Direct-current converter device suitable for DVR (Digital Video Recorder) and circulating current suppression modulation method

Abstract

The invention discloses a direct current converter device suitable for a DVR and a circulating current suppression modulation method, and relates to the technical field of DC-DC direct current conversion, the direct current converter device comprises a first conversion module, a second conversion module and a transformer, and the first conversion module is connected with the second conversion module through the transformer; the first conversion module comprises a first DC power supply, a first inductor, a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a first capacitor, a second capacitor and a third capacitor. The converter can achieve zero current ripples under any conduction duty ratio, any direct current voltage and any transformer turn ratio, the converter has higher working efficiency, the heat dissipation design of a system can be reduced, the power density is further improved, and the converter can be applied to a 50V / 400V buck-boost conversion condition. According to the circulating current suppression modulation method, power circulating current on two sides of the converter can be eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of DC-DC direct current conversion, in particular to a direct current converter device suitable for 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 used to improve transient voltage problems such as voltage sag and voltage swell in power systems. In energy conversion and distributed power systems, the dynamic voltage restorer converts the DC power of the energy storage device into AC, thereby compensating for voltage fluctuations caused by faults or interference to ensure voltage stability of critical loads. The front-stage DC-DC link and the back-stage DC-AC link in the energy storage type dynamic voltage restorer both have the function of bidirectional energy flow. When the energy storage device is insufficient and the grid conditions permit, the device needs to absorb electricity from the grid and charge the energy storage device to ensure that there is enough energy to compensate when a voltage sag occurs; when a voltage sag or other power quality problems occur, the device draws power from the energy storage device, converts DC power into AC and injects it into the grid for voltage compensation. This bidirectional energy flow requirement has prompted the introduction of efficient bidirectional DC-DC converters in energy storage type dynamic voltage restorers.

[0003] Typically, the voltage level in energy storage equipment is about 50V, while the DC-AC inverter link at the rear stage requires a DC voltage of no less than 400V. Therefore, high requirements are placed on the step-up and step-down of the DC-DC converter at the front stage. The traditional dual active bridge converter is one of the most widely used converters, but in the case of voltage mismatch at both ends and a wide voltage conversion ratio, the current stress of the converter is large. In addition, the existing modulation schemes all require the use of circulating current (reactive power) to achieve active power transmission, especially under light load conditions, the proportion of circulating current power increases, causing 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 use of supercapacitors or batteries in the energy storage system, the larger current ripple will reduce the energy conversion efficiency of the entire system, increase thermal stress and loss, induce mechanical stress and vibration, accelerate the aging of components and battery materials, and shorten the service life. The global high-tech industry led by technology continues to make breakthroughs, and various precision equipment has higher requirements for the reliability and stability of power supply. In response to the above-mentioned problems, the bidirectional DC-DC converter with full-range current zero ripple and elimination of circulating power modulation is studied, which is of great significance to the application and further research of energy storage dynamic voltage restorers. 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 and a circulating current suppression modulation method suitable for DVR, which solves the problem of bidirectional dynamic voltage restorer required for energy storage type. DC-DC Technical issues with the converter.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: In a first aspect, the present invention provides a DC converter device suitable for a DVR, comprising a first conversion module, a second conversion module and a transformer, wherein the first conversion module is connected to the second conversion module via 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 second conversion module includes a second direct current 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.

[0008] As a preferred solution of the DC converter device suitable for DVR described in the present invention, wherein: the positive electrode of the first DC source is connected to the positive electrode of the first inductor, the negative electrode of the first DC source is connected to the negative electrode of the first capacitor, the negative electrode of the third capacitor, and the source electrode of the fourth switch tube, the positive electrode of the first capacitor is connected to the negative electrode of the first inductor, the positive electrode of the second capacitor, and the drain electrode of the first switch tube, the negative electrode of the second capacitor is connected to the drain electrode of the second switch tube, the positive electrode of the third capacitor, and the same-name end 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 end 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.

[0009] As a preferred solution of the DC converter device suitable for DVR described in the present invention, wherein: the positive electrode of the second DC source is connected to the positive electrode of the fourth capacitor and the drain of the fifth switch tube, the negative electrode of the second DC source is connected to the negative electrode of the fifth capacitor and the source of the eighth switch tube, the drain of the seventh switch tube is connected to the negative electrode of the fourth capacitor, the positive electrode of the fifth capacitor, and the non-same-name end of the secondary side of the transformer, the source of the sixth switch tube is connected to the source of the seventh switch tube, and the drain of the sixth switch tube is connected to the source of the fifth switch tube, the drain of the eighth switch tube, and the same-name end of the secondary side of the transformer.

[0010] In a second aspect, the present invention provides a circulating current suppression modulation method, comprising 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.

[0011] As a preferred solution of the circulating current suppression modulation method of the present invention, the modulation further 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.

[0012] As a preferred solution of the circulating current suppression modulation method of the present invention, wherein: the transformer turns ratio is 1:n.

[0013] As a preferred solution of the circulating current suppression modulation method of the present invention, the voltages across the first capacitor, the second capacitor, the third capacitor, the fourth capacitor and the fifth capacitor remain constant during the switching cycle.

[0014] As a preferred embodiment of the circulating current suppression modulation method of the present invention, 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).

[0015] 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 higher working efficiency, can reduce the heat dissipation design of the system, and further improve the power density. For the 50V / 400V step-up and step-down conversion situation, the circulating current suppression modulation method of the present invention can eliminate the power circulation existing on both sides of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0017] Figure 1 This is a circuit diagram of a DC converter device suitable for DVR in Example 1.

[0018] Figure 2 It includes the working principle and structure diagram of the energy storage type dynamic voltage restorer.

[0019] Figure 3 This is the main waveform diagram of the circulating current suppression modulation method proposed in the present invention.

[0020] Figure 4 This is the waveform diagram of the main components under the converter circulating current elimination modulation.

[0021] Figure 5 This is one of the operating mode diagrams of the converter under circulating current elimination modulation.

[0022] Figure 6 This is the second working mode diagram of the converter under circulating current elimination modulation.

[0023] Figure 7 This is the third operating mode diagram of the converter under circulating current elimination modulation.

[0024] Figure 8 This is the fourth operating mode diagram of the converter under circulating current elimination modulation.

[0025] Fig. 9 This is the fifth mode diagram of the converter working under circulating current elimination modulation.

[0026] Fig.10 This is the sixth mode diagram of the converter working under circulating current elimination modulation.

[0027] Fig.11 This is one of the experimental waveforms of the converter under circulating current elimination modulation.

[0028] Fig.12 This is the second experimental waveform diagram of the converter under circulating current elimination modulation.

[0029] Fig.13 This is the third experimental waveform diagram of the converter under circulating current elimination modulation.

[0030] Fig.14 This is the fourth experimental waveform diagram of the converter under circulating current elimination modulation.

[0031] Fig.15 This is the overall efficiency curve of the converter from 0.54kW to 2.2kW.

[0032] In the figure: T Transformer, V1 first DC power supply, L1 first inductor, S1 first switch tube, S2 second switch tube, S3 third switch tube, S4 fourth switch tube, C1 first capacitor, C2 second capacitor, C3 third capacitor, V2 second DC power supply, Q1 fifth switch tube, Q2 sixth switch tube, Q3 seventh switch tube, Q4 eighth switch tube, C4 fourth capacitor, C5 fifth capacitor, Lk transformer leakage inductance, Lm excitation inductance. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] Example 1, reference Figure 1 to Figure 10 , which is the first embodiment of the present invention, provides a DC converter device suitable for DVR, including the following contents: A first conversion module, a second conversion module and a transformer T The first conversion module uses a transformer T connected with the second transformation module; The first conversion module includes a first DC 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 positive electrode of the first DC source V1 is connected to the positive electrode of the first inductor L1, the negative electrode of the first DC source 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 terminal 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 terminal 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 second conversion module includes a second DC 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 second DC source V2 is connected to the positive electrode of the fourth capacitor C4 and the drain of the fifth switch tube Q1, the negative electrode of the second DC source V2 is connected to the negative electrode of the fifth capacitor C5 and the source of the eighth switch tube Q4, the drain 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 of the sixth switch tube Q2 is connected to the source of the seventh switch tube Q3, and the drain of the sixth switch tube Q2 is connected to the source of the fifth switch tube Q1, the drain of the eighth switch tube Q4, and the same-name end of the secondary side of the transformer T.

[0037] This embodiment also provides a circulating current suppression modulation method, including: Figure 3 As shown, a switching cycle is divided into , , , , as well as Six working stages are modulated.

[0038] Specifically, transformer T The turns ratio is 1:n.

[0039] 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 during the switching cycle.

[0040] Specifically, , as well as The analysis is as follows: When the first switch tube S1, the second switch tube S2 and the third switch tube S3 on the first DC power source V1 are turned off, the fourth switch tube S4 is turned on, the fifth switch tube Q1 and the eighth switch tube Q4 on the second DC power source V2 are turned off, and the sixth switch tube Q2 and the seventh switch tube Q3 are turned on. At this time: ; ; ; ; in is the potential difference between points a and b, is the voltage of the third capacitor C3, is the voltage of the first DC source V1, For transformer T The voltage on the first conversion module side, For transformer T The voltage on the second conversion module side; The current of the transformer leakage inductance Lk starts to rise from 0, and the relationship between its voltage and current is: ; ; in 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; When the first switch tube S1, the second switch tube S2 and the third switch tube S3 on the first DC power source V1 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 source V2 are turned off, and the fifth switch tube Q1 is turned on. At this time: ; ; in is the voltage of the fourth capacitor C4, is the voltage of the second DC power supply V2; The current of the transformer leakage inductance Lk begins to drop to 0, and the relationship between the current and voltage is: ; ; in For time The current of the transformer leakage inductance Lk; When the first switch tube S1 and the fourth switch tube S4 on the first DC power source V1 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 source V2 are turned off, and the sixth switch tube Q2 and the seventh switch tube Q3 are turned on. At this time: ; ; The relationship between the current and voltage flowing through the transformer leakage inductance Lk is: ; ; in For time The current of the transformer leakage inductance Lk; The first half cycle is obtained The current expression flowing through the transformer leakage inductance Lk is: ; in and are the voltages of the first DC power supply V1 and the second DC power supply V2 respectively.

[0041] Further, , as well as The analysis is as follows: , as well as Compared with the first half cycle Symmetry, analysis content and first half cycle similar; When , the first switch tube S1 on the first DC power source 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 source 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; When , the first switch tube S1 on the first DC power source 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 source 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; 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.

[0042] Furthermore, the modulation 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; If the leakage inductance current changes from 0, then: ; We can further get: ; The maximum value of leakage inductance current is: ; The current flowing into the second DC power supply V2 for: ; Its maximum value and average for; ; ; From this, the transmission power P of the converter can be obtained as: ; when When the converter reaches the maximum transmission power, the maximum power of the converter is obtained by calculation and maximum duty cycle for: ; ; At this time, the maximum current of the transformer leakage inductance for: ; in For time The current of the transformer leakage inductance Lk; according to Figure 4 From the currents i1 and i2 in the circuit, we can see that the current is always positive or 0, which means 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 suppresses the circulating power by limiting the direction of current flow, greatly improving the working efficiency of the converter.

[0043] Furthermore, the modulation analysis also includes performing a zero current ripple analysis on the first inductor L1. It is known that the voltage across the first inductor L1 for ; in is the current of the first inductor L1, is the inductance of the first inductor L1; During the entire switching cycle, the first inductor L1 is clamped by the first DC power supply V1 and the first capacitor C1. In a steady state, the voltage of the first capacitor C1 is equal to that of the first DC power supply V1, that is: ; in is the voltage of the first capacitor C1; When the voltage of the first inductor L1 is 0, the current flowing through the first inductor L1 is Always a constant value.

[0044] 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, and further improve the power density. For the 50V / 400V step-up and step-down conversion situation, the circulating current suppression modulation method of the present invention can eliminate the power circulation on both sides of the converter.

[0045] Example 2, reference Figure 11~Figure 15 And Table 1 is the second embodiment of the present invention. In order 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 suitable for DVR are provided.

[0046] Table 1: Parameter selection of each component in the converter ; The converter operating power is set to 1.5kW. From the converter parameters, we can know that the converter boost ratio is V2 / V1=400 / 50=8.

[0047] Under the improved synchronous PWM modulation method, D1=0.3, D2=0.1, the actual power of the converter is 1.528kW, which is slightly different 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 flowing through the first inductor L1 are as follows: Fig.11 , 12 As shown, it can be seen that the current flowing through the inductor is almost constant, and its variation range is only 0.7A. The current ripple rate is only 2.29%, which completely achieves zero ripple. The voltage across the inductor is about 0V, and it fluctuates only 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 variation 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 shown in Fig.13 , 14 As shown, the current on the V1 side always flows out or is zero, the current on the V2 side always flows in or is zero, there is no reverse current, and the circulating power is completely eliminated.

[0048] Fig.15The figure shows the overall efficiency curve of the proposed converter when the output power is 0.5kW~2.2kW based on the improved synchronous PWM modulation method. In the entire 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. After comparison, the high efficiency performance of the proposed converter and the modulation method is reflected. When the output power Po=540W, the efficiency of the converter is 99.54%, and when the output power Po is 2kW, the efficiency of the converter is 99.21%, while the efficiency of the traditional DAB converter is only 78.96%.

[0049] In summary, the theoretical analysis and experimental results consistently verify the correctness of the circuit and realize the functions of zero current ripple and high efficiency, eliminating the circulating power on both sides of the converter. The high efficiency characteristics of the proposed converter and the proposed modulation method enable the patented bidirectional DC-DC converter of the present invention to be used in situations where there are high requirements for actual efficiency, and therefore can be applied to the front-stage DC-DC link of the energy storage type dynamic voltage restorer.

[0050] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A DC converter device suitable for DVR, characterized in that: include, 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 DC 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).

2. The DC converter device suitable for DVR according to claim 1, characterized in that: The positive electrode of the first direct current source (V1) is connected to the positive electrode of the first inductor (L1); the negative electrode of the first direct current source (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).

3. The DC converter device suitable for DVR as claimed in claim 2, characterized in that: The positive electrode of the second DC source (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 source (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); 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).

4. A circulating current suppression modulation method, based on a DC converter device suitable for a DVR as claimed in any one of claims 1 to 3, 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.

5. The circulating current suppression modulation method according to claim 4, 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.

6. The circulating current suppression modulation method according to claim 5, characterized in that: The transformer ( T )The turns ratio is 1:n.

7. The circulating current suppression modulation method according to claim 6, 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.

8. The circulating current suppression modulation method according to claim 7, 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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