Battery equalization method for hybrid electric vehicle under cold working condition

Abstract

The invention discloses a battery equalization method for a hybrid electric vehicle under a cold working condition, and belongs to the technical field of battery energy. The method is suitable for the hybrid electric vehicle under the cold working condition, waste heat of the engine is transmitted to the battery pack for preheating through the cooling circulation pipeline, the whole vehicle control strategy considering battery preheating under the low-temperature environment is optimized based on the model prediction control algorithm, the consistency problem is divided into a non-aging scene and an aging scene, and the consistency is improved. Active equalization control strategies are respectively designed, a top-layer algorithm mainly judges whether the battery pack needs to start active equalization and whether aged monomers exist and preliminarily marks the aged monomers, a bottom-layer algorithm is responsible for specific implementation of non-aged and aged active equalization control, and finally an active equalization algorithm of the battery pack under the cold working condition is integrally designed. And application and popularization of the hybrid electric vehicle in the cold region are promoted, so that the battery equalization method for the hybrid electric vehicle under the cold working condition has a wide prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery energy, and in particular relates to a battery balancing method for a hybrid electric vehicle under cold working conditions. Background Art

[0002] Lithium-ion batteries are a crucial power source for hybrid vehicles, and their performance directly determines the overall vehicle's performance. However, lithium-ion batteries are significantly affected by temperature fluctuations during use. Low temperatures, in particular, can cause the battery's electrochemical reaction rate to drop dramatically, leading to a decrease in lithium ion concentration. This leads to rapid capacity degradation and can even cause electrolyte freezing, severely impacting power output. Unlike the long-term cumulative effects of high temperatures, the effects of low temperatures are more sudden and immediate. Furthermore, lithium-ion batteries used in hybrid vehicles typically combine multiple battery cells. Due to variations in production processes and operating conditions, individual cell characteristics, such as voltage and internal resistance, vary. This inconsistency exacerbates with age, limiting the overall performance of the battery pack. Ultimately, the performance of a battery pack is limited by its weakest cell. Over time, the pack's capacity gradually degrades, directly impacting the vehicle's power output and range, hindering the application and promotion of hybrid vehicles in cold regions. Regarding power battery balancing methods, relevant scholars have proposed many methods, such as the invention patent (publication number: CN119812571A) published on April 11, 2025, which describes a battery balancing device and battery balancing method. This invention patent uses a heat-conducting shield installed on the top of the power battery to achieve heating and heat dissipation of the power battery while the resistor consumes energy for voltage balancing, avoiding the single-mindedness of using resistors for voltage balancing in traditional settings. However, this invention patent does not consider the issue of battery pack balancing under cold conditions and ignores the impact of temperature on battery pack inconsistency. Another example is the invention patent (publication number: CN119659417A) published on March 21, 2025, which describes a power battery pack balancing control method, device, equipment, and storage medium. This invention patent, based on the discharge or charge state of the battery pack, temporarily excludes the battery cell with the maximum or minimum state of charge at a certain moment from participating in the charge and discharge process, without consuming energy through resistors. This improves the charge and discharge capacity of each battery and the performance and service life of the entire battery system. However, this invention patent also fails to consider the impact of temperature on the battery pack during use, and has certain difficulties in identifying the charge and discharge status of the battery pack. Based on the above discussion, the present invention discloses a battery balancing method for hybrid vehicles under cold conditions. Summary of the Invention

[0003] To address the deficiencies of the prior art, the present invention discloses a battery balancing method for hybrid electric vehicles under cold conditions. It is characterized by:

[0004] Step 1: Battery preheating control strategy based on model predictive control: The engine is first started to heat the coolant, and the cooling heat is transferred to the battery pack through the cooling circulation pipeline. Based on the modeling of the vehicle power system, an integrated thermal management system model is built, and a vehicle control strategy for low temperature conditions is formulated. The control strategy is optimized based on the model predictive control algorithm (MPC):

[0005] (1) Control variable sequence and state variable sequence in the prediction time domain:

[0006]

[0007]

[0008] (2) Objective function of thermal management system model prediction:

[0009]

[0010] Where x(k) represents the engine temperature (°C); u(k) represents the thermostat opening and fan opening (%); N represents the prediction time domain ( / ); Q and R represent the diagonal weighted matrix ( / ); X r represents the output reference trajectory ( / ); X represents the output variable (°C); U represents the control variable (%);

[0011] Step 2: Active balancing control considering battery aging at room temperature: Based on the good preheating of the battery pack in step 1, the consistency problem is divided into two scenarios: non-aging and aging according to the different degrees of battery pack capacity attenuation. Active balancing control strategies are designed for each scenario. The top-level algorithm mainly determines whether the battery pack needs to enable active balancing and whether there are aging cells, and preliminarily marks the aging cells. The bottom-level algorithm is responsible for the specific implementation of active balancing control for non-aging and aging cells. The limit capacity of the aging cell is calculated as follows:

[0012] (1) Voltage of cell i during normal discharge:

[0013]

[0014] (2) Calculation of monomer capacity limit:

[0015]

[0016]

[0017] Where, I i represents the current of the monomer (A); R i Represents the internal resistance of the monomer (Ω); V i Represents the voltage of the monomer (V); CI_C Represents the maximum charge capacity of the monomer when no equalization is applied (Ah); C B_C Represents the maximum charging capacity when equalizing the battery (Ah); C I_D Represents the minimum capacity (Ah) remaining after discharge when the monomer is not balanced; C B_D Represents the minimum discharge maximum capacity remaining when equalizing the battery (Ah);

[0018] Step three, active balancing control of batteries under cold working conditions: Based on the active balancing control algorithm that considers battery aging under normal temperature conditions in step two, the battery preheating system and the battery active balancing control system are integrated. With battery pack preheating as a prerequisite, the battery pack capacity that has been attenuated due to low temperature conditions is restored through sufficient preheating, and then active balancing control of the battery pack is added to further increase the capacity of the battery pack.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The battery preheating control strategy based on model predictive control described in this patent can effectively use the engine's waste heat to preheat the battery to the target temperature, while controlling the engine temperature to maintain within the optimal operating temperature range. The engine can reach the preheating target temperature earlier and better follow the cooling target temperature, thereby improving the energy consumption of the thermal management system.

[0021] 2. The active balancing control considering battery aging at room temperature described in this patent can effectively eliminate the inconsistency between cells in the battery pack, accurately identify aging cells and reduce the impact of aging cells on the battery pack by applying balancing current, thereby reducing the capacity decay of the battery pack and increasing the available capacity of the battery pack, and has certain promotional capabilities;

[0022] 3. The active battery balancing control under cold working conditions described in this patent realizes the preheating of the battery system in cold regions before operation and the consistent balancing during operation, which can effectively reduce the attenuation of battery capacity, thereby outputting more power in hybrid vehicles, thereby achieving a certain fuel-saving effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following description of the embodiments will become easier to understand with reference to the accompanying drawings, in which:

[0024] Figure 1 This is a flow chart of a battery balancing method for a hybrid electric vehicle under cold working conditions according to an embodiment of the present invention; DETAILED DESCRIPTION

[0025] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0026] Reference Attachment Figure 1 A battery balancing method for a hybrid vehicle under cold conditions is described below, but the present invention is not limited to these embodiments.

[0027] 1. A battery balancing method for a hybrid electric vehicle under cold operating conditions, characterized by:

[0028] Step 1: Battery preheating control strategy based on model predictive control: The engine is first started to heat the coolant, and the cooling heat is transferred to the battery pack through the cooling circulation pipeline. Based on the modeling of the vehicle power system, an integrated thermal management system model is built, and a vehicle control strategy for low temperature conditions is formulated. The control strategy is optimized based on the model predictive control algorithm (MPC):

[0029] (1) Control variable sequence and state variable sequence in the prediction time domain:

[0030]

[0031]

[0032] (2) Objective function of thermal management system model prediction:

[0033]

[0034] Where x(k) represents the engine temperature (°C); u(k) represents the thermostat opening and fan opening (%); N represents the prediction time domain ( / ); Q and R represent the diagonal weighted matrix ( / ); X r represents the output reference trajectory ( / ); X represents the output variable (°C); U represents the control variable (%);

[0035] Step 2: Active balancing control considering battery aging at room temperature: Based on the good preheating of the battery pack in step 1, the consistency problem is divided into two scenarios: non-aging and aging according to the different degrees of battery pack capacity attenuation. Active balancing control strategies are designed for each scenario. The top-level algorithm mainly determines whether the battery pack needs to enable active balancing and whether there are aging cells, and preliminarily marks the aging cells. The bottom-level algorithm is responsible for the specific implementation of active balancing control for non-aging and aging cells. The limit capacity of the aging cell is calculated as follows:

[0036] (1) Voltage of cell i during normal discharge:

[0037]

[0038] (2) Calculation of monomer capacity limit:

[0039]

[0040]

[0041] Where, I i represents the current of the monomer (A); R i Represents the internal resistance of the monomer (Ω); V i Represents the voltage of the monomer (V); C I_C Represents the maximum charge capacity of the monomer when no equalization is applied (Ah); C B_C Represents the maximum charging capacity when equalizing the battery (Ah); C I_D Represents the minimum capacity (Ah) remaining after discharge when the monomer is not balanced; C B_D Represents the minimum discharge maximum capacity remaining when equalizing the battery (Ah);

[0042] Step three, active balancing control of batteries under cold working conditions: Based on the active balancing control algorithm that considers battery aging under normal temperature conditions in step two, the battery preheating system and the battery active balancing control system are integrated. With battery pack preheating as a prerequisite, the battery pack capacity that has been attenuated due to low temperature conditions is restored through sufficient preheating, and then active balancing control of the battery pack is added to further increase the capacity of the battery pack.

[0043] The present invention uses more terms such as MPC, but does not exclude the possibility of using other terms. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention.

[0044] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A battery balancing method for a hybrid electric vehicle under cold conditions, characterized by: Step 1: Battery preheating control strategy based on model predictive control: The engine is first started to heat the coolant, and the cooling heat is transferred to the battery pack through the cooling circulation pipeline. Based on the modeling of the vehicle power system, an integrated thermal management system model is built, and a vehicle control strategy for low temperature conditions is formulated. The control strategy is optimized based on the model predictive control algorithm (MPC): (1) Control variable sequence and state variable sequence in the prediction time domain: ， ， (2) Objective function of thermal management system model prediction: ， Where x(k) represents the engine temperature (°C); u(k) represents the thermostat opening and fan opening (%); N represents the prediction time domain ( / ); Q and R represent the diagonal weighted matrix ( / ); X r represents the output reference trajectory ( / ); X represents the output variable (°C); U represents the control variable (%); Step 2: Active balancing control considering battery aging at room temperature: Based on the good preheating of the battery pack in step 1, the consistency problem is divided into two scenarios: non-aging and aging according to the different degrees of battery pack capacity attenuation. Active balancing control strategies are designed for each scenario. The top-level algorithm mainly determines whether the battery pack needs to enable active balancing and whether there are aging cells, and preliminarily marks the aging cells. The bottom-level algorithm is responsible for the specific implementation of active balancing control for non-aging and aging cells. The limit capacity of the aging cell is calculated as follows: (1) Voltage of cell i during normal discharge: ， (2) Calculation of monomer capacity limit: ， ， Where, I i represents the current of the monomer (A); R i Represents the internal resistance of the monomer (Ω); V i Represents the voltage of the monomer (V); C I_C Represents the maximum charge capacity of the monomer when no equalization is applied (Ah); C B_C Represents the maximum charging capacity when equalizing the battery (Ah); C I_D Represents the minimum capacity (Ah) remaining after discharge when the monomer is not balanced; C B_D Represents the minimum discharge maximum capacity remaining when equalizing the battery (Ah); Step three, active balancing control of batteries under cold working conditions: Based on the active balancing control algorithm that considers battery aging under normal temperature conditions in step two, the battery preheating system and the battery active balancing control system are integrated. With battery pack preheating as a prerequisite, the battery pack capacity that has been attenuated due to low temperature conditions is restored through sufficient preheating, and then active balancing control of the battery pack is added to further increase the capacity of the battery pack.

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