Prediction method for allowable operation duration of oil-filled permanent magnet motor under short-time high-torque overload working condition

Abstract

The invention discloses a method for predicting allowable operation duration of an oil-filled permanent magnet motor under a short-time high-torque overload condition, and belongs to the technical field of motors. The method comprises the steps that a motor loss model considering the temperature influence is established according to the loss characteristics of all components of the oil-filled permanent magnet motor, and the loss model comprises stator copper loss, iron loss, permanent magnet eddy current loss and rotor friction loss; based on a motor loss model, constructing a heat balance factor used for representing a relation between internal heat generation and heat dissipation capability of the permanent magnet motor, and analyzing change characteristics of the heat balance factor under a short-time high-torque overload working condition; according to the heat balance factor, the heat balance state of the oil-filled permanent magnet motor under the short-time high-torque overload working condition is evaluated, and therefore the permissible operation duration of the permanent magnet motor is predicted. According to the method, the loss characteristic of the permanent magnet motor and the balance relation between heat generation and heat dissipation capacity are comprehensively considered, so that accurate prediction of the allowable operation duration of the permanent magnet motor under the short-time high-torque overload condition can be realized.

Description

Technical Field

[0001] This invention belongs to the field of motor technology, specifically relating to a method for predicting the allowable running time of an oil-filled permanent magnet motor under short-term high torque overload conditions based on thermal balance factors. Background Technology

[0002] Permanent magnet motors, as key power equipment in industrial systems, are widely used in metallurgy, petrochemicals, mining, shipbuilding, and new energy fields. With the increasing demands for power density and torque output capacity in industrial equipment, motors often need to withstand torque outputs several times higher than their rated values ​​for short periods during actual operation to meet requirements such as starting, impact loads, and fluctuations in operating conditions. Therefore, the short-term torque overload capability of permanent magnet motors has become an important indicator for measuring their operational safety and reliability. To meet these application requirements, oil-filled permanent magnet motors use oil as a heat sink to cool key components such as windings and cores, thus possessing excellent heat dissipation capabilities and gaining widespread application. However, under short-term high torque overload operating conditions, the copper loss, iron loss, and additional losses inside the permanent magnet motor increase significantly, easily leading to a rapid temperature rise. When the generated heat exceeds its heat dissipation capacity, it may cause problems such as insulation aging, permanent magnet demagnetization, and decreased reliability. Therefore, during short-term high torque overload operation, the internal thermal balance state of the oil-filled permanent magnet motor has a significant impact on its permissible operating time. How to accurately predict the overload operating time based on thermal balance characteristics remains a technical problem that needs to be solved in this field.

[0003] In existing technologies, the assessment of the short-term high-torque overload operating capability of permanent magnet motors often relies on empirical margins, fixed duration limits, or estimations based on thermal models under rated operating conditions. These methods typically assume a relatively simple thermal state change process for permanent magnet motors, making it difficult to accurately reflect the impact of different overload torque levels, initial temperature conditions, and cooling conditions on the heat accumulation process. Especially in the application scenarios of oil-filled permanent magnet motors, due to the dynamic changes in the heat capacity and heat dissipation characteristics of the oil medium, assessment methods based on static parameters struggle to accurately predict the sustainable operating time under short-term high-torque overload conditions. Furthermore, some existing methods focus on post-event monitoring or over-temperature protection control, lacking the ability to effectively predict the remaining safe operating time during overload operation, thus limiting the optimization of permanent magnet motor operation scheduling and protection strategies.

[0004] Therefore, there is an urgent need for a method to accurately predict the short-term high-torque overload operation duration of oil-filled permanent magnet motors, taking into account the thermal balance characteristics of permanent magnet motors. Summary of the Invention

[0005] The purpose of this invention is to address the problem of insufficient accuracy in evaluating the short-term high-torque overload operation duration of oil-filled permanent magnet motors based on empirical margins or static thermal models in the prior art. By fully considering the thermal balance characteristics between the heat generation and heat dissipation capacity inside the motor under overload conditions, this invention proposes a method for predicting the allowable operation duration of oil-filled permanent magnet motors under short-term high-torque overload conditions, thereby providing an effective basis for the formulation of overload operation control and protection strategies for permanent magnet motors.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for predicting the permissible operating time of an oil-filled permanent magnet motor under short-time high-torque overload conditions, the method comprising the following steps:

[0008] S1. Based on the loss characteristics of the stator, rotor and permanent magnet of the oil-filled permanent magnet motor, a motor loss model considering the effect of temperature is established. The loss model includes stator copper loss, iron loss, permanent magnet eddy current loss and rotor friction loss.

[0009] S2, Based on the motor loss model established in step S1, construct a thermal balance factor to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor, and analyze the variation characteristics of the thermal balance factor under short-term torque overload conditions, and fit an expression based on the variation characteristic curve.

[0010] S3. Based on the thermal balance factor constructed in step S2 and the expression fitted according to the change characteristic curve, the thermal balance state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated, thereby predicting the allowable operating time of the permanent magnet motor under short-term high torque overload conditions.

[0011] Furthermore, in step S1, establishing a motor loss model that considers the effect of temperature includes the following steps:

[0012] S11, Establish a stator copper loss model that considers the effect of temperature:

[0013]

[0014] in, It is the number of phases of the motor; The temperature is Motor phase resistance at that time; It is the temperature coefficient of resistance of the motor winding; The temperature is The current flowing through the winding; It is the remanence temperature coefficient of permanent magnets; The temperature at which losses are calculated;

[0015] S12, Establish a stator iron loss separation model that considers the effect of temperature:

[0016]

[0017] in, It is the electrical frequency of the motor; It is the amplitude of magnetic flux density; and It is the empirical coefficient of hysteresis loss; It is an empirical coefficient for additional losses; The temperature is Empirical coefficient for eddy current loss at time; It is the temperature coefficient of the empirical coefficient of eddy current loss;

[0018] S13, Establish the permanent magnet eddy current loss model:

[0019]

[0020] in, It is the conductivity of permanent magnets; It is the volume of the permanent magnet; It is the thickness of the permanent magnet;

[0021] S14, Establish a rotor friction loss model that considers temperature factors:

[0022]

[0023] in, It is the rotational speed, in units of 1000 rad / min; , , , , These are undetermined coefficients; It is Euler's constant.

[0024] Furthermore, in step S2, the thermal balance factor used to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor is constructed, and the variation characteristics of this thermal balance factor under short-term torque overload conditions are analyzed. An expression is then fitted based on the variation characteristic curve. The specific process is as follows:

[0025] The heat balance factor is defined as the ratio of heat dissipated from the surface of the motor to heat generated inside. It takes into account the heat loss and heat transfer characteristics of the motor. The heat balance factor can effectively measure whether the cooling capacity of the motor is sufficient to cope with internal heat generation, especially under dynamic or overload conditions.

[0026] The thermal balance factor is defined as:

[0027]

[0028] in, It is a correction factor; It is the heat transfer coefficient; It is the effective heat dissipation surface area of ​​the motor; This is the temperature difference between the motor surface and the ambient temperature, also known as motor temperature rise; subscript These correspond to the various components in the motor that generate losses, including the stator, rotor, and permanent magnets; It is a component The resulting power loss; It is the average temperature of the motor stator, rotor, and permanent magnets when calculating losses;

[0029] It depends on the cooling method of the motor surface. The value is determined based on the Nusselt number as follows:

[0030]

[0031] in, These are Nusselt numbers; It is the thermal conductivity of the fluid; It is the feature length;

[0032] Total loss is expressed as:

[0033]

[0034] As a correction factor to adjust for deviations under different heat transfer coefficients, this parameter is adjusted through simulation methods, taking into account the known properties of the motor housing. , and As a molecule, the total motor loss The result is then compared with the simulation output; when the motor temperature stabilizes, the motor's cooling power equals its heating power. Thus, the value of the correction factor is obtained;

[0035] Treating the thermal equilibrium factor as a function of time, and considering that cooling conditions affect the thermal equilibrium factor, the formula must include the heat transfer coefficient. By using a fitting method, an approximately linear relationship between the thermal equilibrium factor and time was obtained, and the specific expression is as follows:

[0036]

[0037] in, It is the proportionality coefficient; It's time.

[0038] Furthermore, in step S3, the thermal equilibrium state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated to predict the allowable operating time of the permanent magnet motor under short-term high torque overload conditions; the prediction process is as follows:

[0039] A model based on heat capacity and power balance is used to describe short-term torque overload conditions:

[0040]

[0041] in, It is the total heat capacity of the motor; It's the heat generated by the motor; It is the heat dissipation power of the motor;

[0042] Transforming the expression on the right side of equation (9), we get:

[0043]

[0044] in,

[0045] By substituting equation (8) into equation (10) and simplifying the differential equation, we obtain:

[0046]

[0047] Finally, the solution for the time and temperature rise functions is obtained as follows:

[0048]

[0049] The expression based on the predicted short-term torque overload operating time is:

[0050] .

[0051] The advantages of this invention compared to existing technologies are as follows: This invention provides an accurate prediction method for the allowable operating time of an oil-filled permanent magnet motor under short-term high-torque overload conditions based on a thermal balance factor. By comprehensively considering the loss characteristics of the permanent magnet motor and the balance between heat generation and heat dissipation capacity, it can accurately predict the allowable operating time of the permanent magnet motor under short-term high-torque overload conditions. This invention fully considers the impact of temperature rise changes and cooling condition changes on the heat accumulation process of the permanent magnet motor. Compared with evaluation methods that rely on empirical margins or static thermal models, it improves the adaptability and reliability of the overload operating time prediction results, providing an effective reference for the formulation of overload operation control and protection strategies for permanent magnet motors. In addition, the method of this invention has a clear structure and a relatively simple implementation process, making it easy to integrate with existing permanent magnet motor control systems or monitoring systems. It helps to reduce the risk of insulation aging and demagnetization of permanent magnets caused by thermal imbalance during the operation of oil-filled permanent magnet motors under short-term high-torque overload conditions, and has good engineering application value. Attached Figure Description

[0052] Figure 1 The flowchart shows the method for predicting the allowable running time of an oil-filled permanent magnet motor under short-time high torque overload conditions according to the present invention.

[0053] Figure 2 The figure shows the simulation calculation results of the rotor friction loss of the oil-filled motor considering the temperature effect in Embodiment 1 of the present invention;

[0054] Figure 3 This is a graph showing the relationship between the heat balance factor and the running time under different load conditions in Embodiment 1 of the present invention.

[0055] Figure 4 This is a comparison chart of the predicted running time under a 2x torque overload condition in Embodiment 1 of the present invention and the running time obtained from simulation calculations, where the safe temperature threshold is set to 120°C. ;

[0056] Figure 5 The figures for Embodiment 1 of the present invention are the measured and predicted values ​​of cooling air velocities under 1.5 times torque overload and 2 times torque overload, where the temperature threshold is set to 120°C. . Detailed Implementation

[0057] like Figure 1 As shown in the figure, this embodiment describes a method for predicting the permissible operating time of an oil-filled permanent magnet motor under short-term high torque overload conditions. The method includes the following steps:

[0058] S1. Based on the loss characteristics of the stator, rotor and permanent magnet of the oil-filled permanent magnet motor, a motor loss model considering the effect of temperature is established. The loss model includes stator copper loss, iron loss, permanent magnet eddy current loss and rotor friction loss.

[0059] S2, Based on the motor loss model established in step S1, construct a thermal balance factor to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor, and analyze the variation characteristics of the thermal balance factor under short-term torque overload conditions, and fit an expression based on the variation characteristic curve.

[0060] S3. Based on the thermal balance factor constructed in step S2 and the expression fitted according to the change characteristic curve, the thermal balance state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated, thereby predicting the allowable operating time of the permanent magnet motor under short-term high torque overload conditions.

[0061] Furthermore, in step S1, establishing a motor loss model that considers the effect of temperature includes the following steps:

[0062] S11, Establish a stator copper loss model that considers the effect of temperature:

[0063]

[0064] in, It is the number of phases of the motor; The temperature is Motor phase resistance at that time; It is the temperature coefficient of resistance of the motor winding; The temperature is The current flowing through the winding; It is the remanence temperature coefficient of permanent magnets; The temperature at which losses are calculated;

[0065] S12, Establish a stator iron loss separation model that considers the effect of temperature:

[0066]

[0067] in, It is the electrical frequency of the motor; It is the amplitude of magnetic flux density; and It is the empirical coefficient of hysteresis loss; It is an empirical coefficient for additional losses; The temperature is Empirical coefficient for eddy current loss at time; It is the temperature coefficient of the empirical coefficient of eddy current loss;

[0068] S13, Establish the permanent magnet eddy current loss model:

[0069]

[0070] in, It is the conductivity of permanent magnets; It is the volume of the permanent magnet; It is the thickness of the permanent magnet;

[0071] S14, Establish a rotor friction loss model that considers temperature factors:

[0072]

[0073] in, It is the rotational speed, in units of 1000 rad / min; , , , , These are undetermined coefficients. It is Euler's constant.

[0074] Furthermore, in step S2, the thermal balance factor used to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor is constructed, and the variation characteristics of this thermal balance factor under short-term torque overload conditions are analyzed. An expression is then fitted based on the variation characteristic curve. The specific process is as follows:

[0075] The heat balance factor is defined as the ratio of heat dissipated from the surface of the motor to heat generated inside. It takes into account the heat loss and heat transfer characteristics of the motor. The heat balance factor can effectively measure whether the cooling capacity of the motor is sufficient to cope with internal heat generation, especially under dynamic or overload conditions.

[0076] The thermal balance factor is defined as:

[0077]

[0078] in, It is a correction factor; It is the heat transfer coefficient; It is the effective heat dissipation surface area of ​​the motor; This is the temperature difference between the motor surface and the ambient temperature, also known as motor temperature rise; subscript These correspond to the various components in the motor that generate losses, including the stator, rotor, and permanent magnets; It is a component The resulting power loss; It is the average temperature of the motor stator, rotor, and permanent magnets when calculating losses;

[0079] It depends on the cooling method of the motor surface. The value is determined based on the Nusselt number as follows:

[0080]

[0081] in, These are Nusselt numbers; It is the thermal conductivity of the fluid; It is the feature length;

[0082] Total loss is expressed as:

[0083]

[0084] As a correction factor (correction coefficient), this parameter is adjusted to account for deviations under different heat transfer coefficients. The parameter is adjusted using simulation methods, taking into account the known properties of the motor housing. , and As a molecule, the total motor loss The result is then compared with the simulation output; when the motor temperature stabilizes, the motor's cooling power equals its heating power. Thus, the value of the correction factor is obtained;

[0085] according to Figure 3 The characteristic curve in the equation treats the heat balance factor as a function of time. Since cooling conditions affect the heat balance factor, the formula must include the heat transfer coefficient h. Using a fitting method, an approximately linear relationship between the heat balance factor and time is obtained, as shown in the following expression:

[0086]

[0087] in, It is the proportionality coefficient; It's time.

[0088] Furthermore, in step S3, the thermal equilibrium state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated to predict the allowable operating time of the permanent magnet motor under short-term high torque overload conditions; the prediction process is as follows:

[0089] A model based on heat capacity and power balance is used to describe short-term torque overload conditions:

[0090]

[0091] in, It is the total heat capacity of the motor; It's the heat generated by the motor. It is the heat dissipation power of the motor;

[0092] Transforming the expression on the right side of equation (9), we get:

[0093]

[0094] in,

[0095] By substituting equation (8) into equation (10) and simplifying the differential equation, we obtain:

[0096]

[0097] Finally, the solution for the time and temperature rise functions is obtained as follows:

[0098] (12)

[0099] The expression based on the predicted short-term torque overload operating time is:

[0100] .

[0101] Example 1

[0102] like Figure 1 As shown in the figure, this embodiment describes a method for predicting the permissible operating time of an oil-filled permanent magnet motor under short-term high torque overload conditions. The method includes the following steps:

[0103] S1. Based on the loss characteristics of each component (including stator, rotor and permanent magnet) of the oil-filled permanent magnet motor, a motor loss model considering the effect of temperature is established. The loss model includes stator copper loss, iron loss, permanent magnet eddy current loss and rotor friction loss.

[0104] S2, Based on the motor loss model established in step S1, construct a thermal balance factor to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor, and analyze the variation characteristics of the thermal balance factor under short-term torque overload conditions, and fit an expression based on the variation characteristic curve.

[0105] S3. Based on the thermal balance factor constructed in step S2 and the expression fitted according to the change characteristic curve, the thermal balance state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated, thereby predicting the allowable operating time of the permanent magnet motor under short-term high torque overload conditions.

[0106] Furthermore, in step S1, establishing a motor loss model that considers the effect of temperature includes the following steps:

[0107] S11, Establish a stator copper loss model that considers the effect of temperature:

[0108]

[0109] in, It is the number of phases of the motor; The temperature is Motor phase resistance at that time; This is the temperature coefficient of resistance of the motor windings, which is taken as 0.00393 in Example 1. ; The temperature is The current flowing through the motor windings; This is the temperature coefficient of remanence of the permanent magnet. Because temperature changes will cause the remanence of the permanent magnet to decrease, and in order to maintain torque output, the current needs to be increased, this coefficient will affect the current. In Example 1, the value is taken as -0.0011. ; The temperature at which losses are calculated;

[0110] S12, Establish a stator iron loss separation model that considers the effect of temperature:

[0111]

[0112] in, It is the electrical frequency of the motor; It is the amplitude of magnetic flux density; and These are empirical coefficients for hysteresis loss, which are taken as 0.0032 and 1.98 in Example 1, respectively; It is the empirical coefficient for additional losses, which is 0.00037 in Example 1; The temperature is The empirical coefficient for eddy current loss at room temperature (20°C) is 0.000035 in Example 1. This is the temperature coefficient of the empirical coefficient for eddy current loss, which is taken as -0.00583 in Example 1. ;

[0113] S13, Establish the permanent magnet eddy current loss model:

[0114]

[0115] in, It is the conductivity of permanent magnets; It is the volume of the permanent magnet; It is the thickness of the permanent magnet;

[0116] S14, Establish a rotor friction loss model that considers temperature factors:

[0117] Table 1. Basic Dimensions of the Motor

[0118]

[0119] The rotor friction loss was calculated using Workbench simulation based on the motor parameters in Table 1. Figure 2 .right Figure 2 By fitting the data in the model, a rotor friction loss model considering temperature factors is obtained:

[0120]

[0121] in, It is the rotational speed, in units of 1000 rad / min; , , , , These are undetermined coefficients. It is Euler's constant. In Embodiment 1 of this invention, =-0.392, =71, =0.2295, =0.58, =105.

[0122] Therefore, the rotor friction loss model considering temperature factors described above can be written as:

[0123] .

[0124] Furthermore, in step S2, the thermal balance factor used to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor is constructed, and the variation characteristics of this thermal balance factor under short-term torque overload conditions are analyzed. An expression is then fitted based on the variation characteristic curve. The specific process is as follows:

[0125] The thermal balance factor (TEF) is defined as the ratio of heat dissipated from the motor surface to heat generated internally, taking into account both the motor's heat loss and heat transfer characteristics. The TEF effectively measures whether the motor's cooling capacity is sufficient to handle internal heat generation, especially under dynamic or overload conditions.

[0126] The thermal balance factor is defined as:

[0127]

[0128] in, It is a correction factor; It is the heat transfer coefficient; It is the effective heat dissipation surface area of ​​the motor; This is the temperature difference between the motor surface and the ambient temperature, also known as motor temperature rise; subscript These correspond to the various components in the motor that generate losses, including the stator, rotor, and permanent magnets; It is a component The resulting power loss; It is the average temperature of the motor stator, rotor, and permanent magnets when calculating losses;

[0129] It depends on the cooling method of the motor surface, namely natural convection or forced convection. The value is determined based on the Nusselt number as follows:

[0130]

[0131] in, These are Nusselt numbers; It refers to the thermal conductivity of the fluid; in Example 1, the fluid is air. It is a characteristic length (e.g., the length or diameter of the motor housing);

[0132] Total loss is expressed as:

[0133]

[0134] This parameter, used as a correction factor to adjust for deviations under different heat transfer coefficients, can be adjusted through simulation. The known properties of the motor housing... , and As a molecule, the total motor loss The result is then compared with the simulation output; when the motor temperature stabilizes, the motor's cooling power equals its heating power. Thus, the value of the correction factor is obtained.

[0135] The relationship between the rated load and the thermal balance factor of twice the overload versus time at a wind speed of 12 m / s is shown in the figure below. Figure 3 The results show that the heat balance factor is approximately linearly related to time. Furthermore, heat dissipation conditions affect the heat balance factor. Therefore, by treating the heat balance factor as a function of time and employing a fitting method, an approximately linear relationship between the heat balance factor and time is obtained (this change characteristic is obtained through...). Figure 3 This is reflected in the following specific characteristic: under short-term high-torque overload conditions, the thermal balance factor exhibits a linear relationship with time, and the specific expression is as follows:

[0136]

[0137] in, It is the proportionality coefficient; It's time.

[0138] Furthermore, in step S3, the thermal equilibrium state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated to predict the allowable operating time of the permanent magnet motor under short-term high torque overload conditions; the prediction process is as follows:

[0139] A model based on heat capacity and power balance is used to describe short-term torque overload conditions:

[0140]

[0141] in, It is the total heat capacity of the motor; It's the heat generated by the motor; It is the heat dissipation power of the motor;

[0142] Transforming the expression on the right side of equation (9), we get:

[0143]

[0144] in,

[0145] By substituting equation (8) into equation (10) and simplifying the differential equation, we obtain:

[0146]

[0147] Finally, the solution for the time and temperature rise functions is obtained as follows:

[0148] (12)

[0149] Set the temperature threshold to 120. By comparing the obtained solution with the results obtained from the co-simulation, the results are as follows: Figure 4 Therefore, the expression based on the predicted short-term torque overload operating time is:

[0150]

[0151] Under 1.5x and 2x overload conditions, the temperature threshold is 120°C. The measured values ​​in Example 1 are compared with the results of the present invention as follows: Figure 5 As shown.

[0152] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention. Moreover, the scope of protection of the present invention is not limited thereto. Any variations or substitutions 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 method for predicting the permissible operating time of an oil-filled permanent magnet motor under short-term high-torque overload conditions, characterized in that: The method includes the following steps: S1. Based on the loss characteristics of the stator, rotor and permanent magnet of the oil-filled permanent magnet motor, a motor loss model considering the effect of temperature is established. The loss model includes stator copper loss, iron loss, permanent magnet eddy current loss and rotor friction loss. S2, Based on the motor loss model established in step S1, construct a thermal balance factor to characterize the relationship between heat generation and heat dissipation capacity inside the permanent magnet motor, and analyze the variation characteristics of the thermal balance factor under short-term torque overload conditions, and fit an expression based on the variation characteristic curve. S3. Based on the thermal balance factor constructed in step S2 and the expression fitted according to the change characteristic curve, the thermal balance state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated, thereby predicting the allowable operating time of the permanent magnet motor under short-term high torque overload conditions.

2. The prediction method according to claim 1, characterized in that: In step S1, establishing a motor loss model that considers the effect of temperature includes the following steps: S11, Establish a stator copper loss model that considers the effect of temperature: in, It is the number of phases of the motor; The temperature is Motor phase resistance at that time; It is the temperature coefficient of resistance of the motor winding; The temperature is The current flowing through the winding; It is the remanence temperature coefficient of permanent magnets; The temperature at which losses are calculated; S12, Establish a stator iron loss separation model that considers the effect of temperature: in, It is the electrical frequency of the motor; It is the amplitude of magnetic flux density; and It is the empirical coefficient of hysteresis loss; It is an empirical coefficient for additional losses; The temperature is Empirical coefficient for eddy current loss at time; It is the temperature coefficient of the empirical coefficient of eddy current loss; S13, Establish the permanent magnet eddy current loss model: in, It is the conductivity of permanent magnets; It is the volume of the permanent magnet; It is the thickness of the permanent magnet; S14, Establish a rotor friction loss model that considers temperature factors: in, It is the rotational speed, in units of 1000 rad / min; , , , , These are undetermined coefficients; It is Euler's constant.

3. The prediction method according to claim 2, characterized in that: In step S2, a thermal balance factor is constructed to characterize the relationship between heat generation and heat dissipation capacity within the permanent magnet motor, and the variation characteristics of this thermal balance factor under short-term torque overload conditions are analyzed. An expression is then fitted based on the variation characteristic curve. The specific process is as follows: The heat balance factor is defined as the ratio of heat dissipated from the surface of the motor to heat generated inside. It takes into account the heat loss and heat transfer characteristics of the motor. The heat balance factor can effectively measure whether the cooling capacity of the motor is sufficient to cope with internal heat generation, especially under dynamic or overload conditions. The thermal balance factor is defined as: in, It is a correction factor; It is the heat transfer coefficient; It is the effective heat dissipation surface area of ​​the motor; This is the temperature difference between the motor surface and the ambient temperature, also known as motor temperature rise; subscript These correspond to the various components in the motor that generate losses, including the stator, rotor, and permanent magnets; It is a component The resulting power loss; It is the average temperature of the motor stator, rotor, and permanent magnets when calculating losses; It depends on the cooling method of the motor surface. The value is determined based on the Nusselt number as follows: in, These are Nusselt numbers; It is the thermal conductivity of the fluid; It is the feature length; Total loss is expressed as: As a correction factor to adjust for deviations under different heat transfer coefficients, this parameter is adjusted through simulation methods, taking into account the known properties of the motor housing. , and As a molecule, the total motor loss The result is then compared with the simulation output; when the motor temperature stabilizes, the motor's cooling power equals its heating power. Thus, the value of the correction factor is obtained; Treating the thermal equilibrium factor as a function of time, and considering that cooling conditions affect the thermal equilibrium factor, the formula must include the heat transfer coefficient. By using a fitting method, an approximately linear relationship between the thermal equilibrium factor and time was obtained, and the specific expression is as follows: in, It is the proportionality coefficient; It's time.

4. The prediction method according to claim 3, characterized in that: In step S3, the thermal equilibrium state of the oil-filled permanent magnet motor under short-term high torque overload conditions is evaluated to predict the allowable operating time of the permanent magnet motor under short-term high torque overload conditions; the prediction process is as follows: A model based on heat capacity and power balance is used to describe short-term torque overload conditions: in, It is the total heat capacity of the motor; It's the heat generated by the motor; It is the heat dissipation power of the motor; Transforming the expression on the right side of equation (9), we get: in, By substituting equation (8) into equation (10) and simplifying the differential equation, we obtain: Finally, the solution for the time and temperature rise functions is obtained as follows: (12) The expression based on the predicted short-term torque overload operating time is: 。

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