阅读说明：本技术 Cllc双向直流-直流变换器及低增益控制方法 (C LL C bidirectional DC-DC converter and low gain control method ) 是由 肖克 蒋劲松 王大鹏 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-直流变换器及低增益控制方法,属于电力电子技术领域。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；其低增益控制方法包括：获取三相交错CLLC电路输入电压、输入电流、输出电压和输出电流；根据输入电压、输入电流、输出电压和输出电流确定三相交错CLLC电路的直流增益,如果直流增益处于三相交错CLLC电路预设增益为低的直流增益区间内,将变换器从三相交错CLLC电路切换为双相交错CLLC电路。本发明在电路直流增益为低时,三相交错CLLC电路切换为双相交错CLLC电路,控制逻辑简单,可确保能量传输连续,降低了电压纹波。(The embodiment of the invention discloses a C LL C bidirectional direct current-direct current converter and a low gain control method, and belongs to the technical field of power electronics.)

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

when the direct current gain of the circuit of the converter is not in the direct current gain interval with low preset gain, the converter is a three-phase interleaved C LL C circuit, and when the direct current gain of the circuit of the converter is in the direct current gain interval with low preset gain, the converter is a two-phase interleaved C LL C circuit.

2. The converter according to claim 1, wherein the primary side three-phase bridge comprises a first switching tube to a sixth switching tube, the first switching tube and the second switching tube are connected in series to form a first primary side half-bridge, the third switching tube and the fourth switching tube are connected in series to form a second primary side half-bridge, the fifth switching tube and the sixth switching tube are connected in series to form a third primary side half-bridge, two ends of each switching tube are connected in parallel with a backward diode, a first end of the first switching tube is connected with a first end of the third switching tube, a first end of the fifth switching tube and an anode of the primary side filter capacitor, a second end of the first switching tube is connected with a first end of the second switching tube and the primary side resonator, a second end of the second switching tube is connected with a cathode of the primary side filter capacitor, a second end of the fourth switching tube and a second end of the sixth switching tube, and a second end of the third switching tube is connected with a first end of the fourth switching tube, a third end, And the second end of the fifth switching tube is connected with the first end of the sixth switching tube and the primary side resonance device.

3. The converter of claim 2, wherein the primary side resonant devices comprise a first group of primary side series resonant devices to a third group of primary side series resonant devices, the first group 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 end of a transformer in the voltage transformer device, the second group 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 end of a transformer in the voltage transformer device, the third group 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, the third inductor is also connected to one end of one of the transformers in the transformer arrangement.

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

5. The converter according to claim 4, wherein the secondary resonant device comprises a first set of secondary resonant devices 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 converter according to claim 5, wherein the secondary three-phase bridge comprises a seventh switch tube to a twelfth switch tube, the seventh switch tube and the eighth switch tube are connected in series to form a first secondary half-bridge, the ninth switch tube and the tenth switch tube are connected in series to form a second secondary half-bridge, the eleventh switch tube and the twelfth switch tube are connected in series to form a third secondary half-bridge, two ends of each switch tube are connected in parallel with a backward diode, a first end of the seventh switch tube is connected with a first end of the ninth switch tube, a first end of the eleventh switch tube and an anode of the secondary filter capacitor, a second end of the seventh switch tube is connected with a first end of the eighth switch tube and the secondary resonant device, a second end of the eighth switch tube is connected with a cathode of the secondary filter capacitor, a second end of the tenth switch tube and a second end of the twelfth switch tube, and a second end of the ninth switch tube is connected with a first end of the tenth switch tube, And the second end of the eleventh switching tube is connected with the first end of the twelfth switching tube and the secondary side resonance device.

7. The converter of claim 6, wherein the first to twelfth switching tubes are all field effect transistors.

8. The converter according to claim 6, wherein the first to sixth switching tubes further comprise a primary control terminal, the converter further comprises a control unit, the control unit is connected to each primary control terminal for controlling the on/off of the first to sixth switching tubes, the seventh to twelfth switching tubes further comprise a secondary control terminal, and the control unit is connected to each secondary control terminal for controlling the on/off of the seventh to twelfth switching tubes.

9. The converter of claim 6, wherein when energy is required to be transferred from the primary side to the secondary side, the primary side three-phase bridge is used as an active control, and the secondary side three-phase bridge is used as a rectification control, so that forward power conversion from the primary side to the secondary side is realized; when the required 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 is realized.

10. The converter of claim 6, wherein when the converter is a two-phase interleaved C LL C circuit, energy is transferred from the primary side to the secondary side, the switching period of each half bridge is the same, and the switching timing between the half bridges is staggered by 120 °.

11. A method for controlling low gain of a C LL C bi-directional dc-dc converter, the method comprising:

acquiring input voltage and input current of a three-phase interleaved C LL C circuit, and acquiring output voltage and output current of the three-phase interleaved C LL C circuit;

determining a DC gain of the three-phase interleaved C LL C circuit from the input voltage, the input current, the output voltage, and the output current;

and if the direct current gain is in a direct current gain interval in which the preset gain of the three-phase interleaved C LL C circuit is low, switching the converter from the three-phase interleaved C LL C circuit to a double-phase interleaved C LL C circuit.

12. The control method according to claim 11, characterized by further comprising:

if the output voltage is smaller than a first preset voltage and the output current is smaller than a first preset current, the three-phase interleaved C LL C circuit is switched into a double-phase interleaved C LL C circuit by controlling the working state of each switching tube of the three-phase interleaved C LL C circuit.

13. The control method according to claim 12, characterized by further comprising:

the sampling moment is any moment after the three-phase interleaved C LL C circuit is switched to the two-phase interleaved C LL C circuit, the second preset current is larger than the first preset current, if the output current is larger than the first preset current and smaller than the second preset current at the sampling moment, the converter is the two-phase interleaved C LL C circuit, and if the output current is larger than the second preset current at the sampling moment, the converter is switched from the two-phase interleaved C LL C circuit to the three-phase interleaved C LL C circuit.

14. The control method according to claim 11, characterized by comprising:

the method comprises the steps of obtaining the input voltage and the input current of the three-phase interleaved C LL C circuit, obtaining the output voltage and the output current of the three-phase interleaved C LL C circuit, obtaining the working frequency of a switch tube corresponding to the output voltage and the output current, and if the working frequency of the switch tube is larger than a preset frequency, switching the three-phase interleaved C LL C circuit into the two-phase interleaved C LL C circuit by controlling the working state of each switch tube of the three-phase interleaved C LL C circuit.

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 and a low gain control method.

Background

When the dc-dc converter is used as the charging module of the electric vehicle, the dc gain (the dc gain is a logarithm of a ratio of the output voltage to the input voltage) of the dc-dc converter is low when the battery voltage is low. The DC-DC converter can reduce the DC gain of the DC-DC converter by controlling the intermittent operation of the switching tube or reduce the output of the converter by changing the topological structure.

However, when the battery voltage is lower than the output range of the dc-dc converter, the dc-dc converter enters an intermittent operation mode to reduce the power output, thereby causing discontinuous energy output, too large output ripple of the circuit, which easily causes increased loss and reduced power, and thus poor user experience.

Disclosure of Invention

The invention provides a C LL C bidirectional DC-DC converter and a low-gain control method, when a three-phase interleaved C LL C circuit is obtained by calculation and is in a DC gain interval with low preset gain, the three-phase interleaved C LL C circuit is switched into a double-phase interleaved C LL C circuit, the control logic is simple, the energy transmission is ensured to be continuous, and the voltage ripple is reduced.

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, a secondary side resonance device, a secondary side three-phase bridge and a secondary side filter capacitor which are sequentially connected, 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 device comprises three groups of primary side series resonance devices, each group of primary side series resonance devices is 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 of each transformer is connected with one group of primary side series resonance devices, the other primary side terminal of each transformer is connected with the primary side terminals of the other two transformers, one secondary side terminal of each transformer is connected with one group of secondary side resonance devices, the other secondary side terminals of the other are connected with the other in a star-shaped connection on the primary side of the other, when each secondary side resonance device is connected with the other, each secondary side converter, when each secondary side resonance device comprises one of the three groups of the three-phase filter capacitors, the secondary side half bridge is connected with the three-phase-bridge, the three-phase filter capacitors, the three-alternating-phase filter capacitors, the secondary side converter, when the secondary side converter is connected with the secondary side converter, the secondary side converter is connected with the three-phase converter is connected with the three-phase-alternating-.

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

In a preferred embodiment of the present invention, the primary side resonant devices include a first group of primary side series resonant devices to a third group 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 one 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 primary side inductor is further connected to one end of one transformer in the voltage transformer device, the third group of 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 one transformer in the voltage transformer device.

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

In a preferred embodiment of the present invention, the secondary resonant device includes a first group of secondary resonant devices 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 secondary half-bridge 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 secondary half-bridge 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 secondary half-bridge of the secondary three-phase bridge.

In a preferred embodiment of the present invention, the secondary three-phase bridge includes a seventh switching tube to a twelfth switching tube, a first secondary half-bridge is formed by connecting the seventh switching tube and the eighth switching tube in series, a second secondary half-bridge is formed by connecting the ninth switching tube and the tenth switching tube in series, a third secondary half-bridge is formed by connecting the eleventh switching tube and the twelfth switching tube 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 with a first end of the ninth switching tube, a first end of the eleventh switching tube and an anode of the secondary filter capacitor, a second end of the seventh switching tube is connected with a first end of the eighth switching tube and the secondary resonant device, a second end of the eighth switching tube is connected with 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 with a first end of the tenth switching tube and the secondary resonant device, and the second end of the eleventh switching tube is connected with the first end of the twelfth switching tube and the secondary side resonance device.

In a preferred embodiment of the present invention, the first to twelfth 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 respectively, the converter further includes a control unit, the control unit is connected to each primary side control end and is configured to control the on and off of the first to sixth switching tubes, the seventh to twelfth switching tubes further include a secondary side control end respectively, and the control unit is connected to each secondary side control end and is configured to control the on and off of the seventh to twelfth switching tubes.

In the preferred embodiment of the invention, when the required energy is transferred from the primary side to the secondary side, the primary side three-phase bridge is used as the active control, and the secondary side three-phase bridge is used as the rectification control, so that the forward power conversion from the primary side to the secondary side is realized; when the required 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 is realized.

In the preferred embodiment of the present invention, when the converter is a double-phase interleaved C LL C circuit, energy is transferred from the primary side to the secondary side, the switching period of each half-bridge is the same, and the switching timing between the half-bridges is staggered by 120 °.

The embodiment of the invention also provides a low-gain control method of the C LL C bidirectional DC-DC converter, which comprises the steps of obtaining input voltage and input current of a three-phase interleaved C LL C circuit, obtaining output voltage and output current of the three-phase interleaved C LL C circuit, determining DC gain of the three-phase interleaved C LL C circuit according to the input voltage, the input current, the output voltage and the output current, and switching the converter from the three-phase interleaved C LL C circuit to a double-phase interleaved C LL C circuit if the DC gain is in a DC gain interval with low preset gain of the three-phase interleaved C LL C circuit.

In the preferred embodiment of the invention, if the output voltage is less than a first preset voltage and the output current is less than a first preset current, the three-phase interleaved C LL C circuit is switched to a double-phase interleaved C LL C circuit by controlling the working state of each switch tube of the three-phase interleaved C LL C circuit.

In a preferred embodiment of the present invention, the method further includes switching the converter from the bi-phase interleaved C LL C circuit to a three-phase interleaved C LL C circuit if the output current is greater than the first preset current and less than the second preset current at the sampling time, and switching the converter from the bi-phase interleaved C LL C circuit to a three-phase interleaved C LL C circuit if the output current is greater than the second preset current at the sampling time.

In a preferred embodiment of the present invention, the method further includes obtaining the input voltage and the input current of the three-phase interleaved C LL C circuit, obtaining the output voltage and the output current of the three-phase interleaved C LL C circuit, obtaining operating frequencies of the switching tubes corresponding to the output voltage and the output current, and if the operating frequencies of the switching tubes are greater than a preset frequency, switching the three-phase interleaved C LL C circuit to the two-phase interleaved C LL C circuit by controlling operating states of the switching tubes of the three-phase interleaved C LL C circuit.

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

the C LL C bidirectional DC-DC converter and the low gain control method can judge the DC gain of the circuit, and if the DC gain is in the DC gain interval with the preset gain of the three-phase interleaved C LL C circuit being low, the converter can be switched from the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit, the control logic is simple, the energy output is continuous, the output ripple of the circuit is small, and the user experience is improved.

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 a first embodiment of the present invention;

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

fig. 3 is a waveform diagram of driving waveforms of the switching tube when the C LL C bidirectional dc-dc converter is a two-phase interleaved C LL C circuit according to the first embodiment of the present invention.

FIG. 4a is a current-holding loop diagram of the C LL C bidirectional DC-DC converter in a first operating mode;

FIG. 4b is a current-storing loop diagram of the bidirectional DC-DC converter C LL C in the second operation mode;

FIG. 4C is a current-holding loop diagram of the C LL C bi-directional DC-DC converter in mode three;

FIG. 4d is a current-storing loop diagram of the C LL C bi-directional DC-DC converter in the fourth operating mode;

FIG. 5 is a flowchart illustrating the steps of a method for controlling the low gain of the C LL C bidirectional DC-DC converter according to the second embodiment of the present invention;

FIG. 6 is a flow chart of the steps of a low gain control method for a C LL C bi-directional DC-DC converter according to a first embodiment of the present invention;

fig. 7 is a flowchart illustrating the steps of a low gain control method for the C LL C bi-directional dc-dc converter according to the second embodiment of the present invention.

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 and the low gain control method 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.

First embodiment

Fig. 1 is a block diagram of a C LL C bidirectional dc-dc converter according to a first 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 this embodiment includes a primary side filter capacitor C1, a primary side three-phase bridge 10, a primary side resonant device 11, a voltage transformation device 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.

When the dc gain of the circuit of the C LL C bidirectional dc-dc converter of this embodiment is not in the dc gain section where the preset gain is low, the converter is a three-phase interleaved C LL C circuit, and when the dc gain of the circuit of the converter is in the dc gain section where the preset gain is low, the converter is a two-phase interleaved C LL C circuit.

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, a gate G), and the C LL C bidirectional dc-dc converter further includes a control unit (not shown in the figure), which is connected to each primary side control terminal, for controlling the first to sixth switching tubes S1-S6 to turn on and off.

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 resonant device 13 includes three sets of secondary resonant devices C5, C6, and C7, each set of secondary resonant devices includes a resonant capacitor, one end of each resonant capacitor is connected to a secondary terminal of a transformer, and the other end of each resonant capacitor is connected to a secondary half bridge of a secondary three-phase bridge. Specifically, the first group of secondary resonant devices comprises a first resonant capacitor C5, the second group of secondary resonant devices comprises a second resonant capacitor C6, the third group of secondary resonant devices comprises a third resonant capacitor C7, one end of the first resonant capacitor C5 is connected with the first transformer, the other end of the resonant capacitor C5 is connected with one secondary half-bridge in the secondary three-phase bridge, one end of the second resonant capacitor C6 is connected with the second transformer, the other end of the second resonant capacitor C6 is connected with one secondary half-bridge in the secondary three-phase bridge, one end of the third resonant capacitor C7 is connected with the third transformer, and the other end of the third resonant capacitor C7 is connected with one secondary half-bridge in the secondary three-phase bridge.

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 the control unit is connected to each of the secondary control terminals for controlling the seventh to twelfth switching tubes S7-S12 to be turned on and off.

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. In one embodiment, when the primary three-phase resonant tank is actively controlled, the switching period of each primary half-bridge of the primary three-phase bridge is the same, but the switching timing phases of each primary half-bridge are sequentially staggered by 120 °, that is, the switching timing phases of the first switching tube S1, the third switching tube S3 and the fifth switching tube S5 are sequentially staggered by 120 °, so that three-phase staggered resonance of the primary three-phase resonant tank is realized.

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. In one embodiment, when the secondary three-phase resonant circuit is used for rectification control, the semiconductor switch tube of each half bridge of the primary three-phase bridge can be kept closed, so that the anti-parallel diode of the semiconductor switch tube can perform 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 one embodiment, when the star-connected secondary three-phase resonant tank is used as an active control, the switching period of each half-bridge of the secondary three-phase bridge is the same, but the switching timing phases of each secondary half-bridge are sequentially staggered by 120 degrees, so that three-phase staggered resonance of the secondary three-phase resonant tank 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.

Preferably, when the required 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 the forward power conversion from the primary side to the secondary side is realized; when the required 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 is realized.

Preferably, when the converter is a double-phase interleaved C LL C circuit, energy can be transferred from the primary side to the secondary side, the switching period of each half-bridge is the same, the switching timing between the half-bridges is staggered by 120 °, and the driving waveforms of the switching tubes of the converter in the double-phase interleaved C LL C circuit are as shown in fig. 3.

The C LL C bidirectional dc-dc converter of this embodiment can have four operation modes when it is a two-phase interleaved C LL C circuit, wherein the operation mode one is that the switching tube states of the primary three-phase bridge are S1 closed, S2 open, S3 open, S4 closed, S5 open, and S6 closed, respectively, and the switching tube states of the secondary three-phase bridge are S11 closed, S12 open, S9 open, S10 closed, S7 open, and S8 open, respectively, and the energy flow loop is shown in fig. 4 a.

In the second operation mode, the switching tube states of the primary three-phase bridge are respectively S1 closed, S2 open, S3 closed, S4 open, S5 open and S6 closed, the switching tube states of the secondary three-phase bridge are respectively S11 closed, S12 open, S9 closed, S10 open, S7 open and S8 closed, and the energy flow loop is shown in fig. 4 b.

In the third operating mode, the switching tube states of the primary three-phase bridge are respectively S1 open, S2 closed, S3 closed, S4 open, S5 open and S6 closed, the switching tube states of the secondary three-phase bridge are respectively S11 open, S12 closed, S9 closed, S10 open, S7 open and S8 open, and the energy flow loop is shown in fig. 4 c.

In the fourth operation mode, the switching tube states of the primary three-phase bridge are respectively S1 open, S2 closed, S3 open, S4 closed, S5 open and S6 closed, the switching tube states of the secondary three-phase bridge are respectively S11 open, S12 closed, S9 open, S10 closed, S7 closed and S8 open, and the energy flow loop is shown in fig. 4 d.

The C LL C bidirectional DC-DC converter can realize high-voltage high-power bidirectional soft switching DC-DC power conversion, and because a three-phase bridge is in three-phase interleaved control, high-frequency current ripples of filter capacitors on a primary side and a secondary side can be reduced, namely, the capacity of the filter capacitors on the primary side and the secondary side can be reduced, so that the volume and the cost of the bidirectional DC-DC converter are reduced.

The following are embodiments of the method of the present invention, details of which are not described in detail in the method embodiments, and reference may be made to the corresponding apparatus embodiments described above.

Second embodiment

However, when the battery voltage is lower than the output range of the DC-DC converter, the C LL C bidirectional DC-DC converter enters an intermittent working mode to reduce power output, so that energy output is discontinuous.

In order to solve the above problems, the present invention provides a low gain control method for a C LL C bidirectional dc-dc converter, and fig. 5 is a flowchart of a low gain control method for a C LL C bidirectional dc-dc converter according to a second embodiment of the present invention, the control method for a C LL C bidirectional dc-dc converter according to the present embodiment may include the following steps:

in step S1, an input voltage and an input current of the three-phase interleaved C LL C circuit are obtained, and an output voltage and an output current of the three-phase interleaved C LL C circuit are obtained.

Step S2, determining the DC gain of the three-phase interleaved C LL C circuit according to the input voltage, the input current, the output voltage and the output current.

In step S3, if the dc gain is in the dc gain section where the preset gain of the three-phase interleaved C LL C circuit is low, the converter is switched from the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit.

When the converter is in a low gain state, the converter is switched from the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit, so that when the converter outputs low power, the output is not output in an intermittent working mode, the discontinuity of energy output is avoided, the voltage ripple is small, and the user experience is improved.

Preferably, as shown in fig. 6, step S2 may further include:

in step S21, if the output voltage is less than the first predetermined voltage and the output current is less than the first predetermined current, the three-phase interleaved C LL C circuit is switched to the double-phase interleaved C LL C circuit by controlling the operating states of the respective switching tubes of the three-phase interleaved C LL C circuit.

Preferably, as shown in fig. 6, step S2 may further include:

in step S22, the sampling time is any time after the three-phase interleaved C LL C circuit is switched to the double-interleaved C LL C circuit, the second preset current is greater than the first preset current, if the output current is greater than the first preset current and less than the second preset current at the sampling time, the converter is a double-phase interleaved C LL C circuit, and if the output current is greater than the second preset current at the sampling time, the converter is switched from the double-phase interleaved C LL C circuit to the three-phase interleaved C LL C circuit.

For example, the first predetermined voltage is 200V, the first predetermined current is 16A, and the second predetermined current is 20A. if the output voltage 190V is less than the first predetermined voltage 200V, the output current 15A is less than the first predetermined current 16A, and therefore, it is determined that the dc gain of the circuit is low according to step S21, the converter is switched from the three-phase interleaved C LL C circuit to the double-interleaved C LL C circuit, if the output current rises from 15A to 17A, the output current 17A is greater than the first predetermined current 16A but less than the second predetermined current 20A according to step S22, it is determined that the dc gain of the circuit is low, the two-phase interleaved C LL C circuit is maintained, and if the output current rises to 21A, the output current is greater than the second predetermined current, it is determined that the dc gain is high, and the converter is switched from the two-phase interleaved C LL C circuit to the three-phase interleaved C LL C circuit.

Step S22 may be performed after step S21, that is, if step S21 switches the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit, step S22 satisfies the condition of the sampling timing of the two-phase interleaved C LL C circuit, and step S22 may be performed.

Preferably, as shown in fig. 7, step S2 may include:

step S23, acquiring input voltage and input current of the three-phase interleaved C LL C circuit, acquiring output voltage and output current of the three-phase interleaved C LL C circuit, acquiring working frequency of a switching tube corresponding to the output voltage and the output current, and switching the three-phase interleaved C LL C circuit into a double-phase interleaved C LL C circuit by controlling working states of all switching tubes of the three-phase interleaved C LL C circuit if the working frequency of the switching tube is greater than preset frequency.

For example, when the output voltage is 200V and the output current is 16A, the corresponding switching frequency is 300KHZ, and if the operating frequency of the switching tube is 400KHZ at this time, it may be determined that the dc gain of the circuit of the C LL C bidirectional dc-dc converter is low, and the converter needs to be switched from the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit, so as to ensure continuous energy output, and reduce the output ripple of the circuit, thereby improving the user experience.

In summary, the low gain control method of the C LL C bidirectional dc-dc converter of the present invention can determine the dc gain of the circuit, and if the dc gain is in the dc gain range where the preset gain of the three-phase interleaved C LL C circuit is low, the converter is switched from the three-phase interleaved C LL C circuit to the double-phase interleaved C LL C circuit, which has simple control logic, continuous energy output, and small output ripple of the circuit, thereby improving user experience.

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.