Cluster admittance passivity control method based on inverter transformation

Abstract

The invention discloses a cluster admittance passivity control method based on inverter transformation, and the method comprises the steps: firstly obtaining an original anti-resonant frequency and an original sampling frequency of an inverter cluster; then, according to the original anti-resonant frequency, the original sampling frequency and the heterogeneous inverter, determining a target sampling frequency of the heterogeneous inverter; and then, according to the target sampling frequency, determining a filtering parameter of the heterogeneous inverter, and obtaining the configured heterogeneous inverter. And then, the configured heterogeneous inverters are put into an original inverter cluster, so that a target inverter cluster is constructed. The admittance phase of the target inverter cluster can be effectively controlled within a preset range. Through the mode, passive control in a broadband range is realized, dynamic harmonic resonance is effectively inhibited, and the interaction stability of the system is greatly improved. According to the embodiment of the invention, the stability and applicability of the inverter cluster can be improved while the complexity and cost of the system are reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to, but are not limited to, the field of inverter control technology, and in particular, to a cluster admittance passivity control method based on inverter transformation. Background Art

[0002] Inverter clusters are widely used in distributed power sources, microgrids, and renewable energy grid connections due to their high-efficiency energy conversion capabilities. However, the broadband and dynamically changing harmonic currents generated during operation can affect the power quality of the power grid and the reliability of equipment operation. The harmonic currents mainly originate from the differences in the switching frequencies of power devices and the harmonic resonance excited by the interaction of the equivalent impedances inside and outside the cluster.

[0003] To reduce the interaction between the inverter and the grid impedance and avoid harmonic instability, the equivalent impedance of the inverter needs to be passive, that is, the real part of the admittance (impedance) is positive in the broadband range, and the phase angle is from -90° to 90°. However, the existing methods have the following deficiencies: 1. Active damping inner loop design: It enhances the stability of the inverter in the harmonic frequency band, but as the cluster scale increases, multiple sensors are required, which increases the complexity and cost of the system, and the control algorithm is complex, with high hardware requirements. 2. Equipped with auxiliary devices: For example, the shunt active power filter is limited by the control bandwidth and is difficult to suppress broadband dynamic harmonic resonance; although the series inverter reshapes the equivalent impedance and improves the stability, it needs to bear the full-system current, reducing the system reliability and is not suitable for medium-voltage scenarios. In addition, the active damper or auxiliary device also faces problems such as limited control bandwidth, insufficient voltage withstand of power devices, high equipment cost, and complex implementation.

[0004] Therefore, how to improve the stability of the inverter cluster while reducing complexity and cost has become a key problem to be solved urgently. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail in this article. This overview is not intended to limit the scope of protection of the claims.

[0006] The embodiments of the present application provide a cluster admittance passivity control method based on inverter transformation, which can improve the stability and applicability of the inverter cluster while reducing the system complexity and cost.

[0007] A cluster admittance passivity control method based on inverter transformation provided by an embodiment of the present application is applied to an inverter cluster and a heterogeneous inverter for inputting the inverter cluster. The method includes: obtaining the original anti-resonant frequency and the original sampling frequency of the inverter cluster; determining the target sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency, the original sampling frequency and the heterogeneous inverter; determining the filtering parameters of the heterogeneous inverter according to the target sampling frequency to obtain a configured heterogeneous inverter; and incorporating the configured heterogeneous inverter into the inverter cluster to obtain a target inverter cluster, where the admittance phase of the target inverter cluster is within a preset range.

[0008] In an embodiment of the present application, the determining the target sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency, the original sampling frequency and the heterogeneous inverter includes: obtaining the target frequency parameters of the heterogeneous inverter; calculating the sampling frequency range of the heterogeneous inverter according to the original anti-resonant frequency, the original sampling frequency and the target frequency parameters; and determining the target sampling frequency of the heterogeneous inverter within the sampling frequency range.

[0009] In an embodiment of the present application, the target frequency parameters of the heterogeneous inverter include an anti-resonant frequency and a resonant frequency. The calculating the sampling frequency range of the heterogeneous inverter according to the original anti-resonant frequency, the original sampling frequency and the target frequency parameters includes: calculating the upper limit of the sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency and the anti-resonant frequency of the heterogeneous inverter; calculating the lower limit of the sampling frequency of the heterogeneous inverter according to the original sampling frequency; and obtaining the sampling frequency range of the heterogeneous inverter according to the upper limit of the sampling frequency and the lower limit of the sampling frequency.

[0010] In an embodiment of the present application, the calculating the upper limit of the sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency and the anti-resonant frequency of the heterogeneous inverter includes: determining the upper limit of the value of the anti-resonant frequency of the heterogeneous inverter according to the original anti-resonant frequency and the anti-resonant frequency of the heterogeneous inverter; determining the configuration relationship between the original anti-resonant frequency and the sampling frequency of the heterogeneous inverter; and calculating the upper limit of the sampling frequency of the heterogeneous inverter according to the upper limit of the value of the anti-resonant frequency and the configuration relationship.

[0011] In an embodiment of the present application, obtaining the target frequency parameter of the heterogeneous inverter includes: obtaining the filtering parameter of the heterogeneous inverter, where the filtering parameter includes a first filtering inductor, a filtering capacitor, and a second filtering inductor; defining the resonance frequency of the heterogeneous inverter according to the first filtering inductor, the filtering capacitor, and the second filtering inductor; defining the anti-resonance frequency of the heterogeneous inverter according to the first filtering inductor and the filtering capacitor; and obtaining the target frequency parameter of the heterogeneous inverter according to the anti-resonance frequency and the resonance frequency.

[0012] In an embodiment of the present application, the filtering parameter includes a first filtering inductor, a second filtering inductor, and a filtering capacitor; determining the filtering parameter of the heterogeneous inverter according to the target sampling frequency to obtain a configured heterogeneous inverter, including: configuring the value range of the target frequency parameter of the heterogeneous inverter according to the target sampling frequency to obtain a target frequency configuration result; determining the value of the first filtering inductor and the value of the second filtering inductor according to the target frequency configuration result; determining the value of the filtering capacitor according to the target sampling frequency; and calculating the anti-resonance frequency and the resonance frequency of the heterogeneous inverter according to the value of the first filtering inductor, the value of the second filtering inductor, and the value of the filtering capacitor to obtain a configured heterogeneous inverter.

[0013] In an embodiment of the present application, configuring the value range of the target frequency parameter of the heterogeneous inverter according to the target sampling frequency to obtain a target frequency configuration result includes: configuring the resonance frequency of the heterogeneous inverter as a first preset value of the target sampling frequency to obtain a first configuration result; configuring the anti-resonance frequency of the heterogeneous inverter as a second preset value of the target sampling frequency to obtain a second configuration result; and obtaining the target frequency configuration result according to the first configuration result and the second configuration result.

[0014] In an embodiment of the present application, before incorporating the configured heterogeneous inverter into the inverter cluster, the method further includes: adjusting the phase margin and amplitude margin of the heterogeneous inverter according to the proportional gain, resonance gain, and cut-off frequency of the proportional resonance controller of the heterogeneous inverter to obtain an adjusted heterogeneous inverter.

[0015] In an embodiment of the present application, incorporating the configured heterogeneous inverter into the inverter cluster includes: incorporating the configured heterogeneous inverter into the inverter cluster when it is determined that the phase of the heterogeneous inverter does not exceed 80° at the original anti-resonance frequency and the amplitude margin is greater than 4 dB.

[0016] In an embodiment of the present application, the preset range is [-90°, +90°].

[0017] A cluster admittance passivity control method based on inverter transformation provided by an embodiment of the present application. First, obtain the original anti-resonant frequency and original sampling frequency of the inverter cluster; then, determine the target sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency, original sampling frequency, and heterogeneous inverter; next, configure the filtering parameters of the heterogeneous inverter according to the target sampling frequency to obtain the configured heterogeneous inverter. In this step, the reasonable setting of the filtering parameters plays a key role in optimizing the inverter performance and suppressing harmonics. Subsequently, put the configured heterogeneous inverter into the original inverter cluster to construct the target inverter cluster. This target inverter cluster has significant advantages, and its admittance phase can be effectively controlled within a preset range. In this way, passivity control in a wide frequency range is achieved, dynamic harmonic resonance is effectively suppressed, and the interaction stability of the system is greatly improved. This embodiment has many outstanding advantages. On the one hand, by directly transforming the inverter, only adjusting its sampling frequency and filtering parameters, no additional hardware devices need to be added, and no complex control loops need to be constructed, thus effectively reducing the complexity and cost of the system. On the other hand, by accurately calculating and reasonably configuring the target sampling frequency and filtering parameters of the heterogeneous inverter, the admittance phase of the inverter cluster is always within the preset range, significantly improving the harmonic stability of the inverter cluster, greatly reducing the occurrence of harmonic instability phenomena, and effectively improving the stability and reliability of the entire system. It is worth emphasizing that the application scope of this embodiment is wide, and it is not only applicable to a single type of inverter cluster, but also can be flexibly applied to heterogeneous clusters containing multiple types of inverters. This characteristic greatly enhances the applicability of this control method and provides a reliable solution for the stable operation of power systems in different scenarios. Description of the Drawings

[0018] Figure 1 is a flowchart of the cluster admittance passivity control method based on inverter transformation provided by an embodiment of the present application;

[0019] Figure 2 is a schematic diagram of a grid-connected inverter cluster system provided by an embodiment of the present application;

[0020] Figure 3 is a control block diagram of an inverter provided by an embodiment of the present application;

[0021] Figure 4 is a flowchart of obtaining the target frequency parameters of the heterogeneous inverter provided by an embodiment of the present application;

[0022] Figure 5 is a flowchart of obtaining the sampling frequency range of the heterogeneous inverter provided by an embodiment of the present application;

[0023] Figure 6 is provided by an embodiment of the present applicationFigure 5 The specific flowchart of step 510 in

[0024] Figure 7 provided by an embodiment of the present application Figure 1 The specific flowchart of step 130 in

[0025] Figure 8 provided by an embodiment of the present application Figure 7 The specific flowchart of step 710 in

[0026] Figure 9(a) and 9(b) are the experimental result diagrams of the 10kHz inverter case provided by a specific example of the present application;

[0027] Figure 10 are the experimental result diagrams of the 6kHz inverter case provided by a specific example of the present application;

[0028] Figure 11(a) and 11(b) are the experimental results of the 11kHz inverter case provided by a specific example of the present application;

[0029] Figure 12 are the experimental result diagrams of the 5kHz inverter case provided by a specific example of the present application. Specific implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0031] It should be noted that although the logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order from that in the flowchart. Terms such as "first", "second", etc. in the specification, claims and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions for the implementation of this application. Therefore, they do not have substantial technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the efficacy that this application can produce and the purpose that can be achieved, should still fall within the scope covered by the technical content disclosed in this application. At the same time, terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of clear narration, and are not used to limit the scope of implementation of this application. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope within which this application can be implemented.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used herein are only for the purpose of describing the embodiments of this application and are not intended to limit this application.

[0033] Inverter clusters are widely used in distributed power sources, microgrids, and renewable energy grid connection due to their high-efficiency energy conversion capabilities. However, the operation of inverter clusters also generates broadband and dynamically changing harmonic currents. The generation of these harmonic currents mainly stems from two factors: one is the difference in the switching frequencies of power devices, and the other is the harmonic resonance phenomenon excited by the interaction of the equivalent impedances within the cluster and between the cluster and the power grid. This harmonic instability not only affects the power quality of the power grid but also may pose a threat to the operational reliability of equipment.

[0034] To reduce the interaction of the equivalent impedance between the inverter and the power grid and avoid harmonic instability, it is usually required that the equivalent impedance of the inverter be passive. Specifically, the equivalent admittance (or impedance) of the inverter needs to have a positive real part in a wide frequency range, that is, its phase angle should always be maintained between -90° and 90°. However, to achieve the goal of broadband passivity of the inverter, most existing methods rely on the following two means: active damping inner-loop design or the installation of auxiliary devices.

[0035] Active damping technology enhances the stability of inverters in the harmonic frequency band by introducing a feedback control loop into the inverter control system. However, such designs typically require the configuration of multiple current or voltage sensors, resulting in a significant increase in system complexity and cost as the scale of the inverter cluster increases. In addition, complex control algorithms and high-precision requirements for hardware further increase the implementation difficulty.

[0036] To improve harmonic stability, auxiliary devices (such as shunt active power filters) are widely used. However, their effectiveness is limited by the control bandwidth, making it difficult to effectively suppress dynamic harmonic resonance in a wide frequency range. In addition, the interaction between the active power filtering device and the nonlinear load may lead to system instability. Although the equivalent impedance can be reshaped to some extent and the interaction stability can be improved by introducing broadband inverters (such as series or parallel configurations), the series inverters significantly reduce the system reliability because they need to bear the full-system current and are not suitable for medium-voltage scenarios.

[0037] On the other hand, the practical application of active dampers or auxiliary devices also faces the following challenges: the limited control bandwidth makes it difficult to achieve ideal impedance characteristics in a wide frequency range; the voltage withstand level of power devices is insufficient to meet the requirements of complex working conditions; the high equipment cost, complex implementation, and limited applicable scenarios result in unsatisfactory effects of existing technologies in improving the stability of inverter clusters. In summary, how to improve the self-stabilizing ability of inverter clusters while reducing system complexity and cost has become a key problem that urgently needs to be solved.

[0038] In view of this, an embodiment of the present application provides a cluster admittance passivity control method based on inverter transformation. First, the original anti-resonant frequency and the original sampling frequency of the inverter cluster are obtained; then, according to the original anti-resonant frequency, the original sampling frequency, and the heterogeneous inverters, the target sampling frequency of the heterogeneous inverters is determined; next, according to the target sampling frequency, the filtering parameters of the heterogeneous inverters are configured to obtain the configured heterogeneous inverters. In this step, the reasonable setting of the filtering parameters plays a key role in optimizing the inverter performance and suppressing harmonics. Subsequently, the configured heterogeneous inverters are put into the original inverter cluster, thereby constructing the target inverter cluster. This target inverter cluster has significant advantages, and its admittance phase can be effectively controlled within a preset range. In this way, passivity control in a wide frequency range is achieved, dynamic harmonic resonance is effectively suppressed, and the interaction stability of the system is greatly improved. This embodiment has many outstanding advantages. On the one hand, by directly transforming the inverter, only adjusting its sampling frequency and filtering parameters, no additional hardware devices need to be added, and no complex control loops need to be constructed, thus effectively reducing the complexity and cost of the system. On the other hand, by accurately calculating and reasonably configuring the target sampling frequency and filtering parameters of the heterogeneous inverters, the admittance phase of the inverter cluster is always within the preset range, significantly improving the harmonic stability of the inverter cluster, greatly reducing the occurrence of harmonic instability phenomena, and effectively enhancing the stability and reliability of the entire system. It should be emphasized that the application scope of this embodiment is wide, and it is not only applicable to a single type of inverter cluster, but also can be flexibly applied to heterogeneous clusters containing multiple types of inverters. This characteristic greatly enhances the applicability of this control method and provides a reliable solution for the stable operation of power systems in different scenarios.

[0039] The following further elaborates on the embodiments of the present application with reference to the accompanying drawings.

[0040] Refer to Figure 1 , Figure 1 which is a flowchart of the cluster admittance passivity control method based on inverter transformation provided by an embodiment of the present application. This method can be applied to an inverter cluster and heterogeneous inverters for putting into the inverter cluster, and its process includes but is not limited to steps 110 to 140.

[0041] Step 110: Obtain the original anti-resonant frequency and the original sampling frequency of the inverter cluster;

[0042] Step 120: Determine the target sampling frequency of the heterogeneous inverters according to the original anti-resonant frequency, the original sampling frequency, and the heterogeneous inverters;

[0043] Step 130: Determine the filtering parameters of the heterogeneous inverters according to the target sampling frequency to obtain the configured heterogeneous inverters;

[0044] Step 140: Incorporate the configured heterogeneous inverter into the inverter cluster to obtain a target inverter cluster, where the admittance phase of the target inverter cluster is within a preset range.

[0045] The following elaborates on Steps 110 to 140 in detail.

[0046] In a feasible embodiment, an inverter cluster refers to a cluster system composed of multiple grid-connected inverters. Among them, the original anti-resonant frequency of the inverter cluster refers to the anti-resonant frequency presented by the inverter cluster without being affected by external special interference or under initial design and ideal conditions. In an inverter cluster, anti-resonance is an electrical circuit phenomenon. When the system is in the anti-resonant state, its impedance reaches the maximum and the current is the minimum. Physically speaking, an inverter cluster is a complex system composed of multiple electrical components and circuits, with energy storage components such as inductors and capacitors. The interaction of these components will form specific oscillation characteristics, and the original anti-resonant frequency is an important parameter of this oscillation characteristic under the initial or ideal state. In addition, the original sampling frequency refers to the sampling frequency initially set or used under ideal conditions during the data acquisition and control process of the inverter cluster. For example, in the control of an inverter cluster, various electrical quantities (such as voltage, current, etc.) need to be sampled to achieve precise control and protection functions. The original sampling frequency determines the number of times these electrical quantities are sampled per unit time.

[0047] In a feasible embodiment, when obtaining the original anti-resonant frequency of the inverter cluster, a signal generator can be used to input sine signals with different frequencies into the inverter cluster, and at the same time, an oscilloscope or spectrum analyzer can be used to measure the output response of the inverter cluster. Gradually change the frequency of the input signal and record the amplitude and phase changes of the output response. When the output response shows a minimum amplitude value, the corresponding frequency is the anti-resonant frequency.

[0048] In a feasible embodiment, when obtaining the original sampling frequency of the inverter cluster, an oscilloscope can be used to observe the waveform of the sampling signal in the inverter control system. By measuring the period of the sampling signal and according to the reciprocal relationship between frequency and period, the sampling frequency can be calculated. It should be noted that when measuring, select appropriate measurement points and oscilloscope settings to ensure the accuracy of the measurement results.

[0049] It should be noted that the embodiments of the present application do not limit the specific ways of obtaining the original anti-resonant frequency and original sampling frequency of the inverter cluster. These parameters can be obtained through various methods, including but not limited to direct measurement, simulation analysis, historical data query, or prediction based on system models.

[0050] In a feasible embodiment, a heterogeneous inverter refers to an inverter that can be configured with heterogeneous parameters. The sampling frequency of a heterogeneous inverter refers to the frequency at which electrical quantities related to the operation of the inverter (such as voltage, current, etc.) are sampled in the inverter control system. After obtaining the original anti-resonant frequency and the original sampling frequency of the inverter cluster, the target sampling frequency of the heterogeneous inverter can be determined based on the original anti-resonant frequency, the original sampling frequency, and the heterogeneous inverter. In this process, in order to determine the target sampling frequency of the heterogeneous inverter, the original anti-resonant frequency, the original sampling frequency, and the target frequency parameters of the heterogeneous inverter itself can be comprehensively considered. In the specific implementation process, the relevant target frequency parameters of the heterogeneous inverter (such as anti-resonant frequency and resonant frequency) can be obtained first. Then, using these parameters, combined with the known original anti-resonant frequency and original sampling frequency, the appropriate sampling frequency range of the heterogeneous inverter can be obtained through calculation and analysis. Finally, within this range, the target sampling frequency of the heterogeneous inverter is selected and determined to ensure the stability and efficiency of the system operation.

[0051] See Figure 2 , Figure 2 which is a schematic diagram of a grid-connected inverter cluster system provided by an embodiment of the present application. Among them, Figure 2 (a) in it is a schematic diagram of the main circuit wiring, Figure 2 (b) in it is a circuit model diagram. In Figure 2 (a), U dc is the DC-side voltage, U pcc is the common connection point voltage, U g is the grid voltage. L 1 , C f and L 2 are the filter inductance on the inverter side, the filter capacitor, and the filter inductance on the grid side respectively. i g is the grid-side current of a single inverter, i grid is the grid-connected current of the inverter cluster. Y g is the grid admittance, and its expression is Y g = 1 / (R g + sL g ), where R g represents the grid resistance, L g represents the grid inductance, and s is the Laplace operator. In Figure 2 (b), I inv and Y inv respectively represent the Norton equivalent current source of the inverter and its admittance. Adopting Figure 3 the grid-side current feedback control method shown, the expression of the inverter admittance Y inv is as shown in Equation (1).

[0052]

[0053] In Equation (1), K pwm is the inverter gain, D(s) is the Proportional-Resonant (PR) controller, and G g (s) is the control delay. The expressions of D(s) and Gd(s) correspond to Equation (2) and Equation (3), respectively.

[0054]

[0055] In Equation (2), K p and K r are the proportional gain and resonant gain of the PR controller, respectively; ω cd is the cut-off frequency; ω n is the resonant frequency; the controller factor m = K p / K r .

[0056] Gd(s) = exp(-1.5sT) (3), where T refers to the sampling period.

[0057] In a feasible embodiment, after determining the circuit topology of the inverter cluster and the circuit control model of the heterogeneous inverter according to the grid-connected inverter cluster system and the grid-side current feedback control method, the key parameters such as the operating frequency and switching frequency of the heterogeneous inverter can be determined based on the resonant frequency f LCL and anti-resonant frequency f LC of the LCL filter connected to the output end of the heterogeneous inverter, in combination with the internal circuit design and control method of the inverter. It can be understood that the LCL filter is a filter commonly used at the output end of the inverter and consists of two inductors and a capacitor. Its resonant frequency refers to the frequency at which the reactances of the inductor and capacitor are equal in the LCL filter circuit. In the inverter system, the resonant frequency of the inverter is an inherent frequency characteristic jointly determined by various factors such as its internal circuit structure, component parameters, and control strategy. The LCL filter is usually connected to the output end of the inverter, and there is a close relationship between its resonant frequency and the resonant frequency of the inverter, which has a key impact on the system performance.

[0058] It should be noted that the anti-resonant frequency and resonant frequency can be determined based on the inductor and capacitor parameters of the LCL filter at the output end of the heterogeneous inverter in combination with the circuit principle.

[0059] In a feasible embodiment, the specific process of obtaining the target frequency parameters of the heterogeneous inverter is as Figure 4 shown, and this process can at least include Step 410 to Step 440.

[0060] Step 410: Obtain the filtering parameters of the heterogeneous inverter, where the filtering parameters include the first filtering inductor, filtering capacitor, and second filtering inductor;

[0061] Step 420: Define the resonance frequency of the heterogeneous inverter according to the first filter inductor, filter capacitor, and second filter inductor;

[0062] Step 430: Define the anti-resonance frequency of the heterogeneous inverter according to the first filter inductor and filter capacitor;

[0063] Step 440: Obtain the target frequency parameter of the heterogeneous inverter according to the anti-resonance frequency and resonance frequency.

[0064] In a feasible embodiment, the filter parameters of the heterogeneous inverter correspond to the filter parameters of the LCL filter connected to the output end, specifically including the first filter inductor L 1 , filter capacitor C f and the second filter inductor L 2 . It should be noted that these parameters are respectively equivalent to the inverter-side filter inductor L 1 , filter capacitor C f , grid-side filter inductor L 2 . These parameters can be obtained by referring to the equipment manual, actual measurement, etc. For example, for the heterogeneous inverter, the nominal values of the relevant filter parameters can be obtained from the product manual.

[0065] In a feasible embodiment, combining Figure 2 and Figure 3 , at the anti-resonance frequency f LC , the amplitude of the open-loop system will not be affected by the fluctuation of the grid inductor L g . To ensure that the system has good stability, usually the -180° phase crossover frequency f g(-180°) of the open-loop control system can be configured near f LC , and ideally make f g(-180°) = f LC . When this condition is met, the gain margin (GM) of the system can remain constant, thereby ensuring the robust stability of the inverter. In the actual parameter configuration of the inverter system, usually the sampling frequency is matched with f LC , and specifically, the configuration method of f s / 6 = f LC is adopted. At the same time, in the PR controller, the controller factor m = 50 is selected. Under this parameter configuration, there will be a phenomenon that f g(-180°) is slightly lower than f s / 6. Among them, the variable f g(-180°) is defined as the -180° phase crossover frequency of the open-loop control system.

[0066] In a feasible embodiment, according to the first filter inductor L 1 , filter capacitor Cf and the second filter inductor L 2 and the grid inductor L g , the resonant frequency f of the LCL filter can be defined by Equation (4) LCL so as to define the resonant frequency f of the heterogeneous inverter LCLx . Equation (4) is derived based on circuit principles and reflects the resonant characteristics formed by the inductors and capacitors in the LCL filter.

[0067]

[0068] Furthermore, according to the filter inductor L 1 and the filter capacitor C f , the anti-resonant frequency f of the LCL filter can be defined by Equation (5) LC so as to define the anti-resonant frequency f of the heterogeneous inverter LCx .

[0069]

[0070] It should be noted that both f LCLx and f LCL essentially represent the resonant frequency of the LCL filter, and both f lCx and f LC essentially represent the anti-resonant frequency of the LCL filter. Only the subscript "x" is used to distinguish specific heterogeneous inverters. f lCLx is used to represent the resonant frequency corresponding to the heterogeneous inverter, and f LCx is used to represent the anti-resonant frequency corresponding to the heterogeneous inverter. The two are the same in concept and calculation method.

[0071] In a feasible embodiment, as shown in Figure 5 , according to the original anti-resonant frequency, the original sampling frequency of the inverter cluster, and the target frequency parameters of the heterogeneous inverter, the specific process of calculating the sampling frequency range of the heterogeneous inverter can at least include Step 510 to Step 530.

[0072] Step 510: Calculate the upper limit of the sampling frequency of the heterogeneous inverter according to the original anti-resonant frequency and the anti-resonant frequency of the heterogeneous inverter;

[0073] Step 520: Calculate the lower limit of the sampling frequency according to the original sampling frequency;

[0074] Step 530: Obtain the sampling frequency range of the heterogeneous inverter according to the upper limit and the lower limit of the sampling frequency.

[0075] In a feasible embodiment, according to the original anti-resonant frequency f of the inverter cluster LCoriginand the anti-resonant frequency f of the heterogeneous inverter LCx , considering the variation characteristics of the admittance phase angle of the heterogeneous inverter within a specific frequency range, and to ensure that the interaction phase margin is a valid positive value, relevant parameters are configured, and the upper limit of the sampling frequency of the heterogeneous inverter can be calculated.

[0076] In a feasible embodiment, as Figure 6 shown, the specific process of step 510 may include, but is not limited to, steps 610 to 630.

[0077] Step 610: Determine the upper limit of the value of the anti-resonant frequency of the heterogeneous inverter according to the original anti-resonant frequency and the anti-resonant frequency of the heterogeneous inverter;

[0078] Step 620: Determine the configuration relationship between the original anti-resonant frequency and the sampling frequency of the heterogeneous inverter;

[0079] Step 630: Calculate the upper limit of the sampling frequency of the heterogeneous inverter according to the upper limit of the value of the anti-resonant frequency and the configuration relationship.

[0080] In a feasible embodiment, the configuration of relevant parameters includes: at f LCorigin , the admittance phase angle of the heterogeneous inverter should not exceed 80°, that is, it satisfies Based on this,[[]] in the frequency band (f LCx , f LCorigin ), the monotonic decrease should be no less than 10°. At the same time, considering that the descent speed of is slightly slower than that of the delay link, the delay link G dx (s)+5° correction term is used to approximately represent

[0081] Based on these conditions and relationships, the upper limit of the value of the anti-resonant frequency f LCx(max) can be deduced from the following inequality (6):

[0082]

[0083] In formula (6), T x is the control period of the heterogeneous inverter to be selected, and T x is related to the sampling frequency and the anti-resonant frequency f LCx and satisfies the relationship as shown in formula (7):

[0084]

[0085] Substitute formula (7) into formula (6) and organize to get the upper limit of the anti-resonant frequency as shown in formula (8):

[0086]

[0087] That is, the upper limit f of the anti-resonant frequency of the inverter LCx(max) is six-sevenths of the anti-resonant frequency f of the original inverter cluster LCorigin . Further, combining the robust stability configuration requirements, the configuration relationship between the anti-resonant frequency and the sampling frequency of the heterogeneous inverter can be determined as f LCx = f sx / 6. Substituting it into Equation (8), the upper limit of the sampling frequency of the heterogeneous inverter is as shown in Equation (9):

[0088]

[0089] That is, the sampling frequency of the newly configured inverter shall not be higher than thirty-six sevenths of the anti-resonant frequency of the original inverter cluster, that is, the upper limit of the sampling frequency f sx is

[0090] It should be noted that although Equation (9) provides the upper limit of the sampling frequency f sx , too low a sampling frequency may also lead to instability. Based on this, in a feasible embodiment, the heterogeneous inverter at the frequency point (corresponding to the -540° phase crossover frequency f gx(-540°) ≈ f sx / 2) coincides with the frequency point of the original inverter cluster at (corresponding to the -180° phase crossover frequency f gorigin(-180°) ≈ f sorigin / 6), eliminating the potential unstable region. Based on this condition, the sampling frequency f of the heterogeneous inverter sx and the original sampling frequency f of the original inverter cluster sorigin satisfy the relationship: f sx / 2 = f sorigin / 6.

[0091] Thus, the lower limit f of the sampling frequency of the heterogeneous inverter can be obtained sx(max) = f sorigin / 3, that is, f sx shall not be lower than one-third of the sampling frequency f of the original inverter cluster sorigin .

[0092] In a feasible embodiment, after determining the upper limit and the lower limit of the sampling frequency, the value range of the sampling frequency f of the heterogeneous inverter is obtained as shown in Equation (10). sx

[0093]

[0094] Further, select a suitable f according to the sampling frequency rangesx The value is used as the target sampling frequency. Preferably, the target sampling frequency f sx can take a value close to its upper limit value rather than the lower limit value to avoid the ripple problem caused by too low sampling frequency and ensure the filtering effect of the LCL filter.

[0095] In a feasible embodiment, as Figure 7 shown, the specific process of determining the filtering parameters of the heterogeneous inverter according to the target sampling frequency in step 130, so as to obtain the configured heterogeneous inverter, may include but is not limited to steps 710 to 740.

[0096] Step 710: Configure the value range of the target frequency parameters of the heterogeneous inverter according to the target sampling frequency to obtain the target frequency configuration result;

[0097] Step 720: Determine the value of the first filter inductor and the value of the second filter inductor according to the target frequency configuration result;

[0098] Step 730: Determine the value of the filter capacitor according to the target sampling frequency;

[0099] Step 740: Calculate the anti-resonant frequency and resonant frequency of the heterogeneous inverter according to the value of the first filter inductor, the value of the second filter inductor and the value of the filter capacitor, so as to obtain the configured heterogeneous inverter.

[0100] In a feasible embodiment, the specific process of configuring the value range of the target frequency parameters (i.e., anti-resonant frequency and resonant frequency) of the heterogeneous inverter according to the target sampling frequency in step 710 to obtain the target frequency configuration result is as Figure 8 shown, and this process may include but is not limited to steps 810 to 830.

[0101] Step 810: Configure the resonant frequency of the heterogeneous inverter to the first preset value of the target sampling frequency to obtain the first configuration result;

[0102] Step 820: Configure the anti-resonant frequency of the heterogeneous inverter to the second preset value of the target sampling frequency to obtain the second configuration result;

[0103] Step 830: Obtain the target frequency configuration result according to the first configuration result and the second configuration result.

[0104] In a feasible embodiment, according to equations (4) and (5), the resonant frequency f LCL and the anti-resonant frequency f LC of the LCL filter have the relationship shown in equation (11), that is, determine the anti-resonant frequency f LCx and the resonant frequency f LCLxRatio relationship.

[0105]

[0106] Furthermore, according to Equation (11), to ensure sufficient gain margin GM and moderate controller gain, the resonant frequency f LCLx can be configured within a range close to one-third of f sx (i.e., f LCLx ≈ f sx / 3), and the anti-resonant frequency f LCx is configured as f sx / 6 to meet robust stability. Based on the above frequency configuration results, by setting the first filter inductor L 1x (equivalent to L 1 ) and the second filter inductor L 2x (equivalent to L 2 ), the ratio of the resonant frequency to the anti-resonant frequency f LCLx / f LCx is slightly greater than 2 to ensure sufficient gain margin GM. Preferably, f LCLx / f LCx can be selected as 2.18. Corresponding to this configuration result, L 1x can be selected as 3 mH, and L 2x as 0.8 mH.

[0107] In a feasible embodiment, after determining the value of the target sampling frequency, the filter capacitor C LCx of the heterogeneous inverter can be determined according to the relationship f sx = f fx (equivalent to C f ).

[0108] In a feasible embodiment, after determining the values of the first filter inductor, the second filter inductor, and the filter capacitor C fx , the resonant frequency and anti-resonant frequency of the heterogeneous inverter can be calculated respectively according to Equations (4) and (5), thereby obtaining the configured heterogeneous inverter.

[0109] In a feasible embodiment, before integrating the configured heterogeneous inverter into the inverter cluster, the following operations are also required: According to the proportional gain K p , resonant frequency ω n , and cut-off frequency ω cd of the proportional-resonant controller (PR controller) of the heterogeneous inverter, the phase margin PM and gain margin GM of the heterogeneous inverter are adjusted to obtain the adjusted heterogeneous inverter. Among them, according to the resonant gain K r of the PR controller and the proportional gain K pThe controller factor m defined by the ratio satisfies m < ω n / ω cd -1. For example, m = 50 to ensure steady-state tracking accuracy and minimize the mid-frequency phase angle lag effect of the PR controller. After the above adjustments are completed, under ideal grid conditions (i.e., grid inductance L g = 0 mH), verify whether the phase margin PM and gain margin GM of the heterogeneous inverter meet the design requirements. After meeting the requirements, then incorporate the configured heterogeneous inverter into the inverter cluster. For example, when it is determined that the phase of the heterogeneous inverter does not exceed 80° at the original anti-resonant frequency and the gain margin GM is greater than 4 dB, incorporate the configured heterogeneous inverter into the inverter cluster. It can be understood that in a power electronics system, the phase margin and gain margin are important indicators for measuring system stability. The proportional gain K p of the proportional-resonant (PR) controller, the resonant frequency ω n and the cut-off frequency ω cd have a significant impact on the phase margin PM and gain margin GM of the inverter. By adjusting these parameters, the open-loop frequency response characteristics of the system can be changed, and then the phase margin and gain margin can be adjusted. For example, increasing the proportional gain K p may improve the amplitude response of the system, but may also cause a decrease in the phase margin. Therefore, it is necessary to comprehensively consider the influence of each parameter and find appropriate values to ensure that the system has good stability and dynamic performance. In addition, the phase of the heterogeneous inverter does not exceed 80° at the original anti-resonant frequency and the gain margin is greater than 4 dB before it is allowed to be incorporated into the inverter cluster, which is to ensure the stability of the entire cluster after incorporation. If the phase margin and gain margin do not meet these conditions, the inverter may experience unstable oscillations during operation, or even cause the system to collapse. Insufficient phase margin may cause the system to over-respond to interference, while insufficient gain margin may cause the gain of the system to be too large at certain frequencies, leading to instability.

[0110] In a feasible embodiment, after the heterogeneous inverter is put into operation, the admittance phase of the obtained target inverter cluster can be maintained within a preset range (i.e., [-90°, +90°]), thereby ensuring the overall interactive stability of the system. It can be understood that when the admittance phase is within this range, the equivalent impedance of the inverter has passivity, which can effectively reduce the equivalent impedance interaction between the inverter and the grid and avoid harmonic instability. If the admittance phase exceeds this range, it may cause an increase in harmonic current, affect the power quality of the grid, and even threaten the operation reliability of the equipment.

[0111] The following uses a specific example to illustrate the target sampling frequency configuration in this embodiment.

[0112] I. Experiment preparation

[0113] In this example, three inverters are used for experiments, including two 18 kHz inverters with the same configuration and one inverter that can be configured with heterogeneous parameters (i.e., a heterogeneous inverter). Among them, by replacing the output filter, the heterogeneous inverter can be adjusted to meet the configuration requirements for sampling frequencies of 5 kHz, 6 kHz, 10 kHz, 11 kHz, and 12 kHz. In the experiment, all inverters use Infineon IGBT modules (model FF50R12RT4), the supporting driver is of the Bronze Sword series, and the control is implemented with a TMS320F28335 digital signal processor. The equivalent inductance of the 220V grid terminal of the experimental platform is 0.1 mH, and its influence on the experiment can be ignored. The grid parameters and inverter parameters used in the experiment are the same as those in Table 1, ensuring the comparability and authenticity of the experimental results.

[0114] Table 1 shows the non-general part of the inverter parameter data, which is applicable to different inverters, and Table 1 also shows the general part of the inverter parameter data, which is applicable to all inverters.

[0115] Table 1 Non-general part of the inverter parameter data

[0116]

[0117]

[0118] Table 2 General part of the inverter parameter data

[0119]

[0120] II. Experimental analysis at different sampling frequencies

[0121] 1. Sampling frequency of the new inverter within the sampling frequency range

[0122] (1) Case of the 10 kHz inverter

[0123] Calculated according to Equation (10), the lower limit of the sampling frequency range of the new inverter is f sx(min) = 6 kHz, and the upper limit is f sx(max) = 10.566 kHz. Considering avoiding the ripple problem caused by too low sampling frequency, f sx close to the upper limit is selected as 10 kHz. Figure 9 shows the transient experimental waveforms of the grid-connected current i grid of the inverter cluster configured at 10 kHz. Among them, Figure 9(a) is the transient experimental waveform of i grid when the second 18 kHz and the third 10 kHz inverters are put into operation; Figure 9(b) is the transient experimental waveform of i g when the grid inductance L grid increases from 1 mH to 5 mH.

[0124] As shown in Fig. 9(a), under the condition that the grid inductance L g = 1 mH, a single 18 kHz inverter can operate stably, and the total harmonic distortion (THD) of the cluster grid-connected current i grid is 4.03%. When the second 18 kHz inverter is put into operation, high-frequency oscillation appears in i grid , and the THD increases to 8.99%. Subsequently, when the third inverter is connected and the sampling frequency is configured to be 10 kHz, the THD of i grid drops to 1.7%. Fig. 9(b) shows that when the inductance L g increases from 1 mH to 5 mH, i grid can maintain a good sinusoidal waveform, and the THD drops from 1.60% to 1.50%. This indicates that the system has high stability under different grid impedance conditions.

[0125] (2) Case of 6 kHz inverter

[0126] Figure 10 Shows the transient experimental waveforms of the cluster grid-connected current i sx(min) under the condition that the lowest sampling frequency f grid = 6 kHz. When L g = 1 mH, after the 6 kHz inverter is put into operation, the system quickly tends to be stable, and the THD of i grid is only 2.44%. When the grid inductance L g increases to 5 mH, the THD of i grid is only 2.08%, showing high anti-disturbance performance.

[0127] In summary, the experimental results in Fig. 9 and Figure 10 show that as long as the sampling frequency of the third inverter is selected within the recommended range from f sx(min) to f sx(max) , the cluster system can effectively eliminate the unstable region of admittance interaction. At the same time, the system has strong robustness to both grid impedance fluctuations and perturbations of its own structural parameters.

[0128] 2. The sampling frequency of the new inverter exceeds the upper limit of the sampling frequency range

[0129] Case of 11 kHz inverter

[0130] Fig. 11 shows the experimental results of the 11 kHz inverter case. Among them, (a) is the cluster current waveform when the inverter filtering parameters are given values; (b) is the cluster current waveform when the filtering capacitor of the 11 kHz inverter is reduced to 85% of the original value.

[0131] When the sampling frequency of the new inverter is set to f sxAt 11 kHz, the unstable region of the cluster system was temporarily eliminated. Figure 11(a) shows that when the 11 kHz inverter was put into operation, the stability of the cluster system was restored. At L g = 1 mH, the THD of i grid was 3.29%; when L g increased to 5 mH, the THD dropped to 1.94%. Since the sampling frequency f sx = 11 kHz was higher than the recommended upper limit value f sx(max) , the interaction stability margin between the cluster system and the grid admittance was insufficient. When the inverter parameters were perturbed, new unstable regions were likely to occur. Figure 11(b) shows the waveform change of i x when the filter capacitor C grid was reduced to 85% of the original value. When L g was set to 1 mH, i grid did not diverge, but the THD deteriorated to 5.36%. When L g increased to 5 mH, higher harmonic components appeared in i grid , triggering overcurrent protection and the system shut down.

[0132] Obviously, the experimental case of the 11 kHz inverter fully shows that when the sampling frequency of the new inverter exceeds the recommended upper limit value, although the unstable region of the cluster system can be eliminated in the short term, making the system seemingly operate stably, the internal structure parameters of the inverter will inevitably be perturbed during the actual operation process. This perturbation may lead to the emergence of new unstable intervals, which will pose a serious threat to the safe and stable operation of the cluster system. In-depth analysis of the 11 kHz inverter case shows that when the sampling frequency is higher than the recommended upper limit, the interaction stability margin between the cluster system and the grid admittance is necessarily insufficient. In this case, the stability of the system is extremely fragile. Even a small change in internal parameters or external interference may cause the deterioration of system performance and even lead to system collapse.

[0133] This case further confirms that to ensure the stable and reliable operation of the inverter cluster system, the sampling frequency of the new inverter must be strictly controlled within the recommended range of f sx(min) to f sx(max) .

[0134] 3. The sampling frequency of the new inverter is lower than the lower limit of the sampling frequency

[0135] Figure 12 shows that when the sampling frequency of the new inverter is set to f sx = 5 kHz, at L g = 1 mH, although the cluster grid-connected current i gridThe THD is reduced to 4.01%, but the interaction between internal inverters deteriorates. The THDs of the grid-connected currents of the 18 kHz and 5 kHz inverters are relatively high, being 8.22% and 14.05% respectively. When L g increases to 5 mH, characteristic harmonic components appear in i grid and the grid-connected currents of each inverter, and the current waveforms all show varying degrees of oscillatory divergence, ultimately triggering overcurrent protection and causing the cluster system to shut down. The 5 kHz inverter case shows that when the sampling frequency is lower than the recommended lower limit f sx(min) , the admittance interaction problem inside and outside the cluster system intensifies, leading to multi-level interaction instability.

[0136] In summary, the experimental results from Figure 9 to Figure 12 show that the sampling frequency of the new inverter (i.e., the heterogeneous inverter) must be strictly limited within the recommended range f sx(min) to f sx(max) to ensure the robustness and stability of the system.

[0137] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cluster admittance passivity control method based on inverter transformation, characterized in that: Applied to an inverter cluster and a heterogeneous inverter used to be put into the inverter cluster, the method comprises: Obtaining an original anti-resonance frequency and an original sampling frequency of the inverter cluster; Determining a target sampling frequency of the heterogeneous inverter according to the original anti-resonance frequency, the original sampling frequency and the heterogeneous inverter; Determining filtering parameters of the heterogeneous inverter according to the target sampling frequency to obtain a configured heterogeneous inverter; The configured heterogeneous inverters are merged into the inverter cluster to obtain a target inverter cluster, and the admittance phase of the target inverter cluster is within a preset range.

2. The cluster admittance passivity control method according to claim 1, characterized in that: The determining, according to the original anti-resonance frequency, the original sampling frequency and the heterogeneous inverter, a target sampling frequency of the heterogeneous inverter comprises: Obtaining a target frequency parameter of the heterogeneous inverter; Calculating a sampling frequency range of the heterogeneous inverter according to the original anti-resonance frequency, the original sampling frequency and the target frequency parameter; In the sampling frequency range, a target sampling frequency of the heterogeneous inverter is determined.

3. The cluster admittance passivity control method according to claim 2, characterized in that: The target frequency parameters of the heterogeneous inverter include an anti-resonance frequency and a resonant frequency; The calculating, according to the original anti-resonance frequency, the original sampling frequency and the target frequency parameter, a sampling frequency range of the heterogeneous inverter comprises: Calculating an upper limit of a sampling frequency of the heterogeneous inverter according to the original anti-resonance frequency and the anti-resonance frequency of the heterogeneous inverter; According to the original sampling frequency, a lower limit of the sampling frequency of the heterogeneous inverter is calculated; According to the sampling frequency upper limit and the sampling frequency lower limit, a sampling frequency range of the heterogeneous inverter is obtained.

4. The cluster admittance passivity control method according to claim 3, characterized in that: The calculating, according to the original anti-resonance frequency and the anti-resonance frequency of the heterogeneous inverter, an upper limit of the sampling frequency of the heterogeneous inverter comprises: Determining an upper limit of the anti-resonance frequency of the heterogeneous inverter according to the original anti-resonance frequency and the anti-resonance frequency of the heterogeneous inverter; Determining a configuration relationship between the original anti-resonance frequency and the sampling frequency of the heterogeneous inverter; According to the upper limit of the anti-resonance frequency and the configuration relationship, the upper limit of the sampling frequency of the heterogeneous inverter is calculated.

5. The cluster admittance passivity control method according to claim 2, characterized in that: The obtaining of a target frequency parameter of the heterogeneous inverter includes: Acquire filtering parameters of the heterogeneous inverter, where the filtering parameters include a first filtering inductor, a filtering capacitor, and a second filtering inductor; Defining a resonant frequency of the heterogeneous inverter according to the first filter inductor, the filter capacitor and the second filter inductor; Defining an anti-resonance frequency of the heterogeneous inverter according to the first filter inductor and the filter capacitor; A target frequency parameter of the heterogeneous inverter is obtained according to the anti-resonance frequency and the resonant frequency.

6. The cluster admittance passivity control method according to claim 3, characterized in that: The filtering parameters include a first filtering inductor, a second filtering inductor and a filtering capacitor; According to the target sampling frequency, determining the filtering parameters of the heterogeneous inverter, and obtaining a configured heterogeneous inverter, including: According to the target sampling frequency, configuring a value range of a target frequency parameter of the heterogeneous inverter to obtain a target frequency configuration result; Determining a value of the first filter inductor and a value of the second filter inductor according to the target frequency configuration result; Determining the value of the filter capacitor according to the target sampling frequency; According to the value of the first filter inductor, the value of the second filter inductor and the value of the filter capacitor, the anti-resonance frequency and the resonant frequency of the heterogeneous inverter are calculated to obtain a configured heterogeneous inverter.

7. The cluster admittance passivity control method according to claim 6, characterized in that: According to the target sampling frequency, a value range of a target frequency parameter of the heterogeneous inverter is configured to obtain a target frequency configuration result, including: Configuring the resonant frequency of the heterogeneous inverter to be a first preset value of the target sampling frequency to obtain a first configuration result; Configuring the anti-resonance frequency of the heterogeneous inverter to be a second preset value of the target sampling frequency to obtain a second configuration result; A target frequency configuration result is obtained according to the first configuration result and the second configuration result.

8. The cluster admittance passivity control method according to claim 1, characterized in that: Before incorporating the configured heterogeneous inverter into the inverter cluster, the method further includes: According to the proportional gain, resonant gain and cut-off frequency of the proportional resonant controller of the heterogeneous inverter, the phase margin and amplitude margin of the heterogeneous inverter are adjusted to obtain an adjusted heterogeneous inverter.

9. The cluster admittance passivity control method according to claim 8, characterized in that: Integrating the configured heterogeneous inverter into the inverter cluster, including: When it is determined that the phase of the heterogeneous inverter does not exceed 80° at the original anti-resonance frequency and the amplitude margin is greater than 4 dB, the configured heterogeneous inverter is incorporated into the inverter cluster.

10. The cluster admittance passivity control method according to claim 1, characterized in that: The preset range is [-90°, +90°].

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