A 48V system low-voltage battery charging control method and vehicle

Abstract

The present invention discloses a method for controlling the charging of a low-voltage battery in a 48V system. After the vehicle is started, the engine control system EMS calls the low-voltage battery charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network. The DCDC converter obtains the target voltage of the low-voltage battery through the CAN network and controls the DCDC converter to output the target voltage to charge the low-voltage battery; the low-voltage battery charging MAP is a pre-calibrated charging relationship table with the charging voltage as a variable. The advantages of the present invention are as follows: the charging control of the low-voltage battery can be realized without using an EBS battery sensor, which saves costs while ensuring reliable control and high cost performance; the control scheme fully controls the charging, discharging, energy recovery, BSG assistance and other working conditions of the low-voltage battery, and the entire charging control logic is more reliable and meets the requirements of the charging control of the low-voltage battery.

Description

Technical Field

[0001] The present invention relates to the field of automotive battery control and management, and particularly to a charging control method for a low-voltage battery in a 48V system. Background Art

[0002] With the increasingly strict restrictions on fuel consumption and emission regulations, energy conservation and emission reduction have evolved from a policy level to a technical requirement for each automobile enterprise. Therefore, various hybrid and pure electric technologies have developed rapidly. Among them, the 48V mild hybrid system has several working modes such as idle start-stop, braking energy recovery, power assist, and coasting start-stop. In addition, it has advantages such as shorter ignition time, less noise and vibration during starting, more comfortable for passengers and drivers, electrification of high-power accessories, and low engine loss, and thus has been widely concerned.

[0003] At present, the 48V + 12V dual-voltage system solution adopted by the 48V mild hybrid system has two power grids of 12V and 48V to supply power to different systems. Among them, the 12V voltage can be introduced by converting the 48V power supply through a DC / DC converter. The 48V power supply supplies power to the idle start-stop and braking recovery systems, and the 12V power supply is reserved for other low-power electrical components. Therefore, the electrical components with the in-vehicle 12V voltage standard continue to be used, with less modification to the whole vehicle and lower cost. Currently, intelligent battery sensors EBS are used for all low-voltage batteries of the models on the market to monitor the battery capacity of the low-voltage battery in real time, and then control the charging of the low-voltage battery. Although installing EBS can control charging more precisely, the cost is relatively high; and in the prior art, the engine control system EMS can read a low-voltage value through an internal circuit at the moment of starting, which is the voltage value of the low-voltage battery at the starting moment, but the voltage value obtained after starting is not the voltage of the low-voltage battery. Therefore, how to control the charging of the low-voltage battery through a control strategy while saving the EBS sensor and eliminating an intelligent battery sensor and the corresponding wiring harness is the technical problem to be solved in this application. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a charging control method for a low-voltage battery in a 48V system, which is used to realize the charging control of the low-voltage battery through logical control without an EBS sensor.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for controlling the charging of a low-voltage battery in a 48V system. After the vehicle is started, the engine control system EMS calls the low-voltage battery charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network. The DCDC converter obtains the target voltage of the low-voltage battery through the CAN network and controls the DCDC converter to output the target voltage to charge the low-voltage battery; the low-voltage battery charging MAP is a pre-calibrated charging relationship table with the charging voltage as a variable.

[0006] The low-voltage battery charging MAP includes ChargMAP, and the ChargMAP is the relationship between the initial voltage of the low-voltage battery, the charging time, and the charging target voltage;

[0007] When the vehicle is in the driving condition, the EMS, through the engine control system EMS, at the moment when the system is just powered on, reads the voltage value read at the moment of power-on through the EMS and uses it as the initial voltage of the low-voltage battery when the low-voltage battery is powered on; the EMS calls the ChargMAP to obtain the target voltage that changes with time under the initial voltage and sends the target voltage to the CAN network. The DCDC converter receives the target voltage on the CAN network and controls the output of the target voltage to the low-voltage battery.

[0008] Under the initial voltage of the ChargMAP, the target voltage gradually decreases with the increase of time until the target voltage decreases to the set threshold voltage. The ChargMAP calibrates the relationship among the initial voltage, time, and target voltage through pre-tests.

[0009] The set voltage threshold satisfies the following conditions during calibration: According to the pre-calibrated relationship between the battery voltage and the SOC, the set threshold voltage is converted into the SOC of the low-voltage battery. At this time, the battery SOC corresponding to the set voltage threshold is less than the fully charged SOC and the difference is the set margin threshold.

[0010] When the vehicle is in the energy recovery condition, monitor the state of the 48V battery SOC. If the power of the 48V battery is higher than the set SOC threshold, the EMS calls the ReChargMAP to obtain the target voltage of the low-voltage battery during energy recovery and sends it to the DCDC converter through the CAN network for energy recovery control to charge the low-voltage battery; where ReChargMAP is a corresponding relationship table of the target voltage changing with time.

[0011] The ReChargMAP forms the relationship between the corresponding target voltages changing with the energy recovery time through pre-calibration; where the starting voltage of the ReChargMAP is greater than the set threshold voltage to ensure that the energy recovery power charges the low-voltage battery.

[0012] When in the BSG boosting working condition, the DCDC converter is controlled to be in the boosting working state, and the low-voltage battery is boosted and then supplies current together with the 48V battery to assist the BSG.

[0013] When the DCDC converter boosts and jointly assists the BSG, after the working time of the DCDC converter reaches the set time threshold, it stops working to assist the BSG.

[0014] The set margin threshold corresponding to the difference between the battery SOC corresponding to the set voltage threshold and the fully charged SOC is 15 - 20%.

[0015] A vehicle, which uses the described 48V system low-voltage battery charging control method to control the charging of the low-voltage battery in the 48V mild hybrid system.

[0016] The advantages of the present invention are as follows: Without using the EBS battery sensor, the charging control of the low-voltage battery can be realized, which saves costs while ensuring reliable control and high cost performance; The control scheme fully controls the charging, discharging, energy recovery, BSG assistance and other working conditions of the low-voltage battery, and the entire charging control logic is more reliable and meets the requirements of the charging control of the low-voltage battery. Brief Description of the Drawings

[0017] The following briefly describes the content expressed in each drawing of the specification of the present invention and the marks in the drawings:

[0018] Figure 1 It shows the connection relationship between the components in the low-voltage battery charging control system of the present invention. Detailed Embodiments

[0019] The following further details the specific embodiments of the present invention by describing the optimal embodiments with reference to the drawings.

[0020] The present invention provides a method for completing the charging control of a low-voltage battery without using an EBS battery sensor, thereby saving costs and meeting the use of charging, energy recovery, BSG assistance and other working conditions of the low-voltage battery. The specific solution is as follows:

[0021] Such as Figure 1As shown, the 48V system of this application refers to a 48V mild hybrid system, including a 48V battery system and a 12V low-voltage battery system. It mainly aims at how to achieve the charging control of the low-voltage battery after canceling the EBS of the 12V low-voltage battery. The main method of this application is that after the vehicle starts, the engine control system EMS calls the low-voltage battery charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network. The DCDC converter obtains the target voltage of the low-voltage battery through the CAN network and controls the DCDC converter to output the target voltage to charge the low-voltage battery; the low-voltage battery charging MAP is a pre-calibrated charging relationship table with the charging voltage as a variable.

[0022] Among them, the engine control system EMS obtains and calculates a voltage value at the moment when the vehicle is powered on. This voltage value is the voltage of the low-voltage battery at the moment of power-on. After the power-on is completed, due to the influence of 48V and the generator, etc., the voltage obtained by the EMS will be different from the voltage of the low-voltage battery. Therefore, the voltage of the low-voltage battery can be obtained at the moment of power-on, and then based on this voltage, the estimation of the battery's power can be realized. Furthermore, based on the estimation of the power, the low-voltage battery can be charged through the charging MAP, thus realizing the charging of the low-voltage battery. How to charge the battery when the voltage of the low-voltage battery at the moment of power-on is obtained is the main feature of this application, which specifically includes:

[0023] After the vehicle is powered on, ChargMAP is used to control the charging of the low-voltage battery. The low-voltage battery charging MAP includes ChargMAP, and ChargMAP is the relationship between the initial voltage of the low-voltage battery, the charging time, and the charging target voltage; under different initial voltages, there will be corresponding relationships between different charging times and charging target voltages. It is a three-dimensional corresponding relationship, which can be a relationship comparison table or a comparison curve. The comparison table can divide the time more finely, and it also has high accuracy in the case of small time and voltage intervals. Table 1 is a schematic diagram of the relationship of ChargMAP. The specific values are not written in the table, only for illustration:

[0024] Table 1

[0025]

[0026] When the vehicle is in the driving condition, the EMS reads the voltage value at the moment of power-on through the engine control system EMS at the moment when the system is just powered on and uses it as the initial voltage of the low-voltage battery when the low-voltage battery is powered on. After obtaining the initial voltage, the EMS calls ChargMAP to obtain the target voltage that changes with time at the initial voltage and sends the target voltage to the CAN network. The DCDC converter receives the target voltage on the CAN network and controls the output of the target voltage to the low-voltage battery. As shown in Table 1, when the initial voltage is V2, the relationship between the time corresponding to V2 and the target voltage is obtained by querying Table 1. During the process of the time changing from T1 to T3, the target voltage will also change according to the corresponding table, and the DCDC is controlled with this voltage to charge the low-voltage battery. ChargMAP can be formed by collecting and calibrating the working conditions of the low-voltage battery equipped with an EBS sensor. Charging the low-voltage battery immediately based on the MAP after power-on ensures that the power of the low-voltage battery is within the set charging range, thus realizing the charging guarantee of the low-voltage battery and avoiding the occurrence of power shortage.

[0027] At the initial voltage, the target voltage gradually decreases with the increase of time until the target voltage decreases to the set threshold voltage. ChargMAP calibrates the relationship among the initial voltage, time and target voltage through pre-tests. After reaching the set threshold voltage, the charging ends, thus ensuring that the low-voltage battery starts to be charged at power-on and ensuring the power safety of the low-voltage battery.

[0028] In a preferred embodiment, the set voltage threshold satisfies the following conditions during calibration: the set threshold voltage is converted into the SOC of the low-voltage battery according to the pre-calibrated relationship between the battery voltage and the SOC. At this time, the battery SOC corresponding to the set voltage threshold is less than the full-charge SOC and the difference is the set margin threshold. The purpose of setting the margin threshold and not charging the low-voltage battery is to enable the low-voltage battery to recover part of the energy recovered by braking when the 48V battery is in a full-charge or high-power state during the energy recovery stage. The set margin threshold corresponding to the difference between the battery SOC corresponding to the set voltage threshold and the full-charge SOC is 15-20%. ChargMAP is calibrated according to the actual vehicle of the battery to ensure that the battery SOC is 75-85%. According to the battery capacity and the instantaneous energy situation of the 48V system, 15-20% of the battery capacity of the low-voltage battery is used for energy recovery and energy storage, improving the energy recovery utilization rate.

[0029] When the vehicle is in the energy recovery mode, monitor the state of the 48V battery SOC. If the power of the 48V battery is higher than the set SOC threshold, the EMS calls ReChargMAP to obtain the target voltage of the low-voltage battery during energy recovery and sends it to the DCDC converter via the CAN network for energy recovery control to charge the low-voltage battery; where ReChargMAP is a correspondence table of the target voltage varying with time.

[0030] ReChargMAP forms the relationship between the corresponding target voltages varying with the energy recovery time through pre-calibration; where the starting voltage of ReChargMAP is greater than the set threshold voltage to ensure that the energy recovered is used to charge the low-voltage battery. As shown in Table 2, the relationship between the energy recovery time and the energy recovery target voltage under the calibrated set voltage threshold is obtained, so that during the energy recovery stage, the corresponding energy recovery target voltage is obtained by looking up the table according to time, and then the low-voltage battery is charged with the recovered energy:

[0031] Table 2:

[0032] Charging time DCDC target voltage

[0033] As the charging time increases, the energy recovery target voltage (i.e., the DCDC target voltage) gradually decreases until it reaches the cut-off voltage corresponding to full charge, so as to complete the purpose of stopping step-down operation when fully charged (stopping the energy recovery function for charging the low-voltage battery), or after the charging time reaches a certain time threshold, the DCDC converter stops step-down operation to stop charging the low-voltage battery.

[0034] When in the BSG boosting mode, control the DCDC converter to be in the boosting working state, boost the low-voltage battery and jointly provide current with the 48V battery to assist the BSG. When the DCDC converter is boosting to jointly assist the BSG, it stops working to assist the BSG after the working time of the DCDC converter reaches the set time threshold.

[0035] This patent provides a control technology for the charging strategy of the low-voltage battery in a 48V system. For the 48V + 12V dual-voltage system solution adopted by the 48V system, the low-voltage battery needs to be charged during the driving condition and assist in recovering part of the energy during the energy recovery condition. Currently, the biggest bottleneck in the development of 48V technology by enterprises is the high cost. For the dual-voltage system, intelligent battery sensors EBS are adopted in the production models, with a relatively high cost. Aiming at this practical problem, this patent aims to pursue cost performance, saves an intelligent battery sensor and the corresponding wiring harness, and develops a control technology for the charging strategy of the low-voltage battery in a 48V system, and controls the charging of the low-voltage battery through a strategy.

[0036] Overall technical solution: Whether in the driving condition or the energy recovery condition, the EMS calls the charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network architecture; the DCDC receives this target voltage and performs dynamic control of the voltage at the DCDC output terminal 1 to charge the low-voltage battery.

[0037] When the vehicle is in the driving condition, according to the EMS to obtain the state of charge of the low-voltage battery, the EMS calls the ChargMAP and sends the charging voltage requirement of the low-voltage battery to the CAN network architecture. The DCDC receives this signal and the DCDC performs output to the target voltage control of the battery. When the vehicle is in the energy recovery condition, if the 48V battery management system BMS sends that the 48V battery SOC is at a relatively high level, the EMS calls the ReCharg MAP and sends the charging voltage requirement of the low-voltage battery to the CAN network, and the DCDC performs energy recovery charging for the low-voltage battery. In the 48V BSG boosting condition, the DCDC performs low-voltage to high-voltage work, that is, raises the voltage of the low-voltage battery and jointly provides current with the 48V battery to the BSG for boosting.

[0038] A control technology for the charging strategy of the low-voltage battery in a 48V system. Whether in the driving condition or the energy recovery condition, the EMS calls the charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network architecture; the DCDC receives this target voltage and performs dynamic control of the voltage at the DCDC output terminal 1 to charge the low-voltage battery.

[0039] When the vehicle is in the driving condition, the EMS calculates the battery voltage through the built-in circuit of the system engine controller EMS when the vehicle system is just powered on, and estimates the state of charge of the battery through the calculation logic. Based on the initial battery voltage value, the EMS calls the ChargMAP (a three-dimensional MAP about the DCDC conversion voltage relationship under different initial battery voltages and charging times), and sends the charging voltage requirement of the low-voltage battery (this voltage requirement changes with the charging time) to the CAN network architecture. The DCDC receives this signal and the DCDC performs output to the target voltage control of the battery; at a certain initial battery voltage, the required voltage of the ChargMAP gradually decreases with time, that is, at the beginning of time t1, a high voltage is used to charge the low-voltage battery, and then it gradually decreases over time t until the required voltage balances with the low-voltage battery voltage and the charging automatically ends. This voltage needs to be finely calibrated according to the relationship between the battery voltage and the SOC, and a certain battery capacity is reserved for use in the energy recovery condition; since after the vehicle starts and runs, the 48V generator BSG generates electricity for the vehicle's low-voltage power supply and supplies power to the vehicle system through DCDC conversion, generally there is no need for the low-voltage battery to supply power. Therefore, the above logic can keep the low-voltage battery in the driving condition at a relatively high state of charge.

[0040] When the whole vehicle is in the energy recovery working condition, if the 48V battery management system (BMS) sends a signal indicating that the state of charge (SOC) of the 48V battery is relatively high, the engine management system (EMS) receives this signal through the CAN network. The EMS then calls the ReCharg MAP (a two-dimensional MAP regarding the DCDC conversion voltage relationship under charging time), and sends the low-voltage battery charging voltage requirement to the CAN network. The DCDC then conducts energy recovery charging for the low-voltage battery. The voltage of the ReCharg MAP is higher than that of the Charg MAP, by approximately 0.4 - 0.7V. The specific value is determined according to the instantaneous withstand voltage of the low-voltage battery.

[0041] In the 48V BSG boosting working condition, the DCDC performs low-voltage to high-voltage conversion, that is, it raises the voltage of the low-voltage battery and jointly provides current with the 48V battery to the BSG for boosting. Specifically, the DCDC needs to set a reasonable time threshold. Only when the charge of the high-voltage battery is relatively sufficient can the DCDC perform the boosting operation. This logic is mainly to ensure that the low-voltage battery always dynamically retains a certain capacity (15 - 20% of the low-voltage battery capacity) to receive the low-voltage battery charging during the energy recovery working condition (when coasting at high speed and during forced braking, the 48V battery is easily fully charged, and at this time the low-voltage battery receives additional energy to improve energy utilization efficiency).

[0042] It should be specifically noted that the implementation scheme only illustrates the logical idea. The specific low-voltage charging Charg MAP / ReCharg MAP, as well as the charging voltage threshold, need to be specifically measured and calibrated to a reasonable value in combination with the vehicle weight, 48V battery capacity, BSG charging current, and low-voltage battery attributes, and then verified on the whole vehicle.

[0043] Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made using the method concept and technical solution of the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for controlling the charging of a low-voltage battery in a 48V system, characterized in that: After the vehicle is started, the engine management system (EMS) calls the low-voltage battery charging MAP to obtain the target voltage of the low-voltage battery and sends it to the CAN network. The DCDC converter obtains the target voltage of the low-voltage battery through the CAN network and controls the DCDC converter to output the target voltage to charge the low-voltage battery; the low-voltage battery charging MAP is a pre-calibrated charging relationship table with the charging voltage as a variable. The low-voltage battery charging MAP includes ChargMAP, and ChargMAP is the relationship among the initial voltage of the low-voltage battery, the charging time, and the charging target voltage. When the vehicle is in the driving condition, when the system is just powered on, the EMS reads the voltage value read at the moment of power-on through the engine management system (EMS) and uses it as the initial voltage of the low-voltage battery when the low-voltage battery is powered on. The EMS calls ChargMAP to obtain the target voltage that changes with time at the initial voltage and sends the target voltage to the CAN network. The DCDC converter receives the target voltage on the CAN network and controls the output of the target voltage to the low-voltage battery.

2. The low-voltage battery charging control method for a 48V system according to claim 1, characterized in that: At the initial voltage, the target voltage gradually decreases with the increase of time until the target voltage decreases to the set threshold voltage in ChargMAP. The relationship among the initial voltage, time, and target voltage in ChargMAP is calibrated through pre-tests.

3. The 48V system low-voltage battery charging control method according to claim 2, characterized in that: The set threshold voltage satisfies the following conditions during calibration: according to the pre-calibrated relationship between the battery voltage and the state of charge (SOC), the set threshold voltage is converted into the SOC of the low-voltage battery. At this time, the battery SOC corresponding to the set threshold voltage is less than the full charge SOC, and the difference is the set margin threshold.

4. A 48V system low-voltage battery charging control method according to any one of claims 1-3, characterized in that: When the vehicle is in the energy recovery condition, monitor the state of the 48V battery SOC. If the power of the 48V battery is higher than the set SOC threshold, the EMS calls ReChargMAP to obtain the target voltage of the low-voltage battery during energy recovery and sends it to the DCDC converter through the CAN network for energy recovery control to charge the low-voltage battery; where ReChargMAP is a corresponding relationship table of the target voltage changing with time.

5. The 48V system low-voltage battery charging control method according to claim 4, characterized in that: ReChargMAP forms the relationship between the corresponding target voltages changing with the energy recovery time through pre-calibration; the starting voltage of ReChargMAP is greater than the set threshold voltage to ensure that the energy recovered is used to charge the low-voltage battery.

6. A 48V system low-voltage battery charging control method according to any one of claims 1-3, characterized in that: In the BSG boosting condition, control the DCDC converter to be in the boost working state, boost the low-voltage battery, and jointly provide current with the 48V battery to boost the BSG.

7. A 48V system low-voltage battery charging control method according to claim 6, characterized in that: When the DCDC converter is boosting jointly to boost the BSG, the DCDC converter stops working to boost the BSG after working for the set time threshold.

8. The 48V system low-voltage battery charging control method according to claim 3, wherein: The set margin threshold corresponding to the difference between the battery SOC corresponding to the set threshold voltage and the full charge SOC is 15 - 20%.

9. An automobile, characterized in that: The vehicle uses a method for controlling the charging of the low-voltage battery in a 48V system as described in any one of claims 1 - 8 to control the charging of the low-voltage battery in the 48V mild hybrid system.

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