Filter parameter design method and system of energy storage converter

Abstract

The invention relates to the technical field of filters, and particularly provides a filter parameter design method and system for an energy storage converter, and the method comprises the steps: obtaining the rated active power of the energy storage converter, calculating the resistance of a rated load based on the rated active power, and deducing a transfer function of an LC filter based on the resistance of the rated load; calculating an inductance minimum value according to the maximum value of the allowed current ripple, and calculating a capacitance maximum value according to the allowed reactive power; determining the resonant frequency of the filter, and determining initial inductance and initial capacitance based on the resonant frequency, the inductance minimum value and the capacitance maximum value; and drawing a Bode diagram based on the transfer function, and adjusting initial inductance and initial capacitance according to the Bode diagram to obtain inductance and capacitance. The characteristics of the LC filter can be reflected more completely, and the limitation of an existing filter design scheme is effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of filters, and in particular relates to a filter parameter design method and system for an energy storage converter. Background Art

[0002] As an indispensable key component of modern power grids, energy storage devices play an important role in regulating the balance of power supply and demand and optimizing energy allocation. They are seamlessly connected to the power grid through grid-connected inverters, achieving efficient storage and release of energy. In this grid-connected process, power electronic converters play a bridging role, but if the harmonic currents generated during their operation are not properly handled, they will pollute the power grid and affect the quality of power.

[0003] In order to meet this challenge, a large number of power electronic converters generally use filters composed of inductors and capacitors when connected to the grid. This type of filter can effectively filter out the high-frequency harmonic components on the bridge arm side, ensuring that the current waveform on the AC side of the converter is pure and smooth, thereby meeting the high standards of the grid for grid-connected power quality. However, there are a wide variety of filter design solutions on the current market, and the design process is often complicated and cumbersome, involving the precise calculation and matching of many parameters, which places high demands on the professional skills of designers.

[0004] More importantly, some filters have poor filtering effects in actual applications and are difficult to achieve the expected performance indicators, which not only affects the stable operation of power electronic equipment, but also may cause potential safety hazards to the power grid. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a filter parameter design method and system for an energy storage converter to solve the above-mentioned technical problems.

[0006] In a first aspect, the present invention provides a filter parameter design method for an energy storage converter, comprising: Acquiring a rated active power of the energy storage converter, calculating a rated load resistance based on the rated active power, and deriving a transfer function of the LC filter based on the rated load resistance; The minimum inductance is calculated based on the maximum value of the allowed current ripple, and the maximum capacitance is calculated based on the allowed reactive power. Determining a resonant frequency of the filter, and determining an initial inductance and an initial capacitance based on the resonant frequency, a minimum inductance, and a maximum capacitance; A Bode diagram is drawn based on the transfer function, and an initial inductance and an initial capacitance are adjusted according to the Bode diagram to obtain an inductance and a capacitance.

[0007] In a second aspect, the present invention provides a filter parameter design system for an energy storage converter, comprising: A function derivation module, used for obtaining the rated active power of the energy storage converter, calculating the resistance of the rated load based on the rated active power, and deriving the transfer function of the LC filter based on the resistance of the rated load; A limit value calculation module is used to calculate the minimum inductance value according to the maximum value of the allowed current ripple, and calculate the maximum capacitance value according to the allowed reactive power; An initial setting module, used to determine the resonant frequency of the filter, and determine the initial inductance and initial capacitance based on the resonant frequency, the minimum inductance and the maximum capacitance; The parameter optimization module is used to draw a Bode diagram based on the transfer function, and adjust the initial inductance and initial capacitance according to the Bode diagram to obtain the inductance and capacitance.

[0008] The beneficial effect of the present invention is that the filter parameter design method and system of the energy storage converter provided by the present invention determines the power, DC bus voltage value, AC side voltage value, and ripple current of the converter, and then determines the rated load of the AC side according to the power and the voltage of the AC side, and then determines the minimum value of the inductance according to the DC bus voltage value, the ripple coefficient of the AC side current, and the switching frequency, calculates the maximum value of C based on the introduced maximum reactive power, and finally determines the appropriate inductance and capacitance values ​​according to the resonant frequency and the Bode diagram. The present invention can more completely reflect the characteristics of the LC filter, effectively avoid the limitations of the existing filter design scheme, and the operation steps are simple, easy to implement, and the filtering effect is good.

[0009] In addition, the invention has a reliable design principle, a simple structure and a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0011] Figure 1 is a schematic flow chart of a method according to an embodiment of the present invention.

[0012] Figure 2 This is the circuit diagram of the energy storage grid-connected inverter.

[0013] Figure 3 This is a simplified single-phase LC filter circuit diagram.

[0014] Figure 4 Another schematic flow chart of a method according to an embodiment of the present invention.

[0015] Figure 5This is the Bode plot of the LC filter in case 1.

[0016] Figure 6 This is the Bode plot of the LC filter in case 2.

[0017] Figure 7 is a schematic block diagram of a system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] The filter parameter design method for the energy storage converter provided in the embodiment of the present invention is executed by a computer device. Accordingly, the filter parameter design system for the energy storage converter runs in the computer device.

[0021] Figure 1 is a schematic flow chart of a method according to an embodiment of the present invention. Figure 1 The execution subject may be a filter parameter design system for an energy storage converter. According to different requirements, the order of the steps in the flow chart may be changed, and some may be omitted.

[0022] like Figure 1 As shown, the method includes: S1. Obtaining the rated active power of the energy storage converter, calculating the rated load resistance based on the rated active power, and deriving the transfer function of the LC filter based on the rated load resistance; S2. Calculate the minimum inductance value based on the maximum value of the allowed current ripple, and calculate the maximum capacitance value based on the allowed reactive power; S3. Determine the resonant frequency of the filter, and determine the initial inductance and initial capacitance based on the resonant frequency, the minimum inductance and the maximum capacitance; S4. Drawing a Bode diagram based on the transfer function, and adjusting the initial inductance and initial capacitance according to the Bode diagram to obtain inductance and capacitance.

[0023] To facilitate understanding of the present invention, the filter parameter design method for the energy storage inverter provided by the present invention is further described below based on the principle of the filter parameter design method for the energy storage inverter of the present invention and in combination with the process of designing the filter parameters of the energy storage inverter in the embodiment.

[0024] Figure 2 Middle,U dc is the voltage value of the DC bus capacitor; T is the insulated gate bipolar transistor; L is the filter inductor on the bridge arm side, C is the filter capacitor, i ga , i gb , i gc is the three-phase grid-connected current, u ga , u gb , u gc is the three-phase grid voltage. The grid-connected inverter consists of a DC bus support capacitor, an insulated gate bipolar transistor, three filter inductors and three filter capacitors. The voltage before the LC filter has high-order harmonics, which in turn generates high-order harmonic currents. Harmonic currents and harmonic voltages will endanger the stability of the grid, so they cannot be directly connected to the grid. The function of the LC filter composed of inductors and capacitors in the figure is to filter out high-order harmonic currents, generate power frequency currents, and then only allow the voltage on the grid-connected side to have only power frequency voltage, and further smoothly connect to the grid. The LC filter acts as a bridge between the grid-connected inverter and the grid. Selecting appropriate LC filter parameters can provide guarantees for the stable operation of the grid. The AC side grid voltage of the energy storage converter is generally 690V.

[0025] like Figure 3 As shown in the figure, it is a simplified single-phase LC filter circuit diagram. It can be understood that Figure 2 It is a circuit from the single-phase converter bridge arm voltage to the load. Figure 3 In the equation, R is the equivalent load resistance; u i is the voltage before the filter; u o is the voltage after filtering; i L is the current flowing through the filter inductor; i c is the current flowing through the filter capacitor; i g is the current flowing through the load. The filter satisfies Kirchhoff's voltage and current laws of the circuit.

[0026] Please refer to Figure 4 , the specific parameter design steps are as follows: Take a 2MW converter as an example. Since the AC power is 3-phase, P 额定 =0.333*2MW. First, we need to calculate the resistance R under rated load. The calculation formula of R is: , Among them, 690 is the line voltage value of the AC power grid. Common energy storage converters connected to the power grid have 380V and 690V. This application is described with 690V. P is the rated active power of the energy storage converter, and R is the resistance of the rated load.

[0027] In this embodiment, R = 0.2381Ω.

[0028] The transfer function of the LC filter including the resistor with rated load is listed according to Kirchhoff's voltage law and Kirchhoff's current law: , Among them, u i is the input voltage of the filter; u o is the output voltage of the filter; L is the filter inductance on the bridge arm side, and C is the filter capacitor; i c is the current flowing through the filter capacitor; i g is the current flowing through the load; i L is the current flowing through the filter inductor; u c is the voltage of the filter capacitor; The transfer function is simplified and transformed to obtain a second-order system: , in, s is the Laplace operator; u o ( s ), u i ( s ) are the Laplace transforms of the output voltage and the input voltage respectively; The slope of the second order system at high frequencies is -40 dB per decade of range.

[0029] Further, determine L min For a three-level converter, the voltage across the inductor is: ; Where, dt=Δt; Δt=DT s ;di L =Δi L ; T s is the switching period, D is the duty cycle, u dc is the voltage value of the DC bus capacitor; According to the characteristics of the sinusoidal converter, there is a relationship between the duty cycle and the output voltage: , Where m is the amplitude, ω is the angular frequency, and the relationship between ω and frequency f is ω=2πf; Based on the voltage across the inductor, the current ripple expression across the inductor is calculated as: ; Substituting the relationship between duty cycle and output voltage into the current ripple expression across the inductor, the current ripple function can be obtained: ; By taking the derivative of the current ripple function, we can obtain: ; Let the derivative of the current ripple be 0, and we can get: ; Will Substituting into the current ripple function, the maximum current ripple can be obtained: ; Simplifying the maximum current ripple, we can get: , in, f s is the switching frequency; By shifting the terms of the simplified maximum current ripple formula, the minimum inductance calculation formula can be obtained: , Since the ripple of the three-level converter is small, the maximum ripple current is selected as 10% by comprehensively considering the volume of the inductor. The maximum ripple current of 10% is substituted into the calculation formula of the minimum inductance to solve the minimum inductance; Considering the introduced reactive power, which is theoretically less than 5% of the single-phase rated active power of the rectifier, the calculation formula for the maximum capacitance is: , in, f 0 is the power frequency voltage of the power grid, 50Hz; U Rms is the effective value of the phase voltage on the AC side.

[0030] Further, the resonant frequency of the LC filter is determined. The resonant frequency expression of the filter is: , According to the experience in actual engineering, the range of the resonant frequency is set to 10 f 0~ 0.5 f s . f 0 is the base frequency, f s is the switching frequency.

[0031] Given R = 0.2381Ω, set the DC bus voltageu dc is 1500V, the switching frequency f s The minimum inductance can be calculated based on the minimum inductance calculation formula. L min = 0.3169mH.

[0032] According to the maximum capacitance calculation formula, the maximum capacitance can be calculated C max = 0.66858mF.

[0033] Next, we substitute the minimum inductance Lmin and the maximum capacitance Cmax into the expression of the resonant frequency and calculate the corresponding resonant frequency value fr.

[0034] The calculated resonant frequency value f r will be set with the range 10f0 to 0.5f s For comparison, if f r Within this range, we can set the minimum inductance L min Set to the initial inductance value and the maximum capacitance C max Set to the initial capacitance value.

[0035] However, if the calculated resonant frequency value f r If the value is not within the set range, further adjustment is required. In this case, select r The closest range boundary value is used as the new resonant frequency value f r ′. Then, the minimum inductance L min Set to the initial inductance value, and the initial inductance and the new resonant frequency value f r Substitute ' into the expression of resonant frequency to solve the corresponding initial capacitance value C init : ; In this way, the resonant frequency of the LC filter can be ensured to meet the performance requirements of the system, thereby optimizing the filter design.

[0036] Furthermore, the inductance value is selected based on the reactor volume, and the final inductance and capacitance settings are determined by screening candidate inductance and capacitance values ​​and analyzing the Bode plot. The specific steps include: The volume of the reactor is usually proportional to its inductance value. A larger inductance value often requires a larger volume and heavier materials. Therefore, when selecting the inductance value, it is necessary to comprehensively consider factors such as the performance requirements of the filter, the volume limit of the reactor, and the cost.

[0037] The minimum inductance L calculated previouslymin Based on this, we can set multiple candidate inductance values. These candidate inductance values ​​can be min We can then fine-tune the inductor based on the actual filter performance to explore the effect of different inductor values ​​on the filter performance. At the same time, we also need to ensure that the selected inductor value does not make the reactor too large, thus exceeding the space limitations of the system.

[0038] For each candidate inductance value, substitute it into the expression for the resonant frequency to solve for the corresponding capacitance value. These capacitance values ​​will be used as candidate capacitance values ​​for subsequent filter performance analysis and comparison. It should be noted that since the expression for the resonant frequency contains both inductance and capacitance values, when we change the inductance value, the capacitance value will also change accordingly. Therefore, when solving for the candidate capacitance value, we need to ensure that the inductance value used is accurate and corresponds one-to-one with the candidate inductance value.

[0039] In order to evaluate the impact of different candidate inductor and capacitor values ​​on the filter performance, a Bode plot of the transfer function is plotted. A Bode plot is a graphical tool that can intuitively display the gain and phase response of the filter at different frequencies. For each candidate inductor value and corresponding candidate capacitor value combination, a corresponding Bode plot is plotted. Then, by comparing the shapes and characteristics of different Bode plots, the impact of different inductor and capacitor values ​​on the filter performance can be analyzed, including key indicators such as the filter's cutoff frequency, passband gain, and stopband attenuation.

[0040] After analyzing the filtering effects of all candidate inductor and capacitor values, the combination with the best filtering effect is selected as the final inductor and capacitor settings. These settings will ensure that the LC filter can meet the performance requirements of the system and achieve the best balance in terms of size, cost, and reliability.

[0041] like Figure 5 The Bode diagram of the LC filter in case 1 is shown in FIG.

[0042] Considering the volume of the reactor, first assign L1 to 1mH, L2 to 10mH, L3 to 100mH, and set the resonant frequency to 1000Hz. According to the resonant frequency expression, C1 can be obtained as 2.5330*10 -5 F, C2 is 2.5330*10 -6 F, C3 is 2.5330*10 - 7 F.

[0043] It can be understood that the next step is to draw the Bode diagram of the LC filter based on the second-order system of the transfer function. The code for drawing the transfer function is: sys1=tf([1 / (L1*C1)],[1 1 / (R*C1) 1 / (L1*C1)]); sys2=tf([1 / (L2*C2)],[1 1 / (R*C2) 1 / (L2*C2)]); sys3=tf([1 / (L3*C3)],[1 1 / (R*C3) 1 / (L3*C3)]); bode(sys1,sys2,sys3).

[0044] according to Figure 5 It can be seen that the larger L is, the smaller the gain value of the filter at the power frequency is. When L is 1mH, the gain is large. Therefore, L should not be too large.

[0045] like Figure 6 The Bode diagram of the LC filter in case 2 is shown in FIG.

[0046] Assign L1 to 0.5mH, L2 to 5mH, L3 to 50mH, set the resonant frequency to 1000Hz, and according to the resonant frequency expression, C1 can be obtained as 5.0661*10 -5 F, C2 is 5.0661*10 -6 F, C3 is 5.0661*10 -7 F. Bode diagram Figure 6 shown.

[0047] Further, by Figure 6 It can be seen that sys1 maintains a good filtering effect on the components above the industrial frequency 314rad / s, and the inductance L should be as close as possible to 0.5mH. After L is determined, the C value is determined according to the resonant frequency.

[0048] Therefore, this patent proposes a filter design method suitable for energy storage converters, taking into account the difficulty of operation and the filtering effect. First, the rated load is calculated according to the power of the converter and the voltage level of the grid connection point; second, the transfer function of the LC filter under the rated load is derived; third, the minimum inductance is calculated according to the maximum value of the allowed current ripple, and the maximum value of the capacitor C is calculated according to the allowed reactive power; finally, the resonant frequency and the Bode diagram are considered to select the appropriate inductance and capacitance values.

[0049] In some embodiments, the filter parameter design system for the energy storage converter may include a plurality of functional modules composed of computer program segments. The computer program of each program segment in the filter parameter design system for the energy storage converter may be stored in a memory of a computer device and executed by at least one processor to perform (see Figure 1 Description) Function of filter parameter design for energy storage converter.

[0050] In this embodiment, the filter parameter design system of the energy storage converter can be divided into multiple functional modules according to the functions it performs, such as Figure 7 As shown. The functional modules of the system 700 may include: a function derivation module 710, a limit value calculation module 720, an initial setting module 730 and a parameter optimization module 740. The module referred to in the present invention refers to a series of computer program segments that can be executed by at least one processor and can complete fixed functions, which are stored in a memory. In this embodiment, the functions of each module will be described in detail in subsequent embodiments.

[0051] A function derivation module, used for obtaining the rated active power of the energy storage converter, calculating the resistance of the rated load based on the rated active power, and deriving the transfer function of the LC filter based on the resistance of the rated load; A limit value calculation module is used to calculate the minimum inductance value according to the maximum value of the allowed current ripple, and calculate the maximum capacitance value according to the allowed reactive power; An initial setting module, used to determine the resonant frequency of the filter, and determine the initial inductance and initial capacitance based on the resonant frequency, the minimum inductance and the maximum capacitance; The parameter optimization module is used to draw a Bode diagram based on the transfer function, and adjust the initial inductance and initial capacitance according to the Bode diagram to obtain the inductance and capacitance.

[0052] Optionally, as an embodiment of the present invention, the function derivation module includes: , in, P 额定 is the rated active power of the energy storage converter, and R is the resistance of the rated load; The transfer function of the LC filter including the resistor with rated load is listed according to Kirchhoff's voltage law and Kirchhoff's current law: , Among them, u i is the input voltage of the filter; u o is the output voltage of the filter; L is the filter inductance on the bridge arm side, and C is the filter capacitor; i c is the current flowing through the filter capacitor; i g is the current flowing through the load; i L is the current flowing through the filter inductor; u c is the voltage of the filter capacitor; The transfer function is simplified and transformed to obtain a second-order system: , in, s is the Laplace operator;u o ( s ), u i ( s ) are the Laplace transforms of the output voltage and the input voltage respectively; The slope of the second order system at high frequencies is -40 dB per decade of range.

[0053] Optionally, as an embodiment of the present invention, the limit value calculation module includes: For a three-level converter, the voltage across the inductor is: ; Where, dt=Δt; Δt=DT s ;di L =Δi L ; T s is the switching period, D is the duty cycle, u dc is the voltage value of the DC bus capacitor; According to the characteristics of the sinusoidal converter, there is a relationship between the duty cycle and the output voltage: , Where m is the amplitude, ω is the angular frequency, and the relationship between ω and frequency f is ω=2πf; Based on the voltage across the inductor, the current ripple expression across the inductor is calculated as: ; Substituting the relationship between duty cycle and output voltage into the current ripple expression across the inductor, the current ripple function can be obtained: ; By taking the derivative of the current ripple function, we can obtain: ; Let the derivative of the current ripple be 0, and we can get: ; Will Substituting into the current ripple function, the maximum current ripple can be obtained: ; Simplifying the maximum current ripple, we can get: , in, f s is the switching frequency; By shifting the terms of the simplified maximum current ripple formula, the minimum inductance calculation formula can be obtained: , Since the ripple of the three-level converter is small, the maximum ripple current is selected as 10% by comprehensively considering the volume of the inductor. The maximum ripple current of 10% is substituted into the calculation formula of the minimum inductance to solve the minimum inductance; Considering the introduced reactive power, which is theoretically less than 5% of the single-phase rated active power of the rectifier, the calculation formula for the maximum capacitance is: , in, f 0 is the power frequency voltage of the power grid, 50Hz; U Rms is the effective value of the phase voltage on the AC side.

[0054] Optionally, as an embodiment of the present invention, the initial setting module includes: The resonant frequency expression of the filter is: , According to the experience in actual engineering, the range of the resonant frequency is set to 10 f 0~ 0.5 f s ; Substituting the minimum inductance and the maximum capacitance into the resonant frequency expression to obtain the resonant frequency value; If the resonant frequency value is within the range, the minimum inductance is set as the initial inductance, and the maximum capacitance is set as the initial capacitance; If the resonant frequency value is not within the range, the range boundary value closest to the resonant frequency value is set as the new resonant frequency value, the minimum inductance is set as the initial inductance, and the initial inductance and the new resonant frequency value are substituted into the expression of the resonant frequency to obtain the initial capacitance.

[0055] Optionally, as an embodiment of the present invention, the parameter optimization module includes: Based on the volume of the reactor, a plurality of candidate inductance values ​​are set based on the initial inductance; Inputting the candidate inductance value into the resonant frequency expression to obtain the candidate capacitance value corresponding to the candidate inductance value; Based on the candidate inductance values ​​and the corresponding candidate capacitance values, draw the Bode plot of the transfer function, and analyze the filtering effect based on the Bode plot; The candidate inductance value and the candidate capacitance value with the best filtering effect are set as the inductance and the capacitance.

[0056] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A filter parameter design method for an energy storage converter, characterized in that: include: Acquiring a rated active power of the energy storage converter, calculating a rated load resistance based on the rated active power, and deriving a transfer function of the LC filter based on the rated load resistance; The minimum inductance is calculated based on the maximum value of the allowed current ripple, and the maximum capacitance is calculated based on the allowed reactive power. Determining a resonant frequency of the filter, and determining an initial inductance and an initial capacitance based on the resonant frequency, a minimum inductance, and a maximum capacitance; A Bode diagram is drawn based on the transfer function, and an initial inductance and an initial capacitance are adjusted according to the Bode diagram to obtain an inductance and a capacitance.

2. The method according to claim 1, characterized in that The rated active power of the energy storage converter is obtained, the resistance of the rated load is calculated based on the rated active power, and the transfer function of the LC filter is derived based on the resistance of the rated load, including: ， in, P 额定 is the rated active power of the energy storage converter, and R is the resistance of the rated load; The transfer function of the LC filter including the resistor with rated load is listed according to Kirchhoff's voltage law and Kirchhoff's current law: ， Among them, u i is the input voltage of the filter; u o is the output voltage of the filter; L is the filter inductance on the bridge arm side, and C is the filter capacitor; i c is the current flowing through the filter capacitor; i g is the current flowing through the load; i L is the current flowing through the filter inductor; u c is the voltage of the filter capacitor; The transfer function is simplified and transformed to obtain a second-order system: ， in, s is the Laplace operator; u o ( s ), u i ( s ) are the Laplace transforms of the output voltage and the input voltage respectively; The slope of the second order system at high frequencies is -40 dB per decade of range.

3. The method according to claim 2, characterized in that The minimum inductance is calculated based on the maximum value of the allowed current ripple, and the maximum capacitance is calculated based on the allowed reactive power, including: For a three-level converter, the voltage across the inductor is: ； Where, dt=Δt; Δt=DT s ;di L =Δi L ; T s is the switching period, D is the duty cycle, u dc is the voltage value of the DC bus capacitor; According to the characteristics of the sinusoidal converter, there is a relationship between the duty cycle and the output voltage: ， Where m is the amplitude, ω is the angular frequency, and the relationship between ω and frequency f is ω=2πf; Based on the voltage across the inductor, the current ripple expression across the inductor is calculated as: ； Substituting the relationship between duty cycle and output voltage into the current ripple expression across the inductor, the current ripple function can be obtained: ； By taking the derivative of the current ripple function, we can obtain: ； Let the derivative of the current ripple be 0, and we can get: ； Will Substituting into the current ripple function, the maximum current ripple can be obtained: ； Simplifying the maximum current ripple, we can get: ， in, f s is the switching frequency; By shifting the terms of the simplified maximum current ripple formula, the minimum inductance calculation formula can be obtained: ， Since the ripple of the three-level converter is small, the maximum ripple current is selected as 10% by comprehensively considering the volume of the inductor. The maximum ripple current of 10% is substituted into the calculation formula of the minimum inductance to solve the minimum inductance; Considering the introduced reactive power, which is theoretically less than 5% of the single-phase rated active power of the rectifier, the calculation formula for the maximum capacitance is: ， in, f 0 is the power frequency voltage of the power grid, 50Hz; U Rms is the effective value of the phase voltage on the AC side.

4. The method according to claim 3, characterized in that Determining a resonant frequency of the filter, and determining an initial inductance and an initial capacitance based on the resonant frequency, a minimum inductance, and a maximum capacitance, comprising: The resonant frequency expression of the filter is: ， According to the experience in actual engineering, the range of the resonant frequency is set to 10 f 0 ~ 0.5 f s ; Substituting the minimum inductance and the maximum capacitance into the resonant frequency expression to obtain the resonant frequency value; If the resonant frequency value is within the range, the minimum inductance is set as the initial inductance, and the maximum capacitance is set as the initial capacitance; If the resonant frequency value is not within the range, the range boundary value with the smallest difference from the resonant frequency value is set as the new resonant frequency value, the minimum inductance value is set as the initial inductance, and the initial inductance and the new resonant frequency value are substituted into the expression of the resonant frequency to obtain the initial capacitance.

5. The method according to claim 4, characterized in that Drawing a Bode diagram based on the transfer function, adjusting the initial inductance and the initial capacitance according to the Bode diagram to obtain the inductance and the capacitance, including: Based on the volume of the reactor, a plurality of candidate inductance values ​​are set based on the initial inductance; Inputting the candidate inductance value into the resonant frequency expression to obtain the candidate capacitance value corresponding to the candidate inductance value; Based on the candidate inductance values ​​and the corresponding candidate capacitance values, draw the Bode plot of the transfer function, and analyze the filtering effect based on the Bode plot; The candidate inductance value and the candidate capacitance value with the best filtering effect are set as the inductance and the capacitance.

6. A filter parameter design system for an energy storage converter, characterized in that: include: A function derivation module, used for obtaining the rated active power of the energy storage converter, calculating the resistance of the rated load based on the rated active power, and deriving the transfer function of the LC filter based on the resistance of the rated load; A limit value calculation module is used to calculate the minimum inductance value according to the maximum value of the allowed current ripple, and calculate the maximum capacitance value according to the allowed reactive power; An initial setting module, used to determine the resonant frequency of the filter, and determine the initial inductance and initial capacitance based on the resonant frequency, the minimum inductance and the maximum capacitance; The parameter optimization module is used to draw a Bode diagram based on the transfer function, and adjust the initial inductance and initial capacitance according to the Bode diagram to obtain the inductance and capacitance.

7. The system according to claim 6, characterized in that The function derivation module comprises: ， in, P 额定 is the rated active power of the energy storage converter, and R is the resistance of the rated load; The transfer function of the LC filter including the resistor with rated load is listed according to Kirchhoff's voltage law and Kirchhoff's current law: ， Among them, u i is the input voltage of the filter; u o is the output voltage of the filter; L is the filter inductance on the bridge arm side, and C is the filter capacitor; i c is the current flowing through the filter capacitor; i g is the current flowing through the load; i L is the current flowing through the filter inductor; u c is the voltage of the filter capacitor; The transfer function is simplified and transformed to obtain a second-order system: ， in, s is the Laplace operator; u o ( s ), u i ( s ) are the Laplace transforms of the output voltage and the input voltage respectively; The slope of the second order system at high frequencies is -40 dB per decade of range.

8. The system according to claim 7, characterized in that The limit value calculation module comprises: For a three-level converter, the voltage across the inductor is: ； Where, dt=Δt; Δt=DT s ;di L =Δi L ; T s is the switching period, D is the duty cycle, u dc is the voltage value of the DC bus capacitor; According to the characteristics of the sinusoidal converter, there is a relationship between the duty cycle and the output voltage: ， Where m is the amplitude, ω is the angular frequency, and the relationship between ω and frequency f is ω=2πf; Based on the voltage across the inductor, the current ripple expression across the inductor is calculated as: ； Substituting the relationship between duty cycle and output voltage into the current ripple expression across the inductor, the current ripple function can be obtained: ； By taking the derivative of the current ripple function, we can obtain: ； Let the derivative of the current ripple be 0, and we can get: ； Will Substituting into the current ripple function, the maximum current ripple can be obtained: ； Simplifying the maximum current ripple, we can get: ， in, f s is the switching frequency; By shifting the terms of the simplified maximum current ripple formula, the minimum inductance calculation formula can be obtained: ， Since the ripple of the three-level converter is small, the maximum ripple current is selected as 10% by comprehensively considering the volume of the inductor. The maximum ripple current of 10% is substituted into the calculation formula of the minimum inductance to solve the minimum inductance; Considering the introduced reactive power, which is theoretically less than 5% of the single-phase rated active power of the rectifier, the calculation formula for the maximum capacitance is: ， in, f 0 is the power frequency voltage of the power grid, 50Hz; U Rms is the effective value of the phase voltage on the AC side.

9. The system according to claim 8, characterized in that The initial setting module includes: The resonant frequency expression of the filter is: ， According to the experience in actual engineering, the range of the resonant frequency is set to 10 f 0 ~ 0.5 f s ; Substituting the minimum inductance and the maximum capacitance into the resonant frequency expression to obtain the resonant frequency value; If the resonant frequency value is within the range, the minimum inductance is set as the initial inductance, and the maximum capacitance is set as the initial capacitance; If the resonant frequency value is not within the range, the range boundary value with the smallest difference from the resonant frequency value is set as the new resonant frequency value, the minimum inductance value is set as the initial inductance, and the initial inductance and the new resonant frequency value are substituted into the expression of the resonant frequency to obtain the initial capacitance.

10. The system according to claim 9, characterized in that The parameter optimization module comprises: Based on the volume of the reactor, a plurality of candidate inductance values ​​are set based on the initial inductance; Inputting the candidate inductance value into the resonant frequency expression to obtain the candidate capacitance value corresponding to the candidate inductance value; Based on the candidate inductance values ​​and the corresponding candidate capacitance values, draw the Bode plot of the transfer function, and analyze the filtering effect based on the Bode plot; The candidate inductance value and the candidate capacitance value with the best filtering effect are set as the inductance and the capacitance.

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