A converter with interleaved parallel integrated Buck-Boost LLC circuit topology

Abstract

The invention discloses a converter with staggered parallel integrated Buck-Boost LLC circuit topology, belonging to the field of DC power electronic conversion, wherein the primary circuit includes two-stage staggered parallel Buck-Boost circuits and LLC resonant circuits; each stage of Buck-Boost circuit includes four switch tubes and choke inductors, the first two switch tubes constitute Buck bridge arms, the latter two switch tubes constitute Boost bridge arms, and the choke inductors are connected between the midpoints of the Buck bridge arms and the midpoints of the Boost bridge arms; in each stage of Buck-Boost circuit, the phase shift angle between the Boost bridge arms and the Buck bridge arms is the minimum phase shift angle when each switch tube is soft-switched, and under the minimum phase shift angle, the converter loss is a single-valued function related to the inductance value of the choke inductor, and the inductance value of the choke inductor is the inductance value when the converter loss is the smallest. Two-stage phase shift 180-degree staggered parallel connection solves the problem of secondary current asymmetry, realizes secondary synchronous rectification, and designs the phase shift angle and choke inductance values ​​to realize soft switching and minimum loss at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of direct current power electronic conversion, and more specifically, relates to a converter with staggered parallel integrated Buck-Boost LLC circuit topology. Background Art

[0002] In order to achieve the goal of energy saving and consumption reduction, and to conform to the development trend of miniaturization and lightweight, efficiency and power density have always been the core requirements and important indicators of power electronic converters. Reducing power loss and increasing switching frequency are the key to achieving high efficiency and high power density. Soft switching technology is an effective way to reduce high switching losses at high frequencies. LLC resonant converter can achieve zero voltage switching (Zero Voltage Switch, ZVS) of the primary switch and zero current switching (Zero Current Switch, ZCS) of the secondary switch in a wide voltage range and a wide load range. It is a good candidate topology for high efficiency and high power density isolated DC-DC applications. In order to achieve high efficiency and high power density under adjustable conditions, a two-stage circuit of the LLC circuit with a PWM regulator cascaded to work at a fixed frequency is proposed. However, due to the increase in the number of power transmission stages, the efficiency is inevitably reduced, so an integrated two-stage solution is proposed.

[0003] The choke inductor current in the integrated Buck-Boost LLC converter can reduce the current stress of the LLC primary switch. At the same time, this current can help achieve ZVS instead of relying on the excitation current of the transformer. Therefore, the air gap of the high-frequency transformer can be eliminated, thereby reducing eddy current losses. Although the integrated Buck-Boost LLC converter has the advantages mentioned above, due to the integration of the two-stage topology, the choke inductor current will make the ZVS of the upper and lower tubes of the bridge arm asymmetric, resulting in asymmetric input voltage of the resonant cavity, and then distort the resonant current and the secondary winding current, which will make the dead time and effective current of the two secondary switches different. These differences bring great difficulties to synchronous rectification. At the same time, the choke inductance in the converter will have a significant impact on the converter efficiency. By analyzing the loss of the converter under different working conditions, the choke inductance value can be reasonably selected to achieve the optimal design of the loss. Summary of the invention

[0004] In view of the defects of the prior art and the need for improvement, the present invention provides a converter with an interleaved parallel integrated Buck-Boost LLC circuit topology, the purpose of which is to apply the interleaved parallel technology to the Buck-Boost LLC circuit topology to solve the problem of secondary side current asymmetry, thereby conveniently realizing secondary side synchronous rectification, and at the same time designing the phase shift angle and choke inductance, while ensuring soft switching of all switch tubes and minimum loss.

[0005] To achieve the above object, the present invention provides a staggered parallel integrated Buck-Boost A converter with LLC circuit topology comprises a transformer and a primary circuit and a secondary circuit connected at both sides of the transformer, wherein the secondary circuit is a push-pull synchronous rectification circuit; the primary circuit comprises two-stage staggered parallel Buck-Boost circuits and an LLC resonant circuit; each stage of the Buck-Boost circuit comprises four switch tubes and a choke inductor, wherein the first two switch tubes are located between the positive and negative poles of a DC bus and constitute a Buck bridge arm, and the last two switch tubes are located between an intermediate bus and a negative pole of the DC bus and constitute a Boost bridge arm, and the choke inductor is connected between a midpoint of the Buck bridge arm and a midpoint of the Boost bridge arm; the two ends of the LLC resonant circuit are respectively connected to the midpoints of the two Boost bridge arms; in each stage of the Buck-Boost circuit, the phase shift angle between the Boost bridge arm and the Buck bridge arm is the minimum phase shift angle when each switch tube is soft-switched, and at the minimum phase shift angle, the converter loss is a single-valued function related to the inductance value of the choke inductor, and the inductance value of the choke inductor is the inductance value when the converter loss is minimum.

[0006] Furthermore, the minimum phase shift angle is:

[0007] e min =max{e 1min ,e 2min ,e 3min ,e 4min}

[0008]

[0009]

[0010]

[0011]

[0012] Among them, e min is the minimum phase shift angle, e 1min 、e 2min 、e 3min 、e 4min are the minimum phase shift angles for soft switching of the upper switch tube of the Buck bridge arm, the lower switch tube of the Buck bridge arm, the upper switch tube of the Boost bridge arm, and the lower switch tube of the Boost bridge arm, respectively; D is the duty cycle of the upper switch tube of the Buck bridge arm, and f s is the switching frequency, L I is the inductance value of the choke coil, P in is the input power of the converter, V in is the input voltage of the converter, C o(TR)12is the time-dependent equivalent junction capacitance of the upper and lower switches in the Buck bridge arm, I ZVSmin For the switch tube S I-3 And switch tube S I-4 Minimum current to achieve ZVS.

[0013] Furthermore, it also includes: a control unit, which is used to control the on and off of each switch tube, so that in each level of Buck-Boost circuit, the two switch tubes of the Buck bridge arm are complementary turned on and the duty cycle is adjustable, the two switch tubes of the Boost bridge arm are complementary turned on and the duty cycle is fixed at 0.5, the phase shift angle between the Boost bridge arm and the Buck bridge arm is the minimum phase shift angle, and the conduction phase difference between the corresponding switch tubes in the two-stage Buck-Boost circuit is 180°, so that in a stable operating state, the resonant tank voltage input into the LLC resonant circuit is a symmetrical voltage.

[0014] Furthermore, in the buck mode, the control unit is used to control the duty cycle D of the upper switch tube in the Buck bridge arm to be less than 0.5, so that the Buck-Boost circuit operates in the Buck mode.

[0015] Furthermore, in buck mode, 0<e min <D,e min is the minimum phase shift angle.

[0016] Furthermore, in the boost mode, the control unit is used to control the duty cycle D of the upper switch tube in the Buck bridge arm to be greater than 0.5, so that the Buck-Boost circuit operates in the Boost mode.

[0017] Furthermore, in boost mode, D-0.5<e min <0.5, e min is the minimum phase shift angle.

[0018] Furthermore, the push-pull synchronous rectification circuit includes a switch tube S5, a switch tube S6 and an output filter capacitor C o ; The switch tube S5 and the switch tube S6 are connected to the common ground and are respectively located in the two winding branches of the secondary winding of the transformer to form a push-pull rectifier; the output filter capacitor C o connected in parallel to the output port of the push-pull rectifier.

[0019] In general, the above technical scheme conceived by the present invention can achieve the following beneficial effects: a two-stage staggered parallel Buck-Boost circuit is designed on the primary side of the transformer, and the two ends of the LLC resonant circuit are respectively connected to the output nodes of the two-stage staggered parallel Buck-Boost circuit. In the stable operation state, although the voltages of the output nodes of each stage of the Buck-Boost circuit are still asymmetric, due to the staggered parallel structure of the two, the voltage acting on the subsequent resonant tank is the difference between the output voltages of the two, and the difference is naturally symmetrical, thereby making the input voltage of the resonant tank symmetrical, so the resonant current and the secondary current can also be symmetrical, thereby realizing synchronous rectification; in addition, the converter loss increases with the increase of the phase shift angle, and is related to the choke inductance. After finding the minimum phase shift angle according to the soft switching condition, the loss under the minimum phase shift angle is a single-valued function of the choke inductance, and the optimal choke inductance value can be selected to achieve minimum loss, while realizing soft switching and minimum loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A circuit structure diagram of a converter with staggered parallel integrated Buck-Boost LLC circuit topology provided in an embodiment of the present invention;

[0021] Figure 2 A voltage waveform diagram of relevant nodes of a corresponding topology provided by an embodiment of the present invention;

[0022] Figure 3 A relevant waveform diagram of a corresponding topology provided in an embodiment of the present invention in a buck working mode;

[0023] Figure 4 A relevant waveform diagram of a corresponding topology in a boost working mode provided by an embodiment of the present invention;

[0024] Figure 5A The switch tube S in the corresponding topology provided in the embodiment of the present invention I-1 Soft switching process waveform;

[0025] Figure 5B The switch tube S in the corresponding topology provided in the embodiment of the present invention I-2 Soft switching process waveform;

[0026] Figure 6 A graph showing the trend of the total loss of the corresponding topology provided in the embodiment of the present invention as the converter operating conditions and the choke inductance value change. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0029] Figure 1 The circuit structure diagram of the converter with staggered parallel integrated Buck-Boost LLC circuit topology provided by the embodiment of the present invention. Figure 1 , combined with Figure 2-Figure 6 , the converter of the staggered parallel integrated Buck-Boost LLC circuit topology in this embodiment is described in detail.

[0030] See also Figure 1 The converter of the interleaved parallel integrated Buck-Boost LLC circuit topology includes a transformer T and a primary circuit and a secondary circuit connected on both sides of the transformer T. The transformer T is, for example, a high-frequency transformer. The secondary circuit is a push-pull synchronous rectification circuit. The primary circuit includes two-stage interleaved parallel Buck-Boost circuits and an LLC resonant circuit. The LLC resonant circuit is located at the output side of the two-stage interleaved parallel Buck-Boost circuit.

[0031] For each level of Buck-Boost circuit, it includes four switches and choke inductors, two of which form the Buck bridge arm and are located between the positive and negative poles of the DC bus, and the other two form the Boost bridge arm and are located between the intermediate bus and the negative pole of the DC bus. The choke inductor is connected between the midpoint of the Buck bridge arm and the midpoint of the Boost bridge arm. I Connect one end of the LLC resonant circuit to the midpoint B of the Boost bridge arm in the other Buck-Boost circuit. II Connect the other end of the LLC resonant circuit. Therefore, the resonant tank voltage input to the LLC resonant circuit is B I Point voltage V BI With B II Point voltage V BII The difference between the two Buck-Boost circuits is that V BI -V BIIIt is a symmetrical voltage, so the resonant current and the secondary current can also be symmetrical, thus achieving synchronous rectification.

[0032] In each stage of the Buck-Boost circuit, the phase shift angle between the Boost bridge arm and the Buck bridge arm is the minimum phase shift angle that allows each switch tube to soft switch. At the minimum phase shift angle, the converter loss is a single-valued function related to the inductance value of the choke inductor. The inductance value of the choke inductor is the inductance value that minimizes the converter loss. In this way, soft switching and minimum loss are achieved at the same time.

[0033] See also Figure 1 The two-stage interleaved parallel Buck-Boost circuit includes the switch tube S I-1 -S I-4 , S II-1 -S II-4 , input capacitor C i , choke inductance L I -L II , bus capacitance C M ; LLC resonant circuit includes resonant capacitor C r , resonant inductor L r and the magnetizing inductance L m (There is no air gap transformer L in the figure m The push-pull synchronous rectification circuit includes switch tubes S5-S6 and output filter capacitor C o .

[0034] In each switch tube on the primary side, S I-1 and S I-2 Connect to form a half bridge, S II-1 and S II-2 Connect to form a half bridge, S I-3 and S I-4 Connect to form a half bridge, S II-3 and S II-4 Connect to form a half bridge. I-1 and S I-2 The midpoint of the half bridge is connected through the choke inductor L I Connect S I-3 and S I-4 The midpoint of the half bridge forms a first-stage Buck-Boost circuit; S II-1 and S II-2 The midpoint of the half bridge is connected through the choke inductor L II Connect S II-3 and S II-4 The midpoint of the half-bridge forms another Buck-Boost circuit. I and the choke inductance L II The inductance value is the same. Input capacitor C iConnected in parallel at the input end of the two-stage staggered parallel Buck-Boost circuit; bus capacitor C M Connected in parallel between the output bus and ground of the two-stage staggered parallel Buck-Boost circuit. I-3 and S I-4 The midpoint B of the half bridge I , S II-3 and S II-4 The midpoint B of the half bridge II As the input port of the resonant tank, the resonant capacitor C is connected in series r , resonant inductor L r and gapless transformer T, and switch tube S I-3 -S II-4 Together they form a full-bridge LLC circuit. In the two-stage interleaved parallel Buck-Boost circuit, the rear bridge arm of the front-stage Buck-Boost circuit is reused by the rear-stage LLC circuit, and each phase of the two-phase interleaved circuit is reused separately, and a total of 4 semiconductor switch tubes are reused.

[0035] On the secondary side, the switch tube S5 and the switch tube S6 are connected to the common ground and are respectively located in the two winding branches of the secondary winding of the transformer T to form a push-pull rectifier; the output filter capacitor C o Connected in parallel at the output port of the push-pull rectifier.

[0036] According to an embodiment of the present invention, the converter of the staggered parallel integrated Buck-Boost LLC circuit topology further includes a control unit, which is not shown in the figure, and is used to drive and control each switch tube in the converter. Specifically, the control unit is used to control the two switch tubes in one bridge arm of the primary Buck-Boost circuit to be complementary turned on (i.e., control S I-1 and S I-2 The duty ratio of the two switches in the other arm is 0.5 and they are complementary (i.e., control S I-3 and S I-4 Complementary conduction and both duty ratios are 0.5, and the frequency is fixed, the rear full-bridge LLC operates as a DC transformer); the phase difference between the two bridge arms is the phase shift angle e (that is, the control S I-3 and S I-4 The bridge arm and S I-1 and S2 form a bridge arm phase difference of phase shift angle e); and control the conduction phase difference between each switch tube in the bridge arm of the other Buck-Boost circuit and the corresponding switch tube in the bridge arm of the first Buck-Boost circuit by 180° (i.e. control S II-1 , S II-2 , S II-3 , S II-4 Respectively with respect to S I-1 , S I-2 , SI-3 , S I-4 Delay 180°), so that in the stable operation state, the resonant tank voltage input to the LLC resonant circuit is a symmetrical voltage.

[0037] According to an embodiment of the present invention, in the buck mode, the control unit is used to control the switch tube (i.e., the switch tube S) connected to the positive electrode of the DC bus in one bridge arm of the first-stage Buck-Boost circuit. I-1 ) has a duty cycle D less than 0.5, so that the primary Buck-Boost circuit operates in Buck mode. The lower the voltage requirement, the smaller the duty cycle D. Preferably, in buck mode, the control unit is also used to control the minimum phase shift angle e min Satisfying 0<e min <D to achieve ZVS and reduce the current ripple on the choke inductance.

[0038] According to an embodiment of the present invention, in the boost mode, the control unit is used to control the switch tube (i.e., the switch tube S) connected to the positive electrode of the DC bus in one bridge arm of the first-stage Buck-Boost circuit. I-1 ) has a duty cycle D greater than 0.5, so that the primary Buck-Boost circuit operates in the Boost mode. The higher the voltage demand, the greater the duty cycle D. Preferably, in the boost mode, the control unit is also used to control the minimum phase shift angle e min Satisfy D-0.5<e min <0.5 to achieve ZVS and reduce the current ripple on the choke inductor.

[0039] After stable operation, B I Point voltage V BI Still asymmetric, B II Point voltage V BII It is also not symmetrical, but due to the existence of the staggered parallel structure, the voltage acting on the subsequent resonant tank is the difference between the two point voltages V BI -V BII , while V BI -V BII In the case of 180° staggered parallel connection, it is naturally symmetrical, and its waveform is as follows Figure 2 As shown, therefore, synchronous rectification can be achieved.

[0040] In the embodiment of the present invention, the minimum phase shift angle between the Boost bridge arm and the Buck bridge arm is determined based on the realization of soft switching, and then the inductance value of the choke inductor is designed with the minimum loss as the goal. for:

[0041]

[0042] Where I1 is the initial value of the choke inductor current (the switch tube SI-1 The current of the choke inductor before conduction), such as Figure 3 and Figure 4 As shown, V in is the input voltage of the converter, V M is the intermediate bus voltage (capacitor C M voltage on the surface), t is the time, L I is the inductance of the choke coil, e is the phase shift angle between the Boost bridge arm and the Buck bridge arm, T s is the switching period, and D is the duty cycle of the switch tube on the Buck bridge arm.

[0043] Combined with the power relationship, the key current values ​​can be obtained:

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] Among them, P in is the input power of the converter, f s is the switching frequency, I2 is the switch tube S I-2 The current of the choke coil inductor before conduction, I3 is the current of the switch tube S I-3 The current of the choke coil inductor before conduction, I4 is the current of the switch tube S I-4 Current in the choke inductor before conduction.

[0050] According to the conditions for achieving soft switching of each switch tube, the minimum value of the initial current of each dead zone can be obtained:

[0051]

[0052]

[0053]

[0054] Among them, C o(TR)12 The upper switch tube in the Buck bridge arm (S I-1 ) and the lower switch tube (S I-2 )’s time-dependent equivalent junction capacitance, C o(TR)34 The upper switch tube (S I-3 ) and the lower switch tube (S I-4 )’s time-dependent equivalent junction capacitance, C o(TR)56is the time-dependent equivalent junction capacitance of the switch tubes S5 and S6 in the push-pull synchronous rectification circuit. The time-dependent equivalent junction capacitance of each switch tube can be found in the switch tube data sheet, t d The upper switch tube in the Buck bridge arm (S I-1 ) and the lower switch tube (S I-2 ) driving dead time, n is the transformer ratio. I-1 , S I-2 The relevant waveforms of the soft switching process are as follows: Figure 5A and Figure 5B shown.

[0055] Combined with the previous expression of the choke inductor current, we can get the conditions that the phase shift angle needs to meet:

[0056]

[0057]

[0058]

[0059]

[0060] Among them, I ZVSmin For the switch tube S I-3 And switch tube S I-4 The minimum current to achieve ZVS. I-1 ~S I-4 For soft switching, the phase shift angle needs to satisfy:

[0061] e min =max{e 1min ,e 2min ,e 3min ,e 4min}

[0062] After determining the phase shift angle, the converter loss is calculated. The conduction loss is:

[0063]

[0064]

[0065]

[0066] Among them, I SI-1 is the current flowing through the switch tube S I-1 The effective value of the current, I SI-2 is the current flowing through the switch tube S I-2 The effective value of the current, I SI-3 is the current flowing through the switch tube S I-3 The effective value of the current, I SI-4is the current flowing through the switch tube S I-4 The effective value of the current, P con is the conduction loss of the switch tube, R ds(on)1 For S I-1 and S I-2 The on-resistance, R ds(on)2 For S I-3 and S I-4 The on-resistance.

[0067] The switching loss is:

[0068]

[0069]

[0070] P sw =2[P sw-buck (V in ,|I1|)+P sw-buck (V in ,|I2|)+P sw-boost (|I3|)+P sw-boost (|I4|)]

[0071] Among them, k1, k2, k3, k4, k5, k6, l1, l2, l3 are the coefficients k, α and β obtained by fitting, P sw-buck is the switching loss of the Buck bridge arm, I off is the switch off current, P sw-boost is the switching loss of the Boost bridge arm, P sw is the total switching loss.

[0072] The choke inductor core loss is:

[0073]

[0074]

[0075]

[0076] Among them, P cu is the copper loss of the choke inductor, I L is the effective value of the current flowing through the choke inductor, R L is the equivalent DC resistance of the choke inductor, P fe is the iron loss of the choke inductor, V e is the volume of the choke inductor core, B is the peak magnetic induction intensity in the choke inductor core, ΔB is the peak-to-peak value of the magnetic induction intensity in the choke inductor core, α, β, k i are the material parameters of the choke inductor core (given in the data sheet).

[0077] Combining the above loss calculations, we can get the total loss calculation. Under a specific input voltage and power, the total loss is a function of the minimum phase shift angle and the choke inductance. The expressions of the minimum phase shift angle and the choke inductance were calculated above, so the total loss P loss It can be transformed into a single-valued function of the choke inductance:

[0078]

[0079] in, is the total loss with respect to the phase shift angle e and the choke inductance L I The function of is the total loss with respect to the choke inductance L I function (where the phase shift angle e is written as the value of the choke inductance L I Function form), g(L I ) is the phase shift angle e with respect to the choke inductance L I The function of is the total loss with respect to the choke inductance L I It is difficult to express these functions in concise expressions. In practice, they are applied to the design of examples by combining numerical calculation methods.

[0080] Figure 6 This is the result of a calculation example. The input power range of the example is 120W~600W, the input voltage range is 350V~430V, and the output voltage is 24V. The vertical change of the small rectangle in the figure represents the change in loss when the input voltage changes. If you want the converter to have higher efficiency under heavy load and full load, and the equipment will not be damaged by overheating under light load conditions (light load operation time is short or heat dissipation conditions are sufficient), then the choke inductance can be 17uH (serial number ①). If the converter is required to operate stably within the entire load range, the designed choke inductance should ensure that the loss is roughly the same under the two extreme load conditions, and a medium inductance of 23uH (serial number ②) can be selected.

[0081] The converter with staggered parallel integrated Buck-Boost LLC circuit topology in this embodiment can solve the problem of asymmetric resonant current in the existing topology without using a larger quality factor, especially it is still effective under light load, and through the design of the phase shift angle and the inductance value of the choke, the total loss of the main components of the entire circuit is optimized under the premise of ensuring that the switching tubes can achieve soft switching, thereby achieving high efficiency and high power density.

[0082] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A converter with staggered parallel integrated Buck-Boost LLC circuit topology, characterized in that: It includes a transformer and a primary circuit and a secondary circuit connected to both sides of the transformer, wherein the secondary circuit is a push-pull synchronous rectification circuit; The primary circuit includes two stages of staggered parallel Buck-Boost circuits and an LLC resonant circuit; each stage of the Buck-Boost circuit includes four switch tubes and a choke inductor, the first two switch tubes are located between the positive and negative poles of the DC bus and form a Buck bridge arm, the last two switch tubes are located between the intermediate bus and the negative pole of the DC bus and form a Boost bridge arm, and the choke inductor is connected between the midpoint of the Buck bridge arm and the midpoint of the Boost bridge arm; the two ends of the LLC resonant circuit are respectively connected to the midpoints of the two Boost bridge arms; In each Buck-Boost circuit, the phase shift angle between the Boost bridge arm and the Buck bridge arm is the minimum phase shift angle when each switch tube is soft switched. The minimum phase shift angle is: and min =max{and 1min ,and 2min ,and 3min ,and 4min } Among them, e min is the minimum phase shift angle, e 1min 、e 2min 、e 3min 、e 4min are the minimum phase shift angles for soft switching of the upper switch tube of the Buck bridge arm, the lower switch tube of the Buck bridge arm, the upper switch tube of the Boost bridge arm, and the lower switch tube of the Boost bridge arm, respectively; D is the duty cycle of the upper switch tube of the Buck bridge arm, and f s is the switching frequency, L I is the inductance value of the choke coil, P in is the input power of the converter, V in is the input voltage of the converter, C o(TR)12 is the time-dependent equivalent junction capacitance of the upper and lower switches in the Buck bridge arm, I ZVSmin For the switch tube S I-3 And switch tube S I-4 Minimum current to achieve ZVS; At the minimum phase shift angle, the converter loss is a single-valued function related to the inductance value of the choke inductor, and the inductance value of the choke inductor is the inductance value that minimizes the converter loss.

2. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology according to claim 1, characterized in that: Also includes: A control unit is used to control the on and off of each switch tube, so that in each level of Buck-Boost circuit, the two switch tubes of the Buck bridge arm are complementary turned on and the duty cycle is adjustable, the two switch tubes of the Boost bridge arm are complementary turned on and the duty cycle is fixed to 0.5, the phase shift angle between the Boost bridge arm and the Buck bridge arm is the minimum phase shift angle, and the conduction phase difference between the corresponding switch tubes in the two-stage Buck-Boost circuit is 180°, so that in a stable operating state, the resonant tank voltage input to the LLC resonant circuit is a symmetrical voltage.

3. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology as claimed in claim 2, characterized in that: In the buck mode, the control unit is used to control the duty cycle D of the upper switch tube in the Buck bridge arm to be less than 0.5, so that the Buck-Boost circuit works in the Buck mode.

4. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology as claimed in claim 3, characterized in that: In buck mode, 0<e min <D,e min is the minimum phase shift angle.

5. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology as claimed in claim 2, characterized in that: In the boost mode, the control unit is used to control the duty cycle D of the upper switch tube in the Buck bridge arm to be greater than 0.5, so that the Buck-Boost circuit works in the Boost mode.

6. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology as claimed in claim 5, characterized in that: In boost mode, D-0.5<e min <0.5, e min is the minimum phase shift angle.

7. The converter of interleaved parallel integrated Buck-Boost LLC circuit topology according to claim 1, characterized in that: The push-pull synchronous rectification circuit includes a switch tube S5, a switch tube S6 and an output filter capacitor C o ; The switch tube S5 and the switch tube S6 are connected to the common ground and are respectively located in the two winding branches of the secondary winding of the transformer to form a push-pull rectifier; the output filter capacitor C o connected in parallel to the output port of the push-pull rectifier.

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