Thermal protection control method

Abstract

The invention discloses a thermal protection control method, which solves the problem of loss of power caused by zero torque output of a whole vehicle due to overheating of a motor of an electric vehicle under the working conditions of frequent rapid acceleration and rapid deceleration in the prior art, and comprises the following steps of: collecting actual current when a motor controller operates, and calculating a current actual hot melting quantity value; if the actual hot melting quantity value exceeds the heat capacity upper limit value, calculating a derating coefficient according to the actual current at the beginning of derating, and starting current derating until the current derating reaches a sustainable operation current point; and when the actual current value is lower than the sustainable operation current, the I2t value begins to recover, and the current amplitude limiting value is gradually released according to the integral coefficient. When the accumulation amount of the heat capacity value of the motor system reaches the upper limit, derating needs to be carried out to a sustainable operation current point, and the situation that the whole vehicle outputs zero torque and loses power due to overheat of the motor under the working conditions of frequent rapid acceleration and rapid deceleration is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of thermal management control of motor controllers, and in particular to a thermal protection control method. Background Art

[0002] The motor controller is a device that controls the forward and reverse rotation of the motor and the speed and torque of the motor. It plays an important role in the field of new energy vehicles. In the existing motor controller technology, the current threshold is set. When the current exceeds the current threshold, the corresponding protection action is taken to reduce the torque limit.

[0003] However, with the development of electric vehicles, the vehicle has increasingly higher requirements for thermal management control of motor controllers. The temperature sensor measurement value of the motor stator is not necessarily the highest temperature point in the stator winding. If thermal protection is only performed through the motor stator temperature threshold, it will affect the life of key components such as the three-phase current copper busbar. In addition, under extreme conditions of frequent rapid acceleration and deceleration, excessive motor temperature will cause the vehicle to drop to zero torque and lose power, resulting in a very poor user experience. Summary of the invention

[0004] The purpose of the present invention is to solve the problem in the prior art that electric vehicles suffer from motor overheating under frequent rapid acceleration and deceleration conditions, resulting in the whole vehicle outputting zero torque and losing power. A thermal protection control method is provided. When it is determined that the accumulated thermal melt value of the motor system has reached an upper limit, it is necessary to reduce the current to a sustainable operating current point to avoid the motor overheating under frequent rapid acceleration and deceleration conditions, resulting in the whole vehicle outputting zero torque and losing power.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A thermal protection control method based on I2t thermal model comprises the following steps: Collect the actual current when the motor controller is running and calculate the current actual hot melt value; If the actual hot melt value exceeds the upper limit of the hot melt value, the derating factor is calculated according to the actual current at the beginning of the derating, and the limiting current decreases linearly according to the derating factor until the current is reduced to the sustainable operating current point; When the actual current value is lower than the sustainable operating current, the current limit begins to recover and the current limit value is gradually released according to the loss standard.

[0006] The method of the present invention protects the life of the three-phase AC copper busbar by determining that the accumulated amount of the thermal melt value of the motor system reaches an upper limit and needs to be derated to a sustainable operating current point without relying on a temperature sensor. At the same time, it can achieve operation at a sustainable operating current point by thermally protecting the current integral under frequent rapid acceleration and deceleration conditions, thereby avoiding the whole vehicle from outputting zero torque and losing power.

[0007] Preferably, if the actual hot melt value of the motor controller is less than the upper limit of the hot melt value, the limiting current is the peak current. If the current hot melt value of the motor controller increases to between the upper limit of the hot melt value and the maximum value of the hot melt value, the limiting current gradually decreases from the peak current to the sustainable operating current according to the derating factor; when the actual current value is lower than the sustainable operating current, the current hot melt value decreases, and the limiting current recovers to the peak current.

[0008] Preferably, the square of the actual current is integrated, and in the process of repeatedly increasing and decreasing the torque, when the current actual thermal melt value increases from 0, the integral value is initialized by the motor stator temperature; when the power is turned on and off quickly, if derating protection is required, the integral value is initialized according to the motor stator temperature.

[0009] Preferably, the difference between the square of the current actual phase current and the square of the sustainable operating current is calculated to obtain a first difference, the difference between the maximum thermal melt value and the upper limit of the thermal melt value is calculated to obtain a second difference, and the derating factor is obtained according to the ratio of the first difference to the second difference.

[0010] Preferably, the motor stator temperature is collected in real time, and if the motor stator temperature is greater than a first threshold, the integral value is calculated.

[0011] Preferably, the actual thermal melt value is the product of the difference between the square of the actual phase current and the square of the sustainable operating current, an integral coefficient and an integral time, and the integral coefficient is a loss standard.

[0012] Preferably, a fixed value of the upper limit of the hot melt amount is set as a reference value of the loss standard, and the time to reach the upper limit of the hot melt amount at different rotation speeds and different phase currents is recorded. The product of the loss standard and the time is equal to the ratio of the upper limit of the hot melt amount to the difference.

[0013] Preferably, at each water temperature and flow rate, the torque is increased at the rated speed point, starting from a current of x and increasing by x / 2 every t minutes, until the stator temperature stabilizes within a threshold range at the end of t minutes, and the current value at this time is used as the sustainable operating current.

[0014] Preferably, under normal water flow and water temperature conditions, the motor is preheated when the stable water temperature is equal to the stator temperature. When the motor temperature exceeds a preset second threshold, a peak current is output. When the stator temperature reaches 90% of the over-temperature threshold, the upper limit of the hot melt amount is calculated based on the output peak current at this time. When the stator temperature reaches 95% of the over-temperature threshold, the maximum value of the hot melt amount is calculated based on the output peak current at this time.

[0015] Preferably, if the actual hot melt value exceeds the maximum hot melt value, a fault alarm is issued.

[0016] Therefore, the present invention has the following beneficial effects: 1. When it is determined that the accumulated thermal melt value of the motor controller has reached the upper limit, it is necessary to derate to the sustainable operating current point, without relying on the temperature sensor, to protect the life of the three-phase AC copper busbar, and at the same time avoid overheating of the motor under frequent rapid acceleration and deceleration conditions, resulting in zero torque output and loss of power for the vehicle.

[0017] 2. When the torque is frequently increased or decreased and the power is turned on and off quickly, the actual thermal melt value can be initialized by the motor stator temperature to avoid the problem of motor overheating caused by re-integrating the current. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the overall steps of the thermal protection control method of the motor controller in Example 1.

[0019] Figure 2 This is a schematic diagram of the actual heat melting value calculation in Example 2.

[0020] Figure 3 This is a schematic diagram of the derating control principle in the second embodiment. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: Embodiment 1: This embodiment provides a thermal protection control method, such as Figure 1 As shown, the operation process is as follows: Step 1, collect the actual current when the motor controller is running, and calculate the current actual hot melt value; Step 2, if the actual hot melt value exceeds the upper limit of the hot melt value, calculate the derating factor according to the actual current at the beginning of the derating, and limit the current linearly according to the derating factor until the current is reduced to the sustainable operating current point; Step 3, when the actual current value is lower than the sustainable operating current, the limiting current begins to recover, and according to the standard of the loss, the current limit value is gradually released.

[0022] The thermal protection control method provided in this embodiment is mainly aimed at the thermal management control of the motor controller. It uses the I2t thermal model. When it is determined that the accumulated thermal melt value of the motor system has reached the upper limit, the current is reduced to a sustainable operating current point. It does not rely on temperature sensors and can protect the life of the three-phase AC copper busbar. At the same time, it can avoid overheating of the motor under frequent rapid acceleration and deceleration conditions, resulting in zero torque output and loss of power for the entire vehicle.

[0023] The following further illustrates the technical solution and technical effects of the present invention through specific examples and specific application scenarios. The following examples are explanations of the present invention and the present invention is not limited to the following examples.

[0024] The present embodiment provides a thermal protection control method, the basic idea of ​​which is to integrate the square of the motor current to calculate the current actual thermal melt value, and when the actual thermal melt value reaches the threshold, the current derating is started until the current is derated to the sustainable operating current point. When the actual current is lower than the sustainable operating current, the current limit begins to recover, and the current limit value is gradually released according to the integral coefficient.

[0025] The technical problem to be solved is: thermal protection of the motor controller through the motor stator temperature threshold will affect the life of key components such as the three-phase current copper busbar. In addition, under extreme conditions of frequent rapid acceleration and deceleration, excessive motor temperature will cause the entire vehicle to drop to zero torque and lose power, resulting in an extremely poor user experience.

[0026] Specifically, Figure 1 As shown, a thermal protection control method specifically includes the following steps: Step 1: Collect the actual current I when the motor controller is running act , calculate the current actual hot melt value.

[0027] Mainly include: (1) Collect the actual current I when the motor controller is running act , calculate the square of the actual current during operation

[0028] Among them, the square of the actual current is the D-axis current I dact and the square of the Q-axis current.

[0029] (2) Determine the sustainable operating current I const , calculate the square of the sustainable operating current

[0030] At each water temperature and flow rate, the torque is increased at the rated speed point. From the current x, the current increases by x / 2 every t minutes until the stator temperature of the motor stabilizes within the threshold range at the end of the nth t minutes. The current value at this time is taken as the sustainable operating current I const Because the temperature rise value is close to stability after about 15 minutes and is basically close to 90% of the stable temperature point, in this embodiment, t is preferably 15 minutes, which can obtain a stable temperature value without wasting resources due to too long testing time.

[0031] It should be noted that the prerequisite for calculating the sustainable operating current is that the vehicle can provide water temperature and flow data or the MCU is capable of estimating the sustainable operating current.

[0032] (3) Calculate the current actual hot melt value I 2 t act .

[0033] In this embodiment, the current actual hot melt value is calculated by integrating the square of the actual motor current, that is, the current actual hot melt value I 2 t act is the square of the actual phase current The square of the sustainable operating current The difference and the integral coefficient K i The product obtained by integrating the time T.

[0034] The integral coefficient is related to the speed and the actual phase current I act Record different speeds w and different actual phase currents I act Reaching the upper limit of hot melt value I 2 t der Time T wait , calculate the difference between the square of the actual phase current and the square of the sustainable operating current and the time T wait The product of the upper limit of hot melt volume and the ratio of the product is the integral coefficient.

[0035] After multiple calculations, we get K i (w, ΔI 2 ) table, where ΔI 2 It is the difference between the square of the actual phase current and the square of the sustainable operating current.

[0036] Specifically, let the X-axis be the speed w and the Y-axis be ΔI 2 , Z is K i According to the above test method, the corresponding integral coefficient K under different speeds and different currents can be obtained. i , forming a table. Then, when it is needed later, the integral coefficient can be obtained by looking up the table.

[0037] That is, when the square of the phase current Greater than the square of the sustainable operating current Temperature rise will occur when the phase current is squared. Lower than the square of the sustainable operating current The temperature will drop, so the phase current is squared. and the square of the sustainable operating current The actual thermal melting value I of the current motor system is obtained by integrating the difference 2 t act .

[0038] In this embodiment, the motor stator temperature is collected in real time, and the I2t integration is enabled only when the motor stator temperature is greater than 85 degrees Celsius.

[0039] Step 2: If the actual hot melt value exceeds the upper limit of the hot melt value, calculate the derating factor based on the actual current at the beginning of the derating, and limit the current to decrease linearly according to the derating factor until the current is reduced to the sustainable operating current point.

[0040] Derating is a measure to reduce the maximum allowable current of the motor system. 2 t act Exceeding the upper limit of hot melt I 2 t der (i.e. protection threshold), limiting current I limit The microcontroller unit MCU obtains the corresponding phase current command according to the torque request. If the phase current command value exceeds the limit current, the current command is executed according to the limit current, which means that the phase current request value in this embodiment cannot exceed the limit value.

[0041] This embodiment also includes calculating the upper limit value of the hot melt amount and the maximum value of the hot melt amount, and the calculation process is: Set the upper limit value of hot melt volume I 2 t der The fixed value is set as the temperature rise cumulative value of the peak power point under normal water temperature of 25 degrees and flow rate of 8L / min in this embodiment, that is, the integral coefficient K is set i =1, the current at the peak power point is I max Under normal water flow and water temperature conditions, the motor is preheated when the stable water temperature is equal to the stator temperature. When the motor stator temperature exceeds the second threshold, the peak current I max , until the electronic stator temperature reaches 90% of the over-temperature threshold, the hot melt value is calculated by integration, and the upper limit of the hot melt value is recorded. This value is the value for starting derating; when the motor stator temperature reaches 95% of the over-temperature threshold, the hot melt value is calculated by integration, and the maximum hot melt value is recorded. This value is the value that the hot melt value cannot exceed. If this value is exceeded, a fault should be reported.

[0042] Determine whether the current actual hot melt value is greater than the upper limit of the hot melt value. If not, the current limiting current is the peak current. If so, determine whether the current actual hot melt value is less than the maximum value of the hot melt value. If so, if the current actual hot melt value is greater than or equal to the maximum value of the hot melt value, a fault alarm is issued.

[0043] The derating factor is calculated according to the actual current when the derating is started, rather than using a fixed value. In this embodiment, the derating factor K is: the difference between the square of the current actual phase current and the square of the sustainable operating current is calculated to obtain a first difference; the difference between the maximum hot melt value and the upper limit of the hot melt value is calculated to obtain a second difference; the ratio of the first difference to the second difference is calculated to obtain the derating factor.

[0044] Step 3: When the actual current value is lower than the sustainable operating current, the current limit begins to recover and the current limit value is gradually released according to the integral coefficient.

[0045] When the limiting current gradually decreases from the peak current to the sustainable operating current according to the derating factor K, if the current actual hot melt value decreases to less than the upper limit of the hot melt value, the limiting current begins to gradually return to the peak current.

[0046] This embodiment also includes assigning an initial value to the thermal melt value according to the stator temperature to avoid the problem that the thermal melt value drops to 0 after derating and re-integration may cause overheating of the motor.

[0047] The thermal protection control method provided in this embodiment has the following beneficial effects: 1. When it is determined that the accumulated thermal melt value of the motor controller has reached the upper limit, it is necessary to derate to the sustainable operating current point, without relying on the temperature sensor, to protect the life of the three-phase AC copper busbar, and at the same time avoid overheating of the motor under frequent rapid acceleration and deceleration conditions, resulting in zero torque output and loss of power for the vehicle.

[0048] 2. In frequent rapid acceleration and deceleration conditions, the vehicle can be operated at a sustainable operating current point through thermal protection to avoid zero torque output and loss of power.

[0049] Embodiment 2: This embodiment provides a thermal protection control method, which is mainly based on the I2t thermal model. By integrating the square of the motor current, when it is determined that the accumulated thermal melt value of the motor system has reached the upper limit, it is necessary to derate to a sustainable operating current point. It does not rely on temperature sensors, and protects the life of the three-phase AC copper busbar. At the same time, it avoids overheating of the motor under frequent rapid acceleration and deceleration conditions, resulting in zero torque output and loss of power for the entire vehicle.

[0050] The basic idea of ​​I2t is to integrate the square of the motor current. When the integral value reaches the threshold, the current is reduced until the current is reduced to the sustainable operating current point. When the actual current is lower than the sustainable operating current, the I2t value begins to recover, and the current limit value is gradually released according to the integral coefficient. The idea of ​​I2t reflects the relationship between heat generation and thermal melting. The integral coefficient K i It reflects the heat generation, the sustainable operating current reflects the initial value of thermal melting at different temperatures, the threshold for derating reflects the protective thermal melting point of the motor system, and the threshold for the end of derating reflects the maximum thermal melting point of the motor system.

[0051] This embodiment provides a thermal protection control method based on the I2t thermal model, including I2t actual thermal melt value calculation and I2t derating control. Figure 3 As shown, the current melting value I 2 t actExceeding the upper limit of hot melt I 2 t der Gradually increase to the maximum heat melting amount I 2 t top When the current limit I limit (When the protection threshold is not triggered, it is the peak current value) and gradually decreases from the peak current to the corresponding sustainable current I const Similarly, when the actual current I act Becomes smaller, smaller than the sustainable current I const When the current hot melt value I 2 t act Reduce, limit the current I limit It then begins to gradually recover to the peak current.

[0052] Specific: (1) Calculation of actual I2t melting value.

[0053] like Figure 2 As shown, the calculation of the actual hot melt value of I2t includes: calculating the square of the actual current and calculating the square of the sustainable operating current, wherein the sustainable operating current reflects the initial value of the hot melt at different temperatures; setting the integral coefficient, and calculating the actual hot melt value according to the I2t integral.

[0054] The specific calculation process is: The actual thermal melting value calculation formula of the current motor controller is: In the formula, is the square of the actual phase current, and is also the DQ axis current I dact and I qact The sum of the squares of is the square of the sustainable operating current, K i is the integration coefficient, the integration coefficient K i reflects the heat generation, T is the integration time, I 2 t act It is the current actual hot melt value.

[0055] The current hot melt value calculation process can also be seen Figure 2 As shown in the figure, K i Calculate the square of the sustainable current Calculation, 85℃ enable detailed description as follows: I const Selection method.

[0056] At each water temperature T cool and flow rate F coolAt the rated speed point, increase the torque by 50A every fifteen minutes starting from 100A, until the stator temperature is between 130℃ and 140℃ at the end of fifteen minutes (at about 15 minutes, the temperature rise value is close to stable, and is basically close to 90% from the stable temperature point), and the current value at this time is used as the long-term operating current.

[0057] That is, the current increases by 50A every fifteen minutes. After each fifteen minutes, determine whether the motor stator temperature is between 130℃ and 140℃. If so, the current value at this time is used as the long-term operating current. Otherwise, continue to increase the current by 50A. After fifteen minutes, determine again whether the motor stator temperature is between 130℃ and 140℃, until after a certain fifteen minutes, the motor stator temperature is between 130℃ and 140℃, and the current value at this time is used as the long-term operating current.

[0058] This value can sustain the running current I const Relationship with water temperature and flow rate f(F cool , T cool ) The premise is that the vehicle can provide water temperature and flow data or the MCU is capable of estimating the value.

[0059] (1.2)I 2 t der / I 2 t top / K i Selection method.

[0060] Integration coefficient K i In this embodiment, the value is set as the loss standard. Under the same current, the integral coefficient K i The larger the value, the greater the loss and the faster the temperature rise. The loss coefficient usually refers to the loss factor in the motor system, which is used to indicate the proportion of energy loss during power transmission.

[0061] First, set the upper limit value of the hot melt amount I 2 t der The fixed value is used as the reference value of the loss standard. It can be set as the accumulated value of the temperature rise at the peak power point under normal water temperature of 25 degrees and flow rate of 8L / min, that is, set the integral coefficient K i =1, the current at the peak power point is I max Under normal water flow and water temperature conditions, the motor is preheated when the stable water temperature is equal to the stator temperature. When the motor temperature exceeds 75°C, the peak current I max Until the stator temperature reaches 90% of the over-temperature threshold, it is recorded as the upper limit value of the thermal melt I 2 t der, this value is the value for starting derating, which reflects the protective thermal melting point of the motor system. When the stator temperature reaches 95% of the over-temperature threshold, it is recorded as I 2 t top Value, this value is the value that the I2t integral cannot exceed. The value that the I2t integral cannot exceed reflects the maximum thermal melting point of the motor system. If this value is exceeded, an I2t fault should be reported.

[0062] The upper limit value of the hot melt volume recorded in the above process is I 2 t der and maximum heat melting amount I 2 t top are fixed values, so the following test will only change the integral coefficient K i .

[0063] The testing process is: Because K i Value vs. Speed ​​and I act Therefore, different speeds w and different actual current values ​​I are recorded. act Reaching the upper limit of hot melt value I 2 t der Time T wait .

[0064] After obtaining the above data, calculate the integral coefficient K i :

[0065] Substitute the calculation formula of the integral coefficient into the above calculation formula of the actual hot melt value to obtain the actual hot melt value.

[0066] (2)I2t derating control.

[0067] After obtaining the parameters, when the derating threshold is triggered, Figure 3 Derating protection is performed as shown. Figure 3 The figure shows the I2t derating process. During the I2t derating process, the upper limit value of the hot melt I 2 t der As the thermal melt value at which the motor controller system needs to start derating, when the accumulated thermal melt value reaches this value, it is considered that the thermal melt value of the motor controller system has almost reached the upper limit and needs to be derated. The value at which I2t starts derating is set to a fixed value I 2 t der , I2t termination derating means the maximum thermal melt value of the motor system is set to a fixed value I 2 t top .

[0068] The specific calculation process is: If the actual hot melt value of the motor controller system is less than the upper limit value of hot melt I 2t der , limiting current I limit is the peak current; if the current motor controller system thermal melt value increases to the thermal melt upper limit value I 2 t der and maximum heat melting amount I 2 t top When the current is between limit According to the derating factor K, the current is gradually reduced from the peak current to the sustainable operating current I const (If the integral value keeps increasing, the maximum current limit will drop to the sustainable operating current point).

[0069] The calculation formula is as follows:

[0070] When the actual thermal melt value of the motor controller system decreases and is lower than the two upper limits of the thermal melt value I 2 t der , limiting current I limit Gradually returns to the peak current.

[0071] In this embodiment, when designing the derating factor, the derating factor K is calculated according to the actual current when the derating is started, rather than adopting a fixed value and adapting to the current actual current request value.

[0072] If the derating factor K is a fixed value, it may cause a relatively large torque drop in the first cycle of derating. Therefore, the derating factor K value can be calculated by locking the actual current at the moment of derating start. The calculation formula is as follows:

[0073] Substitute the K value into the formula The thermal protection limiting current I can be obtained by calculation. limit .

[0074] The result of the above formula can be used to draw a derating curve. The obtained derating curve is related to the starting current when derating. If the starting current is larger, the derating curve is steeper, and the smaller the starting current is, the derating curve is gentler.

[0075] This embodiment also includes: giving a heat melting amount upper limit value I according to the stator temperature 2 t act Assign initial value to avoid upper limit value of hot melt after derating I 2 t act If it drops to 0, re-integration may cause the motor to overheat.

[0076] Specifically, when the motor system operates at normal temperature, I2t does not need to consider the limiting problem. In this embodiment, an 85°C enabling link is added to the I2t design. When the motor stator temperature is greater than 85°C, I2t integration is enabled. At the same time, in the process of repeatedly increasing and decreasing the torque, when the square of the actual phase current I 2 t act When increasing from 0, the integral is initialized by the motor stator temperature to prevent the square of the actual phase current I after derating. 2 t act The value of the input voltage is reduced to 0, but the motor stator temperature has not dropped below 85°C. Re-integration may cause the motor to overheat.

[0077] It should be noted that 85℃ is required for both normal operation and extreme working conditions.

[0078] The initial value of the upper limit of the heat melting amount corresponding to different motor stator temperatures can be calculated offline and made into a table. During operation, the initial value of the integral can be assigned according to the motor stator temperature.

[0079] This embodiment can also perform I2t protection when rapid power on and off occurs.

[0080] Under more extreme working conditions, the motor may experience I2t derating due to high temperature. The user may power off the vehicle and then power it back on quickly. Without special processing, the integral will be initialized to 0, but the motor is still actually at a high temperature, and I2t will lose its protection capability.

[0081] If I2t derating protection is required when power is turned on and off again, the integral will be initialized according to the stator temperature to avoid motor overheating caused by re-integration.

[0082] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A thermal protection control method, characterized in that: include: Collect the actual current when the motor controller is running and calculate the current actual hot melt value; If the actual hot melt value exceeds the upper limit of the hot melt value, the derating factor is calculated according to the actual current at the beginning of the derating, and the limiting current decreases linearly according to the derating factor until the current is reduced to the sustainable operating current point; When the actual current value is lower than the sustainable operating current, the current limit begins to recover and the current limit value is gradually released according to the loss standard.

2. A thermal protection control method according to claim 1, characterized in that: If the actual hot melt value of the motor controller is less than the upper limit of the hot melt value, the limiting current is the peak current. If the current hot melt value of the motor controller increases to between the upper limit of the hot melt value and the maximum value of the hot melt value, the limiting current gradually decreases from the peak current to the sustainable operating current according to the derating factor; when the actual current value is lower than the sustainable operating current, the current hot melt value decreases, and the limiting current recovers to the peak current.

3. A thermal protection control method according to claim 1, characterized in that: Integrate the square of the actual current. In the process of repeatedly increasing and decreasing the torque, when the current actual thermal melt value increases from 0, the integral value is initialized by the motor stator temperature. When the power is turned on and off quickly, if derating protection is required, the integral value is initialized according to the motor stator temperature.

4. A thermal protection control method according to claim 1, 2 or 3, characterized in that: The difference between the square of the current actual phase current and the square of the sustainable operating current is calculated to obtain a first difference, the difference between the maximum thermal melt value and the upper limit of the thermal melt value is calculated to obtain a second difference, and the derating factor is obtained according to the ratio of the first difference to the second difference.

5. A thermal protection control method according to claim 3, characterized in that: The motor stator temperature is collected in real time, and if the motor stator temperature is greater than a first threshold, the integral value is calculated.

6. A thermal protection control method according to claim 1, 2 or 3, characterized in that: The actual thermal melt value is the product of the difference between the square of the actual phase current and the square of the sustainable operating current, the integral coefficient and the integral time, and the integral coefficient is the loss standard.

7. A thermal protection control method according to claim 6, characterized in that: Set a fixed value for the upper limit of hot melt volume as a reference value for the loss standard, and record the time to reach the upper limit of hot melt volume at different rotation speeds and different phase currents. The product of the loss standard and the time is equal to the ratio of the upper limit of hot melt volume to the difference.

8. A thermal protection control method according to claim 1, characterized in that: At each water temperature and flow rate, the torque is increased at the rated speed point, starting from a current of x and increasing by x / 2 every t minutes until the stator temperature stabilizes within the threshold range at the end of t minutes. The current value at this time is used as the sustainable operating current.

9. A thermal protection control method according to claim 1 or 2 or 3 or 5 or 8, characterized in that: Under normal water flow and water temperature conditions, the motor is preheated when the stable water temperature is equal to the stator temperature. When the motor temperature exceeds the preset second threshold, the peak current is output. When the stator temperature reaches 90% of the over-temperature threshold, the upper limit of the hot melt amount is calculated based on the output peak current at this time. When the stator temperature reaches 95% of the over-temperature threshold, the maximum value of the hot melt amount is calculated based on the output peak current at this time.

10. A thermal protection control method according to claim 1 or 2 or 3 or 5 or 8, characterized in that: If the actual hot melt value exceeds the maximum hot melt value, a fault alarm will be issued.

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