Integrated multi-objective optimization method and system under asymmetric modulation strategy based on dual active bridge converter

Abstract

The invention discloses an integrated multi-objective optimization method and system based on an asymmetric modulation strategy of a dual-active bridge converter, and the method comprises the steps: obtaining an input voltage, an output voltage and an output voltage reference value of the dual-active bridge converter, and an external phase shift angle ratio between a primary side and a secondary side; the working mode of the converter is determined according to the current power demand and the voltage matching ratio, the minimum boundary current value required for soft switching is calculated by analyzing the characteristics of a power switch tube, an optimization objective function and constraint conditions are constructed, and a multi-objective particle swarm optimization algorithm is used for solving to obtain an optimal modulation parameter combination. And further constructing an off-line traversal lookup table, storing optimal modulation parameters and performance data thereof under different working conditions, obtaining the duty ratio and the internal phase shift angle ratio of the primary side full bridge through the lookup table, and finally generating trigger signals of all switching tubes in a digital signal generator. According to the invention, the soft switching range can be expanded, so that the switching loss of a switching tube in the dual-active bridge type converter is effectively reduced, and the efficiency of the dual-active bridge type converter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of dual active bridge converter modulation, and in particular to an integrated multi-objective optimization method and system based on an asymmetric modulation strategy of a dual active bridge converter. Background Art

[0002] For distributed energy storage systems, efficient operation of the DC interface circuit will achieve a highly energy-efficient charging and discharging process for batteries or supercapacitor components. Due to its simple circuit structure, high power density, strong bidirectional power transmission capability, strong wide-range voltage regulation capability, and simple control scheme, dual-active bridge DC converters are often used as the interface circuit for energy storage systems. At the same time, due to the presence of a high-frequency transformer, current isolation on both sides of the converter can be achieved.

[0003] In the modulation strategy of the dual-active bridge DC converter, phase-shift modulation is usually used to perform power control operations and energy efficiency optimization on the dual-active bridge DC converter, including single-phase shift modulation, extended phase-shift modulation, double phase-shift modulation and three-phase phase-shift modulation. In the modulation process, peak current, effective value current, return power and soft switching range can generally be selected as optimization targets to improve the working efficiency of the dual-active bridge DC converter. However, for the traditional phase-shift modulation strategy, under normal circumstances, in the process of optimizing the inductor current peak or the effective value of the inductor current, the soft switching range of the dual-active bridge DC converter will be seriously affected, and its switching loss will be increased, thereby greatly affecting the working efficiency of the dual-active bridge converter. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide an integrated multi-objective optimization method and system based on an asymmetric modulation strategy of a dual active bridge converter, so as to effectively reduce the switching loss of the switch tube in the dual active bridge converter and improve the working efficiency of the dual active bridge converter.

[0005] Technical solution: To achieve the above-mentioned purpose, the present invention provides an integrated multi-objective optimization method based on an asymmetric modulation strategy of a dual active bridge converter, comprising the following steps:

[0006] Step 1: Obtain the input voltage, output voltage and output voltage reference value of the dual active bridge converter;

[0007] Step 2: Obtain a voltage matching ratio according to the input voltage and the output voltage, and obtain an external phase shift angle ratio between the primary full bridge and the secondary full bridge of the dual active bridge converter according to the output voltage and the output voltage reference value;

[0008] Step 3: Based on the maximum transmission power of the dual active bridge converter and the power currently required to be transmitted, the power per unit value currently required to be transmitted is obtained, and the working mode of the dual active bridge converter under the asymmetric modulation strategy is determined according to the power per unit value currently required to be transmitted and the voltage matching ratio requirement;

[0009] Step 4: With the goal of achieving soft turning on of the power switch tube, analyze the power switch tube characteristics of the dual active bridge converter in different working modes to calculate the minimum boundary current value required to achieve soft turning on of the switch tube at each switching moment, thereby obtaining the working boundary conditions for achieving soft turning on of the switch tube;

[0010] Step 5: Take the effective current value and the peak current value as the optimization target to construct the optimization objective function, build the constraint conditions based on the working mode and the soft-turn-on working boundary of the switch tube, and solve the objective function through the multi-objective particle swarm optimization algorithm to obtain the optimal modulation parameter combination;

[0011] Step 6: By optimizing the operating points of each power level and voltage gain, an offline traversal lookup table that can traverse all different working conditions is constructed, which includes the optimal modulation parameter combination and its corresponding performance data under different power levels and voltage gains; according to the voltage matching ratio and external phase shift angle ratio obtained in step 2, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained through the offline lookup table;

[0012] Step 7: According to the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge obtained in step 6, trigger signals of all switches of the dual active bridge converter are generated in the digital signal generator.

[0013] The voltage matching ratio calculation formula in step 2 is:

[0014]

[0015] Among them, k is the voltage matching ratio; V1 is the input voltage, V2 is the output voltage, and n is the high-frequency transformer ratio.

[0016] Among them, the method for obtaining the external phase shift angle ratio of the primary full bridge and the secondary full bridge of the dual active bridge converter described in step 2 is: according to the difference between the output voltage and the output voltage reference value, the external phase shift angle ratio between the primary full bridge power switch tube drive signal and the secondary full bridge power switch tube drive signal is obtained through a proportional integral controller.

[0017] Wherein, the maximum transmission power of the dual active bridge converter in step 3 is:

[0018]

[0019] Where L is the inductance value, f sis the switching frequency;

[0020] The per-unit value of the power currently required to be transmitted is the ratio of the current actual power required to be transmitted to the maximum transmission power, and the value range is 0 to 1;

[0021] The working modes of the dual active bridge converter under the asymmetric modulation strategy include:

[0022] Working mode 1: Applicable to reverse power transmission scenarios;

[0023] Working mode 2: power transmission range is 0~0.33;

[0024] Working mode 4: power transmission range is 0~0.1;

[0025] Working mode 5: power transmission range is 0~0.5;

[0026] Working mode 3 and working mode 6: the power transmission range is 0~1.

[0027] Among them, step 4 aims to realize the soft turning-on of the power switch tube, analyzes the characteristics of the power switch tube of the dual active bridge converter in different working modes, calculates the minimum boundary current value required for realizing soft turning-on at each switching moment, and thus obtains the minimum dead time boundary condition required for realizing soft turning-on. The specific implementation process includes: according to the working mode of the dual active bridge converter, analyzing the characteristics of the power switch tube in different modes to ensure that soft turning-on can be realized under various working conditions, thereby determining the basic conditions for realizing soft turning-on of the power switch tube in different working modes; according to the law of conservation of energy, calculating the minimum boundary current value required for realizing soft turning-on of the switch tube, ensuring that the voltage across the switch tube drops to near zero when the switch tube is in the off state, thereby realizing soft turning-on; analyzing the resonance process of the junction capacitance on both sides of the inductor and the power switch tube, including the discharge of the junction capacitance and the charging of the inductor, deriving the mathematical expression of the resonance time, which reflects the time required for the junction capacitance of the switch tube to discharge to near zero voltage; according to the expression of the resonance time, calculating the minimum dead time boundary value required for realizing soft turning-on.

[0028] Among them, the effective value of the current and the peak-to-peak value of the current described in step 5 are obtained according to the voltage matching ratio, the transmission power requirement and different modulation degrees of freedom; the objective function is iterated by the multi-objective particle swarm algorithm to obtain the optimization solution set of the current stress optimization; the optimal modulation parameter combination is solved by the optimization solution set of the current stress optimization, that is, the optimal external phase shift angle ratio, the optimal duty cycle of the primary full bridge and the optimal internal phase shift angle ratio of the primary full bridge are obtained, and by optimizing the working points of many different power levels and voltage gain conditions, an offline traversal lookup table that can traverse all different working conditions is obtained;

[0029] The current effective value formula and the current peak-to-peak value calculation formula are as follows:

[0030]

[0031] Among them, k is the voltage matching ratio, D1 is the inner phase shift angle ratio between the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal; D2 is the outer phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the dual active bridge converter; D3 is the duty cycle of the primary full-bridge switch tube S1 drive signal in the primary full bridge.

[0032] The process of solving the objective function by the multi-objective particle swarm optimization algorithm is as follows:

[0033]

[0034] Among them, f(x) is the optimization target, x is the relevant variable that affects the solution target, Ax≤b is the non-equality constraint of the target to be optimized, A eq x=b eq is the equality constraint of the objective to be optimized.

[0035] The inequality constraints include the minimum current value for realizing soft-turning of the switch tube and the soft-turning boundary conditions of the switch tube under different working modes;

[0036] The minimum current value for achieving soft-turn on of the switch is:

[0037]

[0038] The soft-turn-on boundary conditions of the switch tube in different working modes are as follows:

[0039]

[0040] Among them, t1 is the time when the power switch tube that needs to realize soft switching is turned on; C oss is the junction capacitance value on both sides of the power switch tube; k is the voltage matching ratio value of the dual active bridge converter, L is the connection inductance value; D1 is the internal phase shift angle ratio between the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal; D2 is the external phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the dual active bridge converter; D3 is the duty cycle of the primary full-bridge switch tube S1 drive signal in the primary full-bridge.

[0041] The equality constraint formula is as follows:

[0042] P=P ref

[0043] Where P is the per-unit value of the transmission power; P *is the per-unit reference value of the transmission power.

[0044] The integrated multi-objective optimization system based on the asymmetric modulation strategy of the dual active bridge converter described in the present invention comprises the following modules:

[0045] Data sampling module: obtains the input voltage, output voltage and output voltage reference value of the dual active bridge converter;

[0046] Data analysis module: obtains a voltage matching ratio according to the input voltage and the output voltage, and obtains an external phase shift angle ratio between the primary full bridge and the secondary full bridge of the dual active bridge converter according to the output voltage and the output voltage reference value;

[0047] Working mode determination module: based on the maximum transmission power of the dual active bridge converter and the power currently required to be transmitted, the power per unit value currently required to be transmitted is obtained, and the working mode of the dual active bridge converter under the asymmetric modulation strategy is determined according to the power per unit value currently required to be transmitted and the voltage matching ratio requirement;

[0048] Working boundary condition determination module: with the goal of achieving soft turning on of the power switch tube, the power switch tube characteristics of the dual active bridge converter in different working modes are analyzed to calculate the minimum boundary current value required to achieve soft turning on of the switch tube at each switching moment, thereby obtaining the working boundary conditions for achieving soft turning on of the switch tube;

[0049] Optimal modulation parameter combination solution module: The current effective value and current peak-to-peak value are used as optimization targets to construct the optimization objective function, and the constraint conditions are constructed based on the working mode and the soft-turn-on working boundary of the switch tube. The objective function is solved by the multi-objective particle swarm optimization algorithm to obtain the optimal modulation parameter combination;

[0050] Offline lookup table construction module: By optimizing the working points of each power level and voltage gain, an offline traversal lookup table that can traverse all different working conditions is constructed, which includes the optimal modulation parameter combination and its corresponding performance data under different power levels and voltage gains; according to the voltage matching ratio and external phase shift angle ratio obtained in step 2, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained through the offline lookup table;

[0051] Drive signal acquisition module: Generates trigger signals for all switches of the dual active bridge converter in the digital signal generator based on the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge obtained in the offline lookup table construction module

[0052] Beneficial effects: The present invention has the following advantages: 1. The present invention can expand the soft switching range, thereby effectively reducing the switching loss of the switch tube in the dual-active bridge converter and improving the efficiency of the dual-active bridge converter;

[0053] 2. The present invention can dynamically adjust the phase shift angle ratio, duty cycle and inner phase shift angle ratio of the dual active bridge converter according to different power requirements and voltage matching ratios, realize an asymmetric modulation strategy, and improve the flexibility and adaptability of the dual active bridge converter; the optimization of parameters ensures that the dual active bridge converter can operate with the lowest switching loss and the highest efficiency under different power levels and voltage gains;

[0054] 3. The present invention constructs an offline traversal lookup table, which enables the dual-active bridge converter to quickly find the optimal modulation parameters corresponding to the current working conditions in actual operation without the need for complex optimization calculations in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a flow chart of the method of the present invention,

[0056] Figure 2 A schematic diagram of a topological structure of a dual-active bridge converter with parasitic parameters according to the present invention;

[0057] Figure 3 Schematic diagram of the calculation of the minimum boundary current at each switching state switching moment under the improved asymmetric modulation of the present invention, wherein: Figure 3 (a) From time t1 to t1+t d time, Figure 3 (b) From time t2 to t2+t d time, Figure 3 (c) From time t3 to t3+t d time, Figure 3 (d) From time t4 to t4+t d time, Figure 3 (e) From time t5 to t5+t d time, Figure 3 (f) is from time t6 to t6+t d time;

[0058] Figure 4 It is the waveform of working mode 1;

[0059] Figure 5 This is the waveform of working mode 2;

[0060] Figure 6 This is the waveform of working mode 3;

[0061] Figure 7 This is the waveform of working mode 4;

[0062] Figure 8 This is the waveform of working mode 5;

[0063] Fig. 9 This is the waveform of working mode 6;

[0064] Fig.10 This is a schematic diagram of optimization performed by the multi-objective particle swarm algorithm of the present invention;

[0065] Fig.11 It is a control execution block diagram of the present invention;

[0066] Fig.12 The current effective value comparison diagram of the present invention and other modulation strategies under different voltage matching ratios, wherein: Fig.12 (a) is the voltage matching ratio of 1, Fig.12 (b) is the voltage matching ratio of 1.5, Fig.12 (c) is the voltage matching ratio of 2, Fig.12 (d) The voltage matching ratio is 3;

[0067] Fig.13 The current peak comparison diagram of the present invention and other modulation strategies under different voltage matching ratios, where: Fig.13 (a) is the voltage matching ratio of 1, Fig.13 (b) is the voltage matching ratio of 1.5, Fig.13 (c) is the voltage matching ratio of 2, Fig.13 (d) The voltage matching ratio is 3;

[0068] Fig.14 This is a comparison chart of the efficiency of the present invention and other modulation strategies. DETAILED DESCRIPTION

[0069] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0070] like Figure 1 As shown in FIG. 1 , it is a flow chart of an integrated multi-objective optimization method based on an asymmetric modulation strategy of a dual active bridge converter in this embodiment, wherein the dual active bridge converter topology with parasitic parameters includes two symmetrical full bridges connected through an inductor L and a high-frequency transformer, the high-frequency transformer is referred to as HFT, wherein the turns ratio of the transformer is n, the input voltage value is recorded as V1, and the output voltage value is recorded as V2. For the equivalent circuit model of the dual active bridge topology, the equivalent AC output voltages of the primary side and the secondary side are recorded as V h1 and V h2 , Ts represents the switching cycle of the switch tube. S1, S2, S3, S4 represent the power switch tubes on the primary full bridge, and Q1, Q2, Q3, Q4 represent the power switch tubes on the secondary full bridge. DSi and DQi represent the anti-parallel diodes on the primary full bridge and the secondary full bridge, respectively. CSi and CQi represent the junction capacitances on both sides of the corresponding switch tubes on the primary full bridge and the secondary full bridge, respectively. Figure 2 shown.

[0071] By controlling the internal phase shift angle ratio D1 of the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal, the external phase shift angle ratio D2 of the primary full-bridge switch tube S1 drive signal and the secondary full-bridge switch tube Q1 drive signal, and the duty cycle D3 of the switch tube S1 drive signal in the primary full-bridge, the current stress under the same transmission power condition is reduced, the soft switching range of the switch tube in the dual-active bridge converter is expanded, and the efficiency of the dual-active bridge converter is effectively improved, and the efficient operation of the dual-active bridge converter is achieved. Figure 3 , which is a schematic diagram of an equivalent circuit for calculating the minimum boundary current at each switching state switching moment under the asymmetric modulation strategy of the present invention.

[0072] The output quantity obtained by the present invention through control is the switch drive signal of the dual active bridge converter, wherein the drive signals of the two switch tubes on each half bridge are complementary. Therefore, the drive signals of all switch devices in the dual active bridge converter can be determined by obtaining D1, D2 and D3.

[0073] The dual active bridge converter of the present invention includes 6 working modes, which are distinguished by the sequence of switching moments, specifically including: working mode 1, the switching sequence is D2TS, D1TS, (1+D1-D3)TS, (D2+0.5)TS, D3TS and TS; working mode 2, the switching sequence is D2TS, D1TS, D3TS, (1+D1-D3)TS, (D2+0.5)TS and TS; working mode 3, the switching sequence is D2TS, D1TS, (1+D1-D3)TS , D3TS, (D2+0.5)TS and TS; in working mode 4, the switching sequence is D1TS, D2TS, (1+D1-D3)TS, (D2+0.5)TS, D3TS and TS; in working mode 5, the switching sequence is D1TS, D2TS, (1+D1-D3)TS, D3TS, (D2+0.5)TS and TS; in working mode 6, the switching sequence is D1TS, D2TS, D3TS, (1+D1-D3)TS, (D2+0.5)TS and TS. Figure 4 is the waveform of working mode 1; Figure 5 is the waveform of working mode 2; Figure 6 is the waveform of working mode 3; Figure 7 is the waveform of working mode 4; Figure 8 is the waveform of working mode 5; Fig. 9 This is the waveform of working mode 6.

[0074] According to the working mode of the dual active bridge converter and the basic characteristics of different power switch tubes, with the goal of achieving soft switching of the power switch tube, many non-ideal factors are analyzed, the minimum boundary current value at each switching moment is obtained, the minimum dead zone boundary condition that can achieve soft switching is obtained, and the charging and discharging process of the switch tube junction capacitance is analyzed in detail;

[0075] The effective current value and the peak-to-peak current value are obtained according to the voltage matching ratio and different modulation degrees of freedom. The effective current value and the peak-to-peak current value are taken as the optimization targets. The optimal modulation scheme is solved by combining the working mode boundary and the soft switching working boundary through the multi-objective particle swarm optimization algorithm.

[0076] The present invention considers in detail the relationship between the dead time, the nonlinear variation law of the junction capacitance, the transient value of the current at the time of shutoff, the inductance value and the voltage gain. On this basis, the resonance process of the junction capacitance on both sides of the switch tube is studied, and the dead time range is estimated. Therefore, by reasonably setting the inductance current value at the switching moment and the length of the dead time, the charge stored in the junction capacitance can be completely released, and the soft opening of a certain switch tube can be realized. The nonlinear variation of the junction capacitance can also be calculated to obtain the equivalent capacitance under the corresponding voltage, and the formula is as follows.

[0077] The equivalent capacitance on the primary side can be expressed as:

[0078]

[0079] The secondary side equivalent capacitance can be expressed as:

[0080]

[0081] Generally speaking, the energy stored in the inductor L should be large enough to charge and discharge the switch junction capacitance. For example, after consuming the energy in the junction capacitance cs1, the drain-source voltage of the switch S1 becomes zero, thereby achieving ZVS of S1. Accordingly, it is necessary to ensure that the minimum iL value when the switch device is turned on or off is I min In order to provide enough energy for ZVS. At the same time, the dead time should be enough for the junction capacitance to complete charging and discharging.

[0082] To calculate the minimum current I min , the ZVS model at each switching moment is as follows Figure 3 The minimum energy stored in the inductor when the switch is turned off is equal to the energy of the DC power supply V1 and nV2 during the dead time t db Energy consumed internally.

[0083] Depend on Figure 3 From the description of d, we can see that at time t4, S1 is turned off and S2 is turned on. The direction of the inductor current is positive, and the current flows through the anti-parallel diode Ds3. d During this period, the inductor current iL starts to charge the junction capacitance Cs1 of S1 and discharge the junction capacitance Cs2 of S2. Figure 3d, in this process, the energy in the junction capacitance Cs2 of S2 is transferred to the junction capacitance Cs1 of S1. The minimum energy stored in L is consumed by the voltage sources V1 and nV2. In addition, at t = t4 and t = t4 + t d When , the voltage in Cs1 and Cs2 is as follows.

[0084]

[0085] Among them, u cs1 The voltage on the junction capacitance Cs1 of S1; u cs2 is the voltage on the junction capacitance Cs2 of S2; u(t) is the junction capacitance voltage of different switch tubes at different times.

[0086] From t4 to t4+t d During this period, the inductor current expression is:

[0087]

[0088] In the formula, C oss is the value of the junction capacitance.

[0089] According to the energy balance principle, from t4 to t4+t d The energy relationship can be expressed as:

[0090]

[0091] in, is the energy stored in the junction capacitance and inductance at time t4; E delivered is the energy consumed by the voltage source.

[0092] At t4, for the ZVS model, the total energy including the energy stored in cs2 and inductor L can be expressed as:

[0093]

[0094] in, is the energy stored in cs2; E L (I L ) is the energy stored in the inductor L.

[0095] At t4, the minimum energy stored in the inductor L can be expressed as:

[0096]

[0097] In the formula, I min To achieve the minimum inductor current value of ZVS.

[0098] At t4+t dWhen , for the ZVS model, the total energy includes the energy stored in cs1:

[0099]

[0100] in, is the energy stored in the junction capacitance and inductance at time t4; is the energy stored in cs1.

[0101] The energy consumed by a voltage source can be expressed as:

[0102]

[0103] Among them, i Cs2 is the current flowing through the junction capacitance cs2;

[0104] The minimum current value to achieve ZVS can be expressed as:

[0105]

[0106] Among them, I min is the minimum current value to achieve ZVS; V1 is the input voltage, V2 is the output voltage; k is the voltage conversion ratio; L is the inductance value.

[0107] In order to achieve zero voltage switching of all semiconductors, the current value at each switching moment should meet the limits in Table 1.

[0108] Table 1 ZVS boundaries at each switching moment:

[0109]

[0110] like Fig.10 As shown, the process of using a multi-objective particle swarm optimization algorithm to optimize the effective current value and current peak value in the soft switching boundary establishment and dead zone optimization method of the dual active bridge converter is shown.

[0111] The present invention takes the effective value of current and the peak value of current as optimization targets, and optimizes with the help of a multi-objective particle swarm optimization algorithm. The optimal modulation scheme is solved by combining the working mode boundary and the soft switch working boundary through the multi-objective particle swarm optimization algorithm. The formula of the effective value of current and the formula of the peak-to-peak value of current are as follows:

[0112]

[0113] Among them, k is the voltage matching ratio, D1 is the inner phase shift angle ratio between the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal; D2 is the outer phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the dual active bridge converter; D3 is the duty cycle of the primary full-bridge switch tube S1 drive signal in the primary full bridge.

[0114] The mathematical model of the multi-objective particle swarm optimization algorithm is as follows:

[0115] min f(x)

[0116]

[0117] Among them, f(x) is the optimization target, x is the relevant variable that affects the solution target, Ax≤b is the non-equality constraint of the target to be optimized, A eq x=b eq is the equality constraint of the objective to be optimized.

[0118] The multi-objective particle swarm algorithm includes inequality constraints and equality constraints;

[0119] The inequality constraints mainly include the minimum current value that can achieve soft-turn on of the switch tube and the boundary conditions of different working modes:

[0120] In order to achieve soft turn-on of the dual active bridge converter during operation to reduce switching losses and improve the operating efficiency of the dual active bridge converter, at the switching moment of each switch tube, the current flowing through the switch tube has constraints:

[0121]

[0122] The boundary conditions of different working modes are as follows:

[0123]

[0124] Among them, t1 is the time when the power switch tube that needs to realize soft switching is turned on; C oss is the junction capacitance value on both sides of the power switch tube; k is the voltage matching ratio value of the dual active bridge converter, and L is the connection inductance value.

[0125] The equality constraint formula is as follows:

[0126] P=P ref

[0127] Where P is the per-unit value of the transmission power; P * is the per-unit reference value of the transmission power;

[0128] like Fig.11 As shown in FIG. 1 , it is a flow chart of the improved asymmetric duty cycle modulation method of the present invention, and its specific implementation process includes the following process:

[0129] 1. Measure the input voltage V1 and output voltage V2 of the dual active bridge converter;

[0130] 2. Calculate the voltage matching ratio k based on the measured input voltage V1 and output voltage V2, and compare the output voltage V2 with the output voltage given value V 2ref , after making a difference, the external phase shift angle ratio D2 of the primary full-bridge switch tube S1 drive signal and the secondary full-bridge switch tube Q1 drive signal is obtained through the proportional-integral controller, and the duty cycle D3 of the primary full-bridge and the internal phase shift angle ratio D1 of the primary full-bridge are obtained through the offline lookup table;

[0131] 3. Determine the power that the current converter needs to transmit, and compare it with the maximum transmission power to obtain the transmission power per unit value P*, based on which the boundary constraints of the current working mode are determined. When P*<0.33, working mode 2 is preferred, otherwise, working mode 5 is preferred;

[0132] Fourth, taking the effective value of current and the peak-to-peak value of current as the optimization targets, the optimization solution is obtained by the multi-objective particle swarm optimization algorithm, where the equality constraint is determined by the per-unit value of the transmission power, and the inequality constraints are the soft switching boundary constraint and the working mode operation boundary constraint, respectively, to obtain the optimal modulation scheme (D1(opt), (D2(opt), (D3(opt));

[0133] 5. After obtaining the optimal modulation scheme (D1(opt), (D2(opt), (D3(opt)), the trigger signals of all switch tubes S1, S2, S3, S4, Q1, Q2, Q3, and Q4 of the dual active bridge converter are obtained according to the improved asymmetric duty cycle modulation strategy.

[0134] The present invention compares and analyzes the current effective value and efficiency of the unilateral asymmetric duty cycle modulation strategy provided by the present invention under the same transmission power, such as Fig.12 As shown in (a)-(d), under different voltage conversion ratios k, the unilateral asymmetric duty cycle modulation strategy and optimization method proposed in the present invention have the lowest current effective value. Fig.13 As shown in (a)-(d), under different voltage conversion ratios k, the unilateral asymmetric duty cycle modulation strategy and optimization method proposed in the present invention have the lowest current peak value. Fig.14 In the efficiency comparison shown, the improved asymmetric duty cycle modulation strategy and optimization method proposed by the present invention have the highest efficiency, which indirectly proves that the optimization method can achieve soft switching of the switch tube in the largest range. It shows that the improved asymmetric duty cycle modulation strategy of the present invention can effectively reduce current stress, expand the soft switching range, and thus effectively reduce the switching loss of the switch tube in the dual active bridge converter, and improve the efficiency of the dual active bridge converter.

[0135] The present invention can analyze the influence of non-ideal factors on the soft switching characteristics of the switch tube, and effectively optimize the current stress in the dual active bridge converter through the multi-objective particle swarm algorithm, thereby improving the working efficiency of the dual active bridge converter. In order to optimize the switching loss, the present invention provides a method for accurately establishing the zero voltage switch boundary and optimizing the dead time through comprehensive analysis. On this basis, based on the multi-objective particle swarm optimization algorithm, the peak current and the root mean square current are optimized, and a lower peak current and a lower root mean square current under the improved asymmetric modulation are achieved. By comparing the existing modulation schemes, the proposed optimization method can achieve the lowest peak current, the lowest effective value current and the widest ZVS range.

Claims

1. An integrated multi-objective optimization method based on an asymmetric modulation strategy for a dual active bridge converter, characterized in that: The following steps are involved: Step 1: Obtain the input voltage, output voltage and output voltage reference value of the dual active bridge converter; Step 2: Obtain a voltage matching ratio according to the input voltage and the output voltage, and obtain an external phase shift angle ratio between the primary full bridge and the secondary full bridge of the dual active bridge converter according to the output voltage and the output voltage reference value; Step 3: Based on the maximum transmission power of the dual active bridge converter and the power currently required to be transmitted, the power per unit value currently required to be transmitted is obtained, and the working mode of the dual active bridge converter under the asymmetric modulation strategy is determined according to the power per unit value currently required to be transmitted and the voltage matching ratio requirement; Step 4: With the goal of achieving soft turning on of the power switch tube, analyze the power switch tube characteristics of the dual active bridge converter in different working modes to calculate the minimum boundary current value required to achieve soft turning on of the switch tube at each switching moment, thereby obtaining the working boundary conditions for achieving soft turning on of the switch tube; Step 5: Take the effective current value and the peak current value as the optimization target to construct the optimization objective function, build the constraint conditions based on the working mode and the soft-turn-on working boundary of the switch tube, and solve the objective function through the multi-objective particle swarm optimization algorithm to obtain the optimal modulation parameter combination; Step 6: By optimizing the operating points of each power level and voltage gain, an offline traversal lookup table that can traverse all different working conditions is constructed, which includes the optimal modulation parameter combination and its corresponding performance data under different power levels and voltage gains; according to the voltage matching ratio and external phase shift angle ratio obtained in step 2, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained through the offline lookup table; Step 7: According to the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge obtained in step 6, trigger signals of all switches of the dual active bridge converter are generated in the digital signal generator.

2. The integrated multi-objective optimization method based on the asymmetric modulation strategy of the dual active bridge converter according to claim 1, characterized in that: The voltage matching ratio calculation formula in step 2 is: Among them, k is the voltage matching ratio; V1 is the input voltage, V2 is the output voltage, and n is the high-frequency transformer ratio.

3. The integrated multi-objective optimization method based on the asymmetric modulation strategy of the dual active bridge converter according to claim 1, characterized in that: The method for obtaining the external phase shift angle ratio of the primary full bridge and the secondary full bridge of the dual active bridge converter described in step 2 is: according to the difference between the output voltage and the output voltage reference value, the external phase shift angle ratio between the primary full bridge power switch tube drive signal and the secondary full bridge power switch tube drive signal is obtained through a proportional integral controller.

4. The integrated multi-objective optimization method based on the asymmetric modulation strategy of the dual active bridge converter according to claim 1, characterized in that: The maximum transmission power of the dual active bridge converter in step 3 is: Where L is the inductance value, f s is the switching frequency, V1 is the input voltage, and V2 is the output voltage; The per-unit value of the power currently required to be transmitted is the ratio of the current actual power required to be transmitted to the maximum transmission power, and the value range is 0 to 1; The working modes of the dual active bridge converter under the asymmetric modulation strategy include: Working mode 1: Applicable to reverse power transmission scenarios; Working mode 2: power transmission range is 0~0.33; Working mode 4: power transmission range is 0~0.1; Working mode 5: power transmission range is 0~0.5; Working mode 3 and working mode 6: the power transmission range is 0~1.

5. The integrated multi-objective optimization method based on the asymmetric modulation strategy of the dual active bridge converter according to claim 1, characterized in that: In step 4, the power switch characteristics of the dual active bridge converter in different working modes are analyzed with the goal of realizing soft turning-on of the power switch tube, and the minimum boundary current value required for realizing soft turning-on at each switching moment is calculated, so as to obtain the minimum dead time boundary condition required for realizing soft turning-on. The specific implementation process includes: according to the working mode of the dual active bridge converter, the characteristics of the power switch tube in different modes are analyzed to ensure that soft turning-on can be realized under various working conditions, so as to determine the basic conditions for realizing soft turning-on of the power switch tube in different working modes; according to the law of conservation of energy, the minimum boundary current value required for realizing soft turning-on of the switch tube is calculated to ensure that the voltage across the switch tube drops to near zero when the switch tube is in the off state, so as to realize soft turning-on; the resonance process of the junction capacitance on both sides of the inductor and the power switch tube is analyzed, including the discharge of the junction capacitance and the charging of the inductor, and the mathematical expression of the resonance time is derived, which reflects the time required for the junction capacitance of the switch tube to discharge to near zero voltage; according to the expression of the resonance time, the minimum dead time boundary value required for realizing soft turning-on is calculated.

6. The integrated multi-objective optimization method based on the asymmetric modulation strategy of the dual active bridge converter according to claim 1, characterized in that: The effective current value and the peak-to-peak current value described in step 5 are obtained according to the voltage matching ratio, the transmission power requirement and different modulation degrees of freedom; the objective function is iterated by the multi-objective particle swarm algorithm to obtain the optimization solution set of the current stress optimization; the optimal modulation parameter combination is solved by the optimization solution set of the current stress optimization, that is, the optimal external phase shift angle ratio, the optimal duty cycle of the primary full bridge and the optimal internal phase shift angle ratio of the primary full bridge are obtained, and an offline traversal lookup table that can traverse all different working conditions is obtained by optimizing the working points of many different power levels and voltage gain conditions; The current effective value formula and the current peak-to-peak value calculation formula are as follows: Among them, k is the voltage matching ratio, D1 is the inner phase shift angle ratio between the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal; D2 is the outer phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the dual active bridge converter; D3 is the duty cycle of the primary full-bridge switch tube S1 drive signal in the primary full bridge.

7. The integrated multi-objective optimization method under improved asymmetric modulation optimization based on dual active bridge converter according to claim 1, characterized in that: The process of solving the objective function by the multi-objective particle swarm optimization algorithm is as follows: Among them, f(x) is the optimization target, x is the relevant variable that affects the solution target, Ax≤b is the non-equality constraint of the target to be optimized, A eq x=b eq is the equality constraint of the objective to be optimized.

8. The integrated multi-objective optimization method under improved asymmetric modulation optimization based on dual active bridge converter according to claim 7, characterized in that: The inequality constraints include the minimum current value to achieve soft-turn on of the switch tube and the soft-turn on boundary conditions of the switch tube under different working modes; wherein, The minimum current value for achieving soft-turn on of the switch is: The soft-turn-on boundary conditions of the switch tube in different working modes are as follows: Among them, t1 is the time when the power switch tube that needs to realize soft switching is turned on; C oss is the junction capacitance value on both sides of the power switch tube; k is the voltage matching ratio value of the dual active bridge converter, L is the connection inductance value; D1 is the internal phase shift angle ratio between the primary full-bridge switch tube S1 drive signal and the switch tube S4 drive signal; D2 is the external phase shift angle ratio between the primary full-bridge switch tube S1 and the secondary full-bridge switch tube Q1 of the dual active bridge converter; D3 is the duty cycle of the primary full-bridge switch tube S1 drive signal in the primary full-bridge.

9. The integrated multi-objective optimization method under improved asymmetric modulation optimization based on dual active bridge converter according to claim 7, characterized in that: The equality constraint condition formula is as follows: P=P ref Where P is the per-unit value of the transmission power; P * is the per-unit reference value of the transmission power.

10. An integrated multi-objective optimization system based on an asymmetric modulation strategy of a dual active bridge converter, characterized in that: Includes the following modules: Data sampling module: obtains the input voltage, output voltage and output voltage reference value of the dual active bridge converter; Data analysis module: obtains a voltage matching ratio according to the input voltage and the output voltage, and obtains an external phase shift angle ratio between the primary full bridge and the secondary full bridge of the dual active bridge converter according to the output voltage and the output voltage reference value; Working mode determination module: based on the maximum transmission power of the dual active bridge converter and the power currently required to be transmitted, the power per unit value currently required to be transmitted is obtained, and the working mode of the dual active bridge converter under the asymmetric modulation strategy is determined according to the power per unit value currently required to be transmitted and the voltage matching ratio requirement; Working boundary condition determination module: with the goal of achieving soft turning on of the power switch tube, the power switch tube characteristics of the dual active bridge converter in different working modes are analyzed to calculate the minimum boundary current value required to achieve soft turning on of the switch tube at each switching moment, thereby obtaining the working boundary conditions for achieving soft turning on of the switch tube; Optimal modulation parameter combination solution module: The current effective value and current peak-to-peak value are used as optimization targets to construct the optimization objective function, and the constraint conditions are constructed based on the working mode and the soft-turn-on working boundary of the switch tube. The objective function is solved by the multi-objective particle swarm optimization algorithm to obtain the optimal modulation parameter combination; Offline lookup table construction module: By optimizing the working points of each power level and voltage gain, an offline traversal lookup table that can traverse all different working conditions is constructed, which includes the optimal modulation parameter combination and its corresponding performance data under different power levels and voltage gains; according to the voltage matching ratio and external phase shift angle ratio obtained in step 2, the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge are obtained through the offline lookup table; Driving signal acquisition module: According to the duty cycle of the primary full bridge and the internal phase shift angle ratio of the primary full bridge obtained in the offline lookup table construction module, the trigger signals of all the switch tubes of the dual active bridge converter are generated in the digital signal generator.

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