Method for reconstructing transformer equivalent turn ratio through dual transformer and improved bridge circuit for wide voltage gain DAB converter

Abstract

The invention relates to a method for reconstructing the equivalent turn ratio of transformers through double transformers and an improved bridge circuit for a wide voltage gain DAB converter. According to the method, the two transformers T1 and T2, an inductor L, a blocking capacitor Cdc, primary and secondary direct current voltages V1 and V2, and primary and secondary filter capacitors C1 and C2 are included; primary side switch tubes S1-S4 form a full-bridge circuit and are connected in parallel with C1 at two ends of V1; five or four secondary side switch tubes form an improved bridge circuit and are connected in parallel with C2 at two ends of V2; according to the scheme, bridge arm midpoints of S1 and S2, an inductor L, primary windings of T1 and T2 and bridge arm midpoints of S3 and S4 are sequentially connected to the primary side of the converter; the improved bridge circuit and the secondary winding of the double transformers are connected at the secondary side according to the characteristics of different schemes, and a blocking capacitor Cdc is added to prevent the saturation of the magnetic cores of the transformers. According to the method, the number of switching tubes is small, the equivalent turn ratios of more than three transformers can be reconstructed without an auxiliary switch, and the efficiency of the dual-active bridge converter under the wide voltage gain can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and in particular to a method for reconstructing the equivalent turns ratio of a transformer for a wide voltage gain DAB converter by using a double transformer and an improved bridge circuit. Background Art

[0002] The dual active bridge (DAB) DC-DC converter is the most popular high-power isolated bidirectional DC-DC converter at this stage. It is widely used in energy storage systems, electric transportation, renewable energy and other occasions. The circuit topology of the DAB converter is as follows: Figure 1 However, the inductor RMS current of a DAB converter under wide voltage gain conditions increases significantly, and some switches fail to achieve soft switching under medium and light load conditions. This increases conduction loss, switching loss, and failure rate, and reduces the converter's transmission efficiency. These issues with the DAB converter under wide voltage gain conditions restrict its application in scenarios with wide voltage range requirements.

[0003] By reconstructing the transformer turns ratio, the voltage gain of the DAB converter can be reconstructed under different secondary voltage conditions, thereby improving the performance of the converter under wide voltage gain. Figure 2-4 The solution of using two full-bridge series-parallel switching on the secondary side is shown in Figure 2 As shown in the figure. By controlling the auxiliary switches R1, R2 and R3, the two full bridges on the secondary side are connected in parallel under low voltage conditions and in series under high voltage conditions. The converter obtains two different transformer turns ratios, which can achieve higher efficiency under wide voltage conditions. The scheme of reconstructing the transformer turns ratio using a multi-winding transformer and a three-bridge circuit is shown in the figure. Figure 3 The solution consists of a 4-winding transformer, 3 auxiliary switches R 1.2 , R 2.3 and R 1.3 , and three-arm bridge circuit, by controlling R 1.2 , R 2.3 and R 1.3 The opening and closing of the transformer can realize the conversion between the six working modes of the transformer turns ratio. The solution of reconstructing the transformer turns ratio using a dual transformer and a three-bridge circuit is as follows: Figure 4 As shown in Figure 1. This solution consists of two transformers and a three-arm bridge circuit without an auxiliary switch. By controlling the drive logic of the secondary-side three-arm bridge circuit, it can achieve conversion between three transformer turn ratio operating modes. The problems with the above solution are: (1) Operation over a wide voltage range requires an auxiliary switch, resulting in poor dynamic performance of the converter. (2) The bridge circuit used has a large number of active switches, which is expensive. Summary of the Invention

[0004] The object of the present invention is to provide a method for reconstructing the transformer equivalent turns ratio of a wide voltage gain DAB converter through a dual transformer and an improved bridge circuit. The method has a smaller number of active switching tubes and can reconstruct different transformer equivalent turns ratios without the need for auxiliary switches.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for reconstructing the equivalent turns ratio of the transformer using dual transformers and an improved bridge circuit for a wide voltage gain DAB converter. By controlling the drive signals of different forms of the improved bridge circuit on the secondary side, different voltages are formed on the primary side of the dual transformer, ensuring that the voltages on both sides of the inductor of the DAB converter remain closely matched under wide voltage gain conditions, thereby reconstructing different transformer equivalent turns ratios.

[0006] In the first implementation of this method, the transformer equivalent turns ratio is reconstructed through a dual transformer and H5 bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, five active switches Q1 to Q5 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a full-bridge circuit, the full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3, Q4 and Q5 are connected in parallel to form an H5 bridge circuit, the H5 bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the potential point between S1 and S2 Lead wire a is connected to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary of transformer T1. The other end of the primary of transformer T1 is connected to one end of the primary of transformer T2. The other end of the primary of transformer T2 is connected to the potential point c between S1 and S2. Lead wire d is connected to one end of the secondary of transformer T1. The other end of the secondary of transformer T1 is connected to one end of the secondary of transformer T2. The other end of the secondary of transformer T2 is connected to the potential point f between Q4 and Q5. DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2.

[0007] In the second implementation of this method, the transformer equivalent turns ratio is reconstructed through a dual transformer and full-bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc, primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a primary full-bridge circuit, the primary full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3 and Q4 are connected in parallel to form a secondary full-bridge circuit, the secondary full-bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the voltage between S1 and S2 Lead out from point a and connect to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary side of transformer T1. The other end of the primary side of transformer T1 is connected to one end of the primary side of transformer T2. The other end of the primary side of transformer T2 is connected to the potential point c between S1 and S2. Lead out from point d between Q3 and Q4 and connect to one end of the secondary side of transformer T1. The other end of the secondary side of transformer T1 is connected to one end of the secondary side of transformer T2. The other end of the secondary side of transformer T2 is connected to the potential point f between Q2 and Q4. The DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2.

[0008] In the third implementation of this method, the transformer equivalent turns ratio is reconstructed through a dual transformer and full-bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a primary full-bridge circuit, the primary full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3 and Q4 are connected in parallel to form a secondary full-bridge circuit, the secondary full-bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the voltage between S1 and S2 Lead out from point a and connect to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary side of transformer T1. The other end of the primary side of transformer T1 is connected to one end of the primary side of transformer T2. The other end of the primary side of transformer T2 is connected to the potential point c between S1 and S2. Lead out from point d between Q3 and Q4 and connect to one end of the secondary side of transformer T1. The other end of the secondary side of transformer T1 is connected to one end of the secondary side of transformer T2. The other end of the secondary side of transformer T2 is connected to the potential point e between Q1 and Q2. The DC blocking capacitor C dc One end is connected to the potential point g between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point f between Q2 and Q4.

[0009] Compared with the prior art, the present invention has the following beneficial effects:

[0010] (1) No additional auxiliary switch is required. The present invention reconstructs the equivalent turns ratio of the transformer by changing the driving logic of the secondary side switch tube. Without any auxiliary switch, the operating modes of different transformer turns ratios can be smoothly switched, which has the advantages of low cost and good dynamic performance.

[0011] (2) Fewer active switches and lower cost: The method of reconstructing the transformer equivalent turns ratio through dual transformers proposed in the present invention requires fewer active switches and has the advantage of low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a circuit topology diagram of a DAB converter in the prior art;

[0013] Figure 2 This is a circuit topology diagram for reconstructing the transformer turns ratio based on series-parallel switching of two secondary full-bridge circuits in the prior art;

[0014] Figure 3 This is a circuit topology diagram of reconstructing the transformer turns ratio using a multi-winding transformer and a three-bridge-arm circuit in the prior art;

[0015] Figure 4 This is a circuit topology diagram of reconstructing the transformer turns ratio using a dual transformer and a three-bridge-arm circuit in the prior art;

[0016] Figure 5 This is a circuit topology diagram implemented by the method for reconstructing the transformer equivalent turns ratio by using dual transformers and an improved bridge circuit, as provided in the first embodiment of the present invention;

[0017] Figure 6 1 is a circuit topology and key waveform diagram of the first embodiment of the present invention in the working mode;

[0018] Figure 7 1 is a circuit topology and key waveform diagram of working mode 2 in embodiment 1 of the present invention;

[0019] Figure 8 1 is a circuit topology and key waveform diagram of working mode 3 in embodiment 1 of the present invention;

[0020] Figure 9 1 is a circuit topology and key waveform diagram of working mode 4 in embodiment 1 of the present invention;

[0021] Figure 10 This is a circuit topology diagram implemented by a method for reconstructing the transformer equivalent turns ratio using dual transformers and an improved bridge circuit, as provided in the second embodiment of the present invention;

[0022] Figure 11 This is the circuit topology and key waveform diagram of the second embodiment of the present invention in the working mode;

[0023] Figure 12 1 is a circuit topology and key waveform diagram of working mode 2 in embodiment 2 of the present invention;

[0024] Figure 13 1 is a circuit topology and key waveform diagram of working mode 3 in embodiment 2 of the present invention;

[0025] Figure 14 This is a circuit topology diagram implemented by a method for reconstructing the transformer equivalent turns ratio using a dual transformer and an improved bridge circuit, as provided in the third embodiment of the present invention;

[0026] Figure 15 This is the circuit topology and key waveform diagram of the third embodiment of the present invention in the working mode;

[0027] Figure 16 1 is a circuit topology and key waveform diagram of working mode 2 in embodiment 3 of the present invention;

[0028] Figure 17 1 is a circuit topology and key waveform diagram of working mode 3 in embodiment 3 of the present invention;

[0029] Figure 18 1 is a circuit topology and key waveform diagram of working mode 4 in embodiment 3 of the present invention;

[0030] Figure 19 1 is a comparison diagram of the optimized control schemes of Example 1 and Example 2 of the present invention;

[0031] Figure 20 This is a flow chart of an implementation of a method for reconstructing the transformer equivalent turns ratio through dual transformers and an improved bridge circuit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0034] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0035] The present invention provides a method for reconstructing the transformer equivalent turns ratio for a wide voltage gain DAB converter using dual transformers and an improved bridge circuit. By controlling the drive signals of different improved bridge circuits on the secondary side, different voltages are generated on the primary side of the dual transformers, ensuring that the voltages on both sides of the DAB converter's inductor remain closely matched under wide voltage gain conditions, thereby reconstructing different transformer equivalent turns ratios. By reconstructing the transformer equivalent turns ratio, this method can achieve a wider soft switching range and lower inductor effective current, thereby improving the efficiency of the wide voltage gain DAB converter by reducing switching losses and conduction losses. Compared to existing wide voltage gain solutions for DAB converters, this method does not require auxiliary switches and can reconstruct more than three equivalent turns ratio combinations with the addition of a small number of components. This method can achieve higher efficiency over a wider voltage gain range without significantly increasing costs.

[0036] The first embodiment of the present invention provides a method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter. Figure 5 As shown in the figure, it reconstructs the transformer equivalent turns ratio through a dual transformer and H5 bridge circuit. The circuit includes: two transformers T1 and T2, with turns ratios of n1 and n1 respectively; four active switches S1 to S4 on the primary side; five active switches Q1 to Q5 on the secondary side; a series inductor L; and a DC blocking capacitor C. dc Primary DC voltage V1; secondary DC voltage V2; primary filter capacitor C1; secondary filter capacitor C2. The series circuit of S1 and S2 is connected in parallel with the series circuit of S3 and S4 to form a full-bridge circuit. The full-bridge circuit and primary filter capacitor C1 are connected in parallel across the primary DC voltage V1. The series circuit of Q1 and Q2 is connected in parallel with the series circuit of Q3, Q4, and Q5 to form the H5 bridge circuit. The H5 bridge circuit and secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2. Lead a wire from potential point a between S1 and S2 to one end of the series inductor L. Connect the other end of the series inductor L to one end of the primary side of transformer T1 at potential point b. Connect the other end of the primary side of transformer T1 to one end of the primary side of transformer T2. Connect the other end of the primary side of transformer T2 to potential point c between S1 and S2. Lead a wire from potential point d between Q3 and Q4 to one end of the secondary side of transformer T1. Connect the other end of the secondary side of transformer T1 to one end of the secondary side of transformer T2. Connect the other end of the secondary side of transformer T2 to potential point f between Q4 and Q5. DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2. L is the inductor current; i C is the current flowing through the capacitor; i Q34 ,i q45 ,i q56is the current flowing through each bridge arm of the secondary side; points a~f are the potential points in the circuit.

[0037] The method proposed in this embodiment for reconstructing the transformer equivalent turns ratio by using dual transformers and an H5 bridge circuit has four working modes, and each working mode has a different transformer equivalent turns ratio.

[0038] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and H5 bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 1 are as follows: Figure 6 As shown. Figure 6 As shown in (a), the switch Q4 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q3 and Q5 form two bridge arms; the voltage waveforms between the switch drive signal and the potential points of the circuit are as follows Figure 6 As shown in (b). The AC square wave voltage of +V1 or -V1 generated by the primary full-bridge circuit at the potential point is V ac ; The secondary side H5 bridge circuit generates an AC square wave voltage with a level of +V2 or -V2 on the secondary side of transformers T1 and T2; de and V ef has opposite phases and the same-name terminals of transformers T1 and T2. The AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer with a value of V bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V1 / n1+V2 / n2). At this time, the equivalent turns ratio of the transformer is expressed as:

[0039]

[0040] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and H5 bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 2 are as follows: Figure 7 As shown. Figure 7 As shown in (a), the switch Q5 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q3 and Q4 form two bridge arms; the voltage waveforms between the switch drive signal and the potential points of the circuit are as follows Figure 7 As shown in (b). The AC square wave voltage of +V1 or -V1 generated by the primary full-bridge circuit at the potential point is V ac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or -V2 on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T2 side. ef ; Due to V de and V efWith opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer, which is V bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V1 / n1+V2 / (2n2)). At this time, the equivalent turns ratio of the transformer is expressed as:

[0041]

[0042] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and H5 bridge circuits to reconstruct the transformer equivalent turns ratio in working mode three are as follows: Figure 8 As shown. Figure 8 As shown in (a), the switch tube Q3 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q4 and Q5 form two bridge arms; the voltage waveform between the switch drive signal and each potential point of the circuit is as follows Figure 8 As shown in (b). The AC square wave voltage of +V1 or -V1 generated by the primary full-bridge circuit at the potential point is V ac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or -V2 on the transformer T2 side. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary H5 bridge circuit is reflected to the voltage V on the primary side of the transformer. bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V2 / (2n1)+V2 / n2). At this time, the equivalent turns ratio of the transformer is expressed as:

[0043]

[0044] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and H5 bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 4 are as follows: Figure 9 As shown. Figure 9 As shown in (a), the switches Q3 and Q5 of the secondary side H5 bridge circuit remain on, Q4 remains off, and Q1 and Q2 form a bridge arm; the voltage waveforms between the switch drive signal and the potential points of the circuit are as follows: Figure 9 As shown in (b). The AC square wave voltage of +V1 or -V1 generated by the primary full-bridge circuit at the potential point is Vac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T2 side. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer, which is V bc =V de / n1-V ef / n2,V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0045]

[0046] In summary, the transformer equivalent turns ratio reconfiguration solution proposed in this embodiment achieves four operating modes with different transformer equivalent turns ratios by changing the drive logic of the secondary-side H5 bridge circuit switches, without the need for auxiliary switches. By varying the transformer equivalent turns ratio, the efficiency of the DAB converter can be improved over a wide voltage range.

[0047] The second embodiment of the present invention provides a method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter, such as Figure 10 As shown in the figure, it reconstructs the transformer equivalent turns ratio through a dual transformer and full-bridge circuit. The circuit includes: two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc, primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2. The series circuit of S1 and S2 is connected in parallel with the series circuit of S3 and S4 to form a primary full-bridge circuit. The primary full-bridge circuit and primary filter capacitor C1 are connected in parallel across the primary DC voltage V1. The series circuit of Q1 and Q2 is connected in parallel with the series circuit of Q3 and Q4 to form a secondary full-bridge circuit. The secondary full-bridge circuit and secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2. Lead a wire from potential point a between S1 and S2 to one end of the series inductor L. Connect the other end of the series inductor L to one end of the primary side of transformer T1 at potential point b. Connect the other end of the primary side of transformer T1 to one end of the primary side of transformer T2. Connect the other end of the primary side of transformer T2 to potential point c between S1 and S2. Lead a wire from potential point d between Q3 and Q4 to one end of the secondary side of transformer T1. Connect the other end of the secondary side of transformer T1 to one end of the secondary side of transformer T2. Connect the other end of the secondary side of transformer T2 to potential point f between Q2 and Q4. DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2. In the figure, points a to f are the potential points in the circuit.

[0048] The method proposed in this embodiment for reconstructing the transformer equivalent turns ratio by using dual transformers and a full-bridge circuit has three working modes, and each working mode has a different transformer equivalent turns ratio.

[0049] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 1 are as follows: Figure 11 As shown in the figure. The driving signal of the active switch and the voltage waveform between each potential point of the circuit are as follows: Figure 11 As shown in (b). The primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 on the secondary side of transformer T1. de The secondary full-bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the secondary side of transformer T2. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / n2-V de / n1,V bc The level is ±(V2 / n1+V2 / (2n2)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0050]

[0051] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 2 are as follows: Figure 12 As shown. Figure 12 As shown in (a), the switch tube Q4 of the secondary full-bridge circuit remains on, Q3 remains off, and Q1 and Q2 form a bridge arm; the voltage waveform between the switch drive signal and each potential point of the circuit is as follows Figure 12 As shown in (b). The primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of -V2 or 0V on the secondary side of transformer T1. de The secondary full-bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the secondary side of transformer T2. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / n2-V de / n1,V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0052]

[0053] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode three are as follows: Figure 13 As shown. Figure 13 As shown in (a), the switch tube Q2 of the secondary full-bridge circuit remains on, Q1 remains off, and Q4 and Q3 are the bridge arms that work normally; the voltage waveforms between the switch drive signal and the potential points of the circuit are as follows: Figure 13 As shown in (b). The primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of -V2 or 0V on the secondary side of transformer T1. de ; The secondary full-bridge circuit short-circuits the secondary winding of transformer T2, and the voltage V ef is 0V; by V de The AC square wave voltage on the secondary side of the transformer generated by the secondary full-bridge circuit is reflected to the primary side of the transformer as V bc =V de / n1,V bcThe level is ±(V2 / (2n1)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0054]

[0055] In summary, the second transformer equivalent turns ratio reconfiguration scheme proposed in this embodiment achieves three operating modes with different transformer equivalent turns ratios by changing the drive logic of the secondary full-bridge circuit switches, without the need for auxiliary switches. By varying the transformer equivalent turns ratio, the efficiency of the DAB converter can be improved over a wide voltage range.

[0056] The third embodiment of the present invention provides a method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter, such as Figure 14 As shown in the figure, it reconstructs the transformer equivalent turns ratio through a dual transformer and full-bridge circuit. The circuit includes: two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2. The series circuit of S1 and S2 is connected in parallel with the series circuit of S3 and S4 to form a primary full-bridge circuit. The primary full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1. The series circuit of Q1 and Q2 is connected in parallel with the series circuit of Q3 and Q4 to form a secondary full-bridge circuit. The secondary full-bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2. A wiring is drawn from the potential point a between S1 and S2 to connect one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary side of the transformer T1. The other end of the primary side of the transformer T1 is connected to one end of the primary side of the transformer T2. The other end of the primary side of the transformer T2 is connected to the potential point c between S1 and S2. A wiring is drawn from the potential point d between Q3 and Q4 to connect one end of the secondary side of the transformer T1. The other end of the secondary side of the transformer T1 is connected to one end of the secondary side of the transformer T2. The other end of the secondary side of the transformer T2 is connected to the potential point e between Q1 and Q2. The DC blocking capacitor C dc One end is connected to the potential point g between the secondary sides of transformers T1 and T2, and the other end is connected to the potential point f between Q2 and Q4. In the figure, points a to g are the potential points in the circuit.

[0057] The method proposed in this embodiment for reconstructing the transformer equivalent turns ratio by using dual transformers and a full-bridge circuit has four working modes, and each working mode has a different transformer equivalent turns ratio.

[0058] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 1 are as follows: Figure 15As shown in the figure. The driving signal of the active switch and the voltage waveform between each potential point of the circuit are as follows: Figure 15 As shown in (b). In the secondary front-end bridge circuit, Q1 and Q4 are turned on synchronously, and Q2 and Q3 are turned on synchronously; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. dg The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ge The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n2)+V de / (2n1), V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0059]

[0060] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 2 are as follows: Figure 16 As shown in the figure. The driving signal of the active switch and the voltage waveform between each potential point of the circuit are as follows: Figure 16 As shown in (b). In the secondary front bridge circuit, Q1 and Q3 are turned on synchronously, and Q2 and Q4 are turned on synchronously; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. df The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ef The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n1)-V de / (2n2), V bc The level is ±(V2 / (2n1)-V2 / (2n2)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0061]

[0062] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode three are as follows: Figure 17 As shown in the figure. The driving signal of the active switch and the voltage waveform between each potential point of the circuit are as follows: Figure 17 As shown in (b). In the secondary front-end bridge circuit, Q1 remains off and Q2 remains on; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. df The secondary full-bridge circuit short-circuits the secondary side of transformer T2. The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n1), V bc The level is ±V2 / (2n1) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0063]

[0064] The circuit topology and key waveforms of the solution proposed in this embodiment using dual transformers and full-bridge circuits to reconstruct the transformer equivalent turns ratio in working mode 4 are as follows: Figure 18 As shown in the figure. The driving signal of the active switch and the voltage waveform between each potential point of the circuit are as follows: Figure 18 As shown in (b). In the secondary front bridge circuit, Q3 remains off and Q4 remains on; the primary full bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ef The secondary full-bridge circuit short-circuits the secondary side of transformer T1. The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, and the voltage is V bc =V de / (2n2), V bc The level is ±V2 / (2n2) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

[0065]

[0066] In summary, the third transformer equivalent turns ratio reconfiguration scheme proposed in this embodiment achieves four operating modes with different transformer equivalent turns ratios by changing the drive logic of the secondary full-bridge circuit switches, without the need for auxiliary switches. By varying the transformer equivalent turns ratio, the efficiency of the DAB converter can be improved over a wide voltage range.

[0067] The primary circuits of the two schemes proposed in this invention, which use dual transformers and an improved bridge circuit to reconstruct the transformer equivalent turns ratio, are consistent with those of the traditional DAB converter. Inner shifting can be introduced to further reduce the inductor current and widen the ZVS range. Taking the respective working modes 1 as an example, the optimized control schemes of schemes 1 and 2 are as follows: Figure 19 As shown, D1 is the phase shift between the primary and secondary bridge arms, and D2 is the internal phase shift of the primary full-bridge circuit. After the internal phase shift D2 is introduced, the primary full-bridge circuit generates a three-level AC square wave voltage V with ±V1 and 0V at the potential point. ac By introducing the zero level and rationally designing the control algorithm of the two phase shift ratios, the inductor current can be further reduced and the ZVS range can be widened under wide voltage gain conditions.

[0068] The implementation method of the method of reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit proposed in the present invention is as follows: Figure 20 As shown. Based on the wide voltage gain DAB converter with reconfigurable transformer turns ratio proposed in the invention, according to Figure 20 The proposed process can improve efficiency under wide voltage gain conditions. First, the parameters of the DAB converter prototype are sampled, including voltage (primary and secondary DC voltage) and current (primary and secondary DC current), and the transmission power and voltage gain are calculated. Second, the operating mode of the wide voltage gain DAB converter proposed in this invention is determined based on the transmission power and voltage gain, taking into account the optimal optimization target (such as the inductor RMS current, the switch soft switching range, or the reactive power optimization target). Finally, the controller determines the shift ratio of the DAB converter according to the corresponding operating mode and generates a corresponding drive signal to control the proposed wide voltage gain DAB converter with a reconfigurable transformer turns ratio.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for reconstructing the transformer equivalent turns ratio using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter, characterized in that: By controlling the driving signals of different forms of improved bridge circuits on the secondary side, different voltages are formed on the primary side of the dual transformer, ensuring that the voltages on both sides of the inductor of the DAB converter remain closely matched under wide voltage gain conditions, and reconstructing different transformer equivalent turns ratios.

2. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 1, characterized in that: The transformer equivalent turns ratio is reconstructed through a dual transformer and H5 bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, five active switches Q1 to Q5 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a full-bridge circuit, the full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3, Q4 and Q5 are connected in parallel to form an H5 bridge circuit, the H5 bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the potential point between S1 and S2 Lead wire a is connected to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary of transformer T1. The other end of the primary of transformer T1 is connected to one end of the primary of transformer T2. The other end of the primary of transformer T2 is connected to the potential point c between S1 and S2. Lead wire d is connected to one end of the secondary of transformer T1. The other end of the secondary of transformer T1 is connected to one end of the secondary of transformer T2. The other end of the secondary of transformer T2 is connected to the potential point f between Q4 and Q5. DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2.

3. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 2, characterized in that: The transformer equivalent turns ratio is reconstructed by using a dual transformer and H5 bridge. The implementation method of working mode 1 is as follows: The switch tube Q4 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q3 and Q5 form two bridge arms; the AC square wave voltage with a level of +V1 or -V1 generated by the primary side full bridge circuit at the potential point is V ac ; The secondary side H5 bridge circuit generates an AC square wave voltage with a level of +V2 or -V2 on the secondary side of transformers T1 and T2; de and V ef has opposite phases and the same-name terminals of transformers T1 and T2. The AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer with a value of V bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V1 / n1+V2 / n2); at this time, the equivalent turns ratio of the transformer is expressed as:

4. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 2, characterized in that: The transformer equivalent turns ratio is reconstructed by using a dual transformer and H5 bridge. The implementation method of the second working mode is as follows: The switch tube Q5 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q3 and Q4 form two bridge arms; the AC square wave voltage with a level of +V1 or -V1 generated by the primary side full bridge circuit at the potential point is V ac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or -V2 on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T2 side. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer, which is V bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V1 / n1+V2 / (2n2)). At this time, the equivalent turns ratio of the transformer is expressed as:

5. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 2, characterized in that: By reconstructing the transformer equivalent turns ratio through dual transformers and H5 bridge, the implementation method of its working mode 3 is as follows: The switch tube Q3 of the secondary side H5 bridge circuit remains on, and Q1, Q2, Q4 and Q5 form two bridge arms; the AC square wave voltage with a level of +V1 or -V1 generated by the primary side full bridge circuit at the potential point is V ac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or -V2 on the transformer T2 side. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the voltage V on the primary side of the transformer. bc =V de / n1-V ef / n2,V bc is an AC square wave voltage with a level of ±(V2 / (2n1)+V2 / n2); at this time, the equivalent turns ratio of the transformer is expressed as:

6. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 2, characterized in that: By reconstructing the transformer equivalent turns ratio through dual transformers and H5 bridge, the implementation method of its working mode 4 is as follows: The switches Q3 and Q5 of the secondary side H5 bridge circuit remain on, Q4 remains off, and Q1 and Q2 form a bridge arm; the AC square wave voltage with a level of +V1 or -V1 generated by the primary side full bridge circuit at the potential point is V ac The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T1 side. de The secondary side H5 bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the transformer T2 side. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary side H5 bridge circuit is reflected to the primary side of the transformer, which is V bc =V de / n1-V ef / n2,V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as:

7. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 1, characterized in that: The transformer equivalent turns ratio is reconstructed through a dual transformer and full-bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a primary full-bridge circuit, the primary full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3 and Q4 are connected in parallel to form a secondary full-bridge circuit, the secondary full-bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the voltage between S1 and S2 Lead out from point a and connect to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary side of transformer T1. The other end of the primary side of transformer T1 is connected to one end of the primary side of transformer T2. The other end of the primary side of transformer T2 is connected to the potential point c between S1 and S2. Lead out from point d between Q3 and Q4 and connect to one end of the secondary side of transformer T1. The other end of the secondary side of transformer T1 is connected to one end of the secondary side of transformer T2. The other end of the secondary side of transformer T2 is connected to the potential point f between Q2 and Q4. The DC blocking capacitor C dc One end is connected between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point e between Q1 and Q2.

8. The method for reconstructing the transformer equivalent turns ratio by using a double transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 7, characterized in that: The transformer equivalent turns ratio is reconstructed by using a dual transformer and full-bridge circuit. The implementation method of working mode 1 is as follows: The primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 on the secondary side of transformer T1. de The secondary full-bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the secondary side of transformer T2. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / n2-V de / n1,V bc The level is ±(V2 / n1+V2 / (2n2)) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as: The implementation method of working mode 2 is: The switch tube Q4 of the secondary full-bridge circuit remains on, Q3 remains off, and Q1 and Q2 form a bridge arm; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of -V2 or 0V on the secondary side of transformer T1. de The secondary full-bridge circuit generates an AC square wave voltage V with a level of +V2 or 0V on the secondary side of transformer T2. ef ; Due to V de and V ef With opposite phases and the same-name terminals of transformers T1 and T2, the AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / n2-V de / n1,V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as: The implementation method of working mode three is: The switch tube Q2 of the secondary full-bridge circuit remains on, Q1 remains off, and Q4 and Q3 are the bridge arms that work normally; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of -V2 or 0V on the secondary side of transformer T1. de ; The secondary full-bridge circuit short-circuits the secondary winding of transformer T2, and the voltage V ef is 0V; by V de The AC square wave voltage on the secondary side of the transformer generated by the secondary full-bridge circuit is reflected to the primary side of the transformer as V bc =V de / n1,V bc The voltage level is ±(V2 / (2n1)) AC square wave voltage. At this time, the equivalent turns ratio of the transformer is expressed as:

9. The method for reconstructing the transformer equivalent turns ratio by using a dual transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 1, characterized in that: The transformer equivalent turns ratio is reconstructed through a dual transformer and full-bridge circuit, including two transformers T1 and T2, four active switches S1 to S4 on the primary side, four active switches Q1 to Q4 on the secondary side, a series inductor L, and a DC blocking capacitor C. dc , primary DC voltage V1, secondary DC voltage V2, primary filter capacitor C1 and secondary filter capacitor C2, the series circuit of S1 and S2 and the series circuit of S3 and S4 are connected in parallel to form a primary full-bridge circuit, the primary full-bridge circuit and the primary filter capacitor C1 are connected in parallel across the primary DC voltage V1, the series circuit of Q1 and Q2 and the series circuit of Q3 and Q4 are connected in parallel to form a secondary full-bridge circuit, the secondary full-bridge circuit and the secondary filter capacitor C2 are connected in parallel across the secondary DC voltage V2; from the voltage between S1 and S2 Lead out from point a and connect to one end of the series inductor L. The potential point b at the other end of the series inductor L is connected to one end of the primary side of transformer T1. The other end of the primary side of transformer T1 is connected to one end of the primary side of transformer T2. The other end of the primary side of transformer T2 is connected to the potential point c between S1 and S2. Lead out from point d between Q3 and Q4 and connect to one end of the secondary side of transformer T1. The other end of the secondary side of transformer T1 is connected to one end of the secondary side of transformer T2. The other end of the secondary side of transformer T2 is connected to the potential point e between Q1 and Q2. The DC blocking capacitor C dc One end is connected to the potential point g between the secondary side of transformer T1 and the secondary side of transformer T2, and the other end is connected to the potential point f between Q2 and Q4.

10. The method for reconstructing the transformer equivalent turns ratio by using a double transformer and an improved bridge circuit for a wide voltage gain DAB converter according to claim 9, characterized in that: The transformer equivalent turns ratio is reconstructed by using a dual transformer and full-bridge circuit. The implementation method of working mode 1 is as follows: In the secondary front bridge circuit, Q1 and Q4 are turned on synchronously, and Q2 and Q3 are turned on synchronously; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. dg The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ge The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n2)+V de / (2n1), V bc The level is ±(V2 / (2n1)+V2 / (2n2)) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as: The implementation method of working mode 2 is: In the secondary front bridge circuit, Q1 and Q3 are turned on synchronously, and Q2 and Q4 are turned on synchronously; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. df The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ef The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n1)-V de / (2n2), V bc The level is ±(V2 / (2n1)-V2 / (2n2)) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as: The implementation method of working mode three is: In the secondary front-bridge circuit, Q1 remains off and Q2 remains on; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T1. df The secondary full-bridge circuit short-circuits the secondary side of transformer T2. The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, which is V bc =V ef / (2n1), V bc The voltage level is ±V2 / (2n1) AC square wave. At this time, the equivalent turns ratio of the transformer is expressed as: The implementation method of working mode 4 is: In the secondary front bridge circuit, Q3 remains off and Q4 remains on; the primary full-bridge circuit generates an AC square wave voltage V with a level of ±V1 at the potential point. ac The secondary full-bridge circuit generates an AC square wave voltage V with a level of ±V2 / 2 on the secondary side of transformer T2. ef The secondary full-bridge circuit short-circuits the secondary side of transformer T1. The AC square wave voltage generated by the secondary full-bridge circuit is reflected to the primary side of the transformer, and the voltage is V bc =V de / (2n2), V bc The level is ±V2 / (2n2) AC square wave voltage; at this time, the equivalent turns ratio of the transformer is expressed as:

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