Stability analysis method and equipment for energy storage power station connected to AC / DC hybrid system

Abstract

The present invention relates to the field of power grid system stability analysis, and discloses a stability analysis method and device for energy storage power stations connected to an AC-DC hybrid system, the method comprising: constructing an energy storage power system; using a system small signal stability criterion analysis method to perform stability analysis on the energy storage power system through the voltage or current of the system grid connection point; performing equivalent aggregation of different converters within the energy storage power system; performing equivalent simplification and modeling of the LCC-HVDC transmission system of the energy storage power system; and performing system stability analysis on the energy storage power system through the control parameters in the simplified LCC-HVDC transmission system. The present invention can reduce the complexity of the model, reduce the simulation time, facilitate various aspects of analysis of large-scale grid-connected energy storage power stations connected to an AC-DC hybrid system, and ensure the accuracy and reliability of the analysis results.

Description

Technical Field

[0001] The present invention relates to the field of power grid system stability analysis, and in particular to a stability analysis method and device for connecting an energy storage power station to an AC / DC hybrid system. Background Art

[0002] At present, the main method for long-distance and large-capacity power transmission in the world is to use high-voltage direct current transmission, combined with the flexible characteristics of AC transmission for power transmission and distribution, to form an AC-DC hybrid transmission system. However, with the rapid development of high-voltage direct current transmission, it has also brought some safety and stability problems to the power grid, and it is necessary to study how to improve the safety and stability of the AC-DC hybrid system.

[0003] Today, energy storage technology is developing rapidly, and the scale of energy storage power stations is constantly expanding. There are even energy storage power stations of hundreds of megawatts. The rise of large-scale energy storage technology will provide support for the stable operation of AC / DC hybrid power grids. Energy storage technology is an ideal flexibility resource with good dynamic active and reactive power regulation capabilities, and can adapt to the operation and control requirements of different time scales. Its large-scale application and coordinated optimization operation with "source-grid-load" are expected to improve the flexibility of power grid operation. At the same time, it can also support voltage and frequency to improve system strength, thereby improving system stability and ensuring the safe, reliable and efficient operation of AC / DC hybrid systems.

[0004] Energy storage power stations can be used for voltage support, reactive power control, improvement of commutation failure and frequency modulation of power grids. In terms of response speed, regulation accuracy and construction flexibility, energy storage power stations have obvious technical advantages and provide important solutions for improving the characteristics of AC / DC hybrid systems. At the same time, with the large-scale access of power electronic equipment, the inertia of today's power system is gradually decreasing. Today, the world is gradually adopting converter network control strategies to deal with such problems. Network control technology in the field of energy storage is gradually being widely used.

[0005] With the construction of a large number of energy storage power stations, relevant research on the impact of energy storage power stations on the stability of AC / DC hybrid systems has gradually been carried out. However, as the scale of energy storage grid connection continues to increase, the simulation model results of energy storage systems have become more complex, resulting in problems such as slow simulation speed and low efficiency, which is not conducive to actual analysis and calculation. Summary of the invention

[0006] The purpose of the present invention is to propose a stability analysis method and device for an energy storage power station connected to an AC / DC hybrid system, so as to make up for the problems of slow simulation speed, low efficiency, and disadvantages in actual analysis and calculation in the stability analysis of the existing power grid energy storage system.

[0007] The present invention uses an equivalent model to replace the detailed model for simulation calculation, thereby simplifying the model, improving efficiency, and ensuring the accuracy of the analysis results. At the same time, a simplified analysis of LCC-HVDC is performed, focusing on the sending end system, and its inverter side is equivalent to a DC voltage source, and a model is built for the rectifier side.

[0008] The present invention specifically comprises the following steps:

[0009] S1: constructing an energy storage power system; the energy storage power system comprises: an AC power grid, a grid-type energy storage power station, and an LCC-HVDC transmission system; the grid-type energy storage power station comprises a converter;

[0010] S2: Use the system small signal stability criterion analysis method to analyze the stability of the energy storage power system through the voltage or current of the system grid connection point;

[0011] S3: Equi-aggregate different converters within the energy storage power system;

[0012] S4: Equivalently simplify and model the LCC-HVDC transmission system of the energy storage power system;

[0013] S5: System stability analysis of the energy storage power system is performed through the control parameters in the simplified LCC-HVDC transmission system.

[0014] A storage medium stores instructions and data for implementing a stability analysis method for connecting an energy storage power station to an AC / DC hybrid system.

[0015] A stability analysis device for connecting an energy storage power station to an AC / DC hybrid system comprises: a processor and a storage medium; the processor loads and executes instructions and data in the storage medium to implement a stability analysis method for connecting an energy storage power station to an AC / DC hybrid system.

[0016] The beneficial effects provided by the present invention are:

[0017] When analyzing the connection of large-capacity grid-connected energy storage power stations to AC / DC hybrid systems, simplified models are generally used or a converter is used to replace the entire energy storage power station equivalently, without considering the differences in its internal converters, resulting in insufficient accuracy of the analysis results. Or the system model is considered but the result is too complex, which is not conducive to simulation analysis and calculation.

[0018] The present invention proposes a stability analysis method for energy storage power stations connected to an AC / DC hybrid system, which aggregates different converters inside the energy storage power station, focuses on the sending end system, simplifies the DC transmission model, and combines the energy storage converter with the LCC-HVDC small signal impedance model to analyze the system stability. This method is conducive to the analysis of the relevant influence of the control parameters of the AC / DC hybrid system connected to a large-capacity energy storage power station on the stability in different frequency bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic flow chart of the method of the present invention;

[0020] Figure 2 is the topology of the power system under test;

[0021] Figure 3 It is a schematic diagram of the system small signal impedance equivalent model;

[0022] Figure 4 It is a verification diagram of the effect of the coherent equivalent aggregation dynamic characteristics of the energy storage power station;

[0023] Figure 5 This is a verification diagram of the effect of the coherent equivalent aggregate impedance characteristics of the energy storage power station;

[0024] Figure 6 It is a system schematic diagram of the energy storage power station equivalent simplified model;

[0025] Figure 7 It is LCC-HVDC impedance sweep verification;

[0026] Figure 8 It is the frequency sweep verification of the small signal impedance pn coordinate system of the grid-connected converter;

[0027] Fig. 9 This is the Nyquis analysis diagram of the system under normal parameters;

[0028] Fig.10 This is the Nyquist diagram of the system when the inertia coefficient J increases from left to right;

[0029] Fig.11 is the output power of the grid when the detailed model J changes;

[0030] Fig.12 is the inertia coefficient D from left to right p Nyquist plot of the system when it becomes larger;

[0031] Fig.13 Detailed model D p The output power of the power grid changes;

[0032] Fig.14 is the inertia coefficient D from left to right qNyquist plot of the system when it becomes larger;

[0033] Fig.15 Detailed model D q The output power of the power grid changes;

[0034] Fig.16 This is the Nyquist diagram of the system when the inertia coefficient k increases from left to right;

[0035] Fig.17 is the output power of the grid when the detailed model k changes;

[0036] Fig.18 It is a working schematic diagram of the hardware device of the present invention. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0038] Before formally describing the present invention, the scheme of the present invention is first generally described for easy understanding.

[0039] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the process of the present invention.

[0040] The present invention provides a stability analysis method for connecting an energy storage power station to an AC / DC hybrid system, comprising the following steps:

[0041] S1: constructing an energy storage power system; the energy storage power system comprises: an AC power grid, a grid-type energy storage power station, and an LCC-HVDC transmission system; the grid-type energy storage power station comprises a converter;

[0042] As an example, please refer to Figure 2 , Figure 2 It is the topological structure of the tested power system, that is, a schematic diagram of the topological structure of the energy storage power system.

[0043] In the embodiment of the present invention, six energy storage converters are set inside the energy storage power station, and the control parameters of the internal energy storage converters are somewhat different.

[0044] S2: Use the system small signal stability criterion analysis method to analyze the stability of the energy storage power system through the voltage or current of the system grid connection point;

[0045] As an embodiment, the stability analysis method of the present invention is used to perform corresponding analysis on the embodiment.

[0046] The analysis method of the system small signal stability criterion in step S2 is as follows:

[0047] S21. Construct a small signal impedance equivalent model of the system;

[0048] As an example, please refer to Figure 3 , first we need to get the system small signal impedance equivalent model, such as Figure 3 As shown, the specific equivalent methods are as follows:

[0049] The grid side is equivalent to a Thevenin branch in which an ideal voltage source and an equivalent impedance are connected in series. The high-voltage direct current transmission LCC-HVDC is equivalent to a Norton branch in which a current source and an output impedance are connected in parallel. The energy storage power station is equivalent to an equivalent output impedance. In addition, the equivalent impedance of the AC filter and reactive power compensation equipment on the AC side is connected in parallel with the above circuit.

[0050] S22. Based on the equivalent impedance model, the voltage expression of the system grid connection point is obtained:

[0051]

[0052] Among them, I LCC It represents the DC current of LCC-HVDC transmission system, Z g Represents the line impedance of the AC power grid, V g Represents the voltage of the local AC power grid, Z GFM Represents the equivalent impedance of the grid-type energy storage power station, Z f is the equivalent impedance of the AC filter and reactive power compensation equipment on the AC side of the LCC-HVDC transmission system, V OUT Indicates the equivalent voltage at the grid connection point;

[0053] S23. Perform stability analysis on the system grid connection point voltage expression based on the Nyquist stability criterion.

[0054] It should be noted that step S23 is specifically as follows: according to the Nyquist stability criterion, it is only necessary to determine the stability of the second term on the right side of the system grid-connected point voltage expression, and record the right side as H(s), as shown in the following formula:

[0055]

[0056] H(s) has the form of a closed-loop transfer function of a negative feedback system, where the feedback gain is Z g / (Z GFM ||Z LCC ||Z f ), which is its open-loop transfer function; according to linear control theory, as long as the feedback gain satisfies the Nyquist criterion, H(s) is stable. Therefore, the system stability is only related to the impedance of the energy storage power station and the LCC-HVDC transmission system.

[0057] S3: Equi-aggregate different converters within the energy storage power system;

[0058] It should be noted that due to the differences in control parameters of the energy storage converters within the system energy storage power station, their differences cannot be ignored, and they need to perform equivalent aggregation operations to reduce their complexity and facilitate system stability analysis.

[0059] Step S3 is specifically as follows:

[0060] When the dynamic characteristics of the converter differ greatly from the line parameters, the coherence equivalence method is adopted for aggregation. The coherence criterion of the coherence equivalence is:

[0061]

[0062] Among them, i p (t) represents the instantaneous value of the grid-connected current of the converter, P(t) represents the instantaneous value of the grid-connected power of the converter, and P ref Indicates the rated power of the converter, ε i Indicates the allowable error of the current criterion, ε p Represents the allowable error of power criterion, ε δ Indicates the allowable error of the power angle criterion;

[0063] In the τ time after the fault occurs, as long as the two converters meet three or two synchronization criteria, they can be judged to be synchronized and divided into a subgroup.

[0064] As an example, in this example, the current criterion allowable error is selected as 2*10 -5 (Since it is divided by the rated power value, the error magnitude is also reduced accordingly), the allowable error of the power criterion is selected as 3, and the allowable error of the power angle criterion is selected as 4°. In the τ time after the fault occurs, as long as the two converters meet the three synchronization criteria, they can be judged as synchronized and divided into a subgroup. In the case of non-strict judgment, it is allowed to meet two synchronization criteria for synchronization.

[0065] In this example, the per-unit parameters of the six converters are set to be different, and the above grouping operation is performed. Finally, the six converters are divided into two synchronous groups. Within the group, the dynamic characteristics and impedance characteristics of the converters are similar without significant differences.

[0066] The present invention selects three coherence criteria for grouping determination, proposes a power criterion, and performs certain normalization processing on the current criterion and the power criterion, thereby achieving optimization, being beneficial to the actual grouping operation, and making the result more obvious and accurate.

[0067] On the other hand, after the converters in the energy storage power station are grouped for synchronization, the present invention performs a single-machine aggregation operation in each group according to the following formula:

[0068]

[0069] P eq Indicates the equivalent rated output active power after equalization within the group, Q eq Indicates the equivalent rated output reactive power after equalization within the group.

[0070]

[0071] Where, J represents the active damping coefficient, J eq represents the active damping coefficient of the converter after equal value aggregation, D p Denotes the inertia coefficient, D peq represents the inertia coefficient of the converter after equal value aggregation, K represents the reactive integral coefficient, K eq Represents the reactive power integral coefficient of the converter after equal value aggregation, D q Indicates voltage virtual inertia, D qeq Represents the converter voltage virtual inertia after equal value aggregation.

[0072]

[0073] Among them, k Pv Represents the voltage loop proportional gain coefficient, k Iv Represents the voltage loop integral gain coefficient, k Pi Represents the current loop proportional gain coefficient, k Ii represents the current loop integral gain coefficient, c i represents the rated power weight of the i-th converter, and n represents the number of converters in the cluster performing aggregation operation.

[0074]

[0075] L represents the inductance inside the converter, R represents the resistance inside the converter, and C represents the capacitance inside the converter. The above LRCs all include filtering and line impedance devices, that is, the filtering devices and line impedance devices are aggregated and equalized in parallel using the method of equalization.

[0076] As an embodiment, the present invention verifies the equivalent effect after performing the equivalent on two groups.

[0077] Please refer to Figure 4-Figure 6 . Figure 4 The solid line in the middle is the detailed model result, and the dashed line is the response result after equalization. Figure 5 The solid line in the middle is the detailed model admittance result, and the dashed line is the coherent equivalent admittance result. Figure 4 It can be seen that the dynamic characteristic curves before and after the equal value are in good agreement. Figure 5This shows that the admittance characteristics before and after the equivalent value are well matched, with only a certain difference in the amplitude-frequency characteristics near 10Hz. Overall, the admittance characteristics before and after the equivalent value are not much different, which can meet the equivalent value requirements. After the equivalent value aggregation, the energy storage power station is equivalent to two grid-connected converters. The schematic diagram of the entire system is shown in Figure 6 shown.

[0078] S4: Equivalently simplify and model the LCC-HVDC transmission system of the energy storage power system;

[0079] It should be noted that after obtaining the impedance model of the energy storage power station, focus on the DC side of LCC-HVDC, equate the inverter side to a DC voltage source, perform small signal modeling on the rectifier converter, and establish the sequence impedance model of LCC-HVDC in the pn positive and negative sequence coordinate system. The core is to add voltage harmonic interference signals to the system, use Fourier closed loop to extract the corresponding frequency components, and thus establish a linearized transfer function model in the frequency domain. It is based on positive and negative sequence modeling, and the physical meaning is clearer than that of dq coordinate system modeling. At the same time, the workload of LCC-HVDC modeling in the pn coordinate system will be clearer and simpler than that of dq axis establishment.

[0080] The LCC-HVDC small signal model was verified by frequency sweeping between 0.1-1000Hz, and a total of 25 discrete frequency sweep points were obtained. Figure 7 The solid line in the middle is the small signal interface result, and the discrete points are the LCC-HVDC impedance obtained by frequency sweep. It can be seen that the small signal model and the frequency sweep result have a good agreement effect, which can be applied to subsequent analysis.

[0081] In addition, the impedance model of the energy storage power station established in the dq coordinate system needs to be converted to the pn positive and negative sequence coordinate system to unify the coordinate system of the entire system for subsequent stability and parameter influencing factor analysis. The conversion is performed according to the following formula:

[0082]

[0083]

[0084] Among them, Y GFMPN is the admittance matrix of the grid-connected converter in the pn positive and negative sequence coordinate system, Y GFMdd , Y GFMdq , Y GFMqd , Y GFMqq They are grid-connected converters.

[0085] Figure 8The figure shows the conversion of the small signal dq impedance of the energy storage power station, and the frequency sweep is performed in the pn coordinate system to verify the correctness of the conversion result. The frequency sweep is performed between 1-1000Hz, and a total of 15 discrete frequency sweep points are obtained. The solid line in the figure above is the small signal modeling result, and the discrete points are the LCC-HVDC impedance we obtained by the frequency sweep. It can be seen that the small signal model and the frequency sweep result have a good match effect, indicating that the result of the conversion according to the formula is correct and can be applied to subsequent analysis.

[0086] Here, the coordinate system is unified, and the small signal impedance model of grid energy storage and LCC-HVDC in the pn coordinate system is obtained.

[0087] S5: System stability analysis of the energy storage power system is performed through the control parameters in the simplified LCC-HVDC transmission system.

[0088] As an embodiment, the impedance value of each part in the pn coordinate system can be obtained according to the time domain model. g / (Z GFM ||Z LCC ||Z f ) to obtain its characteristic roots and obtain its Nyquist curve.

[0089] Because the impedance matrix is ​​a second-order matrix with two characteristic roots, there are two Nyquist curves, such as Fig. 9 As shown. The Nyquist curve of characteristic root 1 is represented by orange, and the Nyquist curve of characteristic root 2 is represented by green. It can be seen from the figure that the Nyquist diagram composed of the two curves is symmetrical along the real axis. At the same time, neither curve contains the (-1,0) point, which meets the stability condition. In this case, the system should be stable, which is consistent with the time domain model results.

[0090] Finally, in this embodiment, the method described in the invention is used to analyze the system stability and the influence of control parameters. Fig.10 and Fig.11 They are the Nyquist diagram and the time domain output power diagram when the inertia coefficient J is changed. The inertia coefficient increases from left to right. It can be seen that with the increase of the inertia coefficient J, the stability margin gradually decreases. When J is too large, the curve goes around (-1,0) many times and the system is unstable. The result is consistent with the simulation result of the time domain model. When J is too large, the power output of the power grid oscillates with equal amplitude.

[0091] Fig.12 and Fig.13 They are respectively changing the active damping coefficient D p The Nyquist diagram and the time domain output power diagram increase from left to right. pWhen the time is too small, the curve goes around (-1,0) many times, and the system is unstable. The result is consistent with the simulation result of the time domain model. When the time is too small, the system loses stability completely and the system oscillates violently and becomes unstable. p As increases, the trend of the system curve around (-1,0) becomes smaller, and the stability margin is relatively larger.

[0092] Fig.14 and Fig.16 They are respectively changing the reactive power droop coefficient D q The Nyquist diagram and the time domain output power diagram increase from left to right. q As the value increases, the system does not have the risk of instability and has a large stability margin. However, the Nyquist plot actually has a trend of gradually surrounding (-1, 0), but the change is small and has limited impact on stability. In these cases, the time domain model is stable and consistent with the Nyquist plot results, indicating that the conclusions obtained are correct and verifying the correctness of the homology equivalence.

[0093] Fig.16 and Fig.17 They are the Nyquist diagram and the time domain output power diagram when the reactive integral coefficient k is changed, which increases from left to right. It can be seen from the figure that the change of k has a greater impact on the Nyquist diagram. When k is too small, from the zoomed diagram in the upper left corner, both curves do not pass through this point, nor do they surround the point (-1,0), so the system should be stable in this case. As k increases, the stability margin gradually decreases, and the curves under 5k and 10k both surround the point (-1,0), and the system is in an unstable state. Fig.17 It can be seen that when k is too small, the system curve oscillates greatly in the early stage, and then enters stability after 0.5s, which fully demonstrates that a small k will cause a certain oscillation before the system enters stability, but it can stabilize. When k is too large, the system oscillates more and the oscillation gradually increases. This is consistent with the results of the Nyquist diagram and the equivalent model.

[0094] In summary, the method of the present invention includes the following parts:

[0095] System small signal stability criterion analysis method, single grid energy storage unit impedance modeling method, grid energy storage power station equivalent aggregation method, LCC-HVDC equivalent simplification and modeling method, system stability and parameter impact analysis method.

[0096] Among them, the system small signal stability criterion analysis method is applicable to complex systems. The impedance models of the energy storage power station, LCC-HVDC and the power grid are established respectively, and the voltage or current of the system grid connection point is judged to obtain the stability of the entire system;

[0097] Among them, the equivalent aggregation method of the grid-connected energy storage power station is suitable for the case where the control parameters of the converters of the energy storage units in the grid-connected energy storage power station are inconsistent, the dynamic characteristics and the impedance characteristics are different, and it is necessary to perform synchronization and equivalent values, and then perform parameter aggregation to reduce the number of converters;

[0098] Among them, the LCC-HVDC equivalent simplification and modeling method is suitable for simplifying the DC sending end system when studying it, focusing on the DC transmission rectifier side, and obtaining the corresponding impedance model in its pn coordinate system;

[0099] Finally, the system stability and parameter impact analysis method is applicable to the analysis of the influence of grid-connected energy storage power stations and LCC-HVDC control parameters on stability, unifying the impedance coordinates of each part of the system and performing Nyquist analysis.

[0100] See also Fig.18 , Fig.18 4 is a schematic diagram of the working of the hardware device of an embodiment of the present invention, wherein the hardware device specifically comprises: a stability analysis device 401 for connecting an energy storage power station to an AC / DC hybrid system, a processor 402 and a storage medium 403.

[0101] A stability analysis device 401 for connecting an energy storage power station to an AC / DC hybrid system: The stability analysis device 401 for connecting an energy storage power station to an AC / DC hybrid system implements a stability analysis method for connecting an energy storage power station to an AC / DC hybrid system.

[0102] Processor 402: The processor 402 loads and executes the instructions and data in the storage medium 403 to implement the stability analysis method for connecting an energy storage power station to an AC / DC hybrid system.

[0103] Storage medium 403: The storage medium 403 stores instructions and data; the storage medium 403 is used to implement the stability analysis method of a storage power station connected to an AC / DC hybrid system.

[0104] The beneficial effects of the present invention are:

[0105] When analyzing the connection of large-capacity grid-connected energy storage power stations to AC / DC hybrid systems, simplified models are generally used or a converter is used to replace the entire energy storage power station equivalently, without considering the differences in its internal converters, resulting in insufficient accuracy of the analysis results. Or the system model is considered but the result is too complex, which is not conducive to simulation analysis and calculation.

[0106] The present invention proposes a stability analysis method for energy storage power stations connected to an AC / DC hybrid system, which aggregates different converters inside the energy storage power station, focuses on the sending end system, simplifies the DC transmission model, and combines the energy storage converter with the LCC-HVDC small signal impedance model to analyze the system stability. This method is conducive to the analysis of the relevant influence of the control parameters of the AC / DC hybrid system connected to a large-capacity energy storage power station on the stability in different frequency bands.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A stability analysis method for energy storage power station connected to an AC / DC hybrid system, characterized in that: Methods include: S1: Building energy storage power system; The energy storage power system includes: an AC power grid, a grid-type energy storage power station, and an LCC-HVDC transmission system; The grid-type energy storage power station includes a converter; S2: Use the system small signal stability criterion analysis method to analyze the stability of the energy storage power system through the voltage or current of the system grid connection point; S3: Equi-aggregate different converters within the energy storage power system; S4: Equivalently simplify and model the LCC-HVDC transmission system of the energy storage power system; S5: System stability analysis of the energy storage power system is performed through the control parameters in the simplified LCC-HVDC transmission system.

2. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system according to claim 1, characterized in that: The analysis method of the system small signal stability criterion in step S2 is as follows: S21. Construct a small signal impedance equivalent model of the system; S22. Based on the equivalent impedance model, the voltage expression of the system grid connection point is obtained: Among them, I LCC represents the DC current of the LCC-HVDC transmission system, Z g Represents the line impedance of the AC power grid, V g Represents the voltage of the local AC power grid, Z GFM Represents the equivalent impedance of the grid-type energy storage power station, Z f is the equivalent impedance of the AC filter and reactive power compensation equipment on the AC side of the LCC-HVDC transmission system, V OUT Indicates the equivalent voltage at the grid connection point; S23. Perform stability analysis on the system grid connection point voltage expression based on the Nyquist stability criterion.

3. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as claimed in claim 2, characterized in that: In step S21, the equivalent method of the system small signal impedance equivalent model is specifically as follows: the AC power grid side is equivalent to a Thevenin branch in which an ideal voltage source and an equivalent impedance are connected in series, the LCC-HVDC transmission system is equivalent to a Norton branch in the form of a current source and an output impedance in parallel, the grid-type energy storage power station is equivalent to an equivalent output impedance, and the equivalent impedance of the AC filter and reactive compensation equipment on the AC side of the LCC-HVDC transmission system is connected in parallel with the grid-type energy storage power station.

4. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as claimed in claim 2, characterized in that: Step S23 is specifically as follows: According to the Nyquist stability criterion, it is only necessary to determine the stability of the second equation on the right side of the system grid-connected point voltage expression, and record the right side as H(s), as shown in the following formula: H(s) has the form of a closed-loop transfer function of a negative feedback system, where the feedback gain is Z g / (Z GFM ||Z LCC ||Z f ), which is its open-loop transfer function; according to linear control theory, as long as the feedback gain satisfies the Nyquist criterion, H(s) is stable.

5. The stability analysis method for connecting an energy storage power station to an AC / DC hybrid system according to claim 1, characterized in that: Step S3 is specifically as follows: When the dynamic characteristics of the converter differ greatly from the line parameters, the coherence equivalence method is adopted for aggregation. The coherence criterion of the coherence equivalence is: Among them, i p (t) represents the instantaneous value of the grid-connected current of the converter, P(t) represents the instantaneous value of the grid-connected power of the converter, and P ref Indicates the rated power of the converter, ε i Indicates the allowable error of the current criterion, ε p Represents the allowable error of power criterion, ε δ Indicates the allowable error of the power angle criterion; In the τ time after the fault occurs, as long as the two converters meet three or two synchronization criteria, they can be judged to be synchronized and divided into a subgroup.

6. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as claimed in claim 5, characterized in that: After the converters inside the energy storage power station are grouped, the single-machine aggregation operation is performed in each group according to the following formula: P eq Indicates the equivalent rated output active power after equalization within the group, Q eq Indicates the equivalent rated output reactive power after equalization within the group; Where, J represents the active damping coefficient, J eq represents the active damping coefficient of the converter after equal value aggregation, D p Denotes the inertia coefficient, D peq represents the inertia coefficient of the converter after equal value aggregation, K represents the reactive integral coefficient, K eq Represents the reactive power integral coefficient of the converter after equal value aggregation, D q Indicates voltage virtual inertia, D qeq It represents the converter voltage virtual inertia after equal value aggregation; Among them, k Pv Represents the voltage loop proportional gain coefficient, k Iv Represents the voltage loop integral gain coefficient, k Pi Represents the current loop proportional gain coefficient, k Ii represents the current loop integral gain coefficient, c i represents the rated power weight of the i-th converter, and n represents the number of converters in the cluster for aggregation operation; L represents the inductance inside the converter, R represents the resistance inside the converter, and C represents the capacitance inside the converter. The above LRCs all include filtering and line impedance devices, that is, the filtering devices and line impedance devices are aggregated and equalized in parallel using the method of equalization.

7. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as claimed in claim 4, characterized in that: The equivalent simplification and modeling process in step S4 is as follows: The research system is the sending-side system, focusing on the DC side of the LCC-HVDC transmission system. The inverter side is equivalent to a DC voltage source, the rectifier converter is modeled for small signals, and the sequence impedance model of LCC-HVDC is established uniformly in the pn positive and negative sequence coordinate system. The specific impedance coordinate system conversion of each part is as follows: Convert the dq coordinate system of the grid-type energy storage power station to the pn positive and negative sequence coordinate system Among them, Y GFMPN is the admittance matrix of the grid-connected converter in the pn positive and negative sequence coordinate system, Y GFMdd , Y GFMdq , Y GFMqd , Y GFMqq They are different converters in the grid-connected energy storage power station.

8. A stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as claimed in claim 7, characterized in that: Step S5 is specifically as follows: After unifying the coordinate system, Nyquist analysis is performed on the feedback gain in H(s). If the graph curve is around (-1,0), the system is unstable. By changing the control parameters of the energy storage power station and LCC-HVDC, and combining the corresponding impedance changes with the Nyquist curve, the influence of the corresponding control parameters on the system stability can be analyzed.

9. A storage medium, characterized in that: The storage medium stores instructions and data for implementing the stability analysis method for connecting an energy storage power station to an AC / DC hybrid system as described in any one of claims 1 to 8.

10. A stability analysis device for an energy storage power station connected to an AC / DC hybrid system, characterized in that: include: Processor and storage medium; the processor loads and executes instructions and data in the storage medium to implement the stability analysis method of a storage power station connected to an AC / DC hybrid system as described in any one of claims 1 to 8.

Images