A soft-switching full-bridge converter based on a buck-type auxiliary circuit

Abstract

This invention discloses a soft-switching full-bridge converter based on a buck-type auxiliary circuit. The DC voltage module provides DC input voltage to other modules. A passive buck-type auxiliary network with a return flow assists the soft-switching of the lagging bridge arm in the four-switch main power bridge arm with loss-reduction capacitors. The four-switch main power bridge arm with loss-reduction capacitors outputs a high-frequency square wave through the transformer primary side and reduces the circulating current loss of the transformer primary side, while smoothing the auxiliary circuit current. An asymmetric magnetically coupled LC ripple suppression network rectifies and filters the high-frequency square wave, outputting a smooth DC voltage. The soft-switching implementation of this invention is independent of the load state, i.e., independent of the main power circuit. The loss-reduction capacitor reduces the circulating current in the main power circuit without disrupting the soft-switching conditions, while smoothing the buck-type auxiliary circuit current. This results in low switching and conduction losses, improved efficiency, and helps to increase the system's operating frequency, leading to high reliability.

Description

Technical Field

[0001] This invention relates to the field of DC / DC converter technology in power conversion devices, and more particularly to a soft-switching full-bridge converter based on a buck-type auxiliary circuit. Background Technology

[0002] The trend towards higher operating frequencies profoundly impacts transformers and magnetic components in filter circuits of switching power supplies. Increasing the operating frequency effectively reduces the size and weight of magnetic devices, significantly improving the power density and volumetric efficiency of the power system, while also reducing system cost to some extent. However, the increase in switching frequency also brings new technical challenges: due to significant voltage and current overlap during traditional hard switching, the combined effect of junction capacitance and parasitic inductance generates substantial switching losses during the turn-on and turn-off of the switching transistor, accompanied by strong high-frequency electromagnetic interference (EMI). These problems not only limit further improvements in converter efficiency but also constitute a bottleneck for high-frequency power supply design.

[0003] To alleviate the aforementioned problems, soft-switching technology has become a key path to resolving the contradiction between high frequency and high efficiency. Among these, soft-switching schemes, represented by zero-voltage switching (ZVS) and zero-current switching (ZCS), have received widespread attention. Among various topologies, the full-bridge converter is widely used due to its high power handling capability and good engineering adaptability. However, in practical designs, the soft-switching implementation of a full-bridge converter typically relies on the load current, especially under light load conditions, where the system needs to maintain a high circulating current to avoid disrupting the soft-switching conditions. Although this circulating current can assist in achieving soft switching, it itself has circulating current conduction losses. Especially under light load conditions, the circulating current conduction losses may even exceed the power of the load itself, leading to a significant decrease in the overall system efficiency. Therefore, how to effectively suppress circulating current losses while achieving soft switching has become a key technical challenge in the design of full-bridge converters for both high frequency and high efficiency. Summary of the Invention

[0004] Technical Objective: To address the shortcomings of existing full-bridge converters, this invention discloses a soft-switching full-bridge converter based on a buck-type auxiliary circuit. It constructs a buck-type auxiliary circuit with independent load and independent of the transformer primary-side circulating current to achieve full-range soft switching. Simultaneously, a small-value loss-reduction capacitor C is connected in series with the transformer primary side. b To achieve smooth buck-type auxiliary circuit current, while simultaneously reducing circulating current on the primary side of the fast step-down transformer, and minimizing circulating current conduction losses.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution.

[0006] A soft-switching full-bridge converter based on a buck-type auxiliary circuit includes a DC voltage module, a return-current buck passive auxiliary network, a four-switch main power bridge arm with loss reduction capacitors, and an asymmetric magnetically coupled LC ripple suppression network.

[0007] The DC voltage module is used to provide DC input voltage to the return buck passive auxiliary network and the four-switch main power bridge arm with loss reduction capacitors;

[0008] A passive auxiliary buck network is used to assist in the soft switching of the lagging bridge arm in the main power bridge arm with a four-switch transistor and loss reduction capacitor. It includes a first energy storage capacitor C1, a second energy storage capacitor C2, and a return buck inductor L1, which form a buck-like circuit. The buck-like circuit is used to provide DC return current for independent loads. The input capacitors C1 and C2 are connected in series to form a capacitor bridge arm that is connected across the two ends of the DC voltage module. The return buck inductor L1 is connected between the midpoint of the capacitor bridge arm and the opposite terminal on the primary side of the transformer.

[0009] The main power bridge arm, equipped with a loss-reduction capacitor and four switching transistors, is used for finite bipolar modulation of DC-DC converters. It outputs a high-frequency square wave through the primary side of the transformer and reduces circulating current losses on the primary side, while smoothing the buck-type auxiliary circuit current. It includes the main power bridge and the primary side of transformer T1. The main power bridge includes power switches Q1 through Q4. A leakage inductance L is connected in series between the midpoints of the upper and lower bridge arms of the main power bridge. r Transformer T1 primary side, loss reduction capacitor C b Furthermore, the magnetizing inductor L is connected in parallel across the primary side of transformer T1. m ;

[0010] An asymmetric magnetically coupled LC ripple suppression network is used to rectify and filter the high-frequency square wave output from the primary side of transformer T1 in the four-switch main power bridge arm with loss reduction capacitor, resulting in a smooth DC voltage output.

[0011] Furthermore, the first power switch Q1 and the second power switch Q2 form the upper bridge arm, and the third power switch Q3 and the fourth power switch Q4 form the lower bridge arm. The gates of the first power switch Q1 to the fourth power switch Q4 are controlled by a bipolar modulation signal.

[0012] Furthermore, the gates of the first power switch Q1 to the fourth power switch Q4 are controlled by bipolar modulation signals, including: the leading bridge arm adopts variable duty cycle control and the lagging bridge arm adopts a limited bipolar control mode with a constant duty cycle.

[0013] Furthermore, the source of the first power switch Q1 is connected to the positive output terminal of the DC voltage module, and its drain is connected to the source and leakage inductance L of the second power switch Q2. r One end, leakage Lr The other end is connected to the corresponding terminal on the primary side of transformer T1; the corresponding terminal on the primary side of transformer T1 is also connected to the magnetizing inductor L. m One end is connected to the magnetizing inductor L m The other end is connected to the opposite end of the primary side of transformer T1; the opposite end of the primary side of transformer T1 is also connected to one end of the return buck inductor L1, and the other end of the return buck inductor L1 is connected to the midpoint of the capacitor bridge arm of input capacitor C1 and input capacitor C2.

[0014] The drain of the second power switch Q2 is connected to the source and leakage inductance L of the first power switch Q1. r One end of the circuit has its source connected to the negative output terminal of the DC voltage module;

[0015] The third power switch Q3 has its drain connected to the positive output terminal of the DC voltage module, and its source connected to the drain of the fourth power switch Q4 and the loss reduction capacitor C. b One end, loss reduction capacitor C b The other end is connected to the opposite-named terminal on the primary side of transformer T1;

[0016] The fourth power switch Q4 has its drain connected to the source of the third power switch Q3 and the loss reduction capacitor C. b One end of the circuit has its source connected to the negative output terminal of the DC voltage module.

[0017] Furthermore, the loss reduction capacitor C b For the nanofat level, the calculation formula includes:

[0018]

[0019] V cbp ≤2D effmax (V in -2nV out )

[0020] Among them, I out For the output current, D effmax T is the maximum effective duty cycle of the secondary side of transformer T1. s For the switching cycle, C oss For the output capacitor of the power switch transistor, V in V is the input voltage. cbp To reduce the peak voltage of the capacitor, n is the turns ratio of transformer T1, V out This is the output voltage.

[0021] Furthermore, the formula for calculating the return buck inductor L1 includes:

[0022]

[0023] Among them, Ts For the switching cycle, I peak To accommodate the peak current flowing back through buck inductor L1, V in For the input voltage, C oss The output capacitor of the power switch is n, where n is the turns ratio of transformer T1, and V is V. out This is the output voltage.

[0024] Furthermore, the full-wave rectifier circuit includes diodes D1 and D2, and the filter circuit includes filter inductor L. f and filter capacitor C f This forms an LC filter circuit; in the asymmetric magnetic coupling LC ripple suppression network, diodes D1 and D2 perform full-wave rectification on the high-frequency square wave output from the primary side of the transformer, and LC filter the output, thereby outputting a smooth DC voltage.

[0025] Furthermore, the anode of diode D1 is connected to the same-name terminal on the secondary side of transformer T1, and the center tap on the secondary side of transformer T1 is connected to filter capacitor C. f One end of the transformer T1 is connected to the anode of diode D2 at the opposite end of the secondary side.

[0026] The anode of diode D1 is connected to the same-name terminal on the secondary side of transformer T1, and the cathode of diode D1 is connected to the cathode of diode D2 and the filter inductor L. f One end;

[0027] The anode of diode D2 is connected to the opposite terminal on the secondary side of transformer T1, and the cathode of diode D2 is connected to the cathode of diode D1 and the filter inductor L. f One end;

[0028] Filter inductor L f One end is connected to the cathodes of diode D1 and D2, and the other end is connected to the output filter capacitor C. f One end.

[0029] Filter capacitor C f One end is connected to the filter inductor L f One end is connected to the center tap on the secondary side of transformer T1, and the other end is connected to the filter capacitor C. f The two ends serve as the positive and negative terminals of the output DC voltage, which are also the positive and negative terminals of the output DC voltage of the soft-switching full-bridge converter of this invention, and are used to connect with the load resistor R. L in parallel.

[0030] Beneficial effects:

[0031] (1) Provide full-range soft-switching hardware circuit conditions for the full-bridge converter by using the backflow buck passive auxiliary network;

[0032] (2) The return buck passive auxiliary network generates soft switching current by using two power switches Q3 and Q4 in the four-switch main power bridge arm with loss reduction capacitor, without the need for additional switching transistors and with fewer passive auxiliary components.

[0033] (3) Under finite bipolar modulation, i.e., under the condition of fixed duty cycle control of the hysteresis arm, the value of the return buck inductor L1 is designed to meet the minimum peak inductance current required for soft switching while reducing the loss capacitor C. b It smooths the auxiliary circuit current and reduces the circulating current velocity to zero, resulting in low circuit circulating current conduction loss.

[0034] (4) The passive auxiliary network of the return buck is independent of the main power bridge arm of the four-switch transistor with loss reduction capacitor. That is, the soft switching is independent of the main power circuit. The switching loss and conduction loss are low, the efficiency is improved, which helps to increase the operating frequency of the system, reduce the size of the output filter, and improve the reliability. Attached Figure Description

[0035] Figure 1 This is a topology diagram of a soft-switching full-bridge converter based on a buck-type auxiliary circuit according to the present invention;

[0036] Figure 2 This is a timing diagram of the drive signal, bridge arm midpoint voltage difference, junction capacitance voltage, transformer primary current, inductor current, and secondary rectifier diode current of a soft-switching full-bridge converter based on a buck-type auxiliary circuit according to the present invention.

[0037] Figures 3 to 8 This is a topology mode diagram of the first stage of a soft-switching full-bridge converter based on a buck-type auxiliary circuit according to the present invention.

[0038] Figures 9-14 This is a topology mode diagram of the second stage of a soft-switching full-bridge converter based on a buck-type auxiliary circuit according to the present invention. Detailed Implementation

[0039] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0040] As attached Figure 1As shown, a soft-switching full-bridge converter based on a buck-type auxiliary circuit includes a DC voltage module 1, a return-flow buck passive auxiliary network 2, a four-switch main power bridge arm with loss reduction capacitor 3, and an asymmetric magnetic coupling LC ripple suppression network 4.

[0041] DC voltage module 1 is used to provide DC input voltage to the return buck passive auxiliary network 2 and the four-switch main power bridge arm 3 with loss reduction capacitor;

[0042] DC input voltage U i The positive terminal is used as the positive output terminal of DC voltage module 1, and the DC input voltage U i The negative terminal is used as the negative output terminal of DC voltage module 1.

[0043] The passive auxiliary network 2 is used to assist the soft switching of the hysteresis bridge arm in the main power bridge arm 3 with a four-switch transistor and a loss reduction capacitor. It includes a first energy storage capacitor C1, a second energy storage capacitor C2, and a return buck inductor L1 that form the buck circuit. The buck circuit is used to provide the return current for the independent four-switch transistor main power bridge arm with a loss reduction capacitor. The input capacitors C1 and C2 are connected in series to form a capacitor bridge arm that is connected across the two ends of the DC voltage module 1. The return buck inductor L1 is connected between the midpoint of the capacitor bridge arm and the opposite terminal on the primary side of the transformer in the four-switch transistor main power bridge arm 3 with a loss reduction capacitor.

[0044] Among them, input capacitors C1 and C2 are connected in series to form a capacitor bridge arm. One end is connected to the positive output terminal of DC voltage module 1, and the other end is connected to the negative output terminal of DC voltage module 1. The midpoint of the capacitor bridge arm is connected to one end of the return buck inductor L1, and the other end of the return buck inductor L1 is connected to the midpoint of the opposite-name terminal on the primary side of the transformer in the main power bridge arm 3 of the four-switch transistor power bridge arm 3 of the loss reduction capacitor.

[0045] The main power bridge arm 3, with a loss-reduction capacitor and four switching transistors, is used for finite bipolar modulation of DC-DC converters and outputs a high-frequency square wave through the primary side of the transformer while reducing the circulating current loss on the primary side of the transformer. It includes the main power bridge and the primary side of transformer T1. The main power bridge includes power switches Q1 through Q4. A leakage inductance L is connected in series between the midpoints of the upper and lower arms of the main power bridge. r Transformer T1 primary side, loss reduction capacitor C b Furthermore, the magnetizing inductor L is connected in parallel across the primary side of transformer T1. m ;

[0046] In this configuration, the first power switch Q1 and the second power switch Q2 form the upper bridge arm, with a fixed phase difference of 180° between them; the third power switch Q3 and the fourth power switch Q4 form the lower bridge arm, with a fixed phase difference of 180° between them; the gates of the first power switch Q1 to the fourth power switch Q4 are controlled by a bipolar modulation signal, with the first power switch Q1 and the fourth power switch Q4 simultaneously turned on, the second power switch Q2 and the third power switch Q3 simultaneously turned on, the third power switch Q3 and the fourth power switch Q4 operating with a fixed duty cycle, and the first power switch Q1 and the second power switch Q2 operating with a variable duty cycle;

[0047] The drain of the first power switch Q1 is connected to the positive output terminal of the DC voltage module 1, and its source is connected to the drain and leakage inductance L of the second power switch Q2. r One end, leakage L r The other end is connected to the corresponding terminal on the primary side of transformer T1; the corresponding terminal on the primary side of transformer T1 is also connected to the magnetizing inductor L. m One end is connected to the magnetizing inductor L m The other end is connected to the opposite end of the primary side of transformer T1; the opposite end of the primary side of transformer T1 is also connected to one end of the return buck inductor L1, and the other end of the return buck inductor L1 is connected to the midpoint of the capacitor bridge arm of input capacitor C1 and input capacitor C2.

[0048] The drain of the second power switch Q2 is connected to the source and leakage inductance L of the first power switch Q1. r One end of the circuit has its source connected to the negative output terminal of the DC voltage module;

[0049] The third power switch Q3 has its drain connected to the positive output terminal of the DC voltage module, and its source connected to the drain of the fourth power switch Q4 and the loss reduction capacitor C. b One end, loss reduction capacitor C b The other end is connected to the opposite-named terminal on the primary side of transformer T1;

[0050] The fourth power switch Q4 has its drain connected to the source of the third power switch Q3 and the loss reduction capacitor C. b One end of the circuit has its source connected to the negative output terminal of the DC voltage module.

[0051] The asymmetric magnetically coupled LC ripple suppression network 4 is used to rectify and filter the high-frequency square wave output from the primary side of transformer T1 in the four-switch main power bridge arm 3 with loss reduction capacitor, resulting in a smooth DC voltage output. The asymmetric magnetically coupled LC ripple suppression network 4 includes the secondary side of transformer T1, a full-wave rectifier circuit, and a filter circuit. The full-wave rectifier circuit includes diodes D1 and D2, and the filter circuit includes a filter inductor L. f and filter capacitor C f This forms an LC filter circuit;

[0052] The anode of diode D1 is connected to the same-name terminal on the secondary side of transformer T1, and the center tap on the secondary side of transformer T1 is connected to filter capacitor C. f One end of the transformer T1 is connected to the anode of diode D2 at the opposite end of the secondary side.

[0053] The anode of diode D1 is connected to the same-name terminal on the secondary side of transformer T1, and the cathode of diode D1 is connected to the cathode of diode D2 and the filter inductor L. f One end;

[0054] The anode of diode D2 is connected to the opposite terminal on the secondary side of transformer T1, and the cathode of diode D2 is connected to the cathode of diode D1 and the filter inductor L. f One end;

[0055] Filter inductor L f One end is connected to the cathodes of diode D1 and D2, and the other end is connected to the output filter capacitor C. f One end.

[0056] Filter capacitor C f One end is connected to the filter inductor L f One end is connected to the center tap on the secondary side of transformer T1, and the other end is connected to the filter capacitor C. f The two ends serve as the positive and negative terminals of the output DC voltage, which are also the positive and negative terminals of the output DC voltage of the soft-switching full-bridge converter of this invention, and are used to connect with the load resistor R. L in parallel.

[0057] In other words, the asymmetric magnetically coupled LC ripple suppression network 4 uses diodes D1 and D2 to perform full-wave rectification and LC filtering on the high-frequency square wave output from the primary side of the transformer, thereby producing a smooth DC voltage.

[0058] Loss reduction capacitor C b For nanofarads, reduce the loss capacitor C b The value is much smaller than that of traditional DC blocking capacitors, and its calculation formula is:

[0059]

[0060] Among them, Iout For the output current, i.e., the output current of the soft-switching full-bridge converter, D effmax T is the maximum effective duty cycle of the secondary side of transformer T1. s For the switching cycle, C oss For the output capacitor of the power switch transistors, the first power switch transistors Q1 to the fourth power switch transistors Q4 of the main power full bridge in this application are the same, V in The input voltage, specifically the input voltage provided by the DC voltage module, is V. cbp The peak voltage of the loss-reducing capacitor is given by n, where n is the turns ratio of transformer T1; here, the peak voltage V of the loss-reducing capacitor can be selected. cbp ≤2D effmax (V in -2nV out ), where V out The output voltage refers to the output voltage of the soft-switching full-bridge converter. A higher peak voltage of the loss-reduction capacitor results in lower circulating current conduction losses during commutation, but also higher voltage stress. Conversely, a lower peak voltage reduces additional voltage stress but also reduces circulating current conduction losses less, eventually rendering the loss-reduction function ineffective and only serving to prevent transformer bias. Therefore, a trade-off must be struck. Reducing the circulating current here will not violate the ZVS soft-switching condition.

[0061] The value of the return buck inductor L1 is determined based on the minimum current required for the soft switching of the hysteresis arm, and its calculation formula is as follows:

[0062]

[0063] Among them, T s For the switching cycle, I peak To accommodate the peak current flowing back through buck inductor L1, V in The input voltage is used; the peak current of the return buck inductor L1 is a smoothed peak current, which can be selected here. Among them, L r For leakage sensing, L m The inductor is the excitation inductor. The higher the peak current of the inductor, the easier it is to achieve soft switching, but the higher the conduction loss of the auxiliary circuit. The lower the peak current of the inductor, the lower the conduction loss of the auxiliary circuit, but it may destroy the soft switching condition of the hysteresis arm. Therefore, there exists a minimum value to ensure the realization of soft switching while minimizing the conduction loss of the auxiliary circuit.

[0064] This invention employs a finite bipolar control mode with variable duty cycle control of the leading arm (including the first power switch Q1 and the second power switch Q2) and constant duty cycle control of the lagging arm (including the third power switch Q3 and the fourth power switch Q4). By bridging the lagging arm with a synchronous rectified buck return circuit independent of the load, it achieves independent energy storage and release of junction capacitance without relying on circulating current, thus enabling full-range soft switching of all switches. Simultaneously, it smooths the auxiliary circuit current through loss-reducing capacitors, and reduces the velocity drop of the circulating current on the primary side of the transformer, thereby reducing conduction losses. In the primary current i... p In the positive first half-cycle, the first power switch Q1 turns from on to off, the second power switch Q2 is normally closed, the third power switch Q3 is normally closed, and the fourth power switch Q4 is normally on; the primary current i p In the negative second half-cycle, the first power switch Q1 is normally closed, the second power switch Q2 changes from on to off, the third power switch Q3 is normally on, and the fourth power switch Q4 is normally closed. The following uses an ideal signal waveform. Figure 2 Modal diagrams Figures 3-14 The working principle and two-stage operating modes of the soft-switching full-bridge converter of this invention are specifically analyzed, wherein the primary current i of the transformer in the first stage is... p Greater than zero, the primary current i of the second-stage transformer p Less than zero.

[0065] Phase 1 Working Mode 1: Figure 3 The circuit shown corresponds to Figure 2 In the interval [t0, t1] shown, during this operating state, the first power switch Q1 and the fourth power switch Q4 are turned on, while the second power switch Q2 and the third power switch Q3 are turned off, and diodes D1 and D2 are turned on simultaneously. The DC input voltage U... i Since it is applied across the leakage inductance, the primary current i can be considered as... p DC input voltage U i Under the influence of [the current], the return buck inductor current i1 rises rapidly and linearly. The magnitude of the return buck inductor current i1 decreases smoothly, and the primary current i […]. p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b During discharge, the current in diode D1 increases linearly, while the current in diode D2 decreases linearly. The first energy storage capacitor C1 and the second energy storage capacitor C2 in the return-to-bus passive auxiliary network 2 have the same capacitance value, and the current flowing through both capacitors is half of the return-to-bus inductor current i1. At time t1, the current in diode D2 drops to zero, and the current in diode D1 is solely due to the load resistance R. L Power supply complete; this phase ends.

[0066] Phase 1 Working Mode 2: Figure 4 The circuit shown corresponds to Figure 2 In the interval [t1, t2] shown, during this operating state, the first power switch Q1 and the fourth power switch Q4 are turned on, while the second power switch Q2 and the third power switch Q3 are turned off. Diode D1 is turned on, and all diodes D2 are turned off. The DC input voltage U... i The primary current i is applied across the leakage inductance and the magnetizing inductance. p DC input voltage U i Under the influence of [various factors], the current increases linearly, but the slope of the increase is lower than that of the previous mode. The return buck inductor current i1 increases smoothly, and the primary current i [increases / decreases]. p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b The circuit discharges to zero and continues to charge forward. During this time, the current in diode D1 increases linearly and supplies power to the load independently. At time t2, the first power switch Q1 turns off, and this phase ends.

[0067] Phase 1 Working Mode 3: Figure 5 The circuit shown corresponds to Figure 2 In the interval [t2, t3] shown, during this operating state, the fourth power switch Q4 is turned on, while the first power switch Q1, the second power switch Q2, and the third power switch Q3 are turned off, and diodes D1 and D2 are turned on simultaneously. The primary current i p The junction capacitances of the first power switch Q1 and the second power switch Q2 are charged and discharged, and due to the primary current i p This is the peak value, allowing for easy charging and discharging. The return buck inductor current i1 rises smoothly, and the primary current i... p Together with the return buck inductor current i1, C b During charging, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. Since the junction capacitances of the power switching transistors are equal, the charging and discharging currents of both capacitors are the primary current i. p Half of it. This stage ends when the junction capacitances of the first power switch Q1 and the second power switch Q2 are fully charged and discharged at time t3.

[0068] Phase 1 Working Mode 4: Figure 6 The circuit shown corresponds to Figure 2 In the interval [t3, t4] shown, during this operating state, the fourth power switch Q4 is turned on, while the first power switch Q1, the second power switch Q2, and the third power switch Q3 are turned off. Diodes D1 and D2 are simultaneously turned on, and the secondary side enters freewheeling mode. Due to the loss reduction capacitor C of the nanofarad stage... b The large reverse voltage drop U formed during charging at its two ends previously b Apply to leakage sensing L r At both ends, the primary current i is realized. pThe rapid decrease reduces conduction losses, and the return buck inductor current i1 rises smoothly, while the primary current i p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b During charging, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. At time t4, the fourth power switch Q4 is turned off, ending this phase.

[0069] Phase 1 Working Mode 5: Figure 7 The circuit shown corresponds to Figure 2 In the interval [t4, t5] shown, during this operating state, all power switches are off, and diodes D1 and D2 are simultaneously on, in a freewheeling state on the secondary side. The primary current i... p The return buck inductor current i1 simultaneously charges and discharges the junction capacitance of the fourth power switch Q4 and the third power switch Q3, and due to the primary current i p At this point, the current is very small, while the return buck inductor current i1 is approximately at its peak value. This is sufficient to achieve charging and discharging solely through the return buck inductor current i1. Furthermore, due to the fixed duty cycle of the lag arm, the maximum L1 value required by the design to meet the minimum peak current needed for soft switching can be supplied to reduce unnecessary inductor losses. The return buck inductor current i1 is at the junction capacitance of the third power switch Q3 from V... in During the discharge to 0V, the voltage first rises and then falls, and the primary current i p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b During charging, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. This stage ends at time t5 when the junction capacitances of the fourth power switch Q4 and the third power switch Q3 are fully charged and discharged.

[0070] Phase 1 Working Mode 6: Figure 8 The circuit shown corresponds to Figure 2 In the interval [t5, t6] shown, during this operating state, all power switches are off, diodes D1 and D2 are simultaneously on, and the secondary side is in freewheeling mode. The return buck inductor current i1 decreases smoothly, and the primary side current i p The primary current i is approximately zero and about to reverse. p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b During charging, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. At time t6, the first power switch Q2 and the fourth power switch Q3 are turned on, and this stage ends.

[0071] Second-stage working mode 1: Figure 9 The circuit shown corresponds to Figure 2In the interval [t6, t7] shown, during this operating state, the second power switch Q2 and the third power switch Q3 are turned on, while the first power switch Q1 and the fourth power switch Q4 are turned off, and diodes D1 and D2 are turned on simultaneously. The DC input voltage is applied across the leakage inductance, therefore the primary current i can be considered... p Under the influence of DC input voltage, it rises rapidly in reverse linearly. The magnitude of the return buck inductor current i1 decreases smoothly, and the primary current i p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b During discharge, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. At time t7, the current in diode D1 drops to zero, and the current in diode D2 supplies power to the load alone, marking the end of this phase.

[0072] Second-stage working mode 2: Figure 10 The circuit shown corresponds to Figure 2 In the interval [t7, t8] shown, during this operating state, the second power switch Q2 and the third power switch Q3 are turned on, while the first power switch Q1 and the fourth power switch Q4 are turned off. Diode D2 is turned on, and diode D1 is turned off. A DC input voltage is applied across the leakage inductance and the magnetizing inductance, and the primary current i... p Under the influence of DC input voltage, the reverse linear rise occurs, but the rise slope is lower than that of the previous mode. The return buck inductor current i1 decreases smoothly, and the primary current i p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b The circuit discharges to zero and continues to reverse charge; during this time, the current from diode D2 supplies power to the load alone. At time t8, the second power switch Q2 turns off, ending this phase.

[0073] Second-stage working mode 3: Figure 11 The circuit shown corresponds to Figure 2 In the interval [t8, t9] shown, during this operating state, the third power switch Q3 is turned on, while the first power switch Q1, the second power switch Q2, and the fourth power switch Q4 are turned off, and diodes D1 and D2 are turned on simultaneously. The primary current i p The junction capacitances of the second power switch Q2 and the first power switch Q1 are charged and discharged, and due to the primary current i p The magnitude is at its peak at this point, allowing for easy charging and discharging. The return buck inductor current i1 rises smoothly in the reverse direction, and the primary current i... p Together with the return buck inductor current i1, C b Reverse charging. This stage ends when the junction capacitance of the second power switch Q2 and the first power switch Q1 is fully charged and discharged at time t9.

[0074] Second-stage working mode 4: Figure 12 The circuit shown corresponds to Figure 2 As shown [t9, t 10 In this operating range, the third power switch Q3 is turned on, while the first power switch Q1, the second power switch Q2, and the fourth power switch Q4 are turned off, and diodes D1 and D2 are turned on simultaneously. The secondary side enters freewheeling mode. Due to the very small loss reduction capacitor C... b The value, the large reverse voltage drop U formed during the previous charging. b Apply to leakage sensing L r At both ends, the primary current i is realized. p The magnitude of the current decreases rapidly, reducing conduction losses. The return buck inductor current i1 rises smoothly in the reverse direction, and the primary current i... p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b Reverse charging. (In t) 10 At the moment the fourth power switch Q4 is turned off, this stage ends.

[0075] Second-stage working mode 5: Figure 13 The circuit shown corresponds to Figure 2 As shown [t] 10 , t 11 In this operating range, all switches are off, and diodes D1 and D2 are simultaneously on, resulting in freewheeling current on the secondary side. The primary current i... p The return buck inductor current i1 simultaneously charges and discharges the junction capacitance of the third power switch Q3 and the fourth power switch Q4, and due to the primary current i p At this point, the value is very small, while the magnitude of the return buck inductor current i1 is approximately at its peak, sufficient to achieve charging and discharging solely through the return buck inductor current i1. The magnitude of the return buck inductor current i1 is determined by the junction capacitance of the fourth power switch Q4 from V... in During the discharge to 0V, the voltage first rises and then falls, and the primary current i p Together with the return buck inductor current i1, it affects the loss reduction capacitor C. b Reverse charging. This stage ends when the junction capacitance of the third power switch Q3 and the fourth power switch Q4 is fully charged and discharged.

[0076] Second-stage working mode 6: Figure 14 The circuit shown corresponds to Figure 2 As shown [t] 11 , t 12 In this operating range, all switches are off, and diodes D1 and D2 are simultaneously on, resulting in freewheeling current on the secondary side. The primary current i... p The return buck inductor current i1 decreases smoothly as it approaches zero and is about to reverse, while the primary current i... pTogether with the return buck inductor current i1, it affects the loss reduction capacitor C. b Reverse charging. (In t) 12 At this moment, the first power switch Q1 and the fourth power switch Q4 are turned on, and this stage ends.

[0077] Analysis of the inverter's operating modes reveals the following advantages of this circuit:

[0078] (1) All power switching transistors can achieve full-range soft switching, and the converter has few passive auxiliary devices.

[0079] (2) The return buck passive auxiliary network generates soft switching current by using two power switches Q3 and Q4 in the four-switch main power bridge arm with loss reduction capacitors, without the need for additional switching transistors and with fewer passive auxiliary devices.

[0080] (3) Under finite bipolar modulation, i.e., under the condition of fixed duty cycle control of the hysteresis arm, the value of the return buck inductor L1 is designed to meet the minimum peak inductance current required for soft switching while reducing the loss capacitor C. b It smooths the auxiliary circuit current and reduces the circulating current velocity to zero, resulting in low circuit circulating current conduction loss.

[0081] (4) The passive auxiliary network of the return buck is independent of the main power bridge arm of the four-switch transistor with loss reduction capacitor. That is, the soft switching is independent of the main power circuit. The switching loss and conduction loss are low, the efficiency is improved, which helps to increase the operating frequency of the system, reduce the size of the output filter, and improve the reliability.

[0082] In the embodiments of this application, the terms "first" and "second" are used only as name identifiers and do not represent their importance ranking.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A soft-switching full-bridge converter based on a buck-type auxiliary circuit, characterized in that, The direct current voltage module, the backflow buck passive auxiliary network, the four-switch main power bridge arm with loss-reducing capacitor, and the asymmetric magnetic coupling LC ripple suppression network are connected in series. The direct current voltage module is used for providing a direct current input voltage for the backflow buck passive auxiliary network and the four-switch main power bridge arm with loss-reducing capacitor. The application discloses a reflux buck passive auxiliary network for assisting in realizing soft switching of a lagging bridge arm in a main power bridge arm with a loss-reducing capacitor four-switch tube, and comprises an input capacitor for constituting a buck circuit , an input capacitor , a reflux buck inductor ; the buck circuit is used for providing stable reflux current of the independent loss-reducing capacitor four-switch tube main power bridge arm; the input capacitor , an input capacitor is connected in series with the input capacitor , and the series connection is connected across the two ends of a direct-current voltage module; a reflux buck inductor is connected between the midpoint of the capacitor bridge arm and the opposite-phase end of the transformer primary side . The application discloses a main power bridge arm with four switching tubes and a loss-reducing capacitor, which is used for limited bipolar modulation of an inverter direct current and outputs a high-frequency square wave through a transformer primary side and reduces the transformer primary side circulating current loss, simultaneously smoothes a buck type auxiliary loop current, and comprises a main power full bridge and a transformer The main power full bridge comprises first to fourth power switching tubes The first to fourth power switching tubes are connected in series The main power full bridge is connected in series between the upper and lower bridge arm midpoints of the main power full bridge The transformer The main power full bridge comprises a loss-reducing capacitor The transformer The main power full bridge is connected in parallel with an excitation inductance at the two ends of the transformer primary side ​ Asymmetric magnetic coupled LC ripple rejection network for transformer in a four switch main power bridge leg with lossy capacitance The high-frequency square wave of the primary side is rectified and filtered to output a smooth DC voltage.

2. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 1, characterized in that: a first power switch tube a second power switch tube a third power switch tube a fourth power switch tube a fifth power switch tube a sixth power switch tube the gates of the first to fourth power switch tubes are controlled by a bipolar modulation signal 3. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 2, characterized in that: The first power switch tube The fourth power switch tube The gate of the fourth power switch tube is controlled by a bipolar modulation signal, including: the upper bridge arm, that is, the leading bridge arm adopts variable duty cycle control, and the lower bridge arm, that is, the lagging bridge arm adopts a limited bipolar control mode with a fixed duty cycle.

4. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 1, characterized in that: First power switch transistor Its drain is connected to the positive output terminal of the DC voltage module, and its source is connected to the second power switch. Source, leakage One end, leakage sensation The other end is connected to the transformer The same-name terminal on the original side; transformer The same terminal on the original side is also related to the magnetizing inductor. One end is connected to the magnetizing inductor. The other end is connected to the transformer The opposite terminal on the original side; transformer The non-standard terminal on the original side is also connected to the return buck inductor. One end is connected to the return buck inductor. The other end is connected to the input capacitor. Input capacitor Connect the midpoints of the capacitor bridge arms; The second power switch tube The drain of the first power switch tube The source of the first power switch tube The negative output end of the direct current voltage module Third power switch Its drain is connected to the positive output terminal of the DC voltage module, and its source is connected to the fourth power switch. Drain capacitor, loss reduction capacitor One end, loss reduction capacitor The other end is connected to the transformer The synonymous end of the original side; The fourth power switch tube The drain of the third power switch tube The source of the fourth power switch tube The negative output end of the DC voltage module 5. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 1, characterized in that: Lossy capacitor For nano farad level, its calculation formula includes: ， wherein, is the output current, is the transformer is the maximum effective duty cycle of the secondary side, is the switching period, is the output capacitance of the power switch, is the input voltage, is the peak voltage of the loss reduction capacitor, is the transformer is the turns ratio, is the output voltage.

6. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 1, characterized in that: A buck inductor for a flyback buck converter A formula for calculating The direct current voltage module, the backflow buck passive auxiliary network, the four-switch main power bridge arm with loss-reducing capacitor, and the asymmetric magnetic coupling LC ripple suppression network are connected in series. ， wherein, is the switching period, is the peak current of the flyback buck inductor is the peak current of the flyback buck inductor, is the input voltage, is the output capacitance of the power switch, is the transformer turns ratio, is the output voltage.

7. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 1, characterized in that: Asymmetric magnetic coupling LC ripple suppression network comprising a transformer connected The secondary side, full-wave rectifier circuit and filter circuit; the full-wave rectifier circuit comprises a diode And a diode The filter circuit comprises a filter inductor And a filter capacitor , constitute LC filter circuit; in asymmetric magnetic coupling LC ripple suppression network, through the diode And a diode Full-wave rectification is carried out on the high-frequency square wave output by the primary side of the transformer, and LC filtering is carried out, so as to output a smooth DC voltage.

8. The soft-switching full-bridge converter based on a buck-type auxiliary circuit according to claim 7, characterized in that: transformer secondary side same name end connection diode anode of the transformer secondary side center tap connection filter capacitor one end of the transformer secondary side opposite name end connection diode anode of the transformer diode anode of the transformer the same name end of the secondary side, diode cathode of the diode cathode, filter inductor one end; diode anode of the transformer secondary side of the transformer cathode of the diode cathode of the filter inductor one end of the filter inductor filtering inductance one end of the diode cathode of the diode cathode of the diode, the other end of the diode one end of the output filtering capacitor filtering capacitor one end of the filtering inductor one end of the transformer the center tap of the secondary side, two ends of the filtering capacitor respectively as the positive and negative poles of the output DC voltage, that is, the positive and negative poles of the output DC voltage of the soft switching full-bridge converter, for parallel connection with the load resistor ​

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