LLCL filter design method

Abstract

The invention discloses an LLCL filter design method, and relates to the technical field of power electronics. The method comprises the following steps: acquiring an initial filter capacitance, an initial inverter side filter inductance, a power grid side filter inductance and a target frequency; calculating filtering branch inductance based on the filtering capacitance and the target frequency; calculating a positive harmonic peak frequency based on the filter capacitor, the inverter side filter inductor, the power grid side filter inductor and the filter branch inductor; calculating damping resistance, damping inductance and damping capacitance based on the positive harmonic peak frequency, the filter capacitance, the resonant frequency value constraint, the first value range constraint and the second value range constraint of the quality factor; and when the target parameter does not meet the grid-connected current harmonic standard, updating the filter capacitor and / or the inverter side filter inductance, and skipping to the step of calculating the filter branch inductance based on the filter capacitor and the target frequency so as to carry out iteration until the grid-connected current harmonic standard is met. According to the embodiment of the invention, the design optimization of the parameter value of the filter element in the LLCL filter is realized.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a LLCL filter design method. Background Art

[0002] In the current field of power electronics technology, flexible converters represented by voltage source inverters are the core equipment of flexible distribution networks. They can realize AC / DC power conversion, thereby achieving power mutual assistance, improved reliability, and enhanced new energy carrying capacity of distribution networks.

[0003] As the power levels of flexible distribution systems increase, the power levels of flexible converters are required to be further increased. One feasible approach is to construct three-level converters using high-power semiconductor devices, thereby increasing the power capacity of each converter. High-power semiconductor devices, such as IGBTs (Insulated Gate Bipolar Transistors), IEGTs (Injection Enhanced Gate Transistors), and IGCTs (Integrated Gate-Commutated Thyristors), are characterized by high switching losses. To meet system efficiency and equipment heat dissipation requirements, their switching frequencies are often limited to only a few hundred Hz, significantly increasing the size and cost of the grid-side filter. Commonly used grid-side filters include L-type and LCL-type. LCL filters offer better attenuation characteristics at high frequencies for the same filter inductor capacitance, making them widely used in grid-connected inverters. However, for high-capacity inverters with low switching frequencies, where harmonic content is high, LCL filters have insufficient attenuation characteristics at mid-frequency ranges, resulting in a similarly large capacity. The LLCL filter can introduce a negative resonance peak in the mid-frequency band, thereby significantly improving the attenuation characteristics of the mid-frequency band and is more suitable for high-power inverter devices.

[0004] However, LLCL filters exhibit not only negative resonance peaks but also positive resonance peaks, necessitating the addition of a damping network to suppress these peaks. An RLC damping network, consisting of a resistor, inductor, and capacitor in parallel, is a particularly effective damping network. While LLCL filters with RLC damping networks offer excellent filtering performance and a relatively small filter size, they require parameter design for seven filter elements, making their design challenging. Currently, LLCL filters lack a clear and feasible parameter design process for large-capacity grid-connected inverters, hindering their widespread adoption in the industry. Summary of the Invention

[0005] The embodiments of the present application provide an LLCL filter design method, which can optimize the parameter value design of the filter elements in the LLCL filter, thereby optimizing the filter cost and volume.

[0006] In a first aspect, an embodiment of the present application provides an LLCL filter design method, wherein the LLCL filter is provided with an RLC damping network and is arranged between an inverter voltage output terminal and a power grid; the LLCL filter design method includes:

[0007] Obtaining the initial filter capacitance, initial inverter-side filter inductance, grid-side filter inductance, and target frequency of the LLCL filter. The target frequency is determined based on the inverter voltage harmonic amplitude-frequency characteristics corresponding to the inverter voltage output terminal.

[0008] Based on the filter capacitance and target frequency, the filter branch inductance of the LLCL filter is calculated.

[0009] Based on the filter capacitor, inverter-side filter inductor, grid-side filter inductor, and filter branch inductor, the positive resonant peak frequency of the LLCL filter is calculated.

[0010] Based on the positive resonance peak frequency, the filter capacitor, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistor, and the second value range constraint of the quality factor of the RLC damping network, the damping resistor, the damping inductor, and the damping capacitor of the RLC damping network are calculated;

[0011] If the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, update the filter capacitor and / or the inverter-side filter inductor, and jump to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard;

[0012] Among them, the target parameters include filter capacitor, inverter side filter inductor, grid side filter inductor, filter branch inductor, damping resistor, damping inductor and damping capacitor.

[0013] In some possible implementations, calculating the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency includes:

[0014] In the initial iteration round, the filter branch inductance is calculated using the first calculation formula based on the filter capacitance and the target frequency;

[0015] The first calculation formula includes:

[0016]

[0017] Among them, f r-is the negative resonance peak frequency of the LLCL filter, and the value of the negative resonance peak frequency is the target frequency. f is the filter branch inductance, C f For the filter capacitor.

[0018] In some possible implementations, calculating the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency includes:

[0019] In a non-initial iteration round, the filter branch inductance is calculated using the second calculation formula based on the filter capacitor, the damping capacitor in the previous iteration round, and the target frequency;

[0020] The second calculation formula includes:

[0021]

[0022] Among them, f r-_actual is the corrected negative resonance peak frequency of the LLCL filter. The corrected negative resonance peak frequency is the target frequency. C eq is the equivalent capacitance, L f is the filter branch inductance, C f is the filter capacitor, C d is the damping capacitance in the previous iteration.

[0023] In some possible implementations, the positive resonant peak frequency of the LLCL filter is calculated based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor, including:

[0024] Based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor, the positive resonance peak frequency is calculated using the third calculation formula;

[0025] The third calculation formula includes:

[0026]

[0027] Among them, f r+ is the positive resonance peak frequency, C f is the filter capacitor, L1 is the filter inductor on the inverter side, L2 is the filter inductor on the grid side, L f is the filter branch inductor.

[0028] In some possible implementations, the damping resistance, damping inductance, and damping capacitance of the RLC damping network are calculated based on the positive resonance peak frequency, the filter capacitance, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistance, and the second value range constraint of the quality factor of the RLC damping network, including:

[0029] Calculate the damping resistance based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint;

[0030] Based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, the damping inductor and the damping capacitor are calculated.

[0031] In some possible implementations, calculating the damping resistance based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint includes:

[0032] The target impedance is calculated based on the inverse of the product of the positive resonance peak frequency and the filter capacitance;

[0033] Based on the target impedance and the first value range constraint, a damping resistance is calculated;

[0034] The first value range constraint includes: the value of the damping resistance is 1 / 5 to 1 / 3 of the target impedance.

[0035] In some possible implementations, the damping inductance and the damping capacitance are calculated based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, including:

[0036] Based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, the damping inductor and the damping capacitor are calculated using the fourth calculation formula and the fifth calculation formula;

[0037] The fourth calculation formula includes:

[0038] The fifth calculation formula includes:

[0039] Among them, f n is the resonant frequency of the RLC damping network, Q is the quality factor of the RLC damping network, L d is the damping inductance, C d is the damping capacitor, R d is the damping resistor;

[0040] The resonant frequency of the RLC damping network is constrained to be consistent with the positive resonance peak frequency.

[0041] The second value range constraint includes: the value range of the quality factor is set to 1 to 1.5.

[0042] In some possible implementations, after calculating the damping resistance, damping inductance, and damping capacitance of the RLC damping network, the LLCL filter design method further includes:

[0043] Based on the target parameters of the current iteration round and the transfer function expression of the LLCL filter from the inverter voltage to the grid current, determine whether the target parameters meet the grid current harmonic standards;

[0044] The transfer function expression is shown in the sixth calculation formula, which includes:

[0045]

[0046] Among them, G LLCL_RLC is the transfer function of LLCL filter from inverter voltage to grid current, L d is the damping inductance, C d is the damping capacitor, R d is the damping resistor, C f is the filter capacitor, L1 is the filter inductor on the inverter side, L2 is the filter inductor on the grid side, L f is the filter branch inductance, and s is the complex frequency variable.

[0047] In some possible implementations, updating the filter capacitor and / or the inverter-side filter inductor includes:

[0048] When the filter capacitance in the current iteration round is less than the upper limit of the filter capacitance, the filter capacitance is increased according to the preset first step value;

[0049] And / or, when the inverter-side filter inductance in the current iteration round is less than the inverter-side filter inductance upper limit, the inverter-side filter inductance is increased according to a preset second step value.

[0050] In some possible implementations, obtaining an initial filter capacitor and an initial inverter-side filter inductor of the LLCL filter includes:

[0051] Obtain a reference capacitance value corresponding to the rated impedance of a target power system at the power frequency, and a reference inductance value corresponding to the rated impedance at the power frequency, where the power system is a power system corresponding to the LLCL filter;

[0052] Based on the reference capacitance value, the reference inductance value and the preset filter coefficient, an initial filter capacitance and an initial inverter-side filter inductance are calculated.

[0053] In some possible implementations, obtaining a grid-side filter inductor includes:

[0054] The transformer leakage inductance of the grid-connected transformer in the target power system is obtained, and the transformer leakage inductance is determined as the grid-side filter inductance. The target power system is the power system corresponding to the LLCL filter.

[0055] In some possible implementations, obtaining a target frequency includes:

[0056] Obtaining the inverter voltage harmonic amplitude-frequency characteristics corresponding to the inverter voltage output terminal;

[0057] Based on the inverter voltage harmonic amplitude-frequency characteristics, the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined, and the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined as the target frequency.

[0058] Based on the same inventive concept, in a second aspect, an embodiment of the present application provides an LLCL filter design device, wherein the LLCL filter is provided with an RLC damping network and is arranged between an inverter voltage output terminal and a power grid; the LLCL filter design device includes:

[0059] A first acquisition module is used to obtain an initial filter capacitor, an initial inverter-side filter inductor, a grid-side filter inductor, and a target frequency of the LLCL filter, where the target frequency is determined based on an inverter voltage harmonic amplitude-frequency characteristic corresponding to an inverter voltage output terminal;

[0060] A first calculation module is used to calculate the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency;

[0061] A second calculation module is used to calculate the positive resonance peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor;

[0062] a third calculation module, configured to calculate the damping resistance, damping inductance, and damping capacitance of the RLC damping network based on the positive resonance peak frequency, the filter capacitance, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistance, and the second value range constraint of the quality factor of the RLC damping network;

[0063] an iterative update module, configured to update the filter capacitor and / or the inverter-side filter inductor if the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, and jump to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard;

[0064] Among them, the target parameters include filter capacitor, inverter side filter inductor, grid side filter inductor, filter branch inductor, damping resistor, damping inductor and damping capacitor.

[0065] In a third aspect, an embodiment of the present application provides an LLCL filter design device, the LLCL filter design device comprising:

[0066] a processor and a memory storing computer program instructions;

[0067] When the processor executes the computer program instructions, the LLCL filter design method provided in any one of the above embodiments of the present application is implemented.

[0068] In a fourth aspect, an embodiment of the present application provides a computer storage medium having computer program instructions stored thereon. When the computer program instructions are executed by a processor, an LLCL filter design method as provided in any one of the above embodiments of the present application is implemented.

[0069] In a fifth aspect, an embodiment of the present application provides a computer program product. When the instructions in the computer program product are executed by a processor of an electronic device, the electronic device executes the LLCL filter design method provided in any one of the above-mentioned embodiments of the present application.

[0070] An embodiment of the present application provides a method for designing an LLCL filter, which obtains the initial filter capacitor, initial inverter-side filter inductor, grid-side filter inductor, and target frequency of the LLCL filter. The target frequency is determined based on the harmonic amplitude-frequency characteristics of the inverter voltage corresponding to the inverter voltage output terminal. Based on the filter capacitor and the target frequency, the filter branch inductance of the LLCL filter is calculated; and then based on the filter capacitor, inverter-side filter inductor, grid-side filter inductor, and filter branch inductance, the positive resonance peak frequency of the LLCL filter is calculated. Then, based on the positive resonance peak frequency, the filter capacitor, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistor, and the second value range constraint of the quality factor of the RLC damping network, the damping resistor, damping inductor, and damping capacitor of the RLC damping network are calculated. Finally, if the target parameters in the current iteration do not meet the grid-connected current harmonic standards, the filter capacitor and / or inverter-side filter inductor are updated, and the process jumps to the step of calculating the LLCL filter's filter branch inductance based on the filter capacitor and target frequency to iterate until the target parameters meet the grid-connected current harmonic standards, thereby obtaining the final design parameters of the LLCL filter. The target parameters include the filter capacitor, inverter-side filter inductor, grid-side filter inductor, filter branch inductor, damping resistor, damping inductor, and damping capacitor.

[0071] From the above description, it can be seen that an LLCL filter design method according to an embodiment of the present application comprehensively determines the specific parameters of each filter element in the LLCL filter by the harmonic characteristics of the inverter output voltage and the grid-connected current harmonic standard, combined with the engineering constraints of different component parameters, and when the component parameters do not meet the grid-connected current harmonic standard, the scheme can select the filter capacitor and / or the inverter-side filter inductor for update to perform iterative update of the overall filter element parameters. In this way, the design scheme realizes the parameter value optimization of the LLCL filter parameters in the parameter iterative update. Compared with the related art that has not yet formed a clear and feasible parameter design process, the LLCL filter design method provided by the embodiment of the present application provides clear and feasible parameter design constraints and optimization processes, which can fully realize the parameter value design optimization of the filter element in the LLCL filter under the premise that the filter element parameters meet the grid-connected current harmonic requirements, so as to reduce the parameter value of the filter element as much as possible and avoid over-configuration of the LLCL filter capacity, thereby achieving the optimization of the cost and volume of the LLCL filter, which is conducive to the widespread promotion and application of LLCL filters in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0073] Figure 1 1 is a flow chart of an LLCL filter design method provided in one embodiment of the present application;

[0074] Figure 2 This is a schematic diagram of a single-phase circuit principle of an LLCL filter with an RLC damping network provided in one embodiment of the present application;

[0075] Figure 3 This is a scenario flow diagram of the LLCL filter design method provided by an embodiment of the present application;

[0076] Figure 4 1 is a schematic structural diagram of an LLCL filter design device provided in one embodiment of the present application;

[0077] Figure 5 Schematic diagram of the structure of an LLCL filter design device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0078] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0079] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, the elements defined by the phrase "comprising..." do not exclude the presence of other identical elements in the process, method, article, or device comprising the elements.

[0080] It should be noted that in the embodiments of the present application, certain software, components, models and other existing solutions in the industry may be mentioned. They should be regarded as exemplary. Their purpose is only to illustrate the feasibility of implementing the technical solution of the present application, but it does not mean that the applicant has or will necessarily use the solution.

[0081] As mentioned in the background technology section, LLCL filters currently lack a clear and feasible parameter design process for large-capacity grid-connected inverters, which has become a limiting factor in the widespread application of LLCL filters in the industry. Based on this, and to address the existing technical issues, the present application provides an LLCL filter design method.

[0082] It should be noted that the embodiments provided in this application are not intended to limit the scope of disclosure of this application.

[0083] The following first introduces the LLCL filter design method provided in the embodiment of the present application.

[0084] Figure 1 The flow chart of the LLCL filter design method provided by an embodiment of the present application is shown. The LLCL filter is provided with an RLC damping network, and the LLCL filter is used to be provided between the inverter voltage output terminal and the power grid. Figure 1 As shown, the LLCL filter design method includes the following steps:

[0085] S110, obtaining an initial filter capacitor, an initial inverter-side filter inductor, a grid-side filter inductor, and a target frequency of the LLCL filter, where the target frequency is determined based on an inverter voltage harmonic amplitude-frequency characteristic corresponding to an inverter voltage output terminal;

[0086] S120, calculating the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency;

[0087] S130, calculating a positive resonant peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor;

[0088] S140, calculating a damping resistance, a damping inductance, and a damping capacitance of the RLC damping network based on the positive resonance peak frequency, the filter capacitance, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistance, and the second value range constraint of the quality factor of the RLC damping network;

[0089] S150: If the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, update the filter capacitor and / or the inverter-side filter inductor, and jump to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard.

[0090] Among them, the target parameters include filter capacitor, inverter side filter inductor, grid side filter inductor, filter branch inductor, damping resistor, damping inductor and damping capacitor.

[0091] As can be seen from the above description, an LLCL filter design method according to an embodiment of the present application comprehensively determines the specific parameters of each filter element in the LLCL filter by using the harmonic characteristics of the inverter output voltage and the grid-connected current harmonic standards, combined with the engineering constraints of different component parameters. Furthermore, if the component parameters do not meet the grid-connected current harmonic standards, the scheme can select the filter capacitor and / or the inverter-side filter inductor for update to iteratively update the overall filter element parameters. In this way, the design scheme optimizes the parameter values of the LLCL filter parameters during the iterative parameter update.

[0092] Compared with the related technologies that have not yet formed a clear and feasible parameter design process, the LLCL filter design method provided in the embodiment of the present application provides clear and feasible parameter design constraints and optimization processes. It can fully realize the parameter value design optimization of the filter elements in the LLCL filter on the premise that the filter element parameters meet the grid-connected current harmonic requirements, so as to minimize the parameter value of the filter element and avoid over-configuration of the LLCL filter capacity, thereby optimizing the cost and volume of the LLCL filter, which is conducive to the widespread promotion and application of LLCL filters in the industry.

[0093] To understand the LLCL filter provided by the present invention, please refer to Figure 2 , Figure 2 This is a schematic diagram of a single-phase circuit principle of an LLCL filter with an RLC damping network provided in one embodiment of the present application.

[0094] like Figure 2 As shown, the LLCL filter is provided with an RLC damping network, and the LLCL filter can be used to be provided between the inverter voltage output terminal and the power grid. Figure 2 In the figure, L1 and L2 are the inverter side filter inductor and grid side filter inductor respectively, C f and L f They are filter capacitor and branch inductor, R d , L d and C d An RLC damping network is formed in parallel to suppress the forward resonance peak of the LLCL filter, thereby preventing the circuit from resonating.

[0095] Depend on Figure 2 It can be seen that there are seven filter elements in the LLCL filter with an RLC damping network whose parameters need to be designed. The embodiment of the present application will provide clear parameter design constraints and optimization processes for these seven filter elements, so as to minimize the parameter values of the filter elements as much as possible while meeting the grid-connected current harmonic requirements, thereby optimizing the filter cost and volume.

[0096] The specific implementation of the above steps 110 to 150 is described in detail below.

[0097] In S110, during specific implementation, the initial filter capacitor, initial inverter-side filter inductor, grid-side filter inductor, and target frequency of the LLCL filter are obtained. The target frequency is determined based on the inverter voltage harmonic amplitude-frequency characteristics corresponding to the inverter voltage output terminal.

[0098] The initial filter capacitor and initial inverter-side filter inductor values can be set based on actual LLCL filter design experience. To avoid over-configuration of filter parameters, the initial filter capacitor and initial inverter-side filter inductor values can be set relatively small, allowing for incremental updates in subsequent iterations, thereby facilitating parameter design optimization.

[0099] More specifically, optionally, obtaining an initial filter capacitor and an initial inverter-side filter inductor of the LLCL filter includes:

[0100] Obtain a reference capacitance value corresponding to the rated impedance of a target power system at the power frequency, and a reference inductance value corresponding to the rated impedance at the power frequency, where the power system is a power system corresponding to the LLCL filter;

[0101] Based on the reference capacitance value, the reference inductance value and the preset filter coefficient, an initial filter capacitance and an initial inverter-side filter inductance are calculated.

[0102] The above-mentioned preset filter coefficients, such as 0.02 and 0.03, are not strictly limited here, and their values can be set based on actual filter design experience and design requirements. It should be noted that in some embodiments, the filter coefficient corresponding to the filter capacitor and the filter coefficient corresponding to the inverter-side filter inductor can be different or the same.

[0103] In this embodiment, the initial filter capacitance value is calculated by multiplying the reference capacitance value corresponding to the system rated impedance at the power frequency by the filter coefficient; the initial inverter-side filter inductance value is calculated by multiplying the reference inductance value corresponding to the system rated impedance at the power frequency by the filter coefficient. These initial filter capacitance and initial inverter-side filter inductance can be used in the initial iteration of the LLCL filter design of the embodiment of the present application to start the LLCL filter design iteration process of the embodiment of the present application.

[0104] According to some embodiments of the present application, optionally, obtaining a grid-side filter inductor includes:

[0105] The transformer leakage inductance of the grid-connected transformer in the target power system is obtained, and the transformer leakage inductance is determined as the grid-side filter inductance. The target power system is the power system corresponding to the LLCL filter.

[0106] In this embodiment, considering the actual system grid-connected scenario, the grid-side filter inductor can be realized by utilizing the leakage inductance of the grid-connected transformer, thereby avoiding the need for additional filter inductance. Therefore, the value of the grid-side filter inductor in this embodiment of the application is the transformer leakage inductance.

[0107] It should be added that, in the LLCL filter design iterative process of the embodiment of the present application, the grid-side filter inductance can be regarded as a fixed known quantity and substituted into the subsequent parameter iterative calculation to reduce the repeated determination and calculation operations of the grid-side filter inductance.

[0108] According to some embodiments of the present application, optionally, obtaining a target frequency includes:

[0109] Obtaining the inverter voltage harmonic amplitude-frequency characteristics corresponding to the inverter voltage output terminal;

[0110] Based on the inverter voltage harmonic amplitude-frequency characteristics, the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined, and the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined as the target frequency.

[0111] The harmonic amplitude-frequency characteristic of the inverter voltage output terminal refers to the relationship between the amplitude and frequency of each harmonic in the system inverter output voltage. The inverter output voltage usually contains a fundamental wave and multiple harmonic components.

[0112] In specific implementation, the time domain signal output by the inverter can be converted into a frequency domain signal through Fourier transform, and the corresponding inverter voltage harmonic amplitude-frequency characteristics can be obtained, so that the amplitude and frequency of each harmonic can be analyzed.

[0113] Then, the inventors of the present application discovered that, through studying the characteristics of the LLCL filter, the LLCL filter has a strong attenuation characteristic near the negative resonance peak frequency band, so the negative resonance peak frequency is set at the frequency where the harmonic amplitude of the inverter output voltage is the largest.

[0114] Based on the above findings, in this embodiment, after obtaining the inverter voltage harmonic amplitude-frequency characteristics, the frequency corresponding to the maximum harmonic amplitude of the inverter-side output voltage is further determined based on the inverter voltage harmonic amplitude-frequency characteristics, and the frequency corresponding to the maximum harmonic amplitude of the inverter-side output voltage is determined as the target frequency. This target frequency can be used to determine the value of the negative resonant peak frequency in the iterative design process of the LLCL filter in this embodiment of the application.

[0115] In this way, the reliability and practical value of the actual LLCL filter design process can be guaranteed, thereby contributing to the widespread promotion and application of LLCL filters in the industry.

[0116] In S120, in a specific implementation, the filter branch inductance of the LLCL filter is calculated based on the filter capacitance and the target frequency. For example, in combination with the above embodiment, the negative resonant peak frequency is set at the target frequency, and then based on the calculation formula for the negative resonant peak frequency of the LLCL filter, the target frequency and the filter capacitance are substituted into the calculation formula to calculate the filter branch inductance of the LLCL filter.

[0117] According to some embodiments of the present application, optionally, calculating the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency includes:

[0118] In the initial iteration round, the filter branch inductance is calculated using the first calculation formula based on the filter capacitance and the target frequency;

[0119] The first calculation formula is shown in formula (1):

[0120]

[0121] Among them, formula (1) is the expression of the negative resonant frequency of the LLCL filter in the initial iteration round without considering the RLC damping network. In formula (1), f r- is the negative resonance peak frequency of the LLCL filter, and the value of the negative resonance peak frequency is the target frequency. f is the filter branch inductance, C f For the filter capacitor.

[0122] It should be understood that in the iterative design process of the LLCL filter of the present application, for the LLCL filter with an RLC damping network, since the relevant parameters in the RLC damping network have not yet been determined in the initial iterative round, the above formula (1) is used to start the calculation of the filter branch inductance to ensure the flow calculation of the subsequent design process.

[0123] According to some embodiments of the present application, optionally, calculating the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency includes:

[0124] In a non-initial iteration round, the filter branch inductance is calculated using the second calculation formula based on the filter capacitor, the damping capacitor in the previous iteration round, and the target frequency;

[0125] The second calculation formula is shown in formula (2):

[0126]

[0127] Wherein, formula (2) is an expression for the corrected negative resonance peak frequency of the LLCL filter after considering the RLC damping network, and this expression is applicable to non-initial iteration rounds in the LLCL filter design process of this application.

[0128] In formula (2), f r-_actual is the corrected negative resonance peak frequency of the LLCL filter. The corrected negative resonance peak frequency is the target frequency. C eq is the equivalent capacitance, L f is the filter branch inductance, C fis the filter capacitor, C d is the damping capacitance in the previous iteration.

[0129] In this embodiment, in non-initial iterations, since the relevant parameters of the RLC damping network have already been calculated in the previous iteration, in order to improve the calculation accuracy of the negative resonant peak frequency of the LLCL filter with an RLC damping network, the damping capacitor in the previous iteration is introduced to calculate the equivalent capacitance of the filter capacitor and the damping capacitor.

[0130] In this way, based on the equivalent capacitance, the correction calculation of the negative resonant peak frequency can be fully realized, further improving the reliability and accuracy of the filter branch inductance calculation in non-initial iteration rounds, thereby ensuring the reliability and practical value of the actual LLCL filter design process.

[0131] It should be noted that LLCL filters with RLC damping networks have strong attenuation characteristics near the negative resonant peak frequency. To fully guarantee the performance of this LLCL filter, the modified negative resonant peak frequency of the LLCL filter is still set at the frequency with the maximum harmonic amplitude of the inverter output voltage. In other words, the modified negative resonant peak frequency in non-initial iterations is set to the target frequency.

[0132] In S130, in a specific implementation, the positive resonance peak frequency of the LLCL filter is calculated based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor. For example, based on a calculation formula for the positive resonance peak frequency of the LLCL filter, the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor are substituted into the calculation formula for the positive resonance peak frequency, thereby calculating the positive resonance peak frequency of the LLCL filter. This positive resonance peak frequency can be used to determine the RLC damping network parameter values in subsequent steps.

[0133] More specifically, the positive resonant peak frequency of the LLCL filter is calculated based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor, including:

[0134] Based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor, the positive resonance peak frequency is calculated using the third calculation formula;

[0135] The third calculation formula is shown in formula (3):

[0136]

[0137] Wherein, formula (3) is the expression of the positive resonance peak frequency of LLCL filter. In formula (3), f r+ is the positive resonance peak frequency, Cf is the filter capacitor, L1 is the filter inductor on the inverter side, L2 is the filter inductor on the grid side, L f is the filter branch inductor.

[0138] In this way, the above parameters, namely, filter capacitor, inverter-side filter inductor, grid-side filter inductor, and filter branch inductor, are reasonably introduced into the calculation of the positive resonance peak frequency of the LLCL filter through the above formula (3). This can fully guarantee the reliability of the calculation result of the positive resonance peak frequency, thereby facilitating the accurate determination of the subsequent RLC damping network parameter values and ultimately improving the reliability of the overall LLCL filter design process.

[0139] In S140, during specific implementation, the damping resistance, damping inductance, and damping capacitance of the RLC damping network are calculated based on the positive resonance peak frequency, the filter capacitance, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistance, and the second value range constraint of the quality factor of the RLC damping network.

[0140] In this embodiment, after the positive resonance peak frequency is calculated, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistor, and the second value range constraint of the quality factor of the RLC damping network are set by combining the relevant performance requirements of the RLC damping network in the engineering design requirements of the actual LLCL filter.

[0141] In this way, by combining these constraints to parameterize the RLC damping network in the LLCL filter, it can be fully guaranteed that the resulting RLC damping network can effectively suppress the positive resonance peak of the LLCL filter while taking into account the robustness and damping characteristics of the RLC damping network.

[0142] Specifically, optionally, based on the positive resonance peak frequency, the filter capacitor, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistor, and the second value range constraint of the quality factor of the RLC damping network, the damping resistance, damping inductance, and damping capacitance of the RLC damping network are calculated, including:

[0143] Calculate the damping resistance based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint;

[0144] Based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, the damping inductor and the damping capacitor are calculated.

[0145] More specifically, optionally, the damping resistance is calculated based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint, including:

[0146] The target impedance is calculated based on the inverse of the product of the positive resonance peak frequency and the filter capacitance;

[0147] Based on the target impedance and the first value range constraint, a damping resistance is calculated;

[0148] The first value range constraint includes: the value of the damping resistance is 1 / 5 to 1 / 3 of the target impedance.

[0149] In one example, f r+ is the positive resonance peak frequency, C f is the filter capacitor. f *2πf r+ ) calculates the target impedance and sets the damping resistance R according to the first value range constraint d The value of is 1 / 5 to 1 / 3 of the target resistance, for example, 1 / 4 of 1 / (C f *2πf r+ The setting of the first value range constraint can ensure that the RLC damping network can effectively suppress the resonance peak of the LLCL filter, thereby improving the stability and filtering performance of the system, while also avoiding unnecessary power loss and energy loss caused by setting the damping resistance too large.

[0150] By combining the previously calculated positive resonance peak frequency and filter capacitance, a reliable and reasonable calculation of the damping resistor in the RLC damping network is achieved, while fully satisfying the engineering constraints of the damping resistor. This damping resistor effectively improves the performance of the LLCL filter, suppressing the resonance peak while maintaining good high-frequency filtering capability and system stability, while also reducing unnecessary power loss.

[0151] According to some embodiments of the present application, optionally, the damping inductance and the damping capacitance are calculated based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, including:

[0152] Based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, the damping inductor and the damping capacitor are calculated using the fourth calculation formula and the fifth calculation formula;

[0153] The fourth calculation formula is shown in formula (4):

[0154]

[0155] The fifth calculation formula is shown in formula (5):

[0156]

[0157] Wherein, formula (4) is the expression of the resonant frequency of the RLC damping network, and formula (5) is the expression of the quality factor of the RLC damping network. In the above formulas (4) and (5), f n is the resonant frequency of the RLC damping network, Q is the quality factor of the RLC damping network, L d is the damping inductance, C d is the damping capacitor, R d is the damping resistor;

[0158] The resonant frequency of the RLC damping network is constrained to be consistent with the positive resonance peak frequency.

[0159] The second value range constraint includes: the value range of the quality factor is set to 1 to 1.5.

[0160] In this embodiment, by setting the resonant frequency value constraint for the RLC damping network, the resonant frequency of the RLC damping network is set to be consistent with the positive resonant peak frequency. As a result, the resulting RLC damping network can provide effective damping at the resonant peak, thereby effectively suppressing the positive resonant peak frequency of the LLCL filter. This constraint setting can effectively suppress overshoot and oscillation in the system, improving system stability.

[0161] At the same time, by setting a second value range constraint for the quality factor of the RLC damping network, the quality factor range is set to 1 to 1.5, for example, a quality factor of 1.3 is selected. This balances the robustness and damping characteristics of the RLC damping network. This constraint sets a moderate quality factor range, thereby avoiding the high energy loss and oscillation risk associated with an excessively high quality factor, while ensuring the stability of the RLC damping network near the resonant frequency.

[0162] In this way, through the above-mentioned constraints on the resonant frequency value of the RLC damping network and the second value range constraint of the quality factor, and based on the calculation expression of the resonant frequency of the RLC damping network and the calculation expression of the quality factor provided by the above formulas (4) and (5), the damping resistance and the positive resonance peak frequency are substituted into the above formulas (4) and (5), and the unknown damping inductance and damping capacitance in the RLC damping network can be effectively calculated.

[0163] In this embodiment, by combining the damping resistance and positive resonant peak frequency calculated above, reliable and reasonable calculation of the damping capacitance and damping inductance in the RLC damping network is achieved, while fully satisfying the constraints on the resonant frequency and quality factor of the RLC damping network. The resulting RLC damping network effectively suppresses the resonant peak, optimizes filtering performance, improves system stability, and reduces design complexity.

[0164] In S150, during specific implementation, when the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, the filter capacitor and / or the inverter-side filter inductor are updated, and the process jumps to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency for iteration until the target parameters meet the grid-connected current harmonic standard.

[0165] Among them, the target parameters include filter capacitor, inverter side filter inductor, grid side filter inductor, filter branch inductor, damping resistor, damping inductor and damping capacitor.

[0166] In this embodiment, after determining the filter component parameters of the LLCL filter with an RLC damping network, it is necessary to ensure that the LLCL filter parameter design in the current iteration meets the grid current harmonic requirements to ensure high inverter output current quality and system stability. The grid current harmonic requirements can be based on domestic and international grid current standards such as IEEE std519-2014 or GBT 14549-1993 "Power Quality Public Grid Harmonics."

[0167] Therefore, if the verification finds that the target parameters in the current iteration round do not meet the grid-connected current harmonic standards, the filter capacitor and / or the inverter-side filter inductor are updated, and the process jumps to step S120 for iteration.

[0168] By iteratively executing steps S120 to S150, the filter parameters are continuously updated and optimized until the target parameters obtained in the current iteration round meet the grid-connected current harmonic standards. In this case, the iteration is terminated, the parameter design process for the LLCL filter ends, and the target parameters in the current iteration round are determined to be the desired LLCL filter design parameters.

[0169] This solution allows for iterative updates of the overall filter component parameters, by selectively updating the filter capacitor and / or inverter-side filter inductor if component parameters do not meet the grid-connected current harmonic standards. This design optimizes the LLCL filter parameters during iterative parameter updates, ultimately achieving LLCL filter parameters that meet the grid-connected current harmonic standards.

[0170] Moreover, since the embodiment of this scenario can adopt the method of gradually iteratively verifying by slightly increasing the filtering parameters during the parameter iterative update design process, it is possible to reduce the parameter value of the final filter element as much as possible while meeting the grid-connected current harmonic standard, effectively avoiding over-configuration of the LLCL filter capacity, thereby effectively reducing the volume and cost of the LLCL filter, realizing the optimization of the cost and volume of the LLCL filter, and contributing to the widespread promotion and application of LLCL filters in the industry.

[0171] According to some embodiments of the present application, optionally, after calculating the damping resistance, damping inductance, and damping capacitance of the RLC damping network, the LLCL filter design method further includes:

[0172] Based on the target parameters of the current iteration round and the transfer function expression of the LLCL filter from the inverter voltage to the grid current, determine whether the target parameters meet the grid current harmonic standards;

[0173] The transfer function expression is shown in the sixth calculation formula, which is shown in formula (6):

[0174]

[0175] Among them, formula (6) is the transfer function expression of LLCL filter from inverter voltage to grid current. In the above formula (6), G LLCL_RLC is the transfer function of LLCL filter from inverter voltage to grid current, L d is the damping inductance, C d is the damping capacitor, R d is the damping resistor, C f is the filter capacitor, L1 is the filter inductor on the inverter side, L2 is the filter inductor on the grid side, L f is the filter branch inductance, and s is the complex frequency variable.

[0176] It should be noted that in the LLCL filter transfer function, the parameter s is a complex frequency variable used for Laplace transform. It is a complex number and is usually expressed as s = σ + jω.

[0177] In this embodiment, by substituting the filter capacitor, inverter-side filter inductor, grid-side filter inductor, filter branch inductor, damping resistor, damping inductor, and damping capacitor in the current iteration round into the above formula (6), the amplitude-frequency and phase-frequency characteristics of the LLCL filter from the inverter voltage to the grid-connected current can be analyzed, thereby verifying whether the current target parameters meet the grid-connected current harmonic standards.

[0178] It should be added that, in combination with the actual grid-connected current harmonic requirements, when verifying whether the grid-connected current harmonic standards are met, the amplitude-frequency characteristics of the LLCL filter from the inverter voltage to the grid-connected current can be analyzed and judged in detail.

[0179] And, in a more specific embodiment, when determining whether the target parameters meet the grid-connected current harmonic standards based on the above-mentioned transfer function expression, it is possible to draw a Bode diagram to achieve intuitive and rapid observation and analysis of its amplitude-frequency characteristics and phase-frequency characteristics, thereby fully verifying whether the current target parameters meet the grid-connected current harmonic standards.

[0180] When drawing the Bode diagram corresponding to the above transfer function expression, manual calculation and drawing can be performed, or professional software tools (such as MATLAB, Python's Matplotlib library, etc.) can be used, and no strict restrictions are made here.

[0181] According to some embodiments of the present application, optionally, updating the filter capacitor and / or the inverter-side filter inductor includes:

[0182] When the filter capacitance in the current iteration round is less than the upper limit of the filter capacitance, the filter capacitance is increased according to the preset first step value;

[0183] And / or, when the inverter-side filter inductance in the current iteration round is less than the inverter-side filter inductance upper limit, the inverter-side filter inductance is increased according to a preset second step value.

[0184] In this embodiment, the step value of the filter capacitor is set to the first step value ΔC f The step value of the inverter-side filter inductor is set to a second step value ΔL1. If it is determined that the filtering parameters in the LLCL filter do not meet the grid-connected current harmonic standard, the filter capacitor and / or the inverter-side filter inductor are increased according to the corresponding step value.

[0185] It should be noted that in order to fully reduce the size and cost of the LLCL filter, thereby optimizing the cost and size of the LLCL filter, the upper limit value of the filter capacitor C can be pre-set. f_max and the upper limit value L of the inverter side filter inductance 1_max , to avoid over-configuration of filter component parameters, and to avoid excessive size and cost of filter components. Before a specific iterative update, determine whether the filter capacitor and inverter-side filter inductor are less than their upper limit values. If they are less than their upper limit values, the parameters can be updated normally according to the corresponding step value. When one of the filter components, the filter capacitor and the inverter-side filter inductor, increases to its upper limit value, stops increasing the parameter value of the filter component and only increases the value of the other filter component.

[0186] For example, when it is necessary to increase the filter capacitor C f Before, first determine whether the filter capacitance is less than the filter capacitance upper limit C f_max If the filter capacitor is less than the upper limit of the filter capacitor C f <C f_max , then it is allowed to follow the first step value ΔC f Increase the filter capacitor C f =C f +ΔC f , to achieve the filter capacitor C f If the filter capacitor Cf The filter capacitor does not meet the C f <C f_max , and the inverter side filter inductor meets L1 <L 1_max , it is allowed to increase the inverter side filter inductance L1=L1+ΔL1 according to the second step value ΔL1.

[0187] To facilitate understanding of the LLCL filter design method provided in the above embodiment, the above method is described below using a specific scenario embodiment. Figure 3 This is a flow chart of a scenario embodiment of the LLCL filter design method provided in one embodiment of the present application. This scenario embodiment proposes an LLCL filter design method that, on the one hand, can meet the grid-connected current harmonic requirements of actual inverters, and on the other hand, can optimize the parameter values of the filter elements in the LLCL filter.

[0188] The proposed LLCL filter design method is described below. In the LLCL filter design method, the following six constraints are first set:

[0189] The first constraint: From the characteristics of LLCL filter, it can be seen that it has a strong attenuation characteristic near the negative resonance peak frequency band, so the negative resonance peak frequency f of LLCL filter is set to r- And the modified negative resonant peak frequency f of the LLCL filter r-_actual The first constraint condition for LLCL filter design is set at the frequency where the harmonic amplitude of the inverter output voltage is the largest. The frequency where the harmonic amplitude of the inverter output voltage is the largest may correspond to the target frequency in the aforementioned embodiment.

[0190] Second constraint: For large-capacity inverters, they are usually connected to the grid through a grid-connected transformer. In this case, the grid-side filter inductor L2 is implemented using the transformer leakage inductance. This is the second constraint of the LLCL filter.

[0191] The third constraint: The RLC damping network is used to suppress the positive resonance peak frequency of the LLCL filter, so the resonant frequency of the RLC damping network is f n It should be consistent with the LLCL filter’s positive resonant peak frequency f r+ This is the third constraint condition for LLCL filter design, which corresponds to the resonant frequency value constraint of the RLC damping network in the aforementioned embodiment.

[0192] Fourth constraint: The damping resistor Rd is set to the positive resonance peak frequency f r+ Filter capacitor C fThe corresponding impedance is 1 / 5 to 1 / 3, which is the fourth constraint condition for LLCL filter design. The fourth constraint condition may correspond to the first value range constraint of the damping resistor in the aforementioned embodiment.

[0193] Fifth Constraint: To balance the robustness and damping characteristics of the RLC damping network, the quality factor Q is set between 1 and 1.5. This is the fifth constraint in LLCL filter design. This fifth constraint corresponds to the second value range constraint for the quality factor of the RLC damping network in the aforementioned embodiment.

[0194] Constraint 6: The final designed filter parameters, i.e., the target parameters in the aforementioned embodiment, including the filter capacitor, inverter-side filter inductor, grid-side filter inductor, filter branch inductor, damping resistor, damping inductor, and damping capacitor, must meet IEEE std 519-2014 or GBT 14549-1993 "Power Quality Public Grid Harmonics"

[0195] The sixth constraint of LLCL filter is the grid-connected current harmonic standard at home and abroad.

[0196] According to the first to sixth constraints mentioned above, this scenario embodiment proposes to Figure 3 The design process shown in the figure is used to carry out parameter optimization design of LLCL filter. Figure 3 For understanding, this scenario embodiment may specifically include the following steps:

[0197] Step 1: Based on the first constraint, determine the negative resonance peak frequency point f according to the inverter voltage harmonic amplitude-frequency characteristics. r- In the initial iteration round, determine the initial value of the filter capacitor C f =0.02C b , the initial value of the inverter side filter inductor L1=0.02L b Among them, C b L is the capacitance value corresponding to the rated impedance of the system at the power frequency, which corresponds to the reference capacitance value in the above embodiment; b is the inductance value corresponding to the rated impedance of the system at the power frequency, which corresponds to the reference inductance value in the above embodiment. The system here can be understood as the target power system in the above embodiment, which corresponds to the LLCL filter. In the initial iteration round, based on the above first constraint condition, the filter branch inductance L of the LLCL filter is calculated using formula (1): f .

[0198] Step 2: Next, the positive resonance peak frequency f of the LLCL filter is calculated based on the second constraint and formula (3): r+It should be noted that after the grid-side filter inductance L2 is initially obtained as the transformer leakage inductance according to the second constraint condition, in the subsequent iteration process, L2 = transformer leakage inductance can be directly substituted into the subsequent parameter calculation as a fixed known quantity to reduce iterative repetition operations.

[0199] Step 3: Based on the fourth constraint, calculate the damping resistance R in the RLC damping network. d .

[0200] Step 4: Based on the third and fifth constraints, the damping inductance L in the RLC damping network is calculated using formulas (4) and (5). d and damping capacitor C d .

[0201] Step 5. At this point, the first iteration design of all filter parameters is completed, that is, the first iteration round of LLCL filter design is completed. Next, according to the sixth constraint condition, the Bode diagram is drawn in combination with formula (6) to verify whether the seven filter parameters obtained in the above steps meet the grid current harmonic standard. The seven filter parameters are the target parameters in the above embodiment, specifically including the filter capacitor C f , inverter side filter inductor L1, grid side filter inductor L2, filter branch inductor L f , damping resistor R d , damping inductance L d and damping capacitor C d .

[0202] It should be noted that once the LLCL filter parameters are determined to meet the grid-connected current harmonic standards, the LLCL filter parameter design is complete, and the LLCL filter design process ends. However, in practice, because the initial values of the filter capacitor and the inverter-side filter inductor are typically small, the filter parameter design in the initial iteration may not meet the grid-connected current harmonic standards for low-switching-frequency grid-connected inverters.

[0203] Step 6: If it is determined that the filter parameters in the LLCL filter do not meet the grid-connected current harmonic standard, the filter capacitor and / or the inverter-side filter inductor are increased according to a certain step value. For example, the step value of the filter capacitor is set to the first step value ΔC. f ; Set the step value of the inverter side filter inductor to the second step value ΔL1.

[0204] When one of the filter components increases to its upper limit value (filter capacitor upper limit value C f_max Or the upper limit value of the inverter side filter inductance L 1_max), stop increasing the value of the filter component and only increase the value of another filter component. In this way, in a non-initial iteration round, based on the updated filter capacitor and / or inverter-side filter inductor, combined with the first constraint condition, the filter branch inductance L in the new iteration round is calculated by the above formula (2): f .

[0205] It should be noted that Figure 3 The parameter update method for the filter capacitor and the inverter-side filter inductor shown is merely an example. In some embodiments, a determination of whether the inverter-side filter inductor is equal to its upper limit value and a parameter update may be performed before the determination of whether the filter capacitor is equal to its upper limit value and a parameter update. Alternatively, the determination of whether the filter capacitor and the inverter-side filter inductor are equal to their upper limit values and the corresponding parameter updates may be performed simultaneously.

[0206] In other feasible embodiments, either the filter capacitor or the inverter-side filter inductor may be selectively updated in one round of iteration, which is not strictly limited in this embodiment.

[0207] Step 7: Repeat the iterative process of steps 2 to 6 until the filtering parameters of the LLCL filter finally meet the grid-connected current harmonic standard. The LLCL filter design process ends and the filtering parameters of the LLCL filter that meet the grid-connected current harmonic standard are obtained.

[0208] In this embodiment scenario, based on the aforementioned design constraints and design process for an LLCL filter with an RLC damping network, LLCL filter parameters that meet the grid-connected current harmonic standards can ultimately be designed. Furthermore, because this embodiment scenario employs a design method that incrementally increases the filter parameters during the parameter iterative update design process, the parameter values of the final filter components can be minimized while still meeting the grid-connected current harmonic standards. This effectively avoids over-configuration of the LLCL filter capacity, thereby effectively reducing the size and cost of the LLCL filter and achieving cost and volume optimization for the LLCL filter.

[0209] Based on the LLCL filter design method provided in the above embodiment, for the same inventive concept, the present application also provides an LLCL filter design device corresponding to the above LLCL filter design method. Figure 4 The LLCL filter design device is introduced in detail.

[0210] Figure 4 A structural schematic diagram of an LLCL filter design device provided in an embodiment of the present application is shown. The LLCL filter is provided with an RLC damping network. The LLCL filter is used to be arranged between the inverter voltage output terminal and the power grid.

[0211] Figure 4 The LLCL filter design apparatus 400 shown includes:

[0212] A first acquisition module 410 is configured to acquire an initial filter capacitor, an initial inverter-side filter inductor, a grid-side filter inductor, and a target frequency of the LLCL filter, where the target frequency is determined based on an amplitude-frequency characteristic of an inverter voltage harmonic corresponding to an inverter voltage output terminal.

[0213] A first calculation module 420 is configured to calculate the filter branch inductance of the LLCL filter based on the filter capacitance and the target frequency;

[0214] A second calculation module 430 is configured to calculate the positive resonance peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor;

[0215] a third calculation module 440 configured to calculate the damping resistance, damping inductance, and damping capacitance of the RLC damping network based on the positive resonance peak frequency, the filter capacitance, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistance, and the second value range constraint of the quality factor of the RLC damping network;

[0216] An iterative update module 450 is configured to update the filter capacitor and / or the inverter-side filter inductor if the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, and jump to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard;

[0217] Among them, the target parameters include filter capacitor, inverter side filter inductor, grid side filter inductor, filter branch inductor, damping resistor, damping inductor and damping capacitor.

[0218] An embodiment of the present application provides an LLCL filter design device that, by configuring corresponding functional modules, comprehensively determines the specific parameters of each filter component in the LLCL filter based on the harmonic characteristics of the inverter output voltage and the grid-connected current harmonic standards, combined with the engineering constraints of different component parameters. Furthermore, if the component parameters do not meet the grid-connected current harmonic standards, this solution can select the filter capacitor and / or inverter-side filter inductor for update to iteratively update the overall filter component parameters. In this way, this design solution optimizes the parameter values of the LLCL filter during iterative parameter updates.

[0219] Compared with the related technologies that have not yet formed a clear and feasible parameter design process, the LLCL filter design method provided in the embodiment of the present application provides clear and feasible parameter design constraints and optimization processes. It can fully realize the parameter value design optimization of the filter elements in the LLCL filter on the premise that the filter element parameters meet the grid-connected current harmonic requirements, so as to minimize the parameter value of the filter element, thereby avoiding over-configuration of the LLCL filter capacity, and thus effectively realizing the optimization of the cost and volume of the LLCL filter, which is conducive to the widespread promotion and application of LLCL filters in the industry.

[0220] Based on the LLCL filter design method provided in the above embodiment, for the same inventive concept, the present application also provides an LLCL filter design device corresponding to the above LLCL filter design method. Figure 5 A detailed introduction to LLCL filter design equipment is given.

[0221] See below Figure 5 , Figure 5 Schematic diagram of the structure of an LLCL filter design device provided in one embodiment of the present application.

[0222] The LLCL filter design apparatus may include a processor 501 and a memory 502 storing computer program instructions.

[0223] Specifically, the processor 501 may include a central processing unit (CPU), or an application-specific integrated circuit (ASIC), or may be configured to implement one or more integrated circuits of the embodiments of the present application.

[0224] The memory 502 may include a large capacity memory for data or instructions. By way of example and not limitation, the memory 502 may include a hard disk drive (HDD), a floppy disk drive, a flash memory, an optical disk, a magneto-optical disk, a magnetic tape, or a universal serial bus (USB) drive, or a combination of two or more of these. Where appropriate, the memory 502 may include removable or non-removable (or fixed) media. Where appropriate, the memory 502 may be inside or outside the integrated gateway disaster recovery device. In a specific embodiment, the memory 502 is a non-volatile solid-state memory.

[0225] The memory may include read-only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical or other physical / tangible memory storage devices. Thus, generally, the memory includes one or more tangible (non-transitory) computer-readable storage media (e.g., memory devices) encoded with software including computer-executable instructions, and when the software is executed (e.g., by one or more processors), it is operable to perform the operations described with reference to the method according to an aspect of the present disclosure.

[0226] The processor 501 reads and executes computer program instructions stored in the memory 502 to implement any one of the LLCL filter design methods in the above embodiments.

[0227] In one example, the data LLCL filter design device may further include a communication interface 503 and a bus 510. Figure 5 As shown, the processor 501, the memory 502, and the communication interface 503 are connected via a bus 510 and communicate with each other.

[0228] The communication interface 503 is mainly used to implement communication between various modules, devices, units and / or equipment in the embodiments of the present application.

[0229] Bus 510 includes hardware, software, or both that couples the components of the LLCL filter design device to each other. By way of example and not limitation, the bus may include an Accelerated Graphics Port (AGP) or other graphics bus, an Enhanced Industrial Standard Architecture (EISA) bus, a Front Side Bus (FSB), a HyperTransport (HT) interconnect, an Industrial Standard Architecture (ISA) bus, an InfiniBand interconnect, a Low Pin Count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a Serial Advanced Technology Attachment (SATA) bus, a Video Electronics Standards Association Local (VLB) bus, or other suitable buses or a combination of two or more of these. Where appropriate, bus 510 may include one or more buses. Although the present application describes and illustrates a specific bus, the present application contemplates any suitable bus or interconnect.

[0230] The LLCL filter design device executes the LLCL filter design method in the embodiment of the present application, thereby realizing the LLCL filter design method described in the embodiment of the present application.

[0231] In addition, in conjunction with the LLCL filter design method in the above embodiments, embodiments of the present application may provide a computer storage medium for implementation. The computer storage medium stores computer program instructions; when the computer program instructions are executed by a processor, any of the LLCL filter design methods in the above embodiments is implemented.

[0232] Based on the LLCL filter design method in the above embodiment, an embodiment of the present application provides a computer program product. When the instructions in the computer program product are executed by a processor of an electronic device, the electronic device executes the LLCL filter design method provided in any one of the above embodiments of the present application.

[0233] It should be understood that the present application is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, a detailed description of known methods is omitted here. In the above embodiments, several specific steps are described and illustrated as examples. However, the method process of the present application is not limited to the specific steps described and illustrated. Those skilled in the art can make various changes, modifications, and additions, or change the order of the steps after understanding the spirit of the present application.

[0234] The functional blocks shown in the above-described block diagram can be implemented as hardware, software, firmware or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of the present application are programs or code segments that are used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link by a data signal carried in a carrier wave. "Machine-readable medium" can include any medium that can store or transmit information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROMs, flash memories, erasable ROMs (EROMs), floppy disks, CD-ROMs, optical disks, hard disks, optical fiber media, radio frequency (RF) links, etc. The code segment can be downloaded via a computer network such as the Internet, an intranet, etc.

[0235] It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, this application is not limited to the order of the above steps. In other words, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0236] Aspects of the present disclosure have been described above with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present disclosure. It should be understood that each box in the flowchart and / or block diagram and the combination of each box in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer or other programmable data processing device to produce a machine so that these instructions executed by the processor of the computer or other programmable data processing device enable the implementation of the function / action specified in one or more boxes of the flowchart and / or block diagram. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor or a field programmable logic circuit. It is also understood that each box in the block diagram and / or flowchart and the combination of the boxes in the block diagram and / or flowchart can also be implemented by dedicated hardware that performs the specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions.

[0237] The above description is only a specific embodiment of the present application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the scope of protection of the present application.

Claims

1. A LLCL filter design method, characterized in that: An LLCL filter is provided with an RLC damping network, and the LLCL filter is used to be provided between an inverter voltage output terminal and a power grid; the method comprises: Obtaining an initial filter capacitor, an initial inverter-side filter inductor, a grid-side filter inductor, and a target frequency of the LLCL filter, where the target frequency is determined based on an inverter voltage harmonic amplitude-frequency characteristic corresponding to the inverter voltage output terminal; Calculating a filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency; Calculating a positive resonant peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor; Calculating a damping resistor, a damping inductor, and a damping capacitor of the RLC damping network based on the positive resonance peak frequency, the filter capacitor, a resonant frequency value constraint of the RLC damping network, a first value range constraint of the damping resistor, and a second value range constraint of the quality factor of the RLC damping network; If the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, updating the filter capacitor and / or the inverter-side filter inductor, and jumping to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard; The target parameters include the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, the filter branch inductor, the damping resistor, the damping inductor, and the damping capacitor.

2. The method according to claim 1, characterized in that The calculating, based on the filter capacitor and the target frequency, the filter branch inductance of the LLCL filter includes: In an initial iteration round, the filter branch inductance is calculated using a first calculation formula based on the filter capacitor and the target frequency; The first calculation formula includes: Among them, f r- is the negative resonance peak frequency of the LLCL filter, the value of the negative resonance peak frequency is the target frequency, L f is the filter branch inductance, C f is the filter capacitor.

3. The method according to claim 1, characterized in that The calculating, based on the filter capacitor and the target frequency, the filter branch inductance of the LLCL filter includes: In a non-initial iteration round, the filter branch inductance is calculated using a second calculation formula based on the filter capacitor, the damping capacitor in the previous iteration round, and the target frequency; The second calculation formula includes: Among them, f r-_actual is the corrected negative resonance peak frequency of the LLCL filter, the value of the corrected negative resonance peak frequency is the target frequency, C eq is the equivalent capacitance, L f is the filter branch inductance, C f is the filter capacitor, C d is the damping capacitor in the previous iteration round.

4. The method according to claim 1, wherein The calculating the positive resonance peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor includes: The positive resonance peak frequency is calculated by a third calculation formula based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor; The third calculation formula includes: Among them, f r+ is the positive resonance peak frequency, C f is the filter capacitor, L1 is the inverter side filter inductor, L2 is the grid side filter inductor, L f is the inductance of the filter branch.

5. The method according to claim 1, wherein The calculating of the damping resistance, damping inductance, and damping capacitance of the RLC damping network based on the positive resonance peak frequency, the filter capacitor, the resonant frequency value constraint of the RLC damping network, the first value range constraint of the damping resistor, and the second value range constraint of the quality factor of the RLC damping network includes: Calculating the damping resistor based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint; The damping inductor and the damping capacitor are calculated based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint.

6. The method according to claim 5, characterized in that The calculating the damping resistance based on the positive resonance peak frequency, the filter capacitance, and the first value range constraint includes: Calculating a target impedance based on the inverse of the product of the positive resonance peak frequency and the filter capacitance; Calculating the damping resistor based on the target impedance and the first value range constraint; The first value range constraint includes: the value of the damping resistor is 1 / 5 to 1 / 3 of the target impedance.

7. The method according to claim 5, characterized in that The calculating the damping inductor and the damping capacitor based on the damping resistance, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint includes: Based on the damping resistor, the positive resonance peak frequency, the resonant frequency value constraint of the RLC damping network, and the second value range constraint, the damping inductor and the damping capacitor are calculated using a fourth calculation formula and a fifth calculation formula; The fourth calculation formula includes: The fifth calculation formula includes: Among them, f n is the resonant frequency of the RLC damping network, Q is the quality factor of the RLC damping network, L d is the damping inductor, C d is the damping capacitor, R d is the damping resistor; The resonant frequency value constraint of the RLC damping network is: the resonant frequency value of the RLC damping network is consistent with the positive resonance peak frequency; The second value range constraint includes: the value range of the quality factor is set to 1 to 1.

5.

8. The method according to claim 1, characterized in that After obtaining the damping resistance, damping inductance, and damping capacitance of the RLC damping network by calculation, the method further includes: Determining whether the target parameter meets the grid-connected current harmonic standard based on the target parameter of the current iteration round and a transfer function expression of the LLCL filter from the inverter voltage to the grid-connected current; The transfer function expression is shown in the sixth calculation formula, which includes: Among them, G LLCL_RLC is the transfer function of the LLCL filter from inverter voltage to grid current, L d is the damping inductor, C d is the damping capacitor, R d is the damping resistor, C f is the filter capacitor, L1 is the inverter side filter inductor, L2 is the grid side filter inductor, L f is the filter branch inductance, and s is a complex frequency variable.

9. The method according to any one of claims 1 to 8, characterized in that The updating of the filter capacitor and / or the inverter-side filter inductor includes: When the filter capacitance in the current iteration round is less than the filter capacitance upper limit, increasing the filter capacitance according to a preset first step value; And / or, when the inverter-side filter inductance in the current iteration round is less than the inverter-side filter inductance upper limit, the inverter-side filter inductance is increased according to a preset second step value.

10. The method according to any one of claims 1 to 8, characterized in that Obtaining an initial filter capacitor and an initial inverter-side filter inductor of the LLCL filter, including: Obtaining a reference capacitance value corresponding to the rated impedance of a target power system at the power frequency, and a reference inductance value corresponding to the rated impedance at the power frequency, wherein the power system is the power system corresponding to the LLCL filter; The initial filter capacitor and the initial inverter-side filter inductor are calculated based on the reference capacitance value, the reference inductance value, and a preset filter coefficient.

11. The method according to any one of claims 1 to 8, characterized in that Obtaining the grid-side filter inductance includes: The transformer leakage inductance of the grid-connected transformer in the target power system is obtained, and the transformer leakage inductance is determined as the grid-side filter inductance, where the target power system is the power system corresponding to the LLCL filter.

12. The method according to any one of claims 1 to 8, characterized in that Acquiring the target frequency includes: Obtaining the inverter voltage harmonic amplitude-frequency characteristics corresponding to the inverter voltage output terminal; Based on the inverter voltage harmonic amplitude-frequency characteristics, the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined, and the frequency corresponding to the maximum harmonic amplitude of the inverter side output voltage is determined as the target frequency.

13. An LLCL filter design device, characterized in that: The LLCL filter is provided with an RLC damping network, and the LLCL filter is used to be arranged between the inverter voltage output terminal and the power grid; the device includes: a first acquisition module, configured to acquire an initial filter capacitor, an initial inverter-side filter inductor, a grid-side filter inductor, and a target frequency of the LLCL filter, wherein the target frequency is determined based on an inverter voltage harmonic amplitude-frequency characteristic corresponding to the inverter voltage output terminal; A first calculation module is configured to calculate a filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency; A second calculation module is configured to calculate a positive resonance peak frequency of the LLCL filter based on the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, and the filter branch inductor; a third calculation module, configured to calculate a damping resistance, a damping inductance, and a damping capacitance of the RLC damping network based on the positive resonance peak frequency, the filter capacitance, a resonant frequency value constraint of the RLC damping network, a first value range constraint of the damping resistance, and a second value range constraint of the quality factor of the RLC damping network; an iterative update module, configured to, if the target parameters in the current iteration round do not meet the grid-connected current harmonic standard, update the filter capacitor and / or the inverter-side filter inductor, and jump to the step of calculating the filter branch inductance of the LLCL filter based on the filter capacitor and the target frequency to iterate until the target parameters meet the grid-connected current harmonic standard; The target parameters include the filter capacitor, the inverter-side filter inductor, the grid-side filter inductor, the filter branch inductor, the damping resistor, the damping inductor, and the damping capacitor.

14. An LLCL filter design device, characterized in that: The device includes: a processor and a memory storing computer program instructions; When the processor executes the computer program instructions, the LLCL filter design method according to any one of claims 1 to 12 is implemented.

15. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer program instructions, and when the computer program instructions are executed by a processor, the LLCL filter design method according to any one of claims 1 to 12 is implemented.

16. A computer program product, characterized in that When the instructions in the computer program product are executed by a processor of an electronic device, the electronic device performs the LLCL filter design method according to any one of claims 1 to 12.

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