DAB efficiency optimization method considering dead time

Abstract

The invention belongs to the technical field of power electronics, and relates to a DAB efficiency optimization method considering dead time, which comprises the following steps of: comparing transmission power Ppu required by a dual-active full-bridge DAB converter with boundaries P1, P2 and P3 of each power range to judge the power range of the dual-active full-bridge DAB converter; respectively calculating optimal control variables in different power ranges of the dual-active full-bridge DAB converter; and applying the calculated optimal control variable to the dual-active full-bridge DAB converter, and if the output voltage vo of the dual-active full-bridge DAB converter is equal to the reference value vo, ref thereof, determining that the dual-active full-bridge DAB converter operates normally. According to the DAB efficiency optimization method considering the dead time, in a low power range, a dual-active full-bridge DAB converter always works on the boundary of a ZVS condition, and the current stress is minimized on the basis of ensuring the ZVS; within a medium power range, the ZVS of all switching devices cannot be realized, and the method can realize the ZVS of six switching devices and maximize the efficiency of the DAB.

Description

Technical Field

[0001] The 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 transformation 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. At present, 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) Reduce switching losses, which needs to be achieved by optimizing the ZVS range of DAB. The optimization goal of maximizing the ZVS range of DAB is generally not independent, but is combined with other optimization goals (minimizing current stress, minimizing effective value, or minimizing return power). And the realization of ZVS is usually achieved under light load conditions by sacrificing a small part of current performance (increasing current stress, effective value, or return power).

[0005] The Chinese patent with publication number CN107425729A and publication date 20171201 discloses a soft switching method of DAB 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 parameter of dead time 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 give 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 current stress and maximizing the ZVS range are the most appropriate optimization goals.

[0006] Although the 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. In addition, due to the discontinuous change of the control variables, the inductance and output current may change suddenly, 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 considering dead time, 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 in that it comprises the following steps:

[0010] S1: Obtain system parameters, which specifically include: the input voltage v of the dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter is 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 of the primary side of the dual active full-bridge DAB converter to achieve ZVS p,min and the minimum current I on the secondary side to achieve ZVS s,min ;

[0012] S3: Based on the obtained voltage transformation ratio d, the minimum current I that can achieve ZVS on the primary side of the dual active full-bridge DAB converter p,min and the minimum current I on the secondary side to achieve ZVS 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 respectively in different power ranges of the dual active full-bridge DAB converter;

[0015] S6: Apply the calculated optimal control variable 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 If the output voltage v of the adjusted dual active bridge DAB converter is equal to 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 leakage inductance and auxiliary inductance of the high-frequency transformer, I b Indicates the inductor current reference value.

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

[0023]

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

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

[0032]

[0033] Among them, K p Represents the proportional coefficient of the controller, K i represents 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] Further, in S5, the transmission power P required by 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 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 comprises the following steps:

[0035] S5.1: If the required transmission power P of the dual active full-bridge DAB converter pu If it 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 variable compared with the outward shift The calculation formula is as follows:

[0036]

[0037] Where d represents the voltage transformation 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 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, 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 variable compared with the outward shift The calculation formula is as follows:

[0039]

[0040] Where d represents the voltage transformation 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 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, 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 variable compared with the outward shift The calculation formula is as follows:

[0042]

[0043] Where d represents the voltage transformation 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 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 D 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 variable compared with the outward shift The calculation formula is as follows:

[0045]

[0046] Where d represents the voltage transformation 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 indicates 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 prior art, the DAB efficiency optimization method considering dead time in the low power range always makes the dual active full-bridge DAB converter operate on the boundary of ZVS conditions, minimizing the current stress on the basis of ensuring ZVS; in the medium power range, ZVS of all switching devices cannot be achieved, and the method can achieve ZVS of 6 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 realize seamless switching of various power ranges.

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

[0051] The DAB efficiency optimization method considering dead time has a small computational 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 by the present invention;

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

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

[0055] Figure 4 This is a working waveform diagram of the efficiency improvement method proposed by the present invention in a low power range, wherein: Figure 4 (a) is the experimental waveform under SPS; Figure 4 (b) is the experimental waveform of the method proposed by the present invention; Figure 4 (c) is the experimental waveform when the switch 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, wherein: Figure 5 (a) is the experimental waveform under SPS; Figure 5 (b) is the experimental waveform of the method proposed by the present invention; Figure 5 (c) is the experimental waveform when the switch 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, wherein: Figure 6 (a) is the experimental waveform under SPS; Figure 6 (b) is the experimental waveform of the method proposed by the present invention; Figure 6 (c) is the experimental waveform when the switch 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 by the present invention in a high power range, wherein: Figure 7 (a) is the experimental waveform under SPS; Figure 7 (b) is the experimental waveform of the method proposed by 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 is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope 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 ), so that the dual active full-bridge DAB converter can achieve both ZVS and minimum current stress. Then, in the low power range, the optimization method of the present invention enables DAB to always work on the boundary of the ZVS condition, thereby minimizing the current stress on the basis of ensuring ZVS; in the medium power range, although ZVS of all switching devices cannot be achieved, in order to maximize the efficiency of DAB, the optimization method of the present invention can achieve ZVS of 6 switching devices by adjusting the ZVS constraint conditions. In the high power range, since 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 specifically include: the input voltage v of the dual active bridge DAB converterin , the output voltage of the dual active bridge DAB converter is 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 of the primary side of the dual active full-bridge DAB converter that can achieve ZVS p,min and the minimum current I on the secondary side to achieve ZVS s,min ; The minimum current I that can achieve ZVS on the primary side p,min and the minimum current I on the secondary side to achieve ZVS s,min The calculation formulas are:

[0065]

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

[0067]

[0068] The calculation formula of 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 of 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 Represents the proportional coefficient of the controller, K i represents 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 it is greater than the power dividing line P3, 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 it is less than or equal to the power dividing line P3 and greater than the power dividing line P2, then S5.2 is executed and the dual active full-bridge DAB converter is in the medium power range 2;

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

[0079] If the required transmission power P pu If it is less than or equal to the power dividing line P1, S5.4 is executed 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 variable compared with the outward shift 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 variable compared with the outward shift 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 variable compared with the outward shift 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 variable compared with the outward shift The calculation formula is:

[0088]

[0089] S6: Apply the calculated optimal control variable 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 If the output voltage v of the adjusted dual active bridge DAB converter is equal to 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 a primary full bridge (T1-T4), a secondary full bridge (T5-T8), and an 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, and 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, vab 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 method of a DAB efficiency optimization method considering dead time, wherein the specific process includes:

[0092] First, obtain the system parameters, which specifically include: the input voltage v of the dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter is 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 transformation ratio d, the minimum current I that can achieve ZVS on the primary side of the dual active bridge DAB converter p,min , the minimum current I that can achieve ZVS on the secondary side of the dual active bridge DAB converter 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 The power range of the dual active full-bridge DAB converter is determined by comparing it with the dividing lines P1, P2, and P3 of each power range. pu If the required transmission power P of the dual active full-bridge DAB converter is greater than the power dividing line P3, the dual active full-bridge DAB converter is in the high power range, and the corresponding optimal control variables are calculated; pu If the required transmission power P of 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 required transmission power P of 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 of the dual active bridge DAB converter 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 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 the present invention, one working point is selected in each of the four power ranges for experimental verification. Figure 4-7 As shown. Select P in the low power range 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, and 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, and the comparison 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 switch device is turned on according to the method proposed in the present invention. It can be seen that all switch devices can achieve ZVS.

[0100] Figure 5 is the transmission power P pu =0.18 (P = 270W) when the steady-state waveform. Among them, Figure 5 (a) is the experimental waveform under SPS, and the current stress is about 16A; Figure 5 (b) is the experimental waveform of the method proposed by the present invention, the current stress is about 10.5A, compared with Figure 5 From the current stress of (a) and 5(b), it can be seen that the method proposed in the present invention can optimize the current stress within 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 switch 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) when the steady-state waveform. Among them, Figure 6 (a) is the experimental waveform under SPS, and the current stress is about 17A; Figure 6 (b) is the experimental waveform of the method proposed by the present invention, the current stress is about 13A, compared with 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, and the current stress is about 18A; Figure 7 (b) is the experimental waveform of the method proposed by the present invention, the current stress is about 15.5A, compared with 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 appreciate 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 in that: The steps include: S1: Obtain system parameters, which specifically include: the input voltage v of the dual active bridge DAB converter in , the output voltage of the dual active bridge DAB converter is 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 of the primary side of the dual active full-bridge DAB converter to achieve ZVS p,min and the minimum current I on the secondary side to achieve ZVS s,min ; S3: Based on the obtained voltage transformation ratio d, the minimum current I that can achieve ZVS on the primary side of the dual active full-bridge DAB converter p,min and the minimum current I on the secondary side to achieve ZVS 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; 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 respectively in different power ranges of the dual active full-bridge DAB converter; S6: Apply the calculated optimal control variable 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 If the output voltage v of the adjusted dual active bridge DAB converter is equal to 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 S2, the primary side of the dual active full-bridge DAB converter can achieve the minimum current I p,min and the minimum current I on the secondary side to achieve ZVS s,min The calculation formulas 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, T dead Indicates the dead time, L r Represents the sum of the leakage inductance and auxiliary inductance of the high-frequency transformer, I b Indicates the inductor current reference value.

4. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: In S3, the calculation formula of the boundary line P1 between the low power range and the medium power range 1 is: Where, d represents the voltage transformation 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 indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

5. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: The calculation formula of the dividing line P2 between the medium power range 1 and the medium power range 2 is: P2=(d-I s,min )(1-d+I s,min ) Where, d represents the voltage transformation ratio, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

6. The DAB efficiency optimization method considering dead time according to claim 1, characterized in that: The calculation formula of the dividing line P3 between the medium power range 2 and the high power range is: Where, d represents the voltage transformation ratio, I s,min It indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

7. 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 Represents the proportional coefficient of the controller, K i represents 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.

8. 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 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 comprises the following steps: S5.1: If the required transmission power P of the dual active full-bridge DAB converter pu If it 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 variable compared with the outward shift The calculation formula is as follows: Where d represents the voltage transformation 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 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, 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 variable compared with the outward shift The calculation formula is as follows: D s,mid2 ＝1， Δ=(1+d-I s,min )(1-d+I s,min )-2P pu Where d represents the voltage transformation 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 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, 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 variable compared with the outward shift The calculation formula is as follows: D p,mid1 =d-I s,min ,D s,mid1 =1, Where d represents the voltage transformation 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 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 D 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 variable compared with the outward shift The calculation formula is as follows: Where d represents the voltage transformation 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 indicates the minimum current that can achieve ZVS on the secondary side of the dual active full-bridge DAB converter.

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