Single-freedom hybrid modulation and light load efficiency optimization method for DAB converter

Abstract

This invention discloses a method for single-degree-of-freedom hybrid modulation and light-load efficiency optimization of a DAB converter, including: acquiring the input voltage V1, output voltage V2, and output current I2 of the DAB converter, and calculating the output power P of the DAB transformer. out The voltage transfer ratio k and the per-unit value of the transmission power P are used to obtain the efficiency-optimized power range of the DAB transformer in PS-IPS modulation mode. The voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal is determined. Based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency-optimized power range, the modulation mode of the converter is determined. Based on the modulation mode of the converter, the phase shift value is determined, the phase between the drive pulses is changed, and the power of the dual active bridge converter is controlled to optimize the light-load efficiency of the DAB converter.

Description

Technical Field

[0001] This invention belongs to the field of modulation technology of dual active bridge converters, and relates to a method for single-degree-of-freedom hybrid modulation and light-load efficiency optimization of DAB converters. Background Technology

[0002] With the development of DC microgrids and energy storage technologies, bidirectional DC / DC converters have been widely used in applications such as power electronic transformers, electric vehicles, smart grids, and energy storage systems. Dual active bridge converters (DABs) feature symmetrical structure, flexible control, high power density, bidirectional energy flow, and ease of achieving zero-voltage switching (ZVS).

[0003] DAB converters typically employ single-degree-of-freedom phase-shift modulation, also known as single-phase-shift (SPS) modulation. This method has only one control variable, making it easy to implement, but it cannot achieve globally optimal control and suffers from low efficiency under light loads. In SPS modulation, both the primary and secondary voltage duty cycles are 50%, with a phase shift between the primary and secondary sides. The converter's power transfer can be controlled by adjusting the phase shift value. When the voltage transfer ratio (defined as the ratio of the voltages across the inductor) equals 1, SPS modulation can achieve soft switching across the entire power range. However, when the voltage ratio deviates from 1, the soft-switching range shrinks rapidly, and some soft switching is lost under light loads. Simultaneously, the return power increases the converter current stress and the effective current value, leading to increased circuit conduction losses. Therefore, the efficiency of DAB converters drops rapidly under light loads.

[0004] To address the issues with SPS, degrees of freedom can be increased, such as Extended Phase Shift (EPS), Dual Phase Shift (DPS), Triple Phase Shift (TPS), and asymmetric modulation of the aforementioned modulation modes. EPS adds a control variable within the primary-side H-bridge, based on SPS, allowing optimization of the ZVS region and current stress in the DAB converter, thus improving transmission efficiency. DPS adds an equal phase shift value to both the primary and secondary-side H-bridges, also optimizing ZVS and current stress in the DAB converter, further improving transmission efficiency. TPS includes three control variables: three phase shift values ​​within the primary-side H-bridge, three within the secondary-side H-bridge, and three between the primary and secondary-side H-bridges. TPS offers greater control flexibility compared to SPS, EPS, and DPS, but the large number of control variables complicates the modulation strategy. Asymmetric modulation, compared to SPS, EPS, DPS, and TPS, no longer uses 50% duty cycles for the primary and secondary voltages, causing the current flowing through the inductor to no longer be symmetrical about zero, potentially leading to transformer and inductor saturation. The aforementioned multi-degree-of-freedom modulation method requires high model accuracy and has a coupling relationship between degrees of freedom, making it computationally complex and difficult to apply well in practical engineering. Summary of the Invention

[0005] The purpose of this invention is to provide a method for optimizing the single-degree-of-freedom hybrid modulation and light-load efficiency of DAB converters, which solves the problem that the existing multi-degree-of-freedom modulation methods for DAB converters are complex in calculation and difficult to apply in practical engineering.

[0006] The technical solution adopted in this invention is a method for optimizing the single-degree-of-freedom hybrid modulation and light-load efficiency of a DAB converter, comprising the following steps: Step 1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2. Calculate the output power P of the DAB converter. out Voltage transmission ratio k and per-unit transmission power P; Step 2: Obtain the efficiency-optimized power range of the DAB converter in PS-IPS modulation mode, and determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. Step 3: Determine the converter modulation method based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency optimization power range; Step 4: Determine the phase shift value according to the converter modulation method, change the phase between the drive pulses, control the power of the dual active bridge converter, and optimize the light-load efficiency of the DAB converter.

[0007] The specific process of step 1 is as follows: Step 1.1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2; Step 1.2: Calculate the output power P of the DAB converter out Voltage transfer ratio k: (1) (2) In the formula, N is the ratio of the primary to the secondary winding of the transformer, and N > 0; Step 1.3: Calculate the DAB converter at the input voltage V 1. Output voltage V 2. Maximum transmission power when the transformer turns ratio is N P N : (3) In the formula, For switching frequency, L This refers to the inductance value; Step 1.4: Calculate the per-unit power P of the DAB converter: (4) Step 2 is as follows: Step 2.1: Plot the phase shift value-power per-unit value curve based on the per-unit value expression of the DAB converter's transmission power under SPS and PS-IPS modulation modes, and read the efficiency optimization power range of the DAB converter in PS-IPS modulation mode from the plotted curve. Step 2.2: Determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal using the converter current stress expression under PS-IPS and SPS modulation modes.

[0008] Step 2.1 The specific process is as follows: Step 2.1.1: Determine the per-unit value of the transmission power of the DAB converter under SPS modulation. P The expression is: (5) P SPS = (6) In the formula, This represents the transmission power corresponding to SPS modulation. This refers to the phase shift value corresponding to the SPS modulation method; Step 2.1.2: Determine the per-unit value of the transmission power of the DAB converter under PS-IPS modulation. P The expression is: (7) P PS-IPS = (8) In the formula, This refers to the transmission power corresponding to PS-IPS modulation. This refers to the phase shift value corresponding to the PS-IPS modulation method; Step 2.1.3: Plot the phase shift value-power per unit value curves corresponding to SPS and PS-IPS modulation modes according to formulas (5) and (7), and obtain the efficiency optimization power range of the DAB converter in PS-IPS modulation mode as (0, 0.5).

[0009] The specific process of step 2.2 is as follows: Step 2.2.1: Determine the expression for the current stress of the DAB converter under SPS modulation as follows: (9) (10) I SPS_max= (11) In the formula, G 1 represents the per-unit value of the current stress in the DAB converter under SPS modulation. I N This represents the maximum transfer current of the DAB converter. I SPS_max Current stress of the DAB converter under SPS modulation; Step 2.2.2: Determine the expression for the current stress of the DAB converter under PS-IPS modulation as follows: (12) I PS-IPS_max = (13) In the formula, G 2 represents the per-unit value of the current stress in the DAB converter under PS-IPS modulation. I PS-IPS_max Current stress in DAB converters under PS-IPS modulation; Step 2.2.3: Based on formulas (5), (7), (9), and (12), plot the three-dimensional kPG curves for SPS and PS-IPS modulation methods. From the plotted three-dimensional kPG curves, obtain the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. .

[0010] Step 3 specifically includes the following steps: Step 3.1: If 0 < P < 0.5 and Formula (14) is obtained from formulas (5)-(12), and the reference value of voltage transfer ratio during PS-IPS and SPS switching is determined by formula (14). : (14) The switching expression within the mixed modulation region is: (15) like k < If k ≥ 0, then SPS modulation is used. In this case, PS-IPS modulation is used; Step 3.2: If 0 < P < 0.5 and In this case, PS-IPS modulation is used; Step 3.3: If P≥0.5 and k≥1, then SPS modulation is used.

[0011] Step 4 is as follows: The DAB converter drive pulse includes four drive pulses: ePWM1A, ePWM1B, ePWM2A, and ePWM2B. ePWM1A is connected to the switches S1 and S4 in the converter, ePWM1B is connected to the switches S2 and S3 in the converter, ePWM2A is connected to the switches Q1 and Q4 in the converter, and ePWM2B is connected to the switches Q2 and Q3 in the converter. Step 4.1: If the modulation method is SPS, then change the phase between ePWM1A and ePWM2A. The phase shift value and power expression are (16): (16) Step 4.2: If the modulation method is PS-IPS, then change the phase between ePWM1A and ePWM1B. The phase shift value and power expression are (17): (17) The beneficial effects of this invention are that by judging the output power and inductor voltage transfer ratio of the dual active bridge converter, a suitable modulation strategy is selected to drive the switching transistors in the DAB converter, thereby controlling the converter power and optimizing the light-load efficiency of the DAB converter. In terms of applicability, this invention can be applied to dual active bridge converters in scenarios such as energy storage and electric vehicles. In terms of complexity, this invention does not require complex calculations and does not have coupling problems between degrees of freedom, which can further improve converter performance and optimize the light-load efficiency of the DAB converter. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the single-degree-of-freedom hybrid modulation and light-load efficiency optimization method for DAB converters of the present invention. Figure 2 This is a schematic diagram of the dual active bridge converter (DAB) circuit of the present invention; Figure 3 This is a graph showing the phase shift value versus power per unit value in this invention. Figure 4 This is a three-dimensional curve of kPG under SPS and PS-IPS modulation methods in this invention; Figure 5 This is a schematic diagram of the PS-IPS modulation power range in this invention; Figure 6 This is a schematic diagram of the SPS modulation power range in this invention; Figure 7 The simulation waveform diagram shows the hybrid modulation strategy of switching from PS-IPS to SPS when P=0.2 in this invention. Figure 8 The simulation waveform diagram shows the hybrid modulation strategy of switching from SPS to PS-IPS when P=0.5 in this invention. Figure 9 The waveform diagram is an experimental waveform of the SPS modulation strategy in this invention; Figure 10 The waveform diagram is an experimental waveform of the PS-IPS modulation strategy in this invention. Detailed Implementation

[0013] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0014] Example 1 A method for optimizing single-degree-of-freedom hybrid modulation and light-load efficiency of DAB converters, referring to... Figure 1 This includes the following steps: Step 1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2. Calculate the output power P of the DAB converter. out Voltage transmission ratio k and per-unit transmission power P; The circuit diagram of the DAB converter is as follows: Figure 2 As shown, the circuit includes switching transistors S1, S2, S3, S4 and Q1, Q2, Q3, Q4, voltage dividing capacitors C1 and C2, inductor L, and transformer T. In the DAB converter, switching transistors S1 and S2 are connected in series, switching transistors S3 and S4 are connected in series and in parallel on the primary side H1, switching transistors Q1 and Q2 are connected in series, switching transistors Q3 and Q4 are connected in series and in parallel on the secondary side H2. The connection between the primary side H1 and the secondary side H2 is achieved through inductor L and transformer T. Step 2: Obtain the efficiency-optimized power range of the DAB converter in PS-IPS modulation mode, and determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. Step 3: Determine the converter modulation method based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency optimization power range; Step 4: Determine the phase shift value according to the converter modulation method, change the phase between the drive pulses, control the power of the dual active bridge converter, and optimize the light-load efficiency of the DAB converter.

[0015] Example 2 A method for optimizing single-degree-of-freedom hybrid modulation and light-load efficiency of a DAB converter includes the following steps: Step 1: Acquire DAB converter data and calculate output power P out Voltage transmission ratio k and per-unit transmission power P; Step 1.1: Acquire the input voltage of the DAB converter V 1. Output voltageV 2 and output current I 2; Step 1.2: Calculate the output power P of the DAB converter out Voltage transfer ratio k: (1) (2) In the formula, N is the ratio of the primary to the secondary winding of the transformer, and N > 0; Step 1.3: Calculate the DAB converter at the input voltage V 1. Output voltage V 2. Maximum transmission power when the transformer turns ratio is N P N : (3) In the formula, For switching frequency, L This refers to the inductance value; Step 1.4: Calculate the per-unit power P of the DAB converter: (4) Step 2: Obtain the efficiency-optimized power range of the DAB converter in PS-IPS modulation mode, and determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. The specific process is as follows: Step 2.1: See Figure 3 Based on the per-unit power expression of the DAB converter under SPS and PS-IPS modulation, a phase shift value-power per-unit curve was plotted. From the plotted curve, it can be seen that the transmission power overlaps between SPS and PS-IPS modulation in the range of (0, 0.5). Therefore, it is determined that PS-IPS can be optimized for light load power. The efficiency optimization power range of the DAB converter under PS-IPS modulation mode is read from the plotted curve (0, 0.5). Step 2.2: Determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal using the converter current stress expressions. .

[0016] Step 3: Determine the converter modulation method based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency optimization power range; Step 3.1: If 0 < P < 0.5 and Calculate the reference value of voltage transfer ratio during PS-IPS and SPS switching. : (5) The switching expression within the mixed modulation region is: (6) Step 3.2: If 0 < P < 0.5 and In this case, PS-IPS modulation is used; Step 3.3: If P≥0.5 and k≥1, then SPS modulation is used.

[0017] Step 4: The DAB converter drive pulse includes four drive pulses: ePWM1A, ePWM1B, ePWM2A, and ePWM2B. ePWM1A is connected to the switches S1 and S4 in the converter, ePWM1B is connected to the switches S2 and S3 in the converter, ePWM2A is connected to the switches Q1 and Q4 in the converter, and ePWM2B is connected to the switches Q2 and Q3 in the converter. Step 4 is as follows: Step 4.1: If the modulation method is SPS, then change the phase between ePWM1A and ePWM2A. The phase shift value and power expression are (7): (7) Step 4.2: If the modulation method is PS-IPS, then change the phase between ePWM1A and ePWM1B. The phase shift value and power expression are (8): (8) By changing the phase between drive pulses, the power transmission of the dual active bridge converter (DAB) can be controlled, thereby optimizing the light-load efficiency of the DAB converter.

[0018] Example 3 A method for optimizing single-degree-of-freedom hybrid modulation and light-load efficiency of a DAB converter includes the following steps: Step 1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2. Calculate the output power P of the DAB converter. out Voltage transmission ratio k and per-unit transmission power P; The specific process of step 1 is as follows: Step 1.1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2; Step 1.2: Calculate the output power P of the DAB converter out Voltage transfer ratio k: (1) (2) In the formula, N is the ratio of the primary to the secondary winding of the transformer, and N > 0; Step 1.3: Calculate the DAB converter at the input voltage V 1. Output voltage V 2. Maximum transmission power when the transformer turns ratio is N P N : (3) In the formula, For switching frequency, L This refers to the inductance value; Step 1.3: Calculate the per-unit power P of the DAB converter: (4) Step 2: Obtain the efficiency-optimized power range of the DAB converter in PS-IPS modulation mode, and determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. The specific process is as follows: Step 2.1: Plot the phase shift value-power per-unit value curve based on the per-unit value expression of the DAB converter's transmission power under SPS and PS-IPS modulation modes, and read the efficiency optimization power range of the DAB converter in PS-IPS modulation mode from the plotted curve. Step 2.1 The specific process is as follows: Step 2.1.1: Determine the per-unit value of the transmission power of the DAB converter under SPS modulation. P The expression is: (5) P SPS = (6) In the formula, This represents the transmission power corresponding to SPS modulation. This refers to the phase shift value corresponding to the SPS modulation method; Step 2.1.2: Determine the per-unit value of the transmission power of the DAB converter under PS-IPS modulation. P The expression is: (7) P PS-IPS = (8) In the formula, This refers to the transmission power corresponding to PS-IPS modulation. This refers to the phase shift value corresponding to the PS-IPS modulation method; Step 2.1.3: Plot the phase shift value-power per unit value curves corresponding to SPS and PS-IPS modulation modes according to formulas (5) and (7), and obtain the efficiency optimization power range of the DAB converter in PS-IPS modulation mode as (0, 0.5).

[0019] Step 2.2: Determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal using the converter current stress expression under PS-IPS and SPS modulation modes.

[0020] The specific process of step 2.2 is as follows: Step 2.2.1: Determine the expression for the current stress of the DAB converter under SPS modulation as follows: (9) (10) I SPS_max= (11) In the formula, G 1 represents the per-unit value of the current stress in the DAB converter under SPS modulation. I N This represents the maximum transfer current of the DAB converter. I SPS_max The current stress of the DAB converter under SPS modulation; Step 2.2.2: Determine the expression for the current stress of the DAB converter under PS-IPS modulation as follows: (12) I PS-IPS_max = (13) In the formula, G 2 represents the per-unit value of the current stress in the DAB converter under PS-IPS modulation. I PS-IPS_max Current stress in DAB converters under PS-IPS modulation; Step 2.2.3: Refer to Figure 4 Based on formulas (5), (7), (9), and (12), three-dimensional kPG curves for SPS and PS-IPS modulation are plotted. From the plotted three-dimensional kPG curves, the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal is obtained as follows: ; Step 3: Determine the converter modulation method based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency optimization power range; Step 3 specifically includes the following steps: Step 3.1: If 0 < P < 0.5 and Formula (14) is obtained from formula (5)-(12), including converting formula (5) and formula (7) into... and P 1. and P The relationship between 2 is then substituted into formulas (9) and (12), and G1 = G2 is set to obtain formula (14). Formula (14) determines the relationship between 2 and 3. , This indicates the reference value for the voltage transfer ratio during PS-IPS and SPS switching. (14) The switching expression within the mixed modulation region is: (15) Step 3.2: If 0 < P < 0.5 and Then, PS-IPS modulation is used, referring to... Figure 5 In the picture This is the primary-side H-bridge waveform of a dual active bridge converter. The waveform of the secondary H-bridge of the dual active bridge converter is shown. Power transmission of the dual active bridge converter is controlled by controlling the phase shift within the primary H-bridge. The phase shift value within the bridge is... and The phase between; Step 3.3: If P ≥ 0.5 and k ≥ 1, then SPS modulation is adopted, referring to... Figure 6 In SPS modulation, both the primary and secondary H-bridges are modulated with a 50% duty cycle. This is the primary-side H-bridge waveform of a dual active bridge converter. The waveform of the secondary H-bridge of the dual active bridge converter is obtained by controlling... and The phase between them enables power transfer in dual active converters.

[0021] Step 4: Determine the phase shift value according to the converter modulation method, change the phase between the drive pulses, control the DAB transmission power of the dual active bridge converter, and optimize the light-load efficiency of the DAB converter.

[0022] Step 4 is as follows: The DAB converter drive pulse includes four drive pulses: ePWM1A, ePWM1B, ePWM2A, and ePWM2B. ePWM1A is connected to the switches S1 and S4 in the converter, ePWM1B is connected to the switches S2 and S3 in the converter, ePWM2A is connected to the switches Q1 and Q4 in the converter, and ePWM2B is connected to the switches Q2 and Q3 in the converter. Step 4.1: If the modulation method is SPS, then change the phase between ePWM1A and ePWM2A. The phase shift value and power expression are (16): (16) Step 4.2: If the modulation method is PS-IPS, then change the phase between ePWM1A and ePWM1B. The phase shift value and power expression are (17): (17) Figure 7 The simulation waveform diagram shows the hybrid modulation strategy of switching from PS-IPS to SPS when P=0.2. Figure 8 The simulation waveform diagram shows the hybrid modulation strategy of switching from SPS to PS-IPS when P=0.5. Figure 9 The waveform diagram is from an experiment using the SPS modulation strategy. Figure 10 The waveform diagram shows the experimental results of the PS-IPS modulation strategy. It can be seen from the waveform results that the hybrid modulation of SPS and PS-IPS can optimize current stress and improve the transmission efficiency of the converter throughout the power range.

Claims

1. A method for optimizing single-degree-of-freedom hybrid modulation and light-load efficiency of DAB converters, characterized in that, Includes the following steps: Step 1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2. Calculate the output power P of the DAB converter. out Voltage transmission ratio k and per-unit transmission power P; The specific process of step 1 is as follows: Step 1.1: Acquire the input voltage of the DAB converter V 1. Output voltage V 2 and output current I 2; Step 1.2: Calculate the output power P of the DAB converter out Voltage transfer ratio k: （1） （2） In the formula, N is the ratio of the primary to the secondary winding of the transformer, and N > 0; Step 1.3: Calculate the DAB converter at the input voltage V 1. Output voltage V 2. Maximum transmission power when the transformer turns ratio is N P N : （3） In the formula, For switching frequency, L This refers to the inductance value; Step 1.4: Calculate the per-unit power P of the DAB converter: （4） Step 2: Obtain the efficiency-optimized power range of the DAB converter in PS-IPS modulation mode, and determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. The specific process of step 2 is as follows: Step 2.1: Plot the phase shift value-power per-unit value curve based on the per-unit value expression of the DAB converter's transmission power under SPS and PS-IPS modulation modes, and read the efficiency optimization power range of the DAB converter in PS-IPS modulation mode from the plotted curve. The specific process of step 2.1 is as follows: Step 2.1.1: Determine the per-unit value of the transmission power of the DAB converter under SPS modulation. P The expression is: （5） P SPS = （6） In the formula, This represents the transmission power corresponding to SPS modulation. This refers to the phase shift value corresponding to the SPS modulation method; Step 2.1.2: Determine the per-unit value of the transmission power of the DAB converter under PS-IPS modulation. P The expression is: （7） P PS-IPS = （8） In the formula, This refers to the transmission power corresponding to PS-IPS modulation. This refers to the phase shift value corresponding to the PS-IPS modulation method; Step 2.1.3: Plot the phase shift value-power per unit value curves corresponding to SPS and PS-IPS modulation modes according to formulas (5) and (7), and obtain the efficiency optimization power range of the DAB converter in PS-IPS modulation mode as (0, 0.5). Step 2.2: Determine the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal using the converter current stress expression under PS-IPS and SPS modulation methods; The specific process of step 2.2 is as follows: Step 2.2.1: Determine the expression for the current stress of the DAB converter under SPS modulation as follows: （9） （10） I SPS_max= （11） In the formula, G 1 represents the per-unit value of the current stress in the DAB converter under SPS modulation. I N This represents the maximum transfer current of the DAB converter. I SPS_max Current stress of the DAB converter under SPS modulation; Step 2.2.2: Determine the expression for the current stress of the DAB converter under PS-IPS modulation as follows: （12） I PS-IPS_max = （13） In the formula, G 2 represents the per-unit value of the current stress in the DAB converter under PS-IPS modulation. I PS-IPS_max Current stress in DAB converters under PS-IPS modulation; Step 2.2.3: Based on formulas (5), (7), (9), and (12), plot the three-dimensional kPG curves for SPS and PS-IPS modulation methods. From the plotted three-dimensional kPG curves, obtain the voltage transfer ratio when the current stress of PS-IPS and SPS modulation is equal. ; Step 3: Determine the converter modulation method based on the relationship between the voltage transfer ratio and k when the current stress of PS-IPS and SPS modulation is equal, and the relationship between P and the efficiency optimization power range; Step 3 specifically includes the following steps: Step 3.1: If 0 < P < 0.5 and Formula (14) is obtained from formulas (5)-(12), and the reference value of voltage transfer ratio during PS-IPS and SPS switching is determined by formula (14). kt : （14） The switching expression within the mixed modulation region is: （15） like k < If k ≥ 0, then SPS modulation is used. In this case, PS-IPS modulation is used; Step 3.2: If 0 < P < 0.5 and In this case, PS-IPS modulation is used; Step 3.3: If P ≥ 0.5 and k ≥ 1, then SPS modulation is used; Step 4: Determine the phase shift value according to the converter modulation method, change the phase between the drive pulses, control the power of the dual active bridge converter, and optimize the light-load efficiency of the DAB converter.

2. The method for single-degree-of-freedom hybrid modulation and light-load efficiency optimization of DAB converter according to claim 1, characterized in that, The specific process of step 4 is as follows: The DAB converter drive pulse includes four drive pulses: ePWM1A, ePWM1B, ePWM2A, and ePWM2B. ePWM1A is connected to the switches S1 and S4 in the converter; ePWM1B is connected to the switches S2 and S3 in the converter; ePWM2A is connected to the switches Q1 and Q4 in the converter; and ePWM2B is connected to the switches Q2 and Q3 in the converter. In the DAB converter, switches S1 and S2 are connected in series, switches S3 and S4 are connected in series, and they are connected in parallel on the primary side H1. Switches Q1 and Q2 are connected in series, switches Q3 and Q4 are connected in series, and they are connected in parallel on the secondary side H2. The connection between the primary side H1 and the secondary side H2 is achieved through inductor L and transformer T. Step 4.1: If the modulation method is SPS, then change the phase between ePWM1A and ePWM2A. The phase shift value and power expression are (16): （16） Step 4.2: If the modulation method is PS-IPS, then change the phase between ePWM1A and ePWM1B. The phase shift value and power expression are (17): （17）。

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