Non-isolated flexible interconnection system common-mode interference suppression method, controller and medium

Abstract

The invention relates to the technical field of filters, particularly provides a common-mode interference suppression method for a non-isolated flexible interconnection system, a controller and a storage medium, and aims to solve the problem that the power density and the system stability of the non-isolated low-voltage flexible interconnection system cannot be considered in an existing method. For the purpose, the method provided by the invention comprises the steps of obtaining a resonant frequency range of common-mode interference generated by a system according to the capacitance of a capacitor and the inductance value of an inductor in a low-voltage flexible module, obtaining a parameter range of a common-mode inductor and a Y capacitor in the low-voltage flexible module, and constructing a target optimization function of the common-mode inductor and the Y capacitor; and obtaining an optimal solution of the target optimization function according to the target optimization function and the constraint condition thereof so as to realize common-mode interference suppression of the system. Therefore, not only can the power density of the system be reduced according to the target optimization function, but also the parameter optimal solutions of the common mode inductor and the Y capacitor in the electromagnetic interference filter can be determined, the common mode interference is effectively inhibited, and the stable operation of the system is ensured.

Description

Technical Field

[0001] The present application relates to the field of filter technology, and in particular to a common-mode interference suppression method, a controller and a storage medium for a non-isolated flexible interconnection system. Background Art

[0002] The flexible interconnection system is a highly flexible and adaptable network connection solution that achieves seamless connection and efficient collaboration between devices by using advanced communication technology and intelligent algorithms. The non-isolated low-voltage flexible interconnection system eliminates the isolation transformer in the traditional flexible interconnection system, which not only avoids the energy loss caused by the transformer and improves the overall efficiency of the system, but also reduces the size and weight of the equipment and reduces the cost of the equipment, and has broad application prospects.

[0003] However, compared with the traditional flexible interconnection system, the common-mode interference level in this non-isolated low-voltage flexible interconnection system is significantly improved. In addition, the common-mode leakage current generated by high-frequency common-mode interference excitation in the system flows in the distribution network, which also increases the network loss and affects the safe and stable operation of the power grid. Therefore, it is necessary to suppress the common-mode leakage current and reduce the common-mode interference level in the system to ensure the safe, reliable and efficient operation of the entire flexible interconnection system. The existing common-mode interference suppression methods are generally software control methods based on various improved pulse width modulation strategies. However, the non-isolated low-voltage flexible interconnection system contains a large number of complexly coupled power electronic equipment, and the asynchronous hardware modulation increases the complexity of the software control method and the control efficiency is low. Hardware optimization based on the improvement of the common-mode flow path, such as parameter optimization methods such as increasing common-mode inductance and impedance matching, will greatly reduce the system power density and is difficult to implement.

[0004] Accordingly, a new solution is needed in the art to solve the above problems. Application Contents

[0005] The present application aims to solve the above-mentioned technical problem, that is, to solve the problem that the existing common-mode interference suppression method cannot take into account both the power density and stability of the non-isolated low-voltage flexible interconnection system.

[0006] In a first aspect, the present application provides a common-mode interference suppression method for a non-isolated flexible interconnection system, the method being applied to a non-isolated low-voltage flexible interconnection system, the system comprising two low-voltage flexible modules, the low-voltage flexible module comprising an AC-DC conversion unit and an electromagnetic interference filter; the input end of the electromagnetic interference filter is connected to the AC side of the AC-DC conversion unit, and the output end of the electromagnetic interference filter is connected to a common connection point of a load; the DC side of the AC-DC conversion unit of each of the low-voltage flexible modules is respectively connected to a DC bus; the method comprises:

[0007] Obtaining a resonant frequency range in which a common-mode leakage current in each of the low-voltage flexible modules generates common-mode interference according to the capacitance of the capacitor and the inductance of the inductor in each of the low-voltage flexible modules;

[0008] According to the connection relationship of the electromagnetic interference filter of each of the low-voltage flexible modules, the parameter range of the common-mode inductor and the Y capacitor of each of the low-voltage flexible modules is obtained;

[0009] According to the inductance ratio between the inductance volume and the inductance of all inductors in the system and the capacitance ratio between the capacitance volume and the capacitance of all capacitors, a target optimization function of the common mode inductor and the Y capacitor is constructed; the constraint condition of the target optimization function is determined according to the resonant frequency range and the parameter range of the two low-voltage flexible modules;

[0010] According to the objective optimization function and the constraint conditions, an optimal solution of the objective optimization function is obtained, so as to achieve common-mode interference suppression of the system according to the common-mode inductance and Y capacitance corresponding to the optimal solution.

[0011] In a technical solution of the common-mode interference suppression method of the non-isolated flexible interconnection system, the step of obtaining the parameter range of the common-mode inductance and Y capacitance of the electromagnetic interference filter includes:

[0012] For each of the low-voltage flexible modules, the minimum inductance of the common-mode inductor of the low-voltage flexible module and the minimum capacitance of the Y capacitor are determined according to the ratio of the ground current to the common-mode leakage current after the electromagnetic interference filter of the low-voltage flexible module shuns the common-mode leakage current;

[0013] A stability analysis is performed on the system to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor.

[0014] In a technical solution of the common-mode interference suppression method of the above-mentioned non-isolated flexible interconnection system, the shunt current of the electromagnetic interference filter for the common-mode leakage current is the current flowing through the Y capacitor; the common-mode leakage current is the current flowing through the grid-side inductor connected in series with the common-mode inductor;

[0015] The determining of the minimum inductance of the common-mode inductor of the low-voltage flexible module and the minimum capacitance of the Y capacitor includes:

[0016] The common-mode leakage current after Laplace transformation is used as an input of a transfer function, and the shunt current after Laplace transformation is used as an output of the transfer function, wherein the Laplace transformation is used to establish a relationship between the inductance of the common-mode inductor and the capacitance of the Y capacitor and the values ​​of the common-mode leakage current and the shunt current;

[0017] constructing the transfer function according to the output quantity and the input quantity, wherein the transfer function is used to represent the ratio of the shunt current to the common-mode leakage current;

[0018] When the ratio reaches a preset lower limit, the inductance of the corresponding common-mode inductor is determined to be the minimum inductance according to the transfer function, and the capacitance of the corresponding Y capacitor is determined to be the minimum capacitance according to the transfer function.

[0019] In a technical solution of the common-mode interference suppression method of the above-mentioned non-isolated flexible interconnection system, the stability analysis of the system is performed to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor, including:

[0020] According to the outer loop control strategy of the system and the connection relationship of the electromagnetic interference filter in the system, a small signal model of the system is obtained;

[0021] Constructing a state space model of the system according to the small signal model, wherein the state variable of the state space model is the current value of the common mode leakage current;

[0022] Solving the state equation in the state space model to obtain a state matrix of the state space model, wherein the elements in the state matrix are used to represent the relationship between the inductance of the common mode inductor, the capacitance of the Y capacitor, and the common mode leakage current;

[0023] The eigenvalue of the state matrix is ​​solved, and the corresponding maximum capacitance of the Y capacitor and the maximum inductance of the common-mode inductor are determined according to the relationship between the eigenvalue and the stability of the system.

[0024] In a technical solution of the common-mode interference suppression method of the above-mentioned non-isolated flexible interconnection system, the inductance in the low-voltage flexible module includes the inductance of the common-mode inductor, the inductance of the filter inductor and the inductance of the grid-side inductor; the capacitance in the low-voltage flexible module includes the capacitance of the Y capacitor, the capacitance of the DC bus parasitic capacitance to ground generated by the grounding of the DC bus, and the parasitic capacitance of the power tube to ground generated in the AC-DC conversion unit;

[0025] The obtaining of the resonant frequency range of the common-mode leakage current in each of the low-voltage flexible modules generating the common-mode interference comprises:

[0026] For each low-voltage flexible module, obtaining a first comprehensive inductance according to the inductance of the common-mode inductor and the inductance of the filter inductor;

[0027] Obtaining a comprehensive capacitance according to the capacitance of the parasitic capacitance of the power tube to the ground and the capacitance of the parasitic capacitance of the DC bus to the ground;

[0028] Acquire a first resonant angular frequency according to the first comprehensive inductance and the comprehensive capacitance;

[0029] Obtaining a second comprehensive inductance according to the first comprehensive inductance and the inductance of the grid-side inductance;

[0030] Obtaining a second resonant angular frequency according to the second comprehensive inductance and the capacitance of the Y capacitor;

[0031] A resonant frequency range of the low-voltage flexible module is determined according to the first resonant angular frequency and the second resonant angular frequency.

[0032] In a technical solution of the common mode interference suppression method of the non-isolated flexible interconnection system, the method further includes determining the constraint conditions of the target optimization function according to the following steps;

[0033] According to the resonant frequency range of each of the low-voltage flexible modules, an upper limit of the resonant frequency and a lower limit of the resonant frequency of each of the low-voltage flexible modules are determined;

[0034] Determining a maximum upper resonance frequency limit from the upper resonance frequency limits of the two low-voltage flexible modules;

[0035] Determining a minimum resonant frequency lower limit from the resonant frequency lower limits of the two low-voltage flexible modules;

[0036] The resonant frequency range required for suppressing common-mode interference of the system is determined according to the maximum resonant frequency upper limit and the minimum resonant frequency lower limit.

[0037] In a technical solution of the common mode interference suppression method of the non-isolated flexible interconnection system, the electromagnetic interference filters in the two low voltage flexible modules include a common mode inductor L cm1 and L cm2 And Y capacitor C y1 and C y2 ;

[0038] The constructing the target optimization function of the common mode inductor and the Y capacitor includes constructing the target optimization function according to the following formula:

[0039] f(L cm1 , L cm2 , C y1 , C y2 )=min(k L (L cm1 +L cm2 )+k C (C y1 +C y2 ))

[0041] Among them, k L is the first coefficient, k C is the second coefficient, L cm1 is the common mode inductance of the first low voltage flexible module, L cm2 is the common mode inductor of the second low voltage flexible module, C y1 is the Y capacitor of the first low voltage flexible module, C y2 It is the Y capacitor of the second low voltage flexible module.

[0042] In a technical solution of the common-mode interference suppression method of the non-isolated flexible interconnection system, the method further includes obtaining the first coefficient and the second coefficient according to the following steps:

[0043] The first coefficient k is determined according to the average value of the maximum magnetic flux density of all inductors in the system and the maximum ripple current in each low-voltage flexible module. L ;

[0044] The second coefficient k is determined by dividing the ratio between the spacing between the capacitor plates of all capacitors in the system and the dielectric constant of the dielectric C .

[0045] In a second aspect, a controller is provided, comprising at least one processor; and a memory communicatively connected to the at least one processor; wherein a computer program is stored in the memory, and when the computer program is executed by the at least one processor, the method described in any one of the technical solutions of the above-mentioned method for suppressing common-mode interference of the non-isolated flexible interconnection system is implemented.

[0046] In a third aspect, a computer-readable storage medium is provided, wherein a plurality of program codes are stored therein, wherein the program codes are suitable for being loaded and run by a processor to execute the method described in any one of the technical solutions of the above-mentioned method for suppressing common-mode interference of the non-isolated flexible interconnection system.

[0047] The above one or more technical solutions of the present application have at least one or more of the following beneficial effects:

[0048] In the case of adopting the above technical solution, the method provided by the present application is applied to a non-isolated low-voltage flexible interconnection system, including: according to the inherent resonance peak value of the system, obtaining the resonant frequency range of the common-mode leakage current in the system to generate common-mode interference, according to the connection relationship of the electromagnetic interference filter in the system, obtaining the parameter range of the common-mode inductance and Y capacitor of the electromagnetic interference filter, and constructing the target optimization function of the common-mode inductance and Y capacitor according to the inductance ratio of the inductance volume to the inductance of the common-mode inductance and the capacitance ratio between the capacitance volume and the capacitance of the Y capacitor; the constraint conditions of the target optimization function are determined according to the resonant frequency range and the parameter range, and according to the target optimization function and its constraint conditions, the optimal solution of the target optimization function is obtained, so as to realize the common-mode interference suppression of the system according to the common-mode inductance and Y capacitor corresponding to the optimal solution. Among them, the system includes two low-voltage flexible modules, the low-voltage flexible module includes an AC-DC conversion unit and an electromagnetic interference filter; the input end of the electromagnetic interference filter is connected to the AC side of the AC-DC conversion unit, and the output end of the electromagnetic interference filter is connected to the common connection point of the load; the DC side of the AC-DC conversion unit of each low-voltage flexible module is connected to the DC bus respectively.

[0049] Through the above configuration, the present application can determine the resonant frequency range of common-mode interference generated by the common-mode leakage current in each low-voltage flexible module through the capacitance of the capacitor and the inductance of the inductor in the low-voltage flexible module, thereby constructing the relationship between the resonant frequency range and the electromagnetic interference filter parameters, and providing more accurate constraints for the optimization of the electromagnetic interference filter parameters. The target optimization function is constructed according to the ratio of the inductance volume to the inductance value of all inductors in the low-voltage flexible module and the ratio of the capacitance volume to the capacitance value of all capacitors to obtain the optimal solution of the inductance value and the capacitance value, and effectively optimizes the power density of the entire interconnected system. In this way, not only can the power density of the non-isolated low-voltage flexible interconnected system be reduced, but also the optimal solution of the parameters of the common-mode inductor and the Y capacitor in the electromagnetic interference filter can be determined to effectively suppress the common-mode interference in the non-isolated low-voltage flexible interconnected system, and ensure the stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The disclosure of the present application will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present application. Among them:

[0051] Figure 1 It is a schematic flow chart of the main steps of a common-mode interference suppression method for a non-isolated flexible interconnection system according to an embodiment of the present application;

[0052] Figure 2 Schematic diagram of the topological structure of the non-isolated low-voltage flexible interconnection system in the embodiment of the present application;

[0053] Figure 3 is a schematic structural diagram of a back-to-back flexible interconnection device in an embodiment of the present application;

[0054] Figure 4 It is a circuit diagram of a refined common-mode interference analysis model in an embodiment of the present application;

[0055] Figure 5 It is a circuit structure diagram of an implementation method of the common-mode leakage current and the flow direction of the ground current in the embodiment of the present application. DETAILED DESCRIPTION

[0056] Some embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the protection scope of the present application.

[0057] In the description of the present application, "module" and "processor" may include hardware, software or a combination of the two. A module may include hardware circuits, various suitable sensors, communication ports, memory, and may also include software parts, such as program code, or a combination of software and hardware. The processor may be a central processing unit, a microprocessor, an image processor, a digital signal processor or any other suitable processor. The processor has data and / or signal processing functions. The processor may be implemented in software, hardware or a combination of the two. Computer-readable storage media include any suitable medium that can store program code, such as a disk, a hard disk, an optical disk, a flash memory, a read-only memory, a random access memory, etc. The term "A and / or B" means all possible combinations of A and B, such as only A, only B or A and B. The term "at least one A or B" or "at least one of A and B" has a similar meaning to "A and / or B" and may include only A, only B or A and B. The singular terms "one" and "the" may also include plural forms.

[0058] Here we first explain some terms involved in this application.

[0059] The non-isolated low-voltage flexible interconnection system is a configuration of the power system. It uses voltage source converter (VSC) technology to achieve flexible transmission and distribution of DC power at a lower voltage level. The non-isolated low-voltage flexible interconnection system solves the problems of large size, heavy weight, low efficiency and high price of the existing low-voltage area flexible interconnection devices. By adopting a design without isolation transformer, it avoids the problem of flexible interconnection equipment circulation caused by the neutral point grounding on the low-voltage side of the distribution transformer. This system connects the first AC / DC converter through the first controller and the second controller to the second AC / DC converter, so that there is no need to configure an isolation transformer, thereby improving the efficiency and reliability of the system.

[0060] See attached Figure 1 , Figure 1 1 is a flow chart of the main steps of a method for suppressing common-mode interference in a non-isolated flexible interconnection system according to an embodiment of the present application. Figure 1 As shown, the common-mode interference suppression method of the non-isolated flexible interconnection system in the embodiment of the present application mainly includes the following steps S101 to S104.

[0061] Step S101: obtaining a resonant frequency range in which a common-mode leakage current in each low-voltage flexible module generates common-mode interference according to the capacitance of the capacitor and the inductance of the inductor in each low-voltage flexible module.

[0062] In this embodiment, this method is applied to a non-isolated low-voltage flexible interconnection system, which includes two low-voltage flexible modules, and the low-voltage flexible module includes an AC-DC conversion unit and an electromagnetic interference filter; the input end of the electromagnetic interference filter is connected to the AC side of the AC-DC conversion unit, and the output end of the electromagnetic interference filter is connected to the common connection point of the load; the DC side of the AC-DC conversion unit of each low-voltage flexible module is respectively connected to the DC bus.

[0063] The AC / DC conversion unit refers to a direct-current-alternating-current converter (AC / DC), which can be used to convert alternating current (AC) into direct current (DC) or convert direct current into alternating current.

[0064] Among them, electromagnetic interference filter refers to electromagnetic interference (EMI) filter, which is usually a low-pass filter circuit composed of a series inductor and a parallel capacitor. Its function is to eliminate electromagnetic interference in the interconnected system and has a greater blocking effect on high-frequency interference signals.

[0065] In this embodiment, the load common point is a key node in the power system that connects the user load and the power grid, wherein the user load can be power loads such as photovoltaics, energy storage, and charging piles.

[0066] In one embodiment, please refer to the attached Figure 2 , Figure 2 Schematic diagram of the topological structure of the non-isolated low-voltage flexible interconnection system in the embodiment of the present application. Figure 2 As shown, it can be used Figure 2 Non-isolated low voltage flexible interconnection system.

[0067] Among them, photovoltaics, energy storage, charging piles and other loads are connected to the public load point (Point of Common Coupling, PCC) through their respective converters, and the distribution stations at both ends are interconnected through non-isolated back-to-back flexible interconnection equipment.

[0068] Among them, please refer to the attached Figure 3 , Figure 3 Schematic diagram of the structure of the back-to-back flexible interconnection device in the embodiment of the present application. Figure 3 As shown, the back-to-back flexible interconnection device may include an electromagnetic interference filter (ie Figure 3 EMI filter in), passive filter (i.e. Figure 3 LC filter in the AC / DC converter (i.e. Figure 3 AC / DC conversion circuit in the circuit) and DC bus. Among them, Figure 3 Point o in the figure is the neutral point of the DC bus.

[0069] In this embodiment, if Figure 3 As shown, the input end of the EMI filter is connected to the output end of the LC filter, the input end of the LC filter is connected to the AC side of the AC / DC conversion circuit, the DC side of the AC / DC conversion circuit is connected to the DC bus, and the output ends of the EMI filters on both sides are respectively connected to Figure 2 The PCC point in the circuit forms the entire non-isolated low-voltage flexible interconnection system.

[0070] In this embodiment, the EMI filter, LC filter, AC / DC conversion circuit and the inductor or capacitor device connected to the EMI filter on one side of the DC bus can be used as a low-voltage flexible module. In some embodiments, the low-voltage flexible modules connected on both sides of the DC bus can be completely symmetrical and have consistent parameters, which is convenient for simplified analysis and calculation of actual circuits.

[0071] In this embodiment, a passive filter (LC passive filter) is a filter circuit formed by a combination of an inductor, a capacitor and a resistor, which can filter out one or more harmonics. The most common and easily adopted passive filter structure is to connect an inductor and a capacitor in series, which can form a low-impedance bypass for the main harmonics.

[0072] In this embodiment, when the parasitic capacitors are charged, they will form an electric field between the wires and the ground, causing current to flow from the live parts of the device or line to the ground, generating common-mode leakage current. That is, the common-mode leakage current is the current flowing to the ground through the parasitic capacitance to the ground in the circuit of the non-isolated low-voltage flexible interconnection system. In some embodiments, the causes of common-mode interference in the non-isolated low-voltage flexible interconnection system may include common-mode interference voltage series-connected to the power grid, radiation interference, different ground voltages, and common-mode interference caused by the internal circuit of the device to the power line.

[0073] In one embodiment, the inductance of the low-voltage flexible module may include the inductance of the common-mode inductor, the inductance of the filter inductor and the inductance of the grid-side inductor; the capacitance in the low-voltage flexible module includes the capacitance of the Y capacitor, the capacitance of the DC bus parasitic capacitance to ground generated by the DC bus grounding, and the parasitic capacitance of the power tube to ground generated in the AC-DC conversion unit.

[0074] In this implementation, step S101 may further include:

[0075] Step S1011: for each low-voltage flexible module, a first comprehensive inductance is obtained according to the inductance of the common-mode inductor and the inductance of the filter inductor.

[0076] Step S1012: Obtaining a comprehensive capacitance according to the capacitance of the parasitic capacitance of the power tube to the ground and the capacitance of the parasitic capacitance of the DC bus to the ground.

[0077] Step S1013: Obtain a first resonant angular frequency according to the first comprehensive inductance and the comprehensive capacitance.

[0078] Step S1014: obtaining a second comprehensive inductance according to the first comprehensive inductance and the inductance of the grid-side inductance.

[0079] Step S1015: acquiring a second resonant angular frequency according to the second comprehensive inductance and the capacitance of the Y capacitor.

[0080] Step S1016: determining a resonant frequency range of the low-voltage flexible module according to the first resonant angular frequency and the second resonant angular frequency.

[0081] In this embodiment, the resonant frequency range is the resonant frequency range when the common-mode leakage current of the low-voltage flexible module causes common-mode interference. The common-mode interference caused by the common-mode leakage current refers to the interference voltage generated by the leakage current in the circuit, which will cause charge accumulation and magnetic field changes, and then form a common-mode interference signal. The resonant frequency refers to the frequency when the common-mode interference reaches the resonant state in the circuit, and the resonant frequency range refers to the frequency range when the common-mode interference reaches the resonant state in the circuit.

[0082] In one embodiment, the connection between the inductors and capacitors in the two low-voltage flexible modules can be completely symmetrical, and the inductance of each inductor is equal to each other, and the capacitance of each capacitor is equal to each other. In this way, when constructing the target optimization function later, the constraint conditions of the target optimization function can be determined according to the resonant frequency range and parameter range of one of the low-voltage flexible modules, thereby saving computing resources.

[0083] In this embodiment, in each low-voltage flexible module, the grid-side inductor, the filter inductor and the common-mode inductor are connected in series. The Y capacitor is connected in parallel with the common-mode inductor, one end of the Y capacitor is grounded, and the other end is connected to the connection point between the common-mode inductor and the grid-side inductor.

[0084] Step S102: acquiring parameter ranges of common mode inductance and Y capacitance of each low voltage flexible module according to the connection relationship of the electromagnetic interference filter of each low voltage flexible module.

[0085] In this embodiment, the circuit of the electromagnetic interference filter includes a common-mode inductor and a Y capacitor, and the common-mode inductor and the Y capacitor are connected in parallel. Among them, the common-mode inductor is an electronic component used to suppress common-mode electromagnetic interference. Its main function is to filter the common-mode electromagnetic interference signal and play the role of EMI filtering. It can effectively suppress the common-mode interference signal in the balanced line without affecting the differential mode signal normally transmitted by the line. The Y capacitor refers to a safety capacitor, and its main function is to remove electromagnetic interference. In the circuit, the Y capacitor is generally used as a filter device to filter out electromagnetic noise and high-frequency noise in the circuit.

[0086] In this embodiment, the parameter range of the common mode inductor in the electromagnetic interference filter refers to the numerical range of the inductance of the common mode inductor, and the parameter range of the Y capacitor of the electromagnetic interference filter refers to the numerical range of the inductance of the Y capacitor.

[0087] In one implementation, step S102 may further include:

[0088] Step S1021: for each low-voltage flexible module, the minimum inductance of the common-mode inductor and the minimum capacitance of the Y capacitor of the low-voltage flexible module are determined according to the ratio of the ground current to the common-mode leakage current after the electromagnetic interference filter of the low-voltage flexible module shuns the common-mode leakage current.

[0089] Step S1022: Perform stability analysis on the system to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor.

[0090] In this embodiment, in the non-isolated low-voltage flexible interconnection system, the low-voltage flexible module is connected in series with the grid-side inductor and the grid-side inductor of the distribution network, and then connected in series with the neutral point grounding resistor on the grid side. The common-mode leakage current of each low-voltage flexible module is the current passing through the grid-side inductor and the grid-side resistor, and finally flows to the ground through the neutral point grounding resistor on the grid side.

[0091] In one embodiment, the electromagnetic interference filter of each low-voltage flexible module can shunt the common-mode leakage current through the Y capacitor. The shunt current of the common-mode leakage current by the electromagnetic interference filter is the current flowing through the Y capacitor; the common-mode leakage current is the current flowing through the grid-side inductor connected in series with the common-mode inductor.

[0092] In this implementation, step S1021 may further include:

[0093] Step S10211: taking the common-mode leakage current after Laplace transformation as the input of the transfer function, and taking the shunt current after Laplace transformation as the output of the transfer function.

[0094] Step S10212: construct a transfer function based on the output quantity and the input quantity.

[0095] Step S10213: when the ratio reaches a preset lower limit, the inductance of the corresponding common-mode inductor is determined to be the minimum inductance according to the transfer function, and the capacitance of the corresponding Y capacitor is determined to be the minimum capacitance according to the transfer function.

[0096] In this embodiment, Laplace transform is used to establish the relationship between the inductance of the common-mode inductor and the capacitance of the Y capacitor and the values ​​of the common-mode leakage current and the shunt current; the transfer function is used to represent the ratio of the shunt current to the common-mode leakage current.

[0097] In one embodiment, after the electromagnetic interference filter shunts the common-mode leakage current, each low-voltage flexible module can also shunt the common-mode leakage current through the common-mode inductor and the parasitic capacitance of the power tube to the ground generated by the AC-DC conversion unit as another shunt current. Therefore, the shunt current of the parasitic capacitance of the power tube to the ground generated by the common-mode inductor and the AC-DC conversion unit can also be used as the output of the transfer function, and the common-mode leakage current can be used as the input of the transfer function to construct a transfer function. In this way, each low-voltage flexible module can construct two transfer functions.

[0098] In one embodiment, the preset lower limit can be 0.01, that is, the shunting effect of the electromagnetic interference filter on the common-mode leakage current is only one percent of the common-mode leakage current, and the electromagnetic interference filter can no longer achieve the preset effect of suppressing the common-mode leakage current. At this time, the inductance of the common-mode inductor is the minimum inductance, and the capacitance of the Y capacitor is the minimum capacitance.

[0099] In one implementation, step S1022 may further include:

[0100] Step S10221: Obtain a small signal model of the system according to the outer loop control strategy of the system and the connection relationship of the electromagnetic interference filter in the system.

[0101] In this embodiment, the outer loop control strategy of the flexible interconnection system in step 10221 mainly participates in the coordinated control of the DC voltage and has the ability to maintain the stability of the AC voltage. Through this control strategy, the flexible interconnection system can maintain stable operation in a complex power grid environment and improve the overall efficiency and reliability of the power system.

[0102] In this embodiment, step S10221 can also list the small signal model according to the device information and line information of the capacitors and inductors in the non-isolated low-voltage flexible interconnection system. Among them, the device information can include the device rated capacity, rated voltage, switching frequency and other information of the EMI filter, LC filter and AC / DC conversion circuit in the system. The line information can include the AC line impedance, EMI filter parameters, LC filter parameters and the connection mode between each capacitor and inductor in the system.

[0103] In this embodiment, the small signal model is a mathematical analysis model used to describe the dynamic behavior of the system, especially the response under small disturbances. The small signal model uses linear equations to approximate the properties of nonlinear elements and is suitable for describing the interaction between small amplitude signals and electronic systems, circuits or components. The dynamic behavior of the system can be analyzed by linearizing the system equations.

[0104] Step S10222: construct a state space model of the system according to the small signal model.

[0105] In this embodiment, the state space model is a type of statistical model used to describe the dynamic changes of a variable in a random process. Especially in an interconnected system, this model can more flexibly and accurately describe the dynamic changes of time series data.

[0106] In this implementation, the state variable of the state-space model may be the current value of the common-mode leakage current.

[0107] In one embodiment, the small signal model can be converted into a state space model through the following steps: first, the state variables of the system are determined according to the small signal model, and the state variables may include the voltage, current or power of the system; then, the state equation is determined according to the linearized system equation in the small signal model, and the state equation is used to describe how the state variables change over time; secondly, the output variables and input variables of the system are determined, the input variable is the common mode voltage input to the entire non-isolated low-voltage flexible interconnection system, and the output variable is the current or voltage output by the entire non-isolated low-voltage flexible interconnection system; finally, a state space expression is formed according to the state equation, input variables and output variables, and the state space expression is expressed in matrix form, in which the state variable is a column vector, and the input variable and the output variable appear in matrix form.

[0108] As an example, the state equation of the state space model can be determined according to the following formula (1):

[0109]

[0110] Among them, A sys is the state matrix of the state space model, B sys is the input matrix of the state-space model, Δx sys is the state vector of the state space model, t is the time variable, Δu sys is the input variable of the state space variable.

[0111] Among them, the input variable Δu sys Used to represent the external input voltage, current or control signal of the entire system; input matrix B sys Used to express the relationship between input variables and system states.

[0112] Step S10223: Solve the state equation in the state-space model to obtain the state matrix of the state-space model.

[0113] In this embodiment, the elements in the state matrix are used to represent the relationship between the inductance of the common mode inductor and the capacitance of the Y capacitor and the common mode leakage current. In some embodiments, the elements in the state matrix may include an expression including the inductance of the common mode inductor and the capacitance of the Y capacitor.

[0114] Step S10224: solve the eigenvalue of the state matrix, and determine the maximum capacitance of the corresponding Y capacitor and the maximum inductance of the common-mode inductor according to the relationship between the eigenvalue and the stability of the system.

[0115] In one implementation, the following steps may be used to obtain the eigenvalues ​​of the state matrix: first, the characteristic polynomial of the state matrix is ​​obtained by expanding the determinant of the state matrix; then, the root of the characteristic polynomial equal to zero is solved and the obtained root is used as the final eigenvalue.

[0116] In this implementation, since the elements in the state matrix may have a quantitative relationship with the inductance of the common mode inductor and the capacitance of the Y capacitor, the eigenvalue also has a quantitative relationship with the inductance of the common mode inductor and the capacitance of the Y capacitor.

[0117] In this embodiment, the relationship between the eigenvalue and the stability of the system can be: if the real part of the eigenvalue is negative, it means that the system tends to a stable state in an oscillating manner; if the real part of the eigenvalue is positive, it means that the system may be in an unstable state.

[0118] In this embodiment, the real part of the eigenvalue can be set to 0, and the inductance of the common-mode inductor and the capacitance of the Y capacitor when the real part of the eigenvalue is 0 are determined, so as to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor in a stable state of the system.

[0119] Step S103: constructing a target optimization function of the common-mode inductor and the Y capacitor according to the inductance ratio between the inductance volume and the inductance of the common-mode inductor of the two low-voltage flexible modules and the capacitance ratio between the capacitance volume and the capacitance of the Y capacitor; the constraint conditions of the target optimization function are determined according to the resonant frequency range and parameter range of the two low-voltage flexible modules.

[0120] In this embodiment, the inductance ratio between the volume and the inductance of all inductors in the two low-voltage flexible modules can be used as a coefficient, and the capacitance ratio between the capacitance volume and the capacitance of all capacitors can be used as another coefficient to construct a target optimization function.

[0121] In one embodiment, the electromagnetic interference filters in the two low voltage flexible modules include a common mode inductor L cm1 and L cm2 And Y capacitor C y1 and C y2 .

[0122] In this embodiment, step S103 further includes: constructing a target optimization function f according to the following formula (2):

[0123] f(L cm1 , L cm2 , C y1 , C y2 )=min(k L (L cm1 +L cm2 )+k C (C y1 +Cy2 )) (2)

[0124] Among them, k L is the first coefficient, k C is the second coefficient, L cm1 is the common mode inductance of the first low voltage flexible module, L cm2 is the common mode inductor of the second low voltage flexible module, C y1 is the Y capacitor of the first low voltage flexible module, C y2 It is the Y capacitor of the second low voltage flexible module.

[0125] In one embodiment, the method further comprises obtaining the first coefficient k according to the following steps: L and the second coefficient k C :

[0126] Step S201: Determine the first coefficient k according to the average value of the maximum magnetic flux density of all inductors in the system and the maximum ripple current in the system L .

[0127] Step S202: Determine the second coefficient k based on the ratio between the distance between the capacitor plates of all capacitors in the system and the dielectric constant of the dielectric C .

[0128] In this embodiment, the maximum magnetic flux density is an important parameter of the inductor, the maximum ripple current refers to the maximum value of the ripple part in the current output by the DC power supply in the AC power supply, the capacitor plate spacing refers to the distance between the two plates of the capacitor, and the dielectric constant is a physical quantity that describes the ability of the dielectric material to store charge in an electric field.

[0129] As an example, the first coefficient k can be determined according to the following formula (3) and formula (4): L and the second coefficient k C .

[0130]

[0131]

[0132] Among them, ΔI max is the maximum ripple current of the system, B max is the maximum magnetic flux density of the inductor, d is the distance between the capacitor plates of the capacitor, and ε is the dielectric constant of the capacitor.

[0133] In one embodiment, step S103 further includes determining the constraint conditions of the target optimization function according to the following steps:

[0134] Step S301: for the resonant frequency range of each low-voltage flexible module, determine the upper limit and lower limit of the resonant frequency of each high-voltage flexible module.

[0135] Step S302: determining a maximum resonant frequency upper limit from the resonant frequency upper limits of the two low-voltage flexible modules.

[0136] Step S303: determining the minimum resonance frequency lower limit from the resonance frequency lower limits of the two low-voltage flexible modules.

[0137] Step S304: determining the resonance frequency range that the system needs to achieve in order to suppress common-mode interference according to the maximum resonance frequency upper limit and the minimum resonance frequency lower limit.

[0138] In one implementation, the resonant frequency range required for the system to suppress common-mode interference may be set to a resonant frequency range in which the resonant frequency is greater than the maximum resonant frequency upper limit and less than the minimum resonant frequency lower limit.

[0139] Step S104: according to the target optimization function and the constraint conditions, an optimal solution of the target optimization function is obtained, so as to achieve common-mode interference suppression of the system according to the common-mode inductance and Y-capacitance corresponding to the optimal solution.

[0140] In this embodiment, the optimal inductance of the corresponding common-mode inductor and the optimal capacitance of the Y capacitor in the system can be determined according to the optimal solution, so as to achieve effective shunting of the common-mode leakage current, suppress the common-mode interference invading both ends of the AC and DC power distribution system, and realize the common-mode interference suppression of the system.

[0141] In one implementation, the optimal solution of the objective optimization function may be obtained by using methods such as the translation straight line method, the test merit method, or the adjustment merit method. In other implementations, other methods may be used to obtain the optimal solution of the objective function according to the constraints.

[0142] In an application scenario according to an embodiment of the present application, Figure 3 A common-mode interference refinement analysis model of a non-isolated low-voltage flexible interconnection system connected with a back-to-back flexible interconnection device is built based on the back-to-back flexible interconnection device to facilitate circuit analysis and achieve parameter optimization of common-mode inductance and Y capacitor in EMI filters.

[0143] In this embodiment, the entire system may include an EMI filter, an LC filter, an AC / DC conversion circuit, and a DC bus. The input end of the EMI filter is connected to the output end of the LC filter, the input end of the LC filter is connected to the AC side of the AC / DC conversion circuit, the DC side of the AC / DC conversion circuit is connected to the DC bus, and the output ends of the EMI filters on both sides are respectively connected to the PCC point.

[0144] In this implementation, a common-mode interference refinement analysis model of the system can be further constructed according to the following steps:

[0145] Step S401: making an idealized assumption on a non-isolated low-voltage flexible interconnection system connected with back-to-back flexible interconnection devices.

[0146] In this embodiment, idealized assumptions may include: the PCC point is directly grounded and there is no ground leakage current path at the PCC point; all power tubes in the system are ideal components and all energy flows under working conditions; the AC / DC conversion circuits, LC filters and EMI filters on both sides of the DC bus are completely symmetrical and the parameters are consistent; the switching frequency of the power tube is much greater than the grid frequency, and the dead zone and transition process are not considered; the system adopts a mid-point balance control strategy, and the influence of the differential mode voltage on the common mode voltage can be ignored.

[0147] Step S402: constructing a refined common-mode interference analysis model according to the circuit of the non-isolated low-voltage flexible interconnection system.

[0148] The refined common mode interference analysis model can be found in the attached Figure 4 , Figure 4 : is a circuit diagram of a refined common mode interference analysis model in an embodiment of the present application. Figure 4 L s1 and L s2 The inductance of the filter inductor, L cm1 and L cm2 are the inductance of the common mode inductors of the two EMI filters at both ends, C y1 and C y2 L is the capacitance of the grounded Y capacitor in the EMI filter at both ends. g1 and L g2 are the inductance of the grid-side inductance on both sides of the grid, R g1 and R g2 are the resistance values ​​of the grid-side resistors on both sides of the grid, R s1 and R s2 Respectively represent the resistance value of the neutral point grounding resistance on both sides of the power grid, C sg1 and C sg2 They represent the capacitance values ​​of the parasitic capacitance to ground generated by the power switch tubes in the AC / DC converter on both sides of the DC bus, C dg Indicates the capacitance value of the DC bus parasitic capacitance to ground generated by the system, G is the system grounding point, V cm1 and V cm2 They respectively represent the voltage values ​​of the common mode voltage on the AC side of the AC / DC converter.

[0149] In this embodiment, the common mode interference suppression method of the non-isolated flexible interconnection system may include steps S501 to S505:

[0150] Step S501: Calculate the main resonant frequency of common-mode interference caused by common-mode leakage current in the system according to the refined common-mode interference analysis model of the non-isolated low-voltage flexible interconnection system.

[0151] In this embodiment, the main resonant frequency is a resonant frequency peak value caused by the line parameters of the system circuit, and the subsequent common-mode interference suppression is mainly used to suppress the common-mode interference at the resonant frequency peak value.

[0152] In this embodiment, the common mode leakage current can be divided into two currents, which flow through the neutral point grounding resistors R at both ends of the interconnection system. s1 and R s2 .

[0153] In one embodiment, please refer to the attached Figure 5 , Figure 5 1 is a schematic diagram of a circuit structure of an implementation method of the present application showing the common mode leakage current and the direction of the current to ground. Figure 5 As shown in Figure 2, there are multiple current paths to ground in the system, among which i cm0 is the parasitic capacitance C flowing through the DC bus to ground dg Current flowing into the grounding grid; i″ cm1 andi″ cm2 The parasitic capacitance C between the power switches on both sides sg1 and C sg2 Current flowing into the grounding grid; i′ cm1 and i′ cm2 The Y capacitor C y1 and C y2 The current flowing into the ground grid; i cm1 and i cm2 It is the current that flows through the AC line and the grounding impedance and invades the grounding network of the AC power grid on both sides.

[0154] In this embodiment, the common mode current i can be determined based on the relationship between the resonant angular frequency and the inductance and capacitance. cm1 The main resonant frequency.

[0155] As an example, the common mode current i can be determined according to the following formulas (5) to (7): cm1 The main resonant frequency ω 01 ,ω 02 and ω 03 :

[0156]

[0157]

[0158]

[0159] Among them, L eq1 =L cm1 / 3+L s1 / 3, C all =2C dg +6C sg1 +6C sg2 , R eq1 =R g1 / 3+R s1 .

[0160] Similarly, the common-mode current i can be determined according to the following formulas (8) to (10): cm2 The main resonant frequency ω 11 ,ω 12 and ω 13 :

[0161]

[0162]

[0163]

[0164] Among them, L eq2 =L cm2 / 3+L s2 / 3, R eq2 =R g2 / 3+R s2 .

[0165] Step S502: Determine the minimum inductance of the common-mode inductor and the minimum capacitance of the Y capacitor of the EMI filter according to the ratio of the common-mode leakage current to other ground currents.

[0166] In this embodiment, the ratio between other ground currents and common-mode leakage current can be obtained according to the following formulas (11) to (14), where H i15 (s) is the ground current i′ cm1 and common mode leakage current i cm1 The ratio between i13 (s) is i″ cm1 with i cm1 The ratio between i24 (s) is the ground current i′ cm2 and common mode leakage current i cm2 The ratio between i22 (s) is the ground current i″ cm2 and common mode leakage current i cm2 The ratio between .

[0167]

[0168]

[0169]

[0170]

[0171] Among them, i cm1 (s) and i cm2 (s) is the common mode leakage current i cm1 and i cm2 The expression after Laplace transformation, i′ cm1 (s) and i′ cm2 (s) is the ground current i′ cm1 and i′ cm2 The expression after Laplace transformation, i″ cm1 (s) and i″ cm2 (s) is the ground current i″ cm1 andi″ cm2 The Laplace transformed expression.

[0172] In one implementation, the lower limit of the ratio of the common-mode leakage current to other ground currents may be set to 0.01, at which point the inductance of the common-mode inductor is minimized and the capacitance of the Y capacitor is minimized.

[0173] In this embodiment, the minimum inductance L of the corresponding common-mode inductor can be determined according to formula (15) to formula (16): cm1_min and Lc m2_min :

[0174]

[0175]

[0176] Among them, f max It is the upper limit of the resonant frequency range f for the system to suppress common-mode interference.

[0177] Where k1 = L g1 (2πf max ) 2 +3R eq1 (2πf max ), k2=L g2 (2πf max ) 2 +3R eq2 (2πf max ).

[0178] In this embodiment, the minimum capacitance C of the corresponding Y capacitor can be determined according to formula (17) to formula (18): y1_min and C y2_min :

[0179]

[0180]

[0181] Among them, f max It is the upper limit of the resonant frequency range f for the system to suppress common-mode interference.

[0182] Step S503: constructing a state space model according to the refined common mode interference analysis model, and determining the maximum inductance of the common mode inductor and the maximum capacitance of the Y capacitor.

[0183] In this implementation, the manner of constructing the state space model and the manner of determining the maximum inductance and the maximum capacitance are the same as those in the above embodiment, and are not described in detail herein.

[0184] Step S504: constructing a target optimization function, and determining the constraint conditions of the target optimization function according to the maximum inductance and the minimum inductance of the common mode inductor, the maximum capacitance and the minimum inductance of the Y capacitor, and the main resonant frequency.

[0185] In this implementation, the target optimization function is constructed in the same manner as described in the above embodiment, and will not be described in detail here.

[0186] In one implementation, the constraints of the objective optimization function may be determined according to formula (19) to formula (24):

[0187]

[0188]

[0189] L cm1_min <L cm1 <L cm1_max (twenty one)

[0190] C y1_min <C y1 <Cy 1_max (twenty two)

[0191] L cm2_min <L cm2 <L cm2_max (twenty three)

[0192] C y2_min <C y2 <C y2_max(twenty four)

[0193] In this embodiment, f max The upper limit of the resonant frequency range f for common mode interference suppression of the system; f min It is the lower limit of the resonant frequency range f for the system to suppress common mode interference. cm1_min is the common mode inductance L cm1 The lower limit of the parameter range, L cm1_max is the common mode inductance L cm1 The upper limit of the parameter. y1_min is the Y capacitor C y1 The lower limit of the parameter range, C y1_max is the Y capacitor C y1 The upper limit of the parameter range. cm2_min is the common mode inductance L cm2 The lower limit of the parameter range, L cm2_max is the common mode inductance L cm2 The upper limit of the parameter. y2_min is the Y capacitor C y2 The lower limit of the parameter range, C y2_max is the Y capacitor C y2 The upper limit of the parameter range.

[0194] Step S505: solving the target optimization model to obtain the optimal inductance of the common mode inductor and the optimal capacitance of the Y capacitor.

[0195] Based on the method described in the above steps S101 to S104, the present application can determine the resonant frequency range of the common-mode leakage current in each low-voltage flexible module to generate common-mode interference through the capacitance of the capacitor and the inductance of the inductor in the low-voltage flexible module, thereby constructing the relationship between the resonant frequency range and the electromagnetic interference filter parameters, and providing more accurate constraints for the optimization of the electromagnetic interference filter parameters. The target optimization function is constructed according to the ratio of the inductance volume to the inductance value of all inductors in the low-voltage flexible module and the ratio of the capacitance volume to the capacitance value of all capacitors to obtain the optimal solution of the inductance value and the capacitance value, and effectively optimizes the power density of the entire interconnected system. In this way, not only can the power density of the non-isolated low-voltage flexible interconnected system be reduced, but also the optimal solution of the parameters of the common-mode inductor and the Y capacitor in the electromagnetic interference filter can be determined to effectively suppress the common-mode interference in the non-isolated low-voltage flexible interconnected system, and ensure the stable operation of the system.

[0196] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art can understand that in order to achieve the effect of the present application, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders. These adjusted schemes are equivalent to the technical schemes described in this application, and therefore will also fall within the scope of protection of this application.

[0197] It is understood by those skilled in the art that all or part of the processes in the method for implementing the above-mentioned embodiment of the present application can also be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable storage medium may include: any entity or device, medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium, etc. that can carry the computer program code.

[0198] Another aspect of the present application also provides a computer-readable storage medium.

[0199] In an embodiment of a computer-readable storage medium according to the present application, the computer-readable storage medium can be configured to store a program for executing the common-mode interference suppression method of a non-isolated flexible interconnection system of the above-mentioned method embodiment, and the program can be loaded and run by a processor to implement the above-mentioned common-mode interference suppression method of a non-isolated flexible interconnection system. For ease of explanation, only the parts related to the embodiment of the present application are shown. For specific technical details not disclosed, please refer to the method part of the embodiment of the present application. The computer-readable storage medium can be a storage device formed by various electronic devices. Optionally, the computer-readable storage medium in the embodiment of the present application is a non-temporary computer-readable storage medium.

[0200] Another aspect of the present application also provides a controller.

[0201] In an embodiment of a controller according to the present application, the controller may include at least one processor; and a memory communicatively connected to the at least one processor; wherein a computer program is stored in the memory, and when the computer program is executed by the at least one processor, the method described in any of the above embodiments is implemented.

[0202] So far, the technical solution of the present application has been described in conjunction with an embodiment shown in the accompanying drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present application.

Claims

1. A method for suppressing common-mode interference in a non-isolated flexible interconnection system. It is characterized in that The method is applied to a non-isolated low-voltage flexible interconnection system, the system comprising two low-voltage flexible modules, the low-voltage flexible modules comprising an AC-DC conversion unit and an electromagnetic interference filter; the input end of the electromagnetic interference filter is connected to the AC side of the AC-DC conversion unit, and the output end of the electromagnetic interference filter is connected to a load common connection point; the DC side of the AC-DC conversion unit of each low-voltage flexible module is respectively connected to a DC bus; the method comprises: Obtaining a resonant frequency range in which a common-mode leakage current in each of the low-voltage flexible modules generates common-mode interference according to the capacitance of the capacitor and the inductance of the inductor in each of the low-voltage flexible modules; According to the connection relationship of the electromagnetic interference filter of each of the low-voltage flexible modules, the parameter range of the common-mode inductor and the Y capacitor of each of the low-voltage flexible modules is obtained; According to the inductance ratio between the inductance volume and the inductance of all inductors in the system and the capacitance ratio between the capacitance volume and the capacitance of all capacitors, a target optimization function of the common mode inductor and the Y capacitor is constructed; the constraint condition of the target optimization function is determined according to the resonant frequency range and the parameter range of the two low-voltage flexible modules; According to the objective optimization function and the constraint conditions, an optimal solution of the objective optimization function is obtained, so as to achieve common-mode interference suppression of the system according to the common-mode inductance and Y capacitance corresponding to the optimal solution.

2. The method for suppressing common-mode interference of a non-isolated flexible interconnection system according to claim 1, It is characterized in that The obtaining of the parameter range of the common mode inductor and the Y capacitor of the electromagnetic interference filter includes: For each of the low-voltage flexible modules, the minimum inductance of the common-mode inductor of the low-voltage flexible module and the minimum capacitance of the Y capacitor are determined according to the ratio of the ground current to the common-mode leakage current after the electromagnetic interference filter of the low-voltage flexible module shuns the common-mode leakage current; A stability analysis is performed on the system to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor.

3. The method for suppressing common-mode interference of a non-isolated flexible interconnection system according to claim 2, It is characterized in that The shunt current of the electromagnetic interference filter for the common-mode leakage current is the current flowing through the Y capacitor; the common-mode leakage current is the current flowing through the grid-side inductor connected in series with the common-mode inductor; The determining of the minimum inductance of the common-mode inductor of the low-voltage flexible module and the minimum capacitance of the Y capacitor includes: The common-mode leakage current after Laplace transformation is used as an input of a transfer function, and the shunt current after Laplace transformation is used as an output of the transfer function, wherein the Laplace transformation is used to establish a relationship between the inductance of the common-mode inductor and the capacitance of the Y capacitor and the values ​​of the common-mode leakage current and the shunt current; constructing the transfer function according to the output quantity and the input quantity, wherein the transfer function is used to represent the ratio of the shunt current to the common-mode leakage current; When the ratio reaches a preset lower limit, the inductance of the corresponding common-mode inductor is determined to be the minimum inductance according to the transfer function, and the capacitance of the corresponding Y capacitor is determined to be the minimum capacitance according to the transfer function.

4. The common mode interference suppression method of the non-isolated flexible interconnection system according to claim 2, It is characterized in that The performing stability analysis on the system to determine the maximum inductance of the common-mode inductor and the maximum capacitance of the Y capacitor includes: According to the outer loop control strategy of the system and the connection relationship of the electromagnetic interference filter in the system, a small signal model of the system is obtained; Constructing a state space model of the system according to the small signal model, wherein the state variable of the state space model is the current value of the common mode leakage current; Solving the state equation in the state space model to obtain a state matrix of the state space model, wherein the elements in the state matrix are used to represent the relationship between the inductance of the common mode inductor, the capacitance of the Y capacitor, and the common mode leakage current; The eigenvalue of the state matrix is ​​solved, and the corresponding maximum capacitance of the Y capacitor and the maximum inductance of the common-mode inductor are determined according to the relationship between the eigenvalue and the stability of the system.

5. The method for suppressing common-mode interference of a non-isolated flexible interconnection system according to claim 1, It is characterized in that The inductance in the low-voltage flexible module includes the inductance of the common-mode inductor, the inductance of the filter inductor and the inductance of the grid-side inductor; the capacitance in the low-voltage flexible module includes the capacitance of the Y capacitor, the capacitance of the DC bus parasitic capacitance to ground generated by the grounding of the DC bus, and the parasitic capacitance of the power tube to ground generated in the AC-DC conversion unit; The obtaining of the resonant frequency range of the common-mode leakage current in each of the low-voltage flexible modules generating the common-mode interference comprises: For each low-voltage flexible module, obtaining a first comprehensive inductance according to the inductance of the common-mode inductor and the inductance of the filter inductor; Obtaining a comprehensive capacitance according to the capacitance of the parasitic capacitance of the power tube to the ground and the capacitance of the parasitic capacitance of the DC bus to the ground; Acquire a first resonant angular frequency according to the first comprehensive inductance and the comprehensive capacitance; Obtaining a second comprehensive inductance according to the first comprehensive inductance and the inductance of the grid-side inductance; Obtaining a second resonant angular frequency according to the second comprehensive inductance and the capacitance of the Y capacitor; A resonant frequency range of the low-voltage flexible module is determined according to the first resonant angular frequency and the second resonant angular frequency.

6. The method for suppressing common-mode interference of a non-isolated flexible interconnection system according to claim 5, It is characterized in that The method further comprises determining the constraint conditions of the objective optimization function according to the following steps; According to the resonant frequency range of each of the low-voltage flexible modules, an upper limit of the resonant frequency and a lower limit of the resonant frequency of each of the low-voltage flexible modules are determined; Determining a maximum upper resonance frequency limit from the upper resonance frequency limits of the two low-voltage flexible modules; Determining a minimum resonant frequency lower limit from the resonant frequency lower limits of the two low-voltage flexible modules; The resonant frequency range required for suppressing common-mode interference of the system is determined according to the maximum resonant frequency upper limit and the minimum resonant frequency lower limit.

7. The method for suppressing common-mode interference of a non-isolated flexible interconnection system according to claim 1, It is characterized in that The electromagnetic interference filters in the two low-voltage flexible modules include a common-mode inductor L cm1 and L cm2 And Y capacitor C y1 and C y2 ; The constructing the target optimization function of the common mode inductor and the Y capacitor includes constructing the target optimization function according to the following formula: f(L cm1 ,L cm2 ,C y1 ,C y2 )=min(k L (L cm1 +L cm2 )+k C (C y1 +C y2 )) Among them, k L is the first coefficient, k C is the second coefficient, L cm1 is the common mode inductance of the first low voltage flexible module, L cm2 is the common mode inductor of the second low voltage flexible module, C y1 is the Y capacitor of the first low voltage flexible module, C y2 It is the Y capacitor of the second low voltage flexible module.

8. The common mode interference suppression method of the non-isolated flexible interconnection system according to claim 7, It is characterized in that The method further comprises obtaining the first coefficient and the second coefficient according to the following steps: The first coefficient k is determined according to the average value of the maximum magnetic flux density of all inductors in the system and the maximum ripple current in each low-voltage flexible module. L ; The second coefficient k is determined based on the ratio between the spacing between the capacitor plates and the dielectric constant of all capacitors in the system. C .

9. A controller, It is characterized in that include: at least one processor; and, a memory communicatively coupled to the at least one processor; The memory stores a computer program, and when the computer program is executed by the at least one processor, the method for suppressing common-mode interference of a non-isolated flexible interconnection system according to any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a plurality of program codes stored therein, It is characterized in that The program code is suitable for being loaded and run by a processor to execute the common-mode interference suppression method for a non-isolated flexible interconnection system according to any one of claims 1 to 8.

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