Broadband self-adaptive impedance remodeling method based on energy storage

Abstract

The invention provides a broadband self-adaptive impedance remodeling method based on energy storage, which comprises the following steps of: dividing an impedance frequency band of an energy storage system according to analysis on a PLL (Phase Locked Loop), a voltage loop, a current loop and a filter, and constructing an improved self-adaptive impedance remodeling control strategy based on combination of active damping and virtual admittance based on the divided frequency band; according to the impedance remodeling control strategy, establishing an energy storage inverter system impedance model considering impedance remodeling; based on an impedance model, the frequency band overlapping effect between different frequency bands and between different control links is comprehensively considered, and the impedance near a system oscillation frequency point is remodeled through sequential optimization design of PLL control, virtual admittance control and active damping control. The purposes of broadband oscillation suppression of the diversified new energy cluster sending-out system and safe and stable operation of a power system are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system stability control, and in particular relates to a wide-band adaptive impedance reshaping method based on energy storage. Background Art

[0002] With the continuous advancement of the dual carbon goals, on the one hand, the installed capacity of new energy such as wind power and photovoltaics will be further greatly increased. It is estimated that by 2025, the proportion of renewable energy in total energy consumption will reach about 18%. On the other hand, the State Grid Gansu Electric Power Company is fully committed to building a new power system of UHV DC transmission type and regional power grid hub type. As of the end of April, the installed capacity of new energy grid-connected in Gansu Province reached 31.2228 million kilowatts, accounting for 48.95% of the total installed capacity of the province, and the proportion of new energy in the transmitted electricity reached 50%, a record high. It can be seen that the AC and DC power grid with a high proportion of power electronic equipment and new energy access will become the basic form of the power grid architecture in our province in the future. The large-scale access of power electronic equipment and new energy has significantly changed the operation mode and dynamic characteristics of the power system. Power electronic equipment represented by converters and inverters will be used on a large scale. The multi-scale cascade and sequential switching characteristics of power electronic equipment will cause fundamental changes in the physical coupling mechanism of traditional power systems. Traditional electromagnetic equipment and power electronic equipment and their control systems have nonlinear strong coupling characteristics, which makes the dynamic behavior of power systems more complex and changeable, and prone to safety problems such as wide-band oscillations.

[0003] In the early 20th century, the oscillation problem of the power system was electromechanical oscillation dominated by synchronous machines. In the 21st century, the oscillation problem of the power system has transitioned to electromagnetic transient oscillation dominated by power electronic equipment. This type of oscillation problem is jointly involved by multiple devices and power grids, with a frequency range of several Hz to thousands of Hz. Its root cause is the multi-time scale dynamic interaction of the source / device network formed by the coupling of new energy units / AC / DC converters and their controls through complex power grids, which is essentially different from the oscillation problem of traditional power grids. It is urgent to study its generation mechanism, identification technology and suppression measures. For the broadband oscillation problem of large-scale diversified new energy cluster transmission systems, the existing suppression strategy is limited to the suppression of a single frequency band, and does not consider the system band overlap effect. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a wide-band adaptive impedance reshaping method based on energy storage, which at least partially solves the problem that the prior art is limited to suppression of a single frequency band and does not consider the system band overlapping effect.

[0005] The embodiment of the present invention provides a wideband adaptive impedance reshaping method based on energy storage, comprising:

[0006] According to the analysis of PLL, voltage loop, current loop and filter, the impedance frequency band of energy storage system is divided, and based on the divided frequency band, an improved adaptive impedance reshaping control strategy based on active damping and virtual admittance is constructed;

[0007] According to the impedance reshaping control strategy, an impedance model of the energy storage inverter system taking impedance reshaping into account is established;

[0008] Based on the impedance model, the frequency band overlapping effects between different frequency bands and different control links are comprehensively considered, and the impedance near the system oscillation frequency point is reshaped through the sequential optimization design of PLL control, virtual admittance control and active damping control.

[0009] Optionally, in the division of the impedance bands of the energy storage system, the bands are divided into band I, band II, band III and band IV.

[0010] Optionally, the improved adaptive impedance reshaping control strategy based on the combination of active damping and virtual admittance constructed based on the divided frequency bands includes: a frequency band II impedance reshaping control strategy, a frequency band III impedance reshaping control strategy and a frequency band IV impedance reshaping control strategy.

[0011] Optionally, the Band II impedance reshaping control strategy comprises:

[0012] Using the impedance reshaping method based on a dual phase-locked loop, the original capacitive negative damping characteristic of band II is transformed into a capacitive positive damping characteristic without sacrificing the dynamic response performance of the unit, thereby enhancing the stability margin of the unit in band II. Optionally, the impedance reshaping control strategy for band III includes:

[0013] By setting a virtual admittance controller, the virtual admittance controller performs phase compensation on the impedance of frequency band III, thereby improving the damping characteristics and increasing the stability margin of the unit within frequency band III.

[0014] Optionally, the virtual admittance controller includes a bandpass filter, and the bandpass filter is:

[0015] ,

[0016] in, is a bandpass filter, The desired damping for Band III is, , and are the upper and lower limits of the frequency of the virtual admittance, that is, by setting and Determines the control band of the virtual admittance controller.

[0017] Optionally, the band IV impedance reshaping control strategy includes:

[0018] The impedance of Band IV is adjusted through phase compensation to optimize the damping characteristics and enhance the stability margin of the unit within Band IV.

[0019] Optionally, adjusting the impedance of band IV by phase compensation includes performing phase compensation by an active damping controller, wherein the active damping controller is:

[0020] ,

[0021] in: is the desired damping for Band IV, , and are the lower and upper frequency limits of active damping respectively.

[0022] Optionally, after the step of reshaping the impedance near the system oscillation frequency point, the step further includes:

[0023] Conduct wide range impedance stability checks to verify whether the system can adaptively reshape impedance according to analysis and set parameters when oscillation occurs in different frequency bands, and adjust the control parameters of units that fail to meet the standards.

[0024] The wide-band adaptive impedance reshaping method based on energy storage provided by the present invention studies the frequency band division of clustered new energy systems, explores the potential of energy storage units in diversified new energy cluster transmission systems, and proposes a wide-band adaptive impedance reshaping method based on energy storage. It also comprehensively considers the frequency band overlapping effects between different frequency bands of energy storage units and different controllers, designs an adaptive impedance reshaping controller to suppress wide-band oscillations, and realizes wide-band impedance reshaping, thereby achieving the suppression of wide-band oscillations of the diversified new energy cluster transmission system and the purpose of safe and stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0026] Figure 1 A block diagram of the control principle of the energy storage system disclosed in the embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the frequency band distribution law of each control link disclosed in an embodiment of the present invention;

[0028] Figure 3A principle block diagram of an energy storage system control strategy taking impedance reshaping into account according to an embodiment of the present invention;

[0029] Figure 4 This is a flow chart of broadband impedance reshaping of an energy storage system disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] It should be clear that the following embodiments of the present invention are described by specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0032] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. It should be understood by those skilled in the art based on the invention that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0033] It should also be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention. The illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0034] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the aspects described may be practiced without these specific details.

[0035] Aiming at the problem of broadband oscillation in different frequency bands caused by the interaction between power electronic equipment and the power grid, a control strategy based on adaptive impedance reshaping of energy storage is invented. First, the frequency band of the energy storage system is divided, and an improved adaptive impedance reshaping control strategy based on the combination of active damping and virtual admittance is proposed. Then, according to the impedance reshaping strategy, an impedance model of the energy storage inverter system under the control of broadband adaptive impedance reshaping is established. Finally, the frequency band overlap effect between different frequency bands and different control links is comprehensively considered, and the impedance near the system oscillation frequency point is reshaped through the sequential optimization design of PLL control, virtual admittance control and active damping control. This invention can give full play to the flexibility of energy storage and realize the effective suppression of broadband oscillations of the diversified new energy cluster transmission system.

[0036] For ease of understanding, this embodiment discloses a broadband adaptive impedance reshaping method based on energy storage, including:

[0037] According to the analysis of PLL, voltage loop, current loop and filter, the impedance frequency band of energy storage system is divided, and based on the divided frequency band, an improved adaptive impedance reshaping control strategy based on active damping and virtual admittance is constructed;

[0038] According to the impedance reshaping control strategy, an impedance model of the energy storage inverter system taking impedance reshaping into account is established;

[0039] Based on the impedance model, the frequency band overlapping effects between different frequency bands and different control links are comprehensively considered, and the impedance near the system oscillation frequency point is reshaped through the sequential optimization design of PLL control, virtual admittance control and active damping control.

[0040] Optionally, in the division of the impedance bands of the energy storage system, the bands are divided into band I, band II, band III and band IV.

[0041] Optionally, the improved adaptive impedance reshaping control strategy based on the combination of active damping and virtual admittance constructed based on the divided frequency bands includes: a frequency band II impedance reshaping control strategy, a frequency band III impedance reshaping control strategy and a frequency band IV impedance reshaping control strategy.

[0042] Optionally, the Band II impedance reshaping control strategy comprises:

[0043] For Band II, an impedance reshaping method based on a dual phase-locked loop is used to transform the original capacitive negative damping characteristic of Band II into a capacitive positive damping characteristic without sacrificing the dynamic response performance of the unit, thereby enhancing the stability margin of the unit in Band II.

[0044] Optionally, the Band III impedance reshaping control strategy comprises:

[0045] By setting a virtual admittance controller, the virtual admittance controller performs phase compensation on the impedance of frequency band III, thereby improving the damping characteristics and increasing the stability margin of the unit within frequency band III.

[0046] Optionally, the virtual admittance controller includes a bandpass filter, and the bandpass filter is:

[0047] ,

[0048] in, is a bandpass filter, The desired damping for Band III is, , and are the upper and lower limits of the frequency of the virtual admittance, that is, by setting and Determines the control band of the virtual admittance controller.

[0049] Optionally, the band IV impedance reshaping control strategy includes:

[0050] The impedance of Band IV is adjusted through phase compensation to optimize the damping characteristics and enhance the stability margin of the unit within Band IV.

[0051] Optionally, adjusting the impedance of band IV by phase compensation includes performing phase compensation by an active damping controller, wherein the active damping controller is:

[0052] ,

[0053] in: is the desired damping for Band IV, , and are the lower and upper frequency limits of active damping respectively.

[0054] Optionally, after the step of reshaping the impedance near the system oscillation frequency point, the step further includes:

[0055] Conduct wide range impedance stability checks to verify whether the system can adaptively reshape impedance according to analysis and set parameters when oscillation occurs in different frequency bands, and adjust the control parameters of units that fail to meet the standards.

[0056] The wide-band adaptive impedance reshaping method based on energy storage disclosed in this embodiment aims to adjust the impedance characteristics of the energy storage system, design voltage loop control, PLL control, virtual admittance control and active damping controller, adaptively use different controllers for different frequency bands, and reshape the impedance near the system oscillation frequency point, thereby achieving effective suppression of wide-band oscillations of the diversified new energy cluster transmission system.

[0057] Wideband impedance model before impedance reshaping:

[0058] A typical control block diagram of an energy storage system is shown in the figure below: Figure 1 As shown, u abc 、i abc are the three-phase voltage and current of the port respectively; m abc is a three-phase modulation signal; is the given value of DC bus voltage; I loud is the equivalent DC current source; L f , C f is the AC side filter inductor and capacitor; C dc is the DC bus capacitance, is the voltage phase angle at the grid connection point.

[0059] The impedance of the energy storage system port is defined as the ratio of the voltage small signal to the current small signal. The voltage and current small signals have the following relationship:

[0060] ,

[0061] In the formula Indicates the frequency Small voltage signal; Indicates the frequency The positive sequence current small signal; Indicates the frequency The negative sequence current small signal.

[0062] The above formula can be expressed as follows through the admittance matrix:

[0063] ,

[0064] The frequency-coupled sequence impedance model of the energy storage system can be expressed as:

[0065] ,

[0066] ,

[0067] Among them, K m is the modulation coefficient; ; I is the unit matrix.

[0068] Unit positive sequence admittance The expression is as follows:

[0069] ,

[0070] Where: I1 is the fundamental AC phase current vector; is the fundamental AC phase voltage vector; .

[0071] Controller / link frequency band distribution law:

[0072] The controllers involved in the energy storage system cooperate with each other to ensure that the system is controlled and operated according to the expected goals. The interaction of controllers with different control bandwidths affects the impedance characteristics of the unit. Therefore, the frequency bands must be divided first, and wide-band impedance reshaping must be performed for different frequency bands.

[0073] The impedance characteristics of the energy storage system are affected by PLL, voltage loop, current loop and LC filter. This section analyzes the frequency domain relationship between the control bandwidth performance indicators of each controller and the impedance model, and describes the frequency band distribution law of each controller / link.

[0074] PLL controller usually adopts PI control. The PI controller transfer function and PLL closed-loop transfer function are:

[0075] ,

[0076] Where K pp , K pi are the proportional coefficient and integral coefficient of the PI controller.

[0077] Where T PLL (s) can be expressed as a typical second-order system:

[0078] ,

[0079] Where: is the PLL damping ratio; is the natural frequency. According to H PLL (s) can be obtained:

[0080] ,

[0081] Where: f tc is the PLL control bandwidth. From Equation 7, we can see that by selecting different control bandwidths f tc With damping ratio , different control characteristics of the PLL can be obtained.

[0082] The DC bus voltage loop adopts PI control, and the transfer function is:

[0083] ,

[0084] Where K vp , K ii are the proportional coefficient and integral coefficient of the PI controller.

[0085] Similar to the PLL analysis process, the open-loop transfer function of the DC voltage controller is transformed into the distribution band after abc-dq coordinate transformation: .

[0086] The current loop usually also uses PI control, and the transfer function is:

[0087] ,

[0088] Similar to the PLL analysis process, the open-loop transfer function of the DC voltage controller is transformed into the distribution band after abc-dq coordinate transformation: .

[0089] The resonant frequency of the main circuit LC filter is

[0090] ,

[0091] The filters are distributed over the entire frequency band and have an impact on the impedance characteristics of the entire frequency band.

[0092] Based on the analysis of PLL, voltage loop, current loop and filter, the impedance band division of the energy storage system can be defined as: is frequency band I, For frequency band II, For band III, is frequency band IV. Its distribution law is given by Figure 2 shown.

[0093] In summary, for the oscillation problems in frequency band II around 70 Hz, the oscillation problems in frequency band III around 240 Hz, and the oscillation problems in frequency band IV between 500 and 1000 Hz, the impedance of the energy storage system can be reshaped.

[0094] Wideband adaptive impedance reshaping control strategy:

[0095] Since the impedance characteristics of different frequency bands are affected by different dominant factors, and the causes of capacitive negative damping characteristics are also different, different methods are required for impedance reshaping of each frequency band. This paper proposes a wideband adaptive impedance reshaping scheme that combines control strategy improvement and control parameter optimization. This scheme optimizes the damping characteristics by adaptively compensating the impedance of different frequency bands of the energy storage system, introduces active damping and virtual admittance control strategies, and realizes impedance reshaping of frequency bands III and IV. Figure 3 shown.

[0096] Band II Impedance Reshaping Method:

[0097] The impedance-capacitive negative damping characteristics of band II are mainly determined by the PLL control parameters, so this embodiment mainly optimizes the PLL to achieve impedance reshaping, both of which have a great impact on the dynamic performance of the energy storage system. Because the maximum output power of the inverter is subject to both static power limit and dynamic power limit, when the grid-side impedance ratio is given, the static power limit is proportional to the short-circuit ratio.

[0098] ,

[0099] ,

[0100] When SCR=1, the static power limit is 1 pu, but according to the results of small signal stability analysis in various literatures, the dynamic power limit is only 0.61 pu. It can be seen that the dynamic power limit is more stringent than the static power limit. Therefore, the maximum output power of the inverter is mainly affected by the dynamic power limit. If the wideband adaptive impedance reshaping method is used to improve the stability boundary, the dynamic power limit can be extended to the vicinity of the static power limit.

[0101] The commonly used simplified admittance matrix is:

[0102] ,

[0103] in , , .

[0104] The ideal globally stable admittance matrix is:

[0105] ,

[0106] Contrast and It can be seen that the negative resistance term introduced by the PLL is the main instability factor, and the negative inductance and resistance introduced by the control loop are secondary factors. Since the control parameters of the PLL mainly dominate the impedance characteristics in Band II, reducing the bandwidth of the phase-locked loop will help improve the stability of the system, but at the cost of reduced dynamic performance. In order to have a faster dynamic response while improving stability, a wide-band adaptive impedance reshaping method is used to optimize the impedance performance of the unit in a wide band and improve the dynamic response capability of the system.

[0107] This embodiment uses an impedance reshaping method based on a dual phase-locked loop, and its control block diagram is as follows: Figure 3 As shown in Figure 1, considering that the grid frequency may have deviations, if it is not restricted, it will continue to increase or decrease under the action of the integrator, causing the system to lose control. Therefore, an auxiliary PLL is introduced, and its bandwidth is made much smaller than the main PLL (this paper takes ), then the auxiliary PLL in steady state Equal to the grid frequency, at this time even if the grid frequency and There is a deviation, the main PLL , but also , thus ensuring is a constant.

[0108] Band III Impedance Reshaping Method:

[0109] In the first half of Band III, the frequency ranges of the DC voltage loop and the current loop overlap. If the control parameters of the DC voltage loop are not properly selected, this band will exhibit the characteristics of capacitive negative damping. In the second half of Band III, the delay and the frequency range of the current loop also overlap, which leads to another capacitive negative damping characteristic near the cutoff frequency of the current loop, and this negative damping characteristic becomes more obvious as the delay increases. The problem of capacitive negative damping in the first half of the band can be avoided by optimizing the control parameter design of the voltage loop. However, since the delay is an inherent characteristic of the unit itself and is difficult to eliminate by simple control parameter adjustments, it is difficult to solve the problem of capacitive negative damping in the second half of Band III. Therefore, this paper proposes a virtual admittance control strategy, such as Figure 2 The additional controller can perform phase compensation on the impedance of Band III, thereby improving the damping characteristics and increasing the stability margin of the unit within Band III.

[0110] Depend on Figure 2 It can be seen that the virtual admittance controller H y (s) The voltage signals of the dq axis are respectively superimposed on the current command value, thereby shaping the impedance characteristics of the inverse band III. In order to reduce the impact on band II and band IV, H y The structure of (s) is a bandpass filter as shown in formula 11:

[0111] ,

[0112] Where k y is the expected damping of Band III. You can set the expected damping to adjust the damping characteristics of the internal impedance of Band III. and Determine the operating frequency band of the virtual admittance controller.

[0113] Band IV impedance reshaping method:

[0114] The impedance performance of band IV is mainly dominated by the capacitance properties of the filter capacitor. When this capacitance property is superimposed on the negative damping effect generated by the delay link, a capacitive negative damping characteristic will appear in band IV. As inherent properties of the unit, the filter capacitor and the delay link are difficult to remove directly. Therefore, this paper proposes an innovative control strategy - active damping control of filter capacitor current feedback. Figure 2 The additional controller is designed to adjust the impedance of Band IV through phase compensation, thereby optimizing the damping characteristics and ultimately enhancing the stability margin of the unit within Band IV.

[0115] When the power grid encounters oscillation in band IV, the filter capacitor has a relatively small component of fundamental current due to its high-pass filtering characteristics, and most of the oscillation frequency current will choose to flow through the filter capacitor. In order to ensure that the impedance adjustment of band IV does not interfere with the impedance characteristics of other bands, this paper cleverly uses the phase adjustment capability of the lead-lag correction link to design an active damping controller for the energy storage system, the specific form of which is shown in Equation 2.

[0116] ,

[0117] Where: k c For the desired damping of band IV, the damping characteristics of the impedance in band IV are adjusted by setting the desired damping: ,fc1 and fc2 are the lower and upper limits of the frequency of the active damping, that is, the working frequency band of the active damping is adjusted by setting the upper and lower limits of the frequency.

[0118] In summary, the design method of broadband adaptive impedance reshaping using energy storage system is summarized as follows:

[0119] 1) For Band II, an impedance reshaping method based on a dual phase-locked loop is proposed. Without sacrificing the dynamic response performance of the unit, the original capacitive negative damping characteristic of Band II is transformed into a capacitive positive damping characteristic, thereby enhancing the stability margin of the unit in Band II.

[0120] 2) For Band III, an impedance regulation strategy based on virtual admittance control is proposed. This strategy introduces an additional controller to achieve phase compensation for Band III impedance, thereby optimizing its damping characteristics and ensuring that the stability margin of the unit in Band III is significantly improved.

[0121] 3) For band IV, an active damping impedance reshaping method based on filter capacitor current feedback is proposed. This strategy achieves flexible adjustment of the impedance damping characteristics of this band through the damping system. At the same time, by adjusting the cutoff frequency, the working frequency band of the active damping can be accurately controlled, thereby effectively reshaping the capacitive negative damping characteristics generated by the current loop and the delay link in band IV.

[0122] 4) When the system oscillates in different frequency bands, this method can adaptively select different control strategies according to the oscillation frequency band to improve the anti-disturbance capability of the energy storage system.

[0123] Impedance Modeling Taking Impedance Reshaping into Account:

[0124] A typical control block diagram of an energy storage system is shown in the figure below: Figure 2 As shown. The three-phase system is decomposed into three symmetrical subsystems using the symmetrical component method: positive sequence, negative sequence and zero sequence subsystems. The sequence impedance model admittance matrix of the typical topology and control structure of the energy storage inverter is as follows:

[0125] ,

[0126] Where: is the given value of DC bus voltage; is the modulation coefficient; ; ; is the identity matrix; , These are the AC side filter inductors and capacitors.

[0127] Under the control strategy of wide-band adaptive impedance reshaping, The frequency domain small signal component of the axis modulation signal can be expressed as:

[0128] ,

[0129] Due to the introduction of the wideband adaptive impedance reshaping control strategy, the small signal component of the modulated signal is superimposed with Shaft voltage, Components related to the shaft filter capacitor current , ,and and With Virtual Admittance Controller and active damping controller related.

[0130] ,

[0131] for The disturbance component of the shaft filter capacitance and current is calculated according to Figure 3 The circuit relationship shown can be obtained by The shaft voltage disturbance component is expressed as:

[0132] ,

[0133] Therefore, it can be seen from equations 14-16 that the wideband adaptive impedance reshaping control strategy reshapes the impedance characteristics of the energy storage inverter by introducing an additional branch of the modulation signal affected by the voltage small signal component. According to the definition structure of the modulation signal frequency domain expression in equation 14, after the wideband impedance reshaping control strategy is introduced, the impact on the impedance characteristics of the energy storage inverter is reflected in the The impact of specific expressions.

[0134] Therefore, based on Figure 3 According to the above analysis, the modulation signal disturbance component expression shown in Equation 16 is recalculated, and the frequency coupling model of the energy storage inverter under the above wide-band adaptive impedance reshaping control strategy can be obtained:

[0135] ,

[0136] In the formula The specific expression of the additional component introduced for the wideband adaptive impedance reshaping control strategy is shown in Figure 18.

[0137] ,

[0138] Wideband impedance reshaping design considering the band overlap effect:

[0139] The impedance characteristics between bands II, III, and IV have a band overlap effect. Bands II and IV will affect the impedance characteristics of band III. Therefore, this paper follows the order of adaptive impedance reshaping of bands II, IV, and III. The specific design process is as follows: Figure 4 shown.

[0140] Step 1: Design impedance adjustment for Band II, which is selected based on the control parameters of the dual phase-locked loop and the DC voltage loop. When determining these parameters, it is necessary to verify the dynamic response to ensure that the selected control parameters can meet both the steady-state control requirements of the system and the requirements of its dynamic characteristics.

[0141] Step 2: Perform impedance reshaping design for Band IV based on the selection of active damping coefficient. Subsequently, stability verification of the selected damping coefficient is performed to ensure that the set parameters can meet the requirements of the system steady-state characteristics.

[0142] Step 3: Impedance reshaping of band III. Based on the design of the PLL control bandwidth of band II and the current loop control bandwidth of band III, the parameters of the virtual admittance bandpass filter are selected to reshape the damping characteristics of band III. Generally, the parameters are selected as and , and They are the control bandwidth of PLL and current loop respectively. The design of band III impedance reshaping is realized by selecting the damping coefficient of current loop control.

[0143] Step 4: Perform wide range impedance stability check to verify whether the system can adaptively reshape the impedance according to the above analysis and setting parameters when oscillation occurs in different frequency bands. For the unit control parameters that fail to meet the standards, repeated design adjustments are required. This process ultimately aims to adaptively select appropriate control parameters to ensure safe and stable operation of the unit.

[0144] Band II Impedance Reshaping Method:

[0145] The impedance characteristics in Band II are mainly dominated by the control parameters of the phase-locked loop (PLL), which have a significant impact on the capacitive negative damping characteristics of the system. When the control bandwidth of the DC voltage loop is less than that of the PLL, the frequency range between the two will overlap, causing the control parameters of the DC voltage loop to also affect the capacitive negative damping characteristics. Therefore, this method introduces an auxiliary PLL and designs the control parameters of the dual phase-locked loop and the DC voltage loop to ensure that the unit maintains good dynamic performance while also achieving the set stability margin standard in Band II.

[0146] Band IV impedance reshaping method:

[0147] The impedance characteristics of band IV are mainly affected by the LC filter in the main circuit, and its impedance characteristics change from inductive to capacitive. Therefore, the parameter design method of active damping control can be used to ensure that the unit can meet the established stability margin requirements within band IV.

[0148] From equation 12, the active damping coefficient k can be usedc The impedance reshaping of band IV is achieved, but at the same time, due to the band overlap effect of band III and band IV, k c The value of needs to take into account the damping characteristics of frequency band IV and frequency band III and cannot be too large.

[0149] Band III impedance reshaping method:

[0150] In Band III, the impedance characteristics are mainly determined by the current loop control and exhibit capacitive behavior characteristics. In this band, the delay phenomenon overlaps with the frequency response range of the current loop, which in turn induces a capacitive negative damping effect around the cutoff frequency of the current loop. This effect increases the possibility of oscillation between the power unit and the grid in Band III. To address this problem, a parameter optimization method of virtual admittance control will be used to ensure that the power unit can achieve the predetermined stability margin standard in Band III.

[0151] According to formula 11, different virtual admittance coefficients k are selected y The impedance of band III can be reshaped, so that the capacitive negative damping characteristics of the unit in band III can be improved; however, due to the band overlap effect between band III and band II, k y The value of needs to take into account the impedance characteristics of band III and band II and cannot be too large. Therefore, the impedance of band III can be reshaped by designing the virtual admittance coefficient.

[0152] In summary, by orderly designing the impedance of the units in band II, band IV and band III for the energy storage system, when oscillation occurs in different frequency bands, this method can adaptively select different control strategies according to the oscillation frequency band, realize the adaptive impedance reshaping of the unit within the wide band range, and eliminate the capacitive negative damping characteristics of the unit within the wide band. Therefore, the above-mentioned wide-band adaptive impedance reshaping method can effectively optimize the impedance performance of the unit within the wide band, thereby effectively suppressing the wide-band oscillation problem.

[0153] This embodiment targets high-proportion renewable energy power generation grid-connected systems represented by wind, solar, and storage. By studying the frequency band division of clustered renewable energy systems, the potential of energy storage units in diversified renewable energy cluster transmission systems is explored, and a wide-band adaptive impedance reshaping method based on energy storage is proposed. The frequency band overlapping effects between different frequency bands of energy storage units and different controllers are comprehensively considered, and an adaptive impedance reshaping controller is designed using PLL, voltage loop, active damping control, and virtual admittance control to suppress broadband oscillations, and broadband (Band II, Band IV, Band III) impedance reshaping is achieved respectively, thereby achieving suppression of broadband oscillations in the diversified renewable energy cluster transmission system, and ensuring safe and stable operation of the power system.

[0154] The basic principle of the present invention is described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and facilitation of understanding, rather than limitation, and the above details do not limit the present invention to being implemented by adopting the above specific details.

[0155] In the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Words such as "including", "comprising", "having", etc. are open words, meaning "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably with them, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to", and can be used interchangeably with it.

[0156] Additionally, as used herein, "or" used in a list of items beginning with "at least one" indicates a separate list, so that, for example, a list of "at least one of A, B, or C" means A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). Furthermore, the word "exemplary" does not mean that the example described is preferred or better than other examples.

[0157] It should also be noted that in the system and method of the present invention, each component or each step can be decomposed and / or recombined. Such decomposition and / or recombination should be regarded as equivalent solutions of the present invention.

[0158] Various changes, substitutions, and modifications of the techniques described herein may be made without departing from the teachings defined by the appended claims. Furthermore, the scope of the claims of the present invention is not limited to the specific aspects of the processes, machines, manufactures, compositions of events, means, methods, and actions described above. Currently existing or later to be developed processes, machines, manufactures, compositions of events, means, methods, or actions that perform substantially the same functions or achieve substantially the same results as the corresponding aspects described herein may be utilized. Thus, the appended claims include such processes, machines, manufactures, compositions of events, means, methods, or actions within their scope.

[0159] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0160] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. A broadband adaptive impedance reshaping method based on energy storage, characterized in that: include: According to the analysis of PLL, voltage loop, current loop and filter, the impedance frequency band of energy storage system is divided, and based on the divided frequency band, an improved adaptive impedance reshaping control strategy based on active damping and virtual admittance is constructed; According to the impedance reshaping control strategy, an impedance model of the energy storage inverter system taking impedance reshaping into account is established; Based on the impedance model, the frequency band overlapping effects between different frequency bands and different control links are comprehensively considered, and the impedance near the system oscillation frequency point is reshaped through the sequential optimization design of PLL control, virtual admittance control and active damping control.

2. The method for broadband adaptive impedance reshaping based on energy storage according to claim 1, characterized in that: In the division of the impedance bands of the energy storage system, the bands are divided into band I, band II, band III and band IV.

3. The method for broadband adaptive impedance reshaping based on energy storage according to claim 2, characterized in that: The improved adaptive impedance reshaping control strategy based on the combination of active damping and virtual admittance constructed based on the divided frequency bands includes: a frequency band II impedance reshaping control strategy, a frequency band III impedance reshaping control strategy and a frequency band IV impedance reshaping control strategy.

4. The method for broadband adaptive impedance reshaping based on energy storage according to claim 3, characterized in that: The Band II impedance reshaping control strategy includes: Using the impedance reshaping method based on a dual phase-locked loop, the original capacitive negative damping characteristic of Band II is transformed into a capacitive positive damping characteristic without sacrificing the dynamic response performance of the unit, thereby enhancing the stability margin of the unit in Band II.

5. The method for broadband adaptive impedance reshaping based on energy storage according to claim 3, characterized in that: The Band III impedance reshaping control strategy includes: By setting a virtual admittance controller, the virtual admittance controller performs phase compensation on the impedance of frequency band III, thereby improving the damping characteristics and increasing the stability margin of the unit within frequency band III.

6. The method for broadband adaptive impedance reshaping based on energy storage according to claim 5, characterized in that: The virtual admittance controller includes a bandpass filter, and the bandpass filter is: ， in, is a bandpass filter, The desired damping for Band III is, , and are the upper and lower limits of the frequency of the virtual admittance, that is, by setting and Determines the control band of the virtual admittance controller.

7. The method for broadband adaptive impedance reshaping based on energy storage according to claim 3, characterized in that: The Band IV impedance reshaping control strategy includes: The impedance of Band IV is adjusted through phase compensation to optimize the damping characteristics and enhance the stability margin of the unit within Band IV.

8. The method for broadband adaptive impedance reshaping based on energy storage according to claim 7, characterized in that: The adjusting the impedance of band IV by phase compensation includes performing phase compensation by an active damping controller, wherein the active damping controller is: ， in: is the desired damping for Band IV, , and are the lower and upper frequency limits of active damping respectively.

9. The method for broadband adaptive impedance reshaping based on energy storage according to claim 1, characterized in that: The step of reshaping the impedance near the system oscillation frequency point also includes: Conduct wide range impedance stability checks to verify whether the system can adaptively reshape impedance according to analysis and set parameters when oscillation occurs in different frequency bands, and adjust the control parameters of units that fail to meet the standards.

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