Soft-switching full-bridge converter based on buck-type auxiliary loop

Abstract

The invention discloses a buck-type auxiliary loop-based soft-switching full-bridge converter, and the converter is characterized in that a DC voltage module is used for providing DC input voltage for other modules; the backflow buck passive auxiliary network is used for assisting the realization of a lagging bridge arm soft switch in a four-switch tube main power bridge arm with a loss reduction capacitor; the four-switch-tube main power bridge arm with the loss reduction capacitor is used for outputting high-frequency square waves through the primary side of the transformer, reducing the circulation loss of the primary side of the transformer and smoothing the current of an auxiliary loop. And the asymmetric magnetic coupling LC ripple suppression network is used for rectifying and filtering the high-frequency square waves and outputting smooth direct-current voltage. The soft switch is independent of the load state, namely independent of the main power loop, the loss reduction capacitor reduces the circulating current of the main power loop and does not damage the soft switch condition, meanwhile, the buck type auxiliary loop current is smoothed, the switching loss and the conduction loss are low, the efficiency is improved, the working frequency of the system is improved, and the reliability is high.

Description

Technical Field

[0001] The present invention relates to the technical field of DC / DC converters in electric energy conversion devices, and in particular to a soft-switching full-bridge converter based on a buck-type auxiliary loop. Background Art

[0002] The trend toward higher frequencies has a profound impact on the transformers and magnetic components in filter circuits within switching power supply circuits. Increasing operating frequencies can effectively reduce the size and weight of magnetic components, significantly improving the power density and volumetric efficiency of power supply systems while also reducing system costs to a certain extent. However, the increase in switching frequency also presents new technical challenges: due to the significant voltage and current overlap in traditional hard switching processes, the combined effects of junction capacitance and parasitic inductance result in significant switching losses at the moment the switch turns on and off, accompanied by strong high-frequency electromagnetic interference (EMI). These issues not only limit further improvements in converter efficiency but also pose a bottleneck to high-frequency power supply design.

[0003] To alleviate these issues, soft-switching technology has become a key path to resolving the conflict between high frequency and high efficiency. Soft-switching solutions, represented by zero-voltage switching (ZVS) and zero-current switching (ZCS), have garnered widespread attention. Among various topologies, the full-bridge converter is widely used due to its high power handling capability and excellent engineering adaptability. However, in practical designs, the implementation of soft switching in full-bridge converters often depends on the load current. Especially under light load conditions, the system must maintain a high circulating current to prevent the soft-switching condition from being compromised. While this circulating current can aid in soft switching, it also carries its own circulating current conduction losses. Especially under light load conditions, these losses can even exceed the load power, significantly reducing overall system efficiency. Therefore, how to achieve soft switching while effectively suppressing circulating current losses has become a key technical challenge in achieving high frequency and high efficiency in full-bridge converters. Summary of the Invention

[0004] Technical purpose: In view of the defects of the full-bridge converter in the prior art, the present invention discloses a soft-switching full-bridge converter based on a buck-type auxiliary circuit, which constructs a buck-type auxiliary circuit with independent load and no dependence on the primary circulating current of the transformer to achieve full-range soft switching. At the same time, a small capacitance value loss-reducing capacitor C is connected in series with the primary side of the transformer. b Achieve smooth buck-type auxiliary loop current, while speeding up the primary side circulating current of the buck converter and minimizing the circulating current conduction loss.

[0005] Technical solution: In order to achieve the above technical objectives, the present invention adopts a technical solution.

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

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

[0008] A passive buck assisted circuit is used to assist in soft switching of the lagging bridge arm in the main power bridge arm of the four-switch transistor with loss-reducing capacitors. The circuit comprises a first energy storage capacitor C1, a second energy storage capacitor C2, and a buck assisted inductor L1, forming a buck-type circuit. The buck-type circuit is used to provide DC return current for an independent load. Input capacitors C1 and C2 are connected in series to form a capacitor bridge arm that spans the DC voltage module. The buck assisted inductor L1 is connected between the midpoint of the capacitor bridge arm and the opposite-signal terminal on the primary side of the transformer.

[0009] The main power bridge arm with four switch tubes with loss-reducing capacitors is used for limited bipolar modulation and inverter DC power. It outputs high-frequency square waves through the primary side of the transformer and reduces the circulating current loss of the primary side of the transformer. At the same time, it smoothes the buck-type auxiliary loop current. It includes the main power full bridge and the primary side of the transformer T1. The main power full bridge includes the first power switch tube Q1 to the fourth power switch tube Q4. The leakage inductor L is connected in series between the midpoints of the upper and lower bridge arms of the main power full bridge. r , transformer T1 primary side, loss reduction capacitor C b , and the excitation inductance L is connected in parallel at both ends of the primary side of transformer T1 m ;

[0010] The 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 main power bridge arm of the four-switch tube with loss-reducing capacitors, and output a smooth DC voltage.

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

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

[0013] Furthermore, the source of the first power switch tube Q1 is connected to the positive output terminal of the DC voltage module, and the drain of the first power switch tube Q2 is connected to the source of the second power switch tube Q2 and the leakage inductor L. r One end of the leakage inductance Lr The other end is connected to the same-name terminal on the primary side of transformer T1; the same-name terminal on the primary side of transformer T1 is also connected to the excitation inductor L m One end of the excitation inductor L m The other end of the transformer is connected to the opposite-name terminal on the primary side of the transformer T1; the opposite-name terminal on the primary side of the 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 the input capacitor C1 and the input capacitor C2;

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

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

[0016] The fourth power switch tube Q4 has a drain connected to the source of the third power switch tube Q3 and the loss-reducing capacitor C b One end of the MOSFET has its source connected to the negative output end of the DC voltage module.

[0017] Furthermore, the loss-reducing capacitor C b It is at the nanofarad level, and its calculation formula includes:

[0018]

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

[0020] Among them, I out is the output current, D effmax is the maximum effective duty cycle of the secondary side of transformer T1, T s is the switching period, C oss is the output capacitance of the power switch tube, V in is the input voltage, V cbp is the peak voltage of the loss-reducing capacitor, n is the turns ratio of transformer T1, V out is the output voltage.

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

[0022]

[0023] Among them, Ts is the switching period, I peak is the peak current of the return buck inductor L1, V in is the input voltage, C oss is the output capacitance of the power switch tube, n is the turns ratio of transformer T1, V out is the output voltage.

[0024] Furthermore, 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 , forming an LC filtering circuit; in the asymmetric magnetic coupling LC ripple suppression network, the high-frequency square wave output from the primary side of the transformer is full-wave rectified through diodes D1 and D2, and the LC filtering output is used to output a smooth DC voltage.

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

[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 of 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 cathode of diode D1 and the cathode of diode 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 of the filter capacitor C f The two ends of the DC voltage are respectively used as the positive and negative electrodes of the output DC voltage, that is, the positive and negative electrodes of the output DC voltage of the soft-switching full-bridge converter of the present invention, for connecting 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 through the return buck passive auxiliary network;

[0032] (2) The passive auxiliary network of the reflux buck generates soft switching current by using two power switches Q3 and Q4 in the main power bridge arm of the four-switch tube with loss reduction capacitors. No additional switches are required and there are fewer passive auxiliary devices.

[0033] (3) Under limited bipolar modulation, that is, under the condition of fixed duty cycle control of the lagging arm, the return buck inductor L1 value is designed to meet the minimum inductor peak current required for soft switching while reducing the loss capacitor C b Smooth auxiliary loop current and reduce the circulating current speed to zero, with low circuit circulating current conduction loss;

[0034] (4) The passive auxiliary network of the reflux buck is independent of the main power bridge arm of the four-switch tube with loss-reducing capacitors, that is, the soft switch is independent of the main power circuit, with low switching loss and conduction loss, improved efficiency, and helpful to increase the operating frequency of the system, reduce the size of the output filter, and improve reliability. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0037] Figures 3 to 8 This is a topological modal diagram of the first stage of a soft-switching full-bridge converter based on a buck-type auxiliary loop according to the present invention;

[0038] Figures 9-14 This is a topological modal diagram of the second stage of a soft-switching full-bridge converter based on a buck-type auxiliary loop according to the present invention. DETAILED DESCRIPTION

[0039] In order to help those skilled in the art better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0040] As attached Figure 1As shown, a soft-switching full-bridge converter based on a buck-type auxiliary loop includes a DC voltage module 1, a backflow buck passive auxiliary network 2, a main power bridge arm 3 with four switch tubes with loss-reducing capacitors, and an asymmetric magnetically coupled LC ripple suppression network 4;

[0041] The DC voltage module 1 is used to provide DC input voltage for the backflow buck passive auxiliary network 2 and the main power bridge arm 3 with four switching tubes with loss reduction capacitors;

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

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

[0044] The input capacitor C1 and the input capacitor C2 are connected in series to form a capacitor bridge arm, one end of which is connected to the positive output terminal of the DC voltage module 1, and the other end is connected to the negative output terminal of the 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 loss-reducing capacitor four-switch tube;

[0045] The main power bridge arm 3 with four switching tubes with loss-reducing capacitors is used for limited bipolar modulation and inverter DC power and outputs high-frequency square waves through the primary side of the transformer and reduces the circulating current loss of the primary side of the transformer. It includes a main power full bridge and the primary side of the transformer T1. The main power full bridge includes the first power switch tube Q1 to the fourth power switch tube Q4; the leakage inductor L is connected in series between the midpoints of the upper and lower bridge arms of the main power full bridge. r , transformer T1 primary side, loss reduction capacitor C b , and the excitation inductance L is connected in parallel at both ends of the primary side of transformer T1 m ;

[0046] The first power switch tube Q1 and the second power switch tube Q2 form an upper bridge arm, and the first power switch tube Q1 and the second power switch tube Q2 have a fixed phase difference of 180°; the third power switch tube Q3 and the fourth power switch tube Q4 form a lower bridge arm, and the third power switch tube Q3 and the fourth power switch tube Q4 have a fixed phase difference of 180°; the gates of the first power switch tubes Q1 to the fourth power switch tube Q4 are controlled by a bipolar modulation signal, the first power switch tube Q1 and the fourth power switch tube Q4 are turned on simultaneously, the second power switch tube Q2 and the third power switch tube Q3 are turned on simultaneously, the third power switch tube Q3 and the fourth power switch tube Q4 operate with a fixed duty cycle, and the first power switch tube Q1 and the second power switch tube Q2 operate with a variable duty cycle;

[0047] The drain of the first power switch tube Q1 is connected to the positive output terminal of the DC voltage module 1, and the source of the first power switch tube Q2 is connected to the drain of the second power switch tube Q2 and the leakage inductor L r One end of the leakage inductance L r The other end is connected to the same-name terminal on the primary side of transformer T1; the same-name terminal on the primary side of transformer T1 is also connected to the excitation inductor L m One end of the excitation inductor L m The other end of the transformer is connected to the opposite-name terminal on the primary side of the transformer T1; the opposite-name terminal on the primary side of the 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 the input capacitor C1 and the input capacitor C2;

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

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

[0050] The fourth power switch tube Q4 has a drain connected to the source of the third power switch tube Q3 and the loss-reducing capacitor C b One end of the MOSFET has its source connected to the negative output end of the DC voltage module.

[0051] The asymmetric magnetic coupling LC ripple suppression network 4 is used to rectify and filter the high-frequency square wave output from the primary side of the transformer T1 in the main power bridge arm 3 of the four-switch tube with loss-reducing capacitors, and output a smooth DC voltage; the asymmetric magnetic coupling LC ripple suppression network 4 includes the connected secondary side of the transformer T1, a full-wave rectifier circuit and a filter circuit; wherein 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 , forming an LC filter circuit;

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

[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 of 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 cathode of diode D1 and the cathode of diode 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 of the filter capacitor C f The two ends of the DC voltage are respectively used as the positive and negative electrodes of the output DC voltage, that is, the positive and negative electrodes of the output DC voltage of the soft-switching full-bridge converter of the present invention, for connecting with the load resistor R L in parallel.

[0057] That is, in the asymmetric magnetic coupling LC ripple suppression network 4, the high-frequency square wave output from the primary side of the transformer is full-wave rectified by diodes D1 and D2, and the LC filtering output is output, thereby outputting a smooth DC voltage.

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

[0059]

[0060] Among them, Iout is the output current, that is, the output current of the soft-switching full-bridge converter, D effmax is the maximum effective duty cycle of the secondary side of transformer T1, T s is the switching period, C oss is the output capacitor of the power switch tube. In this application, the first power switch tube Q1 to the fourth power switch tube Q4 of the main power full bridge are the same. V in is the input voltage, that is, the input voltage provided by the DC voltage module, V cbp is the peak voltage of the loss-reducing capacitor, n is the turns ratio of transformer T1; here we can choose the peak voltage of the loss-reducing capacitor V cbp ≤2D effmax (V in -2nV out ), where V out =output voltage, i.e., the output voltage of the soft-switching full-bridge converter. A higher peak voltage for the loss-reduction capacitor reduces circulating current conduction losses during commutation, but also increases voltage stress. A lower peak voltage for the loss-reduction capacitor reduces additional voltage stress, but also reduces circulating current conduction losses, until the loss-reduction function is lost and the capacitor only serves to prevent transformer demagnetization. Therefore, a trade-off must be made. Reducing circulating current here does not violate the ZVS soft-switching condition.

[0061] The return buck inductor L1 value is determined by the minimum current required for the lagging bridge arm soft switching, and its calculation formula is:

[0062]

[0063] Among them, T s is the switching period, I peak is the peak current of the return buck inductor L1, V in is the input voltage; the peak current of the return buck inductor L1 is the smoothed peak current, which can be selected here Among them, L r is the leakage inductance, L m is the excitation inductor; the higher the peak current of the inductor is, the easier it is to implement soft switching, but the conduction loss of the auxiliary circuit is higher; the lower the peak current of the inductor is, the lower the conduction loss of the auxiliary circuit is, but it may destroy the soft switching condition of the lagging arm. Therefore, a minimum value exists to ensure the implementation of soft switching while minimizing the conduction loss of the auxiliary circuit.

[0064] The present invention adopts a limited bipolar control mode with variable duty cycle control of the leading bridge arm (including the first power switch tube Q1 and the second power switch tube Q2) and fixed duty cycle of the lagging bridge arm (including the third power switch tube Q3 and the fourth power switch tube Q4). By connecting the lagging bridge arm across a synchronous rectification buck return circuit independent of the load, the energy storage and release of the junction capacitance is achieved independently without relying on the circulating current, thereby achieving full-range soft switching of all switch tubes. At the same time, the auxiliary loop current is smoothed by the loss-reducing capacitor, and the circulating current speed of the primary side of the transformer is reduced, thereby reducing the conduction loss. p In the positive first half cycle, the first power switch tube Q1 switches from on to off, the second power switch tube Q2 is normally closed, the third power switch tube Q3 is normally closed, and the fourth power switch tube Q4 is normally on. p In the negative second half cycle, the first power switch tube Q1 is normally closed, the second power switch tube Q2 changes from on to off, the third power switch tube Q3 is normally on, and the fourth power switch tube Q4 is normally closed. Figure 2 , modal diagram Figure 3-Figure 14 , specifically analyze the working principle and two-stage working mode of the soft-switching full-bridge converter of the present invention, in which the primary current i 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 in the figure, in this working state, the first power switch tube Q1 and the fourth power switch tube Q4 are turned on, while the second power switch tube Q2 and the third power switch tube Q3 are turned off, and the diode D1 and the diode D2 are turned on at the same time. i Added across the leakage inductance, it can be considered that the primary current i p At the DC input voltage U i The return buck inductor current i1 decreases smoothly, and the primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b Discharge, the current of diode D1 increases linearly, and the current of diode D2 decreases linearly. Among them, the capacitance of the first energy storage capacitor C1 and the second energy storage capacitor C2 in the passive auxiliary network 2 of the return buck is the same, and the current flowing through the first energy storage capacitor C1 and the second energy storage capacitor C2 is half of the return buck inductor current i1. At time t1, the current of diode D2 drops to zero, and the current of diode D1 alone is the load resistance R L Power is supplied and this phase ends.

[0066] Phase 1 working mode 2: Figure 4 The circuit shown corresponds to Figure 2 In the interval [t1, t2] shown in the figure, in this working state, the first power switch tube Q1 and the fourth power switch tube Q4 are turned on, while the second power switch tube Q2 and the third power switch tube Q3 are turned off, the diode D1 is turned on, and all diodes D2 are turned off. i Added across the leakage inductance and the magnetizing inductance, the primary current i p At the DC input voltage U i The return buck inductor current i1 rises smoothly, and the primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b Discharge to zero and continue forward charging, during which time the current in diode D1 increases linearly and supplies power to the load alone. At time t2, the first power switch Q1 is turned off, and this stage ends.

[0067] Phase 1 working mode 3: Figure 5 The circuit shown corresponds to Figure 2 In the interval [t2, t3] shown in the figure, in this working state, the fourth power switch tube Q4 is turned on, while the first power switch tube Q1, the second power switch tube Q2 and the third power switch tube Q3 are turned off, and the diodes D1 and D2 are turned on at the same time. p The junction capacitance of the first power switch tube Q1 and the second power switch tube Q2 is charged and discharged, and due to the primary current i p This is the peak value, and charging and discharging can be easily achieved. The return buck inductor current i1 rises smoothly, and the primary current i p and the return buck inductor current i1 together with C b During charging, the current of diode D1 decreases linearly, and the current of diode D2 increases linearly. Since the junction capacitance of the power switch tube is equal, the charging and discharging currents of the two capacitors are both the primary current i p This phase ends at time t3 when the junction capacitance of the first power switch tube Q1 and the second power switch tube Q2 is fully charged and discharged.

[0068] Phase 1 working mode 4: Figure 6 The circuit shown corresponds to Figure 2 In the interval [t3, t4] shown in the figure, in this working state, the fourth power switch tube Q4 is turned on, while the first power switch tube Q1, the second power switch tube Q2 and the third power switch tube Q3 are turned off, the diodes D1 and D2 are turned on at the same time, and the secondary side enters the freewheeling state. b , the large reverse voltage drop U formed by charging at both ends b Applied to the leakage inductance L r At both ends, the primary current i pRapidly decreases, reducing the conduction loss, the return buck inductor current i1 rises smoothly, and the primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b During charging, the current of diode D1 decreases linearly, while the current of diode D2 increases linearly. At time t4, the fourth power switch Q4 is turned off, and this stage ends.

[0069] Phase 1 working mode 5: Figure 7 The circuit shown corresponds to Figure 2 In the interval [t4, t5] shown in the figure, in this working state, all power switches are turned off, diodes D1 and D2 are turned on at the same time, and the secondary side is in freewheeling state. p The buck inductor current i1 and the fourth power switch Q4 and the third power switch Q3 junction capacitance are charged and discharged at the same time, and due to the primary current i p At this time, the reflux buck inductor current i1 is very small, and the reflux buck inductor current i1 is approximately at its peak value, which is sufficient to achieve charging and discharging by relying solely on the reflux buck inductor current i1. Moreover, due to the fixed duty cycle of the lagging bridge arm, the maximum L1 value required for the design of the minimum peak current required for soft switching can be supplied to reduce unnecessary inductor losses. The reflux buck inductor current i1 is connected to the junction capacitance of the third power switch tube Q3 from V in During the discharge to 0V process, it first rises and then falls. The primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b The current of diode D1 decreases linearly, and the current of diode D2 increases linearly. This stage ends at time t5 when the junction capacitance of the fourth power switch tube Q4 and the third power switch tube Q3 is charged and discharged.

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

[0071] The second stage working mode 1: Figure 9 The circuit shown corresponds to Figure 2In the interval [t6, t7] shown in the figure, in this working state, the second power switch tube Q2 and the third power switch tube Q3 are turned on, while the first power switch tube Q1 and the fourth power switch tube Q4 are turned off, and the diodes D1 and D2 are turned on at the same time. The DC input voltage is applied to both ends of the leakage inductance, so it can be considered that the primary current i p Under the action of DC input voltage, it quickly reverses and linearly rises. 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 reduces the loss of capacitor C b During discharge, the current in diode D1 decreases linearly, while the current in diode D2 increases linearly. At 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] The second stage working mode 2: Figure 10 The circuit shown corresponds to Figure 2 In the interval [t7, t8] shown in the figure, in this working state, the second power switch tube Q2 and the third power switch tube Q3 are turned on, while the first power switch tube Q1 and the fourth power switch tube Q4 are turned off, the diode D2 is turned on, and the diode D1 is turned off. The DC input voltage is applied to both ends of the leakage inductance and the excitation inductance, and the primary current i p Under the action of DC input voltage, it rises linearly in the reverse direction, and the rising 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 reduces the loss of capacitor C b The diode D2 discharges to zero and continues to charge in reverse. During this time, the current in the diode D2 alone supplies power to the load. At time t8, the second power switch Q2 is turned off, and this phase ends.

[0073] The second stage working mode 3: Figure 11 The circuit shown corresponds to Figure 2 In the interval [t8, t9] shown in the figure, in this working state, the third power switch tube Q3 is turned on, while the first power switch tube Q1, the second power switch tube Q2 and the fourth power switch tube Q4 are turned off, and the diodes D1 and D2 are turned on at the same time. p The junction capacitance of the second power switch tube Q2 and the first power switch tube Q1 is charged and discharged, and due to the primary current i p The magnitude is at its peak value at this time, and charging and discharging can be easily achieved. The reflux buck inductor current i1 rises smoothly in the reverse direction, and the primary current i p and the return buck inductor current i1 together with C b Reverse charging: This phase ends at time t9 when the junction capacitance of the second power switch tube Q2 and the first power switch tube Q1 is fully charged and discharged.

[0074] Second stage working mode 4: Figure 12 The circuit shown corresponds to Figure 2 As shown in [t9, t 10 ] interval, in this working state, the third power switch tube Q3 is turned on, while the first power switch tube Q1, the second power switch tube Q2 and the fourth power switch tube Q4 are turned off, and the diodes D1 and D2 are turned on at the same time. The secondary side enters the freewheeling state. Due to the small loss-reducing capacitor C b value, the large reverse voltage drop U formed by the previous charging b Applied to the leakage inductance L r At both ends, the primary current i p The magnitude of the reverse current i1 decreases rapidly, reducing the conduction loss, and the return buck inductor current i1 rises smoothly in the reverse direction. The primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b Reverse charging. 10 At this moment, the fourth power switch tube Q4 is turned off, and this stage ends.

[0075] Second stage working mode 5: Figure 13 The circuit shown corresponds to Figure 2 As shown [t 10 , t 11 ] interval, in this working state, all switches are turned off, diodes D1 and D2 are turned on at the same time, and the secondary side is in freewheeling state. p The return buck inductor current i1 and the junction capacitance of the third power switch Q3 and the fourth power switch Q4 are charged and discharged at the same time, and due to the primary current i p At this time, the magnitude of the return buck inductor current i1 is very small, and the magnitude of the return buck inductor current i1 is close to the peak value, which is sufficient to achieve charging and discharging by relying solely on the return buck inductor current i1. The magnitude of the return buck inductor current i1 is when the junction capacitance of the fourth power switch tube Q4 is from V in During the discharge to 0V process, it first rises and then falls. The primary current i p Together with the return buck inductor current i1, it reduces the loss of capacitor C b Reverse charging: This phase ends when the junction capacitance of the third power switch tube Q3 and the fourth power switch tube Q4 is fully charged and discharged.

[0076] The second stage working mode 6: Figure 14 The circuit shown corresponds to Figure 2 As shown [t 11 , t 12 ] interval, in this working state, all switches are turned off, diodes D1 and D2 are turned on at the same time, and the secondary side is in freewheeling state. p Approximately zero and about to reverse, the magnitude of the return buck inductor current i1 decreases smoothly, and the primary current i pTogether with the return buck inductor current i1, it reduces the loss of capacitor C b Reverse charging. 12 At this moment, the first power switch tube Q1 and the fourth power switch tube Q4 are turned on, and this stage ends.

[0077] Analysis of the inverter operating mode of the present invention shows that the circuit has the following advantages:

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

[0079] (2) The reflux buck passive auxiliary network generates soft switching current with the help of two power switch tubes Q3 and Q4 in the main power bridge arm of the four-switch tube with loss reduction capacitors. No additional switch tubes are required and there are fewer passive auxiliary devices.

[0080] (3) Under limited bipolar modulation, that is, under the condition of fixed duty cycle control of the lagging arm, the return buck inductor L1 value is designed to meet the minimum inductor peak current required for soft switching while reducing the loss capacitor C b Smooth auxiliary loop current and reduce the circulating current speed to zero, with low circuit circulating current conduction loss;

[0081] (4) The passive auxiliary network of the reflux buck is independent of the main power bridge arm of the four-switch tube with loss-reducing capacitors, that is, the soft switch is independent of the main power circuit, with low switching loss and conduction loss, improved efficiency, and helpful to increase the operating frequency of the system, reduce the size of the output filter, and improve reliability.

[0082] The "first" and "second" in the names of "first" and "second" mentioned in the embodiments of this application are only used as name identifiers and do not represent their importance ranking.

[0083] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as 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: It includes a DC voltage module, a return buck passive auxiliary network, a main power bridge arm with four switch tubes with loss-reducing capacitors, and an asymmetric magnetically coupled LC ripple suppression network; The DC voltage module is used to provide DC input voltage for the passive auxiliary network of the return buck and the main power bridge arm of the four-switch tube with loss-reducing capacitors; The passive buck breaker network assists in soft switching of the lagging bridge arm in the main power bridge arm with loss-reducing capacitors. It includes a first energy storage capacitor C1, a second energy storage capacitor C2, and a buck breaker inductor L1, which form the buck circuit. The buck circuit provides a stable return current for the main power bridge arm of the four-switch tube with independent loss-reducing capacitors. Input capacitors C1 and C2 are connected in series to form a capacitor bridge arm, which is connected across the DC voltage module. The buck breaker inductor L1 is connected between the midpoint of the capacitor bridge arm and the opposite-terminal terminal of the transformer primary. The main power bridge arm with four switch tubes with loss-reducing capacitors is used for limited bipolar modulation and inverter DC power. It outputs high-frequency square waves through the primary side of the transformer and reduces the circulating current loss of the primary side of the transformer. At the same time, it smoothes the buck-type auxiliary loop current. It includes the main power full bridge and the primary side of the transformer T1. The main power full bridge includes the first power switch tube Q1 to the fourth power switch tube Q4. The leakage inductor L is connected in series between the midpoints of the upper and lower bridge arms of the main power full bridge. r , transformer T1 primary side, loss reduction capacitor C b , and the excitation inductance L is connected in parallel at both ends of the primary side of transformer T1 m ; The asymmetric magnetically coupled LC ripple suppression network is used to rectify and filter the high-frequency square wave output from the primary side of the transformer T in the main power bridge arm of the four-switch tube with loss-reducing capacitors, and output a smooth DC voltage.

2. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 1, characterized in that: The first power switch tube Q1 and the second power switch tube Q2 form an upper bridge arm, the third power switch tube Q3 and the fourth power switch tube Q4 form a lower bridge arm, and the gates of the first power switch tube Q1 to the fourth power switch tube Q4 are controlled by bipolar modulation signals.

3. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 2, characterized in that: The gates of the first to fourth power switch tubes Q1 to Q4 are controlled by bipolar modulation signals, including: the upper bridge arm, i.e. the leading bridge arm, adopts variable duty cycle control, and the lower bridge arm, i.e. 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 loop according to claim 1, characterized in that: The drain of the first power switch tube Q1 is connected to the positive output terminal of the DC voltage module, and the source of the first power switch tube Q2 is connected to the source of the second power switch tube Q2 and the leakage inductance L r One end of the leakage inductance L r The other end is connected to the same-name terminal on the primary side of transformer T1; the same-name terminal on the primary side of transformer T1 is also connected to the excitation inductor L m One end of the excitation inductor L m The other end of the transformer is connected to the opposite-name terminal of the primary side of the transformer T1; the opposite-name terminal of the primary side of the 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 the input capacitor C1 and the input capacitor C2; The drain of the second power switch tube Q2 is connected to the source of the first power switch tube Q1 and the leakage inductor L r One end of the MOSFET has its source connected to the negative output end of the DC voltage module; The drain of the third power switch tube Q3 is connected to the positive output terminal of the DC voltage module, and the source is connected to the drain of the fourth power switch tube Q4 and the loss reduction capacitor C b One end of the capacitor C b The other end is connected to the opposite end of the primary side of transformer T1; The fourth power switch tube Q4 has a drain connected to the source of the third power switch tube Q3 and the loss-reducing capacitor C b One end of the MOSFET has its source connected to the negative output end of the DC voltage module.

5. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 1, characterized in that: Loss reduction capacitor C b It is at the nanofarad level, and its calculation formula includes: IN cbp ≤2D effmax (IN in -2nV out ) Among them, I out is the output current, D effmax is the maximum effective duty cycle of the secondary side of transformer T1, T s is the switching period, C oss is the output capacitance of the power switch tube, V in is the input voltage, V cbp is the peak voltage of the loss-reducing capacitor, n is the turns ratio of transformer T1, V out is the output voltage.

6. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 1, characterized in that: The calculation formula for the return buck inductor L1 includes: Among them, T s is the switching period, I peak is the peak current of the return buck inductor L1, V in is the input voltage, C oss is the output capacitance of the power switch tube, n is the turns ratio of transformer T1, V out is the output voltage.

7. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 1, characterized in that: The asymmetric magnetically coupled LC ripple suppression network includes the connected transformer T1 secondary side, 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 , forming an LC filtering circuit; in the asymmetric magnetic coupling LC ripple suppression network, the high-frequency square wave output from the primary side of the transformer is full-wave rectified through diodes D1 and D2, and the LC filtering output is used to output a smooth DC voltage.

8. The soft-switching full-bridge converter based on a buck-type auxiliary loop according to claim 7, characterized in that: The same-name terminal on the secondary side of transformer T1 is connected to the anode of diode D1, and the center tap on the secondary side of transformer T1 is connected to the filter capacitor C f One end of the transformer T1, the opposite end of the secondary side is connected to the anode of the diode D2; 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; The anode of diode D2 is connected to the opposite terminal of 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; Filter inductor L f One end is connected to the cathode of diode D1 and the cathode of diode D2, and the other end is connected to the output filter capacitor C f one end. Filter capacitor C f One end is connected to the filter inductor L f One end of the filter capacitor C f The two ends of the DC voltage are respectively used as the positive and negative electrodes of the output DC voltage, that is, the positive and negative electrodes of the output DC voltage of the soft-switching full-bridge converter of the present invention, for connecting with the load resistor R L in parallel.

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