Modularized multi-level direct current transformer broadband impedance online calculation method and device

Abstract

The invention discloses an online calculation method and device for broadband impedance of a modular multi-level direct-current transformer, and relates to the field of direct-current transformers, and the method comprises the steps: obtaining the relation of all electric quantities during the steady-state operation of the modular multi-level direct-current transformer based on a circuit topological structure of the modular multi-level direct-current transformer; establishing a power circuit model based on the relation of each electrical quantity during steady-state operation; establishing a control circuit model based on the input and output of the controller group of the modularized multi-level direct current transformer; establishing a small signal impedance model based on the power circuit model and the control circuit model; and calculating the broadband impedance of the modularized multi-level direct-current transformer based on the small-signal impedance model. According to the invention, the broadband impedance of the DC transformer can be calculated on line with high precision and high efficiency in different application scenarios.

Description

Technical Field

[0001] The present application relates to the field of direct current transformers, and in particular to a method and device for online calculation of broadband impedance of a modular multi-level direct current transformer. Background Art

[0002] DC grid technology can realize large-scale DC interconnection of multiple energy bases and is an important direction for the development of DC transmission in the future. Due to the rapid response and control characteristics of power electronic equipment, broadband oscillation accidents in power systems occur frequently. Small signal impedance analysis is an effective method to study broadband oscillation problems in power systems. The key premise is to obtain the impedance characteristics of power electronic equipment through impedance modeling.

[0003] As the core equipment for building DC power grid, the broadband impedance model of high-voltage and large-capacity modular multi-level DC transformer is a prerequisite for analyzing the stability of DC power grid. At present, the broadband impedance modeling technology of new energy and power electronic converters is relatively mature, but the research on impedance modeling and stability analysis of modular multi-level DC transformer is almost blank, and most of the existing impedance measurement methods are based on electromagnetic transient simulation software for sweep frequency measurement, which is inefficient and has complex algorithms. Summary of the invention

[0004] The purpose of this application is to provide a modular multi-level DC transformer broadband impedance online calculation method and device, which can calculate the broadband impedance of the DC transformer online with high accuracy and high efficiency in different application scenarios.

[0005] To achieve the above objectives, this application provides the following solutions.

[0006] In a first aspect, the present application provides an online calculation method for the broadband impedance of a modular multilevel DC transformer, comprising: obtaining the relationship between various electrical quantities of the modular multilevel DC transformer during steady-state operation based on the circuit topology of the modular multilevel DC transformer; establishing a power circuit model based on the relationship between various electrical quantities during steady-state operation; establishing a control circuit model based on the input and output of a controller group of the modular multilevel DC transformer; establishing a small signal impedance model based on the power circuit model and the control circuit model; and calculating the broadband impedance of the modular multilevel DC transformer based on the small signal impedance model.

[0007] In a second aspect, the present application provides an online calculation device for broadband impedance of a modular multi-level DC transformer, comprising: a signal processing unit, used to process the time domain signal of the modular multi-level DC transformer using an FFT algorithm to obtain frequency domain signals at different frequency points; a power circuit modeling unit, used to establish a power circuit model; a control circuit modeling unit, used to establish a control circuit model; a broadband impedance calculation board, respectively connected to the signal processing unit, the power circuit modeling unit and the control circuit modeling unit, for calculating broadband impedance according to the frequency domain signals at different frequency points, the power circuit model and the control circuit model; a data storage device, connected to the broadband impedance calculation board, for storing calculation data of the broadband impedance calculation board; a display, connected to the broadband impedance calculation board, for displaying the calculation data of the broadband impedance calculation board.

[0008] According to the specific embodiments provided in this application, this application has the following technical effects.

[0009] (1) Efficient and flexible calculation: This application adopts an efficient algorithm and calculation model and is not restricted by a specific DC transformer circuit topology and control method. It can calculate different power circuit models and control circuit models under different working conditions according to the needs of actual application scenarios. There is no need to use a computer to scan impedance data point by point, thus achieving high efficiency and flexibility in broadband impedance calculation.

[0010] (2) High calculation accuracy: This application adopts a high-precision mathematical model and calculation method, which can collect and process small signal disturbances in real time according to changes in the system operating conditions, so that the broadband impedance calculation results are dynamically updated and can accurately reflect the dynamic behavior of the system at different times and under different disturbances. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 A schematic flow chart of a method for online calculation of broadband impedance of a modular multi-level DC transformer provided in one embodiment of the present application.

[0013] Figure 2 Schematic diagram of the circuit topology of a modular multi-level DC transformer.

[0014] Figure 3 This is the control block diagram of the modular multilevel DC transformer.

[0015] Figure 4 Schematic diagram of the simulation verification results of the DC transformer port model, where (a) is a schematic diagram of the simulation verification results of the low-voltage side port impedance model, and (b) is a schematic diagram of the simulation verification results of the high-voltage side port admittance model.

[0016] Figure 5 Schematic diagram of simulation verification results of simplified model of DC transformer port, where (a) is the schematic diagram of simulation verification results of simplified model of low-voltage side port impedance, and (b) is the schematic diagram of simulation verification results of simplified model of high-voltage side port admittance.

[0017] Figure 6 The block diagram is a structural diagram of a modular multi-level DC transformer broadband impedance online calculation device. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0019] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0020] In an exemplary embodiment, Figure 1 As shown, a modular multi-level DC transformer broadband impedance online calculation method is provided. The method is executed by a computer device, and can be specifically executed by a computer device such as a terminal or a server alone, or can be executed by a terminal and a server together. In an embodiment of the present application, the method is applied to a server as an example for explanation, including the following steps S1 to S5.

[0021] S1: Based on the circuit topology of the modular multilevel DC transformer, the relationship between the electrical quantities of the modular multilevel DC transformer during steady-state operation is obtained.

[0022] This embodiment only takes a circuit topology structure of a DC transformer as an example for explanation, and in practice it can also be applied to other circuit structures and is not limited to this topology. Figure 2 As shown in FIG. 1 , the modular multilevel DC transformer includes a high voltage bridge arm, a common bridge arm and a low voltage bridge arm. The high voltage bridge arm contains The common bridge arm contains The low voltage bridge arm contains The high-voltage bridge arm and the common bridge arm both use half-bridge sub-modules (HBSM), which can only output positive voltage, and the low-voltage bridge arm uses full-bridge sub-modules (FBSM), which can output voltage polarity positive or negative. For the convenience of description, the valve output voltage of each bridge arm sub-module is uniformly defined as ,in, , , respectively , Two phases, , , , respectively represent the high voltage bridge arm, common bridge arm and low voltage bridge arm. The current of each bridge arm is , the submodule capacitor voltage is , the sum of the submodule capacitor voltages is ;The submodule capacitance value is , the bridge arm inductance is , the modulation coefficient of each bridge arm is .

[0023] according to Figure 2 The circuit structure topology shown can obtain the dynamic characteristic relationship inside each bridge arm of the modular multi-level DC transformer during steady-state operation.

[0024] (1)

[0025] in, is the number of sub-modules put into use in each bridge arm.

[0026] like Figure 3 As shown, the controller group of the modular multi-level DC transformer includes a half-bridge module energy balance controller, a full-bridge arm current controller and a low-voltage side DC voltage controller. The number of each arm sub-module input can be represented by the arm modulation voltage (common-mode AC modulation voltage, differential-mode AC modulation voltage, differential-mode DC modulation voltage) output by each controller.

[0027] (2)

[0028] in, for The number of phase high voltage bridge arm submodules put into use, for The number of phase common bridge arm submodules put into use, for The number of low-voltage bridge arm submodules put into use, for The number of phase high voltage bridge arm submodules put into use, for The number of phase common bridge arm submodules put into use, for The number of low-voltage bridge arm submodules put into use, It is the differential mode AC modulation voltage output by the half-bridge module energy balance controller. It is the common-mode AC modulation voltage output by the half-bridge module energy balance controller. is the submodule capacitor voltage rating, is the differential mode AC modulation voltage output by the full-bridge arm current controller, It is the differential-mode DC modulation voltage output by the low-voltage side DC voltage controller. is the common mode AC modulation voltage distribution coefficient.

[0029] According to Kirchhoff's voltage / current law, the relationship between the internal electrical quantity of the modular multi-level DC transformer and the external DC voltage / current can be obtained.

[0030] (3)

[0031] In the formula, , are the high voltage side DC voltage and the low voltage side DC voltage respectively, and are the DC current on the high voltage side and the DC current on the low voltage side, respectively. is the high voltage bridge arm submodule valve output voltage, is the common bridge arm submodule valve output voltage, is the low voltage bridge arm submodule valve output voltage, is the resistance value of the bridge arm inductor, is the high voltage bridge arm current, is the common bridge arm current, is the low voltage bridge arm current, for Phase high voltage bridge arm current, for Phase high voltage bridge arm current, for Phase low voltage bridge arm current, for Phase low voltage bridge arm current.

[0032] S2: Establish a power circuit model based on the relationship between various electrical quantities during steady-state operation. The power circuit model includes a first constraint relationship, a second constraint relationship, a third constraint relationship, and a fourth constraint relationship. Step S2 specifically includes: performing frequency domain transformation on the relationship between various electrical quantities during steady-state operation to obtain a steady-state model of the power circuit; performing small signal processing on the steady-state model of the power circuit using the small signal disturbance components of various electrical quantities and the bridge arm modulation voltage to obtain a small signal model of the power circuit; determining the small signal disturbance constraint relationship between the common-mode component of the sub-module capacitor voltage difference between the high-voltage bridge arm and the common bridge arm and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current based on the small signal model of the power circuit, which is defined as the first constraint relationship; determining the small signal disturbance constraint relationship between the differential-mode component of the low-voltage bridge arm current and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current based on the small signal model of the power circuit, which is defined as the second constraint relationship; determining the small signal disturbance constraint relationship between the low-voltage side DC voltage and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current based on the small signal model of the power circuit, which is defined as the third constraint relationship; determining the small signal disturbance constraint relationship between the high-voltage side DC current and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current based on the small signal model of the power circuit, which is defined as the fourth constraint relationship.

[0033] In this embodiment, the power circuit of the modular multilevel DC transformer is modeled by a multi-harmonic linearization method, which mainly includes two steps: first, the relationship between the electrical quantities of the modular multilevel DC transformer in steady-state operation in formulas (1)-(3) is converted from the time domain to the frequency domain to obtain a steady-state model of the power circuit; then, a small signal linearization method is used to further obtain a small signal model of the power circuit.

[0034] First, define the seventh-order steady-state vector , mainly including fundamental frequency, second frequency and third harmonic components.

[0035] (4)

[0036] in," " represents the conjugate operation, is the steady-state DC component vector of variable z, Respectively represent their frequencies , and The steady-state vector of the components.

[0037] Further, The corresponding Toeplitz matrix is ​​defined as formula (5).

[0038] (5)

[0039] In the formula, the symbol “ ” represents the Toeplitz operation.

[0040] Then, the relationship between the electrical quantities in formulas (1)-(3) is transformed into the frequency domain to obtain the corresponding steady-state model of the power circuit.

[0041] (6)

[0042] in, is the steady-state frequency domain vector of the valve output voltage of each bridge arm submodule, , , respectively , Two phases, , , , respectively represent the high voltage bridge arm, the common bridge arm and the low voltage bridge arm, The steady-state frequency domain vector of the number of inputs to each bridge arm submodule, is the steady-state matrix of the submodule capacitance, is the steady-state frequency domain vector of the capacitor voltage of each bridge arm submodule, is the steady-state frequency domain vector of each bridge arm current, for The steady-state frequency domain vector of the number of phase high-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the differential-mode AC modulation voltage output by the half-bridge module energy balance controller, for Partition coefficient, is the steady-state frequency domain vector of the common-mode AC modulation voltage output by the half-bridge module energy balance controller, is the steady-state frequency domain vector of the differential-mode DC modulation voltage output by the low-voltage side DC voltage controller, is the submodule capacitor voltage rating, for The steady-state frequency domain vector of the number of phase common bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase low-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the differential-mode AC modulation voltage output by the full-bridge arm current controller, for The steady-state frequency domain vector of the number of phase high-voltage bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase common bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase low-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the DC voltage on the high-voltage side, is the steady-state frequency domain vector of the high-voltage bridge arm submodule valve output voltage, is the steady-state frequency domain vector of the common bridge arm submodule valve output voltage, is the steady-state matrix of the bridge arm inductance, is the steady-state frequency domain vector of the high-voltage bridge arm current, is the steady-state frequency domain vector of the common bridge arm current, is the steady-state frequency domain vector of the low-voltage side DC voltage, is the steady-state frequency domain vector of the low-voltage bridge arm submodule valve output voltage, is the steady-state frequency domain vector of the low-voltage bridge arm current, is the steady-state frequency domain vector of the DC current on the high-voltage side, for The steady-state frequency domain vector of the phase high-voltage bridge arm current, for The steady-state frequency domain vector of the phase high-voltage bridge arm current, is the steady-state frequency domain vector of the DC current on the low-voltage side, for The steady-state frequency domain vector of the phase low-voltage bridge arm current, for The steady-state frequency domain vector of the phase low-voltage bridge arm current.

[0043] and The specific expression of is as follows.

[0044] (7)

[0045] In the above formula, represents a diagonal matrix, is the seventh-order identity matrix, is the fundamental angular frequency.

[0046] In this embodiment, the small signal disturbance component of each electrical quantity and the bridge arm modulation voltage output by each controller is used to perform small signal processing on the power circuit steady-state model (Formula (6)) to obtain the power circuit small signal model.

[0047] (8)

[0048] In the formula, the subscripts “0” and “ " represent the steady-state frequency domain component and the small signal disturbance component respectively, is the small signal disturbance vector of the valve output voltage of each bridge arm submodule, is the small signal disturbance vector of the capacitor voltage of each bridge arm submodule, The number of small signal disturbance vectors input to each bridge arm submodule, is the small signal perturbation matrix of the submodule capacitance, is the small signal disturbance vector of each bridge arm current, for The small signal disturbance vector of the number of phase high voltage bridge arm submodules put into operation, is the small signal disturbance vector of the differential mode AC modulation voltage output by the half-bridge module energy balance controller, is the small signal disturbance vector of the common-mode AC modulation voltage output by the half-bridge module energy balance controller, is the small signal disturbance vector of the differential mode DC modulation voltage output by the low voltage side DC voltage controller, for The small signal disturbance vector of the number of phase common bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase high voltage bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase common bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase low-voltage bridge arm submodules put into operation, is the small signal disturbance vector of the differential-mode AC modulation voltage output by the full-bridge arm current controller, for The small signal disturbance vector of the number of phase low-voltage bridge arm submodules put into operation, is the small signal disturbance vector of the DC voltage on the high voltage side, is the small signal disturbance vector of the high-voltage bridge arm submodule valve output voltage, is the small signal disturbance vector of the common bridge arm submodule valve output voltage is the small signal disturbance matrix of the bridge arm inductance, is the small signal disturbance vector of the DC voltage on the low voltage side, is the small signal disturbance vector of the common bridge arm current, is the small signal disturbance vector of the high voltage bridge arm current, is the small signal disturbance vector of the low voltage bridge arm submodule valve output voltage, is the small signal disturbance vector of the low voltage bridge arm current, is the small signal disturbance vector of the DC current on the high voltage side, for The small signal disturbance vector of the phase high voltage bridge arm current, for The small signal disturbance vector of the phase high voltage bridge arm current, is the small signal disturbance vector of the DC current on the low voltage side, for The small signal disturbance vector of the phase low voltage bridge arm current, for Small signal disturbance vector of the phase low-voltage bridge arm current.

[0049] and The expression of is as follows.

[0050] (9)

[0051] In the formula, Represents the small signal disturbance angular frequency.

[0052] Formula (8) can be used to obtain the small signal disturbance relationship between the high-voltage bridge arm modulation coefficient, the common bridge arm modulation coefficient, the high-voltage side DC voltage, the low-voltage side DC voltage, the high-voltage bridge arm current, and the common bridge arm current.

[0053] (10)

[0054] in, is the small signal disturbance vector of the high voltage bridge arm modulation coefficient, is the small signal disturbance vector of the common bridge arm modulation coefficient, is the small signal disturbance vector of the low voltage bridge arm modulation coefficient. The coefficient matrix , , , , , , , , , The detailed expression of is as follows.

[0055] (11)

[0056] (12)

[0057] In the above formula, , , , , , , , , are coefficient matrices, , , They are the frequency domain vectors of submodule capacitor voltage, bridge arm current, and modulation coefficient respectively.

[0058] From the relationship between the low-voltage bridge arm current of the two-phase DC transformer and the low-voltage side DC current in formula (8), the small signal disturbance relationship between the bridge arm modulation coefficient, the high-voltage side DC voltage, the low-voltage side DC current and the low-voltage side DC voltage can be obtained as follows.

[0059] (13)

[0060] In the formula, , , , , , are coefficient matrices.

[0061] Substituting formula (13) into (10) and eliminating the variables, the small signal disturbance constraint relationship between the bridge arm modulation coefficient, the high-voltage side DC voltage, the low-voltage side DC current and the bridge arm current can be obtained as follows.

[0062] (14)

[0063] Among them, the coefficient matrix (All subscripts omitted) The expression is as follows.

[0064]

[0065] (15)

[0066] Then, substitute the relationship between the modulation coefficient of each bridge arm and the modulation voltage of the bridge arm in formula (8) into formula (14) to obtain formula (16).

[0067] (16)

[0068] In the formula, , , are coefficient matrices.

[0069] Substituting formula (16) into formula (8), we can obtain the small signal disturbance constraint relationship between the common-mode component of the sub-module capacitor voltage difference between the high-voltage bridge arm and the common bridge arm and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current as follows.

[0070] (17)

[0071] in, It is the small signal disturbance vector of the common mode component of the submodule capacitor voltage difference between the high voltage bridge arm and the common bridge arm.

[0072] Coefficient Matrix - The expression is as follows.

[0073] (18)

[0074] In the formula, is the small signal impedance matrix of the submodule capacitors, , , , , are coefficient matrices.

[0075] The small signal disturbance constraint relationship between the differential mode component of the low-voltage bridge arm current and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current can be obtained from formula (16).

[0076] (19)

[0077] in, is the small signal disturbance vector of the differential mode component of the low-voltage bridge arm current.

[0078] Coefficient Matrix The expression is as follows.

[0079] (20)

[0080] Substituting the constraint relationship between the bridge arm modulation voltage output by the controller and the number of sub-modules put into formula (13), the small signal disturbance constraint relationship between the low-voltage side DC voltage and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current is obtained as follows.

[0081] (twenty one)

[0082] Among them, the coefficient matrix - The expression is as follows.

[0083] (twenty two)

[0084] In the above formula, , , , , are coefficient matrices.

[0085] Substituting formula (16) into the relationship between the high-voltage side DC current and the bridge arm current in formula (8), the small signal disturbance constraint relationship between the high-voltage side DC current and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current is obtained as follows.

[0086] (twenty three)

[0087] Among them, the coefficient matrix - The expression is as follows.

[0088] (twenty four)

[0089] In summary, the power circuit model of the modular multilevel DC transformer can be expressed as follows by formulas (17), (19), (21), and (23).

[0090] (25)

[0091] S3: Establish a control circuit model based on the input and output of the controller group of the modular multi-level DC transformer. The controller group includes a half-bridge module energy balance controller, a full-bridge arm current controller and a low-voltage side DC voltage controller. The control circuit model includes: a small signal frequency domain model of the half-bridge module energy balance controller, a small signal frequency domain model of the full-bridge arm current controller and a small signal frequency domain model of the low-voltage side DC voltage controller.

[0092] The half-bridge module energy balance controller establishes the small signal component of the common-mode AC modulation voltage generated by the common-mode component of the capacitor voltage difference between the high-voltage bridge arm and the common bridge arm submodule through the half-bridge module energy balance control; the full-bridge bridge arm current controller establishes the small signal component of the differential-mode AC modulation voltage generated by the low-voltage bridge arm circulating current through the full-bridge bridge arm current control; the low-voltage side DC voltage controller establishes the small signal component of the differential-mode DC modulation voltage generated by the low-voltage side DC voltage through the low-voltage side DC voltage control. After integrating the small signal components of the above bridge arm modulation voltages, the total modulation signal of each bridge arm can be obtained, thereby establishing a control circuit model.

[0093] In a specific embodiment, the modular multi-level DC transformer control structure is as follows: Figure 3 As shown in the figure, it includes three parts: half-bridge module energy balance control, full-bridge arm current control and low-voltage side DC voltage control. Half-bridge module energy balance control controls the common-mode AC modulation voltage To balance the charging and discharging energy of the submodules of the high-voltage bridge arm and the common bridge arm. The full-bridge bridge arm current control is achieved by adjusting the full-bridge submodule valve output voltage To offset the differential AC voltage output by the high-voltage bridge arm and the common bridge arm, so as to eliminate the circulating current between the low-voltage bridge arms. The low-voltage side DC voltage control adjusts the differential DC component of the voltage between the high-voltage bridge arm and the common bridge arm by tracking the changes in the DC voltage output on the low-voltage side. To maintain the stability of the DC voltage on the low voltage side. Finally, the number of bridge arm submodules turned on output by the three-level controllers is added together to obtain the total number of each bridge arm submodule turned on. Figure 3 middle, Represents the number of bridge arm submodules put into operation for the output of the low-voltage side DC voltage controller. Represents the total number of bridge arm sub-modules put into use for the controller output.

[0094] First, based on Figure 3 The small signal frequency domain model of the half-bridge module energy balance controller can be obtained.

[0095] (26)

[0096] in, is the small signal disturbance vector of the common mode AC modulation voltage reference value, is the small signal disturbance vector of the common mode component reference value of the submodule capacitor voltage difference between the high voltage bridge arm and the common bridge arm, , , are the transfer function matrices of PI controller, low-pass filter and cosine function respectively, and Represents the PI controller and low-pass filter at frequencies The transfer function at .

[0097] The small signal frequency domain model of the full-bridge arm current controller is as follows.

[0098] (27)

[0099] in, is the small signal disturbance vector of the differential mode AC modulation voltage reference value, is the small signal disturbance vector of the reference value of the differential mode component of the low voltage bridge arm current, , are the transfer function matrices of the PR controller and high-pass filter respectively, and Represents the PR controller and high-pass filter at frequencies The transfer function at .

[0100] Similarly, the small signal frequency domain model of the low-voltage side DC voltage controller is as follows.

[0101] (28)

[0102] in, is the differential mode DC modulation voltage reference value small signal disturbance vector, is the small signal disturbance vector of the low voltage side DC voltage reference value, , are the transfer function matrices of the PI controller and low-pass filter respectively, and Represents the PI controller and low-pass filter at frequencies The transfer function at .

[0103] S4: Establishing a small signal impedance model based on the power circuit model and the control circuit model.

[0104] In this embodiment, the power circuit model (Formula (25)) and the control circuit model (Formula (26)-Formula (28)) are combined to obtain a small signal impedance model that characterizes the dual-port dynamic characteristics of the DC transformer as follows.

[0105] (29)

[0106] In the formula, and They are the high-voltage side port admittance matrix and the low-voltage side port impedance matrix, and and Represents the coupling matrix between the high and low voltage side systems.

[0107] The detailed expressions are as follows.

[0108] (30)

[0109] Among them, the coefficient matrix The expression of is as follows.

[0110] (31)

[0111] In the above formula, , , , , , , , , , , , , , , , , , are coefficient matrices.

[0112] When the disturbance frequency is very high, due to the high-frequency filtering effect of the capacitor, the influence of the high-frequency disturbance of the sub-module capacitor voltage can be ignored. Therefore, the small signal impedance model can be greatly simplified. The simplified small signal impedance model is expressed as follows.

[0113] (32)

[0114] in, represents the simplified model of high-voltage side port admittance, Represents the simplified model of low-voltage side port impedance, represents the influence of control delay, S is the complex frequency, and L is the inductance of the bridge arm.

[0115] S5: Calculating the broadband impedance of the modular multi-level DC transformer based on the small signal impedance model.

[0116] The method for calculating the broadband impedance of the modular multi-level DC transformer proposed in this application first establishes a power circuit model based on the operating condition information and circuit topology structure, combined with Kirchhoff's voltage / current law; then uses the input / output signal of the controller and the transfer function of the control link to establish a control circuit model; after substituting the control circuit model into the power circuit model, the small signal impedance model can be obtained by eliminating the intermediate variables. The fast Fourier transform algorithm is used to extract the steady-state signals of the modulation coefficient of each bridge arm, the bridge arm current, the bridge arm valve output voltage, and the submodule capacitor voltage at the corresponding frequency point of each phase in real time, and input them into the small signal impedance model to calculate the broadband impedance under the current operating condition and control mode, which can be directly used for the small signal stability analysis of the modular multi-level DC transformer, which enhances the flexibility of impedance calculation and improves the efficiency of small signal stability analysis.

[0117] According to the contents of this application, Figure 2 The corresponding two-phase single-pole simulation model of the circuit topology shown in MATLAB / Si-mulink was built, and the rated parameters of the simulation circuit are shown in Table 1.

[0118] Table 1

[0119]

[0120] In order to verify the correctness of this application, a modular multi-level DC transformer electromagnetic transient simulation model was built in Matlab / Simulink, and the high-voltage side port admittance matrix and the low-voltage side port impedance matrix model were measured point by point and compared with the analytical calculation results. The specific scanning process is as follows.

[0121] (1) The superimposed frequencies at the high voltage side DC voltage and the low voltage side DC current are The small signal disturbance component of the system is detected and the system is waited for to enter a new steady-state cycle.

[0122] (2) Sample the DC voltage / current and use FFT analysis to extract the frequency Fourier coefficients of the harmonics of a small perturbation.

[0123] (3) Calculate based on the definition of small disturbance harmonic impedance in the previous article.

[0124] (4) Change the frequency of the small signal disturbance component superimposed on the high-voltage side DC voltage and the low-voltage side DC current and repeat steps (1) to (3) to measure the small signal disturbance harmonic impedance values ​​at other frequency points.

[0125] Figure 4(a) and (b) in the figure compare the simulation measurement results and analytical calculation results of the low-voltage side port impedance and high-voltage side port admittance of the modular multi-level DC transformer in the frequency range of 1~2500Hz, respectively. The red circle is the simulation calculation result, and the blue curve is the theoretical calculation result. It can be found that the high-voltage side port admittance and low-voltage side port impedance models of the modular multi-level DC transformer obtained by electromagnetic transient simulation sweep frequency measurement are highly consistent with its detailed analytical model.

[0126] Figure 5 (a) is the simulation verification result of the simplified model of low-voltage side port impedance. Figure 5 (b) is the simulation verification result of the simplified model of the high-voltage side port admittance. It can be seen that the simplified analytical model has a high consistency with the detailed theoretical model in the frequency range of 300 Hz and above.

[0127] The above results fully demonstrate the effectiveness and practicality of the online calculation method for broadband impedance of modular multi-level DC transformer proposed in this application.

[0128] Based on the same inventive concept, in an exemplary embodiment, Figure 6 As shown, a modular multi-level DC transformer broadband impedance online calculation device is provided, comprising the following units.

[0129] (1) A signal processing unit, used to process the time domain signal of the modular multi-level DC transformer using an FFT algorithm to obtain frequency domain signals at different frequency points.

[0130] The signal processing unit measures the time domain signal values ​​of the bridge arm modulation coefficient, bridge arm current, bridge arm valve output voltage, and sub-module capacitor voltage of each phase in the modular multi-level DC transformer in real time, and uses the FFT algorithm to extract the DC component, fundamental wave, double frequency and triple frequency components of the corresponding signal to obtain the amplitude and phase angle of each signal frequency domain component, and input the frequency domain signals at different frequency points into the broadband impedance calculation board.

[0131] (2) A power circuit modeling unit, used to establish a power circuit model.

[0132] The power circuit model is determined by the DC transformer circuit topology and current operating condition information in the actual application scenario, and is often imported from an external system. When performing impedance calculation, the broadband impedance calculation board will directly obtain the data in the power circuit modeling unit under the current operating condition for impedance calculation and analysis.

[0133] (3) Control circuit modeling unit, used to establish a control circuit model.

[0134] The control circuit model is established by using the small signal disturbance components of the electrical quantity input by each controller and the small signal disturbance components of the modulation voltage output. The small signal impedance model can be obtained by combining it with the power circuit model.

[0135] (4) A broadband impedance calculation board, connected to the signal processing unit, the power circuit modeling unit and the control circuit modeling unit, respectively, for calculating broadband impedance according to frequency domain signals at different frequency points, the power circuit model and the control circuit model.

[0136] The broadband impedance calculation board is the core part of this device. It is embedded with a matching broadband impedance calculation program. It is mainly responsible for calculating the impedance amplitude and phase angle data of the modular multi-level DC transformer under different disturbance frequencies based on the collected signals, power circuit modeling unit, and control circuit modeling unit data, and outputs the data to the data storage and display. The board contains a high-performance processor, dedicated calculation circuits and algorithms, which can calculate broadband impedance in real time and dynamically output it to the display.

[0137] (5) A data storage device connected to the broadband impedance calculation board and used to store calculation data of the broadband impedance calculation board.

[0138] The data storage device is used to store the impedance amplitude and phase angle calculation results of the DC transformer at different disturbance frequency points, which can be directly used for the small signal disturbance stability analysis of the modular multi-level DC transformer. It includes high-speed cache and long-term storage devices to ensure the reliability and persistence of data.

[0139] (6) A display connected to the broadband impedance calculation board and used to display the calculation data of the broadband impedance calculation board.

[0140] The display is the user interface of the device, which is mainly responsible for displaying the broadband impedance calculation results in the form of waveforms for reference and subsequent broadband stability analysis. The display includes display devices such as LCD screens and touch screens.

[0141] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0142] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0143] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0144] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A modular multi-level DC transformer broadband impedance online calculation method, characterized in that: include: Based on the circuit topology of modular multilevel DC transformer, the relationship between various electrical quantities of modular multilevel DC transformer in steady-state operation is obtained; Establish a power circuit model based on the relationship between various electrical quantities during steady-state operation; Establishing a control circuit model based on the input and output of the controller group of the modular multi-level DC transformer; Establishing a small signal impedance model based on the power circuit model and the control circuit model; The broadband impedance of the modular multi-level DC transformer is calculated based on the small signal impedance model.

2. The online calculation method for broadband impedance of modular multi-level DC transformer according to claim 1 is characterized in that: The modular multi-level DC transformer includes a high-voltage bridge arm, a common bridge arm and a low-voltage bridge arm; the controller group includes a half-bridge module energy balance controller, a full-bridge bridge arm current controller and a low-voltage side DC voltage controller.

3. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 2, characterized in that: The power circuit model includes a first constraint relationship, a second constraint relationship, a third constraint relationship and a fourth constraint relationship; Among them, the power circuit model is established based on the relationship between various electrical quantities during steady-state operation, including: The relationship between various electrical quantities during steady-state operation is transformed into the frequency domain to obtain a steady-state model of the power circuit; The small signal disturbance component of the bridge arm modulation voltage output by each electrical quantity and the controller group is used to perform small signal processing on the steady-state model of the power circuit to obtain a small signal model of the power circuit; the bridge arm modulation voltage includes a common mode AC modulation voltage, a differential mode AC modulation voltage and a differential mode DC modulation voltage; Based on the power circuit small signal model, determine the small signal disturbance constraint relationship between the common mode component of the submodule capacitor voltage difference between the high-voltage bridge arm and the common bridge arm and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current, which is defined as the first constraint relationship; Based on the power circuit small signal model, determine the small signal disturbance constraint relationship between the differential mode component of the low voltage bridge arm current and the bridge arm modulation voltage, the high voltage side DC voltage and the low voltage side DC current, which is defined as the second constraint relationship; Based on the power circuit small signal model, determine the small signal disturbance constraint relationship between the low-voltage side DC voltage and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current, which is defined as the third constraint relationship; Based on the small signal model of the power circuit, the small signal disturbance constraint relationship between the high-voltage side DC current and the bridge arm modulation voltage, the high-voltage side DC voltage and the low-voltage side DC current is determined, which is defined as the fourth constraint relationship.

4. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 3, characterized in that: The expression of the steady-state model of the power circuit is: ； in, is the steady-state frequency domain vector of the valve output voltage of each bridge arm submodule, , , respectively , Two phases, , , , respectively represent the high voltage bridge arm, the common bridge arm and the low voltage bridge arm, represents the Toeplitz operation, The steady-state frequency domain vector of the number of inputs to each bridge arm submodule, is the steady-state matrix of the submodule capacitance, is the steady-state frequency domain vector of the capacitor voltage of each bridge arm submodule, is the steady-state frequency domain vector of each bridge arm current, for The steady-state frequency domain vector of the number of phase high-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the differential-mode AC modulation voltage output by the half-bridge module energy balance controller, is the common mode AC modulation voltage distribution coefficient, is the steady-state frequency domain vector of the common-mode AC modulation voltage output by the half-bridge module energy balance controller, is the steady-state frequency domain vector of the differential-mode DC modulation voltage output by the low-voltage side DC voltage controller, is the submodule capacitor voltage rating, for The steady-state frequency domain vector of the number of phase common bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase low-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the differential-mode AC modulation voltage output by the full-bridge arm current controller, for The steady-state frequency domain vector of the number of phase high-voltage bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase common bridge arm submodules put into operation, for The steady-state frequency domain vector of the number of phase low-voltage bridge arm submodules put into operation, is the steady-state frequency domain vector of the DC voltage on the high-voltage side, is the steady-state frequency domain vector of the high-voltage bridge arm submodule valve output voltage, is the steady-state frequency domain vector of the common bridge arm submodule valve output voltage, is the steady-state matrix of the bridge arm inductance, is the steady-state frequency domain vector of the high-voltage bridge arm current, is the steady-state frequency domain vector of the common bridge arm current, is the steady-state frequency domain vector of the low-voltage side DC voltage, is the steady-state frequency domain vector of the low-voltage bridge arm submodule valve output voltage, is the steady-state frequency domain vector of the low-voltage bridge arm current, is the steady-state frequency domain vector of the DC current on the high-voltage side, for The steady-state frequency domain vector of the phase high-voltage bridge arm current, for The steady-state frequency domain vector of the phase high-voltage bridge arm current, is the steady-state frequency domain vector of the DC current on the low-voltage side, for The steady-state frequency domain vector of the phase low-voltage bridge arm current, for The steady-state frequency domain vector of the phase low-voltage bridge arm current.

5. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 4, characterized in that: The expression of the small signal model of the power circuit is: ； in, is the small signal disturbance vector of the valve output voltage of each bridge arm submodule, is the small signal disturbance vector of the capacitor voltage of each bridge arm submodule, The number of small signal disturbance vectors input to each bridge arm submodule, is the small signal perturbation matrix of the submodule capacitance, is the small signal disturbance vector of each bridge arm current, for The small signal disturbance vector of the number of phase high voltage bridge arm submodules put into operation, is the small signal disturbance vector of the differential mode AC modulation voltage output by the half-bridge module energy balance controller, is the small signal disturbance vector of the common-mode AC modulation voltage output by the half-bridge module energy balance controller, is the small signal disturbance vector of the differential mode DC modulation voltage output by the low voltage side DC voltage controller, for The small signal disturbance vector of the number of phase common bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase high voltage bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase common bridge arm submodules put into operation, for The small signal disturbance vector of the number of phase low-voltage bridge arm submodules put into operation, is the small signal disturbance vector of the differential-mode AC modulation voltage output by the full-bridge arm current controller, for The small signal disturbance vector of the number of phase low-voltage bridge arm submodules put into operation, is the small signal disturbance vector of the DC voltage on the high voltage side, is the small signal disturbance vector of the high-voltage bridge arm submodule valve output voltage, is the small signal disturbance vector of the common bridge arm submodule valve output voltage is the small signal disturbance matrix of the bridge arm inductance, is the small signal disturbance vector of the DC voltage on the low voltage side, is the small signal disturbance vector of the common bridge arm current, is the small signal disturbance vector of the high voltage bridge arm current, Small signal disturbance vector of the valve output voltage of the low voltage bridge arm submodule is the small signal disturbance vector of the low voltage bridge arm current, is the small signal disturbance vector of the DC current on the high voltage side, for The small signal disturbance vector of the phase high voltage bridge arm current, for The small signal disturbance vector of the phase high voltage bridge arm current, is the small signal disturbance vector of the DC current on the low voltage side, for The small signal disturbance vector of the phase low voltage bridge arm current, for Small signal disturbance vector of the phase low-voltage bridge arm current.

6. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 5, characterized in that: The expression of the power circuit model is: ； in, is the small signal disturbance vector of the common mode component of the capacitor voltage differential mode of the high-voltage bridge arm and the common bridge arm submodule, is the small signal disturbance vector of the differential mode component of the low voltage bridge arm current, - , - , - , - are coefficient matrices.

7. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 2, characterized in that: The control circuit model includes: a small signal frequency domain model of a half-bridge module energy balance controller, a small signal frequency domain model of a full-bridge arm current controller, and a small signal frequency domain model of a low-voltage side DC voltage controller.

8. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 6, characterized in that: The expression of the small signal impedance model is: ； in, is the high-voltage side port admittance matrix, , They are all coupling matrices between high and low voltage side systems. is the low voltage side port impedance matrix.

9. The method for online calculation of broadband impedance of modular multi-level DC transformer according to claim 8, characterized in that: When the disturbance frequency exceeds the frequency threshold, the small signal impedance model is simplified to obtain a simplified small signal impedance model; The expression of the simplified small signal impedance model is: ； in, is the simplified model of the high-voltage side port admittance, Simplified model for low voltage side port impedance, represents the influence of control delay, , They are PI controller and low-pass filter at a frequency of Transfer function at , S is the complex frequency, L is the bridge arm inductance.

10. A modular multi-level DC transformer broadband impedance online calculation device, characterized in that: include: A signal processing unit, used to process the time domain signal of the modular multi-level DC transformer by using an FFT algorithm to obtain frequency domain signals at different frequency points; A power circuit modeling unit, used for establishing a power circuit model; A control circuit modeling unit, used for establishing a control circuit model; A broadband impedance calculation board is connected to the signal processing unit, the power circuit modeling unit and the control circuit modeling unit respectively, and is used to calculate broadband impedance according to frequency domain signals at different frequency points, the power circuit model and the control circuit model; A data storage device connected to the broadband impedance calculation board and used to store calculation data of the broadband impedance calculation board; A display is connected to the broadband impedance calculation board and is used to display the calculation data of the broadband impedance calculation board.

Images