Common-mode voltage rejection three-phase four-wire converter lcl filter parameter determination method

Abstract

The present application relates to the field of power electronics, in particular to a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method, wherein the method comprises: using double Fourier decomposition, analyzing the entire frequency spectrum of the common-mode voltage suppression PWM of the two-level four-bridge arm converter, obtaining the frequency domain distribution of the PWM modulation voltage; based on the frequency domain distribution of the PWM modulation voltage, according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system, establishing the functional relationship of the filter parameters to the circuit characteristic output parameters; based on the preset constraint condition, solving the functional relationship to obtain the filter parameter feasible region, and determining the final LCL filter parameter according to the filter parameter feasible region. Therefore, the problems of parameter design depending on artificial experience, circuit simulation, and time-consuming and laborious design process are solved, and the efficiency and reliability of parameter design are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method. BACKGROUND

[0002] The three-phase four-wire converter is widely used in low-voltage applications such as power distribution networks, and the two-level four-bridge converter is a commonly used topology in three-phase four-wire converters.

[0003] In related technologies, in order to ensure grid power quality, the two-level four-bridge converter is often connected to the grid through an L filter or an LCL filter, and there is an extended form of LCL+L filter in the three-phase four-wire system. In some application scenarios, the two-level four-bridge converter must use a special common-mode voltage suppression PWM to avoid leakage current caused by common-mode voltage, which in turn causes the protection system to act.

[0004] However, some LCL filter parameter analysis design processes focus more on three-phase three-wire systems under ordinary PWM methods, and there is less research on three-phase four-wire systems. Moreover, due to the lack of reliable LCL+L parameter design processes or methods for three-phase four-wire system common-mode voltage suppression PWM algorithms, the LCL filter parameter design of three-phase four-wire two-level four-bridge converters under common-mode voltage suppression PWM relies on artificial experience and circuit simulation, and the design process is time-consuming and laborious, which needs to be solved urgently. SUMMARY

[0005] The present application provides a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method to solve the problem of LCL filter parameter design of three-phase four-wire two-level four-bridge converters under common-mode voltage suppression PWM relying on artificial experience and circuit simulation, and the time-consuming and laborious design process. Improve the efficiency and reliability of parameter design.

[0006] The first aspect of the present application provides a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method, comprising the following steps: using double Fourier decomposition, analyzing the entire frequency spectrum of the common-mode voltage suppression PWM of the two-level four-bridge converter to obtain the frequency domain distribution of the PWM modulation voltage; based on the frequency domain distribution of the PWM modulation voltage, according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system, a function relationship between the filter parameters and the circuit characteristic output parameters is established; based on the predetermined constraint condition, the function relationship is solved to obtain the filter parameter feasible region, and the final LCL filter parameter is determined according to the filter parameter feasible region.

[0007] Further, in some embodiments, the utilizing the double Fourier decomposition to analyze the full spectrum of the common-mode voltage suppression PWM of the two-level four-leg converter obtains a frequency domain distribution of the PWM modulation voltage, including: determining coefficients of all harmonic components of an ABC three-phase bridge arm switching function of the two-level four-leg converter and an expression of an output switching signal of the fourth bridge arm; determining output voltage functions of the first to fourth bridge arms; and obtaining the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0008] Further, in some embodiments, the differential-mode transfer function is:

[0009]

[0010] The common-mode transfer function is:

[0011]

[0012] wherein i1 is a bridge arm output current, i2 is a grid-connected current, L0 is a neutral line inductance, L1 is a converter-side inductance, L2 is a grid-side inductance, C f is a three-phase filter capacitance, s is a complex frequency, R f is an active or passive damping equivalent capacitance parallel resistance, u g is a grid voltage, and u is a differential-mode or common-mode voltage excitation.

[0013] Further, in some embodiments, the preset constraint condition is:

[0014]

[0015] wherein f0 is a grid frequency, f c is a switching frequency of the converter, P rated is a rated power, U g,ph is a grid-side rated phase voltage effective value; a switching sub-current harmonic in L1 is less than or equal to a first multiple of a rated fundamental current effective value; when operating in a grid-connected mode, a THD of the grid-connected current is less than or equal to a first preset threshold, and a first mapping relationship between each odd harmonic order of the grid-connected current and a proportion of a rated grid-connected current, and a second mapping relationship between each even harmonic order of the grid-connected current and the proportion of the rated grid-connected current; for the common-mode voltage suppression PWM of the two-level four-leg converter, L0 = L1.

[0016] The method for determining LCL filter parameters of a common-mode voltage suppression three-phase four-wire converter provided by the embodiment of the present application can obtain the frequency domain distribution of PWM modulation voltage by using double Fourier decomposition, establish the function relationship from filter parameters to circuit characteristic output parameters by combining the differential mode and common mode equivalent circuits of the three-phase four-wire system and the transfer functions thereof, and solve the filter parameter feasible region by using various inequality constraint relationships, thereby solving the problems of the LCL filter parameter design of the three-phase four-wire two-level four-leg converter under common-mode voltage suppression PWM, such as the dependence on artificial experience and circuit simulation, and the time-consuming and laborious design process, and improving the efficiency and reliability of parameter design.

[0017] The second embodiment of the present application provides a device for determining LCL filter parameters of a common-mode voltage suppression three-phase four-wire converter, comprising: an analysis module configured to analyze the entire frequency spectrum of common-mode voltage suppression PWM of a two-level four-leg converter by using double Fourier decomposition to obtain the frequency domain distribution of PWM modulation voltage; a mathematical modeling module configured to establish the function relationship from filter parameters to circuit characteristic output parameters according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system based on the frequency domain distribution of the PWM modulation voltage; and a calculation module configured to solve the filter parameter feasible region by solving the function relationship based on the preset constraint condition, and determine the final LCL filter parameters according to the filter parameter feasible region.

[0018] Further, in some embodiments, the analysis module is specifically configured to: determine the coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm; determine the output voltage functions of the first to fourth bridge arms; and obtain the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0019] Further, in some embodiments, the analysis module is specifically configured to: determine the coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm; determine the output voltage functions of the first to fourth bridge arms; and obtain the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0020] Further, in some embodiments, the differential mode transfer function is:

[0021]

[0022] The common-mode transfer function is:

[0023]

[0024] Wherein, i1 is the bridge arm output current, i2 is the grid-connected current, L0 is the neutral line inductance, L1 is the converter side inductance, L2 is the grid side inductance, C f is the three-phase filter capacitance, s is the complex frequency, R f is the equivalent capacitance parallel resistance of active or passive damping, u g is the grid voltage, and u is the differential mode or common mode voltage excitation.

[0025] Further, in some embodiments, the preset constraint condition is:

[0026]

[0027] Wherein, f0 is the grid frequency, f c is the switching frequency of the converter, P rated is the rated power, U g,ph is the grid side rated phase voltage effective value; the switching sub-current harmonic in L1 is less than or equal to the first multiple of the rated fundamental current effective value; when operating in the grid-connected mode, the THD of the grid-connected current is less than or equal to the first preset threshold, and the first mapping relationship between the odd harmonic order of the grid-connected current and the proportion of the rated grid-connected current, and the second mapping relationship between the even harmonic order of the grid-connected current and the proportion of the rated grid-connected current; for the common-mode voltage suppression PWM of the two-level four-bridge arm, L0=L1.

[0028] The common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination device provided by the embodiment of the application can obtain the frequency domain distribution of the PWM modulation voltage by using double Fourier decomposition, establish the function relationship from the filter parameter to the circuit characteristic output parameter by combining the differential mode and common mode equivalent circuits and their transfer functions of the three-phase four-wire system, and solve the filter parameter feasible region by using various inequality constraint relationships, so that the problems of the LCL filter parameter design of the three-phase four-wire two-level four-bridge arm converter under the common-mode voltage suppression PWM depending on artificial experience and circuit simulation and the time-consuming and laborious design process are solved, and the efficiency and reliability of parameter design are improved.

[0029] The third aspect embodiment of the application provides an electronic device, comprising: at least one processor; and a memory in communication connection with the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are configured to execute the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method as described in the above embodiments.

[0030] The fourth aspect of the present application provides a computer readable storage medium, which stores a computer program, and the program is executed by a processor to implement the common-mode voltage restrained three-phase four-wire converter LCL filter parameter determination method according to the above-mentioned embodiments.

[0031] The fifth aspect of the present application provides a computer program product, which comprises a computer program, and the computer program is executed by a processor to implement the common-mode voltage restrained three-phase four-wire converter LCL filter parameter determination method according to the above-mentioned embodiments.

[0032] Additional aspects and advantages of the present application will be made apparent by the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0033] The above and / or additional aspects and advantages of the present application will become apparent and be more readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0034] Figure 1 A flow chart of a common-mode voltage restrained three-phase four-wire converter LCL filter parameter determination method according to an embodiment of the present application is provided.

[0035] Figure 2 A common-mode voltage restrained three-phase four-wire converter LCL filter circuit topology structure diagram according to an embodiment of the present application is provided.

[0036] Figure 3 A common-mode voltage restrained three-phase four-wire converter LCL filter equivalent circuit topology structure diagram according to an embodiment of the present application is provided.

[0037] Figure 4 An αβ-axis voltage vector diagram of AZSPWM1 according to an embodiment of the present application is provided.

[0038] Figure 5 A carrier comparison modulation diagram of AZSPWM1 according to an embodiment of the present application is provided.

[0039] Figure 6 A value range diagram of a switching function of AZSPWM1 in x, y plane according to an embodiment of the present application is provided.

[0040] Figure 7 An example diagram of a common-mode voltage restrained three-phase four-wire converter LCL filter parameter determination device according to an embodiment of the present application is provided.

[0041] Figure 8 A structure diagram of an electronic device according to an embodiment of the present application is provided. DETAILED DESCRIPTION

[0042] Embodiments of the present application are described below in detail with reference to the accompanying drawings, wherein the same or similar components or components having the same or similar functions are denoted by the same or similar reference numerals throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0043] A common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method of an embodiment of the present application is described below with reference to the accompanying drawings. In view of the problems of the LCL filter parameter design of the common-mode voltage suppression PWM three-phase four-wire two-level four-bridge arm converter relying on artificial experience and circuit simulation, and the time-consuming and laborious design process, the present application provides a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method. In the method, the frequency domain distribution of the PWM modulation voltage can be obtained by using double Fourier decomposition, the function relationship from the filter parameters to the circuit characteristic output parameters can be established by combining the differential mode and common mode equivalent circuits and their transfer functions of the three-phase four-wire system, and the filter parameter feasible region can be solved by using various inequality constraint relationships. Thus, the problems of the LCL filter parameter design of the common-mode voltage suppression PWM three-phase four-wire two-level four-bridge arm converter relying on artificial experience and circuit simulation, and the time-consuming and laborious design process are solved.

[0044] Specifically, Figure 1 A flowchart of a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method provided by an embodiment of the present application is shown in FIG. 1.

[0045] In this embodiment, a common-mode voltage suppression three-phase four-wire converter LCL filter circuit topology diagram can be as shown in FIG. 2. Figure 2

[0046] Specifically, in the circuit topology diagram, O is the equivalent midpoint of the converter DC side, N is the AC side neutral point; L0 is the neutral line inductance, L1 is the converter side inductance, L2 is the grid side inductance, and Cf is the three-phase filter capacitance, which together constitute the grid-connected LCL filter; point a is the A-phase bridge arm output point, point b is the B-phase bridge arm output point, point c is the C-phase bridge arm output point, and point f is the fourth bridge arm output point.

[0047] Further, the circuit topology diagram can be simplified as shown in FIG. 3. Figure 3 The four-phase bridge arm and the DC side are simplified into four square wave output power supplies, wherein, v ao represents the output voltage of point a relative to point O, v bo represents the output voltage of point b relative to point O, v co represents the output voltage of point c relative to point O, and v fo ​The output voltage at point f relative to point O represents the output voltage of these four square wave voltage sources, which can only be 0.5U. dc and -0.5U dc The transitions between these two states are abrupt.

[0048] like Figure 1 As shown, the method for determining the LCL filter parameters of this common-mode voltage suppression three-phase four-wire converter includes the following steps:

[0049] In step S101, the entire spectrum of the common-mode voltage suppression PWM of the two-level four-arm converter is analyzed using double Fourier decomposition to obtain the frequency domain distribution of the PWM modulation voltage.

[0050] In some embodiments, double Fourier decomposition is used to analyze the entire spectrum of the common-mode voltage suppression PWM of the two-level four-arm converter to obtain the frequency domain distribution of the PWM modulation voltage. This includes: determining the coefficients of all harmonic components of the switching function of the ABC three-phase bridge arms of the two-level four-arm converter and the expression of the output switching signal of the fourth bridge arm; determining the output voltage functions of the first to fourth bridge arms; and obtaining the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the switching function of the ABC three-phase bridge arms, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0051] There are various types of two-level four-arm common-mode voltage suppression PWM. This invention takes AZSPWM1 (active zero state PWM1) as an example for analysis. This method can be applied to other types of two-level four-arm common-mode voltage suppression PWM.

[0052] Figure 4 This is a schematic diagram of the αβ axis voltage vector of AZSPWM1 provided in an embodiment of the present invention.

[0053] The two-level four-arm bridge system has a total of 16 vectors, of which 6 vectors do not generate common-mode voltage. These 6 vectors are V1 (PNNP), V2 (PPNN), V3 (NPNP), V4 (NPPN), V5 (NNPP), and V6 (PNPN). The AZSPWM1 modulation method utilizes the distance-to-reference voltage vector V from these 6 vectors within any switching cycle. ref The four most recent vectors are combined in a symmetrical manner, first counterclockwise and then clockwise, to form the reference voltage vector. As shown in Table 1, Table 1 is a table of vector selection and arrangement for the AZSPWM1 in this embodiment of the invention.

[0054] Table 1

[0055]

[0056] This vector modulation method is completely equivalent to, for example:Figure 5 The carrier wave is compared with the modulation wave. Taking phase A as an example, the two phases B and C are the same. When the reference voltage vector is located in the region above the α axis (A+ in the figure), the A-phase modulation wave should be compared with the carrier wave Λ with the opening facing downward; and when the reference voltage vector is located in the region below the α axis (A- in the figure), the A-phase modulation wave should be compared with the carrier wave with the opening facing upward The comparison is made.

[0057] Further, the carrier wave independent variable x and the modulation wave independent variable y are defined as follows:

[0058]

[0059] where ω c is the carrier wave angular frequency, ω0is the modulation wave angular frequency, for power frequency 50 Hz, ω0= 2πf0= 100π rad / s. θ c and θ0are the initial phases of the carrier wave and the modulation wave respectively, which can be selected at will. The appropriate initial phase angle is selected so that the modulation wave and the carrier wave are both symmetrical about the y axis, and at this time, the A-phase carrier wave u M and the modulation wave u C , the expressions are respectively:

[0060] u M (y) = M cos y

[0061]

[0062] Further, according to the basic principle of carrier wave modulation, the value range of the switching function q(x, y) of AZSPWM1 in the x, y plane can be obtained. Figure 6 The value range of the switching function of AZSPWM1 in the x, y plane provided by the embodiment of the present application is shown in the schematic diagram. As Figure 6 shown, the expressions of the four boundary lines are:

[0063]

[0064] Further, according to the basic principle of double Fourier decomposition, the embodiment of the present application can utilize the substitution z = y-ω0 / ω c (x-2pπ) and double integral to obtain the coefficients A mn and B mn of all harmonic components of the A-phase switching function corresponding to the AZSPWM1 method:

[0065] A 00 +jB 00 = 1

[0066]

[0067] Where, α = m + nω0 / ω c , J v (n) is Bessel function. Similarly, the expressions of B phase and C phase can be obtained by replacing y with and According to the basic principle of AZSPWM1, the expression of the output signal of the fourth bridge arm should be:

[0068] q f (t) = 2-q a (t) - q b (t) - q c (t) (5)

[0069] Further, in some embodiments, the output voltage functions of the first to fourth bridge arms are:

[0070] v(t) = U dc (q(t) - 0.5) (6)

[0071] Where, U dc is the rated voltage of the DC side, and q(t) is the output signal of each bridge arm.

[0072] Thus, the double Fourier decomposition expression of the output voltage of the four bridge arms can be obtained.

[0073] In step S102, based on the frequency domain distribution of the PWM modulated voltage, the function relationship of the filter parameters to the circuit characteristic output parameters is established according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system.

[0074] It should be noted that in the LCL filter, due to the existence of the resonance point, active damping or passive damping is usually needed to be designed, and in the embodiment of the present application, it is considered that for any set of filter parameters (L0, L1, L2, C f ), appropriate damping methods can be designed, and it can be equivalent to a capacitor in parallel with a resistor passive damping, and the equivalent resistance may be a pure resistance, a resistance-capacitance characteristic or a resistance-inductance characteristic according to different feedback methods and control systems.

[0075] In combination with Figure 2 the embodiment, the voltages of ABCN four-phase output points relative to the midpoint O of the DC side are v ao , v bo , v co , v fo , respectively. The state equations of the nine state variables can be listed as:

[0076]

[0077] Where, u pu is the equivalent output voltage of the ABC three bridge arms p = v po -v fo , p = a, b, c. u gp is the three-phase grid voltage. i 1p is the current through L1, positive direction out of the converter; i 2p is the current through L2, positive direction into the grid; v Cp is the voltage on the three-phase filter capacitor, respectively v Cp

[0078] Further, the Clark transformation is used to convert it to the differential mode circuit αβ axis and the common mode circuit 0 axis, and the Laplace transform is used to convert to the frequency domain to obtain the following state equation.

[0079] Among them, for the differential mode circuit αβ axis:

[0080]

[0081] Further, for the common mode circuit 0 axis:

[0082]

[0083] Further, the transfer function of the system from the input voltage u αβ0 to the converter output current i1, grid-connected current i2 in the αβ0 axis can be solved.

[0084] Further, in some embodiments, the differential mode circuit αβ axis transfer function is:

[0085]

[0086] The common mode circuit 0 axis transfer function is:

[0087]

[0088] Among them, i1 is the bridge arm output current, i2 is the grid-connected current, L0 is the middle line inductance, L1 is the converter side inductance, L2 is the grid side inductance, C f is the three-phase filter capacitor, s is the complex frequency, R f is the equivalent capacitor parallel resistance of active or passive damping, u g is the grid voltage, and u is the differential mode or common mode voltage excitation.

[0089] Thus, the double Fourier series of the four bridge arm output voltage can be solved, and the frequency domain distribution of the current circuit characteristic quantity can be solved by using the frequency domain distribution of the voltage excitation and the above transfer function.

[0090] In step S103, based on the preset constraint condition, a function relationship is solved to obtain a filter parameter feasible region, and final LCL filter parameters are determined according to the filter parameter feasible region.

[0091] Further, in some embodiments, the preset constraint condition will be introduced in detail respectively.

[0092] Firstly, the LCL resonant frequency is higher than 10 times of the power frequency and lower than 0.5 times of the switching frequency. Since there are two resonant frequencies of the differential mode resonant frequency and the common mode resonant frequency in the circuit, the constraint condition of the embodiment of the application can be written as the following inequalities:

[0093]

[0094] Wherein, f0 is the power grid frequency, f c is the switching frequency of the converter.

[0095] Secondly, the converter output does not exceed the maximum linear modulation ratio under all operating conditions. For the common mode voltage suppression PWM, the maximum linear modulation ratio is 1, and the maximum phase voltage effective value that the converter can output is Under all operating conditions, the phase voltage output by the converter should not exceed this limit, that is:

[0096]

[0097] Wherein: U dc is the DC side rated voltage, I max is the maximum output current effective value, U g,ph is the grid side rated phase voltage effective value.

[0098] Thirdly, the total reactive power on the filter capacitor is 2% to 5% of the rated capacity:

[0099]

[0100] Wherein: f0 is the power grid frequency, P rated is the rated power, U g,ph is the grid side rated phase voltage effective value.

[0101] Finally, the L f switching secondary current harmonic is less than or equal to the first multiple of the rated fundamental current effective value. Wherein, the L h switching secondary current harmonic is less than or equal to 0.3 times of the rated fundamental current effective value. When operating in the grid-connected mode, the THD of the grid-connected current is less than or equal to the first preset threshold, and the first mapping relationship between the odd harmonic order of the grid-connected current and the proportion of the rated grid-connected current, and the second mapping relationship between the even harmonic order of the grid-connected current and the proportion of the rated grid-connected current.

[0102] Specifically, the THD of the grid-connected current is not more than 3%, and each harmonic of the grid-connected current meets the requirements of IEEE Std. 1547-2003 as shown in Table 2.

[0103] Table 2

[0104] Harmonic number h (odd harmonics) Percentage of rated grid current / % h<11 4.0 11≤h<17 2.0 17≤h<23 1.5 23≤h<35 0.6 35≤h 0.3

[0105] It should be noted that the maximum limit of the even harmonic is 1 / 4 of the odd harmonic shown in the table.

[0106] In particular, for the two-level four-leg common-mode voltage suppression PWM, L0 = L h .

[0107] Therefore, the feasible region of the circuit parameters (L0, L1, L2, C f ) can be inversely solved, and the optimal solution can be determined by using a numerical method as long as an arbitrary optimization target is determined. For example, if L1 is required to be selected in order of priority, C f is required to be the smallest, and L2 is required to be the smallest, the optimization target f(L0, L1, L2, C f ) = 10 6 L1 + 10 3 C f + L2. If the relationship between the volume and the inductance of the reactor can be modeled, the optimization target can also be the minimum overall volume.

[0108] It should be noted that the above constraint conditions are only examples, and according to the double Fourier decomposition method provided by the present application, various constraint conditions based on the frequency domain and harmonics can be solved, and the application range is far beyond the cases given in this chapter. Similarly, the optimization target can also be arbitrarily selected, as long as it can be solved by using various optimization algorithms such as linear programming and genetic algorithm.

[0109] According to the LCL filter parameter determination method for a common-mode voltage suppression three-phase four-wire converter provided by the embodiment of the present application, the frequency domain distribution of the PWM modulation voltage can be obtained by using double Fourier decomposition, the function relationship from the filter parameters to the circuit characteristic output parameters is established by combining the differential mode and common mode equivalent circuits and their transfer functions of the three-phase four-wire system, and the filter parameter feasible region is solved by using various inequality constraint relationships, thereby solving the problems that the LCL filter parameter design of the three-phase four-wire two-level four-leg converter under the common-mode voltage suppression PWM depends on artificial experience and circuit simulation, and the design process is time-consuming and laborious, and improving the efficiency and reliability of the parameter design.

[0110] Secondly, the LCL filter parameter determination device for a common-mode voltage suppression three-phase four-wire converter provided by the embodiment of the present application is described with reference to the accompanying drawings.

[0111] Figure 7is a block schematic view of a common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination device according to an embodiment of the present application.

[0112] As shown in Figure 7 The common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination device 10 includes an analysis module 100, a mathematical modeling module 200, and a calculation module 300.

[0113] The analysis module 100 is configured to analyze the entire frequency spectrum of the common-mode voltage suppression PWM of the two-level four-leg converter by using double Fourier decomposition to obtain the frequency domain distribution of the PWM modulation voltage. The mathematical modeling module 200 is configured to establish a functional relationship between the filter parameters and the circuit characteristic output parameters based on the frequency domain distribution of the PWM modulation voltage and according to the differential-mode transfer function and the common-mode transfer function of the equivalent circuit of the three-phase four-wire system. The calculation module 300 is configured to solve the functional relationship to obtain a filter parameter feasible region based on a preset constraint condition, and determine the final LCL filter parameters according to the filter parameter feasible region.

[0114] Further, in some embodiments, the analysis module 100 is specifically configured to: determine the coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm; determine the output voltage functions of the first to fourth bridge arms; and obtain the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0115] Further, in some embodiments, the analysis module is specifically configured to: determine the coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm; determine the output voltage functions of the first to fourth bridge arms; and obtain the frequency domain distribution of the PWM modulation voltage based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage functions of the first to fourth bridge arms.

[0116] Further, in some embodiments, the differential-mode transfer function is:

[0117]

[0118] The common-mode transfer function is:

[0119]

[0120] Wherein, i1 is the bridge arm output current, i2 is the grid-connected current, L0 is the middle line inductance, L1 is the converter side inductance, L2 is the grid side inductance, C f is the three-phase filter capacitance, s is the complex frequency, R f is the active or passive damping equivalent capacitor parallel resistance, u g is the grid voltage, u is the differential mode or common mode voltage excitation.

[0121] Further, in some embodiments, the preset constraint condition is:

[0122]

[0123] Wherein, f0 is the grid frequency, f c is the switching frequency of the converter;The switching sub-current harmonic of L1 is less than or equal to the first multiple of the effective value of the rated fundamental current;When operating in grid-connected mode, the THD of the grid-connected current is less than or equal to the first preset threshold, and the first mapping relationship between the odd harmonic order of the grid-connected current and the proportion of the rated grid-connected current, and the second mapping relationship between the even harmonic order of the grid-connected current and the proportion of the rated grid-connected current;For two-level four-bridge common mode voltage suppression PWM, L0=L1.

[0124] It should be noted that the aforementioned explanation and description of the common mode voltage suppression three-phase four-wire converter LCL filter parameter determination method embodiment also applies to the common mode voltage suppression three-phase four-wire converter LCL filter parameter determination device of the embodiment, which will not be described here.

[0125] According to the common mode voltage suppression three-phase four-wire converter LCL filter parameter determination device provided by the embodiment of the application, the frequency domain distribution of the PWM modulation voltage can be obtained by using double Fourier decomposition, the function relationship from the filter parameter to the circuit characteristic output parameter is established by combining the differential mode and common mode equivalent circuit and its transfer function of the three-phase four-wire system, and the filter parameter feasible region is solved by using various inequality constraint relationships, so that the problems of relying on artificial experience and circuit simulation for the LCL filter parameter design of the three-phase four-wire two-level four-bridge converter under common mode voltage suppression PWM, and the time-consuming and laborious design process are solved, and the efficiency and reliability of parameter design are improved.

[0126] Figure 8 The structure schematic diagram of the electronic equipment provided by the embodiment of the application is shown. The electronic equipment can include:

[0127] The memory 801, the processor 802 and the computer program stored in the memory 801 and executable on the processor 802.

[0128] When the processor 802 executes the program, the common mode voltage suppression three-phase four-wire converter LCL filter parameter determination method provided in the above embodiment is realized.

[0129] Further, the electronic device further comprises:

[0130] A communication interface 803 is configured to communicate between the memory 801 and the processor 802.

[0131] The memory 801 is configured to store a computer program executable by the processor 802.

[0132] The memory 801 can include a high-speed RAM memory, and can further include a non-volatile memory, for example, at least one disk memory.

[0133] If the memory 801, the processor 802 and the communication interface 803 are implemented independently, the communication interface 803, the memory 801 and the processor 802 can be connected to each other through a bus and complete communication between each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For convenience of representation, Figure 8 In the figure, only one thick line is used to represent, but it does not mean that there is only one bus or one type of bus.

[0134] Optionally, in a specific implementation, if the memory 801, the processor 802 and the communication interface 803 are integrated on a chip, the memory 801, the processor 802 and the communication interface 803 can complete communication between each other through an internal interface.

[0135] The processor 802 can be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present application.

[0136] The embodiments of the present application also provide a computer readable storage medium, which stores a computer program, and the program is executed by a processor to implement the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method as above.

[0137] The embodiment of the present application also provides a computer program product comprising a computer program, which, when executed by a processor, implements the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method as described in the above embodiment.

[0138] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or N embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction.

[0139] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "N" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0140] Any process or method descriptions in flow charts or described elsewhere herein can be understood as representing code modules, segments, or portions of code that include one or more executable instructions for implementing the specified logical functions or steps, and the preferred embodiments of the present application also include the possibility that the described processes or methods can be implemented using hardware that can be generally processed by a processor, and that the processes or methods described as codes can be implemented with software and firmware that can be stored in memory that can be executed by a general purpose processor or a digital signal processor. It should be understood by those skilled in the art that the functions of the preferred embodiments of the present application can be implemented using any combination of hardware and software.

[0141] It should be understood that parts of the present application can be implemented in hardware, software, firmware or a combination thereof. In the above-described embodiments, N steps or methods can be implemented with software or firmware stored in a memory and executed by a suitable instruction execution system. As in another embodiment, if implemented with hardware, any one or a combination of the following technologies known in the art can be used: discrete logic circuit with logic gate circuit for implementing logical functions on data signals, application specific integrated circuit with suitable combination of logic gate circuit, etc.

[0142] Those skilled in the art can understand that all or part of the steps of the foregoing method embodiments can be completed by programs instructing relevant hardware, and the programs can be stored in a computer readable storage medium. When the programs are executed, the steps of the method embodiments or combinations thereof are included.

Claims

1. A method for determining LCL filter parameters of a common-mode voltage rejection three-phase four-wire converter, characterized in that, The method comprises the following steps: The full spectrum of the common-mode voltage suppression PWM of the two-level four-leg converter is analyzed by using double Fourier decomposition, and the frequency domain distribution of the PWM modulation voltage is obtained; Based on the frequency domain distribution of the PWM modulation voltage, the function relationship between the filter parameters and the circuit characteristic output parameters is established according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system; Based on the preset constraint condition, the function relationship is solved to obtain the feasible region of the filter parameters, and the final LCL filter parameters are determined according to the feasible region of the filter parameters; The preset constraint condition is: ； ； ； wherein is the DC side rated voltage, is the maximum output current root mean square value, L0 is the neutral line inductance, L1 is the converter side inductance, L2 is the grid side inductance, is the grid frequency, is the switching frequency of the converter, is the rated power, is the grid side rated phase voltage root mean square value; The middle switch sub-current harmonic is less than or equal to the first multiple of the rated fundamental current effective value. When running in the grid-connected mode, the total harmonic distortion value THD of the grid-connected current is less than or equal to a first preset threshold, and there is a first mapping relationship between each odd harmonic order of the grid-connected current and the proportion of the rated grid-connected current, and there is a second mapping relationship between each even harmonic order of the grid-connected current and the proportion of the rated grid-connected current; For two-level four-leg common-mode voltage suppression PWM, .

2. The method of claim 1, wherein, The method comprises the following steps: The coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm are determined; The output voltage functions of the first to fourth bridge arms are determined; The frequency domain distribution of the PWM modulation voltage is obtained based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm and the output voltage functions of the first to fourth bridge arms.

3. The method of claim 1, wherein, The differential mode transfer function is: ； The common mode transfer function is: ； wherein is the bridge arm output current, is the grid current, L0 is the neutral inductance, L1 is the converter side inductance, L2 is the grid side inductance, C f is the three-phase filter capacitance, is the complex frequency, R f is the capacitance parallel resistance equivalent to active or passive damping, u g is the grid voltage, u is the differential or common mode voltage excitation.

4. A common-mode voltage rejection three-phase four-wire converter LCL filter parameter determination apparatus, characterized in that, The device comprises: The analysis module is configured to analyze the full spectrum of the common-mode voltage suppression PWM of the two-level four-leg converter by using double Fourier decomposition, and obtain the frequency domain distribution of the PWM modulation voltage; The mathematical modeling module is configured to establish the function relationship between the filter parameters and the circuit characteristic output parameters according to the differential mode transfer function and the common mode transfer function of the equivalent circuit of the three-phase four-wire system based on the frequency domain distribution of the PWM modulation voltage; The calculation module is configured to solve the function relationship to obtain the feasible region of the filter parameters based on the preset constraint condition, and determine the final LCL filter parameters according to the feasible region of the filter parameters; The preset constraint condition is: ； ； ； wherein is the DC side rated voltage, is the maximum output current root mean square value, L0 is the neutral line inductance, L1 is the inverter side inductance, L2 is the grid side inductance, is the grid frequency, is the inverter switching frequency, is the rated power, is the grid side rated phase voltage root mean square value; The middle switch sub-current harmonic is less than or equal to the first multiple of the rated fundamental current effective value. When running in the grid-connected mode, the total harmonic distortion value THD of the grid-connected current is less than or equal to a first preset threshold, and there is a first mapping relationship between each odd harmonic order of the grid-connected current and the proportion of the rated grid-connected current, and there is a second mapping relationship between each even harmonic order of the grid-connected current and the proportion of the rated grid-connected current; For two-level four-leg common-mode voltage suppression PWM, .

5. The apparatus of claim 4, wherein, The analysis module is configured to analyze the full spectrum of the common-mode voltage suppression PWM of the two-level four-leg converter by using double Fourier decomposition, and obtain the frequency domain distribution of the PWM modulation voltage; The coefficients of all harmonic components of the ABC three-phase bridge arm switching function of the two-level four-leg converter and the expression of the output switching signal of the fourth bridge arm are determined; The output voltage functions of the first to fourth bridge arms are determined; The frequency domain distribution of the PWM modulation voltage is obtained based on the coefficients of all harmonic components of the ABC three-phase bridge arm switching function, the expression of the output switching signal of the fourth bridge arm, and the output voltage function of the first to fourth bridge arms.

6. The apparatus of claim 4, wherein, The differential mode transfer function is: ； The common mode transfer function is: ； wherein is the bridge arm output current, is the grid current, L0 is the neutral inductance, L1 is the converter side inductance, L2 is the grid side inductance, C f is the three-phase filter capacitance, is the complex frequency, R f is the active or passive damping equivalent capacitance parallel resistance, u g is the grid voltage, u is the differential or common mode voltage excitation.

7. An electronic device, comprising: Comprising: A memory, a processor, and a computer program stored on the memory and executable on the processor, the processor executing the program to implement the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method according to any one of claims 1-3.

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method according to any one of claims 1-3.

9. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to implement the common-mode voltage suppression three-phase four-wire converter LCL filter parameter determination method according to any one of claims 1-3.

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