Energy balance control method, system and storage medium
By dynamically adjusting the frequency and phase-shift control mode in the DAB converter, the loss problem caused by fixed frequency and rigid control strategies is solved, achieving efficient energy transfer and improving the overall performance of the battery system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN POWEROAK NEWENER CO LTD
- Filing Date
- 2026-06-22
- Publication Date
- 2026-07-21
AI Technical Summary
Existing DAB converters have fixed switching frequencies and rigid control strategies, which cause the circuit to leave the ZVS region when the voltage difference at different ports changes, increasing the losses of the switching transistors and magnetic cores, and making it difficult to balance the energy transfer efficiency and complexity in different directions.
The operating frequency is determined by the input and output voltages of the DAB converter, and the phase-shift control mode is dynamically adjusted by combining the energy transfer direction and voltage ratio. An adaptive frequency switching and phase-shift control strategy is adopted, including first dual-phase-shift control, single-phase-shift control and second dual-phase-shift control, to optimize the generation of switching frequency and phase-shift angle.
It achieves high-efficiency operation of DAB converter across the entire operating range, reduces switching transistor and core losses, improves energy transmission efficiency, expands the high-efficiency operating range, and achieves an overall efficiency of over 98%.
Smart Images
Figure CN122437195A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of battery management technology, specifically relating to an energy balance control method, system, and storage medium. Background Technology
[0002] In energy storage systems composed of multiple battery packs connected in series, inconsistencies in initial capacity, internal resistance, self-discharge rate, and operating temperature among the battery packs lead to significant differences in the state of charge (SOC) of each pack after multiple charge-discharge cycles. This inconsistency directly results in a decrease in the overall usable capacity and shortened lifespan of the series-connected battery pack system, and may also trigger safety risks such as localized overcharging or over-discharging. Therefore, battery balancing technology is an indispensable key function in battery management systems. Energy transfer between the primary and secondary sides can be achieved through a Dual Active Bridge (DAB) converter, that is, the DAB converter directly transfers energy from the battery pack with higher charge to the battery pack with lower charge.
[0003] In the energy equalization process of a DAB converter, to achieve energy flow, it is necessary to control the switching frequency of the DAB converter's switching transistors and the phase difference of the switching transistor drive signals. In existing DAB converter energy equalization switching frequency control processes, a fixed switching frequency is used. However, with a fixed switching frequency, when the voltage difference between the two ports of the DAB converter (used to connect the two battery packs) changes, the circuit may deviate from the ZVS (Zero Voltage Switching) region, resulting in a significant increase in switching transistor losses and transformer core losses. Furthermore, the use of a fixed single phase shift control (SPS) or a fixed extended phase shift control (EPS) method throughout the energy equalization phase difference process makes it difficult to simultaneously account for the efficiency and complexity of energy transfer in different directions, from the primary side to the secondary side or from the secondary side to the primary side. Summary of the Invention
[0004] The purpose of this application is to provide an energy balance control method, system, and storage medium to solve the technical problems of rigid control strategies and inability to maintain high efficiency across the entire operating range in the prior art.
[0005] In a first aspect, embodiments of this application provide an energy balancing control method applied to a DAB converter, wherein a main battery pack is connected to the primary side of the DAB converter to provide primary-side energy, and a secondary battery pack is connected to the secondary side of the DAB converter to provide secondary-side energy. The method includes: Based on the input voltage and output voltage of the DAB converter in the energy transmission direction, determine the voltage ratio between the input and output terminals of the DAB converter; The operating frequency of the DAB converter is determined based on the input voltage, the output voltage, and the voltage difference between two adjacent moments. The operating frequency is either a first preset frequency or a second preset frequency higher than the first preset frequency. The port voltage difference is the absolute difference between the input voltage and the output voltage. The phase-shift control mode of the DAB converter at the operating frequency is determined based on the energy transmission direction and the voltage ratio.
[0006] Optionally, the operating frequency of the DAB converter is determined based on the input voltage, the output voltage, and the voltage difference between two adjacent moments, including: Based on the operating frequency of the DAB converter at the previous moment, the input voltage at the current moment, and the output voltage at the current moment, the dynamic differential voltage threshold at the current moment is determined, and the dynamic differential voltage threshold includes a high differential voltage threshold and a low differential voltage threshold. If the input voltage at the current moment is less than or equal to the voltage difference, then the operating frequency of the DAB converter is set to the first preset frequency, and the voltage difference is the absolute difference between the output voltage at the current moment and the high voltage difference threshold at the current moment. If the input voltage at the current moment is greater than the voltage difference, then based on the comparison results of the port voltage difference and the dynamic voltage difference threshold corresponding to the previous moment and the current moment, respectively, and the operating frequency at the previous moment, a switching operation between the first preset frequency and the second preset frequency is performed.
[0007] Optionally, based on the comparison results of the port voltage difference and the dynamic voltage difference threshold corresponding to the previous time and the current time respectively, and the operating frequency of the previous time, a switching operation between the first preset frequency and the second preset frequency is performed, including: If the current port voltage difference is less than the current low voltage difference threshold, the previous port voltage difference is greater than the previous high voltage difference threshold, and the previous operating frequency is the second preset frequency, then the operating frequency of the DAB converter is switched to the first preset frequency. If the current port voltage difference is greater than the current high voltage difference threshold, the previous port voltage difference is less than the previous low voltage difference threshold, and the previous operating frequency is the first preset frequency, then the operating frequency of the DAB converter is switched to the second preset frequency. If neither of the above two conditions is met, the operating frequency of the DAB converter will remain unchanged.
[0008] Optionally, based on the operating frequency of the DAB converter at the previous moment, the input voltage at the current moment, and the output voltage at the current moment, the dynamic differential voltage threshold at the current moment is determined, including: The first voltage value is determined based on the product of the transformer turns ratio of the DAB converter and the output voltage; The second voltage value is determined based on the sum of the first voltage value and the input voltage; Based on the dead time of the drive signal of the switching transistor of the DAB converter and the switching period of the previous moment, the time ratio is determined, wherein the switching period is the reciprocal of the operating frequency of the previous moment. The proportional voltage value is determined based on the product of the time ratio and the second voltage value; The high voltage difference threshold is determined based on the sum of the proportional voltage value and the preset voltage value. The low voltage drop threshold is determined based on the difference between the proportional voltage value and the preset voltage value.
[0009] Optionally, based on the energy transfer direction and the voltage ratio, the phase-shift control mode of the DAB converter at the operating frequency is determined, including: If the energy transmission direction is from the primary side to the secondary side and the voltage ratio is greater than or equal to 1, then the phase shift control mode is a first dual phase shift control mode that controls the external phase shift angle and the internal phase shift angle. If the energy transmission direction is from the primary side to the secondary side and the voltage ratio is less than 1, then the phase shift control mode is a single phase shift control mode that controls the external phase shift angle. If the energy transmission direction is from the secondary side to the primary side and the voltage ratio is greater than or equal to 1, then the phase shift control mode is the first dual phase shift control mode that controls the external phase shift angle and the internal phase shift angle. If the energy transmission direction is from the secondary side to the primary side and the voltage ratio is less than 1, then the phase shift control mode is a second dual-phase shift control mode that controls the external phase shift angle and the internal phase shift angle.
[0010] Optionally, in the first dual-phase-shift control mode, the inner phase-shift angle is determined as:
[0011] The outward phase angle is determined as follows:
[0012] in, and As an intermediate variable, , , For the target transmission power, For transformer leakage inductance, The transformer turns ratio For PWM switching frequency, The voltage ratio is... The input voltage is... The output voltage is denoted as .
[0013] Optionally, in the single-phase-shift control mode, the outer phase-shift angle is dynamically generated by running a proportional-integral (PI) current loop, using the desired equalization current as input and the real-time sampled inductor current as feedback.
[0014] Optional, In the second dual-phase shift control mode, the inner phase shift angle is determined as:
[0015] The outward phase angle is determined as follows:
[0016] in, The voltage ratio is... For normalized power, , For the target transmission power, Characteristic power, , The transformer turns ratio The input voltage is... The output voltage is... For transformer leakage inductance, This is the PWM switching frequency.
[0017] Optionally, the voltage ratio can be determined based on the input and output voltages, including: Determine the ratio of the input voltage to the output voltage at the same time. The voltage ratio is determined by multiplying the ratio and the turns ratio of the transformer in the DAB converter.
[0018] Optionally, the first preset frequency is determined based on the leakage inductance of the transformer of the DAB converter and the equivalent resonant capacitance of the DAB converter; The second preset frequency is a preset multiple of the first preset frequency.
[0019] Secondly, embodiments of this application provide an energy balancing system, including: A DAB converter includes a transformer, a primary-side bridge circuit connected to the primary side of the transformer, and a secondary-side bridge circuit connected to the secondary side of the transformer. The primary-side bridge circuit and the secondary-side bridge circuit are respectively used to connect a main battery pack and a slave battery pack. A controller, connected to the DAB converter, is configured to execute the energy balancing control method described above to balance the energy of the main battery pack and the slave battery pack.
[0020] Thirdly, embodiments of this application provide a computer storage medium storing instructions or programs that, when executed by at least one processor, cause the at least one processor to perform the method described above.
[0021] This application provides an energy equalization control method for DAB converters. First, based on the input and output voltages of the DAB converter in the energy transmission direction, the voltage ratio between the input and output terminals of the DAB converter is determined. Then, based on the input voltage, output voltage, and the voltage difference between the ports at two adjacent moments, the operating frequency of the DAB converter is determined. This operating frequency is either a first preset frequency or a second preset frequency higher than the first preset frequency. Finally, based on the energy transmission direction and the voltage ratio, the phase-shifting control mode of the DAB converter at this operating frequency is determined. This method adaptively determines the current operating frequency from the first and second preset frequencies for each composite operating condition, and jointly determines the phase-shifting control mode of the DAB converter at the current operating frequency based on the energy transmission direction and the voltage ratio. This solves the problem of circuit deviating from the ZVS region or unnecessary switching and core losses caused by changes in the voltage difference between different ports when using a fixed frequency, thus maximizing the efficiency of the DAB converter across its entire operating range. Attached Figure Description
[0022] Figure 1 This is a structural block diagram of the energy balance control system in the embodiments of this application; Figure 2 This is a schematic diagram of the controller 20 in an embodiment of this application; Figure 3 This is a flowchart of the startup and self-test of the energy balance control system in the embodiments of this application; Figure 4This is a flowchart of the energy balance control method in the embodiments of this application; Figure 5 This is a flowchart illustrating frequency adaptive determination based on operating conditions in an embodiment of this application; Figure 6 This is a schematic diagram of the input and output voltages of the DAB converter in different energy transmission directions in the embodiments of this application. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0024] It should be noted that, in the embodiments of this application, the primary side refers to the non-isolated side, i.e., the main battery pack side; the secondary side refers to the isolated side, i.e., the secondary battery pack side.
[0025] Please refer to Figure 1 , Figure 1 A block diagram of the energy balance control system is shown. Figure 1 As shown in the figure, this application provides an energy balancing control system for a series battery pack, including: The DAB converter 10 includes a transformer T, a primary-side bridge circuit connected to the primary side of the transformer T, and a secondary-side bridge circuit connected to the secondary side of the transformer T. The primary-side bridge circuit is connected to the main battery pack, and the secondary-side bridge circuit is connected to the slave battery pack. Each of these circuits consists of four power switching transistors (Q1~Q4 and Q5~Q8) and their anti-parallel diodes. Furthermore, a power inductor L is connected between the primary-side bridge circuit and the transformer T, and filter capacitors CE1 and CE2 are connected in parallel between the primary and secondary bridge circuits, respectively.
[0026] The controller 20, connected to each switch of the DAB converter 10, is configured to perform any of the energy equalization control methods described below.
[0027] In one embodiment, the controller 20 includes an ARM-based microcontroller (MCU, such as the ARM Cortex-M series), whose PWM output is connected to the gates of the switching transistors in the primary-side bridge circuit and the secondary-side bridge circuit, respectively. To handle the high real-time execution of the active balancing algorithm, the controller 20 adopts a layered real-time architecture, which internally includes a task management layer, a current loop control layer, a hardware protection layer, and a PWM drive layer.
[0028] The system comprises the following layers: The task management layer operates in the first cycle and performs frequency selection and mode decision-making based on the input voltage, output voltage, and port voltage difference between the primary and secondary sides of the DAB converter 10 in the energy transmission direction, thereby determining the phase shift angle parameters (i.e., outer and inner phase shift angles) corresponding to the phase shift control mode; the current loop control layer operates in the second cycle and dynamically generates the outer phase shift angle by running the proportional-integral current loop when the phase shift control mode is a single phase shift control mode; the hardware protection layer operates in the third cycle and monitors and identifies various hardware faults and executes corresponding protection actions; the PWM drive layer, connected to the task management layer, current loop control layer, and hardware protection layer, generates PWM drive signals for the primary and secondary bridge circuits of the DAB converter based on the switching frequency and phase shift angle parameters determined by the task management layer (when the phase shift control mode is the first or second dual phase shift control mode) or the outer phase shift angle dynamically generated by the current loop control layer (when the phase shift control mode is a single phase shift control mode), and executes the blocking and restoring of the PWM output according to the protection action instructions of the hardware protection layer.
[0029] In one embodiment, the task management layer is also used to monitor software-level or time-insensitive faults and execute corresponding protection actions. For example, in each first cycle, the task management layer reads information such as voltage, current, and temperature values sampled by the ADC (Analog-to-Digital Converter), compares them with preset thresholds, and determines whether the limits are exceeded. If the limits are exceeded and persist for a certain period of time, corresponding protection actions are executed, such as stopping equalization, shutting down PWM output, and reporting the fault to the BMS.
[0030] For example, the task management layer runs on a 10-millisecond cycle and is responsible for acquiring operating parameters, determining frequency adaptation, making mode decisions, and monitoring fault conditions. Based on the decision results, this layer determines the phase shift angle parameters corresponding to the phase shift control mode at the current switching frequency and sends these parameters to the PWM drive layer or the current loop control layer. This layer has a large computational load but relatively low real-time requirements.
[0031] The current loop control layer operates with a 200-microsecond cycle and is activated only in single-phase-shift control mode. This layer runs a high-speed PI current loop, using the desired equalization current as a given and the real-time sampled inductor current as feedback to dynamically calculate the outer phase shift angle, which is then updated to the PWM drive layer in real time. This layer requires high real-time performance to ensure the bandwidth and stability of the current loop.
[0032] The hardware protection layer operates on a 20-microsecond cycle (or is triggered by an interrupt from a hardware comparator) to monitor hardware-level fault signals such as overvoltage, overcurrent, and short circuits. Upon detecting a fault, this layer immediately sends a blocking command to the PWM driver layer and records the fault status. After the fault is cleared, the blocking can be lifted according to instructions from the task management layer. This layer has the highest priority, ensuring system safety.
[0033] The PWM driver layer interacts directly with the MCU's high-level timer peripherals. It receives switching frequency configuration and phase shift parameters from the task management layer, or dynamic phase shift updates from the current loop control layer, generates complementary PWM drive signals for the primary and secondary bridge circuits, and automatically inserts dead time. Simultaneously, the PWM driver layer responds to hardware protection layer blocking commands, immediately forcing the PWM output to a safe level (e.g., all low levels) upon fault occurrence, and restoring the PWM output according to the task management layer's instructions after fault recovery.
[0034] The four layers communicate with each other through shared memory and flag bits, with the first cycle > the second cycle > the third cycle. The response time of the PWM drive layer is directly determined by the hardware timer (up to nanosecond level), realizing a layered multi-task design. It also makes full use of the high-performance computing capabilities of the ARM MCU and advanced timer peripherals (such as timer cascading to generate complex PWM). The real-time performance and execution accuracy of the algorithm are jointly guaranteed from both software and hardware levels, so that all the above adaptive optimization functions can run stably and smoothly in the actual chip, rather than remaining at the theoretical simulation level.
[0035] Please see Figure 2 , Figure 2 One structure of the controller 20 is shown. For example... Figure 2 As shown, the controller 20 includes at least one processor 21 and a memory 22. The memory 22 can be built into the controller 20 or external to the controller 20. The memory 22 can also be a remotely configured memory connected to the controller 20 via a network.
[0036] Memory 22, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. Memory 22 may include a program storage area and a data storage area, wherein the program storage area may store the operating system and application programs required for at least one function; the data storage area may store data created based on the use of the terminal, etc. Furthermore, memory 22 may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, memory 22 may optionally include memory remotely located relative to processor 21, and these remote memories can be connected to the terminal via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.
[0037] The processor 21 performs various functions of the terminal and processes data by running or executing software programs and / or modules stored in the memory 22 and calling data stored in the memory 22, thereby performing overall monitoring of the terminal, such as implementing the energy balance control method described in any embodiment of this application.
[0038] Processor 21 can be one or more. Figure 2 The example provided is a processor 21. Processor 21 and memory 22 can be connected via a bus or other means. Processor 21 may include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field-programmable gate array (FPGA) device, etc. Processor 21 can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.
[0039] Please refer to Figure 3 , Figure 3 The flowchart of the startup and self-test of the energy balance control system is shown.
[0040] like Figure 3 As shown, after the controller of the energy balance control system is powered on, if it receives an energy balance command, it first performs a self-test and system initialization. The self-test includes verifying voltage sampling (i.e., verifying whether the voltage sampled from the main battery pack and the secondary battery pack deviates from the voltage sampled by the controller) and confirming whether the hardware status is normal (e.g., confirming whether the sampling module, power supply module, and hardware overcurrent signal are normal). System initialization includes reading preset parameters and configuring the system. These preset parameters may include: transformer turns ratio, transformer leakage inductance, equivalent resonant capacitance, dead time, hysteresis width, etc. Initialization configuration includes configuring the PWM timer, ADC sampling channel, fault protection threshold, etc.
[0041] After completing self-test and system initialization, the controller acquires relevant operating parameters to determine the input and output voltages of the DAB converter in the energy transfer direction. These operating parameters include the primary-side voltage, secondary-side voltage, main battery pack SOC value, and secondary battery pack SOC value. In one embodiment, the controller compares the main battery pack SOC value and the secondary battery pack SOC value to determine the energy transfer direction. Specifically, when the main battery pack SOC value is greater than the secondary battery pack SOC value, the energy transfer direction is from the primary side to the secondary side, and the input voltage of the DAB converter in the energy transfer direction is determined to be the primary-side voltage, and the output voltage is determined to be the secondary-side voltage. When the main battery pack SOC value is less than the secondary battery pack SOC value, the energy transfer direction is from the secondary side to the primary side, and the input voltage of the DAB converter in the energy transfer direction is determined to be the secondary-side voltage, and the output voltage is determined to be the primary-side voltage. In other embodiments, the controller can also directly acquire the energy transfer direction and determine the input and output voltages based on the energy transfer direction.
[0042] Furthermore, the controller calculates the port voltage difference and sets the initial switching frequency based on the port voltage difference, thereby initiating energy balancing control (i.e., executing...). Figure 4 (Energy equalization control method in the embodiment). Here, the port voltage difference is the absolute difference between the input voltage and the output voltage. If the initially calculated port voltage difference is greater than a preset initial threshold (which may be the same as the low-voltage threshold described below), then a second preset frequency is selected as the initial switching frequency; otherwise, a first preset frequency is selected as the initial switching frequency.
[0043] In one embodiment, the first preset frequency and the second preset frequency are preset empirical values (such as 30Hz and 50Hz), and the second preset frequency is higher than the first preset frequency.
[0044] In another implementation, the first preset frequency is determined based on the leakage inductance of the transformer in the DAB converter and the equivalent resonant capacitance of the DAB converter, and the second preset frequency is a preset multiple of the first preset frequency. For example, the formulas for calculating the first and second preset frequencies are as follows: (1) (2) in, The first preset frequency, For the second preset frequency, For transformer leakage inductance, This is the equivalent resonant capacitance of the DAB converter.
[0045] Please refer to Figure 4 , Figure 4 A flowchart of the energy balance control method is shown. (For example...) Figure 4 As shown, the energy balance control method includes the following steps S401 to S404.
[0046] Step S401: Based on the input voltage and output voltage of the DAB converter in the energy transmission direction, determine the voltage ratio between the input and output terminals of the DAB converter.
[0047] After the equalization control is initiated, the controller's task management layer operates in the first cycle. It first calculates the ratio based on the input and output voltages at the same moment, and then determines the voltage ratio by multiplying the ratio by the turns ratio of the DAB converter's transformer. The calculation formula is as follows: (3) in, The transformer turns ratio Input voltage, This is the output voltage.
[0048] Please refer to Figure 6 , Figure 6 The diagram illustrates the input and output voltages of a DAB converter under different energy transfer directions. Figure 6 As shown in (a), when the SOC value of the main battery pack is greater than the SOC value of the secondary battery pack, the energy transfer direction is from the primary side to the secondary side. Therefore, the input terminal of the DAB converter is the primary side, the input voltage is the primary side voltage, and the output terminal is the secondary side, the output voltage is the secondary side voltage. Figure 6 As shown in (b), when the SOC value of the main battery pack is less than the SOC value of the secondary battery pack, the energy transfer direction is from the secondary side to the primary side. Therefore, the input terminal of the DAB converter is the secondary side, the input voltage is the secondary side voltage, the output terminal is the primary side, and the output voltage is the primary side voltage.
[0049] Step S402: Determine the operating frequency of the DAB converter based on the input voltage, output voltage, and the magnitude of the voltage difference between two adjacent moments at the port.
[0050] Traditional phase-shift control schemes typically preset the PWM carrier frequency (i.e., switching frequency) to a fixed value. However, the inventors discovered through experiments and research that the optimal switching frequency required to maintain high efficiency (especially ZVS) of the DAB circuit varies with changes in port voltage difference. Under large port voltage differences, a fixed frequency may cause the circuit to deviate from the ZVS region, resulting in a significant increase in switching losses; conversely, under smaller port voltage differences, an excessively high fixed frequency can lead to unnecessary switching and core losses. Based on this, this application proposes a method for adaptive frequency determination based on operating conditions, as detailed below. Figure 5 The description.
[0051] Step S403: Determine the phase-shift control mode of the DAB converter at the operating frequency based on the energy transmission direction and voltage ratio.
[0052] After determining the current switching frequency, the system enters the phase-shift control decision-making and phase-shift angle calculation stage. This application proposes a lookup table-based decision-making method based on the energy transfer direction and voltage ratio, combined with three different phase-shift angle generation paths, to achieve precise matching of the control strategy and optimal performance.
[0053] Specifically, the controller determines the phase-shift control mode under the current operating condition by consulting the following table based on the real-time calculated voltage ratio and the energy transmission direction:
[0054] According to the table above, if the energy transmission direction is from the primary side to the secondary side and the voltage ratio is greater than or equal to 1, the phase shift control mode is the first dual-phase shift control mode that controls the external and internal phase shift angles; if the energy transmission direction is from the primary side to the secondary side and the voltage ratio is less than 1, the phase shift control mode is the single-phase shift control mode that controls the external phase shift angle; if the energy transmission direction is from the secondary side to the primary side and the voltage ratio is greater than or equal to 1, the phase shift control mode is the first dual-phase shift control mode that controls the external and internal phase shift angles; if the energy transmission direction is from the secondary side to the primary side and the voltage ratio is less than 1, the phase shift control mode is the second dual-phase shift control mode that controls the external and internal phase shift angles.
[0055] When the voltage ratio is greater than or equal to 1, the input voltage is high and the output voltage is low (i.e., the port voltage difference is large), resulting in significant voltage stress when the switching transistor is turned off during energy transfer. The first dual-phase-shift control mode introduces two independent phase-shift angles, an outer phase shift angle and an inner phase shift angle, to control the overlap time of the conduction of the primary and secondary bridge circuit arms separately. This ensures that the switching transistor can switch under zero-voltage conditions even with a large port voltage difference, reducing switching losses. Furthermore, if the switching frequency is adaptively increased, the response speed can be accelerated and current ripple reduced under a large port voltage difference, which is beneficial for the ZVS range.
[0056] When the voltage ratio is less than 1 and the energy transfer direction is from the primary side to the secondary side, the port voltage difference is small, and both switching and conduction losses are low. The system's requirements for ZVS are relatively relaxed, and a simple single-phase-shift control mode can meet the performance requirements. The single-phase-shift control mode has only one phase shift angle (i.e., the external phase shift angle), resulting in a simple control structure, low computational load, and suitability for real-time control.
[0057] When the voltage ratio is less than 1 and the energy transmission direction is from the secondary side to the primary side, this application proposes a second dual-phase-shift control mode based on a variant of the first dual-phase-shift control mode. Compared with the first dual-phase-shift control mode, the second dual-phase-shift control mode can further reduce conduction and switching losses and ensure high efficiency.
[0058] In the table above, each phase-shift control mode corresponds to a phase-shift angle generation method. Once the phase-shift control method is determined, the corresponding phase-shift angle can be generated by calling the appropriate phase-shift angle generation engine.
[0059] When the phase-shift control mode is the first dual-phase-shift control mode, the system calls the first set of feedforward calculation formulas based on the DAB precise mathematical model to calculate the inner and outer phase-shift angles, thereby achieving a fast, overshoot-free dynamic response. Specifically, the target transmission power is first obtained. P (Can be calculated or preset by the BMS based on the imbalance), combined with the current switching frequency. Transformer leakage inductance Transformer turns ratio Input voltage Output voltage and voltage ratio Calculate intermediate variables and : (4) (5) Then, based on the intermediate variables , and voltage ratio Calculate the outer phase angle and inward phase angle : (6) (7) In the first dual-phase-shift control mode, by optimizing the phase shift ratio (i.e., the outer and inner phase shift angles), the circulating current and conduction losses can be minimized under different load and voltage conditions. The phase shift angle is directly output based on the real-time voltage ratio through feedforward calculation, avoiding the delay and oscillation of closed-loop regulation. The system has fast dynamic response and high efficiency.
[0060] When the phase-shift control mode is single-phase-shift control mode, the high-speed PI current loop runs in the second cycle, using the desired equalization current as a given and the real-time sampled inductor current as feedback. The PI controller dynamically generates the external phase shift angle (typically ranging from 0 to 0.5). This mode does not rely on precise circuit parameters and has strong robustness.
[0061] In single-phase-shift control mode, the PI current loop closed-loop regulation can ensure stable output current, avoid over-adjustment or oscillation, and further optimize efficiency.
[0062] When the phase-shift control mode is the second dual-phase-shift control mode, the system calls the second set of feedforward calculation formulas, derived from a deep mathematical derivation of the specific current waveform and soft-switching boundary under this operating condition, to calculate the inner and outer phase-shift angles. Specifically, it first calculates the inner and outer phase-shift angles based on the current switching frequency. Transformer leakage inductance Transformer turns ratio Input voltage and output voltage Calculate characteristic power : (8) Then based on the target transmission power and characteristic power Calculate normalized power : (9) Then, based on the normalized power and voltage ratio Calculate the outer phase angle and inward phase angle : (10) (11) The second dual-phase-shift control mode is specifically optimized for the condition where energy transfer direction is from the secondary side to the primary side and K<1, which can significantly reduce current stress and maintain ZVS. Experimental results show that this algorithm can stably improve the efficiency of this extreme condition from less than 90% under the general algorithm to over 96%, solving a long-standing performance bottleneck in existing technologies.
[0063] Finally, the calculated phase shift angle is written into the PWM timer's compare register, and the PWM timer is set according to the current operating frequency to generate the drive waveforms for the primary and secondary bridge circuits. To eliminate the risk of bridge arm shoot-through or current surge during frequency switching, this application also proposes a "safe stop first, then reinitialize" hardware operation sequence. Specifically, during frequency switching, the new frequency is switched according to a safety protocol of "first turning off the PWM output, then reconfiguring the timer period, and then re-enabling the PWM output." In energy balance control, this application uses a hybrid approach of feedforward open-loop calculation and closed-loop PI regulation, balancing fast dynamic response and strong robustness.
[0064] Please refer to Figure 5 , Figure 5A flowchart illustrating frequency adaptive determination based on operating conditions is shown. In this embodiment, the controller periodically monitors the input voltage, output voltage, and port voltage difference in a first cycle, and executes frequency switching logic with hysteresis and state memory.
[0065] like Figure 5 As shown, the method for adaptive frequency determination based on operating conditions includes the following steps S501 to S508: Step S501: Based on the operating frequency of the DAB converter at the previous moment, the input voltage at the current moment, and the output voltage at the current moment, determine the dynamic differential voltage threshold at the current moment.
[0066] The dynamic differential voltage threshold includes a high differential voltage threshold and a low differential voltage threshold, with the previous moment separated from the current moment by one control cycle (i.e., the first cycle). In one embodiment, the dynamic differential voltage threshold is determined as follows: a first voltage value is determined based on the product of the transformer turns ratio and the output voltage of the DAB converter; a second voltage value is determined based on the sum of the first voltage value and the input voltage; a time ratio is determined based on the dead time of the drive signal of the DAB converter's switching transistor and the switching cycle of the previous moment; a proportional voltage value is determined based on the product of the time ratio and the second voltage value; a high differential voltage threshold is determined based on the sum of the proportional voltage value and a preset voltage value; and a low differential voltage threshold is determined based on the difference between the proportional voltage value and the preset voltage value. The switching cycle of the previous moment is the reciprocal of the operating frequency of the previous moment.
[0067] For example, high voltage differential threshold and low pressure threshold The following formula can be used for dynamic calculation: (12) (13) in, Input voltage, For output voltage, The transformer turns ratio The dead time of the power switch. The previous PWM switching cycle. This is the preset hysteresis width.
[0068] In the example above, the first voltage value is... The second voltage value is: The time ratio is The proportional voltage value is The preset voltage value is .
[0069] Step S502: Determine whether the current input voltage is less than or equal to the voltage difference. If yes, proceed to step S503; otherwise, proceed to step S504.
[0070] The voltage difference is the absolute difference between the current output voltage and the current high voltage difference threshold.
[0071] If the current input voltage is less than or equal to the voltage difference, proceed to step S503 and set the operating frequency of the DAB converter to the first preset frequency. If the current input voltage is greater than the voltage difference, execute the frequency switching logic with hysteresis and state memory from steps S504 to S508. This frequency switching logic performs a switching operation between the first preset frequency and the second preset frequency based on the comparison results of the port voltage difference and dynamic voltage difference threshold corresponding to the previous and current times, respectively, and the operating frequency of the previous time.
[0072] Step S503: Set the operating frequency of the DAB converter to the first preset frequency.
[0073] Step S504: Determine whether the current port voltage difference is less than the current low voltage difference threshold, whether the previous port voltage difference is greater than the previous high voltage difference threshold, and whether the previous operating frequency is the second preset frequency. If yes, proceed to step S505; otherwise, proceed to step S506.
[0074] Step S505: Switch the operating frequency of the DAB converter to the first preset frequency.
[0075] Step S506: Determine whether the current port voltage difference is greater than the current high voltage difference threshold, whether the previous port voltage difference is less than the previous low voltage difference threshold, and whether the previous operating frequency is the first preset frequency. If yes, proceed to step S507; otherwise, proceed to step S508.
[0076] Step S507: Switch the operating frequency of the DAB converter to the second preset frequency.
[0077] Step S508: Maintain the operating frequency of the DAB converter unchanged.
[0078] In this embodiment, when the port voltage difference is small, the energy stored in the junction capacitance of the switching transistor when it is turned off is small, resulting in a low commutation energy threshold required to achieve zero-voltage switching (ZVS), and soft switching (ZVS) is easily established and maintained naturally. In the total system losses, conduction losses related to circulating current account for a small proportion, while high-frequency losses directly related to switching behavior account for a large proportion. Therefore, setting the switching frequency to a relatively low and pre-optimized first preset frequency can effectively suppress high-frequency losses that are positively correlated with frequency. When the port voltage difference is large, the commutation energy threshold required to achieve ZVS is high. Increasing the frequency can optimize the current waveform and reduce the effective current value. This achieves the elimination of catastrophic hard-switching losses at the cost of a controllable and limited increase in the number of switching operations, and minimizes the total losses under optimized control. Furthermore, a dead zone is formed between the high and low voltage difference thresholds through hysteresis, effectively preventing frequent frequency switching when the voltage difference fluctuates near the threshold. By using the switching frequency as a dynamic optimization variable and employing a hysteresis comparison strategy based on the port voltage difference to intelligently switch the frequency, the system maintains zero voltage difference (ZVS) under large voltage differences and reduces switching losses under small voltage differences, significantly expanding the high-efficiency operating range. The measured overall efficiency can reach over 98%.
[0079] This application also provides a non-volatile computer-readable storage medium storing computer-executable instructions that are executed by one or more processors, for example, to perform the energy balancing control method steps described above.
[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. An energy balancing control method applied to a DAB converter, wherein a main battery pack is connected to the primary side of the DAB converter to provide primary-side energy and a secondary battery pack is connected to the secondary side of the DAB converter to provide secondary-side energy, characterized in that, The method includes: Based on the input voltage and output voltage of the DAB converter in the energy transmission direction, determine the voltage ratio between the input and output terminals of the DAB converter; The operating frequency of the DAB converter is determined based on the input voltage, the output voltage, and the voltage difference between two adjacent moments. The operating frequency is either a first preset frequency or a second preset frequency higher than the first preset frequency. The port voltage difference is the absolute difference between the input voltage and the output voltage. The phase-shift control mode of the DAB converter at the operating frequency is determined based on the energy transmission direction and the voltage ratio.
2. The method according to claim 1, characterized in that, The operating frequency of the DAB converter is determined based on the input voltage, the output voltage, and the voltage difference between two adjacent moments at the port, including: Based on the operating frequency of the DAB converter at the previous moment, the input voltage at the current moment, and the output voltage at the current moment, the dynamic differential voltage threshold at the current moment is determined, and the dynamic differential voltage threshold includes a high differential voltage threshold and a low differential voltage threshold. If the input voltage at the current moment is less than or equal to the voltage difference, then the operating frequency of the DAB converter is set to the first preset frequency, and the voltage difference is the absolute difference between the output voltage at the current moment and the high voltage difference threshold at the current moment. If the input voltage at the current moment is greater than the voltage difference, then based on the comparison results of the port voltage difference and the dynamic voltage difference threshold corresponding to the previous moment and the current moment, respectively, and the operating frequency at the previous moment, a switching operation between the first preset frequency and the second preset frequency is performed.
3. The method according to claim 2, characterized in that, Based on the comparison results of the port voltage difference and the dynamic voltage difference threshold corresponding to the previous time and the current time respectively, and the operating frequency of the previous time, a switching operation between the first preset frequency and the second preset frequency is performed, including: If the current port voltage difference is less than the current low voltage difference threshold, the previous port voltage difference is greater than the previous high voltage difference threshold, and the previous operating frequency is the second preset frequency, then the operating frequency of the DAB converter is switched to the first preset frequency. If the current port voltage difference is greater than the current high voltage difference threshold, the previous port voltage difference is less than the previous low voltage difference threshold, and the previous operating frequency is the first preset frequency, then the operating frequency of the DAB converter is switched to the second preset frequency. If neither of the above two conditions is met, the operating frequency of the DAB converter will remain unchanged.
4. The method according to claim 2, characterized in that, Based on the operating frequency of the DAB converter at the previous moment, the input voltage at the current moment, and the output voltage at the current moment, the dynamic differential voltage threshold at the current moment is determined, including: The first voltage value is determined based on the product of the transformer turns ratio of the DAB converter and the output voltage; The second voltage value is determined based on the sum of the first voltage value and the input voltage; Based on the dead time of the drive signal of the switching transistor of the DAB converter and the switching period of the previous moment, the time ratio is determined, wherein the switching period is the reciprocal of the operating frequency of the previous moment. The proportional voltage value is determined based on the product of the time ratio and the second voltage value; The high voltage difference threshold is determined based on the sum of the proportional voltage value and the preset voltage value; The low voltage drop threshold is determined based on the difference between the proportional voltage value and the preset voltage value.
5. The method according to claim 1, characterized in that, Based on the energy transfer direction and the voltage ratio, the phase-shift control mode of the DAB converter at the operating frequency is determined, including: If the energy transmission direction is from the primary side to the secondary side and the voltage ratio is greater than or equal to 1, then the phase shift control mode is a first dual-phase shift control mode that controls the external phase shift angle and the internal phase shift angle. If the energy transmission direction is from the primary side to the secondary side and the voltage ratio is less than 1, then the phase shift control mode is a single phase shift control mode that controls the external phase shift angle. If the energy transmission direction is from the secondary side to the primary side and the voltage ratio is greater than or equal to 1, then the phase shift control mode is the first dual phase shift control mode that controls the external phase shift angle and the internal phase shift angle. If the energy transmission direction is from the secondary side to the primary side and the voltage ratio is less than 1, then the phase shift control mode is a second dual-phase shift control mode that controls the external phase shift angle and the internal phase shift angle.
6. The method according to claim 5, characterized in that, In the first dual-phase shift control mode, the inner phase shift angle is determined as: The outward phase angle is determined as follows: in, and As an intermediate variable, , , For the target transmission power, For transformer leakage inductance, The transformer turns ratio For PWM switching frequency, The voltage ratio is... The input voltage is... The output voltage is denoted as .
7. The method according to claim 5, characterized in that, In the single-phase-shift control mode, the outer phase-shift angle is dynamically generated by running a proportional-integral (PI) current loop, with the desired equalization current as input and the inductor current sampled in real time as feedback.
8. The method according to claim 5, characterized in that, In the second dual-phase shift control mode, the inner phase shift angle is determined as: The outward phase angle is determined as follows: in, The voltage ratio is... For normalized power, , For the target transmission power, Characteristic power, , The transformer turns ratio The input voltage is... The output voltage is... For transformer leakage inductance, This is the PWM switching frequency.
9. The method according to claim 1, characterized in that, Based on the input voltage and output voltage, determine the voltage ratio, including: Determine the ratio of the input voltage to the output voltage at the same time. The voltage ratio is determined by multiplying the ratio and the turns ratio of the transformer in the DAB converter.
10. The method according to claim 1, characterized in that, The first preset frequency is determined based on the leakage inductance of the transformer of the DAB converter and the equivalent resonant capacitance of the DAB converter; The second preset frequency is a preset multiple of the first preset frequency.
11. An energy balancing system, characterized in that, include: A DAB converter includes a transformer, a primary-side bridge circuit connected to the primary side of the transformer, and a secondary-side bridge circuit connected to the secondary side of the transformer. The primary-side bridge circuit and the secondary-side bridge circuit are respectively used to connect a main battery pack and a slave battery pack. A controller, connected to the DAB converter, is configured to perform the energy balancing control method as described in any one of claims 1 to 10 to balance the energy of the main battery pack and the slave battery pack.
12. A computer storage medium, characterized in that, The computer storage medium stores instructions or programs that, when executed by at least one processor, cause the at least one processor to perform the method as described in any one of claims 1 to 10.