WO2021088537A1 - Method and system for controlling parallel charging and discharging of battery pack - Google Patents

Abstract

A method for controlling parallel charging and discharging of a battery pack comprises the following steps: performing real-time measurement on an actual current value of each of battery branches connected in parallel; comparing the actual current values of all of battery branches to acquire a maximum actual current value; determining a safe current value of a battery system; comparing the maximum actual current value with the safe current value; and adjusting the battery system on the basis of the comparison between the maximum actual current value and the safe current value. The method performs real-time monitoring on changes in the current of batteries in different branches connected in parallel, dynamically adjusts a load or a charging voltage of the battery system according to an upper limit of a current resistance characteristic of the battery so as to control charging and discharging performed on the battery system, and eliminates an overly large circulating current caused by inconsistencies in capacity, open-circuit voltages, states of charge, internal resistance, and the like in the battery system throughout the entire process of use. In addition, the control method meets the starting power requirements of a locomotive, and leverages the characteristics of the power battery system.

Description

Method and system for controlling parallel charging and discharging of battery packs Technical field

The invention relates to the field of charging and discharging control of locomotive power batteries, and more particularly to a method and system for parallel charging and discharging control of battery packs.

Background technique

As the country advocates green energy, the rolling stock industry (such as high-speed rail, high-speed rail, urban rail, subway, and railway locomotives) has gradually increased the number of projects using power batteries.

Power batteries for locomotives have the characteristics of large capacity and large power, especially from the perspective of locomotive redundancy, most of them use multi-branch parallel circuit topologies. However, in the process of long-term cycling of power batteries, due to the influence of self-discharge, temperature difference, etc., inconsistencies in the state of charge, capacity, and internal resistance will occur. In the parallel circuit topology, the voltage between different branches is the same, but when the state of charge and internal resistance are greatly different, there will be obvious current inconsistencies, that is, circulating current. Circulating current phenomenon will cause the current of some batteries to be very small, while the current of other batteries is too large, which may exceed the current range that the battery can withstand, leading to accelerated aging of the battery pack, which greatly affects the battery life and the performance of power and energy characteristics.

It is necessary to design a charging and discharging control method that can meet the use requirements of locomotives and vehicles such as high-speed railways and high-speed trains, and maximize the characteristics of the power battery system while ensuring system safety and battery performance.

Summary of the invention

According to the current design topology of the locomotive power battery system, the present invention proposes a charging and discharging safety control method suitable for parallel battery packs, which maximizes the power battery while ensuring system safety and battery performance. System characteristics.

In order to achieve the above object, the present invention provides a parallel charging and discharging control method for battery packs. The method includes the following steps: real-time detection of the actual current value of each battery branch of multiple battery branches connected in parallel; The actual current value is compared to obtain the maximum actual current value; the safe current value of the battery system is determined; the maximum actual current value is compared with the safe current value; the battery system is adjusted based on the comparison between the maximum actual current value and the safe current value.

According to an embodiment of the present invention, the method further includes determining whether the battery system is in a charging or discharging state before detecting the actual current value of each battery branch connected in parallel in real time.

According to an embodiment of the present invention, the safe current value is the maximum tolerable current value of the battery branch with the largest current.

According to an embodiment of the present invention, the maximum tolerable current value is determined according to the battery type and grouping mode in the branch.

According to an embodiment of the present invention, the adjustment includes reducing the charging voltage of the battery system in response to determining that the battery system is in a charging state and the maximum actual current value is greater than the safe current value.

According to an embodiment of the present invention, the adjustment includes increasing the charging voltage of the battery system in response to determining that the battery system is in a charging state and the maximum actual current value is less than the safe current value.

According to an embodiment of the present invention, the adjustment includes reducing the load of the battery system in response to determining that the battery system is in a discharged state and the maximum actual current value is greater than the safe current value.

According to an embodiment of the present invention, the adjustment includes increasing the load of the battery system as needed in response to determining that the battery system is in a discharged state and the maximum actual current value is less than the safe current value.

The present invention also provides a parallel charging and discharging control system for battery packs. The system includes: a current detection device for real-time detection of the actual current value of each battery branch of a plurality of battery branches connected in parallel; A safe current determination device for safe current value; a comparison device used to compare the actual current values of all battery branches to obtain the maximum actual current value and compare the maximum actual current value with the safe current value; based on the maximum actual current value and The comparison of the safe current value adjusts the adjustment device of the battery system.

The present invention also provides a locomotive, which uses the above method to control the parallel charging and discharging of the battery pack.

The present invention can obtain the following beneficial effects:

Through real-time monitoring of the current changes of the batteries in different parallel branches, and according to the upper threshold of the battery's current resistance characteristics, the load or charging voltage of the battery system is dynamically adjusted to realize the charge and discharge control of the battery system, and eliminate the internal battery system during the entire use process. Excessive influence of circulating current caused by inconsistencies in capacity, open circuit voltage, state of charge, internal resistance, etc. Moreover, this control method can meet the starting power requirements of the locomotive, and can also maximize the characteristics of the power battery system.

Description of the drawings

According to one or more embodiments described in detail below in conjunction with the accompanying drawings, one or more features and or advantages of the present invention will be apparent.

Fig. 1 is a schematic structural diagram of parallel discharge control of battery packs according to an embodiment of the present invention;

2 is a flowchart of a method for controlling parallel discharge of battery packs according to an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of parallel charging control of battery packs according to an embodiment of the present invention;

Fig. 4 is a flowchart of a method for controlling parallel charging of battery packs according to an embodiment of the present invention.

Detailed ways

As needed, the specification of the present invention discloses specific embodiments of the present invention; however, it should be understood that the embodiments disclosed herein are only examples of the present invention that can be implemented in various and alternative forms. The drawings need not be drawn to scale; some features can be enlarged or reduced to show details of specific components. The same or similar reference signs may indicate the same parameters and components or similar modifications and alternatives. In the following description, a number of operating parameters and components are described in a number of contemplated embodiments. These specific parameters and components are only used as examples in this specification and are not meant to be limiting. Therefore, the specific structure and functional details disclosed in this specification should not be construed as limiting, but merely serving as a representative basis for teaching those skilled in the art to implement the present invention in various forms.

Among the several embodiments provided in this application, the system embodiment described is only illustrative, for example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation, such as Multiple modules or components can be combined or integrated into another system, or some features can be omitted or not implemented. In addition, the displayed or discussed mutual coupling or direct coupling or communication connection may be indirect coupling or communication connection through some interfaces, modules or units, and may be in electrical or other forms.

The modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical modules, that is, they may be located in one place, or they may be distributed on multiple network modules. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments.

In addition, the functional units in the various embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units may be integrated into one module. The above-mentioned integrated unit can be implemented in the form of hardware or software functional unit.

The prior art has proposed a charging method in which the battery packs are used in parallel according to the voltage levels between the battery branches and are put into use sequentially, which can solve the problem of excessive circulating current caused by inconsistent voltages in the battery system at the initial stage of charging. However, as the degree of battery charge and discharge deepens, due to the change of the state of charge, the open circuit voltage and internal resistance of the battery will change non-linearly. After all the batteries are put into use, there may still be differences between the battery branches. Too large causes excessive circulating current, thereby impairing battery performance. Moreover, according to this solution, the battery initially connected to the loop during discharge has only one branch, which cannot meet the starting power requirements of the rolling stock, and the performance of the battery system cannot be fully utilized.

According to the current design topology of the locomotive power battery system, the present invention proposes a charging and discharging safety control method suitable for parallel battery packs. This method ensures that the upper threshold of the current resistance characteristic of the battery pack in each branch is basically the same before each battery branch is put into use. The method generally includes the following steps: real-time detection of the actual current value of each battery branch of multiple battery branches in parallel; comparing the actual current values of all battery branches to obtain the maximum actual current value; determining the safety of the battery system Current value; compare the maximum actual current value with the safe current value; adjust the battery system based on the comparison between the maximum actual current value and the safe current value. In the following, the parallel charging and discharging control method of the battery pack of the present invention will be described in detail in combination with the specific charging state and discharging state.

Fig. 1 shows a schematic structural diagram of parallel discharge control of battery packs according to an embodiment of the present invention. As shown in the figure, the battery system includes 4 parallel branches, and each branch is provided with a group of batteries, namely battery pack 1, battery pack 2, battery pack 3, and battery pack 4. Each battery pack may include a plurality of battery cells connected in series or in parallel. In the process of long-term cycling of battery cells, due to the influence of self-discharge, temperature difference, etc., inconsistencies in the state of charge, capacity, and internal resistance will occur. The inconsistency of the battery cells leads to inconsistencies in the battery packs they consist of. As shown in Figure 1, when the battery pack 1, the battery pack 2, the battery pack 3, and the battery pack 4 are connected in parallel and an external load M is connected, the inconsistency between the battery packs of each branch may lead to different branches Produce circulation phenomenon. Although the size of the external load of the battery system is predetermined according to the characteristics of the battery pack in actual use to ensure that the current of the circuit is within a safe range, the circulating current may cause the current of some batteries to exceed the current range that they can withstand, and the size of the circulating current is also It will change with the change of the battery's depth of discharge, state of charge, internal resistance, etc. If it is not monitored and adjusted in real time, it may accelerate the aging of the battery.

The parallel discharge control method of the battery pack of the present invention is further described in conjunction with FIG. 1 and FIG. 2. During the discharging process of the battery system, the currents I ₁ , I ₂ , I ₃ , and I ₄ of each branch in the system are collected at all times. Send the collected current data of each branch to the battery management system (BMS), compare the current data inside the BMS to obtain the maximum discharge current I _{max_d} , and use the current data as the control signal of the PI controller. After the maximum discharge current I _{max_d is} determined, the maximum tolerable discharge current I _{limt_d} of the battery branch is determined according to the battery type and grouping method contained in the battery pack in the branch where the maximum discharge current I _{max_d occurs} , and I _{limt_d is} used as a safe current for judging whether the branch has an overcurrent risk. It is compared with the _I max_d _I limt_d, and by comparing the _I max_d _I limt_d, decide whether to adjust the load cell system. If I _{max_d} = I _{limt_d} , it indicates that the current maximum current does not exceed the maximum tolerable discharge current, and the power performance of the battery system at this time has been fully utilized, and the battery can continue to discharge under the load. If I _{max_d} > I _{limt_d} , it means that some batteries are at risk of overcurrent. At this time, it is necessary to reduce the battery load to reduce the battery output current and prevent battery performance damage caused by excessive current. If I _{max_d} <I _{limt_d} , it means that the power performance of the battery system has not been fully utilized. At this time, if necessary, the load of the battery system can be increased and the discharge current of the battery system can be increased. The PI regulator controls the battery system load and regulates the output current of the battery system through the output, and uses this as a control basis to realize the real-time closed-loop control of the battery system discharge process, which can maximize the discharge performance of the battery.

The parallel discharge control method of the battery pack of the present invention continuously monitors the current of each branch during the discharge process. When the battery branch with the maximum discharge current changes, the safe current compared with the maximum discharge current needs to be replaced with the current maximum The maximum tolerable discharge current of the branch where the discharge current is located. As a result, even when the battery branch with the maximum discharge current changes with the difference in the depth of discharge, the risk of overcurrent in the battery system can be avoided.

Next, the parallel charging control method of the battery pack of the present invention will be described with reference to FIG. 3 and FIG. 4. During the charging process of the battery system, the currents I ₁ , I ₂ , I ₃ , and I ₄ of each branch in the system are collected at all times. The collected current data of each branch is sent to the battery management system (BMS) and compared within the battery management system (BMS) to obtain the maximum charging current I _{max_c} as the control signal of the PI controller. After the maximum charging current I _{max_c is} determined, according to the battery type and grouping mode included in the battery pack in the branch where the maximum charging current I _{max_c occurs, it is determined to obtain the maximum tolerable charging current I limt_c of the} battery branch. Use I _{limt_c} as a safe current for judging whether the branch has an overcurrent risk. By comparing I _{max_c} and I _{limt_c} , it is decided whether to adjust the battery charging system voltage. If I _{max_c} = I _{limt_c} , it indicates that the current maximum current does not exceed the maximum tolerable charging current, indicating that the charging characteristics of the battery system are fully utilized at this time, and the battery system can continue to be charged at this voltage. If I _{max_c} ＞I _{limt_c} , it means that some batteries have the risk of overcurrent, and the voltage of the battery charging system needs to be lowered to reduce the battery charging current and prevent excessive current from causing battery performance damage or safety hazards. If I _{max_c} <I _{limt_c} , it means that the charging characteristics of the battery system are not fully utilized at this time. At this time, the voltage of the battery charging system can be increased, and the charging current of the battery system can be increased to shorten the charging time of the battery system. The PI regulator controls the battery charging system voltage and regulates the battery system charging current through the output, and uses this as a control basis to realize real-time closed-loop control of the battery system charging process, and can complete the battery charging process in the shortest time within a safe and controllable range.

The invention also discloses a parallel charging and discharging control system for the battery packs. The control system may include a current detection device, a safety current determination device, a comparison device, and an adjustment device. The current detection device may be an ammeter conventionally used in the art. The safe current can be obtained according to the corresponding model and test, and the corresponding data is stored in the memory for use by the controller. In the embodiment shown in Figure 1 and Figure 3, the current size comparison is implemented by the battery management system. The comparison between the maximum charge and discharge current and the maximum withstand current is implemented by the PI controller, and the PI controller performs the comparison based on the result of the comparison. Corresponding adjustments as described above.

The control method of the present invention monitors the actual current in each branch in real time, and uses the actual current as the input signal of the adjustment control, which can eliminate the safety problem caused by the circulating current during the parallel use of the battery. The battery system can be divided into a multi-subsystem parallel topology , Which greatly increases the redundancy of the system. The current of each branch and the upper threshold are simply compared, which avoids the complicated calculation process and simplifies the control logic. The control method of the present invention can be applied to the battery charging process and the discharging process, and is also applicable to the case where the battery polarization has not faded, which greatly increases the reliability of the charge and discharge control of the battery system. At the same time, it can avoid some over-current problems caused by factors such as capacity, internal resistance, state of charge, temperature, etc. during battery use, effectively slow down battery aging, prolong the service life of the battery system, and improve the economy of the full life cycle of rolling stock.

It should be understood that, where technically feasible, the technical features listed above for different embodiments can be combined with each other to form another embodiment within the scope of the present invention. In addition, the specific examples and embodiments described herein are non-limiting, and the structures, dimensions, and materials described above can be modified accordingly without departing from the protection scope of the present invention.

The above-mentioned embodiments, especially any "preferred" embodiments are possible examples of implementations, and are presented only for a clear understanding of the principles of the present invention. Many changes and modifications can be made to the above-mentioned embodiment without basically departing from the spirit and principle of the technology described herein. All modifications are intended to be included within the scope of this disclosure.

Claims (10)

A parallel charging and discharging control method for battery packs is characterized in that it comprises the following steps: Real-time detection of the actual current value of each of the multiple battery branches connected in parallel; Compare the actual current values of all battery branches to obtain the maximum actual current value; Determine the safe current value of the battery system; Compare the maximum actual current value with the safe current value; The battery system is adjusted based on the comparison between the maximum actual current value and the safe current value. The method according to claim 1, characterized in that the method further comprises determining whether the battery system is in a charging or discharging state before detecting the actual current value of each battery branch connected in parallel in real time. The method according to claim 1, wherein the safe current value is the maximum tolerable current value of the branch with the largest current. The method according to claim 1, wherein the maximum tolerable current value is determined according to the battery type and the grouping manner in the branch. 3. The method of claim 2, wherein the adjusting comprises reducing the charging voltage of the battery system in response to determining that the battery system is in a charging state and the maximum actual current value is greater than the safe current value. The method of claim 2, wherein the adjusting comprises increasing the charging voltage of the battery system in response to determining that the battery system is in a charging state and the maximum actual current value is less than the safe current value . The method of claim 2, wherein the adjustment comprises reducing the load of the battery system in response to determining that the battery system is in a discharged state and the maximum actual current value is greater than the safe current value. The method according to claim 2, wherein the adjusting comprises increasing the battery system's battery system as needed in response to determining that the battery system is in a discharged state and the maximum actual current value is less than the safe current value. load. A parallel charging and discharging control system for battery packs, characterized in that the system includes: A current detection device, which is used for real-time detection of the actual current value of each battery branch of the multiple battery branches connected in parallel; A device for determining a safe current, the device for determining a safe current is used to determine a safe current value of the battery system; A comparison device, which is used to compare the actual current values of all battery branches to obtain the maximum actual current value, and to compare the maximum actual current value with the safe current value; An adjustment device that adjusts the battery system based on the comparison between the maximum actual current value and the safe current value. A locomotive, characterized in that the locomotive uses the method according to any one of claims 1-9 to control the parallel charging and discharging of battery packs.

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