阅读说明：本技术 Cllc双向直流-直流变换器 (C LL C bidirectional DC-DC converter ) 是由 蒋劲松 杜晓笏 桂杰明 庄启超 郭水保 于 2020-04-13 设计创作，主要内容包括：本发明实施例公开了一种CLLC双向直流-直流变换器,属于电力电子技术领域。其中所述CLLC双向直流-直流变换器包括：依序连接的原边滤波电容、原边三相桥、原边谐振器件、变压装置、副边谐振器件、副边三相桥以及副边滤波电容。本发明在硬件上自带均流能力,不需要额外的均流控制电路,极大地降低了成本。(The embodiment of the invention discloses a C LL C bidirectional direct current-direct current converter, which belongs to the technical field of power electronics, wherein the C LL C bidirectional direct current-direct current converter comprises a primary side filter capacitor, a primary side three-phase bridge, a primary side resonance device, a transformation device, a secondary side resonance device, a secondary side three-phase bridge and a secondary side filter capacitor which are sequentially connected.)

1. A C LL C bidirectional DC-DC converter is characterized by comprising a primary side filter capacitor, a primary side three-phase bridge, a primary side resonance device, a voltage transformation device, a secondary side resonance device, a secondary side three-phase bridge and a secondary side filter capacitor which are connected in sequence, wherein,

the primary side three-phase bridge comprises three primary side half-bridges, each primary side half-bridge is formed by connecting two switching tubes in series, and each primary side half-bridge is connected with the positive electrode and the negative electrode of a primary side filter capacitor;

the primary side resonance device comprises three groups of primary side series resonance devices, and each group of primary side series resonance devices is connected with one primary side half bridge;

the transformer device comprises three transformers, each transformer comprises a primary side and a secondary side, the primary side of each transformer is provided with two primary side terminals, one primary side terminal is connected with one group of primary side series resonance devices, the other primary side terminal is connected with the primary side terminals of the other two transformers, and the primary sides of the transformers are in star connection; the secondary side of each transformer is provided with two secondary side terminals, one secondary side terminal is connected with a group of secondary side resonance devices, the other secondary side terminal is connected with the secondary side terminals of the other two transformers, and star connection is formed on the secondary side of the transformers;

the secondary side resonant devices comprise three groups, each group of secondary side resonant devices comprises a resonant capacitor, one end of each resonant capacitor is connected with one secondary side terminal of one transformer, and the other end of each resonant capacitor is connected with one secondary side half bridge in the secondary side three-phase bridge;

the secondary three-phase bridge comprises three secondary half-bridges, each secondary half-bridge is formed by connecting two switching tubes in series, and each secondary half-bridge is connected with the anode and the cathode of the secondary filter capacitor.

2. The C LL C bidirectional dc-dc converter according to claim 1, wherein the primary side three-phase bridge comprises first to sixth switching tubes, the first primary side half-bridge is formed by connecting the first and second switching tubes in series, the second primary side half-bridge is formed by connecting the third and fourth switching tubes in series, the third primary side half-bridge is formed by connecting the fifth and sixth switching tubes in series, each switching tube has a reverse diode connected in parallel at both ends, the first end of the first switching tube is connected to the first end of the third switching tube, the first end of the fifth switching tube and the anode of the primary side filter capacitor, the second end of the first switching tube is connected to the first end of the second switching tube and the primary side resonator, the second end of the second switching tube is connected to the cathode of the primary side filter capacitor, the second end of the fourth switching tube and the second end of the sixth switching tube, the second end of the third switching tube is connected to the first end of the fourth switching tube and the primary side resonator, and the second end of the fifth switching tube is connected to the primary side resonator and the anode of the sixth switching tube.

3. The C LL C bidirectional dc-dc converter of claim 2, wherein the primary side resonant devices comprise first through third sets of primary side series resonant devices, the first set of primary side series resonant devices comprises a first capacitor and a first inductor connected in series with the first capacitor, the first capacitor is further connected between a first switching tube and a second switching tube, the first inductor is further connected to one terminal of a transformer in the voltage converter, the second set of primary side series resonant devices comprises a second capacitor and a second inductor connected in series with the second capacitor, the second capacitor is further connected between a third switching tube and a fourth switching tube, the second inductor is further connected to one terminal of a transformer in the voltage converter, the third set of primary side series resonant devices comprises a third capacitor and a third inductor connected in series with the third capacitor, the third capacitor is further connected between a fifth switching tube and a sixth switching tube, and the third inductor is further connected to one terminal of a transformer in the voltage converter.

4. The C LL C bidirectional DC-DC converter of claim 3, wherein the three transformers are respectively first to third transformers, one primary terminal of the first transformer is connected to a first inductor of the first set of primary side series resonant devices, the other primary terminal of the first transformer is connected to one primary terminal of the second transformer and one primary terminal of the third transformer, the other primary terminal of the second transformer is connected to a second inductor of the second set of primary side series resonant devices, the other primary terminal of the third transformer is connected to a third inductor of the third set of primary side series resonant devices, one secondary terminal of the first transformer, one secondary terminal of the second transformer, one secondary terminal of the third transformer is connected to the secondary resonant devices, and the other secondary terminal of the first transformer is connected to the other secondary terminal of the second transformer and the other secondary terminal of the third transformer.

5. The C LL C bidirectional DC-DC converter according to claim 4, wherein the secondary resonant device comprises a first to a third set of secondary resonant devices, the first set of secondary resonant devices comprises a first resonant capacitor, the second set of secondary resonant devices comprises a second resonant capacitor, the third set of secondary resonant devices comprises a third resonant capacitor, one end of the first resonant capacitor is connected to the first transformer, the other end of the first resonant capacitor is connected to one of the secondary half-bridges, one end of the second resonant capacitor is connected to the second transformer, the other end of the second resonant capacitor is connected to one of the secondary half-bridges, one end of the third resonant capacitor is connected to the third transformer, and the other end of the third resonant capacitor is connected to one of the secondary half-bridges.

6. The C LL C bidirectional dc-dc converter according to claim 3, wherein the secondary three-phase bridge comprises seventh to twelfth switching transistors, a first secondary half-bridge is formed by connecting the seventh and eighth switching transistors in series, a second secondary half-bridge is formed by connecting the ninth and tenth switching transistors in series, a third secondary half-bridge is formed by connecting the eleventh and twelfth switching transistors in series, each switching transistor has two ends connected in parallel with a backward diode, a first end of the seventh switching transistor is connected to a first end of the ninth switching transistor, a first end of the eleventh switching transistor and a positive electrode of the secondary filter capacitor, a second end of the seventh switching transistor is connected to a first end of the eighth switching transistor and the secondary resonant device, a second end of the eighth switching transistor is connected to a negative electrode of the secondary filter capacitor, a second end of the tenth switching transistor and a second end of the twelfth switching transistor, a second end of the ninth switching transistor is connected to a first end of the tenth switching transistor and the secondary resonant device, and a second end of the eleventh switching transistor is connected to the secondary resonant device.

7. The C LL C bidirectional DC-DC converter according to any one of claims 3 and 6, wherein the switching tubes are all field effect transistors.

8. The C LL C bidirectional DC-DC converter according to claim 3, wherein the first to sixth switching tubes further include a primary side control terminal, respectively, and the C LL C bidirectional DC-DC converter further includes a control unit connected to each primary side control terminal for controlling the first to sixth switching tubes to turn on and off, and the switching timing of each primary side half-bridge is sequentially shifted by 120 ° in phase from each other.

9. The C LL C bidirectional DC-DC converter according to claim 6, wherein the seventh to twelfth switching transistors further include a secondary control terminal, respectively, the C LL C bidirectional DC-DC converter further includes a control unit connected to each secondary control terminal for controlling the seventh to twelfth switching transistors to be turned on and off, and the switching timing phases of each secondary half-bridge are sequentially shifted by 120 °.

Technical Field

The invention relates to the technical field of power electronics, in particular to a C LL C bidirectional direct current-direct current converter.

Background

At present, in the application occasions of a high-voltage high-power isolated bidirectional DC-DC converter, the selection of power devices is limited, a single full-bridge C LL C is difficult to realize, a common circuit topology structure adopts two full-bridges C LL C in parallel, the parallel connection of the two full-bridges C LL C means that the two full-bridges C LL C work in parallel, each full-bridge C LL C shares half of power, the number of power semiconductor devices is 16, each full-bridge C LL C can realize the bidirectional conversion of energy, however, the technical scheme of the parallel connection of the two full-bridges C LL C adopted at present mainly has the following three disadvantages:

(1) the number of power semiconductor devices is large, and the number of corresponding driving circuits is large, so that the size of the bidirectional direct current-direct current converter is large, and the cost is high;

(2) the two full-bridges C LL C are connected in parallel or alternately connected in parallel in control, so that the high-frequency ripple current of the output filter capacitor is relatively large, the effective value of the ripple current can reach 32% of the output current at most, and the number of the required output filter capacitors is relatively large;

(3) the parallel connection of two full bridges C LL C requires the addition of a current sharing control circuit, which also increases the cost.

Disclosure of Invention

The invention provides a C LL C bidirectional DC-DC converter, which has current sharing capability on hardware, does not need an additional current sharing control circuit and greatly reduces the cost.

The technical scheme is as follows:

the embodiment of the invention provides a C LL C bidirectional direct current-direct current converter which comprises a primary side filter capacitor, a primary side three-phase bridge, a primary side resonance device, a transformation device, secondary side resonance devices, a secondary side three-phase bridge and a secondary side filter capacitor, wherein the primary side three-phase bridge comprises three primary side half bridges, each primary side half bridge is formed by connecting two switching tubes in series, each primary side half bridge is connected with the positive electrode and the negative electrode of the primary side filter capacitor, the primary side resonance devices comprise three groups of primary side series resonance devices, each group of primary side series resonance devices are connected with one primary side half bridge, the transformation device comprises three transformers, each transformer comprises a primary side and a secondary side, the primary side of each transformer is provided with two primary side terminals, one primary side terminal is connected with one group of primary side series resonance devices, the other primary side terminal is connected with the primary side terminals of the other two transformers, the primary side terminals of each transformer are in star connection, the secondary side of each transformer is provided with two secondary side terminals, one secondary side terminal is connected with one group of secondary side resonance devices, the other secondary side resonance devices are connected with the other secondary side resonance devices, one secondary side of each secondary side resonance device is connected with one secondary side of each secondary side bridge, one secondary side resonance device is connected with one secondary side resonance device, and one secondary side resonance device is connected with one secondary side resonance device, one secondary side resonance device in series resonance device, each secondary side resonance device is connected with one secondary side of each secondary side resonance device, each secondary side resonance.

In a preferred embodiment of the present invention, the primary side three-phase bridge includes first to sixth switching tubes, a first primary side half-bridge is formed by connecting the first and second switching tubes in series, a second primary side half-bridge is formed by connecting the third and fourth switching tubes in series, a third primary side half-bridge is formed by connecting the fifth and sixth switching tubes in series, a backward diode is connected in parallel with two ends of each switching tube, the first end of the first switching tube is connected to the first end of the third switching tube, the first end of the fifth switching tube and the anode of the primary side filter capacitor, the second end of the first switching tube is connected to the first end of the second switching tube and the primary side resonator, the second end of the second switching tube is connected to the cathode of the primary side filter capacitor, the second end of the fourth switching tube and the second end of the sixth switching tube, the second end of the third switching tube is connected to the first end of the fourth switching tube and the primary side resonator, the second end of the fifth switching tube is connected to the first end of the sixth switching tube, the, The primary side resonant device is connected.

In a preferred embodiment of the present invention, the primary side resonant devices include first to third groups of primary side series resonant devices, the first group of primary side series resonant devices includes a first capacitor and a first inductor connected in series with the first capacitor, the first capacitor is further connected between a first switching tube and a second switching tube, the first inductor is further connected to one end of a transformer in the voltage transformer device, the second group of primary side series resonant devices includes a second capacitor and a second inductor connected in series with the second capacitor, the second capacitor is further connected between a third switching tube and a fourth switching tube, the second inductor is further connected to one end of a transformer in the voltage transformer device, the third group of primary side series resonant devices includes a third capacitor and a third inductor connected in series with the third capacitor, the third capacitor is further connected between a fifth switching tube and a sixth switching tube, and the third inductor is further connected to one end of a transformer in the voltage transformer device.

In a preferred embodiment of the present invention, the three transformers are respectively first to third transformers, one primary terminal of the first transformer is connected to a first inductance of the first group of primary side series resonant devices, the other primary terminal of the first transformer is connected to one primary terminal of the second transformer and one primary terminal of the third transformer, the other primary terminal of the second transformer is connected to a second inductance of the second group of primary side series resonant devices, the other primary terminal of the third transformer is connected to a third inductance of the third group of primary side series resonant devices, one secondary terminal of the first transformer and one secondary terminal of the second transformer, one secondary terminal of the third transformer is connected to the secondary resonant device, and the other secondary terminal of the first transformer is connected to the other secondary terminal of the second transformer and the other secondary terminal of the third transformer.

In a preferred embodiment of the present invention, the secondary resonant device includes a first group to a third group of secondary resonant devices, the first group of secondary resonant devices includes a first resonant capacitor, the second group of secondary resonant devices includes a second resonant capacitor, the third group of secondary resonant devices includes a third resonant capacitor, one end of the first resonant capacitor is connected to the first transformer, the other end of the first resonant capacitor is connected to one of the secondary half-bridges of the secondary three-phase bridge, one end of the second resonant capacitor is connected to the second transformer, the other end of the second resonant capacitor is connected to one of the secondary half-bridges of the secondary three-phase bridge, one end of the third resonant capacitor is connected to the third transformer, and the other end of the third resonant capacitor is connected to one of the secondary half-bridges of the secondary three-phase bridge.

In a preferred embodiment of the present invention, the secondary three-phase bridge includes seventh to twelfth switching tubes, a first secondary half-bridge is formed by connecting the seventh and eighth switching tubes in series, a second secondary half-bridge is formed by connecting the ninth and tenth switching tubes in series, a third secondary half-bridge is formed by connecting the eleventh and twelfth switching tubes in series, two ends of each switching tube are connected in parallel with a backward diode, a first end of the seventh switching tube is connected to a first end of the ninth switching tube, a first end of the eleventh switching tube and an anode of a secondary filter capacitor, a second end of the seventh switching tube is connected to a first end of the eighth switching tube and a secondary resonant device, a second end of the eighth switching tube is connected to a cathode of the secondary filter capacitor, a second end of the tenth switching tube and a second end of the twelfth switching tube, a second end of the ninth switching tube is connected to a first end of the tenth switching tube, a secondary resonant device, and a second end of the eleventh switching tube is connected to a first end of the twelfth switching tube, The secondary resonant devices are connected.

In a preferred embodiment of the present invention, the switching transistors are all field effect transistors.

In a preferred embodiment of the present invention, the first to sixth switching tubes further include a primary side control end, and the C LL C bidirectional dc-dc converter further includes a control unit, connected to each primary side control end, for controlling the on and off of the first to sixth switching tubes, and the switching timing phases of each primary side half-bridge are sequentially shifted by 120 °.

In a preferred embodiment of the present invention, the seventh to twelfth switching tubes further include a secondary control end, respectively, the C LL C bidirectional dc-dc converter further includes a control unit, connected to each secondary control end, for controlling the seventh to twelfth switching tubes to be turned on and off, and the switching timing phases of each secondary half-bridge are sequentially staggered by 120 °.

The technical scheme provided by the embodiment of the invention has the following beneficial effects:

when energy is transmitted from the primary side to the secondary side, the primary side three-phase bridge is used as active control, the secondary side three-phase bridge is used as rectification control, forward power conversion from the primary side to the secondary side can be achieved, when energy is transmitted from the secondary side to the primary side, the secondary side three-phase bridge is used as active control, the primary side three-phase bridge is used as rectification control, reverse power conversion from the secondary side to the primary side can be achieved, zero-voltage-switching-on soft switching of a secondary side switching tube can be achieved during reverse discharging, and hard switching is not achieved, so that high-frequency current ripples of filter capacitors of the primary side and the secondary side can be reduced, performance of a converter is improved, size and cost of a bidirectional direct current-direct current converter are reduced, the primary side and the secondary side of a transformation device of a three-phase alternating C LL C bidirectional direct current-direct current converter are connected in a star mode, three-phase currents are mutually looped, current sharing capability is achieved on hardware, an additional current sharing control circuit is not needed.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.

Drawings

Fig. 1 is a block diagram of a C LL C bidirectional dc-dc converter according to an embodiment of the present invention;

FIG. 2 is a circuit diagram of the C LL C bidirectional DC-DC converter of FIG. 1;

FIG. 3a is a current-holding loop diagram of the C LL C bidirectional DC-DC converter in a first operating mode;

FIG. 3b is a current-storing loop diagram of the bidirectional DC-DC converter C LL C in the second operation mode;

FIG. 3C is a current-holding loop diagram of the C LL C bi-directional DC-DC converter in the third operating mode;

FIG. 3d is a current-storing loop diagram of the C LL C bi-directional DC-DC converter in the fourth operating mode;

FIG. 3e is a current-holding loop diagram of the C LL C bi-directional DC-DC converter in the fifth operating mode;

FIG. 3f is a current-holding loop diagram of the C LL C bidirectional DC-DC converter in the sixth operating mode;

fig. 4 is a graph of the operating waveform, the primary current and the secondary current of a typical synchronous rectification output of a C LL C bidirectional dc-dc converter during forward power conversion.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, structures, features and effects of the C LL C bi-directional dc-dc converter according to the present invention will be made with reference to the accompanying drawings and preferred embodiments.

The foregoing and other technical and scientific aspects, features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings. While the present invention has been described in connection with the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications, equivalent arrangements, and specific embodiments thereof.

Fig. 1 is a block diagram of a C LL C bidirectional dc-dc converter according to an embodiment of the present invention, fig. 2 is a circuit diagram of a C LL C bidirectional dc-dc converter in fig. 1, the C LL C bidirectional dc-dc converter has a current sharing capability in hardware, and an additional current sharing control circuit is not required, so that the cost is greatly reduced, referring to fig. 1 and fig. 2, the C LL C bidirectional dc-dc converter of the present embodiment includes a primary side filter capacitor C1, a primary side three-phase bridge 10, a primary side resonant device 11, a transformer 12, a secondary side resonant device 13, a secondary side three-phase bridge 14, and a secondary side filter capacitor C8, which are sequentially connected.

Specifically, the primary three-phase bridge 10 includes three primary half-bridges, each of which is formed by connecting two switching tubes in series, and each of the primary half-bridges is connected to the positive electrode and the negative electrode of the primary filter capacitor. Specifically, the primary side three-phase bridge 10 includes first to sixth switching tubes S1-S6, a first primary side half-bridge is formed by connecting the first and second switching tubes S1 and S2 in series, a second primary side half-bridge is formed by connecting the third and fourth switching tubes S3 and S4 in series, a third primary side half-bridge is formed by connecting the fifth and sixth switching tubes S5 and S6 in series, and two ends of each switching tube are connected with a backward diode in parallel. A first end of the first switch tube S1 is connected to a first end of the third switch tube S3, a first end of the fifth switch tube S5, and an anode of the primary side filter capacitor C1, a second end of the first switch tube S1 is connected to a first end of the second switch tube S2 and the primary side resonator 11, a second end of the second switch tube S2 is connected to a cathode of the primary side filter capacitor C1, a second end of the fourth switch tube S4, and a second end of the sixth switch tube S6, a second end of the third switch tube S3 is connected to a first end of the fourth switch tube S4 and the primary side resonator 11, and a second end of the fifth switch tube S5 is connected to a first end of the sixth switch tube S6 and the primary side resonator 11.

When energy is required to be transmitted from the primary side to the secondary side, the primary side three-phase bridge 10 is required to be used as active control, and the secondary side three-phase bridge 14 is used as rectification control, so that the forward power conversion from the primary side to the secondary side can be realized; when the required energy is transferred from the secondary side to the primary side, the secondary three-phase bridge 14 is required to be used as active control, and the primary three-phase bridge 10 is used as rectification control, so that reverse power conversion from the secondary side to the primary side can be realized.

Preferably, each of the first to sixth switching tubes S1-S6 is a semiconductor switch, and may be, for example, a field effect transistor, and the first terminal may be a source (S) or a drain (D) of the transistor, and correspondingly, the second terminal may be a drain or a source of the transistor.

Preferably, the first to sixth switching tubes S1-S6 may further include a primary side control terminal (for example, the gate G), and the C LL C bidirectional dc-dc converter further includes a control unit (not shown in the figure), the control unit is connected to each primary side control terminal for controlling the first to sixth switching tubes S1-S6 to be turned on and off, and the switching timing phases of each primary side half bridge are sequentially shifted by 120 °.

Specifically, the primary side resonant device 11 comprises first to third groups of primary side series resonant devices, the first group of primary side series resonant devices comprises a first capacitor C2 and a first inductor L connected in series with the first capacitor C2, the first capacitor C2 is further connected between a first switching tube S1 and a second switching tube S2, the first inductor L is further connected to one end of a transformer in the transformation device 12, the second group of primary side series resonant devices comprises a second capacitor C3 and a second inductor L2 connected in series with the second capacitor C3, the second capacitor C3 is further connected between the third switching tube S3 and a fourth switching tube S4, the second inductor L2 is further connected to one end of a transformer in the transformation device 12, the third group of primary side series resonant devices comprises a third capacitor C4 and a third inductor 463 connected in series with the third capacitor C4, the third inductor is further connected between a third inductor S465 and a sixth switching tube S L connected between the third capacitor C4624 and a fifth switching tube S5.

The transformation device 12 comprises three transformers m, m and 0m, each transformer comprises a primary side and a secondary side, the primary side of each transformer is provided with two primary side terminals, one of the primary side terminals is connected with one group of primary side series resonance devices, the other primary side terminal is connected with the primary side terminals of the other two transformers, star connection is formed on the primary side of each transformer, the secondary side of each transformer is provided with two secondary side terminals, one of the secondary side terminals is connected with one group of secondary side resonance devices, the other secondary side terminal is connected with the secondary side terminals of the other two transformers, star connection is formed on the secondary side of each transformer, specifically, the three transformers are respectively 1m, 2m and 3m of the first to third transformers, one primary side terminal of the first transformer 4m is connected with a first inductance 51 of the first group of primary side series resonance devices, the other primary side terminal of the first transformer 6m is connected with one primary side terminal of the second transformer 7m, one primary side terminal of the third transformer 8m is connected with one primary side terminal of the second transformer 9m is connected with a second inductance 2 of the second group of series resonance devices, the other primary side terminal of the third transformer 0m is connected with the other secondary side terminal of the third transformer, and the other secondary side terminal of the third secondary side transformer is connected with the third secondary side resonance devices, and the other secondary side terminal of the third secondary side of the third transformer m is connected with the secondary side resonance devices.

The secondary side resonant device 13 comprises three groups of secondary side resonant devices C5, C6 and C7 from the first group to the third group, each group of secondary side resonant devices comprises a resonant capacitor, one end of each resonant capacitor is connected with a secondary side terminal of a transformer, and the other end of each resonant capacitor is connected with a secondary side half bridge in a secondary side three-phase bridge, specifically, the first group of secondary side resonant devices comprises a first resonant capacitor C5, the second group of secondary side resonant devices comprises a second resonant capacitor C6, the third group of secondary side resonant devices comprises a third resonant capacitor C7, one end of the first resonant capacitor C5 is connected with a first transformer, the other end of the resonant capacitor C5 is connected with a secondary side half bridge in the secondary side three-phase bridge, one end of the second resonant capacitor C6 is connected with a second transformer, the other end of the second resonant capacitor C6 is connected with a secondary side half bridge in the secondary side three-phase bridge, one end of the third resonant capacitor C7 is connected with a third transformer, the other end of the third resonant capacitor C7 is connected with a secondary side half bridge, and when the primary side soft switch C5 is connected with a primary side switch, zero, the secondary side switch energy of the secondary side soft switch can be transferred from a primary side soft switch C6313 to a primary side switch, and zero when the secondary side soft switch of the secondary side soft switch is switched on, the secondary side switch can be switched on, and zero, therefore, zero energy transfer of the secondary side switch of the secondary side soft switch of the secondary side three-soft switch of the secondary side three-soft side three-side.

The secondary three-phase bridge 14 includes three secondary half-bridges, each of which is formed by two switching tubes connected in series. Specifically, the secondary three-phase bridge 10 includes seventh to twelfth switching tubes S7-S12, a first secondary half-bridge is formed by connecting seventh and eighth switching tubes S7, S8 in series, a second secondary half-bridge is formed by connecting ninth and tenth switching tubes S9, S10 in series, a third secondary half-bridge is formed by connecting eleventh and twelfth switching tubes S11, S12 in series, and a reverse diode is connected in parallel at two ends of each switching tube. A first end of the seventh switching tube S7 is connected to a first end of the ninth switching tube S9, a first end of the eleventh switching tube S11 and an anode of the secondary filter capacitor C8, a second end of the seventh switching tube S7 is connected to a first end of the eighth switching tube S8 and the secondary resonant device 13, a second end of the eighth switching tube S8 is connected to a cathode of the secondary filter capacitor C8, a second end of the tenth switching tube S10 and a second end of the twelfth switching tube S12, a second end of the ninth switching tube S9 is connected to a first end of the tenth switching tube S10 and the secondary resonant device 13, and a second end of the eleventh switching tube S11 is connected to a first end of the twelfth switching tube S12 and the secondary resonant device 13.

Preferably, the seventh to twelfth switching tubes S7-S12 are all semiconductor switches, and may be field effect transistors, for example, the first terminal may be a source (S) or a drain (D) of the transistor, and correspondingly, the second terminal may be a drain or a source of the transistor. And the first primary half-bridge, the second primary half-bridge and the third primary half-bridge of the primary three-phase bridge respectively correspond to the first secondary half-bridge, the second secondary half-bridge and the third secondary half-bridge of the secondary three-phase bridge.

Preferably, the seventh to twelfth switching tubes S7-S12 may further include a secondary control terminal (for example, a gate G), and a control unit is connected to each secondary control terminal for controlling the seventh to twelfth switching tubes S7-S12 to turn on and off, and the switching timing phases of each secondary half-bridge are sequentially shifted by 120 °.

A primary side three-phase resonant circuit in star connection is formed by a primary side three-phase bridge, a primary side resonant device and a primary side of a voltage transformation device. When the primary three-phase resonant circuit is used for active control, the switching cycles of each primary half-bridge of the primary three-phase bridge are the same (namely the switching cycles of the switching tubes S1-S6 are the same), but the switching time sequence phases of each primary half-bridge are sequentially staggered by 120 degrees, namely the switching time sequences of the first switching tube S1, the third switching tube S3 and the fifth switching tube S5 are sequentially staggered by 120 degrees, so that three-phase staggered resonance of the primary three-phase resonant circuit is realized. When a primary side three-phase resonant circuit (comprising a primary side three-phase bridge, a primary side resonant device and a primary side winding of a voltage transformation device) is used for rectification control, a semiconductor switching tube of each half bridge of the primary side three-phase bridge can be kept closed, and an anti-parallel diode of the semiconductor switching tube can bear the rectification function; the semiconductor switching tubes of the half-bridges corresponding to the secondary three-phase bridge (i.e., the switching tubes S1, S3, and S5 correspond to the switching tubes S11, S9, and S7, respectively, and the switching tubes S2, S4, and S6 correspond to the switching tubes S12, S10, and S8, respectively) may be maintained in the same switching state, so that the semiconductor switching tube body may perform the rectification function.

In addition, a star-connected secondary three-phase resonant loop is formed by the secondary three-phase bridge, the secondary resonant device and the secondary side of the transformer. When the secondary three-phase resonant circuit (comprising a secondary transformer winding, a secondary resonant capacitor and a secondary three-phase bridge) in star connection is used for active control, the switching cycles of each half bridge of the secondary three-phase bridge are the same (the switching cycles of the switching tubes S7-S12 are the same), but the switching time sequence phases of each secondary half bridge are staggered by 120 degrees in sequence, so that three-phase staggered resonance of the secondary three-phase resonant circuit is realized.

In addition, when the star-connected secondary three-phase resonant circuit is used for rectification control, the semiconductor switch tube of each half bridge of the secondary three-phase bridge can be kept closed, and the anti-parallel diode of the semiconductor switch tube can play a role in rectification; the semiconductor switch tube can also keep the same switch state as the semiconductor switch tube of the half bridge at the corresponding position of the primary three-phase bridge, and the semiconductor switch tube body can bear the rectification function.

The invention can realize high-voltage high-power bidirectional soft switch DC-DC power conversion, and because the three-phase bridge is in three-phase interleaved control, the invention can reduce the high-frequency current ripple of the filter capacitors of the primary side and the secondary side, namely the capacity of the filter capacitors of the primary side and the secondary side, thereby reducing the volume and the cost of the bidirectional DC-DC converter.

The three-phase alternating C LL C bidirectional DC-DC converter has the following six working modes when energy is transferred from a primary side to a secondary side:

the first working mode is as follows: the switching tube states of the primary three-phase bridge are respectively switching tube S1 closed, switching tube S2 open, switching tube S3 open, switching tube S4 closed, switching tube S5 closed and switching tube S6 open, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 closed, switching tube S12 open, switching tube S9 open, switching tube S10 closed, switching tube S7 closed and switching tube S8 open, and the energy flow loop is shown in FIG. 3 a.

And a second working mode: the switching tube states of the primary three-phase bridge are respectively switching tube S1 closed, switching tube S2 open, switching tube S3 open, switching tube S4 closed, switching tube S5 open and switching tube S6 closed, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 closed, switching tube S12 open, switching tube S9 open, switching tube S10 closed, switching tube S7 open and switching tube S8 closed, and the energy flow loop is shown in FIG. 3 b.

And a third working mode: the switching tube states of the primary three-phase bridge are respectively switching tube S1 closed, switching tube S2 open, switching tube S3 closed, switching tube S4 open, switching tube S5 open and switching tube S6 closed, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 closed, switching tube S12 open, switching tube S9 closed, switching tube S10 open, switching tube S7 open and switching tube S8 closed, and the energy flow loop is shown in FIG. 3 c.

And a fourth working mode: the switching tube states of the primary three-phase bridge are respectively switching tube S1 open, switching tube S2 closed, switching tube S3 closed, switching tube S4 open, switching tube S5 open and switching tube S6 closed, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 open, switching tube S12 closed, switching tube S9 closed, switching tube S10 open, switching tube S7 open and switching tube S8 closed, and the energy flow loop is shown in FIG. 3 d.

And a fifth working mode: the switching tube states of the primary three-phase bridge are respectively switching tube S1 open, switching tube S2 closed, switching tube S3 closed, switching tube S4 open, switching tube S5 closed and switching tube S6 open, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 open, switching tube S12 closed, switching tube S9 closed, switching tube S10 open, switching tube S7 closed and switching tube S8 open, and the energy flow loop is shown in FIG. 3 e.

And a sixth working mode: the switching tube states of the primary three-phase bridge are respectively switching tube S1 open, switching tube S2 closed, switching tube S3 open, switching tube S4 closed, switching tube S5 closed and switching tube S6 open, the switching tube states of the secondary three-phase bridge are respectively switching tube S11 open, switching tube S12 closed, switching tube S9 open, switching tube S10 closed, switching tube S7 closed and switching tube S8 open, and the energy flow loop is shown in FIG. 3 f.

The C LL C bi-directional dc-dc converter also has six operating modes when energy is transferred from the secondary side to the primary side, one for each mode when energy is transferred from the primary side to the secondary side.

In the three-phase interleaved C LL C bidirectional dc-dc converter, the control of power conversion is a frequency modulation control, the driving waveforms of the two switching tubes of each half-bridge are complementary, the duty ratio is close to 50% (considering dead time), and the typical synchronous rectification output working waveform, the primary current and the secondary current are as shown in fig. 4.

In summary, in the C LL C bidirectional dc-dc converter provided in the embodiments of the present invention, when energy is transferred from the primary side to the secondary side, the primary side three-phase bridge is used as active control, and the secondary side three-phase bridge is used as rectification control, so that forward power conversion from the primary side to the secondary side can be achieved, when energy is transferred from the secondary side to the primary side, the secondary side three-phase bridge is used as active control, and the primary side three-phase bridge is used as rectification control, so that reverse power conversion from the secondary side to the primary side can be achieved, and during reverse discharge, a soft switch is turned on at zero voltage of a secondary side switching tube instead of a hard switch, so that high-frequency current ripples of filter capacitors of the primary side and the secondary side can be reduced, performance of the converter is improved, and volume and cost of the bidirectional dc-dc converter are reduced.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.