A time-domain EMI modeling method for large-capacity short-time working isolated DC-DC charger

Abstract

The application discloses a time domain EMI modeling method for an isolated DC-DC direct current charger with large capacity and short-time work, and steps include: 1) according to the circuit topology of a high-power DC-DC direct current conversion device of a ship platform, an equivalent circuit model with a super capacitor as a time-varying load is established; 2) a control mode of the high-power DC-DC direct current conversion device charging system is determined; 3) the parasitic parameters of each component in the equivalent circuit model are extracted; 4) according to the parasitic parameters, the electromagnetic interference characteristics of the direct current charging system on the direct current power grid side under the constant current charging mode and the constant voltage charging mode are analyzed. The application establishes an EMI equivalent circuit model of the direct current charging system on the basis of the theoretical analysis of the electromagnetic interference coupling path of the isolated DC-DC direct current charger, obtains the time domain result of the electromagnetic interference voltage of the direct current power grid side, and then can directly analyze the EMI characteristics of the direct current charger in a wide frequency domain through time-frequency transformation.

Description

TECHNICAL FIELD

[0001] The application relates to the field of electromagnetic compatibility, and particularly relates to a time-domain EMI modeling method for an isolated DC-DC charger with large capacity and short-time operation. BACKGROUND

[0002] A ship platform needs to be loaded with various strong electromagnetic equipment with large power and short-time operation to improve the electrification level of the ship platform. However, the working characteristics of the strong electromagnetic equipment with large power and short-time operation will cause great power impact on the DC power grid of the ship, so that the electromagnetic interference problem caused by the power impact is reduced, and the independent power grid can work stably. Therefore, the super capacitor energy storage cabinet is pre-charged through the DC power grid. When the electric quantity of the energy storage cabinet meets the peak power and energy consumption demand of the subsequent instantaneous working strong electromagnetic equipment such as a motor, the different strong electromagnetic equipment is driven to work, so that the large-capacity DC-DC charger is needed to perform short-time large-power DC charging between the DC power grid and the energy storage cabinet.

[0003] At present, the electromagnetic environment in the modern ship platform is more complex than that in the traditional ship, and the electromagnetic compatibility problem to be solved is more prominent. The main reason is that the newly added strong electromagnetic equipment of the modern ship contains many high-power switching devices, is connected by high-power cables, and has a high working voltage level. Therefore, great dv / dt and di / dt are generated in the moment of high-frequency turn-on and turn-off, and serious electromagnetic interference is caused in a wide frequency range. The DC-DC charger is one of the main electric energy conversion devices of the ship DC power grid, and needs to have working characteristics such as large power, high efficiency and safety. The full-bridge isolated DC-DC charger is widely used. The use scene of the DC charger is usually to charge the energy storage device by using the isolated DC-DC charger, and then to supply energy to the instantaneous large-power and strong electromagnetic interference equipment by the energy storage device, so as to reduce the electromagnetic interference influence of the instantaneous large-power load on the DC power grid. However, since the super capacitor has time-varying impedance characteristics when it is used as a load, when the conducted electromagnetic interference of the system on the DC power grid side is analyzed, the equivalent circuit model needs to be established under the time-domain analysis to simulate the actual operation process. SUMMARY

[0004] The purpose of the application is to provide a time-domain EMI modeling method for an isolated DC-DC charger with large capacity and short-time operation, which comprises the following steps:

[0005] 1) An equivalent circuit model of a super capacitor as a time-varying load is established according to the circuit topology of a large-power DC-DC conversion device of a ship platform;

[0006] 2) The control mode of the large-power DC-DC conversion device charging system is determined;

[0007] 3) Extracting the parasitic parameters of each component in the equivalent circuit model;

[0008] 4) Analyzing the electromagnetic interference characteristics of the DC charging system under constant current charging mode and constant voltage charging mode according to the parasitic parameters.

[0009] Further, the circuit topology of the equivalent circuit model is as follows:

[0010] Let the positive terminal of the power source u(t) be A terminal, and the negative terminal be B terminal;

[0011] A terminal is connected to B terminal in series with resistor R0, capacitor C f0 .

[0012] A terminal is connected to B terminal in series with resistor R0, super capacitor C f .

[0013] A terminal is connected to B terminal in series with resistor R1, capacitor C1.

[0014] A terminal is connected to B terminal in series with load R L .

[0015] Further, during the constant current charging process of the super capacitor, after charging t1 time, the resistor R0 of the equivalent circuit model is as follows:

[0016]

[0017] In the formula, U1 represents the terminal voltage after increasing ΔU; ΔU represents the voltage increment; U0 represents the initial voltage;

[0018] After charging t2 time, the current I in the equivalent circuit model satisfies the following formula:

[0019]

[0020] In the formula, Q represents the charge quantity; capacitor C f =C f0 +C f1 (u); C f1 (u)C f1 (u) = ku(t); k is a coefficient; u(t) is the terminal voltage of the super capacitor;

[0021] The capacitor C f0 is as follows:

[0022]

[0023] Further, after the constant current charging of the super capacitor is stopped, the accumulated charge quantity Q of the super capacitor C f is as follows:

[0024] Q = I * (t4 - t1) (4)

[0025] wherein t4 represents time.

[0026] Further, when the supercapacitor is fully charged and the external power supply is disconnected, when the supercapacitor is fully charged and the external power supply is disconnected, the supercapacitor C f as a power supply to the branch where the load Rl is located, the branch where the capacitor C1 is located, and the charge provided to the branch where the capacitor C1 is located is greater than the branch where the load Rl is located, that is, the supercapacitor C f as a power supply to the latter two branches, mainly to the C1 branch, internal charge redistribution occurs, and at time t5, the internal equivalent current I0 of the equivalent circuit model is as follows:

[0027]

[0028] The resistance R1 in the equivalent circuit model is as follows:

[0029]

[0030] The time when the internal charge redistribution ends is denoted as t6, that is:

[0031] t6 = t5 + 3(R1 * C1) (7)

[0032] At the end of the internal charge redistribution, the charge amount Q of the supercapacitor C f is as follows:

[0033]

[0034] wherein U6 is the terminal voltage at the end of the internal charge redistribution;

[0035] wherein the coefficient k is as follows:

[0036]

[0037] wherein U4 represents the terminal voltage after the constant current charging of the supercapacitor is stopped;

[0038] The capacitor C1 is as follows:

[0039]

[0040] Further, after the equivalent circuit model is completely static, the voltage across the resistance R1 is as follows:

[0041]

[0042] In the formula, U7 is the terminal voltage after the equivalent circuit model is completely stationary;

[0043] Self-discharge current I l As shown below:

[0044]

[0045] Resistance R l As shown below:

[0046]

[0047] Further, the super capacitor is connected to a DC power grid through a large-capacity isolated DC-DC converter to form a charging system.

[0048] Further, the control mode of the large-power DC-DC converter charging system includes the control modes of a first controller, a second controller, and a third controller.

[0049] The first controller collects the charging current I SC of the super capacitor and the terminal voltage V SC of the super capacitor, and controls the constant-current charging and constant-voltage charging modes of the DC-DC converter according to the rated working voltage of the super capacitor, so as to stabilize the terminal voltage and the charging current of the super capacitor.

[0050] The second controller collects the charging current of the super capacitor, and performs constant-current charging according to the reference value I ref of the super capacitor charging current set by the user, so as to stabilize the charging current of the super capacitor at the set value at all times, thereby realizing constant-current charging of the super capacitor by the DC charger.

[0051] The third controller collects the terminal voltage of the super capacitor, and performs constant-voltage and current-limiting charging according to the reference value V ref of the super capacitor terminal voltage set by the user, so as to maintain the voltage of the super capacitor at the set value at all times, thereby realizing constant-voltage charging of the super capacitor by the DC charger.

[0052] Further, the parasitic parameters include the primary-side high-frequency parasitic capacitance C n1 of the transformer and the secondary-side high-frequency parasitic capacitance C n2 of the transformer, the parasitic capacitance C i of the secondary side of the transformer to ground, and the parasitic capacitance C p of the output side of the inverter bridge to ground.

[0053] Further, the software for extracting the parasitic parameters includes ANSYS Q3D Extractor software.

[0054] It is worth noting that for the isolated DC-DC charger with super capacitor load, the present application first establishes a time-varying equivalent circuit model of the energy storage cabinet (super capacitor) based on the short-time working characteristics. Then, according to the actual working condition of the energy storage cabinet composed of super capacitors in the ship, the control mode of the DC-DC charger is determined. Secondly, based on the circuit topology structure of the isolated DC-DC charger, the common mode interference coupling path and the differential mode interference coupling path are analyzed, and the parasitic parameters of each component are extracted. Finally, the circuit model of the isolated DC-DC charger with time-varying load under the short-time working mode is built in Matlab / Simulink, and the EMI characteristics of the DC charging system on the DC power grid side under the constant current charging mode and the constant voltage charging mode are compared, that is, a time-domain EMI modeling method of the isolated DC-DC charger under the short-time working mode is formed. The present application can provide a method for time-domain EMI modeling of the isolated DC-DC charger with short-time working characteristics, and provide a simulation model and technical support for electromagnetic compatibility prediction and design of the DC power grid side.

[0055] The technical effect of the present application is self-evident. The present application proposes a time-domain EMI modeling method of the isolated DC-DC charger with large capacity and short-time working, which can be used to predict the short-time electromagnetic interference characteristics of the DC-DC charger, and lays a foundation for the analysis of conducted electromagnetic interference of the high-power equipment under the short-time working of the ship platform and the suppression of conducted electromagnetic interference.

[0056] The present application provides modeling of the time-varying equivalent circuit of the super capacitor and the circuit model of the constant current charging and constant voltage charging mode, which has clear physical concept and simple control mode, and provides model support for short-time EMI characteristic analysis of the super capacitor energy storage cabinet under different charging modes.

[0057] Based on the theoretical analysis of the electromagnetic interference coupling path of the isolated DC-DC charger, the present application establishes an EMI equivalent circuit model of the DC charging system, obtains the time-domain results of the electromagnetic interference voltage on the DC power grid side, and can directly analyze the wide frequency domain EMI characteristics of the DC charger through time-frequency transformation.

[0058] Based on the isolated full-bridge DC-DC charger circuit with super capacitor as time-varying load, the present application proposes a time-domain EMI modeling method of strong electromagnetic equipment and system, which provides model and EMI simulation data support for subsequent electromagnetic interference quantification analysis of independent DC power system, can provide guidance for targeted suppression measures, and can be extended to other topological structures of DC-DC circuits with time-varying load, and has wide application value. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1Flow chart for DC-DC charger time domain EMI theoretical modeling

[0060] Figure 2 Circuit topology for isolated DC-DC charger

[0061] Figure 3 Super capacitor charging characteristic graph

[0062] Figure 4 Time-varying equivalent circuit model for super capacitor

[0063] Figure 5 Variable equivalent capacitor sub-module

[0064] Figure 6 Super capacitor module equivalent circuit model

[0065] Figure 7 Super capacitor simulation and test terminal voltage comparison graph

[0066] Figure 8 Super capacitor simulation and test terminal voltage relative error graph

[0067] Figure 9 Super capacitor energy storage system control principle diagram

[0068] Figure 10 Simulink simulation control diagram

[0069] Figure 11 DC-DC charger differential mode electromagnetic interference transmission path graph

[0070] Figure 12 Equivalent model of parasitic capacitance of switching device

[0071] Figure 13 DC-DC charger common mode electromagnetic interference transmission path graph

[0072] Figure 14 Q3D parasitic parameter model extraction graph

[0073] Figure 15 Super capacitor terminal voltage change graph

[0074] Figure 16 Super capacitor charging current change graph

[0075] Figure 17 DC power grid side differential mode voltage under constant current charging mode

[0076] Figure 18 DC power grid side common mode voltage under constant current charging mode

[0077] Figure 19DC grid side differential mode voltage under constant voltage charging mode;

[0078] Figure 20 DC grid side common mode voltage under constant voltage charging mode;

[0079] Figure 21 DC grid side differential mode voltage comparison chart under different charging modes;

[0080] Figure 22 DC grid side common mode voltage comparison chart under different charging modes. DETAILED DESCRIPTION

[0081] The application will be further described in conjunction with the embodiments, but should not be understood as limiting the above-mentioned subject matter of the application to the following embodiments. Various substitutions and modifications can be made according to ordinary technical knowledge and conventional means without departing from the above-mentioned technical idea of the application, and all should be included in the protection scope of the application.

[0082] Example 1:

[0083] Referring to Figures 1 to 22 A time domain EMI modeling method of a large-capacity short-time working isolation type DC-DC direct current charger includes the following steps:

[0084] 1) According to the circuit topology of the large-power DC-DC direct current conversion device of the ship platform, an equivalent circuit model of a super capacitor as a time-varying load is established;

[0085] 2) Determine the control mode of the charging system of the large-power DC-DC direct current conversion device;

[0086] 3) Extract the parasitic parameters of each component in the equivalent circuit model;

[0087] 4) According to the parasitic parameters, analyze the electromagnetic interference characteristics of the direct current charging system under constant current charging mode and constant voltage charging mode on the DC grid side. The electromagnetic interference characteristic analysis is to analyze the electromagnetic interference characteristics by analyzing the frequency spectrum chart under different charging modes in the simulation circuit. The electromagnetic interference characteristics of the direct current charging system under constant current charging mode and constant voltage charging mode on the DC grid side are reflected by the parasitic parameters.

[0088] The circuit topology of the equivalent circuit model is as follows:

[0089] Let the positive pole of the power source u(t) be A end and the negative pole be B end;

[0090] A end is connected to B end in turn through resistance R0, capacitor C f0 and super capacitor C

[0091] A end is connected to B end in turn through resistance R0, capacitor C fThe B end is connected to the A end after connecting a resistor R1 and a capacitor C1 in series.

[0092] The B end is connected to the A end after connecting a resistor R1 and a capacitor C1 in series.

[0093] The B end is connected to the A end after connecting a resistor R1 and a capacitor C1 in series. L The B end is connected to the A end after connecting a resistor R1 and a capacitor C1 in series.

[0094] During the constant current charging process of the super capacitor, after a charging time t1, the resistor R0 of the equivalent circuit model is as follows:

[0095]

[0096] In the formula, U1 represents the terminal voltage after the increase of ΔU; ΔU represents the voltage increase; and U0 represents the initial voltage.

[0097] After a charging time t2, the current I in the equivalent circuit model satisfies the following formula:

[0098]

[0099] In the formula, Q represents the charge quantity; the capacitor C f =C f0 +C f1 (u); C f1 (u)C f1 (u) = ku(t); k is a coefficient; and u(t) is the terminal voltage of the super capacitor.

[0100] The capacitor C f0 is as follows:

[0101]

[0102] After the constant current charging of the super capacitor is stopped, the super capacitor C f The accumulated charge quantity Q is as follows:

[0103] Q = I * (t4-t1) (4)

[0104] In the formula, t4 represents time.

[0105] When the super capacitor is fully charged and the external power supply is disconnected, the super capacitor Cf serves as a power supply to the two branches behind, mainly supplying power to the C1 branch, and internal charge redistribution occurs. At t5, the internal equivalent current I0 of the equivalent circuit model is as follows:

[0106]

[0107] The resistor R1 in the equivalent circuit model is as follows:

[0108]

[0109] The time when the internal charge redistribution ends is denoted as t6, that is:

[0110] t6=t5+3(R1*C1) (7)

[0111] When the internal charge redistribution ends, the supercapacitor C f The charge Q is shown below:

[0112]

[0113] In the formula, U6 is the terminal voltage at the end of the internal charge redistribution;

[0114] The coefficient k is shown below:

[0115]

[0116] In the formula, U4 represents the terminal voltage of the supercapacitor after constant current charging stops;

[0117] Capacitor C1 is shown below:

[0118]

[0119] After the equivalent circuit model is completely stationary, the voltage across resistor R1 is... As shown below:

[0120]

[0121] In the formula, U7 is the terminal voltage of the equivalent circuit model after it is completely stationary;

[0122] Self-discharge current I l As shown below:

[0123]

[0124] resistor R l As shown below:

[0125]

[0126] The supercapacitor is connected to the DC power grid through a large-capacity isolated DC-DC converter to form a charging system.

[0127] The control methods of the high-power DC-DC converter charging system include control methods using a first controller, a second controller, and a third controller.

[0128] The first controller collects the charging current I of the supercapacitor. SC With terminal voltage V SCAnd according to the rated working voltage of the super capacitor, the constant current charging and constant voltage charging of the DC-DC converter are controlled, so that the terminal voltage and charging current of the super capacitor are stabilized.

[0129] The second controller collects the charging current of the super capacitor, and according to the set reference value I ref The constant current charging is performed, so that the charging current of the super capacitor is stabilized at the set value at any time, so that the DC charger performs constant current charging on the super capacitor.

[0130] The third controller collects the terminal voltage of the super capacitor, and according to the set reference value V ref The constant voltage limiting current charging is performed, so that the voltage of the super capacitor is maintained at the set value at any time, so that the DC charger performs constant voltage charging on the super capacitor.

[0131] The parasitic parameters include the primary side high frequency parasitic capacitance C n1 And the secondary side high frequency parasitic capacitance C n2 The parasitic capacitance C i The parasitic capacitance C p .

[0132] The software for extracting the parasitic parameters includes ANSYS Q3D Extractor software.

[0133] Embodiment 2:

[0134] A time domain EMI modeling method of an isolated DC-DC direct current charger with large capacity and short time working, comprising the following steps:

[0135] Based on the circuit topology form of the high-power DC-DC direct current conversion device on the ship platform, an equivalent circuit model of the super capacitor as a time-varying load is established in the short time working mode. Then, according to the actual working mode of the energy storage cabinet composed of the super capacitor on the ship platform, the control mode of the charging system is determined. Secondly, based on the circuit topology structure of the isolated DC-DC direct current charger, the common mode interference coupling path and the differential mode interference coupling path are analyzed, and the parasitic parameters of each component are extracted. Finally, in Matlab / Simulink, a simulation circuit model of the isolated DC-DC direct current charger with super capacitor load in the short time working mode is built, and the common mode voltage and differential mode voltage of the direct current power grid side of the direct current charging system in the constant current charging mode and the constant voltage charging mode are compared through time domain circuit simulation, that is, the time domain EMI modeling of the isolated DC-DC direct current charger in the short time working mode is realized.

[0136] The specific implementation technical solutions are as follows:

[0137] (1) Based on the short-time operation characteristics of high-power DC-DC converter circuits, an equivalent circuit model of supercapacitor as time-varying load is established.

[0138] according to Figure 3 The charging characteristic curves of supercapacitors show that the sharp voltage rise at the beginning of charging indicates that the capacitor has a certain internal resistance. The voltage self-recovery process after charging indicates that supercapacitors cannot be represented by a simple RC series circuit, but should be represented by RC circuits with different time constants connected in parallel. Furthermore, the relationship between voltage and time during charging is actually non-linear; therefore, the capacitance is affected by changes in capacitor voltage. Thus, a voltage-dependent capacitor needs to be added to the circuit model. In summary, a circuit model for supercapacitors should be established as follows: Figure 4 The time-varying equivalent circuit diagram shown is shown, where C f =C f0 +C f1 (u), C f1 (u) has a linear relationship with the terminal voltage of the supercapacitor, i.e., C f1 (u)=ku(t)

[0139] a) Instantaneous branch parameters: The initial voltage U0 of the supercapacitor module is too small. The supercapacitor module starts constant current charging from time t0, let the constant current be I. After a short time t1, U1 represents the voltage after the module terminal voltage increases by ΔU. At this time, it can be assumed that the module terminal voltage is equal to the voltage across resistor R0, then:

[0140]

[0141] When the supercapacitor continues charging for a short period until t2, the voltage across the supercapacitor becomes U2, which is still very small. The variable capacitor C... f1 (u)=ku(t) can be approximated as 0. The terminal voltage of the supercapacitor module is determined by the resistor R0 and the fixed capacitor C. f0 Shared responsibility, the current I is represented as:

[0142]

[0143] Where Q represents C f =C f0 +C f1 The amount of charge on (u).

[0144]

[0145] U3 represents the rated voltage of the supercapacitor module at time t3, when constant current charging stops and the current rapidly drops from I to 0. Then, after a minimum time t4, the voltage is U4, and the instantaneous branch has a charge Q, i.e., the variable capacitor C. f The accumulated charge is expressed as

[0146] Q = I * (t4 - t1)

[0147] Therefore its coefficient k is expressed as:

[0148]

[0149] b) Voltage balancing branch parameters: When the supercapacitor is fully charged and the external power supply is disconnected, the capacitor C f stores the charge Q, C f As the power supply to the two branches behind, the internal charge redistribution process occurs. The voltage decreases ΔU from U4 to U5. When time t5, the internal equivalent current I0 can be expressed as:

[0150]

[0151] The equivalent current I0 can also be expressed as:

[0152]

[0153] R1 is derived, which is expressed as

[0154]

[0155] At time t6, the charge redistribution of the charging branch ends, and the voltage at this time is U6. The time period from the transient branch to the balancing branch should be 3 times the time constant, so it can be expressed as:

[0156] t6 = t5 + 3 (R1 * C1)

[0157] According to the previous charging, the electric quantity Q can be expressed as:

[0158]

[0159] From the above formula, C1 is obtained, which is expressed as:

[0160]

[0161] c) Self-discharge branch parameters: R l is the internal resistance that describes the self-discharge phenomenon of the supercapacitor under long-term static conditions. After the module is completely static, until its terminal voltage changes very slowly, record the time t7, U7 represents the terminal voltage of the module. After the first two branches are stable, the terminal voltage is U6. After complete static, the terminal voltage is U7. The voltage across the resistance R1 in the voltage balancing branch is obtained, which is expressed as

[0162]

[0163] Self-discharge current I l is represented as

[0164]

[0165] Therefore, a self-discharge resistance R l is introduced, which is represented as

[0166]

[0167] (2) According to the actual working characteristics of the energy storage system composed of supercapacitors on the ship platform, determine the appropriate charging control mode, and establish the charging control equivalent circuit model in the isolated full-bridge DC-DC direct current charger.

[0168] The supercapacitor is connected to the DC power grid through a large-capacity isolated DC-DC converter to form an energy storage system. In order to realize the actual working requirements of short-time charging and voltage and current that do not change rapidly, three controllers are designed in the charging control of the energy storage system to realize constant current charging, constant voltage charging and switching between each other, and the control principle diagram is as shown in Figure 9 .

[0169] Controller 1 collects the charging current I SC and the terminal voltage V SC of the supercapacitor, and controls the constant current charging and constant voltage charging of the DC-DC converter according to the rated working voltage of the supercapacitor, to stabilize the terminal voltage and charging current of the supercapacitor. Controller 2 collects the charging current of the supercapacitor, and performs constant current charging according to the set reference value I ref of the supercapacitor charging current, which can stabilize the charging current of the supercapacitor at the set value at all times, to realize constant current charging of the supercapacitor by the DC charger. Controller 3 collects the terminal voltage of the supercapacitor, and performs constant voltage current limiting charging according to the set reference value V ref of the supercapacitor terminal voltage, which can maintain the voltage of the supercapacitor at the set value at all times, to realize constant voltage charging of the supercapacitor by the DC charger.

[0170] (3) Based on the circuit topology of the isolated full-bridge DC-DC converter with supercapacitor load, the differential mode interference and common mode interference coupling paths are analyzed, and the parasitic parameters of each component in the interference coupling path are extracted.

[0171] ① Analysis of differential mode interference transmission path

[0172] The differential mode electromagnetic interference is mainly generated by the electromagnetic interference source of the switch tube, and forms the main electromagnetic interference loop through the primary side of the high-frequency transformer and the LISN. In addition, the differential mode electromagnetic interference will form a channel through the coupling capacitor between the primary side and the secondary side of the high-frequency transformer, and transmit the differential mode electromagnetic interference to the secondary side of the transformer to form an interference loop. Since the differential mode interference transmission path is the same as the current transmission path of the original circuit, as shown by the arrow in Figure 11 , parasitic parameter extraction is not required.

[0173] ②Common mode interference transmission path analysis

[0174] The coupling capacitor between the primary and secondary sides of the high-frequency transformer in the isolated DC-DC direct current charger is an important channel for common mode interference, which can provide a low impedance path for high-frequency EMI propagation. In addition, there is a parasitic capacitor between the heat sink of the MOSFET switching device and the heat sink, and high-frequency EMI will propagate to the heat sink through the parasitic capacitor effect, forming common mode interference and affecting other systems. The final common mode interference transmission path is shown by the arrow in Figure 13 , in which the main elements are the high-frequency parasitic capacitors C n1 and C n2 between the primary and secondary sides of the transformer, the parasitic capacitor C i of the transformer secondary side to ground, the parasitic capacitor C p of the output side of the inverter bridge to ground, and the LISN of the high-voltage DC side.

[0175] ③Component parasitic parameter extraction method

[0176] The parasitic parameters are extracted by using ANSYS Q3D Extractor software. First, a geometric model of the switching device is established as shown in Figure 14 , which mainly includes four parts of the switching tube, the heat-conducting silicone grease, the insulating gasket and the heat sink. Then, set the material properties of various materials in Q3D. Finally, add the Solve Setup to solve the capacitor parameter matrix (Spice Matrix) separately, that is, to solve the parasitic capacitor C p of the output side of the inverter bridge to ground, and then use the same method to extract the remaining circuit parameters C n1 , C n2 and C i .

[0177] (4) Build a circuit model of the isolated DC-DC direct current charging system under short-time working mode, and simulate the electromagnetic interference characteristics of the direct current charging system on the direct current grid side under constant current charging mode and constant voltage charging mode.

[0178] The simulation circuit of the large-capacity short-time working isolated DC-DC charging system is built in Matlab / Simulink, wherein the super capacitor load is built by using the equivalent circuit method in (1). The control method in step (2) is used in Simulink to ensure that the isolated DC-DC charger charges the super capacitor at a constant current and a constant voltage, and the charging mode is switched according to the terminal voltage of the super capacitor. Meanwhile, the parasitic parameter values extracted in step (3) are imported into the simulation circuit model, and then the conduction electromagnetic interference voltage is calculated by using the ode23t rigid algorithm. Finally, the common-mode voltage and the differential-mode voltage of the DC grid side under the constant-current charging mode and the constant-voltage charging mode are compared to verify the electromagnetic interference characteristics under different charging modes.

[0179] Embodiment 3

[0180] A time-domain EMI modeling method for a large-capacity short-time working isolated DC-DC charger, comprising the following steps:

[0181] The time-domain EMI modeling process of the modeling method for the large-capacity short-time working isolated DC-DC charger is shown in Figure 1 The isolated full-bridge DC-DC circuit topology in the present case is shown in Figure 2 , wherein the DC grid voltage is V g = 900V, the phase-shifted full-bridge control mode is adopted, the carrier signal frequency is 4kHz, and the initial voltage of the super capacitor is 540V, and the voltage variation range is 540V-660V. The time-domain EMI modeling method for the large-capacity short-time working isolated DC-DC charger according to the present application comprises the following steps:

[0182] (1) The equivalent circuit model of the super capacitor with transient branch, charge balance branch and self-discharge branch is shown in Figure 4 . The single-port equivalent circuit model of the super capacitor is established in Simulink as shown in Figure 6 . The super capacitor is first left for 30s and then charged at a constant current of 1A. The circuit simulation results are compared with the measured voltage data as shown in Figure 7 , and the relative error of the super capacitor terminal voltage with time is calculated as shown in Figure 8 . Figure 8 There is a large error at the initial charging moment in

[0183] (2) By the charging demand of the energy storage system and the charging mode of the super capacitor, the charging process is divided into constant current charging and constant voltage charging mode, and the main switching process is related to the terminal voltage of the super capacitor. The control principle diagram is shown in Figure 9 . By using the terminal voltage of the super capacitor as the judgment condition, when the terminal voltage of the super capacitor is lower than the set voltage value 660V, the charging mode of the charging system is constant current charging; when the terminal voltage of the super capacitor is equal to the set voltage value 660V, the charging mode of the charging system changes from constant current charging to constant voltage charging.

[0184] (3) According to the analysis of the differential mode conducted electromagnetic interference transmission path and the common mode conducted electromagnetic interference transmission path of the circuit topology, as shown in Figure 11 and Figure 13 , the parasitic capacitance parameters of the switching elements in the circuit are modeled and extracted by using ANSYS Q3DExtractor software, as shown in Figure 14 . When analyzing the transmission path, the DC power supply is considered as short circuit, C n1 , C n2 represent the parasitic capacitance parameters between the primary and secondary sides of the high-frequency transformer, C p represents the equivalent capacitance of the switching tube emitter to the reference ground and the connecting line, C i represents the equivalent parasitic capacitance of the rectifier bridge input to the reference ground.

[0185] (4) In Matlab / Simulink, the simulation circuit of large-capacity short-time working isolation type DC-DC direct current charger is built, and the load is built by using the equivalent circuit method in (1). The control method in step (2) is used to control the constant current and constant voltage charging of the super capacitor in Simulink, and the charging mode is controlled according to the terminal voltage of the super capacitor, as shown in Figure 10 . At the same time, the extracted parasitic parameter values in step (3) are imported into the equivalent circuit model of the system, and then the conducted electromagnetic interference voltage on the DC grid side is calculated by using the ode23t rigid algorithm. The super capacitor terminal voltage and charging current diagram are shown in Figure 15 and Figure 16 , respectively. The differential mode and common mode voltage on the DC grid side under the constant current charging mode of the super capacitor are shown in Figure 17 and Figure 18 , respectively; the differential mode and common mode voltage on the DC grid side under the constant current charging mode of the super capacitor are shown in Figure 19 and Figure 20 , respectively, and are compared to determine the electromagnetic interference characteristics of the DC charger on the DC grid side under different charging modes, as shown in Figure 21 and Figure 22The circuit simulation results are consistent with the time-varying working characteristics of the actual charging circuit in time domain calculation, and good fitting effect can be obtained, that is, the time domain EMI modeling of the isolated DC-DC charger in short-time working mode is finally realized.

[0186] The super capacitor voltage can finally stabilize at 660 V, and the initial charging voltage variation is due to the transient initial voltage jump of the super capacitor in the transient branch caused by the equivalent resistance under the charging current of 35 A, so the charging starts at about 600 V. When the super capacitor is disconnected as a load at 28 s, there will be a voltage jump, and the charging current is temporarily changed to 0. The interference frequency points when the super capacitor is charged in constant current mode are compared with the interference frequency points in constant voltage mode, and from the comparison results, it can be seen that: for the common-mode interference voltage of the DC power grid side, the interference voltage amplitude in constant voltage charging mode is higher than that in constant current charging mode, and the amplitude difference of the main interference frequency points is nearly 5 dB; for the differential-mode interference voltage of the DC power grid side, similar to the common-mode interference voltage, the differential-mode interference voltage amplitude in constant voltage charging mode is higher than that in constant current charging mode, and the amplitude difference of the main interference frequency points is nearly 10 dB.

[0187] The embodiment proposes a time domain EMI modeling method of an isolated DC-DC charger with large capacity and short-time working. For the DC charging system of the full-bridge isolated DC-DC charger with super capacitor load, the patent first establishes a time-varying equivalent circuit model of the energy storage cabinet (super capacitor) based on the short-time working characteristics. Then, according to the actual working mode of the super capacitor, the charging control mode of the charging system is determined. Secondly, based on the circuit topology structure of the isolated DC-DC charger, the common-mode interference coupling path and the differential-mode interference coupling path are analyzed, and the parasitic parameters of each component are extracted. Finally, the circuit model of the isolated DC-DC charger in short-time working mode is built in Matlab / Simulink, the EMI characteristics of the DC charging system on the DC power grid side in constant current charging mode and constant voltage charging mode are compared, and a time domain EMI modeling method of the isolated DC-DC charger in short-time working mode is formed.

Claims

1. A time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger, characterized in that, Includes the following steps: 1) Based on the circuit topology of the high-power DC-DC converter on the ship platform, establish an equivalent circuit model with a supercapacitor as the time-varying load; 2) Determine the control method for the charging system of the high-power DC-DC converter; 3) Extract the parasitic parameters of each component in the equivalent circuit model; 4) Analyze the electromagnetic interference characteristics of DC charging systems under constant current charging and constant voltage charging modes on the DC grid side based on parasitic parameters; The circuit topology of the equivalent circuit model is shown below: Let the end of the power supply u(t) with the positive terminal be terminal A and the end with the negative terminal be terminal B; A is connected in series with a resistor R0 and a capacitor C. f0 Then connect to end B; At end A, a resistor R0 and a supercapacitor C are connected in series. f Then connect to end B; Terminal A is connected to terminal B after a resistor R1 and a capacitor C1 are connected in series. A is connected in series with a load R. L Then connect to end B; The control methods of the high-power DC-DC converter charging system include control methods using a first controller, a second controller, and a third controller. The first controller collects the charging current I of the supercapacitor. SC With terminal voltage V SC The constant current charging and constant voltage charging of the DC-DC converter are controlled according to the rated operating voltage of the supercapacitor to stabilize the terminal voltage and charging current of the supercapacitor. The second controller collects the charging current of the supercapacitor and calculates it based on the set reference value I for the supercapacitor charging current. ref Constant current charging is performed to keep the charging current of the supercapacitor stable at a set value at all times, so that the DC charger can charge the supercapacitor with constant current. The third controller acquires the supercapacitor terminal voltage and, based on the set supercapacitor terminal voltage reference value V... ref Constant voltage and current limiting charging is performed to keep the voltage of the supercapacitor at a set value at all times, so that the DC charger can charge the supercapacitor at a constant voltage.

2. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, During the constant current charging process of the supercapacitor, after a charging time t1, the equivalent circuit model resistor R0 is shown below: In the formula, U1 represents the terminal voltage after increasing ΔU; ΔU represents the voltage increase; U0 represents the initial voltage; After charging time t2, the current I in the equivalent circuit model satisfies the following equation: In the formula, Q represents the amount of charge; capacitance C f rC f0 +C f1 (u); C f1 (u)C f1 (u) = ku(t); k is a coefficient; u(t) is the terminal voltage of the supercapacitor; Capacitor C f0 As shown below:

3. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, After the constant current charging of the supercapacitor stops, the supercapacitor C f The accumulated charge Q is shown below: Q=I*(t4-t1) (4) In the formula, t4 represents time.

4. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, When the supercapacitor is fully charged and the external power supply is disconnected, the supercapacitor C... f As a power source, it supplies power to the branch containing the load Rl and the branch containing the capacitor C1, and the charge supplied to the branch containing the capacitor C1 is greater than that supplied to the branch containing the load Rl, resulting in an internal charge redistribution. At time t5, the internal equivalent current I0 of the equivalent circuit model is as follows: The resistor R1 in the equivalent circuit model is shown below: The time when the internal charge redistribution ends is denoted as t6, that is: t6=t5+3(R1*C1)(7) When the internal charge redistribution ends, the supercapacitor C f The charge Q is shown below: In the formula, U6 is the terminal voltage at the end of the internal charge redistribution; The coefficient k is shown below: In the formula, U4 represents the terminal voltage of the supercapacitor after constant current charging stops; Capacitor C1 is shown below:

5. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, After the equivalent circuit model is completely stationary, the voltage across resistor R1 is... As shown below: In the formula, U7 is the terminal voltage of the equivalent circuit model after it is completely stationary; Self-discharge current I l As shown below: resistor R l As shown below:

6. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, The supercapacitor is connected to the DC power grid through a large-capacity isolated DC-DC converter to form a charging system.

7. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, The parasitic parameters include the high-frequency parasitic capacitance C on the primary side of the transformer. n1 and the high-frequency parasitic capacitance C on the secondary side n2 Parasitic capacitance C of the transformer secondary side to ground i Parasitic capacitance C of the output side of the inverter bridge to ground p .

8. The time-domain EMI modeling method for a high-capacity, short-time operating isolated DC-DC charger according to claim 1, characterized in that, Software used for extracting parasitic parameters includes ANSYS Q3D Extractor.

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