A bidirectional asymmetric operating parameter design method for CLLC resonant converter

Abstract

The present invention discloses a method for designing bidirectional asymmetric operation parameters of a CLLC resonant converter. First, a quantitative relationship is established between the forward and reverse circuit factors, and then the forward and reverse circuit factors are unified into an inductance ratio k, a capacitance ratio b, and a quality factor Q; and k, b, Q and a normalized frequency ω are used to represent the bidirectional unified input impedance and voltage gain expressions of the CLLC resonant converter, respectively, to obtain the selection principle and range of k, b, and Q; finally, according to the different bidirectional gain ranges of battery charging and discharging applications, the bidirectional gain curves are linked to design specific values ​​of k, b, and Q, and the resonant parameters of the CLLC resonant converter are calculated. The scheme of the present invention links the bidirectional gain curves to design the CLLC resonant converter parameters, avoids a large number of calculations and repeated iterations in the traditional design process, and reduces the design difficulty of the CLLC resonant converter parameters; it can not only make the bidirectional gain reach a higher range, but also reduce the range of the bidirectional switching frequency.

Description

Technical Field

[0001] The invention belongs to the field of DC / DC converters, relates to a bidirectional CLLC resonant converter, and specifically relates to a bidirectional asymmetric operating parameter design method for a CLLC resonant converter. Background Art

[0002] With the rapid development of energy storage systems and the popularity of electric vehicles, battery charging equipment has gradually become a hot topic in the field of power electronic converter research. Traditional unidirectional battery charging equipment can no longer meet the challenge of feeding energy back to the power grid, and new bidirectional charging equipment is receiving more and more attention. As the core component of bidirectional charging equipment, isolated bidirectional DC-DC converters have the characteristics of electrical isolation, bidirectional transmission, and level conversion.

[0003] In isolated bidirectional DC-DC converters, the CLLC resonant converter uses resonance to achieve soft switching. It not only has the characteristics of high switching frequency, but also has the advantages of full-range soft switching in the forward and reverse directions. It can achieve zero voltage turn-on and zero current turn-off at the same time, with low switching stress, significantly reducing circulating energy and switching losses. The use of frequency modulation control makes it easy to achieve high frequency, high efficiency and high power density. However, in current research, most of the parameter design methods of CLLC resonant converters are to design the forward and reverse voltage gain curves to be the same curve, that is, the LC resonant element on the secondary side is designed to be equal to the primary LC element after being equivalent to the primary side (L r1 =n 2 L r2 , C r1 =C r2 / n 2 ), such as the bidirectional resonant CLLC converter parameter optimization design method disclosed in patent document 202011585866.5. This symmetrical parameter design method is mainly used in DC transformer applications with consistent bidirectional gain and a narrow range, and is not suitable for battery charging equipment with inconsistent bidirectional gain and a wide range.

[0004] For battery charging equipment applications with bidirectional asymmetric operation and a wide gain range, the asymmetric operating parameters of the converter are currently determined mainly through a large number of calculations and repeated forward and reverse iterations. The iterative process not only determines whether the gain curve meets the forward and reverse design requirements, but also determines whether the gain curve decreases monotonically within the operating frequency range. Although this method can obtain the asymmetric operating parameters of the converter, it has a large amount of calculations and requires repeated forward and reverse iterations. It is impossible to design the forward and reverse voltage gains at the same time, it is difficult to achieve a bidirectional wide gain, and it cannot reduce the range of the bidirectional switching frequency. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter. The method has the advantage that the bidirectional gain curve can be linked to design the CLLC resonant converter parameters, thereby avoiding a large amount of calculation and repeated iterations in the traditional design process, and reducing the difficulty of designing the CLLC resonant converter parameters; the method can not only make the bidirectional gain reach a higher range, but also reduce the range of the bidirectional switching frequency.

[0006] Technical solution: The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter of the present invention comprises the following steps:

[0007] (1) Establish corresponding quantitative relationships between the positive and negative circuit factors and express them with unified circuit factors: inductance ratio k, capacitance ratio b, and quality factor Q;

[0008] (2) Based on the forward and reverse fundamental wave equivalent model of the CLLC resonant converter, the bidirectional unified input impedance and voltage gain expressions of the CLLC resonant converter are expressed using k, b, Q and normalized frequency ω;

[0009] (3) Analyze the influence of k, b, and Q on the bidirectional unified input impedance angle and voltage gain of the CLLC resonant converter, and obtain the selection principle and range of k, b, and Q;

[0010] (4) Determine the input voltage V according to design requirements in , Output voltage range V omin ~V omax , forward resonant frequency ω rf , output voltage V at resonant frequency o , power P, transformer primary-to-secondary turns ratio n = V in / V o , forward gain range nV omin / V in ~nV omax / V in , reverse gain range V in / nV omax ~V in / nV omin ;

[0011] (5) Combine the forward and reverse input impedance angles and link the forward and reverse gain curves to design specific values ​​of k, b, and Q that meet the bidirectional gain range and soft switching requirements;

[0012] (6) According to the specific values ​​of k, b, Q, and the forward resonant frequency ω rf , forward equivalent resistance R ef , the resonant parameters of the CLLC resonant converter are calculated.

[0013] In the step (1), the forward and reverse resonant frequencies are set to be the same, and the corresponding relationship between the forward and reverse circuit factors is obtained as follows:

[0014]

[0015] In the formula, k f 、b f , Q f represents the forward circuit factor, where k f Indicates the ratio of the excitation inductance to the primary resonant inductance, b f Indicates the ratio of the resonant capacitance coupled to the primary side to the resonant capacitance of the primary side, Q f Represents the positive quality factor; a f Indicates the ratio of the resonant inductance coupled to the primary side to the resonant inductance of the primary side; k r 、b r , Q r represents the reverse circuit factor, where k r Indicates the ratio of the magnetizing inductance coupled to the secondary side to the secondary side resonant inductance, b r Indicates the ratio of the resonant capacitance coupled to the secondary side to the resonant capacitance of the secondary side, Q r Represents the reverse quality factor; a r It represents the ratio of the resonant inductance coupled to the secondary side to the resonant inductance of the secondary side.

[0016] In step (1), the expressions of the forward and reverse circuit factors are as follows:

[0017]

[0018] In the formula, ω rf Represents the forward resonant frequency; ω s represents the switching frequency; ω represents the normalized frequency; L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; C r1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; R ef Represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; V o represents the forward rated output voltage; P represents the output power; ω rr Represents the reverse resonant frequency; R er Represents the equivalent resistance of the reverse output resistance coupled to the secondary side of the transformer; V in Indicates the forward rated input voltage.

[0019] In the step (2), according to the forward and reverse fundamental wave equivalent model of the CLLC resonant converter, the bidirectional unified input impedance angle and voltage gain expression of the CLLC resonant converter are expressed by k, b, Q, and ω as follows:

[0020]

[0021]

[0022] In the formula, Z inu Indicates the input impedance of the forward and reverse directions; M u Represents the voltage gain of the forward and reverse directions; R e Represents the forward and reverse equivalent resistance.

[0023] In the step (3), the influence of k, b, and Q on the forward and reverse input impedance angles and the voltage gain is as follows: the smaller the k, the larger the gain range obtained, the narrower the frequency adjustment range, and no two peaks will appear, but the soft switching range will become narrower and the efficiency of the converter will be lower. Since the forward and reverse k are positively correlated, k is maximized while ensuring the forward and reverse voltage gain, soft switching range, and single peak value; the smaller the b, the higher the voltage gain, the steeper the gain curve, and the wider the soft switching range, but two peaks will appear; the smaller the Q, the higher the voltage gain, the steeper the gain curve when ω<1, and the gentler the gain curve when ω>1, the wider the soft switching range, and no two peaks will appear.

[0024] In step (3), the selection principles and ranges of k, b, and Q are as follows: the range of Q is 0 to 0.5; the range of b is 0.8 to 1.25. When the maximum forward gain is smaller than the maximum reverse gain, b is greater than 1. At this time, Q r Less than Q f ; The range of k is 3 to 8.

[0025] In the step (5), within the range of k, b, Q, a set of initial values ​​is selected as the specific values ​​of the forward circuit factor, and the specific values ​​of the reverse circuit factor are calculated; the specific values ​​of the forward circuit factor are substituted into M u and Z inu Draw the curve of forward gain, input impedance angle and normalized frequency ω in the figure, and substitute the specific value of the reverse circuit factor into M u and Z inu The curves of reverse gain, input impedance angle and normalized frequency ω are drawn in; when the forward and reverse gain range, soft switching and single peak requirements are met at the same time, a set of specific values ​​of k, b, and Q are obtained.

[0026] In step (6), the formula for the resonance parameter of the CLLC resonant converter is:

[0027]

[0028] Where, L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; C r1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; ω rf Represents the forward resonant frequency; R ef It represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; k represents the inductance ratio in the unified circuit factor; b represents the capacitance ratio in the unified circuit factor; Q represents the quality factor in the unified circuit factor.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: (1) a quantitative relationship is established between the forward and reverse circuit factors of the CLLC resonant converter, unifying the forward and reverse input impedance and voltage gain expressions; (2) the forward and reverse voltage gain curves are linked together for design, avoiding a large amount of calculation and repeated forward and reverse iterations; (3) the bidirectional gain can be brought to a higher range, while reducing the range of the bidirectional switching frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a topological diagram of the CLLC resonant converter of the present invention;

[0031] Figure 2 It is a flow chart of the method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to the present invention;

[0032] Figure 3 is the forward and reverse equivalent circuit model of the CLLC resonant converter of the present invention;

[0033] Figure 4 is the gain M in the present invention u and input impedance angle θ u Relationship diagram with normalized frequency ω and inductance ratio k;

[0034] Figure 5 is the gain M in the present invention u and input impedance angle θ u Relationship diagram with normalized frequency ω and capacitance ratio b;

[0035] Figure 6 is the gain M in the present invention u and input impedance angle θ u Plot of normalized frequency ω and quality factor Q;

[0036] Figure 7This is a relationship curve diagram of the forward and reverse gains and input impedance angles with the normalized frequency ω when k=3.6, b=1.2, and Q=0.375 in the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] The definitions of the parameters in the present invention are as follows: V in —Input voltage; C in —Input side filter capacitor; V o —Output voltage; C o —Output side filter capacitor; I o —output current; i 1 、i 2 —primary and secondary side resonant current; L r1 , L r2 —CLLC resonant converter primary and secondary resonant inductors; L m —CLLC resonant converter transformer excitation inductance; C r1 , C r2 —The primary and secondary resonant capacitors of the CLLC resonant converter; n—The primary and secondary turns ratio of the CLLC resonant converter transformer; V inf —Forward input voltage; V of —Forward output voltage; R ef —Equivalent resistance coupled to the primary side of the transformer; V inr —Reverse input voltage; V or —Reverse output voltage; R er Equivalent resistance reversely coupled to the secondary side of the transformer; k—inductance ratio; b—capacitance ratio; Q—quality factor; ω—normalized frequency; M u —voltage gain; θ u —Input impedance angle.

[0039] like Figure 1 As shown in Figure 1, the circuit of the CLLC resonant converter mainly consists of three parts: the primary full-bridge circuit, the secondary full-bridge circuit and the CLLC resonant cavity. When the converter works in the forward direction, the primary full-bridge S 1 ~S 4 is the main switch (ignoring the synchronous rectification of the secondary full bridge for the time being), S 1 , S 4 Signal synchronization, S 2 , S 3 The signal is synchronized, and the switch tubes in the same bridge arm work symmetrically with a driving signal of 50% (ignoring the dead time) duty cycle. The voltage between points AB is v AB (t) is a high-frequency square wave, the frequency is equal to the switching frequency ω s , the amplitude is equal to the input voltage V in, and then rectified by the resonant cavity and the secondary full-bridge circuit before output. When the converter works in reverse, the secondary full-bridge S 5 ~S 8 is the main switch tube, the voltage between CD and V CD (t) is a high-frequency square wave, the frequency is equal to the switching frequency ω s , the amplitude is equal to the reverse input voltage V o , and then rectified by the resonant cavity and the primary full-bridge circuit.

[0040] like Figure 2 As shown, the bidirectional asymmetric operating parameter design method of the CLLC resonant converter of the present invention specifically includes the following steps:

[0041] Step 1: Establish the corresponding relationship between the forward and reverse circuit factors and express them with unified circuit factors k, b, Q, which specifically include the following:

[0042] Assuming the forward and reverse resonant frequencies are the same, the corresponding relationship between the forward and reverse circuit factors is as follows:

[0043]

[0044] In the formula, k f 、b f , Q f represents the forward circuit factor, where k f Indicates the ratio of the excitation inductance to the primary resonant inductance, b f (a f ) represents the ratio of the resonant capacitance (inductance) coupled to the primary side to the resonant capacitance (inductance) of the primary side, Q f represents the positive quality factor; k r 、b r , Q r represents the reverse circuit factor, where k r Indicates the ratio of the magnetizing inductance coupled to the secondary side to the secondary side resonant inductance, b r (a r ) represents the ratio of the resonant capacitance (inductance) coupled to the secondary side to the resonant capacitance (inductance) of the secondary side, Q r Represents the reverse quality factor; the expressions for the forward and reverse circuit factors are as follows:

[0045]

[0046] In the formula, ω rf Represents the forward resonant frequency; ω s represents the switching frequency; ω represents the normalized frequency; L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; Cr1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; R ef Represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; V o represents the forward rated output voltage; P represents the output power; ω rr Represents the reverse resonant frequency; R er Represents the equivalent resistance of the reverse output resistance coupled to the secondary side of the transformer; V in Indicates the forward rated input voltage;

[0047] Reverse circuit factor (k r , b r , Q r ) can be completely calculated using the forward circuit factor (k f , b f , Q f ) indicates that the forward and reverse circuit factors can be expressed in a unified form using unified circuit factors (inductance ratio k, capacitance ratio b, quality factor Q).

[0048] Step 2: Use k, b, and Q to express the forward and reverse unified input impedance and voltage gain expressions of the CLLC resonant converter, which include the following:

[0049] According to the forward and reverse fundamental wave equivalent model of the CLLC resonant converter, the forward and reverse unified input impedance and gain expressions of the CLLC resonant converter are expressed by k, b, Q, and ω as follows:

[0050]

[0051]

[0052] In the formula, Z inu Indicates the input impedance of the forward and reverse directions; M u Represents the voltage gain of the forward and reverse directions; R e Represents the forward and reverse equivalent resistance.

[0053] Step 3: Analyze the influence of k, b, and Q on the input impedance angle and voltage gain, and obtain the selection principle and range of k, b, and Q, including the following:

[0054] The effects of k, b, and Q on the forward and reverse input impedance and voltage gain are as follows: the smaller k is, the larger the gain range is, the narrower the frequency adjustment range is, and there will be no two peaks, but the soft switching range will become narrower and the efficiency of the converter will be lower. Since the forward and reverse k are positively correlated, k should be as large as possible while ensuring the forward and reverse voltage gain, soft switching range, and single peak value. The smaller b is, the higher the voltage gain is, the steeper the gain curve is, and the soft switching range is wider, but two peaks will appear. Since b is reciprocal in the forward and reverse directions, the smaller b is in one direction, the larger 1 / b is in the other direction. Therefore, both the forward and reverse directions need to be taken into consideration when selecting, and b is closer to 1. The smaller Q is, the higher the voltage gain is, the steeper the gain curve is when ω<1, and the slower the gain curve is when ω>1, the soft switching range is wider, and there will be no two peaks.

[0055] The selection principles and ranges of k, b, and Q are as follows: Compared with the decrease of k and b, the decrease of Q has a more obvious effect on the gain, and has a smaller effect on the input impedance angle. Therefore, first determine the Q range to be 0 to 0.5. Since the forward and reverse b are reciprocal, the forward maximum gain is smaller than the reverse maximum gain, and b should be greater than 1, so that Q r The value will be higher than Q f Smaller, so that the maximum reverse voltage gain is larger, generally b ranges from 0.8 to 1.25. Although the reduction of k also helps to improve the voltage gain, k cannot be too small, and the range of k is 3 to 8.

[0056] Step 4: Determine the converter parameter index, transformer turns ratio, and forward and reverse gain range according to the design requirements;

[0057] According to the design requirements, determine the input voltage V in , Output voltage range V omin ~V omax , resonant frequency ω r , output voltage V at resonant frequency o , power P, transformer primary-to-secondary turns ratio n=V in / V o , forward gain range nV omin / V in ~nV omax / V in , reverse gain range V in / nV omax ~V in / nV omin .

[0058] Step 5, combining the forward and reverse input impedance angles, linking the forward and reverse gain curves to design specific values ​​of k, b, and Q that meet the bidirectional gain range and soft switching requirements, including the following;

[0059] Within the range of k, b, Q, select a set of initial values ​​as the specific values ​​of the forward circuit factor, and calculate the specific values ​​of the reverse circuit factor. Substitute the specific values ​​of the forward circuit factor into M u and Z inu Draw the curve of forward gain, input impedance angle and normalized frequency ω in the figure, and substitute the specific value of the reverse circuit factor into M u and Z inu The reverse gain, input impedance angle and normalized frequency ω are plotted in Figure 1. When the forward and reverse gain range, soft switching and single peak requirements can be met at the same time, a set of specific values ​​of k, b and Q are obtained.

[0060] Step 6: According to the specific values ​​of k, b, Q, and the forward resonant frequency ω rf , forward equivalent resistance R ef , the resonant parameters of the CLLC resonant converter are calculated, including the following:

[0061] The formula for the resonant parameters of the CLLC resonant converter is:

[0062]

[0063] Where, L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; C r1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; ω rf Represents the forward resonant frequency; R ef It represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; k represents the inductance ratio in the unified circuit factor; b represents the capacitance ratio in the unified circuit factor; Q represents the quality factor in the unified circuit factor.

[0064] Figure 3 To invent the forward and reverse equivalent circuit model of CLLC resonant converter. r1 , L r2 is the primary and secondary resonant inductance of the CLLC resonant converter, L m is the CLLC resonant converter transformer excitation inductance, C r1 , C r2 is the primary and secondary resonant capacitors of the CLLC resonant converter, n is the primary and secondary turns ratio of the transformer of the CLLC resonant converter, ±V inf 、±nV of is the positive input and output square wave voltage of the CLLC resonant converter, R efis the equivalent resistance of the forward output resistance coupled to the primary side of the transformer. The forward equivalent circuit model of the CLLC resonant converter can be obtained by coupling the secondary resonant inductor, capacitor, and output resistance of the transformer to the primary side. ±V inr 、±nV or is the reverse input and output square wave voltage of the CLLC resonant converter, R er is the equivalent resistance of the reverse output resistance coupled to the secondary side of the transformer. The reverse equivalent circuit model of the CLLC resonant converter can be obtained by coupling the primary resonant inductance, capacitance, and output resistance of the transformer to the secondary side.

[0065] Figure 4 is the gain M in the present invention u and input impedance angle θ u The relationship diagram of normalized frequency ω and inductance ratio k, where b = 1.2, Q = 0.4 remains unchanged, the range of normalized frequency ω is 0-2, and k is 2, 4, 5, 10, 50 respectively. It can be seen that: the smaller k is, the larger the voltage gain range is, the narrower the frequency adjustment range is under the same output voltage range, and there will be no two peaks. However, the smaller k is, the soft switching range may become narrower, and the efficiency of the converter will be lower. Since the forward and reverse k are positively correlated, k should be as large as possible while ensuring the reverse voltage gain, soft switching range and single peak value.

[0066] Figure 5 The gain M in the present invention u and input impedance angle θ u The relationship diagram between normalized frequency ω and capacitance ratio b, where k = 4, Q = 0.4 remains unchanged, the normalized frequency ω varies from 0 to 2, and b is 0.6, 0.8, 1.2, 3, and 5 respectively. It can be seen that the smaller b is, the higher the voltage gain can be, the steeper the voltage gain curve is, and the wider the soft switching range is. However, the smaller b is, the two peaks will appear, and since b is reciprocal in the forward and reverse directions, the smaller b is in one direction, the larger 1 / b is in the other direction. Therefore, both the forward and reverse directions need to be taken into consideration when selecting, and b close to 1 is better.

[0067] Figure 6 is the gain M in the present invention u and input impedance angle θ uThe relationship between the normalized frequency ω and the quality factor Q, where k = 4, b = 1.2 remains unchanged, the normalized frequency ω varies from 0 to 2, and Q is 0.3, 0.35, 0.375, 0.4, and 0.5 respectively. It can be seen that: the smaller the Q, the higher the voltage gain can be obtained. When ω < 1, the steeper the voltage gain curve is, and when ω > 1, the voltage gain curve is slower. At the same time, it has a wider soft switching range, and there will be no two peaks. However, when the circuit parameters are determined, the larger the load, the larger the Q is. Therefore, when designing the parameters, it is necessary to ensure that the voltage gain range, soft switching range, and single peak requirements are still met under the maximum load.

[0068] Figure 7 The relationship curve between the forward and reverse gain and input impedance angle and the normalized frequency ω of k = 3.6, b = 1.2, Q = 0.375 in the present invention. Taking 3.6, 1.2, 0.375 as a set of specific values ​​of the forward circuit factor, a set of specific values ​​of the reverse circuit factor can be calculated to be 4.3, 0.83, 0.3125. Substituting 3.6, 1.2, 0.375 into M u and Z inu Draw the curve of forward gain, input impedance angle and normalized frequency ω, and substitute 4.3, 0.83, and 0.3125 into M u and Z inu The reverse gain, input impedance angle and normalized frequency ω are plotted in Figure 1. It can be seen that both the forward and reverse directions can achieve a wide gain range, the switching frequency range is relatively small, and both the forward and reverse gain curves have only a single peak. It should be noted that when the forward normalized frequency ω>ω 1 And the reverse normalized frequency ω>ω 2 , both the forward and reverse directions meet the soft switching requirements.

[0069] The method provided by the present invention can design the parameters of the CLLC resonant converter by linking the bidirectional gain curve, avoiding a large amount of calculation and repeated iteration in the traditional design process, and reducing the difficulty of designing the parameters of the CLLC resonant converter. It can not only make the bidirectional gain reach a higher range, but also reduce the range of the bidirectional switching frequency. When combined with efficiency optimization schemes such as high-performance switching devices and synchronous rectification, the CLLC resonant converter can achieve higher efficiency in both bidirectional operation and have lower implementation cost.

Claims

1. A method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter, characterized in that: The following steps are involved: (1) Establish corresponding quantitative relationships between the positive and negative circuit factors and express them with unified circuit factors: inductance ratio k, capacitance ratio b, and quality factor Q; (2) Based on the forward and reverse fundamental wave equivalent model of the CLLC resonant converter, the bidirectional unified input impedance and voltage gain expressions of the CLLC resonant converter are expressed using k, b, Q and normalized frequency ω; (3) Analyze the influence of k, b, and Q on the bidirectional unified input impedance angle and voltage gain of the CLLC resonant converter, and obtain the selection principle and range of k, b, and Q; (4) Determine the input voltage V according to design requirements in , Output voltage range V omin ~V omax , forward resonant frequency ω rf , output voltage V at resonant frequency o , power P, transformer primary-to-secondary turns ratio n = V in / V o , forward gain range nV omin / V in ~nV omax / V in , reverse gain range V in / nV omax ~V in / nV omin ; (5) Combine the forward and reverse input impedance angles and link the forward and reverse gain curves to design specific values ​​of k, b, and Q that meet the bidirectional gain range and soft switching requirements; (6) According to the specific values ​​of k, b, Q, and the forward resonant frequency ω rf , forward equivalent resistance R ef , the resonant parameters of the CLLC resonant converter are calculated; In the step (1), the forward and reverse resonant frequencies are set to be the same, and the corresponding relationship between the forward and reverse circuit factors is obtained as follows: In the formula, k f 、b f , Q f represents the forward circuit factor, where k f Indicates the ratio of the excitation inductance to the primary resonant inductance, b f Indicates the ratio of the resonant capacitance coupled to the primary side to the resonant capacitance of the primary side, Q f Represents the positive quality factor; a f Indicates the ratio of the resonant inductance coupled to the primary side to the resonant inductance of the primary side; k r 、b r , Q r represents the reverse circuit factor, where k r Indicates the ratio of the magnetizing inductance coupled to the secondary side to the secondary side resonant inductance, b r Indicates the ratio of the resonant capacitance coupled to the secondary side to the resonant capacitance of the secondary side, Q r Represents the reverse quality factor; a r It represents the ratio of the resonant inductance coupled to the secondary side to the resonant inductance of the secondary side; In the step (2), according to the forward and reverse fundamental wave equivalent model of the CLLC resonant converter, the bidirectional unified input impedance and voltage gain expression of the CLLC resonant converter are expressed by k, b, Q, and ω as follows: In the formula, Z inu Indicates the input impedance of the forward and reverse directions; M u Represents the voltage gain of the forward and reverse directions; R e Represents the forward and reverse equivalent resistance.

2. The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to claim 1, characterized in that: In step (1), the expressions of the forward and reverse circuit factors are as follows: In the formula, ω rf Represents the forward resonant frequency; ω s represents the switching frequency; ω represents the normalized frequency; L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; C r1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; R ef Represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; V o represents the forward rated output voltage; P represents the output power; ω rr Represents the reverse resonant frequency; R er Represents the equivalent resistance of the reverse output resistance coupled to the secondary side of the transformer; V in Indicates the forward rated input voltage.

3. The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to claim 1, characterized in that: In step (3), the effects of k, b, and Q on the forward and reverse input impedance angles and voltage gain are as follows: The smaller k is, the larger the gain range is, the narrower the frequency adjustment range is, and there will be no two peaks, but the soft switching range will become narrower and the efficiency of the converter will be lower. Since the forward and reverse k are positively correlated, k is maximized while ensuring the forward and reverse voltage gain, soft switching range and single peak value. The smaller b is, the higher the voltage gain is, the steeper the gain curve is, and the soft switching range is wider, but two peaks will appear; The smaller Q is, the higher the voltage gain is. When ω<1, the gain curve is steeper, and when ω>1, the gain curve is gentler, the soft switching range is wider, and there will be no two peaks.

4. The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to claim 3, characterized in that: In step (3), the selection principles and ranges of k, b, and Q are as follows: the range of Q is 0 to 0.5; the range of b is 0.8 to 1.

25. When the maximum forward gain is smaller than the maximum reverse gain, b is greater than 1. At this time, Q r Less than Q f ; The range of k is 3 to 8.

5. The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to claim 1, characterized in that: In the step (5), within the range of k, b, Q, a set of initial values ​​is selected as the specific values ​​of the forward circuit factor, and the specific values ​​of the reverse circuit factor are calculated; the specific values ​​of the forward circuit factor are substituted into M u and Z inu Draw the curve of forward gain, input impedance angle and normalized frequency ω in the figure, and substitute the specific value of the reverse circuit factor into M u and Z inu The curves of reverse gain, input impedance angle and normalized frequency ω are drawn; when the forward and reverse gain range, soft switching and single peak requirements are met at the same time, a set of specific values ​​of k, b, and Q are obtained.

6. The method for designing bidirectional asymmetric operating parameters of a CLLC resonant converter according to claim 1, characterized in that: In step (6), the formula for the resonance parameter of the CLLC resonant converter is: Where, L r1 , L r2 Represents the primary and secondary resonant inductance of the CLLC resonant converter; L m represents the excitation inductance of the CLLC resonant transformer; C r1 , C r2 represents the primary and secondary resonant capacitors of the CLLC resonant converter; n represents the primary and secondary turns ratio of the transformer of the CLLC resonant converter; ω rf Represents the forward resonant frequency; R ef It represents the equivalent resistance of the forward output resistance coupled to the primary side of the transformer; k represents the inductance ratio in the unified circuit factor; b represents the capacitance ratio in the unified circuit factor; Q represents the quality factor in the unified circuit factor.

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