Design method and system of direct-current high-voltage self-starting converter

Abstract

The invention discloses a design method and system for a direct-current high-voltage self-starting converter, and relates to the technical field of power electronic direct-current converters. A BUCK converter in a DCM control mode is matched with an LLC converter in a full-load range ZVS, so that the working efficiency of the whole converter is improved; meanwhile, by designing the magnetic core shape of a magnetic element and determining the air gap length of the converter, the maximum magnetic induction intensity of the magnetic core of the converter under the magnetic core shape, the number of turns of a primary winding and the total sectional area of the magnetic core winding are determined, so that the optimal maximum magnetic induction intensity of the magnetic core is determined, and converter winding parameters are determined according to the optimal maximum magnetic induction intensity of the magnetic core; the converter is wound in combination with the shape of a magnetic core and the air gap length of the converter, the problem that the leakage inductance of the high-isolation transformer is too large is solved, the optimal number of turns of windings is arranged, and the converter completes voltage conversion when high voltage is input.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic DC converters, and in particular to a design method and system for a DC high-voltage self-starting converter. Background Art

[0002] With the rapid development of renewable energy in my country, the total installed capacity in the country has been steadily increasing year by year. The distribution network is mainly composed of 3kv~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 loss and cost advantages. As the medium-voltage distribution network improves voltage and current loss by using power electronic converter units with higher withstand voltage, improves voltage converter stability, and reduces converter control difficulty, it also puts forward higher requirements for the insulation of the converter and the reliable power supply of the control circuit. Therefore, in the current situation of continuous development of the medium-voltage distribution network, reliable power supply to the control part and drive part 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 the medium-voltage distribution network.

[0003] For medium-voltage AC distribution networks, industrial frequency transformers can be used to solve the problem of excessively high withstand voltage of switching devices. However, medium-voltage DC distribution network self-powered devices have rigid requirements for high-voltage power electronic switching devices. To improve efficiency, experimental 10kV SiC switch chips are often used to package them into independent devices in conjunction with flyback or push-pull structures, but the final efficiency is still relatively low, generally between 40% and 60%. The isolated SiC switch devices currently available on the market have a withstand voltage of 3.3kV, and a single independent device cannot complete medium-voltage voltage conversion. In addition, medium-voltage DC distribution network self-powered devices require a higher isolation level, which places higher requirements on high-frequency transformer isolation. The increased isolation of high-frequency transformers will also increase the leakage inductance problem of the transformer, and the high-voltage input of the transformer will increase the number of transformer windings and cause insulation problems.

[0004] Therefore, the technology currently used is limited by efficiency, high isolation and high turns number issues, making it difficult for the designed converter to complete voltage conversion when a high voltage input is used. Summary of the Invention

[0005] The embodiments of the present invention provide 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 when a high voltage input is used due to the limitations of efficiency, high isolation and high number of turns.

[0006] An embodiment of the present 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 to construct a design variable model of the primary DC high-voltage self-starting converter.

[0008] Based on the maximum inductance condition in the discontinuous DCM control requirements of the buck converter inductor current and the critical conditions of input voltage no-load and full-load 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 calculated.

[0009] Determine the core shape of the magnetic component of the primary DC high-voltage self-starting converter according to the proximity propagation algorithm (AP) method; and determine the air gap length of the primary DC high-voltage self-starting converter according to the core shape and the air gap of the primary DC high-voltage self-starting converter including marginal effects;

[0010] According to the maximum value of the inductance of the BUCK converter and the maximum value of the resonant inductance of the LLC converter, the maximum magnetic induction intensity of the magnetic core of the primary DC high-voltage self-starting converter under the magnetic core shape of the magnetic element of the primary DC high-voltage self-starting converter is obtained;

[0011] The number of primary winding turns of the primary DC high-voltage self-starting converter is obtained based on the number of primary turns, secondary turns, 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; and the total cross-sectional area of ​​the magnetic core winding of the primary DC high-voltage self-starting converter is obtained in combination with the design variable model;

[0012] Determine the optimal maximum magnetic induction intensity of the magnetic core according to the maximum magnetic induction intensity of the primary DC high-voltage self-starting converter, the number of turns of the primary winding, and the total cross-sectional area of ​​the magnetic core winding, and determine the winding parameters of the primary DC high-voltage self-starting converter according to the optimal maximum magnetic induction intensity of the magnetic core;

[0013] The DC high-voltage self-starting converter is wound according to the magnetic core shape, air gap length and turn winding parameters of the primary DC high-voltage self-starting converter.

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

[0015] According to the set power requirement of the primary DC high-voltage self-starting converter, the input voltage V of the BUCK converter is determined. in , output voltage V out and power P, and the frequency f of the BUCK converter s ;

[0016] At the same time, the input voltage V of the LLC converter is determined according to the set power requirement of the converter.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 of the primary DC high-voltage self-starting converter includes:

[0018] According to 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 primary turns of the primary DC high-voltage self-starting converter, the secondary turns of the primary DC high-voltage self-starting converter, and the auxiliary turns of the primary DC high-voltage self-starting converter.

[0019] Preferably, the discontinuous DCM control requirements of the BUCK converter inductor current include:

[0020] The maximum value of the inductor L of the BUCK converter is to make the BUCK converter meet the DCM condition of the inductor current. max The following equation should be satisfied. At this time, the inductor current is in a continuous state:

[0021]

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

[0023] Preferably, the requirements for full-range zero voltage switching (ZVS) of the LLC converter include:

[0024] The LLC converter meets the requirements of zero voltage switching (ZVS) in the full load range, including the two critical ZVS conditions of full load at minimum input voltage and no load at maximum input voltage. In actual application, the design index is 0.9 to 0.95 times the smaller of the two quality factors (Q); and the dead time T is also combined with the dead time T. D and ZVS equivalent capacitance C ZVS Design;

[0025] The design process of LLC converter with full load range zero voltage switching ZVS is as follows:

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

[0027]

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

[0029]

[0030] Let the voltage gain at no load be the required maximum voltage gain and find the maximum normalized frequency:

[0031]

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

[0033]

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

[0035]

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

[0037]

[0038] In order to ensure the ZVS state in the entire operating range, the maximum quality factor of the converter must be lower than Q ZVS1 and Q ZVS2 The smallest one among them, and taking a 5% to 10% margin to ensure that the conditions are met, we have:

[0039] Q s =90~95%·min{Q zvs1 ,Q zvs2}

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

[0041] Z o =Q S ·R ac

[0042]

[0043] Where: C r is the LLC resonant capacitance value; L r is the LLC resonant inductance value; L m is the LLC primary excitation inductance; V in Represents the input voltage of the LLC converter; V0 represents the output voltage of the converter; V in_minRepresents the BUCK converter input voltage V in The minimum value of V in_max Represents the BUCK converter input voltage V in The maximum value of f s Represents the frequency of the BUCK converter; f max Represents the maximum frequency V of the BUCK converter out Represents the converter output voltage; P out represents the output power of the converter; n represents the number of primary turns of the converter.

[0044] Preferably, the determining of 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 of the primary winding, the greater the maximum magnetic induction intensity B of the core. max The smaller the inductance, the smaller the total loss. However, the required air gap is also larger under a certain inductance value. At this time, the air gap length l under ideal conditions is g for:

[0046]

[0047] When there is a marginal effect in the air gap, the air gap length of the converter is:

[0048]

[0049] Where: μ0 is the magnetic permeability of vacuum; R c_total and R o_total The equivalent total magnetic resistance of the transformer center column and side column in the x and y directions is considered respectively; A e is the effective cross-sectional area of ​​the inductor core; N is the number of inductor turns; L P Represents the resonant inductor; R b represents the equivalent resistance of the transformer; a represents the distance between the upper side arm and the side arm of the transformer center column; b represents the width of the transformer side column, and h represents the height of the upper side arm of the transformer center column.

[0050] Preferably, the method for obtaining the maximum magnetic induction intensity of the magnetic core of the primary DC high-voltage self-starting converter is:

[0051]

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

[0053] An embodiment of the present invention further 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 a BUCK converter and an LLC converter in series and their output terminals in parallel to form a primary DC high-voltage self-starting converter; and the electrical parameters of the BUCK converter and the LLC converter in the primary DC high-voltage self-starting converter are determined to construct a design variable model of the primary DC high-voltage self-starting converter.

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

[0056] Determine the core shape of the magnetic component of the primary DC high-voltage self-starting converter according to the proximity propagation algorithm (AP) method; and determine the air gap length of the primary DC high-voltage self-starting converter according to the core shape and the air gap of the primary DC high-voltage self-starting converter including marginal effects;

[0057] According to the maximum value of the inductance of the BUCK converter and the maximum value of the resonant inductance of the LLC converter, the maximum magnetic induction intensity of the magnetic core of the primary DC high-voltage self-starting converter under the magnetic core shape of the magnetic element of the primary DC high-voltage self-starting converter is obtained;

[0058] The number of primary winding turns of the primary DC high-voltage self-starting converter is obtained based on the number of primary turns, secondary turns, 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; and the total cross-sectional area of ​​the magnetic core winding of the primary DC high-voltage self-starting converter is obtained in combination with the design variable model;

[0059] Determine the optimal maximum magnetic induction intensity of the magnetic core according to the maximum magnetic induction intensity of the primary DC high-voltage self-starting converter, the number of turns of the primary winding, and the total cross-sectional area of ​​the magnetic core winding, and determine the winding parameters of the primary DC high-voltage self-starting converter according to the optimal maximum magnetic induction intensity of the magnetic core;

[0060] The winding simulation module winds the DC high-voltage self-starting converter according to the core shape, air gap length and turn winding parameters of the primary DC high-voltage self-starting converter.

[0061] The embodiments of the present invention provide a design method and system for a DC high-voltage self-starting converter. Compared with the prior art, the advantageous effects thereof are as follows:

[0062] The present invention connects a BUCK converter and an LLC converter in series input and in parallel output to improve the operating efficiency of the DC high-voltage self-starting converter. At the same time, multiple magnetic circuit calculations and simulations are performed on the DC high-voltage self-starting converter formed by combining the BUCK converter and the LLC converter to obtain the optimal maximum magnetic induction intensity, air gap length, and wire turn winding parameters for the DC high-voltage self-starting converter. These parameters are then used to wind the DC high-voltage self-starting converter, 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 conversion when a high voltage input is applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 A schematic diagram of a design process of a DC high-voltage self-starting converter and a system according to an embodiment of the present invention;

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

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

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

[0067] Figure 5 A schematic diagram of a design method and system for a DC high-voltage self-starting converter provided by an embodiment of the present invention, showing an improved high-isolation transformer magnetic circuit calculation method. DETAILED DESCRIPTION

[0068] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

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

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

[0071] Step 2: Establish a magnetic component design variable model based on circuit constraints according to the two converter parameters.

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

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

[0074] In step 1, 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 ; Investigate the parasitic parameters and total gate charge Qg of the specific MOSFET model to determine the MOSFET model.

[0075] In step 2, it specifically includes:

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

[0077] According to the discontinuous conduction mode (DCM) control requirements of the BUCK converter and the full range zero voltage switch (ZVS) requirements of the LLC converter, the BUCK converter inductor L and the LLC converter resonant inductor L are calculated respectively. r , resonant capacitor C r and the magnetizing inductance L m The value of .

[0078] The discontinuous DCM control of the buck converter's inductor current requires that the inductor current be continuous at full load and minimum input voltage. The full-range zero-voltage switching (ZVS) requirement for the LLC converter includes two critical ZVS conditions: full load at minimum input voltage and no load at maximum input voltage. In practical applications, the smaller quality factor (Q) of 0.9 to 0.95 times is used as the design indicator.

[0079] In step three, specifically include:

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

[0081] According to the relationship between magnetic component loss, inductance value and winding turns, calculate the transformer's primary winding turns N1 and the core's maximum magnetic induction intensity B. max , total winding cross-sectional area A Lw(wire) .

[0082] For magnetic components that require an air gap, the air gap has a marginal effect. Theoretically, the more turns N1 of the primary winding, the greater the maximum magnetic induction intensity B of the core. max The smaller the inductance, the smaller the total loss. However, the required air gap is also larger under a certain inductance value. At this time, the ideal air gap calculation formula loses its meaning and requires more precise theoretical calculation and evaluation. At the same time, Maxwell simulation is performed to determine the air gap size. Inappropriate adjustment of LLC converter C ZVS The value returns to step 2 for calculation.

[0083] According to the above relationship, the number of turns of the primary winding N1 and the maximum magnetic induction intensity of the core B max , perform multiple optimizations on the primary inductance of the transformer to find the maximum magnetic induction intensity B of the core max Minimum air gap to ensure the best insulation distance of magnetic components design.

[0084] In step 4, specifically include:

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

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

[0087] Specifically:

[0088] Step 1: Determine the topology parameters and design variables of the designed DAB converter, where 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 ; Investigate 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 magnetic components; design variables include the buck converter core shape, the LLC converter core shape, the transformer primary turns N1, the transformer secondary turns N2, and the transformer auxiliary turns N3; calculate the buck converter inductor L and the LLC converter resonant inductor L according to the buck converter inductor current discontinuous DCM control requirements and the LLC converter full range ZVS requirements. r , resonant capacitor C r and the magnetizing inductance L m The value of .

[0090] ① Make the BUCK converter meet the DCM condition of inductor current discontinuous, the maximum value of the BUCK converter inductor L max It should be satisfied that the inductor current is just continuous at this time, and its formula is:

[0091]

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

[0093] ② Make the LLC converter meet the requirements of zero voltage switching (ZVS) in the full load range, mainly including the two critical ZVS conditions of full load at minimum input voltage and no load at maximum input voltage. In actual application, the design index is 0.9 to 0.95 times the smaller quality factor Q of the two. It is necessary to combine the dead time T D and ZVS equivalent capacitance C ZVS (usually 2 times the output capacitance of the MOSFET C oss ) for comprehensive consideration; Figure 4 shown.

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

[0095] Calculate the transformer turns ratio using the formula:

[0096]

[0097] Calculate the maximum and minimum gains within the input voltage range using the following formulas:

[0098]

[0099] Let the voltage gain at no load be the required maximum voltage gain, and calculate the maximum normalized frequency. The formula is:

[0100]

[0101] Calculate the equivalent resistance equivalent to the primary side of the transformer. The formula is:

[0102]

[0103] The inductance ratio is calculated under the conditions of maximum input voltage and no-load output. The formula is:

[0104]

[0105] Calculate the maximum quality factor Q of the converter operating in the ZVS region under minimum input voltage and full load conditions ZVS1 , calculate the maximum quality factor Q of the converter working in the ZVS region under the maximum input voltage and no-load conditions ZVS2 , and their formulas are:

[0106]

[0107] To ensure the ZVS state over 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 that the condition is met. The formula is:

[0108] Q s =90~95%·min{Q zvs1 ,Q zvs2}

[0109] Calculate the characteristic impedance and LLC main circuit parameters, the formulas are:

[0110] Z o =Q S ·R ac

[0111]

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

[0113] For the BUCK converter inductor and LLC resonant inductor L r , the maximum magnetic induction intensity of the core B Lmax for:

[0114]

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

[0116] For LLC transformer, the maximum magnetic induction intensity of the core is B Tmax Approximately:

[0117]

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

[0119] The AP method is often used to simplify the evaluation of transformer windings:

[0120] To calculate the apparent power of the LLC transformer, the formula is:

[0121]

[0122] Provisional maximum magnetic induction intensity B of the core Tmax , calculate the AP value of LLC transformer, the formula is:

[0123]

[0124] Among them: K f is the waveform coefficient (4 for square wave); K w is the window effective utilization coefficient (usually 0.2); K J is the current density, taking 4×10 6 A / m 2 .

[0125] Calculate the penetration depth of the primary and secondary sides of the LLC transformer, determine the primary and secondary winding wire diameters and bus cross-sectional area, check whether the winding space is sufficient, and determine the winding plan. The formula is:

[0126]

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

[0128] Calculate the number of turns of the primary and secondary windings. Ideally, the air gap length formula is:

[0129]

[0130] However, there is a marginal effect of air gap. Considering the marginal effect, Figure 5 Determine the transformer air gap length:

[0131]

[0132] Where: μ0 is the magnetic permeability of vacuum; R c_total and R o_total The equivalent total magnetic resistance of the transformer center column and side column in the x and y directions are considered respectively; a represents the distance between the upper side arm and the side arm of the transformer center column; b represents the width of the transformer side column, and h represents the height of the upper side arm of the transformer center column.

[0133] Finally, continue to adjust the air gap length through Maxwell and check whether the transformer air gap length meets the transformer insulation requirements. If not, increase the maximum magnetic induction intensity B of the core. Tmax Repeat the calculation until the requirement is met.

[0134] Step 4: After a series of iterative calculations, the final calculations for a single power unit are: the input voltage of the preceding BUCK is 1000-2400V, the output voltage is 500V, the BUCK operating frequency is 20kHz, the LLC output voltage is 24V, the rated operating frequency is 150kHz, and the maximum output power is 40W. The accuracy and effectiveness of this design method are verified. Substituting the experimental conditions into the design method proposed in this invention, the design parameters of the magnetic component under these experimental conditions are obtained as follows:

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

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

[0137] This is basically consistent with the design requirements of LLC resonant inductance of 120μH and excitation inductance of 384uH. The detection air gap size is 2.2mm, which is larger than the predetermined safety distance of 2mm and meets the 4kV isolation design requirements. It has also been verified that the LLC's ZVS operating mode can be achieved, with high power transmission efficiency. This method can also be quickly adjusted according to the conditions required to meet universality requirements.

[0138] The present invention adopts a front-stage BUCK converter plus a rear-stage LLC converter as a 2kV self-power module, and connects the two self-power modules in series input and output in parallel to form a DC high-voltage self-power converter device; the efficiency is improved to 80% or above by the front-stage BUCK converter plus the rear-stage LLC; the output power of the two power-taking units is adjusted to solve the voltage withstand problem of the device caused by the two units being input in series; the rear-stage LLC converter uses the transformer leakage inductance to resonate, which solves the problem of excessive leakage inductance of the high-isolation transformer, and the front and rear two-stage structure reduces the LLC converter input, making it more convenient to manufacture the transformer.

[0139] The design method of a two-stage cascaded DC high-voltage self-powered converter device provided by the present invention can avoid the use of high-voltage switching devices and reduce the cost of the entire device compared with existing design methods; the use of a BUCK converter in DCM control mode combined with an LLC converter in full-load range ZVS improves the working efficiency of the entire power-taking device while also improving the reliability of the device. Through an improved magnetic circuit calculation method combined with multiple simulation optimizations, the efficiency of the entire transformer is improved while ensuring the insulation capacity of the transformer, reducing the difficulty of manufacturing high-insulation transformers. In addition, the design method is universal and can be expanded to different voltage levels.

[0140] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall 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 ends of the BUCK converter and the LLC converter are connected in series and the output ends 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 a design variable model of the primary DC high-voltage self-starting converter; According to the maximum inductance condition in the discontinuous DCM control requirement of the BUCK converter inductor current and the critical conditions of input voltage no-load and full-load in the full-range zero voltage switching ZVS requirement of the LLC converter, the maximum inductance of the BUCK converter and the maximum resonant inductance of the LLC converter are obtained; Determine the core shape of the magnetic element of the primary DC high-voltage self-starting converter according to the AP algorithm; and determine the air gap length of the primary DC high-voltage self-starting converter according to the core shape and the air gap of the primary DC high-voltage self-starting converter including the marginal effect; According to the maximum value of the inductance of the BUCK converter and the maximum value of the resonant inductance of the LLC converter, the maximum magnetic induction intensity of the magnetic core of the primary DC high-voltage self-starting converter under the magnetic core shape of the magnetic element of the primary DC high-voltage self-starting converter is obtained; According to the primary turns, secondary turns 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 primary winding turns of the primary DC high-voltage self-starting converter are obtained; and in combination with the design variable model, the total cross-sectional area of ​​the magnetic core winding of the primary DC high-voltage self-starting converter is obtained; According to the maximum magnetic induction intensity of the primary DC high-voltage self-starting converter magnetic core, the number of turns of the primary winding and the total cross-sectional area of ​​the magnetic core winding, the optimal maximum magnetic induction intensity of the magnetic core is determined, and the wire turn winding parameters of the primary DC high-voltage self-starting converter are determined according to the optimal maximum magnetic induction intensity of the magnetic core; The DC high voltage self-starting converter is wound according to the magnetic core shape, air gap length and wire turn winding parameters of the primary DC high voltage self-starting converter.

2. The design method of a DC high voltage self-starting converter according to claim 1 is characterized in that: The determination of the electrical parameters of the BUCK converter and the LLC converter includes: According to the set power requirement of the primary DC high-voltage self-starting converter, the input voltage V of the BUCK converter is determined. in , output voltage V out and power P, and the frequency f of the BUCK converter s ; At the same time, the input voltage V of the LLC converter is determined according to the set power requirement of the converter. in , output voltage V out and power P, and the rated frequency f of the LLC converter sn .

3. The design method of a DC high voltage self-starting converter according to claim 1 is characterized in that: The establishment of the design variable model of the primary DC high-voltage self-starting converter includes: According to the electrical parameters of the BUCK converter and the LLC converter, a design variable model is established, which includes the core shape of the BUCK converter, the core shape of the LLC converter, the primary turns of the primary DC high-voltage self-starting converter, the secondary turns of the primary DC high-voltage self-starting converter and the 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 BUCK converter inductor current discontinuous DCM control requirements include: The maximum value of the inductor L of the BUCK converter is to make the BUCK converter meet the discontinuous DCM condition of the inductor current. max The following equation should be satisfied. At this time, the inductor current is in a continuous state: Where: V BULK_max Represents the BUCK converter inductor L max The maximum value of V in_min Represents the BUCK converter input voltage V in The minimum value of f s represents the BUCK converter frequency; V0 represents the output voltage of the converter; I0 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 LLC converter full range zero voltage switching ZVS requirements include: The LLC converter meets the requirements of zero voltage switching (ZVS) in the full load range, including the two critical ZVS conditions of full load at the minimum input voltage and no load at the maximum input voltage. In practical application, the design index is 0.9 to 0.95 times the smaller of the two quality factors (Q); and the dead time T D and ZVS equivalent capacitance C ZVS Conduct design; The design process of LLC converter with full load range zero voltage switching ZVS is as follows: To find the transformer turns ratio, we have: To find the maximum and minimum gain within the input voltage range, we have: Let the voltage gain at no load be the required maximum voltage gain, and find the maximum normalized frequency: To find the equivalent resistance of the transformer primary side, we have: To find the inductance ratio under the condition of maximum input voltage and no-load output, we have: Find the maximum quality factor Q of the converter operating in the ZVS region under minimum input voltage and full load conditions ZVS1 ; Obtain the maximum quality factor Q of the converter operating in the ZVS region under the maximum input voltage and no-load conditions ZVS2 ,have: To ensure ZVS in the entire operating range, the maximum quality factor of the converter must be lower than Q ZVS1 and Q ZVS2 The smallest one among them, and taking a margin of 5% to 10% to ensure that the conditions are met, we have: Q s =90~95%·min{Q zvs1 ,Q zvs2 } Then the characteristic impedance Z0 and LLC main circuit parameters are obtained as follows: Where: C r is the LLC resonant capacitance value; L r is the LLC resonant inductance value; L m is the LLC primary magnetizing inductance; V in represents the input voltage of the LLC converter; V0 represents the output voltage of the converter; V in_min Represents the BUCK converter input voltage V in The minimum value of V in_max Represents the BUCK converter input voltage V in The maximum value of f s represents the frequency of the BUCK converter; f max Represents the maximum frequency V of the BUCK converter out Represents the converter output voltage; P out represents the output power of the converter; n represents the number of primary turns of the converter.

6. The design method of a DC high voltage self-starting converter according to claim 1, characterized in that: The method of determining the air gap length of the primary DC high voltage self-starting converter comprises: The air gap has a marginal effect. The more turns N1 of the primary winding, the greater the maximum magnetic induction intensity B of the core. max The smaller the inductance is, the smaller the total loss is. However, the required air gap is also larger under a certain inductance value. At this time, the air gap length l under ideal conditions is g for: When there is a marginal effect in the air gap, the air gap length of the converter is: Where: μ0 is the vacuum magnetic permeability; R c_total and R o_total The equivalent total magnetic resistance of the transformer center column and side column in the x and y directions is considered respectively; A e is the effective cross-sectional area of ​​the inductor core; N is the number of inductor turns; L P Represents the resonant inductor; R b represents the equivalent resistance of the transformer; a represents the distance between the side arm on the transformer center column; b represents the width of the transformer side column, and h represents the height of the side arm on the transformer center 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 induction intensity of the magnetic core of the primary DC high-voltage self-starting converter is as follows: Where: I Lmax is the maximum value of the inductor current, N is the number of inductor turns, A eL is the effective cross-sectional area of ​​the inductor core; L ex is the effective inductance 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 ends of the BUCK converter and the LLC converter in series and the output ends in parallel to form a primary DC high-voltage self-starting converter; and to determine the electrical parameters of the BUCK converter and the LLC converter in the primary DC high-voltage self-starting converter respectively to construct a design variable model of the primary DC high-voltage self-starting converter; The magnetic circuit simulation module obtains the maximum value of the inductance of the BUCK converter and the maximum value of the resonant inductance of the LLC converter according to the maximum value of the inductance in the discontinuous DCM control requirements of the BUCK converter and the critical conditions of the input voltage no-load and full-load in the full-range zero voltage switching ZVS requirements of the LLC converter; Determine the core shape of the magnetic element of the primary DC high-voltage self-starting converter according to the AP algorithm; and determine the air gap length of the primary DC high-voltage self-starting converter according to the core shape and the air gap of the primary DC high-voltage self-starting converter including the marginal effect; According to the maximum value of the inductance of the BUCK converter and the maximum value of the resonant inductance of the LLC converter, the maximum magnetic induction intensity of the magnetic core of the primary DC high-voltage self-starting converter under the magnetic core shape of the magnetic element of the primary DC high-voltage self-starting converter is obtained; According to the primary turns, secondary turns 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 primary winding turns of the primary DC high-voltage self-starting converter are obtained; and in combination with the design variable model, the total cross-sectional area of ​​the magnetic core winding of the primary DC high-voltage self-starting converter is obtained; According to the maximum magnetic induction intensity of the primary DC high-voltage self-starting converter magnetic core, the number of turns of the primary winding and the total cross-sectional area of ​​the magnetic core winding, the optimal maximum magnetic induction intensity of the magnetic core is determined, and the wire turn winding parameters of the primary DC high-voltage self-starting converter are determined according to the optimal maximum magnetic induction intensity of the magnetic core; The winding simulation module winds the DC high-voltage self-starting converter according to the magnetic core shape, air gap length and turn winding parameters of the primary DC high-voltage self-starting converter.

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