A modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform

Abstract

The present invention discloses a modeling method for time-domain EMI of a DC-DC charger working for a short time on a ship platform, the steps of which include: 1) obtaining the equivalent interference source spectrum information of the switching process according to the switching function of the switch tube in the power circuit of the DC-DC charger; 2) establishing a common-mode interference equivalent circuit model and a differential-mode interference equivalent circuit; 3) establishing a time-domain expression of the common-mode electromagnetic interference voltage and the differential-mode electromagnetic interference voltage on the output side of the DC-DC charger. The present invention provides a time-domain calculation analytical solution for the common-mode voltage and the differential-mode voltage of a DC charger using a Buck circuit topology, and the EMI characteristics of a DC charger in a wide frequency range can be directly obtained through time-frequency changes.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic compatibility, and in particular to a modeling method for time-domain EMI of a DC-DC charger working for a short time on a ship platform. Background Art

[0002] The propulsion motors currently used in ship platforms have the characteristics of short-term high-power operation, which will produce huge power impacts on the DC power grid of the ship platform. Therefore, in order to reduce the electromagnetic interference caused by power impacts and enable the independent power grid to work smoothly, it is necessary to charge the energy storage cabinet through the DC power grid first, and drive different motors when the power of the energy storage cabinet meets the peak power and energy consumption requirements of the subsequent short-term operation of the propulsion motor. Therefore, a large-capacity DC-DC charger is required to perform short-term high-power DC charging between the DC power grid and the energy storage cabinet.

[0003] High-power semiconductor devices are used in DC-DC chargers. When turned on, the terminal voltage is close to 0, which is approximately equivalent to a short-circuit state, while the terminal voltage in the off state is the power supply voltage. Therefore, when the semiconductor switch device switches quickly between the on and off states, it will inevitably generate large du / dt and di / dt, which will cause electromagnetic interference problems and cause serious electromagnetic interference risks to other electrical equipment working on independent power grids at the same time. At the same time, the capacity of DC-DC chargers used on ship platforms at this stage has reached MW level, and the switching frequency and power of the semiconductor switch devices used will be higher, which will generate greater electromagnetic interference in the circuit. Therefore, the problem of modeling the short-term working characteristics of DC-DC chargers to predict EMI characteristics needs to be solved urgently. However, the DC charger used for the short-term working characteristics of the power system is quite different from the steady-state working characteristics of the traditional DC chargers in the past, and there is no good method for time domain modeling and analysis.

[0004] Buck circuits are increasingly used in DC charging scenarios on ships and other platforms due to their simple circuit structure, high transmission power, and high circuit efficiency. However, from the perspective of electromagnetic interference analysis, the use of switching tubes in the circuit topology and the nonlinear switching characteristics of the switching tube devices themselves will cause serious electromagnetic interference problems, affecting the normal and safe operation of the equipment. Summary of the invention

[0005] The object of the present invention is to provide a modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform, comprising the following steps:

[0006] 1) According to the switching function of the switch tube in the power circuit of the DC-DC charger, the equivalent interference source spectrum information of the switching process is obtained;

[0007] The power circuit includes a Buck circuit;

[0008] Among them, the power circuit uses PWM control to control the on and off of the switch tube;

[0009] The switching function of the switch tube is as follows:

[0010]

[0011] In the formula, S=1 means the switch is on; S=0 means the switch is off.

[0012] The steps of obtaining the spectrum information of the equivalent interference source of the switching process include:

[0013] 1.1) Obtain the time domain waveform of the switch tube at the moment of opening and closing as the time domain information of the interference source;

[0014] 1.2) Perform fast Fourier transform on the time domain information of the interference source to obtain the spectrum information of the interference source.

[0015] 2) Establish common mode interference equivalent circuit model and differential mode interference equivalent circuit;

[0016] The differential mode interference equivalent circuit is the same as the power circuit.

[0017] The steps to establish a common-mode interference equivalent circuit include:

[0018] 2.1) Establishing a geometric model of the switch device, including a switch tube, thermal grease, an insulating pad and a heat sink; wherein the insulating pad is located on the heat sink; the thermal grease is located on the insulating pad; and the switch tube is located on the thermal grease;

[0019] 2.2) According to the geometric model of the switching device, solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm ;

[0020] 2.3) According to the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm , establish a common-mode interference equivalent circuit.

[0021] The circuit topology of the common mode interference equivalent circuit is shown below:

[0022] The positive terminal of the power supply is A, and the negative terminal is B.

[0023] Terminal A is connected to the collector of the switch tube S;

[0024] The base of the switch tube S is suspended, and the emitter is connected in series with the inductor L and the resistor R and then connected to the B terminal;

[0025] The emitter of the switch tube S is connected in series with the capacitor C p Rear grounding;

[0026] The emitter of the switch tube S is connected to the cathode of the diode D1; the anode of the diode D1 is connected to the B terminal;

[0027] Terminal A is connected to capacitor C, capacitor C1, resistor R1 and then grounded;

[0028] Terminal A is connected to capacitor C2, resistor R2 and then grounded;

[0029] The B terminal is connected to capacitor C2, resistor R2 and then grounded; the B terminal is connected to capacitor C1, resistor R1 and then grounded.

[0030] Solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm Tools include Q3D software.

[0031] 3) Establish the time domain expressions of the common-mode electromagnetic interference voltage and differential-mode electromagnetic interference voltage on the output side of the DC-DC charger.

[0032] 3.1) Establish the time domain expression of the differential mode electromagnetic interference voltage at the output side of the DC-DC charger, the steps include:

[0033] 3.1.1) During the conduction period of the switch tube S, the relationship between the input voltage and the output current of the differential mode interference equivalent circuit is established, that is:

[0034]

[0035] Where, E is the input voltage; i O1 is the output current when the switch tube S is turned on; R is the resistance; L is the inductance;

[0036] 3.1.2) According to the relationship between input voltage and output current, establish the output current i O1 The expression is:

[0037]

[0038] In the formula, I O1 is the initial value of the output current when the switch tube S is turned on; is the time constant; t is the time;

[0039] 3.1.3) During the off period of the switch tube S, the output current i is established O2 The time domain expression of is:

[0040]

[0041] In the formula, i O2 is the output current when the switch tube S is turned off;

[0042] 3.1.4) According to the output current i O1 With the output current i O2 The relationship between the output current i O2 The expression is:

[0043]

[0044] In the formula, I O2 is the initial value of the output current when the switch tube S is turned off;

[0045] 3.1.5) Establish the steady-state current constraint when the switch tube S works in the current continuous state, that is:

[0046]

[0047] Where T is the time of a switching cycle;

[0048] 3.1.6) Solve equations (2) to (6) to obtain the initial value of the output current I when the switch S is turned on. O1 When the switch tube S is turned off, the initial value of the output current I O2 ,Right now:

[0049]

[0050] 3.1.7) Establish the time domain expression of differential mode electromagnetic interference voltage, namely:

[0051]

[0052] In the formula, u dm (t) is the instantaneous value of the differential mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S.

[0053] 3.2) Establishing the time domain expression of the common mode electromagnetic interference voltage at the output side of the DC-DC charger, the steps include:

[0054] 3.2.1) When the switch tube S is turned on, the expression of the potential difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the midpoint of the input side power supply is established, that is:

[0055]

[0056] Where U + , U -It represents the difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the potential between the midpoint of the input side power supply;

[0057] 3.2.2) Establish the common mode voltage u when the switch tube S is turned on cm (t) expression, that is:

[0058]

[0059] 3.2.3) Establish the output current i during the conduction period of the switch tube S O3 The expression is:

[0060]

[0061] 3.2.4) According to formula (11), establish the output current i O3 The expression is:

[0062]

[0063] In the formula, I O3 is the initial value of the output current when the switch tube S is turned on;

[0064] 3.2.5) Update the common mode voltage u during the conduction period of the switch tube S cm (t) expression, that is:

[0065]

[0066] 3.2.6) Establish an expression for the potential difference between the potential at both ends of the output side of the common-mode interference equivalent circuit and the midpoint of the input side power supply when the switch tube S is turned off, that is:

[0067]

[0068] In the formula, i O4 is the output current when the switch tube is turned off;

[0069] 3.2.7) Establish the common mode voltage u when the switch tube S is turned off cm (t) expression, that is:

[0070]

[0071] 3.2.8) Establish the output current i during the off period of the switch tube S O4 The expression is:

[0072]

[0073] 3.2.9) According to formula (16), the output current i during the off period of the switch tube S is established O4 The expression is:

[0074]

[0075] In the formula, I O4 is the initial value of the output current when the switch tube S is turned off;

[0076] 3.2.10) Update the common mode voltage u during the switch S off period cm (t) expression, that is:

[0077]

[0078] 3.2.11) Combine formula (13) and formula (18) to establish the time domain expression of common mode electromagnetic interference voltage, namely:

[0079]

[0080] In the formula, u cm (t) is the instantaneous value of the common-mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S.

[0081] Output current initial value I o3 =I o1 ; Output current initial value I o4 =I o2 .

[0082] It is worth noting that the present invention first obtains a mathematical model of the switching function based on the circuit topology and the conduction mode of the switch tube, and then establishes an equivalent interference source model. Then, a theoretical analysis is performed on the electromagnetic interference path, and the parasitic parameters therein are extracted using Q3D software and equivalent to parasitic capacitance elements, thereby establishing an equivalent circuit model of the interference transmission path. Finally, the theoretical calculation formula of the conducted electromagnetic interference voltage in different time periods is obtained through equivalent circuit calculation, which forms a method for theoretical modeling of time domain EMI of a DC-DC charger based on a short-time operation of a ship platform.

[0083] The technical effect of the present invention is unquestionable. The present invention proposes a time domain EMI theoretical modeling method for a DC-DC charger working for a short time on a ship platform, which can be used to predict the conducted electromagnetic interference characteristics of the DC charger on the grid side, and can be used to analyze the propagation characteristics of the interference source in the ship power system, support the research on conducted electromagnetic interference analysis of independent power systems on ship platforms, and carry out targeted design and control of conducted electromagnetic interference, etc.

[0084] The modeling method of the present invention is based on the switching state of the switch tube, has clear physical concepts and simple calculation methods, and can model and characterize the time domain electromagnetic interference source of the DC charger of the Buck circuit topology, laying the foundation for subsequent targeted electromagnetic interference suppression measures.

[0085] The present invention provides a time domain calculation analytical solution for the common mode voltage and differential mode voltage of a DC charger using a Buck circuit topology, and the EMI characteristics of the DC charger in a wide frequency band can be directly obtained through time-frequency changes.

[0086] The present invention provides a modeling method and a calculation model for time-domain electromagnetic interference of a direct current charger circuit based on a Buck circuit, which can also be directly extended and applied to other types of DC-DC conversion circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 This is the Buck circuit topology diagram;

[0088] Figure 2 It is the equivalent circuit diagram of the input side power supply;

[0089] Figure 3 It is the conduction mode diagram of the switch tube;

[0090] Figure 4 Is the interference source waveform; Figure 4 (a) is the time domain waveform of the interference source; Figure 4 (b) is the interference source waveform spectrum;

[0091] Figure 5 It is the differential mode interference transmission path diagram;

[0092] Figure 6 It is the common mode interference transmission path diagram;

[0093] Figure 7 Extract equivalent capacitance for Q3D geometry modeling;

[0094] Figure 8 This is the common mode interference equivalent circuit diagram of the BUCK circuit;

[0095] Fig. 9 This is the time domain comparison result of common mode voltage;

[0096] Fig.10 This is the time domain comparison result diagram of differential mode voltage;

[0097] Fig.11 This is the comparison result of common mode voltage in frequency domain;

[0098] Fig.12 This is the frequency domain comparison result of differential mode voltage. DETAILED DESCRIPTION

[0099] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0100] Embodiment 1:

[0101] See also Figures 1 to 12 A modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform includes the following steps:

[0102] 1) According to the switching function of the switch tube in the power circuit of the DC-DC charger, the equivalent interference source spectrum information of the switching process is obtained;

[0103] The power circuit includes a Buck circuit;

[0104] Among them, the power circuit uses PWM control to control the on and off of the switch tube;

[0105] The switching function of the switch tube is as follows:

[0106]

[0107] In the formula, S=1 means the switch is on; S=0 means the switch is off.

[0108] The steps of obtaining the spectrum information of the equivalent interference source of the switching process include:

[0109] 1.1) Obtain the time domain waveform of the switch tube at the moment of opening and closing as the time domain information of the interference source;

[0110] 1.2) Perform fast Fourier transform on the time domain information of the interference source to obtain the spectrum information of the interference source.

[0111] 2) Establish common mode interference equivalent circuit model and differential mode interference equivalent circuit;

[0112] The differential mode interference equivalent circuit is the same as the power circuit.

[0113] The steps to establish a common-mode interference equivalent circuit include:

[0114] 2.1) Establishing a geometric model of the switch device, including a switch tube, thermal grease, an insulating pad and a heat sink; wherein the insulating pad is located on the heat sink; the thermal grease is located on the insulating pad; and the switch tube is located on the thermal grease;

[0115] 2.2) According to the geometric model of the switching device, solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference groundcm ;

[0116] 2.3) According to the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm , establish a common-mode interference equivalent circuit.

[0117] The circuit topology of the common mode interference equivalent circuit is shown below:

[0118] The positive terminal of the power supply is A, and the negative terminal is B.

[0119] Terminal A is connected to the collector of the switch tube S;

[0120] The base of the switch tube S is suspended, and the emitter is connected in series with the inductor L and the resistor R and then connected to the B terminal;

[0121] The emitter of the switch tube S is connected in series with the capacitor C p Rear grounding;

[0122] The emitter of the switch tube S is connected to the cathode of the diode D1; the anode of the diode D1 is connected to the B terminal;

[0123] Terminal A is connected to capacitor C, capacitor C1, resistor R1 and then grounded;

[0124] Terminal A is connected to capacitor C2, resistor R2 and then grounded;

[0125] The B terminal is connected to capacitor C2, resistor R2 and then grounded; the B terminal is connected to capacitor C1, resistor R1 and then grounded.

[0126] Solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm Tools include Q3D software.

[0127] 3) Establish the time domain expressions of the common-mode electromagnetic interference voltage and differential-mode electromagnetic interference voltage on the output side of the DC-DC charger.

[0128] 3.1) Establish the time domain expression of the differential mode electromagnetic interference voltage at the output side of the DC-DC charger, the steps include:

[0129] 3.1.1) During the conduction period of the switch tube S, the relationship between the input voltage and the output current of the differential mode interference equivalent circuit is established, that is:

[0130]

[0131] Where, E is the input voltage; i O1 is the output current when the switch tube S is turned on; R is the resistance; L is the inductance;

[0132] 3.1.2) According to the relationship between input voltage and output current, establish the output current i O1 The expression is:

[0133]

[0134] In the formula, I O1 is the initial value of the output current when the switch tube S is turned on; is the time constant; t is the time;

[0135] 3.1.3) During the off period of the switch tube S, the output current i is established O2 The time domain expression of is:

[0136]

[0137] In the formula, i O2 is the output current when the switch tube S is turned off;

[0138] 3.1.4) According to the output current i O1 With the output current i O2 The relationship between the output current i O2 The expression is:

[0139]

[0140] In the formula, I O2 is the initial value of the output current when the switch tube S is turned off;

[0141] 3.1.5) Establish the steady-state current constraint when the switch tube S works in the current continuous state, that is:

[0142]

[0143] Where T is the time of a switching cycle;

[0144] 3.1.6) Solve equations (2) to (6) to obtain the initial value of the output current I when the switch S is turned on. O1 When the switch tube S is turned off, the initial value of the output current I O2 ,Right now:

[0145]

[0146] 3.1.7) Establish the time domain expression of differential mode electromagnetic interference voltage, namely:

[0147]

[0148] In the formula, u dm(t) is the instantaneous value of the differential mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S.

[0149] 3.2) Establishing the time domain expression of the common mode electromagnetic interference voltage at the output side of the DC-DC charger, the steps include:

[0150] 3.2.1) When the switch tube S is turned on, the expression of the potential difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the midpoint of the input side power supply is established, that is:

[0151]

[0152] Where U + , U - It represents the difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the potential between the midpoint of the input side power supply;

[0153] 3.2.2) Establish the common mode voltage u when the switch tube S is turned on cm (t) expression, that is:

[0154]

[0155] 3.2.3) Establish the output current i during the conduction period of the switch tube S O3 The expression is:

[0156]

[0157] 3.2.4) According to formula (11), establish the output current i O3 The expression is:

[0158]

[0159] In the formula, I O3 is the initial value of the output current when the switch tube S is turned on;

[0160] 3.2.5) Update the common mode voltage u during the conduction period of the switch tube S cm (t) expression, that is:

[0161]

[0162] 3.2.6) Establish an expression for the potential difference between the potential at both ends of the output side of the common-mode interference equivalent circuit and the midpoint of the input side power supply when the switch tube S is turned off, that is:

[0163]

[0164] In the formula, i O4 is the output current when the switch tube is turned off;

[0165] 3.2.7) Establish the common mode voltage u when the switch tube S is turned off cm (t) expression, that is:

[0166]

[0167] 3.2.8) Establish the output current i during the off period of the switch tube S O4 The expression is:

[0168]

[0169] 3.2.9) According to formula (16), the output current i during the off period of the switch tube S is established O4 The expression is:

[0170]

[0171] In the formula, I O4 is the initial value of the output current when the switch tube S is turned off;

[0172] 3.2.10) Update the common mode voltage u during the switch S off period cm (t) expression, that is:

[0173]

[0174] 3.2.11) Combine formula (13) and formula (18) to establish the time domain expression of common mode electromagnetic interference voltage, namely:

[0175]

[0176] In the formula, u cm (t) is the instantaneous value of the common-mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S.

[0177] Output current initial value I o3 =I o1 ; Output current initial value I o4 =I o2 .

[0178] Embodiment 2:

[0179] See also Figures 1 to 12 A modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform includes the following steps:

[0180] First, the Buck circuit, a power circuit commonly used in DC-DC chargers, is analyzed. Then, a mathematical function model of the switching process is established based on the conduction mode of the switch tube, and then an equivalent interference source model is established. Secondly, for electromagnetic interference path analysis, the parasitic parameters are extracted using Q3D software, and an equivalent circuit model is established through theoretical analysis of the conducted electromagnetic interference paths of common-mode interference and differential-mode interference. Finally, the time domain expressions of the common-mode electromagnetic interference voltage and the differential-mode electromagnetic interference voltage on the output side are derived, which forms a method for theoretical modeling of time domain EMI of DC-DC chargers under short-term working conditions of ship platforms. The present invention can provide a time domain EMI calculation method for equipment under similar working conditions, which is suitable for simulation of conducted electromagnetic interference in power systems, and can provide model support for the overall electromagnetic compatibility prediction of power systems.

[0181] The present invention can theoretically analyze the conducted electromagnetic interference generated by a switch tube in a power circuit when it is in a high-frequency on and off state.

[0182] The time-domain EMI theoretical modeling method of the DC-DC charger proposed in the present invention can be used for the time-domain EMI modeling of the short-term working characteristics of the DC-DC charger in various DC power grids, and can further be used for the analysis of the short-term electromagnetic interference of the ship's DC power grid, and can provide method guidance for the time-domain EMI modeling and analysis of short-term high-power power systems.

[0183] Embodiment 3:

[0184] See also Figures 1 to 12 , a modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform, including the following contents:

[0185] Based on the commonly used circuit topology of high-power DC-DC chargers, a theoretical analysis is conducted on the EMI problems caused by the short-term changes in voltage and current during the opening and closing of semiconductor devices. Then, the electromagnetic interference calculation under short-term working mode is performed using time domain expressions based on the switching state of the switch tube. Secondly, based on the time domain analysis of the interference source, the equivalent circuit modeling of the electromagnetic interference coupling path is performed, and finally the time domain expression for the theoretical calculation of EMI in different time periods is derived. The specific steps are as follows:

[0186] 1) Based on the working state of the switch tube in the Buck circuit, the interference source calculation model in the DC-DC charger is derived.

[0187] The main theoretical derivation process of the present invention is a theoretical analysis of the Buck circuit with inductive load. In the theoretical derivation process, the control method used for the on and off states of the switch tube is PWM control. The switching method is as follows: Figure 3The switch conduction state in this derivation can be set as follows: at time t1 to t2, the switch is in the conduction state; at time t2 to t3, the switch is in the off state.

[0188] Therefore, the switching function in the Buck circuit topology can be equivalent to the following formula:

[0189]

[0190] Among them, S = 1 means the switch is on, and S = 0 means the switch is off. At the moment of turning on and off the switch, its time domain waveform is as follows Figure 4 (a), since a large du / dt is generated in the on and off states, the interference source can be equivalent to a square wave. Then, the interference source is subjected to a fast Fourier transform to obtain its spectrum diagram as shown below: Figure 4 (b) as shown.

[0191] 2) Analyze the transmission path of the interference signal and establish the differential mode and common mode conducted interference equivalent circuits.

[0192] The paths of differential-mode conducted electromagnetic interference and common-mode conducted electromagnetic interference signals are generated for different reasons. Therefore, it is necessary to analyze the transmission paths of differential-mode interference and common-mode interference separately and establish corresponding equivalent circuit models.

[0193] Differential Mode Interference Transmission Path Analysis

[0194] The transmission path of differential mode conducted electromagnetic interference is mainly formed through the switch tube T, the load inductor L and resistor R on the output side, and the electrolytic capacitor on the DC side. Figure 5 As indicated by the arrow in the figure. Since the differential mode interference transmission path is the same as the current transmission path of the original circuit, no parasitic parameter extraction is required, so the differential mode interference equivalent circuit is the same as the original circuit.

[0195] Common Mode Interference Transmission Path Analysis

[0196] The transmission path of common-mode conducted electromagnetic interference is the switch tube T. The DC power supply is considered to be short-circuited. The equivalent inductance L between the connection line between the heat sink and the reference ground is cm It is also an important link in the transmission path. In addition, the common-mode interference transmission path also has the equivalent parasitic capacitance C between the emitter of the switch tube and the reference ground, which cannot be ignored under the high-frequency switching of the switch tube. p In summary, the common mode interference transmission path is as follows Figure 6 As indicated by the arrow in the middle.

[0197] In the common mode interference path theoretical analysis, the equivalent parasitic capacitance of the switch emitter to the reference ground and the equivalent inductance between the heat sink and the reference ground need to be extracted using Q3D software. First, the geometric model of the switch device must be established. Figure 7 As shown in the figure, it mainly includes four parts: switch tube, thermal grease, insulating pad and heat sink. Then, define various material properties in Q3D material settings. Finally, add Solve Setup to solve the capacitance parameter matrix (Spice Matrix) and equivalent inductance parameters separately, that is, solve the equivalent parasitic capacitance C of the switch tube emitter to the reference ground. p The equivalent inductance L between the heat sink and the reference ground cm .

[0198] 3) Based on the equivalent circuits of differential mode and common mode, the theoretical calculation formulas for differential mode and common mode interference time domain EMI are given.

[0199] Theoretical calculation formula for time domain EMI of differential mode voltage

[0200] Assume that α is the duty cycle in the Buck circuit, t on is the conduction time, and E is the input voltage, which are all known. The specific process is analyzed through each time period:

[0201] When t1~t2, the switch tube V is turned on, and the output current is i O1 , then:

[0202]

[0203] Assume the initial value of the output current is I O1 , the time constant is Available O1 (t):

[0204]

[0205] When t2~t3, the switch tube V is turned off, and the output current is i O2 , then:

[0206]

[0207] Assume that the initial value of the output current at this time is I O2 , the time constant is

[0208]

[0209] When working in the continuous current state, the current in the steady state satisfies the following relationship:

[0210]

[0211] Solving the simultaneous equations (2) to (6) yields the initial value of the current:

[0212]

[0213] Therefore, the instantaneous value of its differential mode voltage is u dm (t) is

[0214]

[0215] Theoretical calculation formula for time domain EMI of common mode voltage

[0216] When t1~t2, the switch tube V is turned on, at this time:

[0217]

[0218] Among them, U + , U - Represents the difference between the potential at both ends of the circuit output side and the potential between the midpoint of the input power supply, such as Figure 2 So the common mode voltage is expressed as:

[0219]

[0220] There are

[0221]

[0222] Similar to the differential mode voltage calculation in the above calculation process, the initial value of the current is set to I O3 ,

[0223]

[0224] but:

[0225]

[0226] When t2~t3, the switch tube V is turned off and the output current is set to i O4 , at this time:

[0227]

[0228] So the common mode voltage is expressed as:

[0229]

[0230] There are

[0231]

[0232] Set the initial value of current to I O4 , so

[0233]

[0234] but:

[0235]

[0236] Therefore, the instantaneous value of its common mode voltage is u cm (t) is

[0237]

[0238] In the above derivation and calculation process, since the circuit operation process and the time of switch on and off are the same, the initial value of the steady-state current involved in the calculation of the common-mode voltage is equal to the initial value of the current in the differential-mode current calculation process, that is, I o3 =I o1 ,I o4 =I o2 , so the final calculation expression for the common-mode voltage is obtained.

[0239] Embodiment 4:

[0240] A modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform includes the following contents:

[0241] 1) Determine the circuit parameters. The specific modeling and analysis object topology of the Buck circuit is as follows: Figure 1 As shown. According to U dm =αE to set the input voltage and the duty cycle of the switch control signal, thereby achieving DC-DC voltage conversion. The input voltage is 900V, the duty cycle is 50%, and the switching frequency is 50kHz. According to the conduction time, the output differential voltage can be obtained as follows

[0242] As shown in Table 1.

[0243] Table 1 Differential mode voltage output at different times

[0244]

[0245] 2) In the theoretical analysis of differential mode voltage, the circuit operation state is first determined based on the on and off state of the switch tube. Since the circuit load is inductive, the current will not change transiently when the switch tube is turned on and off. The KVL equation is written for the output side, and the initial value of the current I can be obtained. O1 ,I O2 The time domain expression of the differential mode current on the output side of the circuit is obtained according to the time constant in the circuit, and finally the time domain expression of the differential mode voltage on the output side is obtained according to the load form.

[0246] 3) In the theoretical analysis of common-mode voltage, the voltage change at both ends of the switch tube in the circuit is used and the common-mode voltage expression U is used. cm =(U + +U - ) / 2. Using an analysis method similar to the theoretical derivation of differential mode voltage, it is also necessary to write the KVL equation based on the load current. Since the initial values ​​of the currents in the circuits are the same, the time domain expression of the common mode voltage on the output side is finally obtained by solving the common mode current formula.

[0247] 4) Build and Figure 5 —— Figure 8 The simulation circuits of the common mode and differential mode interference transmission circuits shown in the figure are used to verify the correctness of the theoretical analysis results. By programming the time domain EMI theoretical calculation process, the calculation results are compared with the simulation results of the time domain circuit in the time domain and frequency domain. Fig. 9 —— Fig.12 As shown. It can be found that the main frequency points and amplitudes in the circuit can get a good fitting effect, which verifies the correctness of the time domain EMI theoretical modeling method of the short-time DC charger. However, since the MATLAB / Simulink simulation software will take the symmetry of the circuit into consideration, the interference frequency points of the simulation circuit will be reduced, which will lead to relatively dense interference frequency points in the frequency domain calculation results of the theoretical calculation results, resulting in errors in the comparison results.

Claims

1. A modeling method for time domain EMI of a DC-DC charger working for a short time on a ship platform, characterized in that: The following steps are involved: 1) According to the switching function of the switch tube in the power circuit of the DC-DC charger, the equivalent interference source spectrum information of the switching process is obtained; 2) Establish common mode interference equivalent circuit model and differential mode interference equivalent circuit; 3) Establish the time domain expressions of the common-mode electromagnetic interference voltage and differential-mode electromagnetic interference voltage on the output side of the DC-DC charger; The steps to establish the time domain expression of the differential mode electromagnetic interference voltage at the output side of the DC-DC charger include: a1) During the conduction period of the switch tube S, the relationship between the input voltage and the output current of the differential mode interference equivalent circuit is established, that is: Where, E is the input voltage; i O1 is the output current when the switch tube S is turned on; R is the resistance; L is the inductance; a2) According to the relationship between input voltage and output current, establish the output current i O1 The expression is: In the formula, I O1 is the initial value of the output current when the switch tube S is turned on; is the time constant; t is the time; a3) During the period when the switch tube S is turned off, the output current i is established O2 The time domain expression of is: In the formula, i O2 is the output current when the switch tube S is turned off; a4) According to the output current i O1 With the output current i O2 The relationship between the output current i O2 The expression is: In the formula, I O2 is the initial value of the output current when the switch tube S is turned off; a5) Establish the steady-state current constraint when the switch tube S works in the current continuous state, that is: Where T is the time of a switching cycle; a6) Solve equations (1) to (5) to obtain the initial value of the output current I when the switch S is turned on. O1 When the switch tube S is turned off, the initial value of the output current I O2 ,Right now: a7) Establish the time domain expression of differential mode electromagnetic interference voltage, namely: In the formula, u dm (t) is the instantaneous value of the differential mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S; The steps to establish the time domain expression of the common mode electromagnetic interference voltage at the output side of the DC-DC charger include: b1) Establish an expression for the potential difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the midpoint of the input side power supply when the switch tube S is turned on, that is: Where U + , U - It represents the difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the potential between the midpoint of the input side power supply; b2) Establish the common mode voltage u when the switch tube S is turned on cm (t) expression, that is: b3) Establish the output current i during the conduction period of the switch tube S O3 The expression is: b4) According to formula (10), establish the output current i O3 The expression is: In the formula, I O3 is the initial value of the output current when the switch tube S is turned on; b5) Update the common mode voltage u during the conduction period of the switch tube S cm (t) expression, that is: b6) Establish an expression for the potential difference between the potential at both ends of the output side of the common mode interference equivalent circuit and the midpoint of the input side power supply when the switch tube S is turned off, that is: In the formula, i O4 is the output current when the switch is turned off; b7) Establish the common mode voltage u when the switch tube S is turned off cm (t) expression, that is: b8) Establish the output current i during the off period of the switch tube S O4 The expression is: b9) According to formula (15), establish the output current i during the off period of the switch tube S O4 The expression is: In the formula, I O4 is the initial value of the output current when the switch tube S is turned off; b10) Update the common mode voltage u during the switch S off period cm (t) expression, that is: b11) Combine formula (12) and formula (17) to establish the time domain expression of common mode electromagnetic interference voltage, namely: In the formula, u cm (t) is the instantaneous value of the common-mode electromagnetic interference voltage; [t1, t2) is the on-time period of the switch tube S; [t2, t3) is the off-time period of the switch tube S.

2. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 1 is characterized in that: The power circuit includes a Buck circuit; Among them, the power circuit uses PWM control to control the on and off of the switch tube; The switching function of the switch tube is as follows: In the formula, S=1 indicates that the switch is turned on; S=0 indicates that the switch is turned off; [t1, t2) is the on-time period of the switch S; [t2, t3) is the off-time period of the switch S.

3. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 1 is characterized in that: The steps of obtaining the spectrum information of the equivalent interference source of the switching process include: 1) Obtain the time domain waveform of the switch tube at the moment of opening and closing as the time domain information of the interference source; 2) Perform fast Fourier transform on the time domain information of the interference source to obtain the spectrum information of the interference source.

4. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 1 is characterized in that: The differential mode interference equivalent circuit is the same as the power circuit.

5. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 1 is characterized in that: The steps to establish a common-mode interference equivalent circuit include: 1) Establish a geometric model of the switch device, including a switch tube, thermal conductive silicone grease, an insulating pad and a heat sink; wherein the insulating pad is located on the heat sink; the thermal conductive silicone grease is located on the insulating pad; and the switch tube is located on the thermal conductive silicone grease; 2) According to the geometric model of the switching device, solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm ; 3) According to the equivalent parasitic capacitance C of the switch tube emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm , establish a common-mode interference equivalent circuit.

6. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 5 is characterized in that: The circuit topology of the common mode interference equivalent circuit is shown below: The positive terminal of the power supply is A, and the negative terminal is B. Terminal A is connected to the collector of the switch tube S; The base of the switch tube S is suspended, and the emitter is connected in series with the inductor L and the resistor R and then connected to the B terminal; The emitter of the switch tube S is connected in series with the capacitor C p Rear grounding; The emitter of the switch tube S is connected to the cathode of the diode D1; the anode of the diode D1 is connected to the B terminal; Terminal A is connected to capacitor C, capacitor C1, resistor R1 and then grounded; Terminal A is connected to capacitor C2, resistor R2 and then grounded; The B terminal is connected to capacitor C2, resistor R2 and then grounded; the B terminal is connected to capacitor C1, resistor R1 and then grounded.

7. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 5 is characterized in that: Solve the equivalent parasitic capacitance C of the switch emitter to the reference ground p , the equivalent inductance L between the heat sink and the reference ground cm Tools include Q3D software.

8. The modeling method of time domain EMI of a DC-DC charger working for a short time on a ship platform according to claim 1 is characterized by: Output current initial value I o3 =I o1 ; Output current initial value I o4 =I o2 .

Images