LLC-DCT and variable frequency voltage regulation dual characteristic compatible direct-current-direct-current resonant converter and working method thereof

Abstract

The application provides an LLC-DCT and variable-frequency voltage-regulation dual-characteristic compatible DC-DC resonant converter and a working method thereof. The converter is integrated with a flyback converter bypass through multiplexing of primary full-bridge power switch tubes, and simultaneously realizes LLC resonant wide-range variable-frequency voltage-regulation output and flyback uncontrolled DCT constant-voltage output in a single topology. The two output paths are decoupled and do not affect each other. The application significantly expands the functionality and application scenarios while maintaining high efficiency and soft switching characteristics, and is suitable for charging power supplies and auxiliary power supply systems with multiple output requirements.

Description

Technical Field

[0001] This invention relates to a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation, and its operating method, belonging to the field of power electronics technology. Background Technology

[0002] Resonant converters are increasingly widely used in new energy applications due to their advantages of soft switching and high efficiency. Among resonant converters, LLC resonant converters are particularly advantageous in terms of topology, efficiency, and soft-switching performance. However, the converter parameter design to achieve LLC-DCT characteristics will flatten the frequency conversion and voltage regulation range near the resonant frequency, leading to a decrease in voltage gain G. v The wide range of operating frequency variations resulting from wide-range adjustment is detrimental to the design and stable operation of the converter's magnetic components.

[0003] Therefore, it is necessary to propose a DC-DC resonant converter that is compatible with both LLC-DCT and frequency conversion voltage regulation based on the LLC resonant converter. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of the prior art by proposing a DC-DC resonant converter that is compatible with both LLC-DCT and variable frequency voltage regulation.

[0005] The technical solution implemented by this invention is as follows: A DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation, characterized in that: it includes a converter input voltage U in LLC resonant output voltage U o LLC resonant cavity module, flyback converter bypass, converter DCT output voltage U f The flyback converter bypass and the resonant inductor L in the LLC resonant cavity module r The primary-side switching transistor full-bridge circuit is connected, and the secondary-side diode full-bridge circuit is connected to the secondary winding of the main transformer TX1 in the LLC resonant cavity module.

[0006] Preferably, the LLC resonant cavity module includes a main transformer TX1 and a resonant inductor L. r Resonant capacitor C r .

[0007] Preferably, the flyback converter bypass includes a flyback transformer TX. f , flyback primary diode D f1 , flyback secondary-side diode D f2 flyback output capacitor C f .

[0008] Preferably, the primary-side switching full-bridge circuit includes an input capacitor C.in The system comprises four power switching transistors, each with a diode and a parasitic capacitance connected in anti-parallel; the power switching transistors include a first power switching transistor Q1, a second power switching transistor Q2, a third power switching transistor Q3, and a fourth power switching transistor Q4; the anti-parallel diodes include a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4; and the parasitic capacitance includes a first capacitor C. oss1 Second capacitor C oss2 Third capacitor C oss3 and the fourth capacitor C oss4 .

[0009] Preferably, the positive terminal of the converter input voltage is connected to the input capacitor C. in The upper end of the first power switch Q1 and the drain of the fourth power switch Q4 are connected; the source of the first power switch Q1 is connected to the drain of the third power switch Q3 and the flyback primary diode D. f1 anode, resonant inductor L r The left end; the source of the fourth power switch Q4 is connected to the drain of the second power switch Q2 and the flyback transformer TX. f primary winding N p Different-name terminal, primary winding L of main transformer TX1 m The source of the third power switch Q3 is connected to the source of the second power switch Q2 and the input capacitor C. in The lower end of the converter is the negative terminal of the input voltage.

[0010] Preferably, each power switch of the converter has its gate and source terminals individually receiving a switching signal provided by an external circuit, and when the switching signal is high, the corresponding power switch is turned on; when the switching signal is low, the corresponding power switch is turned off.

[0011] Preferably, the flyback primary-side diode D in the flyback converter bypass... f1 Cathode-connected flyback transformer TX f primary winding N p Same name terminal; flyback transformer TX f secondary winding N s The opposite terminal is connected to the flyback secondary diode D. f2 anode; flyback transformer TX f secondary winding N s Connect the same terminal to the flyback output capacitor C f The lower end of the converter DCT output voltage is the negative terminal; the flyback secondary diode D... f2 Cathode connected to flyback output capacitor C f The upper end of the converter is the positive terminal of the DCT output voltage.

[0012] A method for operating a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation is characterized by: implementation based on the aforementioned LLC-DCT and variable frequency voltage regulation compatible DC-DC resonant converter; the converter's operation synchronously includes an uncontrolled DCT output mode and an LLC variable frequency voltage regulation output mode; the power switching transistors in both modes employ pulse frequency modulation (PFM); and the switching frequency is adjusted during the full switching cycle T. s The process is divided into four stages, from t0 to t4, with the following sequence of actions: (1) [t0~t1] stage: U gs1 U gs2 Output high level, U gs3 U gs4 Output low level; (2) [t1~t2] stage: U gs1 U gs2 U gs3 U gs4 Output low level; (3) [t2~t3] stage: U gs3 U gs4 Output high level, U gs1 U gs2 Output low level; (4) [t3~t4] stage: U gs1 U gs2 U gs3 U gs4 Output low level; In the switching timing of each mode, t0~t2 and t2~t4 are each switching periods T. s Half of it.

[0013] The beneficial effects of this invention are as follows: 1. By adding only a small number of components to the traditional unidirectional full-bridge LLC resonant converter topology and reusing power switches, a DC voltage output based on the flyback converter principle is constructed. This approach expands the converter's functionality while effectively reducing the number of power switches, thereby lowering the converter's construction cost. Furthermore, during LLC resonant frequency conversion and voltage regulation, the resonant freewheeling current enables zero-voltage switching (ZVS) of all power switches, overcoming the problem of excessive extreme voltage stress on the transformer primary-side power switches in traditional flyback converters. This effectively extends the lifespan of the power switches and significantly improves the converter's operational reliability.

[0014] 2. The addition of a flyback converter bypass in this invention does not affect the original LLC resonant converter's power transfer and frequency conversion voltage regulation mechanism. Furthermore, during frequency conversion voltage regulation, the PFM used will maintain the duty cycle of the two complementary power switches in the full-bridge structure at approximately 50% at different power switch operating frequencies. When the flyback transformer winding inductance is sufficiently large, the added flyback converter bypass operates in Continuous Conduction Mode (CCM). At this time, a fixed voltage gain relationship is maintained between the flyback converter bypass DC output voltage and the converter input voltage of this invention, thereby achieving the constant voltage output capability of the DCT. The addition of the flyback converter bypass does not affect the design of parameters related to widening the LLC resonant frequency conversion voltage regulation range, resulting in a high degree of decoupling between the two functions and a more flexible expansion of the invention's application scenarios.

[0015] 3. Traditional LLC resonant converters cannot simultaneously achieve both DCT characteristics and wide-range frequency conversion and voltage regulation characteristics. This application possesses both the constant voltage output capability of a DCT and a wide frequency conversion and voltage regulation output range, thus expanding into a wider range of applications. This invention is applicable to various charging power supplies and auxiliary power supplies requiring a wide voltage range and constant voltage output. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of Embodiment 1 of the present invention; Figure 2 This is a circuit diagram of Embodiment 2 of the present invention; Figure 3 This is a circuit diagram of Embodiment 3 of the present invention; Figure 4 This is the current path diagram of the converter during the [t0~t1] stage of the present invention; Figure 5 This is the current path diagram for the converter during the [t1~t2] stage of the present invention; Figure 6 This is the current path diagram of the converter during the [t2~t3] stage of the present invention; Figure 7 This is the current path diagram for the converter during the [t3~t4] stage of the present invention; Figure 8 The key waveforms obtained from the experiment of the compatibility process of the two output modes of this invention; Figure 9 This is the waveform of the frequency conversion voltage regulation PI control signal of the present invention; Figure 10 For the present invention Figure 8 Transient waveform of constant voltage output in interval 1; Figure 11 For the present invention Figure 8 Transient waveform of constant voltage output in interval 2; Figure 12 For the present invention Figure 8 The soft switch in section 1 realizes the transient waveform; Figure 13 For the present invention Figure 8 The soft switch in interval 2 realizes the transient waveform. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Other systems, methods, and / or features of this embodiment will become apparent to those skilled in the art after reviewing the following detailed description. All such additional systems, methods, features, and advantages are intended to be included within this specification, within the scope of the invention, and protected by the appended claims. Further features of the disclosed embodiments are described in the following detailed description, and these features will become apparent from the following detailed description.

[0018] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0019] Example 1:

[0020] like Figure 1 and Figure 2 As shown, the present invention includes a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation, characterized in that: it includes a converter input voltage U in LLC resonant output voltage U o LLC resonant cavity module, flyback converter bypass, converter DCT output voltage U f The flyback converter bypass and the resonant inductor L in the LLC resonant cavity module r The primary-side switching transistor full-bridge circuit is connected, and the secondary-side diode full-bridge circuit is connected to the secondary winding of the main transformer TX1 in the LLC resonant cavity module.

[0021] Preferably, the transformer also includes a frequency conversion voltage regulation feedback closed loop, which internally contains a reference voltage U refPI controller, voltage-controlled oscillator (VCO), NOT gate, dead-time addition unit.

[0022] Preferably, the LLC resonant cavity module includes a main transformer TX1 and a resonant inductor L. r Resonant capacitor C r .

[0023] Preferably, the flyback converter bypass includes a flyback transformer TX. f , flyback primary diode D f1 , flyback secondary-side diode D f2 flyback output capacitor C f .

[0024] Preferably, the primary-side switching full-bridge circuit includes an input capacitor C. in The system comprises four power switching transistors, each with a diode and a parasitic capacitance connected in anti-parallel; the power switching transistors include a first power switching transistor Q1, a second power switching transistor Q2, a third power switching transistor Q3, and a fourth power switching transistor Q4; the anti-parallel diodes include a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4; and the parasitic capacitance includes a first capacitor C. oss1 Second capacitor C oss2 Third capacitor C oss3 and the fourth capacitor C oss4 .

[0025] Preferably, the positive terminal of the converter input voltage is connected to the input capacitor C. in The upper end of the first power switch Q1 and the drain of the fourth power switch Q4 are connected; the source of the first power switch Q1 is connected to the drain of the third power switch Q3 and the flyback primary diode D. f1 anode, resonant inductor L r The left end; the source of the fourth power switch Q4 is connected to the drain of the second power switch Q2 and the flyback transformer TX. f primary winding N p Different-name terminal, primary winding L of main transformer TX1 m The source of the third power switch Q3 is connected to the source of the second power switch Q2 and the input capacitor C. in The lower end of the converter is the negative terminal of the input voltage.

[0026] Preferably, each power switch of the converter has its gate and source terminals individually receiving a switching signal provided by an external circuit, and when the switching signal is high, the corresponding power switch is turned on; when the switching signal is low, the corresponding power switch is turned off.

[0027] Preferably, the flyback primary-side diode D in the flyback converter bypass...f1 Cathode-connected flyback transformer TX f primary winding N p Same name terminal; flyback transformer TX f secondary winding N s The opposite terminal is connected to the flyback secondary diode D. f2 anode; flyback transformer TX f secondary winding N s Connect the same terminal to the flyback output capacitor C f The lower end of the converter DCT output voltage is the negative terminal; the flyback secondary diode D... f2 Cathode connected to flyback output capacitor C f The upper end of the converter is the positive terminal of the DCT output voltage.

[0028] A method for operating a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation is characterized by: implementation based on the aforementioned LLC-DCT and variable frequency voltage regulation compatible DC-DC resonant converter; the converter's operation synchronously includes an uncontrolled DCT output mode and an LLC variable frequency voltage regulation output mode; the power switching transistors in both modes employ pulse frequency modulation (PFM); and the switching frequency is adjusted during the full switching cycle T. s The process is divided into four stages, from t0 to t4, with the following sequence of actions: (1) [t0~t1] stage: such as Figure 4 As shown, U gs1 U gs2 Output high level, U gs3 U gs4 Output low level; (2) [t1~t2] stage: such as Figure 5 As shown, U gs1 U gs2 U gs3 U gs4 Output low level; (3) [t2~t3] stage: such as Figure 6 As shown, U gs3 U gs4 Output high level, U gs1 U gs2 Output low level; (4) [t3~t4] stage: such as Figure 7 As shown, U gs1 U gs2 U gs3 U gs4 Output low level; In the switching timing of each mode, t0~t2 and t2~t4 are each switching periods T. sHalf of it.

[0029] The beneficial effects of this embodiment are as follows: By adding only a small number of components to the traditional unidirectional full-bridge LLC resonant converter topology and reusing power switches, a DC voltage output based on the flyback converter principle is constructed. This approach expands the converter's functionality while effectively reducing the number of power switches, thereby lowering the converter's construction cost. Furthermore, during LLC resonant frequency conversion and voltage regulation, the resonant freewheeling current not only enables zero-voltage switching (ZVS) of all power switches but also overcomes the problem of excessive extreme voltage stress on the transformer primary-side power switches in traditional flyback converters, effectively extending the lifespan of the power switches and significantly improving the converter's operational reliability.

[0030] Example 2:

[0031] This embodiment should be understood to include all the features of any of the foregoing embodiments, and to further improve upon them.

[0032] like Figure 2 As shown, based on the aforementioned LLC-DCT and frequency conversion voltage regulation dual-characteristic compatible DC-DC resonant converter, the resonant inductor L... r The right end is connected to a resonant capacitor C. r At the left end, the resonant capacitor C r The right end is connected to the primary winding L of the main transformer TX1. m Same name.

[0033] Preferably, the secondary diode full-bridge circuit connected to the secondary winding of the main transformer TX1 includes an output capacitor C. o The fifth diode D5, the sixth diode D6, the seventh diode D7, and the eighth diode D8.

[0034] Preferably, the positive terminal of the LLC resonant output voltage is connected to the output capacitor C. o The upper end of the fifth diode D5 and the cathode of the seventh diode D7; the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6, and the secondary winding L of the main transformer TX1. s Same terminal; the anode of the seventh diode D7 is connected to the cathode of the eighth diode D8, and the secondary winding L of the main transformer TX1. s The opposite terminal; the anode of the sixth diode D6 is connected to the anode of the eighth diode D8, and the output capacitor C. o The lower end of the LLC resonant output voltage is the negative terminal.

[0035] Preferably, in the variable frequency voltage regulation feedback closed loop, the collected LLC resonant output voltage U o With reference voltage Uref The subtraction results in an error signal that is input to a PI controller. The PI controller outputs a control signal, which is then fed into a voltage-controlled oscillator (VCO). The VCO outputs a modulation pulse signal, which is then processed by a dead-time addition unit to output a switching signal U. gs1 with U gs2 This signal is then synchronously passed through a NOT gate and a dead-time addition unit to output a switching signal U. gs3 with U gs4 .

[0036] Assuming that all capacitors, inductors, switching transistors, diodes, and transformers are ideal devices, and that the primary-to-secondary turns ratio of all transformers is 1, and that the flyback transformer winding inductance is large enough to enable the newly added flyback converter to operate in Continuous Conduction Mode (CCM) by bypass.

[0037] The beneficial effects of this embodiment are: successful implementation of LLC resonant output voltage regulation control under wide load variations, that is, achieving a wide range of LLC resonant frequency conversion voltage regulation characteristics. Simultaneously, the DCT output voltage U of the converter... f Keep it constant.

[0038] Example 3: This example should be understood as including at least all the features of any of the foregoing examples, and further improving upon them; A method for operating a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation is proposed. The operating principles of the uncontrolled DCT output mode and the LLC variable frequency voltage regulation output mode can be found in [reference needed]. Figure 2 , Figure 3 , Figure 4 In both modes, the power switch uses pulse frequency modulation (PFM) during the full switching cycle T. s The process is divided into four stages, from t0 to t4, with the following sequence of actions: (1) [t0~t1] stage: U gs1 U gs2 Output high level, U gs3 U gs4 Output low level; (2) [t1~t2] stage: U gs1 U gs2 U gs3 U gs4 Output low level; (3) [t2~t3] stage: U gs3 U gs4 Output high level, U gs1 U gs2 Output low level; (4) [t3~t4] stage: U gs1 U gs2 U gs3 U gs4 Output low level; In the switching timing of each mode, t0~t2 and t2~t4 are each switching periods T. s Half of it.

[0039] Specifically as follows: (1) [t0~t1] Resonant cavity LC resonance + flyback transformer primary winding charging stage, such as Figure 4 As shown: At time t0, Q1 and Q2 achieve ZVS turn-on, making the resonant inductor L r With resonant capacitor C r Series LC resonance occurs, and then i p Increase and crosses zero, and is greater than the excitation current i. Lm Then there exists i s =i p -i Lm This enables the main transformer TX1 to transfer power from the primary side to the secondary side via LC resonance. s The current flows through the secondary diode full-bridge circuit connected to the secondary winding of the main transformer TX1, i Lm The output voltage U of the LLC resonant circuit o The voltage is clamped and rises linearly. Before time t1, due to the LC resonance characteristics, i p It will revert to equal i Lm Make the resonant inductance L r With resonant capacitor C r Magnetizing inductance L m A three-element series resonance occurs, entering the LLC freewheeling phase. Furthermore, Q1 and Q2 conduct simultaneously, subjecting the flyback converter bypass input to a positive current u. ab Voltage, then the flyback primary diode D f1 Turn on, and then the flyback transformer TX f The primary winding and Q1, Q2, and flyback primary diode D f1 The input terminals of the converter and the primary winding of the flyback transformer together form a charging loop, causing the primary current i of the flyback transformer to... f1 The voltage rises linearly, while the output voltage U of the converter DCT increases linearly. f From the flyback output capacitor C f maintain.

[0040] (2) [t1~t2] LLC freewheeling + flyback power transfer stage, such as Figure 5 As shown: at time t1, Q1 and Q2 are off, i p For C oss1 With C oss2 Charging, while simultaneously charging Coss3 With C oss4 The discharge constitutes the ZVS commutation process. Before time t2, C oss3 With C oss4 After discharge, the voltage across the terminals drops to 0, and D3 and D4 are turned on. ab byU in Reduced to -U in During the continuation phase, due to i s =0, LLC resonant output voltage U o From the output capacitor C o Maintain. Furthermore, at the moment Q1 and Q2 are turned off, the positive u... ab The voltage drops and becomes less than the output voltage U of the DCT converter. f Converted to flyback transformer TX f The voltage on the primary winding causes the flyback primary diode D to... f1 When turned off, the primary current i of the flyback transformer f1 Instantly press flyback transformer TX f The turns ratio is transferred to the secondary current i of the flyback transformer. f2 Furthermore, due to the ZVS commutation process, the drain-source voltage U between Q1 and Q2... ds1 with U ds2 Both are the input voltage U of the converter in Clamping, thereby suppressing excessive extreme voltage stress at the turn-off moment of the flyback switch.

[0041] (3) [t2~t3] Resonant cavity LC resonance + flyback transformer secondary winding energy release stage, such as Figure 6 As shown: At time t2, Q3 and Q4 achieve ZVS turn-on, exciting series LC resonance. This process is similar to the [t0~t1] stage, but the current is reversed. Before time t3, due to the LC resonance characteristics, i p It will revert to equal i Lm Make the resonant inductance L r With resonant capacitor C r Magnetizing inductance L m A three-element series resonance occurs, entering the LLC freewheeling phase. Furthermore, Q3 and Q4 conduct simultaneously, causing the flyback converter bypass input to experience reverse current. ab Voltage, then the flyback primary diode D f1 Keep it off, then the flyback transformer TX f Secondary winding and flyback secondary diode D f2 flyback output capacitor C f The output terminals of the converter and the DCT together form an energy release loop in the secondary winding of the flyback transformer, causing the secondary current i of the flyback transformer to... f2 Linear decrease.

[0042] (4) [t3~t4] LLC freewheeling + flyback power feedback stage, such as Figure 7 As shown: at time t3, Q3 and Q4 are off, i p For C oss3 With C oss4 Charging, while simultaneously charging C oss1 With C oss2 The discharge constitutes the ZVS commutation process. Before time t4, C oss1 With C oss2 After discharge, the voltage across the terminals drops to 0, and D1 and D2 are turned on. ab By -U in Upgrade to U in During the continuation phase, due to i s =0, LLC resonant output voltage U o From the output capacitor C o Maintain. Furthermore, at the moment of shutdown in Q3 and Q4. Reverse u. ab The voltage rises and exceeds the output voltage U of the DCT converter. f Converted to flyback transformer TX f The voltage on the primary winding causes the flyback primary diode D to... f1 When the circuit is turned on, the secondary current i of the flyback transformer... f2 Instantly press flyback transformer TX f The turns ratio is transferred to the primary current i of the flyback transformer. f1 .

[0043] in, Figure 3 It reflects the key waveform of a complete cycle, which is transient.

[0044] The principle by which the converter achieves compatibility between uncontrolled DCT output and LLC frequency conversion voltage regulation output dual characteristics is as follows: When the bypass input of the flyback converter is subjected to a positive u ab Voltage, flyback primary diode D f1 The circuit is switched on to initiate the charging process of the primary winding of the flyback transformer, and the charging circuit reuses Q1 and Q2. Simultaneously, the forward u... ab A voltage is applied in parallel to the LLC resonant cavity module, exciting a change in the resonant current and realizing the transfer of resonant power. However, the direction of the resonant current is different from that of the primary current i of the flyback transformer. f1 The current flows in the same direction as the flyback converter bypass and will not flow into the flyback transformer primary current i. f1 The fact that the power flows into both Q1 and Q2 indicates that the charging process of the primary winding of the flyback transformer and the power transfer of the LLC resonant circuit are carried out in parallel and synchronously, and that the two are decoupled.

[0045] When the bypass input of the flyback converter is subjected to reverse u ab Voltage, flyback primary diode Df1 When the flyback transformer is turned off, the charging loop of the primary winding is also turned off. At this time, the energy release loop of the secondary winding of the flyback transformer is enabled, but due to the isolation effect of the flyback transformer, plus the reverse u ab The direction of the resonant current excited by the parallel application of voltage to the LLC resonant cavity module is the same as that of the flyback primary diode D. f1 The opposite conduction direction means that the resonant current will not flow into the flyback converter bypass, indicating that the energy release loop of the flyback transformer secondary winding and the resonant power transfer of the LLC are still carried out in parallel and synchronously, and the two are still decoupled.

[0046] The converter proposed in this invention can be simplified in its working principle as a parallel superposition of a flyback converter and a unidirectional full-bridge LLC resonant converter. Therefore, the converter proposed in this invention retains the frequency conversion and voltage regulation characteristics of the unidirectional full-bridge LLC resonant converter, and can adopt the existing design method of broadening the frequency conversion and voltage regulation parameters, which greatly reduces the difficulty of engineering application. On the other hand, when the inductance of the flyback transformer winding is large enough, the bypass operation of the newly added flyback converter is in the continuous conduction mode (CCM). At this time, the voltage gain relationship of the flyback converter is as shown in equation (1): (1) G F The voltage gain of the flyback converter bypass output is D. f This refers to the duty cycle of the flyback power switch, specifically the duty cycle of Q1 and Q2. In the process of implementing LLC resonant frequency conversion voltage regulation, since the PFM used will maintain the duty cycle of the two complementary power switches in the full-bridge structure at approximately 50% at different power switch operating frequencies, this indicates that D... f G remains constant at 0.5. F The voltage U at the output terminal of the DCT converter remains constant at 1. f It is always equal to the input voltage U of the converter. in This achieves constant voltage output bypass of the flyback converter, forming uncontrolled DCT characteristics.

[0047] Preferably, the converter input voltage U in The voltage is 200V, with main transformer TX1 and flyback transformer TX. f The primary and secondary turns ratios are both 1, and the resonant inductance L r =22uH, resonant capacitor C r =110nF, magnetizing inductance L of main transformer TX1 m 90uH, flyback transformer TX f The magnetizing inductance is 500uH, and the input capacitance C in flyback output capacitor Cf With output capacitor C o Both are 4×470uF. Resonant frequency f r =100kHz, the load resistor at the LLC resonant output terminal is a variable resistor with a resistance range of 16 ohms to 48 ohms, and the bypass load resistor of the flyback converter is 80 ohms.

[0048] The following is Figures 8 to 13 Detailed introduction: Figure 8 The key waveforms obtained from the experiment for compatibility between the two output modes (from top to bottom: LLC resonant output voltage U) o (Red) LLC resonant output load current i o (Green) Voltage U at the output terminal of the DCT converter f (Black) Primary current i of flyback transformer f1 (Blue) and flyback transformer secondary current i f2 (Purple)), from U o with i o The change indicates that the variable frequency voltage regulation feedback closed loop in the embodiment successfully achieves stable voltage control at the LLC resonant output under wide load variations, that is, it achieves a wide range of LLC resonant variable frequency voltage regulation characteristics. Simultaneously, the voltage U at the DCT output of the converter... f Keep it constant. In addition, to observe the bypass transient situation of the flyback converter, different output stages of the LLC resonant frequency converter voltage regulation were selected, namely interval 1 and interval 2. Figure 8 based on Figure 2 The implementation reflects the corresponding LLC output voltage stabilization and regulation process and the constant voltage output of the flyback bypass uncontrolled DCT during the closed-loop operation of the converter.

[0049] Figure 9 The waveform of the frequency converter voltage regulation PI control signal (blue) shows that the operating frequency of the power switch changes during the frequency converter voltage regulation feedback closed-loop control process.

[0050] Figure 10 for Figure 8 The transient waveform of constant voltage output in interval 1 (from top to bottom, the output voltage U of the LLC resonant circuit) o (Red) LLC resonant output load current i o (Green) Voltage U at the output terminal of the DCT converter f (Black) Primary current i of flyback transformer f1 (Blue) and flyback transformer secondary current i f2 (purple)), from i f1 and i f2 The waveform changes indicate that the bypass of the flyback converter realizes the working mechanism of the flyback converter.

[0051] Figure 11 for Figure 8 Interval 2 constant voltage output transient waveform (from top to bottom: LLC resonant output voltage U) o (Red) LLC resonant output load current i o (Green) Voltage U at the output terminal of the DCT converter f (Black) Primary current i of flyback transformer f1 (Blue) and flyback transformer secondary current i f2 (purple)), from i o i f1 and i f2 The waveform changes, and with Figure 10 The comparison shows that the flyback converter bypass realizes the flyback converter operating mechanism at different power switch operating frequencies, and maintains a constant duty cycle D. f It is 0.5.

[0052] Figure 12 for Figure 8 The soft switching in section 1 realizes the transient waveform (from top to bottom, the drain-source voltage U of the first power switch Q1) ds1 (Red) and switch signal U gs1 (Blue) Drain-source voltage U of the third power switch Q3 ds3 (Red) and switch signal U gs3 (Blue) Drain-source voltage U of the second power switch Q2 ds2 (Red) and switch signal U gs2 (Blue) The drain-source voltage U of the fourth power switch Q4 ds4 (Red) and switch signal U gs4 (Blue)), from U ds The waveform changes indicate that after the full-bridge power switches were reused as flyback power switches, excessive extreme voltage stress was significantly suppressed. And from U... ds with U gs The waveform phase relationship indicates that all power switches in the full bridge have achieved ZVS soft switching.

[0053] Figure 13 for Figure 8 The soft switching in section 2 realizes the transient waveform (from top to bottom, the drain-source voltage U of the first power switch Q1) ds1 (Red) and switch signal U gs1 (Blue) Drain-source voltage U of the third power switch Q3 ds3 (Red) and switch signal U gs3 (Blue) Drain-source voltage U of the second power switch Q2 ds2 (Red) and switch signal U gs2(Blue) The drain-source voltage U of the fourth power switch Q4 ds4 (Red) and switch signal U gs4 (Blue)), from U ds The waveform changes indicate that, at different power switch operating frequencies, even after the full-bridge power switches are reused as flyback power switches, excessive extreme voltage stress is still significantly suppressed. Furthermore, from U... ds with U gs The waveform phase relationship indicates that all power switches in the full bridge still achieve ZVS soft switching.

Claims

1. A DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation, characterized in that: Including the converter input voltage U in LLC resonant output voltage U o LLC resonant cavity module, flyback converter bypass, converter DCT output voltage U f The flyback converter bypass and the resonant inductor L in the LLC resonant cavity module r The primary-side switching transistor full-bridge circuit is connected, and the secondary-side diode full-bridge circuit is connected to the secondary winding of the main transformer TX1 in the LLC resonant cavity module. The LLC resonant cavity module includes a main transformer TX1 and a resonant inductor L. r Resonant capacitor C r ; The flyback converter bypass includes the flyback transformer TX f , flyback primary diode D f1 , flyback secondary-side diode D f2 flyback output capacitor C f ; The primary-side switching full-bridge circuit includes an input capacitor C. in The system consists of four power switching transistors, each with a diode and a parasitic capacitance connected in anti-parallel. The power switching transistors include Q1, Q2, Q3, and Q4. The anti-parallel diodes include D1, D2, D3, and D4. The parasitic capacitance includes a first capacitor C. oss1 Second capacitor C oss2 Third capacitor C oss3 and the fourth capacitor C oss4 ; The positive terminal of the converter input voltage is connected to the input capacitor C. in The upper end of the first power switch Q1 and the drain of the fourth power switch Q4 are connected; the source of the first power switch Q1 is connected to the drain of the third power switch Q3 and the flyback primary diode D. f1 anode, resonant inductor L r The left end; the source of the fourth power switch Q4 is connected to the drain of the second power switch Q2 and the flyback transformer TX. f primary winding N p Different-name terminal, primary winding L of main transformer TX1 m The source of the third power switch Q3 is connected to the source of the second power switch Q2 and the input capacitor C. in The lower end of the converter is the negative terminal of the input voltage.

2. The LLC-DCT and frequency conversion voltage regulation dual-characteristic compatible DC-DC resonant converter as described in claim 1, characterized in that: Each power switch of the converter has its own gate and source terminal that receives a switching signal provided by an external circuit. When the switching signal is high, the corresponding power switch is turned on; when the switching signal is low, the corresponding power switch is turned off.

3. The LLC-DCT and frequency conversion voltage regulation dual-characteristic compatible DC-DC resonant converter as described in claim 2, characterized in that: The flyback primary diode D in the flyback converter bypass f1 Cathode-connected flyback transformer TX f primary winding N p Same name terminal; flyback transformer TX f secondary winding N s The opposite terminal is connected to the flyback secondary diode D. f2 anode; flyback transformer TX f secondary winding N s Connect the same terminal to the flyback output capacitor C f The lower end of the converter DCT output voltage is the negative terminal; the flyback secondary diode D... f2 Cathode connected to flyback output capacitor C f The upper end of the converter is the positive terminal of the DCT output voltage.

4. A method for operating a DC-DC resonant converter compatible with both LLC-DCT and variable frequency voltage regulation, characterized in that: Based on the LLC-DCT and variable frequency voltage regulation dual-characteristic compatible DC-DC resonant converter described in claim 3, the converter's operation synchronously includes an uncontrolled DCT output mode and an LLC variable frequency voltage regulation output mode. In both modes, the power switching transistors employ pulse frequency modulation (PFM) during the full switching cycle T. s The process is divided into four stages, from t0 to t4, with the following sequence of actions: (1) [t0~t1] stage: U gs1 U gs2 Output high level, U gs3 U gs4 Output low level; (2) [t1~t2] stage: U gs1 U gs2 U gs3 U gs4 Output low level; (3) [t2~t3] stage: U gs3 U gs4 Output high level, U gs1 U gs2 Output low level; (4) [t3~t4] stage: U gs1 U gs2 U gs3 U gs4 Output low level; In the switching sequence of each mode, t0~t2 and t2~t4 are each the switching period T. s Half of it.

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