A single-stage converter for step-down conversion and control method

Abstract

The present application is applicable to the field of power electronic conversion technology, and provides a single-stage converter and control method for step-down conversion, the single-stage converter comprising: an LLC resonant converter and a Buck converter, the LLC resonant converter comprising a first switch loop, a second switch loop, an external leakage inductor, a resonant capacitor, a rear-stage output capacitor and a transformer, the Buck converter comprising a first switch tube, a second switch tube, a reuse capacitor, a front-stage output capacitor and a first inductor; one end of the first inductor is respectively connected to one end of the front-stage output capacitor and the source of the fourth switch tube in the first switch loop. The present application can simultaneously achieve electrical isolation of the converter and efficient power conversion.

Description

Technical Field

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

[0002] With the continuous development of the new energy industry in recent years, higher requirements have been put forward for power electronic converters. Improving the power, power density and conversion efficiency of converters has been pursued by a considerable number of researchers and a lot of research has been carried out. In power conversion, DC converters play a very important role and have 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 converter with a dual active bridge LLC resonant converter in cascade. The buck 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, no path for the current to flow directly between the two areas is established. 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 a Buck converter for voltage reduction. This solution is a unipolar topology structure, which has the advantages of simple structure and flexible control. However, the unipolar structure leads to low power conversion efficiency.

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

[0006] The embodiments of the present application provide a single-stage converter and a control method for step-down conversion, which can solve the problem that the converter cannot take into account both electrical isolation and power conversion efficiency.

[0007] In a first aspect, an embodiment of the present application provides a single-stage converter for step-down conversion, including an LLC resonant converter and a Buck converter, wherein the LLC resonant converter includes a first switch loop, a second switch loop, an external leakage inductor, a resonant capacitor, a subsequent output capacitor, and a transformer, and the Buck converter includes a first switch tube, a second switch tube, a reuse capacitor, a previous output capacitor, and a first inductor;

[0008] Among them, the first end of the reused capacitor is respectively connected to the positive electrode of the power supply, the drain of the first switch tube, the drain of the third switch tube in the first switch loop, and the first end of the first split capacitor in the first switch loop; the second end of the reused capacitor is respectively connected to the negative electrode of the power supply, the source of the second switch tube, the first end of the previous-stage output capacitor, and the first end of the second split capacitor in the first switch loop; the source of the first switch tube is respectively connected to the drain of the second switch tube and the first end of the first inductor; the second end of the first inductor is respectively connected to the second end of the previous-stage output capacitor and the source of the fourth switch tube in the first switch loop.

[0009] Optionally, the source of the third switching tube is connected to the first end of the resonant capacitor and the drain of the fourth switching tube, the second end of the resonant capacitor is connected to the first end of the primary winding of the transformer, and the second end of the first split capacitor is respectively connected to the second end of the primary winding of the transformer and the second end of the second split capacitor.

[0010] Optionally, the second switching loop includes a fifth switching tube, a sixth switching tube, a third split capacitor and a fourth split capacitor, the source of the fifth switching tube is respectively connected to the first end of the secondary winding of the transformer and the drain of the sixth switching tube, the drain of the fifth switching tube is respectively connected to the first end of the third split capacitor, the first end of the subsequent output capacitor, and the first end of the load, the source of the sixth switching tube is respectively connected to the first end of the fourth split capacitor, the second end of the subsequent output capacitor, and the second end of the load, and the second end of the third split capacitor is respectively connected to the second end of the secondary winding of the transformer and the second end of the fourth split capacitor.

[0011] 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.

[0012] In a second aspect, an embodiment of the present application provides a control method for a single-stage converter, which is applied to the above-mentioned single-stage converter for buck conversion, and the control method includes:

[0013] Obtain the input voltage of the power supply, the actual voltage of the reuse capacitor, and the actual output voltage of the LLC resonant converter;

[0014] Calculate the expected voltage of the reuse capacitor based on the input voltage;

[0015] According to the expected voltage and the actual voltage of the reused capacitor, the duty cycle of the first switch tube in the Buck converter is obtained;

[0016] Obtaining the duty cycle of the primary and secondary sides of the LLC resonant converter according to the actual output voltage and the expected output voltage of the LLC resonant converter;

[0017] Generate a drive signal for each switch tube in the Buck converter and the LLC resonant converter according to the duty cycle of the first switch tube and the duty cycle of the primary and secondary sides of the LLC resonant converter;

[0018] The generated driving signal is used to control the on and off of each switch tube in the Buck converter and the LLC resonant converter.

[0019] Optionally, the expected voltage of the reuse capacitor is calculated based on the input voltage, including:

[0020] By formula Calculate the expected voltage across the multiplexed capacitor ;

[0021] in, represents the desired output voltage of the LLC resonant converter, It represents the transformation ratio of the transformer. Indicates the input voltage.

[0022] Optionally, obtaining a duty cycle of a first switch tube in a Buck converter according to an expected voltage and an actual voltage of the reuse capacitor includes:

[0023] The difference between the expected voltage of the reused capacitor and the actual voltage of the reused capacitor is calculated, and the calculated difference is input into the digital PI regulator to obtain the duty cycle of the first switch tube in the Buck converter.

[0024] Optionally, according to the actual output voltage and the expected output voltage of the LLC resonant converter, the duty cycle of the primary and secondary sides of the LLC resonant converter is obtained, including:

[0025] The difference between the actual output voltage and the expected output voltage of the LLC resonant converter is calculated, and the calculated difference is input into the digital PI regulator to obtain the duty cycle of the primary and secondary sides of the LLC resonant converter.

[0026] Optionally, the driving signal of the first switch tube is complementary to the driving signal of the second switch tube, the driving signal of the third switch tube is complementary to the driving signal of the fourth switch tube, the driving signal of the third switch tube is the same as the driving signal of the sixth switch tube in the second switch loop, and the driving signal of the fifth switch tube in the second switch loop is complementary to the driving signal of the sixth switch tube.

[0027] Optionally, generating a driving signal for each switch tube in the Buck converter and the LLC resonant converter according to the duty cycle of the first switch tube and the duty cycle of the primary and secondary sides of the LLC resonant converter includes:

[0028] Inputting the duty cycle of the first switch tube into the PWM generation unit to obtain a drive signal of the first switch tube, and generating a drive signal of the second switch tube according to the drive signal of the first switch tube;

[0029] The duty cycle of the primary and secondary sides of the LLC resonant converter is input into the PWM generation unit to obtain a driving signal of the fifth switch tube, and driving signals of the sixth switch tube, the third switch tube and the fourth switch tube are generated according to the driving signal of the fifth switch tube.

[0030] The above solution of the present application has the following beneficial effects:

[0031] In an embodiment of the present application, a novel quasi-single-stage converter is constructed by connecting the source of the fourth switch tube in the first switch loop of the LLC resonant converter to the first inductor and the front-stage output capacitor in the Buck converter respectively. The novel quasi-single-stage converter is electrically isolated by the transformer in the LLC resonant converter. At the same time, the structure of the single-stage converter enables it to expand or reduce the voltage gain of the single-stage converter by increasing or reducing the conduction time of the Buck converter switch tube, thereby ensuring that the LLC resonant converter can operate in a voltage matching working mode within a wide voltage range, achieving high-efficiency gain conversion, and ensuring that the power transmitted by the Buck converter is less than or equal to the system power, thereby further improving the system efficiency. By increasing the conduction time difference between the primary and secondary side switches of the LLC converter, the output power of the single-stage converter can be increased, thereby achieving efficient power conversion.

[0032] Other beneficial effects of the present application will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] Figure 1 A schematic diagram of the structure of a single-stage converter for step-down conversion provided in one embodiment of the present application;

[0035] Figure 2 An operating waveform diagram of a single-stage converter is provided for an embodiment of the present application;

[0036] Figure 3 A flow chart of a control method for a single-stage converter is provided for one embodiment of the present application. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In response to the problem that current converters cannot take into account both electrical isolation and power conversion efficiency, an embodiment of the present application provides a single-stage converter for step-down conversion, by connecting the source of the fourth switch tube in the first switch loop of the LLC resonant converter to the first inductor and the front-stage output capacitor in the Buck converter to form a new quasi-single-stage converter, the new quasi-single-stage converter is electrically isolated through the transformer in the LLC resonant converter, and the structure of the single-stage converter enables it to increase or decrease the conduction time of the Buck converter switch tube, expand or reduce the voltage gain of the single-stage converter, ensure that within a wide voltage range, the LLC resonant converter can operate in a voltage matching working mode, achieve high-efficiency gain conversion, and ensure that the power transmitted by the Buck converter is less than or equal to the system power, further improve the system efficiency, and increase the conduction time difference between the primary and secondary side switches of the LLC converter. The output power of the single-stage converter can be increased, thereby achieving efficient power conversion.

[0044] The single-stage converter for step-down conversion provided in the embodiment of the present application is exemplarily described below in conjunction with specific embodiments.

[0045] like Figure 1 As shown, the single-stage converter for step-down conversion provided in the embodiment of the present application includes an LLC resonant converter and a Buck converter, and the LLC resonant converter includes a first switching loop, a second switching loop, an external leakage inductor , resonant capacitor , the output capacitor of the next stage and a transformer T, the Buck converter includes a first switch tube , the second switch tube , multiplexed capacitor , front stage output capacitor and the first inductor The first switch loop includes a third switch tube , the fourth switch tube 、The first split capacitor And the second split capacitor The second switch loop includes a fifth switch tube , the sixth switch tube 、The third split capacitor And the fourth split capacitor .

[0046] Among them, the reuse capacitor The first end is respectively connected to the positive electrode of the power supply and the first switch tube The drain of the third switch tube in the first switch loop The drain of the first switch circuit and the first split capacitor The first end of the multiplexing capacitor is connected The second end of the The source and the front-stage output capacitor The first end of the second split capacitor in the first switch loop The first end of the first switch tube is connected to The source of the second switch tube The drain, first inductor The first end of the first inductor is connected The second end of the capacitor is connected to the front stage output capacitor The second end of the fourth switch tube in the first switch loop Source connection.

[0047] The third switch The source and resonant capacitor The first end of the fourth switch tube The drain connection, resonant capacitor The second end of the first split capacitor is connected to the first end of the primary winding of the transformer T. The second end of the transformer T primary winding and the second split capacitor The second end of the connection.

[0048] Fifth switch The source of the transformer T is connected to the first end of the secondary winding of the transformer T, the sixth switch tube The drain of the fifth switch is connected The drain of the third split capacitor The first end and the output capacitor of the next stage The first end, load The first end of the sixth switch tube is connected to The source of the fourth split capacitor The first end and the output capacitor of the next stage The second end of the load The second end of the third split capacitor is connected The second end of the transformer T secondary winding is connected to the second end of the fourth split capacitor The transformer T includes a primary winding and a secondary winding, and the ratio of the primary winding to the secondary winding is the transformation ratio of the transformer T, specifically: the transformation ratio of the transformer T=the number of turns of the primary winding / the number of turns of the secondary winding.

[0049] It should be noted that Figure 1 middle represents the voltage of the above power supply, that is, the input voltage of the single-stage converter, Represents the current flowing through the external leakage inductance The current, represents the transformation ratio of transformer T, The third switch And the fourth switch The middle point of The first split capacitor And the second split capacitor The middle point of The fifth switch And the sixth switch The middle point of The third split capacitor And the fourth split capacitor The middle point.

[0050] In some embodiments of the present application, the first switch tube , the second switch tube , the third switch tube , the fourth switch tube , the fifth switch tube And the sixth switch N-type MOS tubes with anti-parallel diodes and parasitic capacitances can be used.

[0051] It is worth mentioning that the fourth switch in the first switch loop of the LLC resonant converter The source of the first inductor in the Buck converter And the front stage output capacitor connection, so that the first switch tube is adjusted The ratio of the on-time to the switching period has a significant impact on the output capacitance of the previous stage. The voltage across the two ends is regulated so that the third switch tube , the fourth switch tube The midpoint of the first split capacitor And the second split capacitor The voltage between the midpoints of The amplitude of changes, thereby adjusting the voltage gain of the single-stage converter.

[0052] By controlling the first switch With the fifth switch The ratio of the on-time difference to the switching period can regulate the voltage and voltage ( express Figure 1 The voltage between the two points cd, i.e. the fifth switch tube , the sixth switch tube The middle point and the third split capacitor And the fourth split capacitor The voltage difference between the midpoints of the two stages is used to adjust the output power of the single-stage converter, thereby achieving efficient power conversion.

[0053] Specifically, the embodiment of the present application constructs a new quasi-single-stage converter by connecting the source of the fourth switch tube in the first switch loop of the LLC resonant converter to the first inductor and the front-stage output capacitor in the Buck converter respectively. The new quasi-single-stage converter is electrically isolated by the transformer in the LLC resonant converter. At the same time, the structure of the single-stage converter enables it to expand or reduce the voltage gain of the single-stage converter by increasing or reducing the conduction time of the Buck converter switch tube, thereby ensuring that the LLC resonant converter can operate in a voltage matching working mode within a wide voltage range, achieving high-efficiency gain conversion, and ensuring that the power transmitted by the Buck converter is less than or equal to the system power, thereby further improving the system efficiency. By increasing the conduction time difference between the primary and secondary side switches of the LLC converter, the output power of the single-stage converter can be increased, thereby achieving efficient power conversion.

[0054] Among them, the above structure of the Buck converter enables it to have partial power transmission characteristics, and can only transmit a part of the system output power, which is conducive to the improvement of the power conversion efficiency of the new quasi-single-stage converter, and the topological structure of the new quasi-single-stage converter provided by the present application has the function of electrical isolation. Therefore, the new quasi-single-stage converter provided by the present application can achieve electrical isolation while taking into account power conversion. It can be understood that the Buck converter is a step-down converter, and therefore, the new quasi-single-stage converter provided by the present application is used for step-down conversion.

[0055] Based on the characteristics of the above-mentioned novel quasi-single-stage converter, in practical applications, the voltage gain expression of the novel quasi-single-stage converter is as follows:

[0056]

[0057] in, represents the output voltage of the LLC resonant converter, that is, the voltage of the load, represents the input voltage of the single-stage converter, represents the duty cycle of the first switch tube, Indicates the transformation ratio of transformer T.

[0058] The working process of the novel quasi-single-stage converter provided in the present application is exemplarily described below.

[0059] like Figure 2 As shown, in At this moment, the third switch , the first switch tube Zero voltage turn-on, first inductor Current Linear increase, at the same time, the external leakage inductance Current Linear increase; At this moment, the fifth switch Zero voltage turn-on, first inductor Current Continue to rise linearly, at the same time, due to the external leakage inductance The voltage on both sides is 0, the external leakage inductance Current Remains unchanged, it can be seen that at this time, because of the output capacitance of the previous stage The voltage is adjusted to ensure that the LLC resonant converter works in a mode where the primary and secondary voltages match, thus ensuring high system efficiency. At this moment, the second switch Zero voltage turn-on, the first switch Zero voltage turn-off, the first inductor Current Linear decrease; At this moment, the fourth switch Zero voltage turn-on, the third switch tube Zero voltage shutdown, external leakage inductance Current Linear decrease; At this moment, the sixth switch tube Zero voltage turn-on, the fifth switch Zero voltage turn-off, the first inductor Current Continue to decrease linearly, at the same time, the external leakage inductance Current Remain unchanged.

[0060] It should be noted that Figure 2 The horizontal axis represents the unit time. Indicates 4 different moments, Indicates the first switch The on-time, express and The time difference between express , express .

[0061] The control method of the single-stage converter applied to the above-mentioned single-stage converter for step-down conversion is exemplarily described below in conjunction with specific embodiments.

[0062] like Figure 3As shown, the control method of the single-stage converter provided in the embodiment of the present application includes the following steps:

[0063] Step 31, obtaining the input voltage of the power supply, the actual voltage of the reuse capacitor, and the actual output voltage of the LLC resonant converter.

[0064] The above actual output voltage is the output voltage of the single-stage converter, that is, the voltage of the load. Specifically, the above input voltage, actual voltage and actual output voltage can all be acquired by a voltage sensor and output to a controller for controlling the single-stage converter, which can be a digital signal processor.

[0065] Step 32, calculating the expected voltage of the reuse capacitor according to the input voltage.

[0066] In some embodiments of the present application, the formula Calculate the expected voltage across the multiplexed capacitor Where, represents the desired output voltage of the LLC resonant converter. It can be given according to the actual situation. It represents the transformation ratio of the transformer. Indicates the input voltage.

[0067] Step 33, obtaining the duty cycle of the first switch tube in the Buck converter according to the expected voltage and the actual voltage of the reuse capacitor.

[0068] In some embodiments of the present application, the difference between the expected voltage of the reused capacitor and the actual voltage of the reused capacitor can be calculated first, and then the calculated difference is input into the digital PI regulator to obtain the duty cycle of the first switch tube in the Buck converter. It can be understood that after receiving the difference between the expected voltage and the actual voltage of the reused capacitor, the digital PI regulator can use its own control strategy to process the difference and output the duty cycle of the first switch tube in the Buck converter.

[0069] Step 34, obtaining the duty cycle of the primary and secondary sides of the LLC resonant converter according to the actual output voltage and the expected output voltage of the LLC resonant converter.

[0070] In some embodiments of the present application, the difference between the actual output voltage of the LLC resonant converter and the expected output voltage of the LLC resonant converter can be calculated first, and then the calculated difference is input into the digital PI regulator to obtain the duty cycle of the primary and secondary sides of the LLC resonant converter. It can be understood that after receiving the difference between the actual output voltage and the expected output voltage of the LLC resonant converter, the digital PI regulator can process the difference using its own control strategy and output the duty cycle of the primary and secondary sides of the LLC resonant converter.

[0071] Step 35, generating a driving signal for each switch tube in the Buck converter and the LLC resonant converter according to the duty cycle of the first switch tube and the duty cycle of the primary and secondary sides of the LLC resonant converter.

[0072] In the above-mentioned single-stage converter, the driving signal of the first switch tube is complementary to the driving signal of the second switch tube, the driving signal of the third switch tube is complementary to the driving signal of the fourth switch tube, the driving signal of the third switch tube is the same as the driving signal of the sixth switch tube in the second switch loop, and the driving signal of the fifth switch tube in the second switch loop is complementary to the driving signal of the sixth switch tube.

[0073] Based on this, the driving signals of each switch in the Buck converter and LLC resonant converter can be obtained as follows:

[0074] The duty cycle of the first switch tube is input into the PWM generation unit to obtain a drive signal of the first switch tube, and a drive signal of the second switch tube is generated according to the drive signal of the first switch tube; the duty cycle of the primary and secondary sides of the LLC resonant converter is input into the PWM generation unit to obtain a drive signal of the fifth switch tube, and drive signals of the sixth switch tube, the third switch tube and the fourth switch tube are generated according to the drive signal of the fifth switch tube.

[0075] It can be understood that after using the PWM generation unit to generate the driving signals of the first switch tube and the fifth switch tube, the driving signals of the second switch tube, the third switch tube, the fourth switch tube and the sixth switch tube can be obtained based on the relationship between the driving signals of the above-mentioned switch tubes.

[0076] It should be noted that the above-mentioned driving signals may all be PWM driving signals.

[0077] Step 36, using the generated driving signal to control the on and off of each switch tube in the Buck converter and the LLC resonant converter.

[0078] In some embodiments of the present application, after obtaining the driving signal of each switch tube, the on and off of each switch tube can be controlled by inputting the driving signal into the gate of the corresponding switch tube to obtain the on time of the switch tube.

[0079] It is worth mentioning that by increasing or decreasing the on-time of the Buck converter switch tube, the voltage gain of the single-stage converter is expanded or reduced, ensuring that the LLC resonant converter can operate in a voltage matching working mode within a wide voltage range, achieving high-efficiency gain conversion, and ensuring that the power transmitted by the Buck converter is less than or equal to the system power, further improving the system efficiency, and by increasing the on-time difference between the primary and secondary side switches of the LLC converter, the output power of the single-stage converter can be increased, thereby achieving efficient power conversion.

[0080] In order to verify the feasibility of a single-stage converter and control method for step-down conversion provided by the present application, an embodiment of the present application refers to Figure 1 The topology shown in the figure builds a 1000W quasi-unipolar converter prototype with an input voltage of 100V~300V and an output voltage of 400V. The driving signals of the LLC resonant converter and the Buck converter are generated by the TI digital signal processor (DSP) TMS320F28377S. Under the experimental conditions, the new quasi-single-stage converter (i.e., the single-stage converter of the embodiment of the present application) can work normally in a closed loop under its control method, and realize electrical isolation and efficient power conversion at the same time. Moreover, the converter prototype can operate normally under different input voltages and different loads, indicating that the quasi-unipolar converter provided in the present application can make up for the shortcomings of the prior art and has the applicability under diverse working conditions.

[0081] It can be seen that the new quasi-single-stage converter provided by the present application constructs a new quasi-single-stage converter by combining a Buck converter and an LLC resonant converter. By increasing or decreasing the conduction time of the Buck switch tube, the voltage gain of the new quasi-single-stage converter can be expanded or reduced, thereby ensuring that within a wide voltage range, the LLC resonant converter in the new quasi-single-stage converter can operate in a voltage matching working mode to achieve high-efficiency gain conversion; by increasing the conduction time difference between the primary and secondary side switches of the LLC resonant converter, the output power of the new quasi-single-stage converter can be increased, and by increasing or decreasing the conduction time of the Buck converter switch tube, the output voltage of the quasi-unipolar converter can be increased or decreased, thereby achieving efficient power conversion.

[0082] Based on the above description, the advantages of the single-stage converter and the control method thereof provided by the present application are: a new cascade topology is formed between the Buck converter and the LLC resonant converter, so that it has the advantages of both the Buck converter and the LLC resonant converter, and the duty cycle (the first switch tube) is adjusted. The ratio of the on-time to the switching period) to the output capacitance of the previous stage The voltage at both ends is adjusted to make the first bridge arm (the third switch tube The source of the fourth switch tube The drain connection is composed of the second bridge arm (the first split capacitor And the second split capacitor The voltage amplitude between the midpoints of the connection composition) changes to adjust the voltage gain of the new quasi-single-stage converter. With the first switch The output power of the converter is adjusted by the ratio of the on-time difference to the switching period, while achieving electrical isolation and efficient power conversion of the converter.

[0083] In addition, the Buck converter has a partial power transmission feature and only transmits a portion of the system output power, which is beneficial to improving the efficiency of the converter. The LLC resonant converter always operates under the working condition of matching the original and secondary side voltages, which can enable all switch tubes to be turned on at zero voltage.

[0084] 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 control method for a single-stage converter, characterized in that: A single-stage converter for step-down conversion, the single-stage converter comprising an LLC resonant converter and a Buck converter, the LLC resonant converter comprising a first switch loop, a second switch loop, an external leakage inductor, a resonant capacitor, a subsequent output capacitor and a transformer, characterized in that the Buck converter comprises a first switch tube, a second switch tube, a reuse capacitor, a previous output capacitor and a first inductor; The first end of the reused capacitor is respectively connected to the positive electrode of the power supply, the drain of the first switch tube, the drain of the third switch tube in the first switch loop, and the first end of the first split capacitor in the first switch loop; the second end of the reused capacitor is respectively connected to the negative electrode of the power supply, the source of the second switch tube, the first end of the previous stage output capacitor, and the first end of the second split capacitor in the first switch loop; the source of the first switch tube is respectively connected to the drain of the second switch tube and the first end of the first inductor; the second end of the first inductor is respectively connected to the second end of the previous stage output capacitor and the source of the fourth switch tube in the first switch loop; The control method comprises: Obtain the input voltage of the power supply, the actual voltage of the reuse capacitor, and the actual output voltage of the LLC resonant converter; Calculating the expected voltage of the reuse capacitor according to the input voltage; Obtaining a duty cycle of a first switch tube in a Buck converter according to an expected voltage and an actual voltage of the reused capacitor; Obtaining a duty cycle of the primary and secondary sides of the LLC resonant converter according to the actual output voltage and the expected output voltage of the LLC resonant converter; Generate a drive signal for each switch tube in the Buck converter and the LLC resonant converter according to the duty cycle of the first switch tube and the duty cycle of the primary and secondary sides of the LLC resonant converter; The generated driving signal is used to control the on and off of each switch tube in the Buck converter and the LLC resonant converter.

2. The control method according to claim 1, characterized in that: The source of the third switching tube is connected to the first end of the resonant capacitor and the drain of the fourth switching tube, the second end of the resonant capacitor is connected to the first end of the primary winding of the transformer, and the second end of the first split capacitor is respectively connected to the second end of the primary winding of the transformer and the second end of the second split capacitor.

3. The control method according to claim 2, characterized in that: The second switch loop includes a fifth switch tube, a sixth switch tube, a third split capacitor and a fourth split capacitor. The source of the fifth switch tube is respectively connected to the first end of the secondary winding of the transformer and the drain of the sixth switch tube, the drain of the fifth switch tube is respectively connected to the first end of the third split capacitor, the first end of the subsequent output capacitor, and the first end of the load, the source of the sixth switch tube is respectively connected to the first end of the fourth split capacitor, the second end of the subsequent output capacitor, and the second end of the load, and the second end of the third split capacitor is respectively connected to the second end of the secondary winding of the transformer and the second end of the fourth split capacitor.

4. The control method according to claim 3, 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.

5. The control method according to claim 1, characterized in that: The calculating the expected voltage of the reuse capacitor according to the input voltage includes: By formula Calculate the expected voltage of the reuse capacitor ; in, represents the desired output voltage of the LLC resonant converter, It represents the transformation ratio of the transformer. represents the input voltage.

6. The control method according to claim 1, characterized in that: The step of obtaining the duty cycle of the first switch tube in the Buck converter according to the expected voltage and the actual voltage of the reuse capacitor includes: The difference between the expected voltage of the multiplexed capacitor and the actual voltage of the multiplexed capacitor is calculated, and the calculated difference is input into the digital PI regulator to obtain the duty cycle of the first switch tube in the Buck converter.

7. The control method according to claim 1, characterized in that: The step of obtaining the duty cycle of the primary and secondary sides of the LLC resonant converter according to the actual output voltage and the expected output voltage of the LLC resonant converter includes: The difference between the actual output voltage and the expected output voltage of the LLC resonant converter is calculated, and the calculated difference is input into a digital PI regulator to obtain the duty cycle of the primary and secondary sides of the LLC resonant converter.

8. The control method according to claim 1, characterized in that: The driving signal of the first switch tube is complementary to the driving signal of the second switch tube, the driving signal of the third switch tube is complementary to the driving signal of the fourth switch tube, the driving signal of the third switch tube is the same as the driving signal of the sixth switch tube in the second switch loop, and the driving signal of the fifth switch tube in the second switch loop is complementary to the driving signal of the sixth switch tube.

9. The control method according to claim 8, characterized in that: The step of generating a driving signal for each switch tube in the Buck converter and the LLC resonant converter according to the duty cycle of the first switch tube and the duty cycle of the primary and secondary sides of the LLC resonant converter comprises: Inputting the duty cycle of the first switch tube into a PWM generation unit to obtain a drive signal of the first switch tube, and generating a drive signal of the second switch tube according to the drive signal of the first switch tube; The duty cycle of the primary and secondary sides of the LLC resonant converter is input into a PWM generation unit to obtain a drive signal of the fifth switch tube, and drive signals of the sixth switch tube, the third switch tube and the fourth switch tube are generated according to the drive signal of the fifth switch tube.

Images