Method for suppressing wide frequency oscillation of direct current collection system based on impedance reshaping

Abstract

The application discloses a wide-frequency oscillation suppression method based on impedance remodeling for a direct-current collection system, and relates to the technical field of power electronics. The method comprises the following steps: S1, a wide-frequency impedance coupling model is constructed to determine a wide-frequency oscillation range and a dominant frequency; S2, a dynamic self-adaptive impedance remodeling controller comprising a detection module, a calculation module, a compensation module and a closed-loop adjustment module is designed; S3, bus voltage and branch current signals are collected, and oscillation characteristic quantities are extracted; S4, target impedance and compensation impedance are calculated based on the characteristic quantities and system parameters; S5, adaptive compensation impedance is injected to realize impedance remodeling; and S6, compensation impedance parameters are corrected through closed-loop feedback. The application realizes accurate suppression of wide-frequency oscillation, improves system stability, reduces control complexity, and can be adapted to upgrading and reconstruction of various direct-current collection systems.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a broadband oscillation suppression method for DC-DC collector systems based on impedance reshaping. Background Technology

[0002] With the continuous expansion of new energy power generation, DC collection systems are widely used in large-scale new energy bases such as offshore wind power and desert photovoltaic power due to their advantages such as low loss, high transmission efficiency, and no need for reactive power compensation. DC collection systems are mainly composed of DC generation units, DC transformers (DCTs), collection lines, energy storage devices, and grid-side modular multilevel converters (MMCs) and other power electronic equipment. The system exhibits a high proportion of power electronics characteristics, has inherently insufficient damping, and is prone to broadband oscillation problems.

[0003] Wideband oscillations can cause voltage and current distortions in the system, increase equipment losses, and in severe cases, damage power electronic devices, threatening the safe and stable operation of the system. Currently, methods for suppressing wideband oscillations in DC-DC converter systems mainly fall into two categories: one is to optimize existing control strategies by adjusting controller parameters and adding damping control loops to improve system damping. However, this method is not highly targeted and struggles to address the suppression needs of oscillations at different frequencies across a wide frequency range. Furthermore, it is prone to coupling with other control loops in the system, leading to increased control complexity. The other category employs impedance reshaping technology, adjusting the system impedance characteristics by introducing virtual impedance and paralleling active dampers to achieve oscillation suppression.

[0004] However, existing impedance reshaping technologies have significant drawbacks: First, most methods are designed only for single-frequency or narrow-band oscillations, failing to achieve full-coverage suppression across a wide frequency range (10Hz~10kHz), and are ineffective at suppressing multi-frequency component oscillations generated by equipment interaction in DC aggregation systems; Second, the parameters of virtual impedances or active dampers are mostly fixed values ​​or simply adaptively adjusted, without considering the dynamic impact of system operating conditions, resulting in low impedance reshaping accuracy and poor oscillation suppression stability; Third, existing impedance reshaping strategies do not fully consider the impedance coupling characteristics of each unit (generator unit, DCT, aggregation line) in the DC aggregation system, easily leading to secondary oscillations.

[0005] Therefore, there is an urgent need for an impedance reshaping method that can take into account wide frequency band coverage, dynamic adaptation, and low complexity, in order to solve the above-mentioned problems of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to propose a broadband oscillation suppression method for DC-DC collector systems based on impedance reshaping. By using a dynamic adaptive impedance reshaping strategy, this method addresses the technical shortcomings of existing technologies, such as insufficient broadband coverage, low impedance reshaping accuracy, and poor adaptability, thereby achieving precise suppression of broadband oscillations and improving system operational stability.

[0007] To achieve the above objectives, this invention proposes a broadband oscillation suppression method for DC-DC converging systems based on impedance reshaping, comprising the following steps: S1. Construct a broadband impedance coupling model of the DC collection system, obtain the impedance parameters and operating status parameters of each unit of the DC collection system, and determine the frequency range and dominant oscillation frequency of the broadband oscillation. S2. Design a dynamic adaptive impedance reshaping controller, which includes a wideband oscillation detection module, an impedance parameter calculation module, an impedance compensation module, and a closed-loop adjustment module. S3. Through the wideband oscillation detection module, the bus voltage and branch current signals of the DC collection system are collected in real time, the oscillation characteristic quantities are extracted and the current oscillation frequency and oscillation amplitude are identified. S4. Based on the oscillation characteristic quantities and system operating state parameters, the target impedance and compensation impedance required for impedance reshaping are dynamically calculated through the impedance parameter calculation module. S5. Inject adaptive compensation impedance into the DC collection system through the impedance compensation module and the compensation impedance parameters. S6. The closed-loop adjustment module provides real-time feedback on the system impedance reshaping effect and oscillation suppression, and dynamically corrects the compensation impedance parameters.

[0008] Preferably, in step S1, the steps for determining the frequency range and dominant oscillation frequency of the broadband oscillation are as follows: Step S11: Obtain the basic parameters of each unit in the system: the equivalent impedance of the DC power generation unit. , i =1,2,..., n The equivalent resistance of the collection line and equivalent inductance , j =1,2,..., n DC bus equivalent capacitance Equivalent impedance of DCT Equivalent impedance of the DC port of the grid-side MMC Equivalent impedance of energy storage device ;in, n The number of DC power generation units. i , j It is an integer; Step S12: Based on the impedance coupling effect between each unit and the influence of bidirectional power flow, a broadband impedance coupling model is constructed, and the total equivalent impedance of the DC collection system is calculated as follows: ; in, The total equivalent impedance is... For complex frequencies, Angular frequency; Step S13: Determine the frequency range of the broadband oscillation using impedance sweep frequency testing and small-signal analysis, and identify the dominant oscillation frequency; the formula for the dominant oscillation frequency is as follows: ; in, As the dominant oscillation frequency, The oscillation frequency is denoted as .

[0009] Preferably, in step S2, the functions of each module are as follows: Wideband oscillation detection module: Employs an improved wavelet packet transform algorithm to acquire DC bus voltage in real time. and the current in each branch Extract oscillation features, including oscillation frequency. f Oscillation amplitude A and oscillation damping ratio ; Impedance parameter calculation module: dynamically calculates the target impedance parameter and compensation impedance parameter based on oscillation characteristic quantities and system operating state parameters; Impedance compensation module: Employs a virtual impedance injection method, injecting compensation impedance into the system through power electronic switching devices. This enables the reshaping of the system's equivalent impedance. Closed-loop control module: Real-time acquisition of the reshaped system equivalent impedance and oscillation amplitude A The damping ratio relative to the preset target and allowable oscillation amplitude By comparing and dynamically adjusting the compensation impedance parameters, a closed-loop control is formed.

[0010] Preferably, in step S3, the oscillation characteristic quantity includes the oscillation frequency. f Oscillation amplitude A and oscillation damping ratio Among them, the oscillation damping ratio Extracted using an improved wavelet packet transform algorithm, the formula is as follows: ; in, , For two adjacent oscillation peaks, The time interval between the two peaks. The oscillation period is [the period of time].

[0011] The preferred steps of the improved wavelet packet transform algorithm are as follows: Step S31: Denoise the acquired time-domain signal to remove the power frequency component and random noise, and obtain the denoised signal. Step S32: Use wavelet packet transform to perform 8-level multi-scale decomposition on the denoised signal, covering the frequency range of wideband oscillation, and obtain the wavelet packet coefficients of each level. Step S33: Calculate the energy of each layer, using the following formula: ; in, For the first m The energy of the layer, These are wavelet packet coefficients. m The number of decomposition layers, k The sampling point number, N This represents the total number of sampling points; Step S34: Identify the oscillation frequency, oscillation amplitude, and oscillation damping ratio based on the energy of each layer.

[0012] Preferably, in step S4, the target impedance is calculated using the following formula: ; ; ; ; in, For the target impedance, For the target resistance, For the target inductor, For the target capacitance, , , This is the impedance adjustment coefficient. This is the steady-state value of the DC bus voltage. For the system's real-time power, The rated power of the system, The number of units to be put into operation is the rated quantity. n The quantity allocated to the aggregation unit; Compensation impedance The calculation formula is as follows: ; The compensation impedance meets the amplitude limit condition: .

[0013] Preferably, in step S5, the adaptive compensation impedance injection method is virtual impedance injection, and the specific steps are as follows: Step S51: Compensate impedance Decomposed into resistive components Inductive component and capacitance components ; Step S52: By using pulse width modulation (PWM) technology, control the on and off of power electronic switching devices to simulate the impedance characteristics of virtual resistance, virtual inductance, and virtual capacitance. Step S53: Inject the compensation impedance into the connection node between the DC bus and the collection line to reshape the system's equivalent impedance.

[0014] Preferably, in step S6, the specific steps are as follows: Step S61: Real-time detection of the reshaped oscillation amplitude A and the reshaped damping ratio , and the preset allowable oscillation amplitude Damping ratio with target Compare; Step S62, if and If so, the current compensation impedance parameters remain unchanged; Step S63, if or Then based on the deviation and Correct the compensation impedance parameters; among which, For the deviation of oscillation amplitude, This refers to the damping ratio deviation; Step S64: Adjust the compensation impedance. Re-inject into the system and repeat steps S3 to S6 to form a closed-loop control.

[0015] Preferably, in step S63, the dynamic correction formula for the compensation impedance parameter is as follows: ; in, , This is the deviation adjustment coefficient.

[0016] Preferably, the DC collection system consists of n It consists of a DC power generation unit, a collection line, a DC bus, a DC transformer (DCT), a grid-side MMC, and an energy storage device. Each DC power generation unit is connected in parallel to the DC bus through the collection line. The DC bus is connected to the AC power grid via the DCT and the grid-side MMC. The energy storage device is connected in parallel to the DC bus.

[0017] Therefore, this invention proposes a broadband oscillation suppression method for DC-DC collector systems based on impedance reshaping, and demonstrates it through a related system. Its beneficial effects are as follows: (1) This invention innovatively constructs a broadband impedance coupling model for DC collection system, which fully considers the impedance coupling characteristics of each unit (generator unit, DCT, collection line) and the influence of bidirectional power flow on impedance, solves the problem of low impedance reshaping accuracy caused by the failure of existing models to consider coupling effects, and provides accurate model support for broadband oscillation suppression. (2) The present invention designs a dynamic adaptive impedance reshaping controller, which realizes real-time dynamic adjustment of the compensation impedance parameter. It can adaptively match the oscillation suppression requirements of different frequencies according to the changes in the system operating state and oscillation characteristics, covering a wide frequency band of 10Hz~10kHz, and solves the defects of narrow frequency band suppression and poor adaptability of the existing methods. (3) The present invention adopts a closed-loop control architecture of "detection-calculation-compensation-feedback", which corrects the compensation impedance parameters through real-time feedback, avoids secondary oscillation caused by excessive or insufficient impedance reshaping, and improves the stability and reliability of oscillation suppression.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a flowchart of the broadband oscillation suppression method for DC collection systems based on impedance reshaping according to the present invention; Figure 2 The following are comparison diagrams of voltage and current waveforms before and after oscillation suppression using the prior art in the embodiments of the present invention; wherein, (a) is the voltage and current waveform before oscillation suppression, and (b) is the voltage and current waveform after oscillation suppression using the prior art. Figure 3 The figures are comparison diagrams of voltage and current waveforms before and after oscillation suppression using the method of the present invention in the embodiments of the present invention; wherein, (a) is the voltage and current waveform diagram before oscillation suppression, and (b) is the voltage and current waveform diagram after oscillation suppression using the method of the present invention. Detailed Implementation

[0020] To make the technical solutions, advantages, and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] like Figure 1As shown, this invention provides a broadband oscillation suppression method for DC-DC charging systems based on impedance reshaping, with the following specific steps: Step S1: Construct a wideband impedance coupling model for the DC collection system.

[0023] DC collection system mainly consists of n It consists of a DC power generation unit, a collection line, a DC bus, a DC transformer (DCT), a grid-side MMC, and an energy storage device. Each DC power generation unit is connected in parallel to the DC bus through the collection line. The DC bus is connected to the AC grid through the DCT and the grid-side MMC. The energy storage device is connected in parallel to the DC bus to smooth out power fluctuations.

[0024] Step S11: Obtain the basic parameters of each unit in the system: the equivalent impedance of the DC power generation unit. , i =1,2,..., n The equivalent resistance of the collection line and equivalent inductance , j =1,2,..., n DC bus equivalent capacitance Equivalent impedance of DCT Equivalent impedance of the DC port of the grid-side MMC Equivalent impedance of energy storage device ;in, n The number of DC power generation units. i , j It is an integer; Step S12: Based on the impedance coupling effect between each unit and the influence of bidirectional power flow, a broadband impedance coupling model is constructed, and the total equivalent impedance of the DC collection system is calculated as follows: ; in, The total equivalent impedance is... For complex frequencies, Angular frequency; Step S13: Through impedance sweep frequency testing and small signal analysis, the frequency range of the broadband oscillation is determined to be 10Hz~10kHz, and the dominant oscillation frequency is identified; the formula for the dominant oscillation frequency is as follows: ; in, As the dominant oscillation frequency, The oscillation frequency is denoted as .

[0025] Step S2: Design a dynamic adaptive impedance reshaping controller.

[0026] The dynamic adaptive impedance reshaping controller includes a wideband oscillation detection module, an impedance parameter calculation module, an impedance compensation module, and a closed-loop adjustment module. The functions of each module are as follows: Wideband oscillation detection module: Employs an improved wavelet packet transform algorithm to acquire DC bus voltage in real time. and the current in each branch Extract oscillation features, including oscillation frequency. f Oscillation amplitude A and oscillation damping ratio ; Impedance parameter calculation module: dynamically calculates the target impedance parameter and compensation impedance parameter based on oscillation characteristic quantities and system operating state parameters; Impedance compensation module: Employs a virtual impedance injection method, injecting compensation impedance into the system through power electronic switching devices. This enables the reshaping of the system's equivalent impedance. Closed-loop control module: Real-time acquisition of the reshaped system equivalent impedance and oscillation amplitude A The damping ratio relative to the preset target and allowable oscillation amplitude By comparing and dynamically adjusting the compensation impedance parameters, a closed-loop control is formed.

[0027] Step S3: Detection of wideband oscillation characteristics.

[0028] The broadband oscillation detection module uses an improved wavelet packet transform algorithm to decompose the acquired bus voltage and branch current signals. The specific steps are as follows: Step S31: Denoise the acquired time-domain signal to remove the power frequency component and random noise, and obtain the denoised signal. Step S32: Use wavelet packet transform to perform 8-level multi-scale decomposition on the denoised signal, covering a wide frequency band of 10Hz~10kHz, and obtain the wavelet packet coefficients of each level. Step S33: Calculate the energy of each layer, using the following formula: ; in, For the first m The energy of the layer, These are wavelet packet coefficients. m The number of decomposition layers, k The sampling point number, N This represents the total number of sampling points; Step S34: Based on the energy of each layer The oscillation frequency, oscillation amplitude, and oscillation damping ratio are identified; among them, the oscillation damping ratio... The formula is as follows: ; in, , For two adjacent oscillation peaks, The time interval between the two peaks. The oscillation period is [the period of time].

[0029] Step S4: Dynamic calculation of impedance parameters.

[0030] Based on oscillation characteristic quantities and system operating state parameters, the target impedance and compensation impedance required for impedance reshaping are dynamically calculated through the impedance parameter calculation module. The specific calculation formula is as follows: First, calculate the target impedance, which must meet the preset target damping ratio across a wide frequency band. : ; ; ; ; in, For the target impedance, For the target resistance, For the target inductor, For the target capacitance, , , The impedance adjustment factor (adjusted according to the actual engineering scenario) , , ), This is the steady-state value of the DC bus voltage. For the system's real-time power, The rated power of the system, The rated number of units to be invested in the collection unit, where n is the number of units to be invested in the collection unit; Next, calculate the compensation impedance. The formula is as follows: ; The compensation impedance meets the amplitude limit condition: .

[0031] Step S5: Adaptive impedance compensation and reshaping.

[0032] The impedance compensation module uses a virtual impedance injection method to inject the compensation impedance calculated in step S4. The injection DC collection system is implemented as follows: Step S51: Compensate impedance Decomposed into resistive components Inductive component and capacitance components ; Step S52: By using pulse width modulation (PWM) technology, control the on and off of power electronic switching devices to simulate the impedance characteristics of virtual resistance, virtual inductance, and virtual capacitance, and inject the compensation impedance into the connection node between the DC bus and the collection line. Step S53: Inject the compensation impedance into the connection node between the DC bus and the collection line to reshape the system's equivalent impedance, offset the negative damping component of the broadband oscillation, and suppress the oscillation amplitude.

[0033] Step S6: Closed-loop regulation and stability control.

[0034] The closed-loop control module collects the reshaped system equivalent impedance in real time. and oscillation amplitude A To perform closed-loop feedback adjustment, the specific steps are as follows: Step S61: Real-time detection of the reshaped oscillation amplitude A and the reshaped damping ratio , and the preset allowable oscillation amplitude Damping ratio with target Compare; Step S62, if and If so, the current compensation impedance parameters remain unchanged; Step S63, if or Then based on the deviation and Correct the compensation impedance parameters; among which, For the deviation of oscillation amplitude, This refers to the damping ratio deviation; Step S64: Adjust the compensation impedance. Re-inject into the system and repeat steps S3 to S6 to form a closed-loop control, ensuring that wideband oscillations are continuously suppressed and the system maintains stable operation.

[0035] To verify the effectiveness of the method of the present invention, a simulation model of a DC collection system was built. The system parameters are as follows: n=6 DC power generation units, each with a rated power of 500kW, and equivalent impedance... =0.1+j0.05Ω; The line length is 10km, and the equivalent resistance is... =0.02Ω / km, equivalent inductance =0.1mH / km; DC bus capacitance =10mF; DCT equivalent impedance =0.2+j0.1Ω; Equivalent impedance of the DC port of the grid-side MMC =0.15+j0.08Ω; Equivalent impedance of energy storage device =0.05+j0.02Ω; Preset target damping ratio =0.4, allowable oscillation amplitude =3% Impedance adjustment coefficient =1.0, =0.7, =1.2; Deviation adjustment coefficient =0.2, =0.3.

[0036] like Figure 2 It is evident that when using existing technology, the system exhibits significant broadband oscillations; for example... Figure 3 As can be seen, after adopting the method of the present invention, the oscillation is quickly suppressed, meeting the preset requirements, and there is no obvious oscillation in the wide frequency band of 10Hz~10kHz, which verifies the effectiveness and superiority of the method of the present invention.

[0037] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art.

[0038] Therefore, this invention provides a broadband oscillation suppression method for DC bundling systems based on impedance reshaping. By constructing a broadband impedance coupling model, designing a dynamic adaptive impedance reshaping controller, and adopting a closed-loop control architecture, it achieves accurate suppression of broadband oscillations, improves system stability, and reduces control complexity. It can be adapted to the upgrade and transformation of various DC bundling systems.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A broadband oscillation suppression method for DC collecting systems based on impedance reshaping, characterized in that, Includes the following steps: S1. Construct a broadband impedance coupling model of the DC collection system, obtain the impedance parameters and operating status parameters of each unit of the DC collection system, and determine the frequency range and dominant oscillation frequency of the broadband oscillation. S2. Design a dynamic adaptive impedance reshaping controller, which includes a wideband oscillation detection module, an impedance parameter calculation module, an impedance compensation module, and a closed-loop adjustment module. S3. Through the wideband oscillation detection module, the bus voltage and branch current signals of the DC collection system are collected in real time, the oscillation characteristic quantities are extracted and the current oscillation frequency and oscillation amplitude are identified. S4. Based on the oscillation characteristic quantities and system operating state parameters, the target impedance and compensation impedance required for impedance reshaping are dynamically calculated through the impedance parameter calculation module. S5. Inject adaptive compensation impedance into the DC collection system through the impedance compensation module and the compensation impedance parameters. S6. The closed-loop adjustment module provides real-time feedback on the system impedance reshaping effect and oscillation suppression, and dynamically corrects the compensation impedance parameters.

2. The broadband oscillation suppression method for DC collecting systems based on impedance reshaping according to claim 1, characterized in that, In step S1, the steps for determining the frequency range and dominant oscillation frequency of the broadband oscillation are as follows: Step S11: Obtain the basic parameters of each unit in the system: the equivalent impedance of the DC power generation unit. , i =1,2,..., n The equivalent resistance of the collection line and equivalent inductance , j =1,2,..., n DC bus equivalent capacitance Equivalent impedance of DCT Equivalent impedance of the DC port of the grid-side MMC Equivalent impedance of energy storage device ;in, n The number of DC power generation units. i , j It is an integer; Step S12: Based on the impedance coupling effect between each unit and the influence of bidirectional power flow, a broadband impedance coupling model is constructed, and the total equivalent impedance of the DC collection system is calculated as follows: ； in, The total equivalent impedance is... For complex frequencies, Angular frequency; Step S13: Determine the frequency range of the broadband oscillation using impedance sweep frequency testing and small-signal analysis, and identify the dominant oscillation frequency; the formula for the dominant oscillation frequency is as follows: ； in, As the dominant oscillation frequency, The oscillation frequency is denoted as .

3. The broadband oscillation suppression method for DC-DC collecting systems based on impedance reshaping according to claim 2, characterized in that, In step S2, the functions of each module are as follows: Wideband oscillation detection module: Employs an improved wavelet packet transform algorithm to acquire DC bus voltage in real time. and the current in each branch Extract oscillation features, including oscillation frequency. f Oscillation amplitude A and oscillation damping ratio ; Impedance parameter calculation module: dynamically calculates the target impedance parameter and compensation impedance parameter based on oscillation characteristic quantities and system operating state parameters; Impedance compensation module: Employs a virtual impedance injection method, injecting compensation impedance into the system through power electronic switching devices. This enables the reshaping of the system's equivalent impedance. Closed-loop control module: Real-time acquisition of the reshaped system equivalent impedance and oscillation amplitude A The damping ratio relative to the preset target and allowable oscillation amplitude By comparing and dynamically adjusting the compensation impedance parameters, a closed-loop control is formed.

4. The broadband oscillation suppression method for DC collecting systems based on impedance reshaping according to claim 3, characterized in that, In step S3, the oscillation characteristic quantity includes the oscillation frequency. f Oscillation amplitude A and oscillation damping ratio Among them, the oscillation damping ratio Extracted using an improved wavelet packet transform algorithm, the formula is as follows: ； in, , For two adjacent oscillation peaks, The time interval between the two peaks. The oscillation period is [the period of time].

5. The broadband oscillation suppression method for DC-DC collecting systems based on impedance reshaping according to claim 4, characterized in that, The specific steps of the improved wavelet packet transform algorithm are as follows: Step S31: Denoise the acquired time-domain signal to remove the power frequency component and random noise, and obtain the denoised signal. Step S32: Use wavelet packet transform to perform 8-level multi-scale decomposition on the denoised signal, covering the frequency range of wideband oscillation, and obtain the wavelet packet coefficients of each level. Step S33: Calculate the energy of each layer, using the following formula: ； in, For the first m The energy of the layer, These are wavelet packet coefficients. m The number of decomposition layers, k The sampling point number, N This represents the total number of sampling points; Step S34: Identify the oscillation frequency, oscillation amplitude, and oscillation damping ratio based on the energy of each layer.

6. The broadband oscillation suppression method for DC-DC collecting systems based on impedance reshaping according to claim 5, characterized in that, In step S4, the target impedance is calculated using the following formula: ； ； ； ； in, For the target impedance, For the target resistance, For the target inductor, For the target capacitance, , , This is the impedance adjustment coefficient. This is the steady-state value of the DC bus voltage. For the system's real-time power, The rated power of the system, The number of units to be put into operation is the rated quantity. n The quantity allocated to the aggregation unit; Compensation impedance The calculation formula is as follows: ； The compensation impedance meets the amplitude limit condition: 。 7. The broadband oscillation suppression method for DC-DC collecting systems based on impedance reshaping according to claim 6, characterized in that, In step S5, the adaptive compensation impedance injection method is virtual impedance injection, and the specific steps are as follows: Step S51: Compensate impedance Decomposed into resistive components Inductive component and capacitance components ; Step S52: By using pulse width modulation (PWM) technology, control the on and off of power electronic switching devices to simulate the impedance characteristics of virtual resistance, virtual inductance, and virtual capacitance. Step S53: Inject the compensation impedance into the connection node between the DC bus and the collection line to reshape the system's equivalent impedance.

8. The broadband oscillation suppression method for DC collecting systems based on impedance reshaping according to claim 7, characterized in that, In step S6, the specific steps are as follows: Step S61: Real-time detection of the reshaped oscillation amplitude A and the reshaped damping ratio , and the preset allowable oscillation amplitude Damping ratio with target Compare; Step S62, if and If so, the current compensation impedance parameters remain unchanged; Step S63, if or Then based on the deviation and Correct the compensation impedance parameters; among which, For the deviation of oscillation amplitude, This refers to the damping ratio deviation; Step S64: Adjust the compensation impedance. Re-inject into the system and repeat steps S3 to S6 to form a closed-loop control.

9. The broadband oscillation suppression method for DC collecting systems based on impedance reshaping according to claim 8, characterized in that, In step S63, the dynamic correction formula for the compensation impedance parameter is as follows: ； in, , This is the deviation adjustment coefficient.

10. The broadband oscillation suppression method for DC-DC collecting systems based on impedance reshaping according to claim 1, characterized in that, The DC collection system consists of n It consists of a DC power generation unit, a collection line, a DC bus, a DC transformer (DCT), a grid-side MMC, and an energy storage device. Each DC power generation unit is connected in parallel to the DC bus through the collection line. The DC bus is connected to the AC power grid via the DCT and the grid-side MMC. The energy storage device is connected in parallel to the DC bus.

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