Parameter optimization method for improving near power frequency stability of new energy flexible direct transmission system

Abstract

The application provides a parameter optimization method for improving the near power frequency stability of a new energy flexible direct transmission system, and the method comprises the following steps: dividing the new energy flexible direct transmission system into a source side subsystem and a load side subsystem, and respectively establishing positive and negative sequence impedance models of the source side subsystem and the load side subsystem; evaluating the stability margin of the system in the near power frequency band based on the above models; if the stability margin of the system in the near power frequency band is low, extracting dominant parameters affecting the near power frequency stability of the new energy flexible direct transmission system based on the phase margin sensitivity; determining the optimization interval of the dominant parameters based on the equivalent impedance criterion and the upper and lower limits of the parameter values; establishing the input and disturbance response transfer functions of the source side subsystem and the load side subsystem, evaluating the influence of the change of the dominant parameters on the power frequency control performance, and finally determining the optimal parameter values. The parameter optimization method can improve the near power frequency stability of the new energy flexible direct transmission system while minimizing the influence on the power frequency control performance of the system.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and more specifically, to a parameter optimization method, system, medium, and terminal for improving the near-power frequency stability of a new energy flexible direct transmission system. Background Technology

[0002] In recent years, flexible DC transmission technology has developed rapidly. With the gradual maturation of modular multilevel converter (MMC) technology, the voltage and power levels of flexible DC systems have been greatly improved, making them more suitable for long-distance, large-scale renewable energy integration systems. Renewable energy transmission projects via flexible DC involve a large number of power electronic devices. The interaction between renewable energy and the flexible DC converter station causes frequent system oscillations, seriously affecting the safe and stable operation of the system.

[0003] Recently, a new energy flexible DC transmission project has repeatedly experienced near-power frequency positive and negative sequence oscillations of 40-60Hz. Because the oscillation frequency is close to the fundamental frequency, these near-power frequency oscillations are difficult to suppress. The system's operating characteristics near the power frequency are influenced by a combination of factors, and existing parameter optimization methods are insufficient to simultaneously address power frequency control performance. Therefore, a parameter optimization method and system are needed to improve the near-power frequency stability of new energy flexible DC transmission systems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, a parameter optimization method, system, medium, and terminal for improving the near-power frequency stability of new energy flexible direct transmission systems are proposed.

[0005] According to one aspect of the present invention, a parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system is provided, comprising:

[0006] The new energy flexible direct transmission system is divided into a source-side subsystem and a load-side subsystem; the source-side subsystem is the flexible direct transmission end MMC converter; the load-side subsystem is the new energy power station.

[0007] Based on the source-side subsystem and the load-side subsystem, AC-side positive and negative sequence impedance models of the source-side subsystem and the load-side subsystem are established respectively.

[0008] Based on the aforementioned AC-side positive and negative sequence impedance model, the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band is evaluated.

[0009] When the near-power frequency stability margin of the new energy flexible direct transmission system is determined to be lower than the set threshold, the dominant parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter.

[0010] Based on the original parameters, the dominant parameters that need to be optimized are determined by iterating through the upper and lower limits of the actual parameter values, and the parameter optimization range is determined based on the equivalent impedance criterion.

[0011] Within the determined parameter optimization range, the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem are constructed, the impact of parameter changes on the power frequency control performance of the system is evaluated, and the determined optimization range of the dominant parameters is optimized again.

[0012] Preferably, the source-side subsystem AC-side positive and negative sequence impedance model includes the flexible DC-side MMC converter main circuit and the MMC control system, wherein the MMC control system includes a positive and negative sequence AC voltage control loop, a positive and negative sequence current control loop, a positive and negative sequence separation algorithm, and a control delay.

[0013] The load-side subsystem AC side positive and negative sequence impedance model includes the full-power wind turbine main circuit and the full-power wind turbine control system. The full-power wind turbine control system includes a DC voltage control loop, a positive and negative sequence current control loop, a phase-locked loop, a positive and negative sequence separation algorithm, and a control delay loop.

[0014] Preferably, the process of establishing the source-side subsystem AC-side positive and negative sequence impedance models and the load-side subsystem AC-side positive and negative sequence impedance models includes:

[0015] Based on the harmonic state-space method, small-signal harmonic state-space models of MMC and full-power wind turbines are established respectively, and the relationship between the main circuit and the controller is established according to the modulation function and control structure.

[0016] Preferably, the evaluation of the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band based on the AC-side positive and negative sequence impedance model includes:

[0017] Using the positive and negative sequence voltage of small disturbance on the AC side as the input of the positive and negative sequence impedance model on the AC side, the positive and negative sequence current of small disturbance on the AC side is obtained by solving the small signal harmonic state space equation, and the positive and negative sequence impedances on the AC side of the flexible DC MMC converter and the full-power wind turbine are obtained.

[0018] Based on the positive and negative sequence impedances of the AC side of the flexible DC MMC converter and the full-power wind turbine, the equivalent loop gains of the new energy flexible DC transmission system are defined as follows:

[0019] L mp =Z MMCp (s) / Z WFp (s);

[0020] L mn =Z MMCn (s) / Z loadn (s);

[0021] In the formula: Z MMCp (s) and Z WFp (s) represent the near-power frequency positive sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively.MMCn (s) and Z WFn (s) represent the near-power frequency negative sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively; s represents the Laplace operator.

[0022] L in the s domain mp and L mn Transform to the frequency domain and write it as the sum of the real and imaginary parts:

[0023] L p =Re(L mp )+jIm(L mp );

[0024] L n =Re(L mn )+jIm(L mn );

[0025] The necessary and sufficient conditions for the stability of a new energy flexible direct transmission system are defined as follows:

[0026] L p and L n The imaginary part Im(L) mp ) and Im(L mn When crossing the frequency axis, the corresponding real part Re(L) mp ) and Re(L mn If the value is greater than the set threshold, the system is stable;

[0027] Based on the aforementioned necessary and sufficient conditions, determine whether the new energy flexible direct transmission system is stable.

[0028] Preferably, the process of extracting the dominant parameters affecting near-power frequency stability includes:

[0029] If the stability margin of the new energy flexible direct transmission system in the near-power frequency band is lower than a set threshold, the positive and negative sequence phase margin sensitivity of the interconnected system parameters is defined as follows:

[0030]

[0031]

[0032] Where: PM p and PM n These represent the positive and negative sequence phase margins, f, respectively. os For the potential oscillation frequency, a i For a specific main circuit or control parameter of a flexible DC-DC MMC converter or a full-power wind turbine, Δa i For the infinitesimal increment of this parameter, Δa i Select a i 0.1% of;

[0033] The dominant parameter affecting near-power frequency stability is determined by the magnitude of the absolute value of the positive and negative sequence phase margin sensitivity.

[0034] Preferably, the step of determining the dominant parameter to be optimized based on the original parameters and by iterating through the upper and lower limits of the actual parameter values, and determining the parameter optimization range based on the equivalent impedance criterion, includes:

[0035] Observe L as the dominant parameter changes. p and L n Imaginary part Im(L) of the frequency domain curve mp ) and Im(L mn At the point where the frequency axis is crossed, all corresponding L p and L n The real part of the frequency domain curve Re(L) mp ) and Re(L mn The relationship between the minimum value of a parameter and a set threshold, combined with the upper and lower limits of the parameter's value, determines the optimal range of the parameter's value; that is, it can be expressed mathematically as:

[0036]

[0037] In the formula: C1 and C2 are the upper and lower limits of the parameter values, respectively, and a satisfies the formula. i The optimal range of values ​​for the dominant parameter.

[0038] Preferably, the process of further optimizing the determined optimization range of the dominant parameter includes:

[0039] Construct the source-side subsystem input-response transfer function T input1 (s)=Δu gd / Δu gdref and disturbance response transfer function T disturb1 (s)=Δu gd / Δu d They are as follows:

[0040]

[0041]

[0042] In the formula: L arm and R arm Z represents the equivalent inductance and resistance of the flexible DC MMC converter arm; L H represents the equivalent resistance on the AC side of the flexible DC MMC converter. vp and H ip These are PI controllers for the outer loop of positive-sequence AC voltage and the inner loop of positive-sequence current, respectively; G d1 s represents the control delay of the flexible DC MMC converter, and s is the Laplace operator;

[0043] Construct the input-response transfer function T of the load-side subsystem input2 (s)=Δu dc / Δu dcref and disturbance response transfer function T disturb2 (s)=Δu dc / Δu d They are as follows:

[0044]

[0045]

[0046] In the formula: L f and R f The equivalent series inductance and resistance of the AC side filter for a full-power wind turbine; C dc For DC side capacitor; H dc and H cp These are PI controllers with an outer loop for DC voltage and an inner loop for positive sequence current, respectively; G d2 Control delay for full-power wind turbine units; u sd0 The steady-state value of the d-axis component of the AC bus voltage; u dc0 This is the steady-state value of the DC voltage;

[0047] Based on the input response and disturbance response transfer functions, the impact of parameter changes on the system's power frequency control performance is evaluated, and the optimal value range of the dominant parameters is further determined based on the already determined parameter optimization range.

[0048] According to a second aspect of the present invention, a parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system is provided, comprising:

[0049] Module division: The new energy flexible direct transmission system is divided into source-side subsystem and load-side subsystem; the source-side subsystem is the flexible direct transmission end MMC converter; the load-side subsystem is the new energy power station;

[0050] Modeling module: Based on the source-side subsystem and the load-side subsystem, establish AC-side positive and negative sequence impedance models for the source-side subsystem and the load-side subsystem, respectively;

[0051] Stability assessment module: Based on the AC side positive and negative sequence impedance model, evaluate the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band;

[0052] The main parameter acquisition module: When the near-power frequency stability margin of the new energy flexible direct transmission system is determined to be lower than the set threshold, the main parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter.

[0053] Initial optimization module: Based on the original parameters, the module iterates through the upper and lower limits of the actual parameter values ​​to determine the dominant parameters that need to be optimized, and determines the parameter optimization range based on the equivalent impedance criterion.

[0054] The module is further optimized as follows: Within the determined parameter optimization range, the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem are constructed, the impact of parameter changes on the power frequency control performance of the system is evaluated, and the determined optimization range of the dominant parameters is optimized again.

[0055] According to a third aspect of the present invention, a terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to execute any of the parameter optimization methods for improving the near-power frequency stability of a new energy flexible direct transmission system, or to run the parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system.

[0056] According to a fourth aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, can be used to perform any of the parameter optimization methods for improving the near-power frequency stability of a new energy flexible direct transmission system, or to perform the parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system.

[0057] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0058] The parameter optimization method and system for improving the near-power frequency stability of the new energy flexible direct current transmission system in the embodiments of the present invention establish an impedance model that considers the positive / negative sequence control links of the new energy generator set and the flexible direct current MMC converter, which can be used to accurately assess the near-power frequency positive / negative sequence oscillation risk of the new energy flexible direct current transmission system.

[0059] The parameter optimization method and system for improving the near-power frequency stability of the new energy flexible direct transmission system in this embodiment of the invention extracts the dominant control parameters that affect the near-power frequency positive / negative sequence oscillation stability of the new energy flexible direct transmission system based on the phase margin parameter sensitivity index. By optimizing the dominant positive or negative sequence control parameters, the near-power frequency positive / negative sequence stability of the system can be improved to the maximum extent.

[0060] The parameter optimization method and system for improving the near-power frequency stability of the new energy flexible direct transmission system in this embodiment of the invention can improve the near-power frequency positive / negative sequence stability of the new energy flexible direct transmission system while minimizing the impact of parameter optimization on the system's power frequency control performance. Attached Figure Description

[0061] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0062] Figure 1 This is a flowchart illustrating a preferred embodiment of the parameter optimization design method of the present invention.

[0063] Figure 2 This is a topology and control system structure diagram of the source-side subsystem according to a preferred embodiment of the present invention. a is a schematic diagram of the MMC main circuit, and b is a schematic diagram of the MMC control system.

[0064] Figure 3 This is a topology and control system structure diagram of a preferred embodiment of the present invention;

[0065] Figure 4 This is a schematic diagram of the equivalent loop gain frequency domain curve of a preferred embodiment of the present invention;

[0066] Figure 5 This is a graph showing the phase margin sensitivity analysis results of a preferred embodiment of the present invention;

[0067] Figure 6 A preferred embodiment of the present invention provides a parameter optimization design curve (using the proportional coefficient K of the phase-locked loop PI controller for a full-power wind turbine). ppll (For example);

[0068] Figure 7 This is a structural diagram of the input response and disturbance response transfer function of the source-side subsystem according to a preferred embodiment of the present invention;

[0069] Figure 8 This is a structural diagram of the input response and disturbance response transfer function of the load-side subsystem according to a preferred embodiment of the present invention;

[0070] Figure 9 This is a schematic diagram illustrating the effect of a specific embodiment of the present invention. Detailed Implementation

[0071] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0072] The purpose of this invention is to provide a parameter optimization method to improve the near-power frequency stability of a new energy flexible direct transmission system, thereby minimizing the impact on the system's power frequency control performance while improving the near-power frequency stability of the new energy flexible direct transmission system.

[0073] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0074] Figure 1This is a schematic diagram of a parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system provided by the present invention, as shown in the figure. Figure 1 As shown, the parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system provided by the present invention includes:

[0075] S11, the new energy flexible direct transmission system is divided into source-side subsystem and load-side subsystem; the source-side subsystem is the flexible direct transmission end MMC converter; the load-side subsystem is the new energy power station.

[0076] S12, based on the source-side subsystem and load-side subsystem determined in S11, establish the AC-side positive and negative sequence impedance models of the source-side subsystem and load-side subsystem respectively;

[0077] S13, based on the AC side positive and negative sequence impedance model established in S12, evaluates the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band.

[0078] S14, in S13, the stability result is: when the stability margin of the new energy flexible direct transmission system in the near-power frequency band is determined to be lower than the set threshold, the dominant parameters affecting the near-power frequency stability are extracted based on the sensitivity of the phase margin parameter.

[0079] S15, based on the original parameters, combined with the upper and lower limits of the actual parameter values ​​to determine the dominant parameters extracted in S14 that need to be optimized, and the parameter optimization range is determined based on the equivalent impedance criterion.

[0080] S16. Within the parameter optimization range determined in S15, construct the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem, evaluate the impact of parameter changes on the system's power frequency control performance, and further optimize the determined optimization range of the dominant parameters.

[0081] This embodiment improves the near-power frequency stability of the new energy flexible direct transmission system while minimizing the impact on the system's power frequency control performance.

[0082] In a preferred embodiment of the invention, S12 is implemented. See also Figure 2 This is a topology and control system structure diagram of the source-side subsystem. The impedance model of the source-side subsystem includes the main circuit of the flexible DC-side MMC converter, the positive and negative sequence AC voltage control loop, the positive and negative sequence current control loop, the positive and negative sequence separation algorithm, control delay, and other components. See also... Figure 3 This is a topology and control system structure diagram of the load-side subsystem. The impedance model of the load-side subsystem includes the main circuit of the full-power wind turbine, DC voltage control loop, positive and negative sequence current control loop, phase-locked loop, positive and negative sequence separation algorithm, control delay and other components.

[0083] Furthermore, the process of establishing the AC side positive and negative sequence impedance models of the above source-side subsystem and load-side subsystem is as follows: Based on the harmonic state-space method, small-signal harmonic state-space models of MMC and full-power wind turbine are established respectively, and the relationship between the main circuit and the controller is established according to the modulation function and control structure.

[0084] Using the small disturbance positive and negative sequence voltage on the AC side as input, the small disturbance positive and negative sequence current on the AC side is obtained by solving the small signal harmonic state space equation, and then the positive and negative sequence impedance on the AC side of the flexible DC MMC converter and the full-power wind turbine is obtained.

[0085] In a preferred embodiment of the present invention, step S13 is implemented to evaluate the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band (40-60Hz) based on the impedance model established in step S12; specifically,

[0086] S131, based on the above impedance model, the positive and negative sequence impedances of the AC side of the flexible DC MMC converter and the full-power wind turbine are obtained. The positive and negative sequence equivalent loop gains of the new energy flexible DC transmission system are defined as follows:

[0087] L mp =Z MMCp (s) / Z WFp (s);

[0088] L mn =Z MMCn (s) / Z loadn (s);

[0089] In the formula: Z MMCp (s) and Z WFp (s) represent the near-power frequency positive sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively. MMCn (s) and Z loadn (s) represent the near-power frequency negative sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively; s represents the Laplace operator.

[0090] S132, L in the s field mp and L mn Transform to the frequency domain and write it as the sum of the real and imaginary parts:

[0091] L p =Re(L mp )+jIm(L mp );

[0092] L n =Re(L mn )+jIm(L mn );

[0093] S133, the necessary and sufficient conditions for obtaining a stable interconnected system are as follows:

[0094] L p and L n The imaginary part Im(L) mp ) and Im(L mn When crossing the frequency axis, the corresponding real part Re(L) mp ) and Re(L mn If the value is greater than -1, then the system is stable.

[0095] Furthermore, S131-133 are applied to the instance. Figure 4 This is a schematic diagram of the gain curve of a new energy flexible direct transmission system in the prior art. From the figure, it can be seen that at 59.4Hz, L... n The imaginary part Im(L) mn When the frequency axis is crossed, the corresponding real part Re(L) is... mn = -1.01494 < -1, the system is unstable.

[0096] This embodiment provides a method for judging system stability, which is intuitive, accurate, and fast.

[0097] In one embodiment of this invention, step S14 is performed: If, in step S13, it is determined that the near-power frequency stability margin of the new energy flexible direct transmission system is low, the dominant parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter. It should be noted that "low stability margin" here refers to L... p and L n The imaginary part Im(L) mp ) and Im(L mn When crossing the frequency axis, the corresponding real part Re(L) mp ) and Re(L mn At least one of them is less than -1.

[0098] Specifically, the implementation process of S14 is as follows:

[0099] S141, If ​​S13 determines that the stability margin of the new energy flexible direct transmission system is low in the near-power frequency band, define the positive and negative sequence phase margin sensitivity of the interconnected system parameters:

[0100]

[0101]

[0102] Where: PM p and PM n These represent the positive and negative sequence phase margins, f, respectively. os For the potential oscillation frequency, a i For a specific main circuit or control parameter of a flexible DC-DC MMC converter or a full-power wind turbine, Δa iFor the infinitesimal increment of this parameter, Δa i Select a i 0.1%; Positive sequence phase margin PM p That is, L p The imaginary part Im(L) mp The point (f) that crosses the frequency axis os The point at which the impedance amplitudes of the wind turbine and the flexible DC MMC intersect is defined as follows:

[0103] PM p =180°-(∠Z) MMCp (f os )-∠Z WFp (f os Negative sequence phase margin PM n That is, L n The imaginary part Im(L) mn The point (f) that crosses the frequency axis os At this location, PM is defined as follows: n =180°-(∠Z) MMCn (f os )-∠Z WFn (f os )).

[0104] S142, the dominant parameters affecting near-power frequency stability are determined by the magnitude of the absolute values ​​of the positive and negative sequence phase margin sensitivity. In this embodiment, the dominant parameters affecting near-power frequency stability are extracted by comparing the damping sensitivity of different parameters within the near-power frequency band. Since there are many parameters, the first three absolute values ​​are selected here.

[0105] Furthermore, S141-S142 are applied to the instance. Figure 5 The negative-sequence phase margin sensitivity analysis results in this embodiment are shown in the figure. From the figure, it can be determined that, under different wind farm output conditions on the renewable energy side, the dominant parameter affecting near-power frequency negative-sequence stability is mainly the proportional coefficient K of the full-power wind turbine phase-locked loop PI controller. ppll The integral coefficient K of the negative sequence current loop PI controller for full-power wind turbine generators iin .

[0106] In a preferred embodiment of the present invention, step S15 is implemented, based on the original parameters and combined with the upper and lower limits of the actual parameter values ​​to determine the dominant parameters extracted in S14 that need to be optimized, and the parameter optimization range is determined based on the equivalent impedance criterion. It should be noted that the original parameters here refer to the main circuit and control parameters of the new energy flexible direct transmission system when the interconnected system generates near-power frequency oscillation risk; the actual parameters refer to the actual values ​​of the main circuit and control parameters of the new energy flexible direct transmission system: taking the current inner loop PI parameter as an example, its actual control bandwidth is between 100-400Hz. The original parameters are also within this range, but due to unreasonable parameter selection or control interaction, the interconnected system generates oscillation risk, therefore, the original parameters are optimized based on the actual parameter values.

[0107] The specific process of S15 is that when the dominant parameter changes, L... p and L n Imaginary part Im(L) of the frequency domain curve mp ) and Im(L mn The frequency corresponding to crossing the frequency axis will also change, and the range of parameter selection can be optimized based on the equivalent impedance criterion.

[0108] Furthermore, observe L as the parameters change. p and L n Imaginary part Im(L) of the frequency domain curve mp ) and Im(L mn At the point where the frequency axis is crossed, all corresponding L p and L n The real part of the frequency domain curve Re(L) mp ) and Re(L mn The relationship between the minimum value of () and -1, combined with the upper and lower limits of the parameter's value, determines the optimal range of the parameter's value. This can be abstracted mathematically as follows:

[0109]

[0110] In the formula: C1 and C2 are the upper and lower limits of the parameter values, respectively, and a satisfies the formula. i The optimal range of values ​​for the dominant parameter.

[0111] Furthermore, this embodiment S15 is applied to an example. Figure 6 The parameter optimization design curves of this embodiment are given, with the proportional coefficient K of the full-power wind turbine phase-locked loop PI controller as an example. ppll For example, using the original value of this control parameter as a baseline, the proportional coefficient of the original sequence current loop of the wind turbine is changed from 0.1 pu to 1.3 pu. Based on the above design method, the proportional coefficient K of the phase-locked loop PI controller of the full-power wind turbine can be obtained. ppll The optimized value range is 0.1-0.67pu.

[0112] In a preferred embodiment of the present invention, S16 is implemented to construct the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem within the parameter optimization range determined in S15, evaluate the impact of parameter changes on the power frequency control performance of the system, and further determine the optimization range of the dominant parameters.

[0113] The specific implementation process of S16 is as follows:

[0114] S161, Construct the source-side subsystem input response transfer function T input1 (s)=Δu gd / Δu gdref and disturbance response transfer function T disturb1 (s)=Δu gd / Δu d They are as follows:

[0115]

[0116]

[0117] In the formula: L arm and R arm Z represents the equivalent inductance and resistance of the flexible DC MMC converter arm; L H represents the equivalent resistance on the AC side of the flexible DC MMC converter. vp and H ip These are PI controllers for the outer loop of positive-sequence AC voltage and the inner loop of positive-sequence current, respectively; G d1 For the control delay of the flexible DC MMC converter, please refer to [link / reference]. Figure 7 It provides a structural diagram of the input response and disturbance response transfer function of the source-side subsystem in this embodiment.

[0118] S152, Construct the input response transfer function T of the load-side subsystem. input2 (s)=Δu dc / Δu dcref and disturbance response transfer function T disturb2 (s)=Δu dc / Δu d They are as follows:

[0119]

[0120]

[0121] In the formula: Lf and Rf are the equivalent series inductance and resistance of the AC side filter of the full-power wind turbine; Cdc is the DC side capacitor; Hdc and Hcp are the DC voltage outer loop and positive sequence current inner loop PI controllers, respectively; Gd2 is the control delay of the full-power wind turbine; usd0 is the steady-state value of the d-axis component of the AC bus voltage; udc0 is the steady-state value of the DC voltage, which can be found in [reference]. Figure 8 It provides a structural diagram of the input response and disturbance response transfer function of the load-side subsystem in this embodiment.

[0122] S163. Based on the aforementioned input response and disturbance response transfer functions, assess the impact of parameter changes on the system's power frequency control performance. Further determine the optimal value range of the dominant parameters based on the already established parameter optimization range. That is, after determining the parameter optimization range based on the equivalent impedance criterion mentioned earlier, observe the changes in the system's input response and disturbance response as the parameters change within the optimization range to evaluate the impact on power frequency control performance. Combined with the control system's dynamic response indicators (overshoot, peak time, settling time, etc.), further optimize the parameter value range.

[0123] Furthermore, S16 is applied to an example. The effectiveness of this parameter optimization design method is verified through simulation. 2.2 seconds after the simulation begins, the new energy control parameters change to the optimized values, and the resulting PCC current waveform is shown below. Figure 9 As shown. Figure 9 Before 2.2 seconds, the new energy flexible direct transmission system experienced near-power frequency negative sequence oscillations. After optimization of the control parameters, the PCC current gradually stabilized. This demonstrates that the proposed parameter optimization design method can effectively improve the near-power frequency stability of the new energy flexible direct transmission system.

[0124] Based on the same inventive concept, this invention provides a parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system, including a partitioning module, a modeling module, a stability judgment module, a main parameter acquisition module, an initial optimization module, and a secondary optimization module. Among these,

[0125] Module division: The new energy flexible direct transmission system is divided into source-side subsystem and load-side subsystem; the source-side subsystem is the flexible direct transmission end MMC converter; the load-side subsystem is the new energy power station;

[0126] Modeling module: Based on the source-side subsystem and the load-side subsystem, establish AC-side positive and negative sequence impedance models for the source-side subsystem and the load-side subsystem, respectively;

[0127] Stability assessment module: Based on the AC side positive and negative sequence impedance model, evaluate the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band;

[0128] The main parameter acquisition module: When the near-power frequency stability margin of the new energy flexible direct transmission system is determined to be lower than the set threshold, the main parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter.

[0129] Initial optimization module: Based on the original parameters, the module iterates through the upper and lower limits of the actual parameter values ​​to determine the dominant parameters that need to be optimized, and determines the parameter optimization range based on the equivalent impedance criterion.

[0130] The module is further optimized as follows: Within the determined parameter optimization range, the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem are constructed, the impact of parameter changes on the power frequency control performance of the system is evaluated, and the determined optimization range of the dominant parameters is optimized again.

[0131] The specific implementation techniques of each module / unit in the above examples of the present invention can be referred to the parameter optimization method for improving the near-power frequency stability of the new energy flexible direct transmission system in the above embodiments, and will not be repeated here.

[0132] Based on the same inventive concept, in other embodiments of the present invention, a terminal is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to execute any of the parameter optimization methods for improving the near-power frequency stability of the new energy flexible direct transmission system, or to run the parameter optimization system for improving the near-power frequency stability of the new energy flexible direct transmission system.

[0133] Optionally, the memory is used to store programs; the memory may include volatile memory, such as random-access memory (RAM), such as static random-access memory (SRAM), double data rate synchronous dynamic random-access memory (DDR SDRAM), etc.; the memory may also include non-volatile memory, such as flash memory. The memory is used to store computer programs (such as application programs, functional modules, etc. that implement the above methods), computer instructions, etc., and the aforementioned computer programs, computer instructions, etc., can be partitioned and stored in one or more memories. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by the processor.

[0134] The aforementioned computer programs, computer instructions, etc., can be stored in partitions within one or more memory locations. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by a processor.

[0135] A processor is used to execute a computer program stored in memory to implement the various steps of the methods involved in the above embodiments. For details, please refer to the relevant descriptions in the preceding method embodiments.

[0136] The processor and memory can be separate structures or integrated structures. When the processor and memory are separate structures, they can be coupled together via a bus.

[0137] Based on the same inventive concept, in other embodiments of the present invention, a computer-readable storage medium is provided, on which a computer program is stored, which, when executed by a processor, can be used to perform any of the parameter optimization methods for improving the near-power frequency stability of a new energy flexible direct transmission system, or the parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system.

[0138] Computer-readable media include computer storage media and communication media, wherein communication media include any medium that facilitates the transfer of computer programs from one place to another. Storage media can be any available medium accessible to a general-purpose or special-purpose computer. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in a user device. Of course, the processor and storage medium can also exist as discrete components in a communication device.

[0139] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0140] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to this application. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0141] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0142] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0143] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system, characterized in that, include: The new energy flexible direct transmission system is divided into source-side subsystem and load-side subsystem; The source-side subsystem is a flexible direct-feed MMC converter. The load-side subsystem is a new energy power station; Based on the source-side subsystem and the load-side subsystem, AC-side positive and negative sequence impedance models of the source-side subsystem and the load-side subsystem are established respectively. Based on the aforementioned AC-side positive and negative sequence impedance model, the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band is evaluated. When the near-power frequency stability margin of the new energy flexible direct transmission system is determined to be lower than the set threshold, the dominant parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter. Based on the original parameters, the dominant parameters that need to be optimized are determined by iterating through the upper and lower limits of the actual parameter values, and the parameter optimization range is determined based on the equivalent impedance criterion. Within the determined parameter optimization range, the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem are constructed, the impact of parameter changes on the power frequency control performance of the system is evaluated, and the determined optimization range of the dominant parameters is optimized again. The process of extracting the dominant parameters affecting near-power frequency stability includes: If the stability margin of the new energy flexible direct transmission system in the near-power frequency band is lower than a set threshold, the positive and negative sequence phase margin sensitivity of the interconnected system parameters is defined as follows: ； In the formula: PM p and PM n These represent the positive and negative phase margins, respectively. f os For the potential oscillation frequency, a i For a specific main circuit or control parameter of a flexible DC-DC MMC converter or a full-power wind turbine, Δ a i For the infinitesimal increment of this parameter, Δ a i Select a i 0.1%; The dominant parameter affecting near-power frequency stability is determined by the magnitude of the absolute value of the positive and negative sequence phase margin sensitivity.

2. The parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system according to claim 1, characterized in that, The source-side subsystem AC-side positive and negative sequence impedance model includes the flexible DC-side MMC converter main circuit and the MMC control system, wherein the MMC control system includes a positive and negative sequence AC voltage control loop, a positive and negative sequence current control loop, a positive and negative sequence separation algorithm, and a control delay. The load-side subsystem AC side positive and negative sequence impedance model includes the full-power wind turbine main circuit and the full-power wind turbine control system. The full-power wind turbine control system includes a DC voltage control loop, a positive and negative sequence current control loop, a phase-locked loop, a positive and negative sequence separation algorithm, and a control delay loop.

3. The parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system according to claim 2, characterized in that, The process of establishing the source-side subsystem AC side positive and negative sequence impedance models and the load-side subsystem AC side positive and negative sequence impedance models includes: Based on the harmonic state-space method, small-signal harmonic state-space models of MMC and full-power wind turbines are established respectively, and the relationship between the main circuit and the controller is established according to the modulation function and control structure.

4. The parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system according to claim 3, characterized in that, The evaluation of the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band based on the AC-side positive and negative sequence impedance model includes: Using the positive and negative sequence voltage of small disturbance on the AC side as the input of the positive and negative sequence impedance model on the AC side, the positive and negative sequence current of small disturbance on the AC side is obtained by solving the small signal harmonic state space equation, and the positive and negative sequence impedances on the AC side of the flexible DC MMC converter and the full-power wind turbine are obtained. Based on the positive and negative sequence impedances of the AC side of the flexible DC MMC converter and the full-power wind turbine, the equivalent loop gains of the new energy flexible DC transmission system are defined as follows: L mp = Z MMCp ( s ) / Z WFp ( s )； L mn = Z MMCn ( s ) / Z loadn ( s )； In the formula: Z MMCp ( s )and Z WFp ( s These are the near-power frequency positive sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively. Z MMCn ( s )and Z WFn ( s These are the near-power frequency negative sequence impedances of the flexible DC MMC converter and the full-power wind turbine, respectively. s Represents the Laplace operator; The s In the domain L mp and L mn Transform to the frequency domain and write it as the sum of the real and imaginary parts: L p =Re( L mp )+ j Im( L mp ); L n =Re( L mn )+ j Im( L mn ); The necessary and sufficient conditions for the stability of a new energy flexible direct transmission system are defined as follows: L p and L n The imaginary part Im ( L mp ) and Im( L mn When ) crosses the frequency axis, the corresponding real part Re( L mp ) and Re( L mn If the value is greater than the set threshold, the system is stable; Based on the aforementioned necessary and sufficient conditions, determine whether the new energy flexible direct transmission system is stable.

5. The parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system according to claim 1, characterized in that, The process involves determining the dominant parameters to be optimized based on the original parameters and by iterating through the upper and lower limits of actual parameter values. The optimization range is then determined based on the equivalent impedance criterion, including: Observe when the dominant parameter changes L p and L n Imaginary part of the frequency domain curve Im( L mp ) and Im( L mn At the point where it crosses the frequency axis, all of its corresponding points L p and L n The real part of the frequency domain curve Re( L mp ) and Re( L mn The relationship between the minimum value of a parameter and a set threshold, combined with the upper and lower limits of the parameter's value, determines the optimal range of the parameter's value; that is, it can be expressed mathematically as: ； In the formula: C 1. C 2 represents the upper and lower limits of the parameter values, which satisfy the formula. a i The optimal range of values ​​for the dominant parameter.

6. The parameter optimization method for improving the near-power frequency stability of a new energy flexible direct transmission system according to claim 5, characterized in that, The process of further optimizing the optimization range of the dominant parameter includes: Construct the input-response transfer function of the source-side subsystem T input1 ( s )=Δ u gd / Δ u gdref and disturbance response transfer function T disturb1 ( s )= Δ u gd / Δ u d They are as follows: ； In the formula: L arm and R arm Z represents the equivalent inductance and resistance of the flexible DC MMC converter arm; L This represents the equivalent resistance on the AC side of the flexible DC MMC converter; H vp and H ip These are PI controllers for the outer loop of positive-sequence AC voltage and the inner loop of positive-sequence current, respectively. G d1 s represents the control delay of the flexible DC MMC converter, and s is the Laplace operator; Construct the input-response transfer function of the load-side subsystem T input2 ( s )=Δ u dc / Δ u dcref and disturbance response transfer function T disturb2 ( s )=Δ u dc / Δ u d They are as follows: ； In the formula: L f and R f The equivalent series inductance and resistance of the AC side filter for a full-power wind turbine; C dc For DC side capacitors; H dc and H cp These are PI controllers for the outer loop of DC voltage and the inner loop of positive sequence current, respectively. G d2 Control delay for full-power wind turbine units; u sd0 This represents the steady-state value of the d-axis component of the AC bus voltage. u dc0 This is the steady-state value of the DC voltage; Based on the input response and disturbance response transfer functions, the impact of parameter changes on the system's power frequency control performance is evaluated, and the optimal value range of the dominant parameters is further determined based on the already determined parameter optimization range.

7. A parameter optimization system for improving the near-power frequency stability of a new energy flexible direct transmission system, used to implement the method described in claim 1, characterized in that, include: Module division: The new energy flexible direct transmission system is divided into source-side subsystems and load-side subsystems; The source-side subsystem is a flexible direct-transmission MMC converter; the load-side subsystem is a new energy power station. Modeling module: Based on the source-side subsystem and the load-side subsystem, establish AC-side positive and negative sequence impedance models for the source-side subsystem and the load-side subsystem, respectively; Stability assessment module: Based on the AC side positive and negative sequence impedance model, evaluate the stability of the new energy transmission system via flexible direct transmission in the near-power frequency band; The main parameter acquisition module: When the near-power frequency stability margin of the new energy flexible direct transmission system is determined to be lower than the set threshold, the main parameters affecting near-power frequency stability are extracted based on the sensitivity of the phase margin parameter. Initial optimization module: Based on the original parameters, the module iterates through the upper and lower limits of the actual parameter values ​​to determine the dominant parameters that need to be optimized, and determines the parameter optimization range based on the equivalent impedance criterion. The module is further optimized as follows: Within the determined parameter optimization range, the input and disturbance response transfer functions of the source-side subsystem and the load-side subsystem are constructed, the impact of parameter changes on the power frequency control performance of the system is evaluated, and the determined optimization range of the dominant parameters is optimized again.

8. A terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it can be used to perform the method of any one of claims 1-6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, this program can be used to perform the method of any one of claims 1-6.

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