Broadband oscillation suppression method based on impedance sensitivity in multiple operation modes

Abstract

The invention relates to a broadband oscillation suppression method based on impedance sensitivity in multiple operation modes. The broadband oscillation suppression method comprises the following steps: acquiring N scenes of typical operation modes of a power grid and M control parameters; according to a power grid short-circuit current equivalent method, solving a transfer function of an impedance ratio in an ith power grid typical operation mode; for the jth control parameter, based on the transfer function of the impedance ratio, respectively calculating the sensitivity value of the control parameter to the amplitude of the impedance ratio and the sensitivity value of the control parameter to the phase angle of the impedance ratio, and adjusting the control parameter; and after all given power grid typical operation modes and all control parameters are adjusted, the control range of each control parameter in each scene is fused to obtain an optimized MMC control parameter suitable for each power grid operation mode, and suppression of broadband oscillation is realized. Compared with the prior art, the method has the advantages of being suitable for safe operation of the system in multiple operation modes, high in control reliability and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of flexible DC transmission systems, and relates to a method for suppressing broadband oscillations in flexible DC transmission, particularly a broadband oscillation suppression method based on impedance sensitivity under multiple operating modes. Background Technology

[0002] With the continuous construction of flexible DC transmission system grid connection projects, oscillation problems caused by the interaction between the flexible DC system and the power grid have gradually emerged. Compared with traditional HVDC transmission based on thyristors and VSCs, the equipment and control links of flexible DC systems based on Modular Multilevel Converters (MMCs) are more complex, making the coupling between flexible DC transmission equipment and grid equipment, and between flexible DC control links and grid equipment, more pronounced. This greatly increases the likelihood of multi-frequency oscillations occurring during the interaction between the flexible DC system and the grid. Wideband oscillations involve power oscillations in multiple frequency bands from low-frequency to high-frequency, with complex oscillation mechanisms and significant suppression challenges. Furthermore, due to different grid operating modes, the equivalent impedance of the grid varies under different scenarios, further complicating the suppression of wideband oscillations.

[0003] Currently, there are two main types of measures to suppress broadband oscillations in flexible DC systems. One type is based on optimizing the parameters of the MMC control loop to suppress broadband oscillations. By optimizing and adjusting its control parameters, the ratio of grid impedance to inverter output impedance satisfies the Nyquist stability criterion in the frequency domain. For example, Chinese patent application CN114865680A discloses a method for suppressing specific resonant frequencies of a modular multilevel converter. The other type is based on additional hardware equipment to suppress broadband oscillations. This involves considering installing a dedicated impedance optimization device at the MMC grid connection point to improve the impedance characteristics of the MMC station. Based on the physical characteristics of the additional impedance optimization device, it can be divided into active impedance optimization and passive impedance optimization.

[0004] The two broadband oscillation suppression measures mentioned above each have their own application scenarios. Among them, the method based on control link parameter optimization only requires parameter optimization of the existing MMC equipment. Compared with the suppression method based on additional equipment, its implementation cost is lower and it has a better suppression effect on the low and medium frequency oscillations in broadband oscillations. Therefore, its application scenarios are more extensive.

[0005] Existing parameter optimization methods based on control links are generally only applicable to fixed power grid scenarios, and their optimization objectives are relatively singular, focusing only on optimizing the control parameters of a specific link. However, the actual power grid is constantly changing due to load variations, and its equivalent grid impedance is also constantly changing. In particular, the power grid operation modes differ significantly under different seasons. How to achieve broadband oscillation suppression under multiple operating modes is a problem that needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a broadband oscillation suppression method based on impedance sensitivity under multiple operating modes. By calculating the impedance ratio sensitivity under multiple operating modes and comprehensively adjusting the control parameters of each control link of MMC according to the calculation results, it can be made suitable for the safe operation of the system under multiple operating modes and achieve broadband oscillation control.

[0007] The objective of this invention can be achieved through the following technical solutions: A broadband oscillation suppression method based on impedance sensitivity under multiple operating modes includes the following steps: Obtain N typical power grid operation scenarios and M control parameters; Based on the equivalent method of short-circuit current in the power grid, the transfer function of impedance ratio under typical operating modes of each power grid is solved; For each control parameter, based on the transfer function of the impedance ratio, the sensitivity values ​​of the control parameter to the impedance ratio amplitude and the impedance ratio phase angle are calculated respectively, and the control parameter is adjusted according to the sensitivity values ​​of the impedance ratio amplitude and the impedance ratio phase angle. After adjusting all given typical power grid operating modes and all control parameters, the control ranges of each control parameter under each scenario are integrated to obtain optimized MMC control parameters suitable for each power grid operating mode, thereby suppressing wideband oscillations.

[0008] Furthermore, the typical operation modes of the power grid include peak summer operation mode and off-peak spring and autumn operation mode.

[0009] Furthermore, the control parameters include the loop parameters of the PI circuit.

[0010] Furthermore, the formula for calculating the transfer function of the impedance ratio is: Z b ( s )= Zg ( s ) / Zc ( s ) in, Z g (s () represents the equivalent impedance of the power grid. Z c ( s ) represents the equivalent impedance of the converter.

[0011] Furthermore, the sensitivity calculation formula for the impedance ratio amplitude is as follows: in, d For a certain control parameter, s For the Laplace operator, For impedance comparison control parameters d Sensitivity, The transfer function of impedance ratio, This represents the sensitivity of the impedance ratio amplitude.

[0012] Furthermore, the sensitivity calculation formula for the impedance ratio phase angle is as follows: in, d For a certain control parameter, s For the Laplace operator, The sensitivity is the impedance ratio to the phase angle. The transfer function of impedance ratio.

[0013] Furthermore, adjusting the control parameters based on the sensitivity value of the impedance ratio amplitude specifically involves: Based on the sign and magnitude of the impedance ratio amplitude sensitivity value, adjust the value of the control parameter. If the amplitude margin of the system after adjustment is still within the reasonable range of the given amplitude stability margin, further adjust the value of the control parameter. If the amplitude margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the control parameter and record the control parameter as the limit value of the range that meets the amplitude margin requirements under the typical operating mode of the power grid.

[0014] Furthermore, adjusting the control parameters based on the sensitivity of the impedance ratio phase angle specifically involves: Based on the sign and magnitude of the impedance ratio phase angle sensitivity value, adjust the value of the control parameter. If the phase angle margin of the system after adjustment is still within the reasonable range of the given phase angle stability margin, further adjust the value of the parameter. If the phase angle margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the parameter and record the parameter as the limit value of the range that meets the phase angle margin requirements under the typical operation mode of the power grid.

[0015] Furthermore, the control range of the integrated control parameters under various scenarios is specifically as follows: Take the intersection of the control ranges for the same control parameter.

[0016] The present invention also provides a broadband oscillation suppression device based on impedance sensitivity under multiple operating modes, comprising the following steps: The scenario acquisition module is used to acquire N typical power grid operation modes and M control parameters; The transfer function calculation module is used to solve the transfer function of impedance ratio under typical operating modes of various power grids based on the equivalent method of short-circuit current in the power grid. The parameter adjustment module is used to calculate the sensitivity values ​​of the control parameter to the impedance ratio amplitude and the impedance ratio phase angle for each control parameter based on the transfer function of the impedance ratio, and adjust the control parameter according to the sensitivity values ​​of the impedance ratio amplitude and the impedance ratio phase angle. The optimization parameter acquisition module is used to adjust all given typical power grid operating modes and all control parameters, and then integrate the control range of each control parameter under each scenario to obtain optimized MMC control parameters suitable for each power grid operating mode, thereby achieving the suppression of wideband oscillations.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention fully considers the equivalent impedance of the power grid under various typical power grid operating modes. By calculating the sensitivity of the impedance ratio to the control parameters under different operating modes, the invention provides a control strategy to suppress broadband oscillations based on the comprehensive calculation results. Furthermore, the invention comprehensively adjusts the control parameters of each control link of the MMC based on the calculation results to make it suitable for the safe operation of the system under multiple operating modes, thereby achieving broadband oscillation mitigation.

[0018] 2. This invention obtains the sensitivity of the impedance ratio to the control parameters of each link in the MMC, and then obtains the optimal range of control parameters that meet the system stability conditions, thereby ensuring the stable operation of the system and improving the control reliability. Attached Figure Description

[0019] Figure 1 This is a flowchart of the broadband oscillation suppression method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the broadband oscillation suppression device according to an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0021] Example 1 like Figure 1As shown, this embodiment provides a broadband oscillation suppression method based on impedance sensitivity under multiple operating modes, including the following steps: Step S1: Obtain N typical power grid operation scenarios and M control parameters.

[0022] Specifically, typical power grid operation modes include peak summer operation and off-peak spring and autumn operation. Control parameters include the loop parameters of the PI control.

[0023] For example, control parameters may include PI control parameters for control loops such as the power outer loop, current inner loop, circulating current suppression secondary current loop, and phase-locked loop.

[0024] Step S2: Based on the equivalent method of short-circuit current in the power grid, solve for the transfer function of impedance ratio under typical operating modes of each power grid.

[0025] For MMC converters, the impedance ratio is defined as the ratio of the grid impedance to the output impedance of the MMC converter. Z b ( s This is the equivalent impedance of the power grid. Z g ( s Divide by the converter's equivalent impedance Z c ( s ), if and only if Z b ( s )= Zg ( s ) / Zc ( s A grid-connected system with an MMC converter is stable only if the Nyquist stability criterion is met. When designing a control system using the frequency domain method, a certain stability margin is required, typically expressed as a phase margin. γ and gain margin GM To measure.

[0026] Specifically, the equivalent impedance of the power grid can be calculated based on the equivalent impedance of the connection point on the grid side. This equivalent impedance can be calculated directly using the WARD equivalent method or obtained through the short-circuit calculation function in the BPA software. The equivalent impedance of the converter is calculated using the harmonic linearization method (HSS). Based on the harmonic linearization method, the equivalent impedance of the MMC side considering the frequency coupling effect can be obtained with high accuracy.

[0027] like Figure 1 As shown, Z gi ( s ) is the first iThe transfer function of the equivalent impedance of the power grid under different scenarios reflects the relationship between the power grid impedance and frequency under different scenarios; Z mmci ( s ) is the first i The transfer function of the equivalent impedance of the MMC converter station in different scenarios reflects the relationship between the MMC converter station and the frequency in different scenarios. Z b ( s Let be the transfer function of impedance ratio, and its value is: Z gi ( s ) / Z mmci ( s ), representing the relationship between impedance ratio and frequency.

[0028] Specifically, such as Figure 1 As shown, the process of solving the transfer function of the impedance ratio includes the following steps: S201. Find the transfer function of the equivalent impedance of the power grid under the i-th typical operating mode. Z gi ( s ); S202. Find the transfer function of the equivalent impedance of the power grid's MMC under the i-th typical operating mode. Z mmci ( s ); S203. Solve for the transfer function of the impedance ratio under the i-th typical operating mode: Z b ( s )= Z gi ( s ) / Z mmci ( s ) Step S3: For the j-th control parameter, based on the transfer function of the impedance ratio, calculate the sensitivity values ​​of the control parameter to the impedance ratio amplitude and the impedance ratio phase angle, and adjust the control parameter according to the sensitivity values ​​of the impedance ratio amplitude and the impedance ratio phase angle.

[0029] By calculating the sensitivity of the impedance ratio gain margin and phase margin to all control parameters, the influence weight of the control parameters on the grid-connected stability of the system can be obtained.

[0030] Specifically, the formula for calculating the sensitivity of the impedance ratio amplitude is: (1) (2) in, d For a certain control parameter, s For the Laplace operator, For impedance comparison control parameters d Sensitivity, The transfer function of impedance ratio, This represents the sensitivity of the impedance ratio amplitude.

[0031] The formula for calculating the sensitivity of the impedance ratio phase angle is: (3) in, d For a certain control parameter, s For the Laplace operator, The sensitivity is the impedance ratio to the phase angle. The transfer function of impedance ratio.

[0032] In one possible implementation, adjusting the control parameters based on the sensitivity value of the impedance ratio amplitude specifically involves: Based on the sign and magnitude of the impedance ratio amplitude sensitivity value, adjust the value of the control parameter. If the amplitude margin of the system after adjustment is still within the reasonable range of the given amplitude stability margin, further adjust the value of the control parameter. If the amplitude margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the control parameter and record the control parameter as the limit value of the range that meets the amplitude margin requirements under the typical operating mode of the power grid.

[0033] In one possible implementation, adjusting the control parameters based on the sensitivity of the impedance ratio and phase angle specifically involves: Based on the sign and magnitude of the impedance ratio phase angle sensitivity value, adjust the value of the control parameter. If the phase angle margin of the system after adjustment is still within the reasonable range of the given phase angle stability margin, further adjust the value of the parameter. If the phase angle margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the parameter and record the parameter as the limit value of the range that meets the phase angle margin requirements under the typical operation mode of the power grid.

[0034] like Figure 1 As shown, c j For the first j The control parameter can be the proportional or integral coefficient of the PI controller in components such as the current control loop, voltage control loop, and phase-locked loop. c jMagmin , c jMagmin To consider the stability margin of the impedance ratio amplitude, the first j The range of variation of each control parameter during operation, the firstj The value of a control parameter cannot exceed this range; otherwise, the amplitude stability margin of the system will not meet the requirements. c jPhagmin , c jPhamin is the variation range of the j th control parameter considering the phase angle stability margin of the impedance ratio. During operation, the value of the j th control parameter cannot exceed this range; otherwise, the phase angle stability margin of the system will not meet the requirements.

[0035] Specifically, as Figure 1 shown, the adjustment process of each control parameter includes the adjustment based on the amplitude sensitivity of the impedance ratio and the adjustment based on the phase angle sensitivity of the impedance ratio. Among them, the adjustment based on the amplitude sensitivity of the impedance ratio includes: S301. Select the control parameter c j ; S302. Calculate the sensitivity of the amplitude of the impedance ratio of the c j th scenario to the parameter S303. Fine-tune the value of the parameter c j according to the calculation result of the amplitude sensitivity to make its amplitude margin within the stable range; S304. Record the parameter range that meets the amplitude margin as c jMagmin , c jMagmin ; S305. Judge whether j < M is satisfied, that is, whether all control parameters have been traversed. If so, execute step S306; S306. Further judge whether i < N is satisfied, that is, whether all scenarios have been traversed. If so, end. If not, obtain the transfer function of the impedance ratio of the next scenario and perform the next round of calculation.

[0036] The adjustment based on the phase angle sensitivity of the impedance ratio includes: S311. Select the control parameter c j ; S312. Calculate the sensitivity of the phase angle of the impedance ratio of the c j th scenario to the parameter S313. Fine-tune the value of the parameter c j according to the calculation result of the amplitude sensitivity to make its amplitude margin within the stable range; S314. Record the parameter range that meets the amplitude margin asc jPhagmin , c jPhamin ; S315. Determine whether j < M is satisfied, that is, whether all control parameters have been traversed. If so, execute step S306.

[0037] Step S4. After adjusting all the given typical grid operation modes and all control parameters, fuse the control ranges of each control parameter in each scenario to obtain optimized MMC control parameters suitable for each grid operation mode, and achieve the suppression of broadband oscillations.

[0038] In a possible implementation manner, fusing the control ranges of each control parameter in each scenario specifically means: taking the intersection of the control ranges of the same control parameter, and then obtaining optimized MMC control parameters suitable for each grid operation mode.

[0039] In an embodiment, when suppressing broadband oscillations for a specific flexible DC transmission system, the operation process includes the following steps: 1) Classify typical operation modes according to the grid operation conditions; 2) Control according to the above broadband oscillation suppression method; 3) Enter the value range of each control link of the optimized MMC as a control parameter into the MMC control program, and then return to step 1).

[0040] If the above method is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or a part of this technical solution can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. And the aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0041] Embodiment 2 As Figure 2 shown, based on the same inventive concept, this embodiment provides a broadband oscillation suppression device based on impedance sensitivity under multiple operation modes, including the following steps: A scenario acquisition module 1, configured to acquire scenarios of N typical grid operation modes and M control parameters; The transfer function calculation module 2 is used to solve the transfer function of the impedance ratio under the i-th typical operation mode of the power grid based on the equivalent method of short-circuit current in the power grid. The parameter adjustment module 3 is used to calculate the sensitivity values ​​of the control parameter to the impedance ratio magnitude and the impedance ratio phase angle based on the transfer function of the impedance ratio for the j-th control parameter, and adjust the control parameter according to the sensitivity values ​​of the impedance ratio magnitude and the impedance ratio phase angle. The optimization parameter acquisition module 4 is used to integrate the control range of each control parameter under each scenario after adjusting all given typical power grid operating modes and all control parameters, so as to obtain optimized MMC control parameters suitable for each power grid operating mode and realize the suppression of wideband oscillation.

[0042] The broadband oscillation suppression device based on impedance sensitivity under multiple operating modes provided in this embodiment has all the advantages of the broadband oscillation suppression method based on impedance sensitivity under multiple operating modes provided in Embodiment 1.

[0043] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A broadband oscillation suppression method based on impedance sensitivity under multiple operating modes, characterized in that, Includes the following steps: Obtain N typical power grid operation scenarios and M control parameters; Based on the equivalent method of short-circuit current in the power grid, the transfer function of impedance ratio under typical operating modes of each power grid is solved; For each control parameter, based on the transfer function of the impedance ratio, the sensitivity values ​​of the control parameter to the impedance ratio amplitude and the impedance ratio phase angle are calculated respectively, and the control parameter is adjusted according to the sensitivity values ​​of the impedance ratio amplitude and the impedance ratio phase angle. After adjusting all given typical power grid operating modes and all control parameters, the control ranges of each control parameter under each scenario are integrated to obtain optimized MMC control parameters suitable for each power grid operating mode, thereby suppressing wideband oscillations.

2. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The typical operation modes of the power grid include peak summer operation mode and off-peak spring and autumn operation mode.

3. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The control parameters include the loop parameters of the PI circuit.

4. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The formula for calculating the transfer function of the impedance ratio is: Z b ( s )= Zg ( s ) / Zc ( s ) in, Z g ( s () represents the equivalent impedance of the power grid. Z c ( s ) represents the equivalent impedance of the converter.

5. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The sensitivity calculation formula for the impedance ratio amplitude is as follows: in, d For a certain control parameter, s For the Laplace operator, For impedance comparison control parameters d Sensitivity, The transfer function of impedance ratio, This represents the sensitivity of the impedance ratio amplitude.

6. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The formula for calculating the sensitivity of the impedance ratio phase angle is: in, d For a certain control parameter, s For the Laplace operator, The sensitivity is the impedance ratio to the phase angle. The transfer function of impedance ratio.

7. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The control parameters are adjusted based on the sensitivity value of the impedance ratio amplitude as follows: Based on the sign and magnitude of the impedance ratio amplitude sensitivity value, adjust the value of the control parameter. If the amplitude margin of the system after adjustment is still within the reasonable range of the given amplitude stability margin, further adjust the value of the control parameter. If the amplitude margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the control parameter and record the control parameter as the limit value of the range that meets the amplitude margin requirements under the typical operating mode of the power grid.

8. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The control parameters are adjusted based on the sensitivity of the impedance ratio and phase angle as follows: Based on the sign and magnitude of the impedance ratio phase angle sensitivity value, adjust the value of the control parameter. If the phase angle margin of the system after adjustment is still within the reasonable range of the given phase angle stability margin, further adjust the value of the parameter. If the phase angle margin of the system after adjustment is less than the reasonable range of the given amplitude stability margin, stop adjusting the parameter and record the parameter as the limit value of the range that meets the phase angle margin requirements under the typical operation mode of the power grid.

9. The broadband oscillation suppression method based on impedance sensitivity under multiple operating modes according to claim 1, characterized in that, The control range of the integrated control parameters under various scenarios is specifically as follows: Take the intersection of the control ranges for the same control parameter.

10. A broadband oscillation suppression device based on impedance sensitivity under multiple operating modes, characterized in that, Includes the following steps: The scenario acquisition module is used to acquire N typical power grid operation modes and M control parameters; The transfer function calculation module is used to solve the transfer function of impedance ratio under typical operating modes of various power grids based on the equivalent method of short-circuit current in the power grid. The parameter adjustment module is used to calculate the sensitivity values ​​of the control parameter to the impedance ratio amplitude and the impedance ratio phase angle for each control parameter based on the transfer function of the impedance ratio, and adjust the control parameter according to the sensitivity values ​​of the impedance ratio amplitude and the impedance ratio phase angle. The optimization parameter acquisition module is used to adjust all given typical power grid operating modes and all control parameters, and then integrate the control range of each control parameter under each scenario to obtain optimized MMC control parameters suitable for each power grid operating mode, thereby achieving the suppression of wideband oscillations.

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