Two-stage converter and control method thereof

Abstract

The invention relates to the technical field of power electronic conversion, and provides a two-stage converter and a control method thereof.The two-stage converter comprises an LLC circuit and a Buck circuit; the LLC circuit comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, an external leakage inductor, an excitation inductor, a blocking capacitor, a multiplexing capacitor, a transformer, an output capacitor and a load, and the drain electrode of the first switch tube is connected with the second end of the first inductor and the first end of the multiplexing capacitor of the Buck circuit; the source electrode of the first switch tube is connected with the drain electrode of the second switch tube and the first end of the blocking capacitor. The source electrode of the second switch tube is connected with the second end of the multiplexing capacitor, the second end of the second capacitor, the second end of the switch tube bridge arm of the Buck circuit, the second end of the input capacitor and the negative electrode of the power supply. According to the two-stage converter, the electric energy conversion efficiency can be improved while electric isolation is realized.

Description

Technical Field

[0001] The present application relates to the technical field of power electronic conversion, and in particular to a two-stage converter and a control method thereof. Background Art

[0002] In recent years, with the development of new energy industry, power electronic converters have encountered higher challenges. More and more researchers have carried out a lot of research to pursue high power, high conversion efficiency and high power density of converters. As an important link in power conversion, DC converters have also become the focus of research.

[0003] In order to improve the power conversion efficiency and voltage regulation capability of the converter, the following solutions have been proposed:

[0004] Solution 1: Researchers combined the buck circuit (Buck) with the dual active half-bridge circuit (DAHB) in cascade. The converter works under the working condition of matching the primary and secondary voltages of the transformer to achieve electrical isolation (referring to the way to prevent the current from flowing directly from one area to another in the circuit, that is, not establishing a direct current flow path between the two areas. Although the current cannot flow directly, energy or information can still be transmitted through other means, such as electromagnetic induction or electromagnetic waves, or by optical, acoustic or mechanical means) and high-efficiency power conversion, and uses the Buck circuit for voltage regulation. This solution is a two-stage topology structure, which has the advantages of simple structure and flexible control. However, the two-stage structure leads to low power conversion efficiency and increases the number of switching tubes.

[0005] Solution 2: The researchers connected the DAHB circuit and the Buck circuit in series input and parallel output. The DAHB circuit worked under voltage matching conditions, and the Buck circuit adjusted the duty cycle to regulate the voltage. This solution has improved efficiency compared to the two-stage solution, but its topology does not have the function of electrical isolation.

[0006] This shows that the current converter has the problem of not being able to balance electrical isolation and power conversion efficiency. Summary of the invention

[0007] The present application provides a two-stage converter and a control method thereof, which can solve the problem that electrical isolation and power conversion efficiency cannot be taken into account at the same time.

[0008] In a first aspect, an embodiment of the present application provides a two-stage converter, including an LLC circuit and a Buck circuit consisting of a switch tube bridge arm, a reused capacitor and a first inductor, wherein the LLC circuit includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, an external leakage inductor, an excitation inductor, a DC blocking capacitor, a reused capacitor, a transformer, an output capacitor, and a load;

[0009] Among them, the drain of the first switch tube is respectively connected to the second end of the first inductor of the Buck circuit and the first end of the reused capacitor, the source of the first switch tube is respectively connected to the drain of the second switch tube and the first end of the DC blocking capacitor, the source of the second switch tube is respectively connected to the second end of the reused capacitor, the second end of the second capacitor, the second end of the switch tube bridge arm of the Buck circuit, the second end of the input capacitor, and the negative electrode of the power supply, the first end of the first capacitor is respectively connected to the positive electrode of the power supply, the first end of the input capacitor, and the first end of the switch tube bridge arm of the Buck circuit, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the opposite end of the primary winding of the converter, and the excitation The second end of the inductor is connected, the second end of the DC blocking capacitor is connected to the first end of the external leakage inductor, the second end of the external leakage inductor is respectively connected to the same-name end of the primary winding of the converter and the first end of the excitation inductor, the source of the third switching tube is respectively connected to the same-name end of the secondary winding of the transformer and the drain of the fourth switching tube, the drain of the third switching tube is respectively connected to the first end of the third capacitor, the first end of the input capacitor, and the first end of the load, the source of the fourth switching tube is respectively connected to the second end of the fourth capacitor, the second end of the output capacitor, and the second end of the load, and the second end of the third capacitor is respectively connected to the first end of the fourth capacitor and the opposite-name end of the secondary winding of the transformer.

[0010] Optionally, the switch tube bridge arm includes a fifth switch tube and a sixth switch tube;

[0011] The drain of the fifth switch tube is the first end of the switch tube bridge arm, and the source of the sixth switch tube is the second end of the switch tube bridge arm;

[0012] The source of the fifth switch tube is connected to the drain of the sixth switch tube and the first end of the first inductor respectively.

[0013] Optionally, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are all N-type MOS tubes with anti-parallel diodes and parasitic capacitors.

[0014] In a second aspect, an embodiment of the present application provides a control method for a two-stage converter, which is applied to the above-mentioned two-stage converter. The control method includes:

[0015] Obtaining the actual voltage of the reused capacitor and the input voltage, actual output voltage, and expected output voltage of the two-stage converter;

[0016] Calculate the expected voltage of the reuse capacitor based on the input voltage and the actual output voltage;

[0017] The duty cycle of the switch tube is obtained based on the expected voltage and the actual voltage of the reused capacitor, and the phase shift angle is obtained based on the expected output voltage and the actual output voltage;

[0018] Calculate the output power of the two-stage converter based on the switch duty cycle and phase shift angle;

[0019] Acquire a first PWM drive signal based on the switch duty cycle, and acquire a second PWM drive signal based on the phase shift angle;

[0020] The first PWM drive signal and the second PWM drive signal are used to control the on-off of the switch tube of the two-stage converter, so as to control the output power of the two-stage converter.

[0021] Optionally, the expected voltage of the reuse capacitor is calculated based on the input voltage and the actual output voltage, including:

[0022] By formula:

[0023] V caref =2V o *N p -Vin

[0024] Calculate the expected voltage V of the multiplexed capacitor caref ;

[0025] Among them, V o Represents the actual output voltage of the two-stage converter, N p It represents the transformation ratio of the transformer, and Vin represents the input voltage.

[0026] Optionally, the duty cycle of the switch tube is obtained based on the expected voltage and the actual voltage of the reused capacitor, including:

[0027] Calculating a first difference between an expected voltage and an actual voltage of the reuse capacitor;

[0028] The first difference is input into the digital PI regulator to obtain the duty cycle of the switch tube.

[0029] Optionally, obtaining a phase shift angle based on the expected output voltage and the actual output voltage includes:

[0030] calculating a second difference between the desired output voltage and the actual output voltage;

[0031] The second difference is input into the digital PI regulator to obtain the phase shift angle.

[0032] Optionally, the output power of the two-stage converter is calculated according to the switch duty cycle and the phase shift angle, including:

[0033] By formula:

[0034]

[0035] Calculate the output power p of the two-stage converter;

[0036] Among them, V out Represents the actual output voltage of the two-stage converter, N p It represents the transformation ratio of the transformer. represents the phase shift angle, D represents the duty cycle of the switch tube, and f s Indicates the switching frequency of the transformer, L k Indicates the inductance value.

[0037] The above solution of the present application has the following beneficial effects:

[0038] In an embodiment of the present application, the Buck circuit and the LLC circuit are constructed into an electrically isolated two-stage converter, and the output voltage of the Buck circuit can be adjusted by increasing or decreasing the conduction time of the Buck circuit switch tube, thereby ensuring that within a wide voltage range, the LLC circuit in the two-stage converter can operate in a voltage matching working mode, achieving high-efficiency gain conversion, and ensuring that the power transmitted by the Buck circuit is less than or equal to the system power, thereby further improving the system efficiency; by controlling the switch tube, the output power of the two-stage converter can be increased, thereby achieving efficient power conversion.

[0039] Other beneficial effects of the present application will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 A topological diagram of a two-stage converter provided in one embodiment of the present application;

[0042] Figure 2 A flow chart of a control method for a two-stage converter provided in one embodiment of the present application;

[0043] Figure 3 This is a working waveform diagram of a two-stage converter provided in one embodiment of the present application. DETAILED DESCRIPTION

[0044] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0045] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0046] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0047] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0048] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0049] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0050] In view of the problem that the electrical isolation and power conversion efficiency of the existing converter cannot be taken into account at the same time, the present application provides a two-stage converter and a control method thereof. By constructing a Buck circuit and an LLC circuit into an electrically isolated two-stage converter, the output voltage of the Buck circuit can be adjusted by increasing or decreasing the conduction time of the Buck circuit switch tube, ensuring that within a wide voltage range, the LLC circuit in the two-stage converter can operate in a voltage matching working mode to achieve high-efficiency gain conversion, and ensuring that the power transmitted by the Buck circuit is less than or equal to the system power, thereby further improving the system efficiency; by controlling the switch tube, the output power of the two-stage converter can be increased, thereby achieving efficient power conversion.

[0051] Next, the structure of the two-stage converter provided in the present application is exemplified.

[0052] like Figure 1 As shown, the two-stage converter includes an LLC circuit and a Buck circuit consisting of a switch tube bridge arm, a reused capacitor and a first inductor. The LLC circuit includes a first switch tube (such as Figure 1 S1 in), the second switch tube (such as Figure 1 S2 in), the third switch tube (such as Figure 1 S3 in), the fourth switch tube (such as Figure 1 S4 in), the first capacitor (such as Figure 1 C1 in), the second capacitor (such as Figure 1 C2 in), the third capacitor (such as Figure 1 C3 in), the fourth capacitor (such as Figure 1 C4 in), external leakage inductance (such as Figure 1 L k ), excitation inductance (such as Figure 1 L m ), DC blocking capacitors (such as Figure 1 C b ), multiplexed capacitors (such as Figure 1 C Buck ), transformer (such as Figure 1 T in), output capacitor (such as Figure 1 C out ), load (such as Figure 1 R L ).

[0053] The drain of the first switch tube is respectively connected to the second end of the first inductor of the Buck circuit and the first end of the reused capacitor, the source of the first switch tube is respectively connected to the drain of the second switch tube and the first end of the DC blocking capacitor, the source of the second switch tube is respectively connected to the second end of the reused capacitor, the second end of the second capacitor, the second end of the switch tube bridge arm of the Buck circuit, and the input capacitor (such as Figure 1 Cin ) of the second terminal, power supply (such as Figure 1 V in ), the first end of the first capacitor is respectively connected to the positive electrode of the power supply, the first end of the input capacitor, and the first end of the switch tube bridge arm of the Buck circuit, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the opposite end of the primary winding of the converter, and the second end of the excitation inductor, the second end of the DC blocking capacitor is connected to the first end of the external leakage inductor, the second end of the external leakage inductor is respectively connected to the same end of the primary winding of the converter and the first end of the excitation inductor, the source of the third switch tube is respectively connected to the same end of the secondary winding of the transformer and the drain of the fourth switch tube, the drain of the third switch tube is respectively connected to the first end of the third capacitor, the first end of the input capacitor, and the first end of the load, the source of the fourth switch tube is respectively connected to the second end of the fourth capacitor, the second end of the output capacitor, and the second end of the load, and the second end of the third capacitor is respectively connected to the first end of the fourth capacitor and the opposite end of the secondary winding of the transformer.

[0054] The Buck circuit includes a switch bridge arm, a reuse capacitor and a first inductor (such as Figure 1 L f The switch tube bridge arm includes a fifth switch tube (such as Figure 1 S5 in the figure) and the sixth switch tube (such as Figure 1 S6 in ).

[0055] The drain of the fifth switch tube is the first end of the switch tube bridge arm, the source of the sixth switch tube is the second end of the switch tube bridge arm, and the source of the fifth switch tube is connected to the drain of the sixth switch tube and the first end of the first inductor respectively.

[0056] It should be noted that the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube all use N-type MOS tubes with anti-parallel diodes and parasitic capacitors. The transformer T includes a primary winding and a secondary winding, and the ratio of the primary winding to the secondary winding is the transformer ratio. Figure 1 middle u p Indicates the voltage value of the primary winding of the transformer. represents the current of the first inductor, N p Indicates the transformer's transformation ratio, i Lk Represents the current of the external leakage inductance.

[0057] The working principle of the two-stage converter of the present application is:

[0058] The voltage is regulated by the BUCK circuit of the front stage, and the output of the BUCK is connected to the switch bridge arm of the back stage half-bridge LLC circuit to form an energy transmission circuit. The supporting capacitor bridge arm of the half-bridge LLC is directly connected to the input power supply to form a neutral point b. The input voltage Vin and the output voltage Vout The relationship between them is:

[0059] V out =Vin*D

[0060] Wherein, D represents the duty cycle of the switch tube.

[0061] It is worth mentioning that by constructing the Buck circuit and the LLC circuit into an electrically isolated two-stage converter, the output voltage of the Buck circuit can be adjusted by increasing or decreasing the conduction time of the Buck circuit switch tube, ensuring that within a wide voltage range, the LLC circuit in the two-stage converter can operate in a voltage matching working mode to achieve high-efficiency gain conversion, and ensuring that the power transmitted by the Buck circuit is less than or equal to the system power, further improving the system efficiency; by controlling the switch tube, the output power of the two-stage converter can be increased, thereby achieving efficient power conversion.

[0062] The control method of the two-stage converter provided in the present application is exemplarily described below.

[0063] like Figure 2 As shown, the control method of the two-stage converter provided in the present application includes the following steps:

[0064] Step 21, obtaining the actual voltage of the reused capacitor and the input voltage, actual output voltage, and expected output voltage of the two-stage converter.

[0065] The above input voltage is the power supply voltage of the two-stage converter, and the actual output voltage is the voltage on both sides of the load.

[0066] In some embodiments of the present application, physical measurement tools such as a multimeter and a voltage sensor can be used to measure the actual voltage of the multiplexed capacitor, the input voltage of the two-stage converter, and the actual output voltage, and the expected output voltage can be given based on the transformer transformation ratio, input voltage and other values ​​of the transformer.

[0067] Step 22, calculating the expected voltage of the reuse capacitor according to the input voltage and the actual output voltage.

[0068] Specifically, through the formula:

[0069] V caref =2V o *N p -Vin

[0070] Calculate the expected voltage V of the multiplexed capacitor caref .

[0071] Among them, V o Represents the actual output voltage of the two-stage converter, N pIt represents the transformation ratio of the transformer, and Vin represents the input voltage.

[0072] Step 23, obtaining the switch duty cycle based on the expected voltage and the actual voltage of the reuse capacitor, and obtaining the phase shift angle based on the expected output voltage and the actual output voltage.

[0073] In some embodiments of the present application, the steps of obtaining the duty cycle of the switch tube based on the expected voltage and the actual voltage of the reused capacitor, and obtaining the phase shift angle based on the expected output voltage and the actual output voltage include:

[0074] The first step is to obtain the switch duty cycle based on the expected voltage and actual voltage of the reused capacitor.

[0075] First, a first difference between an expected voltage and an actual voltage of the reused capacitor is calculated; then, the first difference is input into a digital PI regulator to obtain a duty cycle of the switch tube.

[0076] In the second step, the phase shift angle is obtained based on the expected output voltage and the actual output voltage.

[0077] First, a second difference between the desired output voltage and the actual output voltage is calculated; then, the second difference is input into the digital PI regulator to obtain a phase shift angle.

[0078] It should be noted that the above phase shift angle is used to describe the ratio of the conduction time difference between the third switch tube and the fifth switch tube to the switching period.

[0079] Step 24, calculating the output power of the two-stage converter according to the switch duty cycle and the phase shift angle.

[0080] Specifically, through the formula:

[0081]

[0082] Calculate the output power p of the two-stage converter.

[0083] Among them, V out Represents the actual output voltage of the two-stage converter, N p It represents the transformation ratio of the transformer. represents the phase shift angle, D represents the duty cycle of the switch tube, and f s Indicates the switching frequency of the transformer, L k Indicates the inductance value.

[0084] Step 25, obtaining a first PWM drive signal based on the switch duty cycle, and obtaining a second PWM drive signal based on the phase shift angle.

[0085] Exemplarily, the duty cycle of the switch tube can be input into a PWM generation unit to generate a first PWM drive signal, and the phase shift angle can be input into the PWM generation unit to generate a second PWM drive signal. The PWM generation unit can be a unit of a unipolar carrier modulation method and a PWM generation circuit.

[0086] It is worth mentioning that generating a first PWM drive signal according to the duty cycle of the switching tube and generating a second PWM drive signal according to the phase shift angle is a conversion of the duty cycle of the switching tube in data form to a PWM drive signal of actual action, which facilitates the subsequent control of the switching tube according to the first PWM drive signal and the second PWM drive signal.

[0087] Step 26, using the first PWM drive signal and the second PWM drive signal to control the on-off of the switch tube of the two-stage converter, so as to control the output power of the two-stage converter.

[0088] Specifically, the first PWM drive signal is used to control the on-off of the fifth switch tube in the two-stage converter, and the second PWM drive signal is used to control the on-off of the first switch tube in the two-stage converter. By controlling the on-off of the fifth switch tube, the voltage across the reuse capacitor can be adjusted so that the middle point (such as the middle point between the first switch tube and the second switch tube) of the two-stage converter is Figure 1 The middle point of the first capacitor and the second capacitor (such as Figure 1 The voltage V between point b) ab The amplitude of V can be adjusted by controlling the on-off of the first switch tube. ab and V cd (The middle point between the third switch tube and the fourth switch tube (such as Figure 1 The middle point of the third capacitor and the fourth capacitor (such as Figure 1 The phase difference between the voltage at point d) in the middle is used to adjust the output power of the converter, thereby achieving efficient power conversion.

[0089] It should be noted that since the voltage gain of the converter is proportional to the duty cycle of the switch tube, when the first PWM drive signal is used to control the on and off of the fifth switch tube in the two-stage converter, the voltage gain of the two-stage converter can also be controlled, and the voltage gain of the two-stage converter can be adjusted to improve the current waveform efficiency.

[0090] In some embodiments of the present application, the fifth switch tube and the sixth switch tube in the two-stage converter are complementarily turned on, and the conduction time is controlled by the duty cycle. The first switch tube and the second switch tube in the two-stage converter are complementarily turned on, and the connection time is half of an on-off control cycle. The turn-on time of the third switch tube is the same as that of the first switch tube. The third switch tube and the fourth switch tube are complementarily turned on, and the connection time of the third switch tube and the fourth switch tube is half of an on-off control cycle. The fifth switch tube and the sixth switch tube are complementarily turned on, and the conduction time of the fifth switch tube and the sixth switch tube is controlled by the duty cycle.

[0091] It is worth mentioning that by constructing the Buck circuit and the LLC circuit into an electrically isolated two-stage converter, the output voltage of the Buck circuit can be adjusted by increasing or decreasing the conduction time of the Buck circuit switch tube, ensuring that within a wide voltage range, the LLC circuit in the two-stage converter can operate in a voltage matching working mode to achieve high-efficiency gain conversion, and ensuring that the power transmitted by the Buck circuit is less than or equal to the system power, further improving the system efficiency; by controlling the switch tube, the output power of the two-stage converter can be increased, thereby achieving efficient power conversion.

[0092] The above control method is exemplarily described below with reference to a specific example.

[0093] like Figure 3 As shown, at time t0, the first, third, and fifth switches are turned on with zero voltage, and the current i of the first inductor is La At the same time, the current i of the external leakage inductor Lk Linear rise; at t1, the sixth switch is turned on with zero voltage, the fifth switch is turned off with zero voltage, and the current i of the first inductor La Linear decrease; at time t2, the second and fourth switches are turned on with zero voltage, the first and third switches are turned off with zero voltage, and the current i Lk Linear decrease. Figure 3 The t (t0, t1, ..., t3) in the abscissa represents the unit time, DT s represents the conduction time of the fifth switch tube, Indicates u ab and u cd The time difference between ab Indicates the middle point between the first switch tube and the second switch tube (such as Figure 1 The middle point of the first capacitor and the second capacitor (such as Figure 1 The voltage between point b) and cd Indicates the middle point between the third switch tube and the fourth switch tube (such as Figure 1 The middle point of the third capacitor and the fourth capacitor (such as Figure 1 The voltage between point d).

[0094] In order to verify the feasibility of the two-stage converter and the control method thereof provided by the present application, an embodiment of the present application refers to Figure 1 The topology shown in the figure builds a 1000W two-stage converter prototype with an input voltage of 100V~125V and an output voltage of 400V. The driving signals of the LLC circuit and the Buck circuit are generated by the TI digital signal processor (DSP) TMS320F28377S. Under the experimental conditions, the two-stage converter can work normally in a closed loop under its control method, and realize electrical isolation and efficient power conversion. Moreover, the converter prototype can operate normally under different input voltages and different loads, indicating that the two-stage converter provided in the present application can make up for the shortcomings of the prior art and has the applicability under a variety of working conditions.

[0095] It can be seen that the two-stage converter of the present application can well control the output power of the two-stage converter while achieving electrical isolation, thereby improving the power conversion efficiency of the converter.

[0096] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0097] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles described in the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A two-stage converter, comprising an LLC circuit and a Buck circuit consisting of a switch tube bridge arm, a reused capacitor and a first inductor, characterized in that: The LLC circuit includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, an external leakage inductor, an excitation inductor, a DC blocking capacitor, a reuse capacitor, a transformer, an output capacitor, and a load; Among them, the drain of the first switch tube is respectively connected to the second end of the first inductor of the Buck circuit and the first end of the multiplexing capacitor, the source of the first switch tube is respectively connected to the drain of the second switch tube and the first end of the DC blocking capacitor, the source of the second switch tube is respectively connected to the second end of the multiplexing capacitor, the second end of the second capacitor, the second end of the switch tube bridge arm of the Buck circuit, the second end of the input capacitor, and the negative electrode of the power supply, the first end of the first capacitor is respectively connected to the positive electrode of the power supply, the first end of the input capacitor, and the first end of the switch tube bridge arm of the Buck circuit, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the opposite end of the primary winding of the converter, and the excitation electrode. The second end of the inductor is connected to the second end of the DC blocking capacitor, the second end of the external leakage inductor is connected to the same-name end of the primary winding of the converter and the first end of the excitation inductor respectively, the source of the third switching tube is connected to the same-name end of the secondary winding of the transformer and the drain of the fourth switching tube respectively, the drain of the third switching tube is connected to the first end of the third capacitor, the first end of the input capacitor, and the first end of the load respectively, the source of the fourth switching tube is connected to the second end of the fourth capacitor, the second end of the output capacitor, and the second end of the load respectively, and the second end of the third capacitor is connected to the first end of the fourth capacitor and the opposite-name end of the secondary winding of the transformer respectively.

2. The two-stage converter according to claim 1, characterized in that: The switch tube bridge arm includes a fifth switch tube and a sixth switch tube; The drain of the fifth switch tube is the first end of the switch tube bridge arm, and the source of the sixth switch tube is the second end of the switch tube bridge arm; The source of the fifth switch tube is connected to the drain of the sixth switch tube and the first end of the first inductor respectively.

3. The two-stage converter according to claim 2, characterized in that: The first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, and the sixth switch tube are all N-type MOS tubes with anti-parallel diodes and parasitic capacitors.

4. A control method for a two-stage converter, applied to the two-stage converter according to any one of claims 1 to 3, the control method comprising: Obtaining the actual voltage of the reused capacitor and the input voltage, actual output voltage, and expected output voltage of the two-stage converter; Calculate the expected voltage of the reuse capacitor according to the input voltage and the actual output voltage; Acquire a switch duty cycle based on the expected voltage and the actual voltage of the reuse capacitor, and acquire a phase shift angle based on the expected output voltage and the actual output voltage; Calculating the output power of the two-stage converter according to the switch duty cycle and the phase shift angle; Acquire a first PWM drive signal based on the switch duty cycle, and acquire a second PWM drive signal based on the phase shift angle; The first PWM drive signal and the second PWM drive signal are used to control the on-off of the switch tube of the two-stage converter, so as to control the output power of the two-stage converter.

5. The control method according to claim 4, characterized in that: The calculating the expected voltage of the reuse capacitor according to the input voltage and the actual output voltage includes: By formula: V caref =2V o *N p -Vin Calculate the expected voltage V of the reuse capacitor caref ; Among them, the V o represents the actual output voltage of the two-stage converter, N p represents the transformation ratio of the transformer, and Vin represents the input voltage.

6. The control method according to claim 5, characterized in that: The step of obtaining the switch duty cycle based on the expected voltage and the actual voltage of the reused capacitor includes: Calculating a first difference between an expected voltage of the reuse capacitor and the actual voltage; The first difference is input into a digital PI regulator to obtain a duty cycle of the switch tube.

7. The control method according to claim 4, characterized in that: The acquiring a phase shift angle based on the expected output voltage and the actual output voltage comprises: calculating a second difference between the expected output voltage and the actual output voltage; The second difference is input into a digital PI regulator to obtain a phase shift angle.

8. The control method according to claim 4, characterized in that: The step of calculating the output power of the two-stage converter according to the switch duty cycle and the phase shift angle comprises: By formula: Calculating the output power p of the two-stage converter; Among them, V out represents the actual output voltage of the two-stage converter, N p It represents the transformation ratio of the transformer. represents the phase shift angle, D represents the switch duty cycle, f s Indicates the switching frequency of the transformer, L k Indicates the inductance value.

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