Traction motor water cooling system, water cooling method, controller and urban rail vehicle

Abstract

This invention discloses a traction motor water-cooling system, a water-cooling method, a controller, and an urban rail vehicle. The water-cooling system includes a water-cooling unit, a first sensor, a second sensor, and a controller. The water-cooling unit includes a radiator and a cooling fan housed in a cooling tower. The outlet of the radiator is connected to the inlet of the traction motor via a water pump, and the outlet of the traction motor is connected to the inlet of the radiator. The radiator is positioned in the air inlet path of the cooling fan. The controller is used to control the cooling fan to operate at full power when the traction motor temperature is above a temperature threshold, and to control the operating frequency of the cooling fan based on the radiator outlet temperature and the target temperature when the traction motor temperature is below or equal to the temperature threshold, thereby achieving adaptive control of the cooling fan's operating frequency. This invention saves energy, reduces noise, and extends the service life of the water-cooling system while ensuring effective cooling of the traction motor.

Description

Technical Field

[0001] This invention belongs to the field of traction motor water cooling technology, and particularly relates to a traction motor water cooling system, water cooling method, controller and urban rail vehicle. Background Technology

[0002] Traction motors in urban rail vehicles typically employ self-ventilated cooling. Their cooling capacity and efficiency are affected by the vehicle's operating conditions. When the vehicle is running at low speed or the traction motor is running at low speed, the cooling effect is poor, leading to a high temperature rise in the traction motor. This can cause traction motor failure, affecting vehicle operation or the service life of the traction motor.

[0003] With technological advancements, such as permanent magnet direct drive traction motors, the speed of traction motors is relatively low, and the requirements for the power and power density of traction motors are constantly increasing. Traditional self-ventilated heat dissipation methods can no longer meet these demands. Summary of the Invention

[0004] The purpose of this invention is to provide a traction motor water cooling system, water cooling method, controller, and urban rail vehicle, which can provide stable, effective, and operating state-independent heat dissipation for the traction motor of the urban rail vehicle, thereby ensuring the reliability of the traction motor and extending its lifespan. At the same time, it can automatically adjust according to the actual heat load to achieve the optimal cooling effect with the lowest possible energy consumption.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution: a traction motor water cooling system, comprising a water cooling unit, a first sensor, a second sensor, and a controller, wherein the water cooling unit includes a radiator and a cooling fan disposed in a cooling tower, the outlet of the radiator is connected to the inlet of the traction motor via a water pump, and the outlet of the traction motor is connected to the inlet of the radiator; the radiator is disposed in the air inlet path of the cooling fan;

[0006] The first sensor is used to collect the temperature of the traction motor, and the second sensor is used to collect the temperature of the radiator outlet. The controller is used to control the cooling fan to operate at full power when the temperature of the traction motor is greater than the temperature threshold, and to control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature when the temperature of the traction motor is less than or equal to the temperature threshold, so as to realize the adaptive control of the operating frequency of the cooling fan.

[0007] Furthermore, a filter is provided in the air inlet path of the cooling fan, the filter being used to filter the air entering the cooling fan.

[0008] Furthermore, the controller is used to control the cooling fan to operate at full power when the traction motor temperature exceeds a temperature threshold, specifically including:

[0009] When the temperature of the traction motor exceeds the temperature threshold, the operating frequency of the cooling fan is controlled to the rated frequency, so that the cooling fan runs at full power.

[0010] After the cooling fan has been running at full power for a period of time t, it is determined whether the temperature of the traction motor is greater than the temperature threshold. If so, the steps of running the cooling fan at full power for a period of time t and determining whether the temperature of the traction motor is greater than the temperature threshold are repeated. If not, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature to achieve adaptive control of the operating frequency of the cooling fan.

[0011] Furthermore, when the traction motor temperature is less than or equal to the temperature threshold, the operating frequency of the cooling fan is controlled based on the radiator outlet temperature and the target temperature, specifically including:

[0012] After a delay of time t, it is determined whether the radiator outlet temperature is greater than the target temperature. If the radiator outlet temperature is greater than the target temperature, it is determined whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation, it is determined again after a delay of time t. If so, the operating frequency of the cooling fan is controlled to be the sum of the current operating frequency and the frequency deviation.

[0013] If the radiator outlet temperature is less than or equal to the sum of the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant.

[0014] If the radiator outlet temperature is less than or equal to the target temperature, then determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation, then after a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If so, then control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation.

[0015] If the radiator outlet temperature is greater than or equal to the difference between the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant.

[0016] Based on the same concept, the present invention also provides a water-cooling method for a traction motor, implemented based on the traction motor water-cooling system described above, the water-cooling method comprising:

[0017] Step S1: Obtain the temperature of the traction motor;

[0018] Step S2: Determine whether the temperature of the traction motor is greater than the temperature threshold. If yes, proceed to step S3; otherwise, proceed to step S4.

[0019] Step S3: Control the cooling fan to operate at full power.

[0020] Step S4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

[0021] Furthermore, in step S3, controlling the cooling fan to operate at full power specifically includes:

[0022] Step S3.1: Control the operating frequency of the cooling fan to the rated frequency so that the cooling fan operates at full power;

[0023] Step S3.2: Cooling fan full-power operation time t;

[0024] Step S3.3: Obtain the traction motor temperature and determine whether the traction motor temperature is greater than the temperature threshold. If yes, proceed to step S3.2; otherwise, proceed to step S3.4.

[0025] Step S3.4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

[0026] Furthermore, in step S4 or S3.4, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature, specifically including:

[0027] Step S4.1: Obtain the radiator outlet temperature;

[0028] Step S4.2: Delay time t;

[0029] Step S4.3: Determine whether the radiator outlet temperature is greater than the target temperature. If yes, proceed to step S4.4; otherwise, proceed to step S4.6.

[0030] Step S4.4: Determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, proceed to step S4.5; otherwise, proceed to step S4.8.

[0031] Step S4.5: After a delay of time t, determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to the sum of the current operating frequency and the frequency deviation; if no, proceed to step S4.8.

[0032] Step S4.6: Determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, proceed to step S4.7; otherwise, proceed to step S4.8.

[0033] Step S4.7: After a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation; otherwise, proceed to step S4.8.

[0034] Step S4.8: Keep the operating frequency of the cooling fan constant.

[0035] Furthermore, the temperature threshold is the over-temperature warning value for the traction motor.

[0036] Based on the same concept, the present invention also provides a controller for implementing the traction motor water cooling method as described above.

[0037] Based on the same concept, the present invention also provides an urban rail vehicle, wherein each of the cars of the urban rail vehicle is equipped with a traction motor water cooling system as described above, each set of the traction motor water cooling system corresponds to two traction motors on a bogie, and the controller in the traction motor water cooling system is a control unit of the traction converter.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] This invention controls the cooling fan to operate at full power when the traction motor temperature exceeds the temperature threshold, prioritizing the safety of the traction motor, preventing overheating damage, ensuring high reliability, and extending the service life of the traction motor. When the traction motor temperature does not exceed the temperature threshold, the operating frequency of the cooling fan is dynamically adjusted based on the difference between the radiator outlet temperature and the target temperature, achieving on-demand cooling and significantly reducing the average operating power of the cooling fan.

[0040] The dual-loop control proposed in this invention, based on the temperature of the traction motor and the temperature of the radiator outlet, saves energy, reduces noise, and extends the service life of the water cooling system while ensuring the cooling effect of the traction motor, thus achieving the goal of green environmental protection.

[0041] This invention adaptively controls the operating frequency of the cooling fan based on the radiator outlet temperature and the target temperature. Within the temperature range (i.e., target temperature ± temperature deviation), the operating frequency of the cooling fan remains constant. Only when the temperature range is exceeded will the operating frequency of the cooling fan be adjusted, improving system stability and preventing frequent start-stop or oscillation of the cooling fan, thus avoiding energy waste and even damage to the cooling fan. This invention effectively filters out some short-term interference through a delay judgment mechanism, avoiding erroneous adjustments and improving the system's anti-interference capability. This invention uses a fixed frequency deviation for frequency adjustment, making frequency changes smoother, reducing the impact on the cooling fan, and extending the system's lifespan. Attached Figure Description

[0042] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the working principle of the traction motor water cooling system in an embodiment of the present invention;

[0044] Figure 2 This is a control flowchart of the traction motor water cooling method in an embodiment of the present invention. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0047] Example 1

[0048] like Figure 1 As shown, the traction motor water-cooling system provided in this embodiment of the invention includes a water-cooling unit, a first sensor, a second sensor, and a controller. The water-cooling unit includes a radiator and a cooling fan located in a cooling tower. The outlet of the radiator is connected to the inlet of the traction motor via a water pump, and the outlet of the traction motor is connected to the inlet of the radiator. The radiator is located in the air inlet path of the cooling fan. There may be one or more traction motors.

[0049] The first sensor is located on the traction motor and is used to collect the traction motor temperature; the second sensor is located at the radiator outlet and is used to collect the radiator outlet temperature. The controller is used to control the cooling fan to operate at full power when the traction motor temperature is higher than a temperature threshold, and to control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature when the traction motor temperature is lower than or equal to the temperature threshold, thereby achieving adaptive control of the cooling fan operating frequency.

[0050] The controller is used to control the cooling fan to operate at full power when the traction motor temperature exceeds a temperature threshold. Specifically, it includes:

[0051] When the temperature of the traction motor exceeds the temperature threshold, the operating frequency of the cooling fan is controlled to the rated frequency, so that the cooling fan runs at full power.

[0052] After the cooling fan has been running at full power for a period of time t, it is determined whether the temperature of the traction motor is greater than the temperature threshold. If so, the steps of running the cooling fan at full power for a period of time t and determining whether the temperature of the traction motor is greater than the temperature threshold are repeated. If not, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature to achieve adaptive control of the operating frequency of the cooling fan.

[0053] For urban rail vehicles, the normal operating temperature of the traction motor is typically below 150℃, with the over-temperature protection value set at 170℃ and the over-temperature warning value set at 150℃. Setting the over-temperature warning value within the upper limit of the normal operating range allows the system more time (a 20℃ temperature rise margin and time) to issue a warning and take action before reaching the over-temperature protection value. In this embodiment, the temperature threshold is set as the over-temperature warning value of the traction motor, i.e., the temperature threshold is set at 150℃.

[0054] The default operating frequency of the cooling fan when it is powered on is 50% of the rated frequency. For example, if the rated frequency of the cooling fan is 50Hz, then the operating frequency of the cooling fan when it is powered on is 25Hz, and the operating frequency of the cooling fan is controlled to be 50Hz when the traction motor temperature is higher than the temperature threshold.

[0055] Since both traction motor heating and water cooling activation have thermal inertia, meaning it's a slow process, the system waits for the water cooling to take effect by allowing the cooling fan to run at full power for a period of time (i.e., a delay time t). This avoids frequent oscillations in control commands. By controlling the cooling fan's operating frequency to the rated frequency, waiting for activation, and then making a further judgment, the system remains stable and controllable. In this embodiment, the delay time t is set to 5 minutes based on experience.

[0056] In a specific embodiment of the present invention, when the traction motor temperature is less than or equal to a temperature threshold, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature, specifically including:

[0057] After a delay of time t, it is determined whether the radiator outlet temperature is greater than the target temperature. If the radiator outlet temperature is greater than the target temperature, it is determined whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation, it is determined again after a delay of time t. If so, the operating frequency of the cooling fan is controlled to be the sum of the current operating frequency and the frequency deviation.

[0058] If the radiator outlet temperature is less than or equal to the sum of the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant.

[0059] If the radiator outlet temperature is less than or equal to the target temperature, then determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation, then after a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If so, then control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation.

[0060] If the radiator outlet temperature is greater than or equal to the difference between the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant.

[0061] Within the temperature range (i.e., target temperature ± temperature deviation), the operating frequency of the cooling fan remains constant; only when the temperature range is exceeded will the operating frequency of the cooling fan be adjusted, improving system stability and avoiding frequent start-stop or oscillation of the cooling fan, thereby avoiding energy waste or even damage to the cooling fan; the delay judgment mechanism can effectively filter out some short-term interference, avoiding erroneous adjustment and improving the system's anti-interference capability; frequency adjustment with a fixed frequency deviation makes frequency changes smoother, reducing the impact on the cooling fan and extending the system's lifespan.

[0062] In this embodiment, the temperature deviation is set to 3℃, the frequency deviation is set to 5Hz, and the target temperature is set to 55℃.

[0063] In a specific embodiment of the present invention, a filter is provided in the air inlet path of the cooling fan, and the filter is used to filter the air entering the cooling fan.

[0064] Example 2

[0065] like Figure 2 As shown, based on the traction motor water cooling system in Embodiment 1 of the present invention, the present invention provides a traction motor water cooling method comprising the following steps:

[0066] Step S1: Obtain the traction motor temperature; specifically, the traction motor temperature is collected using the first sensor and sent to the controller, which then obtains the traction motor temperature.

[0067] Step S2: The controller determines whether the traction motor temperature is greater than the temperature threshold. If yes, proceed to step S3; otherwise, proceed to step S4 and enter the cooling fan operating frequency adaptive control mode.

[0068] Step S3: Control the cooling fan to operate at full power.

[0069] Step S4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

[0070] In this embodiment, the temperature threshold is set to an over-temperature warning value, such as 150°C.

[0071] In a specific embodiment of the present invention, step S3, controlling the cooling fan to operate at full power, specifically includes:

[0072] Step S3.1: Control the operating frequency of the cooling fan to the rated frequency so that the cooling fan operates at full power;

[0073] Step S3.2: Cooling fan full-power operation time t, i.e. delay time t;

[0074] Step S3.3: Obtain the traction motor temperature and determine whether the traction motor temperature is greater than the temperature threshold. If yes, proceed to step S3.2; otherwise, proceed to step S3.4.

[0075] Step S3.4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

[0076] The default operating frequency of the cooling fan when it is powered on is 50% of the rated frequency. For example, if the rated frequency of the cooling fan is 50Hz, then the operating frequency of the cooling fan when it is powered on is 25Hz, and the operating frequency of the cooling fan is controlled to be 50Hz when the traction motor temperature is higher than the temperature threshold.

[0077] In a specific embodiment of the present invention, in step S3.3, when the temperature of the traction motor is less than or equal to the temperature threshold, a delay time t is applied before proceeding to step S3.4 to enter the adaptive control mode of the cooling fan operating frequency.

[0078] In a specific embodiment of the present invention, step S4 or S3.4, controlling the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature, specifically includes:

[0079] Step S4.1: Obtain the radiator outlet temperature; specifically, use the second sensor to collect the radiator outlet temperature and send it to the controller, which then obtains the radiator outlet temperature.

[0080] Step S4.2: Delay time t;

[0081] Step S4.3: Determine whether the radiator outlet temperature is greater than the target temperature. If yes, proceed to step S4.4; otherwise, proceed to step S4.6.

[0082] Step S4.4: Determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, proceed to step S4.5; otherwise, proceed to step S4.8.

[0083] Step S4.5: After a delay of time t, determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to the sum of the current operating frequency and the frequency deviation; if no, proceed to step S4.8.

[0084] Step S4.6: Determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, proceed to step S4.7; otherwise, proceed to step S4.8.

[0085] Step S4.7: After a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation; otherwise, proceed to step S4.8.

[0086] Step S4.8: Keep the operating frequency of the cooling fan constant.

[0087] In this embodiment, the temperature deviation is set to 3℃, the frequency deviation is set to 5Hz, the target temperature is set to 55℃, and the delay time t is set to 5min.

[0088] Example 3

[0089] This invention provides a traction motor water-cooling system for urban rail vehicles. Each urban rail vehicle is equipped with the traction motor water-cooling system of this invention. Each traction motor water-cooling system corresponds to two traction motors on one bogie. The controller in the traction motor water-cooling system is the control unit of the traction converter, and the traction motor water-cooling control is realized by the control unit of the traction converter.

[0090] The above description only discloses specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or modifications that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A traction motor water-cooling system, characterized in that, The water cooling system includes a water cooling unit, a first sensor, a second sensor, and a controller. The water cooling unit includes a radiator and a cooling fan installed in a cooling tower. The outlet of the radiator is connected to the inlet of the traction motor via a water pump, and the outlet of the traction motor is connected to the inlet of the radiator. The radiator is located in the air inlet path of the cooling fan. The first sensor is used to collect the temperature of the traction motor, and the second sensor is used to collect the temperature of the radiator outlet. The controller is used to control the cooling fan to operate at full power when the temperature of the traction motor is greater than the temperature threshold, and to control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature when the temperature of the traction motor is less than or equal to the temperature threshold, so as to realize the adaptive control of the operating frequency of the cooling fan.

2. The traction motor water-cooling system according to claim 1, characterized in that, A filter is provided in the air inlet path of the cooling fan, and the filter is used to filter the air entering the cooling fan.

3. The traction motor water-cooling system according to claim 1, characterized in that, The controller is used to control the cooling fan to operate at full power when the traction motor temperature exceeds a temperature threshold, specifically including: When the traction motor temperature exceeds the temperature threshold, the operating frequency of the cooling fan is controlled to the rated frequency, so that the cooling fan operates at full power. After the cooling fan has been running at full power for a period of time t, it is determined whether the temperature of the traction motor is greater than the temperature threshold. If so, the steps of running the cooling fan at full power for a period of time t and determining whether the temperature of the traction motor is greater than the temperature threshold are repeated. If not, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature to achieve adaptive control of the operating frequency of the cooling fan.

4. The traction motor water-cooling system according to any one of claims 1 to 3, characterized in that, When the traction motor temperature is less than or equal to the temperature threshold, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature, specifically including: After a delay of time t, it is determined whether the radiator outlet temperature is greater than the target temperature. If the radiator outlet temperature is greater than the target temperature, it is determined whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation, it is determined again after a delay of time t. If so, the operating frequency of the cooling fan is controlled to be the sum of the current operating frequency and the frequency deviation. If the radiator outlet temperature is less than or equal to the sum of the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant. If the radiator outlet temperature is less than or equal to the target temperature, then determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation, then after a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If so, then control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation. If the radiator outlet temperature is greater than or equal to the difference between the target temperature and the temperature deviation, the operating frequency of the cooling fan will be kept constant.

5. A water-cooling method for a traction motor, characterized in that, Based on the traction motor water-cooling system as described in any one of claims 1 to 4, the water-cooling method includes: Step S1: Obtain the temperature of the traction motor; Step S2: Determine whether the temperature of the traction motor is greater than the temperature threshold. If yes, proceed to step S3; otherwise, proceed to step S4. Step S3: Control the cooling fan to operate at full power. Step S4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

6. The water-cooling method for a traction motor according to claim 5, characterized in that, In step S3, controlling the cooling fan to operate at full power includes: Step S3.1: Control the operating frequency of the cooling fan to the rated frequency so that the cooling fan operates at full power; Step S3.2: Cooling fan full-power operation time t; Step S3.3: Obtain the traction motor temperature and determine whether the traction motor temperature is greater than the temperature threshold. If yes, proceed to step S3.2; otherwise, proceed to step S3.

4. Step S3.4: Control the operating frequency of the cooling fan according to the radiator outlet temperature and the target temperature to achieve adaptive control of the cooling fan operating frequency.

7. The traction motor water cooling method according to claim 5 or 6, characterized in that, In step S4 or S3.4, the operating frequency of the cooling fan is controlled according to the radiator outlet temperature and the target temperature, specifically including: Step S4.1: Obtain the radiator outlet temperature; Step S4.2: Delay time t; Step S4.3: Determine whether the radiator outlet temperature is greater than the target temperature. If yes, proceed to step S4.4; otherwise, proceed to step S4.

6. Step S4.4: Determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, proceed to step S4.5; otherwise, proceed to step S4.

8. Step S4.5: After a delay of time t, determine whether the radiator outlet temperature is greater than the sum of the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to the sum of the current operating frequency and the frequency deviation; if no, proceed to step S4.

8. Step S4.6: Determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, proceed to step S4.7; otherwise, proceed to step S4.

8. Step S4.7: After a delay of time t, determine whether the radiator outlet temperature is less than the difference between the target temperature and the temperature deviation. If yes, control the operating frequency of the cooling fan to be the difference between the current operating frequency and the frequency deviation; otherwise, proceed to step S4.

8. Step S4.8: Keep the operating frequency of the cooling fan constant.

8. The traction motor water cooling method according to claim 5, characterized in that, The temperature threshold is the over-temperature warning value for the traction motor.

9. A controller, characterized in that, The controller is used to implement the traction motor water cooling method as described in any one of claims 5 to 8.

10. A type of urban rail vehicle, characterized in that, Each of the urban rail vehicles is equipped with a traction motor water-cooling system as described in any one of claims 1 to 4. Each traction motor water-cooling system corresponds to two traction motors on one bogie. The controller in the traction motor water-cooling system is a control unit of the traction converter.

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