A method and system for cycle power optimization for three-phase dual active bridge

Abstract

The application provides a circulating power optimization method and system for a three-phase dual active bridge, and relates to the field of power electronics, and the method comprises the following steps: determining an optimal backflow modulation strategy set corresponding to a mixed modulation group, the mixed modulation group comprising a triangular wave modulation, a trapezoidal wave modulation, a synchronous modulation and an extended phase-shift modulation, the optimal backflow modulation strategy set corresponding to the mixed modulation group comprising modulation modes and freedom degree relationships corresponding to different transmission power standard values in different voltage conversion ratio ranges; determining a freedom degree and power relationship set corresponding to the mixed modulation group, comprising the relationship between the freedom degree and the power of each mode corresponding to different transmission power standard values; combining real-time voltage conversion ratios and real-time virtual power standard values to determine phase-shift angles, primary side duty cycles and secondary side duty cycles, and controlling the three-phase dual active bridge to operate, which has the advantages of reducing complexity, improving portability and efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, in particular to a circulating power optimization method and system for a three-phase dual-active-bridge. BACKGROUND

[0002] Dual-active-bridge (DAB) converters are widely used in DC microgrids, power conversion systems, distributed power sources, new energy vehicles and other occasions requiring isolation and bidirectional transmission due to their small size, high efficiency, soft switching, bidirectional transmission and other characteristics. However, with the development of technology and energy, more scenarios require high-power operation, low energy consumption, high power quality and other higher demands for DAB. High-power scenarios mean that the size and quantity of the required converter are large, and reducing energy consumption generally requires improvements to the control algorithm, and high power quality requires processing of current ripple, such as using third-generation semiconductors (such as SiC) to increase switching frequency. Three-phase DAB has higher unit power density and smaller inductance current ripple, and has higher efficiency and more research value in high power density transmission. However, due to the large number of switching tubes, only single-phase shift modulation with one degree of freedom cannot achieve zero voltage switching when the voltage conversion ratio deviates, and cannot optimize other performance.

[0003] Like the optimization strategy of single-phase shift modulation, there are many methods to increase the control degree of freedom. For example, there is a single three-phase switching control strategy in the prior art, which makes the three-phase DAB run in a two-phase parallel state at light load and voltage ratio deviation, which improves efficiency but loses the characteristics of three-phase interleaving. The hybrid modulation strategy of single-phase shift and asymmetric phase shift expands the soft switching operation range of the system at light load, but since the minimum phase shift angle for soft switching operation must be determined in advance as the switching point, the leakage inductance and capacitance value must be known in advance, which lacks portability and the calculation is relatively complex. The asymmetric modulation strategy has three degrees of freedom, but the analysis and calculation of three degrees of freedom are very complex, although the existing technology uses numerical methods to avoid modal analysis to optimize it, the portability is poor and the implementation is complex.

[0004] Therefore, it is necessary to provide a circulating power optimization method and system for a three-phase dual-active-bridge, which reduces the complexity of the circulating power optimization of the three-phase dual-active-bridge and improves the portability and efficiency. SUMMARY

[0005] The application provides a circulating power optimization method for a three-phase dual active bridge, comprising: determining an optimal backflow modulation strategy set corresponding to a mixed modulation group, wherein the mixed modulation group comprises triangular wave modulation, trapezoidal wave modulation, synchronous modulation and extended phase-shift modulation, the optimal backflow modulation strategy set corresponding to the mixed modulation group comprises modulation modes and degree of freedom relationships corresponding to different transmission power standard value ranges under different voltage conversion ratio ranges; determining a degree of freedom and power relationship set corresponding to the mixed modulation group, wherein the degree of freedom and power relationship set corresponding to the mixed modulation group comprises relationships between the degree of freedom and power of each mode of the triangular wave modulation, the trapezoidal wave modulation, the synchronous modulation and the extended phase-shift modulation corresponding to different transmission power standard values; determining a phase-shift angle, a primary side duty ratio and a secondary side duty ratio based on a real-time voltage conversion ratio, a real-time virtual power standard value, the optimal backflow modulation strategy set corresponding to the mixed modulation group and the degree of freedom and power relationship set corresponding to the mixed modulation group; and controlling the three-phase dual active bridge to operate according to the phase-shift angle, the primary side duty ratio and the secondary side duty ratio.

[0006] Further, the optimal backflow modulation strategy corresponding to the mixed modulation group is determined, comprising: for each transmission power standard value range, determining constraint conditions of each mode of the triangular wave modulation, the trapezoidal wave modulation, the synchronous modulation and the extended phase-shift modulation corresponding to the transmission power standard value range, calculating optimal solutions of each mode corresponding to the transmission power standard value range, and determining modulation modes and degree of freedom relationships corresponding to the transmission power standard value range based on the optimal solutions of each mode corresponding to the transmission power standard value range according to a screening target, wherein the screening target is that the inductor current is minimum when the backflow power is 0.

[0007] Further, in the synchronous modulation, the secondary side duty ratio is fixed.

[0008] Further, the phase-shift angle, the primary side duty ratio and the secondary side duty ratio are determined based on the real-time voltage conversion ratio, the real-time virtual power standard value, the optimal backflow modulation strategy set corresponding to the mixed modulation group and the degree of freedom and power relationship set corresponding to the mixed modulation group, comprising: determining a target voltage conversion ratio range based on the real-time voltage conversion ratio; obtaining a target degree of freedom conversion relationship from the optimal backflow modulation strategy set corresponding to the mixed modulation group according to the real-time virtual power standard value and the target voltage conversion ratio range; obtaining a relationship between the target degree of freedom and power from the degree of freedom and power relationship set corresponding to the mixed modulation group according to the real-time virtual power standard value; and determining the phase-shift angle, the primary side duty ratio and the secondary side duty ratio based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and power.

[0009] Further, the real-time voltage conversion ratio is determined, comprising: sampling an input voltage; and determining the real-time voltage conversion ratio according to the input voltage and a preset output reference voltage.

[0010] Further, the real-time virtual power unit is determined by: sampling the output voltage; inputting the error voltage, which is obtained by subtracting the reference voltage from the output voltage, into a PI controller to output a virtual voltage; sampling the output current; calculating the virtual power based on the input voltage, the reference voltage, the virtual voltage, the output voltage and the output current; and normalizing the virtual power to determine the real-time virtual power unit.

[0011] Further, the real-time virtual power unit is determined by normalizing the virtual power according to the following formula:

[0012] ,

[0013] wherein, the real-time virtual power unit is Pvirtual, the virtual power is Pvirtual, the reference power is Pbase, the switching frequency is fs, the total value of the auxiliary inductance and the transformer leakage inductance is Ltotal, the transformer ratio is K, the virtual voltage is Vvirtual, the preset output reference voltage is Vref, the output current is Iout, the input voltage is Vin, the output voltage is Vout.

[0014] Further, the proportional parameter of the PI controller is compensated based on the switching frequency, the inductance value and the switching frequency.

[0015] Further, the phase shift angle, the primary side duty ratio and the secondary side duty ratio are determined based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and the power, including: determining the solving formula of each degree of freedom based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and the power; and determining the phase shift angle, the primary side duty ratio and the secondary side duty ratio according to the power and the solving formula of each degree of freedom.

[0016] This invention provides a cyclic power optimization system for a three-phase dual active bridge circuit, applying the aforementioned cyclic power optimization method for a three-phase dual active bridge circuit, comprising: a modulation analysis module for determining the optimal set of return current modulation strategies corresponding to a hybrid modulation group, wherein the hybrid modulation group includes triangular wave modulation, trapezoidal modulation, synchronous modulation, and extended phase-shift modulation, and the optimal set of return current modulation strategies corresponding to the hybrid modulation group includes modulation modes and degrees of freedom relationships corresponding to different per-unit transmission power values ​​under different voltage conversion ratio ranges; the modulation analysis module is further used to determine the degrees of freedom and power corresponding to the hybrid modulation group. The set of relationships, wherein the set of degrees of freedom and power correlations corresponding to the hybrid modulation group includes the relationship between the degrees of freedom and power for each mode of triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase-shift modulation corresponding to different per-unit transmission power values; the degree of freedom determination module is used to determine the phase shift angle, primary side duty cycle and secondary side duty cycle based on the real-time voltage conversion ratio, real-time virtual per-unit power value, the set of optimal return modulation strategies corresponding to the hybrid modulation group and the set of degrees of freedom and power correlations corresponding to the hybrid modulation group; the operation control module is used to control the operation of the three-phase dual active bridge according to the phase shift angle, primary side duty cycle and secondary side duty cycle.

[0017] Compared with existing technologies, the circulating power optimization method and system for a three-phase dual active bridge provided by this invention has at least the following beneficial effects:

[0018] By comparing the characteristics of the numerical optimal solution and the convex function using numerical methods, an analytical solution for hybrid strategy optimization is obtained, making the algorithm portable. Due to the discontinuity in degree-of-freedom control, a virtual power control algorithm is employed. Furthermore, the use of virtual power as the control variable improves control accuracy, significantly reducing overshoot while maintaining a nearly constant response speed. It also exhibits rapid recovery to stability under load and power supply fluctuations, demonstrating disturbance rejection capabilities. Compared to traditional single-phase-shift modulation algorithms, it improves efficiency and extends some ZVS range while minimizing inductor current stress. However, it increases the cost of two sensors.

[0019] Hybrid modulation strategies offer superior performance under light and medium load conditions. This strategy covers the entire power range and can be used when the voltage conversion ratio deviates from its maximum or minimum value. However, when the voltage conversion ratio is 1, single-phase-shift modulation remains the most efficient. Attached Figure Description

[0020] This specification will be further described by way of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting; in these embodiments, the same reference numerals denote the same structures, wherein:

[0021] Figure 1is a flow chart of a circulating power optimization method for a three-phase dual active bridge according to some embodiments of the present specification;

[0022] Figure 2 is a circuit topology diagram of a three-phase DAB according to some embodiments of the present specification;

[0023] Figure 3 is a virtual power control block diagram of a three-phase DAB recirculation optimization according to some embodiments of the present specification;

[0024] Figure 4 is a numerical solution size diagram of a three-phase DAB under constraints according to some embodiments of the present specification;

[0025] Figure 5 is a waveform diagram of triangular modulation and trapezoidal modulation according to some embodiments of the present specification;

[0026] Figure 6 is a waveform diagram of synchronous modulation and extended phase-shift modulation according to some embodiments of the present specification;

[0027] Figure 7 is an inductor current waveform diagram running in low-power triangular modulation in a simulation process according to some embodiments of the present specification;

[0028] Figure 8 is an inductor current waveform diagram running in low-to-medium-power trapezoidal modulation in a simulation process according to some embodiments of the present specification;

[0029] Figure 9 is an inductor current waveform diagram running in medium-power in a simulation process according to some embodiments of the present specification;

[0030] Figure 10 is an inductor current waveform diagram running in high-power in a simulation process according to some embodiments of the present specification;

[0031] Figure 11 is an output voltage fluctuation diagram when input voltage suddenly drops in a simulation process according to some embodiments of the present specification;

[0032] Figure 12 is an output voltage fluctuation diagram when load suddenly drops in a simulation process according to some embodiments of the present specification;

[0033] Figure 13 is a module diagram of a circulating power optimization system for a three-phase dual active bridge according to some embodiments of the present specification. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present specification, the drawings needed to be used in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some examples or embodiments of the present specification, and for those skilled in the art, the present specification can also be applied to other similar scenarios without creative labor on the basis of the drawings. Unless it is obvious from the language environment or otherwise stated, the same reference numbers in the drawings represent the same structure or operation.

[0035] Figure 1 is a flowchart of a circulating power optimization method for a three-phase dual active bridge according to some embodiments of the present specification, as shown in Figure 1 A circulating power optimization method for a three-phase dual active bridge can include the following steps.

[0036] Step 110, determining the optimal set of return flow modulation strategies corresponding to the mixed modulation group, wherein the mixed modulation group includes triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation, and the optimal set of return flow modulation strategies corresponding to the mixed modulation group includes the modulation mode and degree of freedom relationship corresponding to different transmission power unit value ranges under different voltage conversion ratio ranges.

[0037] When deviating from the unit voltage conversion ratio, triangular wave and trapeoidal modulation have good performance, and due to the inductance current characteristics, they can operate at the zero voltage switching boundary and can ensure that the return flow power is 0, and the inductance current stress gradually increases under the three modes. However, the power range of this modulation strategy can only cover the light load range.

[0038] In order to ensure that the modulation strategy can cover the entire possible power range, mixed modulation is used. In order to simplify the mode range and degree of freedom as much as possible, the synchronous modulation strategy is introduced, and for the sake of distinguishing each mode, it is labeled as DPS1 to DPS7.

[0039] In order to exclude the particularity and at the same time not to analyze the three degrees of freedom mode, the secondary side duty cycle is no longer changed to maintain 50%, only the primary side duty cycle and the phase shift ratio are changed, that is, in the synchronous modulation, the secondary side duty cycle is fixed, which is similar to the extended phase shift modulation (EPS) in single-phase DAB. EPS has nine modes, and for the sake of distinguishing each mode, it is labeled as EPS1 to EPS9. In this way, there is no index that must be synchronized, and the range can be further expanded by mixing with synchronous modulation. Since they all have certain particularity, the mode calculation is still much simpler than the three degrees of freedom modulation.

[0040] The power is divided into several power ranges, , the triangle wave and trapezoidal modulation are in the first power range, DPS4, DPS6, EPS7, EPS8, EPS9 are in the second power range, DPS1, DPS2, DPS5, EPS1, EPS2, EPS4, EPS5, EPS6 are in the third power range, EPS3 and DPS3 are in the fourth power range.

[0041] In some embodiments, the optimal backflow modulation strategy corresponding to the hybrid modulation group is determined, comprising:

[0042] For each transmission power unit range, the constraint condition of each mode of the triangle wave modulation, the trapezoidal modulation, the synchronous modulation and the extended phase shift modulation corresponding to the transmission power unit range is determined, the optimal solution of each mode corresponding to the transmission power unit range is calculated, and the modulation mode corresponding to the transmission power unit range and the degree of freedom relationship are determined according to the optimal solution of each mode corresponding to the transmission power unit range based on the screening target, wherein the screening target is that the inductance current is minimum when the backflow power is 0.

[0043] Specifically, the optimal backflow power is selected from the modes in each power range classified above. Since the inductance current of the three-phase DAB no longer has symmetry, the backflow power is 0 as much as possible to meet the mode constraint, and then the zero-voltage switching boundary condition is met as much as possible, and the inductance current is minimum when the backflow power is 0.

[0044] The transmission power range of each mode is affected by the voltage conversion ratio. When the voltage conversion ratio deviates to different degrees, the power range that meets the constraint is also limited. A numerical solution is adopted. The optimal solution under different constraints is obtained under each mode, and then the overall optimal solution is obtained by comparing the optimal solutions under all modes.

[0045] In matlab, the backflow power under each different constraint is expressed by the formula. By drawing the backflow power-transmission power graph, the boundary constraint with the minimum backflow value under the same transmission power is obtained, and the relationship between the degrees of freedom on each boundary is obtained by solving the constraint equation.

[0046] For example, corresponding to the second transmission power unit range, the backflow power of the modes under each constraint is calculated by matlab, as shown in the attached Figure 4 After determining the boundary by matlab, the backflow values of all modes are plotted in the same graph. Figure 4 The horizontal and vertical coordinates of the left graph are power units and backflow values, respectively, as shown in the figure. Figure 4 As can be seen from the figure, in the case of m>1, the backflow value of EPS7 is minimum under the same power unit, so EPS7 is selected as the optimal mode in this range. Figure 4 The right graph is the degree of freedom relationship area under the EPS7 mode,Figure 4 The winning red part is the relationship that should be met under the optimal condition constraint, and the boundary can be obtained by solving the constraint inequality, as follows, where , is the degree of freedom, and m is the voltage conversion ratio:

[0047] ,

[0048] And the corresponding power range can be solved from the above formula:

[0049] ,

[0050] Finally, all the optimal modes in the power range are mixed to make the power range connected, and the optimal backflow modulation strategy is obtained. As an example, for the second transmission power unit value range, the constraint conditions of each mode of synchronous modulation and extended phase-shift modulation corresponding to the transmission power unit value range can be shown in Table 1, where high deviation and low deviation refer to the deviation degree from the unit voltage conversion ratio (i.e. m = 1), such as m > 1 high deviation, which means that the mode can cover a wider power range when the deviation is high (such as m > 1.6), and when the deviation is low, it may fail because the power range is covered less. The final figure drawn in the example Figure 4 determines whether to select.

[0051] Table 1

[0052] ,

[0053] The degree of freedom relationship of the full power range backflow optimal in the case of low deviation is shown in Table 2. In Table 2, each mode is sorted by power in the range of each m. In the region of 1 < m < 2, further subdivision is performed, which is divided into and regions, and the optimal mode corresponding to different regions is different.

[0054] Table 2

[0055] ,

[0056] where m is the voltage conversion ratio, defined as the voltage ratio on both sides of the auxiliary inductor before the transformer, i.e. , where V1 is the input side DC voltage amplitude, n is the transformer ratio, and V2 is the output side DC voltage amplitude. , , are three degrees of freedom, respectively, the transformer primary side bridge arm switch duty cycle, the transformer secondary side bridge arm switch duty cycle, and the phase shift ratio of the primary and secondary switch modulation signals. is the transmission power unit, defined as: where P is the transmission power, is the reference value, is the switching frequency, is the total value of the auxiliary inductance and the transformer leakage inductance.

[0057] Step 120, determine the degree of freedom and power relationship set corresponding to the mixed modulation group, wherein the degree of freedom and power relationship set corresponding to the mixed modulation group includes the relationship between the degree of freedom and power corresponding to each mode of the triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation at different transmission power units.

[0058] For example only, the relationship between the degree of freedom and power corresponding to each mode of the triangular wave modulation and trapezoidal modulation at different transmission power units in the buck state and boost state respectively is shown in Table 3 and Table 4. Taking an example of Figure 5 The left graph is the current waveform of the triangular wave modulation in the buck state, and the current size of each section is as follows:

[0059] ,

[0060] Integrate each section of current and voltage using the power formula as follows, and the power and unit range of each table is obtained. In the following formula, each parameter is the same as above, and t1 to t9 are each time period, as shown in the Figure 4 .

[0061] ,

[0062] Table 3

[0063] ,

[0064] Table 4

[0065] ,

[0066] The relationship between the degree of freedom and power corresponding to each mode of the synchronous modulation and the extended phase shift modulation at different transmission power units can be shown in Table 5 and Table 6 respectively. By example Figure 6 , the calculation examples of the above Table 3 and Table 4 can also be obtained.

[0067] Table 5

[0068] ,

[0069] Table 6

[0070] ,

[0071] At step 130, based on the real-time voltage conversion ratio, the real-time virtual power unit, the optimal return flow modulation strategy set corresponding to the hybrid modulation group, and the degree of freedom and power relationship set corresponding to the hybrid modulation group, the phase shift angle, the primary side duty cycle, and the secondary side duty cycle are determined.

[0072] As shown in Table 1, the range of the degrees of freedom is not continuous, and any degree of freedom cannot be used as a control object. The virtual power control is introduced to use continuous power as a control object, and the degrees of freedom are obtained by optimizing the modulation strategy.

[0073] In some embodiments, step 130 specifically includes:

[0074] Based on the real-time voltage conversion ratio, a target voltage conversion ratio range is determined.

[0075] According to the real-time virtual power unit and the target voltage conversion ratio range, a target degree of freedom conversion relationship is obtained from the optimal return flow modulation strategy set corresponding to the hybrid modulation group. Specifically, according to which interval range m is in Table 2, the range in which the optimization strategy is located and the relationship between the degrees of freedom are determined by looking up the table. For example, if m = 0.7, it is in the range of 0.5 < m < 1, and the strategy uses the corresponding degree of freedom relationship in this range.

[0076] According to the real-time virtual power unit, a relationship between the target degree of freedom and power is obtained from the degree of freedom and power relationship set corresponding to the hybrid modulation group.

[0077] Based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and power, the phase shift angle, the primary side duty cycle, and the secondary side duty cycle are determined.

[0078] In some embodiments, the real-time voltage conversion ratio is determined, including:

[0079] The input voltage is sampled.

[0080] According to the input voltage and the preset output reference voltage, the real-time voltage conversion ratio is determined.

[0081] In some embodiments, the real-time virtual power unit is determined, including:

[0082] The output voltage is sampled.

[0083] The error voltage obtained by subtracting the reference voltage from the output voltage is input into the PI controller, and the virtual voltage is output. wherein, is the virtual voltage, is the output voltage, is the reference voltage, is the proportional gain, is the integral gain, is the Laplace operator.

[0084] sampling output current;

[0085] calculating a virtual power based on the input voltage, the reference voltage, the virtual voltage, the output voltage and the output current;

[0086] normalizing the virtual power to determine a real-time virtual power normalization.

[0087] Specifically, the virtual power is normalized according to the following formula to determine the real-time virtual power normalization:

[0088]

[0089] wherein, is the real-time virtual power normalization, is the virtual power, is the reference power, is the switching frequency, is the total value of the auxiliary inductance and the transformer leakage inductance, is the transformer ratio, is the virtual voltage, is the preset output reference voltage, is the output current, is the input voltage, is the output voltage.

[0090] In some embodiments, the proportional parameter of the PI controller is compensated based on the switching frequency, the inductance value and the inductance value, and specifically, the product of is multiplied into the proportional parameter of the PI to complete the compensation, and the parameter of the PI controller is adjusted so that the value of the virtual voltage is close to .

[0091] In some embodiments, the phase shift angle, the primary side duty ratio and the secondary side duty ratio are determined based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and the power, including:

[0092] The solving formula of each degree of freedom is determined based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and the power.

[0093] The phase shift angle, the primary side duty ratio and the secondary side duty ratio are determined according to the power and the solving formula of each degree of freedom.

[0094] Step 140, controlling the three-phase dual active bridge to operate according to the phase shift angle, the primary side duty ratio and the secondary side duty ratio.

[0095] Specifically, the PWM generator of the MCU outputs the corresponding complementary PWM waveform after receiving the phase shift angle, which is used to control the MOSFET in the circuit after being driven by the driving circuit.

[0096] ​A circulating power optimization method for three-phase dual active bridge is further described below in combination with simulation experiments.

[0097] The circuit topology is shown in Figure 2 The simulation system is built in simulink, the switching frequency is selected as 100 kHz, the transformer ratio is 2.5:1, the circuit auxiliary inductance is 20uH, and the output side capacitor is 470uF.

[0098] The control block diagram of Figure 3 is used to build the control loop. The input voltage, output voltage and output current are sampled, the reference voltage and input voltage are sent to the voltage conversion ratio module to calculate the conversion ratio, and the output voltage and current are sent to the virtual power calculator. The waveforms of triangular modulation and trapezoidal modulation, the waveforms of synchronous modulation, and the waveforms of extended phase-shift modulation are shown in Figures 4-6 .

[0099] The calculated virtual power and conversion ratio are sent to the optimization strategy, and the output three duty cycles are obtained. The delay phase link is used to build the PWM generator and phase-shift circuit, so as to output the driving signal to the converter.

[0100] In step S1, the input voltage is set to 400V, the output reference voltage is 220V, and the conversion ratio is less than 1. According to table 2, the algorithm operating range is in the range of 0.5

[0101] Table 7

[0102] ,

[0103] The parameters of the PI controller are adjusted as follows: K p =2, K i =800.

[0104] According to the different modal transmission power expressions provided in tables 3 to 6 and table 7, the relationship between the degree of freedom and the power under different input powers is calculated as follows. The formula is the algorithm formula in the optimization strategy module, and the required duty cycle and phase-shift ratio can be output by inputting the transmission power and the voltage conversion ratio m. If the known voltage conversion ratio is constant, the simplified formula can be obtained by substituting it into the formula in advance:

[0105] When ,

[0106] ;

[0107] When ,

[0108] ;

[0109] When :

[0110] ;

[0111] When :

[0112] ;

[0113] When :

[0114] ;

[0115] When :

[0116] . Figure 2 In the original three-phase full-bridge by six switch tubes S 1 to S 6 composed of the secondary three-phase full-bridge by six switch tubes Q 1 to Q 6 composed of the transformer has three-phase winding, the original side and the secondary side winding are connected to the midpoint of the three-phase full-bridge, the original side winding L a , L b , L c corresponding to three-phase respectively. After calculating the phase shift angle, the original side duty ratio and the secondary side duty ratio, combined with the input transmission power and the modulation strategy corresponding to the voltage conversion ratio m mode, the PWM signal is generated to drive the switch tubes S 1 to S 6, switch tubes Q 1 to Q 6, the two switch tubes of each phase arm of the original three-phase full-bridge are complementary to the original side duty ratio calculated, and the two switch tubes of each phase arm of the secondary three-phase full-bridge are complementary to the secondary side duty ratio calculated. The phase of the secondary three-phase full-bridge lags behind the original three-phase full-bridge by the calculated phase shift angle.

[0117] To verify that the controller can run in each power range and the optimal backflow, simulation verification is carried out. First, the steady-state performance is verified, so that the converter runs in steady state at each power, and the output voltage reaches 220V.

[0118] The resistance is 25 ohms, so the transmission power per unit is 0.1408, and it runs under triangular wave modulation, Figure 7 that is, the simulation waveform, and the backflow is 0.

[0119] When the resistance is 15 ohms, the transmission power unit is 0.2347, and the converter runs under trapezoidal modulation, Figure 8 That is, the simulation waveform, and the return current is nearly 0.

[0120] When the resistance is 10 ohms, the transmission power unit is 0.352, and the converter runs under EPS7, Figure 9 That is, the simulation waveform, and the return current is nearly 0.

[0121] When the resistance is 5.6 ohms, the transmission power unit is 0.6286, and the converter runs under DPS2, Figure 10 That is, the simulation waveform, and the inductor current i6 is nearly 0, and the return current is optimal.

[0122] The dynamic performance is verified, and the converter runs under steady state 220V at each power, and the resistance is 30 ohms. Then the load and input are fluctuated, and the output fluctuation is observed.

[0123] At 0.12s, the input voltage is temporarily reduced from 400V to 360V, Figure 11 That is, the simulation waveform, and the output voltage is restored to stability within 0.02s. During the dynamic period, the voltage drops by a maximum of 8V, and there is no sudden rise peak.

[0124] At 0.12s, the load resistance is reduced from 30 ohms to 20 ohms, that is, the output current is suddenly increased from 13.3A to 20A, Figure 12 That is, the simulation waveform. The output voltage is restored to stability within 0.02s. During the dynamic period, the voltage drops by a maximum of 6V, and there is no sudden rise peak.

[0125] Figure 13 According to some embodiments of the present application, a module schematic diagram of a circulating power optimization system for a three-phase dual active bridge is shown as follows, Figure 13 As shown in the figure, a circulating power optimization system for a three-phase dual active bridge can include a modulation analysis module, a degree of freedom determination module, and a running control module.

[0126] The modulation analysis module is used to determine the optimal return current modulation strategy set corresponding to the mixed modulation group, wherein the mixed modulation group includes triangular wave modulation, trapezoidal modulation, synchronous modulation, and extended phase shift modulation. The optimal return current modulation strategy set corresponding to the mixed modulation group includes the modulation mode and the degree of freedom relationship corresponding to different transmission power units in different voltage conversion ratio ranges.

[0127] The modulation analysis module is also used to determine the degree of freedom and power relationship set corresponding to the mixed modulation group, wherein the degree of freedom and power relationship set corresponding to the mixed modulation group includes the relationship between the degree of freedom and the power of each mode of triangular wave modulation, trapezoidal modulation, synchronous modulation, and extended phase shift modulation corresponding to different transmission power units.

[0128] The degree of freedom determination module is configured to determine the phase-shifting angle, the primary side duty cycle and the secondary side duty cycle based on the real-time voltage conversion ratio, the real-time virtual power unit, the optimal return flow modulation strategy set corresponding to the hybrid modulation group and the degree of freedom and power relationship set corresponding to the hybrid modulation group.

[0129] The operation control module is configured to control the three-phase dual active bridge to operate according to the phase-shifting angle, the primary side duty cycle and the secondary side duty cycle.

[0130] A circulating power optimization system for a three-phase dual active bridge can be used to perform a circulating power optimization method for a three-phase dual active bridge, which will not be described here.

[0131] Finally, it should be understood that the embodiments described herein are merely for the purpose of illustrating the principles of the embodiments described herein. Other variations can also be within the scope of the present disclosure. Therefore, alternative configurations of the embodiments described herein can be considered as consistent with the teachings of the present disclosure, as an example but not limitation. Accordingly, the embodiments of the present disclosure are not limited to the embodiments explicitly introduced and described in the present disclosure.

Claims

1. A method for cycle power optimization for a three-phase dual active bridge, characterized in that, The method comprises the following steps: determining the optimal return flow modulation strategy set corresponding to the mixed modulation group, wherein the mixed modulation group comprises triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation, and the optimal return flow modulation strategy set corresponding to the mixed modulation group comprises the modulation mode and degree of freedom relationship corresponding to different transmission power unit value ranges under different voltage conversion ratio ranges; determining the degree of freedom and power relationship set corresponding to the mixed modulation group, wherein the degree of freedom and power relationship set corresponding to the mixed modulation group comprises the relationship between the degree of freedom and power of each mode of triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation corresponding to different transmission power unit values; determining the phase shift angle, the primary side duty ratio and the secondary side duty ratio based on the real-time voltage conversion ratio, the real-time virtual power unit value, the optimal return flow modulation strategy set corresponding to the mixed modulation group and the degree of freedom and power relationship set corresponding to the mixed modulation group; controlling the three-phase dual active bridge to operate according to the phase shift angle, the primary side duty ratio and the secondary side duty ratio.

2. A method for cyclic power optimization for a three-phase dual active bridge according to claim 1, characterized in that, The method for determining the optimal return flow modulation strategy corresponding to the mixed modulation group comprises the following steps: for each transmission power unit value range, determining the constraint condition of each mode of triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation corresponding to the transmission power unit value range, calculating the optimal solution of each mode corresponding to the transmission power unit value range, and determining the modulation mode and degree of freedom relationship corresponding to the transmission power unit value range according to the optimal solution of each mode corresponding to the transmission power unit value range based on the screening target, wherein the screening target is that the inductor current is minimum when the return flow power is 0.

3. The method for cyclic power optimization for a three-phase dual active bridge of claim 1, wherein, In the synchronous modulation, the secondary side duty ratio is fixed.

4. The method for cyclic power optimization for a three-phase dual active bridge of claim 1, wherein, The method for determining the phase shift angle, the primary side duty ratio and the secondary side duty ratio based on the real-time voltage conversion ratio, the real-time virtual power unit value, the optimal return flow modulation strategy set corresponding to the mixed modulation group and the degree of freedom and power relationship set corresponding to the mixed modulation group comprises the following steps: determining the target voltage conversion ratio range based on the real-time voltage conversion ratio; obtaining the target degree of freedom conversion relationship from the optimal return flow modulation strategy set corresponding to the mixed modulation group according to the real-time virtual power unit value and the target voltage conversion ratio range; obtaining the relationship between the target degree of freedom and power from the degree of freedom and power relationship set corresponding to the mixed modulation group according to the real-time virtual power unit value; determining the phase shift angle, the primary side duty ratio and the secondary side duty ratio based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and power.

5. A method for cyclic power optimization for a three-phase dual active bridge according to claim 4, characterized in that, The method for determining the real-time voltage conversion ratio comprises the following steps: sampling the input voltage; determining the real-time voltage conversion ratio according to the input voltage and the preset output reference voltage.

6. A method for cyclic power optimization of a three-phase dual active bridge according to claim 5, characterized in that, The method for determining the real-time virtual power unit value comprises the following steps: sampling the output voltage; inputting the error voltage obtained by subtracting the reference voltage from the output voltage into a PI controller to output a virtual voltage; sampling the output current; calculating the virtual power based on the input voltage, the reference voltage, the virtual voltage, the output voltage and the output current; normalizing the virtual power to determine the real-time virtual power unit value.

7. A method for cycle power optimization for a three-phase dual active bridge according to claim 6, characterized in that, The virtual power is normalized to determine the real-time virtual power unit value according to the following formula: ， wherein, is a real-time virtual power unit, is a virtual power, is a reference power, is a switching frequency, is a total value of the auxiliary inductance and the transformer leakage inductance, is a transformer ratio, is a virtual voltage, is a preset output reference voltage, is an output current, is an input voltage, is an output voltage.

8. The method for cyclic power optimization for a three-phase dual active bridge of claim 6, wherein, The proportional parameter of the PI controller is compensated based on the switching frequency, the inductance value and the inductance value.

9. The method for cyclic power optimization for a three-phase dual active bridge of claim 4, wherein, Determine the phase shift angle, the primary side duty ratio and the secondary side duty ratio based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and power, including: Determine the solving formula of each degree of freedom based on the target degree of freedom conversion relationship and the relationship between the target degree of freedom and power; Determine the phase shift angle, the primary side duty ratio and the secondary side duty ratio according to the power and the solving formula of each degree of freedom.

10. A circulating power optimization system for a three-phase dual active bridge, characterized in that, The application of the method for optimizing the circulating power of the three-phase dual active bridge according to any one of claims 1-9, including: The modulation analysis module is used to determine the optimal return flow modulation strategy set corresponding to the mixed modulation group, wherein the mixed modulation group includes triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation, and the optimal return flow modulation strategy set corresponding to the mixed modulation group includes the modulation mode and the degree of freedom relationship corresponding to different transmission power unit values under different voltage conversion ratio ranges; The modulation analysis module is also used to determine the degree of freedom and power relationship set corresponding to the mixed modulation group, wherein the degree of freedom and power relationship set corresponding to the mixed modulation group includes the relationship between the degree of freedom and the power corresponding to different transmission power unit values of each mode of triangular wave modulation, trapezoidal modulation, synchronous modulation and extended phase shift modulation; The degree of freedom determination module is used to determine the phase shift angle, the primary side duty ratio and the secondary side duty ratio based on the real-time voltage conversion ratio, the real-time virtual power unit value, the optimal return flow modulation strategy set corresponding to the mixed modulation group and the degree of freedom and power relationship set corresponding to the mixed modulation group; The operation control module is used to control the three-phase dual active bridge to operate according to the phase shift angle, the primary side duty ratio and the secondary side duty ratio.

Images