A soft-switching bidirectional DC-DC circuit and device based on a self-coupled transformer

Abstract

The application provides a soft-switching bidirectional DC-DC circuit and device based on a self-coupling transformer, wherein a main power circuit comprises a high-voltage DC bus, a battery end, two main switching tubes, a filter inductor and a filter capacitor; an auxiliary network comprises three auxiliary switching tubes and auxiliary diodes, a transformer, a resonant inductor and a resonant capacitor. In view of the defects that the auxiliary switching zero-current turn-on fails due to the maintenance current generated by the discharge of the auxiliary diode parasitic capacitance in the traditional soft-switching Buck circuit, and the soft switching of the bidirectional Boost mode is invalid, the auxiliary switching is used to cut off the resonant loop before the maintenance current is formed, the release of the parasitic capacitance energy is inhibited, and it is ensured that all switching devices in the Buck and Boost two energy flow directions achieve zero-voltage or zero-current switching. Through high-frequency resonant control, the circuit always maintains a soft-switching state in the bidirectional power transmission process, significantly reduces the switching loss, improves the overall efficiency, and is suitable for energy storage and electric vehicles and other scenes requiring efficient bidirectional DC conversion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of DC-DC circuit, in particular to a soft switching bidirectional DC-DC circuit and device based on autotransformer. BACKGROUND

[0002] With the rapid development of new energy power generation, energy storage system and electric vehicle bidirectional charging application scenarios, the DC-DC circuit capable of realizing bidirectional energy flow becomes one of the key components in the power electronic field. Under the design requirements of high frequency, high power density and high efficiency, soft switching technology is widely used in bidirectional DC-DC circuit to reduce switching loss, reduce electromagnetic interference and improve system efficiency.

[0003] At present, the existing scheme tries to combine the resonant soft switching technology with high-frequency transformer or autotransformer to broaden the soft switching range and take into account the step-down capability. For example, Figure 1 The soft switching Buck circuit based on high-frequency transformer shown in the figure injects resonant energy into a specific node through an autotransformer, so that the main power switch and the switching devices in the auxiliary network can realize zero voltage turn-on (ZVS) or zero current turn-on (ZCS), thereby maintaining high conversion efficiency under different input voltages and load conditions. The topology structure theoretically realizes a wide range of soft switching operation and shows good step-down performance in Buck mode.

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

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

[0006] In view of this, the present application is proposed. SUMMARY

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

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A soft switching bidirectional DC-DC circuit based on a self-coupling transformer comprises a high-voltage DC bus, a battery voltage, a main power circuit, and an auxiliary network, the high-voltage DC bus is connected in parallel with the main power circuit, the positive pole of the high-voltage DC bus is electrically connected with the first end of the auxiliary network and the first end of the main power circuit, the negative pole of the high-voltage DC bus is electrically connected with the second end of the auxiliary network, the switch tube of the main power circuit is connected in parallel with the capacitor of the auxiliary network, the battery voltage is connected in parallel with the main power circuit, the third end of the auxiliary network is electrically connected with 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 with an external controller.

[0010] The auxiliary network is configured to cut off the loop before the maintenance current occurs, avoid the occurrence of the maintenance current, and ensure the normal operation of the Boost mode soft switching while realizing the normal turn-on of the switch zero current of the auxiliary network.

[0011] The application further provides a soft switching bidirectional DC-DC device based on a self-coupling transformer, which comprises a controller and the soft switching bidirectional DC-DC circuit based on a self-coupling transformer according to any one of the above, the control end of the main power circuit and the control end of the auxiliary network are electrically connected with the output end of the controller, and the controller is configured to control the switching of the auxiliary switch tube and the main switch tube.

[0012] In summary, the application is based on the existing soft switching Buck circuit based on a high-frequency transformer, and aims at the maintenance current problem caused by the parasitic capacitance of the auxiliary diode and the limitation of one-way power flow, and proposes a soft switching DC-DC conversion circuit and circuit with bidirectional energy transmission capability taking a self-coupling transformer as the core. By adding an auxiliary switch Sa2 in the auxiliary network, the resonant loop is cut off in time before the main switch is turned off, the maintenance current caused by the discharge of the parasitic capacitance is eliminated from the source, and the turn-on and turn-off of all power devices in Buck and Boost modes can realize zero voltage or zero current. The topology structure is simple, the control strategy is compatible with the existing high-frequency resonance control, the soft switching characteristics can be maintained in a wide input voltage and load range, the switching loss and electromagnetic interference are significantly reduced, the system efficiency and reliability are improved, and the application is particularly suitable for energy storage systems, electric vehicle bidirectional charging and discharging and other application scenarios requiring high-efficiency bidirectional DC conversion. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a soft switching Buck circuit based on a high-frequency transformer of the prior art;

[0014] Figure 2 is a soft switching Buck simulation waveform diagram based on a high-frequency transformer of the prior art;

[0015] Figure 3 is a schematic diagram of a soft-switching bidirectional DC-DC circuit based on a self-coupling transformer provided by the present application;

[0016] Figure 4 (a)- Figure 4 (j) is a schematic diagram of the working mode of the circuit in Buck mode provided by the present application;

[0017] Figure 5 is a schematic diagram of the working waveform of the circuit in Buck mode provided by the present application;

[0018] Figure 6 (a)- Figure 6 (h) is a schematic diagram of the working mode of the circuit in Boost mode provided by the present application;

[0019] Figure 7 is a schematic diagram of the working waveform of the circuit in Boost mode provided by the present application;

[0020] Figure 8 is a simulation waveform diagram of the working of the circuit in Buck mode provided by the present application, wherein: Figure 8 (a) is a simulation waveform diagram in which the current of the resonant inductor is kept as zero when the first auxiliary switch tube is turned on, Figure 8 (b) is a simulation waveform diagram in which the main switch tube realizes zero-current switching work, Figure 8 (c) is a simulation waveform diagram in which the second auxiliary switch tube also realizes zero-current soft switching work, Figure 8 (d) is a simulation waveform diagram in which the current injected into the switch node is greater than the filter inductor current;

[0021] Figure 9 is a simulation waveform diagram of the working of the circuit in Boost mode provided by the present application, wherein: Figure 9 (a) is a simulation waveform diagram in which the third auxiliary switch tube realizes zero-current soft switching work, Figure 9 (b) is a simulation waveform diagram in which the second main switch tube realizes zero-voltage switching work, Figure 9 (c) is a simulation waveform diagram in which the current injected into the switch node is greater than the filter inductor current. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0023] Reference Figure 3 As shown in the figure, the first embodiment of the present application discloses a soft-switching bidirectional DC-DC circuit based on a self-coupling transformer, which comprises: a high-voltage DC bus U bus, battery voltage U bat , main power circuit, auxiliary network, high-voltage DC bus U bus parallel to the main power circuit, high-voltage DC bus U bus positive electrode of the high-voltage DC bus U bus negative electrode of the high-voltage DC bus U bat 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 is connected to the control end of the auxiliary network and an external controller;

[0024] The auxiliary network is configured to cut off the loop before the maintenance current occurs, avoid the occurrence of the maintenance current, and ensure the normal operation of the Boost mode soft switch while realizing the normal turn-on of the switch zero current of the auxiliary network.

[0025] Preferably, the main power circuit includes a first main switch S1, a second main switch S2, a filter inductor L f , an output filter capacitor C f2 , and an input filter capacitor C f1 The control end of the first main switch S1 and the control end of the second main switch S2 are connected to the controller, the first end of the first main switch S1 is electrically connected to the positive electrode of the high-voltage DC bus U bus , the second end of the first main switch S1 is electrically connected to the first end of the second main switch S2, the auxiliary network, and one end of the filter inductor L f , the second end of the second main switch S2 is electrically connected to the negative electrode of the high-voltage DC bus U bus , the other end of the filter inductor L f is electrically connected to the output filter capacitor C f2 , the other end of the output filter capacitor C f2 is electrically connected to the negative electrode of the high-voltage DC bus U bus and the second end of the second main switch S2, and the input filter capacitor C f1 is connected in parallel to the high-voltage DC bus U bus .

[0026] Preferably, the auxiliary network includes a first auxiliary switch S a1 , a first auxiliary diode D a1 , a second auxiliary switch S a2 , a second auxiliary diode D a2 , a third auxiliary switch S a3 , a third auxiliary diode D a3 , a transformer T a, resonance inductance L r , resonance capacitance C r , and parasitic capacitance C Da2 , wherein the control end of the first auxiliary switch S a1 , the control end of the second auxiliary switch S a2 , and the control end of the third auxiliary switch S a3 are connected with a controller, the first end of the first auxiliary switch S a1 is electrically connected with the positive pole of a high-voltage DC bus U bus , the second end of the first auxiliary switch S a1 is electrically connected with the negative pole of a first auxiliary diode S a1 and the first end of a resonance inductance L r , the second end of the resonance inductance L r is electrically connected with the first end of a transformer T a , the second end of the transformer T a is electrically connected with the positive pole of a third auxiliary diode D a3 , the third end of the transformer T a is electrically connected with the negative pole of a second auxiliary diode D a2 , the fourth end of the transformer T a is electrically connected with the second end of a first main switch S1, the first end of a second main switch S2, and one end of a filter inductance L f , the negative pole of the third auxiliary diode D a3 is electrically connected with the first end of the third auxiliary switch S a2 , the parasitic capacitance C Da2 is connected in parallel with the second auxiliary diode D a2 , the positive pole of the second auxiliary diode D a3 is electrically connected with the second end of the second auxiliary switch S a2 , the positive pole of the first auxiliary diode D a1 , the first end of the second auxiliary switch S a2 , and the second end of the third auxiliary switch D a3 are electrically connected with the negative pole of the high-voltage DC bus U bus .

[0027] Specifically, in the embodiment, the soft-switching bidirectional DC-DC circuit based on the autotransformer realizes bidirectional, soft-switching, and high-efficiency DC-DC power conversion through a set of compact and complete main power circuit and auxiliary network. The high-voltage DC bus U busThe positive pole 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 resonance branch. The negative pole 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. The battery voltage U bat The filter inductor L f is connected in series with the output filter capacitor C f2 at the output of the main power circuit, serving as both the load in Buck mode and the energy source in Boost mode, achieving bidirectional power flow with the same hardware structure.

[0028] Inside the main power circuit, both the first main switch S1 and the second main switch S2 are NMOS transistors, with their gates uniformly receiving PWM signals from an external digital controller. The source-drain path carries all the load current during switching. The filter inductor L f is connected in series between the source of the first main switch S1 and the positive pole of the battery, and the output filter capacitor C f2 is connected in parallel across the battery, together smoothing the pulsating current to a DC voltage acceptable to the battery and suppressing voltage spikes on the bus side. Since the first main switch S1 and the second main switch S2 are connected in parallel with the resonance capacitor C r , when the controller turns off both main switches during the dead time, the resonance capacitor C r can clamp the voltage rate of change, allowing the first main switch S1 and the second main switch S2 to achieve approximately zero-voltage switching and significantly reduce switching losses.

[0029] The auxiliary network is physically interleaved with the main power circuit, but it solves the problem of maintaining current caused by parasitic capacitance C Da2 discharge in the prior art through a "premature cutoff" strategy. The drain of the first auxiliary switch S a1 is also connected to the high-voltage DC bus U bus positive pole, and its source is connected to one end of the resonance inductor L a1 through the cathode of the first auxiliary diode D r . The other end of the resonance inductor L r is connected to the same end of the transformer T a . The secondary side of the transformer T a has two coupled windings: the third winding is connected in series with the third auxiliary diode D a3 and the third auxiliary switch S a3 and then returns to the negative pole of the bus, and the second winding is connected in series with the second auxiliary diode D a2 and the second auxiliary switch S a2 and then returns to the negative pole of the bus, with a capacitor connected in parallel across the second auxiliary diode D a2 to absorb spikes. In this way, when the controller detects the presence of a maintaining current, it immediately turns off the second auxiliary switch Sa2 so that the second auxiliary diode D a2 loses the discharge path of the parasitic capacitance C Da2 , thereby completely suppressing the generation of the maintenance current; meanwhile, the third winding continues to participate in resonance in the Boost mode, ensuring that the third auxiliary switch S a3 can still be turned on with zero current and maintaining the soft switching performance in the Boost direction. The number of turns of the three windings of the transformer T a is N1, N2 and N3 respectively, Figure 3 L m is the magnetizing inductance of the transformer T a .

[0030] In simple terms, the second auxiliary switch S a2 cuts off the circuit before the maintenance current appears. On the one hand, it solves the problem of the maintenance current generated by the discharge of the parasitic capacitance C a2 of the second auxiliary diode D Da2 , which leads to the failure of the zero-current turn-on of the auxiliary switch; at the same time, it solves the problem of the failure of the soft switching in the Boost mode due to the discharge of the parasitic capacitance C Da2 caused by the coupling of the two secondary windings N2 and N3, thereby ensuring the soft switching operation of the bidirectional DC-DC conversion process and ultimately achieving high-efficiency power conversion of the bidirectional circuit.

[0031] It should be noted that in this embodiment, all the switch devices except the second auxiliary diode D a2 are ideal devices, and all the inductors, capacitors and transformers are ideal devices, and the current ripple of the filter inductor L f and the voltage ripple of the output filter capacitor C f2 can be ignored, i.e. the filter inductor current i Lf is a constant value I Lf , and the output voltage u o is a constant value U o . In addition, the series resonance frequency is much higher than the rectification frequency, and the input rectification voltage is considered constant within each cycle and is set to U bus or U bat . The transformer turns ratios n and m are set to N1 / N2 and N1 / N3 respectively, in order to complete the soft switching operation of the circuit, n is set to less than 1 and m is set to greater than 1.

[0032] Further, in actual operation, when the system is in the Buck mode, the controller first turns on the first auxiliary switch S a1 and the second auxiliary switch S a2 with zero current, and stores energy in the resonant inductor L r ; then the second auxiliary switch S a2 is turned off in advance, cutting off the maintenance current path, and the resonant inductor Lr , resonance capacitor C r Continue resonance to complete ZVS turn-on of the first main switch S1; energy is transferred through the filter inductor L f , output filter capacitor C f2 Smooth injection of the battery. In boost mode, the battery energy is transferred through the filter inductor L f , second main switch S2, transformer T a , third winding, third auxiliary switch S a3 , third auxiliary diode D a3 Feedback bus, early turn-off of the second auxiliary switch S a2 also ensures that the second auxiliary diode D a2 will not introduce additional resonance, and the third auxiliary switch S a3 is naturally turned off at the zero-crossing point due to the coupling winding current, achieving zero-current switching. The two operating modes share the same set of magnetic components and power devices, eliminating the need for additional relays or mechanical switching, significantly reducing size and cost. The circuit solves the problem of maintaining current caused by the parasitic capacitance of the auxiliary diode in the auxiliary network, which leads to the failure of zero-current turn-on of the auxiliary switch. It can realize soft switching in the process of bidirectional DC-DC power conversion, and further realize high-efficiency power conversion of bidirectional circuit.

[0033] Preferably, the first main switch is an NMOS tube, the control end of the first main switch is the gate of the NMOS tube, the first end of the first main switch is the drain of the NMOS tube, and the second end of the first main switch is the source of the NMOS tube.

[0034] Preferably, the second main switch is an NMOS tube, the control end of the second main switch is the gate of the NMOS tube, the first end of the second main switch is the drain of the NMOS tube, and the second end of the second main switch is the source of the NMOS tube.

[0035] Preferably, the first auxiliary switch, the second auxiliary switch, and the third auxiliary switch are all NMOS tubes. The control end of the first auxiliary switch, the control end of the second auxiliary switch, and the control end of the third auxiliary switch are all gates of NMOS tubes, the first end of the first auxiliary switch, the first end of the second auxiliary switch, and the first end of the third auxiliary switch are all drains of NMOS tubes, and the second end of the first auxiliary switch, the second end of the third auxiliary switch, and the second end of the third auxiliary switch are all sources of NMOS tubes.

[0036] 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 f2 The 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.

[0037] 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.

[0038] 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 iLr is the resonant inductor current, i N2 is the transformer secondary current. The basic working principle is analyzed as follows:

[0039] Phase 1 - [t0-t1]: as shown in Figure 4 (a). At t0, i Ta is less than I Lf . The first auxiliary switch S a1 and the second auxiliary switch S a2 are turned on at the same time, and zero-current turn-on (ZCS-ON) can be achieved. The resonant inductor L r is charged, and the resonant inductor current i Lr starts to rise from 0. At the same time, the parasitic capacitor C Da2 begins to discharge. At this time, the primary and secondary sides of the autotransformer are short-circuited, so the resonant inductor L r stores energy while the transformer T a makes the secondary side auxiliary diode D a2 conduct. And because of the existence of the secondary side current, the speed of i Ta increases, so that the circuit can enter the next stage faster. Due to the existence of the parasitic capacitor C Da2 , the magnetizing inductor current i Lm rises in the opposite direction.

[0040] Phase 2 - [t1-t2]: as shown in Figure 4 (b). At t1, when the parasitic capacitor voltage u CDa2 is equal to 0, the parasitic capacitor C Da2 discharges, and the resonant inductor current i Lr begins to continue to rise linearly, and the magnetizing inductor current i Lm begins to rise in the positive direction.

[0041] Phase 3 - [t2-t3]: as shown in Figure 4 (c). At t2, i Ta is equal to I Lf , the resonant inductor L r and the resonant capacitor C r start to resonate. The parasitic diode of the second main switch S2 is turned off. The voltage of the resonant capacitor C r starts to rise from 0. With the resonant rise of the resonant capacitor C r voltage, the voltage of the first main switch S1 continues to drop.

[0042] Phase 4 - [t3-t4]: as shown in Figure 4 (d). At t3, the resonant capacitor voltage u Cr is equal to the high voltage bus voltage U busWhen , 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.

[0043] 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.

[0044] 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 .

[0045] 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.

[0046] 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.

[0047] 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).

[0048] Phase 10——[t9-t 10 ]:like Figure 6 (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.

[0049] Furthermore, in steady-state operation, the Boost mode can be divided into 8 operating modes, such as Figure 7 The waveforms of each stage are shown in Figure 6 As shown, PWM Sa3 、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:

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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 .

[0056] 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.

[0057] Phase 8——[t7-t8-t9]: Figure 8 (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.

[0058] Figure 8This 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 (d) 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 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 2 (c) is shown. Compared with the simulation results of the existing technology, the waveform is as follows Figure 9 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.

[0059] Figure 9 is the simulation result in Boost mode, Figure 9 (a) Shows the third auxiliary switch S a3 It works as zero current soft switching; 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 ​ (b)

[0060] In summary, the application gives a set of simple and systematic hardware-control collaborative solutions around the industry pain point of "how to eliminate the maintenance current caused by the parasitic capacitance of the auxiliary diode and keep the bidirectional DC-DC circuit in soft switching in the full load range": the main power stage and the auxiliary network all use NMOS tubes, which can reduce the conduction loss and switching loss by taking advantage of their low conduction resistance and fast switching characteristics; the self-coupled transformer and the resonant cavity share the magnetic components, reducing the number of magnetic components and the volume; most importantly, before the maintenance current is formed, the second auxiliary switch tube is turned off by the controller in advance, instantaneously cutting off the discharge circuit of the parasitic capacitance, thereby completely cutting off the source of the maintenance current, so that all auxiliary switches can be reliably turned on under zero current conditions, and the main switch can realize zero voltage switching by means of the resonant capacitor. More importantly, the same set of hardware can seamlessly switch between Buck and Boost directions without any relays or mechanical switching, which is suitable for charging and discharging of energy storage converters, and meets the needs of bidirectional, high-frequency, high-power density scenarios such as electric vehicle V2G and data center 48V bus, and truly realizes the design goal of "one topology, two directions, full-soft switching, and full-efficiency".

[0061] The second embodiment of the application provides a self-coupled transformer-based soft switching bidirectional DC-DC device, which comprises a controller and a self-coupled transformer-based soft switching bidirectional DC-DC circuit according to any one of the above, and 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.

[0062] The above is the preferred embodiment of the application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the principles of the application, and these improvements and refinements are also considered within the protection scope of the application.

Claims

1. A soft-switching bidirectional DC-DC circuit based on a self-coupled transformer, characterized in that, The application relates to a high-voltage direct-current bus, a battery voltage, a main power circuit and an auxiliary network, wherein the main power circuit comprises a first main switch tube, a second main switch tube, a filter inductor, an output filter capacitor and an input filter capacitor; the control ends of the first main switch tube and the second main switch tube are connected with a controller; the first end of the first main switch tube is electrically connected with the positive pole of the high-voltage direct-current bus; the second end of the first main switch tube is electrically connected with the first end of the second main switch tube, the auxiliary network and one end of the filter inductor; the second end of the second main switch tube is electrically connected with the negative pole of the high-voltage direct-current bus; the other end of the filter inductor is electrically connected with the output filter capacitor; the other end of the output filter capacitor is electrically connected with the negative pole of the high-voltage direct-current bus and the second end of the second main switch tube; the input filter capacitor is connected in parallel with the high-voltage direct-current bus; the high-voltage direct-current bus is connected in parallel with the main power circuit; the positive pole of the high-voltage direct-current bus is electrically connected with the first end of the auxiliary network and the first end of the main power circuit; the negative pole of the high-voltage direct-current bus is electrically connected with the second end of the auxiliary network; the second switch tube of the main power circuit is connected in parallel with the capacitor of the auxiliary network; the battery voltage is connected in parallel with the main power circuit; the third end of the auxiliary network is electrically connected with the midpoint of the switch bridge arm of the main power circuit; the control ends of the main power circuit and the auxiliary network are connected with an external controller. The auxiliary network is configured to cut off the loop before the maintenance current appears, avoid the appearance of the maintenance current, and ensure the normal operation of the Boost mode soft switch while realizing the normal opening of the switch zero current of the auxiliary network. The auxiliary network comprises 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; the control ends of the first auxiliary switch tube, the second auxiliary switch tube and the third auxiliary switch tube are connected with a controller; the first end of the first auxiliary switch tube is electrically connected with the positive pole of the high-voltage direct-current bus; the second end of the first auxiliary switch tube is electrically connected with the negative pole of the first auxiliary diode and the first end of the resonant inductor; the second end of the resonant inductor is electrically connected with the first end of the transformer; the second end of the transformer is electrically connected with the positive pole of the third auxiliary diode; the third end of the transformer is electrically connected with the negative pole of the second auxiliary diode; the fourth end of the transformer is electrically connected with 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 negative pole of the third auxiliary diode is electrically connected with the first end of the third auxiliary switch tube; the parasitic capacitor is connected in parallel with the second auxiliary diode; the positive pole of the second auxiliary diode is electrically connected with the second end of the second auxiliary switch tube; the positive pole 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 with the negative pole of the high-voltage direct-current bus. ​ 2. The self-coupled transformer-based soft-switching bidirectional DC-DC circuit of claim 1, wherein, The first main switch tube is an NMOS tube, a control end of the first main switch tube is a gate of the NMOS tube, a first end of the first main switch tube is a drain of the NMOS tube, and a second end of the first main switch tube is a source of the NMOS tube.

3. The self-coupled transformer-based soft-switching bidirectional DC-DC circuit of claim 1, wherein, The second main switch tube is an NMOS tube, a control end of the second main switch tube is a gate of the NMOS tube, a first end of the second main switch tube is a drain of the NMOS tube, and a second end of the second main switch tube is a source of the NMOS tube.

4. The self-coupled transformer-based soft-switching bidirectional DC-DC circuit of claim 1, wherein, The first auxiliary switch tube, the second auxiliary switch tube and the third auxiliary switch tube are all NMOS tubes.

5. The self-coupled transformer-based soft-switching bidirectional DC-DC circuit of claim 4, 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 all gates of the NMOS tubes, 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 tubes, and the second end of the first auxiliary switch tube, the second end of the second auxiliary switch tube and the second end of the third auxiliary switch tube are all sources of the NMOS tubes.

6. A self-coupled transformer based soft-switching bidirectional DC-DC device, characterized in that, The controller and the soft-switching bidirectional DC-DC circuit based on the autotransformer are connected electrically, and the controller is configured to control the switching of the auxiliary switch tubes and the main switch tubes.

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