A DAB efficiency optimization method considering dead time

Abstract

The present invention belongs to the technical field of power electronics and relates to a DAB efficiency optimization method considering dead time, which is to optimize the transmission power P of the dual active full-bridge DAB converter by pu The dividing line P of each power range 1、 P 2、 P3 is compared to determine the power range of the dual-active full-bridge DAB converter, and then the optimal control variables are calculated in different power ranges of the dual-active full-bridge DAB converter; and the calculated optimal control variables are applied to the dual-active full-bridge DAB converter. If the output voltage v o and its reference value v o,ref If the values ​​of the DAB converter and the DAB voltage are equal, the DAB converter operates normally. This DAB efficiency optimization method, which considers dead time, consistently keeps the DAB converter operating at the boundary of the ZVS condition in the low-power range, minimizing current stress while ensuring ZVS. In the medium-power range, ZVS for all switching devices is unattainable. This method achieves ZVS for all six switching devices, maximizing DAB efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a DAB efficiency optimization method considering dead time. Background Art

[0002] Dual Active Bridge (DAB) DC / DC converters have been widely used in electric vehicles, DC microgrids, solid-state transformers, power electronic traction transformers and other fields due to their advantages such as bidirectional power flow, zero voltage switching (ZVS), electrical isolation and high power density. However, when the ratio of the input and output voltages of the DAB converter does not match the ratio of its internal high-frequency transformer, the use of the traditional single phase shift (SPS) modulation strategy will cause the converter's circulating current to increase sharply and the ZVS range to decrease, greatly reducing the power transmission efficiency. Currently, there are two main ways to improve the efficiency of DAB converters:

[0003] 1) Reducing conduction losses can be achieved by adopting new modulation strategies such as extended phase-shift modulation, double phase-shift modulation, and triple phase-shift modulation, and optimizing the inductor current stress, effective value, or return power.

[0004] 2) Reducing switching losses requires optimizing the ZVS range of the DAB. The optimization goal of maximizing the ZVS range for DAB is generally not independent but is combined with other optimization goals (minimizing current stress, minimizing RMS value, or minimizing return power). Furthermore, ZVS is typically achieved under light load conditions by sacrificing a small amount of current performance (increasing current stress, RMS value, or return power).

[0005] The Chinese patent with publication number CN107425729A and publication date 20171201 discloses a DAB soft switching method based on current modulation ratio and current efficiency optimization. The invention takes minimizing the effective value of current and ensuring soft switching as the optimization goals. When calculating the soft switching conditions, only the direction of the inductor current is considered, and the dead time parameter is not considered. The conclusion drawn cannot guarantee the realization of DAB soft switching. The coefficient α in the control variable only gives an approximate calculation range, and does not provide detailed calculation steps. However, the conduction loss is mainly related to the effective value current, while the core loss and switching loss are mainly affected by the current stress (this conclusion is drawn from the document ZHANG Hongwei, LIU Zeng, SONG Ying, et al. A current-stress-optimized design method for dual active bridge converters with improved ZVS capability under wide output voltage conditions [J]. IEEE Transactions on Industrial Electronics, 2024, 71 (6): 5807-5817.). Therefore, minimizing the current stress and maximizing the ZVS range are the most appropriate optimization goals.

[0006] Although existing methods can improve the efficiency of the dual-active full-bridge DAB converter to a certain extent and ensure that all switching devices can achieve ZVS within the full power range, they do not take the dead time into consideration. Moreover, due to the discontinuous change of the control variable, the inductance and output current may undergo sudden changes, affecting the stability of the system. Summary of the Invention

[0007] The object of the present invention is to provide a DAB efficiency optimization method taking dead time into consideration, so as to overcome the problems existing in the above-mentioned background technology.

[0008] The present invention solves the technical problem by the following technical solutions:

[0009] A DAB efficiency optimization method considering dead time, characterized by comprising the following steps:

[0010] S1: Obtain system parameters, which include: input voltage v of dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter v o , the transformation ratio N of the dual active bridge DAB converter t , the switching frequency f of the dual active bridge DAB converter s, the sum of the high-frequency transformer leakage inductance and auxiliary inductance L r , dead time T dead ; Then calculate the inductor current reference value I b and voltage transformation ratio d;

[0011] S2: Based on the obtained inductor current reference value I b Calculate the minimum current I required to achieve ZVS on the primary side of a dual-active full-bridge DAB converter p,min The minimum current I that can achieve ZVS on the secondary side s,min ;

[0012] S3: Based on the obtained voltage transformation ratio d, the minimum current I of the primary side of the dual active full-bridge DAB converter that can achieve ZVS p,min The minimum current I that can achieve ZVS on the secondary side s,min Calculate a boundary line P1 between the low power range and the medium power range 1, a boundary line P2 between the medium power range 1 and the medium power range 2, and a boundary line P3 between the medium power range 2 and the high power range;

[0013] S4: According to the output voltage v of the dual active bridge DAB converter o and its reference value v o,ref , calculate the required transmission power P of the dual active full-bridge DAB converter pu ;

[0014] S5: The required transmission power P of the dual active full-bridge DAB converter pu By comparing with the dividing line P1 between the low power range and the medium power range 1, the dividing line P2 between the medium power range 1 and the medium power range 2, and the dividing line P3 between the medium power range 2 and the high power range, the power range of the dual-active full-bridge DAB converter is determined, and then the optimal control variables are calculated in different power ranges of the dual-active full-bridge DAB converter;

[0015] S6: Apply the calculated optimal control variables to the dual-active full-bridge DAB converter to adjust the output voltage v of the dual-active full-bridge DAB converter. o,1 , and then determine the output voltage v of the adjusted dual active bridge DAB converter o,1 and its reference value v o,ref Are they equal? ​​If the output voltage v of the adjusted dual active bridge DAB converter is o,1 and its reference value v o,ref If they are equal, the dual-active full-bridge DAB converter operates normally, otherwise it returns to S4.

[0016] Furthermore, in S1, the inductor current reference value I b The calculation formulas for the voltage transformation ratio d are:

[0017]

[0018] Among them, v in Represents the input voltage of the dual active bridge DAB converter, v o Represents the output voltage of the dual active bridge DAB converter, N t represents the transformation ratio of the dual active bridge DAB converter, f s represents the switching frequency of the dual active bridge DAB converter, L r Represents the sum of the leakage inductance and auxiliary inductance of the high-frequency transformer.

[0019] Furthermore, in S2, the primary side of the dual active full-bridge DAB converter can achieve the minimum current I p,min The minimum current I that can achieve ZVS on the secondary side s,min The calculation formulas are:

[0020]

[0021] Among them, v in Represents the input voltage of the dual active bridge DAB converter, v o Represents the output voltage of the dual active bridge DAB converter, N t represents the transformation ratio of the dual active bridge DAB converter, T dead Indicates the dead time, L r Represents the sum of the high-frequency transformer leakage inductance and auxiliary inductance, I b Indicates the inductor current reference value.

[0022] Furthermore, in S3, the calculation formula of the dividing line P1 between the low power range and the medium power range 1 is:

[0023]

[0024] Where, d represents the voltage ratio, I p,min It represents the minimum current of the primary side of the dual active full-bridge DAB converter that can achieve ZVS, I s,min It represents the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

[0025] Furthermore, the calculation formula of the dividing line P2 between the medium power range 1 and the medium power range 2 is:

[0026] P2=(dI s,min )(1-d+I s,min )

[0027] Where, d represents the voltage ratio, I s,min It represents the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

[0028] Furthermore, the calculation formula of the dividing line P3 between the medium power range 2 and the high power range is:

[0029]

[0030] Where, d represents the voltage ratio, I s,min It represents the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

[0031] Furthermore, in S4, the transmission power required by the dual active full-bridge DAB converter is P pu The calculation formula is:

[0032]

[0033] Among them, K p Indicates the proportional coefficient of the controller, K i Indicates the integral coefficient of the controller, v o Represents the output voltage of the dual active bridge DAB converter, v o,ref It represents the reference value of the output voltage of the dual active bridge DAB converter.

[0034] Furthermore, in S5, the transmission power required by the dual active full-bridge DAB converter P pu The method for determining the power range of the dual-active full-bridge DAB converter by comparing the power range with the boundary line P1 between the low power range and the medium power range 1, the boundary line P2 between the medium power range 1 and the medium power range 2, and the boundary line P3 between the medium power range 2 and the high power range includes the following steps:

[0035] S5.1: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is greater than the dividing line P3 between the medium power range 2 and the high power range, the dual active full-bridge DAB converter is in the high power range. The optimal control variable in the high power range is calculated as follows: p,high , the optimal control variable D compared with the secondary side inward shift s,high , the optimal control variables compared with outward movement The calculation formula is as follows:

[0036]

[0037] Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter;

[0038] S5.2: If the required transmission power P of the dual active full-bridge DAB converter is puIf the value is less than or equal to the dividing line P3 between medium power range 2 and high power range and greater than the dividing line P2 between medium power range 1 and medium power range 2, then the dual active full-bridge DAB converter is in medium power range 2. Calculate the optimal control variable in medium power range 2: the optimal control variable D compared with the original side inward shift p,mid2 , the optimal control variable D compared with the secondary side inward shift s,mid2 , the optimal control variables compared with outward movement The calculation formula is as follows:

[0039]

[0040] Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter;

[0041] S5.3: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is less than or equal to the dividing line P2 between medium power range 1 and medium power range 2 and greater than the dividing line P1 between low power range and medium power range 1, then the dual active full-bridge DAB converter is in medium power range 1. Calculate the optimal control variable in medium power range 1: the optimal control variable D compared with the original side inward shift p,mid1 , the optimal control variable D compared with the secondary side inward shift s,mid1 , the optimal control variables compared with outward movement The calculation formula is as follows:

[0042]

[0043] Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter;

[0044] S5.4: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is less than or equal to the dividing line P1 between the low power range and the medium power range 1, the dual active full-bridge DAB converter is in the low power range. The optimal control variable in the low power range is calculated as follows: p,low , the optimal control variable D compared with the secondary side inward shift s,low , the optimal control variables compared with outward movement The calculation formula is as follows:

[0045]

[0046] Where d represents the voltage ratio, Ppu represents the required transmission power of the dual active full-bridge DAB converter, I p,min It represents the minimum current of the primary side of the dual active full-bridge DAB converter that can achieve ZVS, I s,min It represents the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

[0047] The advantages and beneficial effects of the present invention are:

[0048] Compared with the existing technology, this DAB efficiency optimization method considering dead time always makes the dual-active full-bridge DAB converter operate on the boundary of ZVS conditions in the low power range, minimizing current stress while ensuring ZVS. In the medium power range, ZVS of all switching devices cannot be achieved. This method can achieve ZVS of six switching devices, maximizing the efficiency of DAB.

[0049] The DAB efficiency optimization method considering dead time can ensure the continuity of control variables in the full power range and achieve seamless switching of various power ranges.

[0050] The DAB efficiency optimization method considering dead time does not use the parasitic parameters of the switching devices when calculating the ZVS minimum current, thus simplifying the calculation process.

[0051] The DAB efficiency optimization method considering dead time has low computation burden and can be calculated in real time in a microcontroller. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flow chart of the method for improving the efficiency of the dual-active full-bridge DAB converter proposed in the present invention;

[0053] Figure 2 The topology of the dual active full-bridge DAB converter of the present invention;

[0054] Figure 3 This is a trajectory diagram of the control variables of the efficiency improvement method proposed in the present invention;

[0055] Figure 4 This is a working waveform diagram of the efficiency improvement method proposed in the present invention in a low power range, where: Figure 4 (a) is the experimental waveform under SPS; Figure 4 (b) is the experimental waveform of the method proposed in the present invention; Figure 4 (c) is the experimental waveform when the switching device is turned on according to the method proposed by the present invention;

[0056] Figure 5 This is a working waveform diagram of the efficiency improvement method proposed in the present invention within the medium power range 1, where: Figure 5 (a) is the experimental waveform under SPS; Figure 5 (b) is the experimental waveform of the method proposed in the present invention; Figure 5 (c) is the experimental waveform when the switching device is turned on according to the method proposed by the present invention;

[0057] Figure 6 This is a working waveform diagram of the efficiency improvement method proposed in the present invention within the medium power range 2, where: Figure 6 (a) is the experimental waveform under SPS; Figure 6 (b) is the experimental waveform of the method proposed in the present invention; Figure 6 (c) is the experimental waveform when the switching device is turned on according to the method proposed by the present invention;

[0058] Figure 7 This is a working waveform diagram of the efficiency improvement method proposed in the present invention in the high power range, where: Figure 7 (a) is the experimental waveform under SPS; Figure 7 (b) is the experimental waveform of the method proposed in the present invention; Figure 7 (c) is the experimental waveform when the switching device is turned on according to the method proposed in the present invention. DETAILED DESCRIPTION

[0059] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0060] The present invention proposes a DAB efficiency optimization method considering dead time. First, different optimal control variables are designed according to different power transmission ranges (the control variables include: the optimal control variable D of the primary side inward shift ratio p , the optimal control variable D compared with the secondary side inward shift s Optimal control variables compared to outward migration ), enabling the dual-active full-bridge DAB converter to simultaneously achieve both ZVS and minimize current stress. Then, in the low-power range, the optimization method of the present invention ensures that the DAB always operates on the boundary of ZVS conditions, thereby minimizing current stress while ensuring ZVS. In the medium-power range, although ZVS for all switching devices is unattainable, to maximize DAB efficiency, the optimization method of the present invention achieves ZVS for six switching devices by adjusting the ZVS constraints. In the high-power range, since the DAB can naturally achieve ZVS, its optimization goal is to minimize current stress.

[0061] A DAB efficiency optimization method considering dead time, such as Figure 1 As shown, the method includes:

[0062] S1: Obtain system parameters, which include: input voltage v of dual active bridge DAB converterin , the output voltage of the dual active bridge DAB converter v o , the transformation ratio N of the dual active bridge DAB converter t , the switching frequency f of the dual active bridge DAB converter s , the sum of the high-frequency transformer leakage inductance and auxiliary inductance L r , dead time T dead ; Then, calculate the inductor current reference value I b , transmission power reference value P b and voltage ratio d; inductor current reference value I b The calculation formulas for the voltage transformation ratio d are:

[0063]

[0064] S2: Calculate the minimum current I required to achieve ZVS on the primary side of the dual-active full-bridge DAB converter p,min The minimum current I that can achieve ZVS on the secondary side s,min ; Minimum current I on the primary side to achieve ZVS p,min The minimum current I that can achieve ZVS on the secondary side s,min The calculation formulas are:

[0065]

[0066] S3: Based on the obtained voltage transformation ratio d, the minimum current I of the primary side of the dual active full-bridge DAB converter that can achieve ZVS p,min The minimum current I that can achieve ZVS on the secondary side s,min Calculate the boundary line P1 between the low power range and the medium power range 1, the boundary line P2 between the medium power range 1 and the medium power range 2, and the boundary line P3 between the medium power range 2 and the high power range. The calculation formula for the boundary line P1 between the low power range and the medium power range 1 is:

[0067]

[0068] The calculation formula for the dividing line P2 between the medium power range 1 and the medium power range 2 is:

[0069] P2=(dI s,min )(1-d+I s,min )

[0070] The calculation formula for the dividing line P3 between the medium power range 2 and the high power range is:

[0071]

[0072] S4: According to the output voltage v of the dual active bridge DAB converter o and its reference value vo,ref Calculate the required transmission power P of the dual active full-bridge DAB converter pu ; Required transmission power P pu The calculation formula is:

[0073]

[0074] Among them, K p Indicates the proportional coefficient of the controller, K i Indicates the integral coefficient of the controller, v o Represents the output voltage of the dual active bridge DAB converter, v o,ref It represents the reference value of the output voltage of the dual active bridge DAB converter.

[0075] S5: The required transmission power P pu Compare with the dividing lines P1, P2, and P3 of each power range to determine the power range of the dual-active full-bridge DAB converter:

[0076] If the required transmission power P pu If the power is greater than the power dividing line P3, then S5.1 is executed and the dual-active full-bridge DAB converter is in the high power range;

[0077] If the required transmission power P pu If the power is less than or equal to the power dividing line P3 and greater than the power dividing line P2, then execute S5.2 and the dual-active full-bridge DAB converter is in the medium power range 2;

[0078] If the required transmission power P pu If the power is less than or equal to the power dividing line P2 and greater than the power dividing line P1, then execute S5.3 and the dual-active full-bridge DAB converter is in the medium power range 1;

[0079] If the required transmission power P pu If the power is less than or equal to the power dividing line P1, then execute S5.4 and the dual-active full-bridge DAB converter is in the low power range;

[0080] S5.1: Calculate the optimal control variable in the high power range: the optimal control variable D compared with the original side inward shift p,high , the optimal control variable D compared with the secondary side inward shift s,high , the optimal control variables compared with outward movement The calculation formula is:

[0081]

[0082] S5.2: Calculate the optimal control variable in the medium power range 2: the optimal control variable D compared with the original side inward shift p,mid2 , the optimal control variable D compared with the secondary side inward shift s,mid2, the optimal control variables compared with outward movement The calculation formula is:

[0083]

[0084] Δ=(1+dI s,min )(1-d+I s,min )-2P pu

[0085] S5.3: Calculate the optimal control variable in the medium power range 1: the optimal control variable D compared with the original side inward shift p,mid1 , the optimal control variable D compared with the secondary side inward shift s,mid1 , the optimal control variables compared with outward movement The calculation formula is:

[0086]

[0087] S5.4: Calculate the optimal control variable in the low power range: the optimal control variable D compared with the original side inward shift p,low , the optimal control variable D compared with the secondary side inward shift s,low , the optimal control variables compared with outward movement The calculation formula is:

[0088]

[0089] S6: Apply the calculated optimal control variables to the dual-active full-bridge DAB converter to adjust the output voltage v of the dual-active full-bridge DAB converter. o,1 , and then determine the output voltage v of the adjusted dual active bridge DAB converter o,1 and its reference value v o,ref Are they equal? ​​If the output voltage v of the adjusted dual active bridge DAB converter is o,1 and its reference value v o,ref If they are equal, the dual-active full-bridge DAB converter operates normally, otherwise it returns to S4.

[0090] The topology of DAB is as follows Figure 2 As shown, DAB consists of the primary full bridge (T1-T4), the secondary full bridge (T5-T8), and the input DC side capacitor C in , output DC side capacitor C o , high frequency transformer T and auxiliary inductor L r The DAB primary full-bridge inward shift refers to the ratio of the phase difference of the driving pulses of the switching devices T1 and T4 in the primary full-bridge to the pulse period. The DAB outward shift refers to the ratio of the phase difference of the driving pulses of the switching devices T1 and T5 to the pulse period. The DAB secondary full-bridge inward shift refers to the ratio of the phase difference of the driving pulses of the switching devices T5 and T8 in the primary full-bridge to the pulse period.ab is the square wave voltage on the primary full-bridge AC side, v cd It is the square wave voltage on the secondary full-bridge AC side.

[0091] A specific implementation of a DAB efficiency optimization method considering dead time includes the following steps:

[0092] First, obtain the system parameters, which include: the input voltage v of the dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter v o , the transformation ratio N of the dual active bridge DAB converter t , the switching frequency f of the dual active bridge DAB converter s , the sum of the high-frequency transformer leakage inductance and auxiliary inductance L r , dead time T dead ; Calculate the inductor current reference value I b , voltage ratio d, and the minimum current I required for the primary side of the dual active bridge DAB converter to achieve ZVS. p,min The minimum current I that can achieve ZVS on the secondary side of the dual active bridge DAB converter is s,min ;

[0093] Secondly, calculate the dividing lines P1, P2 and P3 of each power range;

[0094] Then, according to the output voltage v of the dual active bridge DAB converter o and its reference value v o,ref Calculate the required transmission power P of the dual active full-bridge DAB converter pu ;

[0095] Finally, the required transmission power P of the dual active bridge DAB converter is pu Compare with the dividing lines P1, P2, and P3 of each power range to determine the power range of the dual-active full-bridge DAB converter. pu If the power required by the dual-active full-bridge DAB converter is greater than the power boundary P3, the dual-active full-bridge DAB converter is in the high power range, and the corresponding optimal control variables are calculated; if the required transmission power P of the dual-active full-bridge DAB converter is pu If the power required by the dual-active full-bridge DAB converter is less than or equal to the power dividing line P3 and greater than the power dividing line P2, the dual-active full-bridge DAB converter is in the medium power range 2, and the corresponding optimal control variables are calculated; if the required transmission power P of the dual-active full-bridge DAB converter is pu If the power required by the dual-active full-bridge DAB converter is less than or equal to the power dividing line P2 and greater than the power dividing line P1, the dual-active full-bridge DAB converter is in the medium power range 1, and the corresponding optimal control variables are calculated; if the required transmission power P of the dual-active full-bridge DAB converter is puIf it is less than or equal to the power dividing line P1, the dual active full-bridge DAB converter is in the low power range, and the corresponding optimal control variables are calculated;

[0096] The trajectory diagram of the optimal control variable is as follows: Figure 3 As shown, according to Figure 3 It can be seen that the efficiency improvement method proposed in the present invention can ensure the continuity of the control variables within the full power range, that is, each power range can achieve seamless switching.

[0097] according to Figure 2 The topology shown in the figure is used to build a DAB converter experimental prototype. Its parameters are as follows: the input voltage v in =120V, the output voltage reference value of the dual active bridge DAB converter is v o,ref =60V, the switching frequency f of the dual active bridge DAB converter s =20kHz, the transformation ratio of the dual active bridge DAB converter is N t =1, input side capacitance C in =1.12×10 -3 F, output side capacitance C o =1.12×10 -3 F, the sum of the high-frequency transformer leakage inductance and auxiliary inductance L r =60×10 -6 H, dead time T dead =1us. According to the above parameters, we can calculate: P1 = 0.1748, P2 = 0.2484, P3 = 0.2884.

[0098] In order to verify the effectiveness of the method proposed in this invention, an operating point is selected in each of the four power ranges for experimental verification. Figure 4-7 As shown. In the low power range, select P pu =0.1(P=150W), select P in the medium power range 1 pu =0.18(P=270W), select P in the medium power range 2 pu =0.25(P=375W), select P in the high power range pu =0.34(P=510W).

[0099] Figure 4 is the transmission power P pu =0.1(P=150W). Among them, Figure 4 (a) is the experimental waveform under SPS, the current stress is about 14A; Figure 4 (b) is the experimental waveform of the method proposed by the present invention, the current stress is about 8A, compared Figure 4(a) and 4(b), it can be seen that the method proposed in the present invention can optimize the current stress in the low power range; Figure 4 (c) is the experimental waveform when the switching device is turned on according to the method proposed in the present invention. It can be seen that all switching devices can achieve ZVS.

[0100] Figure 5 is the transmission power P pu =0.18 (P = 270W) when the steady-state waveform. Figure 5 (a) is the experimental waveform under SPS, the current stress is about 16A; Figure 5 (b) is the experimental waveform of the method proposed in the present invention, the current stress is about 10.5A, compared Figure 5 (a) and 5(b), the current stress can be optimized in the medium power range 1. Figure 5 (b) It can be seen that i Lr (T1)≈0A, which does not meet the ZVS condition; Figure 5 (c) is the experimental waveform when the switching device is turned on according to the method proposed by the present invention. Figure 5 (c) It can be seen that the switch device T1 does not achieve ZVS, that is, the two switch devices in the first bridge arm of the DAB converter cannot achieve ZVS, and only 6 switch devices can achieve ZVS.

[0101] Figure 6 is the transmission power P pu =0.25(P=375W). Among them, Figure 6 (a) is the experimental waveform under SPS, the current stress is about 17A; Figure 6 (b) is the experimental waveform of the method proposed in the present invention, the current stress is about 13A, compared Figure 6 From the current stress of (a) and 6 (b), it can be seen that the method proposed in the present invention can minimize the current stress in the medium power range 2. Figure 6 (b) It can be seen that i Lr,pu (T1)>-I p,min , does not meet the ZVS condition; Figure 6 (c) is the experimental waveform when the switch device is turned on according to the method proposed by the present invention. Figure 6 (c) It can be seen that the switch device T1 does not achieve ZVS, that is, the two switch devices in the first bridge arm of the DAB converter cannot achieve ZVS, and only 6 switch devices can achieve ZVS.

[0102] Figure 7 is the transmission power P pu =0.34 (P=510W) when the steady-state waveform. Figure 7 (a) is the experimental waveform under SPS, the current stress is about 18A; Figure 7 (b) is the experimental waveform of the method proposed in the present invention, the current stress is about 15.5A, compared Figure 7 (a) and 7(b), it can be seen that the method proposed in the present invention can minimize the current stress; Figure 7 (c) is the experimental waveform when the switch device is turned on according to the method proposed by the present invention. Figure 7 (c) It can be seen that all switching devices achieve ZVS.

[0103] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A DAB efficiency optimization method considering dead time, characterized by: The steps include: S1: Obtain system parameters, which include: input voltage v of dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter v o , the transformation ratio N of the dual active bridge DAB converter t , the switching frequency f of the dual active bridge DAB converter s , the sum of the high-frequency transformer leakage inductance and auxiliary inductance L r , dead time T dead ; Then calculate the inductor current reference value I b and voltage transformation ratio d; S2: Based on the obtained inductor current reference value I b Calculate the minimum current I required to achieve ZVS on the primary side of a dual-active full-bridge DAB converter p,min The minimum current I that can achieve ZVS on the secondary side s,min ; S3: Based on the obtained voltage transformation ratio d, the minimum current I of the primary side of the dual active full-bridge DAB converter that can achieve ZVS p,min The minimum current I that can achieve ZVS on the secondary side s,min Calculate a boundary line P1 between the low power range and the medium power range 1, a boundary line P2 between the medium power range 1 and the medium power range 2, and a boundary line P3 between the medium power range 2 and the high power range; P2=(d-I s,min )(1-d+I s,min ), S4: According to the output voltage v of the dual active bridge DAB converter o and its reference value v o,ref , calculate the required transmission power P of the dual active full-bridge DAB converter pu ; S5: The required transmission power P of the dual active full-bridge DAB converter pu By comparing with the dividing line P1 between the low power range and the medium power range 1, the dividing line P2 between the medium power range 1 and the medium power range 2, and the dividing line P3 between the medium power range 2 and the high power range, the power range of the dual-active full-bridge DAB converter is determined, and then the optimal control variables are calculated in different power ranges of the dual-active full-bridge DAB converter; S6: Apply the calculated optimal control variables to the dual-active full-bridge DAB converter to adjust the output voltage v of the dual-active full-bridge DAB converter. o,1 , and then determine the output voltage v of the adjusted dual active bridge DAB converter o,1 and its reference value v o,ref Are they equal? ​​If the output voltage v of the adjusted dual active bridge DAB converter is o,1 and its reference value v o,ref If they are equal, the dual-active full-bridge DAB converter operates normally, otherwise it returns to S4.

2. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: In S1, the inductor current reference value I b The calculation formulas for the voltage transformation ratio d are: Among them, v in Represents the input voltage of the dual active bridge DAB converter, v o Represents the output voltage of the dual active bridge DAB converter, N t represents the transformation ratio of the dual active bridge DAB converter, f s represents the switching frequency of the dual active bridge DAB converter, L r Represents the sum of the leakage inductance and auxiliary inductance of the high-frequency transformer.

3. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: In S4, the dual active full-bridge DAB converter requires a transmission power P pu The calculation formula is: Among them, K p Indicates the proportional coefficient of the controller, K i Indicates the integral coefficient of the controller, v o Represents the output voltage of the dual active bridge DAB converter, v o,ref It represents the reference value of the output voltage of the dual active bridge DAB converter.

4. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: In S5, the required transmission power P of the dual active full-bridge DAB converter is pu The method for determining the power range of the dual-active full-bridge DAB converter by comparing the power range with the boundary line P1 between the low power range and the medium power range 1, the boundary line P2 between the medium power range 1 and the medium power range 2, and the boundary line P3 between the medium power range 2 and the high power range includes the following steps: S5.1: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is greater than the dividing line P3 between the medium power range 2 and the high power range, the dual active full-bridge DAB converter is in the high power range. The optimal control variable in the high power range is calculated as follows: p,high , the optimal control variable D compared with the secondary side inward shift s,high , the optimal control variables compared with outward movement The calculation formula is as follows: Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter; S5.2: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is less than or equal to the dividing line P3 between medium power range 2 and high power range and greater than the dividing line P2 between medium power range 1 and medium power range 2, then the dual active full-bridge DAB converter is in medium power range 2. Calculate the optimal control variable in medium power range 2: the optimal control variable D compared with the original side inward shift p,mid2 , the optimal control variable D compared with the secondary side inward shift s,mid2 , the optimal control variables compared with outward movement The calculation formula is as follows: Δ=(1+d-I s,min )(1-d+I s,min )-2P pu Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter; S5.3: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is less than or equal to the dividing line P2 between medium power range 1 and medium power range 2 and greater than the dividing line P1 between low power range and medium power range 1, then the dual active full-bridge DAB converter is in medium power range 1. Calculate the optimal control variable in medium power range 1: the optimal control variable D compared with the original side inward shift p,mid1 , the optimal control variable D compared with the secondary side inward shift s,mid1 , the optimal control variables compared with outward movement The calculation formula is as follows: Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter; S5.4: If the required transmission power P of the dual active full-bridge DAB converter is pu If the value is less than or equal to the dividing line P1 between the low power range and the medium power range 1, the dual active full-bridge DAB converter is in the low power range. The optimal control variable in the low power range is calculated as follows: p,low , the optimal control variable D compared with the secondary side inward shift s,low , the optimal control variables compared with outward movement The calculation formula is as follows: Where d represents the voltage ratio, P pu represents the required transmission power of the dual active full-bridge DAB converter, I p,min It represents the minimum current of the primary side of the dual active full-bridge DAB converter that can achieve ZVS, I s,min It represents the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

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