Composite Cuk-SEPIC bidirectional DCDC converter

Abstract

The invention discloses a composite Cuk-SEPIC bidirectional DC-DC converter, and belongs to the technical field of power electronic conversion devices. The converter comprises an input filtering module, a driving control module, a single-tube chopper circuit composed of a first switching tube, an SEPIC and Cuk bidirectional power branch module composed of a second switching tube and a third switching tube, and an output filtering module. Wherein the direct current input voltage source is connected to the first switch tube through the input inductor, and the drain electrode of the switch tube is used as a common switch node to be respectively connected with the second switch tube of the SEPIC branch and the third switch tube of the Cuk branch; a source electrode of the second switching tube is connected with a node of the SEPIC inductor and the SEPIC transfer capacitor, and a drain electrode of the second switching tube is connected with the positive output end; the source electrode of the third switch tube is connected with the negative output capacitor, and the drain electrode is connected with the node of the Cuk inductor and the Cuk transfer capacitor. And the output end of the bidirectional power branch module is connected with the input end of the output filtering module. Through cooperative control of the first switch tube, the second switch tube and the third switch tube by the driving control module, forward boost-buck conversion of energy from the input side to the positive and negative double output sides and reverse energy feedback from the double output sides to the input side are realized. The bidirectional function of the converter is achieved through simplest hardware modification, the bottleneck that energy cannot be flexibly scheduled in application such as photovoltaic energy storage of a traditional unidirectional topology is effectively solved, and the converter has the advantages of being simple in topological structure, high in conversion efficiency and high in adaptability.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and specifically to a composite Cuk-SEPIC bidirectional DC-DC converter. Background Technology

[0002] Currently, in fields such as photovoltaic power generation, most common DC-DC converters adopt a unidirectional topology, mainly used to realize the transformation of the output voltage of photovoltaic modules and maximum power point tracking to ensure that the photovoltaic system can efficiently convert solar energy into electrical energy and transmit it to loads or energy storage devices.

[0003] However, with technological advancements and increasingly complex application scenarios, higher demands are being placed on flexible energy management. Traditional unidirectional converters can only achieve unidirectional energy flow from the input side to the output side, and cannot feed back excess energy from energy storage devices or braking energy from the load side to the input side, thus limiting the improvement of overall system energy efficiency. Although existing bidirectional DC-DC converter technology has made significant progress, most topologies are complex, requiring a large number of switching devices and auxiliary circuits, resulting in high costs, complex control, and challenges to reliability.

[0004] Therefore, the composite Cuk-SEPIC bidirectional DC-DC converter of the present invention is based on the above-mentioned development trend. By innovatively improving the topology of the traditional unidirectional DC-DC converter, it achieves efficient and reliable bidirectional energy flow with a simple structure, thus promoting the further development of photovoltaic power generation technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite Cuk-SEPIC bidirectional DC-DC converter. This converter is based on the traditional Cuk-SEPIC converter topology and is improved by optimizing the configuration of switching devices and introducing a bidirectional control strategy. It achieves flexible bidirectional energy flow with a simple circuit structure, while retaining wide voltage input and bipolar output capabilities, effectively improving the energy utilization efficiency and flexibility of photovoltaic energy storage and other systems.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a composite Cuk-SEPIC bidirectional DC-DC converter, comprising an input filtering module, a drive control module, a single-transistor chopper circuit composed of a first switching transistor, and a SEPIC and Cuk bidirectional power branch module and a dual-output filtering module composed of a second switching transistor and a third switching transistor, respectively. The DC input voltage source is connected to the first switching transistor via an input inductor. The drain of this switching transistor serves as a common switching node, connecting to the second switching transistor of the SEPIC branch and the third switching transistor of the Cuk branch. The source of the second switching transistor is connected to the node of the SEPIC inductor and the SEPIC transfer capacitor, and its drain is connected to the positive output terminal. The source of the third switching transistor is connected to the negative output capacitor, and its drain is connected to the node of the Cuk inductor and the Cuk transfer capacitor. Through the coordinated control of the first, second, and third switching transistors by the drive control module, positive buck-boost conversion of energy from the input side to the positive and negative dual output sides, and reverse energy feedback from the dual output sides to the input side are achieved.

[0007] The input filtering module includes an input inductor Lin, which is connected in series between the DC positive input terminal Vin of the converter and the internal switching node.

[0008] The drive control module includes a signal generation unit configured to generate three pulse width modulation (PWM) signals according to the converter's operating mode, respectively driving the first, second, and third switching transistors. In the forward operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the first switching transistor; and generate synchronous rectification signals for controlling the second and third switching transistors, the synchronous rectification signals being complementary to the master control PWM signal. In the reverse operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the second and third switching transistors; and generate a synchronous rectification signal for controlling the first switching transistor, the synchronous rectification signal being complementary to the master control PWM signals of the second and third switching transistors.

[0009] The bidirectional power branch module is the core of this invention for achieving dual output and bidirectional energy flow. It innovatively transforms the traditional unidirectional SEPIC and Cuk output branches into bidirectional branches that can be actively controlled by a switching transistor. This module mainly includes a SEPIC functional branch, a Cuk functional branch, and a bidirectional energy storage capacitor bank. The SEPIC functional branch generates and regulates the positive output voltage VPOS, and includes a capacitor CS, an inductor LS, and a switching transistor S2. The capacitor CS serves as an energy transfer and coupling capacitor, with one end connected to the common switching node of the bidirectional power branch module, and the other end connected to one end of the inductor LS and the source of the switching transistor S2. The other end of the inductor LS is grounded, forming a SEPIC conversion network together with the capacitor CS. The drain of the switching transistor S2 serves as the positive voltage output terminal VPOS. By controlling the on and off states of the switching transistor S2, the positive output or reverse feedback of energy in this branch can be controlled. The Cuk functional branch generates and regulates the negative output voltage Vneg, and includes a capacitor CC, an inductor LC, and a switching transistor S3. The capacitor CC serves as an energy transfer and coupling capacitor. The energy storage capacitor has one end connected to the common switching node of the bidirectional power branch module, and the other end connected to one end of the inductor LC and the drain of the switching transistor S3. The other end of the inductor LC directly serves as the negative voltage output terminal Vneg, and the source of the switching transistor S3 is directly grounded. This connection method ensures the inherent step-down and negative voltage output characteristics of the Cuk circuit and realizes bidirectional energy control through the switching transistor S3. In the forward power conversion mode, energy is simultaneously injected from the common switching node of the bidirectional power branch module into both the SEPIC and Cuk branches. In the SEPIC branch, the voltage is boosted through the coupling of capacitor CS and inductor LS, and then supplied to capacitor CP and the load through switch S2 or its body diode. In the reverse feedback mode, the energy flow is reversed. The energy of capacitor CP at the positive output terminal is fed back to the common switching node of the bidirectional power branch module through active drive S2, inductor LS and capacitor CS. The energy of capacitor CN at the negative output terminal is fed back to the common switching node of the bidirectional power branch module through active drive switch S3, inductor LC and capacitor CC, ultimately realizing the feedback of energy to the input side.

[0010] The dual-output filter module consists of energy storage capacitors CP and CN. Energy storage capacitor CP is connected between the positive voltage output terminal VPOS of the SEPIC functional branch and ground; energy storage capacitor CN is connected between the negative voltage output terminal Vneg of the Cuk functional branch and ground. These two capacitors are not only used to store output energy, but more importantly, they are used to smooth the output voltage ripple of their respective branches and provide a stable DC voltage for the load.

[0011] Compared with the prior art, the beneficial effects of the present invention are: 1. Based on the original unidirectional circuit topology, the present invention achieves bidirectional energy flow by optimizing the configuration of key components such as switching transistors, and introduces an appropriate bidirectional switching control strategy, breaking through the barrier that unidirectional circuits can only transmit energy in one direction.

[0012] 2. This invention can flexibly switch the energy transmission direction according to system requirements, and adapt to bidirectional energy interaction scenarios such as energy storage system charging and discharging, and braking energy recovery. Unlike unidirectional circuits, it does not require complex and redundant designs such as anti-parallel connection when bidirectional needs are met, which greatly simplifies the circuit structure.

[0013] 3. The optimized bidirectional converter of this invention inherits and optimizes some characteristics of the original unidirectional circuit. With the help of the synergistic effect of components such as inductors and capacitors, it can effectively suppress input and output current ripple and ensure the stability of voltage conversion.

[0014] The accompanying drawings are provided to more clearly illustrate the composite Cuk-SEPIC bidirectional DC-DC converter proposed in this invention. The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] Figure 1 This is a circuit diagram of a composite Cuk-SEPIC bidirectional DC-DC converter according to the present invention.

[0016] Figure 2 This is the positive operating mode where switch S1 is turned on and switches S2 and S3 are turned off.

[0017] Figure 3 This is the positive operating mode where switch S1 is off and switches S2 and S3 are on.

[0018] Figure 4 This is the reverse operating mode where switching transistors S2 and S3 are turned on and switching transistor S1 is turned off.

[0019] Figure 5 This is the reverse operating mode where switching transistors S2 and S3 are off and switching transistor S1 is on. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] Reference Figure 1The present invention provides a circuit structure diagram of a composite Cuk-SEPIC bidirectional DC-DC converter, the specific structure of which is as follows: It includes an input filtering module, a drive control module, a single-transistor chopper circuit composed of a first switching transistor, and a SEPIC and Cuk bidirectional power branch module and a dual-output filtering module composed of a second switching transistor and a third switching transistor, respectively. The DC input voltage source is connected to the first switching transistor via an input inductor. The drain of this switching transistor serves as a common switching node, connecting to the second switching transistor of the SEPIC branch and the third switching transistor of the Cuk branch. The source of the second switching transistor is connected to the node of the SEPIC inductor and the SEPIC transfer capacitor, and its drain is connected to the positive output terminal. The source of the third switching transistor is connected to the negative output capacitor, and its drain is connected to the node of the Cuk inductor and the Cuk transfer capacitor. Through the coordinated control of the first, second, and third switching transistors by the drive control module, positive buck-boost conversion of energy from the input side to the positive and negative dual output sides, and reverse energy feedback from the dual output sides to the input side are achieved.

[0022] The input filtering module includes an input inductor Lin, which is connected in series between the DC positive input terminal Vin of the converter and the internal switching node.

[0023] The drive control module includes a signal generation unit configured to generate three pulse width modulation (PWM) signals according to the converter's operating mode, respectively driving the first, second, and third switching transistors. In the forward operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the first switching transistor; and generate synchronous rectification signals for controlling the second and third switching transistors, the synchronous rectification signals being complementary to the master control PWM signal. In the reverse operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the second and third switching transistors; and generate a synchronous rectification signal for controlling the first switching transistor, the synchronous rectification signal being complementary to the master control PWM signals of the second and third switching transistors.

[0024] The bidirectional power branch module is the core of this invention for achieving dual output and bidirectional energy flow. It innovatively transforms the traditional unidirectional SEPIC and Cuk output branches into bidirectional branches that can be actively controlled by a switching transistor. This module mainly includes a SEPIC functional branch, a Cuk functional branch, and a bidirectional energy storage capacitor bank. The SEPIC functional branch is used to generate and regulate the positive output voltage VPOS. It includes a capacitor CS, an inductor LS, and a switching transistor S2. The capacitor CS serves as an energy transfer and coupling capacitor, with one end connected to the common switching node of the bidirectional power branch module, and the other end connected to one end of the inductor LS and the source of the switching transistor S2. The other end of the inductor LS is grounded, forming a SEPIC conversion network together with the capacitor CS. The drain of the switching transistor S2 serves as the positive voltage output terminal VPOS. By controlling the on and off states of the switching transistor S2, the positive output or reverse feedback of energy in this branch can be controlled. The Cuk functional branch is used to generate and regulate the negative output voltage Vneg. It includes a capacitor CC, an inductor LC, and a switch S3. The capacitor CC serves as an energy transfer and storage capacitor. One end of CC is connected to the common switching node of the bidirectional power branch module, and the other end is connected to one end of the inductor LC and the drain of the switch S3. The other end of the inductor LC directly serves as the negative voltage output terminal Vneg. The source of the switch S3 is directly grounded. This connection method ensures the inherent buck and negative voltage output characteristics of the Cuk circuit and realizes bidirectional energy control through the switch S3. In the forward power conversion mode, energy is injected into both the SEPIC and Cuk branches simultaneously from the common switching node of the bidirectional power branch module. The SEPIC branch achieves voltage boost through the coupling of the capacitor CS and the inductor LS, and supplies power to the capacitor CP and the load through the switch S2 or its body diode. In the reverse feedback mode, the energy flow is reversed. The energy of capacitor CP at the positive output terminal is fed back to the common switching node of the bidirectional power branch module through active drive S2, inductor LS and capacitor CS; the energy of capacitor CN at the negative output terminal is fed back to the common switching node of the bidirectional power branch module through active drive switch S3, inductor LC and capacitor CC, ultimately realizing energy feedback to the input side.

[0025] The dual-output filter module consists of energy storage capacitors CP and CN. Energy storage capacitor CP is connected between the positive voltage output terminal VPOS of the SEPIC functional branch and ground; energy storage capacitor CN is connected between the negative voltage output terminal Vneg of the Cuk functional branch and ground. These two capacitors are not only used to store output energy, but more importantly, they are used to smooth the output voltage ripple of their respective branches and provide a stable DC voltage for the load.

[0026] This invention provides a composite Cuk-SEPIC bidirectional DC-DC converter, which has the following significant differences and innovations compared with traditional unidirectional Cuk or SEPIC converters and other existing bidirectional converters: In traditional converters, diodes are generally used for rectification, and energy can only flow in one direction. This invention uses a second and a third switch to replace the rectifier diodes in the SEPIC and Cuk output branches, respectively. Through a unique connection method (especially the source of the third switch is connected to the negative output capacitor, and the drain is connected to the Cuk inductor and the transfer capacitor node), bidirectional energy flow is fundamentally achieved from the hardware structure. At the same time, compared with some complex bidirectional topologies, this invention achieves bidirectional energy management of positive and negative bipolar outputs through only three switches and their coordinated control. This control architecture achieves complex functions while having lower hardware costs and simpler control logic, thus reducing system complexity and cost.

[0027] Next, please refer to Figure 2 and Figure 3 This invention coordinates the control of the first, second, and third switching transistors via a drive control module. In forward mode, it primarily operates in the following two states to adapt to different energy flow requirements: Figure 2 In state one of the forward operating modes: switch S1 is on, and switches S2 and S3 are off. Voltage source Vin, acting as the energy source, directly supplies power to input inductor Lin. As current flows through inductor Lin, its magnetic field strengthens, storing electrical energy in the form of a magnetic field. In the SEPIC circuit, the already charged transfer capacitor CS begins to discharge through inductor LS. Current flows through inductor LS, strengthening its magnetic field and transferring the stored energy from capacitor CS to the magnetic field of inductor LS. In the Cuk circuit, the already charged transfer capacitor CC discharges through inductor LC. Current flows through inductor LC, strengthening its magnetic field and transferring the stored energy from capacitor CC to the magnetic field of inductor LC. The output voltages of both SEPIC and Cuk are maintained by their respective output capacitors CP and CN. Figure 3In the second state of positive operating mode: switch S1 is off, and switches S2 and S3 are on. In the SEPIC circuit, inductor Lin begins to release energy. Its current no longer flows through switch S1, but is connected in series with the input voltage source Vin, passing through capacitor CS, and then through switch S2 to charge the capacitor and load at the SEPIC output terminal. At the same time, inductor LS releases energy and passes through switch S2 to supply the positive output voltage source. In the Cuk circuit, the energy released by inductor Lin is also connected in series with the input voltage source Vin, passing through capacitor CC, and then through switch S3 to charge the capacitor and load at the Cuk terminal. At the same time, inductor LC releases energy, and its current also passes through switch S3 to supply the output terminal of Cuk. This process repeats continuously. By adjusting the proportion of the on-time of switch S1, the amount of energy supplied can be controlled, thereby achieving a stable buck-boost bipolar output.

[0028] Next, please refer to Figure 4 and Figure 5 This invention coordinates the control of the first, second, and third switching transistors via a drive control module. In reverse mode, it primarily operates in the following two states to adapt to different energy flow requirements: Figure 4 In the reverse operating mode, state one is as follows: switch S1 is off, and switches S2 and S3 are on. The circuit draws current from the positive output voltage source Vpos and the reverse output voltage source Vneg, storing energy in the magnetic and electric fields of inductors LS and LC, as well as transfer capacitors CS and CC. In the SEPIC circuit, current flows out from the positive output capacitor CP, through inductor LS, increasing the inductor current and storing the energy of the positive output voltage source Vpos in the form of a magnetic field. Another part of the current also flows out from capacitor CP, charging the transfer capacitor CS. This path is essentially the energy storage stage of a boost circuit. In the Cuk circuit, current flows out from the negative terminal of the negative output capacitor CN, through switch S3, through inductor LC, increasing the inductor current and storing the energy at the output terminal in the form of a magnetic field. Another part of the current also flows out from capacitor CN, through switch S3, charging the transfer capacitor CC and storing energy in capacitor CC. Figure 5State 2 in reverse operating mode: Switch S1 is on, and switches S2 and S3 are off. This is the key to boost feedback. All the energy stored in State 1 of reverse operating mode is forcibly fed into the input side through series superposition. This is crucial for achieving boost feedback. In the SEPIC circuit, inductor LS maintains its current, and capacitor CS maintains its voltage. Their total voltage after series connection forms a loop through the on-state switch S1. Since the series voltage is much higher than the input voltage Vin, energy is forced to be pushed to the input side Vin through the input inductor Lin. In the Cuk circuit, after switch S3 is off, inductor LC and capacitor CC are forced to be connected in series, forming a loop through switch S1, and forcibly delivering energy to the input side Vin through the input inductor Lin. At this time, the energy stored in the SEPIC and Cuk paths generates a high voltage through the series connection of inductors and capacitors, realizing the boost function. Switch S1 is actively on at this time, providing a low-loss path for energy to the input side. The input inductor Lin here plays the role of smoothing the input current and filtering ripple.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. The purpose of this invention is to provide a composite Cuk-SEPIC bidirectional DC-DC converter to solve some technical problems existing in traditional unidirectional DC-DC converters in photovoltaic power generation systems.

2. The technical solution adopted in this invention is: a composite Cuk-SEPIC bidirectional DC-DC converter, characterized in that, include: The converter consists of an input filtering module, a drive control module, a single-tube chopper circuit composed of a first switching transistor, and a SEPIC and Cuk bidirectional power branch module and a dual-output filtering module composed of a second switching transistor and a third switching transistor, respectively. The DC input voltage source is connected to the first switching transistor via an input inductor, and the drain of the first switching transistor serves as a common switching node, connecting to the second switching transistor of the SEPIC branch and the third switching transistor of the Cuk branch, respectively. The source of the second switch is connected to the node of the SEPIC inductor and the SEPIC transfer capacitor, and the drain is connected to the positive output terminal; the source of the third switch is connected to the negative output capacitor, and the drain is connected to the node of the Cuk inductor and the Cuk transfer capacitor. Through the coordinated control of the first, second and third switches by the drive control module, the positive buck-boost conversion of energy from the input side to the positive and negative dual output sides is realized, as well as the reverse energy feedback from the dual output sides to the input side.

3. The composite Cuk-SEPIC bidirectional DC-DC converter according to claim 1, characterized in that: The input filtering module includes a DC input voltage source Vin, an input inductor Lin, and a first switching transistor S1; one end of the input inductor Lin is connected to the positive terminal of the DC input voltage source Vin, and the other end is connected to the source terminal of the first switching transistor S1; the drain terminal of the first switching transistor S1 is grounded.

4. A composite Cuk-SEPIC bidirectional DC-DC converter according to claim 1, characterized in that: The drive control module includes a signal generation unit configured to generate three pulse width modulation (PWM) signals according to the converter's operating mode, respectively driving the first, second, and third switching transistors. In the forward operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the first switching transistor; and generate synchronous rectification signals for controlling the second and third switching transistors, the synchronous rectification signals being complementary to the master control PWM signal. In the reverse operating mode, the signal generation unit is configured to: generate a master control PWM signal for controlling the second and third switching transistors; and generate a synchronous rectification signal for controlling the first switching transistor, the synchronous rectification signal being complementary to the master control PWM signals of the second and third switching transistors.

5. A composite Cuk-SEPIC bidirectional DC-DC converter according to claim 1, characterized in that: The bidirectional power branch module includes a SEPIC functional branch, a Cuk functional branch, and a bidirectional energy storage capacitor bank. The SEPIC bidirectional branch and the Cuk bidirectional branch are connected in parallel through a common switching node. The SEPIC bidirectional branch includes a SEPIC inductor, a SEPIC transfer capacitor, and a second switching transistor. One end of the SEPIC inductor and one end of the SEPIC transfer capacitor are connected to a first node, and the other end of the SEPIC transfer capacitor is connected to the common switching node. The source of the second switching transistor is connected to the first node, and the drain of the second switching transistor serves as the positive output terminal of the SEPIC bidirectional branch. The Cuk bidirectional branch includes a Cuk inductor, a Cuk transfer capacitor, a negative output capacitor, and a third switching transistor. One end of the Cuk inductor and one end of the Cuk transfer capacitor are connected to a second node, and the other end of the Cuk transfer capacitor is connected to the common switching node. The drain of the third switching transistor is connected to the second node, and the source of the third switching transistor is connected to one end of the negative output capacitor. The other end of the negative output capacitor serves as the negative output terminal of the Cuk bidirectional branch.

6. A composite Cuk-SEPIC bidirectional DC-DC converter according to claim 1, characterized in that: The dual-output filter module includes a first output capacitor and a second output capacitor. The first output capacitor is connected between the positive output terminal of the SEPIC bidirectional branch and the reference ground. The second output capacitor is connected between the negative output terminal of the Cuk bidirectional branch and the reference ground. The positive output terminal, the negative output terminal, and the reference ground together constitute a bipolar DC output port.

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