A design method and system for a DC high-voltage self-starting converter

Abstract

This invention discloses a design method and system for a DC high-voltage self-starting converter, relating to the field of power electronic DC converter technology. This invention combines a DCM-controlled BUCK converter with a full-load-range ZVS LLC converter to improve the overall converter efficiency. Simultaneously, by designing the magnetic core shape and determining the converter's air gap length, the maximum magnetic flux density, primary winding turns, and total cross-sectional area of ​​the core are determined for that core shape, thereby identifying the optimal maximum magnetic flux density. Based on this optimal maximum magnetic flux density, the converter winding parameters are determined. Combining the core shape and air gap length, the converter is wound to solve the problem of excessive leakage inductance in high-isolation transformers and to arrange the optimal number of winding turns, enabling the converter to complete voltage conversion even with high-voltage input.

Description

Technical Field

[0001] This invention relates to the field of power electronic DC-DC converter technology, and in particular to a design method and system for a DC high-voltage self-starting converter. Background Technology

[0002] With the rapid development of renewable energy in my country, the total installed capacity nationwide has been steadily increasing year by year. The distribution network is mainly composed of 3kV to 10kV medium-voltage DC distribution network and 10kV and 20kV medium-voltage AC distribution network. Among them, the medium-voltage distribution network has developed rapidly due to its advantages in loss and cost. As the medium-voltage distribution network uses power electronic converter units with higher withstand voltage to improve voltage and current loss, improve voltage converter stability, and reduce converter control difficulty, it also puts forward higher requirements for the reliable power supply of the converter's insulation and control circuit. Therefore, under the current situation of continuous development of medium-voltage distribution network, reliable power supply to the control and drive parts of the power electronic converter unit from the high-voltage input side of the electronic converter unit shows important research value and plays a vital role in the overall working stability of medium-voltage distribution network.

[0003] For medium-voltage AC distribution networks, power frequency transformers can be used to solve the problem of excessively high withstand voltage of switching devices. However, medium-voltage DC distribution network self-generation devices have strict requirements for high-voltage withstand power electronic switching devices. To improve efficiency, experimental 10kV SiC switching chips are often packaged into independent devices and used in conjunction with flyback or push-pull structures, but the final efficiency is still relatively low, generally between 40% and 60%. Currently available discrete SiC switching devices have a withstand voltage of 3.3kV, and a single independent device is difficult to complete medium-voltage voltage transformation. In addition, medium-voltage DC distribution network self-generation devices require a high level of isolation, which places higher demands on the isolation of high-frequency transformers. Increasing the isolation of high-frequency transformers will also increase the leakage inductance of the transformer, and high voltage input to the transformer will increase the number of transformer windings and cause insulation problems.

[0004] Therefore, the current technology is limited by efficiency, high isolation and high turns ratio issues, making it difficult for the designed converter to complete voltage conversion under high voltage input. Summary of the Invention

[0005] This invention provides a design method and system for a DC high-voltage self-starting converter, which can solve the problem in the prior art that the designed converter is difficult to complete voltage conversion under high voltage input due to limitations in efficiency, high isolation and high turns.

[0006] This invention provides a design method for a DC high-voltage self-starting converter, comprising the following steps:

[0007] The input terminals of the BUCK converter and the LLC converter are connected in series and their output terminals are connected in parallel to form a primary DC high voltage self-starting converter; the electrical parameters of the BUCK converter and the LLC converter in the primary DC high voltage self-starting converter are determined respectively to construct the design variable model of the primary DC high voltage self-starting converter.

[0008] Based on the maximum inductance condition in the discontinuous current control (DCM) requirements of the BUCK converter and the no-load and full-load critical conditions of the input voltage in the full-range zero-voltage switching (ZVS) requirements of the LLC converter, the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter are determined.

[0009] The core shape of the magnetic element of the primary DC-DC high-voltage self-starting converter is determined according to the nearest neighbor propagation algorithm (AP method); and the air gap length of the primary DC-DC high-voltage self-starting converter is determined according to the core shape and the air gap of the primary DC-DC high-voltage self-starting converter including the marginal effect.

[0010] Based on the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter, the maximum magnetic flux density of the core of the primary DC high voltage self-starting converter under the core shape of the magnetic element of the primary DC high voltage self-starting converter is obtained.

[0011] Based on the number of primary, secondary, and auxiliary turns of the primary DC high-voltage self-starting converter in the design variable model, and the air gap length of the primary DC high-voltage self-starting transformer, the number of turns of the primary winding of the primary DC high-voltage self-starting converter is obtained; and combined with the design variable model, the total cross-sectional area of ​​the core winding of the primary DC high-voltage self-starting converter is obtained.

[0012] The optimal maximum magnetic flux density of the primary DC high voltage self-starting converter is determined based on the maximum magnetic flux density of the core, the number of turns in the primary winding, and the total cross-sectional area of ​​the core winding. The parameters of the primary DC high voltage self-starting converter winding are then determined based on the optimal maximum magnetic flux density of the core.

[0013] Based on the core shape, air gap length, and winding parameters of the primary DC high voltage self-starting converter, the DC high voltage self-starting converter is wound.

[0014] Preferably, the determination of the electrical parameters of the BUCK converter and LLC converter includes:

[0015] Based on the set power requirements of the primary DC high-voltage self-starting converter, determine the input voltage V of the BUCK converter. in Output voltage V out and power P, and frequency f of the BUCK converter s ;

[0016] Simultaneously, the input voltage V of the LLC converter is determined based on the converter's set power requirements.in Output voltage V out and power P, and the rated frequency f of the LLC converter. sn .

[0017] Preferably, the establishment of the design variable model for the primary DC high-voltage self-starting converter includes:

[0018] Based on the electrical parameters of the BUCK converter and LLC converter, a design variable model is established, including the core shape of the BUCK converter, the core shape of the LLC converter, the number of primary turns of the primary DC high voltage self-starting converter, the number of secondary turns of the primary DC high voltage self-starting converter, and the number of auxiliary turns of the primary DC high voltage self-starting converter.

[0019] Preferably, the discontinuous current control (DCM) requirement for the BUCK converter inductor includes:

[0020] To ensure the BUCK converter satisfies the discontinuous current discontinuity (DCM) condition for inductor current, the maximum value L of the BUCK converter inductor is... max The following equation must be satisfied for the inductor current to be continuous:

[0021]

[0022] Where: V BULK_max L represents the inductor of the BUCK converter. max The maximum value of V; in_min V represents the input voltage of the BUCK converter. in The minimum value of f; s V0 represents the frequency of the BUCK converter; V0 represents the output voltage of the converter; I0 represents the output current of the converter.

[0023] Preferably, the requirement for the LLC converter to have a full-range zero-voltage switch (ZVS) includes:

[0024] To ensure the LLC converter meets the requirements of zero-voltage switching (ZVS) across the entire load range, including both full-load and no-load ZVS critical conditions at minimum input voltage and maximum input voltage, in practical applications, the design specification is taken as 0.9 to 0.95 times the smaller of the two corresponding quality factors (Q values); and the dead time T must also be considered. D ZVS equivalent capacitance C ZVS Design;

[0025] The design process for an LLC converter with a full-load-range zero-voltage switching (ZVS) converter is as follows:

[0026] To determine the transformer turns ratio, we have:

[0027]

[0028] To find the maximum and minimum gain within the input voltage range, we have:

[0029]

[0030] Let the voltage gain under no-load conditions be the desired maximum voltage gain, and then find the maximum normalized frequency:

[0031]

[0032] To find the equivalent resistance applied to the primary side of the transformer, we have:

[0033]

[0034] To determine the inductance ratio under the conditions of maximum input voltage and no-load output, we have:

[0035]

[0036] Find the minimum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under full load. ZVS1 Find the maximum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under no-load conditions. ZVS2 ,have:

[0037]

[0038] To ensure ZVS status throughout the entire operating range, the converter's maximum quality factor must be lower than Q. ZVS1 and Q ZVS2 The smallest one, with a margin of 5% to 10% to ensure the condition is met, is:

[0039] Q s =90~95%·min{Q zvs1 Q zvs2}

[0040] The characteristic impedance Z0 and LLC main circuit parameters are then obtained as follows:

[0041] Z o =Q S ·R ac

[0042]

[0043] Where: C r The value of the LLC resonant capacitor; L r L is the resonant inductance value of the LLC capacitor. m V is the primary magnetizing inductance value of the LLC; in V represents the input voltage of the LLC converter; V0 represents the output voltage of the converter; V in_minV represents the input voltage of the BUCK converter. in The minimum value of V; in_max V represents the input voltage of the BUCK converter. in The maximum value of f; s f represents the frequency of the BUCK converter; max V represents the maximum frequency of the BUCK converter. out P represents the converter output voltage; out This represents the converter's output power; n represents the number of turns on the primary side of the converter.

[0044] Preferably, determining the air gap length of the primary DC high-voltage self-starting converter includes:

[0045] The air gap has a marginal effect; the more turns N1 in the primary winding, the greater the maximum magnetic induction intensity B of the core. max The smaller the value, the lower the total loss, but the larger the required air gap for a given inductance value. In this case, the ideal air gap length l... g for:

[0046]

[0047] When the air gap exhibits marginal effects, the air gap length of the converter is:

[0048]

[0049] Where: μ0 is the free magnetic permeability; R c_total and R o_total These respectively consider the equivalent total magnetic reluctance of the transformer's middle and side columns in the x and y directions; A e L is the effective cross-sectional area of ​​the inductor core; N is the number of inductor turns; L P Represents resonant inductance; R b 1 represents the equivalent resistance of the transformer; 'a' represents the distance between the upper side arm and the side arm of the transformer's central column; 'b' represents the width of the transformer's side column; and 'h' represents the height of the upper side arm of the transformer's central column.

[0050] Preferably, the method for obtaining the maximum magnetic flux density of the core of the primary DC high-voltage self-starting converter is as follows:

[0051]

[0052] Among them: I Lmax The maximum inductor current is given by A, where N is the number of inductor turns. eL L is the effective cross-sectional area of ​​the inductor core. ex This represents the effective inductance value of the inductor core.

[0053] This invention also provides a design system for a DC high-voltage self-starting converter, comprising:

[0054] A transformer module is used to connect the input terminals of the BUCK converter and the LLC converter in series and the output terminals in parallel to form a primary DC high voltage self-starting converter; the electrical parameters of the BUCK converter and LLC converter in the primary DC high voltage self-starting converter are determined respectively to construct the design variable model of the primary DC high voltage self-starting converter;

[0055] The magnetic circuit simulation module calculates the maximum inductance value of the BUCK converter and the maximum resonant inductance value of the LLC converter based on the maximum inductance value condition in the discontinuous current DCM control requirements of the BUCK converter and the no-load and full-load critical conditions of the input voltage in the full-range zero-voltage switching (ZVS) requirements of the LLC converter.

[0056] The core shape of the magnetic element of the primary DC-DC high-voltage self-starting converter is determined according to the nearest neighbor propagation algorithm (AP method); and the air gap length of the primary DC-DC high-voltage self-starting converter is determined according to the core shape and the air gap of the primary DC-DC high-voltage self-starting converter including the marginal effect.

[0057] Based on the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter, the maximum magnetic flux density of the core of the primary DC high voltage self-starting converter under the core shape of the magnetic element of the primary DC high voltage self-starting converter is obtained.

[0058] Based on the number of primary, secondary, and auxiliary turns of the primary DC high-voltage self-starting converter in the design variable model, and the air gap length of the primary DC high-voltage self-starting transformer, the number of turns of the primary winding of the primary DC high-voltage self-starting converter is obtained; and combined with the design variable model, the total cross-sectional area of ​​the core winding of the primary DC high-voltage self-starting converter is obtained.

[0059] The optimal maximum magnetic flux density of the primary DC high voltage self-starting converter is determined based on the maximum magnetic flux density of the core, the number of turns in the primary winding, and the total cross-sectional area of ​​the core winding. The parameters of the primary DC high voltage self-starting converter winding are then determined based on the optimal maximum magnetic flux density of the core.

[0060] The winding simulation module performs the winding of the DC high voltage self-starting converter based on the core shape, air gap length, and wire winding parameters of the primary DC high voltage self-starting converter.

[0061] This invention provides a design method and system for a DC high-voltage self-starting converter, which has the following advantages compared with the prior art:

[0062] This invention connects a BUCK converter and an LLC converter in series at the input and parallel at the output to improve the working efficiency of the DC high voltage self-starting converter. At the same time, it performs multiple magnetic circuit calculations and simulations on the DC high voltage self-starting converter after combining the BUCK converter and LLC converter to obtain the optimal maximum magnetic induction intensity of the core, air gap length, and winding parameters of the DC high voltage self-starting converter. Based on these parameters, the DC high voltage self-starting converter is wound, solving the problem of excessive leakage inductance of the high isolation transformer and arranging the optimal number of winding turns, so that the converter can complete voltage transformation under high voltage input. Attached Figure Description

[0063] Figure 1 A schematic diagram of the design method and system for a DC high-voltage self-starting converter provided in this embodiment of the invention;

[0064] Figure 2 A typical circuit diagram of a BUCK converter for a design method and system of a DC high-voltage self-starting converter provided in this embodiment of the invention;

[0065] Figure 3 A typical LLC converter circuit diagram of a design method and system for a DC high voltage self-starting converter provided in this embodiment of the invention;

[0066] Figure 4 A schematic diagram of the LLC converter frequency gain of a design method and system for a DC high voltage self-starting converter provided in an embodiment of the present invention;

[0067] Figure 5 This is a schematic diagram of an improved high-isolation transformer magnetic circuit calculation method for a design method and system of a DC high-voltage self-starting converter provided in an embodiment of the present invention. Detailed Implementation

[0068] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0069] See also Figure 1 This invention provides a design method for a DC high-voltage self-starting converter, comprising the following steps:

[0070] Step 1: Determine the parameters of the BUCK converter and LLC converter, as well as the MOSFET model, based on the converter power requirements.

[0071] Step 2: Establish a design variable model for magnetic components based on circuit constraints, using the parameters of the two converters.

[0072] Step 3: Based on the model, construct an optimization model for transformer design variables based on insulation strength and power density.

[0073] Step 4: Change the core shape, repeat step 3, and continue to search for the optimal transformer design model.

[0074] In step one, the BUCK converter circuit diagram is as follows: Figure 2 As shown, the LLC converter circuit diagram is as follows: Figure 3 As shown, determine the parameters of the BUCK converter and LLC converter, including: input voltage V. in Output voltage V out Power P, frequency f s Examine the parasitic parameters and total gate charge Qg of the specific MOSFET model to determine the MOSFET model.

[0075] Step two specifically includes:

[0076] Design variables include the core shape of the BUCK converter, the core shape of the LLC converter, the number of turns on the primary side of the transformer N1, the number of turns on the secondary side of the transformer N2, and the number of auxiliary turns on the transformer N3.

[0077] Based on the discontinuous conduction mode (DCM) control requirements of the BUCK converter and the zero-voltage switch (ZVS) requirements of the LLC converter, calculate the BUCK converter inductance L and the LLC converter resonant inductance L. r Resonant capacitor C r And excitation inductance L m The value of .

[0078] Among them, the discontinuous current control (DCM) of the BUCK converter requires that the inductor current be continuous when the minimum input voltage is fully loaded. The full-range zero-voltage switching (ZVS) requirement of the LLC converter includes two ZVS critical conditions: full load at the minimum input voltage and no load at the maximum input voltage. In practical applications, the design index is taken as 0.9 to 0.95 times the smaller of the two corresponding quality factors Q.

[0079] Step three specifically includes:

[0080] The core shape of the magnetic element is screened and determined according to the AP method, and the frame is checked to see if it can withstand the multi-layer winding design.

[0081] Based on the relationship between magnetic component losses, inductance, and number of turns in the winding, calculate the number of turns N1 in the primary winding of the transformer and the maximum magnetic induction intensity B of the magnetic core. max Total cross-sectional area of ​​winding A Lw(wire) .

[0082] For magnetic components that require an air gap, the air gap has a marginal effect; theoretically, the more turns N1 in the primary winding, the greater the maximum magnetic induction intensity B of the core. max The smaller the inductance, the lower the total loss, but the larger the required air gap for a given inductance value. At this point, the ideal air gap calculation formula becomes meaningless, requiring more refined theoretical calculations for evaluation. Simultaneously, Maxwell simulations are performed to determine the air gap size, and inappropriate adjustments to the LLC converter's CL value are necessary. ZVS The value is then returned to step two for recalculation.

[0083] Based on the above relationships, the number of turns N1 of the primary winding and the maximum magnetic induction intensity B of the magnetic core are... max The primary inductance of the transformer was optimized through multiple steps to find the maximum magnetic flux density B of the core. max The optimal design for insulating magnetic components is one where the air gap is minimized to ensure the insulation distance.

[0084] Step four specifically includes:

[0085] Replace the magnetic core, recalculate the parameters, and check whether the power density of the transformer can be further improved.

[0086] Wind the transformer and measure whether the leakage inductance and primary inductance of the transformer meet the requirements.

[0087] Specifically:

[0088] Step 1: Determine the topology parameters and design variables of the DAB converter to be designed. The required topology parameters include the input voltage V. in Output voltage V out Power P, BUCK converter frequency f s LLC converter rated frequency f sn Examine the parasitic parameters and total gate charge Qg of the specific MOSFET model to determine the MOSFET model.

[0089] Step 2: Calculate the feasibility parameters of the magnetic components; design variables include the core shape of the BUCK converter, the core shape of the LLC converter, the number of turns on the primary side of the transformer N1, the number of turns on the secondary side of the transformer N2, and the number of auxiliary turns of the transformer N3; calculate the BUCK converter inductor L and the LLC converter resonant inductor L based on the discontinuous current discontinuity control (DCM) requirements of the BUCK converter and the full-range zero-voltage switching (ZVS) requirements of the LLC converter. r Resonant capacitor C r And excitation inductance L m The value of .

[0090] ① To ensure the BUCK converter satisfies the discontinuous current discontinuity (DCM) condition for the inductor current, the maximum value L of the BUCK converter inductor is... max This should satisfy the condition that the inductor current is exactly continuous, and its formula is:

[0091]

[0092] Where: V BULK_max L represents the inductor of the BUCK converter. max The maximum value of V; in_min V represents the input voltage of the BUCK converter. in The minimum value of f; s V0 represents the frequency of the BUCK converter; V0 represents the output voltage of the converter; I0 represents the output current of the converter.

[0093] ② To ensure the LLC converter meets the requirements of zero-voltage switching (ZVS) across the entire load range, this mainly includes two ZVS critical conditions: full load at minimum input voltage and no load at maximum input voltage. In practical applications, the design specification is taken as 0.9 to 0.95 times the smaller of the two quality factors Q; this needs to be considered in conjunction with the dead time T. D ZVS equivalent capacitance C ZVS (Typically twice the output capacitance C of the MOSFET) oss ) Take comprehensive consideration; such as Figure 4 As shown.

[0094] The specific design flow of the LLC converter with full-load-range zero-voltage switching (ZVS) is as follows:

[0095] The formula for calculating the transformer turns ratio is as follows:

[0096]

[0097] The formulas for calculating the maximum and minimum gain within the input voltage range are as follows:

[0098]

[0099] Let the voltage gain under no-load conditions be the desired maximum voltage gain, and calculate the maximum normalized frequency using the following formula:

[0100]

[0101] The formula for calculating the equivalent resistance applied to the primary winding of the transformer is as follows:

[0102]

[0103] The formula for calculating the inductance ratio under the conditions of maximum input voltage and no-load output is as follows:

[0104]

[0105] Calculate the minimum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under full load. ZVS1 Calculate the maximum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under no-load conditions. ZVS2 The formulas are as follows:

[0106]

[0107] To ensure ZVS status throughout the entire operating range, the converter's maximum quality factor must be lower than the smallest of the two aforementioned quality factors, with a margin of 5% to 10% to ensure the condition is met. The formula is as follows:

[0108] Q s =90~95%·min{Q zvs1 Q zvs2}

[0109] The formulas for calculating the characteristic impedance and LLC main circuit parameters are as follows:

[0110] Z o =Q S ·R ac

[0111]

[0112] Step 3: Calculate the feasibility parameters of the magnetic components.

[0113] For BUCK converter inductors and LLC resonant inductors L r The maximum magnetic flux density B of the magnetic core Lmax for:

[0114]

[0115] Among them: I Lmax The maximum inductor current is given by A, where N is the number of inductor turns. eL This represents the effective cross-sectional area of ​​the inductor core.

[0116] For an LLC transformer, the maximum magnetic flux density of the core is B. Tmax Approximately:

[0117]

[0118] Among them: A eT N1 is the effective cross-sectional area of ​​the transformer core; N2 is the number of turns of the primary inductance.

[0119] The AP method is often used for simplified evaluation of transformer windings.

[0120] The formula for calculating the apparent power of an LLC transformer is as follows:

[0121]

[0122] Provisional maximum magnetic flux density B of the magnetic core Tmax The formula for calculating the AP value of an LLC transformer is as follows:

[0123]

[0124] Where: K f For waveform coefficients (4 for square wave); K w K is the window's effective utilization factor (typically 0.2); J For current density, take 4 × 10 6 A / m 2 .

[0125] Calculate the transmission depth of the primary and secondary windings of the LLC transformer, determine the wire diameter and cross-sectional area of ​​the primary and secondary windings, check if the winding space is sufficient, and determine the winding scheme. The formula is as follows:

[0126]

[0127] Where μ is the absolute permeability of copper; γ is the electrical conductivity of copper.

[0128] The formula for calculating the number of turns in the primary and secondary windings, under ideal conditions, is:

[0129]

[0130] However, the air gap exhibits marginal effects, which should be considered in accordance with... Figure 5 Determine the air gap length of the transformer:

[0131]

[0132] Where: μ0 is the free magnetic permeability; R c_total and R o_total These figures represent the equivalent total magnetic reluctance of the transformer's center column and side column in the x and y directions, respectively; a represents the distance between the upper side arm and the side arm of the transformer's center column; b represents the width of the transformer's side column; and h represents the height of the upper side arm of the transformer's center column.

[0133] Finally, Maxwell continued to adjust the air gap length and checked whether the transformer air gap length met the transformer insulation requirements. If not, the maximum magnetic induction intensity B of the magnetic core was increased. Tmax Repeat the calculation until the requirement is met.

[0134] Step 4: After a series of iterative calculations, the input voltage of the preamplifier BUCK for a single power supply unit was finally determined to be 1000–2400V, the output voltage to be 500V, the BUCK operating frequency to be 20kHz, the LLC output voltage to be 24V, the rated operating frequency to be 150kHz, and the maximum output power to be 40W. This verifies the accuracy and effectiveness of the design method. Substituting the experimental conditions into the design method proposed in this invention, the design parameters of the magnetic components under these experimental conditions are obtained as follows:

[0135] ①LLC Transformer: The transformer core uses two EE50 cores, PC95 material, N1 / N2 is 42 / 4, the transformer leakage inductance is 21.8μH, and the magnetizing inductance is 375uH.

[0136] ②LLC external inductor: The inductor core is made of EE22 magnetic core and PC95 material, with 34 coil turns and an inductance value of 102.3μH.

[0137] The method is basically consistent with the design requirements of 120μH resonant inductance and 384uH magnetizing inductance for LLC. The detected air gap size is 2.2mm, which is greater than the predetermined safety distance of 2mm, meeting the 4kV isolation design requirements. It has also been verified that the method can achieve the ZVS operating mode of LLC with high power transmission efficiency. Furthermore, the method can be quickly adjusted and changed according to the requirements of the conditions, meeting the requirements of universality.

[0138] This invention employs a front-stage BUCK converter and a rear-stage LLC converter as a 2kV self-powered module. The two self-powered modules are connected in series at the input and in parallel at the output to form a DC high-voltage self-powered converter device. The efficiency is improved to 80% or higher by using the front-stage BUCK converter and the rear-stage LLC converter. The output power of the two power-taking units is adjusted to solve the problem of the series voltage of the two units and solve the device withstand voltage problem. The rear-stage LLC converter uses the leakage inductance of the transformer to resonate, which solves the problem of excessive leakage inductance of the high isolation transformer. The two-stage structure reduces the input of the LLC converter, making the transformer easier to manufacture.

[0139] The design method for a two-stage cascaded DC high-voltage self-powered converter provided by this invention avoids the use of high-voltage switching devices, reducing the overall cost of the device compared to existing design methods. The use of a BUCK converter with DCM control mode, combined with a full-load-range ZVS LLC converter, improves the overall efficiency and reliability of the power supply device. Through an improved magnetic circuit calculation method combined with simulation and multiple optimizations, the efficiency of the transformer is improved while ensuring its insulation capability, reducing the manufacturing difficulty of high-insulation transformers. Furthermore, this design method is universal and can be extended to different voltage levels.

[0140] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A design method for a DC high-voltage self-starting converter, characterized in that, include: The input terminals of the BUCK converter and the LLC converter are connected in series and their output terminals are connected in parallel to form a primary DC high voltage self-starting converter; the electrical parameters of the BUCK converter and the LLC converter in the primary DC high voltage self-starting converter are determined respectively to construct the design variable model of the primary DC high voltage self-starting converter. Based on the maximum inductance condition in the discontinuous current control (DCM) requirements of the BUCK converter and the no-load and full-load critical conditions of the input voltage in the full-range zero-voltage switching (ZVS) requirements of the LLC converter, the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter are determined. The core shape of the magnetic element of the primary DC-DC high-voltage self-starting converter is determined according to the nearest neighbor propagation algorithm (AP method); and the air gap length of the primary DC-DC high-voltage self-starting converter is determined according to the core shape and the air gap of the primary DC-DC high-voltage self-starting converter including the marginal effect. Based on the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter, the maximum magnetic flux density of the core of the primary DC high voltage self-starting converter under the core shape of the magnetic element of the primary DC high voltage self-starting converter is obtained. Based on the number of primary, secondary, and auxiliary turns of the primary DC high-voltage self-starting converter in the design variable model, and the air gap length of the primary DC high-voltage self-starting transformer, the number of turns of the primary winding of the primary DC high-voltage self-starting converter is obtained; and combined with the design variable model, the total cross-sectional area of ​​the core winding of the primary DC high-voltage self-starting converter is obtained. The optimal maximum magnetic flux density of the primary DC high voltage self-starting converter is determined based on the maximum magnetic flux density of the core, the number of turns in the primary winding, and the total cross-sectional area of ​​the core winding. The parameters of the primary DC high voltage self-starting converter winding are then determined based on the optimal maximum magnetic flux density of the core. Based on the core shape, air gap length, and winding parameters of the primary DC high voltage self-starting converter, the DC high voltage self-starting converter is wound.

2. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, The determination of the electrical parameters of the BUCK converter and LLC converter includes: Based on the set power requirements of the primary DC high-voltage self-starting converter, determine the input voltage of the BUCK converter. V in Output voltage V out and power P and the frequency of the BUCK converter f s ; Simultaneously, the input voltage of the LLC converter is determined based on the converter's set power requirements. V in Output voltage V out and power P and the rated frequency of the LLC converter f sn .

3. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, The establishment of the design variable model for the primary DC high-voltage self-starting converter includes: Based on the electrical parameters of the BUCK converter and LLC converter, a design variable model is established, including the core shape of the BUCK converter, the core shape of the LLC converter, the number of primary turns of the primary DC high voltage self-starting converter, the number of secondary turns of the primary DC high voltage self-starting converter, and the number of auxiliary turns of the primary DC high voltage self-starting converter.

4. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, The discontinuous current discontinuity (DCM) control requirements for the BUCK converter inductor include: To ensure the BUCK converter satisfies the discontinuous current discontinuity (DCM) condition for inductor current, the maximum value of the BUCK converter inductor is... L max When the following equation is satisfied, the inductor current is in a continuous state: in: V BULK_max Represents the inductor of the BUCK converter L max The maximum value; V in_min Represents the input voltage of the BUCK converter V in The minimum value; f s This represents the frequency of the BUCK converter; V 0 represents the output voltage of the converter; I 0 represents the output current of the converter.

5. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, The requirements for the full-range zero-voltage switching (ZVS) of the LLC converter include: To ensure the LLC converter meets the requirements of zero-voltage switching (ZVS) across the entire load range, including both full-load and no-load ZVS critical conditions at minimum input voltage and maximum input voltage, in practical applications, a design specification is taken as 0.9 to 0.95 times the smaller of the two corresponding quality factors (Q values). This must also be considered in conjunction with the dead time T. D ZVS equivalent capacitance C ZVS Design; The design process for an LLC converter with a full-load-range zero-voltage switching (ZVS) converter is as follows: To determine the transformer turns ratio, we have: To find the maximum and minimum gain within the input voltage range, we have: Let the voltage gain under no-load conditions be the desired maximum voltage gain, and then find the maximum normalized frequency: To find the equivalent resistance applied to the primary side of the transformer, we have: To determine the inductance ratio under the conditions of maximum input voltage and no-load output, we have: Find the minimum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under full load. ZVS1 Find the maximum input voltage and the maximum quality factor Q of the converter operating in the ZVS region under no-load conditions. ZVS2 ,have: To ensure ZVS status throughout the entire operating range, the converter's maximum quality factor must be lower than Q. ZVS1 and Q ZVS2 The smallest one, with a margin of 5% to 10% to ensure the condition is met, is: Then obtain the characteristic impedance Z The parameters of the 0 and LLC main circuits are as follows: in: C r This refers to the value of the LLC resonant capacitor. L r This is the value of the LLC resonant inductance. L m This is the primary magnetizing inductance value of the LLC. V in This represents the input voltage of the LLC converter. V 0 represents the output voltage of the converter; V in_min Represents the input voltage of the LLC converter V in The minimum value; V in_max Represents the input voltage of the LLC converter V in The maximum value; f s Represents the frequency of the converter; f max This represents the maximum frequency of the converter. V out Represents the converter output voltage; P out This represents the converter's output power; n represents the number of turns on the primary side of the converter.

6. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, Determining the air gap length of the primary DC high-voltage self-starting converter includes: The air gap has a marginal effect, and the number of turns in the primary winding N The more 1s there are, the greater the maximum magnetic flux density of the core. B max The smaller the inductance, the lower the total loss, but the larger the required air gap for a given inductance value. This leads to the optimal air gap length under ideal conditions. l g for: When the air gap exhibits marginal effects, the air gap length of the DC high-voltage self-starting converter is: in: Permeability of free space; R c_total and R o_total The equivalent total magnetic reluctance of the transformer's middle and side columns is considered in the x and y directions, respectively. A e This is the effective cross-sectional area of ​​the inductor core; N This refers to the number of inductor turns. L P Represents a resonant inductor; R b Represents the equivalent resistance of the transformer; a This represents the distance between the upper side arm and the side arm of the transformer's center column; b Represents the width of the transformer's side post. h This represents the height of the upper arm of the transformer's central column.

7. The design method of a DC high-voltage self-starting converter according to claim 1, characterized in that, The method for obtaining the maximum magnetic flux density of the magnetic core of the primary DC high-voltage self-starting converter is as follows: in: I Lmax This is the maximum value of the inductor current. N This refers to the number of inductor turns. A eL This is the effective cross-sectional area of ​​the inductor core; L ex This represents the effective inductance value of the inductor core.

8. A design system for a DC high-voltage self-starting converter, characterized in that, include: A transformer module is used to connect the input terminals of the BUCK converter and the LLC converter in series and the output terminals in parallel to form a primary DC high voltage self-starting converter; the electrical parameters of the BUCK converter and LLC converter in the primary DC high voltage self-starting converter are determined respectively to construct the design variable model of the primary DC high voltage self-starting converter; The magnetic circuit simulation module calculates the maximum inductance value of the BUCK converter and the maximum resonant inductance value of the LLC converter based on the maximum inductance value condition in the discontinuous current DCM control requirements of the BUCK converter and the no-load and full-load critical conditions of the input voltage in the full-range zero-voltage switching (ZVS) requirements of the LLC converter. The core shape of the magnetic element of the primary DC-DC high-voltage self-starting converter is determined according to the nearest neighbor propagation algorithm (AP method); and the air gap length of the primary DC-DC high-voltage self-starting converter is determined according to the core shape and the air gap of the primary DC-DC high-voltage self-starting converter including the marginal effect. Based on the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter, the maximum magnetic flux density of the core of the primary DC high voltage self-starting converter under the core shape of the magnetic element of the primary DC high voltage self-starting converter is obtained. Based on the number of primary, secondary, and auxiliary turns of the primary DC high-voltage self-starting converter in the design variable model, and the air gap length of the primary DC high-voltage self-starting transformer, the number of turns of the primary winding of the primary DC high-voltage self-starting converter is obtained; and combined with the design variable model, the total cross-sectional area of ​​the core winding of the primary DC high-voltage self-starting converter is obtained. The optimal maximum magnetic flux density of the primary DC high voltage self-starting converter is determined based on the maximum magnetic flux density of the core, the number of turns in the primary winding, and the total cross-sectional area of ​​the core winding. The parameters of the primary DC high voltage self-starting converter winding are then determined based on the optimal maximum magnetic flux density of the core. The winding simulation module performs the winding of the DC high voltage self-starting converter based on the core shape, air gap length, and wire winding parameters of the primary DC high voltage self-starting converter.

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