Method for dynamically correcting SOC (state of charge) of battery cell of oil-electric hybrid electric vehicle

Abstract

The invention provides a method for dynamically correcting the SOC (state of charge) of a battery cell of a gas-electric hybrid electric vehicle, which comprises the following steps of: S1, static SOC correction: when the static time of the vehicle exceeds a first threshold time, automatically waking up a battery management system to carry out open-circuit voltage verification, and correcting the static SOC 0 of the battery cell according to a verification result; s2, internal resistance calibration when the engine is started, wherein when the vehicle engine is started, the internal resistance R0 of the battery pack is calibrated according to the instantaneous voltage fluctuation; s3, dynamic SOC measurement, wherein when the vehicle runs normally, dynamic SOCt is obtained through ampere-hour integration and table look-up. According to the method, the SOC is calibrated in combination with the special working condition of the HEV model, and the risk of over-charging and over-discharging of the battery cell is prevented while the precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hybrid vehicle battery thermal management, and in particular relates to a method for dynamically correcting the SOC of a battery cell of an oil-electric hybrid vehicle. Background Art

[0002] With the development of China's automobile industry, the dependence on oil resources is getting heavier. The dependence of new energy vehicles represented by BEV on electricity has aggravated the pressure on power supply. It is urgent to balance oil and gas resources and electricity resources. About 70% of my country's oil and gas resource demand depends on imports. The fuel consumption target value in the "Medium- and Long-Term Development Plan for the Automobile Industry" has been tightened to 4.0L / 100km. HEV models improve fuel economy by adding power batteries. Its market will become the key solution for the balanced development of oil and gas resources and electricity resources in the subsequent market.

[0003] Compared with BEV and PHEV models, HEV models have a demand for power batteries with low power and high power. Therefore, the selection of power battery cells requires smaller capacity and higher charge and discharge rates. Among them, high charge and discharge rates increase the fluctuation of dynamic voltage by multiples, so SOC calibration under severe working conditions is particularly necessary, especially for the protection of battery cells within the range of use.

[0004] Based on the above background, this patent proposes a HEVSOC algorithm for dynamic voltage. Through the relationship between the vehicle start-stop conditions, dynamic voltage, and internal resistance calculation, the SOC is calculated more accurately to solve the potential risks of overcharging and over-discharging of power batteries.

[0005] Invention patent content

[0006] In view of the above problems, the present invention provides a method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle. The method aims at the specific operating conditions of hybrid electric vehicle (HEV) vehicle startup and the need for SOC calibration due to frequent switching of battery cell charge and discharge. The method couples the specific operating conditions of HEV vehicles at rest, starting, and driving with the relationship between the open circuit voltage, dynamic voltage, current, and internal resistance of the power battery to obtain the relevant constraints of SOC calibration and usage restrictions. Different from the traditional SOC calibration scheme that targets the battery itself, the present invention calibrates the SOC in combination with the special operating conditions of HEV models, which improves the accuracy while also preventing the risks of overcharging and over-discharging of the battery cell. The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle, which comprises:

[0008] Step S1-static SOC correction: When the vehicle is stationary for more than the first threshold time, the battery management system is automatically awakened to verify the open circuit voltage, and the static SOC0 of the battery cell is corrected according to the verification result. Preferably, the first threshold time is not less than 0.5h, that is, the BMS is automatically awakened and the SOC is verified and calibrated through the open circuit voltage when the vehicle reaches a stationary state for more than half an hour.

[0009] Step S2-Internal resistance calibration during engine start: When the vehicle engine is started, especially at the moment of engine intervention, the battery SOC and internal resistance need to be calibrated, and the battery pack internal resistance R0 needs to be calibrated according to the instantaneous voltage fluctuation. Specifically, during the vehicle start-up process, the current under the special condition of engine start-up is calculated, and the internal resistance of the battery pack is calculated according to the instantaneous voltage fluctuation, and the internal resistance and battery cell SOC are corrected. Different from the battery's own strategy, when considering the engine start-up process, the battery will release a pulse current. In this process, in the RC model of the battery, R0 can be directly calculated through the open circuit voltage U0 and current I. This is also the core parameter for dynamic voltage calibration. At the same time, the internal resistance at different SOCs is also adjusted proportionally. For the verification of R0, it can be guaranteed that there will be no overcharging or over-discharging during vehicle driving.

[0010] Step S3-Dynamic SOC measurement: When the vehicle is running normally, the dynamic SOC is obtained by integrating ampere-hours and looking up the table. t During vehicle driving, the calibrated R0 obtained by starting the engine is combined with U0 and current I to integrate the SOC of the battery pack in ampere hours to obtain a new result SOC t During the dynamic driving of the vehicle, the HEV battery cell will be charged and discharged at a rate of more than 30C, so the dynamic voltage will fluctuate greatly. The dynamic voltage U obtained after considering R0 can better support the battery to operate within the allowable operating range, while taking into account performance and ensuring life. Unlike BEV and PHEV batteries, the service life of HEV batteries needs to exceed 20,000 times, so its use range must be guaranteed during repeated cycles, which is also an advantage of the present invention in practical applications.

[0011] Step S4-immediate stop SOC correction: When the engine just stops working but not yet in static state, the SOC is corrected by a first correction coefficient because the open circuit voltage of the battery pack cannot be stabilized. Further, the first correction coefficient is 0.4-0.6, preferably the first correction coefficient is 0.5.

[0012] Step S5-Parking SOC correction: When the vehicle stops to a static state, the SOC2 at the time of parking is verified by the open circuit voltage. Generally, the conditions for obtaining the open circuit voltage are directly related to the performance of the battery cell. The vehicle stops to a static state when the voltage fluctuates within ±5mV within 1 minute after the engine stops running, or the engine stops running for 20 minutes.

[0013] Preferably, in step S1, the current SOC is obtained by open circuit voltage verification. p , and the SOC2 of the last parking is fitted. If the verification result does not exceed the preset threshold, the SOC2 of the last parking is used as the static SOC0 of this correction; if the verification result exceeds the preset threshold, the calibration is started and corrected by the second correction coefficient. Preferably, the range of the second correction coefficient is 0.8-1.

[0014] Furthermore, it also includes step S6-forced calibration: when the voltage characterization exceeds the preset confidence interval, forced calibration is initiated. Specifically, if the dynamic voltage characterization of the battery pack exceeds the confidence interval of the open circuit voltage, internal resistance, and current calculation, forced calibration is performed to ensure the user's requirements for safety and life.

[0015] The beneficial effects of the present invention are:

[0016] (1) The HEV power battery SOC algorithm proposed in the present invention utilizes the internal resistance calculation conditions of the power battery of the HEV vehicle model in the special and stable working condition of engine starting, thereby completing the connection between SOC and dynamic voltage, which not only improves the accuracy but also avoids the overcharge and over-discharge problems of HEV battery cells under high charge and discharge rates.

[0017] (2) The technical solution of the present invention performs power battery SOC calibration during engine start-up and vehicle dynamic driving, thereby solving the high error defect caused by current instability during dynamic voltage calibration. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure shows a HEV battery cell dynamic SOC correction method according to embodiment 1 of the present invention;

[0019] Figure 2 Shown is a schematic diagram of the internal resistance calibration during engine startup in the method of the present invention. DETAILED DESCRIPTION

[0020] The technical scheme of the preferred embodiment of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Embodiment 1:

[0022] This embodiment provides a method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle, which includes:

[0023] Step S1-static SOC correction: When the vehicle is stationary for more than the first threshold time, the battery management system is automatically awakened to verify the open circuit voltage, and the static SOC0 of the battery cell is corrected according to the verification result. For example, the BMS is automatically awakened and the open circuit voltage is verified and calibrated after the vehicle reaches a stationary state for more than half an hour.

[0024] In step S1, when the vehicle is stationary (waiting to start), the SOC0 obtained by the last calibration is compared with the SOC p Fitting is performed to verify. If the verification result does not exceed the preset threshold, SOC0 is retained. If it exceeds, calibration is performed. This process is to exclude the possibility that the battery has been stationary for too long or the SOC0 calibration accuracy is insufficient.

[0025] Step S2 - internal resistance calibration at start-up: When the vehicle engine is started, the battery pack internal resistance R0 is calibrated according to the instantaneous voltage fluctuation; specifically, during the vehicle start-up process, the current under the special working condition of engine start-up is calculated, and the battery pack internal resistance is calculated according to the instantaneous voltage fluctuation, and the internal resistance and battery cell SOC are corrected.

[0026] During the vehicle startup process, especially when the engine is engaged, step S2 needs to calibrate the battery's SOC and internal resistance. Different from the battery's own strategy, during the engine startup process, the battery will release a pulse current. During this process, the battery's RC model (see Figure 2 ), R0 can be directly calculated through the open circuit voltage U0 and current I, which is also the core parameter for dynamic voltage calibration. At the same time, the internal resistance under different SOC is also proportionally adjusted. By verifying R0, it can be used to avoid overcharging or over-discharging during vehicle driving.

[0027] Step S3-Dynamic SOC measurement: When the vehicle is running normally, the dynamic SOCt is obtained by integrating the ampere-hour and looking up the table. During the vehicle driving process, the calibrated R0 obtained by starting the engine is combined with U0 and current I to integrate the SOC of the battery pack by ampere-hour to obtain a new result SOC tDuring the dynamic driving of the vehicle, the HEV battery cell will be charged and discharged at a rate of more than 30C, so the dynamic voltage will fluctuate greatly. The dynamic voltage U obtained after considering R0 can better support the battery to operate within the allowable operating range, while taking into account performance and ensuring life. Unlike BEV and PHEV batteries, the service life of HEV batteries needs to exceed 20,000 times, so its use range must be guaranteed during repeated cycles, which is also an advantage of the present invention in practical applications.

[0028] Step S4 - immediate stop SOC correction: When the engine has just stopped working but has not reached a static state, the SOC is corrected by a first correction coefficient. In a preferred embodiment, the first correction coefficient is 0.4 to 0.6, and is usually about 0.5 according to the specific battery cell structure and empirical design.

[0029] Step S5-Parking SOC Correction: When the vehicle stops to a static state, the SOC2 at the time of parking is obtained through the open circuit voltage. After the vehicle stops, the SOC is verified, and SOC2 is obtained under the condition of obtaining the open circuit voltage verification, that is, the SOC0 of the next vehicle start. Usually, the conditions for obtaining the open circuit voltage are directly related to the performance of the battery cell. The reference indexes for the vehicle stopping to a static state include the engine stopping for 20 minutes, or the open circuit voltage fluctuation within 1 minute does not exceed ±5mV, etc.

[0030] Preferably, in step S1, the current SOC is obtained by open circuit voltage verification. p , and fit it with the SOC2 during the previous parking. If the verification result does not exceed the preset threshold, the SOC2 during the previous parking is used as the static SOC0 for this correction; if the verification result exceeds the preset threshold, the calibration is started and corrected by the first correction coefficient. The first correction coefficient is designed according to the specific vehicle model and relevant experience, and the range of the first correction coefficient is 0.8~1.

[0031] In a preferred embodiment, step S6-forced calibration is also included: when the voltage characterization exceeds the preset confidence interval, forced calibration is initiated. Specifically, if the dynamic voltage characterization of the battery pack exceeds the confidence interval of the open circuit voltage, internal resistance, and current calculation, forced calibration is performed to ensure the user's requirements for safety and life.

[0032] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention. The dimensions described in the drawings and embodiments are not related to the specific objects and are not used to limit the protection scope of the present invention. The dimensions of the objects can be selected and changed according to actual needs.

Claims

1. A method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle, comprising: Step S1-static SOC correction: When the vehicle is stationary for more than the first threshold time, the battery management system is automatically awakened to verify the open circuit voltage, and the static SOC0 of the battery cell is corrected according to the verification result; Step S2 - internal resistance calibration when the engine is started: when the vehicle engine is started, the battery pack internal resistance R0 is calibrated according to the instantaneous voltage fluctuation; Step S3-Dynamic SOC measurement: When the vehicle is running normally, the dynamic SOC is obtained by integrating ampere-hours and looking up the table. t .

2. The method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to claim 1, characterized in that: The method also includes: Step S4 - immediate stop SOC correction: when the engine just stops working but has not yet reached a static state, the SOC is corrected by a first correction coefficient.

3. The method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to claim 2, characterized in that: The first correction coefficient is 0.4-0.

6.

4. The method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to claim 2, characterized in that: It also includes: Step S5-Parking SOC correction: when the vehicle stops to a static state, the SOC2 at the time of parking is verified by the open circuit voltage.

5. The method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to claim 4, characterized in that: In step S1, the current SOC is obtained by open circuit voltage verification. p , and fit it with the SOC2 during the previous parking. If the verification result does not exceed the preset threshold, the SOC2 during the previous parking is used as the static SOC0 for this correction; if the verification result exceeds the preset threshold, the calibration is started and corrected by the second correction coefficient.

6. The method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to claim 5, characterized in that: The second correction coefficient is in the range of 0.8-1.

7. A method for dynamically correcting the SOC of a battery cell of a hybrid electric vehicle according to any one of claims 1 to 6, characterized in that: The method further includes step S6 - forced calibration: when the voltage characteristic exceeds a preset confidence interval, forced calibration is initiated.

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