DAB converter coordinated modulation method and system based on regional optimal trajectory

Abstract

The application discloses a DAB converter cooperative modulation method and system based on a region optimal trajectory, and relates to the technical field of power electronic conversion; the method comprises the following steps: dividing the working range of a DAB converter into two voltage regions according to voltage transmission characteristics, and respectively acquiring the inductance current effective values of each working point in a plurality of preset modulation modes in each voltage region, so as to obtain a region modulation trajectory lookup table of a modulation mode corresponding to the minimum inductance current effective value of all working points; determining the target voltage region where the current working point is located according to the input voltage in the operating parameters, and determining the target modulation mode and the target control parameters in the target modulation mode according to the transmission power in the operating parameters and the region modulation trajectory lookup table of the target voltage region; and generating the PWM waveform for driving each bridge arm of the DAB converter according to the target control parameters. The application significantly improves the system efficiency under the premise of guaranteeing the dynamic performance and stability of the system.

Description

Technical Field

[0001] This application relates to the field of power electronic conversion technology, specifically to a DAB converter cooperative modulation method and system based on regional optimal trajectory. Background Technology

[0002] DAB converters are widely used in energy storage systems, electric vehicle charging, and microgrid interconnection due to their electrical isolation, high power density, high efficiency potential, and bidirectional power flow capability. However, the actual performance of DAB converters, especially their efficiency and electromagnetic compatibility, is highly dependent on the modulation strategy employed and its parameter optimization trajectory.

[0003] Currently, most optimization research on DAB modulation strategies focuses on parameter tuning for a single operating mode or local optimization within a limited operating range. There is a lack of a modulation parameter optimization method that can achieve globally optimal performance across the entire voltage and load range and is easily implemented in engineering. In particular, existing methods fail to effectively address the smooth transition and trajectory tracking problems when modulation parameters change continuously over a wide range, resulting in a significant gap between actual operating performance and theoretical optimal values.

[0004] To improve the performance limitations of SPS, the Triple Phase Shift (TPS) modulation strategy was proposed. However, TPS modulation has a variety of complex operating modes, and the switching process between modes is complicated, which can easily cause current surges or transient imbalances. It fails to effectively solve the problem of smooth transition and trajectory tracking when the modulation parameters change continuously over a wide range, resulting in a significant gap between the actual operating performance and the theoretical optimal value.

[0005] Therefore, there is an urgent need to propose a control method that enables smooth transition and trajectory tracking when modulation parameters change continuously over a wide range. Summary of the Invention

[0006] This application aims to at least address the problems of insufficient performance of single modulation strategies and poor practicality of complex strategies in the modulation strategies of DAB converters in the prior art, and provides a DAB converter cooperative modulation method and system based on regional optimal trajectory. By combining offline trajectory optimization and online table lookup tracking, the system efficiency is significantly improved while ensuring the dynamic performance and stability of the system.

[0007] The solution presented in this application example is implemented through the following steps.

[0008] The first aspect of this application provides a DAB converter cooperative modulation method based on regional optimal trajectory, including: Based on voltage transfer characteristics, the operating range of the DAB converter is divided into two voltage regions. The effective value of the inductor current at each operating point within each voltage region under multiple preset modulation modes is obtained to generate a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points. Each operating point has an input voltage and its power traverses within a normalized power range. The preset modulation modes include single-phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode. The regional modulation trajectory lookup table also includes control parameters corresponding to the modulation mode of the operating point. The target voltage region where the current operating point is located is determined based on the input voltage in the operating parameters, and the target modulation mode and the target control parameters under the target modulation mode are determined based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region. The PWM waveforms driving each bridge arm of the DAB converter are generated based on the target control parameters.

[0009] This application first divides the wide operating range into two distinct voltage regions based on voltage transfer characteristics. By introducing a region division concept based on voltage parameters, the complex global optimization problem is decomposed into two independent region optimization problems, providing a novel and efficient engineering approach for the selection of wide-range modulation strategies for DAB. Furthermore, by systematically integrating the SPS modulation mode, the TZ-CCM modulation mode, and the TR-DCM modulation mode within the TPS modulation mode, multiple preset modulation modes adaptable to both single and complex operating conditions are obtained. Then, within each region, a regional modulation trajectory lookup table is generated through global optimization, including the modulation mode corresponding to the minimum effective inductor current value at all operating points. The generated regional modulation trajectory lookup table maintains the minimum effective inductor current value under all operating conditions (wide voltage, wide power), thereby maximizing the overall operating efficiency of the DAB converter and ensuring optimal global performance. Finally, a two-dimensional lookup table method is used to search the regional modulation trajectory lookup table for real-time control of the modulation mode, effectively avoiding the real-time optimization calculation burden of traditional complex TPS strategies while retaining the performance advantages of TPS under wide voltage / light load conditions, demonstrating high engineering practicality.

[0010] The DAB converter cooperative modulation method for region-optimal trajectory described above may optionally include dividing the operating range of the DAB converter into two voltage regions based on voltage transfer characteristics, including: Based on the relationship between the input voltage and the intermediate voltage, the operating range is divided into two voltage regions. The intermediate voltage is the average of the maximum and minimum input voltage values ​​preset by the system. When the input voltage is lower than the intermediate voltage, the voltage transfer ratio k is greater than 1, and the DAB converter operates in Boost mode. When the input voltage is higher than the intermediate voltage, the voltage transfer ratio k is less than 1, and the DAB converter operates in Buck mode.

[0011] By dividing the voltage into two regions to achieve both a single fixed modulation mode and a complex modulation mode, the contradiction between the insufficient performance of a single strategy and the poor practicality of complex strategies in existing technologies can be avoided. This division method greatly simplifies the solution of the global optimization problem, allowing the selection of the optimal strategy to be targeted within each voltage region.

[0012] In the DAB converter cooperative modulation method for region-optimal trajectory described above, optionally, the step of obtaining the effective value of the inductor current at each operating point in each voltage region under multiple preset modulation modes includes: Obtain the normalized inductor current RMS value model under each preset modulation mode; wherein, the inductor current RMS value model is used to analyze the normalized inductor current RMS value under each modulation mode. In each voltage region, the normalized power range is traversed, and the effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode is determined according to the inductor current effective value model.

[0013] By determining the effective value of the inductor current at each operating point within two voltage regions using preset effective value models of inductor current with different modulation modes, the minimum effective value of the inductor current can be obtained quickly.

[0014] In the DAB converter cooperative modulation method for region-optimal trajectories described above, optionally, obtaining the normalized inductor current RMS value model under each of the preset modulation modes includes: The peak value of the inductor current in the SPS modulation mode of the DAB converter is determined as the reference value of the effective value of the inductor current. The inductor current waveform for each modulation mode is determined, and the inductor current waveform is normalized according to the reference value to obtain the corresponding effective value model of the inductor current.

[0015] The normalized inductor current RMS model is established based on the mathematical integral of the inductor current waveform under each modulation mode, and normalized using the peak inductor current under rated power in SPS modulation mode as the benchmark value, so as to achieve a fair comparison of current stress performance under all modulation modes.

[0016] The DAB converter cooperative modulation method described above for region-optimal trajectory can optionally include obtaining a region modulation trajectory lookup table corresponding to the minimum effective value of the inductor current, including: Obtain the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode; The modulation mode corresponding to each of the minimum values ​​is determined as the target modulation mode, and the control parameter corresponding to the minimum value is determined as the target control parameter; A lookup table is used to determine the regional modulation trajectory of each target modulation mode and the target control parameters for each operating point in two voltage regions.

[0017] For each operating point, the corresponding effective value of the inductor current is determined based on its different modulation modes and operating parameters. Then, the magnitudes of the effective values ​​of the inductor current obtained from multiple modulation modes are compared, and the operating mode with the smallest effective value of the inductor current is determined as the target modulation mode. The control parameters at this time are also determined as the target control parameters to ensure that the current stress is minimized under the target modulation mode.

[0018] The DAB converter cooperative modulation method for region-optimal trajectory described above may optionally include, in the step of obtaining the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode, respectively, comprising: When the normalized power at the operating point is lower than the preset power boundary, the minimum value of the effective value of the inductor current in the TZ-CCM modulation mode and the TR-DCM modulation mode is selected. When the normalized power at the operating point is higher than the preset power boundary, the effective value of the inductor current in the SPS modulation mode is selected as the minimum value.

[0019] By selecting appropriate modulation modes under different operating conditions, the DAB converter can maintain a minimum effective value of inductor current under all operating conditions (wide voltage and wide power), thereby maximizing the overall operating efficiency of the DAB converter.

[0020] The DAB converter cooperative modulation method for region-optimal trajectory described above may optionally include, before generating the PWM waveforms driving each bridge arm of the DAB converter according to the target control parameters: Set the power hysteresis bandwidth when the operating point is located at the switching boundary between two modulation modes.

[0021] By setting power hysteresis bandwidth at the switching boundaries of different modulation modes, frequent switching of modulation modes caused by small fluctuations in operating parameters near the boundary points can be avoided, thus ensuring the smoothness and stability of modulation mode switching.

[0022] A second aspect of this application provides a DAB converter cooperative modulation system based on a region-optimal trajectory, comprising: The regional modulation trajectory generation module is used to divide the operating range of the DAB converter into two voltage regions based on the voltage transmission characteristics, and to obtain the effective value of the inductor current of each operating point in each voltage region under multiple preset modulation modes, so as to obtain a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current of all operating points; wherein, each operating point has an input voltage and the power traverses within the normalized power range, and the preset modulation modes include single phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode, and the regional modulation trajectory lookup table also includes the control parameters corresponding to the modulation mode of the operating point; The modulation strategy decision module is used to determine the target voltage region where the current operating point is located based on the input voltage in the operating parameters, and to determine the target modulation mode and the target control parameters under the target modulation mode based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region. The modulation waveform generation module is used to generate PWM waveforms to drive each bridge arm of the DAB converter based on the target control parameters.

[0023] This paper employs multiple functional modules to first divide the wide operating range into two distinct voltage regions based on voltage transmission characteristics. By introducing a region division concept based on voltage parameters, the complex global optimization problem is decomposed into two independent region optimization problems, providing a novel and efficient engineering approach for the selection of wide-range modulation strategies in DAB. Furthermore, by systematically integrating the SPS modulation mode, the TZ-CCM modulation mode, and the TR-DCM modulation mode within the TPS modulation mode, multiple preset modulation modes adaptable to both single and complex operating conditions are obtained. Then, within each region, a regional modulation trajectory lookup table is generated through global optimization, encompassing the modulation modes corresponding to the minimum effective inductor current value at all operating points. The generated regional modulation trajectory lookup table maintains the minimum effective inductor current value under all operating conditions (wide voltage, wide power), thereby maximizing the overall operating efficiency of the DAB converter and ensuring optimal global performance. Finally, a two-dimensional lookup table method is used to search the regional modulation trajectory lookup table for real-time control, effectively avoiding the real-time optimization calculation burden of traditional complex TPS strategies while retaining the performance advantages of TPS under wide voltage / light load conditions, demonstrating high engineering practicality.

[0024] The DAB converter cooperative modulation system for regional optimal trajectory as described above may optionally include a storage module for storing the regional modulation trajectory lookup table and the inductor current RMS value model.

[0025] The regional modulation trajectory lookup table, the inductor current effective value model used to determine the effective value of inductor current, the voltage region division boundary, and the preset power boundary generated by the regional modulation trajectory generation module are all stored in the storage module for easy access by the modulation strategy decision module.

[0026] The DAB converter cooperative modulation system for regional optimal trajectory described above may optionally include a parameter acquisition module for real-time acquisition of the input voltage, output voltage, and transmission power of the DAB converter, and sending them to the modulation strategy decision module.

[0027] The modulation strategy decision module can retrieve the regional modulation trajectory lookup table, inductor current RMS value model, voltage region division boundary, and preset power boundary from the storage module based on the operating parameters to determine the optimal target modulation mode and target control parameters.

[0028] This application aims to at least solve the problem of frequent modulation mode switching caused by power fluctuations at the mode switching boundary when DAB converters use hybrid modulation in the prior art. It provides a dynamic hysteresis control method and system for hybrid modulation of DAB converters. By dynamically adjusting the hysteresis bandwidth coefficient, it achieves a balance between suppressing frequent mode switching and ensuring system response performance, thereby improving system stability and operating efficiency. Attached Figure Description

[0029] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein: Figure 1 A flowchart illustrating a DAB converter cooperative modulation method based on regional optimal trajectory provided in this application embodiment; Figure 2 This application provides a full-range ZVS schematic diagram of a hybrid modulation strategy employed in an embodiment of the present application; Figure 3 A schematic diagram showing the three-dimensional performance surface plot of the normalized effective value of inductor current under five modulation modes and the trajectory of the optimal effective value of inductor current under each mode, provided for embodiments of this application. Figure 4 A schematic diagram of the optimal trajectories of two voltage regions on a performance surface provided for an embodiment of this application; Figure 5 A schematic diagram of the trajectory of the optimal inductor current RMS value in two regions of a test operating point on a performance surface, provided for an embodiment of this application; Figure 6This application provides a schematic diagram comparing the effective value of inductor current and efficiency at the test operating point and non-track point, as illustrated in an embodiment of the present application. Figure 1 ; Figure 7 This application provides a schematic diagram comparing the effective value of inductor current and efficiency at the test operating point and non-track point, as illustrated in an embodiment of the present application. Figure 2 . Detailed Implementation

[0030] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0031] Traditional single-phase-shift (SPS) modulation strategies are simple in structure and easy to implement. However, when the voltage conversion ratio (k = N*V2 / V1) deviates from a unit value, the effective value of its inductor current (I_RMS) rises sharply, leading to a significant increase in conduction losses and a sharp decrease in efficiency. Especially under light load conditions, SPS modulation generates a large amount of reactive circulating current, which not only degrades efficiency but also causes the loss of zero-voltage switching (ZVS) conditions, increasing switching losses and electromagnetic interference.

[0032] To improve the performance limitations of SPS (Short-Side Phase Shift), a triple phase shift (TPS) modulation strategy was proposed. This strategy introduces three control degrees of freedom: the duty cycle of the primary and secondary bridge arms, and the inter-bridge phase shift angle. Theoretically, it can minimize the effective value of the inductor current under specific operating conditions. However, TPS modulation has multiple complex operating modes, and the switching process between these modes is complex, easily leading to current surges or transient imbalances, thus limiting its engineering practicality.

[0033] More importantly, the optimal control parameters for TPS modulation need to be obtained by solving a multivariable nonlinear optimization problem in real time. DAB converters typically operate at high frequencies (tens to hundreds of kHz), requiring the control system to complete optimization calculations within microseconds. This places extremely high demands on the processor's computing power, making it difficult to implement in practical engineering.

[0034] Existing technologies mostly use offline lookup table methods to pre-store optimization parameters, but this method has a contradiction between storage accuracy and generalization ability: high-precision lookup table requires storing massive amounts of data, which places stringent requirements on memory resources; while low-precision lookup table will lead to performance degradation and make it difficult to maintain the best performance across all operating conditions.

[0035] Currently, most optimization research on DAB modulation strategies focuses on parameter tuning for a single operating mode or local optimization within a limited operating range. There is a lack of a modulation parameter optimization method that can achieve globally optimal performance across the entire voltage and load range and is easily implemented in engineering. In particular, existing methods fail to effectively address the smooth transition and trajectory tracking problems when modulation parameters change continuously over a wide range, resulting in a significant gap between actual operating performance and theoretical optimal values.

[0036] Therefore, designing a regional modulation trajectory lookup table for DAB converters that can adapt to a wide voltage range and wide load variation, and achieving efficient and stable tracking of this trajectory, thereby minimizing current stress (i.e., RMS inductor current), reducing losses, and maintaining ZVS conditions across the entire operating range, has become a key technical bottleneck that urgently needs to be overcome in the field of DAB converters. Based on this, this application proposes a DAB converter cooperative modulation method and system based on two regional optimal trajectories. By combining offline trajectory optimization with online lookup table tracking, the system efficiency is significantly improved while ensuring dynamic performance and stability.

[0037] like Figure 1 As shown, this embodiment provides a DAB converter cooperative modulation method based on regional optimal trajectory, including the following steps.

[0038] Step S100: Based on the voltage transfer characteristics, the operating range of the DAB converter is divided into two voltage regions, and the effective value of the inductor current at each operating point in each voltage region under multiple preset modulation modes is obtained to obtain a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points. Each operating point has an input voltage and the power traverses within the normalized power range. The preset modulation modes include single phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode. The regional modulation trajectory lookup table also includes the control parameters corresponding to the modulation mode of the operating point.

[0039] Step S200: Determine the target voltage region where the current operating point is located based on the input voltage in the operating parameters, and determine the target modulation mode and the target control parameters under the target modulation mode based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region.

[0040] Step S300: Generate PWM waveforms for driving each bridge arm of the DAB converter based on the target control parameters.

[0041] This application first divides the wide operating range into two distinct voltage regions based on voltage transfer characteristics. By introducing a region division concept based on voltage parameters, the complex global optimization problem is decomposed into two independent region optimization problems, providing a novel and efficient engineering approach for the selection of wide-range modulation strategies for DAB. Furthermore, by systematically integrating the SPS modulation mode, the TZ-CCM modulation mode, and the TR-DCM modulation mode within the TPS modulation mode, multiple preset modulation modes adaptable to both single and complex operating conditions are obtained. Then, within each region, a regional modulation trajectory lookup table is generated through global optimization, including the modulation mode corresponding to the minimum effective inductor current value at all operating points. The generated regional modulation trajectory lookup table maintains the minimum effective inductor current value under all operating conditions (wide voltage, wide power), thereby maximizing the overall operating efficiency of the DAB converter and ensuring optimal global performance. Finally, a two-dimensional lookup table method is used to search the regional modulation trajectory lookup table for real-time control, effectively avoiding the real-time optimization calculation burden of traditional complex TPS strategies while retaining the performance advantages of TPS under wide voltage / light load conditions, demonstrating high engineering practicality.

[0042] The embodiments of this application will be described below through specific examples.

[0043] For step S100 above, the operating range of the DAB converter is divided into two voltage regions based on the voltage transfer characteristics. The effective value of the inductor current at each operating point within each voltage region under multiple preset modulation modes is obtained to generate a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points. Each operating point has an input voltage and its power traverses within the normalized power range. The preset modulation modes include single-phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode. The regional modulation trajectory lookup table also includes the control parameters corresponding to the modulation mode of the operating point.

[0044] To effectively manage performance optimization issues under wide voltage input (or wide voltage ratio k), the entire operating range is divided into two main voltage regions based on the input voltage relative to the system's preset intermediate voltage. This voltage region division method greatly simplifies the solution of the global optimal problem, allowing the selection of the optimal modulation mode to be targeted within its respective region.

[0045] Within the two voltage regions defined above, offline calculations are used for the full power range (normalized power). Two regional modulation trajectory lookup tables with the minimum effective value of inductor current are generated. Specifically, during the calculation, calculations are performed for each operating point within each voltage region. Each operating point has an input voltage and transmission power, which can be represented as ( ,in, This indicates the input voltage at this operating point. This represents the transmission power at the operating point; for each operating point, the effective value of the inductor current under multiple preset modulation modes is calculated.

[0046] In this embodiment, the multiple preset modulation modes include the aforementioned single-phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode; among them, TZ-CCM and TR-DCM modulation modes are special modulation modes of TPS modulation mode, which can be applied to complex operating conditions. For each operating point, a traversal method is used, specifically, traversing the entire range of transmission power. Each traversal of transmission power corresponds to an operating point, and the transmission power at each operating point... Calculate the effective value of the inductor current under the three modulation modes of SPS, TZ-CCM and TR-DCM respectively. ).

[0047] Then, the effective values ​​of the inductor current at each operating point under the three modulation modes are compared to determine the modulation mode corresponding to the smallest effective value of the inductor current, as well as the control parameters corresponding to the effective value of the inductor current, so as to form a regional modulation trajectory lookup table; to ensure that the effective value of the inductor current in the regional modulation trajectory lookup table is the smallest.

[0048] Within each region, a regional modulation trajectory lookup table with the minimum effective value of inductor current is generated through global optimization. By systematically integrating the advantages of SPS and TPS, the generated regional modulation trajectory lookup table can maintain the minimum effective value of inductor current under all operating conditions (wide voltage and wide power), thereby maximizing the overall operating efficiency of the DAB converter and ensuring optimal global performance.

[0049] Both voltage zones have a regional modulation trajectory lookup table. In subsequent use, the corresponding voltage zone is determined based on the input voltage of the operating point, and then the modulation mode is determined by comparing the regional modulation trajectory lookup table with the transmission power.

[0050] For step S200 above, the target voltage region where the current operating point is located is determined based on the input voltage in the operating parameters, and the target modulation mode and the target control parameters under the target modulation mode are determined based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region.

[0051] Furthermore, the regional modulation trajectory lookup table is a two-dimensional lookup table, including the input voltage and transmission power (as input) for each operating point, and the corresponding modulation mode and control parameters (as output). During DAB converter operation, operating parameters (as operating parameters for a single operating point), such as input voltage, output voltage, and transmission power, can be acquired in real time. Then, by comparing these operating parameters with the regional modulation trajectory lookup table, the target modulation mode that minimizes the effective value of the induced inductor current at that operating point, along with the target control parameters under that mode, is determined.

[0052] By combining a two-dimensional lookup table method to search the regional modulation trajectory lookup table for real-time control, the real-time optimization calculation burden of traditional complex TPS strategies is effectively avoided, while retaining the performance advantages of TPS under wide voltage / light load conditions, and it has extremely high engineering practicality.

[0053] For step S300 above, the PWM waveforms driving each bridge arm of the DAB converter are generated according to the target control parameters. This not only avoids the real-time optimization calculation burden of the traditional complex TPS strategy, but also retains the performance advantages of TPS under wide voltage / light load, and has extremely high engineering practicality.

[0054] As one implementation method, the operating range of the DAB converter is divided into two voltage regions based on the voltage transfer characteristics. This includes dividing the operating range into two voltage regions according to the relationship between the input voltage and the intermediate voltage. The intermediate voltage is the average of the maximum and minimum input voltage values ​​preset by the system. When the input voltage is lower than the intermediate voltage, the voltage transfer ratio k is greater than 1, and the DAB converter operates in Boost mode. When the input voltage is higher than the intermediate voltage, the voltage transfer ratio k is less than 1, and the DAB converter operates in Buck mode.

[0055] In practical implementation, the DAB converter has preset parameters, including the minimum and maximum values ​​of the input voltage range, voltage transfer ratio, etc. The midpoint between the maximum and minimum values ​​of the input voltage is defined as the intermediate voltage, and the operating range is divided into two voltage regions based on the relationship between the input voltage and the intermediate voltage. At the intermediate voltage, the voltage transfer ratio k is equal to 1.

[0056] Specifically, based on the relationship between the input voltage and the system's preset intermediate voltage, the entire operating range is divided into two main voltage regions; one where the input voltage is lower than the intermediate voltage ( In the region where the voltage transfer ratio k is greater than 1, the power transfer mode is mainly Boost type, which dominates in terms of modulation mode complexity and performance; another input voltage is higher than the intermediate voltage ( In the region where the voltage transfer ratio k is less than 1, the power transfer mode is predominantly Buck type, which is the opposite of the dominant mode in region 1, and is dominant in a single fixed modulation mode.

[0057] By dividing the voltage into two regions to achieve both a single fixed modulation mode and a complex modulation mode, the contradiction between the insufficient performance of a single strategy and the poor practicality of complex strategies in existing technologies can be avoided. This division method greatly simplifies the solution of the global optimization problem, allowing the selection of the optimal strategy to be targeted within each voltage region.

[0058] In one embodiment, the effective value of the inductor current at each operating point in each voltage region under multiple preset modulation modes is obtained, including the following steps.

[0059] Step 1: Obtain the normalized inductor current RMS value model under each preset modulation mode; wherein, the inductor current RMS value model is used to analyze the normalized inductor current RMS value under each modulation mode.

[0060] Step 2: Traverse the normalized power range within each voltage region and determine the effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode based on the inductor current effective value model.

[0061] The effective value model of inductor current is a mathematical model that characterizes the effective value of inductor current under various modulation modes (SPS modulation mode, TZ-CCM modulation mode, TR-DCM modulation mode). It can also be understood as a formula for calculating the effective value of inductor current; for example, a complex piecewise function, or a general expression using a two-variable function.

[0062] Different modulation modes employ different RMS inductor current models. Each RMS inductor current model is related to operating parameters, such as input voltage and transmitted power. By traversing each voltage region based on the normalized power at each operating point, and inputting the operating parameters into the RMS inductor current model, the RMS inductor current value at each operating point under the three modulation modes can be determined.

[0063] By determining the effective value of the inductor current at each operating point within two voltage regions using preset effective value models of inductor current with different modulation modes, the minimum effective value of the inductor current can be obtained quickly.

[0064] In this embodiment, the inductor current RMS model and the regional modulation trajectory lookup table can be stored after generation. When needed during the operation of the DAB converter, they can be called online for lookup and comparison, which significantly improves system efficiency while ensuring system dynamic performance and stability.

[0065] In one embodiment, a method for obtaining a normalized effective value model of inductor current under each preset modulation mode includes the following steps.

[0066] Step 1: Determine the peak value of the inductor current of the DAB converter in SPS modulation mode as the reference value of the effective value of the inductor current.

[0067] Step 2: Determine the inductor current waveform for each modulation mode, and normalize the inductor current waveform according to the reference value to obtain the corresponding effective value model of the inductor current.

[0068] First, a normalization reference is determined, using the peak inductor current of the DAB converter in SPS modulation mode as the reference value for current stress. Then, analytical expressions are obtained. For TZ-CCM and TR-DCM modulation modes, the inductor current waveforms under triple phase-shift control parameters are solved respectively, and the analytical expressions (inductor current RMS model) are obtained by square integration of the waveforms.

[0069] The above-mentioned normalized inductor current RMS value model is established based on the mathematical integral of the inductor current waveform under each modulation mode, and normalized using the peak value of the inductor current under rated power in SPS modulation mode as the benchmark value, so as to achieve a fair comparison of current stress performance under all modulation modes.

[0070] When using SPS, the peak inductor current is taken as a unified normalized reference. All calculation results are normalized values. The analytical models of normalized transmission power and effective inductor current for the three modulation modes of SPS, TZ-CCM and TR-DCM are shown in Table 1 below.

[0071] Table 1

[0072] In the table above, k represents the voltage transfer ratio, calculated from the input and output voltages. Both the TZ-CCM and TR-DCM modulation modes in the table include Buck and Boost modes. It can be observed that different modes have different characteristics.

[0073] Figure 2 This embodiment provides a full-range ZVS diagram of the hybrid modulation strategy employed.

[0074] In one implementation, obtaining a lookup table of the regional modulation trajectory corresponding to the minimum effective value of the inductor current includes the following steps.

[0075] Step 1: Obtain the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode.

[0076] Step 2: Determine the modulation mode corresponding to each minimum value as the target modulation mode, and determine the control parameter corresponding to the minimum value as the target control parameter.

[0077] Step 3: Determine the target modulation mode and target control parameters for each operating point in the two voltage regions using the regional modulation trajectory lookup table.

[0078] Specifically, for each operating point, the corresponding effective value of the inductor current is determined based on its different modulation modes and operating parameters. Then, the magnitudes of the effective values ​​of the inductor current obtained from multiple modulation modes are compared, and the operating mode with the smallest effective value of the inductor current is determined as the target modulation mode. The control parameters at this time are also determined as the target control parameters to ensure that the current stress is minimized under the target modulation mode.

[0079] After traversing all operating points in the two voltage zones according to the normalized transmission power, the optimal modulation mode (target modulation mode) and its optimal control parameters (target control parameters) at each operating point are recorded to form two two-dimensional lookup table data, namely the regional modulation trajectory lookup table for each of the two voltage zones.

[0080] As shown in Table 2 below, the optimal control parameter group of the regional modulation trajectory lookup table for each of the two voltage regions is partially displayed.

[0081] Table 2

[0082] In the table above, Region1 represents one voltage region, and Region2 represents another voltage region.

[0083] like Figure 3 As shown in the figure, this embodiment illustrates a three-dimensional performance surface plot of the normalized inductor current RMS value under five modulation modes and a schematic diagram of the optimal inductor current RMS value trajectory for each mode.

[0084] Figure 4 This is a schematic diagram of the optimal trajectories of two voltage regions on the performance surface provided in an embodiment of this application, which clearly shows the cooperative switching boundary of the modulation mode.

[0085] In one implementation, obtaining the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode includes the following steps.

[0086] When the normalized power at the operating point is lower than the preset power boundary, the minimum effective value of the inductor current in the TZ-CCM modulation mode and the TR-DCM modulation mode is selected; when the normalized power at the operating point is higher than the preset power boundary, the minimum effective value of the inductor current in the SPS modulation mode is selected.

[0087] DAB converters operate under various conditions, such as light load and medium-to-high load. Under different conditions, an appropriate modulation mode is selected. Specifically, under light load conditions, the TPS modulation modes (TR-DCM, TZ-CCM) exhibit lower current stress. Therefore, when the transmitted power is below a preset power threshold, the optimal modulation mode is preferentially selected from TR-DCM and TZ-CCM as the target modulation mode.

[0088] Correspondingly, under medium to high load conditions, when the preset power boundary is exceeded, the SPS modulation mode has advantages in power density and implementation complexity. At the same time, its performance gap with the TPS modulation mode is reduced. Therefore, the SPS modulation mode is used to make up for the shortfall, so as to ensure that the effective value of the inductor current covers the full power range.

[0089] By selecting appropriate modulation modes under different operating conditions, the DAB converter can maintain a minimum effective value of inductor current under all operating conditions (wide voltage and wide power), thereby maximizing the overall operating efficiency of the DAB converter.

[0090] In one implementation, before generating the PWM waveforms for each bridge arm of the DAB converter based on the target control parameters, the method further includes setting the power hysteresis bandwidth when the operating point is located at the switching boundary between two modulation modes.

[0091] At the switching boundaries of different modulation modes, such as the boundary between TR-DCM / TZ-CCM and SPS, a power hysteresis bandwidth is set to avoid frequent switching of modulation modes caused by small fluctuations in operating parameters near the boundary point, thus ensuring the smoothness and stability of modulation mode switching.

[0092] For example, this embodiment provides a specific implementation method.

[0093] This embodiment takes a typical DAB converter for an energy storage system as an example, and its design parameters are as follows: switching frequency. Transformer turns ratio Input voltage range to Stable output voltage Voltage ratio The device used is Wolfspeed's C3M0021120K.

[0094] Step 1: Establish a normalized model of the effective value of inductor current for various modulation modes.

[0095] Specifically, normalized analytical models (inductor current RMS models) for three modulation modes—SPS, TZ-CCM, and TR-DCM—and schematic diagrams of the full-range ZVS are established. Figure 2 Peak current when using SPS. To ensure a unified normalization benchmark, all calculation results are normalized, as shown in Table 1 above.

[0096] Step 2: Divide the voltage region.

[0097] Specifically, based on the system characteristics, the intermediate voltage is calculated. The voltage range is then divided as follows: Region 1: Vi < 800V (corresponding to k > 1), the system mainly operates in Boost mode.

[0098] Region 2: Vi > 800V (corresponding to k < 1), the system mainly operates in Buck mode.

[0099] Step 3: Solve for the optimal trajectory in the region (minimum effective value of inductor current).

[0100] Specifically, within region 1 (640V to 800V), the following optimization selections are made for all power points from 0 to 1: Light load condition optimization ( Compare all control parameter combinations that can transmit the target power under the two modulation modes TR-DCM and TZ-CCM, and select the effective value of the inductor current. The smallest combination is the optimal modulation mode.

[0101] Heavy-duty working condition supplement ( Using the SPS modulation strategy, calculate the phase shift angle required to transmit the target power. , as the optimal modulation mode.

[0102] All optimal ( The optimal modulation mode and control parameters corresponding to the region are packaged to form the effective value trajectory of the inductor current in region 1 (region modulation trajectory lookup table).

[0103] Repeat the above process for region 2 (800V to 960V) to form the RMS value trajectory of the inductor current in region 2 (region modulation trajectory lookup table). The region modulation trajectory lookup tables for regions 1 and 2 are shown in Table 2 above.

[0104] like Figure 5As shown in the figure, this embodiment also provides a schematic diagram of the trajectory of the optimal inductor current RMS value in two regions selected for the test operating point on the performance surface; wherein, the test operating point is selected as... .

[0105] Figure 6 and Figure 7 Both values ​​represent the effective value of the inductor current and the efficiency at the operating point and non-track point. A comparison diagram, in which, Figure 6 A comparison chart of larger measurement time ranges. Figure 7 This is a comparison chart for a smaller measurement time range. It can be observed that when the modulation mode is selected using a regional modulation trajectory lookup table at the operating point, the effective value of the inductor current can be reduced and efficiency improved.

[0106] Based on the unified application concept, this embodiment also provides a DAB converter cooperative modulation system based on regional optimal trajectory, including a regional modulation trajectory generation module, a modulation strategy decision module, and a modulation wave generation module.

[0107] Specifically, the regional modulation trajectory generation module is used to divide the operating range of the DAB converter into two voltage regions based on the voltage transmission characteristics, and to obtain the effective value of the inductor current of each operating point in each voltage region under multiple preset modulation modes, so as to obtain a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current of all operating points. Each operating point has an input voltage and the power traverses within the normalized power range. The preset modulation modes include single phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode. The regional modulation trajectory lookup table also includes the control parameters corresponding to the modulation mode of the operating point.

[0108] The modulation strategy decision module is used to determine the target voltage region where the current operating point is located based on the input voltage in the operating parameters, and to determine the target modulation mode and the target control parameters under the target modulation mode based on the transmission power and the regional modulation trajectory lookup table of the target voltage region in the operating parameters; the modulation waveform generation module is used to generate PWM waveforms to drive each bridge arm of the DAB converter based on the target control parameters in order to control the power transmission.

[0109] The aforementioned functional modules first divide the wide operating range into two distinct voltage regions based on voltage transmission characteristics. By introducing a region division concept based on voltage parameters, the complex global optimization problem is decomposed into two independent region optimization problems, providing a novel and efficient engineering approach for the selection of wide-range modulation strategies for DAB. Furthermore, by systematically integrating the SPS modulation mode, the TZ-CCM modulation mode, and the TR-DCM modulation mode within the TPS modulation mode, multiple preset modulation modes adaptable to both single and complex operating conditions are obtained. Then, within each region, a regional modulation trajectory lookup table is generated through global optimization, encompassing the modulation modes corresponding to the minimum effective inductor current value at all operating points. The generated regional modulation trajectory lookup table maintains the minimum effective inductor current value under all operating conditions (wide voltage, wide power), thereby maximizing the overall operating efficiency of the DAB converter and ensuring optimal global performance. Finally, a two-dimensional lookup table method is used to search the regional modulation trajectory lookup table for real-time control, effectively avoiding the real-time optimization calculation burden of traditional complex TPS strategies while retaining the performance advantages of TPS under wide voltage / light load conditions, demonstrating high engineering practicality.

[0110] In one implementation, the DAB converter cooperative modulation system based on the regional optimal trajectory further includes a storage module for storing a regional modulation trajectory lookup table and an inductor current RMS model.

[0111] The regional modulation trajectory lookup table, the inductor current effective value model used to determine the effective value of the inductor current, the voltage region division boundary, and the preset power boundary generated by the aforementioned regional modulation trajectory generation module are all stored in the storage module for easy access by the modulation strategy decision module.

[0112] In one embodiment, the DAB converter cooperative modulation system based on the optimal regional trajectory further includes a parameter acquisition module, which is used to acquire the input voltage, output voltage, and transmission power of the DAB converter in real time and send them to the modulation strategy decision module. This allows the modulation strategy decision module to retrieve the regional modulation trajectory lookup table, the inductor current RMS model, the voltage region division boundary, and the preset power boundary from the storage module based on the operating parameters to determine the optimal target modulation mode and target control parameters.

[0113] In the foregoing description of this application, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "linked" should be interpreted broadly. For example, the term "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this application, those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0114] Based on the above description of this application, those skilled in the art will also understand that terms used, such as "upper," "lower," "length," "width," "top," "bottom," "inner," "outer," "axial," "longitudinal," "transverse," "clockwise," or "counterclockwise," indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings of this application. These terms are used only for the purpose of facilitating the explanation of the application and simplifying the description, and are not intended to explicitly or implicitly suggest that the device or element involved must have the stated specific orientation, or be constructed and operated in a specific orientation. Therefore, the aforementioned orientation or positional relationship terms should not be understood or interpreted as limitations on the application.

[0115] Furthermore, the terms "first" or "second," etc., used in this application to refer to numbers or ordinal numbers are for convenience of description only and should not be construed as explicitly or implicitly indicating relative importance or specifying the number of indicated technical features. Also, a feature specified as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0116] While numerous embodiments of this application have been shown and described herein, it will be appreciated by those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise in the mind and spirit of this application without departing from its intent. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A DAB converter cooperative modulation method based on regional optimal trajectory, characterized in that, include: Based on voltage transfer characteristics, the operating range of the DAB converter is divided into two voltage regions. The effective value of the inductor current at each operating point within each voltage region under multiple preset modulation modes is obtained to generate a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points. Each operating point has an input voltage and its power traverses within a normalized power range. The preset modulation modes include single-phase shift (SPS) modulation mode, trapezoidal continuous conduction (TZ-CCM) modulation mode, and triangular discontinuous conduction (TR-DCM) modulation mode. The regional modulation trajectory lookup table also includes control parameters corresponding to the modulation mode of the operating point. The target voltage region where the current operating point is located is determined based on the input voltage in the operating parameters, and the target modulation mode and the target control parameters under the target modulation mode are determined based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region. Based on the target control parameters, generate PWM waveforms to drive each bridge arm of the DAB converter; The process of obtaining the regional modulation trajectory lookup table, which includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points, includes: Obtain the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode; The modulation modes corresponding to all the minimum values ​​are determined as the target modulation modes, and the control parameters corresponding to the minimum values ​​are determined as the target control parameters; Determine the regional modulation trajectory lookup table for each target modulation mode and the target control parameters as operating points in two voltage regions; Furthermore, obtaining the minimum effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode includes: When the normalized power at the operating point is lower than the preset power boundary, the minimum value of the effective value of the inductor current in the TZ-CCM modulation mode and the TR-DCM modulation mode is selected. When the normalized power at the operating point is higher than the preset power boundary, the effective value of the inductor current in the SPS modulation mode is selected as the minimum value.

2. The DAB converter cooperative modulation method based on regional optimal trajectory according to claim 1, characterized in that, The operating range of the DAB converter is divided into two voltage regions based on voltage transfer characteristics, including: Based on the relationship between the input voltage and the intermediate voltage, the operating range is divided into two voltage regions. The intermediate voltage is the average of the maximum and minimum input voltage values ​​preset by the system. When the input voltage is lower than the intermediate voltage, the voltage transfer ratio k is greater than 1, and the DAB converter operates in Boost mode. When the input voltage is higher than the intermediate voltage, the voltage transfer ratio k is less than 1, and the DAB converter operates in Buck mode.

3. The DAB converter cooperative modulation method based on regional optimal trajectory according to claim 1, characterized in that, The step of acquiring the effective value of the inductor current at each operating point in each voltage region under multiple preset modulation modes includes: Obtain the normalized inductor current RMS value model under each preset modulation mode; wherein, the inductor current RMS value model is used to analyze the normalized inductor current RMS value under each modulation mode. In each voltage region, the normalized power range is traversed, and the effective value of the inductor current at each operating point in SPS modulation mode, TZ-CCM modulation mode, and TR-DCM modulation mode is determined according to the inductor current effective value model.

4. The DAB converter cooperative modulation method based on regional optimal trajectory according to claim 3, characterized in that, The step of obtaining the normalized inductor current RMS value model under each of the preset modulation modes includes: The peak value of the inductor current in the SPS modulation mode of the DAB converter is determined as the reference value of the effective value of the inductor current. The inductor current waveform for each modulation mode is determined, and the inductor current waveform is normalized according to the reference value to obtain the corresponding effective value model of the inductor current.

5. The DAB converter cooperative modulation method based on regional optimal trajectory according to claim 1, characterized in that, Before generating the PWM waveforms for each bridge arm of the DAB converter based on the target control parameters, the method further includes: Set the power hysteresis bandwidth when the operating point is located at the switching boundary between two modulation modes.

6. A DAB converter cooperative modulation system based on a region-optimal trajectory, the DAB converter cooperative modulation system being based on the DAB converter cooperative modulation method based on a region-optimal trajectory as described in claim 1, characterized in that, include: The regional modulation trajectory generation module is used to divide the operating range of the DAB converter into two voltage regions based on the voltage transmission characteristics, and to obtain the effective value of the inductor current at each operating point in each voltage region under multiple preset modulation modes, so as to obtain a regional modulation trajectory lookup table that includes the modulation mode corresponding to the minimum effective value of the inductor current at all operating points; wherein, each operating point has an input voltage and the power traverses within the normalized power range, and the preset modulation modes include single phase shift (SPS) modulation mode, trapezoidal continuous conduction TZ-CCM modulation mode, and triangular discontinuous conduction TR-DCM modulation mode, and the regional modulation trajectory lookup table also includes the control parameters corresponding to the modulation mode of the operating point; The modulation strategy decision module is used to determine the target voltage region where the current operating point is located based on the input voltage in the operating parameters, and to determine the target modulation mode and the target control parameters under the target modulation mode based on the transmission power in the operating parameters and the regional modulation trajectory lookup table of the target voltage region. The modulation waveform generation module is used to generate PWM waveforms to drive each bridge arm of the DAB converter based on the target control parameters.

7. The DAB converter cooperative modulation system according to claim 6, characterized in that, It also includes a storage module for storing the regional modulation trajectory lookup table and the inductor current RMS value model.

8. The DAB converter cooperative modulation system according to claim 6, characterized in that, It also includes a parameter acquisition module, which is used to acquire the input voltage, output voltage, and transmission power of the DAB converter in real time and send them to the modulation strategy decision module.

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