Four-degree-of-freedom efficiency optimization control method for bidirectional DC converter of electric locomotive

Abstract

The present invention relates to a four-degree-of-freedom efficiency optimization control method suitable for a bidirectional DC converter of an electric locomotive, comprising: based on the inductor current model and soft switching constraints of the converter under triple phase shift control, calculating the external phase shift that satisfies the soft switching of all switch tubes; according to the converter return power expression, obtaining the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero under the full soft switching constraint; combining the Lagrangian function and the power expression of the dual active full-bridge DC-DC converter under three-degree-of-freedom control, introducing the switching frequency as the fourth control degree of freedom, solving the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization on the basis of satisfying the full soft switching and zero return power constraints, and optimizing the converter with the obtained solution. The present invention can realize the comprehensive optimization of the steady-state performance of the bidirectional full-bridge DC-DC converter.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic converters, and in particular to a four-degree-of-freedom efficiency optimization control method suitable for a bidirectional direct current converter of an electric locomotive. Background Art

[0002] At present, the focus of my country's energy structure is gradually shifting from traditional fossil energy to clean energy, and renewable energy is gradually becoming the mainstream. Bidirectional full-bridge DC-DC converters are widely used in distributed power generation systems, battery energy storage systems, electric locomotives and electric vehicle charging and energy feedback due to their simple structure, bidirectional energy flow and high power density.

[0003] Bidirectional full-bridge DC-DC converters usually use phase shift control methods, which are simple to implement and easy to achieve bidirectional energy transmission. However, when the input and output voltages do not match or under light load conditions, large reflux power and current stress will be generated, resulting in reduced converter efficiency. In addition, the increase in switching frequency will lead to increased switching losses, thereby reducing converter efficiency.

[0004] In order to improve the efficiency of the converter, many optimization methods such as return power optimization, minimum current stress optimization or soft switching range expansion have been proposed. Although these methods can improve the working efficiency of the converter, due to the limitation of control freedom, they can only achieve efficiency optimization through one of the following aspects: return power optimization, current stress optimization or soft switching range expansion. They cannot take all influencing factors into account. Therefore, the steady-state performance optimization effect of the converter is not obvious, and comprehensive efficiency improvement cannot be achieved. In addition, most traditional optimization methods use a constant switching frequency and optimize efficiency by controlling the phase shift. At most, they can achieve optimization of three control freedom degrees, which results in the transmission power of the converter being constrained by the optimization conditions, making it difficult to apply the converter within a wider power range. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a four-degree-of-freedom efficiency optimization control method suitable for a bidirectional DC converter of an electric locomotive, which can achieve comprehensive optimization of the working efficiency of a bidirectional full-bridge DC-DC converter and significantly improve the efficiency of the converter.

[0006] The technical solution adopted by the present invention to solve the technical problem is: to provide a four-degree-of-freedom efficiency optimization control method suitable for a bidirectional DC converter of an electric locomotive, comprising the following steps:

[0007] According to the inductor current model and soft switching constraint conditions of the converter under triple phase shift control, the external phase shift amount satisfying the soft switching of all switches is calculated, and the obtained external phase shift amount satisfying the soft switching of all switches is used as the full soft switching constraint condition;

[0008] According to the converter return power expression, the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero is obtained under the full soft switching constraint condition, and the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle is used as the zero return power constraint condition;

[0009] The external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle are taken as three degrees of freedom, combined with the Lagrangian function and the power expression of the dual active full-bridge DC converter under three-degree-of-freedom control, the switching frequency is introduced as the fourth control degree of freedom, and on the basis of satisfying the full soft switching and zero return power constraints, the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization are solved;

[0010] The dual active full-bridge DC converter is optimally controlled based on the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

[0011] The method for obtaining the full soft switching constraint condition is specifically as follows: using the combination of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as independent variables, using the segmented analysis method to solve the inductance and current expressions at all switch-on moments, and then combining the current polarity required to achieve soft switching at each moment to construct an inequality equation group, and jointly solving them to obtain the required size of the external shift phase as the full soft switching constraint condition.

[0012] The full soft switching constraint condition is: D2=0, where D2 represents the external phase shift.

[0013] The method for obtaining the zero return power constraint condition is specifically as follows: a return power expression is derived using a combination of an external phase shift, a primary side internal phase shift angle, and a secondary side internal phase shift angle as independent variables, and then the return power is set to zero, and the relationship between the corresponding primary side internal phase shift angle and the secondary side internal phase shift angle is calculated as the zero return power constraint condition.

[0014] The zero reflux power constraint condition is: D1=1-k(1-D3), wherein D1 represents the phase shift angle within the primary side, D3 represents the phase shift angle within the secondary side, and k represents the voltage conversion ratio of the dual active full-bridge DC converter.

[0015] The Lagrangian function is expressed as: E = I peak (D1,D2,D3,f s )+λ(PP * ), where E is the Lagrangian function, λ is the Lagrangian multiplier, and I peak (·) is the current stress function, D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, P is the actual power, P * For a given power.

[0016] The relationship between the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization is:

[0017]

[0018] Where D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, k represents the voltage conversion ratio of the dual active full-bridge DC converter, P′ is the transmission power of the dual active full-bridge DC converter, L is the inductance value of the auxiliary inductor, U i is the input voltage of the dual active full-bridge DC converter.

[0019] The optimization control of the dual active full-bridge DC-DC converter based on the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency is specifically: power transmission is achieved by adjusting the switching frequency, minimum current stress control is achieved by adjusting the primary side internal phase shift angle, and zero reflux power and full soft switching optimization are achieved by adjusting the external phase shift angle and the secondary side internal phase shift angle.

[0020] The technical solution adopted by the present invention to solve the technical problem is: to provide a four-degree-of-freedom efficiency optimization control device suitable for a bidirectional DC converter of an electric locomotive, comprising:

[0021] The first calculation module is used to calculate the external phase shift amount that satisfies the soft switching of all switches based on the inductor current model of the converter under triple phase shift control and the soft switching constraint condition, and use the obtained external phase shift amount that satisfies the soft switching of all switches as the full soft switching constraint condition;

[0022] The second calculation module is used to obtain the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero under the full soft switching constraint condition according to the converter return power expression, and use the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle as the zero return power constraint condition;

[0023] A third calculation module is used to take the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as three degrees of freedom, combine the Lagrangian function and the power expression of the dual active full-bridge DC converter under three-degree-of-freedom control, introduce the switching frequency as the fourth control degree of freedom, and solve the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization on the basis of satisfying the full soft switching and zero return power constraints;

[0024] The optimization control module is used for optimizing the control of the dual active full-bridge DC converter based on the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

[0025] The technical solution adopted by the present invention to solve its technical problem is: to provide an electronic device, including a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the above-mentioned four-degree-of-freedom efficiency optimization control method applicable to the bidirectional DC converter of an electric locomotive are implemented.

[0026] The technical solution adopted by the present invention to solve its technical problem is: providing a computer-readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above-mentioned four-degree-of-freedom efficiency optimization control method applicable to a bidirectional DC converter of an electric locomotive are implemented.

[0027] Beneficial Effects

[0028] Due to the adoption of the above technical scheme, the present invention has the following advantages and positive effects compared with the prior art: According to the three-degree-of-freedom soft switching conditions and the reflux power model of the bidirectional full-bridge DC-DC converter in the electric locomotive, the present invention solves the constraints of the three degrees of freedom D1, D2 and D3 while ensuring the soft switching of all switch tubes and zero reflux power, and obtains the combination of the optimal phase shift angle and switching frequency that simultaneously satisfies the full soft switching, zero reflux power and minimum inductor current stress according to the Lagrangian function and the power model of the converter under the three-degree-of-freedom control. Due to the comprehensive consideration of the optimization of full soft switching, zero reflux power and minimum inductor current stress, the switching frequency is introduced as the fourth control degree of freedom, which can expand the transmission power range of the converter, have higher control freedom and more significant optimization effect, can further improve the converter efficiency, and realize energy-saving and efficient operation of the converter system. In addition, the four-degree-of-freedom efficiency optimization control method proposed by the present invention has a simple algorithm, simple calculation, easy digitization, and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of a four-degree-of-freedom efficiency optimization control method applicable to a bidirectional DC converter of an electric locomotive according to a first embodiment of the present invention;

[0030] Figure 2 is a topological structure diagram of a bidirectional full-bridge DC-DC converter according to an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the switch control signal, the AC side voltage of the primary bridge and the secondary bridge, and the inductor current waveform of the bidirectional full-bridge DC-DC converter under three-degree-of-freedom control in an embodiment of the present invention;

[0032] Figure 4 is a flow chart of optimization control in an embodiment of the present invention;

[0033] Figure 5 It is the waveform diagram of the primary and secondary full-bridge AC side voltage and inductor current under traditional single-phase shift control;

[0034] Figure 6 It is the waveform diagram of the primary and secondary full-bridge AC side voltage and inductor current under fundamental wave optimization control;

[0035] Figure 7 It is a waveform diagram of the primary and secondary full-bridge AC side voltage and the inductor current using the implementation mode of the present invention;

[0036] Figure 8 Efficiency comparison diagram among traditional single phase shift control, fundamental wave optimization control and implementation mode of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0038] The first embodiment of the present invention relates to a four-degree-of-freedom efficiency optimization control method applicable to a bidirectional DC converter of an electric locomotive, such as Figure 1 As shown, the following steps are included:

[0039] Step 1: Based on the inductor current model and soft switching constraints of the converter under triple phase shift control, the external phase shift that satisfies the soft switching of all switches is calculated, and the external phase shift that satisfies the soft switching of all switches is used as the full soft switching constraint.

[0040] In this step, the combination of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle is used as the independent variable, and the segmented analysis method is used to solve the inductance and current expressions at all switch-on moments. Then, a group of inequality equations is constructed in combination with the current polarity required to achieve soft switching at each moment. The required size of the external shift phase is obtained by simultaneous solution as the full soft switching constraint condition.

[0041] by Figure 2 Taking the bidirectional full-bridge DC-DC converter topology shown in the figure as an example, since the soft switching of the switch tubes on both sides of the bidirectional full-bridge DC-DC converter is closely related to the direction of the inductor current, in order to achieve full soft switching, it is necessary to analyze the inductor current direction corresponding to the opening moment of each switch. Figure 3As shown in the figure, according to the voltage and current waveform of the converter under the combined control of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle, the inductor current value at each moment can be obtained by using the segmented analysis method:

[0042]

[0043] Among them, i L (t0),i L (t1),i L (t2),i L (t3),i L (t4) represents the inductor current value at t0, t1, t2, t3, and t4 respectively, L is the auxiliary inductor, U i is the converter input voltage, f s is the switching frequency, D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, and D3 represents the internal phase shift angle of the secondary side.

[0044] according to Figure 2 The topological structure shown and the soft switching conditions of the switches on both sides are used to obtain the inductor current polarity required to satisfy the soft switching of all switches, and construct a set of inequality equations:

[0045]

[0046] Combining equations (1) and (2), the constraint conditions for achieving soft switching of all switches are solved, which is only related to the external phase shift D2. The required external phase shift angle D2 is:

[0047] D2=0 (3)

[0048] Step 2, according to the converter return power expression, under the full soft switching constraint condition, obtain the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero, and use the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle as the zero return power constraint condition.

[0049] In this step, the return power expression is derived by taking the combination of the external phase shift, the primary side internal phase shift angle, and the secondary side internal phase shift angle as independent variables. Then, the return power is set to zero, and the relationship between the corresponding primary side internal phase shift angle and the secondary side internal phase shift angle is calculated as the constraint condition for zero return power.

[0050] refer to Figure 3 By integrating the product of voltage and current during the power reflux period, the reflux power of the converter can be calculated as:

[0051]

[0052] By setting equation (4) to zero, we can obtain the phase shift constraint condition for the return power to be zero:

[0053] D1=1-k(1-D3) (5)

[0054] Step 3, taking the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as three degrees of freedom, combining the Lagrangian function and the power expression of the dual active full-bridge DC-DC converter under three-degree-of-freedom control, introducing the switching frequency as the fourth control degree of freedom, and solving the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization on the basis of satisfying the full soft switching and zero return power constraints.

[0055] This step uses full soft switching and zero reflux power as constraints, and takes the phase shift (D1, D2, D3) and switching frequency f s As four degrees of freedom, the Lagrangian function and the converter power model are combined to minimize the inductor current stress, and the phase shift combination and switching frequency expression that meet multi-objective optimization are solved. Specifically:

[0056] In order to optimize the current stress at a given output power, the current stress is expressed as a function of the phase shift amount and the switching frequency, and the Lagrangian function is constructed as:

[0057] E=I peak (D1,D2,D3,f s )+λ(PP * ) (6)

[0058] Where E is the Lagrangian function, λ is the Lagrangian multiplier, I peak (·) is the current stress function, P is the actual power of the bidirectional full-bridge DC-DC converter, P * is the given transmission power of the bidirectional full-bridge DC-DC converter.

[0059] The independent variables in equation (6) are derived, and combined with the constraints of full soft switching and zero backflow power, the optimal combination of the three degrees of freedom (D1, D2, D3) and the fourth degree of freedom switching frequency that simultaneously satisfies full soft switching, zero backflow power and minimum inductor current stress is calculated:

[0060]

[0061]

[0062] Step 4, optimizing and controlling the dual active full-bridge DC-DC converter based on the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

[0063] The optimal combination of phase shift and switching frequency that can simultaneously meet full soft switching, zero backflow power and minimum inductor current stress is obtained by reference. Figure 4By collecting the input voltage and output voltage of the converter in real time, the voltage conversion ratio of the converter can be calculated, and then the required optimal phase shift can be obtained. In order to compensate for the influence of inaccurate parameters such as transformer leakage inductance and transformer ratio on the output voltage, a PI controller is used to adjust the switching frequency to ensure that the output voltage reaches the reference voltage. By adjusting the switching frequency f s To achieve power transmission, the minimum current stress control is achieved by adjusting the internal phase shift angle D1 of the primary side, and the zero reflux power and full soft switching optimization are achieved by adjusting the external phase shift angle D2 and the internal phase shift angle D3 of the secondary side.

[0064] like Figure 5-Figure 7 As shown in the figure, under the same voltage conversion ratio and transmission power, compared with the traditional single-phase shift control and fundamental wave optimization control methods, the method of this embodiment has better soft switching characteristics and can also achieve zero reflux power and minimum inductor current stress at the same time. Compared with other optimization control methods, the control method of this embodiment achieves zero reflux power and minimum current stress optimization under the premise of ensuring soft switching, and at the same time, introduces the switching frequency f s As the fourth degree of freedom, it expands the power transmission range of the converter and solves the influence of efficiency optimization constraints on the converter transmission power. Figure 8 As shown, when the voltage parameters do not match, the method of this embodiment has the highest efficiency in the full power range, and the efficiency improvement is most obvious under light load conditions.

[0065] It is not difficult to find that the present invention solves the constraints of the three degrees of freedom D1, D2 and D3 based on the three-degree-of-freedom soft switching conditions and the reflux power model of the bidirectional full-bridge DC-DC converter in the electric locomotive while ensuring the soft switching of all switch tubes and zero reflux power, and obtains the optimal phase shift angle combination and switching frequency combination that simultaneously satisfies full soft switching, zero reflux power and minimum inductor current stress based on the Lagrangian function and the power model of the converter under three-degree-of-freedom control. Due to the comprehensive consideration of optimizations such as full soft switching, zero reflux power and minimum inductor current stress, the switching frequency is introduced as the fourth control degree of freedom, which can expand the transmission power range of the converter, have higher control freedom and more significant optimization effect, can further improve the converter efficiency, and realize energy-saving and efficient operation of the converter system. In addition, the four-degree-of-freedom efficiency optimization control method proposed in the present invention has a simple algorithm, simple calculation, and is easy to digitize, and has strong practicality.

[0066] A second embodiment of the present invention relates to a four-degree-of-freedom efficiency optimization control device suitable for a bidirectional DC converter of an electric locomotive, comprising:

[0067] The first calculation module is used to calculate the external phase shift amount that satisfies the soft switching of all switches based on the inductor current model of the converter under triple phase shift control and the soft switching constraint condition, and use the obtained external phase shift amount that satisfies the soft switching of all switches as the full soft switching constraint condition;

[0068] The second calculation module is used to obtain the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero under the full soft switching constraint condition according to the converter return power expression, and use the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle as the zero return power constraint condition;

[0069] A third calculation module is used to take the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as three degrees of freedom, combine the Lagrangian function and the power expression of the dual active full-bridge DC converter under three-degree-of-freedom control, introduce the switching frequency as the fourth control degree of freedom, and solve the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization on the basis of satisfying the full soft switching and zero return power constraints;

[0070] The optimization control module is used for optimizing the control of the dual active full-bridge DC converter based on the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

[0071] The first calculation module uses the combination of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as independent variables, and uses the segmented analysis method to solve the inductance and current expressions at all switch-on moments, and then constructs an inequality equation group in combination with the current polarity required to achieve soft switching at each moment, and solves them jointly to obtain the required size of the external shift phase as a full soft switching constraint.

[0072] The full soft switching constraint condition is: D2=0, where D2 represents the external phase shift.

[0073] The second calculation module derives the return power expression using the combination of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as independent variables, and then sets the return power to zero, and calculates the relationship between the corresponding primary side internal phase shift angle and the secondary side internal phase shift angle as a constraint condition for zero return power.

[0074] The zero reflux power constraint condition is: D1=1-k(1-D3), wherein D1 represents the phase shift angle within the primary side, D3 represents the phase shift angle within the secondary side, and k represents the voltage conversion ratio of the dual active full-bridge DC converter.

[0075] The Lagrangian function is expressed as: E = I peak (D1,D2,D3,f s )+λ(PP * ), where E is the Lagrangian function, λ is the Lagrangian multiplier, and Ipeak (·) is the current stress function, D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, P is the actual power, P * For a given power.

[0076] The relationship between the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization is:

[0077]

[0078] Where D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, k represents the voltage conversion ratio of the dual active full-bridge DC converter, P′ is the transmission power of the dual active full-bridge DC converter, L is the inductance value of the auxiliary inductor, U i is the input voltage of the dual active full-bridge DC converter.

[0079] The optimization control module realizes power transmission by adjusting the switching frequency, realizes minimum current stress control by adjusting the phase shift angle inside the primary side, and realizes zero reflux power and full soft switching optimization by adjusting the external phase shift angle and the secondary side internal phase shift angle.

[0080] The third embodiment of the present invention relates to an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the four-degree-of-freedom efficiency optimization control method of the first embodiment applicable to a bidirectional DC converter of an electric locomotive when executing the computer program.

[0081] The fourth embodiment of the present invention relates to a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the four-degree-of-freedom efficiency optimization control method of the first embodiment applicable to a bidirectional DC converter of an electric locomotive.

[0082] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0083] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0084] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0086] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0087] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive, characterized in that: The following steps are involved: Based on the inductor current model and soft switching constraints of the converter under triple phase shift control, the external phase shift that satisfies the soft switching of all switches is calculated, and the obtained external phase shift that satisfies the soft switching of all switches is used as the full soft switching constraint; According to the converter return power expression, the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero is obtained under the full soft switching constraint condition, and the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle is used as the zero return power constraint condition; The external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle are taken as three degrees of freedom, combined with the Lagrangian function and the power expression of the dual active full-bridge DC converter under three-degree-of-freedom control, the switching frequency is introduced as the fourth control degree of freedom, and on the basis of satisfying the full soft switching and zero return power constraints, the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization are solved; The dual active full-bridge DC converter is optimally controlled based on the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

2. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 1, characterized in that: The method for obtaining the full soft switching constraint condition is specifically as follows: using the combination of the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as independent variables, using the segmented analysis method to solve the inductance and current expressions at all switch-on moments, and then combining the current polarity required to achieve soft switching at each moment to construct an inequality equation group, and jointly solving them to obtain the required size of the external shift phase as the full soft switching constraint condition.

3. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 2, characterized in that: The full soft switching constraint condition is: D2=0, where D2 represents the external phase shift.

4. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 1, characterized in that: The method for obtaining the zero return power constraint condition is specifically as follows: a return power expression is derived using a combination of an external phase shift, a primary side internal phase shift angle, and a secondary side internal phase shift angle as independent variables, and then the return power is set to zero, and the relationship between the corresponding primary side internal phase shift angle and the secondary side internal phase shift angle is calculated as the zero return power constraint condition.

5. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 4, characterized in that: The zero reflux power constraint condition is: D1=1-k(1-D3), wherein D1 represents the phase shift angle within the primary side, D3 represents the phase shift angle within the secondary side, and k represents the voltage conversion ratio of the dual active full-bridge DC converter.

6. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 1, characterized in that: The Lagrangian function is expressed as: E = I peak (D1,D2,D3,f s )+λ(PP * ), where E is the Lagrangian function, λ is the Lagrangian multiplier, and I peak (·) is the current stress function, D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, P is the actual power, P * For a given power.

7. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 1, characterized in that: The relationship between the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization is: Where D1 represents the internal phase shift angle of the primary side, D2 represents the external phase shift, D3 represents the internal phase shift angle of the secondary side, and f s represents the switching frequency, k represents the voltage conversion ratio of the dual active full-bridge DC converter, P′ is the transmission power of the dual active full-bridge DC converter, L is the inductance value of the auxiliary inductor, U i is the input voltage of the dual active full-bridge DC converter.

8. The four-degree-of-freedom efficiency optimization control method for a bidirectional DC converter of an electric locomotive according to claim 1, characterized in that: The optimization control of the dual active full-bridge DC converter based on the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency is specifically: power transmission is achieved by adjusting the switching frequency, minimum current stress control is achieved by adjusting the primary side internal phase shift angle, and reflux power and full soft switching optimization are achieved by adjusting the external phase shift angle and the secondary side internal phase shift angle.

9. A four-degree-of-freedom efficiency optimization control device based on a bidirectional DC converter suitable for electric locomotives, characterized in that: include: The first calculation module is used to calculate the external phase shift amount that satisfies the soft switching of all switches based on the inductor current model of the converter under triple phase shift control and the soft switching constraint condition, and use the obtained external phase shift amount that satisfies the soft switching of all switches as the full soft switching constraint condition; The second calculation module is used to obtain the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle that makes the return power zero under the full soft switching constraint condition according to the converter return power expression, and use the relationship between the primary side internal phase shift angle and the secondary side internal phase shift angle as the zero return power constraint condition; A third calculation module is used to take the external phase shift, the primary side internal phase shift angle and the secondary side internal phase shift angle as three degrees of freedom, combine the Lagrangian function and the power expression of the dual active full-bridge DC converter under three-degree-of-freedom control, introduce the switching frequency as the fourth control degree of freedom, and solve the expressions of the external phase shift, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency that meet the minimum current stress optimization on the basis of satisfying the full soft switching and zero return power constraints; The optimization control module is used for optimizing the control of the dual active full-bridge DC converter based on the external phase shift amount, the primary side internal phase shift angle, the secondary side internal phase shift angle and the switching frequency.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the four-degree-of-freedom efficiency optimization control method applicable to the bidirectional DC converter of an electric locomotive are implemented as described in any one of claims 1-8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, the steps of the four-degree-of-freedom efficiency optimization control method applicable to the bidirectional DC converter of an electric locomotive are implemented as described in any one of claims 1-8.

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