stability criterion, and facilitates stability analysis.

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] Renewable energy has experienced rapid development in recent years, and with continuous technological advancements, their penetration into power grids is increasing. Currently, grid-connected renewable energy sources primarily rely on grid-following converters, which use a phase-locked loop (PLL) to collect voltage at the common connection point for control. However, this can easily lead to subsynchronous and supersynchronous oscillations in weak grids. Grid-connecting converters widely utilize droop control, and most feature power synchronization, actively supporting grid voltage and frequency. The combined use of these two types of converters is becoming a new trend, creating heterogeneous renewable energy systems. Therefore, studying the nonlinear dynamic behavior of heterogeneous renewable energy systems and analyzing their transient stability is of paramount importance. However, currently used transient simulation methods for analyzing system stability suffer from long computation times and low efficiency, making them inefficient and unable to meet the requirements for rapid analysis and assessment of system stability. Existing research also lacks robustness for the stability analysis of heterogeneous systems. Therefore, efficiently and accurately determining the nonlinear dynamic behavior of heterogeneous systems and deriving stability criteria for stability analysis becomes a key issue. Summary of the Invention

[0003] In response to 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. It can also 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 objectives, the present invention adopts the following technical solution: 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 is established based on a 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, wherein one end of the line module is connected to the first control module via the first node, and the other end of the line module is connected to the second control module via 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, obtaining a first phase angle and a second phase angle according to the heterogeneous system, where 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;

[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 dynamic simplified model is obtained by subtracting the second second-order derivative from the first second-order derivative;

[0010] Solving the nonlinear dynamic model using an averaging method to obtain an analytical solution, wherein the analytical solution is an expression of the square of the system amplitude;

[0011] Derivative 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 determined according to the stability criterion.

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

[0015] Based on the simplified model topology, a common angular frequency, a first electrical quantity variable, and a first 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, and the first control parameter is the control parameter of the grid-connected converter;

[0016] Obtaining a first expression according to the first electrical 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] Furthermore, the step of obtaining the first second-order derivative is:

[0020] Differentiating 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] Derivative 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] Furthermore, the step of obtaining the second second-order derivative is:

[0024] Based on the simplified model topology, a common angular frequency, a first electrical quantity variable, a second electrical quantity variable, a line parameter, and a 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-connected 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] Derivative the second first-order derivative with respect to time to obtain a third expression, where the third expression is an initial expression of the second second-order derivative;

[0027] Obtaining a q-axis voltage at 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 yields 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-following converter PLL, k i is the integral parameter of the grid-following converter PLL, V a is the first node voltage, L abis the line inductance between the first node and the second node, I ad The d-axis component of the current injected into the first node, D p is the droop coefficient of the grid-type converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value for droop control of grid-type converter.

[0034] Furthermore, the steps of using the averaging 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] Where, f is a nonlinear function;

[0038] Based on the simplified model topology, a relationship between a system amplitude, an initial phase angle, and a 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 the initial expression of the analytical solution; the fourth expression is:

[0040]

[0041]

[0042] Where 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 yields 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 yields the averaged equation for the heterogeneous system, which is:

[0048]

[0049] Where, 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, and the nonlinear dynamics simplified model is constructed based on the simplified model topology structure.

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

[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 applies the averaging method to 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 the state equation model of the heterogeneous system. While reducing the model order, the nonlinear characteristics of the system are retained 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] Based on the obtained simplified second-order nonlinear dynamics model of the heterogeneous system, the present invention performs analytical solution based on the generalized averaging method, analyzes the amplitude of the system analytical solution, and proposes a system stability criterion.

[0063] The present invention solves the problems of traditional heterogeneous system models being complex, inefficient, and lacking in prominent nonlinear characteristics, and combines nonlinear vibration theory to achieve further analysis of system stability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0065] Figure 2 This is a flow chart of the heterogeneous system stability analysis method based on the simplified nonlinear dynamics model of the present invention. DETAILED DESCRIPTION

[0066] Grid-following converters primarily use a phase-locked loop (PLL) for control. From the perspective of the external grid, they are equivalent to a current source. The current source amplitude is determined by the controller's current reference, and the phase is determined by the phase angle output by the PLL.

[0067] Grid-connected converters often use droop control. Since they don't require external grid support and inherently have voltage-supporting capabilities, they can be viewed as a voltage source from the perspective of the external grid. This voltage source doesn't consider reactive loop control, and its voltage amplitude remains constant, with its phase angle affected by droop control.

[0068] A heterogeneous system is formed by using grid-type converters and grid-forming converters together. Regarding heterogeneous systems, most 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-type converter, and the second control module is obtained based on the grid-type converter. The grid-type converter is equivalent to a voltage source, and the grid-type 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 box 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, 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 based on the first phase angle and the second phase angle. 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 electrical quantity variable, and a first 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, and the first control parameter is the control parameter of the grid-connected converter;

[0076] A first expression is obtained according to the first electric quantity variable. 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 The 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 active power of the first node is obtained according to the first expression and the phase angle difference; the active power of the first node 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 active power of the first node. 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 of the active power of the first node is obtained by taking the derivative with respect to time. The third first-order derivative is:

[0087]

[0088] Substituting the third first-order derivative into the second expression yields the first and second-order derivatives, which are:

[0089]

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

[0091] Based on the simplified model topology, a common angular frequency, a first electrical quantity variable, a second electrical quantity variable, a line parameter, and a 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-connected 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, 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-type 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 differentiating 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-following converter PLL, k i is the integral parameter of the grid-following 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-type converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value for droop control of grid-type 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 an analytical solution for a nonlinear dynamic model using the averaging method are as follows:

[0111] The process expression is obtained by Taylor expansion of the simplified nonlinear dynamics model. The process expression is:

[0112]

[0113] Where, 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. The fourth expression is the initial expression of the analytical solution; the fourth expression is:

[0116] in,

[0117]

[0118] Where 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 yields the fifth expression, which is:

[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] Where, 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 the 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 heterogeneous system stability analysis method 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 including a stored program, which controls the 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: Establishing a simplified model topology structure 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, wherein one end of the line module is connected to the first control module via the first node, and the other end of the line module is connected to the second control module via the second node; Obtaining the first control module based on the grid-forming converter, and obtaining the second control module based on the grid-following converter; Based on the simplified model topology, obtaining a first phase angle and a second phase angle according to the heterogeneous system, where 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; 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 dynamic simplified model is obtained by subtracting the second second-order derivative from the first second-order derivative; Solving the nonlinear dynamic model using an averaging method to obtain an analytical solution, wherein the analytical solution is an expression of the square of the system amplitude; Derivative 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 determined 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 is characterized by: The steps for obtaining the first first-order derivative are: Based on the simplified model topology, a common angular frequency, a first electrical quantity variable, and a first 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, and the first control parameter is the control parameter of the grid-connected converter; Obtaining a first expression according to the first electrical 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, characterized in that: The steps to obtain the first second-order derivative are: Differentiating 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; Derivative 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 electrical quantity variable, a second electrical quantity variable, a line parameter, and a 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-connected 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; Derivative the second first-order derivative with respect to time to obtain a third expression, where the third expression is an initial expression of the second second-order derivative; Obtaining a q-axis voltage at 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 yields 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 is characterized by: The simplified nonlinear dynamics 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-following converter PLL, k i is the integral parameter of the grid-following 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 The d-axis component of the current injected into the first node, D p is the droop coefficient of the grid-type converter, ω0 is the common angular frequency of the grid, P aref It is the active power reference value for droop control of grid-type converter.

6. The method for analyzing the stability of heterogeneous systems based on a simplified nonlinear dynamics model according to claim 5, characterized in that: The steps of using the averaging 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: Where, f is a nonlinear function; Based on the simplified model topology, a relationship between a system amplitude, an initial phase angle, and a 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 the initial expression of the analytical solution; the fourth expression is: Where A is the system amplitude, θ is the initial phase angle, and t is the time; Substituting the fourth expression into the nonlinear function yields 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 yields the averaged equation for the heterogeneous system, which is: Where, 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: Its characteristics are: 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 for implementing 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: The invention comprises a stored program, which 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 when the program is run.

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