A high overload permanent magnet servo motor cooling structure and method with phase change material

Abstract

The present invention discloses a high-overload permanent magnet servo motor cooling structure and method with phase change material. The high-overload permanent magnet servo motor cooling structure includes a casing, an end cover, a stator core, a permanent magnet, a rotor core, a rotating shaft, a rotor end cover and a stator winding, and a phase change-epoxy resin composite potting material is arranged on both end faces of the stator core. The method is to select an initial phase change material, and then divide the second layer of phase change material and the third layer of epoxy resin material to obtain a composite material layer and then construct a thermal network model to obtain the end temperature rise of the stator winding, change the selection of phase change material, repeat the experiment, and obtain the optimal phase change material. The structure of the present invention avoids the influence of filling phase change material on the increase of motor volume, and also effectively suppresses the end temperature rise of the stator winding under high overload conditions. The method of the present invention selects the optimal phase change material suitable for the structure of the present invention through multiple experiments.

Description

Technical Field

[0001] The invention belongs to the technical field of motors, and in particular relates to a cooling structure and method for a high-overload permanent magnet servo motor with phase change material. Background Art

[0002] In order to cope with the complex and changing working environment, the robot joint servo motor needs to have a high overload capacity. The compact structural characteristics of the permanent magnet servo motor make it accompanied by severe heat dissipation problems under overload conditions and high loss density. Temperature is a key factor affecting the output power of the motor, so the design of the motor cooling structure is one of the key technologies restricting the development of the motor. The air-cooling and water-cooling structures use external mechanical structures such as fans and pumps to force the internal fluid or cooling medium of the motor to flow to take away the heat of the motor. Although these two types of cooling structures can cool the motor, the increase in volume caused by the addition of external mechanical mechanisms cannot meet the requirements of the robot joint servo motor for small size and high power density.

[0003] The commonly used phase change cooling scheme at present usually slots in the motor casing and fills the phase change material. This cooling structure scheme requires a large casing volume and can only suppress the temperature rise of the motor stator and casing under normal operating conditions. Under high overload conditions, the stator winding end is the hottest point of the motor. There is no direct contact between the phase change material in the casing and the winding end, and the heat transfer path is long. The casing filled with phase change material is not ideal for suppressing the short-term large temperature rise of the motor. Summary of the invention

[0004] In order to overcome the above technical problems, the present invention provides a high overload permanent magnet servo motor cooling structure and method with phase change material. The present invention can suppress the short-term temperature rise of the end of the stator winding of the permanent magnet servo motor under short-term high overload conditions.

[0005] The technical solution adopted by the present invention is:

[0006] 1. A high overload permanent magnet servo motor cooling structure with phase change material

[0007] The structure includes a casing, an end cover, a stator core, a permanent magnet, a rotor core, a rotating shaft, a rotor end cover and a stator winding; two end covers are fixedly installed on the two end faces of the casing respectively, and permanent magnets, a rotor core, a rotating shaft and a stator winding are arranged inside the casing, and two ends of the rotating shaft pass through the two end covers respectively and are coaxially movably connected with the two end covers; the rotor core is coaxially fixedly sleeved on the rotating shaft, and a plurality of circumferentially arranged and axially penetrating permanent magnets are fixedly sleeved on the surface of the rotor core, and two rotor end covers are fixedly installed on the two end faces of the rotor core respectively; the stator core is tightly installed on the circumferential inner wall of the casing, and a plurality of winding axial through grooves are opened in the stator core along the circumferential direction, and corresponding stator windings are respectively embedded in each winding axial through groove; the two end faces of the stator core are provided with phase change-epoxy resin composite potting material.

[0008] The phase change-epoxy resin composite potting material is a three-layer potting material, and the three layers of potting materials are respectively a first layer of epoxy resin material, a second layer of phase change material and a third layer of epoxy resin material; the first layer of epoxy resin material is potted on the two end surfaces of the stator core, the second layer of phase change material is potted on the end surface at both ends of each stator winding, the phase change materials potted on the end surfaces of each two adjacent stator windings are not connected to each other, the third layer of epoxy resin material is potted on the surface of the phase change material, the third layer of epoxy resin material is filled in the space formed between the stator core, the casing and the end cover and is in close contact with the stator core and the casing end cover.

[0009] 2. A method for selecting phase change materials for cooling structure of high overload permanent magnet servo motor

[0010] The phase change material selection method comprises the following steps:

[0011] S1. Select an initial phase change material and obtain the thermal conductivity of the phase change material.

[0012] S2. The second layer of phase change material and the third layer of epoxy resin material are divided to obtain composite material layers, and the equivalent specific heat capacity of the phase change material is obtained by performing analytical modeling on the composite material layers.

[0013] S3. A thermal network model of the high overload permanent magnet servo motor cooling structure is constructed according to the thermal conductivity of the phase change material, the equivalent specific heat capacity of the composite material layer and the phase change material. The high overload permanent magnet servo motor cooling structure is continuously operated until the overload condition ends, and the end temperature rise of the stator winding is obtained according to the thermal network model.

[0014] S4, changing the selection of phase change material, repeating steps S2-S3, obtaining the end temperature rise of the stator winding under different phase change materials, and obtaining the optimal phase change material according to the end temperature rise of the stator winding under different phase change materials.

[0015] The step S2 is specifically as follows:

[0016] S21. Divide the phase change material of the second layer into an inner phase change material layer and an outer phase change material layer according to a preset division ratio, divide the epoxy resin material of the third layer into an inner epoxy resin material layer and an outer epoxy resin material layer according to a preset division ratio, and combine the inner epoxy resin material layer and the outer phase change material layer into an equivalent composite material layer.

[0017] S22. According to the composite material layer, the phase change material of the second layer is subjected to analytical modeling processing by using an equivalent heat capacity method to obtain an equivalent specific heat capacity of the phase change material.

[0018] In the step S21, after being equivalent to the composite material layer, the equivalent specific heat capacity of the composite material layer is obtained according to the following formula:

[0019] c p-mix = ( ηρ pcm c p-pcm +(1- η ) ρ er c p-er ) / ρ mix

[0020] ρ mix = ηρ pcm +(1- η ) ρ er

[0021] in, ρ mix is the equivalent density of the composite material layer, c p-mix is the equivalent specific heat capacity of the composite material layer, η is the volume proportion of the outer phase change material layer in the composite material layer, ρ pcm and ρ er are the densities of phase change material and epoxy resin material, c p-pcm and c p-er are the specific heat capacities of phase change material and epoxy resin material respectively.

[0022] In step S22, the analytical modeling process for the phase change material is set according to the following formula:

[0023] c p = c p-pcm , β = 0 or 1

[0024] c p =(1- β / b 1) ( c p-pcm + L / Δ T )+( β / b1) c p-pcm ,0< β < b 1

[0025] c p =(1-( β - b 1) / b 2)( c p-pcm + L / Δ T )+(( β - b 1) / b 2) c p-pcm , b 1< β <1

[0026] β =( T max - T pcm ) / ( T 2- T 1)

[0027] in, c p is the equivalent specific heat capacity of the phase change material, β is the liquid fraction of the phase change material, b 1 is the volume fraction of the inner phase change material layer in the phase change material, b 2 is the volume fraction of the outer phase change material layer in the phase change material, L is the latent heat of phase change, Δ T is the temperature difference between the starting and ending time of phase change of unit mass phase change material, T 1 and T 2 are the phase change starting temperature and phase change ending temperature of the phase change material, T max is the maximum temperature of the phase change material, T pcm is the phase change temperature of the phase change material.

[0028] The step S3 is specifically as follows:

[0029] S301 , constructing an end thermal network model of the stator winding according to the thermal conductivity of the phase change material in step S1 and the equivalent specific heat capacity of the composite material layer and the phase change material in step S2 .

[0030] S302. According to the end thermal network model of the stator winding, the physical model of the high overload permanent magnet servo motor cooling structure is divided according to the network division method to obtain a plurality of grid units and the grid unit size of each grid unit. Each grid unit is regarded as a node, and thermal resistance is set between each node and connected through the thermal resistance. The initial temperature of each node and the initial temperature rise of the high overload permanent magnet servo motor cooling structure are preset, so as to construct the thermal network model of the high overload permanent magnet servo motor cooling structure.

[0031] The network partitioning method is a conventional method in the field of servo motor structure to decompose a complex physical system into multiple subsystems or modules. The thermal resistance is a component after the equivalent degree of resistance encountered when heat is transferred between two nodes, and the thermal resistance can be a conductive thermal resistance or a convective thermal resistance.

[0032] The high overload refers to operation under multiple overload conditions.

[0033] S303, obtaining material parameters of each component in the physical model of the high overload permanent magnet servo motor cooling structure, and processing according to the grid unit size to obtain the conduction thermal resistance between each node in the thermal network model and the heat capacity of each node.

[0034] The material parameters of each component include the equivalent specific heat capacity of the phase change material, etc.

[0035] S304. According to the material parameters of each component and the size of the grid unit, the convective heat transfer coefficient of the heat exchange surface of the casing, the end cover and the rotor end cover is obtained by using an empirical formula, and the convective thermal resistance between each node is obtained according to the convective heat transfer coefficient.

[0036] S305. Based on the physical model of the high-overload permanent magnet servo motor cooling structure, various losses in the high-overload permanent magnet servo motor cooling structure are obtained by using the electromagnetic field finite element method, and the various losses in the high-overload permanent magnet servo motor cooling structure are added as heat sources to corresponding nodes.

[0037] The various losses include copper loss of stator windings, iron loss of stator cores, eddy current loss of permanent magnets, friction loss of bearings, etc., and the phase change-epoxy resin composite potting material has no loss.

[0038] S306. According to the conduction thermal resistance and convection thermal resistance between each node, the heat capacity of each node and the various losses in the cooling structure of the high overload permanent magnet servo motor, and using Kirchhoff's current law and the law of conservation of energy, a node thermal conductivity matrix, a node thermal capacity matrix and a node heat source matrix of the thermal network model are obtained, and according to the node thermal conductivity matrix, the node thermal capacity matrix and the node heat source matrix, a transient thermal network node equation group is obtained.

[0039] S307, using the finite difference method to process the transient thermal network node equation group to obtain a transient node temperature matrix iteration formula, according to which the transient node temperature matrix iteration formula is used to obtain each node temperature and update the node temperature matrix.

[0040] S308, according to the node temperature matrix, the same method as step S21 is used to obtain the equivalent specific heat capacity of the phase change material after the phase change and update the equivalent specific heat capacity of the phase change material.

[0041] S309. Repeat steps S301 to S308 until the overload condition operation ends.

[0042] The overload condition is preset according to different situations.

[0043] S310, obtaining the end temperature rise of the stator winding by processing according to the thermal conductivity of the phase change material and the node temperature matrix at all times.

[0044] The convection heat transfer coefficient in step S304 is set according to the following formula:

[0045] α c =15(1+0.4(0.2 v r ) 0.9 )

[0046] α e =15(1+0.4(0.7 v r ) 0.9 )

[0047] α r =28(1+(0.45 v r ) 0.5 )

[0048] in, α c , α e and α r are the convective heat transfer coefficients of the heat transfer surfaces of the casing, end cover and rotor end cover, respectively. v r is the air velocity on the rotor core surface.

[0049] The transient node temperature matrix iteration formula is set according to the following formula:

[0050] T i+1 =( E -Δ tC -1 G ) T i +Δ tC -1 P

[0051] in, G is the thermal conductivity matrix, C is the heat capacity matrix, P is the heat source matrix, E is the identity matrix, T i For the i The nodal temperature matrix for the time step, T i+1 For the i +1 time step node temperature matrix, Δ t is the time step.

[0052] The step S4 is specifically as follows:

[0053] S41, changing the selection of phase change material to obtain the thermal conductivity of the changed phase change material, repeating steps S2 to S3, and obtaining the end temperature rise of the stator winding under different thermal conductivities of phase change materials.

[0054] S42. Select the thermal conductivity of the phase change material corresponding to the lowest temperature rise of the end of the stator winding as the optimal thermal conductivity of the phase change material, and the phase change material corresponding to the optimal thermal conductivity as the optimal phase change material.

[0055] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0056] 1. The present invention utilizes the latent heat characteristics of the phase change material to absorb the heat at the end of the stator winding while maintaining a constant temperature, thereby effectively suppressing a short-term large temperature rise at the end of the stator winding.

[0057] 2. The present invention pots the phase change-epoxy resin composite potting material in the end space without changing the mechanical structure such as the stator core and the casing, thus avoiding the problem of increased structural volume of the present invention.

[0058] 3. The present invention optimizes the calculation method of the specific heat capacity of phase change materials under the equivalent heat capacity method, takes into account the influence of the liquid phase ratio of the phase change material on the sensible heat, and more accurately calculates the end temperature of the stator winding during the phase change process.

[0059] 4. The thermal network model of the high-overload permanent magnet servo motor cooling structure constructed by the present invention has a fast processing speed and can quickly perform parameterized scanning processing on the influence of the thermal physical parameters of the phase change material on the temperature rise suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic diagram of the axial cross-section of the high overload permanent magnet servo motor cooling structure without the phase change-epoxy resin composite potting material.

[0061] Figure 2 A partial structural schematic diagram of a high overload permanent magnet servo motor cooling structure provided with a phase change-epoxy resin composite potting material.

[0062] Figure 3 Schematic diagram of the end thermal network model of the stator winding.

[0063] Figure 4 Schematic diagram of the thermal network model of the high overload permanent magnet servo motor cooling structure.

[0064] Figure 5 It is the transient temperature curve of the end of the stator winding and the stator core teeth.

[0065] Figure 6 The temperature change curve of the end of the stator winding under the thermal conductivity corresponding to different phase change materials.

[0066] Among them, 1. casing; 2. end cover; 3. stator core; 4. permanent magnet; 5. rotor core; 6. bearing; 7. rotating shaft; 8. rotor end cover; 9. stator winding; 10. phase change material; 11. epoxy resin material. DETAILED DESCRIPTION

[0067] The present invention is further described below in conjunction with the accompanying drawings. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention, and do not limit the protection scope of the claims of this application. Example 1

[0068] like Figure 1 As shown, this embodiment adopts a 12-slot 14-pole permanent magnet servo motor as the research object. The high overload permanent magnet servo motor cooling structure of this embodiment includes a casing 1, an end cover 2, a stator core 3, a permanent magnet 4, a rotor core 5, a rotating shaft 7, a rotor end cover 8 and a stator winding 9; two end covers 2 are fixedly installed on the two end surfaces of the casing 1, and permanent magnets 4, a rotor core 5, a rotating shaft 7 and a stator winding 9 are arranged inside the casing 1. The two ends of the rotating shaft 7 pass through the two end covers 2 and are coaxially movably connected with the two end covers 2 through their respective bearings 6; the rotor core 5 is coaxially fixedly sleeved on the rotating shaft 7, and a plurality of circumferentially arranged and axially penetrating permanent magnets 4 are fixedly sleeved on the surface of the rotor core 5, and two rotor end covers 8 are fixedly installed on the two end surfaces of the rotor core 5; the stator core 3 is tightly installed on the circumferential inner wall of the casing 1, and a plurality of winding axial through grooves are opened in the stator core 3 along the circumferential direction, and corresponding stator windings 9 are respectively embedded in each winding axial through groove.

[0069] like Figure 2 As shown, both end surfaces of the stator core 3 are provided with phase change-epoxy resin composite potting material.

[0070] The phase change-epoxy resin composite potting material is a three-layer potting material, which includes a first layer of epoxy resin material 11, a second layer of phase change material 10, and a third layer of epoxy resin material 11; the first layer of epoxy resin material 11 is potted on the two end surfaces of the stator core 3, such as Figure 2 As shown, the second layer of phase change material 10 is embedded on the end surface of each stator winding 9 at both ends, and the phase change materials 10 embedded on the end surfaces of each adjacent stator winding 9 are not connected to each other. The third layer of epoxy resin material 11 is embedded on the surface of the phase change material 10. Figure 2 As shown, the third layer of epoxy resin material 11 is filled in the space formed between the stator core 3, the housing 1 and the end cover 2, and the third layer of epoxy resin material 11 is in close contact with the stator core 3 and the end cover 2 of the housing 1, respectively. Figure 2 shown.

[0071] The phase change material selection method of this embodiment includes the following steps:

[0072] S1 . Select an initial phase change material 10 and obtain the thermal conductivity of the initial phase change material 10 .

[0073] S2, the second layer of phase change material 10 and the third layer of epoxy resin material 11 are divided to obtain composite material layers, and an equivalent specific heat capacity of the phase change material 10 is obtained by performing analytical modeling according to the composite material layers.

[0074] S21. Divide the second layer of phase change material 10 into an inner phase change material layer and an outer phase change material layer according to a preset division ratio, divide the third layer of epoxy resin material 11 into an inner epoxy resin material layer and an outer epoxy resin material layer according to a preset division ratio, and combine the inner epoxy resin material layer and the outer phase change material layer into an equivalent composite material layer.

[0075] In step S21, after being equivalent to a composite material layer, the equivalent specific heat capacity of the composite material layer is obtained according to the following formula:

[0076] c p-mix = ( ηρ pcm c p-pcm +(1- η ) ρ er c p-er ) / ρ mix

[0077] ρ mix = ηρ pcm +(1- η ) ρ er

[0078] in, ρ mix is the equivalent density of the composite material layer, c p-mix is the equivalent specific heat capacity of the composite material layer, η is the volume proportion of the outer phase change material layer in the composite material layer, ρ pcm and ρ er are the densities of the phase change material 10 and the epoxy resin material 11, respectively, c p-pcm and c p-er are the specific heat capacities of the phase change material 10 and the epoxy resin material 11 respectively.

[0079] In order to reduce the complexity of analytical modeling of phase change materials, appropriate simplifications and assumptions are made for phase change material 10:

[0080] 1. Ignore the volume change of the phase change material 10 during the melting process, that is, the solid and liquid states of the phase change material 10 have the same density;

[0081] 2. The thermal conductivity of solid-liquid phase change material 10 is equal everywhere and does not change with temperature;

[0082] 3. Ignore the effect of heat convection caused by the flow of the phase change material 10 after melting on the heat transfer effect;

[0083] 4. Ignore the problem of solid-liquid phase boundary movement of phase change materials 10 and the impact of changes in microscopic results on the phase change process.

[0084] In a specific implementation, the inner phase change material layer is 0.1 mm.

[0085] S22, performing analytical modeling processing on the second layer of phase change material 10 according to the composite material layer and using an equivalent heat capacity method to obtain an equivalent specific heat capacity of the phase change material 10.

[0086] In step S22, the phase change material 10 is subjected to analytical modeling and is set according to the following formula:

[0087] c p = c p-pcm , β = 0 or 1

[0088] c p =(1- β / b 1) ( c p-pcm + L / Δ T )+( β / b 1) c p-pcm ,0< β < b 1

[0089] c p =(1-( β - b 1) / b 2)( c p-pcm + L / Δ T )+(( β - b 1) / b 2) c p-pcm , b 1< β <1

[0090] β =( T max - T pcm ) / ( T 2- T 1)

[0091] in, c p is the equivalent specific heat capacity of the phase change material 10, β is the liquid fraction of the phase change material 10, b 1 is the volume fraction of the inner phase change material layer to the phase change material 10, b 2 is the volume fraction of the outer phase change material layer to the phase change material 10, L is the latent heat of phase change, Δ T is the temperature difference between the starting and ending time of phase change of unit mass phase change material 10, T 1 and T 2 are the phase change starting temperature and phase change ending temperature of the phase change material 10, respectively. T max is the maximum temperature of the phase change material 10, T pcm is the phase change temperature of the phase change material 10.

[0092] S3. A thermal network model of the high overload permanent magnet servo motor cooling structure is constructed according to the thermal conductivity of the phase change material 10, the equivalent specific heat capacity of the composite material layer and the phase change material 10. The high overload permanent magnet servo motor cooling structure is continuously operated until the overload condition ends, and the end temperature rise of the stator winding 9 is obtained according to the thermal network model.

[0093] S301, constructing a thermal network model of the end of the stator winding 9 according to the thermal conductivity of the phase change material 10 in step S1, the composite material layer in step S2 and the equivalent specific heat capacity of the latest phase change material 10. The constructed thermal network model of the end of the stator winding 9 is as follows: Figure 3 shown.

[0094] S302. According to the end thermal network model of the stator winding 9, the physical model of the high overload permanent magnet servo motor cooling structure is divided according to the network division method to obtain a plurality of grid units and the grid unit size of each grid unit. Each grid unit is used as a node. A thermal resistance is set between each node and connected through the thermal resistance. The initial temperature of each node and the initial temperature rise of the high overload permanent magnet servo motor cooling structure are preset, thereby constructing a thermal network model of the high overload permanent magnet servo motor cooling structure. The constructed thermal network model of the high overload permanent magnet servo motor cooling structure is as follows: Figure 4 As shown, the thermal network model is symmetrically distributed along the vertical center axis.

[0095] The network partitioning method is a method for decomposing a complex physical system into multiple subsystems or modules in the field of servo motor structure. Thermal resistance is the equivalent of the degree of resistance encountered when heat is transferred between two nodes. Thermal resistance can be conduction thermal resistance or convection thermal resistance.

[0096] The high overload means that the present embodiment operates under a 4-fold overload condition.

[0097] S303, obtaining material parameters of each component in the physical model of the high overload permanent magnet servo motor cooling structure, and processing according to the grid unit size to obtain the conduction thermal resistance between each node in the thermal network model and the heat capacity of each node.

[0098] The material parameters of each component include the equivalent specific heat capacity of the phase change material 10 and the like.

[0099] S304, using empirical formulas to process the material parameters of each component and the size of the grid unit to obtain the convective heat transfer coefficients of the heat exchange surfaces of the casing 1, the end cover 2 and the rotor end cover 8, and obtaining the convective thermal resistance between each node based on the convective heat transfer coefficients.

[0100] Step S304: The convection heat transfer coefficient is set according to the following formula:

[0101] α c=15(1+0.4(0.2 v r ) 0.9 )

[0102] α e =15(1+0.4(0.7 v r ) 0.9 )

[0103] α r =28(1+(0.45 v r ) 0.5 )

[0104] in, α c , α e and α r are the convective heat transfer coefficients of the heat exchange surfaces of the casing 1, the end cover 2 and the rotor end cover 8, v r is the air flow velocity on the surface of the rotor core 5.

[0105] S305, using electromagnetic field finite element method to process the physical model of the high overload permanent magnet servo motor cooling structure to obtain various losses in the high overload permanent magnet servo motor cooling structure, and adding the various losses in the high overload permanent magnet servo motor cooling structure as heat sources to corresponding nodes;

[0106] The various losses include copper loss of the stator winding 9, iron loss of the stator core 3, eddy current loss of the permanent magnet 4 and friction loss of the bearing 6, etc. The phase change-epoxy resin composite potting material has no loss.

[0107] S306. According to the conduction thermal resistance and convection thermal resistance between each node, the heat capacity of each node and the various losses in the cooling structure of the high overload permanent magnet servo motor, and using Kirchhoff's current law and the law of conservation of energy, a node thermal conductivity matrix, a node thermal capacity matrix and a node heat source matrix of the thermal network model are obtained, and according to the node thermal conductivity matrix, the node thermal capacity matrix and the node heat source matrix, a transient thermal network node equation group is obtained.

[0108] The transient thermal network node equations are set up as follows:

[0109] GT + C (d T / d t ) =P

[0110] in,G is the thermal conductivity matrix, C is the heat capacity matrix, P is the heat source matrix, T is the node temperature matrix, and t is the time.

[0111] S307, using the finite difference method to process the transient thermal network node equation group to obtain a transient node temperature matrix iteration formula, according to which the transient node temperature matrix iteration formula is used to obtain each node temperature and update the node temperature matrix.

[0112] S308 , according to the node temperature matrix, the same method as step S21 is used to obtain the equivalent specific heat capacity of the phase change material 10 after the phase change, and the equivalent specific heat capacity of the phase change material 10 is updated.

[0113] S309. Repeat steps S301 to S308 until the overload condition operation ends.

[0114] In this embodiment, the operating condition is 4 times overload operation for 15 seconds.

[0115] S310 , obtaining the end temperature rise of the stator winding 9 by processing according to the thermal conductivity of the phase change material 10 and the node temperature matrix at all times.

[0116] In a specific implementation, the temperature rise of the teeth of the stator core 3 can also be obtained by processing according to the thermal conductivity of the phase change material 10 and the transient node temperature matrix iteration formula.

[0117] The transient node temperature matrix iteration formula in step S307 and step S310 is set according to the following formula:

[0118] T i+1 =( E -Δ tC -1 G ) T i +Δ tC -1 P

[0119] in, G is the thermal conductivity matrix, C is the heat capacity matrix, P is the heat source matrix, E is the identity matrix, T i For the i The nodal temperature matrix for the time step, T i+1 For the i +1 time step node temperature matrix, Δ t is the time step.

[0120] S4, changing the selection of phase change material 10, repeating steps S2-S3, obtaining the end temperature rise of stator winding 9 under different phase change materials 10, and obtaining the optimal phase change material 10 according to the end temperature rise of stator winding 9 under different phase change materials 10.

[0121] S41 , changing the selection of the phase change material 10 to obtain the changed thermal conductivity of the phase change material 10 , repeating steps S2 to S3 to obtain the end temperature rise of the stator winding 9 under different thermal conductivities of the phase change material 10 .

[0122] S42 , selecting the thermal conductivity of the phase change material 10 corresponding to the lowest temperature rise at the end of the stator winding 9 as the optimal thermal conductivity of the phase change material 10 , and the phase change material 10 corresponding to the optimal thermal conductivity is selected as the optimal phase change material 10 .

[0123] This embodiment uses computational fluid dynamics and other methods to verify the temperature rise suppression effect of the high overload permanent magnet servo motor cooling structure and the rationality of the thermal network model, and selects the best phase change material 10 for the high overload permanent magnet servo motor cooling structure according to the phase change material 10 selection method. Example 2

[0124] This embodiment adopts the same structure as that of Embodiment 1 and uses the thermal network model and computational fluid dynamics simulation of the high overload permanent magnet servo motor cooling structure based on phase change-epoxy resin composite potting material to obtain the temperature of each structure at the end of 15s of the motor running under 4 times overload conditions, as shown in Table 1. From the analysis of Table 1, it can be obtained that the error between the calculation results of the thermal network model and the simulation results of the computational fluid dynamics method is less than 5%, which is within the allowable error range. The temperature change curves of the end of the stator winding 9 and the teeth of the stator core 3 within 15s under the 4 times overload condition are shown in Figure 5 As shown by Figure 5 The analysis shows that the transient temperature curves of the stator winding 9 end and the stator teeth under the two calculation methods of thermal network model and computational fluid dynamics are well fitted, which verifies the rationality of the thermal network model of the high overload permanent magnet servo motor cooling structure based on phase change-epoxy resin composite potting material.

[0125] Table 1 Temperature of each structure in the cooling structure of the high overload permanent magnet servo motor at the end of 15s

[0126] Structure Name Node temperature / ℃ CFD simulation temperature / ℃ error End of stator winding 62.69 61.94 1.21% Center of stator winding 66.57 64.79 2.74% Stator core 38.73 37.18 4.17% Rotor core 27.45 27.73 -1.01% permanent magnet 27.71 27.99 -1.00%

[0127] The same method as in Example 1 was used to change the phase change material 10 and then change the thermal conductivity of the phase change material 10 for multiple experiments. According to the phase change material 10 that can be actually obtained, the range of the thermal conductivity of the phase change material 10 is determined, as shown in Table 2. Case 1 is a reference case in which two end surfaces of the stator core 3 are provided with three layers of epoxy resin material 11 (the three layers of epoxy resin material 11 are the phase change material 10 of the second layer of the phase change-epoxy resin composite potting material replaced with epoxy resin material 11, that is, the three layers use epoxy resin material 11), and Cases 2 to 4 are cases in which different phase change-epoxy resin composite potting materials are provided on the two end surfaces of the stator core 3. The temperature rise results of the ends of the stator winding 9 are shown in FIG. Figure 6 As shown. Figure 6 Analysis shows that, based on the encapsulation phase change-epoxy resin composite encapsulation material, the temperature of the end of the stator winding 9 in Case 2-Case 4 is reduced by 0.99°C, 1.66°C and 2.09°C at the maximum, indicating that the high-overload permanent magnet servo motor cooling structure can suppress the temperature of the end of the stator winding 9 under a 4-fold overload condition and the temperature rise suppression effect increases with the increase of thermal conductivity. The thermal network model constructed in the present invention can accurately process the motor temperature under the high-overload permanent magnet servo motor cooling structure, and after changing the parameters of the phase change material 10, it can quickly process the temperature rise result.

[0128] Table 2 Cases with different thermal conductivity

[0129] Case <![CDATA[Thermal conductivity / (W·(m·k) -1 )]]> Phase change temperature / ℃ <![CDATA[Latent heat of phase change / (J·g -1 )]]> Case 1 — — — Case 2 0.2 30 230 Case 3 0.3 30 230 Case 4 0.4 30 230

[0130] According to the cases with different thermal conductivities in Table 2, case 4 is adopted as the best thermal conductivity, and the phase change material 10 adopted in case 4 is the best phase change material 10 of this embodiment.

[0131] The high-overload permanent magnet servo motor cooling structure that can suppress the short-term large temperature rise at the end of the stator winding 9 is mainly due to the use of phase change-epoxy resin composite potting material. The method for selecting the phase change material 10 uses a thermal network model and an equivalent heat capacity method to process the temperature rise at the end of the stator winding 9, and the computational fluid dynamics method is used to verify the temperature rise suppression effect of the high-overload permanent magnet servo motor cooling structure and the rationality of the thermal network model.

[0132] The structure of the present invention avoids the effect of filling phase change materials on the increase of the motor volume, and also effectively suppresses the end temperature rise of the stator winding under high overload conditions. The method of the present invention selects the optimal phase change material suitable for the structure of the present invention through multiple experiments.

[0133] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, a person of ordinary skill in the art can also make many forms of specific changes under the guidance of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for selecting phase change materials for a high overload permanent magnet servo motor cooling structure, characterized in that: The method comprises the following steps: The high overload permanent magnet servo motor cooling structure comprises a casing (1), an end cover (2), a stator core (3), a permanent magnet (4), a rotor core (5), a rotating shaft (7), a rotor end cover (8) and a stator winding (9); two end covers (2) are fixedly mounted on two end surfaces of the casing (1), the permanent magnet (4), the rotor core (5), the rotating shaft (7) and the stator winding (9) are arranged inside the casing (1), and two ends of the rotating shaft (7) pass through the two end covers (2) and are connected to the two end covers (2). ) are coaxially movably connected; the rotor core (5) is coaxially fixedly sleeved on the rotating shaft (7); a plurality of permanent magnets (4) arranged circumferentially and axially penetrating are fixedly sleeved on the surface of the rotor core (5); two rotor end covers (8) are respectively fixedly mounted on the two end faces of the rotor core (5); a stator core (3) is tightly mounted on the circumferential inner wall of the casing (1); a plurality of winding axial through slots are opened in the stator core (3) along the circumferential direction, and a corresponding stator winding (9) is respectively embedded in each winding axial through slot; Both end surfaces of the stator core (3) are provided with a phase change-epoxy resin composite potting material; The phase change-epoxy resin composite potting material is a three-layer potting material, and the three layers of potting materials are respectively a first layer of epoxy resin material (11), a second layer of phase change material (10) and a third layer of epoxy resin material (11); the first layer of epoxy resin material (11) is potted on two end surfaces of the stator core (3), the second layer of phase change material (10) is potted on the end surfaces of both ends of each stator winding (9), the phase change materials (10) potted on the end surfaces of each two adjacent stator windings (9) are not connected to each other, the third layer of epoxy resin material (11) is potted on the surface of the phase change material (10), and the third layer of epoxy resin material (11) is filled in the space formed between the stator core (3), the housing (1) and the end cover (2) and is in close contact with the stator core (3), the housing (1) and the end cover (2); S1, selecting an initial phase change material (10) and obtaining the thermal conductivity of the phase change material (10); S2, dividing the second layer of phase change material (10) and the third layer of epoxy resin material (11) to obtain composite material layers, and performing analytical modeling on the composite material layers to obtain an equivalent specific heat capacity of the phase change material (10); S3, constructing a thermal network model of the high overload permanent magnet servo motor cooling structure according to the thermal conductivity of the phase change material (10), the composite material layer and the equivalent specific heat capacity of the phase change material (10), the high overload permanent magnet servo motor cooling structure continuously operating until the overload condition ends, and obtaining the end temperature rise of the stator winding (9) according to the thermal network model; S4, changing the selection of the phase change material (10), repeating steps S2 to S3, obtaining the temperature rise of the end of the stator winding (9) under different phase change materials (10), and obtaining the optimal phase change material (10) according to the temperature rise of the end of the stator winding (9) under different phase change materials (10); The step S2 is specifically as follows: S21, dividing the second layer of phase change material (10) into an inner phase change material layer and an outer phase change material layer according to a preset division ratio, dividing the third layer of epoxy resin material (11) into an inner epoxy resin material layer and an outer epoxy resin material layer according to a preset division ratio, and combining the inner epoxy resin material layer and the outer phase change material layer to form an equivalent composite material layer; S22, performing analytical modeling processing on the second layer of phase change material (10) based on the composite material layer and using an equivalent heat capacity method to obtain an equivalent specific heat capacity of the phase change material (10); In step S22, the analytical modeling process of the phase change material (10) is set according to the following formula: c p = c p-pcm , β = 0 or 1 c p =(1- β / b 1) ( c p-pcm + L / D T )+( β / b 1) c p-pcm ,0< β < b 1 c p =(1-( β - b 1) / b 2)( c p-pcm + L / D T )+(( β - b 1) / b 2) c p-pcm , b 1< β <1 β =( T max - T pcm ) / ( T 2- T 1) in, c p is the equivalent specific heat capacity of the phase change material (10), c p-pcm is the specific heat capacity of the phase change material (10), β is the liquid fraction of the phase change material (10), b 1 is the volume fraction of the inner phase change material layer in the phase change material (10), b 2 is the volume fraction of the outer phase change material layer in the phase change material (10), L is the latent heat of phase change, Δ T is the temperature difference between the starting and ending time of the phase change of the unit mass phase change material (10), T 1 and T 2 are the phase change starting temperature and phase change ending temperature of the phase change material (10), T max is the maximum temperature of the phase change material (10), T pcm is the phase change temperature of the phase change material (10).

2. The phase change material selection method according to claim 1, characterized in that: In the step S21, after being equivalent to the composite material layer, the equivalent specific heat capacity of the composite material layer is obtained according to the following formula: c p-mix = ( ηρ pcm c p-pcm + (1- η ) ρ er c p-er ) / ρ mix ρ mix = ηρ pcm + (1- η ) ρ er in, ρ mix is the equivalent density of the composite material layer, c p-mix is the equivalent specific heat capacity of the composite material layer, η is the volume proportion of the outer phase change material layer in the composite material layer, ρ pcm and ρ er are the densities of the phase change material (10) and the epoxy resin material (11), c p-pcm and c p-er are the specific heat capacities of the phase change material (10) and the epoxy resin material (11), respectively.

3. The phase change material selection method according to claim 1, characterized in that: The step S3 is specifically as follows: S301, constructing a thermal network model of the end of the stator winding (9) according to the thermal conductivity of the phase change material (10) in step S1 and the equivalent specific heat capacity of the composite material layer and the phase change material (10) in step S2; S302, dividing the physical model of the high overload permanent magnet servo motor cooling structure according to the network division method based on the end thermal network model of the stator winding (9), obtaining a plurality of grid units and the grid unit size of each grid unit, taking each grid unit as a node, providing thermal resistance between each node and connecting them through the thermal resistance, and presetting the initial temperature of each node and the initial temperature rise of the high overload permanent magnet servo motor cooling structure, thereby constructing a thermal network model of the high overload permanent magnet servo motor cooling structure; S303, obtaining material parameters of each component in the physical model of the high overload permanent magnet servo motor cooling structure, and processing according to the grid unit size to obtain the conduction thermal resistance between each node in the thermal network model and the heat capacity of each node; S304, using empirical formulas to process the material parameters of each component and the size of the grid unit to obtain the convective heat transfer coefficients of the heat exchange surfaces of the casing (1), the end cover (2) and the rotor end cover (8), and obtaining the convective thermal resistance between each node based on the convective heat transfer coefficients; S305, using electromagnetic field finite element method to process the physical model of the high overload permanent magnet servo motor cooling structure to obtain various losses in the high overload permanent magnet servo motor cooling structure, and adding the various losses in the high overload permanent magnet servo motor cooling structure as heat sources to corresponding nodes; S306, according to the conduction thermal resistance and convection thermal resistance between each node, the heat capacity of each node and various losses in the cooling structure of the high overload permanent magnet servo motor, and using Kirchhoff's current law and the law of conservation of energy to obtain a node thermal conductivity matrix, a node thermal capacity matrix and a node heat source matrix of the thermal network model, and according to the node thermal conductivity matrix, the node thermal capacity matrix and the node heat source matrix, to obtain a transient thermal network node equation group; S307, using a finite difference method to process the transient thermal network node equation group to obtain a transient node temperature matrix iteration formula, obtaining each node temperature according to the transient node temperature matrix iteration formula and updating the node temperature matrix; S308, using the same method as step S21 to process the node temperature matrix to obtain the equivalent specific heat capacity of the phase change material (10) after the phase change and updating the equivalent specific heat capacity of the phase change material (10); S309, repeating steps S301 to S308 until the overload condition operation ends, and then the operation ends; S310, performing processing based on the thermal conductivity of the phase change material (10) and the node temperature matrix at all times to obtain the end temperature rise of the stator winding (9).

4. The method for selecting a phase change material according to claim 3, characterized in that: The convection heat transfer coefficient in step S304 is set according to the following formula: α c =15(1+0.4(0.2 v r ) 0.9 ) α e =15(1+0.4(0.7 v r ) 0.9 ) α r =28(1+(0.45 v r ) 0.5 ) in, α c , α e and α r are the convective heat transfer coefficients of the heat exchange surfaces of the casing (1), the end cover (2) and the rotor end cover (8), respectively. v r is the air velocity on the surface of the rotor core (5).

5. The method for selecting a phase change material according to claim 3, characterized in that: The transient node temperature matrix iteration formula is set according to the following formula: T i+1 =( E -D tC -1 G ) T i +D tC -1 P in, G is the thermal conductivity matrix, C is the heat capacity matrix, P is the heat source matrix, E is the identity matrix, T i For the i The nodal temperature matrix for the time step, T i+1 For the i +1 time step node temperature matrix, Δ t is the time step.

6. The phase change material selection method according to claim 1, characterized in that: The step S4 is specifically as follows: S41, changing the selection of the phase change material (10) to obtain the thermal conductivity of the changed phase change material (10), repeating steps S2 to S3 to obtain the temperature rise at the end of the stator winding (9) under different thermal conductivities of the phase change material (10); S42, selecting the thermal conductivity of the phase change material (10) corresponding to the lowest temperature rise at the end of the stator winding (9) as the optimal thermal conductivity of the phase change material (10), and the phase change material (10) corresponding to the optimal thermal conductivity as the optimal phase change material (10).

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