A novel LLC resonant converter

Abstract

The present invention discloses a novel LLC resonant converter, which includes a full-bridge switching network, a resonant network, a transformer transmission network, and a rectifier and filter network connected in sequence. The resonant network includes a first inductor L1 and a first capacitor C1, and further includes a first switch S1 and a second inductor L2. The first switch S1 is connected in parallel with the primary side of the second transformer T2. The first transformer T1 and the second transformer T2 are connected in series and then connected in parallel with the second inductor L2. The structure of the present invention is simple. When the battery voltage changes, through the added first switch S1, the normalized DC gain M of the LLC resonant converter n remains unchanged. Specifically, according to the working condition of the battery voltage, that is, by switching the second switch S2, the voltage of the first battery BT1 is equal to V 01 or the voltage of the second battery BT2 is equal to V 02 , and V1 = 2V 02 ; the first switch S1 is switched to operate, thereby changing the number of transformers connected to the resonant cavity network, so as to ensure that the normalized DC gain M of the LLC resonant converter n remains unchanged, and the LLC resonant converter maintains its original working mode.

Description

Technical Field

[0001] The present invention relates to the field of bidirectional DC / DC converters for mutual switching of battery voltages, and particularly to a novel LLC resonant converter. 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 leading to a decrease in the converter efficiency, especially for high-frequency converters. Therefore, in order to reduce the switching losses, the resonant soft-switching technology has emerged.

[0003] However, in some cases, the battery voltage needs to be switched between two different voltage levels. When the DC output voltage changes, the normalized DC gain of the full-bridge LLC resonant converter will change. Under the same conditions, it is possible to cause the LLC resonant converter to enter the capacitive region, resulting in the inability of the switching transistors to achieve zero-voltage switching, significantly increasing the device losses, and seriously leading to irreversible failures of the machine. Therefore, it is very important to obtain an LLC resonant converter that solves the above defects. Summary of the Invention

[0004] In order to solve the above technical problems existing in the existing solutions, the present invention provides a novel LLC resonant converter, which includes a drive circuit, a resonant network, a transformer transmission network, and a rectifier and filter network connected in sequence. The input end of the full-bridge switch network is connected to the input DC source, and the output end of the full-bridge switch network is connected to the input end of the resonant network. The transformer transmission network is connected to the full-bridge switch network through the resonant network. The input end of the rectifier and filter network is connected to the output end of the transformer transmission network; the resonant network includes a first inductor L1 and a first capacitor C1. The transformer transmission network includes a first transformer T1 and a second transformer T2 connected in series with the first transformer T1. The first inductor L1 is connected in series to the primary side of the first transformer T1. The first capacitor C1 is connected in series to the primary side of the second transformer T2. It further includes a first switch S1, and the first switch S1 is connected in parallel to the primary side of the second transformer T2. It further includes a second inductor L2, and the first transformer T1 and the second transformer T2 are connected in parallel to the second inductor L2 after being connected in series.

[0005] 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. 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 through a first capacitor C1.

[0006] 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, 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 and the positive pole of the second rectifier bridge D2 are connected to form a first positive pole, and 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 further 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] The output end of the rectifying and filtering network is connected in parallel with a first battery pack BT1 and a second battery pack BT2. It further includes a second switch S2. The first end of the second switch S2 is electrically connected to the first positive pole, and the second end of the second switch S2 is respectively connected to the first battery pack BT1 and the second battery pack BT2. The voltage of the first battery pack BT1 is twice the voltage of the second battery pack BT2.

[0009] The structure of the present invention is simple. When the battery voltage changes, through the added first switch S1, the normalized DC gain M of the LLC resonant converter n remains unchanged. Specifically, according to the working condition of the battery voltage, that is, by switching the second switch S2, the voltage of the first battery pack BT1 is equal to V 01 or the voltage of the second battery pack BT2 is equal to V 02 , and V1 = 2V 02 ; switch the first switch S1 to change the number of transformers connected to the resonant cavity network, so as to ensure that the normalized DC gain M of the LLC resonant converter n remains unchanged. In this way, even if the battery voltage changes, the LLC resonant converter can still maintain its original working mode. Description of the Drawings

[0010] Figure 1 is an existing dual-active bridge converter;

[0011] Figure 2 is an existing AC equivalent model of an LLC resonant converter;

[0012] Figure 3 A novel LLC resonant converter proposed by the present invention (the first switch S1 is closed);

[0013] Figure 4 A novel LLC resonant converter proposed by the present invention (the first switch S1 is open); Specific embodiments

[0014] To enable those skilled in the art to better understand the present invention and thus more clearly define the scope of protection of 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.

[0015] As Figure 1 shown, 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 01 , and the voltage of the second battery pack BT2 is V 02 , and V o1 = 2V o2 . Ensure that the second switch S2 is switched to the battery pack BT1, and the dual-active bridge converter can achieve zero-voltage switching of the primary and secondary switching tubes within a wide load range. Design the turns ratio N:1 of the primary and secondary sides of the transformer. It can be known that the normalized DC gain of the LLC resonant converter at this time When the second switch S2 is switched to the voltage V o2 of the first battery pack BT2, the normalized DC gain of the LLC resonant converter at this time Since V o1 = 2V o2 , so M n1 = 2 * M n2 , that is, the normalized DC gain curve of the LLC resonant converter changes.

[0016] To illustrate the above problem more specifically, the analysis is as follows: Figure 2 is an existing AC equivalent model of an LLC resonant converter. From Figure 2 the normalized DC gain expression of the full-bridge LLC resonant converter can be derived:

[0017]

[0018] Among them, inductance coefficient k; quality factor Q; normalized frequency f n ; transformer equivalent turns ratio n; DC output voltage V2 of the LLC resonant converter; DC input voltage V1 of the LLC resonant converter. The normalized DC gain Mn of the full-bridge LLC resonant converter is related to the transformer equivalent turns ratio n, DC input voltage V1, and DC output voltage V2. When the DC output voltage changes, the normalized DC gain of the full-bridge LLC resonant converter will change. Under the same conditions, it may cause the LLC resonant converter to enter the capacitive region, resulting in the inability of the switching tube to achieve zero-voltage switching, significantly increasing the device loss, and seriously leading to irreversible failures of the machine.

[0019] Therefore, the present invention provides a novel LLC resonant converter, including a driving circuit, a resonant 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 resonant network. The transformer transmission network is connected to the full-bridge switching network through the resonant network. The input end of the rectifying and filtering network is connected to the output end of the transformer transmission network; the resonant network includes a first inductor L1 and a first capacitor C1. The transformer transmission network includes a first transformer T1 and a second transformer T2 connected in series with the first transformer T1. The first inductor L1 is connected in series to the primary side of the first transformer T1, the first capacitor C1 is connected in series to the primary side of the second transformer T2, and further includes a first switch S1, and the first switch S1 is connected in parallel to the primary side of the second transformer T2. It further includes a second inductor L2, and the first transformer T1 and the second transformer T2 are connected in series and then connected in parallel with the second inductor L2.

[0020] Among them, the turns ratios of the primary and secondary sides of the first transformer T1 and the second transformer T2 are N:1.

[0021] The driving circuit includes a full-bridge switching network, including a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, and a fourth switching tube Q4. 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, the first series branch and the second series branch are connected in parallel to form a first parallel branch, and 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 the 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 through the first capacitor C1. Among them, the driving circuit can also be other circuits for driving and controlling the resonant network.

[0022] The secondary side of the first transformer T1 and the secondary side of the second transformer T2 are respectively connected to the rectifying and filtering network.

[0023] 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, 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 further 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.

[0024] The output end of the rectifying and filtering network is connected in parallel with a first battery pack and a second battery pack. It further includes a second switch S2. The first end of the second switch S2 is electrically connected to the first positive pole, and the second end of the second switch S2 is respectively connected to the first battery pack and the second battery pack. The voltage of the first battery pack is twice that of the second battery pack, that is, the voltage of the first battery BT1 is V 01 , and the voltage of the second battery BT2 is V 02 , and V o1 = 2V o2 .

[0025] As Figure 3 shown, when the first switch S1 is closed and the second switch S2 is switched to the voltage V 01 of the first battery pack BT1, at this time, the normalized DC gain M n1 of the LLC resonant converter = N*V o1 / V1; as Figure 4 shown, when the first switch S1 is closed and the second switch S2 is switched to the voltage V 02 of the second battery pack BT2, at this time, the normalized DC gain M n2 of the LLC resonant converter = 2N*V o2 / V1; since V o1 = 2V o2 , then M n1 = M n2 . According to the above operations of the present invention, even if the battery voltage undergoes a switching operation, it is still possible to ensure that the normalized DC gain curve of the LLC resonant converter remains unchanged, thereby ensuring the stable operation of the system.

[0026] The structure of the present invention is simple. When the battery voltage changes, through the added first switch S1, the normalized DC gain M n of the LLC resonant converter remains unchanged. Specifically, according to the working condition of the battery voltage, that is, by switching the second switch S2, the voltage of the first battery BT1 is equal to V 01 or the voltage of the second battery BT2 is equal to V 02 , and V1 = 2V 02; Switch the first switch S1 to operate, thereby changing the number of transformers connected to the resonant cavity network, so as to ensure that the normalized DC gain M of the LLC resonant converter n remains unchanged. In this way, even if the battery voltage changes, the LLC resonant converter can still maintain its original operating mode.

[0027] 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 scope of the essence of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A novel LLC resonant converter, comprising a driving circuit, a resonant 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 an input DC source, the output end of the full-bridge switching network is connected to the input end of the resonant network, the transformer transmission network is connected to the full-bridge switching network through the resonant network, and the input end of the rectifying and filtering network is connected to the output end of the transformer transmission network; The resonant network includes a first inductor L1 and a first capacitor C1, and the transformer transmission network includes a first transformer T1 and a second transformer T2 connected in series with the first transformer T1. The first inductor L1 is connected in series to the primary side of the first transformer T1, and the first capacitor C1 is connected in series to the primary side of the second transformer T2. It is characterized in that: It further includes a first switch S1, and the first switch S1 is connected in parallel with the primary side of the second transformer T2; The resonant network further includes a second inductor L2, and the first transformer T1 and the second transformer T2 are connected in series and then connected in parallel with the second inductor L2; The output end of the rectifying and filtering network is connected in parallel with a first battery pack BT1 and a second battery pack BT2, and it further includes a second switch S2. The first end of the second switch S2 is electrically connected to a first positive electrode, and the second end of the second switch S2 is respectively connected to the first battery pack BT1 and the second battery pack BT2; The voltage of the first battery pack BT1 is twice the voltage of the second battery pack BT2.

2. The novel LLC resonant converter according to claim 1, wherein: The driving circuit includes a full-bridge switching network, including a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, and a fourth switching tube Q4. 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 through a first capacitor C1.

3. The novel LLC resonant converter according to claim 1, wherein: The secondary sides of the first transformer T1 and the second transformer T2 are respectively connected to the rectifying and filtering network.

4. The novel LLC resonant converter 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 and the positive electrode of the second rectifier bridge D2 are connected to form a first positive electrode, and the negative electrode of the first rectifier bridge D1 and the negative electrode of the second rectifier bridge D2 are connected to form a first negative electrode.

5. The novel LLC resonant converter according to claim 4, characterized in that: 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.

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