Soft switching bidirectional DC-DC circuit and device based on autotransformer

Abstract

The invention provides a soft switching bidirectional DC-DC circuit and device based on an autotransformer. A main power circuit of the soft switching bidirectional DC-DC circuit comprises a high-voltage DC bus, a battery end, two main switching tubes, a filter inductor and a filter capacitor; the auxiliary network comprises three auxiliary switch tubes, an auxiliary diode, a transformer, a resonant inductor and a resonant capacitor. Aiming at the defects that a traditional soft switch Buck circuit causes zero-current turn-on failure of an auxiliary switch and failure of a bidirectional Boost mode soft switch due to holding current generated by discharge of an auxiliary diode stray capacitor, a resonant circuit is cut off through the auxiliary switch before the holding current is formed, energy release of the stray capacitor is suppressed, and the voltage of the bidirectional Boost mode soft switch is reduced. And all switching devices under the two energy flow directions of Buck and Boost are ensured to realize zero-voltage or zero-current switching. Through high-frequency resonance control, the circuit always keeps a soft switching state in a bidirectional power transmission process, the switching loss is remarkably reduced, the overall efficiency is improved, and the circuit is suitable for energy storage and electric automobiles and other scenes needing efficient bidirectional direct current conversion.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC circuits, and in particular to a soft-switching bidirectional DC-DC circuit and device based on an autotransformer. Background Art

[0002] With the rapid development of new energy power generation, energy storage systems, and bidirectional charging for electric vehicles, DC-DC circuits that enable bidirectional energy flow have become key components in the power electronics field. Driven by design requirements for high frequency, high power density, and high efficiency, soft switching technology is widely used in bidirectional DC-DC circuits to reduce switching losses, minimize electromagnetic interference, and improve system efficiency.

[0003] Currently, there are attempts to combine resonant soft switching technology with high-frequency transformers or autotransformers to broaden the soft switching range while taking into account the voltage reduction capability. For example, Figure 1 The high-frequency transformer-based soft-switching Buck circuit shown here injects resonant energy into specific nodes via an autotransformer, enabling both the main power switch and the switching devices in the auxiliary network to achieve zero voltage switching (ZVS) or zero current switching (ZCS), thereby maintaining high conversion efficiency under various input voltage and load conditions. This topology theoretically achieves soft switching operation over a wide range and exhibits excellent step-down performance in Buck mode.

[0004] However, in practical applications, the above existing solutions still have the following shortcomings: First, the parasitic capacitance of the auxiliary diode in the auxiliary network will produce unexpected resonant behavior with the resonant inductor and the excitation inductor during the resonance process, resulting in a large holding current on the resonant inductor after the main switch is turned off. This holding current not only destroys the zero-current turn-on condition of the auxiliary switch and reduces system efficiency, but may also cause additional electromagnetic interference and device stress problems. Second, the existing topology only supports unidirectional Buck mode energy transmission and cannot adapt to application scenarios such as energy storage systems or electric vehicles that require bidirectional energy flow, limiting its versatility and system integration.

[0005] Therefore, how to overcome the holding current problem caused by the parasitic capacitance of the auxiliary diode and, on this basis, realize full-range soft switching operation of the bidirectional DC-DC circuit has become a key issue that needs to be urgently solved in current technology.

[0006] In view of this, this application is filed. Summary of the Invention

[0007] The present invention provides a soft-switching bidirectional DC-DC circuit and device based on an autotransformer, which can effectively improve the above-mentioned problems.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A soft-switching bidirectional DC-DC circuit based on an autotransformer, comprising: a high-voltage DC bus, a battery voltage, a main power circuit, and an auxiliary network, wherein the high-voltage DC bus is connected in parallel with the main power circuit, the positive electrode of the high-voltage DC bus is electrically connected to a first end of the auxiliary network and a first end of the main power circuit, the negative electrode of the high-voltage DC bus is electrically connected to a second end of the auxiliary network, a switch tube of the main power circuit is connected in parallel with a capacitor of the auxiliary network, the battery voltage is connected in parallel with the main power circuit, a third end of the auxiliary network is electrically connected to a midpoint of a switch bridge arm of the main power circuit, and a control end of the main power circuit and a control end of the auxiliary network are connected to an external controller; The auxiliary network is configured to cut off the loop before the holding current appears to avoid the holding current, and ensure the normal operation of the Boost mode soft switch while achieving normal zero-current switching of the auxiliary network switch.

[0009] The present invention also provides a soft-switching bidirectional DC-DC device based on an autotransformer, which includes a controller and a soft-switching bidirectional DC-DC circuit based on an autotransformer as described in any one of the above items, wherein the control end of the main power circuit and the control end of the auxiliary network are electrically connected to the output end of the controller; wherein the controller is configured to control the switching of the auxiliary switch tube and the main switch tube.

[0010] In summary, based on the existing soft-switching Buck circuit based on a high-frequency transformer, the present invention aims to solve the problem of maintaining current caused by the parasitic capacitance of the auxiliary diode and the limitation of unidirectional power flow, and proposes a soft-switching DC-DC conversion circuit and circuit with an autotransformer as the core and capable of bidirectional energy transmission. By adding an auxiliary switch Sa2 in the auxiliary network, the resonant circuit is cut off in time before the main switch is turned off, and the maintaining current caused by the discharge of the parasitic capacitance is eliminated from the source, ensuring that all power devices in both Buck and Boost modes can achieve zero voltage or zero current switching and shutdown. The topology is simple, and the control strategy is compatible with the existing high-frequency resonant control. It can maintain soft switching characteristics within a wide input voltage and load range, significantly reduce switching losses and electromagnetic interference, and improve system efficiency and reliability. It is particularly suitable for energy storage systems, electric vehicle bidirectional charging and discharging, and other application scenarios that require efficient bidirectional DC conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of a soft-switching Buck circuit based on a high-frequency transformer in the prior art solution; Figure 2 This is a schematic diagram of the soft-switching Buck simulation waveform based on a high-frequency transformer in the existing technical solution; Figure 3This is a schematic diagram of a soft-switching bidirectional DC-DC circuit based on an autotransformer provided by the present invention; Figure 4 Schematic diagram of the working mode of the circuit in Buck mode provided by the present invention; Figure 5 This is a schematic diagram of the circuit operating waveform in the Buck mode provided by the present invention; Figure 6 This is a schematic diagram of the working mode of the circuit in the Boost mode provided by the present invention; Figure 7 This is a schematic diagram of the circuit operating waveform in the Boost mode provided by the present invention; Figure 8 This is a circuit operation simulation waveform diagram in Buck mode provided by the present invention, where: Figure 8 (a) is the simulation waveform of the resonant inductor current remaining zero when the first auxiliary switch is turned on. Figure 8 (b) The simulation waveform diagram of the main switch tube to achieve zero current switching operation. Figure 8 (c) is the simulation waveform of the second auxiliary switch tube also working in zero current soft switching. Figure 8 (d) is the simulation waveform when the current injected into the switch node is greater than the filter inductor current; Figure 9 This is a circuit operation simulation waveform diagram in the Boost mode provided by the present invention, wherein: Figure 9 (a) is the simulation waveform of the third auxiliary switch tube working in zero current soft switching. Figure 9 (b) is the simulation waveform of the second main switch tube achieving zero voltage switching operation. Figure 9 (c) is the simulation waveform when the current injected into the switch node is greater than the filter inductor current. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0013] refer to Figure 3 As shown, the first embodiment of the present invention discloses a soft switching bidirectional DC-DC circuit based on an autotransformer, comprising: a high voltage DC bus U bus , battery voltage U bat , main power circuit, auxiliary network, the high voltage DC bus U bus In parallel with the main power circuit, the high voltage DC bus U bus The positive electrode is electrically connected to the first end of the auxiliary network and the first end of the main power circuit, and the high-voltage DC bus U busThe negative electrode of the auxiliary network is electrically connected to the second end, the switch tube of the main power circuit is connected in parallel with the capacitor of the auxiliary network, and the battery voltage U bat The auxiliary network is connected in parallel with the main power circuit, the third end of the auxiliary network is electrically connected to the midpoint of the switch bridge arm of the main power circuit, and the control end of the main power circuit and the control end of the auxiliary network are connected to an external controller; The auxiliary network is configured to cut off the loop before the holding current appears to avoid the holding current, and ensure the normal operation of the Boost mode soft switch while achieving normal zero-current switching of the auxiliary network switch.

[0014] Preferably, the main power circuit includes a first main switch tube S1, a second main switch tube S2, a filter inductor L f , output filter capacitor C f2 And the input filter capacitor C f1 , wherein the control end of the first main switch tube S1 and the control end of the second main switch S2 are connected to the controller, and the first end of the first main switch tube S1 is connected to the high voltage DC bus U bus The positive electrode of the first main switch tube S1 is electrically connected to the first end of the second main switch S2, the auxiliary network, the filter inductor L f One end of the second main switch S2 is electrically connected to the high-voltage DC bus U bus The negative pole of the filter inductor L is electrically connected to f The other end of the output filter capacitor C f2 Electrical connection, the output filter capacitor C f2 The other end is connected to the high voltage DC bus U bus The negative electrode of the second main switch S2 is electrically connected to the second end of the input filter capacitor C f1 With high voltage DC bus U bus in parallel.

[0015] Preferably, the auxiliary network includes a first auxiliary switch tube S a1 , the first auxiliary diode D a1 , the second auxiliary switch tube S a2 , the second auxiliary diode D a2 , the third auxiliary switch tube S a3 , the third auxiliary diode D a3 、Transformer T a , resonant inductor L r , resonant capacitor C r And the parasitic capacitance C Da2 , wherein the first auxiliary switch tube S a1 The control end of the second auxiliary switch tube S a2 The control end of the third auxiliary switch tube S a3The control end is connected to the controller, and the first auxiliary switch tube S a1 The first end is connected to the high voltage DC bus U bus The positive electrode of the first auxiliary switch S is electrically connected to a1 The second end of the first auxiliary diode S a1 The negative pole, resonant inductor L r The first end is electrically connected to the resonant inductor L r The second end of the transformer T a The first end is electrically connected to the transformer T a The second end of the third auxiliary diode D a3 The positive electrical connection of the transformer T a The third terminal of the second auxiliary diode D a2 The negative pole of the transformer T is electrically connected a The fourth end of the first main switch tube S1, the first end of the second main switch tube S2, the filter inductor L f One end of the third auxiliary diode D is electrically connected to a3 The negative electrode and the third auxiliary switch tube S a2 The first end is electrically connected to the parasitic capacitor C Da2 With the second auxiliary diode D a2 In parallel, the second auxiliary diode D a3 The positive electrode and the second auxiliary switch tube S a2 The second end of the first auxiliary diode D is electrically connected to a1 The positive electrode, the second auxiliary switch tube S a2 The first end of the third auxiliary switch tube D a3 The second end is connected to the high voltage DC bus U bus negative electrical connection.

[0016] Specifically, in this embodiment, the autotransformer-based soft-switching bidirectional DC-DC circuit realizes bidirectional, soft-switching, and high-efficiency DC-DC power conversion through a combination of a compact and fully functional main power circuit and an auxiliary network. bus The positive electrode of the bus is directly coupled to the drain of the first main switch S1, and also serves as the starting point of the auxiliary network, providing energy for the resonant branch. The negative electrode of the bus is connected to the source of the second main switch S2 and the common reference point of the auxiliary network, forming a low-impedance current loop. bat Through the filter inductor L f and the output filter capacitor C f2 Connected in parallel with the output end of the main power circuit, it serves as both a load in Buck mode and an energy source in Boost mode, achieving bidirectional power flow under the same hardware structure.

[0017] Inside the main power circuit, the first main switch tube S1 and the second main switch tube S2 are both NMOS tubes, and the gates uniformly receive the PWM signal of the external digital controller. The source-drain path bears all the load current at the switching moment. f Connected in series between the source of the first main switch tube S1 and the positive electrode of the battery, the output filter capacitor C f2 Connected in parallel at both ends of the battery, the two together smooth the pulsating current into a DC current acceptable to the battery, while suppressing the voltage spike on the bus side. r When the controller turns off the two main switches in the dead time, the resonant capacitor C r The voltage change rate can be clamped, so that the first main switch tube S1 and the second main switch tube S2 can be turned off at approximately zero voltage, thereby significantly reducing the turn-off loss.

[0018] The auxiliary network is interlaced with the main power circuit in physical layout, but the functional "early cut-off" strategy is used to solve the parasitic capacitance C in the existing technology. Da2 The problem of maintaining current caused by discharge. The first auxiliary switch tube S a1 The drain is also connected to the high voltage DC bus U bus The positive electrode, its source is connected to the first auxiliary diode D a1 The cathode of the resonant inductor L is connected r One end of the resonant inductor L r The other end is connected to the (autotransformer) T a The same-name terminal of transformer T a The secondary side has two coupled windings: the third winding is connected to the 3rd auxiliary diode D a3 With the third auxiliary switch S a3 After the series connection, it returns to the negative pole of the busbar, and the second winding passes through the second auxiliary diode D a2 With the second auxiliary switch S a2 Back to the negative pole of the bus, and in the second auxiliary diode D a2 The two ends are connected in parallel with capacitors to absorb the peak. In this way, when the controller detects that the holding current is about to appear, it immediately turns off the second auxiliary switch tube S in advance. a2 , so that the second auxiliary diode D a2 The parasitic capacitance C Da2 The discharge path is lost, thus completely suppressing the generation of the holding current; at the same time, the third winding continues to participate in the resonance in the Boost mode, ensuring that the third auxiliary switch tube S a3 It can still be turned on with zero current and maintain the soft switching performance in the Boost direction. a The number of turns of the three windings are N1, N2 and N3 respectively. Figure 3 L in m Transformer Ta The magnetizing inductance.

[0019] In simple terms, the second auxiliary switch tube S a2 The circuit is cut off before the maintenance current appears. On the one hand, the second auxiliary diode D a2 The parasitic capacitance C Da2 The maintenance current generated by the discharge causes the auxiliary switch to fail to turn on at zero current; at the same time, the parasitic capacitance C Da2 The discharge causes the problem of soft switching failure in the Boost mode, thereby ensuring the soft switching operation of the bidirectional DC-DC conversion process, and finally realizing the efficient power conversion of the bidirectional circuit.

[0020] It should be noted that, in this embodiment, except for the second auxiliary diode D a2 Except for the switch tube, the rest of the switching devices are ideal devices, and all inductors, capacitors and transformers are ideal devices, and the filter inductor L can be ignored. f The current ripple and output filter capacitor C f2 The voltage ripple, that is, the filter inductor current i Lf is a constant value I Lf , output voltage u o is a constant value U o In addition, the series resonant frequency is much larger than the rectifier frequency, and the input rectifier voltage is considered constant in each cycle, which is set as U bus or U bat The transformer turns ratios n and m are set to N1 / N2 and N1 / N3 respectively. In order to achieve soft switching of the circuit, n is set to be less than 1 and m is set to be greater than 1.

[0021] Furthermore, in actual operation, when the system is in Buck mode, the controller first turns on the first auxiliary switch S a1 , the second auxiliary switch tube S a2 Zero current turn-on, resonant inductor L r Energy storage; then the second auxiliary switch tube S a2 Turn off in advance, cut off the maintaining current path, and the resonant inductor L r , resonant capacitor C r Continue to resonate to complete the ZVS opening of the first main switch tube S1; the energy passes through the filter inductor L f , output filter capacitor C f2 In Boost mode, the battery energy is injected into the battery through the filter inductor L f , the second main switch tube S2, transformer T a The third winding, the third auxiliary switch tube S a3 , the third auxiliary diode D a3Feedback bus, second auxiliary switch tube S a2 The early shutdown of the second auxiliary diode D a2 No additional resonance is introduced, the third auxiliary switch S a3 Because the coupled winding current naturally shuts off at the zero-crossing point, zero-current switching is achieved. Both operating modes share the same set of magnetic components and power devices, eliminating the need for additional relays or mechanical switches, significantly reducing size and cost. This circuit solves the problem of the auxiliary switch failing to achieve zero-current switching due to the holding current generated by the parasitic capacitance of the auxiliary diode in the auxiliary network. It enables soft switching in the bidirectional DC-DC power conversion process, thereby achieving efficient power conversion in bidirectional circuits.

[0022] Preferably, the first main switch tube is an NMOS tube, the control end of the first main switch tube is the gate of the NMOS tube, the first end of the first main switch tube is the drain of the NMOS tube, and the second end of the first main switch tube is the source of the NMOS tube.

[0023] Preferably, the second main switch tube is an NMOS tube, the control end of the second main switch tube is the gate of the NMOS tube, the first end of the second main switch tube is the drain of the NMOS tube, and the second end of the second main switch tube is the source of the NMOS tube.

[0024] Preferably, the first, second, and third auxiliary switching transistors are all NMOS transistors. The control terminals of the first, second, and third auxiliary switching transistors are all gates of the NMOS transistors, the first terminals of the first, second, and third auxiliary switching transistors are all drains of the NMOS transistors, and the second terminals of the first, second, and third auxiliary switching transistors are all sources of the NMOS transistors.

[0025] In this embodiment, all controllable power devices in the main power and auxiliary networks are N-channel enhancement-mode MOSFETs, taking advantage of their low on-resistance, high-speed switching, and consistent body diode reverse recovery characteristics, thereby minimizing both conduction loss and switching loss on the same silicon platform. bus The positive electrode is directly connected to the drain of the first main switch tube S1. The source of the first main switch tube S1 and the drain of the second main switch tube S2 are connected at the same point, and then connected to the auxiliary network and the filter inductor L f The source of the second main switch tube S2 is connected to the negative electrode of the bus and the output filter capacitor C f2The negative terminal of the MOSFET is shorted to form a low-impedance power ground. The gates of the two main switches are independently controlled by a digital controller via an isolated driver chip. The leading and trailing edges of the gate drive signals, as well as the dead time, are programmable, ensuring that ZVS or ZCS boundary conditions are maintained under varying loads and temperatures.

[0026] The auxiliary network also uses NMOS tubes: the first auxiliary switch tube S a1 The drain of the bus has the same potential as the positive electrode, and its source is connected to the first auxiliary diode D a1 The cathode and resonant inductor L r Series; resonant inductor L r The other end is connected to the transformer T a The same-name end of transformer T a The second winding is connected to the second auxiliary switch tube S a2 The drain-source channel and the second auxiliary diode D a2 Back to the negative pole of the busbar, the third winding is connected to the third auxiliary switch tube S a3 The drain-source channel and the third auxiliary diode D a3 Returning to the negative busbar, since the direction of the NMOS tube's body diode aligns with the current direction required by the topology, when the controller turns off any auxiliary switch during the dead time, the body diode can instantaneously continue current, avoiding additional reverse recovery losses. Furthermore, the direct connection between the NMOS tube's source and the negative busbar stabilizes the gate drive reference potential, eliminating the need for a floating power supply for the drive circuit, simplifying the layout and reducing costs.

[0027] See also Figure 4 Specifically, in this embodiment, when working in steady state, Buck mode can be divided into 10 working modes, and the waveforms of each stage are as follows: Figure 5 As shown, PWM Sa1, Sa2 、PWM S1 They are switch tube S a1 、S a2 , the driving signal of S1, and the autotransformer current i Ta Equal to i Lr +i N2 , where i Lr is the resonant inductor current, i N2 is the secondary current of the transformer. The basic working principle is analyzed as follows: Phase 1——[t0-t1]: Figure 4 (a). At time t0, i Ta Less than I Lf The first auxiliary switch tube S a1 and the second auxiliary switch tube S a2 When both are turned on at the same time, zero current switching (ZCS-ON) can be achieved. r Charging, resonant inductor current iLr Starts to rise from 0. At the same time, the parasitic capacitance C Da2 Start to discharge. At this time, the primary and secondary sides of the autotransformer are short-circuited, so the resonant inductor L r While storing energy, the transformer T a The auxiliary diode D on the secondary side a2 And due to the existence of secondary current, i Ta The speed of increase is accelerated, which enables the circuit to enter the next stage faster. Da2 The existence of the excitation inductance current i Lm Reverse rise.

[0028] Phase 2——[t1-t2]: Figure 4 (b) At time t1, the parasitic capacitor voltage u CDa2 When it is equal to 0, the parasitic capacitance C Da2 After the discharge is completed, the resonant inductor current i Lr Starts to continue to rise linearly, the excitation inductor current i Lm Start to rise positively.

[0029] Phase 3 - [t2-t3]: Figure 4 (c) As shown. At time t2, i Ta Equal to I Lf , resonant inductor L r and resonant inductor C r Resonance starts. The parasitic diode of the second main switch tube S2 is turned off. The resonant capacitor C r The voltage starts to rise from 0. As the resonant capacitor C r The voltage resonates and rises, and the voltage of the first main switch tube S1 continues to drop.

[0030] Phase 4 - [t3-t4]: Figure 4 (d) At t3, the resonant capacitor voltage u Cr Equal to the high-voltage bus voltage U bus When , the resonance ends. The parasitic diode of the first main switch tube S1 is turned on. This provides the conditions for the zero voltage turn-on (ZVS-ON) of the first main switch tube S1. The resonant inductor L r Under back pressure, so i Lr Start to decline linearly.

[0031] Phase 5——[t4-t5]: Figure 4 (e) As shown. At t4, the first main switch S1 is turned on, completing ZVS-ON. Consistent with stage 4, i Lr It continues to decrease linearly until it reaches 0.

[0032] Phase 6 - [t5-t6]: Figure 4(f) As shown. At t5, i Lr Drops to 0. Resonant inductance L r and parasitic capacitance C Da2 Considering the impedance in the circuit, i Lr It will resonate to 0 in an underdamped attenuated oscillation state. At the same time, the parasitic capacitance C Da2 The voltage will remain at 2U bus .

[0033] Phase 7 - [t6-t7]: Figure 4 (g) At t6, the first auxiliary switch tube S a1 and the second auxiliary switch tube S a2 At the same time, the zero current shutdown (ZCS-OFF) is completed. In this stage, the excitation inductor current i Lm The voltage starts to decrease until it reaches 0, completing the reset of the excitation. This process will cause the auxiliary first auxiliary switch tube S a1 The second auxiliary switch tube S a2 The voltage is still 0.

[0034] Phase 8——[t7-t8]: Figure 4 (h) As shown. At t7, i Lm During this period, only the first main switch S1 remains on, and the high-voltage DC bus U bus Through the first main switch S1 and the filter inductor L f Power is supplied to the battery. The auxiliary switch and all diodes remain off.

[0035] Phase 9 - [t8-t9]: Figure 4 (i) As shown in Figure 2. At t8, the first main switch S1 is turned off, and the resonant capacitor C r Due to the clamping effect, the first main switch tube S1 approximately completes zero voltage shutdown (ZVS-OFF).

[0036] Phase 10——[t9-t 10 ]:like Figure 4 (j) At t9, the voltage of the first main switch tube S1 rises to U bus , while the resonant capacitor C r The voltage of the resonant capacitor drops to 0. At t8, the resonant capacitor voltage u Cr When the voltage is 0, the parasitic diode of the second main switch tube S2 is turned on, and the system enters the normal Buck freewheeling state, waiting for the next switching cycle.

[0037] Furthermore, in steady-state operation, the Boost mode can be divided into 8 operating modes, such as Figure 6 The waveforms of each stage are shown in Figure 7 As shown, PWMSa3 、PWM S2 They are switch tube S a3 , the driving signal of S2, and the transformer current i Ta Equal to i Lr +i N3 , where i N3 is the current of the third winding on the secondary side of the transformer. The basic working principle is analyzed as follows: Phase 1——[t0-t1]: Figure 6 (a). At time t0, i Ta Less than I Lf , the first auxiliary switch tube S a1 The parasitic diode of the first main switch tube S1 is turned on. The third auxiliary switch tube S a3 Open, complete ZCS-ON. Resonant inductor L r Charging, resonant inductor current i Lr It starts to rise linearly from 0, and the excitation inductance i Lm It also starts to rise from 0.

[0038] Phase 2——[t1-t2]: Figure 6 (b) As shown. At time t1, i Ta Equal to I Lf , the parasitic diode of the first main switch tube S1 is turned off. The resonant inductor L r and resonant capacitor C r Start to resonate, the resonant capacitor C r The voltage from U bus Start to descend.

[0039] Phase 3 - [t2-t3]: Figure 6 (c) At t2, the resonant capacitor voltage u Cr =0. The parasitic diode of the second main switch tube S2 is turned on, providing the conditions for the ZVS-ON of the second main switch tube S2. At this time, the excitation inductor current i Lm Will remain unchanged.

[0040] Phase 4 - [t3-t4]: Figure 6 As shown in (d). At time t3, the second main switch S2 is turned on, completing ZVS-ON. The resonant inductor L r Under back pressure, so i Lr It starts to decrease linearly until it reaches 0.

[0041] Phase 5——[t4-t5]: Figure 6 (e) As shown. At time t4, i Lr Equal to 0. The first auxiliary switch tube S a1 The parasitic diode is turned off.

[0042] Phase 6 - [t5-t6]: Figure 6 (f) At t5, the third auxiliary switch tube S a3 Turn off, completing ZCS-OFF. At the same time, the first auxiliary diode D a1 conduction, resonant inductor current i Lr At this time, the negative excitation inductor current is -i Lm .

[0043] Phase 7 - [t6-t7]: Figure 6 As shown in (g). At t6, the second main switch tube S2 is turned off, the parasitic diode of the first main switch tube S1 is turned on, and the filter inductor L f Energy is provided to the DC bus terminal through the parasitic diode of the first main switch tube S1. r The existence of the second main switch tube S2 allows the second main switch tube S2 to approximately complete ZVS-OFF. The resonant capacitor voltage will gradually rise from 0 to U bus At this time, the transformer T a The primary side will bear the voltage, making the excitation inductor current i Lm Gradually decrease.

[0044] Phase 8——[t7-t8-t9]: Figure 6 (h) As shown. At t7, u Cr Equal to U bus , in the t7-t8 stage, i Lm Still descending at the same slope. Lm drops to 0, and the excitation inductance is reset. At the same time, the first auxiliary diode D a1 Turn off. Wait for the next switching cycle.

[0045] Figure 8 This is the simulation result in Buck mode. Figure 8 (a) Shows the resonant inductance L r The current i Lr In the first auxiliary switch S a1 When the second auxiliary switch tube S is turned on, it remains zero. a2 The presence of the resonant inductor L r A holding current is generated on the first auxiliary switch S to ensure a1 Zero current soft switching operation. Figure 8 As shown in (d), the current i injected into the switch node Ta Greater than the filter inductor current i Lf , so that the main switch tube can achieve zero current switching operation, such as Figure 8 (b) As shown; at the same time, the second auxiliary switch tube S a2 It also works as zero current soft switching, such as Figure 8(c) is shown. Compared with the simulation results of the existing technology, the waveform is as follows Figure 2 As shown, PWM Qa1 、PWM Q1 They are the driving signals of auxiliary switch Qa1 and switch Q1, and the resonant inductor L k The current i Lk There is a holding current, which causes the auxiliary switch tube Qa1 to be hard turned on (zero current cannot be turned on). The current i flowing through the auxiliary switch tube Qa1 at the moment of turning on Qa1 Generates a large current spike.

[0046] Figure 9 is the simulation result in Boost mode, Figure 9 (a) Shows the third auxiliary switch S a3 It is a zero current soft switching operation; Figure 9 (c) shows that the current i injected into the switch node Ta Greater than the filter inductor current i Lf , so that the main switch tube S2 can achieve zero voltage switching operation, such as Figure 9 (b)

[0047] To summarize, the present invention addresses the industry pain point of "how to eliminate the holding current caused by the parasitic capacitance of the auxiliary diode while maintaining soft switching of the bidirectional DC-DC circuit within the full load range" and provides a concise and systematic hardware-control collaborative solution: the main power stage and the auxiliary network all use NMOS tubes, which take advantage of their low on-resistance and fast switching characteristics to simultaneously reduce the conduction loss and switching loss; the autotransformer and the resonant cavity share magnetic parts to reduce the number of magnetic components and reduce the size; the most critical thing is that before the holding current is formed, the controller turns off the second auxiliary switch tube in advance, instantaneously cuts off the discharge loop of the parasitic capacitance, and thus completely cuts off the source of the holding current, so that all auxiliary switches can be reliably turned on under zero current conditions, and the main switch uses the resonant capacitor to achieve zero voltage switching. More importantly, the same hardware can seamlessly switch between Buck and Boost without any relays or mechanical switches. This makes it suitable for charging and discharging energy storage inverters, and also meets the needs of bidirectional, high-frequency, and high-power density scenarios such as electric vehicle V2G and data center 48V busbars, truly achieving the design goal of "one topology, two directions, full-range soft switching, and full-domain high efficiency."

[0048] A second embodiment of the present invention provides a soft-switching bidirectional DC-DC device based on an autotransformer, which includes a controller and a soft-switching bidirectional DC-DC circuit based on an autotransformer as described in any one of the above items, wherein the control end of the main power circuit and the control end of the auxiliary network are electrically connected to the output end of the controller; wherein the controller is configured to control the switching of the auxiliary switch tube and the main switch tube.

[0049] The above is 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 are also considered to be within the scope of protection of the present invention.

Claims

1. A soft-switching bidirectional DC-DC circuit based on an autotransformer, characterized in that: include: A high-voltage DC bus, a battery voltage, a main power circuit, and an auxiliary network, wherein the high-voltage DC bus is connected in parallel to the main power circuit, the positive electrode of the high-voltage DC bus is electrically connected to a first end of the auxiliary network and a first end of the main power circuit, the negative electrode of the high-voltage DC bus is electrically connected to a second end of the auxiliary network, the switch tube of the main power circuit is connected in parallel to the capacitor of the auxiliary network, the battery voltage is connected in parallel to the main power circuit, the third end of the auxiliary network is electrically connected to the midpoint of the switch bridge arm of the main power circuit, and the control end of the main power circuit and the control end of the auxiliary network are connected to an external controller; The auxiliary network is configured to cut off the loop before the holding current appears to avoid the holding current, and ensure the normal operation of the Boost mode soft switch while achieving normal zero-current switching of the auxiliary network switch.

2. The soft-switching bidirectional DC-DC circuit based on an autotransformer according to claim 1, characterized in that: The main power circuit includes a first main switch, a second main switch, a filter inductor, an output filter capacitor, and an input filter capacitor. The control terminals of the first main switch and the second main switch are connected to a controller. The first terminal of the first main switch is electrically connected to the positive electrode of a high-voltage DC bus. The second terminal of the first main switch is electrically connected to the first terminal of the second main switch, an auxiliary network, and one terminal of the filter inductor. The second terminal of the second main switch is electrically connected to the negative electrode of the high-voltage DC bus. The other terminal of the filter inductor is electrically connected to the output filter capacitor. The other terminal of the output filter capacitor is electrically connected to the negative electrode of the high-voltage DC bus and the second terminal of the second main switch. The input filter capacitor is connected in parallel with the high-voltage DC bus.

3. The autotransformer-based soft-switching bidirectional DC-DC circuit according to claim 2, characterized in that: The first main switch tube is an NMOS tube, the control end of the first main switch tube is the gate of the NMOS tube, the first end of the first main switch tube is the drain of the NMOS tube, and the second end of the first main switch tube is the source of the NMOS tube.

4. The autotransformer-based soft-switching bidirectional DC-DC circuit according to claim 2, characterized in that: The second main switch tube is an NMOS tube, the control end of the second main switch tube is the gate of the NMOS tube, the first end of the second main switch tube is the drain of the NMOS tube, and the second end of the second main switch tube is the source of the NMOS tube.

5. The autotransformer-based soft-switching bidirectional DC-DC circuit according to claim 2, characterized in that: The auxiliary network includes a first auxiliary switch tube, a first auxiliary diode, a second auxiliary switch tube, a second auxiliary diode, a third auxiliary switch tube, a third auxiliary diode, a transformer, a resonant inductor, a resonant capacitor and a parasitic capacitor, wherein the control end of the first auxiliary switch tube, the control end of the second auxiliary switch tube and the control end of the third auxiliary switch tube are connected to the controller, the first end of the first auxiliary switch tube is electrically connected to the positive electrode of the high-voltage DC bus, the second end of the first auxiliary switch tube is electrically connected to the negative electrode of the first auxiliary diode and the first end of the resonant inductor, the second end of the resonant inductor is electrically connected to the first end of the transformer, and the transformer The second end of the transformer is electrically connected to the anode of the third auxiliary diode, the third end of the transformer is electrically connected to the cathode of the second auxiliary diode, the fourth end of the transformer is electrically connected to the second end of the first main switch tube, the first end of the second main switch tube, and one end of the filter inductor, the cathode of the third auxiliary diode is electrically connected to the first end of the third auxiliary switch tube, the parasitic capacitor is connected in parallel with the second auxiliary diode, the anode of the second auxiliary diode is electrically connected to the second end of the second auxiliary switch tube, and the anode of the first auxiliary diode, the first end of the second auxiliary switch tube, and the second end of the third auxiliary switch tube are electrically connected to the negative electrode of the high-voltage DC bus.

6. The autotransformer-based soft-switching bidirectional DC-DC circuit according to claim 5, characterized in that: The first auxiliary switch tube, the second auxiliary switch tube, and the third auxiliary switch tube are all NMOS tubes.

7. The autotransformer-based soft-switching bidirectional DC-DC circuit according to claim 6, characterized in that: The control end of the first auxiliary switch tube, the control end of the second auxiliary switch tube, and the control end of the third auxiliary switch tube are all gates of the NMOS tube, the first end of the first auxiliary switch tube, the first end of the second auxiliary switch tube, and the first end of the third auxiliary switch tube are all drains of the NMOS tube, and the second end of the first auxiliary switch tube, the second end of the third auxiliary switch tube, and the second end of the third auxiliary switch tube are all sources of the NMOS tube.

8. A soft-switching bidirectional DC-DC device based on an autotransformer, characterized in that: It comprises a controller and a soft-switching bidirectional DC-DC circuit based on an autotransformer as described in any one of claims 1 to 7, wherein the control end of the main power circuit and the control end of the auxiliary network are electrically connected to the output end of the controller; wherein the controller is configured to control the switching of the auxiliary switch tube and the main switch tube.

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