Non-isolated high-gain bidirectional DC / DC converter with low voltage stress and control method

Abstract

The invention discloses a non-isolated high-gain bidirectional DC / DC converter with low voltage stress and a control method. An input unit of the converter comprises a power supply, a first independent inductor, a capacitor C1, a first switching tube and a second switching tube, the switched capacitor boosting unit comprises a second independent inductor, a third switching tube, a fourth switching tube, a capacitor C2 and a capacitor C3; the output unit comprises a capacitor C4, a capacitor C5 and a fifth switch tube; the second independent inductor is matched with the first independent inductor and the capacitor C1 to realize charging and discharging of the inductor and the capacitor; and the capacitor C4 and the capacitor C5 are connected in parallel at the output side, so that capacitor voltage and switch tube voltage stress can be effectively reduced. In a boost mode, the first switch tube is turned on. And in a step-down mode, the fourth switch tube is in complementary conduction with the second switch tube, the third switch tube and the fifth switch tube. The invention has the advantages of simple topological structure, convenient switch control, high voltage gain, low switch tube voltage stress and high working efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a non-isolated high-gain bidirectional DC / DC converter with low voltage stress and a control method. Background Art

[0002] Microgrids are studied and developed as an important form of realizing the access of distributed power sources to the grid. Bidirectional DC / DC converters play a vital role in DC microgrids, which can effectively control power flow, energy management, grid integration and voltage regulation. The high-voltage side of the DC bus voltage of grid-connected renewable energy systems and uninterruptible power supplies (UPS) is usually 200-400V, while the low-voltage side voltage powered by batteries is between 24-48V. Therefore, a high-gain DC / DC converter is required to achieve voltage matching.

[0003] In different applications, bidirectional high-gain DC / DC converters can be divided into isolated and non-isolated types. For isolated converters, high voltage gain can be achieved by increasing the transformer winding turns ratio. These converters have the characteristics of simple structure and low cost. However, the voltage stress of high-voltage side devices is large, and the gain range is generally narrow, the volume is large, and magnetic saturation is prone to occur. The leakage inductance and parasitic capacitance formed by the secondary winding of the transformer may cause voltage and current spikes, resulting in damage to the switching device and poor stability.

[0004] Non-isolated converters include Cuk, Sepic / Zeta, coupled inductor, traditional buck-boost, three-level, multi-level, switched capacitor and interleaved structures. Traditional bidirectional DC / DC converters are difficult to obtain high voltage gain due to the presence of parasitic elements, the converter efficiency is low, and the power switch is subjected to high voltage stress. The coupled inductor structure can achieve high voltage gain by changing the turns ratio of the coupled inductor, but it needs to solve the additional problems of leakage inductance, such as high voltage peaks between power switches, and requires additional buffer circuit design. The power conversion and transmission capabilities of the converter are limited by the core capacity. For Cuk and Sepic / Zeta structures, due to the cascade configuration of two power stages, their conversion efficiency is low. Although three-level or multi-level converters can improve voltage gain, multi-level DC / DC converters require more power switches, additional hardware circuits and control strategies, which makes the converter require more devices and more complex control. Converters based on switched capacitor / inductor structures transfer energy to the low-voltage side or high-voltage side through different charging and discharging paths to achieve high voltage gain. However, its high voltage gain requires multiple inductors / capacitors to be connected in series or in parallel, which makes its structure complex and reduces power density. The bidirectional DC / DC converter with an interleaved structure can reduce input current ripple, but this structure requires more switching devices and is easily affected by circuit parasitic parameters, resulting in unbalanced input currents in each phase. There is also a circuit topology that combines switched capacitors with an interleaved structure. This method can greatly improve the voltage gain and the input current ripple can be ignored, but its input and output are not grounded, which will cause serious EMI problems. Summary of the invention

[0005] 1. Technical problem to be solved by the invention

[0006] The present invention provides a non-isolated high-gain bidirectional DC / DC converter with low voltage stress and a control method. The present invention adopts a switched capacitor structure as a boost unit and utilizes the charge and discharge boost technology of an inductor and capacitor to achieve a high voltage gain. The circuit control method is simple and the working reliability is enhanced. The voltage stress of the switch tube can be well reduced, and the problems of power imbalance and complex control can be solved.

[0007] 2. Technical solution

[0008] In order to achieve the above object, the technical solution provided by the present invention is:

[0009] A non-isolated high-gain bidirectional DC / DC converter with low voltage stress of the present invention comprises an input unit, a switch capacitor boost unit and an output parallel unit, wherein the input unit comprises a power supply V in , capacitor C low, a first independent inductor L1, a capacitor C1, a first switch tube S1 and a second switch tube S2; the input unit is connected to a switch capacitor boost unit, the switch capacitor boost unit includes a second independent inductor L2, a third switch tube S3, a fourth switch tube S4, a capacitor C2 and a capacitor C3; the second independent inductor L2 cooperates with the first independent inductor L1 and the capacitor C1 to realize the charging and discharging of the inductor and the capacitor; the switch capacitor boost unit is connected to an output parallel unit, the output parallel unit includes a capacitor C4, a capacitor C5 and a fifth switch tube S5, and the capacitor C4 and the capacitor C5 are connected in series and in parallel at the output end of the converter.

[0010] Furthermore, in the input unit, the power supply V in With capacitor C low Parallel connection, power supply V in The positive electrode of the capacitor C1 is connected to one end of the first independent inductor L1, the other end of the first independent inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2, and the negative electrode of the capacitor C1 is connected to the power supply V in The cathode of the capacitor C1 is connected to the source of the first switch tube S1; the anode of the capacitor C1 is connected to the drain of the second switch tube S2.

[0011] Furthermore, in the switch capacitor boost unit, the drain of the second switch tube S2 is connected to one end of the second independent inductor L2, the other end of the second independent inductor L2 is respectively connected to the positive electrode of the capacitor C2, the negative electrode of the capacitor C3 and the source electrode of the third switch tube S3, the negative electrode of the capacitor C2 is connected to the source electrode of the second switch tube S2 of the input unit, the positive electrode of the capacitor C3 is connected to the drain electrode of the fourth switch tube S4. The drain electrode of the third switch tube S3 is connected to the source electrode of the fourth switch tube S4.

[0012] Furthermore, in the output parallel unit, the source of the fifth switch tube S5 is connected to the positive electrode of the capacitor C3 of the switch capacitor boost unit and the drain of the fourth switch tube S4; the positive electrode of the capacitor C4 is connected to one end of the output side and the drain of the fifth switch tube S5; the negative electrode of the capacitor C4 is connected to the positive electrode of the capacitor C5, the source of the fourth switch tube S4 of the switch capacitor boost unit and the drain of the third switch tube S3; the negative electrode of the capacitor C5 is connected to the other end of the output side.

[0013] The present invention provides a control method for a non-isolated high-gain bidirectional DC / DC converter with low voltage stress. In a boost mode, the duty cycle of a first switch tube S1 is controlled to achieve the purpose of boosting. In a buck mode, the duty cycles of a second switch tube S2, a third switch tube S3, a fourth switch tube S4 and a fifth switch tube S5 are controlled to achieve the purpose of bucking, wherein the fourth switch tube S4 is complementary to the second switch tube S2, the third switch tube S3 and the fifth switch tube S5.

[0014] Furthermore, in the boost mode, the first to third working modes are included, and the first to third working modes are executed in sequence, wherein:

[0015] The first working mode: the first switch tube S1 is controlled to be turned on, the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are all turned off, and the diode D4 of the fourth switch tube S4 is turned on;

[0016] The second working mode: the first switch tube S1 is controlled to remain turned on, the diode D4 of the fourth switch tube S4 is turned off, and the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are still turned off;

[0017] The third working mode: the first switch tube S1 and the fourth switch tube S4 are controlled to be turned off, and the diode D2 of the second switch tube S2, the diode D3 of the third switch tube S3 and the diode D5 of the fifth switch tube S5 are turned on.

[0018] Furthermore, in the buck mode, it includes the first and second working modes, and the first and second working modes are executed in sequence, wherein:

[0019] The first working mode: the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are turned on at the same time, and the first switch tube S1 and the fourth switch tube S4 are turned off;

[0020] The second working mode: the fourth switch tube S4 is controlled to be turned on, the diode D1 of the first switch tube S1 is turned on, and the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are all turned off.

[0021] Furthermore, in boost mode, the voltage gain of the converter is:

[0022]

[0023] When the first switch tube S1 is turned on, the voltage stress of the switch tube is:

[0024]

[0025] Where, d Boost is the boost duty cycle.

[0026] Furthermore, in buck mode, the voltage gain of the converter is:

[0027]

[0028] The second switch tube S2, the third switch tube S3, and the fifth switch tube S5 are complementarily turned on with the fourth switch tube S4, and the voltage stress of the switch tubes is:

[0029]

[0030] Where, d Buck is the step-down duty cycle.

[0031] 3. Beneficial effects

[0032] Compared with the existing known technologies, the technical solution provided by the present invention has the following significant effects:

[0033] (1) A non-isolated high-gain bidirectional DC / DC converter with low voltage stress of the present invention adopts a switched capacitor structure as a boost unit, and realizes high voltage gain by using the charge-discharge boost technology of inductors and capacitors. Specifically, a capacitor C5 is arranged on the output side and connected in series with the capacitor C4; and the source of the fourth switch tube S4 and the drain of the third switch tube S3 of the switched capacitor boost unit are connected between the capacitors C4 and C5, so that the voltage stress of the capacitor and the switch tube is significantly reduced. In this way, a device with low on-resistance and low rated voltage can be used, so that the loss and net cost of the converter are minimized, and the efficiency is also improved.

[0034] (2) The present invention is a non-isolated high-gain bidirectional DC / DC converter with low voltage stress. An inductor L2 is added to the switch capacitor structure to cooperate with the inductor L1 and capacitor C1 on the input side. The inductor and capacitor charging and discharging principle is used to significantly improve the voltage gain of the converter. When the duty cycle reaches 0.7, the boost voltage gain of the converter is 9. When the duty cycle reaches 0.3, the buck gain is 0.1.

[0035] (3) The non-isolated high-gain bidirectional DC / DC converter with low voltage stress of the present invention is versatile and can be applied to various occasions requiring high voltage gain, such as energy storage systems, fuel cell power generation systems, and DC microgrids. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a circuit structure diagram of the converter in the present invention;

[0037] Figure 2 It is a schematic diagram of the main working waveform of the converter in boost mode;

[0038] Figure 3 is a schematic diagram of an equivalent circuit of a converter in a first working mode under a boost mode;

[0039] Figure 4 is a schematic diagram of an equivalent circuit of the converter in the second working mode under the boost mode;

[0040] Figure 5 is a schematic diagram of an equivalent circuit of the converter in the third working mode under the boost mode;

[0041] Figure 6It is a schematic diagram of the relationship between the switch tube voltage stress, the output voltage ratio and the duty cycle of the converter in the boost mode;

[0042] Figure 7 It is a schematic diagram of the main working waveform of the converter in buck mode;

[0043] Figure 8 is a schematic diagram of an equivalent circuit of a converter in a first working mode under a buck mode;

[0044] Fig. 9 is a schematic diagram of an equivalent circuit of the converter in the second working mode under the buck mode;

[0045] Fig.10 It is a schematic diagram of the relationship between the switch tube voltage stress, the output voltage ratio and the duty cycle of the converter in the buck mode;

[0046] Fig.11 It is a schematic diagram of the converter boost mode driving simulation waveform and the inductor current simulation waveform;

[0047] Fig.12 (a)-(c) are schematic diagrams of simulated waveforms of switch voltage and current in boost mode of the converter;

[0048] Fig.13 A schematic diagram of the simulated waveform of the relationship between the input and output voltages of the converter in boost mode;

[0049] Fig.14 It is a schematic diagram of the simulation waveform of the converter buck mode drive and the simulation waveform of the inductor current;

[0050] Fig.15 (a)-(c) are schematic diagrams of simulated waveforms of the voltage and current of the switch tube in the buck mode of the converter;

[0051] Fig.16 A schematic diagram of a simulation waveform of the relationship between the input and output voltages of the converter in buck mode;

[0052] Fig.17 (a)-(b) are schematic diagrams of experimental waveforms of converter boost mode driving and inductor current experiment waveforms;

[0053] Fig.18 (a)-(e) are schematic diagrams of experimental waveforms of switch voltage and current in the converter boost mode;

[0054] Fig.19 (a)-(b) are schematic diagrams of converter buck mode simulation drive waveform and inductor current experimental waveform;

[0055] Fig. 20(a)-(e) are schematic diagrams of experimental waveforms of switch voltage and current in buck mode of converter;

[0056] Fig.21 This is a physical picture of a 400W prototype developed corresponding to the converter described in the present invention. DETAILED DESCRIPTION

[0057] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings and embodiments.

[0058] Example 1

[0059] Figure 1 is a structural schematic diagram of a non-isolated high-gain bidirectional DC / DC converter with low voltage stress in this embodiment. Figure 1 As shown, the switch tubes used in the converter are all MOSFETs, including: input unit, switch capacitor boost unit and output parallel unit. The input unit includes a power supply V in , the first independent inductor L1, the capacitor C low , capacitor C1, a first switch tube S1 and a second switch tube S2; the input unit is connected to a switch capacitor boost unit, the switch capacitor boost unit includes a second independent inductor L2, a third switch tube S3, a fourth switch tube S4, a capacitor C2 and a capacitor C3; the output parallel unit includes a capacitor C4, a capacitor C5 and a fifth switch tube S5.

[0060] Specifically, in the input unit structure, the power supply V in With capacitor C low Parallel connection, power supply V in The positive electrode of the capacitor C1 is connected to one end of the first independent inductor L1, the other end of the first independent inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2, and the negative electrode of the capacitor C1 is connected to the power supply V in The cathode of the capacitor C1 is connected to the source of the first switch tube S1; the anode of the capacitor C1 is connected to the drain of the second switch tube S2.

[0061] In the switch capacitor boost unit, the drain of the second switch tube S2 is connected to one end of the second independent inductor L2, the other end of the second independent inductor L2 is respectively connected to the positive electrode of the capacitor C2, the negative electrode of the capacitor C3 and the source electrode of the third switch tube S3, the negative electrode of the capacitor C2 is connected to the source electrode of the second switch tube S2 of the input unit, the positive electrode of the capacitor C3 is connected to the drain electrode of the fourth switch tube S4. The drain electrode of the third switch tube S3 is connected to the source electrode of the fourth switch tube S4.

[0062] In the output parallel unit, the source of the fifth switch tube S5 is connected to the positive electrode of the capacitor C3 of the switch capacitor boost unit and the drain of the fourth switch tube S4; the positive electrode of the capacitor C4 is connected to one end of the output side and the drain of the fifth switch tube S5; the negative electrode of the capacitor C4 is connected to the positive electrode of the capacitor C5, the source of the fourth switch tube S4 of the switch capacitor boost unit and the drain of the third switch tube S3; the negative electrode of the capacitor C5 is connected to the other end of the output side.

[0063] The converter has the advantages of simple topology and common ground between input and output ends. It adopts a switched capacitor structure as a boost unit and realizes high voltage gain by using the charge and discharge boost technology of inductor and capacitor. Specifically, capacitor C5 is arranged on the output side and connected in series with capacitor C4; and the source of the fourth switch tube S4 and the drain of the third switch tube S3 of the switched capacitor boost unit are connected between capacitor C4 and capacitor C5, so that the voltage stress of the capacitor and the switch tube is significantly reduced. In this way, devices with low on-resistance and low rated voltage can be used, so that the loss and net cost of the converter are minimized and the working efficiency is improved. Inductor L2 is added to the switched capacitor structure, which cooperates with the inductor L1 and capacitor C1 on the input side, and the voltage gain of the converter is significantly improved by using the charge and discharge principle of inductor and capacitor. The converter of this embodiment is very suitable for applications with a wide input voltage range, low voltage input and high voltage gain.

[0064] Example 2

[0065] The converter of this embodiment controls the duty cycle of a switch tube in the boost mode to achieve the purpose of boosting. A switching cycle includes working mode 1, working mode 2 and working mode 3. Figure 2 for Figure 1 The theoretical operating waveform of the equivalent circuit in the boost mode of the converter is shown in the figure. Figure 3-Figure 5 yes Figure 2 The working mode diagrams of the converter equivalent circuit shown in FIG. 1 ; wherein the first to third working modes correspond to working modes 1-3, specifically:

[0066] Working mode 1[t0-t1]:

[0067] At time t0, the first switch tube S1 is turned on, the diode D4 of the fourth switch tube S4 is turned on, the switch tubes S2, S3 and S5 are turned off, and the first independent inductor L1 is connected to the power supply V in After being charged by the first switch tube S1, the capacitor C1 charges the second independent inductor L2, the capacitor C5 charges the capacitor C3, the capacitors C1 and C5 simultaneously supply power to the capacitor C2, and the capacitors C4 and C5 provide energy to the load. Its equivalent circuit and current path are as follows: Figure 3 As shown. Its inductor voltage can be expressed as:

[0068]

[0069] Working mode 2[t1-t2]:

[0070] At time t1, the first switch tube S1 is still turned on, the diode D4 of the fourth switch tube S4 is turned off, the switches S2, S3 and S5 continue to be turned off, and the first independent inductor L1 is connected to the power supply V in After the first switch tube S1 is charged, the capacitor C1 charges the second independent inductor L2, and the capacitor C5 cannot supply power to the capacitors C2 and C3. Figure 4 The inductor voltage expression is the same as that of mode 1.

[0071] Working mode 3[t2-t3]:

[0072] At time t2, diodes D2, D3 and D5 are turned on, the first switch tube S1 and the fourth switch tube S4 are turned off, and the power supply V in , the first independent inductor L1 charges the capacitor C1 through the diode D2, and discharges through the capacitor C2 to charge the capacitor C5 through the diode D3, and the second independent inductor L2 and the capacitor C3 discharge through the diode D5 to the capacitor C4 and the capacitor C5, and provide energy to the load at the same time. Its equivalent circuit and current path are as follows Figure 5 As shown. Its inductor voltage can be expressed as:

[0073]

[0074] In the non-isolated high-gain bidirectional DC / DC converter of this embodiment, in the boost mode, the first switch tube S1 is turned on, and the voltage gain of the converter is:

[0075]

[0076] The curve of the ratio of the switch tube voltage to the output voltage of the converter as the duty cycle changes is shown in Figure 6 As shown, in addition, the voltage stress of the converter switch tube is:

[0077]

[0078] Where, d Boost is the boost duty cycle. The relationship between switch stress, output voltage and duty cycle can be seen from the formula. The voltage stress of the switch tube is between half and one third of the output voltage.

[0079] Example 3

[0080] The present embodiment is a non-isolated high-gain bidirectional DC / DC converter with low voltage stress. In the buck mode, the duty cycle of the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 is controlled to achieve the purpose of bucking, wherein the fourth switch tube S4 is complementary to the second switch tube S2, the third switch tube S3 and the fifth switch tube S5. In one switching cycle, the operating mode 1 and the operating mode 2 are included. Figure 7 for Figure 1 The theoretical operating waveform of the equivalent circuit of the converter in buck mode is shown in Figure 1. Figure 8-Figure 9 yes Figure 1 The various working mode diagrams of the converter equivalent circuit are shown. Among them, the first to second working modes correspond to working modes 1-2, specifically:

[0081] Mode 1 [T0-T1]:

[0082] At time T0, the switches S2, S3 and S5 are turned on, the first switch S1 and the fourth switch S4 are turned off, the capacitor C1 provides energy to the first independent inductor L1 through the second switch S2, the high voltage side V0 and the capacitor C5 supply power to the capacitor C2 and the first independent inductor L1, and provide energy to the load. The capacitor C3, the capacitor C4 and the second independent inductor L2 are powered by V0. Its equivalent circuit and current path are as follows: Figure 8 As shown. Its inductor voltage can be expressed as:

[0083]

[0084] Mode 2 [T1-T2]:

[0085] At time T1, diode D1 and the fourth switch tube S4 are turned on, switches S2, S3 and S5 are turned off, the first independent inductor L1 supplies power to the load through diode D1, capacitor C2 and the second independent inductor L2 charge capacitor C1, capacitor C5 is charged by capacitor C2 and capacitor C3 through diode D1 and the fourth switch tube S4, and capacitor C4 provides energy to the high voltage side V0. Its equivalent circuit and current path are as follows: Fig. 9 As shown. Its inductor voltage can be expressed as:

[0086]

[0087] In the converter of this embodiment, the second switch tube S2, the third switch tube S3, and the fifth switch tube S5 are complementarily turned on with the fourth switch tube S4, and the voltage gain of the converter is:

[0088]

[0089] The curve of the ratio of the converter switch voltage to the output voltage as the duty cycle changes is shown in FIG. Fig.10As shown, in addition, the voltage stress of the converter switch tube is:

[0090]

[0091] Where, d Buck is the step-down duty cycle. The relationship between switch stress, output voltage and duty cycle can be seen from the formula. The voltage stress of the switch tube is between half and one third of the output voltage.

[0092] Furthermore, when the converter of this embodiment is in the boost mode and the duty cycle of the first switch tube S1 is 0.61, the gain of the converter is 6.6 times; if the power supply V in The voltage of the converter is equal to 48V, then the output voltage of the converter is 320V, and the voltage stress of the switch tube is only 122V. In the buck mode, when the duty ratio of the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 is 0.39, and the duty ratio of the fourth switch tube S4 is 0.61, the gain of the converter is 0.15 times; if the power supply V o The voltage is equal to 320V, then the output voltage of the converter is 48V, and the voltage stress of the switch tube is only 122V. The converter simulation parameter table is shown in Table 1:

[0093] Table 1 Converter simulation parameters

[0094] Parameter name Parameter number Parameter Value Output power: <![CDATA[P0]]> 400W Switching frequency: <![CDATA[f s ]]> 20kHz inductance <![CDATA[L1]]> 500μH inductance <![CDATA[L2]]> 3mH Switching tube <![CDATA[S1~S2]]> AGM25T16AT capacitance <![CDATA[C low ~C1]]> 100μF / 250V capacitance <![CDATA[C2~C3]]> 520μF / 300V capacitance <![CDATA[C4]]> 220μF / 250V capacitance <![CDATA[C5]]> 320μF / 400V Boost Mode Input voltage <![CDATA[U in ]]> 40～56V Output voltage U 320V Output load: <![CDATA[R0]]> 256Ω Buck Mode Input voltage <![CDATA[U in ]]> 320～340V Output voltage U 48V Output load: <![CDATA[R0]]> 5.7Ω

[0095] Under the simulation parameters in Table 1, the drive signal in the boost mode and the simulation waveforms of the two inductor currents of the converter of this embodiment are as follows: Fig.11 As shown, the simulated waveforms of the voltage and current of the first, second, third, fourth and fifth switch tubes are as follows Fig.12 As shown in (a)-(c) in Figure 1, it can be seen that the change process is basically consistent with the theoretical analysis. Fig.12 It can be observed that the voltage stress of the switch tube is 122V. It can be seen that the voltage stress of the switch tube is low, which is consistent with the calculation result of the voltage stress expression derived from the theory.

[0096] Input and output voltage simulation waveforms are as follows Fig.13 As shown, it can be observed that when the input voltage is 48V, the output voltage is 320V, which is consistent with the calculation result of the voltage gain expression derived theoretically.

[0097] Under the simulation parameters in Table 1, the drive signal in the buck mode and the simulation waveforms of the two inductor currents of the converter of this embodiment are as follows: Fig.14 As shown, the simulated waveforms of the voltage and current of the first, second, third, fourth and fifth switch tubes are as follows Fig.15 As shown in (a)-(c) in Figure 1, it can be seen that the change process is basically consistent with the theoretical analysis, and the voltage stress of the switch tube is also very low. Fig.15It can be observed that the voltage stress of the switch tube is 122V, which is consistent with the calculation result of the voltage stress expression derived from theory.

[0098] Input and output voltage simulation waveforms are as follows Fig.16 As shown, it can be observed that when the input voltage is 320V, the output voltage is 48V, which is consistent with the calculation result of the voltage gain expression derived theoretically.

[0099] In order to verify the effectiveness of the converter, a 400W prototype was developed to verify its performance. Fig.21 The driving signal of the boost mode and the experimental waveforms of the two inductor currents are shown in Fig.17 As shown in (a)-(b) in the figure, the voltage and current experimental waveforms of the switch tube are as follows Fig.18 As shown in (a)-(e) in .

[0100] The driving signal of the buck mode and the experimental waveforms of the two inductor currents are as follows: Fig.19 As shown in (a)-(b) in the figure, the voltage and current experimental waveforms of the switch tube are as follows Fig. 20 As shown in (a)-(e) in .

[0101] The simulation results and experimental results of the simulation platform built according to the parameters listed in Table 1 verify the correctness of the theoretical analysis results, and further strongly prove the advantages of high voltage gain and low voltage stress of power devices of the non-isolated high-gain bidirectional DC / DC converter with low voltage stress of this embodiment.

[0102] In this embodiment, the converter and control method proposed based on the input unit, the switched capacitor boost unit and the output parallel unit circuit have the characteristics of high voltage gain and low voltage stress. In the boost mode, the voltage gain is The voltage stress of the power device is where d Boost is the boost duty cycle. In buck mode, the voltage gain The voltage stress of the power device is where d Buck In addition, the converter of this embodiment has the advantages of simple topology, low switch tube voltage stress, high output voltage gain, common ground for input and output terminals, and high working efficiency, and is very suitable for applications with a wide input voltage range, low voltage input, and high voltage gain.

[0103] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A non-isolated high-gain bidirectional DC / DC converter with low voltage stress, characterized in that: It includes an input unit, a switch capacitor boost unit and an output parallel unit, wherein the input unit includes a power supply V in , capacitor C low , a first independent inductor L1, a capacitor C1, a first switch tube S1 and a second switch tube S2; the input unit is connected to a switch capacitor boost unit, the switch capacitor boost unit includes a second independent inductor L2, a third switch tube S3, a fourth switch tube S4, a capacitor C2 and a capacitor C3; the second independent inductor L2 cooperates with the first independent inductor L1 and the capacitor C1 to realize the charging and discharging of the inductor and the capacitor; the switch capacitor boost unit is connected to an output parallel unit, the output parallel unit includes a capacitor C4, a capacitor C5 and a fifth switch tube S5, and the capacitor C4 and the capacitor C5 are connected in series and in parallel at the output end of the converter.

2. The non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 1, characterized in that: In the input unit, the power supply V in With capacitor C low Parallel connection, power supply V in The positive electrode of the capacitor C1 is connected to one end of the first independent inductor L1, the other end of the first independent inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2, and the negative electrode of the capacitor C1 is connected to the power supply V in The cathode of the capacitor C1 is connected to the source of the first switch tube S1; the anode of the capacitor C1 is connected to the drain of the second switch tube S2.

3. The non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 2, characterized in that: In the switch capacitor boost unit, the drain of the second switch tube S2 is connected to one end of the second independent inductor L2, the other end of the second independent inductor L2 is respectively connected to the positive electrode of the capacitor C2, the negative electrode of the capacitor C3 and the source electrode of the third switch tube S3, the negative electrode of the capacitor C2 is connected to the source electrode of the second switch tube S2 of the input unit, the positive electrode of the capacitor C3 is connected to the drain electrode of the fourth switch tube S4. The drain electrode of the third switch tube S3 is connected to the source electrode of the fourth switch tube S4.

4. The non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 3, characterized in that: In the output parallel unit, the source of the fifth switch tube S5 is connected to the positive electrode of the capacitor C3 of the switch capacitor boost unit and the drain of the fourth switch tube S4; the positive electrode of the capacitor C4 is connected to one end of the output side and the drain of the fifth switch tube S5; the negative electrode of the capacitor C4 is connected to the positive electrode of the capacitor C5, the source of the fourth switch tube S4 of the switch capacitor boost unit and the drain of the third switch tube S3; the negative electrode of the capacitor C5 is connected to the other end of the output side.

5. A control method for a non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to any one of claims 1 to 4, characterized in that: In the boost mode, the duty cycle of the first switch tube S1 is controlled to achieve the purpose of boosting; in the buck mode, the duty cycles of the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are controlled to achieve the purpose of bucking, wherein the fourth switch tube S4 is complementarily turned on with the second switch tube S2, the third switch tube S3 and the fifth switch tube S5.

6. The control method of a non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 5, characterized in that: In the boost mode, the first to third working modes are included, and the first to third working modes are executed in sequence, wherein: The first working mode: the first switch tube S1 is controlled to be turned on, the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are all turned off, and the diode D4 of the fourth switch tube S4 is turned on; The second working mode: the first switch tube S1 is controlled to remain turned on, the diode D4 of the fourth switch tube S4 is turned off, and the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are still turned off; The third working mode: the first switch tube S1 and the fourth switch tube S4 are controlled to be turned off, and the diode D2 of the second switch tube S2, the diode D3 of the third switch tube S3 and the diode D5 of the fifth switch tube S5 are turned on.

7. The control method of a non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 6, characterized in that: In the step-down mode, the first and second working modes are included, and the first and second working modes are executed in sequence, wherein: The first working mode: the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are turned on at the same time, and the first switch tube S1 and the fourth switch tube S4 are turned off; The second working mode: the fourth switch tube S4 is controlled to be turned on, the diode D1 of the first switch tube S1 is turned on, and the second switch tube S2, the third switch tube S3 and the fifth switch tube S5 are all turned off.

8. The control method of a non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 6 or 7, characterized in that: In boost mode, the voltage gain of the converter is: When the first switch tube S1 is turned on, the voltage stress of the switch tube is: Where, d Boost is the boost duty cycle.

9. The control method of a non-isolated high-gain bidirectional DC / DC converter with low voltage stress according to claim 6 or 7, characterized in that: In buck mode, the voltage gain of the converter is: The second switch tube S2, the third switch tube S3, and the fifth switch tube S5 are complementarily turned on with the fourth switch tube S4, and the voltage stress of the switch tubes is: Where, d Buck is the step-down duty cycle.

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