A design method of integrated filter parameters for a symmetrical hybrid transformer
Patent Information
- Application Number
- CN202611166148.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-03
- Publication Date
- 2026-10-30
AI Technical Summary
通过获取变压器参数、绕组阻抗分配关系、换流器参数及滤波设计参数，实现了变压器参数与两侧换流器滤波设计条件的统一输入。通过由短路电抗确定总漏感并按绕组阻抗分配关系形成两侧绕组漏感，使两侧绕组漏感能够直接作为两侧换流器主滤波电感，减少绕组漏感与外接滤波电感分离设计造成的参数重复。通过依据滤波性能要求确定两侧等效滤波电感，并结合等效负载、目标阻尼比和滤波电容连接方式确定两侧滤波电容，实现了两侧等效滤波电感与两侧滤波电容的联动整定。通过将工频频段、主要谐波频段、开关频率及边带频段和控制带宽频段合并形成禁止谐振频段，能够分别校验第一侧谐振频率和第二侧谐振频率。通过在任一侧谐振频率落入禁止谐振频段时调整两侧等效滤波电感或两侧滤波电容，使输出的滤波参数同时满足滤波性能要求、电容工程约束和两侧谐振避让条件，形成可直接用于两侧换流器滤波配置的滤波参数。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of power electronics technology, and specifically to a method for designing integrated filter parameters for a symmetrical hybrid transformer. Background Technology
[0002] In symmetrical hybrid transformers, the converters on both sides typically require AC-side filter inductors and capacitors to limit switching harmonics, current ripple, and resonant amplification. Current parameter designs often treat the transformer and converter separately: the transformer side is designed with short-circuit impedance based on rated capacity, rated voltage, and short-circuit voltage percentage; the converter side then independently selects external filter inductors and capacitors.
[0003] This approach typically treats winding leakage inductance as a parasitic parameter, failing to incorporate it into the unified calculation as a filter inductance. This easily leads to redundant configuration of external filter inductors, or the equivalent filter inductance deviating from the target value due to the superposition of the actual winding leakage inductance and the designed filter inductance. Some existing designs also rely on single-sided converter parameters or a single resonant frequency for verification, without simultaneously addressing the correspondence between the leakage inductance distribution of both sides of the windings, the switching frequencies of both sides of the converters, the control bandwidth, and the main harmonic frequency bands. When the parameters on both sides are inconsistent, the calculation results of one side cannot fully reflect the resonant frequency of the other side; when the filter capacitor is selected empirically, the resonant frequency may also fall near the power frequency, main harmonics, switching frequency, and sideband or control bandwidth. The aforementioned separate design mechanism can lead to a mismatch between filter parameters and transformer parameters, resulting in insufficient filter attenuation, excessive reactive power capacity, excessive supplementary inductance, or local resonance amplification. Therefore, it is necessary to solve the problems of the lack of unified setting and resonance avoidance verification between the leakage inductance of both sides of the windings, converter parameters, and filter parameters. Summary of the Invention
[0004] This invention addresses the problems existing in the prior art by providing a method for designing integrated filter parameters for a symmetrical hybrid transformer. This method aims to solve at least the problem of how to incorporate the leakage inductance of the windings on both sides into the unified design of the filter parameters of the converters on both sides, and to ensure that the resonant frequencies on both sides avoid the prohibited resonant frequency band while meeting the filter performance requirements and capacitor engineering constraints.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Obtain transformer parameters, winding impedance distribution, converter parameters, and filter design parameters; calculate short-circuit reactance from transformer parameters and determine leakage inductance of both windings according to winding impedance distribution; use the leakage inductance of both windings as the main filter inductance of both converters, and determine the equivalent filter inductance, single-phase equivalent filter capacitance, and filter capacitance of both sides from the filter design parameters; determine the prohibited resonant frequency band from transformer and converter parameters, and determine the resonant frequency of both sides from the equivalent filter inductance and single-phase equivalent filter capacitance of both sides; if the resonant frequency of either side falls into the prohibited resonant frequency band, adjust the equivalent filter inductance or filter capacitance of both sides until the resonant frequency of both sides avoids the prohibited resonant frequency band; output filter parameters.
[0006] In one possible implementation, the symmetrical hybrid transformer includes a two-winding transformer and two converters connected in series with the two windings of the two-winding transformer respectively; the transformer parameters include rated capacity, rated voltage, short-circuit voltage percentage, rated frequency and turns ratio; the converter parameters include switching frequency and control bandwidth; the filter design parameters include equivalent load, target damping ratio, filter performance requirements and filter capacitor connection method; the filter performance requirements include at least one of harmonic attenuation requirements at the switching frequency and current ripple limit; and the winding impedance distribution relationship is used to characterize the distribution ratio of total leakage inductance between the two windings of the two-winding transformer.
[0007] In one possible implementation, the short-circuit reactance is calculated based on transformer parameters, and the leakage inductance of the two windings is obtained according to the winding impedance distribution relationship. This includes: calculating the short-circuit reactance based on the rated capacity, rated voltage, and short-circuit voltage percentage, and converting the short-circuit reactance to a preset reference side according to the turns ratio; determining the total leakage inductance based on the converted short-circuit reactance and rated frequency, and distributing the total leakage inductance to the leakage inductance of the two windings according to the winding impedance distribution relationship.
[0008] In one possible implementation, determining the equivalent filter inductance on both sides according to filter design parameters includes: determining a first-side target filter inductance and a second-side target filter inductance according to filter performance requirements, wherein the leakage inductance of the windings on both sides includes the leakage inductance of the first-side winding and the leakage inductance of the second-side winding; if the leakage inductance of the first-side winding is less than the first-side target filter inductance, determining a first-side supplementary inductance based on the difference between the two; if the leakage inductance of the first-side winding is not less than the first-side target filter inductance, setting the first-side supplementary inductance to zero; if the leakage inductance of the second-side winding is less than the second-side target filter inductance, determining a second-side supplementary inductance based on the difference between the two; if the leakage inductance of the second-side winding is not less than the second-side target filter inductance, setting the second-side supplementary inductance to zero; determining the sum of the first-side winding leakage inductance and the first-side supplementary inductance as the first-side equivalent filter inductance, and determining the sum of the second-side winding leakage inductance and the second-side supplementary inductance as the second-side equivalent filter inductance, wherein the equivalent filter inductance on both sides includes the first-side equivalent filter inductance and the second-side equivalent filter inductance.
[0009] In one possible implementation, the filter capacitors on both sides are determined based on the equivalent filter inductances on both sides and the filter design parameters, including: determining the single-phase equivalent filter capacitors on both sides based on the equivalent filter inductances on both sides, the equivalent load, and the target damping ratio; and determining the filter capacitors on both sides based on the single-phase equivalent filter capacitors on both sides, the filter capacitor connection method, and capacitor engineering constraints, wherein the capacitor engineering constraints include at least one of rated voltage constraints, rated current constraints, and reactive power capacity constraints.
[0010] In one possible implementation, the filter capacitors on both sides are determined based on the single-phase equivalent filter capacitors, the filter capacitor connection method, and capacitor engineering constraints. This includes: when the filter capacitor connection method is an independent connection for each phase or a star connection, the single-phase equivalent filter capacitors on both sides are determined as the branch capacitors of each phase on each side, and when the branch capacitors of each phase on each side meet the capacitor engineering constraints, the branch capacitors of each phase on each side are determined as the filter capacitors on both sides; when the filter capacitor connection method is a delta connection, the single-phase equivalent filter capacitors on both sides are calculated according to the voltage relationship between the line voltage and the phase voltage to obtain the delta branch capacitors on each side, and when the delta branch capacitors on each side meet the capacitor engineering constraints, the delta branch capacitors on each side are determined as the filter capacitors on both sides.
[0011] In one possible implementation, the prohibited resonant frequency band is obtained from the transformer parameters and converter parameters, including: determining the power frequency band and the main harmonic frequency band based on the rated frequency, determining the switching frequency and the sideband frequency band based on the switching frequency, and determining the control bandwidth frequency band based on the control bandwidth; and merging the power frequency band, the main harmonic frequency band, the switching frequency and the sideband frequency band and the control bandwidth frequency band to obtain the prohibited resonant frequency band.
[0012] In one possible implementation, the equivalent filter inductance on both sides includes a first-side equivalent filter inductance and a second-side equivalent filter inductance, and the single-phase equivalent filter capacitor on both sides includes a first-side single-phase equivalent filter capacitor and a second-side single-phase equivalent filter capacitor; the first-side resonant frequency is determined based on the first-side equivalent filter inductance and the first-side single-phase equivalent filter capacitor, and the second-side resonant frequency is determined based on the second-side equivalent filter inductance and the second-side single-phase equivalent filter capacitor, and the resonant frequencies on both sides include the first-side resonant frequency and the second-side resonant frequency.
[0013] In one possible implementation, adjusting the equivalent filter inductance or filter capacitor on both sides includes: adjusting the filter capacitor on both sides according to the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band, to obtain the adjusted filter capacitor on both sides; if the adjusted filter capacitor on both sides meets the capacitor engineering constraints, updating the filter capacitor on both sides based on the adjusted filter capacitor on both sides; if the adjusted filter capacitor on both sides does not meet the capacitor engineering constraints, and adding the equivalent filter inductance on either side can shift the resonant frequency on the same side to a lower frequency direction outside the prohibited resonant frequency band, determining the supplementary inductance on both sides according to the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band, the leakage inductance of the windings on both sides, and the filtering performance requirements, and updating the equivalent filter inductance on both sides based on the supplementary inductance on both sides; if the filter capacitor on both sides is updated, converting the updated filter capacitor on both sides into the updated single-phase equivalent filter capacitor on both sides according to the filter capacitor connection method, and redetermining the resonant frequencies on both sides based on the equivalent filter inductance on both sides and the updated single-phase equivalent filter capacitor on both sides; if the equivalent filter inductance on both sides is updated, redetermining the resonant frequencies on both sides based on the updated equivalent filter inductance on both sides and the single-phase equivalent filter capacitor on both sides; and re-performing resonance avoidance verification according to the prohibited resonant frequency band.
[0014] In one possible implementation, the output of the filter parameters verified by resonance avoidance includes: when the resonant frequencies on both sides avoid the prohibited resonant frequency band, the equivalent filter inductances on both sides meet the filter performance requirements, and the filter capacitors on both sides meet the capacitor engineering constraints, the equivalent filter inductances on both sides and the filter capacitors on both sides are output as filter parameters.
[0015] Compared with the prior art, the present invention has the following beneficial effects: By acquiring transformer parameters, winding impedance distribution relationships, converter parameters, and filter design parameters, a unified input of transformer parameters and filter design conditions for both converters was achieved. By determining the total leakage inductance from the short-circuit reactance and forming the leakage inductance of both windings according to the winding impedance distribution relationship, the leakage inductance of both windings can be directly used as the main filter inductance of both converters, reducing parameter duplication caused by separate design of winding leakage inductance and external filter inductance. By determining the equivalent filter inductance on both sides based on filter performance requirements, and combining the equivalent load, target damping ratio, and filter capacitor connection method to determine the filter capacitors on both sides, the linkage tuning of the equivalent filter inductance and the filter capacitors on both sides was achieved. By merging the power frequency band, main harmonic frequency band, switching frequency, sideband frequency band, and control bandwidth frequency band into a prohibited resonance frequency band, the resonant frequencies of the first and second sides can be verified separately. By adjusting the equivalent filter inductance or filter capacitor on both sides when the resonant frequency on either side falls into the prohibited resonant frequency band, the output filter parameters can simultaneously meet the filter performance requirements, capacitor engineering constraints, and resonant avoidance conditions on both sides, thus forming filter parameters that can be directly used for filter configuration of both converters. Attached Figure Description
[0016] Figure 1 This is a flowchart of the symmetrical hybrid transformer integrated filter parameter design method in an embodiment of the present invention; Figure 2 This is a single-phase topology diagram of the symmetrical hybrid transformer in an embodiment of the present invention; Figure 3 This is a three-phase topology diagram of a symmetrical hybrid transformer in an embodiment of the present invention; Figure 4 This is a diagram of a single-phase equivalent filter circuit in an embodiment of the present invention. Detailed Implementation
[0017] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.
[0018] In this embodiment, the symmetrical hybrid transformer consists of a two-winding transformer and two converters connected in series with the two windings of the two-winding transformer. The parameters processed are the leakage inductance of the two windings, the equivalent filter inductance of the two windings, the filter capacitors of the two windings, and the resonant frequencies of the two windings. The filter parameters correspond to the equivalent filter inductance and filter capacitors used on the AC side of the two converters. The input sources are the rated capacity, rated voltage, short-circuit voltage percentage, rated frequency, and turns ratio of the two-winding transformer, as well as the switching frequency, control bandwidth, and filter design parameters of the two converters. The parameter design process establishes a side-to-side correspondence based on the connection relationship between the two windings and the two converters. The winding impedance distribution relationship is used as the basis for the total leakage inductance distribution, and the equivalent load, target damping ratio, filter performance requirements, and filter capacitor connection method are used as the basis for determining the filter parameters. After the input verification is completed, the transformer parameters are entered into the short-circuit reactance and leakage inductance calculation of both windings. The leakage inductance of both windings serves as the main filter inductance of both converters, further forming the equivalent filter inductance and filter capacitor on both sides. Then, the process of forming the prohibited resonant frequency band, calculating the resonant frequency on both sides, and verifying the resonance avoidance is entered.
[0019] like Figure 1 As shown, a method for designing integrated filter parameters for a symmetrical hybrid transformer includes the following processing steps.
[0020] The integrated filter parameter design method for symmetrical hybrid transformers begins by reading the basic configuration of the dual-winding transformer and the converters on both sides, thus forming transformer parameters, winding impedance distribution relationships, converter parameters, and filter design parameters.
[0021] Transformer parameters are used to determine the short-circuit reactance and leakage inductance of the windings on both sides. The winding impedance distribution relationship is used to limit the distribution of total leakage inductance between the windings on both sides. Converter parameters are used to form the prohibited resonant frequency band. Filter design parameters are used to determine the equivalent filter inductance and filter capacitors on both sides.
[0022] After completing the parameter verification, the transformer parameters, winding impedance distribution relationship, converter parameters, and filter design parameters are collected according to the connection relationship between the windings on both sides and the converters on both sides, forming the input basis required for subsequent calculations of short-circuit reactance, leakage inductance of windings on both sides, equivalent filter inductance on both sides, filter capacitor on both sides, and resonant frequency on both sides.
[0023] like Figure 2 and Figure 3 As shown, in one embodiment, the symmetrical hybrid transformer employs a two-winding transformer and converters on both sides. Figure 2 This illustrates a single-phase topology of a symmetrical hybrid transformer. Figure 3 The diagram illustrates the three-phase topology of a symmetrical hybrid transformer, with the two converters connected in series with the two windings of a two-winding transformer. Parameter readings are performed by establishing a side-to-side correspondence based on the connection relationship between the two windings and the two converters. When the transformer's turns ratio is 1:1 and the impedances of the two windings are consistent, the impedance distribution is determined according to the principle of equal distribution of the total leakage inductance between the two windings. When the turns ratio is not 1:1 or the impedances of the two windings are inconsistent, the winding parameters are converted to a preset reference side, and the distribution ratio is then determined based on the design parameters of the two windings or the decomposition results of short-circuit tests.
[0024] Transformer parameters include rated capacity, rated voltage, short-circuit voltage percentage, rated frequency, and turns ratio. Rated capacity, rated voltage, rated frequency, and turns ratio are obtained from the nameplate parameters or design parameters of the two-winding transformer. The short-circuit voltage percentage is preferentially based on short-circuit test results; if short-circuit test results are not yet available, the design parameters of the two-winding transformer are used. The rated voltage is the rated voltage corresponding to the short-circuit reactance calculation side. The calculated short-circuit reactance is converted to the preset reference side according to the turns ratio. The rated capacity, short-circuit voltage percentage, and rated frequency maintain their corresponding rated values. The form of the rated voltage is consistent with the voltage form used in the short-circuit reactance calculation.
[0025] The converter parameters are determined using the switching frequency and control bandwidth. The switching frequency is read from the modulation settings of both converters, and the control bandwidth is read from the control settings of both converters. When both converters have the same settings, a set of converter parameters is formed. When the two converters have different settings, the switching frequency of the first side, the switching frequency of the second side, the control bandwidth of the first side, and the control bandwidth of the second side are recorded separately to ensure that the prohibited resonant frequency band covers the operating range of both converters. If any switching frequency or control bandwidth is missing, the transmission of converter parameters to subsequent stages is stopped.
[0026] The filter design parameters include equivalent load, target damping ratio, filter performance requirements, and filter capacitor connection method. The equivalent load represents the load impedance determined according to the single-phase equivalent relationship, which is calculated from the rated voltage and rated capacity, or from the voltage and current under actual operating conditions. When multiple operating conditions exist, equivalent loads are formed separately and used for calculating the single-phase equivalent filter capacitors on both sides. The target damping ratio is set according to the damping requirements of the filter network; a target damping ratio of 0.707 is acceptable.
[0027] The filtering performance requirements must meet at least one of the following: harmonic attenuation requirements at the switching frequency and current ripple limits. The harmonic attenuation requirements at the switching frequency are determined by the harmonics allowed to enter the dual-winding transformer from both converters. The current ripple limits are determined by the allowable AC current variation range from both converters. The filter capacitor connection method is selected from independent connection per phase, star connection, and delta connection, for subsequent calculation of the filter capacitors on both sides.
[0028] In a specific set of parameters, the rated voltage is 10 kV, the rated capacity is 1 MVA, the short-circuit voltage percentage is 5%, the rated frequency is 50 Hz, the transformation ratio is 1:1, the switching frequency is 5 kHz, the target damping ratio is 0.707, and the equivalent load is 100 ohms.
[0029] After the parameters are read, the side, reference side, unit, and numerical range are checked. If any necessary parameter is missing or the side relationship is inconsistent, no further input is generated. The verified transformer parameters, winding impedance distribution relationship, converter parameters, and filter design parameters proceed to the calculation stage of short-circuit reactance and leakage inductance of both windings.
[0030] The parameter design process receives transformer parameters, winding impedance distribution relationships, converter parameters, and filter design parameters, and reads rated capacity, rated voltage, short-circuit voltage percentage, rated frequency, and turns ratio from the transformer parameters. Rated capacity, rated voltage, and short-circuit voltage percentage are used to calculate short-circuit reactance; the turns ratio is used to convert the short-circuit reactance to a preset reference side; and the rated frequency is used to convert the converted short-circuit reactance into total leakage inductance.
[0031] After completing the total leakage inductance calculation, the distribution ratio of the total leakage inductance between the two windings of the dual-winding transformer is determined according to the winding impedance distribution relationship, thus obtaining the leakage inductance of the first winding and the second winding. The leakage inductance of both windings is used as the main filter inductance of the converters on both sides, entering the stage of determining the equivalent filter inductance on both sides.
[0032] In one embodiment, the transformer parameters include rated capacity, rated voltage, short-circuit voltage percentage, rated frequency, and turns ratio. The preset reference side is selected from the windings on both sides of the two-winding transformer. When calculating short-circuit reactance, the rated voltage is the rated voltage of the short-circuit reactance calculation side, while the rated capacity remains unchanged with the calculation side; the three-phase parameters are calculated using line voltages. The short-circuit voltage percentage uses short-circuit test data; if short-circuit test data is not yet available, design parameters are used.
[0033] When the winding resistance is negligible compared to the short-circuit reactance, the short-circuit impedance is approximated as the short-circuit reactance, which is calculated using the following formula:
[0034] In the formula, For short-circuit reactance, This represents the percentage of short-circuit voltage. Rated voltage, The rated capacity is used. When the turns ratio is not 1:1, the short-circuit reactance of the non-preset reference side is converted to the preset reference side according to the square of the ratio of the preset reference side rated voltage to the non-preset reference side rated voltage, so that the total leakage inductance and the leakage inductance of both windings adopt the same voltage reference.
[0035] Converting rated frequency to power frequency angular frequency:
[0036] In the formula, It is the power frequency angular frequency. Pi The rated frequency. The total leakage inductance is determined by the converted short-circuit reactance and the power frequency angular frequency according to the following formula:
[0037] In the formula, For total leakage, This is the converted short-circuit reactance. The angular frequency is the power frequency. The total leakage inductance is the sum of the leakage inductance of both windings after being referred to the preset reference side.
[0038] The winding impedance distribution relationship is determined based on the design leakage reactance ratio of the two windings or the decomposition results of the short-circuit test, and is used to distribute the total leakage inductance into the leakage inductance of the first winding and the leakage inductance of the second winding. When the turns ratio is 1:1 and the impedances of the two windings are consistent, the total leakage inductance is evenly distributed between the two windings. The leakage inductance of a single winding is calculated according to the following formula:
[0039] In the formula, For leakage inductance of the first winding or the second winding, This is the converted short-circuit reactance. This refers to the power frequency angular frequency. When the turns ratio is not 1:1 or the impedances of the two windings are inconsistent, the leakage inductance of the first winding and the leakage inductance of the second winding are determined according to the winding impedance distribution relationship.
[0040] Taking a rated voltage of 10 kV, a rated capacity of 1 MVA, a short-circuit voltage percentage of 5%, a rated frequency of 50 Hz, and a turns ratio of 1:1 as an example, the short-circuit reactance is about 5 ohms, the power frequency angular frequency is about 314.16 radians per second, and the total leakage inductance is about 15.9 millihenries. When the impedances of the two windings are the same, the leakage inductance of the first winding and the leakage inductance of the second winding are both about 7.95 millihenries.
[0041] After completing the calculation, verify that the sum of the leakage inductance of the two windings matches the total leakage inductance. If the sum does not match, re-verify the turns ratio, the preset reference side, and the winding impedance distribution relationship. If the winding impedance distribution relationship cannot be determined based on the design parameters, use the results of the short-circuit test to determine the leakage inductance of the two windings. The verified leakage inductance of the two windings is used as the main filter inductance of the two converters, respectively, and the process proceeds to the stage of determining the equivalent filter inductance of the two sides.
[0042] After determining the leakage inductance of both windings, the parameter design process uses the leakage inductance of the first and second windings as the main filter inductors of the converters on both sides, respectively, and takes into account the equivalent load, target damping ratio, filter performance requirements, and filter capacitor connection method. Based on the filter performance requirements, the target filter inductors for the first and second sides are formed. The supplementary inductors for the first and second sides are determined by comparing the leakage inductance of the windings on the same side with the target filter inductors on the same side, thus forming the equivalent filter inductors for the first and second sides.
[0043] The equivalent filter inductances on both sides, along with the equivalent load and target damping ratio, are used to determine the equivalent single-phase filter capacitances on both sides. These capacitances are then combined with the filter capacitor connection method and capacitor engineering constraints to form the filter capacitors on both sides. The equivalent filter inductances and equivalent single-phase filter capacitances on both sides then proceed to the stage of determining the resonant frequencies on both sides.
[0044] In one embodiment, the filtering performance requirement is used to determine the target filter inductance on the first side and the target filter inductance on the second side, respectively. The filtering performance requirement employs at least one of a harmonic attenuation requirement at the switching frequency and a current ripple limit. When using the harmonic attenuation requirement at the switching frequency, different filter inductance values are set for the first-side converter and the second-side converter, the harmonic attenuation amount generated by each filter inductance value at the switching frequency is calculated, and the minimum filter inductance value that meets the harmonic attenuation requirement at the switching frequency is determined as the target filter inductance on the first side and the target filter inductance on the second side, respectively. When using the current ripple limit, the current ripple limit is set according to the allowable AC current variation range of the two converters, the current ripple corresponding to different filter inductance values is checked, and the minimum filter inductance value that meets the current ripple limit is determined as the target filter inductance on the first side and the target filter inductance on the second side, respectively. When verifying different filter inductor values, the single-phase equivalent filter capacitor corresponding to each filter inductor value is determined according to the equivalent load and target damping ratio. The harmonic attenuation and current ripple at the switching frequency are then calculated using the corresponding filter inductor values and single-phase equivalent filter capacitors. When both filtering performance requirements are simultaneously applied, the target filter inductors on the first and second sides are selected to simultaneously meet the harmonic attenuation requirements and current ripple limits at the switching frequency.
[0045] When the leakage inductance of the first winding is less than the target filter inductance on the first side, the first-side supplementary inductance is formed by subtracting the leakage inductance of the first winding from the target filter inductance on the first side; when the leakage inductance of the first winding is not less than the target filter inductance on the first side, the first-side supplementary inductance is zero. When the leakage inductance of the second winding is less than the target filter inductance on the second side, the second-side supplementary inductance is formed by subtracting the leakage inductance of the second winding from the target filter inductance on the second side; when the leakage inductance of the second winding is not less than the target filter inductance on the second side, the second-side supplementary inductance is zero. The first-side supplementary inductance and the second-side supplementary inductance are connected in series with the windings on both sides of the dual-winding transformer, so that the leakage inductance of the first winding and the leakage inductance of the second winding continue to serve as the main filter inductance of the converters on both sides.
[0046] The equivalent filter inductance on the first side and the equivalent filter inductance on the second side are determined according to the following formulas:
[0047] In the formula, This refers to either the equivalent filter inductance on the first side or the equivalent filter inductance on the second side. For leakage inductance of the first winding or the second winding, This provides either a supplementary inductance for the first side or the second side. The calculation relationships are used to combine the leakage inductance of the first-side winding with the supplementary inductance for the first side to form the equivalent filter inductance for the first side, and to combine the leakage inductance of the second-side winding with the supplementary inductance for the second side to form the equivalent filter inductance for the second side. When the supplementary inductance for the first side is zero, the equivalent filter inductance for the first side equals the leakage inductance of the first-side winding; when the supplementary inductance for the second side is zero, the equivalent filter inductance for the second side equals the leakage inductance of the second-side winding.
[0048] After determining the equivalent filter inductances on both sides, verify whether the equivalent filter inductances on the first and second sides meet the filtering performance requirements. If the equivalent filter inductance on either side does not meet the filtering performance requirements, recheck the target filter inductance and the supplementary inductance on the same side. If the equivalent filter inductances on both sides meet the filtering performance requirements, transfer the determination process of the equivalent filter inductances on both sides to the determination process of the single-phase equivalent filter capacitors on both sides.
[0049] like Figure 4 As shown, the single-phase equivalent filter capacitors on both sides form a single-phase equivalent filter circuit with the equivalent filter inductor and equivalent load on the same side, respectively. Figure 4 In this diagram, L represents the equivalent filter inductance on the first side or the equivalent filter inductance on the second side, C represents the equivalent single-phase filter capacitor on the first side or the equivalent single-phase filter capacitor on the second side that matches the equivalent filter inductance on the same side, and R represents the equivalent load. In one embodiment, the equivalent single-phase filter capacitors on both sides are determined based on the equivalent filter inductance on the first side and the equivalent filter inductance on the second side, respectively. The equivalent load adopts a value that matches the operating conditions of the converters on both sides, which can be calculated from the rated voltage and rated capacity, or from the voltage and current under actual operating conditions. When the operating conditions of the converters on both sides are the same, the same equivalent load is used; when the operating conditions of the converters on both sides are different, equivalent loads that match the first-side converter and the second-side converter are used respectively. The target damping ratio is set according to the filter design parameters and is used to constrain the value of the equivalent single-phase filter capacitors on both sides. The target damping ratio can be 0.707.
[0050] The natural angular frequency formed by the equivalent filter inductance on either side and the single-phase equivalent filter capacitor on either side is determined by the following formula:
[0051] In the formula, The natural angular frequency, This refers to either the equivalent filter inductance on the first side or the equivalent filter inductance on the second side. The value is the one that matches the equivalent filter inductance on the same side among the single-phase equivalent filter capacitors on both sides. The natural angular frequency is used to characterize the frequency position formed by the equivalent filter inductance and the single-phase equivalent filter capacitor on the same side, and serves as the basis for subsequent calculations to determine the resonant frequencies on both sides.
[0052] The damping ratio is determined by the following formula:
[0053] In the formula, For the damping ratio, For equivalent load, This refers to either the equivalent filter inductance on the first side or the equivalent filter inductance on the second side. This refers to the values of the single-phase equivalent filter capacitors on both sides that are matched with the equivalent filter inductors on the same side. Substituting the equivalent filter inductance, equivalent load, and target damping ratio of the first side into the damping ratio calculation relationship, the values of the single-phase equivalent filter capacitors on both sides used for the first-side converter are calculated. Similarly, substituting the equivalent filter inductance, equivalent load, and target damping ratio of the second side into the same damping ratio calculation relationship, the values of the single-phase equivalent filter capacitors on both sides used for the second-side converter are calculated.
[0054] The single-phase equivalent filter capacitors on both sides are determined based on the single-phase equivalent relationship established by the phase voltage. Taking an example where the equivalent filter inductance on both sides is 7.95 millihenries, the equivalent load is 100 ohms, and the target damping ratio is 0.707, the single-phase equivalent filter capacitors on both sides are approximately 0.4 microfarads. After calculation, check whether the single-phase equivalent filter capacitors on both sides are positive, and check whether the units of the equivalent load, target damping ratio, and equivalent filter inductances on both sides are consistent. If any calculation condition is inconsistent, stop passing the single-phase equivalent filter capacitors on both sides to the filter capacitor connection method processing process, and recheck the filter design parameters; if the calculation conditions are consistent, pass the single-phase equivalent filter capacitors on both sides, the filter capacitor connection method, and capacitor engineering constraints to the filter capacitor determination process on both sides.
[0055] In one embodiment, the filter capacitor connection method is used to convert the single-phase equivalent filter capacitors on both sides into two-phase filter capacitors. When the filter capacitor connection method is that each phase is independently connected, the single-phase equivalent filter capacitors on both sides are used as the branch capacitors of each phase respectively; when the filter capacitor connection method is a star connection, the single-phase equivalent filter capacitors on both sides are still used as the branch capacitors of each phase respectively. The conversion relationship is as follows:
[0056]
[0057] In the formula, For each phase branch capacitor connected independently, For the capacitance of each phase branch in a star connection, This is a single-phase equivalent filter capacitor matched with the converter on the same side.
[0058] When the filter capacitor is connected in a delta configuration, the delta branch capacitor bears the line voltage, and its capacitance is calculated according to the relationship between line voltage and phase voltage. The three-phase fundamental reactive power capacity for both star and delta connections is determined by the following formula:
[0059]
[0060] In the formula, For a three-phase fundamental reactive power configuration connected in a star configuration, For the three-phase fundamental reactive power capacity connected in a delta configuration, It is the power frequency angular frequency. For a delta branch capacitor, Phase voltage, This is the line voltage. Under three-phase balance conditions:
[0061] When two filter capacitor connection methods provide the same three-phase fundamental reactive power capacity:
[0062] After the filter capacitors on both sides are determined, at least one of the following checks is performed: rated voltage constraint, rated current constraint, and reactive power capacity constraint. The rated voltage constraint is set according to the actual phase voltage or line voltage, the rated current constraint is set according to the power frequency current and the current at the switching frequency, and the reactive power capacity constraint is set according to the relationship between the three-phase fundamental reactive power capacity and the rated capacity.
[0063] Taking a rated voltage of 10 kV, a phase voltage of 5.77 kV, and a single-phase equivalent filter capacitor of 0.4 μF on both sides as an example, the capacitance of each phase branch is 0.4 μF, the capacitance of the delta branch is about 0.133 μF, and the three-phase fundamental reactive power capacity is about 12.5 kVar.
[0064] If any phase branch capacitor or delta branch capacitor does not meet the capacitor engineering constraints, return to the process of determining the single-phase equivalent filter capacitor on both sides; if the capacitor engineering constraints are met, determine the phase branch capacitor or delta branch capacitor as the filter capacitor on both sides, and pass it to the stage of determining the resonant frequency on both sides.
[0065] After determining the equivalent filter inductance and filter capacitors on both sides, the parameter design process involves reading the rated frequency, switching frequency, and control bandwidth. The rated frequency is used to form the power frequency band and the main harmonic frequency band, the switching frequency is used to form the switching frequency and sideband frequency band, and the control bandwidth is used to form the control bandwidth frequency band. Each frequency band is merged according to its coverage area to form a prohibited resonance frequency band.
[0066] The equivalent filter inductance on the first side and the equivalent single-phase filter capacitor on the first side are used together to determine the resonant frequency on the first side. The equivalent filter inductance on the second side and the equivalent single-phase filter capacitor on the second side are used together to determine the resonant frequency on the second side. The resonant frequencies on the first and second sides together form the resonant frequencies on both sides, which are then transmitted to the resonance avoidance verification stage.
[0067] In one embodiment, the prohibited resonant frequency band is formed by the power frequency band, the main harmonic frequency band, the switching frequency and sideband frequency band, and the control bandwidth frequency band. The parameter design process reads the rated frequency from the transformer parameters, the switching frequency and control bandwidth from the converter parameters, and verifies the units, numerical ranges, and applicability relationships of the three parameters. If the rated frequency, switching frequency, or control bandwidth is missing, the formation of the prohibited resonant frequency band is stopped, and the process returns to the parameter acquisition stage to supplement the corresponding parameters.
[0068] The power frequency band is determined based on the rated frequency and is used to limit the operating frequency range so that the resonant frequencies on both sides do not fall near the rated frequency. The lower and upper limits of the power frequency band are determined based on the rated frequency and the allowable operating frequency variation range of the two-winding transformer. When the rated frequency is 50 Hz, the power frequency band is formed around 50 Hz; when the rated frequency is 60 Hz, the power frequency band is formed around 60 Hz. When the two-winding transformer operates at a fixed rated frequency, the power frequency band is determined according to the equipment design parameters; when there is an allowable variation range in the operating frequency, the power frequency band covers the allowable variation range.
[0069] The main harmonic frequency band is also determined based on the rated frequency. The parameter design process, based on the possible main harmonic orders of a symmetrical hybrid transformer, multiplies the rated frequency by each main harmonic order to determine the center frequency of each main harmonic. This, combined with the allowable frequency variation range of each main harmonic, forms the main harmonic frequency band. The main harmonic orders are determined based on the distribution network operating conditions, the modulation methods of the converters on both sides, and existing harmonic analysis results. Frequency not listed as a main harmonic is not included in the main harmonic frequency band to avoid prohibiting the resonant frequency band from covering frequency ranges irrelevant to actual operation.
[0070] The switching frequency and sideband are determined based on the switching frequency. The switching frequency is read from the modulation settings of both converters, and the sideband position is determined based on the frequency relationship between the switching frequency, the rated frequency, and the control bandwidth. When both converters use the same switching frequency, a set of switching frequencies and sidebands is formed; when the two converters use different switching frequencies, a first-side switching frequency and sideband and a second-side switching frequency and sideband are formed respectively, and both sets of bands are included in the prohibited resonance band. When the switching frequency is adjusted, the switching frequency and sideband are updated synchronously.
[0071] The lower and upper limits of the control bandwidth are determined based on the frequency ranges corresponding to the control bandwidth in the control settings of both converters. This is to avoid the frequency range where the control effects of both converters are concentrated. When both converters use the same control bandwidth, the control bandwidth is formed according to the common control bandwidth; when the two converters use different control bandwidths, a first-side control bandwidth and a second-side control bandwidth are formed respectively. When the control bandwidth changes, a new control bandwidth is formed to avoid continuing to use frequency ranges inconsistent with the current converter parameters.
[0072] After determining each frequency band, the power frequency band, main harmonic frequency band, switching frequency and sideband frequency band, and control bandwidth frequency band are arranged from low to high frequency. When adjacent frequency bands overlap, the overlapping frequency ranges are merged into a continuous frequency interval; when adjacent frequency bands do not overlap, their respective lower and upper frequency limits are retained. One or more merged frequency intervals together form the prohibited resonance frequency band. The prohibited resonance frequency band is stored in association with transformer parameters and converter parameters and is transferred to the resonance avoidance verification process.
[0073] In one embodiment, the resonant frequencies on both sides are determined based on the equivalent filter inductance and the equivalent single-phase filter capacitor on the same side, respectively. The equivalent filter inductance on both sides consists of the equivalent filter inductance on the first side and the equivalent filter inductance on the second side, and the equivalent single-phase filter capacitor on both sides consists of the equivalent single-phase filter capacitor on the first side and the equivalent single-phase filter capacitor on the second side. The parameter design process follows the series connection between the two converters and the two windings of the dual-winding transformer, pairing the equivalent filter inductance on the first side with the equivalent single-phase filter capacitor on the first side, and pairing the equivalent filter inductance on the second side with the equivalent single-phase filter capacitor on the second side, thus avoiding the cross-use of parameters from different sides for the same resonant frequency calculation.
[0074] The resonant frequencies on both sides are determined by the following formulas:
[0075] In the formula, This refers to either the first-side resonant frequency or the second-side resonant frequency. Pi This refers to either the equivalent filter inductance on the first side or the equivalent filter inductance on the second side. The first-side single-phase equivalent filter capacitor or the second-side single-phase equivalent filter capacitor is paired with the equivalent filter inductor on the same side. Substituting the first-side equivalent filter inductor and the first-side single-phase equivalent filter capacitor into the calculation expression, the first-side resonant frequency is formed; substituting the second-side equivalent filter inductor and the second-side single-phase equivalent filter capacitor into the calculation expression, the second-side resonant frequency is formed.
[0076] The single-phase equivalent filter capacitors used in the calculation are determined based on the connection method of the filter capacitors. When the filter capacitor connection method is independent connection of each phase or star connection, the single-phase equivalent filter capacitor on each side is equal to the branch capacitor of each phase on the same side; when the filter capacitor connection method is delta connection, the delta branch capacitors on each side are converted into single-phase equivalent filter capacitors on the same side according to the voltage relationship between line voltage and phase voltage.
[0077] Before calculation, the units of the equivalent filter inductance on the first side, the equivalent filter inductance on the second side, the equivalent single-phase filter capacitance on the first side, and the equivalent single-phase filter capacitance on the second side are standardized. The equivalent filter inductances on both sides are uniformly converted to Henry, and the equivalent single-phase filter capacitances on both sides are uniformly converted to Farads. If any parameter is zero, negative, or missing, the resonant frequency calculation on both sides is not performed, and the process returns to the stage of determining the equivalent filter inductances or equivalent single-phase filter capacitances on both sides for verification. When the parameter units and numerical ranges meet the calculation conditions, the resonant frequencies on the first and second sides are generated respectively.
[0078] Taking an example where the equivalent filter inductance on both sides is 7.95 millihenries, and the equivalent single-phase filter capacitance on both sides is 0.4 microfarads, after converting the corresponding parameters to Henry's law and substituting them into the resonant frequency calculation expression, the resonant frequency on both sides is approximately 2.83 kHz. When the parameters on both sides are inconsistent, the resonant frequencies on both sides are retained, and the average value is not used to replace the resonant frequency on either side.
[0079] After the calculation is completed, the first and second resonant frequencies are jointly determined as the two resonant frequencies, and compared with the prohibited resonant frequency bands. When either the first or second resonant frequency falls into the prohibited resonant frequency band, the corresponding side, resonant frequency, and frequency range are transmitted to the filter parameter adjustment stage. When both the first and second resonant frequencies avoid the prohibited resonant frequency band, the two resonant frequencies, along with the equivalent filter inductances and filter capacitors on both sides, are transmitted to the filter parameter output stage.
[0080] After entering the filter parameter adjustment stage, adjust the filter capacitors on the same side according to the position of the resonant frequency falling into the forbidden resonant frequency band within the forbidden resonant frequency band. If the filter capacitors on both sides cannot meet the capacitor engineering constraints after adjustment, and adding the equivalent filter inductance on either side can move the resonant frequency on the same side to a lower frequency direction outside the forbidden resonant frequency band, determine the supplementary inductance on both sides according to the positional relationship between the resonant frequencies on both sides and the forbidden resonant frequency band, the leakage inductance of the windings on both sides, and the filter performance requirements, and update the equivalent filter inductance on both sides accordingly.
[0081] After updating the parameters, the resonant frequencies on both sides are redefined and resonance avoidance verification is performed. When the resonant frequencies on both sides avoid the prohibited resonant frequency band, the equivalent filter inductances on both sides meet the filtering performance requirements, and the filter capacitors on both sides meet the capacitance engineering constraints, the filter parameters after resonance avoidance verification are formed, and the equivalent filter inductances and filter capacitors on both sides are output as filter parameters.
[0082] In one embodiment, parameter adjustment is based on the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band. When the first resonant frequency falls into the prohibited resonant frequency band while the second resonant frequency avoids it, only the first-side filter capacitor is adjusted; when the second-side resonant frequency falls into the prohibited resonant frequency band while the first resonant frequency avoids it, only the second-side filter capacitor is adjusted; when both resonant frequencies fall into the prohibited resonant frequency band, both the first-side and second-side filter capacitors are adjusted.
[0083] When it is necessary to shift the first or second resonant frequency to a higher frequency, the corresponding filter capacitor should be decreased; when it is necessary to shift the first or second resonant frequency to a lower frequency, the corresponding filter capacitor should be increased. The adjustment value of the filter capacitor is determined according to the principle that the newly determined resonant frequency on the same side exceeds the upper or lower limit of the current frequency band. After each adjustment, the resonant frequencies on both sides are redefined, and the resonance avoidance check is continued based on the newly determined resonant frequencies on both sides.
[0084] After adjustment, the adjusted filter capacitors on both sides are formed, and they are checked according to the rated voltage constraint, rated current constraint, and reactive power capacity constraint. When the adjusted filter capacitors on both sides meet the capacitor engineering constraints, the adjusted filter capacitors on both sides replace the original filter capacitors on both sides, while keeping the equivalent filter inductance on both sides unchanged.
[0085] If the adjusted filter capacitors on both sides do not meet the capacitor engineering constraints, the adjustment result will not be adopted. If adding the equivalent filter inductance on either side can shift the resonant frequency on the same side to a lower frequency direction outside the prohibited resonant frequency band, the supplementary inductances on both sides will be determined based on the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band, the leakage inductance of the windings on both sides, and the filtering performance requirements. This ensures that the updated equivalent filter inductances on both sides meet the filtering performance requirements and that the resonant frequency on the same side that needs to be shifted to a lower frequency direction is lower than the lower limit of the current frequency band. The supplementary inductances on both sides, together with the corresponding winding leakage inductance, form the updated equivalent filter inductances on both sides.
[0086] After updating the filter capacitors on both sides, the updated first-side and second-side filter capacitors are converted into first-side single-phase equivalent filter capacitors and second-side single-phase equivalent filter capacitors respectively, according to the filter capacitor connection method. Then, the resonant frequencies on both sides are re-determined by combining the first-side equivalent filter inductance and the second-side equivalent filter inductance. After updating the equivalent filter inductances on both sides, the resonant frequencies on both sides are re-determined by combining the first-side single-phase equivalent filter capacitors and the second-side single-phase equivalent filter capacitors. The newly formed resonant frequencies on both sides are then compared with the forbidden resonant frequency band.
[0087] If the resonant frequency on either side still falls into the prohibited resonant frequency band, continue to adjust the equivalent filter inductance or filter capacitor on both sides; when the resonant frequencies on both sides avoid the prohibited resonant frequency band, stop adjusting and proceed to the review of filter performance requirements and capacitor engineering constraints.
[0088] If continuous adjustment of the filter capacitors on both sides still cannot make the resonant frequency on both sides avoid the prohibited resonant frequency band, or if the filter capacitors on both sides continue to fail to meet the capacitor engineering constraints after adjustment, then retain the filter capacitors on both sides that meet the capacitor engineering constraints before adjustment; when increasing the equivalent filter inductance on the same side can make the resonant frequency on the corresponding side move to a lower frequency direction outside the prohibited resonant frequency band, then update the equivalent filter inductance on the same side by increasing the supplementary inductance on the same side.
[0089] If the corresponding side resonant frequency needs to be shifted to a higher frequency and the reduced same-side filter capacitor does not meet the capacitor engineering constraints, return to the acquisition of converter parameters and filter design parameters, and recheck the control bandwidth, filter performance requirements and filter capacitor connection method.
[0090] If adding supplementary inductors on both sides still cannot simultaneously meet the filtering performance requirements and resonance avoidance verification, then return to obtaining the transformer parameters, converter parameters, and filter design parameters, and recheck the switching frequency, control bandwidth, filtering performance requirements, and filter capacitor connection method to avoid continuing to adjust when the input parameters are inconsistent.
[0091] In one embodiment, the filter parameters verified by resonance avoidance are formed when three conditions are met. The first condition is that both the first-side resonant frequency and the second-side resonant frequency avoid the prohibited resonant frequency band; the second condition is that both the first-side equivalent filter inductance and the second-side equivalent filter inductance meet the filter performance requirements; and the third condition is that both the first-side filter capacitor and the second-side filter capacitor meet the capacitor engineering constraints.
[0092] The three conditions are checked one by one. If any condition is not met, the filter parameters are not output and the parameters that do not meet the conditions are returned to the filter parameter adjustment stage.
[0093] When verifying the resonant frequencies on both sides, the first and second resonant frequencies are compared with the power frequency band, the main harmonic frequency band, the switching frequency and the sideband frequency band, and the control bandwidth frequency band, respectively. If the first resonant frequency does not fall into any frequency band, the first resonant frequency passes the resonance avoidance verification; if the second resonant frequency does not fall into any frequency band, the second resonant frequency passes the resonance avoidance verification.
[0094] If either of the two resonant frequencies fails the resonance avoidance check, the positional relationship between the corresponding resonant frequency and the prohibited resonant frequency band is returned to the filter parameter adjustment stage.
[0095] When verifying the equivalent filter inductances on both sides, check whether the equivalent filter inductances on the first and second sides meet at least one of the harmonic attenuation requirements and current ripple limits at the switching frequency. If the equivalent filter inductance on the first side does not meet the filtering performance requirements, the supplementary inductance on the first side is re-determined; if the equivalent filter inductance on the second side does not meet the filtering performance requirements, the supplementary inductance on the second side is re-determined.
[0096] When both equivalent filter inductances on both sides meet the filtering performance requirements, the current equivalent filter inductances on both sides are retained and the filter capacitors on both sides are checked.
[0097] When verifying the filter capacitors on both sides, determine the actual phase voltage or line voltage borne by the first and second filter capacitors according to the connection method of the filter capacitors, and check the rated voltage constraint; check the rated current constraint according to the power frequency current and the current at the switching frequency; check the reactive capacity constraint according to the relationship between the three-phase fundamental reactive capacity and the rated capacity.
[0098] If the first or second side filter capacitor fails to meet the capacitor engineering constraints, adjust the filter capacitors on both sides while keeping the equivalent filter inductance on both sides, which already meets the filter performance requirements, unchanged.
[0099] When all three conditions are met, the equivalent filter inductance on the first side, the equivalent filter inductance on the second side, the filter capacitor on the first side, and the filter capacitor on the second side together form the filter parameters. The equivalent filter inductances and filter capacitors on both sides are recorded according to the connection relationship between the two converters and the two windings on both sides of the dual-winding transformer, and are output as filter parameters after resonance avoidance verification. Parameters that fail resonance avoidance verification, filter performance requirement verification, or capacitor engineering constraint verification are not included in the filter parameters.
[0100] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.
Claims
1. A method for designing integrated filter parameters for a symmetrical hybrid transformer, characterized in that, The method includes: Obtain transformer parameters, winding impedance distribution relationships, converter parameters, and filter design parameters; The short-circuit reactance is calculated from the transformer parameters and the leakage inductance of the two windings is determined according to the winding impedance distribution relationship. The leakage inductance of the windings on both sides is used as the main filter inductance of the converters on both sides. The equivalent filter inductance, single-phase equivalent filter capacitor and filter capacitor on both sides are determined by the filter design parameters. The prohibited resonant frequency band is determined by the transformer parameters and the converter parameters, and the resonant frequency on both sides is determined by the equivalent filter inductance on both sides and the single-phase equivalent filter capacitor on both sides. When the resonant frequency on either side falls into the prohibited resonant frequency band, adjust the equivalent filter inductance or the filter capacitor on both sides until the resonant frequencies on both sides avoid the prohibited resonant frequency band, and then output the filter parameters.
2. The method according to claim 1, characterized in that, The symmetrical hybrid transformer includes a dual-winding transformer and two converters connected in series with the two windings of the dual-winding transformer. The transformer parameters include rated capacity, rated voltage, short-circuit voltage percentage, rated frequency, and turns ratio. The converter parameters include switching frequency and control bandwidth. The filter design parameters include equivalent load, target damping ratio, filter performance requirements, and filter capacitor connection method. The filter performance requirements include at least one of harmonic attenuation requirements at the switching frequency and current ripple limit. The winding impedance distribution relationship is used to characterize the distribution ratio of total leakage inductance between the windings on both sides of the two-winding transformer.
3. The method according to claim 2, characterized in that, The step of calculating the short-circuit reactance based on the transformer parameters and obtaining the leakage inductance of the windings on both sides according to the winding impedance distribution relationship includes: The short-circuit reactance is calculated based on the rated capacity, the rated voltage, and the percentage of short-circuit voltage, and the short-circuit reactance is converted to a preset reference side based on the turns ratio; The total leakage inductance is determined based on the converted short-circuit reactance and the rated frequency, and then distributed as leakage inductance of the two windings according to the winding impedance distribution relationship.
4. The method according to claim 2, characterized in that, The step of determining the equivalent filter inductance on both sides according to the filter design parameters includes: The target filter inductance on the first side and the target filter inductance on the second side are determined according to the filtering performance requirements, and the leakage inductance of the windings on both sides includes the leakage inductance of the first winding and the leakage inductance of the second winding. When the leakage inductance of the first side winding is less than the target filter inductance of the first side, the supplementary inductance of the first side is determined according to the difference between the two. When the leakage inductance of the first side winding is not less than the target filter inductance of the first side, the supplementary inductance of the first side is determined to be zero. If the leakage inductance of the second-side winding is less than the target filter inductance of the second side, the supplementary inductance of the second side is determined based on the difference between the two. If the leakage inductance of the second-side winding is not less than the target filter inductance of the second side, the supplementary inductance of the second side is determined to be zero. The sum of the leakage inductance of the first-side winding and the supplementary inductance of the first-side winding is determined as the first-side equivalent filter inductance, and the sum of the leakage inductance of the second-side winding and the supplementary inductance of the second-side winding is determined as the second-side equivalent filter inductance. The equivalent filter inductances on both sides include the first-side equivalent filter inductance and the second-side equivalent filter inductance.
5. The method according to claim 2, characterized in that, The step of determining the filter capacitors on both sides based on the equivalent filter inductances on both sides and the filter design parameters includes: The single-phase equivalent filter capacitors on both sides are determined based on the equivalent filter inductance on both sides, the equivalent load, and the target damping ratio. The filter capacitors on both sides are determined based on the single-phase equivalent filter capacitors on both sides, the connection method of the filter capacitors, and the capacitor engineering constraints. The capacitor engineering constraints include at least one of rated voltage constraints, rated current constraints, and reactive power capacity constraints.
6. The method according to claim 5, characterized in that, The step of determining the filter capacitors on both sides based on the single-phase equivalent filter capacitors on both sides, the connection method of the filter capacitors, and the capacitor engineering constraints includes: When the filter capacitor connection method is independent connection of each phase or star connection, the equivalent filter capacitor of each phase on both sides is determined as the branch capacitor of each phase on each side, and when the branch capacitor of each phase on each side meets the capacitor engineering constraints, the branch capacitor of each phase on each side is determined as the filter capacitor of both sides. When the filter capacitor is connected in a delta configuration, the single-phase equivalent filter capacitors on both sides are calculated according to the voltage relationship between the line voltage and the phase voltage to obtain the delta branch capacitors on each side. If the delta branch capacitors on each side satisfy the capacitor engineering constraints, the delta branch capacitors on each side are determined as the filter capacitors on both sides.
7. The method according to claim 2, characterized in that, The process of obtaining the prohibited resonant frequency band from the transformer parameters and the converter parameters includes: The power frequency band and main harmonic frequency band are determined based on the rated frequency; the switching frequency and sideband frequency band are determined based on the switching frequency; and the control bandwidth frequency band is determined based on the control bandwidth. The power frequency band, the main harmonic frequency band, the switching frequency and sideband frequency band, and the control bandwidth frequency band are combined to obtain the forbidden resonance frequency band.
8. The method according to claim 5, characterized in that, The equivalent filter inductors on both sides include a first equivalent filter inductor and a second equivalent filter inductor, and the single-phase equivalent filter capacitors on both sides include a first single-phase equivalent filter capacitor and a second single-phase equivalent filter capacitor. The first-side resonant frequency is determined based on the first-side equivalent filter inductance and the first-side single-phase equivalent filter capacitance, and the second-side resonant frequency is determined based on the second-side equivalent filter inductance and the second-side single-phase equivalent filter capacitance. The resonant frequencies on both sides include the first-side resonant frequency and the second-side resonant frequency.
9. The method according to claim 5, characterized in that, The adjustment of the equivalent filter inductance on both sides or the filter capacitor on both sides includes: Adjust the filter capacitors on both sides according to the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band to obtain the adjusted filter capacitors on both sides; If the adjusted filter capacitors on both sides meet the capacitor engineering constraints, update the filter capacitors on both sides based on the adjusted filter capacitors on both sides. If the adjusted filter capacitors on both sides do not meet the capacitor engineering constraints, and adding the equivalent filter inductor on either side can cause the resonant frequency on the same side to move to a lower frequency direction outside the prohibited resonant frequency band, the supplementary inductors on both sides are determined according to the positional relationship between the resonant frequencies on both sides and the prohibited resonant frequency band, the leakage inductance of the windings on both sides and the filter performance requirements, and the equivalent filter inductors on both sides are updated based on the supplementary inductors on both sides. When updating the filter capacitors on both sides, the updated filter capacitors on both sides are converted into updated single-phase equivalent filter capacitors on both sides according to the filter capacitor connection method, and the resonant frequency on both sides is re-determined based on the equivalent filter inductance on both sides and the updated single-phase equivalent filter capacitors on both sides. When updating the equivalent filter inductances on both sides, the resonant frequencies on both sides are re-determined based on the updated equivalent filter inductances on both sides and the single-phase equivalent filter capacitors on both sides. Resonance avoidance verification should be performed again based on the prohibited resonant frequency band.
10. The method according to claim 5, characterized in that, The output filtering parameters include: When the resonant frequencies on both sides avoid the prohibited resonant frequency band, the equivalent filter inductances on both sides meet the filtering performance requirements, and the filter capacitors on both sides meet the capacitor engineering constraints, the equivalent filter inductances on both sides and the filter capacitors on both sides are output as the filtering parameters.