阅读说明：本技术 直流/直流变换器及其控制方法 (DC/DC converter and control method thereof ) 是由 胡文斐 陆城 于 2019-01-16 设计创作，主要内容包括：本公开提供一种直流/直流变换器的控制方法与直流/直流变换器。直流/直流变换器包括耦接于第一节点的第一电容和第二电容；耦接在第一节点和第二节点之间的第一开关元件和第二开关元件、耦接在第一节点和第三节点之间的第三开关元件和第四开关元件；耦接在第四节点和第五节点之间的第一无源网络,第一无源网络将第四节点和第五节点串联连接至变压器的原边绕组和耦接于变压器的副边绕组的二次侧电路；控制方法包括：控制第一开关元件、第二开关元件互补导通、第三开关元件、第四开关元件互补导通,其中第一开关元件和第四开关元件的控制信号具有第一移相角,调整该第一移相角使第一电容和第二电容的电压差减小。本公开提供的直流/直流变换器的控制方法可以更好地调节直流/直流变换器的中点平衡。(The disclosure provides a control method of a direct current/direct current converter and the direct current/direct current converter. The DC/DC converter comprises a first capacitor and a second capacitor coupled to a first node; a first switching element and a second switching element coupled between a first node and a second node, a third switching element and a fourth switching element coupled between the first node and a third node; a first passive network coupled between a fourth node and a fifth node, the first passive network connecting the fourth node and the fifth node in series to the primary winding of the transformer and a secondary side circuit coupled to the secondary winding of the transformer; the control method comprises the following steps: and controlling the first switching element, the second switching element and the third switching element to be complementarily conducted, and controlling the third switching element and the fourth switching element to be complementarily conducted, wherein control signals of the first switching element and the fourth switching element have a first phase shift angle, and the first phase shift angle is adjusted to reduce the voltage difference between the first capacitor and the second capacitor. The control method of the DC/DC converter can better adjust the midpoint balance of the DC/DC converter.)

1. A control method of a DC/DC converter is applied to the DC/DC converter, the DC/DC converter comprises a first capacitor and a second capacitor which are coupled to a first node, the second end of the first capacitor is coupled to a second node, and the second end of the second capacitor is coupled to a third node; a first leg coupled between the first node and the second node, the first leg including first and second switching elements coupled to a fourth node, a second leg coupled between the first and third nodes, the second leg including third and fourth switching elements coupled to a fifth node; a transformer with a primary winding electrically connected to the fourth node and the fifth node and a secondary side circuit electrically connected to a secondary winding of the transformer; it is characterized by comprising:

outputting a first control signal, a second control signal, a third control signal and a fourth control signal to control terminals of the first switching element, the second switching element, the third switching element and the fourth switching element, wherein the first control signal, the second control signal, the third control signal and the fourth control signal are square wave signals with a preset period, the first control signal is complementary to the second control signal, the third control signal is complementary to the fourth control signal, a first phase shift angle is formed between the first control signal and the fourth control signal, and the first phase shift angle is formed between the second control signal and the third control signal;

and controlling the first phase shifting angle to reduce the voltage difference between the first capacitor and the second capacitor.

2. The control method of claim 1, wherein said controlling the first phase shift angle to reduce the voltage difference between the first capacitance and the second capacitance comprises:

detecting a first voltage across the first capacitor and a second voltage across the second capacitor;

and determining the first phase shifting angle according to the difference value of the first voltage and the second voltage, reducing the first phase shifting angle when the difference value is a positive value, and increasing the first phase shifting angle when the difference value is a negative value.

3. The control method of claim 1, wherein the dc/dc converter further comprises a first passive network and/or a second passive network, the first passive network being coupled between the fourth node, the fifth node, and the primary winding of the transformer, and the second passive network being coupled between the secondary winding of the transformer and the secondary circuit.

4. The control method of claim 3, wherein the first passive network and/or the second passive network comprise only capacitors.

5. The control method of claim 3, wherein the first passive network and/or the second passive network comprises a capacitor and inductor series, parallel, or series-parallel network.

6. The control method of claim 1, wherein the dc/dc converter further comprises:

an input source coupled with the second node and the third node.

7. The control method of claim 1, wherein the dc/dc converter further comprises:

and the input source is coupled with the secondary side circuit.

8. The control method according to any one of claims 1 to 7, wherein the secondary side circuit is a full-bridge rectifier circuit or a full-wave rectifier circuit.

9. The control method according to any one of claims 1 to 7, wherein the secondary side circuit comprises a third capacitor and a fourth capacitor coupled to a tenth node, a second terminal of the third capacitor is coupled to an eleventh node, and a second terminal of the fourth capacitor is coupled to a twelfth node; a third leg coupled between the eleventh node and the tenth node, a fourth leg coupled between the twelfth node and the tenth node, the third leg including a fifth switching element and a sixth switching element coupled to a thirteenth node, the fourth leg including a seventh switching element and an eighth switching element coupled to a fourteenth node, the secondary winding being electrically connected to the thirteenth node and the fourteenth node.

10. The control method according to claim 9, wherein a fifth control signal, a sixth control signal, a seventh control signal, and an eighth control signal are output to control terminals of the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, wherein the fifth control signal, the sixth control signal, the seventh control signal, and the eighth control signal are square wave signals having a preset period, the fifth control signal is complementary to the sixth control signal, the seventh control signal is complementary to the eighth control signal, the fifth control signal and the eighth control signal have a second phase shift angle therebetween, and the sixth control signal and the seventh control signal have the second phase shift angle therebetween;

and controlling the second phase shifting angle to reduce the voltage difference between the third capacitor and the fourth capacitor.

11. The control method of claim 10, wherein said controlling the second phase shift angle to reduce the voltage difference between the third capacitance and the fourth capacitance comprises:

detecting a third voltage across the third capacitor and a fourth voltage across the fourth capacitor;

and determining the second phase shifting angle according to the difference value of the third voltage and the fourth voltage, reducing the second phase shifting angle when the difference value is a positive value, and increasing the second phase shifting angle when the difference value is a negative value.

12. A dc/dc converter, comprising:

a first capacitor, a first end coupled to the first node, and a second end coupled to the second node;

a second capacitor, wherein a first end is coupled to the first node, and a second end is coupled to a third node;

a first leg coupled between the first node and the second node, including a first switching element and a second switching element coupled to a fourth node;

a second leg coupled between the first node and the third node, including a third switching element and a fourth switching element coupled to a fifth node;

a primary winding of the transformer is electrically connected to the fourth node and the fifth node;

a secondary side circuit electrically connected to the secondary winding of the transformer;

a control module, coupled to the first capacitor, the second capacitor, the first leg, the second leg, and the secondary side circuit, configured to:

outputting a first control signal, a second control signal, a third control signal and a fourth control signal to control terminals of the first switching element, the second switching element, the third switching element and the fourth switching element, wherein the first control signal, the second control signal, the third control signal and the fourth control signal are square wave signals with a preset period, the first control signal is complementary to the second control signal, the third control signal is complementary to the fourth control signal, a first phase shift angle is formed between the first control signal and the fourth control signal, and the first phase shift angle is formed between the second control signal and the third control signal;

and controlling the first phase shifting angle to reduce the voltage difference between the first capacitor and the second capacitor.

13. The dc/dc converter of claim 12, wherein the control module comprises:

the voltage detection unit is used for detecting a first voltage at two ends of the first capacitor and a second voltage at two ends of the second capacitor;

a phase difference determining unit, configured to determine the first phase shift angle according to a difference value between the first voltage and the second voltage, decrease the first phase shift angle when the difference value is a positive value, and increase the first phase shift angle when the difference value is a negative value;

and the control signal output unit is used for outputting the first control signal, the second control signal, the third control signal and the fourth control signal according to the first phase shifting angle.

14. The dc/dc converter of claim 12, further comprising:

a first passive network coupled between the fourth node, the fifth node, and the primary winding of the transformer, and/or a second passive network coupled between the secondary winding of the transformer and the secondary side circuit.

15. The dc/dc converter of claim 14, wherein the first passive network and/or the second passive network comprise only capacitors.

16. The dc/dc converter of claim 14, wherein the first passive network and/or the second passive network comprises a capacitor and an inductor in series, parallel, or both.

17. The dc/dc converter of claim 12, further comprising:

an input source coupled with the second node and the third node.

18. The dc/dc converter of claim 12, further comprising:

and the input source is coupled with the secondary side circuit.

19. The dc/dc converter according to any one of claims 12 to 18, wherein the secondary side circuit is a full-bridge rectifier circuit or a full-wave rectifier circuit.

20. The dc/dc converter according to any of claims 12-18, wherein the secondary side circuit comprises a third capacitor and a fourth capacitor coupled to a tenth node, a second terminal of the third capacitor is coupled to an eleventh node, and a second terminal of the fourth capacitor is coupled to a twelfth node; a third leg coupled between the eleventh node and the tenth node, a fourth leg coupled between the twelfth node and the tenth node, the third leg including a fifth switching element and a sixth switching element coupled to a thirteenth node, the fourth leg including a seventh switching element and an eighth switching element coupled to a fourteenth node, the secondary winding being electrically connected to the thirteenth node and the fourteenth node.

21. The dc/dc converter according to claim 20, wherein a fifth control signal, a sixth control signal, a seventh control signal, and an eighth control signal are outputted to control terminals of the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, wherein the fifth control signal, the sixth control signal, the seventh control signal, and the eighth control signal are square wave signals having a predetermined period, the fifth control signal is complementary to the sixth control signal, the seventh control signal is complementary to the eighth control signal, the fifth control signal and the eighth control signal have a second phase shift angle therebetween, and the sixth control signal and the seventh control signal have the second phase shift angle therebetween;

and controlling the second phase shifting angle to reduce the voltage difference between the third capacitor and the fourth capacitor.

22. The dc/dc converter of claim 21, wherein said controlling said second phase shift angle to reduce a voltage difference between said third capacitance and said fourth capacitance comprises:

detecting a third voltage across the third capacitor and a fourth voltage across the fourth capacitor;

and determining the second phase shifting angle according to the difference value of the third voltage and the fourth voltage, reducing the second phase shifting angle when the difference value is a positive value, and increasing the second phase shifting angle when the difference value is a negative value.

Technical Field

The present disclosure relates to the field of power supply technologies, and in particular, to a method for controlling a dc/dc converter and a related dc/dc converter.

Background

The high-voltage direct current/direct current converter is widely applied to a high-power direct current conversion system, a new energy storage system, an electric vehicle charging device and a rail transit power distribution system, and in order to reduce the loss and cost of a conducting wire, improve the voltage grade and reduce the number of cascade units, the high-voltage direct current/direct current converter usually realizes high-voltage input by means of a three-level circuit. Under the influence of factors such as hardware parameter inconsistency, the neutral point potential of the three-level circuit can generate an unbalanced phenomenon, the safety of devices and the normal operation of a converter are influenced, and the neutral point potential needs to be balanced and controlled.

Therefore, a dc/dc converter control method capable of performing neutral point potential adjustment (neutral point balancing) on a dc/dc converter is required.

It is to be noted that the information disclosed in the above background section is only for enhancement of understanding of the background of the present disclosure, and thus may include information that does not constitute prior art known to those of ordinary skill in the art.

Disclosure of Invention

The present disclosure is directed to a method for controlling a dc/dc converter and a control apparatus for a dc/dc converter, which are used to adjust a midpoint potential balance of the dc/dc converter.

According to a first aspect of the embodiments of the present disclosure, a method for controlling a dc/dc converter is provided, which is applied to a dc/dc converter, the dc/dc converter including a first capacitor and a second capacitor coupled to a first node, a second end of the first capacitor being coupled to a second node, and a second end of the second capacitor being coupled to a third node; a first leg coupled between the first node and the second node, the first leg including first and second switching elements coupled to a fourth node, a second leg coupled between the first and third nodes, the second leg including third and fourth switching elements coupled to a fifth node; a transformer with a primary winding electrically connected to the fourth node and the fifth node and a secondary side circuit electrically connected to a secondary winding of the transformer; the method comprises the following steps:

outputting a first control signal, a second control signal, a third control signal and a fourth control signal to control terminals of the first switching element, the second switching element, the third switching element and the fourth switching element, wherein the first control signal, the second control signal, the third control signal and the fourth control signal are square wave signals with a preset period, the first control signal is complementary to the second control signal, the third control signal is complementary to the fourth control signal, a first phase shift angle is formed between the first control signal and the fourth control signal, and the first phase shift angle is formed between the second control signal and the third control signal;

and controlling the first phase shifting angle to reduce the voltage difference between the first capacitor and the second capacitor.

In an exemplary embodiment of the present disclosure, the controlling the first phase shift angle to reduce the voltage difference of the first capacitance and the second capacitance comprises:

detecting a first voltage across the first capacitor and a second voltage across the second capacitor;

and determining the first phase shifting angle according to the difference value of the first voltage and the second voltage, reducing the first phase shifting angle when the difference value is a positive value, and increasing the first phase shifting angle when the difference value is a negative value.

In an exemplary embodiment of the disclosure, the dc/dc converter further includes a first passive network and/or a second passive network, the first passive network is coupled between the fourth node, the fifth node, and the primary winding of the transformer, and the second passive network is coupled between the secondary winding of the transformer and the secondary side circuit.

In an exemplary embodiment of the present disclosure, the first passive network and/or the second passive network include only a capacitance.

In an exemplary embodiment of the disclosure, the first passive network and/or the second passive network comprises a network of capacitors and inductors in series, in parallel, or in series-parallel.

In an exemplary embodiment of the present disclosure, the dc/dc converter further includes:

an input source coupled with the second node and the third node.

In an exemplary embodiment of the present disclosure, the dc/dc converter further includes:

and the input source is coupled with the secondary side circuit.

In an exemplary embodiment of the present disclosure, the secondary-side circuit is a full-bridge rectifier circuit or a full-wave rectifier circuit.

In an exemplary embodiment of the present disclosure, the secondary side circuit includes a third capacitor and a fourth capacitor coupled to a tenth node, a second end of the third capacitor is coupled to an eleventh node, and a second end of the fourth capacitor is coupled to a twelfth node; a third leg coupled between the eleventh node and the tenth node, a fourth leg coupled between the twelfth node and the tenth node, the third leg including a fifth switching element and a sixth switching element coupled to a thirteenth node, the fourth leg including a seventh switching element and an eighth switching element coupled to a fourteenth node, the secondary winding being electrically connected to the thirteenth node and the fourteenth node.

In an exemplary embodiment of the present disclosure, a fifth control signal, a sixth control signal, a seventh control signal, and an eighth control signal are output to control terminals of the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, wherein the fifth control signal, the sixth control signal, the seventh control signal, and the eighth control signal are all square wave signals having a preset period, the fifth control signal is complementary to the sixth control signal, the seventh control signal is complementary to the eighth control signal, a second phase shift angle is provided between the fifth control signal and the eighth control signal, and the second phase shift angle is provided between the sixth control signal and the seventh control signal;

and controlling the second phase shifting angle to reduce the voltage difference between the third capacitor and the fourth capacitor.

In an exemplary embodiment of the present disclosure, the controlling the second phase shift angle to reduce the voltage difference of the third capacitance and the fourth capacitance comprises:

detecting a third voltage across the third capacitor and a fourth voltage across the fourth capacitor;

and determining the second phase shifting angle according to the difference value of the third voltage and the fourth voltage, reducing the second phase shifting angle when the difference value is a positive value, and increasing the second phase shifting angle when the difference value is a negative value.

According to a second aspect of the present disclosure, there is provided a dc/dc converter comprising:

a first capacitor, a first end coupled to the first node, and a second end coupled to the second node;

a second capacitor, wherein a first end is coupled to the first node, and a second end is coupled to a third node;

a first leg coupled between the first node and the second node, including a first switching element and a second switching element coupled to a fourth node;

a second leg coupled between the first node and the third node, including a third switching element and a fourth switching element coupled to a fifth node;

a primary winding of the transformer is electrically connected to the fourth node and the fifth node;

a secondary side circuit electrically connected to the secondary winding of the transformer;

a control module, coupled to the first capacitor, the second capacitor, the first leg, the second leg, and the secondary side circuit, configured to:

outputting a first control signal, a second control signal, a third control signal and a fourth control signal to control terminals of the first switching element, the second switching element, the third switching element and the fourth switching element, wherein the first control signal, the second control signal, the third control signal and the fourth control signal are square wave signals with a preset period, the first control signal is complementary to the second control signal, the third control signal is complementary to the fourth control signal, a first phase shift angle is formed between the first control signal and the fourth control signal, and the first phase shift angle is formed between the second control signal and the third control signal;

and controlling the first phase shifting angle to reduce the voltage difference between the first capacitor and the second capacitor.

In an exemplary embodiment of the present disclosure, the control module includes:

the voltage detection unit is used for detecting a first voltage at two ends of the first capacitor and a second voltage at two ends of the second capacitor;

a phase difference determining unit, configured to determine the first phase shift angle according to a difference value between the first voltage and the second voltage, decrease the first phase shift angle when the difference value is a positive value, and increase the first phase shift angle when the difference value is a negative value;

and the control signal output unit is used for outputting the first control signal, the second control signal, the third control signal and the fourth control signal according to the first phase shifting angle.

In an exemplary embodiment of the present disclosure, further comprising:

a first passive network coupled between the fourth node, the fifth node, and the primary winding of the transformer, and/or a second passive network coupled between the secondary winding of the transformer and the secondary side circuit.

In an exemplary embodiment of the present disclosure, the first passive network and/or the second passive network include only a capacitance.

In an exemplary embodiment of the disclosure, the first passive network and/or the second passive network comprises a network of capacitors and inductors in series, in parallel, or in series-parallel.

In an exemplary embodiment of the present disclosure, the dc/dc converter further includes:

an input source coupled with the second node and the third node.

In an exemplary embodiment of the present disclosure, the dc/dc converter further includes:

and the input source is coupled with the secondary side circuit.

In an exemplary embodiment of the present disclosure, the secondary-side circuit is a full-bridge rectifier circuit or a full-wave rectifier circuit.

In an exemplary embodiment of the present disclosure, the secondary side circuit includes a third capacitor and a fourth capacitor coupled to a tenth node, a second end of the third capacitor is coupled to an eleventh node, and a second end of the fourth capacitor is coupled to a twelfth node; a third leg coupled between the eleventh node and the tenth node, a fourth leg coupled between the twelfth node and the tenth node, the third leg including a fifth switching element and a sixth switching element coupled to a thirteenth node, the fourth leg including a seventh switching element and an eighth switching element coupled to a fourteenth node, the secondary winding being electrically connected to the thirteenth node and the fourteenth node.

In an exemplary embodiment of the present disclosure, a fifth control signal, a sixth control signal, a seventh control signal, and an eighth control signal are output to control terminals of the fifth switching element, the sixth switching element, the seventh switching element, and the eighth switching element, wherein the fifth control signal, the sixth control signal, the seventh control signal, and the eighth control signal are all square wave signals having a preset period, the fifth control signal is complementary to the sixth control signal, the seventh control signal is complementary to the eighth control signal, a second phase shift angle is provided between the fifth control signal and the eighth control signal, and the second phase shift angle is provided between the sixth control signal and the seventh control signal;

and controlling the second phase shifting angle to reduce the voltage difference between the third capacitor and the fourth capacitor.

In an exemplary embodiment of the present disclosure, the controlling the second phase shift angle to reduce the voltage difference of the third capacitance and the fourth capacitance comprises:

detecting a third voltage across the third capacitor and a fourth voltage across the fourth capacitor;

and determining the second phase shifting angle according to the difference value of the third voltage and the fourth voltage, reducing the second phase shifting angle when the difference value is a positive value, and increasing the second phase shifting angle when the difference value is a negative value.

According to the control method of the dc/dc converter provided by the embodiment of the disclosure, the first switching element, the second switching element, the third switching element and the fourth switching element on the two bridge arms of the SHB structure dc/dc converter are controlled to be in complementary conduction, so that the control signals of the first switching element and the fourth switching element have a phase shift angle, and the phase shift angle is adjusted to reduce the voltage difference between the first capacitor and the second capacitor, so that the midpoint potential balance of the dc/dc converter can be effectively adjusted.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure. It is to be understood that the drawings in the following description are merely exemplary of the disclosure, and that other drawings may be derived from those drawings by one of ordinary skill in the art without the exercise of inventive faculty.

Fig. 1 is a schematic diagram of a dc/dc converter employing a three-level circuit.

Fig. 2 is a schematic diagram of still another configuration of the dc/dc converter of the three-level circuit shown in fig. 1.

Fig. 3 is a schematic diagram of a midpoint balancing method in the related art.

Fig. 4 is a schematic diagram of a control method provided by the present disclosure.

Fig. 5A to 5D are schematic diagrams of four switching modes of a series double half-bridge three-level circuit.

Fig. 6 is a block diagram of a control module of the dc/dc converter provided by the present disclosure.

FIG. 7 is a signal relationship diagram of the control module of FIG. 6.

Fig. 8 is a schematic diagram of a passive network structure in an embodiment of the disclosure.

Fig. 9 is a simulation waveform of the control method applied to the circuit shown in fig. 8.

Fig. 10 is a schematic diagram of another passive network structure in an embodiment of the disclosure.

FIG. 11 is a simulated waveform of the control method applied to the circuit of FIG. 10 when power is flowing in the forward direction.

FIG. 12 is a simulated waveform of the control method applied to the circuit of FIG. 10 when power flows in the reverse direction.

Fig. 13 is a schematic diagram of a secondary-side circuit in a full-bridge configuration.

Fig. 14 is a schematic diagram of a secondary-side circuit in a full-wave rectification structure.

Fig. 15 is a schematic diagram of a secondary side circuit in a series double half-bridge configuration.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the subject matter of the present disclosure can be practiced without one or more of the specific details, or with other methods, components, devices, steps, and the like. In other instances, well-known technical solutions have not been shown or described in detail to avoid obscuring aspects of the present disclosure.

Further, the drawings are merely schematic illustrations of the present disclosure, in which the same reference numerals denote the same or similar parts, and thus, a repetitive description thereof will be omitted. Some of the block diagrams shown in the figures are functional entities and do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different networks and/or processor devices and/or microcontroller devices.

The following detailed description of exemplary embodiments of the disclosure refers to the accompanying drawings.

Fig. 1 is a schematic diagram of a dc/dc converter employing a three-level circuit.

Referring to fig. 1, the dc/dc converter 100 may include:

a first capacitor C₁A first terminal coupled to a first node N1, and a second terminal coupled to a second node N2;

second capacitor C₂A first terminal coupled to the first node N1, and a second terminal coupled to the third node N3;

a first leg 1A coupled between a first node N1 and a second node N2, and including a first switching element S1 and a second switching element S2 connected in series, the first switching element S1 and the second switching element S2 being coupled to a fourth node a;

a second leg 1B coupled between the first node N1 and a third node N3, and including a third switching element S3 and a fourth switching element S4 connected in series, the third switching element S3 and the fourth switching element S4 being coupled to a fifth node B;

a primary winding of the transformer 1 is electrically connected to a fourth node A and a fifth node B through a sixth node C and a seventh node D respectively;

a secondary side circuit 2 electrically connected to the secondary winding of the transformer 1 through an eighth node N8 and a ninth node N9;

a control module 3 coupled to the first capacitor C₁A second capacitor C₂A first bridge arm 1A, a second bridge arm 1B and a secondary side circuit 2, which are used for outputting a first control signal, a second control signal, a third control signal and a fourth control signal to a first switch according to the voltage difference between a first capacitor and a second capacitorA control terminal of the switching element S1, the second switching element S2, the third switching element S3, and the fourth switching element S4, wherein the first control signal, the second control signal, the third control signal, and the fourth control signal are square wave signals having a predetermined period, the first control signal is complementary to the second control signal, the third control signal is complementary to the fourth control signal, a first phase shift angle is provided between the first control signal and the fourth control signal, and the first phase shift angle is provided between the second control signal and the third control signal; the first phase shifting angle is controlled to reduce the voltage difference between the first capacitor and the second capacitor.

Fig. 2 is a schematic diagram of still another configuration of the dc/dc converter of the three-level circuit shown in fig. 1.

Referring to fig. 2, the dc/dc converter 100 may further include only the first passive network 4 or the second passive network 5, or may include both the first passive network 4 and the second passive network 5. The first passive network 4 is coupled between the fourth node a, the fifth node B and the primary winding of the transformer 1, and the second passive network 5 is coupled between the secondary winding of the transformer 1 and the secondary side circuit 2. The circuit structure of the first passive network and/or the second passive network may include only a capacitor, or may include a network formed by connecting a capacitor and an inductor in series, in parallel, or in series and parallel, and the disclosure is not limited thereto.

Common three-level circuits include diode midpoint clamped (DNPC) circuits and series double half-bridge (SHB) circuits. In fig. 1 and 2, the first and second legs are two half-bridges connected in series by four active devices connected in series, and this configuration is referred to as a series double half-bridge (SHB) configuration. The SHB structure is composed of 4 switching tubes, and can output three levels of +2, +1 and 0. For a direct current/direct current converter, the series double half-bridge structure is simple, and the system efficiency is higher.

In order to solve the problem of midpoint balance control of the three-level circuit, the related art proposes a midpoint control method based on duty cycle modulation, as shown in fig. 3, control signals of the first switching element S1 and the second switching element S2 are complementarily turned on, control signals of the third switching element S3 and the fourth switching element S4 are complementarily turned on, and duty cycles of the control signals of S1 and S3 are more than 50%And the duty ratio of the control signals of S2 and S4 is less than 50%. In the period from t1 to t2, the control signals of S1 and S3 are conducted to generate a level 1, the primary side current of the transformer is positive, and the current flows into a midpoint (a first node N1) through S1 and S3; during the period t6-t7, the control signals of S1 and S3 are turned on to generate 1 level, the primary side current of the transformer is negative, and the current flows out of the midpoint (the first node N1) through S1 and S3. In one switching period, the 1 level state is opposite to the midpoint in effect twice, so that the midpoint balance can be controlled by adjusting the effect time difference of the 1 level in the positive half cycle and the negative half cycle. When Tpf is reached<Tnf, the current flowing out of the midpoint is larger than that flowing into the midpoint in one switching period, so that the voltage U of the lower half capacitor_dc2Voltage U of falling, upper half capacitor_dc1And (4) rising to realize the adjustment of the midpoint potential.

In the control mode, because the action time of the positive half cycle 1 level and the negative half cycle 1 level are unequal, the working mode of the converter in one switching period is asymmetric, the turn-off current of each switching tube is different, and it is difficult to ensure that all the switching tubes realize Zero Voltage Switching (ZVS), the conduction loss and the switching loss are unequal, and the thermal design is influenced. Therefore, the adjustment performance is poor by controlling the midpoint balance by means of the action time difference of the 1 level.

Aiming at the problems in the related art, the control method provided by the disclosure has stronger neutral point balance adjustment capability, does not influence the realization of Zero Voltage Switching (ZVS) of the converter, can balance the switching loss and the conduction loss of a switching tube, and is suitable for various resonant or non-resonant, unidirectional or bidirectional direct current/direct current circuits with a primary side of a series double-half-bridge three-level structure.

Fig. 4 is a schematic diagram of a control method provided by the present disclosure. The control method shown in fig. 4 can be applied to the circuits shown in fig. 1 and 2.

In FIG. 4, Ugs is the control signal level of each switch tube, i_LrIs the current flowing through the secondary side, i_mIs the excitation current, i, of the transformer 1_NIs the current at the first node, i.e., the midpoint current. The grey part of the figure is the first phase shift angle.

Referring to fig. 4, in the embodiment of the present disclosure, control signals controlling the first switching element S1 and the second switching element S2 are complementarily turned on, and control signals of the third switching element S3 and the fourth switching element S4 are complementarily turned on. Neglecting the dead zone, ideally the duty cycles of all switching tube control signals are 50%, and there is a first phase shift angle Φ x between the control signals of switching elements S1, S2 of first leg 1A and the control signals of switching elements S3, S4 of second leg 1B. Defining the S4 firing phase angle to be positive after S1 and the S4 to be negative before the S1 firing phase angle. In the embodiments of the present disclosure, this method is referred to as a shift modulation method.

Without considering dead time, the series double-half-bridge three-level bridge arm can form 4 switching modes in one switching period, taking the first phase shift angle as a positive example, as shown in fig. 5A to 5D:

when S1 and S4 are turned on simultaneously in FIG. 5A, the two input capacitors C₁、C₂The converter is connected in series, and the total output voltage of the first bridge arm and the second bridge arm is (U)_dc1+U_dc2) The output level is 2, the midpoint (first node N1) is not connected to the circuit, and the mode has no influence on the midpoint potential.

In FIG. 5B, when S2 and S3 are turned on simultaneously, two input capacitors C₁、C₂The converter is not connected, the total output voltage of the first bridge arm 1A and the second bridge arm 1B is 0, the output level is 0, the midpoint (the first node N1) is not connected with the circuit, and the mode has no influence on the midpoint potential.

In fig. 5C, when S1 and S3 are turned on simultaneously, the total output voltage of first arm 1A and second arm 1B is U_dc1When the output level is 1, the midpoint (the first node N1) is connected to the circuit, and the converter primary current flows out of the midpoint through the two switching elements S1 and S3.

In fig. 5D, when S2 and S4 are simultaneously turned on, the total output voltage of the first arm 1A and the second arm 1B is U_dc2When the output level is 1, the midpoint (the first node N1) is connected to the circuit, and the converter primary current flows out of the midpoint through the two switching elements S2 and S4.

In the above four switching modes, the 0 level and the 2 level have no influence on the center potential, and when the primary side circuit operates in the 0/2 two-level modulation mode, the converter itself has no regulation capability on the center. Therefore, when the midpoint balance adjustment is required, the midpoint potential needs to be adjusted by reasonably utilizing the 1-level mode.

In the control method shown in fig. 4, the series double half-bridge three-level leg experiences two 1-level modes in one switching cycle: when the first phase shift angle is positive, the current is always in the direction of the outflow midpoint, and the upper half capacitor C₁Charging, lower half capacitance C₂Discharging to promote the drop of the midpoint potential and reduce the voltage difference between the two capacitors; when the phase shift angle is negative, the current always flows in the direction of the midpoint, and the lower half capacitor C₁Charging, upper half capacitor C₂Discharging to promote the rising of the midpoint potential and reduce the voltage difference between the two capacitors.

Therefore, the direction of the current flowing through the midpoint is determined by the control signal phase shift angles of the two bridge arms, the larger the phase shift angle is, the longer the 1-level action time is, the longer the current flows through the midpoint, the higher the midpoint current average value is, and the stronger the regulating capability is.

Referring to fig. 6, in one embodiment of the present disclosure, the controller 3 of the dc/dc converter may include:

a voltage detection unit 31 for detecting a first voltage across the first capacitor and a second voltage across the second capacitor;

a phase difference determining unit 32, configured to determine a first phase shift angle according to a difference between the first voltage and the second voltage, decrease the first phase shift angle when the difference is a positive value, and increase the first phase shift angle when the difference is a negative value;

the control signal output unit 33 is configured to output a first control signal, a second control signal, a third control signal, and a fourth control signal according to the first phase shift angle to control on/off of the first switching element S1 to the fourth switching element S4.

Referring to fig. 7, in the embodiment of the present disclosure, the phase difference determining unit 32 may be, for example, a regulator, and the control signal output unit 33 receives inputs of the first phase shift angle determined by the regulator and the switching frequency to generate and output the first to fourth control signals.

Compared with the related art, the phase shift modulation-based direct current/direct current converter control method provided by the disclosure has at least the following advantages:

1. the working modes of the positive and negative half control periods are completely symmetrical, the action effects of the positive and negative half control periods on the center are consistent, and stronger adjusting capability can be obtained after the positive and negative half control periods are superposed; 2. the current of the primary side circuit of the transformer is symmetrical, which is beneficial to realizing ZVS of a switching tube in the primary side circuit; 3. stress and loss of four switching tubes in the primary side circuit can be uniform, and energy efficiency is improved.

Fig. 8 is a schematic diagram of a first passive network structure in an embodiment of the disclosure.

Referring to fig. 8, in one embodiment, the first passive network 4 may include:

resonant capacitor C_LAnd the second node is coupled to the fourth node a and is connected in series with the primary winding of the transformer 1 through a sixth node C, or is coupled to the fifth node B and is connected in series with the primary winding of the transformer 1 through a seventh node D. Resonant capacitor C_LCan form a resonance circuit with the excitation inductance and the leakage inductance of the transformer 1.

In the embodiment shown in fig. 8, the primary winding of the transformer 1 is electrically connected to the series double half-bridge three-level circuit (comprising the first capacitor C) via the first passive network 4₁A second capacitor C₂First bridge arm 1A, second bridge arm 1B), first passive network 4 only includes resonant capacitor, forms resonant network with excitation inductance and the leakage inductance of transformer 1. At this time, the control method shown in fig. 4 can be applied to adjust the midpoint potential of the series double half-bridge three-level circuit regardless of the circuit form of the secondary side circuit 2.

Fig. 9 is a simulation waveform of the control method shown in fig. 4 applied to the circuit shown in fig. 8.

Referring to fig. 9, simulation conditions were to use frequency modulation control for the LL C voltage conversion circuit, set the output voltage Uo to a constant voltage, start simulating midpoint imbalance at 6ms, set the voltages of the two input capacitors to the first voltage U_dcPRising, second voltage U_dcNAnd (4) descending. Determining a first phase shift angle using a control method as shown in FIG. 4Positive and negative poles and amplitudeAnd adjusting the first phase shift angle according to the voltage difference of the two input capacitors. After a period of time, the first phase shift angle increasesLarge, 1-level mode with increased action time and midpoint current i_NThe voltage of the two input capacitors is balanced again when the voltage of the middle point is reduced and the action time of the 1 level mode is increased.

In other embodiments, the first passive network 4 may also be a series resonant network or a parallel resonant network, and may include an inductor and a capacitor.

Fig. 10 is a schematic diagram of another first passive network structure 4 in an embodiment of the disclosure.

Referring to fig. 10, in another embodiment, the first passive network 4 may include:

blocking capacitor C_BAnd the second node is coupled to the fourth node a and is connected in series with the primary winding of the transformer 1 through a sixth node C, or is coupled to the fifth node B and is connected in series with the primary winding of the transformer 1 through a seventh node D. Blocking capacitor C_BHas a large capacitance value and does not resonate with the excitation inductance and the leakage inductance of the transformer 1.

In the embodiment shown in fig. 10, the primary-side circuit of the transformer is a DAB circuit with a series double half-bridge circuit, and in this case, the control of the output power magnitude and direction can be realized by adjusting the phase shift angle between the primary-side switching signal and the secondary-side switching signal: when the secondary side circuit lags behind the primary side circuit modulation, power flows in the forward direction (from the left side of the transformer to the right side of the transformer); when the secondary side circuit is modulated before the primary side circuit, power flows in the reverse direction.

FIG. 11 is a simulated waveform of the control method shown in FIG. 4 when power flows in the forward direction in the circuit shown in FIG. 10.

Referring to FIG. 11, when u_CDLags behind u_ABWhen the DAB circuit is running in the forward direction. Simulating the neutral point imbalance at the moment of 6ms, and setting the voltages of the two input capacitors as a first voltage U_dcPRising, second voltage U_dcNAnd (4) descending. Determining a first phase shift angle using a control method as shown in FIG. 4The first phase shift angle is increased according to the voltage difference of the two input capacitorsThe action time of 1 level mode is increased, and the midpoint current i_NThe voltage of the two input capacitors is balanced again after a period of time when the voltage of the middle point is reduced and the action time of the 1 level mode is increased.

Fig. 12 is a simulation waveform of the control method shown in fig. 4 when power flows in the reverse direction in the circuit shown in fig. 10.

Referring to FIG. 12, when u_CDAhead of u_ABThe DAB circuit is operated in reverse. The voltage balance control of the input capacitor can also be realized by adopting the control method shown in fig. 4.

The midpoint balance control method (controlling the input capacitor voltage balance) provided by the embodiment of the disclosure can be applied to voltage conversion circuits in which the secondary side circuit 2 of the transformer is in various forms.

Fig. 13 is a schematic circuit diagram of the secondary side circuit 2.

Referring to fig. 13, the secondary-side circuit 2 may be a full-bridge rectifier circuit including:

a fourth leg 2A including a fifth switching element S5 and a sixth switching element S6 coupled to an eighth node N8;

a fifth leg 2B including seventh switching element S7 and eighth switching element S8 coupled to a ninth node N9;

the fifth switching element S5 and the seventh switching element S7 are coupled to the tenth node N10, the sixth switching element S6 and the eighth switching element S8 are coupled to the eleventh node N11, and the secondary-side circuit 2 is electrically connected to the secondary winding of the transformer 1 through the eighth node N8 and the ninth node N9.

In some embodiments, the eighth node N8 and the ninth node N9 may be directly coupled to the secondary winding of the transformer 1, or may be electrically connected to the secondary winding of the transformer 1 through the second passive network 5. The circuit form of the second passive network 5 may be the same as or different from that of the first passive network 4, and the present disclosure is not limited thereto.

In the embodiment shown in fig. 13, the primary-side circuit of the transformer is a series double half-bridge circuit, and the control method shown in fig. 4 can be used to adjust the midpoint potential balance of the primary-side circuit. The output ports of the two bridge arms 1A and 1B are connected with the primary winding of the transformer 1 through a first passive network 4 (the structure of the first passive network 4 is not limited), and the secondary side circuit 2 is a full-bridge rectification circuit.

Fig. 14 is a schematic diagram of another circuit configuration of the secondary-side circuit 2.

Referring to fig. 14, the transformer secondary-side circuit 2 may be a full-wave rectifier circuit including:

a fifth switching element S5 having a first end electrically connected to one end of the secondary winding of the transformer 1 through an eighth node N8;

a sixth switching element S6 has a first terminal electrically connected to the other terminal of the secondary winding of the transformer 1 via a ninth node N9, and a second terminal coupled to the second terminal of the fifth switching element S5.

In the embodiment shown in fig. 14, the primary side circuit is a series double half-bridge circuit, and the neutral point potential balance can be adjusted by using the phase shift modulation method shown in fig. 4. The output ports of the two bridge arms 1A and 1B are connected with the primary winding of the transformer 1 through a first passive network 4 (the passive network structure is not limited), and the secondary side circuit 2 is a full-wave rectification circuit.

In the present embodiment, when the secondary-side circuit 2 is a rectifier circuit as described above, uncontrolled rectification or synchronous rectification may be adopted for the secondary-side circuit 2, or other modulation methods may be adopted.

Fig. 15 is a schematic diagram of still another circuit configuration of the secondary-side circuit 2.

Referring to fig. 15, in one embodiment, the secondary-side circuit 2 may also be a series double half-bridge (SHB) structure, including:

a third capacitor C coupled to the tenth node N10₃And a fourth capacitance C₄Third capacitor C₃Is coupled to an eleventh node N11, a fourth capacitor C₄Is coupled to a twelfth node N12;

third leg 2A coupled between tenth node N10 and eleventh node N11, fourth leg 2B coupled between twelfth node N12 and tenth node N10, third leg 2A including fifth switching element S5 and sixth switching element S6 coupled to thirteenth node N13, fourth leg 2B including seventh switching element S7 and eighth switching element S8 coupled to fourteenth node N14, and secondary side circuit 2 electrically connected to the secondary winding of transformer 1 through thirteenth node N13 and fourteenth node N14.

In the embodiment shown in fig. 15, the control method may further include:

outputting a fifth control signal, a sixth control signal, a seventh control signal and an eighth control signal to control ends of a fifth switching element, a sixth switching element, a seventh switching element and an eighth switching element, wherein the fifth control signal, the sixth control signal, the seventh control signal and the eighth control signal are square wave signals with a preset period, the fifth control signal is complementary with the sixth control signal, the seventh control signal is complementary with the eighth control signal, a second phase shift angle is formed between the fifth control signal and the eighth control signal, and a second phase shift angle is formed between the sixth control signal and the seventh control signal;

and controlling the second phase shifting angle to reduce the voltage difference between the third capacitor and the fourth capacitor.

Wherein controlling the second phase shift angle to reduce the voltage difference between the third capacitor and the fourth capacitor comprises:

detecting a third voltage at two ends of a third capacitor and a fourth voltage at two ends of a fourth capacitor;

and determining a second phase shifting angle according to the difference value of the third voltage and the fourth voltage, reducing the second phase shifting angle when the difference value is a positive value, and increasing the second phase shifting angle when the difference value is a negative value.

When the secondary-side circuit 2 is in the SHB structure, the midpoint balance of the secondary-side circuit 2 can be adjusted by applying the method shown in fig. 4, and the details of the disclosure are not repeated herein.

Although the embodiment of the present disclosure takes the example that the voltage input source is coupled to the second node and the third node, in other embodiments, the voltage input source may also be coupled to the secondary side circuit 2, that is, the circuit may operate in a forward direction or a reverse direction, or the circuit may operate in a bidirectional direction, which is not limited in this disclosure.

The passive network structure of the dc/dc converter using the three-level circuit and the secondary side circuit structure of the transformer are only examples, and the above examples may be collocated with each other, and in other embodiments, other structures may be included, as long as the primary side circuit of the transformer uses the three-level circuit with the SHB structure, the control method provided by the present disclosure may be applied to adjust the midpoint potential.

In summary, in the embodiment of the present disclosure, by controlling the complementary conduction of the first switching element, the second switching element, the third switching element, and the fourth switching element on the two bridge arms of the SHB structure dc/dc converter, the control signals of the first switching element and the fourth switching element have a phase shift angle, and the phase shift angle is adjusted to reduce the voltage difference between the first capacitor and the second capacitor, so that the midpoint potential balance of the dc/dc converter can be effectively adjusted. In the control method, the working modes of the positive half period and the negative half period are completely symmetrical, the action effect on the center is consistent, the conduction time of the switching elements in the SHB structure is the same, and compared with a method for performing center point adjustment by controlling the action time difference of 1 level to cause uneven stress of the switching tube, the method disclosed by the embodiment of the invention has higher center point adjustment capability, is beneficial to realizing ZVS of four switching elements in a bridge arm, simultaneously enables the stress and the loss of the four switching elements to be uniform, and improves the energy efficiency.

It should be noted that although in the above detailed description several modules or units of the device for action execution are mentioned, such a division is not mandatory. Indeed, the features and functionality of two or more modules or units described above may be embodied in one module or unit, according to embodiments of the present disclosure. Conversely, the features and functions of one module or unit described above may be further divided into embodiments by a plurality of modules or units.

Furthermore, the above-described figures are merely schematic illustrations of processes involved in methods according to exemplary embodiments of the invention, and are not intended to be limiting. It will be readily understood that the processes shown in the above figures are not intended to indicate or limit the chronological order of the processes. In addition, it is also readily understood that these processes may be performed synchronously or asynchronously, e.g., in multiple modules.

Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.