A lithium battery system charging control method, device, controller, and lithium battery system

Abstract

This invention provides a lithium battery system charging control method, device, controller, and lithium battery system, relating to the field of energy storage control technology. The method includes: after the lithium battery system is powered on, acquiring the high-voltage side voltage of each DC-DC converter in real time; controlling each DC-DC converter to gradually increase its high-voltage side voltage; and after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC-DC converter all fall within a preset range, controlling each DC-DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module. The preset range is determined based on the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed. This invention avoids the judgment deviation caused by the internal resistance difference of a single DC-DC converter by comprehensively judging the average voltage of multiple DC-DC converters, ensuring that the relay can be successfully closed and the system enters charging mode after the lithium battery system is powered on.

Description

Technical Field

[0001] This invention relates to the field of energy storage control technology, and in particular to a lithium battery system charging control method, device, controller, and lithium battery system. Background Technology

[0002] A lithium-ion battery system is an energy system that integrates energy storage media, energy conversion devices, and control units to realize the storage, release, and dispatch of electrical energy, thereby mitigating fluctuations in power supply and demand. In a lithium-ion battery system, a single battery module can be connected to multiple DC-DC converters of the same structure. These converters can be switched between series and parallel connections. Different connection methods can adapt to applications with different voltages or power levels.

[0003] When a lithium battery system needs charging after power-on, the relay between the DC bus and the DC converter can be closed to switch to charging mode. For example, if the lithium battery system shuts down due to over-discharge, the relay between the DC bus and the DC converter will open; after power is restored, the lithium battery system can automatically power on, control the relay to close, and switch to charging mode. The DC bus voltage is usually much higher than the battery voltage. During the startup process of the lithium battery system, in order to prevent the inrush current from burning out the internal components of the DC converter, an open-loop slow-start method is usually used. For example, the controller gradually increases the duty cycle of the drive signals of each DC converter in a linear ramp manner, gradually increasing the high-voltage side voltage of each DC converter until the voltage difference across the relay meets the closing condition (e.g., the voltage difference is less than 10V), then the relay closes, switching to closed-loop control mode to charge the battery.

[0004] Because all DC-DC converters have the same structure, their high-voltage side voltages are theoretically the same when connected in parallel. To simplify control, the high-voltage side voltage of one of the DC-DC converters is usually used as a reference, representing the overall voltage after the parallel connection of all DC-DC converters. When the voltage difference between the high-voltage side voltage of that DC-DC converter and the DC bus voltage meets the closing condition, all relays are closed simultaneously. However, existing open-loop soft-start methods may encounter problems in parallel mode, such as the inability to close relays and the lithium battery system failing to switch to charging mode. Summary of the Invention

[0005] This invention provides a lithium battery system charging control method, device, controller, and lithium battery system to solve the problem that existing open-loop slow-start control methods cannot close the relay and cannot switch to charging mode in parallel mode.

[0006] In a first aspect, embodiments of the present invention provide a charging control method for a lithium battery system, the lithium battery system including a battery module and at least two DC-DC converters; the low-voltage side of each DC-DC converter is connected to the battery module, and the high-voltage side is connected to a DC bus via a relay; the method includes: after the lithium battery system is powered on, acquiring the high-voltage side voltage of each DC-DC converter in real time; controlling each DC-DC converter to gradually increase the high-voltage side voltage; wherein, the average value of the high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference, for DC-DC converters with voltages higher than the reference, the voltage increase amplitude is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the voltage increase amplitude is increased in the next cycle; after the average value, maximum value, and minimum value of the high-voltage side voltage of each DC-DC converter all fall within a preset range, controlling each DC-DC converter to stop increasing the high-voltage side voltage, closing the relay, and charging the battery module, wherein the preset range is determined based on the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed.

[0007] In one possible implementation, after acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: performing a weighted average of the high-voltage side voltage of each DC-DC converter to obtain the average value of the high-voltage side voltage of each DC-DC converter.

[0008] In one possible implementation, before the weighted average of the high-voltage side voltages of each DC-DC converter is obtained, the method further includes: controlling each DC-DC converter to increase its high-voltage side voltage with the same modulation parameters during a target period; determining the weight of each DC-DC converter based on its high-voltage side voltage; wherein the weight is positively correlated with the high-voltage side voltage; correspondingly, the weighted average of the high-voltage side voltages of each DC-DC converter is obtained by: after the target period, performing a weighted average of the high-voltage side voltages of each DC-DC converter based on its weight to obtain the average high-voltage side voltage of each DC-DC converter.

[0009] In one possible implementation, before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter have all fallen within a preset range, the method further includes: if there is a first DC converter whose high-voltage side voltage has risen to the upper limit of the preset range, then controlling the first DC converter to stop increasing its high-voltage side voltage, and controlling the other DC converters other than the first DC converter to continue gradually increasing their high-voltage side voltage until the average and minimum values ​​have all fallen within the preset range.

[0010] In one possible implementation, before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltages of each DC converter all fall within a preset range, the method further includes: after the average value of the high-voltage side voltages of each DC converter falls within the preset range, if there is a second DC converter whose high-voltage side voltage is less than the lower limit of the preset range, controlling the other DC converters except the second DC converter to stop increasing their high-voltage side voltage, and controlling the second DC converter to continue gradually increasing its high-voltage side voltage until the high-voltage side voltage of the second DC converter is not less than the lower limit of the preset range.

[0011] In one possible implementation, controlling each DC-DC converter to gradually increase the high-voltage side voltage includes: if the high-voltage side voltage of any DC-DC converter in the previous cycle is greater than the average value, then the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is reduced to reduce the increase in the high-voltage side voltage; if the high-voltage side voltage of any DC-DC converter in the previous cycle is less than the average value, then the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is increased to increase the increase in the high-voltage side voltage.

[0012] In one possible implementation, after acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: performing an arithmetic average of the high-voltage side voltage of each DC-DC converter to obtain the average value of the high-voltage side voltage of each DC-DC converter.

[0013] Secondly, embodiments of the present invention provide a lithium battery system charging control device. The lithium battery system includes a battery module and at least two DC-DC converters. The low-voltage side of each DC-DC converter is connected to the battery module, and the high-voltage side is connected to a DC bus via a relay. The device includes: an acquisition module for acquiring the high-voltage side voltage of each DC-DC converter in real time after the lithium battery system is powered on; a boost module for controlling each DC-DC converter to gradually increase the high-voltage side voltage; wherein, the average value of the high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference, and for DC-DC converters with voltages higher than the reference, the boost amplitude is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the boost amplitude is increased in the next cycle; and a charging module for controlling each DC-DC converter to stop increasing the high-voltage side voltage and closing the relay to charge the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC-DC converter all fall within a preset range, wherein the preset range is determined based on the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed.

[0014] Thirdly, embodiments of the present invention provide a controller, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation thereof.

[0015] Fourthly, embodiments of the present invention provide a lithium battery system, including the controller described in the third aspect above.

[0016] Fifthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in the first aspect or any possible implementation thereof.

[0017] In a sixth aspect, embodiments of the present invention provide a computer program product, including a computer program that, when executed by a processor, implements the method described in the first aspect or any possible implementation thereof.

[0018] This invention, in its embodiment, controls the parallel DC-DC converters to gradually increase their voltage periodically during the startup process of a lithium battery system. Simultaneously, the high-voltage side voltages of all DC-DC converters are collected and their average value is calculated. Using this average value as a benchmark, the subsequent voltage increase of each DC-DC converter is adjusted in reverse. During the voltage increase process, the voltage differences between the DC-DC converters are continuously reduced until the average, maximum, and minimum values ​​all fall within a preset range, at which point the relays of all DC-DC converters are closed. The preset range corresponds to the voltage difference requirement for safe relay closure, determined by the DC bus voltage and the maximum allowable voltage difference between the two sides of the relay. Using the average voltage of each DC-DC converter as a benchmark for the voltage increase process reduces the voltage differences between branches, avoiding misjudgments of partial compliance but overall non-compliance caused by single-branch references. When the average, maximum, and minimum values ​​all fall within the preset range, it indicates that the actual voltage difference between the two sides of the relays in each branch meets the safe closure condition. At this point, the relays are safely closed, allowing the lithium battery system to enter the charging state. Attached Figure Description

[0019] Figure 1 This is an application scenario diagram of the lithium battery system charging control method provided in the embodiments of the present invention; Figure 2 This is a flowchart illustrating the implementation of the lithium battery system charging control method provided in this embodiment of the invention. Figure 3 This is a schematic diagram of the structure of the lithium battery system charging control device provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0020] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] Figure 1 This diagram illustrates an application scenario of the lithium battery system charging control method provided in an embodiment of the present invention. For example... Figure 1 As shown, the lithium battery system includes a battery module 1 and a DC-DC converter 2. The DC-DC converter 2 is connected to a DC bus 4 via a relay 3. The DC bus can be part of the lithium battery system or located outside the lithium battery system. The DC bus can be connected to the power grid via a bidirectional converter.

[0022] A lithium battery system can contain one or more battery modules; however, this explanation focuses on a single battery module. Each battery module corresponds to multiple DC-DC converters. The number of DC-DC converters can be two or more. Figure 1 Only two DC-DC converters are shown for illustration. The output terminals of each DC-DC converter can be connected in series or in parallel, and can be switched between parallel and series connections. It should be noted that the output terminal of the DC-DC converter refers to the port connected to the DC bus. The DC-DC converter is bidirectional, so the output terminal here can discharge to the DC bus when the battery is discharging, and can also receive electrical energy from the DC bus when the battery is charging.

[0023] In series connection, the outputs of each DC-DC converter are connected end-to-end; that is, the negative output of the previous DC-DC converter is connected to the positive output of the next DC-DC converter. The positive output of the first DC-DC converter serves as the positive terminal of the lithium battery system and is connected to the positive DC bus, while the negative output of the last DC-DC converter serves as the negative terminal of the lithium battery system and is connected to the negative DC bus. In parallel connection, the positive outputs of each DC-DC converter are connected in parallel to the positive DC bus, and the negative outputs of each DC-DC converter are connected in parallel to the negative DC bus. Figure 1 Only the parallel connection method is shown in the diagram.

[0024] Regarding the number of relays, one relay can be installed for each DC-DC converter. A relay can be installed only at the positive output terminal of the DC-DC converter; alternatively, a relay can be installed at both the positive and negative output terminals of the DC-DC converter. In this case, a group of relays installed at the positive and negative output terminals of the same DC-DC converter can be considered as one relay.

[0025] Regarding the relay configuration, in parallel connection, for example, the output terminals of each DC-DC converter are connected to the first terminal of the relay, and the second terminals of each relay are connected in parallel. That is, the DC-DC converters are connected in parallel at the second terminals of the relays. Here, the first terminal of the relay is the port facing the DC-DC converter, and the second terminal is the port facing the DC bus. Alternatively, the DC-DC converters can also be connected in parallel at the first terminal of the relay.

[0026] When a lithium battery system shuts down, the voltage on the high-voltage side (output terminal) of the DC-DC converter is 0, and the relay is in the open state. There are many reasons why a lithium battery system might shut down, such as during normal use due to operational needs or due to over-discharge. If the lithium battery system shuts down due to a power outage discharging the load and over-discharge, the battery module voltage will be low and in an undervoltage state.

[0027] When a lithium battery system is powered on from a shutdown state, the battery modules need to be charged under certain circumstances. For example, after over-discharge, the battery module voltage is low, and when power is restored from the grid, the battery modules need to be charged through the grid. During the startup process of charging a lithium battery system, an open-loop slow-start method is typically used. In this method, the DC bus voltage is high after power is restored (e.g., 250V), and the high-voltage side voltage of the DC-DC converter gradually increases from 0 until the voltage difference across the relay meets the closing condition, at which point the relay closes.

[0028] The background section above provides the first open-loop soft start method, which gradually increases the duty cycle and voltage during the start-up phase. After closing the relay, it enters the operation phase and switches to closed-loop control to charge the battery.

[0029] The second open-loop slow-start method is explained below. To maintain consistency between the control logic in the startup phase and the control logic in the operation phase, and to simplify the overall control process, in the startup phase, the high-voltage side voltage of the DC-DC converter can be controlled in a closed loop based on a given value. Simultaneously, the given value is continuously increased, causing the high-voltage side voltage of the DC-DC converter to gradually rise from 0 until the voltage difference across the relay meets the closing condition. After the relay closes, the operation phase begins, switching to closed-loop control to charge the battery. Essentially, the startup phase is a closed-loop control with a gradually increasing given value, while the operation phase is a closed-loop control with a constant given value. The control logic of the two phases is basically the same. It should be noted that in the operation phase, because the output terminals of each DC-DC converter are connected in parallel after the relay closes, if each DC-DC converter were to independently control its own high-voltage side voltage in a closed loop, the voltage fluctuation at the parallel terminals would increase. Therefore, the feedback quantity for the closed-loop control generally uses the high-voltage side voltage of one of the DC-DC converters. Correspondingly, in the startup phase, to maintain consistency, the high-voltage side voltage of one of the DC-DC converters is usually used as a reference.

[0030] However, existing open-loop soft-start methods may encounter problems in parallel mode, such as the inability to close the relay and the inability of the lithium battery system to switch to charging mode.

[0031] Due to manufacturing errors or long-term performance degradation, the internal resistance of each DC-DC converter will vary, which will result in different high-voltage side voltages for each DC-DC converter even when using the same open-loop soft-start method.

[0032] For example, when the voltage difference between the high-voltage side voltage of the reference DC-DC converter and the DC bus voltage meets the closing condition, the high-voltage side voltage of other DC-DC converters may be too low, resulting in a large voltage difference across the relay. In this case, the voltage difference across the relay does not actually meet the closing condition, and the relay with the large voltage difference cannot actually close. However, the open-loop soft start has already ended, and the high-voltage side voltage of each DC-DC converter no longer increases, causing the relay to remain unable to close, and the lithium battery system cannot switch to charging mode.

[0033] For example, when the voltage difference between the high-voltage side voltage and the DC bus voltage of the reference DC-DC converter meets the closing condition, the high-voltage side voltage of other DC-DC converters may be too high, the voltage on the relay battery side may be too high, and the voltage difference across the relay may be too large. In this case, the voltage difference across the relay with a large voltage difference does not actually meet the closing condition, and the relay cannot actually close. However, the open-loop soft start has ended, and the high-voltage side voltage of each DC-DC converter no longer increases, causing the relay to remain unable to close, and the lithium battery system cannot switch to charging mode.

[0034] This invention avoids the judgment deviation caused by the difference in internal resistance of a single DC converter by comprehensively judging the average voltage of multiple DC converters, thereby solving the problem that the existing open-loop soft start control method cannot close the relay and cannot switch to the charging mode in parallel mode.

[0035] Reference Figure 1 The structural basis of the embodiments of the present invention will be explained below.

[0036] In one possible implementation, the lithium battery system includes a battery module 1 and at least two DC-DC converters 2; the low-voltage side of each DC-DC converter 2 is connected to the battery module 1, and the high-voltage side is connected to the DC bus 4 via a relay 3.

[0037] For example, the number of battery modules can be one or more. For example, one battery module may correspond to multiple DC-DC converters. For instance, each battery module may correspond to two DC-DC converters.

[0038] For example, each DC-DC converter includes a low-voltage side and a high-voltage side. The side of the DC-DC converter connected to the battery module is the low-voltage side, and the side connected to the DC bus is the high-voltage side. Further, the low-voltage side includes a positive input terminal and a negative input terminal; the high-voltage side includes a positive output terminal and a negative output terminal. It should be noted that during charging, the voltage of the battery module is typically low (e.g., 57.6V), while the voltage of the DC bus is typically high (e.g., 250V).

[0039] For example, the high-voltage sides of each DC-DC converter are connected in parallel. Furthermore, each DC-DC converter is equipped with one or more relays. The high-voltage side port of each DC-DC converter is connected to the DC bus in parallel through the relays of that DC-DC converter. For instance, the positive output terminal of a DC-DC converter is connected to the positive DC bus through a positive relay; the negative output terminal of a DC-DC converter is connected to the negative DC bus through a negative relay.

[0040] For example, the DC-DC converters have the same structure.

[0041] The above describes the structural basis of the method in the embodiments of the present invention. The following describes the implementation steps of the method in the embodiments of the present invention. It should be noted that the executing entity in the embodiments of the present invention can be a controller built into the lithium battery system, such as a BMU (Battery Management Unit), BMS (Battery Management System), etc. The controller can acquire voltage and output control commands to the DC-DC converter.

[0042] Figure 2 This is a flowchart illustrating the implementation of the lithium battery system charging control method provided in this embodiment of the invention. (Refer to...) Figure 2 The methods include: Step 201: After the lithium battery system is powered on, the high-voltage side voltage of each DC converter is acquired in real time.

[0043] For example, after the lithium battery system is powered on, and when charging is required, the high-voltage side voltage of each DC-DC converter is acquired in real time, and the high-voltage side voltage of each DC-DC converter is gradually increased. It should be noted that the lithium battery system may need to be charged or discharged after power-on. Whether charging or discharging, the high-voltage side voltage of the DC-DC converter needs to increase. In the scenario where charging is required, the DC bus is in a high-voltage state, and the high-voltage side voltage of the DC-DC converter responds by increasing to the voltage level of the DC bus.

[0044] The reason for the shutdown of the lithium battery system before startup is not limited. For example, the lithium battery system may shut down after the battery module has been over-discharged. Furthermore, the reason for the lithium battery system needing to be charged after startup is also not limited. For ease of understanding, it can be considered that the lithium battery system shuts down after the battery module has been over-discharged, and correspondingly, the battery module needs to be charged after the lithium battery system is subsequently powered on. It should be noted that after the lithium battery system shuts down but before startup, the high-voltage side voltage of the DC-DC converter is 0, and the relay is in the open state.

[0045] After the lithium battery system is powered on, the DC bus voltage is higher than the battery module voltage. When the lithium battery system is powered on, the DC bus is energized, and the DC bus voltage is a high voltage, such as 250V.

[0046] The triggering conditions for powering on the lithium battery system are not limited. For example, it could be automatic power-on after power is restored. For instance, after mains power is restored, the DC bus voltage rises, and the lithium battery system determines the power status based on the DC bus voltage and automatically executes the power-on process. Another example is that the trigger signal for powering on the lithium battery system can also come from a host computer command. It should be noted that the application scenario of this embodiment is precisely the power-on startup process of a lithium battery system.

[0047] It should also be noted that the lithium battery system in this embodiment of the invention can switch between series and parallel connections, and the boost modulation strategy and boost target of each DC-DC converter are different under different connection methods. Therefore, it is necessary to first determine the connection method after power-on.

[0048] In one possible implementation, after the lithium battery system is powered on, the real-time acquisition of the high-voltage side voltage of each DC-DC converter includes: acquiring the high-voltage side connection method of each DC-DC converter after the lithium battery system is powered on; if the high-voltage side connection method is parallel connection, acquiring the high-voltage side voltage of each DC-DC converter in real time, and simultaneously controlling each DC-DC converter to gradually increase the high-voltage side voltage according to the strategy corresponding to the parallel connection method.

[0049] The above describes the state of each part of the lithium battery system before and after power-on. The following explains how to control the DC-DC converter to increase the high-voltage side voltage.

[0050] Step 202: Control each DC-DC converter to gradually increase the high-voltage side voltage; wherein, the average high-voltage side voltage of each DC-DC converter in the previous cycle is used as the reference. For DC-DC converters with voltages higher than the reference, the voltage increase will be reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the voltage increase will be increased in the next cycle.

[0051] It should be noted that step 202 involves gradually adjusting the modulation parameters and gradually increasing the high-voltage side voltage of the DC-DC converter. For example, step 201, which involves acquiring the voltage, can be performed synchronously with step 202, which involves increasing the voltage; alternatively, steps 201 and 202 can be executed cyclically.

[0052] In some embodiments, the drive signal for the DC-DC converter is a PWM (Pulse Width Modulation) drive signal. Accordingly, by gradually increasing the duty cycle of the PWM drive signal, the high-voltage side voltage of each DC-DC converter is gradually increased.

[0053] In some embodiments, the DC-DC converter is an LLC resonant converter. Accordingly, by gradually changing the resonant frequency, the high-voltage side voltage of each DC-DC converter is gradually increased.

[0054] The above explains two types of drive signals used as modulation parameters. The control method is described below.

[0055] In one possible implementation, controlling the gradual increase of the high-voltage side voltage of each DC-DC converter includes: using the average high-voltage side voltage of each DC-DC converter as a reference, cyclically controlling the gradual increase of the high-voltage side voltage of each DC-DC converter in a periodic manner. Specifically, the average high-voltage side voltage of each DC-DC converter in the previous cycle is used as the reference; for DC-DC converters with voltages higher than the reference, the voltage increase is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the voltage increase is increased in the next cycle.

[0056] In some embodiments, the cyclic control method can be a simple open-loop control method or a combination of open-loop and closed-loop control methods.

[0057] The following explains the control method based solely on open loop.

[0058] In some embodiments, modulation parameters are adjusted by a preset step size to control the gradual increase of the high-voltage side voltage of each DC-DC converter. The average high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference. For DC-DC converters with voltages higher than the reference, the adjustment step size of the modulation parameters is decreased and the voltage boost amplitude is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the adjustment step size of the modulation parameters is increased and the voltage boost amplitude is increased in the next cycle. Simultaneously, in each cycle, it is determined whether the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC-DC converter fall within a preset range.

[0059] The following describes a control method based on a combination of open-loop and closed-loop control.

[0060] In some embodiments, the average high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference. For DC-DC converters with voltages higher than the reference, the adjustment step size of the given value is decreased and the boost voltage is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the adjustment step size of the given value is increased and the boost voltage is increased in the next cycle. At the same time, in each cycle, it is determined whether the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC-DC converter fall within a preset range.

[0061] For example, for any DC-DC converter, in each cycle, the average high-side voltage of all DC-DC converters is used as the feedback value. Based on a given value, the high-side voltage of that DC-DC converter is controlled in a closed loop. During closed-loop control, the drive signal (e.g., the duty cycle and resonant frequency mentioned above) and the output voltage are adjusted according to the difference between the given value and the feedback value. When the given value increases, the high-side voltage of the DC-DC converter changes accordingly under closed-loop control and eventually stabilizes. Further exemplarily, the given value of the current cycle increases relative to the previous cycle. After the feedback value stabilizes at the given value of the current cycle, the cycle switches to the next cycle and the given value continues to increase. Thus, only the given value needs to be changed gradually, and the specific cycle period does not need to be predetermined.

[0062] In each cycle of controlling each DC converter to gradually increase the high-voltage side voltage, the average value of the high-voltage side voltage of each DC converter is used as a reference to continuously adjust the voltage boosting amplitude of each DC converter in the reverse direction, thereby continuously reducing the voltage difference between each DC converter.

[0063] In some embodiments, the average high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference. DC-DC converters with voltages higher than the reference will reduce the boost voltage in the next cycle by a preset ratio or a preset magnitude; DC-DC converters with voltages lower than the reference will increase the boost voltage in the next cycle by a preset ratio or a preset magnitude.

[0064] In some embodiments, before step 203, a judgment step is included, namely, judging whether the average value, maximum value and minimum value of the high-voltage side voltage of each DC converter fall within a preset range.

[0065] As the high-voltage side voltage of each DC-DC converter gradually increases, the aforementioned average, maximum, and minimum values ​​also gradually increase. Generally, when the average, maximum, and minimum values ​​are higher than the lower limit of the preset range, they fall within the preset range.

[0066] It should be noted that steps 201, 202, and the judgment step can also be executed cyclically. The loop will exit and step 203 will begin once the judgment condition is met.

[0067] Step 203: After the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC-DC converter fall within a preset range, control each DC-DC converter to stop increasing the high-voltage side voltage, close the relay, and charge the battery module. The preset range is determined based on the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed.

[0068] The preset range is determined by two parameters: the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed. The DC bus voltage is the reference value, and the maximum allowable voltage difference between the two sides when the relay is closed is the fluctuation range.

[0069] The specific interval of the preset range can be represented as:

[0070] in, The permissible safe differential voltage threshold for relay closure. When the average voltage of the high-voltage side of each DC-DC converter is within this range, it can be determined that the actual voltage difference across the relay meets the safe closure requirements.

[0071] It should be noted that when the DC-DC converters are controlled to stop increasing the high-voltage side voltage, the modulation parameters of each DC-DC converter will temporarily stop changing, and the high-voltage side voltage of each DC-DC converter will also temporarily stop changing.

[0072] Prior to step 203, each DC-DC converter is in boost mode, with modulation parameters continuously adjusted to increase the voltage. Once the average, maximum, and minimum values ​​are met, continuing to boost the voltage will cause the DC-DC converter side voltage to become too high, resulting in an excessive voltage difference between the DC-DC converter side and the DC bus side when the relay is closed, triggering a surge current that impacts the power devices. Therefore, stopping the boost operation is to lock the current voltage level, ensuring that the voltage difference between the DC-DC converter side and the DC bus side is within a safe range before the relay closes.

[0073] After the relay closes, the high-voltage side of each DC-DC converter is officially connected to the DC bus, and the lithium battery system switches from the open-loop start-up phase to the charging operation phase. At this time, the electrical energy of the DC bus is transferred to the battery module through the DC-DC converter to carry out the battery charging process. The safety of relay closure is guaranteed by the premise that the average, maximum, and minimum values ​​fall within the preset range, avoiding the problem in the prior art where the relay cannot close and the system cannot charge due to voltage imbalance in a single branch.

[0074] In some embodiments, a closing relay refers to a relay that simultaneously closes each DC-DC converter.

[0075] Multiple DC-DC converters are connected in parallel in lithium battery systems to increase the total charging power and meet the charging needs of large-capacity battery modules. Because the hardware specifications of a single DC-DC converter have limitations, its rated output power is limited and cannot meet the needs of high-power charging scenarios on its own.

[0076] If a simultaneous closing strategy is not adopted, but rather the relays of each branch are closed sequentially, the DC-DC converter that closes first will bear the entire charging load current alone. At the moment of closing, the charging current between the DC bus and the battery module will all flow through the first closed branch, causing the current in that branch to momentarily exceed its rated current limit, resulting in an overload. This overload will cause power devices such as switching transistors and inductors to overheat due to overcurrent, triggering protection shutdowns or burning out the devices, preventing normal charging.

[0077] The purpose of simultaneously closing the relays of each DC-DC converter is to achieve load balancing after multiple DC-DC converters are connected in parallel. By closing all the relays at the same time, the charging current will be distributed among the DC-DC converters, avoiding single-circuit overload, achieving load balancing, ensuring that multiple DC-DC converters work together, and fully utilizing the capacity expansion function of parallel connection.

[0078] This invention, in its embodiment, controls the parallel DC-DC converters to gradually increase their voltage periodically during the startup process of a lithium battery system. Simultaneously, the high-voltage side voltages of all DC-DC converters are collected and their average value is calculated. Using this average value as a benchmark, the subsequent voltage increase of each DC-DC converter is adjusted in reverse. During the voltage increase process, the voltage differences between the DC-DC converters are continuously reduced until the average, maximum, and minimum values ​​all fall within a preset range, at which point the relays of all DC-DC converters are closed. The preset range corresponds to the voltage difference requirement for safe relay closure, determined by the DC bus voltage and the maximum allowable voltage difference between the two sides of the relay. Using the average voltage of each DC-DC converter as a benchmark for the voltage increase process reduces the voltage differences between branches, avoiding misjudgments of partial compliance but overall non-compliance caused by single-branch references. When the average, maximum, and minimum values ​​all fall within the preset range, it indicates that the actual voltage difference between the two sides of the relays in each branch meets the safe closure condition. At this point, the relays are safely closed, allowing the lithium battery system to enter the charging state.

[0079] The following explains how to obtain the average value of the high-voltage side voltage of each DC converter.

[0080] In one possible implementation, after acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: performing an arithmetic average of the high-voltage side voltage of each DC-DC converter to obtain the average value of the high-voltage side voltage of each DC-DC converter.

[0081] It should be noted that when the hardware differences between the DC-DC converters (e.g., output internal resistance, manufacturing errors) are small, the overall voltage after the DC-DC converters are connected in parallel can be approximated as an arithmetic mean. Small differences between the DC-DC converters mean their output internal resistances are similar, and under the same modulation parameters, the boost rate and final voltage value deviation of each branch are extremely small. When the arithmetic mean of the high-voltage side voltages of each DC-DC converter is within a preset range, it can be ensured that the overall voltage after the DC-DC converters are connected in parallel is also highly likely to be within the preset range. The arithmetic averaging method is simple and has high execution efficiency.

[0082] In one possible implementation, after acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: performing a weighted average of the high-voltage side voltage of each DC-DC converter to obtain the average value of the high-voltage side voltage of each DC-DC converter.

[0083] Arithmetic averaging ignores the dominant effect of internal resistance on the total voltage. If the internal resistance of each branch differs greatly, the average value will deviate significantly from the actual total voltage after parallel connection. When the hardware of each DC-DC converter differs greatly, a weighted average can be used to calculate the average voltage on the high-voltage side, which can more accurately reflect the actual overall voltage level after multiple parallel connections.

[0084] For example, the weighted average makes the weight inversely proportional to the internal resistance of the branch, that is, the smaller the internal resistance of the branch, the higher the weight ratio.

[0085] For example, weights can be set based on measured internal resistances. For instance, after determining the output internal resistance of each branch experimentally, weights can be set. In this case, the weighted average is equivalent to the total parallel voltage, allowing for a more accurate calculation of the actual overall voltage. However, in the actual use of lithium battery systems, experimental testing conditions are often unavailable, making it difficult to accurately measure the internal resistance of each DC-DC converter. The following embodiment provides a simple method for determining weights.

[0086] In one possible implementation, before weighted averaging of the high-voltage side voltages of each DC-DC converter to obtain the average value of the high-voltage side voltages of each DC-DC converter, the method further includes: controlling each DC-DC converter to increase its high-voltage side voltage with the same modulation parameters during a target period; determining the weight of each DC-DC converter based on its high-voltage side voltage; wherein the weight is positively correlated with the high-voltage side voltage. Accordingly, the high-voltage side voltage of each DC-DC converter is weighted and averaged to obtain the average value of the high-voltage side voltage of each DC-DC converter. This includes: after the target period, the high-voltage side voltage of each DC-DC converter is weighted and averaged to obtain the average value of the high-voltage side voltage of each DC-DC converter.

[0087] It should be noted that, under the same modulation parameters, the boost process of each DC-DC converter is determined solely by its own hardware characteristics, with the core factor being the output internal resistance. For example, the smaller the internal resistance, the faster the boost speed and the higher the final voltage; conversely, the larger the internal resistance, the slower the boost speed and the lower the final voltage. This embodiment of the invention uses a weighted average with weights positively correlated with voltage. This indirectly matches the magnitude of the internal resistance of each branch to the boosted voltage value, allowing the weighted average to represent the actual total voltage after parallel connection.

[0088] It should be further clarified that when multiple DC-DC converters are connected in parallel on their high-voltage sides, the total output voltage is not a simple numerical average, but rather a weighted result of internal resistance, determined by the voltage and internal resistance of each branch. Taking two branches in parallel as an example, let the voltage of branch 1 be... Internal resistance Branch 2 voltage Internal resistance The formula for the total voltage after parallel connection is:

[0089] The final value of the parallel total voltage is determined by the branch voltage with the smaller internal resistance, which has a stronger dominant effect on the total voltage. The influence of internal resistance on the total voltage can be expressed as a weight.

[0090] Therefore, the high-voltage side voltage of each DC-DC converter is inversely proportional to its internal resistance, and the internal resistance is inversely proportional to its weight. Thus, the weight is positively correlated with the high-voltage side voltage. That is, the higher the voltage of the DC-DC converter, the greater its assigned weight; the lower the voltage of the DC-DC converter, the smaller its assigned weight.

[0091] It should be noted that the target period can be any period, but the first period is usually chosen as the target period. In the initial stage of startup, the weights are determined first, and these weights can be directly used in subsequent periods.

[0092] This invention bypasses the complex operation of measuring internal resistance by using the same modulation parameters to boost voltage, assigning weights based on voltage values, and calculating the overall voltage using a weighted average. It directly uses the boosted voltage value to indirectly match the internal resistance weights, simplifying the control algorithm and ensuring the accuracy of voltage determination. Ultimately, the weighted average value accurately represents the total parallel voltage, ensuring that the voltage difference when the relay closes meets safety requirements. In this embodiment, the weights are assigned based on the boosted voltage. Since a smaller internal resistance results in a faster boosting speed for a branch, the magnitude and speed of the boosted voltage indirectly reflect the internal resistance. Therefore, assigning higher weights to branches with faster boosting speeds essentially involves indirectly matching the internal resistance weights through voltage characteristics. This also allows the weighted average value to closely approximate the actual total parallel voltage, avoiding misjudgments due to arithmetic mean deviations and ensuring successful relay closure.

[0093] In one possible implementation, before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter have all fallen within a preset range, the method further includes: if there is a first DC converter whose high-voltage side voltage has risen to the upper limit of the preset range, then controlling the first DC converter to stop increasing its high-voltage side voltage, and controlling the other DC converters other than the first DC converter to continue to gradually increase their high-voltage side voltage until the average and minimum values ​​have all fallen within the preset range.

[0094] In this embodiment of the invention, after the maximum voltage on the high-voltage side rises to the upper limit of a preset range, the DC converter is controlled to stop increasing the voltage, ensuring that the maximum value falls within the preset range.

[0095] In practical applications, the voltage deviation of each DC-DC converter is usually within a small range (e.g., the voltage difference between branches ≤ 5V), while the allowable voltage difference range on both sides when the relay is closed (e.g., ±10V) is sufficient to cover this deviation.

[0096] When a DC-DC converter has significant manufacturing deviations or exhibits significant performance aging after prolonged use, the voltage deviation between branches will further increase, even exceeding the voltage difference range allowed by the relays (e.g., voltage difference between branches > 10V). In this case, even if the average, maximum, and minimum values ​​of the high-voltage side voltages of each DC-DC converter fall within the preset range, the large voltage difference between branches and severe imbalance will generate a large internal circulating current after the high-voltage sides of the DC-DC converters are connected in parallel.

[0097] In a further embodiment of the present invention, to optimize the voltage balance during the parallel boosting process of multiple DC-DC converters and reduce the risk of circulating current in the branches after the relays are closed, a voltage balance adjustment step is added before performing the operation of "controlling each DC-DC converter to stop increasing the high-voltage side voltage, closing the relays, and charging the battery module". The details are as follows.

[0098] In one possible implementation, before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter have all fallen into a preset range, the method further includes: if there is a first DC converter whose high-voltage side voltage has risen into the upper half of the preset range, then the first DC converter is controlled to stop increasing its high-voltage side voltage, and the other DC converters besides the first DC converter are controlled to continue gradually increasing their high-voltage side voltage until the average and minimum values ​​have all fallen into the preset range.

[0099] The triggering conditions for the voltage balancing adjustment step include: the existence of at least one DC-DC converter whose high-voltage side voltage rises into the upper half of the preset range, hereinafter referred to as the first DC-DC converter. This indicates a voltage imbalance condition where the overall average value fails to meet the standard, but the voltage of a single branch exceeds the limit. It should be noted that the high-voltage side voltage continuously rises from 0, which essentially means that the maximum value of the high-voltage side voltage of each DC-DC converter first rises into the upper half of the preset range; that is, the DC-DC converter with the fastest voltage rise is the first DC-DC converter.

[0100] This implementation employs a differentiated control strategy. It controls the first DC-DC converter to stop increasing its high-voltage side voltage, preventing further voltage increases and widening the voltage difference between this branch and other branches. Meanwhile, it controls the other DC-DC converters (excluding the first one) to gradually increase their high-voltage side voltage, continuously raising the overall average voltage until both the average and minimum values ​​reach preset range requirements. In short, this strategy avoids single-path overshooting and reduces the voltage difference between branches through differentiated adjustments.

[0101] This invention, through the aforementioned differentiated control, increases the overall average voltage while limiting the voltage increase of high-voltage branches, effectively reducing the voltage difference between DC-DC converters and avoiding extreme imbalances such as excessively high voltage in one branch and excessively low voltage in multiple branches. Branch voltage difference is the core cause of internal circulating current after relay closure. Reducing the voltage difference directly reduces the amplitude of the circulating current, preventing it from impacting power devices and ensuring the safety and stability of the lithium battery system's charging process. Once the average value falls within a preset range, all DC-DC converters are uniformly controlled to stop boosting voltage, and all relays are simultaneously closed, completing the switching of charging modes.

[0102] In one possible implementation, before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter all fall within a preset range, the method further includes: after the average value of the high-voltage side voltage of each DC converter falls within the preset range, if there is a second DC converter whose high-voltage side voltage is less than the lower limit of the preset range, controlling the other DC converters except the second DC converter to stop increasing their high-voltage side voltage, and controlling the second DC converter to continue gradually increasing its high-voltage side voltage until the high-voltage side voltage of the second DC converter is not less than the lower limit of the preset range.

[0103] In some embodiments, after the maximum and average values ​​of the high-voltage side voltages of each DC converter fall within a preset range, if there is a second DC converter whose high-voltage side voltage is less than the lower limit of the preset range, the other DC converters except the second DC converter are controlled to stop increasing their high-voltage side voltages, and the second DC converter is controlled to continue to gradually increase its high-voltage side voltage until the high-voltage side voltage of the second DC converter is not less than the lower limit of the preset range.

[0104] The application scenario of this invention is a situation where the average value meets the standard but the branch voltage is unbalanced. This situation requires the following conditions to be met: 1. The average value of the high-voltage side voltage of each DC converter has fallen within the preset range; 2. There is at least one second DC converter whose high-voltage side voltage is lower than the lower limit of the preset range, that is, a certain voltage is too low.

[0105] This invention employs differentiated control with high-limit and low-compensation, stopping voltage boosting in all branches except the second DC-DC converter, and driving only the second DC-DC converter to continue boosting to a level not lower than a preset lower limit. If other branches continue boosting, the voltage difference with the second DC-DC converter will further widen, leading to an increase in the circulating current amplitude after parallel connection. Stopping other branches from boosting voltage locks in the current high-voltage side voltage upper limit, preventing the voltage difference from continuing to expand. The second DC-DC converter's voltage being below the preset lower limit is one of the reasons for the excessive branch voltage difference. Driving it to boost voltage individually can quickly increase the voltage of the low-voltage branch without raising the overall voltage upper limit, reducing the voltage difference with other branches; simultaneously, since only a single branch is boosted slightly, the overall average voltage will not exceed the preset range, still meeting the basic conditions for relay closure.

[0106] In one possible implementation, controlling the gradual increase of the high-voltage side voltage of each DC-DC converter includes: if the high-voltage side voltage of any DC-DC converter in the previous cycle is greater than the average value, then the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is reduced to reduce the increase of the high-voltage side voltage; if the high-voltage side voltage of any DC-DC converter in the previous cycle is less than the average value, then the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is increased to increase the increase of the high-voltage side voltage.

[0107] After the lithium battery system is powered on, each DC-DC converter enters the boost phase. The high-voltage side voltage of each circuit is periodically collected, and the average voltage of all branches in the current cycle is calculated as the benchmark for adjustment in this cycle. For each DC-DC converter, its current cycle voltage is compared with the average value, and differentiated adjustments are performed. If the branch voltage is greater than the average value, it indicates that the voltage rise rate of this branch is too fast. In the next cycle, the adjustment range of the modulation parameters will be reduced to slow down the voltage rise rate. If the branch voltage is less than the average value, it indicates that the voltage rise rate of this branch is too slow. In the next cycle, the adjustment range of the modulation parameters will be increased to speed up the voltage rise rate.

[0108] Repeated sampling, calculation of average value, and adjustment of adjustment range are iterated periodically until the voltage of each branch converges to near the average value, and the average value falls within the preset range and the voltage difference between branches meets the requirements.

[0109] Modulation parameters are the switching timing parameters that determine the voltage output of a DC-DC converter. The relationship between these parameters and voltage differs across topologies, and adjustments to the modulation range must be made to match the topology characteristics. For example, in PWM drive, the modulation parameter is the duty cycle, which is positively correlated with voltage. When the branch voltage is greater than the average value, the adjustment step size of the duty cycle decreases; when the branch voltage is less than the average value, the adjustment step size increases. As another example, in an LLC resonant converter, the modulation parameter is the switching frequency, which is negatively correlated with voltage. The lower the frequency, the higher the voltage. When the branch voltage is greater than the average value, the adjustment step size of the switching frequency decreases; when the branch voltage is less than the average value, the adjustment step size increases.

[0110] It should be noted that traditional open-loop control typically relies on prior experimental experience to determine the adjustment range of the modulation parameters in an open-loop soft-start mode, and the adjustment strategy is usually fixed. For example, the adjustment range of the modulation parameters in an open-loop soft-start mode is determined based on experimental data. Furthermore, it should be noted that in a combination of open-loop and closed-loop control, adjusting the increase in the setpoint is essentially adjusting the adjustment range of the modulation parameters.

[0111] This invention employs dynamic modulation parameter adjustment based on real-time voltage deviation to actively reduce the voltage difference between DC-DC converters during open-loop boosting, ultimately ensuring all branches synchronously fall within the target voltage range, guaranteeing simultaneous relay closure and load balancing. This dynamic adjustment based on real-time voltage feedback automatically adapts to actual operating conditions such as manufacturing deviations, hardware aging, and temperature fluctuations, eliminating the need for pre-obtaining high-precision experimental values. With all branches synchronously falling within the target voltage range, relays can close simultaneously, avoiding the time loss of waiting for lagging branches to boost voltage and improving the start-up charging efficiency of the lithium battery system.

[0112] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0113] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0114] Figure 3 A schematic diagram of the structure of a lithium battery system charging control device provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 3 As shown, the lithium battery system includes a battery module and at least two DC-DC converters; the low-voltage side of each DC-DC converter is connected to the battery module, and the high-voltage side is connected to the DC bus via a relay; the lithium battery system charging control device 3 includes: The startup module 31 is used to acquire the high-voltage side voltage of each DC-DC converter in real time after the lithium battery system is powered on. The acquisition module 32 is used to control each DC-DC converter to gradually increase the high-voltage side voltage; wherein, the average high-voltage side voltage of each DC-DC converter in the previous cycle is used as a reference, and DC-DC converters with voltages higher than the reference will have their voltage increase reduced in the next cycle; DC-DC converters with voltages lower than the reference will have their voltage increase increased in the next cycle. The charging module 33 is used to control each DC converter to stop increasing the high-voltage side voltage and close the relay to charge the battery module after the average, maximum and minimum values ​​of the high-voltage side voltage of each DC converter fall within a preset range. The preset range is determined based on the DC bus voltage and the voltage difference between the two sides allowed when the relay is closed.

[0115] This invention, in its embodiment, controls the parallel DC-DC converters to gradually increase their voltage periodically during the startup process of a lithium battery system. Simultaneously, the high-voltage side voltages of all DC-DC converters are collected and their average value is calculated. Using this average value as a benchmark, the subsequent voltage increase of each DC-DC converter is adjusted in reverse. During the voltage increase process, the voltage differences between the DC-DC converters are continuously reduced until the average, maximum, and minimum values ​​all fall within a preset range, at which point the relays of all DC-DC converters are closed. The preset range corresponds to the voltage difference requirement for safe relay closure, determined by the DC bus voltage and the maximum allowable voltage difference between the two sides of the relay. Using the average voltage of each DC-DC converter as a benchmark for the voltage increase process reduces the voltage differences between branches, avoiding misjudgments of partial compliance but overall non-compliance caused by single-branch references. When the average, maximum, and minimum values ​​all fall within the preset range, it indicates that the actual voltage difference between the two sides of the relays in each branch meets the safe closure condition. At this point, the relays are safely closed, allowing the lithium battery system to enter the charging state.

[0116] Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 4 As shown, the controller 4 in this embodiment includes a processor 40 and a memory 41. The memory 41 stores a computer program 42. When the processor 40 executes the computer program 42, it implements the steps in the various method embodiments described above. Alternatively, when the processor 40 executes the computer program 42, it implements the functions of each module / unit in the various device embodiments described above.

[0117] For example, computer program 42 may be divided into one or more modules / units, which are stored in memory 41 and executed by processor 40 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 42 in controller 4.

[0118] The controller 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will understand that... Figure 4 This is merely an example of controller 4 and does not constitute a limitation on controller 4. It may include more or fewer components than shown, or combine certain components, or different components. For example, controller 4 may also include input / output devices, network access devices, buses, etc.

[0119] The processor 40 can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0120] The memory 41 can be an internal storage unit of the controller 4, such as the hard disk or RAM of the controller 4. The memory 41 can also be an external storage device of the controller 4, such as a plug-in hard disk, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 4. Furthermore, the memory 41 can include both internal storage units and external storage devices of the controller 4. The memory 41 is used to store the computer program 42 and other programs and data required by the controller 4. The memory 41 can also be used to temporarily store data that has been output or will be output.

[0121] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0122] This invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the methods described in the above-described method embodiments.

[0123] This invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the methods described in the above-described method embodiments.

[0124] Computer programs include computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. Computer-readable media can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0125] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A charging control method for a lithium battery system, characterized in that, The lithium battery system includes a battery module and at least two DC-DC converters; the low-voltage side of each DC-DC converter is connected to the battery module, and the high-voltage side is connected to a DC bus via a relay; the method includes: After the lithium battery system is powered on, the high-voltage side voltage of each DC-DC converter is acquired in real time. The voltage of each DC-DC converter is gradually increased. The average voltage of the high-voltage side of each DC-DC converter in the previous cycle is used as the reference. For DC-DC converters with voltages higher than the reference, the voltage increase is reduced in the next cycle. For DC-DC converters with voltages lower than the reference, the voltage increase is increased in the next cycle. After the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter fall within the preset range, the DC converter is controlled to stop increasing the high-voltage side voltage, the relay is closed, and the battery module is charged. The preset range is determined based on the DC bus voltage and the allowable voltage difference between the two sides when the relay is closed.

2. The lithium battery system charging control method according to claim 1, characterized in that, After acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: The high-voltage side voltages of each DC-DC converter are weighted and averaged to obtain the average value of the high-voltage side voltages of each DC-DC converter.

3. The lithium battery system charging control method according to claim 2, characterized in that, Before performing a weighted average of the high-voltage side voltages of each DC-DC converter to obtain the average value of the high-voltage side voltages of each DC-DC converter, the method further includes: During the target period, each DC-DC converter is controlled to increase the high-voltage side voltage using the same modulation parameters; The weight of each DC-DC converter is determined based on the high-voltage side voltage of each converter; wherein the weight is positively correlated with the high-voltage side voltage. Accordingly, the high-voltage side voltages of each DC-DC converter are weighted and averaged to obtain the average value of the high-voltage side voltages of each DC-DC converter, including: After the target period, the high-voltage side voltage of each DC-DC converter is weighted and averaged based on the weight of each DC-DC converter to obtain the average value of the high-voltage side voltage of each DC-DC converter.

4. The lithium battery system charging control method according to claim 1, characterized in that, Before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter all fall within a preset range, the procedure further includes: If a first DC-DC converter has a high-voltage side voltage that rises to the upper limit of a preset range, then the first DC-DC converter is controlled to stop increasing the high-voltage side voltage, and other DC-DC converters other than the first DC-DC converter are controlled to continue to gradually increase the high-voltage side voltage until the average value and the minimum value both fall within the preset range.

5. The lithium battery system charging control method according to claim 4, characterized in that, Before controlling each DC converter to stop increasing its high-voltage side voltage, closing the relay, and charging the battery module after the average, maximum, and minimum values ​​of the high-voltage side voltage of each DC converter all fall within a preset range, the procedure further includes: After the average value of the high-voltage side voltage of each DC converter falls into the preset range, if there is a second DC converter whose high-voltage side voltage is less than the lower limit of the preset range, control the other DC converters except the second DC converter to stop increasing the high-voltage side voltage, and control the second DC converter to continue to gradually increase the high-voltage side voltage until the high-voltage side voltage of the second DC converter is not less than the lower limit of the preset range.

6. The lithium battery system charging control method according to claim 1, characterized in that, The method of controlling each DC converter to gradually increase the high-voltage side voltage includes: If the high-voltage side voltage of any DC-DC converter in the previous cycle is greater than the average value, then the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is reduced to reduce the rise in high-voltage side voltage. If the high-voltage side voltage of any DC-DC converter in the previous cycle is less than the average value, the adjustment range of the modulation parameters of the DC-DC converter in the next cycle is increased to increase the rise in high-voltage side voltage.

7. The lithium battery system charging control method according to claim 1, characterized in that, After acquiring the high-voltage side voltage of each DC-DC converter in real time, the method further includes: The arithmetic mean of the high-voltage side voltages of each DC-DC converter is calculated to obtain the average value of the high-voltage side voltages of each DC-DC converter.

8. A lithium battery system charging control device, characterized in that, The lithium battery system includes a battery module and at least two DC-DC converters; the low-voltage side of each DC-DC converter is connected to the battery module, and the high-voltage side is connected to a DC bus via a relay; the device includes: The acquisition module is used to acquire the high-voltage side voltage of each DC-DC converter in real time after the lithium battery system is powered on. The boost module is used to control the DC-DC converter to gradually increase the high-voltage side voltage. The average high-voltage side voltage of the DC-DC converter in the previous cycle is used as the reference. For DC-DC converters with voltages higher than the reference, the boost amplitude is reduced in the next cycle; for DC-DC converters with voltages lower than the reference, the boost amplitude is increased in the next cycle. The charging module is used to control each DC converter to stop increasing the high-voltage side voltage and close the relay to charge the battery module after the average, maximum and minimum values ​​of the high-voltage side voltage of each DC converter fall within a preset range. The preset range is determined based on the DC bus voltage and the voltage difference between the two sides allowed when the relay is closed.

9. A controller, characterized in that, The system includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the lithium battery system charging control method as described in any one of claims 1 to 7.

10. A lithium battery system, characterized in that, Includes the controller as described in claim 9.

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