DC Converter Device Applicable to DVR and Circulating Current Suppression Modulation Method

Abstract

The present invention discloses a DC converter device applicable to a DVR and a circulating current suppression modulation method, which relates to the technical field of DC-DC DC conversion. The device includes a first conversion module, a second conversion module and a transformer. The first conversion module is connected to the second conversion module through the transformer. The first conversion module includes a first DC power supply, a first inductor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first capacitor, a second capacitor and a third capacitor. The converter of the present invention can achieve zero current ripple under any conduction duty cycle, any DC voltage and any transformer turns ratio. The converter has higher working efficiency, can reduce the heat dissipation design of the system, further improve the power density, and for the step-up and step-down conversion of 50V / 400V, the circulating current suppression modulation method of the present invention can eliminate the power circulating current existing on both sides of the converter.

Description

Technical Field

[0001] The present invention relates to the technical field of DC-DC DC conversion, and particularly to a DC converter device applicable to a DVR and a circulating current suppression modulation method. Background Art

[0002] The energy storage type dynamic voltage restorer is a widely used power quality control device for improving transient voltage problems such as voltage sags and voltage swells in a power system. In an energy conversion and distributed power supply system, the dynamic voltage restorer converts the DC electrical energy of an energy storage device into AC, and then compensates for voltage fluctuations caused by faults or disturbances to ensure the voltage stability of critical loads. In the energy storage type dynamic voltage restorer, both the front-stage DC-DC link and the rear-stage DC-AC link have the function of bidirectional energy flow. When the energy storage device has insufficient power and the grid conditions permit, the device needs to absorb electrical energy from the grid and charge the energy storage device to ensure that there is enough energy for compensation when a voltage sag event occurs; when a voltage sag or other power quality problems occur, the device draws power from the energy storage device, converts the DC power into AC and injects it into the grid for voltage compensation. This bidirectional energy flow requirement promotes the introduction of an efficient bidirectional DC-DC converter in the energy storage type dynamic voltage restorer.

[0003] Generally, the voltage level in the energy storage device is about 50V, and the rear-stage DC-AC inverter link requires a DC voltage of not less than 400V. Therefore, there are high requirements for the step-up and step-down of the front-stage DC-DC converter. The traditional dual-active-bridge converter is one of the most widely used converters. However, in the case of mismatched voltages at both ends and a wide voltage conversion ratio, the current stress of the converter is large, and since existing modulation schemes all need to use circulating current (reactive power) to achieve active power transmission, especially under light load conditions, the proportion of circulating current power increases, resulting in a sharp drop in efficiency.

[0004] In addition, the high voltage stress generated by the DC bus voltage also limits the improvement of its efficiency and reliability. At the same time, due to the supercapacitor bank or battery bank in the energy storage system, a large current ripple will reduce the energy conversion efficiency of the entire system, increase thermal stress and losses, cause mechanical stress and vibration, accelerate the aging of components and cell materials, and shorten the service life. The global high-tech industry led by technology continues to make breakthrough progress, and various precision devices have higher requirements for the reliability and stability of power supply. In view of the above problems, researching a bidirectional DC-DC converter with a full-range zero current ripple and a modulation method for eliminating circulating current power is of great significance for the application and further research of the energy storage type dynamic voltage restorer. Summary of the Invention

[0005] In view of the above existing problems, the present invention is proposed.

[0006] Therefore, the present invention provides a DC converter device applicable to a DVR and a circulating current suppression modulation method, which solve the technical problem of the bidirectional DC-DC converter required for an energy storage type dynamic voltage restorer.

[0007] To solve the above technical problems, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a DC converter device applicable to a DVR, which includes a first conversion module, a second conversion module, and a transformer, and the first conversion module is connected to the second conversion module through the transformer;

[0009] The first conversion module includes a first DC power supply, a first inductor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first capacitor, a second capacitor, and a third capacitor;

[0010] The second conversion module includes a second DC power supply, a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube, a fourth capacitor, and a fifth capacitor.

[0011] As a preferred solution of the DC converter device applicable to a DVR according to the present invention, wherein: the positive pole of the first DC source is connected to the positive pole of the first inductor, the negative pole of the first DC source is connected to the negative pole of the first capacitor, the negative pole of the third capacitor, and the source electrode of the fourth switch tube, the positive pole of the first capacitor is connected to the negative pole of the first inductor, the positive pole of the second capacitor, and the drain electrode of the first switch tube, the negative pole of the second capacitor is connected to the drain electrode of the second switch tube, the positive pole of the third capacitor, and the same-name terminal of the primary side of the transformer, the drain electrode of the third switch tube is connected to the source electrode of the first switch tube, the drain electrode of the fourth switch tube, and the non-same-name terminal of the primary side of the transformer, and the source electrode of the third switch tube is connected to the source electrode of the second switch tube.

[0012] As a preferred solution of the DC converter device applicable to a DVR according to the present invention, wherein: the positive pole of the second DC source is connected to the positive pole of the fourth capacitor and the drain electrode of the fifth switch tube, the negative pole of the second DC source is connected to the negative pole of the fifth capacitor and the source electrode of the eighth switch tube, the drain electrode of the seventh switch tube is connected to the negative pole of the fourth capacitor, the positive pole of the fifth capacitor, and the non-same-name terminal of the secondary side of the transformer, the source electrode of the sixth switch tube is connected to the source electrode of the seventh switch tube, and the drain electrode of the sixth switch tube is connected to the source electrode of the fifth switch tube, the drain electrode of the eighth switch tube, and the same-name terminal of the secondary side of the transformer.

[0013] In a second aspect, the present invention provides a circulating current suppression modulation method, which includes dividing a switching period into , , , , and It is modulated in six working stages;

[0014] During the working stage, turn off the first switch tube (S1), the second switch tube (S2), and the third switch tube (S3) on the side of the first DC power supply (V1). At this time, the fourth switch tube (S4) is turned on, the fifth switch tube (Q1) and the eighth switch tube (Q4) on the side of the second DC power supply (V2) are turned off, and the sixth switch tube (Q2) and the seventh switch tube (Q3) are turned on;

[0015] During the working stage, turn off the first switch tube (S1), the second switch tube (S2), and the third switch tube (S3) on the side of the first DC power supply (V1), turn on the fourth switch tube (S4), turn off the sixth switch tube (Q2), the seventh switch tube (Q3), and the eighth switch tube (Q4) on the side of the second DC power supply (V2), and turn on the fifth switch tube (Q1);

[0016] During the working stage, turn off the first switch tube (S1) and the fourth switch tube (S4) on the side of the first DC power supply (V1), turn on the second switch tube (S2) and the third switch tube (S3), turn off the fifth switch tube (Q1) and the eighth switch tube (Q4) on the side of the second DC power supply (V2), and turn on the sixth switch tube (Q2) and the seventh switch tube (Q3);

[0017] During the working stage, turn on the first switch tube (S1) on the side of the first DC power supply (V1), turn off the second switch tube (S2), the third switch tube (S3), and the fourth switch tube (S4), turn on the sixth switch tube (Q2) and the seventh switch tube (Q3) on the side of the second DC power supply (V2), turn off the fifth switch tube (Q1) and the eighth switch tube (Q4), and the current of the transformer leakage inductance (Lk) starts to increase in the reverse direction from 0;

[0018] During the working stage, turn on the first switch tube (S1) on the side of the first DC power supply (V1), turn off the second switch tube (S2), the third switch tube (S3), and the fourth switch tube (S4), turn on the eighth switch tube (Q4) on the side of the second DC power supply (V2), turn off the fifth switch tube (Q1), the sixth switch tube (Q2), and the seventh switch tube (Q3), and the transformer leakage inductance current starts to decrease to 0;

[0019] During During the working stage, turn on the second switch tube (S2) and the third switch tube (S3) on the side of the first DC power supply (V1), turn off the first switch tube (S1) and the fourth switch tube (S4), turn on the sixth switch tube (Q2) and the seventh switch tube (Q3) on the side of the second DC power supply (V2), turn off the fifth switch tube (Q1) and the eighth switch tube (Q4), and the leakage inductance current of the transformer is 0.

[0020] As a preferred embodiment of the circulating current suppression modulation method described in the present invention, wherein: the modulation further includes defining the working stage time as:

[0021] ;

[0022] ;

[0023] ;

[0024] where is the operating frequency of the switch tubes in the circuit, is the time step, and are the duty cycles.

[0025] As a preferred embodiment of the circulating current suppression modulation method described in the present invention, wherein: the turns ratio of the transformer is 1:n.

[0026] As a preferred embodiment of the circulating current suppression modulation method described in the present invention, wherein: the voltages across the first capacitor, the second capacitor, the third capacitor, the fourth capacitor, and the fifth capacitor remain constant within the switching period.

[0027] As a preferred embodiment of the circulating current suppression modulation method described in the present invention, wherein: when , the converter reaches the maximum transmission power, and by calculation, the maximum power of the converter and the maximum duty cycle are:

[0028] ;

[0029] ;

[0030] where is the voltage of the first DC source V1, is the voltage of the second DC power supply V2, is the operating frequency of the switch tubes in the circuit, is the leakage inductance of the transformer leakage inductance (Lk).

[0031] The beneficial effects of the present invention are as follows: The converter of the present invention can achieve zero current ripple under any conduction duty cycle, any DC voltage, and any transformer turns ratio. The converter has a higher working efficiency, can reduce the heat dissipation design of the system, further improve the power density, and for the step-up / step-down conversion of 50V / 400V, the circulating current suppression modulation method of the present invention can eliminate the power circulating current existing on both sides of the converter. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 It is the circuit diagram of the DC converter device applicable to DVR in Embodiment 1.

[0034] Figure 2 It is the working principle and structure diagram of the energy storage type dynamic voltage restorer.

[0035] Figure 3 It is the main waveform diagram of the circulating current suppression modulation method proposed by the present invention.

[0036] Figure 4 It is the main component waveform diagram under the circulating current elimination modulation of the converter.

[0037] Figure 5 It is one of the working mode diagrams of the converter under the circulating current elimination modulation.

[0038] Figure 6 It is the second working mode diagram of the converter under the circulating current elimination modulation.

[0039] Figure 7 It is the third working mode diagram of the converter under the circulating current elimination modulation.

[0040] Figure 8 It is the fourth working mode diagram of the converter under the circulating current elimination modulation.

[0041] Figure 9 It is the fifth working mode diagram of the converter under the circulating current elimination modulation.

[0042] Figure 10 It is the sixth working mode diagram of the converter under the circulating current elimination modulation.

[0043] Figure 11 It is the first experimental waveform diagram of the converter under the circulating current elimination modulation.

[0044] Figure 12It is the second experimental waveform diagram of the converter under circulating-current elimination modulation.

[0045] Figure 13 It is the third experimental waveform diagram of the converter under circulating-current elimination modulation.

[0046] Figure 14 It is the fourth experimental waveform diagram of the converter under circulating-current elimination modulation.

[0047] Figure 15 It is the overall efficiency curve of the converter from 0.54kW to 2.2kW.

[0048] In the figure: T Transformer, V1 is the first DC power supply, L1 is the first inductor, S1 is the first switching tube, S2 is the second switching tube, S3 is the third switching tube, S4 is the fourth switching tube, C1 is the first capacitor, C2 is the second capacitor, C3 is the third capacitor, V2 is the second DC power supply, Q1 is the fifth switching tube, Q2 is the sixth switching tube, Q3 is the seventh switching tube, Q4 is the eighth switching tube, C4 is the fourth capacitor, C5 is the fifth capacitor, Lk is the leakage inductance of the transformer, and Lm is the magnetizing inductance. Specific implementation manners

[0049] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific implementation manners of the present invention will be described in detail below with reference to the accompanying drawings of the specification.

[0050] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0051] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0052] Embodiment 1, referring to Figures 1 to 10 , which is the first embodiment of the present invention. This embodiment provides a DC converter device applicable to a DVR, including the following:

[0053] The first conversion module, the second conversion module, and a transformer T , and the first conversion module is connected to the second conversion module through a transformer T ;

[0054] The first conversion module includes a first DC power supply V1, a first inductor L1, a first switching transistor S1, a second switching transistor S2, a third switching transistor S3, a fourth switching transistor S4, a first capacitor C1, a second capacitor C2, and a third capacitor C3;

[0055] The positive pole of the first DC power supply V1 is connected to the positive pole of the first inductor L1. The negative pole of the first DC power supply V1 is connected to the negative pole of the first capacitor C1, the negative pole of the third capacitor C3, and the source electrode of the fourth switching transistor S4. The positive pole of the first capacitor C1 is connected to the negative pole of the first inductor L1, the positive pole of the second capacitor C2, and the drain electrode of the first switching transistor S1. The negative pole of the second capacitor C2 is connected to the drain electrode of the second switching transistor S2, the positive pole of the third capacitor C3, and the same-named terminal of the primary side of the transformer T. The drain electrode of the third switching transistor S3 is connected to the source electrode of the first switching transistor S1, the drain electrode of the fourth switching transistor S4, and the non-same-named terminal of the primary side of the transformer T. The source electrode of the third switching transistor S3 is connected to the source electrode of the second switching transistor S2;

[0056] The second conversion module includes a second DC power supply V2, a fifth switching transistor Q1, a sixth switching transistor Q2, a seventh switching transistor Q3, an eighth switching transistor Q4, a fourth capacitor C4, and a fifth capacitor C5;

[0057] The positive pole of the second DC power supply V2 is connected to the positive pole of the fourth capacitor C4 and the drain electrode of the fifth switching transistor Q1. The negative pole of the second DC power supply V2 is connected to the negative pole of the fifth capacitor C5 and the source electrode of the eighth switching transistor Q4. The drain electrode of the seventh switching transistor Q3 is connected to the negative pole of the fourth capacitor C4, the positive pole of the fifth capacitor C5, and the non-same-named terminal of the secondary side of the transformer T. The source electrode of the sixth switching transistor Q2 is connected to the source electrode of the seventh switching transistor Q3. The drain electrode of the sixth switching transistor Q2 is connected to the source electrode of the fifth switching transistor Q1, the drain electrode of the eighth switching transistor Q4, and the same-named terminal of the secondary side of the transformer T.

[0058] This embodiment also provides a circulating current suppression modulation method, including: as Figure 3 shown, a switching cycle is divided into , , , , , and six working stages for modulation.

[0059] Specifically, the turns ratio of the transformer T is 1:n.

[0060] It should also be noted that the voltages across the first capacitor C1, the second capacitor C2, the third capacitor C3, the fourth capacitor C4, and the fifth capacitor C5 remain constant within the switching cycle.

[0061] Specifically, , and The analysis is as follows:

[0062] When, on the first DC power supply V1 side, the first switch tube S1, the second switch tube S2, and the third switch tube S3 are turned off, and the fourth switch tube S4 is turned on, and on the second DC power supply V2 side, the fifth switch tube Q1 and the eighth switch tube Q4 are turned off, and the sixth switch tube Q2 and the seventh switch tube Q3 are turned on, at this time:

[0063] ;

[0064] ;

[0065] ;

[0066] ;

[0067] where is the potential difference between points a and b, is the voltage of the third capacitor C3, is the voltage of the first DC power supply V1, is the transformer T voltage on the first conversion module side, is the transformer T voltage on the second conversion module side;

[0068] The current of the transformer leakage inductance Lk starts to rise from 0, and the relationship between its voltage and current is:

[0069] ;

[0070] ;

[0071] where is the voltage of the transformer leakage inductance Lk, is the current of the transformer leakage inductance Lk at time t, is the leakage inductance of the transformer leakage inductance Lk;

[0072] When, on the first DC power supply V1 side, the first switch tube S1, the second switch tube S2, and the third switch tube S3 are turned off, and the fourth switch tube S4 is turned on, and on the second DC power supply V2 side, the sixth switch tube Q2, the seventh switch tube Q3, and the eighth switch tube Q4 are turned off, and the fifth switch tube Q1 is turned on, at this time:

[0073] ;

[0074] ;

[0075] where is the voltage of the fourth capacitor C4, is the voltage of the second DC power supply V2;

[0076] The current of the transformer leakage inductance Lk starts to drop to 0, and its current-voltage relationship is:

[0077] ;

[0078] ;

[0079] where is time and the current of the transformer leakage inductance Lk;

[0080] When, the first switch tube S1 and the fourth switch tube S4 on the first DC power supply V1 side are turned off, the second switch tube S2 and the third switch tube S3 are turned on, the fifth switch tube Q1 and the eighth switch tube Q4 on the second DC power supply V2 side are turned off, and the sixth switch tube Q2 and the seventh switch tube Q3 are turned on. At this time:

[0081] ;

[0082] ;

[0083] The relationship between the current and voltage flowing through the transformer leakage inductance Lk is:

[0084] ;

[0085] ;

[0086] where is time and the current of the transformer leakage inductance Lk;

[0087] Combining to obtain the current expression of the first half cycle flowing through the transformer leakage inductance Lk is:

[0088] ;

[0089] where and are the voltages of the first DC power supply V1 and the second DC power supply V2 respectively.

[0090] Furthermore, 、 and are analyzed as follows:

[0091] 、 and in the first half cycle Symmetry, the analysis content is similar to the first half cycle Similar;

[0092] When, the first switch tube S1 on the first DC power supply V1 side is turned on, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are turned off, the sixth switch tube Q2 and the seventh switch tube Q3 on the second DC power supply V2 side are turned on, the fifth switch tube Q1 and the eighth switch tube Q4 are turned off, and the current of the transformer leakage inductance Lk starts to increase in the reverse direction from 0;

[0093] When, the first switch tube S1 on the first DC power supply V1 side is turned on, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are turned off, the eighth switch tube Q4 on the second DC power supply V2 side is turned on, the fifth switch tube Q1, the sixth switch tube Q2 and the seventh switch tube Q3 are turned off, and the transformer leakage inductance current starts to decrease to 0;

[0094] When, the second switch tube S2 and the third switch tube S3 on the first DC power supply V1 side are turned on, the first switch tube S1 and the fourth switch tube S4 are turned off, the sixth switch tube Q2 and the seventh switch tube Q3 on the second DC power supply V2 side are turned on, the fifth switch tube Q1 and the eighth switch tube Q4 are turned off, and the transformer leakage inductance current is 0.

[0095] Furthermore, the modulation includes defining the working stage time as:

[0096] ;

[0097] ;

[0098] ;

[0099] Wherein is the working frequency of the switch tube in the circuit, is the time step, and are the duty cycles;

[0100] If the leakage inductance current starts to change from 0, then it satisfies:

[0101] ;

[0102] Furthermore, it can be obtained that:

[0103] ;

[0104] The maximum value of the leakage inductance current is:

[0105] ;

[0106] The current flowing into the second DC power supply V2 is:

[0107] ;

[0108] Its maximum value and average value are;

[0109] ;

[0110] ;

[0111] Thus, the transmission power P of the converter can be obtained as:

[0112] ;

[0113] When , the converter reaches the maximum transmission power. By calculation, the maximum power and the maximum duty cycle are:

[0114] ;

[0115] ;

[0116] At this time, the maximum value of the current in the leakage inductance of the transformer is:

[0117] ;

[0118] where is the current in the leakage inductance Lk of the transformer at time ;

[0119] According to Figure 4 the currents i1 and i2, it can be seen that the current is always positive or 0, which indicates that the current on the V1 side always flows out or is zero, and the current on the V2 side always flows in or is zero. The improved synchronous PWM modulation completely realizes the suppression of the circulating power by restricting the current flow direction, greatly improving the working efficiency of the converter.

[0120] Furthermore, the modulation analysis also includes zero-current ripple analysis of the first inductor L1. Given that the voltage across the first inductor L1 is

[0121] ;

[0122] where is the current in the first inductor L1, is the inductance of the first inductor L1;

[0123] During the entire switching cycle, the first inductor L1 is clamped by the first DC power supply V1 and the first capacitor C1. In the steady state, the voltage of the first capacitor C1 is equal to that of the first DC power supply V1, that is:

[0124] ;

[0125] where is the voltage of the first capacitor C1;

[0126] When the voltage of the first inductor L1 is 0, the current flowing through the first inductor L1 is always a constant value.

[0127] In summary, the converter of the present invention can achieve zero current ripple under any conduction duty cycle, any DC voltage, and any transformer turns ratio. The converter has higher working efficiency, can reduce the heat dissipation design of the system, realize further improvement of power density, and for the step-up / step-down conversion of 50V / 400V, the circulating current suppression modulation method of the present invention can eliminate the power circulating current existing on both sides of the converter.

[0128] Example 2, referring to Figures 11 to 15 and Table 1, is the second embodiment of the present invention. To further verify the technical solution of the present invention, experimental simulation data of a DC converter device and a circulating current suppression modulation method applicable to a DVR are given.

[0129] Table 1: Parameter selection of each component in the converter

[0130] ;

[0131] It is set that the working power of the converter is 1.5kW. From the converter parameters, the boost ratio of the converter is V2 / V1 = 400 / 50 = 8.

[0132] Under the improved synchronous PWM modulation method, at this time D1 = 0.3, D2 = 0.1, and the actual power of the converter is 1.528kW at this time, which has a slight difference from the theoretical value of 1.5kW, including the part caused by component losses, which is within a reasonable range. The current and voltage waveforms of the first inductor L1 are as Figure 11 、 12 shown. It can be seen that the current flowing through the inductor is almost a constant value, and its change range is only 0.7A. The current ripple rate is only 2.29%, fully realizing zero ripple; the voltage across the inductor is about 0V, only fluctuating within the range of 0.2V, which is consistent with the theory; increasing the inductance value of the inductor L1 and the capacitance value of the capacitor C1 will further reduce the change range of the inductor voltage and current. The current i1 flowing out of the DC source V1 and the current i2 flowing into the DC source V2 are as Figure 13 、 14As shown, the current on the V1 side always flows out or is zero, and the current on the V2 side always flows in or is zero. There is no reverse current, completely eliminating the circulating current power.

[0133] Figure 15 As shown, it is the overall efficiency curve of the proposed converter when the output power is 0.5 kW to 2.2 kW based on the improved synchronous PWM modulation method. Throughout the power range, the converter efficiency is greater than 99%. At the same time, the efficiency curve of the traditional DAB converter under the single-phase-shift modulation method is given. Through comparison, it reflects the high-efficiency performance of the proposed converter and modulation method. When the output power Po = 540 W, the efficiency of the converter is 99.54%. When the output power Po is 2 kW, the efficiency of the converter is 99.21%, while the efficiency of the traditional DAB converter is only 78.96%.

[0134] In summary, the theoretical analysis and experimental results consistently verify the correctness of the circuit and achieve the functions of zero current ripple and high efficiency, eliminating the circulating current power on both sides of the converter. The high-efficiency characteristics of the proposed converter and the proposed modulation method enable this invention patent bidirectional DC-DC converter to be used in occasions with high requirements for actual efficiency. Therefore, it can be applied to the pre-stage DC-DC link of the energy storage type dynamic voltage restorer.

[0135] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A circulating current suppression modulation method, characterized in that: This involves dividing a switching cycle into , , , , as well as Six working stages for modulation; exist During the working stage, the first switch tube (S1), the second switch tube (S2) and the third switch tube (S3) on the first DC power supply (V1) side are turned off, and the fourth switch tube (S4) is turned on, the fifth switch tube (Q1) and the eighth switch tube (Q4) on the second DC power supply (V2) side are turned off, and the sixth switch tube (Q2) and the seventh switch tube (Q3) are turned on; exist During the working stage, the first switch tube (S1), the second switch tube (S2) and the third switch tube (S3) on the first DC power supply (V1) side are turned off, the fourth switch tube (S4) is turned on, the sixth switch tube (Q2), the seventh switch tube (Q3) and the eighth switch tube (Q4) on the second DC power supply (V2) side are turned off, and the fifth switch tube (Q1) is turned on; exist During the working stage, the first switch tube (S1) and the fourth switch tube (S4) on the first DC power supply (V1) side are turned off, the second switch tube (S2) and the third switch tube (S3) are turned on, the fifth switch tube (Q1) and the eighth switch tube (Q4) on the second DC power supply (V2) side are turned off, and the sixth switch tube (Q2) and the seventh switch tube (Q3) are turned on; exist During the working stage, the first switch tube (S1) on the first DC power supply (V1) side is turned on, the second switch tube (S2), the third switch tube (S3) and the fourth switch tube (S4) are turned off, the sixth switch tube (Q2) and the seventh switch tube (Q3) on the second DC power supply (V2) side are turned on, the fifth switch tube (Q1) and the eighth switch tube (Q4) are turned off, and the current of the transformer leakage inductance (Lk) increases in the reverse direction from 0; exist During the working stage, the first switch tube (S1) on the first DC power supply (V1) side is turned on, the second switch tube (S2), the third switch tube (S3) and the fourth switch tube (S4) are turned off, the eighth switch tube (Q4) on the second DC power supply (V2) side is turned on, the fifth switch tube (Q1), the sixth switch tube (Q2) and the seventh switch tube (Q3) are turned off, and the transformer leakage inductance current begins to decrease to 0; exist During the working stage, the second switch tube (S2) and the third switch tube (S3) on the first DC power supply (V1) side are turned on, the first switch tube (S1) and the fourth switch tube (S4) are turned off, the sixth switch tube (Q2) and the seventh switch tube (Q3) on the second DC power supply (V2) side are turned on, the fifth switch tube (Q1) and the eighth switch tube (Q4) are turned off, and the transformer leakage inductance current is 0; A DC converter device suitable for DVR, comprising a first conversion module, a second conversion module and a transformer ( T ), the first conversion module is through a transformer ( T ) is connected to the second transformation module; The first conversion module includes a first direct current power supply (V1), a first inductor (L1), a first switch tube (S1), a second switch tube (S2), a third switch tube (S3), a fourth switch tube (S4), a first capacitor (C1), a second capacitor (C2) and a third capacitor (C3); The second conversion module includes a second direct current power supply (V2), a fifth switch tube (Q1), a sixth switch tube (Q2), a seventh switch tube (Q3), an eighth switch tube (Q4), a fourth capacitor (C4) and a fifth capacitor (C5); The positive electrode of the first DC power supply (V1) is connected to the positive electrode of the first inductor (L1); the negative electrode of the first DC power supply (V1) is connected to the negative electrode of the first capacitor (C1), the negative electrode of the third capacitor (C3), and the source electrode of the fourth switch tube (S4); the positive electrode of the first capacitor (C1) is connected to the negative electrode of the first inductor (L1), the positive electrode of the second capacitor (C2), and the drain electrode of the first switch tube (S1); the negative electrode of the second capacitor (C2) is connected to the drain electrode of the second switch tube (S2), the positive electrode of the third capacitor (C3), and the same-name end of the primary side of the transformer (T); the drain electrode of the third switch tube (S3) is connected to the source electrode of the first switch tube (S1), the drain electrode of the fourth switch tube (S4), and the non-same-name end of the primary side of the transformer (T); and the source electrode of the third switch tube (S3) is connected to the source electrode of the second switch tube (S2); The positive electrode of the second DC power supply (V2) is connected to the positive electrode of the fourth capacitor (C4) and the drain electrode of the fifth switch tube (Q1); the negative electrode of the second DC power supply (V2) is connected to the negative electrode of the fifth capacitor (C5) and the source electrode of the eighth switch tube (Q4); the drain electrode of the seventh switch tube (Q3) is connected to the negative electrode of the fourth capacitor (C4), the positive electrode of the fifth capacitor (C5) and the non-same-name end of the secondary side of the transformer (T); the source electrode of the sixth switch tube (Q2) is connected to the source electrode of the seventh switch tube (Q3); and the drain electrode of the sixth switch tube (Q2) is connected to the source electrode of the fifth switch tube (Q1), the drain electrode of the eighth switch tube (Q4) and the same-name end of the secondary side of the transformer (T).

2. The circulating current suppression modulation method according to claim 1, characterized in that: The modulation also includes defining the working phase time as: in is the operating frequency of the switch tube in the circuit, is the time step, and is the duty cycle.

3. The circulating current suppression modulation method according to claim 2, characterized in that: The transformer ( T )The turns ratio is 1:n.

4. The circulating current suppression modulation method according to claim 3, characterized in that: The voltages across the first capacitor (C1), the second capacitor (C2), the third capacitor (C3), the fourth capacitor (C4) and the fifth capacitor (C5) remain constant during a switching cycle.

5. The circulating current suppression modulation method according to claim 4, characterized in that: when When the converter reaches the maximum transmission power, the maximum power of the converter is obtained by calculation and maximum duty cycle for: in is the voltage of the first DC source V1, is the voltage of the second DC power supply V2, is the operating frequency of the switch tube in the circuit, is the leakage inductance of the transformer (Lk).

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