Rail transit battery pack online active balancing method

Abstract

This invention relates to the field of power balancing technology, specifically to an online active balancing method for rail transit battery packs. This method constructs an "energy ledger" to historically record the energy absorption capacity of each battery module during multiple braking operations. Therefore, when the central control console triggers the coordinated pulse mode, the BMS can intelligently adjust the power output ratio between the main battery pack and the auxiliary power supply based on real data. Secondly, in the coordinated pulse mode, this invention continuously monitors at high frequency and uses a Kalman filter algorithm to predict the voltage drop curve, enabling early identification of "abnormally low-voltage battery modules" that are about to reach the minimum safety threshold, and triggering "online reverse active balancing operation." Through capacitors and MOSFET switches, the energy of the "main battery module" is rapidly transferred to the abnormal module. This proactive intervention effectively prevents BMS fuse blowouts due to the weak link effect of a single module, greatly improving the safety of system operation.

Description

Technical Field

[0001] This invention relates to the field of power balancing technology, and more specifically, to an online active balancing method for rail transit battery packs. Background Technology

[0002] Rail transit, especially electrified railways and urban rail transit systems, is the backbone of modern urban public transportation. Its vehicles are typically equipped with a main battery pack to provide starting, auxiliary power, and emergency backup power. During train operation, especially during braking, a large amount of recyclable electrical energy is generated; while during starting, acceleration, or climbing, high-power output is required. Traditional battery systems often struggle to efficiently handle these instantaneous, high-intensity power fluctuations.

[0003] In existing technologies, some solutions introduce auxiliary power supplies consisting of multiple battery modules connected in series to recover braking energy and support peak power output. However, this series structure inherently suffers from the "weakest link" effect, meaning the performance of the entire series battery pack is limited by the worst-performing individual battery module with the lowest voltage. Under continuous high power output conditions, due to differences in internal resistance, capacity, and health status, the voltage drop rates of each battery module are not uniform. This can easily lead to individual battery modules' voltages dropping to the lowest safe threshold first, triggering the battery management system's (BMS) protection mechanisms (such as fuse tripping), causing an unexpected interruption of the entire auxiliary power supply and even the power system, severely impacting operational reliability and safety. Summary of the Invention

[0004] The purpose of this invention is to provide an online active balancing method for rail transit battery packs to improve the above-mentioned technical problems.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] This application provides an online active balancing method for rail transit battery packs, applicable to rail transit battery systems. The system includes a main battery pack mounted on the underframe of the power car near the traction inverter and an auxiliary power supply located on one side of the main battery pack. The auxiliary power supply is characterized in that it absorbs braking energy generated during train braking and provides additional power to the main battery pack when the train outputs high power. The auxiliary power supply is composed of multiple battery modules connected in series, with an active balancing capacitor connected in parallel between two battery modules to stabilize the continuous high-power output of the auxiliary power supply. The method includes: continuously and frequently collecting voltage and current data of multiple battery modules via a BMS during multiple train braking events to construct an energy ledger corresponding to the auxiliary power supply; when the central control console or automatic driving system triggers a cooperative pulse mode, the BMS adjusts the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger, while simultaneously monitoring voltage fluctuations of multiple battery modules in the auxiliary power supply in real time. In cases of abnormal voltage fluctuations, the active balancing capacitor replenishes energy to abnormally low-voltage battery modules, thereby preventing excessively low voltage in abnormally low-voltage battery modules from triggering abnormal fuse blowouts in the BMS.

[0007] Optionally, the construction of the energy ledger corresponding to the auxiliary power source includes:

[0008] During train braking, the voltage and current data of multiple battery modules are continuously and frequently collected through the BMS to construct the net charging amount of each battery module during this braking process.

[0009] An energy ledger for the auxiliary power supply is constructed based on the cumulative net charge of each battery module during multiple braking processes. Multiple battery modules are sorted according to their cumulative net charge, and the top 20%-30% of battery modules are marked as primary battery modules, while the rest are marked as secondary battery modules.

[0010] Optionally, when the cooperative pulse mode is triggered by the central console or the autonomous driving system, the BMS adjusts the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger, including:

[0011] In response to the cooperative pulse mode command triggered by the central console or the automatic driving system, the BMS parses the high power demand data and high power duration in the cooperative pulse mode command, and at the same time retrieves the energy reserve parameters of the main battery pack and the latest energy ledger of the auxiliary power supply. The high power demand data and high power duration are obtained by the train itself from the operating parameter list according to the acceleration demand or the climbing section demand.

[0012] The average collaborative power is calculated based on the energy reserve data and high power duration in the energy ledger. The output power of the auxiliary power supply is configured according to 90%-95% of the average collaborative power, so that the 90%-95% average collaborative power plus the output power of the main battery pack meets the high power demand data.

[0013] Optionally, the BMS monitors the voltage fluctuations of multiple battery modules in the auxiliary power supply in real time, and in the event of abnormal voltage fluctuations, replenishes the abnormally low-voltage battery modules with energy through active balancing capacitors, including:

[0014] The BMS continuously and frequently collects voltage and current data from multiple battery modules, constructs a voltage drop curve for each module, and uses a Kalman filter algorithm to correct the predicted voltage drop curve's trend over the coordinated duration. When any voltage drop curve approaches the minimum voltage safety threshold during a sustained high-power period, an online reverse active balancing operation is triggered. This allows the main battery module to replenish the energy of the abnormally low-voltage battery module through parallel capacitors and MOSFET switches, thereby preventing the abnormally low-voltage battery module from triggering the BMS's abnormal fuse due to excessive low voltage.

[0015] Optionally, an online reverse active balancing operation is triggered, enabling the main battery module to replenish the abnormally low-voltage battery module through parallel capacitors and MOSFET switches, including:

[0016] Retrieve the voltage drop curve corresponding to the abnormally low voltage battery module, and obtain the time node where the voltage drop curve intersects with the minimum voltage safety threshold of 110%-115%, which is recorded as the first time node.

[0017] The voltage drop curves of multiple main battery modules are retrieved, and the main battery module with the highest voltage value at the first time point is identified as the first main battery module.

[0018] Based on the interval between the first time node and the high-power end time node, and the current voltage value of the first main battery module, the corresponding capacitor charging voltage value is retrieved from the operating parameter reference table. The first main battery module and the capacitor are connected in parallel through a MOSFET switch. When the capacitor voltage reaches the capacitor charging voltage value, the parallel connection between the capacitor and the first main battery module is disconnected through a MOSFET switch. When the voltage value of the abnormal low-voltage battery module is lower than the capacitor charging voltage value, the capacitor is connected in parallel with the abnormal low-voltage battery module through a MOSFET switch, thereby slowing down the voltage drop trend of the abnormal low-voltage battery module.

[0019] The beneficial effects of this invention are as follows:

[0020] This invention constructs an "energy ledger" to historically record the energy absorption capacity of each battery module during multiple braking events. As a result, when the coordinated pulse mode is triggered at the central control console, the BMS can intelligently adjust the power output ratio of the main battery pack and the auxiliary power supply based on real data.

[0021] Secondly, in the cooperative pulse mode, this invention continuously monitors at high frequency and uses a Kalman filter algorithm to predict the voltage drop curve, enabling it to identify "abnormally low-voltage battery modules" that are about to reach the minimum safety threshold in advance, and trigger "online reverse active balancing operation." Through capacitors and MOSFET switches, the energy of the "main battery module" is rapidly transferred to the abnormal module. This proactive intervention effectively prevents BMS fuse blowouts due to the weak link effect of a single module, greatly improving the continuity and safety of system operation.

[0022] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of an online active balancing method for rail transit battery packs as described in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0026] It should be noted that similar reference numerals or letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0027] Example 1:

[0028] like Figure 1 As shown, this embodiment provides an online active balancing method for rail transit battery packs, applicable to rail transit battery systems. The system includes a main battery pack mounted on the underframe of the power car near the traction inverter and an auxiliary power supply located on one side of the main battery pack. The auxiliary power supply is used to absorb the braking energy generated during train braking and to provide additional power to the main battery pack when the train is outputting high power. The auxiliary power supply is obtained by connecting multiple battery modules in series, and an active balancing capacitor is connected in parallel between two battery modules to stabilize the continuous high power output of the auxiliary power supply. The connection relationship between the battery modules and the capacitor is a common switched capacitor active balancing circuit, which will not be described here. This circuit has the characteristics of being simple, reliable, non-magnetic, and easy to control, making it extremely suitable for reliable transportation vehicles such as trains.

[0029] Secondly, the active balancing of the auxiliary power supply described in this embodiment is an extreme case handling method, which is not applicable to normal situations. For example, before the cooperative pulse mode is triggered, the auxiliary power supply will use the balancing circuit to balance the voltage difference between each battery pack to keep them consistent.

[0030] Secondly, this control method is applicable to high-power scenarios such as temporary train climbing. Such scenarios do not frequently occur at every station, while braking energy recovery occurs frequently. That is, after multiple energy recoverys, only one cycle is needed to use up the energy recovered multiple times, and then the cycle repeats. Therefore, it is necessary to build a corresponding energy recovery ledger for each cycle. However, due to frequent charging and discharging, the damage to the battery itself is relatively large. Therefore, during braking energy recovery, it does not directly act on the main battery pack, but instead uses frequent charging and discharging of the auxiliary power supply to reduce the damage to the main battery pack.

[0031] The method includes:

[0032] Step S100: During multiple train braking operations, the BMS continuously and frequently collects voltage and current data from multiple battery modules to construct an energy ledger corresponding to the auxiliary power supply. During charging, the charging energy is calculated based on the voltage data, current data, and duration, and recorded. The charging energy level depends on the battery's inherent quality. Especially during frequent short-interval charging, the energy absorbed by each battery will differ, and this difference in battery quality will be amplified during high-power discharge. Therefore, a corresponding active balancing control method is required to prevent the BMS from triggering low-voltage fuses. Secondly, due to the different accumulated charging energy, when the cooperative pulse mode is triggered, the BMS will first perform an active balancing to balance the voltage of multiple battery modules in the auxiliary power supply, ensuring that the initial voltage of multiple battery modules remains consistent. This is determined by the charging mode. During charging, multiple battery modules are independent and separate. This function can be achieved by checking the MOSFET switches, which is a conventional technique in this field and will not be elaborated here.

[0033] Step S200: When the coordinated pulse mode is triggered at the central control console or the autonomous driving system, the BMS adjusts the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger. At the same time, it monitors the voltage fluctuations of multiple battery modules in the auxiliary power supply in real time. In the event of abnormal voltage fluctuations, it replenishes the abnormally low-voltage battery modules with energy through the active balancing capacitor, thereby preventing the abnormal low-voltage battery modules from triggering the abnormal fuse of the BMS due to excessive low voltage.

[0034] The approximate power output ratio is calculated by dividing the total collected energy by the duration of the cooperative pulse mode, thereby obtaining the maximum average power that the auxiliary power supply can provide. In order to assist the main battery as much as possible, this assistance will usually consume about 90% of the total power of the auxiliary power supply. Based on 90%-95% of the maximum average output power of the auxiliary power supply plus the output power of the main battery pack, the sum of the two power values ​​should be equal to or slightly higher than the required power in the cooperative pulse mode command, thereby realizing the recovery and reuse of multiple braking energy.

[0035] This embodiment constructs an "energy ledger" to historically record the energy absorption capacity of each battery module during multiple braking events. As a result, when the coordinated pulse mode is triggered at the central control console, the BMS can intelligently adjust the power output ratio of the main battery pack and the auxiliary power supply based on real data.

[0036] Secondly, in the cooperative pulse mode, this invention continuously monitors at high frequency and uses a Kalman filter algorithm to predict the voltage drop curve, enabling it to identify "abnormally low-voltage battery modules" that are about to reach the minimum safety threshold in advance, and trigger "online reverse active balancing operation." Through capacitors and MOSFET switches, the energy of the "main battery module" is rapidly transferred to the abnormal module. This proactive intervention effectively prevents BMS fuse blowouts due to the weak link effect of a single module, greatly improving the continuity and safety of system operation.

[0037] The specific implementation method for constructing the energy ledger corresponding to the auxiliary power source in step S100 is as follows:

[0038] Step S110: During train braking, the voltage and current data of multiple battery modules are continuously and frequently collected through the BMS to construct the net charging amount of each battery module during this braking process.

[0039] Step S120: Construct an energy ledger for the auxiliary power supply based on the cumulative net charge of each battery module during multiple braking processes, and sort the multiple battery modules according to the cumulative net charge. Mark the top 20%-30% of battery modules as primary battery modules, and the rest as secondary battery modules.

[0040] The energy ledger serves two main purposes. First, it calculates the maximum average output power of the auxiliary power supply in the coordinated pulse mode, thereby configuring the power output ratio between the main battery pack and the auxiliary power supply. Second, it screens out battery modules with superior performance. In actual operation scenarios, frequent braking and charging without discharging will cause high-performance battery modules to absorb more regenerative braking energy, while low-performance modules may stop absorbing regenerative braking energy in the later stages due to overcharging. However, due to frequent braking and less coordinated mode, the auxiliary power supply is usually overcharged or has relatively abundant energy storage in most cases.

[0041] Secondly, the specific implementation method of adjusting the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger in step S200 is as follows:

[0042] Step S210: In response to the cooperative pulse mode command triggered by the central console or the automatic driving system, the BMS parses the high power demand data and high power duration in the cooperative pulse mode command, and at the same time retrieves the energy reserve parameters of the main battery pack and the latest energy ledger of the auxiliary power supply. The high power demand data and high power duration are obtained by the train itself from the operating parameter list according to the acceleration demand or the climbing section demand.

[0043] Step S220: Calculate the average collaborative power based on the energy reserve data and high power duration in the energy ledger, and configure the output power value of the auxiliary power supply according to 90%-95% of the average collaborative power value, so that the 90%-95% average collaborative power value plus the output power value of the main battery pack meets the high power demand data.

[0044] In the coordinated pulse mode, i.e. when the dual batteries provide high output power to the power unit, the system will trigger equalization detection. The specific implementation method can be as follows:

[0045] In step S230, the BMS continuously and frequently collects voltage and current data from multiple battery modules and constructs a voltage drop curve for each battery module. The Kalman filter algorithm is used to correct the trend of the predicted voltage drop curve in real time within the coordinated duration. When any voltage drop curve approaches the minimum voltage safety threshold within the high-power duration, an online reverse active balancing operation is triggered. This allows the main battery module to replenish the energy of the abnormally low-voltage battery module through parallel capacitors and MOSFET switches, thereby preventing the abnormally low voltage battery module from triggering the abnormal fuse of the BMS due to excessive low voltage.

[0046] The specific operation of online reverse active balancing is as follows:

[0047] Retrieve the voltage drop curve corresponding to the abnormally low voltage battery module. This abnormally low voltage battery module is usually the previously marked secondary battery module, that is, the battery module with poor quality. Obtain the time point where the voltage drop curve intersects with the minimum voltage safety threshold of 110%-115%, and record it as the first time point.

[0048] The voltage drop curves of multiple main battery modules are retrieved, and the main battery module with the highest voltage value at the first time point is recorded as the first main battery module.

[0049] Based on the interval between the first time node and the high-power end time node, and the current voltage value of the first main battery module, the corresponding capacitor charging value is retrieved from the operating parameter reference table. Specifically, the capacitor charging value is looked up in the operating parameter reference table by the difference between the current voltage value of the first main battery module and the minimum voltage safety threshold of 110%-115% and the interval. This capacitor charging value needs to ensure that the first main battery module can charge the capacitor while ensuring its own output, in order to prepare for the later capacitor replenishment. The first main battery module and the capacitor are connected in parallel through a MOSFET switch. When the capacitor voltage reaches the capacitor charging value, the parallel connection between the capacitor and the first main battery module is disconnected through the MOSFET switch. When the voltage value of the abnormal low-voltage battery module is lower than the capacitor charging value, the capacitor is connected in parallel with the abnormal low-voltage battery module through the MOSFET switch, thereby slowing down the voltage drop trend of the abnormal low-voltage battery module.

[0050] Secondly, if the difference between the voltage value of the first main battery module and the minimum voltage safety threshold of 110%-115% does not meet the energy replenishment requirement, then the main battery module with the second highest voltage value at the first time node is selected and recorded as the second main battery module.

[0051] The second main battery module is connected in parallel with the capacitor via a MOSFET switch. When the capacitor voltage reaches 30% of its charging voltage, the second main battery module is disconnected, and then the first main battery module is connected in parallel again until the capacitor voltage reaches its charging voltage. This constitutes two power replenishments. This measure is only taken when sequential power replenishment is not feasible, and is considered an extreme power replenishment trigger condition.

[0052] The aforementioned balancing operation is not performed blindly, but rather based on precise prediction and optimal selection, specifically the primary battery module with the highest voltage at the first critical moment. By consulting the "Operating Parameter Comparison Table" to determine the "capacitor charging voltage value," the timing and amount of energy transfer are optimized and calculated, making the balancing process fast and accurate. This is particularly suitable for the instantaneous power demands of rail transit, ensuring smooth and stable power output.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An online active balancing method for rail transit battery packs, applicable to rail transit battery systems, the system comprising a main battery pack mounted on the underframe of a power car near the traction inverter and an auxiliary power supply located on one side of the main battery pack, characterized in that, The auxiliary power supply is used to absorb the braking energy generated during train braking and to provide additional power to the main battery pack when the train is outputting high power. The auxiliary power supply is composed of multiple battery modules connected in series, and an active balancing capacitor is connected in parallel between two battery modules to stabilize the continuous high power output of the auxiliary power supply. The method includes: During multiple train braking events, the voltage and current data of multiple battery modules are continuously and frequently collected through the BMS to construct the energy ledger corresponding to the auxiliary power supply. When the coordinated pulse mode is triggered by the central console or the autonomous driving system, the BMS adjusts the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger. At the same time, it monitors the voltage fluctuations of multiple battery modules in the auxiliary power supply in real time. In case of abnormal voltage fluctuations, it replenishes the abnormally low voltage battery modules through active balancing capacitors, thereby preventing the abnormal low voltage battery modules from triggering the abnormal fuse of the BMS due to excessive low voltage. Secondly, the construction of the energy ledger corresponding to the auxiliary power source includes: During train braking, the voltage and current data of multiple battery modules are continuously and frequently collected through the BMS to construct the net charging amount of each battery module during this braking process. An energy ledger for the auxiliary power supply is constructed based on the cumulative net charge of each battery module during multiple braking processes. Multiple battery modules are sorted according to their cumulative net charge, and the top 20%-30% of battery modules are marked as primary battery modules, while the rest are marked as secondary battery modules. Secondly, when the cooperative pulse mode is triggered at the central control console or by the autonomous driving system, the BMS adjusts the power output ratio of the main battery pack and the auxiliary power supply based on the energy ledger, including: In response to the cooperative pulse mode command triggered by the central console or the automatic driving system, the BMS parses the high power demand data and high power duration in the cooperative pulse mode command, and at the same time retrieves the energy reserve parameters of the main battery pack and the latest energy ledger of the auxiliary power supply. The high power demand data and high power duration are obtained by the train itself from the operating parameter list according to the acceleration demand or the climbing section demand. The average collaborative power is calculated based on the energy reserve data and high power duration in the energy ledger. The output power of the auxiliary power supply is configured according to 90%-95% of the average collaborative power, so that the 90%-95% average collaborative power plus the output power of the main battery pack meets the high power demand data.

2. The online active balancing method for rail transit battery packs according to claim 1, characterized in that, The BMS monitors voltage fluctuations in multiple battery modules in the auxiliary power supply in real time, and in the event of abnormal voltage fluctuations, it replenishes power to abnormally low-voltage battery modules through active balancing capacitors, including: The BMS continuously and frequently collects voltage and current data from multiple battery modules, constructs a voltage drop curve for each module, and uses a Kalman filter algorithm to correct the predicted voltage drop curve's trend over the coordinated duration. When any voltage drop curve approaches the minimum voltage safety threshold during a sustained high-power period, an online reverse active balancing operation is triggered. This allows the main battery module to replenish the energy of the abnormally low-voltage battery module through parallel capacitors and MOSFET switches, thereby preventing the abnormally low-voltage battery module from triggering the BMS's abnormal fuse due to excessive low voltage.

3. The online active balancing method for rail transit battery packs according to claim 2, characterized in that, Triggering online reverse active balancing operation enables the main battery module to replenish the abnormally low-voltage battery module through parallel capacitors and MOSFET switches, including: Retrieve the voltage drop curve corresponding to the abnormally low voltage battery module, and obtain the time node where the voltage drop curve intersects with the minimum voltage safety threshold of 110%-115%, which is recorded as the first time node. The voltage drop curves of multiple main battery modules are retrieved, and the main battery module with the highest voltage value at the first time point is recorded as the first main battery module. Based on the interval between the first time node and the high-power end time node, and the current voltage value of the first main battery module, the corresponding capacitor charging voltage value is retrieved from the operating parameter reference table. The first main battery module and the capacitor are connected in parallel through a MOSFET switch. When the capacitor voltage reaches the capacitor charging voltage value, the parallel connection between the capacitor and the first main battery module is disconnected through a MOSFET switch. When the voltage value of the abnormal low-voltage battery module is lower than the capacitor charging voltage value, the capacitor is connected in parallel with the abnormal low-voltage battery module through a MOSFET switch, thereby slowing down the voltage drop trend of the abnormal low-voltage battery module.

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