Optical storage integrated grid-connected DC-DC converter and control method thereof

Abstract

The invention relates to an optical storage integrated grid-connected DC-DC converter and a control method thereof. The converter is characterized in that a high-voltage side adopts a half-bridge three-level structure and comprises at least two input support capacitors and two bridge arms, each bridge arm comprises at least two power switch tubes, and a connection midpoint of the two bridge arms is output to a resonant cavity; the CLLLC resonant cavity module comprises a resonant capacitor and a resonant inductor which are connected in series, an excitation inductor which is connected in parallel, and a transformer primary winding which is connected in series with the excitation inductor; a secondary winding of the transformer is connected in series with a resonant inductor and a resonant capacitor; the low-voltage side adopts a full-bridge rectification structure, comprises at least four power switch tubes and is connected with the secondary side of the resonant cavity; and the control module is used for generating a control signal to drive the switch tube to be switched on or switched off and implementing phase-shift change duty ratio control. According to the invention, the half-bridge three-level topology is adopted to reduce the voltage stress of the device, the CLLLC resonant topology and the phase-shift change duty ratio control are combined, the wide-range voltage gain adjustment and soft switching are realized, and the efficiency of the converter is improved.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology; specifically, this invention relates to a photovoltaic-storage integrated grid-connected DC-DC converter and its control method. Background Technology

[0002] With the transformation of the global energy structure, the development and utilization of renewable energy sources such as photovoltaics are receiving increasing attention. Photovoltaic power generation is characterized by intermittency and volatility; therefore, energy storage systems are typically required to ensure grid stability and power supply reliability. Integrated photovoltaic-energy storage grid-connected systems can effectively mitigate the fluctuations in photovoltaic power generation and improve energy efficiency. In this system, the DC-DC converter is a key component for achieving bidirectional energy flow and voltage matching between photovoltaic modules, energy storage units, and the grid.

[0003] Currently, traditional DC-DC converters, such as those employing hard-switching technology, suffer from high switching losses and struggle to improve efficiency. Resonant converters have attracted considerable attention due to their ability to achieve soft switching of the switching transistors (zero-voltage switching, ZVS, or zero-current switching, ZCS). Among resonant converters, LLC resonant converters are widely used due to their simple structure and ability to achieve a wide range of soft switching. However, in energy storage applications requiring a wider voltage gain range, especially those with large variations in the low-voltage side voltage, the gain regulation capability of traditional LLC converters is limited.

[0004] In terms of control strategies, while traditional frequency converter (PFM) control is simple, its gain curve flattens and regulation sensitivity decreases when the switching frequency is far from the resonant frequency, making precise control difficult, especially when precise output voltage or specific dynamic response is required. Furthermore, frequency converter control can lead to an excessively wide switching frequency range, posing challenges to the design of magnetic components and filters. Summary of the Invention

[0005] In view of this, the present invention provides a photovoltaic-storage integrated grid-connected DC-DC converter and its control method, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0006] To achieve the aforementioned objectives, a first aspect of the present invention provides an integrated photovoltaic-storage grid-connected DC-DC converter, comprising:

[0007] The high-voltage side input module is a half-bridge three-level structure, which includes at least two series-connected input support capacitors, a first bridge arm and a second bridge arm. Each bridge arm includes at least two series-connected power switching transistors. The midpoint of the connection between the first bridge arm and the second bridge arm is output to the resonant cavity.

[0008] The CLLLC resonant cavity module includes a first resonant capacitor and a first resonant inductor connected in series, a magnetizing inductor connected in parallel, and a transformer primary winding connected in series with the magnetizing inductor; the transformer secondary winding is connected in series with a second resonant inductor and a second resonant capacitor.

[0009] The low-voltage side output module is a full-bridge rectifier structure containing at least four power switching transistors, which are connected to the secondary side of the CLLLC resonant cavity module and output to the filter capacitor and the load.

[0010] The control module generates control signals to drive the power switches of the high-voltage side input module and the low-voltage side output module to turn on or off. The control module implements phase-shift duty cycle control on the power switches of the high-voltage side input module.

[0011] In the DC-DC converter described above, optionally, in the high-voltage side input module, the first bridge arm includes a first power switch and a second power switch connected in series, and the second bridge arm includes a third power switch and a fourth power switch connected in series.

[0012] The drive signals for the first power switch and the fourth power switch have the same adjustable duty cycle. The drive signals of the second power switch and the third power switch have a fixed 50% duty cycle.

[0013] There is a dead time between the drive signals of the first power switch and the second power switch, and between the drive signals of the third power switch and the fourth power switch;

[0014] The drive signal of the first power switch has an early turn-off phase angle relative to the drive signal of the second power switch. There is a phase shift angle between the output voltage of the primary bridge arm and the output voltage of the secondary bridge arm. ;

[0015] The phase-shift duty cycle control implemented by the control module includes controlling the adjustable duty cycle. The aforementioned early turn-off phase angle and the phase shift angle .

[0016] In the DC-DC converter described above, optionally, the adjustable duty cycle The adjustment range is 0 to 50%.

[0017] In the DC-DC converter described above, optionally, the relationship between the first resonant inductor and the second resonant inductor in the CLLLC resonant cavity module is as follows:

[0018]

[0019] The relationship between the first resonant capacitor and the second resonant capacitor is as follows:

[0020]

[0021] In the formula, The first resonant inductor, This is the second resonant inductor. This is the first resonant capacitor. is the second resonant capacitor, and N is the turns ratio of the transformer.

[0022] To achieve the aforementioned objective, a second aspect of the present invention provides a control method for a DC-DC converter as described in any one of the first aspects, comprising:

[0023] A phase-shift duty cycle control strategy is used to control the power switching transistors of the high-voltage side input module;

[0024] The first and fourth power switches controlling the high-voltage side input module use the same power switch with the same duty cycle. An adjustable drive signal controls the second and third power switches to use a drive signal with a fixed 50% duty cycle.

[0025] The first power switch and the second power switch are turned on simultaneously, and the third power switch and the fourth power switch are turned on simultaneously. An early turn-off phase angle is introduced into the drive signal of the first power switch relative to the drive signal of the second power switch. ;

[0026] A phase shift angle is introduced between the chopper voltage generated by the high-voltage side input module and the voltage generated by the low-voltage side output module. ;

[0027] Adjust the duty cycle The aforementioned early turn-off phase angle and the phase shift angle This is to adjust the output voltage gain of the DC-DC converter and achieve soft switching of the power switching transistor.

[0028] In the control method described above, optionally, different early turn-off phase angles are set and tested in experiments. and the phase shift angle The combination of these factors determines the combination that enables the DC-DC converter to operate in a soft-switching state under different operating conditions.

[0029] In the control method described above, optionally, the early turn-off phase angle, which is set and tested in the experiment, is... and the phase shift angle Combinations, including , , .

[0030] In the control method described above, optionally, the high-voltage side input module outputs power by combining the on and off states of the power switch. 0 The three-level stepped waveform is applied to the CLLLC resonant cavity, where... This is the input voltage.

[0031] In the control method described above, optionally, the on and off combinations of the power switch include:

[0032] The first power switch and the second power switch are turned on, and the third power switch and the fourth power switch are turned off;

[0033] The second power switch is turned on, and the first power switch, the third power switch, and the fourth power switch are turned off.

[0034] The third power switch is turned on and the fourth power switch is turned off;

[0035] The third power switch is turned on, while the first power switch, the second power switch, and the fourth power switch are turned off.

[0036] In the control method described above, optionally, the early turn-off phase angle can be determined by establishing an equivalent model of the DC-DC converter and combining it with the results of characteristic analysis. and the phase shift angle The value of is determined to achieve the target gain and soft-switching range.

[0037] The photovoltaic-storage integrated grid-connected DC-DC converter of the present invention adopts a half-bridge three-level topology on the high-voltage side to reduce device voltage stress; at the same time, it combines a CLLLC resonant topology with phase-shift duty cycle control to achieve wide-range voltage gain adjustment and soft switching, thereby improving converter efficiency.

[0038] The present invention further provides a control method for the above-mentioned converter, and therefore the control method also has the above-mentioned advantages. Attached Figure Description

[0039] The disclosure of this invention will become more apparent from the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings:

[0040] Figure 1 This is a topology diagram of an integrated photovoltaic and energy storage grid-connected system;

[0041] Figure 2 This is a schematic diagram of a grid-connected DC-DC converter topology that integrates photovoltaic and energy storage, as disclosed in an embodiment of the present invention.

[0042] Figure 3 This is a functional module diagram of a photovoltaic-storage integrated grid-connected DC-DC converter disclosed in an embodiment of the present invention;

[0043] Figure 4 A schematic diagram of the gain curves of a CLLLC resonant cavity under different Q-value parameters under frequency conversion control;

[0044] Figure 5 This is a schematic diagram of the switching transistor drive signal and chopper output voltage waveform of a phase-shift duty cycle control strategy disclosed in an embodiment of the present invention.

[0045] Figure 6 This invention discloses a method for controlling different phase shift duty cycles under different phase shift duty cycles. and A diagram illustrating four working scenarios in relational relationships;

[0046] Figure 7 This is a schematic diagram of an equivalent circuit of a CLLLC resonant cavity disclosed in an embodiment of the present invention;

[0047] Figure 8 This is a schematic diagram of the system gain curve under a phase-shift duty cycle control strategy disclosed in an embodiment of the present invention;

[0048] Figure 9 This is a schematic diagram of the gain curve for achieving soft switching within a phase-shift duty cycle control strategy disclosed in an embodiment of the present invention.

[0049] Figure 10 The experimental waveform diagram is shown below, using frequency conversion control at a working frequency of 40kHz.

[0050] Figure 11 The diagram shows experimental waveforms of phase-shift duty cycle control at different angles, as disclosed in an embodiment of the present invention. Detailed Implementation

[0051] Referring to the accompanying drawings and specific embodiments, the structure, composition, features, and advantages of the integrated photovoltaic and energy storage grid-connected DC-DC converter and its control method of the present invention will be described below by way of example. However, all descriptions should not be construed as limiting the present invention in any way.

[0052] Furthermore, for any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the various figures, the present invention still allows for any combination or deletion of these technical features (or their equivalents) without any technical obstacle, and thus these further embodiments according to the present invention should also be considered within the scope of this description.

[0053] It should be noted that the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "third," or "fourth" may explicitly or implicitly include at least one of those features.

[0054] Furthermore, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0055] An embodiment of the DC-DC converter of the present invention is applied to a photovoltaic energy storage integrated grid-connected system. Figure 1 This is a topology diagram of an integrated photovoltaic and energy storage grid-connected system.

[0056] Figure 1 This diagram illustrates a specific implementation of a photovoltaic-storage grid-connected DC microgrid system. Its hardware structure is as follows: a photovoltaic array is connected to a DC bus via a first DC / DC converter module with a built-in MPPT (Maximum Power Point Tracking) control unit; an energy storage device (ESS) is connected to the DC bus via a second bidirectional DC / DC converter module with bidirectional charge / discharge control functionality; the DC bus simultaneously connects to a photovoltaic grid-connected inverter and DC power-consuming equipment (DEV); the inverter's AC side is connected to the public AC grid. During system operation, when photovoltaic output is sufficient, redundant energy from the photovoltaic-powered load is charged into the energy storage device. Once the energy storage is fully utilized, any remaining energy is transmitted to the grid via the inverter. When photovoltaic output is insufficient, the energy storage discharges and powers the photovoltaic system in tandem; if the output is still insufficient, the inverter draws grid power to supplement the DC bus. In the event of a grid fault, the grid connection switch is disconnected, and the system is off-grid, with the photovoltaic and energy storage systems working together to ensure power supply to the DC load.

[0057] Figure 2 and Figure 3 The circuit topology and module division of an integrated photovoltaic and energy storage grid-connected DC-DC converter disclosed in an embodiment of the present invention are shown.

[0058] Reference Figure 2 and Figure 3 This embodiment discloses a photovoltaic-storage integrated grid-connected DC-DC converter, based on CLLLC topology and phase-shift duty cycle control, which can be applied to applications such as... Figure 1 In the integrated photovoltaic and energy storage grid-connected system shown, the photovoltaic array / high-voltage DC bus is connected to the energy storage battery / low-voltage DC bus.

[0059] like Figure 2 , 3 As shown, the DC-DC converter in this embodiment includes a high-voltage side input module, a low-voltage side output module, and a CLLLC resonant cavity module. The converter also includes a control module (not shown). The high-voltage side (primary side) uses a half-bridge three-level structure to form a chopper unit, and the low-voltage side (secondary side) has a full-bridge rectifier unit connected to a filter and a load. The high-voltage side and the low-voltage side are isolated by a CLLLC resonant cavity and a high-frequency transformer T.

[0060] It should be noted that this converter supports bidirectional energy transfer between the high-voltage side and the low-voltage side. Terms such as "input module," "output module," and "rectifier" are only used for convenience in describing the direction of energy flow under specific operating modes and do not limit the reverse working capability of the converter or its components.

[0061] Figure 4 The curves showing the gain of the CLLLC resonator as a function of frequency for different quality factors Q (Q=0, 0.2, 0.3, 0.4) are presented. Figure 4 As shown, the gain rapidly rises to its peak value near 0.5 with increasing frequency f, then gradually decreases and tends to level off as f increases. Furthermore, the smaller the quality factor Q, the higher the peak gain and the narrower the frequency range corresponding to the peak value. This pattern can be used to select resonant cavity parameters to match the target gain.

[0062] Reference Figure 2 , 3 The high-voltage side input module consists of two series-connected supporting capacitors. and Forming the midpoint of the DC bus; , , , For high-voltage side power switches (such as MOSFETs or IGBTs), the corresponding - Its body diode, - Its parasitic capacitance; , This is a clamping diode. The DC input voltage is... By controlling - The switching on and off of the transformer can generate a three-level circuit on the primary side. ,0, AC square wave voltage For example, specific switch combinations (1100, 0100, 0011, 0010 states, with four digits corresponding to the switching transistors) can be used. - (Switch status), output 0 The three-level stepped waveform is transmitted to the CLLLC resonant cavity, which effectively reduces the voltage stress on the switching devices.

[0063] The high-voltage side adopts a half-bridge three-level topology, which means that the voltage stress on each switch is only half of the input voltage. This allows the use of switches with lower voltage ratings, reducing costs and improving system reliability.

[0064] Reference Figure 2 , 3 The CLLLC resonant cavity module consists of a primary-side resonant capacitor. Primary resonant inductor Magnetizing inductor High-frequency transformer T, secondary resonant inductor and secondary resonant capacitor Composition. For example, the following parameters can be used in the design to satisfy the symmetry condition:

[0065]

[0066] Where N is the transformer turns ratio. This symmetrical structure simplifies parameter design and facilitates wide-range gain and bidirectional energy flow.

[0067] Reference Figure 2 , 3 The low-voltage side output module consists of secondary power switching transistors. , , , (e.g., MOSFETs) and their body diodes - and parasitic capacitance - This forms a full-bridge rectifier circuit (which switches to inverter mode when reverse power flows). R is the output filter capacitor, and R is the load. This is achieved by controlling... - This enables synchronous rectification of the AC output from the resonant cavity to obtain a DC output voltage. .

[0068] The control module, not shown, controls the on / off state of each power switch and implements a phase-shift duty cycle control strategy. The specific control strategy can be found in the subsequent control method implementation examples.

[0069] Accordingly, this invention also discloses a control method for an integrated photovoltaic-storage grid-connected DC-DC converter.

[0070] This embodiment employs a phase-shift duty cycle control strategy to fix the switching frequency. Operation, adjustment of three control degrees of freedom: primary side (primary / high voltage side) outer switch tube and duty cycle , the same-side switch tube in the primary side bridge arm (such as and The phase shift angle between ) and the phase shift angle between the original secondary side bridge and the road. Among them, the phase shift angle Equivalent to turning off the phase angle in advance, for example and The phase shift angle between them is equivalent to Compared to The early shutdown phase angle.

[0071] Figure 5 This is a schematic diagram of the switching transistor drive signal and chopper output voltage waveform under the phase-shift duty cycle control strategy in this embodiment.

[0072] like Figure 5 As shown, - These are primary-side switching transistors. - and secondary side (secondary / low voltage side) switching transistor - The drive signal voltage waveform reflects its on / off timing, duty cycle, and phase shift angle. and Control logic, etc.; This is the primary-side chopped voltage waveform of the transformer, which is a three-level waveform. ,0, AC square wave voltage; The waveform represents the secondary voltage; the current i includes... and waveform, and These are the primary and secondary currents, respectively.

[0073] Reference Figure 5 In one specific implementation of the above control strategy, the primary-side switching transistor... and Using the same drive signal and duty cycle Adjustable, for example, with an adjustment range of 0-50%. Primary-side switching transistor. and Using the same drive signal, the duty cycle is fixed at 50%. Switching transistor and The drive signals are logically enabled synchronously (considering dead time). and The drive signals are logically enabled synchronously.

[0074] Phase shift angle Defined as (or (relative to) (or The early turn-off phase angle. When =50% and When =0, it is equivalent to traditional phase-shift control. By adjusting... and It can change the primary chopper voltage. The pulse width and phase are adjusted to generate an effective three-level waveform.

[0075] Phase shift angle Defined as primary-side chopping voltage The fundamental frequency and secondary voltage The phase difference between the fundamental and the fundamental frequencies. By adjusting... It can control the power transferred from the primary side to the secondary side.

[0076] By adjusting the duty cycle mentioned above Early shutdown phase angle and phase shift angle This allows for adjustment of the converter's output voltage gain and soft switching of the power transistors. For example, a mathematical model of the converter under phase-shift duty cycle control can be established using time-domain analysis, and the duty cycle can be determined based on this model. Early shutdown phase angle and phase shift angle The value of is determined to achieve the target gain and soft-switching range.

[0077] Figure 6 For the different phase-shift duty cycle control strategies mentioned above and A diagram illustrating four working scenarios in relational relationships. (The diagram shows the four scenarios.) and The relations are respectively , , , .

[0078] Figure 6 The primary voltages under the above conditions are presented. With secondary voltage The timing waveforms, with different waveforms corresponding to the early turn-off phase angles. With phase angle Different combinations of timing control techniques can be used to achieve three-level stepped waveform output and ensure the soft-switching state of the switching transistors, adapting to the gain adjustment requirements of photovoltaic-storage grid-connected scenarios.

[0079] Optionally, a parametric equivalence conversion method is used to transform the secondary side parameters of the CLLLC resonator to the primary side, thereby establishing a... Figure 7 The equivalent model of the CLLLC resonant cavity circuit is shown. This modeling method provides a simplified approach to system analysis, helps to deepen the understanding of the working principle of the resonant converter, and obtains analytical results such as the characteristic curves of the converter based on the equivalent model.

[0080] like Figure 7 As shown, the equivalent model includes an intermediate parallel magnetizing inductor. And two symmetrical series branches, both the primary and secondary branches contain resonant inductance. With resonant capacitor The primary-side port voltage is The secondary port voltage is The primary and secondary branch currents are respectively and The corresponding capacitor voltage is and .

[0081] In an optional embodiment, the system gain and phase shift angle can be plotted based on theoretical analysis results. and The changing characteristic curve, such as Figure 8 As shown. Figure 8 The relationship between gain and phase shift angle is shown in both 3D and 2D plots. , The relationship between the values ​​is displayed using color changes to show the varying gain. This image visually illustrates the control parameters. and The influence of the system gain is shown in the red box in the planar diagram, which represents the operating range that meets the gain requirements.

[0082] Furthermore, based on theoretical analysis and experimental verification, the gain characteristic curve of the system under soft-switching conditions can be plotted, such as... Figure 9 As shown. Figure 9 Gain and phase shift angle are also displayed in both 3D and 2D diagrams. , The relationship between the values ​​is illustrated in the red box in the plan view, which represents the effective operating range where the system can simultaneously meet soft-switching conditions and gain requirements. This provides an important reference for system parameter optimization and controller design. By selecting appropriate... and Combining these features allows the converter to operate in a soft-switching state under different operating conditions, thereby reducing switching losses.

[0083] Optionally, the effects of the aforementioned phase-shift duty cycle control and traditional frequency conversion control can be verified and compared through experiments.

[0084] In the experiment, the following prototype parameters were established: input voltage =200V (corresponding to a half-bridge three-level voltage) = =100V input to the resonant cavity), rated load R=2.5Ω, full-load output power 160W. Transformer turns ratio N=5, primary inductance =55µH, secondary inductance =2.2µH, magnetizing inductance =220µH, primary-side capacitance =180nF, secondary capacitor =4.7µF. Operating frequency range 30-70kHz, resonant frequency Approximately 50kHz (according to) , calculate).

[0085] Experiments show that the gain error of frequency conversion control is large when it deviates from the resonant point, especially when it is far from the resonant frequency (such as 70kHz), the error reaches 15%. Figure 10 The experimental waveforms are shown at a working frequency of 40kHz when frequency conversion control is used in the experiment. As can be seen from the experimental waveforms, although frequency conversion control can still achieve ZVS at a working frequency of 40kHz, from... Figure 10 (d) It can be seen that The voltage drop across the terminals is accompanied by obvious high-frequency oscillations, and the peak amplitude of the voltage spike is close to 100V, indicating that the voltage stress during the turn-off transient of the switching transistor is too high at this operating frequency.

[0086] The experiments on phase-shift duty cycle control were conducted in (…). =0°, =90°), ( =60°, =80°), ( =70°, The experiment was conducted under conditions such as (e.g., 100°). Figure 11The experimental waveforms at the aforementioned angles are shown when the phase-shift duty cycle control described above is employed in the experiment. The experimental waveforms demonstrate that under these operating conditions, the switching transistors can achieve soft switching (e.g., ZVS), and compared to… Figure 10 , Voltage oscillations decay faster and peak amplitude decreases. Furthermore, by adjusting... and The system effectively adjusts the output gain, verifying the correctness of the theoretical analysis and the feasibility of the control strategy. For example, under these parameter combinations, a lower DC gain can be achieved, which is crucial for applications with a wide range of output voltages (such as energy storage battery charging, where the voltage varies from low to high).

[0087] Furthermore, under the strategy of variable duty cycle plus phase shift control, the secondary-side switch maintains a 50% duty cycle, ensuring the continuity of the secondary-side current and thus avoiding the phenomenon of the secondary-side resonant circuit de-resonating, enabling the system to maintain the stability of the resonant cavity state within one switching cycle.

[0088] Some embodiments of the present invention may have at least the following beneficial effects:

[0089] (1) Reduce device voltage stress: The high-voltage side adopts a half-bridge three-level topology, so that the voltage stress borne by each switch is only half of the input voltage. Switches with lower withstand voltage ratings can be used, reducing costs and improving system reliability.

[0090] (2) Wide gain range and high precision control: A phase-shift duty cycle control strategy is adopted, and the duty cycle is adjusted in a coordinated manner. Bridge arm inward phase angle Phase angle of the original secondary side shift It can achieve a wider voltage gain range at a fixed switching frequency, and compared with traditional frequency conversion control, the gain adjustment accuracy is higher, especially in the low gain region;

[0091] (3) High efficiency operation: The design of the CLLLC resonant cavity and the implementation of the phase shift duty cycle control strategy help to achieve soft switching (ZVS) of the primary and secondary side switching transistors in a wide load and wide voltage range, significantly reducing switching losses and improving converter efficiency;

[0092] (4) Midpoint voltage balance: The control strategy and switching transistor combination adopted can naturally achieve the balance of the midpoint potential of the half-bridge three-level structure without the need for additional complex balance control circuits;

[0093] (5) Symmetrical resonant cavity design: The CLLLC resonant cavity adopts a symmetrical design, which simplifies the parameter design and is conducive to realizing the symmetrical characteristics of bidirectional power flow.

[0094] The technical scope of this invention is not limited to the contents of the above specification. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the scope of this invention.

Claims

1. A photovoltaic-storage integrated grid-connected DC-DC converter, characterized in that, include: The high-voltage side input module is a half-bridge three-level structure, which includes at least two series-connected input support capacitors, a first bridge arm and a second bridge arm. Each bridge arm includes at least two series-connected power switching transistors. The midpoint of the connection between the first bridge arm and the second bridge arm is output to the resonant cavity. The CLLLC resonant cavity module includes a first resonant capacitor and a first resonant inductor connected in series, a magnetizing inductor connected in parallel, and a transformer primary winding connected in series with the magnetizing inductor; the transformer secondary winding is connected in series with a second resonant inductor and a second resonant capacitor. The low-voltage side output module is a full-bridge rectifier structure containing at least four power switching transistors, which are connected to the secondary side of the CLLLC resonant cavity module and output to the filter capacitor and the load. The control module generates control signals to drive the power switches of the high-voltage side input module and the low-voltage side output module to turn on or off. The control module implements phase-shift duty cycle control on the power switches of the high-voltage side input module.

2. The DC-DC converter according to claim 1, characterized in that, In the high-voltage side input module, the first bridge arm includes a first power switch and a second power switch connected in series, and the second bridge arm includes a third power switch and a fourth power switch connected in series. The drive signals for the first power switch and the fourth power switch have the same adjustable duty cycle. The drive signals of the second power switch and the third power switch have a fixed 50% duty cycle. There is a dead time between the drive signals of the first power switch and the second power switch, and between the drive signals of the third power switch and the fourth power switch; The drive signal of the first power switch has an early turn-off phase angle relative to the drive signal of the second power switch. There is a phase shift angle between the output voltage of the primary bridge arm and the output voltage of the secondary bridge arm. ; The phase-shift duty cycle control implemented by the control module includes controlling the adjustable duty cycle. The aforementioned early turn-off phase angle and the phase shift angle .

3. The DC-DC converter according to claim 2, characterized in that, The adjustable duty cycle The adjustment range is 0 to 50%.

4. The DC-DC converter according to claim 1, characterized in that, In the CLLLC resonant cavity module, the relationship between the first resonant inductor and the second resonant inductor is as follows: The relationship between the first resonant capacitor and the second resonant capacitor is as follows: In the formula, The first resonant inductor, This is the second resonant inductor. This is the first resonant capacitor. is the second resonant capacitor, and N is the turns ratio of the transformer.

5. A control method for a DC-DC converter as described in any one of claims 1 to 4, characterized in that, include: A phase-shift duty cycle control strategy is used to control the power switching transistors of the high-voltage side input module; The first and fourth power switches controlling the high-voltage side input module use the same power switch with the same duty cycle. An adjustable drive signal controls the second and third power switches to use a drive signal with a fixed 50% duty cycle. The first power switch and the second power switch are turned on simultaneously, and the third power switch and the fourth power switch are turned on simultaneously. An early turn-off phase angle is introduced into the drive signal of the first power switch relative to the drive signal of the second power switch. ; A phase shift angle is introduced between the chopper voltage generated by the high-voltage side input module and the voltage generated by the low-voltage side output module. ; Adjust the duty cycle The aforementioned early turn-off phase angle and the phase shift angle This is to adjust the output voltage gain of the DC-DC converter and achieve soft switching of the power switching transistor.

6. The control method according to claim 5, characterized in that, By setting and testing different early turn-off phase angles in the experiment, and the phase shift angle The combination of these factors determines the combination that enables the DC-DC converter to operate in a soft-switching state under different operating conditions.

7. The control method according to claim 6, characterized in that, The early turn-off phase angles that were set and tested in the experiment are described below. and the phase shift angle Combinations, including , , .

8. The control method according to claim 5, characterized in that, The high-voltage side input module outputs power by combining the on and off states of the power switching transistors. 0 The three-level stepped waveform is applied to the CLLLC resonant cavity, where... This is the input voltage.

9. The control method according to claim 8, characterized in that, The on / off combinations of the power switch include: The first power switch and the second power switch are turned on, and the third power switch and the fourth power switch are turned off; The second power switch is turned on, and the first power switch, the third power switch, and the fourth power switch are turned off. The third power switch is turned on and the fourth power switch is turned off; The third power switch is turned on, while the first power switch, the second power switch, and the fourth power switch are turned off.

10. The control method according to claim 5, characterized in that, By establishing an equivalent model of the DC-DC converter and combining it with the results of characteristic analysis, the early turn-off phase angle is determined. and the phase shift angle The value of is determined to achieve the target gain and soft-switching range.

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