Power system stability determination method, device, terminal equipment and storage medium

Abstract

The present invention discloses a method, apparatus, terminal device, and storage medium for determining power system stability. The method includes: constructing a state space equation for a hybrid two-terminal DC power system; using a state variable whose participation factor exceeds a preset threshold as a primary state variable, and obtaining an analytical solution for the dominant oscillation frequency based on the state space and the primary state variable; determining a system stability criterion based on the analytical solution for the dominant oscillation frequency and the state space equation; determining, based on the system stability criterion, the stability conditions that the outer loop control parameters of the VSC must satisfy when the hybrid two-terminal DC power system is stable; obtaining the current outer loop control parameters of the VSC in the current hybrid two-terminal DC power system; and determining that the current hybrid two-terminal DC power system is stable if the current outer loop control parameters satisfy the stability conditions; otherwise, determining that the hybrid two-terminal DC power system is unstable. By implementing the present invention, it is possible to determine whether a hybrid DC power system is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power grids, and in particular to a method, apparatus, terminal equipment and storage medium for determining the stability of an electric power system. Background Art

[0002] Traditional DC transmission, based on line-commutated converters (LCCs), offers low cost, high transmission capacity, minimal transmission losses, and rapid control of active power. However, this can lead to commutation failures and requires filters and bulky reactive power compensation devices. Flexible DC transmission, based on voltage-source converters (VSCs), avoids commutation failures and offers a compact structure, a small footprint, and the ability to independently regulate active and reactive power. However, this comes at the expense of high equipment costs and significant operating losses. Hybrid DC transmission combines the advantages of both LCC-HVDC and VSC-HVDC, reducing costs and operating losses while effectively avoiding commutation failures. This system holds broad application prospects in future power systems. However, due to the interaction between the different converters and the DC link, hybrid DC systems can experience DC-side oscillation and instability.

[0003] How to judge the stability of hybrid DC power systems is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] Embodiments of the present invention provide a method, apparatus, terminal device, and storage medium for determining power system stability, which can determine whether a hybrid direct current power system is stable.

[0005] An embodiment of the present invention provides a method for determining power system stability, comprising: constructing a state space equation for a hybrid two-terminal DC power system, and determining state variables involved in constructing the state space equation;

[0006] Taking the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtaining an analytical solution of the dominant oscillation frequency of the hybrid two-terminal DC power system based on the state space and the main state variable;

[0007] generating a characteristic equation of a hybrid two-terminal direct current power system according to the analytical solution of the dominant oscillation frequency and the state-space equation, and then determining a system stability criterion according to the characteristic equation;

[0008] According to the system stability criterion, determining the stability conditions that the outer loop control parameters of the VSC need to meet when the hybrid double-terminal DC power system is stable;

[0009] Obtain current outer loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer loop control parameters meet the stability condition, determine that the current hybrid two-terminal DC power system is stable; otherwise, determine that the current hybrid two-terminal DC power system is unstable.

[0010] Furthermore, the state space equation is:

[0011]

[0012] in,

[0013]

[0014]

[0015] Δ represents the offset of the equilibrium point; x is the state variable; A is the state matrix; B is the input matrix; u is the input variable; subscript 0 represents the initial steady-state value; is the VSC DC side voltage; is the d-axis current of the VSC converter; i dc is the current of the DC transmission line; x v It is the integral link of VSC outer loop control; x i is the integral link of LCC control; x in It is the integral link of the VSC inner loop control; is the set value of VSC DC voltage; is the setting value of LCC constant current control; g0 is the initial equivalent conductance of VSC; C dc is the DC side equivalent capacitance of VSC; k0 is the voltage coefficient of VSC; is the proportional gain of the VSC inner loop control; is the integral gain of the VSC inner loop control; is the proportional gain of the VSC outer loop voltage control; is the proportional gain of LCC control; R s is the equivalent resistance of the AC side of the converter; L s is the equivalent inductance of the AC side of the converter; L dc is the total equivalent inductance of the transmission line; R eq is the total equivalent resistance of the transmission line; U0 is the ideal DC no-load voltage; α is the trigger angle of the LCC; is the integral gain of the VSC outer loop voltage control; is the integral gain of LCC control.

[0016] Furthermore, the analytical solution of the dominant oscillation frequency is:

[0017] Furthermore, generating the characteristic equation of the hybrid two-terminal DC power system according to the dominant oscillation frequency analytical solution and the state space equation includes:

[0018] Performing Laplace transform on the state space equation to obtain the initial characteristic equation of the hybrid two-terminal DC power system;

[0019] Simplifying the initial characteristic equation according to the analytical solution of the dominant oscillation frequency to obtain the characteristic equation of the hybrid two-terminal DC power system;

[0020] The characteristic equation of the hybrid two-terminal DC power system is:

[0021] F d (s)=b2s 2 +b1s+b0;

[0022] in,

[0023]

[0024]

[0025] s is the Laplace operator; b0, b1 and b2 are all system damping.

[0026] Furthermore, the system stability criterion is:

[0027]

[0028] in, R l is the equivalent resistance of the DC line, d x is the equivalent commutation resistance; Q is the stability criterion.

[0029] Furthermore, the stability conditions that the outer loop control parameters of VSC need to meet are:

[0030]

[0031]

[0032] in, The minimum voltage allowed by the HVDC transmission system; i dcmax The maximum current allowed by the HVDC system.

[0033] Based on the above method embodiment, the present invention provides a corresponding equipment embodiment;

[0034] An embodiment of the present invention provides a power system stability determination device, comprising: a state space equation construction module, a dominant oscillation frequency analytical solution determination module, a system stability criterion determination module, a stability condition determination module, and a stability judgment module;

[0035] The state space equation construction module is used to construct the state space equation of the hybrid two-terminal DC power system and determine the state variables involved in constructing the state space equation;

[0036] The dominant oscillation frequency analytical solution determination module is configured to take the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtain the dominant oscillation frequency analytical solution of the hybrid two-terminal DC power system based on the state space and the main state variable;

[0037] The system stability criterion determination module is configured to generate a characteristic equation of a hybrid two-terminal direct current power system based on the dominant oscillation frequency analytical solution and the state-space equation, and then determine a system stability criterion based on the characteristic equation;

[0038] The stability condition determination module is configured to determine, based on the system stability criterion, stability conditions that the outer loop control parameters of the VSC need to satisfy when the hybrid double-terminal DC power system is stable;

[0039] The stability judgment module is used to obtain current outer-loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer-loop control parameters meet the stability conditions, the current hybrid two-terminal DC power system is determined to be stable; otherwise, the current hybrid two-terminal DC power system is determined to be unstable.

[0040] Based on the above method embodiment, the present invention provides a corresponding terminal device embodiment;

[0041] An embodiment of the present invention provides a terminal device, comprising: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the method for determining the stability of the power system described in any one of the present inventions is implemented.

[0042] Based on the above method embodiment, the present invention provides a corresponding storage medium embodiment;

[0043] An embodiment of the present invention provides a storage medium, wherein the computer-readable storage medium includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the power system stability determination methods described in the present invention.

[0044] The following beneficial effects are achieved by implementing the embodiments of the present invention:

[0045] Embodiments of the present invention provide a method, apparatus, terminal device, and storage medium for determining power system stability. The method constructs a stability criterion for a hybrid two-terminal DC power system based on state-space equations and an analytical solution to the dominant oscillation frequency. Based on the stability criterion, the stability conditions that the outer-loop control parameters of the VSC must satisfy when the hybrid two-terminal DC power system is stable are determined. Finally, based on the stability conditions and the current outer-loop control parameters of the VSC in the hybrid two-terminal DC power system, the stability of the hybrid two-terminal DC power system is determined. By implementing the present invention, stability analysis can be performed on a hybrid two-terminal DC power system, automatically assessing whether the hybrid two-terminal DC power system is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flowchart of a method for determining power system stability provided by one embodiment of the present invention.

[0047] Figure 2 FIG. 1 is a schematic diagram of an equivalent circuit of an LCC provided by an embodiment of the present invention.

[0048] Figure 3 FIG. 1 is a schematic diagram of an equivalent circuit of a VSC provided by an embodiment of the present invention.

[0049] Figure 4 This is a structural diagram of a hybrid double-terminal DC power system provided by an embodiment of the present invention.

[0050] Figure 5 It is a structural diagram of a power system stability determination device provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0052] First, it should be noted that the power system stability determination method provided by the present invention is used to determine the small-disturbance stability of a hybrid two-terminal DC power system.

[0053] like Figure 1 As shown, an embodiment of the present invention provides a method for determining power system stability, which at least includes:

[0054] Step S101: constructing a state space equation of a hybrid two-terminal direct current power system and determining state variables involved in constructing the state space equation.

[0055] Step S102: taking the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtaining an analytical solution of the dominant oscillation frequency of the hybrid two-terminal DC power system according to the state space and the main state variable.

[0056] Step S103: generating a characteristic equation of the hybrid two-terminal direct current power system according to the dominant oscillation frequency analytical solution and the state-space equation, and then determining a system stability criterion according to the characteristic equation.

[0057] Step S104: determining, based on the system stability criterion, stability conditions that the outer loop control parameters of the VSC need to satisfy when the hybrid double-terminal DC power system is stable.

[0058] Step S105: obtaining current outer loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer loop control parameters meet the stability condition, determining that the current hybrid two-terminal DC power system is stable; otherwise, determining that the current hybrid two-terminal DC power system is unstable.

[0059] For step S101, Figure 2 、 3 as well as Figure 4 As shown in Figure 2, the state space equation of the hybrid two-terminal DC power system is constructed based on the converter model.

[0060] Specifically, such as Figure 2 The equivalent circuit of the LCC is shown, and the dynamic model of the LCC is expressed as follows:

[0061]

[0062]

[0063]

[0064] in, i dc are the DC voltage and DC current of the LCC as the rectifier side respectively; U0 is the ideal DC no-load voltage; E is the effective value of the power line electromotive force; d x is the equivalent commutation resistance; d x i dc It indicates the voltage drop caused by the commutation current in the commutation reactance, which results in the LCC AC voltage and DC voltage drop;

[0065] LCC adopts constant DC current control, and its control process is shown as follows:

[0066]

[0067]

[0068] in, and are the proportional gain and integral gain of LCC control respectively; is the setting value of LCC constant current control; α is the trigger angle of LCC, x I It is the integral link of LCC control;

[0069] See also Figure 3 , the relationship between the d-axis voltage and d-axis current of VSC is shown as follows:

[0070]

[0071] in, and are the grid d-axis voltage and the converter d-axis voltage, and are the q-axis and d-axis currents of the VSC converter, Rs and Ls are the equivalent resistance and inductance of the AC side of the converter, respectively;

[0072] When the d-axis and grid voltage coincide, the active power and reactive power of the VSC are decoupled, and its active power is only related to the d-axis current. Therefore, only the d-axis current of the VSC is considered. The relationship between the capacitor current and the VSC DC side voltage is:

[0073]

[0074] Among them, i C is the equivalent capacitor current, is the VSC DC side voltage;

[0075] According to the equivalent circuit diagram of VSC, the equivalent capacitor current i C , VSC DC side current i dc and DC side injection current i d The relationship between them is:

[0076] i dc =i d +i C (8)

[0077] Ignoring the losses of the converter and transformer, the power balance equations on the AC and DC sides are:

[0078]

[0079] Among them, P ac and P dc are the active powers on the AC and DC sides of the VSC respectively;

[0080] According to the characteristics of VSC, the relationship between the AC side voltage and the DC voltage of VSC can be obtained as follows:

[0081]

[0082] in, is the modulation ratio of the VSC and is proportional to the d-axis voltage of the VSC;

[0083] The inner loop control equation of VSC is as follows:

[0084]

[0085]

[0086] in, and are the proportional gain and integral gain of the VSC inner loop control respectively; is the set value of the VSC's d-axis AC current, x in It is the integral link of the VSC inner loop control;

[0087] The VSC outer loop adopts constant DC voltage control and uses a PI controller to keep the DC voltage at a constant value. The control equation is shown in Equation (13):

[0088]

[0089]

[0090] in, and are the proportional gain and integral gain of the VSC outer loop voltage control respectively; is the set value of VSC DC voltage, x V It is the integral link of the VSC outer loop control;

[0091] Since the oscillation frequency of the DC side system does not exceed the feasible frequency of the RL transmission line model, the RL transmission line model is used to simplify the analysis. The relationship between the rectifier side DC voltage and the inverter side DC voltage is expressed as:

[0092]

[0093] Among them, R l and L l are the equivalent resistance and equivalent inductance of the DC line respectively, i dc is the current of the DC transmission line, and the smoothing reactor on the rectifier side is L d Indicates that the smoothing reactor on the inverter side is L T express;

[0094] After linearizing the above equation around the equilibrium point, the state space equation of the hybrid two-terminal DC power system can be obtained as follows:

[0095]

[0096] Where x is the state variable, A is the state matrix, B is the input matrix, and u is the input variable. The state variables and matrices are expressed as follows:

[0097]

[0098]

[0099] In step S102, based on the established system state space equation and the participation factors of each state variable, a state variable highly correlated with the dominant mode is selected to obtain an analytical solution of the dominant oscillation frequency;

[0100] First, all the state variables of the system are divided into variables with large participation factors under the dominant mode (i.e., the main state variables mentioned above) and variables with small participation factors according to the preset threshold. Then, the system state space equation represented by Equation (16) can be rewritten as follows:

[0101]

[0102] Among them, Δx1 is the variable with the greatest influence on the system under the dominant mode (i.e., the main state variable mentioned above), and Δx2 is the variable with the least influence on the system under the dominant mode (i.e., other state variables except the main state variable mentioned above).

[0103] Δx2=[Δi dc ,Δx v ,Δx i ,Δx in ] T ; A11, A12, A21, A22, B1, B2 are represented as follows:

[0104]

[0105]

[0106]

[0107] Ignoring the state variables with low correlation in the dominant mode (i.e., other state variables except the above-mentioned main state variables), the dominant oscillation frequency can be obtained as:

[0108]

[0109] Among them, ω dis the dominant oscillation frequency.

[0110] In step S103, the calculated dominant oscillation frequency is used to obtain a reduced-order system small-disturbance stability analysis model, thereby deriving a system small-disturbance stability analytical criterion;

[0111] Specifically, after performing Laplace transformation on Equation (18), we can obtain:

[0112] sI 11 Δx1=A 11 Δx1+A 12 Δx2+B1Δu (21)

[0113] sI 22 Δx1=A 21 Δx1+A 22 Δx2+B2Δu (22)

[0114] Among them, I 22 is a fourth-order identity matrix, the same order as A22;

[0115] The initial characteristic equation of the original system can be obtained as:

[0116] F(s)=det[(sI 11 -A 11 )+A 12 (sI 22 -A 22 ) -1 A 21 ] (twenty three)

[0117] Among them, (sI 11 -A 11 ) is the main state variable system that has a greater impact on the system under the dominant mode (i.e., the variable system composed of the above main state variables); (sI 22 -A 22 ) is a non-main state variable system that has little influence on the system under the dominant mode (i.e., a variable system composed of other state variables except the main state variables);

[0118] Since the damping under the dominant mode is relatively small, the Laplace operator s under the dominant mode can be expressed as jω d Expressed as (j is an imaginary unit), the characteristic equation of the dominant frequency neighborhood is simplified as follows:

[0119]

[0120] Among them, MR and MI are two-order square matrices, and their values ​​are as follows:

[0121]

[0122]

[0123] Based on (25) and (26), the characteristic equation of the hybrid two-terminal DC power system can be obtained as:

[0124]

[0125] This system can be represented by a second-order characteristic polynomial, where the coefficients are:

[0126]

[0127]

[0128]

[0129] b0, b1, and b2 are all system damping. According to classical control theory, when the system is unstable, the damping is less than 0, and when the system is stable, the damping is greater than 0. Since b0>0 and b2>0, the stability of the hybrid two-terminal DC power system is determined by b1. Therefore, based on formula (28), the system stability criterion can be obtained as:

[0130]

[0131] When Q>0, the hybrid two-terminal DC power system is stable, when Q=0 it reaches the stability boundary, and when Q<0, the system is unstable. Related to the initial operating state of the system, expressed as:

[0132]

[0133] For step S104, since Q Increase and increase, as i dc0 Decrease and increase, we can get the following relationship:

[0134]

[0135] in, The minimum voltage allowed by the HVDC transmission system; i dcmax The high current allowed by the HVDC system;

[0136] Due to the integral gain of the VSC outer loop control It is usually greater than zero, so the following relationship can be obtained:

[0137]

[0138]

[0139] (30) and (31) are the stability conditions that the VSC outer loop control parameters need to meet when the hybrid two-terminal DC power system is stable. Users can design controller parameters based on (30) and (31) to ensure the stability of the system on the DC side and provide theoretical guidance for engineering design. It can be understood that the VSC outer loop control parameters include: and

[0140] For step S105, according to the stability condition determined in step S104, the current outer loop control parameters of the VSC in the current hybrid two-terminal DC power system are obtained, and it is determined whether the current outer loop control parameters simultaneously satisfy formula (32) and formula (33). If so, the current hybrid two-terminal DC power system is determined to be stable; otherwise, it is determined to be unstable.

[0141] Based on the above method embodiment, the present invention provides a corresponding equipment embodiment;

[0142] like Figure 5 As shown, an embodiment of the present invention provides a device for determining the stability of a power system, comprising: a state space equation construction module, a dominant oscillation frequency analytical solution determination module, a system stability criterion determination module, a stability condition determination module, and a stability judgment module;

[0143] The state space equation construction module is used to construct the state space equation of the hybrid two-terminal DC power system and determine the state variables involved in constructing the state space equation;

[0144] The dominant oscillation frequency analytical solution determination module is configured to take the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtain the dominant oscillation frequency analytical solution of the hybrid two-terminal DC power system based on the state space and the main state variable;

[0145] The system stability criterion determination module is configured to generate a characteristic equation of a hybrid two-terminal direct current power system based on the dominant oscillation frequency analytical solution and the state-space equation, and then determine a system stability criterion based on the characteristic equation;

[0146] The stability condition determination module is configured to determine, based on the system stability criterion, stability conditions that the outer loop control parameters of the VSC need to satisfy when the hybrid double-terminal DC power system is stable;

[0147] The stability judgment module is used to obtain current outer-loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer-loop control parameters meet the stability conditions, the current hybrid two-terminal DC power system is determined to be stable; otherwise, the current hybrid two-terminal DC power system is determined to be unstable.

[0148] It should be noted that the device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. In addition, in the drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art can understand and implement the present invention without inventive effort.

[0149] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0150] Based on the above method embodiment, the present invention provides a corresponding terminal device embodiment;

[0151] An embodiment of the present invention provides a terminal device, comprising: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the method for determining the stability of the power system described in any one of the present inventions is implemented.

[0152] The terminal device may be a computing device such as a desktop computer, a notebook computer, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0153] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal device, connecting various parts of the entire terminal device using various interfaces and lines.

[0154] The memory can be used to store the computer program, and the processor realizes various functions of the terminal device by running or executing the computer program stored in the memory and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application required for a function, etc.; the data storage area can store data created based on the use of the mobile phone, etc. In addition, the memory can include a high-speed random access memory and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage device.

[0155] Based on the above method embodiment, the present invention provides a corresponding storage medium embodiment;

[0156] An embodiment of the present invention provides a storage medium, wherein the computer-readable storage medium includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute any one of the power system stability determination methods described in the present invention.

[0157] The storage medium is a computer-readable storage medium, and the computer program is stored in the computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned various method embodiments. The computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0158] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for determining power system stability, characterized in that: include: Construct the state-space equations for the hybrid two-terminal DC power system and determine the state variables involved in constructing the state-space equations; Taking the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtaining an analytical solution of the dominant oscillation frequency of the hybrid two-terminal DC power system based on the state space and the main state variable; generating a characteristic equation of a hybrid two-terminal direct current power system according to the analytical solution of the dominant oscillation frequency and the state-space equation, and then determining a system stability criterion according to the characteristic equation; According to the system stability criterion, determining the stability conditions that the outer loop control parameters of the VSC need to meet when the hybrid double-terminal DC power system is stable; Obtain current outer loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer loop control parameters meet the stability condition, determine that the current hybrid two-terminal DC power system is stable; otherwise, determine that the current hybrid two-terminal DC power system is unstable.

2. The method for determining power system stability according to claim 1, wherein: The state space equation is: in, Δ represents the offset of the equilibrium point; x is the state variable; A is the state matrix; B is the input matrix; u is the input variable; subscript 0 represents the initial steady-state value; is the VSC DC side voltage; is the d-axis current of the VSC converter; i dc is the current of the DC transmission line; x v It is the integral link of VSC outer loop control; x i is the integral link of LCC control; x in It is the integral link of the VSC inner loop control; is the set value of VSC DC voltage; is the setting value of LCC constant current control; g0 is the initial equivalent conductance of VSC; C dc is the DC side equivalent capacitance of VSC; k0 is the voltage coefficient of VSC; is the proportional gain of the VSC inner loop control; is the integral gain of the VSC inner loop control; is the proportional gain of the VSC outer loop voltage control; is the proportional gain of LCC control; R s is the equivalent resistance of the AC side of the converter; L s is the equivalent inductance of the AC side of the converter; L dc is the total equivalent inductance of the transmission line; R eq is the total equivalent resistance of the transmission line; U0 is the ideal DC no-load voltage; α is the trigger angle of the LCC; is the integral gain of the VSC outer loop voltage control; is the integral gain of LCC control.

3. The method for determining power system stability according to claim 2, wherein: The analytical solution of the dominant oscillation frequency is:

4. The method for determining power system stability according to claim 3, wherein: Generating the characteristic equation of the hybrid two-terminal DC power system according to the dominant oscillation frequency analytical solution and the state space equation includes: Performing Laplace transform on the state space equation to obtain the initial characteristic equation of the hybrid two-terminal DC power system; Simplifying the initial characteristic equation according to the analytical solution of the dominant oscillation frequency to obtain the characteristic equation of the hybrid two-terminal DC power system; The characteristic equation of the hybrid two-terminal DC power system is: F d (s)=b2s 2 +b1s+b0; in, s is the Laplace operator; b0, b1 and b2 are all system damping.

5. The method for determining power system stability according to claim 4, wherein: The system stability criterion is: in, R l is the equivalent resistance of the DC line; d x is the equivalent commutation resistance; Q is the stability criterion.

6. The method for determining power system stability according to claim 5, wherein: The stability conditions that the outer loop control parameters of VSC need to meet are: in, The minimum voltage allowed by the HVDC transmission system; i dcmax The maximum current allowed by the HVDC system.

7. A device for determining power system stability, characterized in that: include: State space equation construction module, dominant oscillation frequency analytical solution determination module, system stability criterion determination module, stability condition determination module and stability judgment module; The state space equation construction module is used to construct the state space equation of the hybrid two-terminal DC power system and determine the state variables involved in constructing the state space equation; The dominant oscillation frequency analytical solution determination module is configured to take the state variable whose participation factor exceeds a preset threshold as the main state variable, and then obtain the dominant oscillation frequency analytical solution of the hybrid two-terminal DC power system based on the state space and the main state variable; The system stability criterion determination module is configured to generate a characteristic equation of a hybrid two-terminal direct current power system based on the dominant oscillation frequency analytical solution and the state-space equation, and then determine a system stability criterion based on the characteristic equation; The stability condition determination module is configured to determine, based on the system stability criterion, stability conditions that the outer loop control parameters of the VSC need to satisfy when the hybrid double-terminal DC power system is stable; The stability judgment module is used to obtain current outer-loop control parameters of the VSC in the current hybrid two-terminal DC power system. If the current outer-loop control parameters meet the stability conditions, the current hybrid two-terminal DC power system is determined to be stable; otherwise, the current hybrid two-terminal DC power system is determined to be unstable.

8. A terminal device, characterized in that: The method comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the method for determining the stability of the power system according to any one of claims 1 to 6 is implemented.

9. A storage medium, characterized in that: The storage medium includes a stored computer program, wherein when the computer program is executed, the device where the storage medium is located is controlled to execute the power system stability determination method according to any one of claims 1 to 6.

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