A Dual Active Bridge Converter for Achieving Wide-Range Soft Switching

Abstract

The present invention discloses a dual-active-bridge converter for realizing wide-range soft switching, which includes a full-bridge switching network, an inductive energy storage network, a transformer transmission network, and a rectifier and filter network connected in sequence. The input end of the full-bridge switching network is connected to an input DC source, the output end of the full-bridge switching network is connected to the input end of the inductive energy storage network, and the input end of the rectifier and filter network is connected to the output end of the transformer transmission network. The inductive energy storage network includes a first inductor L1 and a first switch S1, and the first switch S1 is connected in parallel with the primary side of a second transformer T2 of the transformer transmission network to form a second parallel branch. The structure of the present invention is simple. The battery voltage is selected according to the second switching switch S2, and then the first switch S1 is switched, thereby changing the number of transformers in the inductor energy storage network, so as to ensure that even if the load voltage changes, the input-output voltage transmission ratio k of the dual-active-bridge converter remains unchanged.

Description

Technical Field

[0001] The present invention relates to the field of bidirectional DC / DC converters for mutual switching of battery voltages, and more particularly to a dual-active-bridge converter that achieves wide-range soft switching. Background Art

[0002] High efficiency and high power density have always been the goals and development directions pursued by switching power converters. For a converter circuit composed of power devices, an increase in the switching frequency will cause an increase in the switching losses of the power devices, ultimately resulting in a decrease in the converter efficiency. Especially for high-frequency converters, in order to reduce the switching losses, soft-switching technology has emerged, and its main implementation methods include zero-voltage switching (ZVS) and zero-current switching (ZCS). The dual-active-bridge (DAB) converter has been widely used in the field of power conversion due to its characteristics such as electrical isolation, step-up / step-down conversion, bidirectional energy transfer, and high power density.

[0003] However, in some cases, the battery voltage needs to be switched between two different voltage levels. When the DC output voltage changes, the dual-active-bridge converter cannot satisfy the full realization of zero-voltage switching for the primary and secondary switching transistors under light load. Therefore, it is very important to obtain a dual-active-bridge converter that achieves wide-range soft switching to solve the above problems. Summary of the Invention

[0004] In order to solve the above technical problems existing in the existing solutions, the present invention provides a dual-active-bridge converter that achieves wide-range soft switching, which includes a driving circuit, an inductive energy storage network, a transformer transmission network, and a rectifying and filtering network connected in sequence. The input end of the full-bridge switching network is connected to the input DC source, and the output end of the full-bridge switching network is connected to the input end of the inductive energy storage network. The transformer transmission network is connected to the full-bridge switching network through the inductive energy storage network. The input end of the rectifying and filtering network is connected to the output end of the transformer transmission network. The inductive energy storage network includes a first inductor L1 and a first switch S1. The first inductor L1 is connected in series with the primary side of the first transformer T1 of the transformer transmission network. The first switch S1 is connected in parallel with the primary side of the second transformer T2 of the transformer transmission network to form a second parallel branch. The primary side of the first transformer T1 of the transformer transmission network is connected in series with the second parallel branch to form a third series branch.

[0005] The drive circuit includes a full-bridge switching network, which includes a first switching transistor Q1, a second switching transistor Q2, a third switching transistor Q3, and a fourth switching transistor Q4. It also includes a first capacitor C1, and the first capacitor C1 is connected in parallel with the full-bridge switching network. The first switching transistor Q1 and the second switching transistor Q2 are connected in series to form a first series branch. The third switching transistor Q3 and the fourth switching transistor Q4 are connected in series to form a second series branch. The first series branch and the second series branch are connected in parallel to form a first parallel branch. The connection point of the first switching transistor Q1 and the second switching transistor Q2 is connected to the primary side of a first transformer T1 through a first inductor L1. The connection point of the third switching transistor Q3 and the fourth switching transistor Q4 is connected to the primary side of a second transformer T2.

[0006] The primary sides of the first transformer T1 and the second transformer T2 are connected in series to form a fourth series branch. The secondary sides of the first transformer T1 and the second transformer T2 are respectively connected to the rectifying and filtering network.

[0007] The rectifying and filtering network includes a first rectifier bridge D1 and a second rectifier bridge D2. The first rectifier bridge D1 is connected to the secondary side of the first transformer T1. The second rectifier bridge D2 is connected to the secondary side of the second transformer T2. The positive pole of the first rectifier bridge D1 and the positive pole of the second rectifier bridge D2 are connected to form a first positive pole. The negative pole of the first rectifier bridge D1 and the negative pole of the second rectifier bridge D2 are connected to form a first negative pole. It also includes a second capacitor C2. One end of the second capacitor C2 is connected to the first positive pole, and the other end of the second capacitor C2 is connected to the first negative pole.

[0008] A first battery pack BT1 and a second battery pack BT2 are connected in parallel to the output end of the rectifying and filtering network. It also includes a second switching switch S2. The first end of the second switching switch S2 is electrically connected to the first positive pole, and the second end of the second switching switch S2 is respectively connected to the first battery pack BT1 and the second battery pack BT2.

[0009] According to the working condition of the battery voltage, that is, by switching the second switching switch S2, the battery voltage is switched to be equal to V o1 or V o2 , and V o1 = 2V o2 , switch the first switch S1, and then change the number of transformers connected to the inductor energy storage network, so as to ensure that the input-output voltage transfer ratio k of the dual-active-bridge converter remains unchanged, and ensure that the dual-active-bridge converter can still achieve zero-voltage switching of the primary and secondary switching transistors within a wide load range even under the condition that the battery voltage changes.

[0010] The structure of the present invention is simple. The battery voltage is selected according to the second switching switch S2, and then the first switch S1 is switched, thereby changing the number of transformers in the inductor energy storage network, so as to ensure that even if the load voltage changes, the input-output voltage transfer ratio k of the dual-active-bridge converter remains unchanged.

[0011] Let K*V o1 = V1. When the second switching switch S2 switches the battery voltage to be equal to V o1 and the first switch S1 remains closed, the input-output voltage transfer ratio k1 of the dual-active-bridge converter = (K*V o1 ) / V1 = 1; when the second switching switch S2 switches the battery voltage to be equal to V o2 , at this time the first switch S1 remains open, then the input-output voltage transfer ratio of the dual-active-bridge converter: k2 = (2*K*V o2 ) / V1. Since V o1 = 2V o2 , so k1 = k2 = 1. According to the soft-switching range during the phase-shift control of the dual-active-bridge converter, it can be known that the input-output voltage transfer ratio k = 1 of the dual-active-bridge converter can ensure that the dual-active-bridge converter realizes zero-voltage switching of the primary and secondary switching tubes within a wide load range. Description of the Drawings

[0012] Figure 1 is the existing dual-active-bridge converter;

[0013] Figure 2 are the waveforms of the key electrical parameters of the dual-active-bridge converter;

[0014] Figure 3 is the soft-switching range during the phase-shift control of the dual-active-bridge converter;

[0015] Figure 4 is a dual-active-bridge converter for realizing wide-range soft switching proposed by the present invention (the first switch S1 is closed);

[0016] Figure 5 is a dual-active-bridge converter for realizing wide-range soft switching proposed by the present invention (the first switch S1 is open); Detailed Embodiments

[0017] In order to enable those skilled in the art to better understand the present invention and thus more clearly define the scope of protection required by the present invention, the present invention will be described in detail below with respect to certain specific embodiments of the present invention. It should be noted that the following are only some specific embodiments of the concept of the present invention and only a part of the embodiments of the present invention. The specific and direct descriptions of the relevant structures are only for the convenience of understanding the present invention, and each specific feature does not of course and directly limit the scope of implementation of the present invention.

[0018] In some cases, the voltage of the battery needs to be switched between two different voltage levels. For example, the voltage of the first battery pack BT1 is V o1 , and the voltage of the second battery pack BT2 is V o2 , and V o1 = 2V o2 . Ensure that the second switch S2 is switched to the first battery pack BT1. The dual-active-bridge converter can achieve zero-voltage switching of the primary and secondary switching transistors within a wide load range. Design the turns ratio K of the primary and secondary sides of the transformer. Then, the input-output voltage transfer ratio of the dual-active-bridge converter at this time and K * V o1 = V1, that is, k1 = 1; when the second switch S2 is switched to the second battery pack BT2, the input-output voltage transfer ratio of the dual-active-bridge converter at this time V o1 = 2V o2 , k2 = 1 / 2k1 = 0.5.

[0019] Refer to the attached Figure 1 and the attached Figure 2 As shown, when the forward power is transmitted, the average power input to the primary side of the dual-active-bridge (DAB) converter where K is the turns ratio of the primary and secondary sides of the transformer; V1 is the primary-side DC voltage of the dual-active-bridge converter; V2 is the secondary-side DC voltage of the dual-active-bridge converter; L is the energy storage inductance of the dual-active-bridge converter; fs is the operating frequency of the dual-active-bridge converter; D is the phase-shift duty cycle of the primary and secondary PWM signals in half a cycle; define the ratio of K * V2 to V1 equal to k, that is, the input-output voltage transfer ratio of the dual-active-bridge converter Define the reference value of power as Then, the per-unit value of the average power input to the primary side of the dual-active-bridge converter during forward power transmission : Similarly, the per-unit value of the average power input to the primary side during reverse power transmission Then, the unified expression of the average power of the primary side of the dual-active-bridge converter during forward and reverse power transmissions is P* = 4 * k * D * (1 - |D|).

[0020] According to Figure 3 As shown, the necessary conditions for the primary and secondary switching transistors of the dual-active-bridge converter to achieve zero-voltage switching It can be deduced that

[0021] When the primary switching transistor satisfies zero-voltage switching, it is necessary to satisfy When the secondary switching transistor satisfies zero-voltage switching, it is necessary to satisfy Then, the necessary conditions for all the primary and secondary switching transistors to satisfy zero-voltage switching are:

[0022] That is

[0023] Based on the above formula, two boundary lines are drawn, as Figure 3 shown. Among them, the two solid lines are the boundary lines for the primary and secondary side switching tubes to achieve zero-voltage switching respectively. The area enclosed by the two is the power range for all the switching tubes on the primary and secondary sides to achieve zero-voltage switching during the forward power transmission of the converter. It can be seen from Figure 4 that when k≠1, that is, when V1≠KV2, it is difficult to achieve zero-voltage switching under light load; only when k = 1, that is, when V1 = KV2, can the converter achieve zero-voltage switching within a wide load range.

[0024] As Figure 1 shown, when there is a situation of mutual switching of the battery voltages of the dual-active-bridge converter, that is, when there are different input-output voltage transfer ratios in the same circuit system, the soft-switching ranges of the dual-active-bridge converter are not the same. When the load voltage satisfies V o1 = 2V o2 , and the battery voltage is equal to V o1 , that is, when k1 = 1, all the switching tubes on the primary and secondary sides of the dual-active-bridge converter can achieve zero-voltage switching within the entire power range; when the battery voltage is equal to V o2 , that is, when k2 = 0.5, the dual-active-bridge converter cannot meet the requirement that all the switching tubes on the primary and secondary sides achieve zero-voltage switching under light load.

[0025] Therefore, the present invention provides a dual-active-bridge converter that can achieve wide-range soft switching, as Figure 4 and Figure 5 shown. It includes a driving circuit, an inductive energy storage network, a transformer transmission network, and a rectifying and filtering network connected in sequence. The input end of the full-bridge switching network is connected to the input DC source, the output end of the full-bridge switching network is connected to the input end of the inductive energy storage network, and the input end of the rectifying and filtering network is connected to the output end of the transformer transmission network; the transformer transmission network is connected to the full-bridge switching network through the inductive energy storage network. The inductive energy storage network includes a first inductor L1 and a first switch S1. The first inductor L1 is connected in series with the primary side of the first transformer T1 of the transformer transmission network; the first switch S1 is connected in parallel with the primary side of the second transformer T2 of the transformer transmission network to form a second parallel branch; the primary side of the first transformer T1 of the transformer transmission network is connected in series with the second parallel branch to form a third series branch. The turns ratio of the first transformer and the second transformer is K:1.

[0026] The drive circuit includes a full-bridge switching network, which includes a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, and a fourth switching tube Q4. It also includes a first capacitor C1, and the first capacitor C1 is connected in parallel with the full-bridge switching network. The first switching tube Q1 and the second switching tube Q2 are connected in series to form a first series branch, the third switching tube Q3 and the fourth switching tube Q4 are connected in series to form a second series branch, and the first series branch and the second series branch are connected in parallel to form a first parallel branch; the connection point of the first switching tube Q1 and the second switching tube Q2 is connected to the primary side of the first transformer T1 through a first inductor L1; the connection point of the third switching tube Q3 and the fourth switching tube Q4 is connected to the primary side of the second transformer T2. Among them, the drive circuit can also be other circuits that control and drive the resonant network.

[0027] The primary sides of the first transformer T1 and the second transformer T2 are connected in series to form a fourth series branch, and the secondary sides of the first transformer T1 and the second transformer T2 are respectively connected to the rectification and filtering network.

[0028] The rectification and filtering network includes a first rectifier bridge D1 and a second rectifier bridge D2. The first rectifier bridge D1 is connected to the secondary side of the first transformer T1, and the second rectifier bridge D2 is connected to the secondary side of the second transformer T2. The positive pole of the first rectifier bridge D1 is connected to the positive pole of the second rectifier bridge D2 to form a first positive pole, and the negative pole of the first rectifier bridge D1 is connected to the negative pole of the second rectifier bridge D2 to form a first negative pole. It also includes a second capacitor C2, one end of the second capacitor C2 is connected to the first positive pole, and the other end of the second capacitor C2 is connected to the first negative pole.

[0029] A first battery pack BT1 and a second battery pack BT2 are connected in parallel at the output end of the rectification and filtering network. It also includes a second switching switch S2. The first end of the second switching switch S2 is electrically connected to the first positive pole, and the second end of the second switching switch S2 is respectively connected to the first battery pack BT1 and the second battery pack BT2.

[0030] According to the working condition of the battery voltage, that is, by switching the second switching switch S2, the battery voltage is equal to V 01 or V 02 , and V1 = 2V 02 , switch the first switch S1, and then change the number of transformers connected to the inductor energy storage network, so as to ensure that the input-output voltage transfer ratio k of the dual-active-bridge converter remains unchanged, and ensure that the dual-active-bridge converter can still achieve zero-voltage switching of the primary and secondary switching tubes within a wide load range even under the condition of changing battery voltage.

[0031] The structure of the present invention is simple. The battery voltage is selected according to the second switching switch S2, and then the first switch S1 is switched, thereby changing the number of transformers in the inductor energy storage network, so as to ensure that even if the load voltage changes, the input-output voltage transfer ratio k of the dual-active-bridge converter remains unchanged.

[0032] Let K*V o1 = V1. When the second switching switch S2 switches the battery voltage to be equal to V o1 and the first switch S1 remains closed, the input-output voltage transfer ratio k1 of the dual-active-bridge converter = (K*V o1 ) / V1 = 1; when the second switching switch S2 switches the battery voltage to be equal to V o2 at this time, the first switch S1 remains in the open state, then the input-output voltage transfer ratio of the dual-active-bridge converter: k2 = (2*K*V o2 ) / V1. Since V o1 = 2V o2 , so k1 = k2 = 1. According to the soft-switching range during the phase-shift control of the dual-active-bridge converter, the input-output voltage transfer ratio k = 1 of the dual-active-bridge converter can ensure that the primary and secondary switching tubes of the dual-active-bridge converter achieve zero-voltage switching within a wide load range.

[0033] Therefore, for the application of the present invention, even if the load battery voltage undergoes a switching operation, such as the conversion of the battery voltage from V o1 to V o2 , at this time, the input-output voltage transfer ratio k of the dual-active-bridge converter still remains equal to 1, then the dual-active-bridge converter can still achieve zero-voltage switching of the primary and secondary switching tubes within a wide load range.

[0034] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the substantial scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A dual-active-bridge converter for achieving wide-range soft switching, comprising a driving circuit, an inductive energy storage network, a transformer transmission network, and a rectifying and filtering network connected in sequence. The input end of the full-bridge switch network is connected to the input DC source, the output end of the full-bridge switch network is connected to the input end of the inductive energy storage network, the transformer transmission network is connected to the full-bridge switch network through the inductive energy storage network, and the input end of the rectifying and filtering network is connected to the output end of the transformer transmission network; It is characterized in that: The inductive energy storage network includes a first inductor L1 and a first switch S1. The first inductor L1 is connected in series with the primary side of the first transformer T1 of the transformer transmission network; the first switch S1 is connected in parallel with the primary side of the second transformer T2 of the transformer transmission network to form a second parallel branch; the primary side of the first transformer T1 of the transformer transmission network is connected in series with the second parallel branch to form a third series branch; the turns ratio of the first transformer and the second transformer is K:1; A first battery pack BT1 and a second battery pack BT2 are connected in parallel at the output end of the rectifying and filtering network. It further includes a second switching switch S2. The first end of the second switching switch S2 is electrically connected to the first positive electrode, and the second end of the second switching switch S2 is respectively connected to the first battery pack BT1 and the second battery pack BT2; According to the working condition of the battery voltage, the battery voltage is switched through the second switching switch S2, and the first switch S1 is switched, thereby changing the number of transformers connected to the inductor energy storage network, so as to ensure that the input-output voltage transfer ratio k of the dual-active-bridge converter remains unchanged; The voltage of the first battery pack BT1 is V o1 , and the voltage of the second battery pack BT2 is V o2 . When the load voltage satisfies V o1 = 2V o2 , the battery voltage is equal to V o1 . When k = 1, V1 is the DC voltage on the primary side of the dual active bridge converter; let K * V o1 = V1. When the second switching switch S2 switches the battery voltage to be equal to V o1 and the first switch S1 remains closed, the primary and secondary switching transistors of the dual active bridge converter can achieve zero voltage switching in the entire power range to achieve bidirectional transmission.

2. The dual-active-bridge converter for realizing wide-range soft-switching according to claim 1, wherein: The driving circuit includes a full-bridge switch network, including a first switch tube Q1, a second switch tube Q2, a third switch tube Q3, and a fourth switch tube Q4. The first switch tube Q1 and the second switch tube Q2 are connected in series to form a first series branch, the third switch tube Q3 and the fourth switch tube Q4 are connected in series to form a second series branch, and the first series branch and the second series branch are connected in parallel to form a first parallel branch; The connection point of the first switch tube Q1 and the second switch tube Q2 is connected to the primary side of the first transformer T1 through the first inductor L1; the connection point of the third switch tube Q3 and the fourth switch tube Q4 is connected to the primary side of the second transformer T2.

3. The dual-active-bridge converter for achieving wide-range soft-switching according to claim 1, wherein: It further includes a first capacitor C1, and the first capacitor is connected in parallel with the full-bridge switch network.

4. The dual-active-bridge converter for realizing wide-range soft switching according to claim 1, wherein: The primary sides of the first transformer T1 and the second transformer T2 are connected in series to form a fourth series branch, and the secondary sides of the first transformer T1 and the second transformer T2 are respectively connected to the rectifying and filtering network.

5. The dual-active-bridge converter for realizing wide-range soft switching according to claim 1, characterized in that: The rectifying and filtering network includes a first rectifier bridge D1 and a second rectifier bridge D2. The first rectifier bridge D1 is connected to the secondary side of the first transformer T1, the second rectifier bridge D2 is connected to the secondary side of the second transformer T2, the positive electrode of the first rectifier bridge D1 is connected to the positive electrode of the second rectifier bridge D2 to form a first positive electrode, and the negative electrode of the first rectifier bridge D1 is connected to the negative electrode of the second rectifier bridge D2 to form a first negative electrode.

6. The dual-active-bridge converter for achieving wide-range soft switching according to claim 5, wherein: It further includes a second capacitor C2. One end of the second capacitor C2 is connected to the first positive electrode, and the other end of the second capacitor C2 is connected to the first negative electrode.

7. The dual-active-bridge converter for achieving wide-range soft switching according to claim 1, wherein: The voltage of the first battery pack is twice that of the second battery pack.

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