A full power range soft switching control method and system based on DAB circuit

Abstract

The application discloses a full-power-range soft switching control method and system based on a DAB circuit. The method comprises the following steps: connecting a buffer capacitor in parallel with a switching tube to realize soft turn-off of the switching tube at any time; when actual transmission power of the DAB circuit is less than preset mode switching power, a phase shift control strategy with an external phase shift angle not less than 90 degrees and not more than 180 degrees is adopted to make the switching tube of the DAB circuit open with zero voltage, wherein when the external phase shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase turn-off current of the switching tube, the buffer capacitor completes charging and discharging in dead time, and the switching tube is in a soft switching state; and when actual transmission power of the DAB circuit is not less than the preset mode switching power, a single phase shift control strategy is adopted to make the switching tube of the DAB circuit open with zero voltage. The method can realize full-power-range soft switching control of the switching tube, greatly reduce switching loss of the switching device, improve system efficiency and not affect dynamic response of the system.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a full-power range soft switching control method and system based on a DAB circuit. Background Art

[0002] With the development of power electronics technology and the rise of renewable energy generation, the power system has undergone profound changes. Compared to AC transmission, DC transmission and distribution technology offers lower line losses, easier access to distributed power sources, and more flexible dispatching, resulting in unprecedented growth. Large-capacity DC transformers, as core equipment in DC transmission and distribution systems, primarily provide core functions such as electromagnetic isolation and voltage level transformation. Compared to traditional power frequency isolation transformers, they are smaller and offer higher power density. However, due to the introduction of large-capacity switching devices, switching device losses contribute significantly to this loss.

[0003] To improve DC transformer efficiency, a shunt capacitor can be used to implement soft-turn-off of the switching devices. This technology effectively reduces the turn-off losses of the switching devices in a DAB (Dual Active Bridge) circuit under rated load. Combined with its soft-turn-on characteristics, it significantly reduces switching losses and improves system efficiency. However, when the device operates under light load, the dead zone causes the device to lose its zero-voltage turn-on characteristic. The shunt capacitor directly discharges the switching device, generating a large pulse current. Furthermore, the peak current of existing small-capacitance capacitors is low, and there are certain requirements for the current rise rate when the device turns on. Therefore, this pulse current reduces the lifespan of the switching device and capacitor, making the DAB unsafe under light load and no-load conditions. While adding a capacitor in series with the auxiliary inductor can extend the soft-switching range in the presence of voltage mismatches, it still cannot completely resolve the loss of zero-voltage turn-on during no-load operation. Therefore, existing technologies cannot achieve power continuity regulation after the DAB is connected in parallel with the soft-turn-off capacitor. Summary of the Invention

[0004] In view of the above problems, the inventors have made the present invention, and through specific implementation methods, provide a full-power range soft switching control method and system based on a DAB circuit.

[0005] In a first aspect, an embodiment of the present invention provides a full-power range soft switching control method based on a DAB circuit, comprising:

[0006] When the actual transmission power of the DAB circuit is less than the preset mode switching power, a phase shift control strategy with an external phase shift angle of not less than 90 degrees and not more than 180 degrees is adopted to turn on the switch of the DAB circuit at zero voltage. When the external phase shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase the turn-off current of the switch. The buffer capacitor is fully charged and discharged within the dead time, and the switch is in a soft switching state.

[0007] When the actual transmission power of the DAB circuit is not less than the preset mode switching power, a single phase-shift control strategy is adopted to turn on the switch tube of the DAB circuit at zero voltage. Since there is a buffer capacitor when turning off, it is a quasi-soft turn-off, and the switch tube is in a soft switching state.

[0008] Specifically, the phase-shift control strategy includes any one of single-phase-shift control, double-phase-shift control, and triple-phase-shift control.

[0009] Specifically, constructing the DAB circuit includes the following steps:

[0010] The DAB circuit includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer, wherein the primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer;

[0011] The primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1. T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4;

[0012] The secondary full bridge includes four switching tubes T5, T6, T7 and T8, and a DC support capacitor Cs. T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8;

[0013] Each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor, respectively. The collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor, respectively. The emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor, respectively.

[0014] Furthermore, when dual phase shift is used to inject reactive power, after the switch tube is in the soft shutdown state, the reactive power is gradually reduced until the switch tube is no longer in the soft shutdown state. The reactive power at this time is recorded to obtain the dual phase shift soft shutdown minimum reactive power.

[0015] Specifically, determining the mode switching power includes the following steps:

[0016] determining an operating mode according to an actual transmission power of the DAB circuit;

[0017] The mode switching power is determined according to the capacitance, DC voltage, dead time and phase shift inductance in the DAB circuit.

[0018] Specifically, the following steps are also included:

[0019] When the mode is switched, the bias current during switching is controlled to eliminate the bias current.

[0020] Specifically, controlling the bias current during switching to eliminate the bias current includes the following steps:

[0021] By controlling the on-duty cycle of all switching tubes in the first cycle after mode switching, the bias current during mode switching is eliminated.

[0022] Specifically, the bias current during mode switching is eliminated by controlling the on-duty cycle of all switching tubes in the first cycle after mode switching, including the following steps:

[0023] When a light load is switched to a heavy load in the positive direction or a light load is switched to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, and the bias current is eliminated.

[0024] When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference across it to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated.

[0025] When the energy transfer direction changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated;

[0026] The positive direction refers to the direction of energy transfer from the primary side to the secondary side, and the negative direction refers to the direction of energy transfer from the secondary side to the primary side. V1 is the output voltage of the primary side, V2 is the output voltage of the secondary side, and the conduction of T1 is the cycle start signal.

[0027] In a second aspect, an embodiment of the present invention provides a full-power range soft switching control system based on a DAB circuit, comprising:

[0028] A DAB circuit construction module is used to construct the DAB circuit, which includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer. The primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer; the primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1, T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; the secondary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1, T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer. The other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; Switches T5, T6, T7 and T8, a DC support capacitor Cs, T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8; each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor respectively, the collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor respectively, and the emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor respectively;

[0029] A mode switching power determination module is configured to determine an operating mode based on an actual transmission power of the DAB circuit; and determine the mode switching power based on a capacitance, a DC voltage, a dead time, and a phase shift inductance in the DAB circuit;

[0030] a first soft-off control module, configured to, when the actual transmission power of the DAB circuit is less than a preset mode switching power, adopt a phase-shift control strategy with an external phase-shift angle of not less than 90 degrees and not more than 180 degrees to enable the switching tube of the DAB circuit to be turned on at zero voltage; wherein, when the external phase-shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase the turn-off current of the switching tube, so that the buffer capacitor is fully charged and discharged within the dead time, and the switching tube is in a soft switching state;

[0031] The second soft-off control module is configured to, when the actual transmission power of the DAB circuit is not less than the preset mode switching power, adopt a single-phase-shift control strategy to turn on the switch tube of the DAB circuit at zero voltage, and the switch tube is in a soft switching state.

[0032] Specifically, the phase-shift control strategy includes any one of single-phase-shift control, double-phase-shift control, and triple-phase-shift control.

[0033] Furthermore, a full power range soft switching control system based on a DAB circuit further includes:

[0034] A minimum reactive power determination module is used to, when dual-phase shifting is used to inject reactive power, gradually reduce the reactive power after the switch tube is in the soft-off state until the switch tube is no longer in the soft-off state, record the reactive power at this time, and obtain the dual-phase shifting soft-off minimum reactive power;

[0035] The bias current elimination module is used to control the bias current during switching and eliminate the bias current when the mode is switched.

[0036] Specifically, the bias current elimination module is specifically used to:

[0037] By controlling the on-duty cycle of all switches in the first cycle after mode switching, the bias current during mode switching is eliminated.

[0038] When a light load is switched to a heavy load in the positive direction or a light load is switched to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, thereby eliminating the bias current.

[0039] When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference across it to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated.

[0040] When the energy transfer direction changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated;

[0041] The positive direction refers to the direction of energy transfer from the primary side to the secondary side, and the negative direction refers to the direction of energy transfer from the secondary side to the primary side. V1 is the output voltage of the primary side, V2 is the output voltage of the secondary side, and the conduction of T1 is the cycle start signal.

[0042] The beneficial effects of the above technical solutions provided by the embodiments of the present invention include at least:

[0043] Without adding additional components, this system can achieve soft switching across the full power range through reactive power injection, significantly reducing device turn-off losses and improving system efficiency without affecting the system's dynamic response. Furthermore, by controlling reactive power during dual-phase reactive power injection, reactive power is minimized while still meeting soft shutdown requirements, reducing losses in the isolation transformer.

[0044] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0047] Figure 1 This is a flow chart of a full-power range soft switching control method based on a DAB circuit in an embodiment of the present invention;

[0048] Figure 2 1 is a topology diagram of a dual active bridge DC-DC converter with a turn-off buffer capacitor according to an embodiment of the present invention;

[0049] Figure 3 1 is a driving signal diagram of a switching device when switching from a light load to a heavy load in the forward direction according to an embodiment of the present invention;

[0050] Figure 4 1 is a driving signal diagram of a switching device when switching from a heavy load to a light load in the forward direction according to an embodiment of the present invention;

[0051] Figure 5 1 is a driving signal diagram of a switching device when the positive direction switches to the negative direction in an embodiment of the present invention;

[0052] Figure 6 This is a block diagram of a full-power range soft switching control system based on a DAB circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0054] In order to solve the problems existing in the prior art, an embodiment of the present invention provides a full-power range soft switching control method and system based on a DAB circuit.

[0055] Example 1

[0056] The first embodiment of the present invention provides a full power range soft switching control method based on a DAB circuit, the process of which is as follows: Figure 1 As shown, the following steps are included:

[0057] Step S1: Construct a DAB circuit with a cut-off buffer capacitor. Figure 2 As shown, the DAB circuit includes DC support capacitors Cp-Cs, switches T1-T8, diodes D1-D8, auxiliary reactor L1, a high-frequency isolation transformer, and shutdown buffer capacitors C1-C8. The collector or anode of the switch tube Ti is connected to the cathode of the corresponding diode Di, the emitter or cathode of the switch tube Ti is connected to the anode of the corresponding diode Di, the positive electrode of the shutdown buffer capacitor Ci is connected to the collector or anode of the corresponding switch tube Ti, and the negative electrode of the shutdown buffer capacitor Ci is connected to the emitter or cathode of the corresponding switch tube Ti, where i is an integer and 1≤i≤8. The switches T1-T2 are sequentially connected in series to form a primary half-bridge, T1-T4 to form a primary full-bridge, and the output voltage is recorded as V1. T5-T6 are sequentially connected in series to form a secondary half-bridge, and T5-T8 to form a secondary full-bridge, and the output voltage is recorded as V2.

[0058] Constructing the DAB circuit specifically includes the following steps:

[0059] The DAB circuit includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer, wherein the primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer;

[0060] The primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1. T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4;

[0061] The secondary full bridge includes four switching tubes T5, T6, T7 and T8, and a DC support capacitor Cs. T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8;

[0062] Each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor, respectively. The collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor, respectively. The emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor, respectively.

[0063] Step S2: determining the operating mode according to the actual transmission power of the DAB circuit; and determining the mode switching power according to the capacitance, DC voltage, dead time and phase shift inductance in the DAB circuit.

[0064] Step S3: When the actual transmission power of the DAB circuit is less than the preset mode switching power, a phase-shift control strategy with an external phase-shift angle of not less than 90 degrees and not more than 180 degrees is used to enable the DAB circuit's switch to be turned on at zero voltage. When the external phase-shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit, increasing the switch's turn-off current. The buffer capacitor completes charging and discharging within the dead time, placing the switch in a soft switching state. At this point, the device's turn-off current increases, and even under no-load conditions, a significant turn-off current remains, ensuring the device is in a soft switching state. The soft switching state includes a soft-on state and a soft-off state.

[0065] When the system power is less than the mode switching power, a phase-shift control strategy of reactive injection can be used to control DAB. The reactive injection increases the reactive power in the DAB transmission power under light load and improves the turn-off current of the switch tube under light load.

[0066] The phase-shift control strategy includes any one of single-phase-shift control, double-phase-shift control, and triple-phase-shift control.

[0067] Furthermore, when using dual-phase reactive power injection, after the switch is in the soft-off state, the reactive power is gradually reduced until the switch is no longer in the soft-off state. The reactive power at this point is recorded to obtain the dual-phase soft-off minimum reactive power. Compared to single-phase reactive power injection, dual-phase reactive power injection can control reactive power, minimizing reactive power while meeting soft-off requirements, thereby reducing losses in the isolation transformer.

[0068] Step S4: When the actual transmission power of the DAB circuit is not less than the preset mode switching power, a single-phase control strategy is adopted to turn on the switch tube of the DAB circuit at zero voltage, and the switch tube is in a soft switching state.

[0069] When the actual transmission power of the DAB circuit is not less than the preset mode switching power, a single phase shift control strategy can be used to control the DAB. After the buffer capacitor is turned off in parallel, the presence of the buffer capacitor during shutdown allows for a soft shutdown, enabling a soft switching state of the switching device.

[0070] Step S5: When the mode is switched, the bias current during switching is controlled to eliminate the bias current.

[0071] The switching process needs to compensate and eliminate the bias current generated by the switching to ensure the dynamic response of the DAB circuit. The switching can be divided into six switching modes: positive light load switching heavy load, positive heavy load switching light load, positive switching negative, negative switching positive, negative light load switching heavy load, and negative heavy load switching light load. The light load adopts double phase shift based on reactive injection, and the heavy load adopts single phase shift control to analyze the switching process. Among them, Figure 2 As shown, the cycle starts with T1 being turned on, and the energy is transferred from V1 to V2 in the forward direction.

[0072] Specifically, controlling the bias current during switching to eliminate the bias current includes the following steps:

[0073] By controlling the on-duty cycle of all switching tubes in the first cycle after mode switching, the bias current during mode switching is eliminated.

[0074] Specifically, the bias current during mode switching is eliminated by controlling the on-duty cycle of all switching tubes in the first cycle after mode switching, including the following steps:

[0075] When switching from a light load to a heavy load in the positive direction or from a light load to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, and the bias current is eliminated. The switch tube driving signal when switching from a light load to a heavy load in the positive direction is as follows: Figure 3 As shown in the figure, light loads use dual phase shifting based on reactive injection, while heavy loads use single phase shifting to analyze the switching process. Din is the inner phase shift angle, and Dout is the outer phase shift angle. Dinlast is the inner phase shift angle of the previous cycle, and Doutlast is the outer phase shift angle of the previous cycle. Ts represents one cycle, and I represents the current signal.

[0076] When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference between its two ends to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated. The switch tube driving signal when switching from a heavy load to a light load is as follows: Figure 4As shown in the figure, single phase-shift control is used for heavy loads to analyze the switching process, while dual phase-shift control based on reactive injection is used for light loads. Din is the inner phase-shift angle, and Dout is the outer phase-shift angle. Dinlast is the inner phase-shift angle of the previous cycle, and Doutlast is the outer phase-shift angle of the previous cycle. Ts represents one cycle, and I represents the current signal.

[0077] When the direction of energy transfer changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated; when the positive direction is cut to the negative direction, the switch tube driving signal is as follows Figure 5 As shown in Figure 2, Din is the inner phase shift angle, Dout is the outer phase shift angle, Dinlast is the inner phase shift angle of the previous cycle, Doutlast is the outer phase shift angle of the previous cycle, Ts represents one cycle, and I represents the current signal.

[0078] The positive direction refers to the direction in which energy is transferred from the primary side to the secondary side, and the negative direction refers to the direction in which energy is transferred from the secondary side to the primary side.

[0079] The above-described method of this embodiment achieves soft shutdown across the full power range by relying on reactive power injection without adding additional components. This significantly reduces device shutdown losses, improves DAB circuit efficiency, and does not affect the DAB circuit's dynamic response. Furthermore, by controlling reactive power during dual-phase-shifted reactive power injection, reactive power is minimized while still meeting soft shutdown requirements, reducing losses in the isolation transformer.

[0080] Those skilled in the art can change the above sequence without departing from the scope of protection of the present disclosure.

[0081] Example 2

[0082] The second embodiment of the present invention provides a full power range soft switching control system based on a DAB circuit, and its structure is as follows: Figure 6 Shown, including:

[0083] The DAB circuit construction module 100 is used to construct the DAB circuit, which includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer, wherein the primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer; the primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1, T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; the secondary full bridge includes four Switching tubes T5, T6, T7 and T8, a DC support capacitor Cs, T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8; each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor respectively, the collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor respectively, and the emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor respectively;

[0084] The mode switching power determination module 200 is configured to determine an operating mode based on the actual transmission power of the DAB circuit; and determine the mode switching power based on the capacitance, DC voltage, dead time, and phase shift inductance in the DAB circuit;

[0085] A first soft-off control module 300 is configured to, when the actual transmission power of the DAB circuit is less than a preset mode switching power, employ a phase-shift control strategy with an external phase-shift angle of not less than 90 degrees and not more than 180 degrees to enable zero-voltage switching of the switch tube of the DAB circuit. When the external phase-shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase the off-current of the switch tube. The buffer capacitor completes charging and discharging within the dead time, and the switch tube enters a soft-switching state.

[0086] The second soft-off control module 400 is configured to, when the actual transmission power of the DAB circuit is not less than the preset mode switching power, use a single-phase shift control strategy to enable the switching tube of the DAB circuit to be turned on at zero voltage, placing the switching tube in a soft-switching state. The soft-switching state includes a soft-on state and a soft-off state.

[0087] The phase-shift control strategy includes any one of single-phase-shift control, double-phase-shift control, and triple-phase-shift control.

[0088] A full-power range soft switching control system based on a DAB circuit, further comprising:

[0089] The minimum reactive power determination module 500 is configured to, when dual-phase shifting is used to inject reactive power, gradually reduce the reactive power after the switch is in the soft-off state until the switch is no longer in the soft-off state, record the reactive power at this time, and obtain the minimum reactive power for dual-phase shifting soft-off;

[0090] The bias current elimination module 600 is used to control the bias current during switching and eliminate the bias current when the mode is switched.

[0091] Specifically, the bias current elimination module 600 is specifically used to:

[0092] By controlling the on-duty cycle of all switches in the first cycle after mode switching, the bias current during mode switching is eliminated.

[0093] When a light load is switched to a heavy load in the positive direction or a light load is switched to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, thereby eliminating the bias current.

[0094] When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference across it to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated.

[0095] When the energy transfer direction changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated;

[0096] The positive direction refers to the direction of energy transfer from the primary side to the secondary side, and the negative direction refers to the direction of energy transfer from the secondary side to the primary side. V1 is the output voltage of the primary side, V2 is the output voltage of the secondary side, and the conduction of T1 is the cycle start signal.

[0097] This embodiment achieves soft shutdown across the full power range through reactive power injection without adding additional components. This significantly reduces device shutdown losses, improves system efficiency, and does not affect system dynamic response. Furthermore, by controlling reactive power during dual-phase-shifted reactive power injection, reactive power is minimized while still meeting soft shutdown requirements, reducing losses in the isolation transformer.

[0098] Regarding the system in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0099] Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention shall still fall within the scope of the patent coverage of the present invention.

Claims

1. A full power range soft switching control method based on DAB circuit, characterized in that: include: When the actual transmission power of the DAB circuit is less than the preset mode switching power, a single phase-shift control strategy or a double phase-shift control strategy with an external phase-shift angle of not less than 90 degrees and not more than 180 degrees is adopted to make the switch of the DAB circuit turn on at zero voltage. When the external phase-shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase the turn-off current of the switch. The buffer capacitor is fully charged and discharged within the dead time, and the switch is in a soft switching state. When the actual transmission power of the DAB circuit is not less than the preset mode switching power, a single phase shift control strategy is adopted to turn on the switch tube of the DAB circuit at zero voltage, and the switch tube is in a soft switching state; When dual phase shift is used to inject reactive power, after the switch tube is in the soft-on state, the reactive power is gradually reduced until the switch tube is no longer in the soft-on state. The reactive power at this time is recorded to obtain the dual phase shift soft-off minimum reactive power.

2. The method according to claim 1, wherein Constructing the DAB circuit includes the following steps: The DAB circuit includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer, wherein the primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer; The primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1. T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; The secondary full bridge includes four switching tubes T5, T6, T7 and T8, and a DC support capacitor Cs. T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8; Each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor, respectively. The collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor, respectively. The emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor, respectively.

3. The method according to claim 1 or 2, wherein: Determining the mode switching power includes the following steps: determining an operating mode according to an actual transmission power of the DAB circuit; The mode switching power is determined according to the capacitance, DC voltage, dead time and phase shift inductance in the DAB circuit.

4. The method according to claim 1 or 2, wherein: The following steps are also included: When the mode is switched, the bias current during switching is controlled to eliminate the bias current.

5. The method according to claim 4, wherein Controlling the bias current during switching to eliminate the bias current includes the following steps: By controlling the on-duty cycle of all switching tubes in the first cycle after mode switching, the bias current during mode switching is eliminated.

6. The method according to claim 5, wherein By controlling the on-duty cycle of all switches in the first cycle after mode switching, the bias current during mode switching is eliminated, including the following steps: When a light load is switched to a heavy load in the positive direction or a light load is switched to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, and the bias current is eliminated. When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference across it to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated. When the energy transfer direction changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated; The positive direction refers to the direction of energy transfer from the primary side to the secondary side, and the negative direction refers to the direction of energy transfer from the secondary side to the primary side. V1 is the output voltage of the primary side, V2 is the output voltage of the secondary side, and the conduction of T1 is the cycle start signal.

7. A full power range soft switching control system based on DAB circuit, characterized in that: include: A DAB circuit construction module is used to construct the DAB circuit, which includes a primary full bridge, a secondary full bridge and a high-frequency isolation transformer. The primary full bridge and the secondary full bridge are respectively connected to the high-frequency isolation transformer; the primary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1, T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer, and the other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; the secondary full bridge includes four switching tubes T1, T2, T3 and T4, a DC support capacitor Cp and an auxiliary reactor L1, T1 and T2 are connected in series, T3 and T4 are connected in series, one end of the collector of T1, one end of the collector of T3 and one end of the positive electrode of Cp are connected, one end of the emitter of T2, one end of the emitter of T4 and one end of the negative electrode of Cp are connected, one end of L1 is connected to the connection between T1 and T2, and the other end of L1 is connected to one end of the primary side of the high-frequency isolation transformer. The other end of the primary side of the high-frequency isolation transformer is connected to the connection between T3 and T4; Switches T5, T6, T7 and T8, a DC support capacitor Cs, T5 and T6 are connected in series, T7 and T8 are connected in series, one end of the collector of T5, one end of the collector of T7 and one end of the positive electrode of Cs are connected, one end of the emitter of T6, one end of the emitter of T8 and one end of the negative electrode of Cs are connected, one end of the secondary side of the high-frequency isolation transformer is connected to the connection between T5 and T6, and the other end of the secondary side of the high-frequency isolation transformer is connected to the connection between T7 and T8; each of the switching tubes in the primary full bridge and the secondary full bridge corresponds to a diode and a shutdown buffer capacitor respectively, the collector of each switching tube is connected to the cathode of the corresponding diode and the positive electrode of the corresponding shutdown buffer capacitor respectively, and the emitter of each switching tube is connected to the anode of the corresponding diode and the negative electrode of the corresponding shutdown buffer capacitor respectively; A mode switching power determination module is configured to determine an operating mode based on an actual transmission power of the DAB circuit; and determine the mode switching power based on a capacitance, a DC voltage, a dead time, and a phase shift inductance in the DAB circuit; a first soft-off control module, configured to, when the actual transmission power of the DAB circuit is less than a preset mode switching power, adopt a single phase-shift control strategy or a double phase-shift control strategy with an external phase-shift angle of not less than 90 degrees and not more than 180 degrees to enable the switching tube of the DAB circuit to be turned on at zero voltage; wherein, when the external phase-shift angle is greater than 90 degrees, reactive power is injected into the DAB circuit to increase the turn-off current of the switching tube, so that the buffer capacitor is fully charged and discharged within the dead time, and the switching tube is in a soft switching state; A second soft-off control module is configured to, when the actual transmission power of the DAB circuit is not less than a preset mode switching power, adopt a single-phase-shift control strategy to enable the switch tube of the DAB circuit to be turned on at zero voltage, and the switch tube is in a soft switching state; The minimum reactive power determination module is used to gradually reduce the reactive power when the switch tube is in the soft-on state when dual-phase shifting is used to inject reactive power, until the switch tube is no longer in the soft-on state, record the reactive power at this time, and obtain the minimum reactive power of dual-phase shifting soft shutdown.

8. The system according to claim 7, wherein: Also includes: The bias current elimination module is used to control the bias current during switching and eliminate the bias current when the mode is switched.

9. The system according to claim 8, wherein The bias current elimination module is specifically used to: By controlling the on-duty cycle of all switches in the first cycle after mode switching, the bias current during mode switching is eliminated. When a light load is switched to a heavy load in the positive direction or a light load is switched to a heavy load in the negative direction, the low level time of V1 is extended. After the current of the auxiliary inductor passes through zero for the first time, the voltage difference between its two ends is controlled to maintain the same time as after the current passes through zero in the heavy load state, thereby eliminating the bias current. When switching from a heavy load to a light load in the positive direction or from a heavy load to a light load in the negative direction, keep V1 and V2 negative. After the current of the auxiliary inductor passes through zero for the first time, control the voltage difference across it to maintain the same time as after the current passes through zero in the light load state, and the bias current is eliminated. When the energy transfer direction changes, the driving signals of the leading bridge arm and the lagging bridge arm are swapped, and only the driving signal of the second half cycle of the first cycle after the swap is retained, and the bias current is eliminated; The positive direction refers to the direction of energy transfer from the primary side to the secondary side, and the negative direction refers to the direction of energy transfer from the secondary side to the primary side. V1 is the output voltage of the primary side, V2 is the output voltage of the secondary side, and the conduction of T1 is the cycle start signal.

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