Battery thermal management system and control method and device of water pump in battery thermal management system

Abstract

The invention belongs to the technical field of battery external heat management systems, and particularly relates to a battery heat management system and a control method and device of a water pump in the battery heat management system. Comprising the steps that after the starting time of a refrigeration mode of the battery thermal management system exceeds the set starting time, the duty ratio of a water pump in a water circulation loop of the battery thermal management system is adjusted according to the relation between the pressure of the low-pressure side of a compressor in a refrigerant loop of the thermal management system and the duty ratio of the water pump, and therefore the rotating speed of the water pump is controlled; the relation includes that when the pressure of the low-pressure side of the compressor is larger than a high-pressure threshold value, the duty ratio of the water pump is a set refrigeration low duty ratio; when the low-pressure side pressure of the compressor is smaller than a low-pressure threshold value, the duty ratio of the water pump is the set refrigeration high duty ratio; and when the low-pressure-side pressure of the compressor is larger than or equal to the low-pressure threshold value and smaller than or equal to the high-pressure threshold value, the higher the low-pressure-side pressure is, the smaller the corresponding water pump duty ratio is. The rotating speed of the water pump can be adjusted according to the low-pressure side pressure of the compressor, and energy consumption is reduced while the refrigeration effect is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery external thermal management systems, and in particular relates to a battery thermal management system and a control method and device for a water pump therein. Background Art

[0002] In the prior art, the thermal management system of the battery system is controlled by using temperature, temperature difference and other related data to control the rotation speed of the water pump. However, since the thermal management system of the battery system includes two circulation pipelines, the water circulation loop and the refrigerant loop, and the two circulation pipelines exchange heat through a heat exchanger, the two circulation pipelines need to cooperate with each other to achieve a better cooling effect. When the refrigerant flow rate in the refrigerant loop is slow, it cannot exchange heat with the water circulation loop in time, which will cause the temperature of the water circulation loop to be high. At this time, even if the flow rate of the water pipeline is increased, the cooling capacity of the thermal management system cannot be significantly improved. On the contrary, it will increase the energy consumption of the water pump in the water circulation loop. Summary of the invention

[0003] The object of the present invention is to provide a battery thermal management system and a control method and device for a water pump therein, so as to solve the technical problem of energy waste caused by mismatched flow rates of two pipelines in the thermal management system in the prior art.

[0004] In order to solve the above technical problems, the present invention provides a method for controlling a water pump in a battery thermal management system, the method comprising:

[0005] After the battery thermal management system starts the cooling mode beyond the set start time, the low-pressure side pressure of the compressor in the refrigerant circuit is obtained, and the water pump duty cycle of the water pump in the water circulation circuit is adjusted according to the relationship between the low-pressure side pressure and the water pump duty cycle, thereby controlling the speed of the water pump;

[0006] The relationship includes: when the low-pressure side pressure is greater than the high-pressure threshold, the water pump duty cycle is the set cooling low duty cycle; when the low-pressure side pressure is less than the low-pressure threshold, the water pump duty cycle is the set cooling high duty cycle; when the low-pressure side pressure is greater than or equal to the low-pressure threshold and less than or equal to the high-pressure threshold, the greater the low-pressure side pressure, the smaller the water pump duty cycle;

[0007] The low cooling duty cycle is set to be smaller than the high cooling duty cycle; the high pressure threshold is larger than the low pressure threshold; the high cooling duty cycle is set to make the water pump run at a higher speed, and the low cooling duty cycle is set to make the water pump run at a lower speed that does not affect the cooling capacity.

[0008] Furthermore, the low-pressure threshold is a calibrated value, and the low-pressure side pressure of the compressor corresponding to the operation of the water pump at a set refrigeration high duty cycle under the maximum cooling capacity of the thermal management system is calibrated as the low-pressure threshold.

[0009] Furthermore, the high-pressure threshold is a calibrated value, and the low-pressure side pressure of the compressor corresponding to the operation of the water pump at a set refrigeration low duty cycle according to the water pump duty cycle under the minimum cooling capacity of the thermal management system is calibrated as the high-pressure threshold.

[0010] Furthermore, within a set startup time after the cooling mode of the battery thermal management system is started, the water pump is adjusted to operate according to a water pump duty cycle set to a set startup duty cycle, and the set startup duty cycle is used to make the water pump operate at a higher speed.

[0011] Furthermore, when the low-pressure side pressure of the compressor is greater than or equal to the low-pressure threshold and less than or equal to the high-pressure threshold, there is a linear negative correlation between the low-pressure side pressure and the water pump duty cycle.

[0012] Furthermore, after the heating mode of the battery thermal management system is started, the water pump is first adjusted to operate according to the water pump duty cycle as the set heating high duty cycle; when the difference between the target water outlet temperature and the actual water outlet temperature of the heater of the water circulation loop of the thermal management system is less than or equal to the first set difference, the water pump is adjusted to operate according to the water pump duty cycle as the set heating low duty cycle; when the difference between the water outlet temperature and the target temperature is greater than or equal to the second set difference, the water pump stops running after the delayed set shutdown time; the set heating high duty cycle is greater than the set heating low duty cycle, the heating high duty cycle is set as the duty cycle for making the water pump run at a higher speed, and the heating low duty cycle is set as the duty cycle for making the water pump run at a lower speed.

[0013] Furthermore, when the battery thermal management system is in the self-circulation mode, the duty cycle of the water pump is adjusted so that the water pump runs at the set self-circulation speed.

[0014] The present invention is a pioneering invention, and its beneficial effects are as follows: the control method of the water pump in the battery thermal management system of the present invention proposes a new technical solution for adjusting the water pump signal duty cycle of the thermal management system according to the low-pressure side pressure of the compressor, thereby adjusting the water pump speed. The low-pressure side pressure of the compressor reflects the speed of the compressor to a certain extent. The lower the low-pressure side pressure, the higher the compressor speed. Therefore, by adjusting the water pump duty cycle according to the low-pressure pressure of the compressor, the water pump speed and the compressor speed can be matched. When the compressor speed is low, the low-pressure side pressure is high. The control method of the present invention controls the water pump speed not to be too high. When the compressor speed is high, the low-pressure side pressure is low. The water pump control method of the present invention controls the water pump speed not to be too low, ensuring that the water pump speed matches the compressor speed, preventing energy loss caused by mismatched speeds, and improving the energy utilization rate of the thermal management system. In addition, the present invention limits the duty cycle of the water pump. When the pressure on the low-pressure side is higher than the high-pressure threshold, the duty cycle of the water pump is set to a low refrigeration duty cycle and will no longer decrease; when the pressure on the low-pressure side is lower than the low-pressure threshold, the duty cycle of the water pump is set to a high refrigeration duty cycle and will no longer increase; the water pump duty cycle is prevented from reaching unreasonable limit values, thereby ensuring the normal operation of the water pump.

[0015] To solve the above technical problems, the present invention also provides a control device for a water pump in a battery thermal management system, comprising a processor, which implements the method steps described in the control method for a water pump in a battery thermal management system of the present invention when executing a computer program.

[0016] The present invention is a pioneering invention, and its beneficial effects are the same as those of the method for controlling a water pump in a battery thermal management system of the present invention, and will not be described again here.

[0017] In order to solve the above technical problems, the present invention also provides a battery thermal management system, including a water circulation circuit, a refrigerant circuit and a water pump control device, the water circulation circuit is provided with a water pump and a heater, the refrigerant circuit is provided with a compressor, the water circulation circuit and the refrigerant circuit perform heat exchange through a heat exchanger, and the water pump control device includes a processor, and the processor implements the method steps described in the water pump control method in the battery thermal management system of the present invention when executing a computer program.

[0018] The present invention is a pioneering invention, and its beneficial effects are the same as those of the method for controlling a water pump in a battery thermal management system of the present invention, and will not be described again here. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of a battery thermal management system of a system embodiment of the present invention;

[0020] Figure 2is a schematic diagram of a battery thermal management system of a system embodiment of the present invention;

[0021] Figure 3 is a graph showing the relationship between the duty cycle and the water pump speed of a system embodiment of the present invention;

[0022] Figure 4 is a diagram showing the relationship between the duty cycle of the water pump and the pressure on the low-pressure side of the compressor in the refrigeration mode of the system embodiment of the present invention;

[0023] Figure 5 It is a schematic diagram of water pump speed regulation in heating mode of a system embodiment of the present invention. DETAILED DESCRIPTION

[0024] A battery thermal management system and a control method and device for a water pump therein of the present invention propose a new technical solution for adjusting the water pump signal duty cycle of the thermal management system according to the low-pressure side pressure of the compressor, thereby adjusting the water pump speed. The low-pressure side pressure of the compressor reflects the speed of the compressor to a certain extent. The lower the low-pressure side pressure, the higher the compressor speed. Therefore, by adjusting the water pump duty cycle according to the low-pressure pressure of the compressor, the water pump speed and the compressor speed can be matched. When the compressor speed is low, the low-pressure side pressure is high. The control method of the present invention controls the water pump speed not to be too high. When the compressor speed is high, the low-pressure side pressure is low. The water pump control method of the present invention controls the water pump speed not to be too low, thereby ensuring that the water pump speed matches the compressor speed, preventing energy loss caused by mismatched speeds, and improving the energy utilization rate of the thermal management system. In addition, the present invention limits the duty cycle of the water pump. When the pressure on the low-pressure side is higher than the high-pressure threshold, the duty cycle of the water pump is set to a low refrigeration duty cycle and will no longer decrease; when the pressure on the low-pressure side is lower than the low-pressure threshold, the duty cycle of the water pump is set to a high refrigeration duty cycle and will no longer increase; the water pump duty cycle is prevented from reaching unreasonable limit values, thereby ensuring the normal operation of the water pump.

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] System Example:

[0027] The main function of the battery thermal management system (TMS) is to respond to the battery's cooling or heating request, cool down or heat up the battery system, and make the battery system work within a suitable temperature range (usually 20-35°C). It communicates with the battery management system BMS in real time and exchanges information. Common working modes include cooling mode, heating mode, self-circulation mode, shutdown mode, etc. When the battery temperature triggers the temperature threshold set by the battery management system BMS, the battery management system BMS sends a mode command request to the battery thermal management system TMS.

[0028] The structure of the battery thermal management system TMS of this embodiment is as follows: Figure 1 As shown, it includes two circulation pipelines, a water circulation pipeline and a refrigerant circulation pipeline. The two pipelines exchange heat through a heat exchanger. The water circulation pipeline is used to heat the battery system ( Figure 1 The cooling and centering of the battery pack) mainly includes a water pump, a PTC heater, a heater outlet water temperature sensor T1 and a battery pack outlet water temperature sensor T2; the refrigerant pipeline mainly includes a compressor, a condenser, a low-pressure pressure sensor P1, a high-pressure pressure sensor P2, a low-pressure charging valve V1, a high-pressure charging valve V2, an exhaust temperature sensor T3 and an expansion valve TXV.

[0029] The battery thermal management system also includes a water pump control device, which includes a processor. When executing a computer program, the processor is used to control the water pump in the external liquid cooling system of the battery pack using the following battery thermal management system water pump control method.

[0030] The water pump control method of the battery thermal management system of the present invention includes controlling the water pump in three modes: cooling, heating and self-circulation. In different modes, the working conditions of the components in the thermal management system are as follows: Figure 2 shown.

[0031] Generally, the rated power of the water pump configured in the vehicle-mounted battery cooling system is between 200W and 400W, and the rated power of the water pump configured in the energy storage battery cooling system is between 200W and 4000W; from the above data, the power consumption of the water pump is relatively large. Therefore, under the premise of meeting the battery cooling and heating requirements, different operating modes need to give the water pump a more reasonable operating logic to save the power consumption of the water pump and achieve the purpose of energy saving. In order to achieve the purpose of energy saving, the control method of the water pump in the battery thermal management system of the present invention includes:

[0032] 1. Control method of water pump in cooling mode.

[0033] In the cooling mode of the battery thermal management system TMS, both the water pump compressor and the condensing fan need to work. The control of the water pump in the cooling mode includes: when the TMS receives the cooling mode instruction and the cooling target temperature sent by the BMS to enter the cooling mode, after entering the cooling mode, the water pump is adjusted to run according to the water pump duty cycle as the set start duty cycle in the first 60s (set start time), and the start duty cycle is set to a value that can make the water pump speed close to or equal to the maximum speed, which is 90% in this embodiment; after 60s (set start time), the water pump duty cycle is adjusted according to the relationship between the water pump duty cycle and the low pressure of the compressor of the refrigerant circuit of the water cooling system, thereby adjusting the water pump speed.

[0034] Take a certain brand of variable frequency water pump on the market as an example: the working voltage of the water pump is DC18-32V (rated voltage DC24V), and PWM control mode (voltage: 24V, frequency: 250Hz) is adopted, that is, the water pump speed is adjusted by adjusting the duty cycle of the water pump control signal. The relationship between the water pump duty cycle and the water pump speed is as follows: Figure 3 When the duty cycle of the water pump is 0%-15%, the corresponding water pump speed is 0, which is a shutdown command; when the duty cycle of the water pump is 15%-20%, the corresponding water pump speed is the minimum speed of the water pump; when the duty cycle of the water pump is 90%-100%, the corresponding water pump speed is the maximum speed of the water pump; the interval of the water pump duty cycle of 20%-90% is a linear speed regulation interval, and within this interval, the higher the duty cycle, the higher the water pump speed.

[0035] The relationship between the water pump duty cycle and the low-pressure side pressure of the compressor used in this embodiment is as follows: Figure 4 As shown, Figure 4 The middle fluorine circuit is the refrigerant circuit, and the low pressure on the fluorine circuit side is the pressure on the low pressure side of the compressor. Figure 4 and Figure 3 It can be seen that the greater the pressure on the low-pressure side of the compressor, the smaller the corresponding water pump duty cycle and the lower the water pump speed. When the low-pressure side pressure of the compressor is greater than the high-pressure threshold, the duty cycle of the water pump control signal is reduced to the set refrigeration low duty cycle of 60% and no longer decreases; when the low-pressure side pressure of the compressor is lower than the low-pressure threshold of the low-pressure side, the duty cycle of the water pump control signal is the set refrigeration high duty cycle (90%) and no longer increases, and the set refrigeration high duty cycle is greater than the set refrigeration low duty cycle; the high-pressure threshold is greater than the low-pressure threshold.

[0036] The high refrigeration duty cycle is set to a value that can make the water pump speed close to the maximum speed of the water pump, which is generally the minimum duty cycle corresponding to the maximum speed of the water pump. In this embodiment, the high refrigeration duty cycle is set to 90%, at which time the water pump speed is equal to the maximum speed of the water pump. In actual use, the high refrigeration duty cycle, the low refrigeration duty cycle, and the start time can be set as needed. The low refrigeration duty cycle is set to a duty cycle that allows the water pump to run at a lower speed without affecting the cooling capacity. It needs to be determined through experimental verification, that is, fixing factors such as the compressor speed, fan speed, and ambient temperature, setting different water pump duty cycles, and calibrating the inflection point where a certain duty cycle does not have much effect on the cooling capacity, that is, setting the low refrigeration duty cycle.

[0037] When the cooling mode is just started, the battery pack needs to be quickly cooled and cooled, and the system cooling capacity is mainly determined by the water pump speed. Therefore, in this embodiment, within the set startup time after the cooling mode is started, the water pump duty cycle is adjusted to set the startup duty cycle so that the water pump runs at a speed close to the maximum speed of the water pump, and the battery is cooled as soon as possible. After the thermal management system has been running for a period of time, the temperature of the water circulation loop rises, and the cooling capacity of the system is limited by the compressor speed. When the compressor speed is low, even if the water pump speed is increased, the system cooling capacity will not be greatly improved, but the energy consumption will be increased. Therefore, the present invention reflects the compressor speed through the compressor low-pressure side pressure (the higher the compressor speed, the lower the low-pressure side pressure), and adjusts the water pump duty cycle according to the compressor low-pressure side pressure, thereby adjusting the water pump speed. When the compressor low-pressure side pressure is high (the compressor speed is low), the water pump duty cycle will not be too large, so as to control the water pump speed not to be too large, so as to prevent the water pump speed from being too large when the compressor speed is low, which not only wastes energy but also fails to significantly increase the cooling capacity. Similarly, when the pressure on the low-pressure side of the compressor is low (the compressor speed is high), the water pump duty cycle will not be too small and thus the water pump speed will not be too low.

[0038] In this embodiment, the low-pressure threshold A and the high-pressure threshold B are calibration values. The specific calibration method is: make the unit work at the maximum cooling capacity, adjust the water pump to operate according to the water pump duty cycle to set the high cooling duty cycle, record the corresponding low-pressure side pressure of the compressor at this time, and use the low-pressure side pressure value as the low-pressure side low-pressure threshold A; make the unit work at the minimum cooling capacity, record the corresponding low-pressure side pressure of the compressor when the water pump duty cycle is set to the low cooling duty cycle, and use this pressure as the low-pressure side high-pressure threshold B. As other implementation methods, the high-pressure threshold and the low-pressure threshold can also be set according to actual engineering experience.

[0039] After determining the low-pressure threshold A on the low-pressure side and the high-pressure threshold B on the low-pressure side, the relationship between the water pump duty cycle and the low-pressure side pressure of the compressor can be obtained. In this embodiment, between the low-pressure threshold A and the high-pressure threshold B, the relationship between the water pump duty cycle and the low-pressure side pressure is a linear relationship, such as Figure 4 As shown, by directly connecting the two points corresponding to the high-pressure threshold and the low-pressure threshold on the low-pressure side in the coordinate system, a linear relationship with a negative correlation between the water pump duty cycle and the low-pressure side pressure of the compressor can be obtained.

[0040] 2. Control of water pump in heating mode.

[0041] In the heating mode of the battery thermal management system TMS, only the PTC heater and the water pump need to work, and the compressor and the condensing fan in the refrigerant circuit do not work.

[0042] When TMS receives the heating instruction and the target temperature of heating sent by BMS, the water pump is operated according to the water pump duty cycle of the high value of heating. In this embodiment, the high duty cycle of heating is set to 90%, and the corresponding speed of the water pump is the maximum speed. When the difference between the target temperature and the outlet water temperature of the PTC heater of the thermal management system is less than or equal to the first difference threshold a, at this time, the outlet water temperature of the heater is about to reach the target outlet water temperature, and it is no longer necessary to use a higher heating rate for heating. The water pump is adjusted to operate according to the water pump duty cycle of the low duty cycle of heating. At this time, the water pump speed is low, which can reduce the energy consumption of the water pump and prevent the outlet water temperature from being too high in advance. In this embodiment, the low duty cycle of heating is set to 20%, and the corresponding speed of the water pump is the minimum speed, so as to reduce the heating efficiency of the battery pack, prevent the outlet water temperature from being too high, and reduce the energy consumption of the water pump. In actual use, the high duty cycle of heating is set to a value that can make the water pump speed close to the maximum speed of the water pump, which can ensure that the battery is heated at a higher heating rate after the heating mode is started. The heating low duty cycle is set to a value that can make the water pump speed close to the minimum water pump speed. The specific values ​​of the heating high duty cycle and the heating low duty cycle can be set according to actual needs.

[0043] When the difference between the outlet water temperature and the target temperature is greater than or equal to the second difference threshold b, the outlet water temperature exceeds the target temperature. To prevent the outlet water temperature from being too high and to reduce system energy consumption, the PTC heater stops heating, and the water pump stops running after a delay of 2 minutes (set downtime).

[0044] In heating mode, the relationship between the pump duty cycle and the outlet water temperature is as follows: Figure 5 As shown in the figure, T 目标 is the target water temperature for heating, T 出水 It is the outlet water temperature of the PTC heater in the water circulation loop of the thermal management system.

[0045] 3. Control of the water pump in self-circulation mode.

[0046] In the self-circulation mode, the difference between the TMS outlet water temperature and the actual temperature is not large, and neither heating nor cooling is required. Therefore, you only need to turn on the water pump. After multiple cooling water cycles, the TMS outlet water temperature can be equal to the real-time temperature.

[0047] In the self-circulation mode of this embodiment, the duty cycle of the self-circulation mode of the water pump is adjusted, and the specific duty cycle value is 70%. As for other implementation methods, the specific self-circulation mode duty cycle can be set according to actual needs.

[0048] Method Example:

[0049] The specific process, principle, etc. of the control method of the water pump in the battery thermal management system of the present invention have been described in detail in the system embodiment, and will not be repeated in this embodiment.

[0050] Device Example:

[0051] The water pump control device of the battery thermal management system of the present invention includes a processor, and the processor implements the method steps described in the system embodiment when executing the computer program. The specific process, principle, etc. of the method have been described in detail in the system embodiment, and will not be repeated in this embodiment.

[0052] The processor may be any type of processor such as MCU or FPGA.

[0053] A battery thermal management system and a control method and device for a water pump therein of the present invention control the duty cycle of the water pump according to the pressure on the low-pressure side of the compressor on the refrigerant pipeline, thereby adjusting the speed of the water pump, matching the speed of the water pump with the speed of the compressor, improving energy utilization efficiency, and preventing energy waste caused by mismatching the speeds of the two. Furthermore, within the set startup time after the cooling mode is started, the present invention adjusts the water pump to operate at a set startup duty cycle so that the water pump speed is close to or equal to the maximum speed, thereby improving the speed at which the battery system dissipates heat. Furthermore, in the heating mode, the present invention adjusts the duty cycle of the water pump according to the difference between the target temperature and the outlet water temperature of the thermal management system, so that the outlet water temperature of the thermal management system is close to the target temperature, while reducing the energy consumption of the water pump.

Claims

1. A method for controlling a water pump in a battery thermal management system, characterized in that: The method includes: After the battery thermal management system starts the cooling mode beyond the set start time, the low-pressure side pressure of the compressor in the refrigerant circuit is obtained, and the water pump duty cycle of the water pump in the water circulation circuit is adjusted according to the relationship between the low-pressure side pressure and the water pump duty cycle, thereby controlling the speed of the water pump; The relationship includes: when the low-pressure side pressure is greater than the high-pressure threshold, the water pump duty cycle is the set cooling low duty cycle; when the low-pressure side pressure is less than the low-pressure threshold, the water pump duty cycle is the set cooling high duty cycle; when the low-pressure side pressure is greater than or equal to the low-pressure threshold and less than or equal to the high-pressure threshold, the greater the low-pressure side pressure, the smaller the water pump duty cycle; The low cooling duty cycle is set to be smaller than the high cooling duty cycle; the high pressure threshold is larger than the low pressure threshold; the high cooling duty cycle is set to make the water pump run at a higher speed, and the low cooling duty cycle is set to make the water pump run at a lower speed that does not affect the cooling capacity.

2. The method for controlling a water pump in a battery thermal management system according to claim 1, characterized in that: The low-pressure threshold is a calibrated value, and the low-pressure side pressure of the compressor corresponding to the operation of the water pump at a set refrigeration high duty cycle according to the water pump duty cycle under the maximum cooling capacity of the thermal management system is calibrated as the low-pressure threshold.

3. The method for controlling a water pump in a battery thermal management system according to claim 1, characterized in that: The high-pressure threshold is a calibrated value, and the low-pressure side pressure of the compressor corresponding to the operation of the water pump at a set refrigeration low duty cycle according to the water pump duty cycle under the minimum cooling capacity of the thermal management system is calibrated as the high-pressure threshold.

4. The method for controlling a water pump in a battery thermal management system according to claim 1, characterized in that: Within the set startup time after the battery thermal management system cooling mode is started, the water pump is adjusted to operate according to the water pump duty cycle being the set startup duty cycle. The set startup duty cycle is used to make the water pump run at a higher speed.

5. The method for controlling a water pump in a battery thermal management system according to any one of claims 1 to 4, characterized in that: When the low-pressure side pressure of the compressor is greater than or equal to the low-pressure threshold and less than or equal to the high-pressure threshold, there is a linear negative correlation between the low-pressure side pressure and the water pump duty cycle.

6. The method for controlling a water pump in a battery thermal management system according to claim 1, characterized in that: After the heating mode of the battery thermal management system is started, the water pump is first adjusted to operate according to the water pump duty cycle as the set heating high duty cycle; when the difference between the target water outlet temperature and the actual water outlet temperature of the heater of the water circulation loop of the thermal management system is less than or equal to the first set difference, the water pump is adjusted to operate according to the water pump duty cycle as the set heating low duty cycle; when the difference between the water outlet temperature and the target temperature is greater than or equal to the second set difference, the water pump stops running after the delayed set shutdown time; the set heating high duty cycle is greater than the set heating low duty cycle, the heating high duty cycle is set as the duty cycle for making the water pump run at a higher speed, and the heating low duty cycle is set as the duty cycle for making the water pump run at a lower speed.

7. The method for controlling a water pump in a battery thermal management system according to claim 1, characterized in that: When the battery thermal management system is in the self-circulation mode, the water pump duty cycle is adjusted so that the water pump runs at the set self-circulation speed.

8. A control device for a water pump in a battery thermal management system, comprising a processor, characterized in that: The processor implements the steps of the method for controlling a water pump in a battery thermal management system according to any one of claims 1 to 7 when executing the computer program.

9. A battery thermal management system, comprising a water circulation loop, a refrigerant loop and a water pump control device, wherein a water pump and a heater are provided in the water circulation loop, a compressor is provided in the refrigerant loop, the water circulation loop and the refrigerant loop perform heat exchange through a heat exchanger, and the water pump control device comprises a processor, characterized in that: The processor implements the steps of the method for controlling a water pump in a battery thermal management system according to any one of claims 1 to 7 when executing the computer program.

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