A cable simulator, a cable loop modeling method, and an inverter

Abstract

The present invention provides a cable simulator, a modeling method for a cable loop, and an inverter. The method comprises: determining the self-inductance of a cable and the mutual inductance between two conductors in the cable, determining the equivalent inductance of each conductor in the cable according to the self-inductance and the mutual inductance of the cable, determining the resonant frequency of the cable, and determining the equivalent resistance of each conductor in the cable according to the resonant frequency of the cable, so that the cable can be equivalent to an inductance and a resistance, thereby analyzing the influence of the cable on the system by analyzing the influence of the inductance and the resistance on the system, and improving the service life of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of power stations, and more specifically, particularly relates to a cable simulator, a modeling method for a cable loop, and an inverter. Background Art

[0002] In actual photovoltaic power stations, the inverter and photovoltaic strings are connected through photovoltaic cables. Each string corresponds to two positive and negative wires, and the cables are connected to the input end of the inverter through cable troughs or trenches.

[0003] Generally, when analyzing the photovoltaic power station process, only the impact of the corresponding devices on the photovoltaic power station is analyzed, while the impact of the cables is ignored. In addition, the actual photovoltaic power station wiring is complicated, and the impact of the cables cannot be analyzed, which in turn has a certain impact on the power generation function and operation of the photovoltaic power station, reducing the service life of the photovoltaic power station. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a cable simulator, a cable loop modeling method, and an inverter, which are used to equate the cable to an inductor and a resistor, so as to analyze the influence of the cable on the system and improve the service life of the system by analyzing the influence of the inductor and the resistor on the system.

[0005] The first aspect of the present application discloses a cable loop modeling method, comprising:

[0006] determining the self-inductance of a cable and the mutual inductance between two conductors in said cable;

[0007] Determining the equivalent inductance of each of the conductors in the cable according to the self-inductance and mutual inductance of the cable;

[0008] determining a resonant frequency of the cable;

[0009] The equivalent resistance of each of the conductors in the cable is determined according to the resonant frequency of the cable.

[0010] Optionally, in the cable loop modeling method, determining the self-inductance of the cable includes:

[0011] The self-inductance of two of the conductors in the cable is calculated according to the length and radius of the conductors in the cable.

[0012] Optionally, in the cable loop modeling method, determining the mutual inductance between two conductors in the cable includes:

[0013] The mutual inductance between the wires is calculated according to the length of the wires in the cable and the distance between two of the wires.

[0014] Optionally, in the above cable loop modeling method, determining the equivalent inductance of each conductor in the cable according to the self-inductance and mutual inductance of the cable includes:

[0015] Determine the loop type of the cable; wherein the loop type is a common mode loop or a differential mode loop;

[0016] The equivalent inductance of each conductor in the cable is determined according to the loop type of the cable, the self-inductance and the mutual inductance of the cable.

[0017] Optionally, in the cable loop modeling method, determining the equivalent inductance of the cable according to the loop type of the cable includes:

[0018] If the loop type is a differential mode loop, the equivalent inductance of the conductor in the cable is the difference between the self-inductance of the conductor and the mutual inductance.

[0019] Optionally, in the cable loop modeling method, determining the equivalent inductance of the cable according to the loop type of the cable includes:

[0020] If the loop type is a common mode loop, the equivalent inductance of the conductors in the cable is the sum of the self-inductance and the mutual inductance of the conductors.

[0021] Optionally, in the cable loop modeling method, determining the resonant frequency of the cable includes:

[0022] The resonant frequency of the cable is determined according to the loop type of the cable.

[0023] Optionally, in the cable loop modeling method, determining the resonant frequency of the cable according to the loop type of the cable includes:

[0024] If the loop type is a differential mode loop, the resonant frequency of the cable is determined according to the self-inductance and mutual inductance of the cable and the differential mode capacitance value of the inverter input port in the cable simulator.

[0025] Optionally, in the cable loop modeling method, determining the resonant frequency of the cable according to the loop type of the cable includes:

[0026] If the loop type is a common mode loop, the resonant frequency of the cable is determined according to the self-inductance and mutual inductance of the cable and the capacitance value of the inverter to ground and the capacitance value of the new energy power generation unit to ground in the cable simulator.

[0027] Optionally, in the cable loop modeling method, determining the equivalent resistance of the cable according to the resonant frequency of the cable includes:

[0028] Determining the skin depth of the conductor in the cable according to the resonant frequency, the magnetic permeability and the electrical conductivity of the conductor;

[0029] The equivalent resistance of the wire is determined according to the skin depth, wire radius and wire length.

[0030] A second aspect of the present application discloses a cable simulator, wherein the equivalent inductance and equivalent resistance in the cable simulator are obtained by the cable loop modeling method as described in any one of the first aspect of the present application.

[0031] Optionally, in the above-mentioned cable simulator, the cable simulator includes: a cable equivalent inductance and a cable equivalent resistance;

[0032] The cable equivalent inductance and the equivalent resistance are both arranged between the new energy power generation unit and the inverter.

[0033] Optionally, in the above cable simulator, the cable equivalent inductance includes: a positive wire equivalent inductance and a negative wire equivalent inductance; the cable equivalent resistance includes: a positive wire equivalent resistance and a negative wire equivalent resistance;

[0034] The positive wire equivalent inductance and the positive wire equivalent resistance are arranged on the positive branch between the new energy power generation unit and the inverter;

[0035] The negative wire equivalent inductance and the negative wire equivalent resistance are arranged on the negative electrode branch between the new energy power generation unit and the inverter.

[0036] Optionally, in the above cable simulator, if the loop between the new energy power generation unit and the inverter is a differential mode loop:

[0037] The cable equivalent inductance and the cable equivalent resistance are both arranged on the positive branch or the negative branch between the new energy power generation unit and the inverter; or,

[0038] One of the cable equivalent inductance and the cable equivalent resistance is arranged on the positive branch, and the other of the cable equivalent inductance and the cable equivalent resistance is arranged on the negative branch;

[0039] The inductance of the cable equivalent inductance is the sum of the positive wire equivalent inductance and the negative wire equivalent inductance, and the resistance of the cable equivalent resistance is the sum of the positive wire equivalent resistance and the negative wire equivalent resistance.

[0040] Optionally, in the above-mentioned cable simulator, the cable equivalent inductance includes: a wound air-core coil.

[0041] Optionally, in the above-mentioned cable simulator, the cable equivalent inductance further includes: a magnetic core added to the air-core coil.

[0042] Optionally, in the above-mentioned cable simulator, a plurality of taps are provided on the wound hollow coil.

[0043] Optionally, in the above-mentioned cable simulator, the cable equivalent resistance includes: a power resistor and / or an adjustable resistor.

[0044] The third aspect of the present application discloses an inverter, wherein the differential common-mode capacitance parameters of the inverter are obtained by testing when the inverter is connected to a cable simulator as described in any one of the second aspect of the present application.

[0045] It can be seen from the above technical scheme that the present invention provides a modeling method for a cable loop, including: determining the self-inductance of the cable and the mutual inductance between two conductors in the cable, determining the equivalent inductance of each conductor in the cable based on the self-inductance and mutual inductance of the cable, determining the resonant frequency of the cable, and determining the equivalent resistance of each conductor in the cable based on the resonant frequency of the cable, so that the cable can be equivalent to inductance and resistance, thereby analyzing the influence of the inductance and resistance on the system to achieve analysis of the influence of the cable on the system and improve the service life of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 is a flow chart of a cable loop modeling method provided by an embodiment of the present invention;

[0048] Figure 2 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0049] Figure 3 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0050] Figure 4 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0051] Figure 5 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0052] Figure 6 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0053] Figure 7 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0054] Figure 8 is a flow chart of another cable loop modeling method provided by an embodiment of the present invention;

[0055] Fig. 9 is a schematic diagram of a new energy system provided by an embodiment of the present invention;

[0056] Fig.10 is a schematic diagram of another cable simulator provided by an embodiment of the present invention;

[0057] Fig.11 is a schematic diagram of another cable simulator provided by an embodiment of the present invention;

[0058] Fig.12 is a schematic diagram of another cable simulator provided by an embodiment of the present invention;

[0059] Fig.13 is a schematic diagram of another cable simulator provided by an embodiment of the present invention;

[0060] Fig.14 It is a schematic diagram of another cable simulator provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0061] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 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 are within the scope of protection of the present invention.

[0062] In this application, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0063] The embodiment of the present application provides a cable loop modeling method to solve the problem that in the prior art, when analyzing the photovoltaic power station process, only the impact of the corresponding devices on the photovoltaic power station is analyzed, while the impact of the cables is ignored. In addition, the wiring situation of the actual photovoltaic power station is complicated, and the impact of the cables cannot be analyzed, which in turn has a certain impact on the power generation function and operation of the photovoltaic power station, reducing the service life of the photovoltaic power station.

[0064] See also Figure 1 , the modeling method of the cable loop includes:

[0065] S101. Determine the self-inductance of the cable and the mutual inductance between two conductors in the cable.

[0066] It should be noted that when current flows through a wire, the wire will generate self-inductance. In the case of multiple wires, mutual inductance will be generated between the two wires.

[0067] The cable consists of two conductors, a positive conductor and a negative conductor, so the cable has both self-inductance and mutual inductance.

[0068] Both self-inductance and mutual inductance will have a certain impact on the system, so it is also necessary to determine the self-inductance and mutual inductance of the cable first.

[0069] The two devices are connected by a cable. Generally, the two wires are laid in parallel, and there will be mutual inductance between them.

[0070] It should be noted that the positive wire and the negative wire in the cable are not limited to being wrapped in one housing. The positive wire and the negative wire can be two independent wires, as long as they are in the same cable position, they are all within the protection scope of this application.

[0071] S102. Determine the equivalent inductance of each conductor in the cable based on the self-inductance and mutual inductance of the cable.

[0072] It should be noted that the length, spacing, and radius of each conductor of the same cable are equal, so the self-inductance of each conductor is equal, and the mutual inductance is the same, and thus the equivalent inductance of each conductor is equal.

[0073] S103: Determine the resonant frequency of the cable.

[0074] It should be noted that the resonant frequency of the cable can be obtained by calculation, and of course it is not excluded that it can be obtained by detection.

[0075] Determining the resonant frequency of the cable will not be described in detail here, and it can be determined according to the actual situation, which is within the protection scope of this application.

[0076] In addition, the resonant frequency of the cable can be divided into the resonant frequencies of the various conductors. However, as described above, the parameters of the various conductors are equal, and therefore, the resonant frequencies of the various conductors are equal.

[0077] S104: Determine the equivalent resistance of each conductor in the cable according to the resonant frequency of the cable.

[0078] It should be noted that the resonant frequencies of the conductors of the same cable are equal, and thus the equivalent inductances of the conductors are equal.

[0079] In this embodiment, the self-inductance of the cable and the mutual inductance between two conductors in the cable are determined, and based on the self-inductance and mutual inductance of the cable, the equivalent inductance of each conductor in the cable is determined, and the resonant frequency of the cable is determined. Based on the resonant frequency of the cable, the equivalent resistance of each conductor in the cable is determined, so that the cable can be equivalent to an inductor and a resistor, thereby analyzing the influence of the inductor and the resistor on the system to analyze the influence of the cable on the system and improve the service life of the system.

[0080] In practical applications, see Figure 2 The step S101 of determining the self-inductance of the cable includes:

[0081] S201. Calculate the self-inductance of two conductors in the cable according to the length and radius of the conductors in the cable.

[0082] Specifically, the formula used to calculate the self-inductance of the two conductors in the cable is:

[0083]

[0084] Among them, L is the self-inductance of the wire; LineRadius is the radius of the wire; LineDistance is the distance from the PV module to the inverter, that is, the length of the wire; μ0 is the magnetic permeability of the wire. Since the length and radius of each wire in the same cable are equal, the self-inductance of each wire in the same cable is equal.

[0085] In practical applications, see Figure 3 The step S101 of determining the mutual inductance between two conductors in the cable includes:

[0086] S301. Calculate the mutual inductance between the conductors according to the length of the conductors in the cable and the distance between the two conductors.

[0087] The formula used to calculate the mutual inductance of wire 1 to wire 2 is:

[0088]

[0089] Among them, LineDistance is the length of the wire, TwoLineAxisDis is the distance between the two wire axes, that is, the distance between the two wires; μ0 is the magnetic permeability of the wire.

[0090] The calculation process of the mutual inductance between wire 1 and wire 2 is similar, which will not be described here one by one, and all are within the protection scope of this application.

[0091] In practical applications, see Figure 4 The above step S102, determining the equivalent inductance of each conductor in the cable according to the self-inductance and mutual inductance of the cable, includes:

[0092] S401: Determine the loop type of the cable.

[0093] Among them, the loop type is a common mode loop or a differential mode loop.

[0094] That is to say, the loop type of the cable may be a common mode loop, or the loop type of the cable may be a differential mode loop.

[0095] The loop type of the cable can be determined directly or by calculation.

[0096] Specifically, the specific process of determining the loop type of the cable will not be described in detail here, and all are within the scope of protection of this application.

[0097] S402: Determine the equivalent inductance of each conductor in the cable according to the loop type of the cable, the self-inductance and the mutual inductance of the cable.

[0098] That is, under different loop types, the method of determining the equivalent inductance of each conductor is slightly different. Therefore, the equivalent inductance of each conductor in the cable can be determined according to different loop types.

[0099] In practical applications, see Figure 5 The above step S402, determining the equivalent inductance of each conductor in the cable according to the loop type of the cable, includes:

[0100] S501: Determine whether the loop type of the cable is a differential mode loop.

[0101] If the loop type is a differential mode loop, step S502 is executed.

[0102] S502. The equivalent inductance of the conductor in the cable is the difference between the self-inductance of the conductor and the mutual inductance.

[0103] Specifically, the equivalent inductance in the differential mode loop is in the form of: Lp=Ln=LM.

[0104] Among them, Lp is the equivalent inductance of the positive wire; Ln is the equivalent inductance of the negative wire; L is the self-inductance of the wire; M is the mutual inductance between the two wires.

[0105] If the loop type is not a differential mode loop, that is, a common mode loop, then step S503 is executed.

[0106] S503. The equivalent inductance of a conductor in a cable is the sum of the conductor's self-inductance and mutual inductance.

[0107] Specifically, the equivalent inductance in the common mode loop is in the form of: Lp=Ln=L+M.

[0108] Among them, Lp is the equivalent inductance of the positive wire; Ln is the equivalent inductance of the negative wire; L is the self-inductance of the wire; M is the mutual inductance between the two wires.

[0109] In this embodiment, the influence of the common-differential mode loop is taken into consideration, which can be used to design the common-differential mode capacitor parameters inside the inverter, avoid current resonance and reduce the cost of EMI filters, which is of great significance for solving the oscillation current in the differential mode loop and analyzing the leakage current in the common mode loop.

[0110] In practical applications, see Figure 6 , the above step S103 determines the resonant frequency of the cable, including:

[0111] S601. Determine the resonant frequency of the cable according to the loop type of the cable.

[0112] Among them, the loop type is a common mode loop or a differential mode loop.

[0113] That is to say, the loop type of the cable may be a common mode loop, or the loop type of the cable may be a differential mode loop.

[0114] The loop type of the cable can be determined directly or obtained by calculation, such as determining the loop type by the loop oscillation current, etc. The specific process of determining the loop type of the cable will not be repeated here and is within the scope of protection of this application.

[0115] It should be noted that the method of determining the resonant frequency of the cable is slightly different under different loop types. Therefore, the resonant frequency of the cable can be determined according to different loop types.

[0116] For details, see Figure 7 , according to the cable loop type, determine the cable resonant frequency, including:

[0117] S501: Determine whether the loop type of the cable is a differential mode loop.

[0118] If the loop type is a differential mode loop, step S701 is executed.

[0119] S701 : Determine the resonant frequency of the cable according to the inductance and mutual inductance of the cable and the differential mode capacitance value of the inverter input port in the cable simulator.

[0120] In the differential mode circuit, the resonant frequency is estimated as follows:

[0121]

[0122] Wherein, L is the self-inductance of the wire; M is the mutual inductance between the two wires; and Cx is the differential mode capacitance value of the inverter input port.

[0123] If the loop type is not a differential mode loop, that is, a common mode loop, then step S702 is executed.

[0124] S702: Determine the resonant frequency of the cable according to the inductance and mutual inductance of the cable and the capacitance value of the inverter to ground and the capacitance value of the new energy power generation unit to ground in the cable simulator.

[0125] In the common mode loop, the resonant frequency is estimated as follows:

[0126]

[0127] Among them, L is the self-inductance of the wire; M is the mutual inductance between the two wires; CyPV is the capacitance value of the new energy power generation unit to the ground; CyInv is the capacitance value of the inverter to the ground.

[0128] It should be noted that when determining the resonant frequency of the cable, the inverter operating switching frequency can be selected accordingly, which will not be elaborated here one by one, and it can be determined according to the actual situation, all of which are within the protection scope of this application.

[0129] In practical applications, see Figure 8 The above step S104, determining the equivalent resistance of the cable according to the resonant frequency of the cable, includes:

[0130] S801. Determine the skin depth of the conductor in the cable according to the resonant frequency, the magnetic permeability and the electrical conductivity of the conductor.

[0131] Specifically, the formula used to determine the skin depth of the conductor in the cable is:

[0132]

[0133] Among them, δ is the skin depth of the wire; f is the resonant frequency; μ0 is the magnetic permeability; σ is the electrical conductivity.

[0134] S802. Determine the equivalent resistance of the wire based on the skin depth, wire radius and wire length.

[0135] Specifically, the formula used to determine the equivalent resistance of the wire is:

[0136]

[0137] Among them, Rp is the equivalent resistance of the positive wire; Rn is the equivalent resistance of the negative wire; ρ is the conductor resistivity; LineRadius is the wire radius; LineDistance is the distance from the PV module to the inverter, that is, the wire length; δ is the skin depth of the wire.

[0138] Taking the photovoltaic system as an example, this application extracts the model parameters of the differential mode loop and the common mode loop according to the factors such as the line type, routing layout and frequency of interest of the photovoltaic string cable. Among them, the inductance is related to the radius, length and spacing between the positive and negative wires of the cable conductor; the resistance is related to the cable material (copper or aluminum), cross-sectional area, length, temperature and frequency. Considering the component ground capacitance CyPv and the differential mode capacitance Cx and ground capacitance Cy of the photovoltaic inverter input port, the model of the photovoltaic system is as follows: Fig. 9 shown.

[0139] Another embodiment of the present application provides a cable simulator.

[0140] See also Fig. 9 The cable simulator 30 can be arranged between the new energy power generation unit 10 and the inverter 20 .

[0141] It should be noted that a differential mode capacitor Cx is provided at the input port of the inverter 20 .

[0142] The new energy power generation unit 10 has its own ground capacitance CyPv.

[0143] The inverter 20 has its own capacitance Cy to ground.

[0144] The new energy power generation unit 10 includes: at least one of a photovoltaic power generation unit and a wind power generation unit.

[0145] The specific form of the new energy power generation unit 10 is not specifically limited here and can be determined according to actual conditions, all of which are within the protection scope of this application.

[0146] The equivalent inductance and equivalent resistance in the cable simulator 30 are obtained by the cable loop modeling method provided by any of the above embodiments.

[0147] The specific process and principle of the cable loop modeling method will not be described here one by one, and all are within the protection scope of this application.

[0148] In practical applications, the cable simulator 30 includes: cable equivalent inductance (including Fig.10 Lp and Ln shown) and cable equivalent resistance (including Fig.10 Rp and Rn shown).

[0149] The cable equivalent inductance and equivalent resistance are both arranged between the new energy power generation unit 10 and the inverter 20 .

[0150] That is to say, the inductance value of the cable equivalent inductance is the value of the cable equivalent inductance obtained by the cable loop modeling method provided in any of the above embodiments.

[0151] The resistance value of the cable equivalent resistance is the value of the cable equivalent resistance obtained by the cable loop modeling method provided in any of the above embodiments.

[0152] In practical applications, the cable equivalent inductance includes: positive wire equivalent inductance Lp and negative wire equivalent inductance Ln.

[0153] The cable equivalent resistance includes: the positive wire equivalent resistance Rp and the negative wire equivalent resistance Rn.

[0154] The positive wire equivalent inductance Lp and the positive wire equivalent resistance Rp are arranged on the positive branch between the new energy power generation unit 10 and the inverter 20 .

[0155] like Fig.10 As shown, the positive output terminal of the new energy power generation unit 10 is connected to the positive input terminal of the inverter 20 through the positive wire equivalent inductance Lp, the positive wire equivalent resistance Rp. The order between the positive wire equivalent inductance Lp and the positive wire equivalent resistance Rp is not specifically limited here, and it can be determined according to the actual situation, which is within the protection scope of this application.

[0156] The negative wire equivalent inductance Ln and the negative wire equivalent resistance Rn are arranged on the negative electrode branch between the new energy power generation unit 10 and the inverter 20 .

[0157] like Fig.10 As shown, the negative electrode of the output end of the new energy power generation unit 10 is connected to the negative electrode of the input of the inverter 20 through the negative wire equivalent inductance Ln and the negative wire equivalent resistance Rn. The order between the negative wire equivalent inductance Ln and the negative wire equivalent resistance Rn is not specifically limited here, and it can be determined according to the actual situation, which is within the protection scope of this application.

[0158] In practical applications, if the circuit between the new energy power generation unit 10 and the inverter 20 is a differential mode circuit:

[0159] The cable equivalent inductance and the cable equivalent resistance are both arranged on the positive branch or the negative branch between the new energy power generation unit 10 and the inverter 20 .

[0160] Specifically, the cable equivalent inductance and the cable equivalent resistance are both arranged on the positive branch between the new energy power generation unit 10 and the inverter 20 (eg Fig.11or, the cable equivalent inductance and the cable equivalent resistance are both arranged on the negative branch between the new energy power generation unit 10 and the inverter 20 (as shown in FIG. Fig.12 shown).

[0161] Alternatively, one of the cable equivalent inductance and the cable equivalent resistance is set on the positive branch, and the other of the cable equivalent inductance and the cable equivalent resistance is set on the negative branch.

[0162] Specifically, the cable equivalent inductance is set on the positive branch, and the cable equivalent resistance is set on the negative branch (such as Fig.13 or, the cable equivalent resistance is set in the positive branch, and the cable equivalent inductance is set in the negative branch (as shown in Fig.14 shown).

[0163] Among them, the inductance of the cable equivalent inductance is the sum of the positive wire equivalent inductance and the negative wire equivalent inductance, that is, Lp+Ln; the resistance of the cable equivalent resistance is the sum of the positive wire equivalent resistance and the negative wire equivalent resistance, Rp+Rn.

[0164] In this embodiment, the cable equivalent inductance can be realized as the inductance made of Lp+Ln, and the cable equivalent resistance can be realized as the resistance made of Rp+Rn, which can be placed at the positive or negative end of the loop. This has the advantage of reducing the number of components in the cable simulator.

[0165] It should be noted that since the inductance formed by the actual string cables will not decay even under higher current conditions, the inductance value obtained according to the above steps and circuit types can be achieved by winding a hollow coil. The advantage is that it is similar to the actual working conditions and the inductance value will not decay under high current.

[0166] That is, the equivalent inductance of the cable includes: winding an air-core coil.

[0167] If the maximum current under certain working conditions is predicted, adding a magnetic core to the air-core coil can greatly reduce the volume of the air-core inductor, but the key point of its design is that the magnetic core will not saturate under the predicted maximum current of the working conditions.

[0168] That is, the equivalent inductance of the cable also includes: the magnetic core added to the air-core coil.

[0169] In practical applications, a plurality of taps are provided on the wound air-core coil.

[0170] There are multiple taps on the wound hollow coil. The inductance value can be changed by changing the tap connection position to simulate different layouts of actual photovoltaic cables on site.

[0171] In practical applications, the cable equivalent resistance includes: power resistance and / or adjustable resistance.

[0172] That is to say, the setting of the cable equivalent resistance can be achieved through a power resistor or an adjustable resistor.

[0173] Another embodiment of the present application provides an inverter.

[0174] The differential common mode capacitance parameters of the inverter are obtained by testing when the inverter is connected to a cable simulator as described in any one of the above items.

[0175] The specific structure of the inverter will not be described in detail here, and will be determined according to the actual situation, all of which are within the protection scope of this application.

[0176] The specific structure and principle of the cable simulator will not be described in detail here, and all are within the protection scope of this application.

[0177] In this embodiment, the common-mode and differential-mode capacitor parameters inside the inverter are designed by using a cable simulator to avoid current resonance and reduce the cost of EMI filters, which is of great significance for solving the oscillating current in the differential mode loop and analyzing the leakage current in the common mode loop.

[0178] The features recorded in the various embodiments in this specification can be replaced or combined with each other, and the same and similar parts between the various embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0179] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0180] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cable loop modeling method, characterized in that: include: determining the self-inductance of a cable and the mutual inductance between two conductors in said cable; Determining the equivalent inductance of each of the conductors in the cable according to the self-inductance and mutual inductance of the cable; Determining a resonant frequency of the cable according to a loop type of the cable; The equivalent resistance of each of the conductors in the cable is determined according to the resonant frequency and conductor parameters of the cable.

2. The cable loop modeling method according to claim 1, characterized in that: Determine the self-inductance of the cable, including: The self-inductance of two of the conductors in the cable is calculated according to the length and radius of the conductors in the cable.

3. The cable loop modeling method according to claim 1, characterized in that: Determine the mutual inductance between two conductors in a cable, including: The mutual inductance between the wires is calculated according to the length of the wires in the cable and the distance between two of the wires.

4. The cable loop modeling method according to claim 1, characterized in that: Determining the equivalent inductance of each conductor in the cable according to the self-inductance and mutual inductance of the cable includes: Determine the loop type of the cable; wherein the loop type is a common mode loop or a differential mode loop; The equivalent inductance of each conductor in the cable is determined according to the loop type of the cable, the self-inductance and the mutual inductance of the cable.

5. The cable loop modeling method according to claim 4, characterized in that: Determining the equivalent inductance of the cable according to the loop type of the cable includes: If the loop type is a differential mode loop, the equivalent inductance of the conductor in the cable is the difference between the self-inductance of the conductor and the mutual inductance.

6. The cable loop modeling method according to claim 4, characterized in that: Determining the equivalent inductance of the cable according to the loop type of the cable includes: If the loop type is a common mode loop, the equivalent inductance of the conductors in the cable is the sum of the self-inductance and the mutual inductance of the conductors.

7. The cable loop modeling method according to claim 1, characterized in that: Determining the resonant frequency of the cable according to the loop type of the cable includes: If the loop type is a differential mode loop, the resonant frequency of the cable is determined according to the self-inductance and mutual inductance of the cable and the differential mode capacitance value of the inverter input port in the cable simulator.

8. The cable loop modeling method according to claim 1, characterized in that: Determining the resonant frequency of the cable according to the loop type of the cable includes: If the loop type is a common mode loop, the resonant frequency of the cable is determined according to the self-inductance and mutual inductance of the cable and the capacitance value of the inverter to ground and the capacitance value of the new energy power generation unit to ground in the cable simulator.

9. The cable loop modeling method according to any one of claims 1 to 8, characterized in that: The conductor parameters include the magnetic permeability and electrical conductivity of the conductor, as well as the conductor radius and the conductor length; The determining the equivalent resistance of each of the conductors in the cable according to the resonant frequency and conductor parameters of the cable comprises: Determining the skin depth of the conductor in the cable according to the resonant frequency, the magnetic permeability and the electrical conductivity of the conductor; The equivalent resistance of the wire is determined according to the skin depth, wire radius and wire length.

10. A cable simulator, characterized in that: The equivalent inductance and equivalent resistance in the cable simulator are both constructed by the cable loop modeling method according to any one of claims 1 to 9.

11. The cable simulator according to claim 10, characterized in that: The cable simulator includes: a cable equivalent inductance and a cable equivalent resistance; The cable equivalent inductance and the equivalent resistance are both arranged between the new energy power generation unit and the inverter.

12. The cable simulator according to claim 11, characterized in that: The cable equivalent inductance includes: positive wire equivalent inductance and negative wire equivalent inductance; the cable equivalent resistance includes: positive wire equivalent resistance and negative wire equivalent resistance; The positive wire equivalent inductance and the positive wire equivalent resistance are arranged on the positive branch between the new energy power generation unit and the inverter; The negative wire equivalent inductance and the negative wire equivalent resistance are arranged on the negative electrode branch between the new energy power generation unit and the inverter.

13. The cable simulator according to claim 11, characterized in that: If the circuit between the new energy power generation unit and the inverter is a differential mode circuit: The cable equivalent inductance and the cable equivalent resistance are both arranged on the positive branch or the negative branch between the new energy power generation unit and the inverter; or, One of the cable equivalent inductance and the cable equivalent resistance is arranged on the positive branch, and the other of the cable equivalent inductance and the cable equivalent resistance is arranged on the negative branch; The inductance of the cable equivalent inductance is the sum of the positive wire equivalent inductance and the negative wire equivalent inductance, and the resistance of the cable equivalent resistance is the sum of the positive wire equivalent resistance and the negative wire equivalent resistance.

14. The cable simulator according to claim 11, characterized in that: The cable equivalent inductance includes: a wound air-core coil.

15. The cable simulator according to claim 14, characterized in that: The cable equivalent inductance also includes: a magnetic core added to the air-core coil.

16. The cable simulator according to claim 14, characterized in that: The wound hollow coil is provided with a plurality of taps.

17. The cable simulator according to any one of claims 11 to 16, characterized in that: The cable equivalent resistance includes: a power resistance and / or an adjustable resistance.

18. An inverter, characterized in that: The differential common-mode capacitance parameters of the inverter are obtained by testing when the inverter is connected to a cable simulator as described in any one of claims 10-17.

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