Battery system, control method, medium, and vehicle

Abstract

The application provides a battery system, a control method, a medium and a vehicle. The battery system comprises a controller, a first battery and a second battery connected in series, a first capacitor, a main switch and a first conversion branch. A first end of the first capacitor is connected to a positive electrode of the first battery through the main switch, and a second end of the first capacitor is connected to a negative electrode of the second battery. The first conversion branch comprises a branch inductor and two switch tubes. The two switch tubes are connected in series and are connected in parallel with the first capacitor. The branch inductor is connected between a series connection point of the first battery and the second battery and a series connection point of the two switch tubes. When the battery system starts pre-charging and the main switch is in an off state, the controller is used for controlling a duty cycle of the two switch tubes in the first conversion branch until a voltage of the first capacitor reaches a target voltage. The duty cycle of the switch tubes in the first conversion branch increases with an increase in the number of on-off times of the switch tubes. The application can realize pre-charging and has low cost.

Description

[0001] This application claims priority to Chinese Patent Application No. 202411218644.8, filed on August 30, 2024, entitled "Battery System, Control Method, Medium and Vehicle", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a battery system, control method, medium, and vehicle. Background Technology

[0003] A battery system is a system that uses electrochemical cells as an energy storage carrier to store electrical energy for a certain period of time and supply electrical energy for a certain period of time. It can be widely used in various scenarios. Currently, battery systems are used as the power source in electric vehicles.

[0004] A battery system typically includes components such as batteries, inductors, and capacitors. When a battery system starts up, it generally requires pre-charging to ensure stable and safe operation and prevent damage to components like capacitors from sudden high-current surges. Currently, many battery systems achieve pre-charging through a dedicated pre-charge conversion branch. This branch includes a large resistor to prevent instantaneous high current from breaking down other components within the conversion branch; however, this approach leads to higher battery system costs. Summary of the Invention

[0005] This application provides a battery system, control method, medium, and vehicle that can achieve pre-charging at a low cost.

[0006] In a first aspect, embodiments of this application provide a battery system, which includes a controller, a first battery and a second battery connected in series, a first capacitor, a main switch, and a first conversion branch; a first terminal of the first capacitor is connected to the positive terminal of the first battery through the main switch, and a second terminal of the first capacitor is connected to the negative terminal of the second battery; the first conversion branch includes a branch inductor and two switching transistors; the two switching transistors are connected in series and then in parallel with the first capacitor, and the branch inductor is connected between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors;

[0007] When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the two switching transistors in the first conversion branch until the voltage of the first capacitor reaches the target voltage. The duty cycle of the switching transistors in the first conversion branch increases with the increase of the number of times the switching transistors are turned on.

[0008] In one feasible implementation, the switching transistors in the first conversion branch include a first switching transistor and a second switching transistor.

[0009] When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the first switch and the second switch until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switch changes, the rate of change of the current in the first conversion branch is within a preset charging rate range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

[0010] In one feasible implementation, the battery system further includes a second conversion branch; the second conversion branch includes a branch inductor and two switching transistors; the two switching transistors in the second conversion branch are connected in series and then in parallel with the first capacitor; the branch inductor in the second conversion branch is connected in series between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors.

[0011] When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the two switching transistors in the first conversion branch and the duty cycle of the two switching transistors in the second conversion branch until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first and second conversion branches when the duty cycle of the switching transistors in the first and second conversion branches changes is within a preset charging speed range.

[0012] In one feasible implementation, the controller is specifically used for:

[0013] Based on the correspondence between the actual charging power of the first capacitor and the target voltage, a first control signal and a second control signal are obtained. The duty cycle of the two switching transistors in the first conversion branch is controlled based on the first control signal, and the duty cycle of the two switching transistors in the second conversion branch is controlled based on the second control signal, until the voltage of the first capacitor reaches the target voltage.

[0014] Wherein, when the duty cycle of the first control signal changes and the duty cycle of the second control signal changes, the rate of change of the sum of the currents of the first conversion branch and the second conversion branch is within a preset charging speed range; the target correspondence is used to indicate the power distribution relationship when the first conversion branch and the second conversion branch work together.

[0015] In one feasible implementation, the controller is specifically used for:

[0016] The target ratio is obtained based on the actual charging power of the first capacitor and the target correspondence, which is the power allocation ratio corresponding to the maximum working efficiency. The target correspondence is used to describe the correspondence between power, power allocation ratio and working efficiency. The target ratio is used to indicate the ratio between the duty cycle of the first control signal and the duty cycle of the second control signal.

[0017] In one feasible implementation, the first switch and the third switch are 180 degrees out of phase; and / or, the second switch and the fourth switch are 180 degrees out of phase.

[0018] In one feasible implementation, the battery system further includes a first branch switch and a second branch switch. The first branch switch is connected between the branch inductor in the first conversion branch and the negative terminal of the first battery, and the second branch switch is connected between the branch inductor in the second conversion branch and the negative terminal of the first battery. Before controlling the duty cycle of the two switches in the target conversion branch, the controller is also used to control the target branch switch in the target conversion branch to be in a conducting state. The target conversion branch is the first conversion branch and / or the second conversion branch.

[0019] In one feasible implementation, the controller is further configured to:

[0020] The preset charging speed is obtained based on the ratio of the pre-charge current threshold to the set pre-charge time. The lower limit of the preset charging speed range is (1 - floating percentage) * the preset charging speed, and the upper limit of the preset charging speed range is (1 + floating percentage) * the preset charging speed.

[0021] In one feasible implementation, the target voltage is greater than or equal to the difference between the total output voltage and the floating voltage of the battery system, and less than or equal to the sum of the total output voltage and the floating voltage.

[0022] In one feasible implementation, the first battery and the second battery satisfy the condition that the rated capacity of the first battery differs from the rated capacity of the second battery by a first threshold.

[0023] Alternatively, the first battery and the second battery satisfy the following conditions: the energy density of the first battery differs from the energy density of the second battery by a second threshold, and the cycle life of the second battery differs from that of the first battery by a third threshold.

[0024] In one feasible implementation, the cycle life of the first battery is greater than that of the second battery, and the mass energy density and / or volumetric energy density of the second battery is greater than that of the first battery.

[0025] In one feasible implementation, the cycle life of the first battery is greater than 1.2 times the cycle life of the second battery;

[0026] Or the mass energy density and / or volumetric energy density of the second battery is greater than 1.1 times the mass energy density and / or volumetric energy density of the first battery.

[0027] In one feasible implementation, the capacity of the first battery is greater than the capacity of the second battery.

[0028] In one feasible implementation, the capacity of the first battery is greater than 1.1 times the capacity of the second battery.

[0029] Secondly, this application provides a control method applied to a battery system, the battery system including a first battery and a second battery connected in series, a first capacitor, a main switch, and a first conversion branch; a first terminal of the first capacitor is connected to the positive terminal of the first battery through the main switch, and a second terminal of the first capacitor is connected to the negative terminal of the second battery; each of the first conversion branches includes a branch inductor and two switching transistors; the two switching transistors are connected in series and then in parallel with the first capacitor, and the branch inductor is connected between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors; the method includes:

[0030] When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the two switching transistors in the first conversion branch is controlled until the voltage of the first capacitor reaches the target voltage. The duty cycle of the switching transistors in the first conversion branch increases with the increase of the number of times the switching transistors are turned on.

[0031] In one feasible implementation, the switching transistors in the first transformation branch include a first switching transistor and a second switching transistor; the method includes:

[0032] When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the first switch and the second switch is controlled until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switch changes, the rate of change of the current in the first conversion branch is within a preset charging rate range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

[0033] In one feasible implementation, the battery system further includes a second conversion branch; the second conversion branch includes a branch inductor and two switching transistors; the method includes:

[0034] When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the two switches in the first conversion branch and the duty cycle of the two switches in the second conversion branch are controlled until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first conversion branch and the second conversion branch when the duty cycle of the switches in the first conversion branch and the second conversion branch changes is within a preset charging speed range.

[0035] In one feasible implementation, the method includes:

[0036] Based on the correspondence between the actual charging power of the first capacitor and the target voltage, a first control signal and a second control signal are obtained. The duty cycle of the two switching transistors in the first conversion branch is controlled based on the first control signal, and the duty cycle of the two switching transistors in the second conversion branch is controlled based on the second control signal, until the voltage of the first capacitor reaches the target voltage.

[0037] Wherein, when the duty cycle of the first control signal changes and the duty cycle of the second control signal changes, the rate of change of the sum of the currents of the first conversion branch and the second conversion branch is within a preset charging speed range; the target correspondence is used to indicate the power distribution relationship when the first conversion branch and the second conversion branch work together.

[0038] In one feasible implementation, the method includes:

[0039] The target ratio is obtained based on the actual charging power of the first capacitor and the target correspondence, which is the power allocation ratio corresponding to the maximum working efficiency. The target correspondence is used to describe the correspondence between power, power allocation ratio and working efficiency. The target ratio is used to indicate the ratio between the duty cycle of the first control signal and the duty cycle of the second control signal.

[0040] Thirdly, this application provides a computer storage medium having a computer program stored thereon, which, when executed by a processor, implements the control method as described in the second aspect and any feasible implementation thereof.

[0041] Fourthly, this application provides a vehicle including a battery system as described in the first aspect and any feasible implementation thereof.

[0042] In this embodiment, during the pre-charging process of the battery system, the main switch is in the off state, controlling the duty cycle of the two switching transistors in the first conversion branch. By gradually increasing the duty cycle of the switching transistors, the charging speed of the first capacitor is made approximately uniform, thereby ensuring that the current flowing through the first capacitor changes gradually and slowly, without any instantaneous large current. Pre-charging stops when the voltage of the first capacitor reaches the target voltage, achieving dual monitoring of current and voltage, ensuring the smooth completion of the pre-charging process without the need for an additional pre-charging circuit, thus reducing system costs. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the battery system provided in an embodiment of this application;

[0044] Figure 2 This is another structural schematic diagram of the battery system provided in the embodiments of this application;

[0045] Figure 3 This is another structural schematic diagram of the battery system provided in the embodiments of this application;

[0046] Figure 4 This is a flowchart illustrating the control method provided in an embodiment of this application. Detailed Implementation

[0047] 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, and 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.

[0048] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, system, product, or apparatus that comprises a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, products, or apparatuses.

[0049] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0050] Please see Figure 1 , Figure 1 This is a schematic diagram of the battery system provided in an embodiment of this application, as shown below. Figure 1 As shown, the battery system may include a controller, a first battery and a second battery connected in series (e.g., ...). Figure 1 DC1 and DC2 in the middle), the first capacitor (such as Figure 1 C) Main switch (such as Figure 1 In the circuit, K0) and the first conversion branch, the first terminal of the first capacitor is connected to the positive terminal of the first battery through the main switch, and the second terminal of the first capacitor is connected to the negative terminal of the second battery; as shown... Figure 1 As shown, the first terminal of the first capacitor C is connected to one terminal of the main switch K0, the other terminal of the main switch K0 is connected to the positive terminal of the first battery DC1, and the second terminal of the first capacitor C is connected to the negative terminal of the second battery DC2. The first conversion branch includes a branch inductor (such as...). Figure 1 L1 in the middle) and two switching transistors (such as L1 ... Figure 1 (T1 and T2 in the diagram); the two switching transistors are connected in series and then in parallel with the first capacitor. The inductance of this branch is connected between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors.

[0051] When the battery system begins pre-charging and the main switch is off, the controller controls the duty cycle of the two switches in the first conversion branch until the voltage of the first capacitor reaches the target voltage. The duty cycle of the switches in the first conversion branch increases with the number of times the switches are turned on. Controlling the duty cycle of the two switches in the first conversion branch means controlling the two switches to alternately (complementarily) turn on or off.

[0052] The controller is a device with control capabilities. For example, the controller may include a microcontroller unit (MCU).

[0053] This battery system can be applied in electric vehicles. The first and second batteries in the system can provide energy to the electric vehicle, thereby powering it. The first battery may include one or more first cells, which can be connected in series and / or parallel to provide a certain voltage. Similarly, the second battery may include one or more second cells, which can be connected in series and / or parallel to provide a certain voltage.

[0054] The positive electrode materials of the first and second battery cells can be various, such as lithium iron phosphate, ternary materials including nickel, cobalt, and manganese, lithium cobalt oxide, lithium manganese oxide, etc. The negative electrode materials of the first and second battery cells can be various, such as graphite, silicon, lithium metal, and materials without a negative electrode. Depending on the combination of positive and negative electrode materials, the chemical systems of the cells in the first and second batteries can include, but are not limited to, the following chemical systems: lithium iron phosphate-graphite system, lithium iron phosphate-silicon negative electrode system, lithium iron phosphate-silicon-carbon system, lithium iron phosphate-lithium metal negative electrode system, lithium iron phosphate-no-negative electrode system, ternary material-graphite system, ternary material-silicon negative electrode system, ternary material-silicon-carbon system, ternary material-lithium metal negative electrode system, ternary material-no-negative electrode system, etc. Understandably, the first and second battery cells can belong to different chemical systems; or they can belong to the same chemical system, but at least one electrode may have a different material ratio.

[0055] Understandably, the first and second batteries in this battery system satisfy the following condition: the rated capacity of the first battery differs from the rated capacity of the second battery by a first threshold. This first threshold can be set according to the actual scenario; for example, it could be 10%. This rated capacity represents the battery's energy storage capacity and can also represent its discharge capacity. Although there is a certain difference between the rated capacities of the first and second batteries, their rated voltages can be essentially the same, therefore the energy that the two batteries can store differs.

[0056] Optionally, the capacity of the first battery may be greater than the capacity of the second battery, where the capacity may refer to the aforementioned rated capacity.

[0057] For example, the capacity of the first battery can be greater than 1.1 times the capacity of the second battery. Thus, the two batteries in the battery system have different capacities, allowing for subsequent optimization by combining the characteristics of each battery to improve the overall efficiency of the battery system.

[0058] Alternatively, the first and second batteries in the battery system satisfy the following conditions: the energy density of the first battery differs from that of the second battery by a second threshold, and the cycle life of the second battery differs from that of the first battery by a third threshold. The energy density of the battery can include at least one of mass energy density and volumetric energy density. The second and third thresholds can be set according to the actual scenario; for example, the second threshold can be 10%, and the third threshold can be 20%, which is not limited in this application. The cycle life of the battery can refer to the number of cycles in which the battery is repeatedly charged at 0.5C and discharged at 0.5C to its commonly used voltage range, and then decays to 80% of its rated capacity. That is, there are certain differences in both the energy density and cycle life of the first and second batteries. Specifically, the battery with a higher energy density has a shorter cycle life, while the battery with a lower energy density has a longer cycle life; therefore, these two batteries can be referred to as a long-life battery and a high-energy-density battery, respectively.

[0059] Optionally, the cycle life of the first battery is greater than that of the second battery, and the mass energy density and / or volumetric energy density of the second battery is greater than that of the first battery.

[0060] For example, the cycle life of the first battery is greater than 1.2 times that of the second battery; or, the mass energy density and / or volumetric energy density of the second battery is greater than 1.1 times that of the first battery.

[0061] For example, a negative electrode-free battery with an energy density of 400Wh / kg and a cycle life of less than 200 cycles can be used as a high-energy-density battery, while a traditional lithium iron phosphate battery with an energy density of 200Wh / kg and a cycle life of more than 1500 cycles can be used as a long-life battery.

[0062] Understandably, the number of first cells in the first battery and the number of second cells in the second battery can be determined according to actual needs. For example, the first battery and the second battery can be designed to be combined in a 5:5 ratio of total capacity. This application does not impose any restrictions on this.

[0063] The switching transistors mentioned in this application can be transistors, insulated gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), etc., and this application is not limited to any of them. Taking MOSFETs as an example, the first and second terminals of each switching transistor can be the source and drain of the MOSFET, respectively. The control terminal of each switching transistor is used to receive control signals.

[0064] The main switch, such as a DC contactor, is used to connect or disconnect the circuit. In this embodiment, incorporating a main switch into the battery system increases control flexibility. When a circuit fault occurs, the main switch is turned off, preventing damage to components and improving the reliability of the battery system. Furthermore, during periods of battery system inactivity, turning off the main switch reduces system power consumption and extends system lifespan. The target voltage is within a certain voltage range, which is related to the total output voltage of the battery system.

[0065] Specifically, the target voltage is greater than or equal to the difference between the total output voltage of the battery system and the floating voltage value, and less than or equal to the sum of the total output voltage and the floating voltage value. This floating voltage value can be set according to actual needs; for example, the floating voltage value can be 50V, then the target voltage can be within the range of ±50V of the total output voltage of the battery system. This application does not limit the specific value of the target voltage.

[0066] It is understandable that the main switch is turned off during the pre-charging process of the battery system, so as to avoid the first capacitor being subjected to a large current surge before it is pre-charged to the target voltage.

[0067] By pre-charging the battery system to the target voltage (the supply voltage of the first capacitor), and ensuring the target voltage is within the fluctuation range of the total output voltage, the first capacitor can be pre-charged to a reasonable voltage range. This prevents the first capacitor from being subjected to a large current surge after the battery system supplies power to the load. In other words, during pre-charging, the main switch is in the off state, and the first capacitor is pre-charged to the target voltage first. When the battery system subsequently starts working, such as supplying power to the load, the main switch may need to be turned on. At this time, the first capacitor will not be subjected to a sudden large current surge due to the main switch being turned on, reducing the risk of damage to the first capacitor and thus extending the battery system's lifespan.

[0068] Understandably, the first conversion circuit described above includes switching transistors T1 and T2. During the control of the duty cycles of these two transistors, T1 and T2 conduct complementaryly. Specifically, the duty cycle of T1 can increase with the number of times T1 is turned on during the pre-charging process, or the duty cycle of T2 can increase with the number of times T2 is turned on during the pre-charging process. When the duty cycle of one transistor changes, the duty cycle of the other transistor changes accordingly, ensuring that the two transistors conduct complementaryly.

[0069] When the duty cycle of the switching transistor in the first conversion circuit increases with the number of times it is turned on, the duty cycle can change from a first preset value, which can be set according to the actual scenario. For example, the first preset value can be 0, or other smaller values ​​in the range of 0 to 1, and this application does not impose any restrictions.

[0070] Understandably, the duty cycle of the switching transistor in the first conversion circuit increases with the number of times it is turned on. It's possible that the duty cycle initially increases continuously, then fluctuates around a certain value (greater than the initial duty cycle value). Alternatively, the final value of the duty cycle may be greater than the initial value, but it may fluctuate continuously during the change, with the final value also fluctuating around a certain value. This application does not limit the variation of the duty cycle.

[0071] In this embodiment, it is not necessary to set up an additional pre-charge conversion branch in the battery system. Utilizing the existing circuit structure, the controller controls the state of the switching transistor in the first conversion branch to achieve pre-charging, causing the voltage of the first capacitor to rise to the target voltage. By controlling the duty cycle of the switching transistor, damage to the first capacitor caused by instantaneous large current surges can be avoided, thus achieving pre-charging with low system cost. In addition, pre-charging stops when the voltage of the first capacitor reaches the target voltage, realizing dual monitoring of current and voltage, ensuring the smooth completion of the pre-charging process, simplifying the circuit topology, reducing circuit complexity, and achieving high control precision.

[0072] In one possible implementation, the switching transistors in the first switching branch include a first switching transistor and a second switching transistor.

[0073] When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the first and second switching transistors until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switching transistor changes, the rate of change of the current in the first conversion branch is within the preset charging speed range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

[0074] The preset charging range can be calculated. Specifically, the lower limit of the preset charging speed range is (1 - floating percentage) * preset charging speed, and the upper limit is (1 + floating percentage) * preset charging speed. In other words, the preset charging range can include the range of preset charging speed * (1 ± X%), where X% represents the floating percentage. For example, the floating percentage can be 30%, meaning the preset charging range is the range of preset charging speed * (1 ± 30%). The floating percentage can also be other values, which can be determined based on the actual scenario.

[0075] The preset charging speed can be obtained based on the ratio of the pre-charge current threshold to the set pre-charge time. In other words, the preset charging speed = preset charging threshold / set pre-charge time.

[0076] In this application, during the change of the duty cycle of the first switching transistor, the rate of change of the current in the first conversion branch is within the preset charging speed range. That is, by modulating the duty cycle of the first switching transistor in the first conversion branch to track the current I of the first conversion branch, the rate of change of the current is kept within the preset charging speed range. In this way, the charging speed of the first capacitor can be made close to uniform during the pre-charging process, thereby ensuring that the current flowing through the first capacitor changes gradually and slowly, without instantaneous large current, thus improving the safety and reliability of the pre-charging process.

[0077] Please see Figure 2 , Figure 2 This is another schematic diagram of the battery system provided in the embodiments of this application. Figure 2 Is Figure 1 Based on, such as Figure 2 As shown, the battery system also includes a second conversion branch, which includes a branch inductor (such as...). Figure 2 L2 in the middle) and two switching transistors (such as L2 ... Figure 2 (T3 and T4 in the first capacitor), the two switching transistors in the second conversion branch are connected in series and then in parallel with the first capacitor; the branch inductor in the second conversion branch is connected in series between the connection point of the first battery and the second battery and the connection point of the two switching transistors.

[0078] When the battery system begins pre-charging and the main switch is off, the controller can control the duty cycle of the two switches in the target conversion branch, i.e., control the alternating (complementary) on / off of the two switches in the target conversion branch, and control the two switches in another conversion branch to be off (i.e., the two switches in that conversion branch are always inactive), until the voltage of the first capacitor reaches the target voltage. The rate of change of the current in the target conversion branch when the duty cycle of the switches changes is within a preset charging rate range, and the current in the target conversion branch is the current flowing through the branch inductor. The target conversion branch can be either the first conversion branch or the second conversion branch.

[0079] The relevant description of the target voltage can be found above.

[0080] For a description of the preset charging speed range, please refer to the text above.

[0081] Understandably, when the battery system begins pre-charging and the main switch is off, the target conversion branch participates in pre-charging, while the other conversion branch does not. The battery system completes pre-charging by controlling the switch in the target conversion branch. Although the battery system includes two conversion branches, pre-charging can be achieved by controlling only one of them, thus reducing control complexity and making the pre-charging process simple and low-cost.

[0082] In this battery system, when a component in one of the conversion branches fails, the other conversion branch (the target conversion branch) that is still functioning will operate and participate in pre-charging. This provides redundancy and backup, ensuring that the pre-charging process can be completed smoothly and improving system reliability.

[0083] In addition, when the battery system is working after precharging is complete, the switching transistors in the first conversion branch and / or the second conversion branch can be controlled to enable the first battery and / or the second battery to supply power to the load individually or in combination, thereby realizing energy conversion.

[0084] The following section details the control process for achieving pre-charging using a switching branch.

[0085] In such Figure 1 or Figure 2 In the battery system shown, assuming that only the first conversion branch participates in pre-charging, the duty cycle of the first switching transistor can be obtained by controlling the current of the first conversion branch.

[0086] Specifically, the controller can obtain a preset charging speed based on the ratio of the set pre-charging time to the pre-charging current threshold, and perform proportional-integral control on the current of the first conversion branch to obtain the duty cycle of the first switching transistor, wherein the current change rate of the first conversion branch is within the preset charging speed range.

[0087] Here, the preset charging time can be denoted as t0, and the pre-charge current threshold can be denoted as I0. The preset charging time is the desired time to complete the pre-charge, for example, 1 second, which is not limited in this application. The pre-charge current threshold is the desired maximum current flowing through the first capacitor after the pre-charge process is completed. By setting these two parameters, the preset charging speed I0 / t0 is obtained, and the current flowing through the first capacitor during the pre-charge process can be controlled.

[0088] During pre-charging, the controller modulates the duty cycle of the first switch to track the current i of the first conversion branch, ensuring that the rate of change of the current in the first conversion branch is uniquely within the aforementioned preset charging speed range. Here, the rate of change of the current in the first conversion branch is Δi / Δt, where Δi represents the arithmetic mean of the current from n samples, and Δt represents the time interval between n samples. By modulating the duty cycle of the first switch to make Δi / Δt as close as possible to I0 / t0, the average change of the current within the n sampling time is essentially the same as the preset value, thus ensuring that the current flowing through the first capacitor changes slowly during pre-charging.

[0089] In other words, proportional-integral (PI) control is applied to the current of the first conversion branch to obtain the duty cycle of the first switching transistor. This process actually includes the following steps: The difference Δi / Δt - I0 / t0 is calculated and used as the input to the PI controller, causing the PI controller to continuously adjust the duty cycle until the difference approaches zero. When the difference approaches zero, it indicates that the battery system is pre-charging the first capacitor at a preset current rate. When the difference is greater than zero, the PI controller adjusts the control strength by calculating the instantaneous difference and the preceding time integral difference, thereby increasing or decreasing the duty cycle until the difference approaches zero again.

[0090] Understandably, due to the delay in the control process, the rate of change of current in the first conversion branch is not necessarily equal to the preset charging rate at all times. The actual measured rate of change of current in the first conversion branch is within the range of the preset charging rate * (1 ± 30%), and can change dynamically within this range. By setting a certain redundancy, the rate of change of current in the first conversion branch is made as equal to the preset charging rate as possible, ensuring that the current flowing through the first capacitor changes slowly as required during the pre-charging process.

[0091] Understandably, the pre-charging process of the battery system is not necessarily completed within the preset charging time t0. In reality, due to the dynamic adjustment of the control process, it can be completed within the time range of t0*(1±30%).

[0092] Understandably, during pre-charging, the total capacitance of the battery system is fixed, and the voltage across a capacitor is proportional to the integral of the current being charged. Therefore, by setting the preset charging time and pre-charging current threshold, and ensuring that the actual current and time are essentially consistent with the preset conditions, it can be guaranteed that the voltage of the first capacitor will also reach the ideal voltage range synchronously. By checking whether the voltage of the first capacitor reaches the target voltage, the pre-charging process can be stopped. This allows for dual monitoring of voltage and current, ensuring that the voltage and current of the first capacitor meet the requirements when pre-charging is actually completed, reducing the risk of damage and improving system reliability.

[0093] In this embodiment, during the pre-charging process, the main switch is in the off state. The duty cycle of the first and second switching transistors is controlled by the PWM control signal of the first conversion branch, allowing the current in the first conversion branch to change slowly. This, in turn, causes the voltage of the first capacitor to gradually change until it reaches the target voltage, avoiding large current surges during and after pre-charging. Since this pre-charging process is implemented through control logic, no additional pre-charging circuit is required, thus reducing the cost of the battery system. Furthermore, if one conversion branch in the battery system fails, the other conversion branch can still operate, providing redundancy and enhancing the reliability of the battery system.

[0094] The above introduces how Figure 1 or Figure 2 In the battery system shown, only one switching branch participates in the pre-charging process.

[0095] The following introduction is as follows: Figure 2 In the battery system shown, both conversion branches participate in the pre-charging process.

[0096] In such Figure 2In the battery system shown, during the initial pre-charging phase, the controller can control the duty cycles of the two switches in the first conversion branch and the two switches in the second conversion branch until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first and second conversion branches when the duty cycles of the switches in the first and second conversion branches change is within a preset charging rate range. Understandably, since both the first and second conversion branches participate in the pre-charging process of the battery system, it is necessary to control the operation of these two conversion branches and the switching states of the switches included in them. Specifically, the first switch T1 and the third switch T3 are 180 degrees out of phase, and / or the second switch T2 and the fourth switch T4 are 180 degrees out of phase. The control of the duty cycle of the two switches in the first conversion branch and the control of the duty cycle of the two switches in the second conversion branch refer to the first switch T1 and the second switch T2 in the first conversion branch being complementary to be turned on (complementarily turned off), and the third switch T3 and the fourth switch T4 in the second conversion branch being complementary to be turned on (complementarily turned off).

[0097] In this embodiment, during the pre-charging process, the main switch is in the off state, and the controller controls the on / off state of each switch in the first and second conversion branches until the voltage of the first capacitor gradually changes to reach the target voltage. By controlling the total current conversion rate to be within the preset charging speed range, the current flowing through the first capacitor can be guaranteed to change slowly, avoiding large current surges. Since this pre-charging process is implemented through control logic, there is no need to set up an additional pre-charging circuit, thus reducing the cost of the battery system.

[0098] In one possible implementation, the controller is specifically used for:

[0099] The target ratio is obtained by determining the power allocation ratio corresponding to the maximum working efficiency based on the actual charging power of the first capacitor and the target correspondence. This target correspondence is used to describe the correspondence between power, power allocation ratio and working efficiency. The target ratio is used to indicate the ratio between the duty cycle of the first control signal and the duty cycle of the second control signal.

[0100] For example, the target ratio mentioned above can represent the ratio of the duty cycle of the first switch to the duty cycle of the third switch.

[0101] The target ratio can be a fixed ratio, such as 50%. The target ratio can also be a variable ratio, such as one based on the actual charging power of the first capacitor, and can be determined according to the actual situation.

[0102] During pre-charging, the controller modulates the duty cycles of the first and second control signals to track the current *i* flowing through the first capacitor, ensuring that the rate of change of the current flowing through the first capacitor is within a preset charging speed range. Specifically, the rate of change of the current flowing through the first capacitor is made as close as possible to the preset charging speed. Here, the rate of change of the current flowing through the first capacitor is Δi / Δt, where Δi represents the arithmetic mean of the current flowing through the first capacitor from n samples, and Δt represents the time interval between the n samples. By modulating the duty cycles of the first and second control signals to make Δi / Δt as close as possible to the preset charging speed *I0 / t0*, the average change of the current flowing through the first capacitor within the n sampling time is essentially the same as the preset value, thus ensuring that the current flowing through the first capacitor changes slowly during pre-charging.

[0103] Since both the first and second conversion branches participate in the pre-charging process, the current flowing through the first capacitor is the sum of the current in the first conversion branch and the current in the second conversion branch. Therefore, the rate of change of the sum of the currents in the first and second conversion branches is also within the aforementioned preset charging range, and is basically equal to the aforementioned preset charging speed.

[0104] In this embodiment, during the pre-charging process, the main switch is in the off state. The controller controls the on / off state of each switch in the first and second conversion branches, so that the current flowing through the first capacitor changes slowly, thereby causing the voltage of the first capacitor to gradually change to reach the target voltage, avoiding large current surges. Since this pre-charging process is implemented through control logic, there is no need to set up an additional pre-charging circuit, thus reducing the cost of the battery system.

[0105] Understandably, due to the delay in the control process, the rate of change of the current flowing through the first capacitor is not necessarily equal to the preset charging rate at all times. The actual measured rate of change of the current in the first conversion branch is within the range of the preset charging rate * (1 ± 30%), and can change dynamically within this range. By setting a certain redundancy, the rate of change of the current flowing through the first capacitor is made as equal as possible to the preset charging rate, ensuring that the current flowing through the first capacitor changes slowly as required during the pre-charging process.

[0106] Understandably, the pre-charging process of the battery system is not necessarily completed within the preset charging time t0. In reality, due to the dynamic adjustment of the control process, it can be completed within the time range of t0*(1±30%).

[0107] Understandably, during pre-charging, the total capacitance of the battery system is fixed, and the voltage across a capacitor is proportional to the integral of the current being charged. Therefore, by setting the preset charging time and pre-charging current threshold, and ensuring that the actual current and time are essentially consistent with the preset conditions, it can be guaranteed that the voltage of the first capacitor will also reach the ideal voltage range synchronously. By checking whether the voltage of the first capacitor reaches the target voltage, the pre-charging process can be stopped. This allows for dual monitoring of voltage and current, ensuring that the voltage and current of the first capacitor meet the requirements when pre-charging is actually completed, reducing the risk of damage, improving system reliability, and enhancing the stability of the battery system during startup.

[0108] In this embodiment of the application, the controller in the battery system can also be used for:

[0109] The power allocation ratio corresponding to the maximum operating efficiency is obtained based on the actual charging power of the first capacitor and the target correspondence. The power allocation ratio corresponding to the maximum operating efficiency is taken as the target ratio. Here, the target correspondence is used to describe the correspondence between power, power allocation ratio and system efficiency.

[0110] By obtaining the duty cycle of the first and second control signals according to the target ratio, the current flowing through the first capacitor can change slowly during the pre-charging process.

[0111] Understandably, the target correspondence is obtained in advance. The process of obtaining the target correspondence may include: after the battery system is working and the pre-charging process is completed, when both the first and second conversion branches are working, for each requested power, the operating efficiency corresponding to each power allocation ratio is measured to obtain the operating efficiency under different requested power conditions. Specifically, the power allocation ratio can be between 1% and 99%, varying in 1% increments. For example, if the requested power X is allocated according to a power allocation ratio of y%, then the power allocated to the first conversion branch is X*y%, and the power allocated to the second conversion branch is X*(100%-y%). Each switch is controlled based on these requested powers and allocation ratios to obtain the operating efficiency corresponding to the requested power and power allocation ratio. In this way, the correspondence between requested power, power allocation ratio, and operating efficiency can be obtained, i.e., the target correspondence can be obtained.

[0112] In other words, by performing proportional-integral control on the current flowing through the first capacitor, and according to the aforementioned target ratio, the first control signal and the second control signal can be obtained.

[0113] In this embodiment, during the pre-charging process, the main switch is in the off state. The controller controls the on / off state of each switch in the first and second conversion branches, causing the current flowing through the first capacitor to change slowly. This, in turn, causes the voltage of the first capacitor to gradually change until it reaches the target voltage, avoiding large current surges. Since this pre-charging process is implemented through control logic, no additional pre-charging circuit is required, thus reducing the cost of the battery system. Because both conversion branches participate in pre-charging, the charging current can be controlled more quickly and stably. The ripple of the two conversion branches cancels each other out, reducing the ripple of the entire battery system, improving pre-charging efficiency, and reducing the possibility of component damage.

[0114] In addition, since the currents of the two conversion branches are out of phase, each conversion branch carries a portion of the power. While keeping the total power constant, the power can be preferentially allocated to the point of maximum efficiency of one conversion branch to ensure that most of the power corresponds to higher efficiency. This can further improve system efficiency and reduce heat dissipation.

[0115] In one possible implementation, each conversion branch in the battery system may further include a branch switch. For example, in Figure 1 In the battery system shown, a first branch switch is added. For example, in... Figure 2 In the battery system described, one or two branch switches may be added. This application does not impose any limitations.

[0116] Please see Figure 3 , Figure 3 This is another schematic diagram of the battery system provided in the embodiments of this application. Figure 3 Is Figure 2 Based on, such as Figure 3 As shown, the battery system also includes a first branch switch (such as...). Figure 3 K1 in the middle) and the second branch switch (such as K1 ... Figure 3 In K2), the first branch switch is connected between the branch inductor in the first conversion branch and the negative terminal of the first battery, and the second branch switch is connected between the branch inductor in the second conversion branch and the negative terminal of the first battery.

[0117] The first branch switch and the second branch switch can be DC contactors, etc., used to connect or disconnect the circuit connection.

[0118] Before controlling the duty cycle of the two switches in the target transformation branch, the controller is also used to control the target branch switch in the target transformation branch to be in the on state; the target transformation branch can be the first transformation branch and / or the second transformation branch.

[0119] In this embodiment, branch switches are provided in the battery system. Controlling the shutdown of a branch switch disables the corresponding conversion branch, eliminating the need to control the switching transistors within that conversion branch. This simplifies control and facilitates operation. Furthermore, shutting down the branch switches prevents damage to components in the conversion branch during fault conditions, improving the battery system's safety. Additionally, during battery system inactivity, shutting down the branch switches reduces system power consumption and extends system lifespan.

[0120] In the battery system described above, the output terminal of the battery system is also used to connect to the load, and the two ends of the first capacitor are connected to the output terminal of the battery system.

[0121] When the voltage of the first capacitor reaches the target voltage, the controller is also used to control the first battery and / or the second battery in the battery system to supply power to the load.

[0122] Any battery, any conversion branch, and the first capacitor can constitute a conversion circuit that can convert one DC voltage into another. For example, this conversion circuit can be a boost circuit to convert the voltage provided by the battery into a higher output voltage.

[0123] After pre-charging, the main switch can be turned on, allowing the battery system to start working, for example, supplying power to a load. By controlling the operation of some or all switching branches in the battery system, any one battery in the system can independently supply power to the load, or both batteries can supply power to the load together. When the SOC of both batteries in the battery system is high, they can be used together to discharge and provide energy to the load, meeting its needs. When the battery SOC is medium or high, a single battery can be used to supply power to the load. In this way, the battery system can implement different intelligent control modes in different scenarios, adapting to various situations and meeting different needs, with high control flexibility. In addition, since the lifespan and energy density of the two batteries differ, the advantages of long-life batteries and high-energy-density batteries can be combined and utilized by controlling the operation. Long-life batteries can be used for cycling in the high SOC range, and high-energy-density batteries can be used in the low SOC range. This ensures the battery system's lifespan while increasing energy density, thereby achieving significant optimization of driving range and the weight and volume of the battery system.

[0124] Compared to traditional battery topologies, the battery system with two conversion branches provided in this application offers a wider output current range, thus providing more flexible power output options for different scenarios. This battery system can significantly increase the efficient operating current range while using a smaller inductor. Furthermore, the high-efficiency range of a single conversion branch is relatively narrow. By setting multiple conversion branches, their high-efficiency ranges can be combined, and through control strategies, the power-efficiency relationship can be transformed from a single-peak to a multi-peak pattern, thereby increasing the absolute power range of the system within the high-efficiency range. In other words, by controlling the operation of multiple conversion branches, the battery system can operate within the high-efficiency range most of the time, thereby improving overall operating efficiency and energy conversion efficiency.

[0125] Please see Figure 4 , Figure 4 This is a flowchart illustrating a control method provided in an embodiment of this application. This method can be applied to, for example... Figures 1-3 The battery system shown in any of the figures includes a first battery and a second battery connected in series, a first capacitor, a main switch, and a first conversion branch; the first terminal of the first capacitor is connected to the positive terminal of the first battery through the main switch, and the second terminal of the first capacitor is connected to the negative terminal of the second battery; each of the first conversion branches includes a branch inductor and two switching transistors; the two switching transistors are connected in series and then in parallel with the first capacitor, and the branch inductor is connected between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors;

[0126] This method includes, but is not limited to, the following steps:

[0127] S401: When the battery system begins pre-charging and the main switch is in the off state, control the duty cycle of the two switching transistors in the first conversion branch until the voltage of the first capacitor reaches the target voltage.

[0128] In the first conversion branch, the duty cycle of the switching transistor increases with the number of times the switching transistor is turned on.

[0129] In one possible implementation, the switching transistors in the first switching branch include a first switching transistor and a second switching transistor; the above method includes:

[0130] When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the first switch and the second switch is controlled until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switch changes, the rate of change of the current in the first conversion branch is within the preset charging rate range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

[0131] In one possible implementation, the battery system further includes a second conversion branch; the second conversion branch includes a branch inductor and two switching transistors; the method includes:

[0132] When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the two switching transistors in the first conversion branch and the duty cycle of the two switching transistors in the second conversion branch are controlled until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first and second conversion branches when the duty cycle of the switching transistors in the first and second conversion branches changes is within the preset charging speed range.

[0133] In one possible implementation, the above method includes:

[0134] Based on the correspondence between the actual charging power of the first capacitor and the target voltage, a first control signal and a second control signal are obtained. The duty cycle of the two switching transistors in the first conversion branch is controlled based on the first control signal, and the duty cycle of the two switching transistors in the second conversion branch is controlled based on the second control signal, until the voltage of the first capacitor reaches the target voltage.

[0135] Among them, when the duty cycle of the first control signal changes and the duty cycle of the second control signal changes, the rate of change of the sum of the currents of the first conversion branch and the second conversion branch is within the preset charging speed range; the target correspondence is used to indicate the power distribution relationship when the first conversion branch and the second conversion branch work together.

[0136] In one possible implementation, the above method includes:

[0137] The target ratio is obtained by matching the actual charging power of the first capacitor with the target ratio to obtain the power allocation ratio corresponding to the maximum working efficiency. The target ratio is used to describe the correspondence between power, power allocation ratio and working efficiency.

[0138] This application also provides a computer storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described functionality. Figure 4 The method shown.

[0139] This application also provides a vehicle that may include the above-mentioned features. Figures 1-3 Any of the battery systems shown in the diagram.

[0140] In this embodiment, it is not necessary to set up an additional pre-charge conversion branch in the battery system. Pre-charging is achieved by controlling the state of the switching transistor in the first conversion branch, causing the voltage of the first capacitor to rise to the target voltage. By controlling the duty cycle of the switching transistor, damage to the first capacitor from instantaneous large current surges can be avoided, thus achieving pre-charging with low system cost. Furthermore, pre-charging stops when the voltage of the first capacitor reaches the target voltage, enabling dual monitoring of current and voltage, ensuring a smooth pre-charging process, simplifying the circuit topology, reducing circuit complexity, and providing high control precision.

[0141] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A battery system characterized by, The system includes a controller, a first battery and a second battery connected in series, a first capacitor, a main switch, and a first conversion branch. The first terminal of the first capacitor is connected to the positive terminal of the first battery via the main switch, and the second terminal of the first capacitor is connected to the negative terminal of the second battery. The first conversion branch includes a branch inductor and two switching transistors. The two switching transistors are connected in series and then in parallel with the first capacitor. The branch inductor is connected between the series connection point of the first and second batteries and the series connection point of the two switching transistors. When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the two switching transistors in the first conversion branch until the voltage of the first capacitor reaches the target voltage. The duty cycle of the switching transistors in the first conversion branch increases with the number of times the switching transistors are turned on, and the two switching transistors are turned on or off alternately. The battery system further includes a second conversion branch; the second conversion branch includes a branch inductor and two switching transistors; the two switching transistors in the second conversion branch are connected in series and then in parallel with the first capacitor; the branch inductor in the second conversion branch is connected in series between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors. When the battery system begins pre-charging and the main switch is in the off state, the controller is used to control the duty cycle of the two switching transistors in the first conversion branch and the duty cycle of the two switching transistors in the second conversion branch until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first conversion branch and the second conversion branch when the duty cycle of the switching transistors in the first conversion branch and the second conversion branch changes is within a preset charging speed range. The first switching branch includes a first switching transistor and a second switching transistor; the second switching branch includes a third switching transistor and a fourth switching transistor; the first switching transistor and the third switching transistor are 180 degrees out of phase; and / or, the second switching transistor and the fourth switching transistor are 180 degrees out of phase.

2. The battery system of claim 1, wherein, The switching transistors in the first conversion branch include a first switching transistor and a second switching transistor; When the battery system begins pre-charging and the main switch is in the off state, the controller controls the duty cycle of the first switch and the second switch until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switch changes, the rate of change of the current in the first conversion branch is within a preset charging rate range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

3. The battery system of claim 1, wherein, The controller is specifically used for: Based on the correspondence between the actual charging power of the first capacitor and the target voltage, a first control signal and a second control signal are obtained. The duty cycle of the two switching transistors in the first conversion branch is controlled based on the first control signal, and the duty cycle of the two switching transistors in the second conversion branch is controlled based on the second control signal, until the voltage of the first capacitor reaches the target voltage. Wherein, when the duty cycle of the first control signal changes and the duty cycle of the second control signal changes, the rate of change of the sum of the currents of the first conversion branch and the second conversion branch is within a preset charging speed range; the target correspondence is used to indicate the power distribution relationship when the first conversion branch and the second conversion branch work together.

4. The battery system of claim 3, wherein, The controller is specifically used for: The target ratio is obtained based on the actual charging power of the first capacitor and the target correspondence, which is the power allocation ratio corresponding to the maximum working efficiency. The target correspondence is used to describe the correspondence between power, power allocation ratio and working efficiency. The target ratio is used to indicate the ratio between the duty cycle of the first control signal and the duty cycle of the second control signal.

5. The battery system of any one of claims 1-4, wherein, The battery system further includes a first branch switch and a second branch switch. The first branch switch is connected between the branch inductor in the first conversion branch and the negative terminal of the first battery, and the second branch switch is connected between the branch inductor in the second conversion branch and the negative terminal of the first battery. Before controlling the duty cycle of the two switches in the target conversion branch, the controller is also used to control the target branch switch in the target conversion branch to be in the on state. The target conversion branch is the first conversion branch and / or the second conversion branch.

6. The battery system of any one of claims 1-5, wherein, The controller is also used for: The preset charging speed is obtained based on the ratio of the pre-charge current threshold to the set pre-charge time, and the lower limit of the preset charging speed range is (1 - floating percentage). The preset charging speed, the upper limit of the preset charging speed range is (1 + floating percentage). The preset charging speed.

7. The battery system of any one of claims 1-6, wherein, The target voltage is greater than or equal to the difference between the total output voltage and the floating voltage of the battery system, and less than or equal to the sum of the total output voltage and the floating voltage.

8. The battery system of any one of claims 1-7, wherein, The first battery and the second battery satisfy the condition that the rated capacity of the first battery differs from the rated capacity of the second battery by a first threshold. Alternatively, the first battery and the second battery satisfy the following conditions: the energy density of the first battery differs from the energy density of the second battery by a second threshold, and the cycle life of the second battery differs from that of the first battery by a third threshold.

9. The battery system of any one of claims 1-8, wherein, The cycle life of the first battery is greater than that of the second battery, and the mass energy density and / or volumetric energy density of the second battery is greater than that of the first battery.

10. The battery system of claim 9, wherein, The cycle life of the first battery is greater than 1.2 times that of the second battery; Or the mass energy density and / or volumetric energy density of the second battery is greater than 1.1 times the mass energy density and / or volumetric energy density of the first battery.

11. The battery system of claim 9 or 10, wherein, The capacity of the first battery is greater than the capacity of the second battery.

12. The battery system of claim 11, wherein, The capacity of the first battery is greater than 1.1 times the capacity of the second battery.

13. A control method characterized by, The method is applied to a battery system, which includes a first battery and a second battery connected in series, a first capacitor, a main switch, and a first conversion branch; a first terminal of the first capacitor is connected to the positive terminal of the first battery through the main switch, and a second terminal of the first capacitor is connected to the negative terminal of the second battery; the first conversion branch includes a branch inductor and two switching transistors; the two switching transistors are connected in series and then in parallel with the first capacitor, and the branch inductor is connected between the series connection point of the first battery and the second battery and the series connection point of the two switching transistors; the method includes: When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the two switching transistors in the first conversion branch is controlled until the voltage of the first capacitor reaches the target voltage. The duty cycle of the switching transistors in the first conversion branch increases with the increase of the number of times the switching transistors are turned on. The two switching transistors are turned on or off alternately. The battery system further includes a second conversion branch; the second conversion branch includes a branch inductor and two switching transistors; the method further includes: When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the two switching transistors in the first conversion branch and the duty cycle of the two switching transistors in the second conversion branch are controlled until the voltage of the first capacitor reaches the target voltage. The rate of change of the sum of the currents in the first conversion branch and the second conversion branch when the duty cycle of the switching transistors in the first conversion branch and the second conversion branch changes is within a preset charging speed range. The first switching branch includes a first switching transistor and a second switching transistor; the second switching branch includes a third switching transistor and a fourth switching transistor; the first switching transistor and the third switching transistor are 180 degrees out of phase; and / or, the second switching transistor and the fourth switching transistor are 180 degrees out of phase.

14. The control method according to claim 13, characterized by, The switching transistors in the first conversion branch include a first switching transistor and a second switching transistor; the method includes: When the battery system begins pre-charging and the main switch is in the off state, the duty cycle of the first switch and the second switch is controlled until the voltage of the first capacitor reaches the target voltage. When the duty cycle of the first switch changes, the rate of change of the current in the first conversion branch is within a preset charging rate range. The current in the first conversion branch is the current flowing through the branch inductor in the first conversion branch.

15. The control method according to claim 13, characterized by, The method includes: Based on the correspondence between the actual charging power of the first capacitor and the target voltage, a first control signal and a second control signal are obtained. The duty cycle of the two switching transistors in the first conversion branch is controlled based on the first control signal, and the duty cycle of the two switching transistors in the second conversion branch is controlled based on the second control signal, until the voltage of the first capacitor reaches the target voltage. Wherein, when the duty cycle of the first control signal changes and the duty cycle of the second control signal changes, the rate of change of the sum of the currents of the first conversion branch and the second conversion branch is within a preset charging speed range; the target correspondence is used to indicate the power distribution relationship when the first conversion branch and the second conversion branch work together.

16. The control method according to claim 15, characterized by The method includes: The target ratio is obtained based on the actual charging power of the first capacitor and the target correspondence, which is the power allocation ratio corresponding to the maximum working efficiency. The target correspondence is used to describe the correspondence between power, power allocation ratio and working efficiency. The target ratio is used to indicate the ratio between the duty cycle of the first control signal and the duty cycle of the second control signal.

17. A computer storage medium having stored thereon a computer program, characterized in that When the program is executed by the processor, it implements the control method as described in any one of claims 13-16.

18. A vehicle characterized by comprising: Includes the battery system as described in any one of claims 1-12.

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