阅读说明：本技术 基于阻尼比的lcl滤波器参数设计方法、设备及介质 (LCL filter parameter design method, equipment and medium based on damping ratio ) 是由 马柯 唐为禹 于 2020-06-23 设计创作，主要内容包括：本发明提供了一种基于阻尼比的LCL滤波器参数设计方法、设备及介质,首先根据传统LCL滤波器设计方法,选取变流器侧电感及滤波电容参数；然后利用阻尼比,对阻尼电阻和输出侧电感的取值进行优化设计；此外,还提供了针对总电感量和谐振频率的迭代优化方案。本发明优选采用最优阻尼比0.28,该阻尼比能够以最小的阻尼损耗保障带LCL滤波器的变流器系统稳定运行。本发明设计迭代少,能够保障LCL滤波器的高频衰减设计准确,避免阻尼设计不合理所引入的稳定性风险,进而确保电流控制参数的选取简单直接,适用于LCL滤波器的输出侧电压高频分量较低的场合。(The invention provides a damping ratio-based LCL filter parameter design method, equipment and a medium, wherein firstly, according to the traditional LCL filter design method, the parameters of a side inductor and a filter capacitor of a converter are selected; then, optimally designing values of the damping resistor and the output side inductor by using the damping ratio; in addition, an iterative optimization scheme for the total inductance and the resonant frequency is provided. The invention preferably adopts an optimal damping ratio of 0.28, which can ensure the stable operation of the converter system with the LCL filter with the minimum damping loss. The method has less design iteration, can ensure the accuracy of the high-frequency attenuation design of the LCL filter, avoids the stability risk caused by unreasonable damping design, further ensures the simple and direct selection of the current control parameter, and is suitable for occasions with lower high-frequency components of the voltage at the output side of the LCL filter.)

1. A method for designing LCL filter parameters based on damping ratio is characterized by comprising the following steps:

calculating the inductance L of the converter side according to the current ripple design index of the converter side_fTaking the value of (A);

calculating the filter capacitor C according to the ratio of the reactive capacity of the filter capacitor_fTaking the value of (A);

according to the passive damping ratio and the high-frequency current attenuation design index, the side inductor L of the converter is combined_fAnd the value of (C) and the filter capacitance (C)_fCalculating the inductance L of the output side_gThe value of (a) is as follows:

L_f: a converter side inductance of the LCL filter;

L_g: an output side inductor of the LCL filter;

C_f: a filter capacitor of the LCL filter;

ζ: passive damping ratio of LCL filter;

attention: attenuation of high-frequency current of the LCL filter;

ω_sw: the switching angular frequency of the power semiconductor device;

ω_res，f_res: the resonant angular frequency and the resonant frequency of the LCL filter;

abs (…): taking an absolute value for operation;

j: imaginary unit.

2. The LCL filter parameter design method based on damping ratio of claim 1, further comprising: calculating the passive damping resistance R according to the passive damping ratio_dThe calculation formula is as follows:

3. the LCL filter parameter design method based on the damping ratio as claimed in claim 1, wherein the value range of the passive damping ratio is 0.20-0.35.

4. The LCL filter parameter design method based on damping ratio as claimed in claim 3, wherein the optimal value of the passive damping ratio is 0.28, which can ensure the stable operation of the converter system with LCL filter with the minimum damping loss.

5. The LCL filter parameter design method based on damping ratio of claim 1, wherein the calculating of converter side inductance L_fThe values of (a) are calculated according to any one of the following formulas:

in three-phase four-wire systems with SPWM modulation, L_fThe calculation formula of (a) is as follows:

f_sw: the switching frequency of the power semiconductor device;

V_dc: a direct current bus voltage;

△i_f.max: the maximum peak value of the current ripple on the converter side;

in three-phase three-wire systems with SPWM modulation, L_fThe calculation formula of (a) is as follows:

V₁: an effective value of the output side voltage;

max { … }: taking the maximum value for operation;

three in using SVPWM modulationIn a three-phase wire system, L_fThe calculation formula of (a) is as follows:

6. the LCL filter parameter design method based on damping ratio of claim 1, wherein the calculating filter capacitance C_fThe calculation formula is as follows:

I₁: an effective value of the output side current;

λ: the reactive capacity absorbed by the capacitor accounts for the ratio;

f₁: fundamental frequency of the output side voltage;

C_base: a reference capacitance.

7. The LCL filter parameter design method based on damping ratio according to any of claims 1-6, further comprising: performing optional iterative optimization on the total inductance of the LCL filter, namely the converter-side inductance L_fAnd an output side inductor L_gThe sum should be less than the upper limit L of the total inductance_T.Limit；

The optimization iteration is performed when any one of the following occasions:

applications sensitive to filter volume, weight or cost;

-applications where the voltage modulation ratio is greater than 0.85;

the specific operation of the optimization iteration is as follows: when the total inductance of the LCL filter is greater than the upper limit L of the total inductance_T.LimitThen, the reactive capacity ratio lambda absorbed by the capacitor is increased, and the filter capacitor C is redesigned_fAnd an output side inductance L_gOr redesigning the filter capacitor C_fAn output side inductor L_gAnd a passive damping resistor R_d。

8. The LCL filter parameter design method based on damping ratio of claim 7, wherein the total inductance upper limit L_T.LimitTaking 10% of the reference inductance, the formula is as follows:

L_base: a reference inductance.

9. The LCL filter parameter design method based on damping ratio according to any of claims 1-6, further comprising: resonance frequency f for LCL filters_resPerforming iterative optimization;

the resonant frequency of the LCL filter should be greater than 10 times the fundamental frequency and less than 1/2 switching frequencies, as follows:

10f₁＜f_res＜0.5f_sw

if the resonant frequency of the LCL filter is less than 10 times of the fundamental frequency, the reactive capacity occupation ratio lambda absorbed by the capacitor is reduced, or the high-frequency Attenuation value attention of the LCL filter is increased, or the maximum peak value △ i of the current ripple on the side of the converter is increased_f.max；

If the resonant frequency of the LCL filter is greater than 1/2 switching frequency, increasing the reactive capacity ratio lambda absorbed by the capacitor, or reducing the high-frequency Attenuation value attention of the LCL filter, or reducing the maximum peak value △ i of the current ripple on the converter side_f.max。

10. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the program when executed by the processor is operable to perform the LCL filter parameter design method of any of claims 1-9.

11. A computer-readable storage medium, storing a computer program, wherein the program, when executed by a processor, is operable to perform the LCL filter parameter design method of any of claims 1-9.

Technical Field

The invention relates to the field of filter design of a converter, in particular to a damping ratio-based LCL filter parameter design method.

Background

Compared with the traditional inductive filter, the LCL filter has better attenuation performance on high-frequency current harmonics. In recent years, to meet more and more stringent grid-connected criteria, more and more grid-connected converters begin to adopt LCL filters to filter out the switching order harmonics in the grid-connected current. However, there is an inherent resonance peak on the amplitude-frequency characteristic curve of the LCL filter, which easily causes the instability of the converter system, and presents a challenge to the design of the current controller. In order to ensure the stability of control, the converter system with the LCL filter generally adopts an active damping method or a passive damping method to suppress a resonance peak.

The main advantage of active damping is that no damping losses are introduced and the high frequency attenuation performance of the LCL filter is not degraded. However, active damping generally requires the use of additional sensors, which means additional economic cost and more complex control loops. Passive damping is a simpler and more common approach than active damping. In general, a damping resistor may be connected in series with the capacitance of the LCL filter to suppress resonance. The cost of this approach is increased damping loss and poor high frequency attenuation performance. To overcome these drawbacks, some new passive damping methods use additional capacitors or inductors to bypass the high frequency current and the fundamental frequency current on the capacitive branches, respectively, such as the RC damping branch, the RLC damping branch, etc. However, these new damping schemes introduce high order transfer functions and varying eigenfrequencies, which increases the complexity of filter parameter design. Therefore, in practical applications, a simple damping resistor is connected in series with the filter capacitor, which is still a common passive damping method.

How to design the value of the damping resistor is a difficult problem because the value of the damping resistor is related to a plurality of parameters. When using conventional design methods, the damping resistor is typically set to a value on the order of magnitude of the capacitive impedance at the resonant frequency for simplicity of design, and 1/3 is a commonly used empirical value. However, the design of damping based on empirical values is not accurate enough: if the resistance value is too small, the resonance suppression of the filter is insufficient, and the control stability of the converter is adversely affected; if the resistance value is too large, this will result in excessive degradation of the high-frequency current attenuation performance and a decrease in the power conversion efficiency. Therefore, the conventional design method needs to adjust the damping value through continuous iteration. In the literature, "Analysis of Soft skin conference Lotus in LCL-Filter-Based Grid ConverIn ters, R.Alzola et al propose an analytic passive damping design method to ensure control stability. The method is only suitable for the condition that the converter side current of the LCL filter is taken as a controlled object, and the damping design is accurate only when the output side inductance is far larger than the converter side inductance. However, in practical applications, it is common that the output side current of the LCL filter is the controlled object, and the output side inductance is generally smaller than the converter side inductance. Therefore, the method is poorly applicable.

In addition, when the conventional design method is adopted, the damping resistance of the LCL filter is usually performed after the values of the inductance and the capacitance are determined. Considering that the damping resistor partially blocks the high frequency current flowing through the capacitor branch, the high frequency attenuation of the LCL filter inevitably differs from the design initial value. Therefore, conventional design methods require additional iterations to adjust the attenuation behavior.

In summary, the existing passive damping resistor design method mainly has two defects:

1) the design of passive damping values is not accurate, and the instability of the converter or overlarge damping loss can be caused by unreasonable damping values;

2) the passive damping and the high-frequency current attenuation need to be iteratively adjusted for many times, the design efficiency is low, and the design precision is poor.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method, equipment and medium for designing parameters of an LCL filter based on a damping ratio.

According to a first aspect of the present invention, there is provided a method for designing parameters of an LCL filter, including:

calculating the inductance L of the converter side according to the current ripple design index of the converter side_fTaking the value of (A);

calculating the filter capacitor C according to the ratio of the reactive capacity of the filter capacitor_fTaking the value of (A);

according toA passive damping ratio and a high-frequency current attenuation design index are combined with the side inductor L of the converter_fAnd the value of (C) and the filter capacitance (C)_fCalculating the inductance L of the output side_gThe value of (a) is as follows:

L_f: a converter side inductance of the LCL filter;

L_g: an output side inductor of the LCL filter;

C_f: a filter capacitor of the LCL filter;

ζ: passive damping ratio of LCL filter;

attention: attenuation of high-frequency current of the LCL filter;

ω_sw: the switching angular frequency of the power semiconductor device;

ω_res，f_res: the resonant angular frequency and the resonant frequency of the LCL filter;

abs (…): taking an absolute value for operation;

j: imaginary unit.

Further, the method further comprises: calculating the passive damping resistance R according to the passive damping ratio_dThe value of (a).

Optionally, the passive damping resistor R_dThe calculation formula is as follows:

optionally, the calculating filter capacitance C_fThe value of (a) is as follows:

V₁: an effective value of the output side voltage;

I₁: an effective value of the output side current;

λ: the reactive capacity absorbed by the capacitor accounts for the ratio;

f₁: fundamental frequency of the output side voltage;

C_base: a reference capacitance.

Optionally, the passive damping ratio is 0.20-0.35, and further, the optimal passive damping ratio is 0.28, so that a resonance peak on an amplitude-frequency characteristic curve of the LCL filter can be just suppressed.

Optionally, the method further comprises: performing optional iterative optimization on the total inductance of the LCL filter; the total inductance of the LCL filter, i.e. the side inductance L of the converter_fAnd an output side inductor L_gThe sum should be less than the upper limit L of the total inductance_T.Limit。

The optimization iteration is performed when any one of the following occasions:

applications sensitive to filter volume, weight or cost;

-applications where the voltage modulation ratio is greater than 0.85;

the specific operation of the optimization iteration is as follows: when the total inductance of the LCL filter is greater than the upper limit L of the total inductance_T.LimitThen, the reactive capacity ratio lambda absorbed by the capacitor is increased, and the filter capacitor C is redesigned_fAnd an output side inductance L_gOr redesigning the filter capacitor C_fAn output side inductor L_gAnd a passive damping resistor R_d。

Further, the total inductance upper limit L_T.LimitTaking 10% of the reference inductance, the formula is as follows:

L_base: a reference inductance;

f₁: fundamental frequency of the output side voltage;

V₁: output ofAn effective value of the side voltage;

I₁: the effective value of the output side current.

Optionally, the method further comprises: resonance frequency f for LCL filters_resPerforming iterative optimization;

the resonant frequency of the LCL filter should be greater than 10 times the fundamental frequency and less than 1/2 switching frequencies, as follows:

10f₁＜f_res＜0.5f_sw

f₁: fundamental frequency of the output side voltage;

f_sw: the switching frequency of the power semiconductor device;

if the resonant frequency of the LCL filter is less than 10 times of the fundamental frequency, the reactive capacity occupation ratio lambda absorbed by the capacitor is reduced, or the high-frequency Attenuation value attention of the LCL filter is increased, or the maximum peak value △ i of the current ripple on the side of the converter is increased_f.max；

If the resonant frequency of the LCL filter is greater than 1/2 switching frequency, increasing the reactive capacity ratio lambda absorbed by the capacitor, or reducing the high-frequency Attenuation value attention of the LCL filter, or reducing the maximum peak value △ i of the current ripple on the converter side_f.max。

According to a second aspect of the present invention, there is also provided a computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor when executing the program being operable to perform the LCL filter parameter design method described above.

According to a third aspect of the present invention, there is also provided a computer-readable storage medium storing a computer program, wherein the program is usable for the above LCL filter parameter design method when executed by a processor.

Compared with the prior art, the embodiment of the invention has at least one of the following beneficial effects:

the method improves the design formula of the output side inductor based on the damping ratio, ensures the high-frequency current attenuation design of the LCL filter to be accurate, avoids the design iteration of adjusting the attenuation performance, and realizes the accurate design of the output side inductor.

The method improves the design formula of the damping resistor based on the damping ratio, avoids the design iteration of adjusting the damping value, realizes the accurate design of the damping resistor, and can ensure the stable operation of the converter system with the LCL filter with the minimum damping loss.

According to the method, the value of the damping ratio can be in the range of 0.20-0.35, and the damping ratio can ensure that a resonance peak on an amplitude-frequency characteristic curve of the LCL filter is just inhibited, so that the selection of current control parameters is simple and direct; further, the universal optimal damping ratio is 0.28, and the damping ratio can ensure the stable operation of the converter system with the LCL filter with the minimum damping loss.

The method has the advantages of clear design criteria, less design iteration, high design efficiency and high precision, and ensures that the current control parameters are simply and directly selected.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a flow chart of LCL filter parameter design based on damping ratio in a preferred embodiment of the present invention;

FIG. 2 is a topology diagram of an inverter applied under grid-connected conditions according to an embodiment of the present invention;

fig. 3 is a bode plot of the LCL filter transfer function in an embodiment of the invention.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

Fig. 1 is a flow chart of the design of parameters of the LCL filter based on the damping ratio in a preferred embodiment of the present invention, and the method is suitable for the situation where the output side voltage high-frequency component of the LCL filter is low, such as the inverter grid-connected condition. In the method for designing the parameters of the LCL filter based on the damping ratio, firstly, the parameters of a side inductor and a filter capacitor of the converter are selected according to the traditional LCL filter design method; then, optimally designing values of the damping resistor and the output side inductor by using the damping ratio; specifically, as shown in fig. 1, the method may include the following steps:

s1, calculating the current transformer side inductance L according to the current ripple design index of the current transformer side_fTaking the value of (A);

s2, calculating the filter capacitor C according to the reactive capacity ratio of the filter capacitor_fTaking the value of (A);

s3, combining the inductor L on the converter side according to the passive damping ratio and the high-frequency current attenuation design index_fAnd the value of (C) and the filter capacitance (C)_fCalculating the inductance L of the output side_gTaking the value of (A);

s4, calculating the passive damping resistance R according to the passive damping ratio and the parameters obtained in the previous step_dThe value of (a).

Regarding S1 above, taking the three-phase three-wire system using SPWM modulation as an example, the calculation formula of the converter-side inductance is as follows:

regarding S2 above, the calculation formula of the filter capacitance is as follows:

regarding S3 described above, the calculation formula of the output side inductance is as follows:

the formula considers the influence of the passive damping resistor, can ensure the accurate design of high-frequency current attenuation, and avoids unnecessary design iteration. Wherein the content of the first and second substances,

in the preferred embodiment, the damping ratio of the LCL filter can be 0.20-0.35, wherein the optimal damping ratio is 0.28, which can ensure that the resonance peak on the amplitude-frequency characteristic curve of the LCL filter is just suppressed, thereby ensuring the stable operation of the converter system with the LCL filter with the minimum damping loss.

Regarding S4 above, the design of the passive damping resistor of the LCL filter is based on the following formula:

the design formula can ensure that the LCL filter has a specific damping ratio.

In the above examples, the variables used have the following meanings:

L_f: a converter side inductance of the LCL filter;

L_g: an output side inductor of the LCL filter;

C_f: a filter capacitor of the LCL filter;

R_d: a passive damping resistor of the LCL filter;

ζ: passive damping ratio of LCL filter;

attention: attenuation of high-frequency current of the LCL filter;

ω_sw，f_sw: the switching angular frequency and the switching frequency of the power semiconductor device;

ω_res，f_res: the resonant angular frequency and the resonant frequency of the LCL filter;

f₁: fundamental frequency of the output side voltage;

V₁: an effective value of the output side voltage;

I₁: an effective value of the output side current;

V_dc: a direct current bus voltage;

△i_f.max: the maximum peak value of the current ripple on the converter side;

λ: the reactive capacity absorbed by the capacitor accounts for the ratio;

C_base，L_base: a reference capacitor and an inductor;

abs (…): taking an absolute value for operation;

max { … }: and taking the maximum value for operation.

The embodiment of the invention realizes the accurate design of the inductance at the output side, can ensure that the high-frequency attenuation of the LCL filter is highly consistent with the design index, and avoids the design iteration of adjusting the attenuation performance; furthermore, the method also realizes the accurate design of the damping resistor, can ensure the stable operation of the converter system with the LCL filter with the minimum damping loss, and avoids the design iteration of adjusting the damping value.

On the basis of the above embodiment, the other preferred embodiments of the present invention further include an optional optimization scheme for the total inductance and the resonant frequency, which has less iteration, can ensure accurate high-frequency attenuation design of the LCL filter, avoid the stability risk caused by unreasonable damping design, and further ensure simple and direct selection of the current control parameters.

Specifically, in a preferred embodiment, the total inductance of the LCL filter is iteratively optimized, wherein the total inductance of the LCL filter, i.e. the sum of the inductor on the converter side and the inductor on the output side, should be smaller than the upper limit L of the total inductance_T.LimitThe formula is as follows:

L_f+L_g＜L_T.Limit

in general, the upper limit of the total inductance may be 10% of the reference inductance, and the formula is as follows:

the optimization iteration is applied to: 1) applications sensitive to filter volume, weight, or cost, 2) applications with voltage modulation ratios greater than 0.85; in other cases, the optimization iteration may not be used.

The specific operations of the optimization iteration are as follows: when the total inductance of the LCL filter is greater than the upper limit L of the total inductance_T.LimitThen, the reactive capacity ratio lambda absorbed by the capacitor is increased, and the filter capacitor C is redesigned_fAn output side inductor L_gAnd a passive damping resistor R_d。

In another preferred embodiment, the resonant frequency of the LCL filter is iteratively optimized, and should be greater than 10 times the fundamental frequency and less than 1/2 switching frequencies, as follows:

10f₁＜f_res＜0.5f_sw。

if the resonant frequency of the LCL filter is less than 10 times of the fundamental frequency, the reactive capacity occupation ratio lambda absorbed by the capacitor is reduced, or the high-frequency Attenuation value attention of the LCL filter is increased, or the maximum peak value △ i of the current ripple on the side of the converter is increased_f.max。

If the resonant frequency of the LCL filter is greater than 1/2 switching frequency, increasing the reactive capacity ratio lambda absorbed by the capacitor, or reducing the high-frequency Attenuation value attention of the LCL filter, or reducing the maximum peak value △ i of the current ripple on the converter side_f.max。

In order to better understand the technical scheme of the invention, the following description is combined with specific application examples, and it should be understood that the following application examples are not used for limiting the invention.

Fig. 2 is an inverter topology diagram applied to a grid-connected condition according to an embodiment of the present invention, and referring to the topology shown in fig. 2, a three-phase two-level voltage source inverter is connected to an ideal grid through an LCL filter. The design method provided by the invention can be suitable for occasions with low high-frequency components of the voltage at the output side, and the grid-connected working condition is the most common application occasion.

The electrical parameters of the present embodiment are set as follows:

three-phase three-wire system, SPWM modulation mode, DC bus voltage V_dc400V, effective value V of output side voltage₁110V, fundamental frequency f of output side voltage₁50Hz, effective value of output side current I₁＝20AIGBT switching frequency f_sw＝20kHz。

The LCL filter design criteria of this embodiment are as follows:

the maximum value of the current ripple at the converter side is 20% of the output current amplitude; the proportion of the reactive capacity of the capacitor is 5 percent of the rated power; the high-frequency current ripple attenuation is 1/25; the damping ratio takes an optimum value ζ of 0.28.

Referring to the flow of designing parameters of the LCL filter based on the damping ratio in fig. 1, the present embodiment may include the following implementation steps:

step 1, calculating the value of the inductance at the converter side according to the current ripple design index at the converter side;

in this embodiment, the maximum ripple △ i of the current transformer side current_f.maxComprises the following steps:

considering that the system is a three-phase three-wire system and SPWM modulation is used, the converter-side inductance can be calculated by the following formula, and the result is: l is_f＝0.42mH。

Step 2, calculating the value of the filter capacitor according to the reactive capacity ratio of the filter capacitor;

in this embodiment, the ratio of the capacitance reactive capacity is 5% of the rated power, that is, λ is 5%; the capacitance can be calculated by the following equation, resulting in: c_f＝29uF。

Step 3, on the premise that the values of the converter side inductor and the filter capacitor are determined, according to the optimal damping ratio ζ of 0.28 and the high-frequency attenuation design index, the output side inductor can be calculated by the following formula, and the result is: l is₁＝0.27mH。

Wherein the content of the first and second substances,

verifying whether the sum of the converter inductance and the output side inductance of the LCL filter exceeds the total inductance limit or not; in the present embodiment, the upper limit of the total inductance is selected as the reference inductance L _base10% of (a), namely:

the total inductance in the embodiment satisfies the requirement, as follows:

L_f+L_g＝0.42mH+0.27mH＜1.75mH＝L_T.Limit

verifying whether the resonant frequency of the LCL filter is within a reasonable range; in this embodiment, the resonant frequency f of the LCL filter_res2319Hz, the following inequality is satisfied:

10f₁＜f_res＜0.5f_sw→500Hz＜2319Hz＜10000Hz

step 4, according to the determined inductance and capacitance values and the optimal damping ratio ζ equal to 0.28, the passive damping resistance can be calculated by the following formula, and the result is: r_d＝1.33Ω。

So far, the LCL filter parameter design of the present embodiment is completed, no iteration is introduced in the design process, the design criteria are clear, and the design efficiency is high. In this embodiment, the design result of the LCL filter is: l is_f＝0.42mH，C_f＝29uF，L_g＝0.27mH，R_d＝1.33Ω。

Of course, in the above embodiment, since both the total inductance and the resonant frequency are within the limit range, iterative adjustment is not required. In other embodiments, if the total inductance or resonant frequency is outside of a limit, an iteration is required. Compared with the traditional LCL design, the invention has less iteration times, and the best condition is that no iteration is needed.

FIG. 3 is a Bode plot of the LCL filter transfer function according to one embodiment of the present invention; transfer function of LCL filter, from converter side voltage v_sTo the output side current i_gThe following are:

referring to fig. 3, the LCL filter parameter corresponding to the optimal damping is the above design result; the lack of damping corresponds to halving the damping resistance, i.e. R, in the above result_d0.67 Ω, the remaining parameters were unchanged; excessive damping corresponds to doubling the damping resistance in the above result, i.e. R_d2.66 Ω, the remaining parameters were unchanged. By contrast, the adoption of ζ being 0.28 can ensure that a resonance peak on an amplitude-frequency characteristic curve of the LCL filter is just suppressed, so that the stable operation of a converter system is ensured with the minimum damping loss.

The three-phase three-wire system modulated by SPWM is exemplified above, and other systems have universality except for the formula for the inductance of the converter side. For other systems, the calculation formula of the converter side inductance needs to be adaptively changed, and the same is true. For example,

when in a three-phase four-wire system adopting SPWM modulation, the inductance L at the side of the converter is calculated_fThe calculation formula of (a) is as follows:

f_sw: the switching frequency of the power semiconductor device;

V_dc: a direct current bus voltage;

△i_f.max: the maximum peak value of the current ripple on the converter side;

as another example, inIn a three-phase three-wire system modulated by SVPWM, the inductance L at the converter side is calculated_fThe calculation formula of (a) is as follows:

in another embodiment of the present invention, there is also provided a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor when executing the program is operable to execute the LCL filter parameter design method of any one of the above embodiments.

In another embodiment of the present invention, a computer-readable storage medium is further provided, which stores a computer program, wherein the program is operable to be executed by a processor to perform the LCL filter parameter design method of any one of the above embodiments.

In summary, according to the design method of the traditional LCL filter, the embodiment of the invention selects the parameters of the side inductor and the filter capacitor of the converter; then, optimally designing values of the damping resistor and the output side inductor by using the damping ratio; in addition, an iterative optimization scheme for the total inductance and the resonant frequency is provided. In the embodiment of the invention, the optimal damping ratio is 0.28, and the damping ratio can ensure the stable operation of the converter system with the LCL filter with the minimum damping loss. The method has less design iteration, can ensure the accuracy of the high-frequency attenuation design of the LCL filter, avoids the stability risk caused by unreasonable damping design, further ensures the simple and direct selection of the current control parameter, and is suitable for occasions with lower high-frequency components of the output side voltage of the LCL filter.

It should be noted that the above description is only an embodiment of the present invention, and is not intended to limit the present invention. Those skilled in the art can make modifications and substitutions to the proposed design method without departing from the spirit and principles of the present invention. It is intended that all such modifications fall within the scope of the appended claims and their equivalents be covered thereby without departing from the spirit and principles of the invention.