General transient DC bias suppression method for dual-active bridge converter under bidirectional power flow

Abstract

The invention discloses a general transient DC bias suppression method for a dual-active-bridge converter under bidirectional power flow. The method comprises the following steps: when the dual-active-bridge DC converter operates stably, asynchronous carriers are generated; a certain modulation and control strategy is adopted, closed-loop operation is carried out in each switching period, and a primary side inner shift phase ratio D1, a secondary side inner shift phase ratio D2 and an outer shift phase ratio Df are generated; different working modes are selected according to the positive and negative relation of the external shift comparison between the current switching period and the previous switching period, and an asynchronously updated modulation wave is generated; and according to the selected working mode, determining a lead and lag relationship of the modulation wave, comparing the modulation wave with the carrier wave, and generating a driving signal of a power switch of the dual-active bridge converter. According to the method, the problem that an existing transient direct current bias suppression method is only suitable for a specific power flow direction or a specific modulation strategy can be solved, transient direct current bias suppression under power bidirectional flow is achieved, and safe operation of the dual active bridge converter is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of direct current conversion technology in the field of power electronics technology, and in particular relates to a universal transient direct current bias suppression method under bidirectional power flow of a dual active bridge converter. Background Art

[0002] Dual Active Bridge (DAB) converter has been widely used due to its symmetrical topology, wide voltage conversion gain range, high power density, electrical isolation and easy ZVS. DAB converter uses different modulation strategies to improve efficiency, optimize return power and reduce current stress, including single-phase-shift (SPS) modulation, extended-phase-shift (EPS) modulation, dual-phase-shift (DPS) modulation and triple-phase-shift (TPS) modulation.

[0003] When the load of the DAB converter changes suddenly, the power transmission direction changes suddenly, or the given voltage changes suddenly, the update of the shift phase will change suddenly, resulting in unequal positive and negative volt-second products of the voltage across the power transmission inductor, thereby generating transient DC bias current. The transient DC bias current will increase the current stress of the power switch, and easily lead to saturation of the inductor and transformer core, or even burn it. When no measures are taken to deal with the DC bias, due to the existence of line impedance, the DC bias will eventually decrease to zero, and the leakage inductance current will tend to stabilize. The duration of this process is related to the size of the line impedance. The larger the line impedance, the shorter the transient process. However, the overcurrent problem still exists, and the generation of DC bias cannot be suppressed from the source. In order to avoid the various effects of DC bias on the DAB converter, it is necessary to adopt a corresponding modulation strategy to adjust when the power changes.

[0004] The transient DC bias suppression method in the prior art is only applicable to specific modulation schemes and is difficult to be extended to TPS modulation with the best working mode of ZVS and low conduction loss. In addition, the traditional transient DC bias suppression strategy mainly focuses on the working conditions of unidirectional power flow, and cannot guarantee the fast power reverse operation of the DAB converter. For example, the Chinese patent "DC bias suppression method, device and medium for dual active bridge DC converter" with application publication number CN11663123A proposes to distribute the driving signal of the switch tube of the dual active bridge DC converter by comparing the asynchronous carrier with the modulation wave, and eliminate the inductor current bias and excitation current bias generated by the transient process. However, this method is only applicable to transient DC bias suppression during unidirectional power conversion; in the article “Novel Phase-Shift Method for Fast Power Reversal With TransientZero Voltage Switching in a Bidirectional Dual Active Bridge DC–DC Converter” published in IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS in 2021, a transient DC bias suppression method for bidirectional power conversion based on SPS modulation is proposed, which can realize soft switching while realizing bidirectional power conversion. However, this method can only be used for specific SPS modulation and is not universal and portable. In the article “A Simple DC-Offset Eliminating Method of the Series-Inductance Current for the DAB DC–DC Converter” published in IEEE TRANSACTIONS ON POWER ELECTRONICS in 2023, a decoupling method between the modulation method and the DC bias suppression method is proposed, which is applicable to all phase-shift modulation methods. The DC bias suppression method, but the DC bias problem during power reverse mutation is not considered. Summary of the invention

[0005] Therefore, the purpose of the present invention is to provide a universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter, so as to solve the problem that the existing transient DC bias suppression method is only applicable to a specific power flow direction or a specific modulation strategy. The present invention generates a driving signal for a power switch by comparing an asynchronous carrier with an asynchronously updated modulation wave, and realizes transient DC bias suppression under bidirectional power flow by changing the lead-lag relationship between the primary and secondary modulation waves, thereby ensuring the safe operation of the dual active bridge converter.

[0006] In order to achieve the above object, the present invention provides a universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter, comprising the following steps:

[0007] S1. When the dual active bridge converter is in stable operation, an asynchronous carrier is generated. The asynchronous carrier includes: a sawtooth carrier T of the bridge arm L1. L1 , the sawtooth carrier T of bridge arm L2 L2 , the sawtooth carrier T of bridge arm L3 L3 , the sawtooth carrier T of bridge arm L4 L4 ;

[0008] S2, adopt a certain modulation strategy and control strategy, perform closed-loop operation in each switching cycle to generate phase shift, the modulation strategy includes: single phase shift modulation, extended phase shift modulation, double phase shift modulation and triple phase shift modulation, the phase shift includes: primary side inner phase shift D1, secondary side inner phase shift D2 and outer phase shift D f ;

[0009] S3, according to the positive and negative relationship between the current switching cycle outward shift and the previous switching cycle outward shift, select different working modes to generate asynchronously updated modulation waves, the working modes include: working mode 1 and working mode 2, the modulation waves include: the modulation wave C of the bridge arm L1 A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the modulation wave C of bridge arm L3 A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 ;

[0010] S4. According to the selected working mode, the leading and lagging relationship of the modulation wave is determined, the modulation wave is compared with the carrier wave, and a driving signal of the power switch of the dual active bridge converter is generated to achieve the suppression of transient DC bias.

[0011] Further preferably, in S1, the carrier T L1 and carrier T L2 The phase of the carrier T L3 and carrier T L4 The phase of the carrier T L3 , T L4 Lag carrier T L1 , T L2 The phase is 180°.

[0012] Further preferably, in S2, when single phase shift modulation is adopted, D1=D2=0, when extended phase shift modulation is adopted, D1=0, D2≠0 or D1≠0, D2=0, when double phase shift modulation is adopted, D1=D2, and when triple phase shift modulation is adopted, D1≠0 and D2≠0.

[0013] Further preferably, in S3, the working mode selection specifically includes:

[0014] When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is positive, the working mode is not switched and working mode 1 is selected;

[0015] When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is negative, the working mode is not switched and working mode 2 is selected;

[0016] When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is negative, the operation mode 1 is switched to the operation mode 2;

[0017] When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is positive, the operation mode 2 is switched to the operation mode 1.

[0018] Further preferably, the modulation wave calculation expression of each bridge arm is:

[0019]

[0020] Among them, y and z are constants. After calculation, the values ​​of y and z are both 0.5. The calculation formula of x is:

[0021] x=V1 / (V1+nV2) Formula (2)

[0022] Among them, V1 is the primary DC side voltage of the dual active bridge converter, V2 is the secondary DC side voltage of the dual active bridge converter, and n is the ratio of the primary and secondary turns of the high-frequency transformer of the dual active bridge converter.

[0023] Further preferably, in S4, each modulated wave is updated when the carrier wave is equal to zero, and the updating method specifically includes:

[0024] When selecting working mode 1, first update the modulation wave C of bridge arm L3 at the same time A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , and then update the modulation wave C of bridge arm L1 at the same time A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the update time differs by half a switching cycle;

[0025] When selecting working mode 2, first update the modulation wave C of bridge arm L1 at the same time A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , and then update the modulation wave C of bridge arm L3 at the same time A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , the update time differs by half a switching cycle.

[0026] Further preferably, the generating a driving signal of a power switch of the dual active bridge converter comprises:

[0027] When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 A1 When , the upper switch tube driving signal of the bridge arm L1 is set to a high level, and the lower switch tube driving signal is set to a low level;

[0028] When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 B1 When , the upper switch tube driving signal of the bridge arm L1 is set to a low level, and the lower switch tube driving signal is set to a high level;

[0029] When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 A2 When , the lower switch tube driving signal of the bridge arm L2 is set to a high level, and the upper switch tube driving signal is set to a low level;

[0030] When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 B2 When , the lower switch tube driving signal of the bridge arm L2 is set to a low level, and the upper switch tube driving signal is set to a high level;

[0031] When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 A3 When , the upper switch tube driving signal of the bridge arm L3 is set to a high level, and the lower switch tube driving signal is set to a low level;

[0032] When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 B3 When , the upper switch tube driving signal of the bridge arm L3 is set to a low level, and the lower switch tube driving signal is set to a high level;

[0033] When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 A4 When , the lower switch tube driving signal of the bridge arm L4 is set to a high level, and the upper switch tube driving signal is set to a low level;

[0034] When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 B4 When , the lower switch tube driving signal of the bridge arm L4 is set to a low level, and the upper switch tube driving signal is set to a high level.

[0035] Compared with the prior art, the universal transient DC bias suppression method under bidirectional power flow of the dual active bridge converter disclosed in the present invention has the following beneficial effects: (modulation strategy, power forward and reverse)

[0036] 1. The present invention is applicable to a variety of modulation strategies, including single phase shift modulation, extended phase shift modulation, double phase shift modulation and triple phase shift modulation, and is applicable to working conditions with bidirectional power flow;

[0037] 2. During the steady-state operation and transient DC bias suppression of the dual active bridge converter, the calculation expressions used for each modulation wave do not change, achieving the unification of steady state and transient state, avoiding the discontinuity problem caused by expression switching and the resulting disturbance, and avoiding the complex logical judgment and calculation steps in the transient process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a circuit topology diagram of a dual active bridge converter;

[0039] Figure 2 It is a schematic diagram of the implementation process of the present invention;

[0040] Figure 3 It is the key waveform diagram of the method proposed in the present invention in working mode 1;

[0041] Figure 4 It is the key waveform diagram of the method proposed in the present invention in working mode 2;

[0042] Figure 5 This is the experimental waveform diagram when switching from forward power flow to reverse power flow under traditional TPS modulation;

[0043] Figure 6 This is the experimental waveform diagram when switching from reverse power flow to forward power flow under traditional TPS modulation;

[0044] Figure 7 It is an experimental waveform diagram when the method proposed by the present invention is used to switch from a forward light load to a forward heavy load under TPS modulation;

[0045] Figure 8 It is an experimental waveform diagram when the method proposed by the present invention is used to switch from reverse light load to reverse heavy load under TPS modulation;

[0046] Fig. 9This is an experimental waveform diagram when the method proposed in the present invention is used to switch from a forward light load to a reverse heavy load under TPS modulation;

[0047] Fig.10 This is an experimental waveform diagram when the method proposed in the present invention is used to switch from reverse light load to forward heavy load under TPS modulation. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below through the accompanying drawings and specific implementation methods.

[0049] The circuit topology of the dual active bridge converter is as follows: Figure 1 As shown, bridge arms L1 and L2 form a primary H bridge, including power switches S1-S4 and their corresponding body diodes D1-D4; bridge arms L3 and L4 form a secondary H bridge, including power switches S5-S8 and their corresponding body diodes D5-D8; v ab and v cd are the midpoint voltages of the primary H-bridge and the secondary H-bridge respectively; V1 and V2 are the primary and secondary DC voltages respectively; C1 and C2 are the primary and secondary DC filter capacitors respectively; n:1 is the turns ratio of the high-frequency transformer T; L is the leakage inductance; L m is the excitation inductance; i L is the leakage inductance current; i o is the output current.

[0050] like Figure 2 As shown, a general transient DC bias suppression method under bidirectional power flow of a dual active bridge converter provided by an embodiment of one aspect of the present invention comprises the following steps:

[0051] S1, the dual active bridge converter generates an asynchronous carrier when operating stably, such as Figure 3 As shown, the asynchronous carrier includes: a sawtooth carrier T of the bridge arm L1 L1 , the sawtooth carrier T of bridge arm L2 L2 , the sawtooth carrier T of bridge arm L3 L3 , the sawtooth carrier T of bridge arm L4 L4 .

[0052] like Figure 3 and Figure 4 As shown, the carrier T L1 and carrier T L2 The phase of the carrier T L3 and carrier T L4 The phase of the carrier T L3 , T L4 Lag carrier T L1 , T L2 The phase is 180°.

[0053] S2, using triple phase shift modulation and PI control method, each switching cycle performs closed-loop operation to generate phase shifts, the phase shifts include: primary side internal phase shift D1, secondary side internal phase shift D2 and external phase shift D f .

[0054] When single phase shift modulation is used, D1=D2=0; when extended phase shift modulation is used, D1=0, D2≠0 or D1≠0, D2=0; when double phase shift modulation is used, D1=D2; when triple phase shift modulation is used, D1≠0 and D2≠0.

[0055] S3, according to the positive and negative relationship between the current switching cycle shift and the previous switching cycle shift, select different working modes to generate asynchronously updated modulation waves, the working modes include: working mode 1 ( Figure 3 ) and working mode 2( Figure 4 ), the modulation wave includes: the modulation wave C of the bridge arm L1 A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the modulation wave C of bridge arm L3 A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 .

[0056] The working mode selection includes:

[0057] When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is positive, the working mode is not switched and working mode 1 is selected;

[0058] When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is negative, the working mode is not switched and working mode 2 is selected;

[0059] When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is negative, the operation mode 1 is switched to the operation mode 2;

[0060] When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is positive, the operation mode 2 is switched to the operation mode 1.

[0061] The calculation expression of the modulation wave of each bridge arm is:

[0062]

[0063] Wherein, y and z are constants. In the preferred embodiment of the present invention, y and z are both 0.5, and the calculation formula of x is:

[0064] x=V1 / (V1+nV2) Formula (2)

[0065] Among them, V1 is the primary DC side voltage of the dual active bridge converter, V2 is the secondary DC side voltage of the dual active bridge converter, and n is the ratio of the primary and secondary turns of the high-frequency transformer of the dual active bridge converter.

[0066] S4. According to the selected working mode, the leading and lagging relationship of the modulation wave is determined, the modulation wave is compared with the carrier wave, and a driving signal of the power switch of the dual active bridge converter is generated to achieve the suppression of transient DC bias.

[0067] Each modulated wave is updated when the carrier wave is equal to zero. The specific update methods include:

[0068] When selecting working mode 1, Figure 3 As shown, the modulation wave C of bridge arm L3 is updated simultaneously. A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , and then update the modulation wave C of bridge arm L1 at the same time A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the update time differs by half a switching cycle;

[0069] When selecting working mode 2, Figure 4 As shown, the modulation wave C of bridge arm L1 is updated simultaneously. A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , and then update the modulation wave C of bridge arm L3 at the same time A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , the update time differs by half a switching cycle.

[0070] In a preferred embodiment of the present invention, Figure 3 and Figure 4 As shown, the driving signal for generating the power switch of the dual active bridge converter includes:

[0071] When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 A1 When , the upper switch tube driving signal of the bridge arm L1 is set to a high level, and the lower switch tube driving signal is set to a low level;

[0072] When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 B1 When , the upper switch tube driving signal of the bridge arm L1 is set to a low level, and the lower switch tube driving signal is set to a high level;

[0073] When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 A2 When , the lower switch tube driving signal of the bridge arm L2 is set to a high level, and the upper switch tube driving signal is set to a low level;

[0074] When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 B2 When , the lower switch tube driving signal of the bridge arm L2 is set to a low level, and the upper switch tube driving signal is set to a high level;

[0075] When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 A3 When , the upper switch tube driving signal of the bridge arm L3 is set to a high level, and the lower switch tube driving signal is set to a low level;

[0076] When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 B3 When , the upper switch tube driving signal of the bridge arm L3 is set to a low level, and the lower switch tube driving signal is set to a high level;

[0077] When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 A4 When , the lower switch tube driving signal of the bridge arm L4 is set to a high level, and the upper switch tube driving signal is set to a low level;

[0078] When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 B4 When , the lower switch tube driving signal of the bridge arm L4 is set to a low level, and the upper switch tube driving signal is set to a high level.

[0079] Figures 5 to 10 In, v ab is the primary H-bridge midpoint voltage, v cd is the secondary H-bridge midpoint voltage, i L is the inductor current.

[0080] Figure 5 The experimental waveform diagram when switching from forward power flow to reverse power flow under traditional TPS modulation is shown as an example. Figure 6 The experimental waveform diagram when switching from reverse power flow to forward power flow under traditional TPS modulation is shown as an example. It can be seen that under traditional TPS modulation, when the power flow direction changes suddenly, severe transient DC bias will be generated, which will increase the current stress of the power switch and easily saturate the magnetic core of the magnetic component.

[0081] Figures 7 to 10 The experimental waveform diagram of transient DC bias suppression under typical working conditions under TPS modulation using the method proposed in the present invention is exemplified. Figure 7 For the switching process from forward light load to forward heavy load, Figure 8 It is the switching process from reverse light load to reverse heavy load. Fig. 9 It is the switching process from forward light load to reverse heavy load. Fig.10 This is the switching process from reverse light load to forward heavy load. It can be seen that the transient DC bias is effectively suppressed by adopting the method proposed in the present invention.

[0082] Obviously, the above embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A general transient DC bias suppression method for a dual active bridge converter under bidirectional power flow, characterized in that: The following steps are involved: S1. When the dual active bridge converter is in stable operation, an asynchronous carrier is generated. The asynchronous carrier includes: a sawtooth carrier T of the bridge arm L1. L1 , the sawtooth carrier T of bridge arm L2 L2 , the sawtooth carrier T of bridge arm L3 L3 , the sawtooth carrier T of bridge arm L4 L4 ; S2, adopt a certain modulation strategy and control strategy, perform closed-loop operation in each switching cycle to generate phase shift, the modulation strategy includes: single phase shift modulation, extended phase shift modulation, double phase shift modulation and triple phase shift modulation, the phase shift includes: primary side inner phase shift D1, secondary side inner phase shift D2 and outer phase shift D f ; S3, according to the positive and negative relationship between the current switching cycle outward shift and the previous switching cycle outward shift, select different working modes to generate asynchronously updated modulation waves, the working modes include: working mode 1 and working mode 2, the modulation waves include: the modulation wave C of the bridge arm L1 A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the modulation wave C of bridge arm L3 A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 ; S4. According to the selected working mode, the leading and lagging relationship of the modulation wave is determined, the modulation wave is compared with the carrier, and a driving signal of the power switch of the dual active bridge converter is generated to realize the transition from one steady state to another within one switching cycle, eliminate the transient spike of the leakage inductance current, and realize the suppression of transient DC bias.

2. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S1, the carrier T L1 and carrier T L2 The phase of the carrier T L3 and carrier T L4 The phase of the carrier T L3 , T L4 Lag carrier T L1 , T L2 The phase is 180°.

3. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S2, when single phase shift modulation is adopted, D1=D2=0, when extended phase shift modulation is adopted, D1=0, D2≠0 or D1≠0, D2=0, when double phase shift modulation is adopted, D1=D2, when triple phase shift modulation is adopted, D1≠0 and D2≠0.

4. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S3, the working mode selection includes: When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is positive, the working mode is not switched and working mode 1 is selected; When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is negative, the working mode is not switched and working mode 2 is selected; When the outward shift phase ratio of the previous switching cycle is positive and the outward shift phase ratio of the current switching cycle is negative, the operation mode 1 is switched to the operation mode 2; When the outward shift phase ratio of the previous switching cycle is negative and the outward shift phase ratio of the current switching cycle is positive, the operation mode 2 is switched to the operation mode 1.

5. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S3, the modulation wave calculation expression of each bridge arm is: Among them, x, y and z are the time shifts of the modulation wave calculated by D f , D1 and D2. y and z are constants, and their values ​​are both 0.5 after calculation. The calculation formula for x is: x=V1 / (V1+nV2) Formula (2) Among them, V1 is the primary DC side voltage of the dual active bridge converter, V2 is the secondary DC side voltage of the dual active bridge converter, and n is the ratio of the primary and secondary turns of the high-frequency transformer of the dual active bridge converter.

6. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S4, each modulated wave is updated when the carrier is equal to zero, and the updating method specifically includes: When selecting working mode 1, first update the modulation wave C of bridge arm L3 at the same time A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , and then update the modulation wave C of bridge arm L1 at the same time A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , the update time differs by half a switching cycle; When selecting working mode 2, first update the modulation wave C of bridge arm L1 at the same time A1 With C B1 , the modulation wave C of bridge arm L2 A2 With C B2 , and then update the modulation wave C of bridge arm L3 at the same time A3 With C B3 , the modulation wave C of bridge arm L4 A4 With C B4 , the update time differs by half a switching cycle.

7. The universal transient DC bias suppression method under bidirectional power flow of a dual active bridge converter according to claim 1, characterized in that: In S4, generating a driving signal for a power switch of the dual active bridge converter includes: When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 A1 When , the upper switch tube driving signal of the bridge arm L1 is set to a high level, and the lower switch tube driving signal is set to a low level; When the sawtooth carrier T L1 Equal to the modulation wave C of bridge arm L1 B1 When , the upper switch tube driving signal of the bridge arm L1 is set to a low level, and the lower switch tube driving signal is set to a high level; When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 A2 When , the lower switch tube driving signal of the bridge arm L2 is set to a high level, and the upper switch tube driving signal is set to a low level; When the sawtooth carrier T L2 Equal to the modulation wave C of bridge arm L2 B2 When , the lower switch tube driving signal of the bridge arm L2 is set to a low level, and the upper switch tube driving signal is set to a high level; When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 A3 When , the upper switch tube driving signal of the bridge arm L3 is set to a high level, and the lower switch tube driving signal is set to a low level; When the sawtooth carrier T L3 Equal to the modulation wave C of bridge arm L3 B3 When , the upper switch tube driving signal of the bridge arm L3 is set to a low level, and the lower switch tube driving signal is set to a high level; When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 A4 When , the lower switch tube driving signal of the bridge arm L4 is set to a high level, and the upper switch tube driving signal is set to a low level; When the sawtooth carrier T L4 Equal to the modulation wave C of bridge arm L4 B4 When , the lower switch tube driving signal of the bridge arm L4 is set to a low level, and the upper switch tube driving signal is set to a high level.

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