A method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor

Abstract

The present invention proposes a method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor. The method is as follows: first, a physical model of the motor solution domain is established; then, the grid is divided according to the structural characteristics, boundary conditions are set, and the fluid field data is calculated using the computational fluid dynamics method; the thermal resistance of each component is calculated based on the average flow velocity, and then a thermal network model is established, and finally the temperature rise distribution of each component of the motor is solved. This method combines the respective advantages of the computational fluid dynamics method and the lumped parameter thermal network method, and calculates the thermal resistance parameters of the thermal network model with the precise flow field data obtained by the computational fluid dynamics method, avoiding the accuracy defects caused by the use of empirical values ​​in the traditional thermal network method under complex flow fields. The temperature rise distribution of a megawatt-class high-speed permanent magnet motor can be calculated accurately and quickly.

Description

Technical Field

[0001] The present invention relates to the field of motor temperature field calculation, and specifically to a method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor, and specifically to a method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor based on a combination of a computational fluid dynamics method and a thermal network method. Background Art

[0002] High-speed permanent magnet motors have been increasingly widely used in the industrial field due to their high speed, small size, and high power density. Megawatt-class high-speed permanent magnet motors have greater output power and higher power density. Compared with high-speed permanent magnet motors of the same size, they effectively improve the utilization rate of motor materials and reduce production costs, but at the same time they also bring problems such as large losses and temperature rise, as well as heat dissipation difficulties caused by small heat dissipation area. Excessive temperature rise of permanent magnets will cause demagnetization of permanent magnets, increase motor losses, shorten motor service life, and other problems, which restrict the development of high-speed permanent magnet motors. With the rapid growth of the national economy, people's demand for electric energy is also increasing. High-speed permanent magnet motors have higher and higher requirements for thermal performance. Thermal performance analysis of motors is a prerequisite for ensuring high reliability of motors.

[0003] There are two main methods for calculating the temperature rise in motors: computational fluid dynamics and lumped parameter thermal network. The computational fluid dynamics method physically models the target motor and accurately simulates the heat conduction and convection phenomena in the motor. The specific temperature rise distribution of each point in the motor can be obtained through calculation, and the heat transfer phenomenon of the motor can be simulated. However, since this method takes a long time to calculate, it is difficult to achieve rapid parametric modeling of the motor. The lumped parameter thermal network method equates the motor thermal network to a traditional electrical network. The temperature rise corresponds to voltage, power corresponds to current, and thermal resistance corresponds to resistance. Compared with the computational fluid dynamics method, the calculation speed is faster, but the traditional thermal network method often uses empirical flow velocity to calculate the convection thermal resistance, and the calculation accuracy depends largely on the selection of parameters. None of the above methods can take into account both calculation speed and accuracy at the same time, and it is difficult to meet actual needs. Summary of the invention

[0004] Overcome the shortcomings of slow calculation speed of computational fluid dynamics method and the calculation accuracy defects caused by using empirical values ​​to select heat transfer coefficients in lumped parameter thermal network method. Provide a temperature rise calculation method for megawatt-class high-speed permanent magnet motors that can both improve calculation speed and ensure the accuracy of calculation results, and realize the coupled calculation of fluid field and temperature field.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor A method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor, characterized in that it comprises the following steps:

[0007] Step 1: Establish the physical model of the motor solution domain;

[0008] According to the motor structure, select the appropriate solution domain and simplify it reasonably;

[0009] Step 2: Meshing and boundary setting;

[0010] Set appropriate size conditions, divide the grid, use the finite volume method to solve, and set corresponding boundary conditions according to the model structure, including inlet and outlet;

[0011] Step 3: Fluid field calculation;

[0012] Check the quality of the grid, use computational fluid dynamics software to simulate the fluid flow properties in the motor based on the boundary conditions, and calculate the average flow velocity of each fluid domain based on the flow field data;

[0013] Step 4: Establish a thermal circuit model;

[0014] The T-shaped equivalent method is used to construct the thermal network model of the target motor, where T1 and T2 are the average temperature rises of the outer and inner walls of the hollow cylinder, respectively. a , T b are the average temperature rise of the left and right end faces of the hollow cylinder, P is the loss generated by the hollow cylinder, R 1a , R 2a is the axial thermal conduction resistance, R 3a is the additional axial impedance, R 1r , R 2r is the radial conduction thermal resistance, R 3r It is the radial additional impedance. Assuming that the axial and radial heat transfer of the cylinder are independent of each other, the calculation formula of the axial and radial conduction thermal resistance is:

[0015]

[0016] Due to the symmetry of the motor structure, the axial conduction thermal resistance R 1a , R 2a equal;

[0017] The temperature rise of each part of the fluid inside the motor is expressed as the product of loss and air thermal resistance, which reflects the relationship between the temperature rise and energy of each part of the cooling medium. As an important boundary condition for the calculation of the motor temperature rise, it is written in matrix form as follows:

[0018]

[0019] It contains 8 heat sources and 7 controlled sources, with the temperature rise of the air outside the casing as the zero potential energy surface;

[0020] Step 5: Calculate thermal resistance parameters;

[0021] According to the different forms of energy transfer, it can be classified into conduction heat dissipation, convection heat dissipation and radiation heat dissipation. The temperature rise gradient of each structural part of the high-speed permanent magnet motor is small, and radiation heat transfer is negligible compared to other heat transfer pathways. Therefore, only conduction thermal resistance and convection thermal resistance need to be considered;

[0022] The heat conduction of the motor refers to the form of energy transfer when there is no relative displacement between the various structures in the motor. The heat conduction between the various structures in the motor follows Fourier's law of heat conduction:

[0023]

[0024] Where: φ is the heat flow; λ is the thermal conductivity; A is the cross-sectional area of ​​the heat conduction surface; T is the node temperature rise; n is the temperature rise gradient direction; q is the heat flux density along the n direction; the negative sign indicates that the direction of heat transfer is opposite to the direction of temperature rise;

[0025] The stator and rotor core, permanent magnets, and rotor jacket in the motor are equivalent to a hollow cylindrical structure. The calculation formula for the radial conduction thermal resistance between the inner and outer walls is:

[0026]

[0027] Where: r1, r2 are the inner and outer wall radii of the hollow cylinder respectively; l is the axial length of the hollow cylinder;

[0028] According to the axial radial mixed ventilation structure of the motor, the convection heat dissipation coefficient includes the heat dissipation coefficient of the stator and rotor ends, the heat dissipation coefficient at the air gap, the heat dissipation coefficient of the casing, the heat dissipation coefficient in the axial air duct of the stator and rotor, and the heat dissipation coefficient of the stator radial air duct;

[0029] The cooling medium enters the air cavity at the end of the motor from the air inlet, and undergoes convection heat exchange with the ends of the stator and rotor. This is forced convection heat exchange, and the calculation formula for the commutation coefficient is:

[0030] h=15.5(0.39v1+1)

[0031] Where: v1 is the cooling medium flow rate at the ends of the stator and rotor.

[0032] The calculation of the air gap heat dissipation coefficient and the rotor axial duct heat dissipation coefficient depends on the Nusselt number. The calculation formula of the convection heat dissipation coefficient is:

[0033]

[0034] Where: Nu is the Nusselt number; k is the thermal conductivity of air; δ is the radial length of the air gap;

[0035] The chassis adopts natural convection cooling, and the convection heat dissipation coefficient calculation formula is:

[0036]

[0037] Where: v3 is the air velocity outside the casing;

[0038] When the solid surface heat dissipation coefficient is known, the convection thermal resistance of the axial radial mixed ventilation cooling method can be obtained by the above-mentioned stator and rotor end heat dissipation coefficient calculation formula:

[0039]

[0040] Where: A is the contact area between the solid surface and the cooling medium;

[0041] Step 6: Thermal network calculation;

[0042] By building a motor thermal network model, the calculation process of the motor thermal network model is similar to the electrical network solution, and the additional boundary condition equations are combined:

[0043]

[0044] Where: P c is the energy flowing into the cooling medium of each structural part. From the above, it can be known that the temperature rise of each node T c Can be obtained by P c The node temperature rise and the thermal resistance between air give:

[0045] T c =RP c

[0046] The column vector of temperature rise of each node in the network:

[0047]

[0048] Based on the thermal resistance in the thermal circuit diagram, the average temperature of each part of the motor stator and rotor is calculated.

[0049] Furthermore, in step 1, a physical model of the motor solution domain is established, as follows:

[0050] When the motor structure is symmetrical, a partial structural domain is used for solving the problem, the base, chassis and other non-motor parts are ignored, and the multi-turn winding is equivalent to a single-turn coil.

[0051] Furthermore, the flow field calculation in steps 2 and 3 is as follows:

[0052] The finite volume method is used to divide the grid into appropriate sizes according to the model settings. The flow field data of each component is calculated based on the boundary conditions, and the average flow velocity is calculated based on the flow field data.

[0053] Furthermore, the temperature rise calculation of the thermal network in steps 4, 5, and 6 is as follows:

[0054] According to the average flow rate obtained in step 3, the thermal resistance of each area is calculated, and a thermal network model is built. The temperature rise distribution inside the motor is calculated based on the thermal network model.

[0055] Compared with the prior art, the present invention has the following significant advantages: (1) The lumped parameter thermal network method is applied to the temperature rise calculation of megawatt-class high-speed permanent magnet motors, which can effectively analyze the thermal performance of such motors and provide guidance for the design of the motors.

[0056] (2) The computational fluid dynamics method and the lumped parameter thermal network method are combined. The fluid field data of the motor is obtained by the computational fluid dynamics method, and the heat transfer coefficient of each region is calculated based on the average flow rate, thus avoiding the accuracy defects caused by the selection of empirical values ​​by the traditional lumped parameter thermal network method under complex flow fields. This method has both the accuracy advantages of the computational fluid dynamics method and the speed advantages of the thermal network method. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a logical structure diagram of the present invention;

[0058] FIG2 is a diagram showing the stator and rotor structure of a motor according to an example of the present invention; (a) is the stator structure; and (b) is the rotor structure.

[0059] Figure 3 is the air domain flow rate of the present invention example;

[0060] FIG4 is a schematic diagram of the T-shaped equivalent method; (a) is a physical model of a hollow cylinder; (b) is a T-shaped equivalent thermal path of a hollow cylinder;

[0061] Figure 5 This is a motor thermal network model of an example of the present invention. DETAILED DESCRIPTION

[0062] The following is a detailed description of a temperature rise calculation method for a megawatt-class high-speed permanent magnet motor proposed by the present invention in conjunction with the embodiments and drawings. The method comprises the following steps:

[0063] Step 1: Establish the physical model of the motor solution domain:

[0064] Taking a 1MW surface-mounted high-speed permanent magnet motor as an example, the motor's dimensional parameters are shown in Table 1, and the stator and rotor structure is shown in Figure 2. The stator core adopts a laminated silicon steel sheet structure. The winding adopts a double-layer structure, wrapped with insulating material and embedded in the stator slot. The permanent magnet is a surface-mounted structure, made of NdFeB35EH, and a carbon fiber sheath is used to fix the permanent magnet by interference fit.

[0065] Taking into account the symmetry of the motor structure in this example, a one-twelfth motor structural domain is constructed to couple the motor fluid field and temperature field. A 1 / 12 motor unit is used in the circumferential direction and the entire motor domain is taken as the basic solution domain in the axial direction. There are air outlets and air inlets on the left and right casing surfaces respectively.

[0066] Table 11MW high-speed permanent magnet motor size parameters

[0067]

[0068] Step 2: Meshing and boundary settings:

[0069] The model is divided into polyhedral grids of appropriate size and solved by finite volume method. Due to the high-speed rotation of the motor, the Reynolds number of the fluid flow is very large (Re>2300), so the k-ε turbulence model is used to solve the flow field in the motor; during the flow in the motor, the fluid velocity is much smaller than the speed of sound, so the fluid is treated as an incompressible fluid. The nonlinear change of the physical properties of the fluid to the temperature is ignored. The velocity inlet boundary condition is adopted, and the inlet flow rate is 1.5m 3 / s, according to the inlet area, the inlet flow rate can be calculated to be 2.82m / s. The outlet is set as a pressure outlet, and the pressure value is a standard atmospheric pressure; due to the rotation of the motor, the lower wall of the air gap is set as a rotating wall, and the speed is 10000rpm.

[0070] Step 3: Fluid field calculation:

[0071] After checking the mesh quality, the computational fluid dynamics software was used to simulate the fluid flow properties in the motor based on the above boundary conditions. Figure 3 The fluid field in the air domain shown in the figure shows that due to the narrowness of the air gap and the inlet of the rotor axial air duct and the small cross-sectional area, when the cooling medium flows into the air gap from the right air cavity, the flow resistance of the fluid flow path becomes larger, the amount of cooling air entering the ventilation duct is obvious, the flow velocity increases rapidly, and the highest flow velocity occurs at the inlet of the air gap. Considering the friction of the air duct wall, there is energy loss in the process of the cooling medium flowing axially in the air gap, resulting in a decrease in the flow rate in the air gap and a gradual decrease in the wind speed along the flow position. The average flow velocity of each fluid domain is calculated using the flow field data.

[0072] Step 4: Establish thermal circuit model:

[0073] Combined with Figure 4, the T-shaped equivalent method is used to construct the target motor thermal network model. This method is suitable for the radial heat conduction model of the hollow cylinder. In the figure, T1 and T2 are the average temperature rise of the outer wall and inner wall of the hollow cylinder, respectively. a , T b are the average temperature rise of the left and right end faces of the hollow cylinder, P is the loss generated by the hollow cylinder, R 1a , R 2ais the axial thermal conduction resistance, R 3a is the additional axial impedance, R 1r , R 2r is the radial conduction thermal resistance, R 3r It is the radial additional impedance. Assuming that the axial and radial heat transfer of the cylinder are independent of each other, the calculation formula of the axial and radial conduction thermal resistance is:

[0074]

[0075] Due to the symmetry of the motor structure, the axial conduction thermal resistance R 1a , R 2a equal.

[0076] The temperature rise of each part of the fluid inside the motor is expressed as the product of loss and air thermal resistance, reflecting the relationship between the temperature rise and energy of each part of the cooling medium, which serves as an important boundary condition for the calculation of the motor temperature rise. It can be written in matrix form as:

[0077]

[0078] Establish the motor global thermal network model as follows Figure 5 As shown, there are 8 heat sources and 7 controlled sources in total, with the temperature rise of the air outside the casing as the zero potential energy surface.

[0079] Step 5: Calculate thermal resistance parameters:

[0080] According to the different forms of energy transfer, it can be classified into conduction heat dissipation, convection heat dissipation and radiation heat dissipation. The temperature rise gradient of each structural part of the high-speed permanent magnet motor is small, and radiation heat transfer is negligible compared to other heat transfer paths. Therefore, only conduction thermal resistance and convection thermal resistance need to be considered.

[0081] The heat conduction of the motor refers to the form of energy transfer when there is no relative displacement between the various structures in the motor. The heat conduction between the various structures in the motor follows Fourier's law of heat conduction:

[0082]

[0083] In the formula: φ is the heat flow; λ is the thermal conductivity; A is the cross-sectional area of ​​the heat conduction surface; T is the node temperature rise; n is the direction of the temperature rise gradient; q is the heat flux density along the n direction; the negative sign indicates that the direction of heat transfer is opposite to the direction of temperature rise.

[0084] The stator and rotor core, permanent magnets, rotor sleeve and other structural parts in the motor can be equivalent to a hollow cylindrical structure, and the calculation formula for the radial conduction thermal resistance between the inner and outer walls is:

[0085]

[0086] Where: r1, r2 are the inner and outer wall radii of the hollow cylinder respectively; l is the axial length of the hollow cylinder.

[0087] According to the axial radial mixed ventilation structure of the motor, the convection heat dissipation coefficient includes the heat dissipation coefficient of the stator and rotor ends, the heat dissipation coefficient at the air gap, the heat dissipation coefficient of the casing, the heat dissipation coefficient in the axial air duct of the stator and rotor, and the heat dissipation coefficient of the stator radial air duct.

[0088] The cooling medium enters the air cavity at the end of the motor from the air inlet, and undergoes convection heat exchange with the ends of the stator and rotor, which belongs to forced convection heat exchange. The calculation formula for the commutation coefficient is:

[0089] h=15.5(0.39v1+1)

[0090] Where: v1 is the cooling medium flow rate at the ends of the stator and rotor.

[0091] The calculation of the air gap heat dissipation coefficient and the rotor axial duct heat dissipation coefficient depends on the Nusselt number. The calculation formula of the convection heat dissipation coefficient is:

[0092]

[0093] Where: Nu is the Nusselt number; k is the thermal conductivity of air; δ is the radial length of the air gap.

[0094] The chassis adopts natural convection cooling, and the convection heat dissipation coefficient calculation formula is:

[0095]

[0096] Where: v3 is the air velocity outside the casing.

[0097] When the solid surface heat dissipation coefficient is known, the convection thermal resistance of the axial radial mixed ventilation cooling method can still be obtained by the above-mentioned stator and rotor end heat dissipation coefficient calculation formula:

[0098]

[0099] Where: A is the contact area between the solid surface and the cooling medium.

[0100] Step 6: Thermal network calculation,

[0101] The calculation process of the motor thermal network model is similar to the electrical network solution. The additional boundary condition equations are combined:

[0102]

[0103] Where: P c is the energy flowing into the cooling medium of each structural part. From the above, it can be known that the temperature rise of each node T c Can be obtained by P c The node temperature rise and the thermal resistance between air give:

[0104] T c =RP c

[0105] The temperature rise column vector of each node in the network:

[0106]

[0107] According to the thermal resistance in the thermal circuit diagram, the average temperature of each part of the motor stator and rotor is calculated as shown in Table 2.

[0108] Table 2 Calculation results of temperature rise of 1MW high-speed permanent magnet motor

[0109]

[0110]

[0111] In summary, the calculation method of the present invention uses computational fluid dynamics to obtain the average flow velocity of the flow field of each component of the motor, replaces the empirical value to calculate the thermal resistance of the thermal network method, and establishes a thermal network model for motor thermal analysis. At the same time, it takes into account the accuracy and calculation time of temperature rise calculation. It has good application value in the design of megawatt-level high-speed permanent magnet motors.

[0112] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor A method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor, characterized in that: The following steps are involved: Step 1: Establish the physical model of the motor solution domain; According to the motor structure, select the appropriate solution domain and simplify it reasonably; Step 2: Meshing and boundary setting; Set appropriate size conditions, divide the grid, use the finite volume method to solve, and set corresponding boundary conditions according to the model structure, including inlet and outlet; Step 3: Fluid field calculation; Check the quality of the grid, use computational fluid dynamics software to simulate the fluid flow properties in the motor based on the boundary conditions, and calculate the average flow velocity of each fluid domain based on the flow field data; Step 4: Establish a thermal circuit model; The T-shaped equivalent method is used to construct the thermal network model of the target motor, where T1 and T2 are the average temperature rises of the outer and inner walls of the hollow cylinder, respectively. a , T b are the average temperature rise of the left and right end faces of the hollow cylinder, P is the loss generated by the hollow cylinder, R 1a , R 2a is the axial thermal conduction resistance, R 3a is the additional axial impedance, R 1r , R 2r is the radial conduction thermal resistance, R 3r It is the radial additional impedance. Assuming that the axial and radial heat transfer of the cylinder are independent of each other, the calculation formula of the axial and radial conduction thermal resistance is: Due to the symmetry of the motor structure, the axial conduction thermal resistance R 1a , R 2a equal; The temperature rise of each part of the fluid inside the motor is expressed as the product of loss and air thermal resistance, which reflects the relationship between the temperature rise and energy of each part of the cooling medium. As an important boundary condition for the calculation of the motor temperature rise, it is written in matrix form as follows: It contains 8 heat sources and 7 controlled sources, with the temperature rise of the air outside the casing as the zero potential energy surface; Step 5: Calculate thermal resistance parameters; According to the different forms of energy transfer, it can be classified into conduction heat dissipation, convection heat dissipation and radiation heat dissipation. The temperature rise gradient of each structural part of the high-speed permanent magnet motor is small, and radiation heat transfer is negligible compared to other heat transfer paths. Therefore, only conduction thermal resistance and convection thermal resistance need to be considered; The heat conduction of the motor refers to the form of energy transfer when there is no relative displacement between the various structures in the motor. The heat conduction between the various structures in the motor follows Fourier's law of heat conduction: Where: φ is the heat flow; λ is the thermal conductivity; A is the cross-sectional area of ​​the heat conduction surface; T is the node temperature rise; n is the temperature rise gradient direction; q is the heat flux density along the n direction; the negative sign indicates that the direction of heat transfer is opposite to the direction of temperature rise; The stator and rotor core, permanent magnets, and rotor jacket in the motor are equivalent to a hollow cylindrical structure. The calculation formula for the radial conduction thermal resistance between the inner and outer walls is: Where: r1, r2 are the inner and outer wall radii of the hollow cylinder respectively; l is the axial length of the hollow cylinder; According to the axial radial mixed ventilation structure of the motor, the convection heat dissipation coefficient includes the heat dissipation coefficient of the stator and rotor ends, the heat dissipation coefficient at the air gap, the heat dissipation coefficient of the casing, the heat dissipation coefficient in the axial air duct of the stator and rotor, and the heat dissipation coefficient of the stator radial air duct; The cooling medium enters the air cavity at the end of the motor from the air inlet, and undergoes convection heat exchange with the ends of the stator and rotor, which belongs to forced convection heat exchange. The calculation formula for the commutation coefficient is: h=15.5(0.39v1+1) Where: v1 is the cooling medium flow rate at the ends of the stator and rotor; The calculation of the air gap heat dissipation coefficient and the rotor axial duct heat dissipation coefficient depends on the Nusselt number. The calculation formula of the convection heat dissipation coefficient is: Where: Nu is the Nusselt number; k is the thermal conductivity of air; δ is the radial length of the air gap; The chassis adopts natural convection cooling, and the convection heat dissipation coefficient calculation formula is: Where: v3 is the air velocity outside the casing; When the solid surface heat dissipation coefficient is known, the convection thermal resistance of the axial radial mixed ventilation cooling method can be obtained by the above-mentioned stator and rotor end heat dissipation coefficient calculation formula: Where: A is the contact area between the solid surface and the cooling medium; Step 6: Thermal network calculation; By building a motor thermal network model, the calculation process of the motor thermal network model is similar to the electrical network solution, and the additional boundary condition equations are combined: Where: P c is the energy flowing into the cooling medium from each structural part; from the above, it can be known that the temperature rise of each node T c Can be obtained by P c The node temperature rise and the thermal resistance between air give: T c =RP c The temperature rise column vector of each node in the network: Based on the thermal resistance in the thermal circuit diagram, the average temperature of each part of the motor stator and rotor is calculated.

2. The method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor according to claim 1, characterized in that: In step 1, the physical model of the motor solution domain is established as follows: When the motor structure is symmetrical, a partial structural domain is used for solving the problem, the base, chassis and other non-motor parts are ignored, and the multi-turn winding is equivalent to a single-turn coil.

3. The method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor according to claim 1, characterized in that: The flow field calculation in steps 2 and 3 is as follows: The finite volume method is used to divide the grid into appropriate sizes according to the model settings. The flow field data of each component is calculated based on the boundary conditions, and the average flow velocity is calculated based on the flow field data.

4. The method for calculating the temperature rise of a megawatt-class high-speed permanent magnet motor according to claim 1, characterized in that: The calculation of the thermal network temperature rise in steps 4, 5, and 6 is as follows: According to the average flow rate obtained in step 3, the thermal resistance of each area is calculated, and a thermal network model is built. The temperature rise distribution inside the motor is calculated based on the thermal network model.

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