Thermal simulation method for high-protection-level compact distributed marine water-cooling frequency converter

Abstract

The invention discloses a thermal simulation method for a high-protection-level compact distributed marine water-cooling frequency converter, which comprises the following steps of: firstly, carrying out electric-thermal coupling calculation and flow-thermal coupling calculation, and then carrying out thermal field calculation on other heat sources such as capacitors, copper bars and controllers to obtain the temperature of air in a cavity of the frequency converter and the temperature of a shell of the frequency converter; and finally, carrying out electricity-flow-heat three-field coupling calculation, and obtaining a simulation result by setting boundary conditions and dividing grids. According to the thermal simulation method for the high-protection-level compact distributed marine water-cooling frequency converter, the heat dissipation design of the frequency converter is guided through the simulation result, namely temperature distribution, the heat dissipation effect is improved, and therefore higher power density is achieved.

Description

Technical Field

[0001] This invention relates to the field of power control equipment simulation technology, specifically to a thermal simulation method for a high-protection-level compact distributed marine water-cooled frequency converter. Background Technology

[0002] With the development of marine electric propulsion technology, high-protection-level, compact, distributed marine water-cooled frequency converters have been widely used. These converters integrate IGBT modules, capacitors, copper busbars, control boards, heat sinks, and other components. To ensure electrical insulation, epoxy resin boards are pressed onto the copper busbars. The compact structure and concentrated heat sources make heat dissipation design extremely challenging. Therefore, from a physical field perspective, they can be divided as follows: Electric field: primarily electrothermal coupling via the copper busbars; the heat dissipation rates of other components are not simulated, but can be found in the component datasheets; Flow field: primarily coolant in the heat sinks, with additional air within the converter; Thermal field: the largest heat source within the converter is the IGBT module, containing IGBT chips and diodes, along with capacitors, copper busbars, and the control board.

[0003] In this high-protection-level compact distributed marine water-cooled frequency converter, the main heat dissipation methods are forced convection cooling of the coolant in the radiator, natural convection cooling of the air in the frequency converter, and conduction cooling of each component installed in the frequency converter housing through the mounting surface.

[0004] Existing frequency converter simulation methods have many shortcomings: 1. Patent application CN115859713A discloses a method for analyzing the temperature field of a frequency converter based on water-air heat exchanger cooling. This method only focuses on temperature field simulation and does not involve the coupling calculation of electric field and flow field. It ignores the precise influence of Joule heat generated by current conduction on the temperature field and does not consider the changes in contact resistance and material properties with temperature. As a result, the accuracy of temperature field simulation is insufficient and cannot meet the fine heat dissipation design requirements of compact frequency converters. 2. Patent application CN117521468A discloses a performance optimization method for a mine explosion-proof frequency converter. Its core lies in electromagnetic interference analysis and heat dissipation optimization. Although it involves electro-magnetic-thermal coupling, it does not achieve complete three-field coupling of electric field, flow field and thermal field. Furthermore, it does not make targeted designs for the special structure of compact distributed marine frequency converters (such as epoxy resin board pressing and copper busbar contact resistance). The simulation model has low fit with the actual working conditions. 3. Existing simulation methods generally suffer from incomplete consideration of heat sources. They only focus on the heat dissipation of the main power devices and ignore the impact of natural convection and conduction heat dissipation of auxiliary heat sources such as capacitors and control boards on the overall temperature distribution. At the same time, the modeling of the heat transfer path between thermal grease, chips and mounting surfaces is rough and no accurate equivalent model has been established. This results in a large deviation between the simulation results and the actual operating conditions, making it difficult to effectively guide the heat dissipation design of high power density frequency converters.

[0005] Therefore, in order to develop a compact distributed water-cooled frequency converter with high protection level, and to reduce the size of the equipment and increase its power density, higher requirements are placed on the heat dissipation design of the frequency converter. It is necessary to develop a thermal simulation method for this compact topology and optimize the structural design based on the thermal simulation results. Summary of the Invention

[0006] The purpose of this invention is to provide a thermal simulation method for a compact distributed marine water-cooled frequency converter with a high protection level. The simulation results, i.e., temperature distribution, guide the heat dissipation design of the frequency converter, improve the heat dissipation effect, and thus achieve higher power density.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A thermal simulation method for a high-protection-level compact distributed marine water-cooled frequency converter includes the following steps: S1, Electro-thermal coupling calculation: Electro-thermal coupling calculation is performed mainly on the copper busbar, establishing an electric field model and a thermal field model for the copper busbar. During the modeling process, the influence of contact resistance on current density and the resulting Joule heat are considered, and the model is assigned electro-thermal coupling material properties that change with temperature. The temperature distribution of the copper busbar and epoxy resin board is calculated. S2, Fluid-thermal coupling calculation: Fluid-thermal coupling calculation is performed from the IGBT module to the radiator coolant. An equivalent model and flow field model from the IGBT to the radiator are established. A thermal contact method is used to establish a thermal grease model. The accuracy of the equation selection is verified by applying the turbulence equation and combining experiments. The temperature distribution of the copper substrate surface is calculated. S3, Thermal field calculation of other heat sources: For other heat sources such as capacitors and control boards, models of the air domain and each heat source within the frequency converter cavity are established. Through natural convection and conduction heat dissipation calculations, the air temperature inside the frequency converter cavity and the temperature of the frequency converter casing are obtained. S4, Electric field-fluid field-thermal field three-field coupling calculation: Integrating step S1... Based on the calculation results of S3, an overall geometric model is established, electric field, flow field, thermal field and mutually coupled physical fields are added, boundary conditions are summarized and meshed, and the calculation is started. Finally, the surface temperature of each device in the inverter, the air temperature in the cavity, the cooling water temperature distribution and the surface temperature of the module chip are obtained.

[0008] Furthermore, step S1 specifically includes the following sub-steps: S1.1, establishing a three-dimensional model of the copper busbar, querying the material library, and obtaining the conductivity σ and constant-pressure heat capacity C of the copper busbar through research or experimentation.p Relative permittivity ε r Density ρ, thermal conductivity λ T The curve of temperature variation is assigned to the model; S1.2, at the copper busbar overlap, the projection surface of the connecting bolt gasket on the copper busbar interface is equivalent to the current conduction area, and the contact resistance R is obtained through experiments. Contact Calculate the surface resistivity ρ surface And assign values, setting the remaining copper busbar contact positions to electrical insulation; S1.3, establish the epoxy resin plate model pressed onto the copper busbar, and assign it a constant pressure heat capacity C. p Density ρ, thermal conductivity λ T Material properties, setting the surface heat transfer coefficient h and air temperature T at the heat exchange interface of copper busbar, epoxy resin plate and air. amb S1.4 Couple the electric and thermal fields, add the Joule thermophysical field, refine the mesh for the equivalent conductive region of the contact resistance, automatically divide the mesh for the rest, and calculate the temperature distribution of the copper busbar and epoxy resin board step by step.

[0009] Furthermore, in step S1.2, the surface resistivity ρ surface Through the formula ρ surface =R Contact The total area S of the equivalent conductive region of the contact resistance is calculated using the formula... Calculate, where P is the number of equivalent conductive regions for contact resistance, and S... n Let be the area of ​​the equivalent conductive region of the nth contact resistance.

[0010] Furthermore, step S2 specifically includes the following sub-steps: S2.1, establishing a model along the heat transfer path, including the IGBT module, thermal grease, inverter housing, and flow channels; establishing a chip model with the same position based on the chip location and size in the IGBT module; establishing an equivalent model of the structure between the chip and the bottom surface of the copper substrate; and using the IGBT module junction-casing thermal resistance R... thJC As the equivalent model's thermal resistance; S2.2, assigning a constant-pressure heat capacity C to all models. p Thermal conductivity λ T Density ρ is a material property that imparts an additional dynamic viscosity μ to thermal grease and cooling water, while thermal conductivity λ is the equivalent model between the chip and the mounting surface. T Through formula λ T =L / (R thJC∙ S) Calculation: L is the heat transfer path length from the chip to the bottom surface of the copper substrate, and S is the area of ​​the copper substrate of the IGBT module; S2.3, Add a thermal field and set the thickness d of the thermal grease layer through thermal contact. s Set the coolant inflow surface temperature T inS2.4. Add a flow field, set the coolant inflow rate Q and outflow surface, select the turbulence equation, couple the flow field and thermal field and add a non-isothermal flow multiphysics field, perform wall distance initialization calculation, flow field steady-state calculation and thermal field coupling calculation step by step to obtain the temperature distribution of the copper substrate surface.

[0011] Furthermore, the turbulence equations mentioned in step S2.4 include the k-ε equation and the k-ω equation. The suitability of different turbulence equations is verified through experiments, and the optimal equation is selected.

[0012] Furthermore, step S2 also includes using formula T chip-max =T plate-max +R thJC *P chip -273.15 Calculate the highest temperature of the chip, where T chip-max T is the highest temperature on the chip. plate-max P is the highest temperature on the heat exchange plate. chip This refers to the chip's heat dissipation rate.

[0013] Furthermore, step S3 specifically includes the following sub-steps: S3.1, establish the thermal field model of the capacitor, copper busbar, and control board, and assign heat dissipation rate to each model; S3.2, establish the air domain flow field model in the inverter cavity, assign air properties, and set the gravity direction according to the actual layout direction of the inverter; S3.3, couple the thermal field and flow field, add non-isothermal flow multiphysics field, and calculate the air temperature inside the inverter cavity and the inverter shell temperature.

[0014] Furthermore, step S4 specifically includes the following sub-steps: S4.1, synthesizing the model content from steps S1 to S3, establishing the overall geometric model of the frequency converter, giving the material properties of the overall model, and considering the temperature dependence of all material properties; S4.2, adding electric field, flow field, thermal field, and mutually coupled Joule heating and non-isothermal flow physical fields, and using the Joule heating calculation results as a heat source to transfer to the non-isothermal flow physical field for coupling calculation; S4.3, summarizing the boundary conditions from steps S1 to S3, including current or potential and contact resistance in the electric field, inlet and outlet positions and flow rates in the flow field, and ambient temperature, inlet water temperature, equivalent thermal resistance, and heat source heat dissipation rate in the thermal field; S4.4, refining the mesh of the equivalent conductive area of ​​contact resistance, chip structure, and flow channel, and automatically dividing the mesh of the remaining parts according to the physical field, and starting the three-field coupling calculation.

[0015] Furthermore, in step S4.4, the chip structure and flow channels are processed with extremely fine mesh, and the equivalent conductive region of the contact resistance is processed with fine mesh. The mesh refinement density is adjusted according to the simulation convergence requirements.

[0016] Furthermore, the material property assignments for all models in steps S1 to S4 are based on the property-temperature curves, which are obtained through material library queries, experimental testing, or industry research.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Achieve complete coupling of electric field, flow field, and thermal field. For the first time, integrate the electric-thermal coupling of copper busbar, the flow-thermal coupling of IGBT module, and the thermal field calculation of auxiliary heat source into a unified simulation system, which comprehensively reflects the multi-physics interaction mechanism and improves the simulation accuracy by more than 30% compared with the existing technology; 2. An innovative contact resistance equivalent modeling method is introduced, which, combined with the temperature dependence of material properties, accurately simulates the current conduction and heat transfer process, solving the simulation deviation problem caused by neglecting contact resistance and material temperature characteristics in existing technologies; 3. Establish an equivalent thermal resistance model from the chip to the mounting surface and a thermal contact model for thermal grease. Combine this with experimentally verified turbulence equations to significantly improve the realism of flow-thermal coupling calculations and provide accurate data support for IGBT module heat dissipation optimization. 4. Comprehensive coverage of heat dissipation calculations for major power devices and auxiliary heat sources, taking into account the synergistic effect of natural convection, forced convection and conduction heat dissipation, fully presenting the internal temperature distribution of the frequency converter, avoiding the one-sidedness of simulation caused by the omission of heat sources in existing technologies; 5. A differentiated meshing strategy is adopted to refine the mesh in regions with high gradient physical quantities. This improves computational efficiency while ensuring simulation accuracy. The simulation results can directly guide the optimization of the heat dissipation structure of high-protection-level compact distributed marine water-cooled frequency converters, helping to achieve a balance between equipment miniaturization and high power density.

[0018] In summary, the present invention proposes a thermal simulation method for a high-protection-level compact distributed marine water-cooled frequency converter. The simulation results, i.e., temperature distribution, guide the heat dissipation design of the frequency converter, improve the heat dissipation effect, and thus achieve higher power density. Attached Figure Description

[0019] Figure 1 The flowchart shows the thermal simulation method for a high-protection-level compact distributed marine water-cooled frequency converter. Detailed Implementation

[0020] The specific embodiments of the present invention are described below with reference to the figures: like Figure 1 As shown in the figure, the thermal simulation method for a high-protection-level compact distributed marine water-cooled frequency converter proposed in this embodiment of the invention includes the following steps: Step 1, Electro-thermal Coupling Calculation: Electro-thermal coupling calculation is performed primarily using a copper busbar, and is divided into two sub-steps: Step 1.1, Establishing an electric field model for the copper busbar and performing electric field calculations; Step 1.2, Establishing a thermal field model and performing electro-thermal coupling calculations. During the modeling process, the material properties of the electro-thermal coupling in the model are assigned, and the influence of contact resistance on current density and the resulting Joule heating are considered.

[0021] Step 2, Flow-Thermal Coupling Calculation: The flow-thermal coupling calculation from the IGBT module to the heatsink coolant is divided into two sub-steps: Step 2.1, establishing an equivalent model from the IGBT to the heatsink; Step 2.2, establishing a flow field model for flow-thermal coupling calculation. During the modeling process, an equivalent model of the structure between the chip and the mounting surface is established, and a thermal contact method is used to establish a thermal grease model. Multiple turbulence equations are applied, and the accuracy of the selected flow field equations is verified through experiments.

[0022] Step 3: Thermal field calculation for other heat sources: The heat dissipation methods for the remaining capacitors, copper busbars, and control board heat sources are mainly natural convection and conduction. Establish the air domain and models of each heat source within the inverter cavity. This is also divided into two sub-steps: Step 3.1: Establish the thermal field for the capacitors, copper busbars, and control board, and assign heat dissipation rates; Step 3.2: Establish the flow field in the air domain, assign air properties, and set the gravity direction according to the actual layout direction; Step 3.3: Couple the thermal field and flow field, add a non-isothermal flow multiphysics field, and calculate the air temperature inside the inverter cavity and the inverter casing temperature under the influence of the remaining heat sources.

[0023] Step 4: Coupled Calculation of Electric Field, Flow Field, and Thermal Field: The calculations performed in the first three steps are combined and a coupled calculation of the electric field, flow field, and thermal field is executed. This is divided into the following sub-steps: Step 4.1: Integrate the contents of the first three steps to establish an overall geometric model and specify the material properties of the overall model; Step 4.2: Add the electric field, flow field, thermal field, and the coupled Joule heating and non-isothermal flow physical fields. The Joule heating result is used as a heat source to transfer to the non-isothermal flow physical field for coupling calculation; Step 4.3: Summarize the boundary conditions from the first three steps, including the current or potential and contact resistance in the electric field, the inlet and outlet positions and flow rates in the flow field, and the ambient temperature, inlet water temperature, equivalent thermal resistance or equivalent thermal conductivity, and heat source heat dissipation rate in the thermal field; Step 4.4: Mesh the data and begin the calculation.

[0024] The final results yielded the surface temperatures of various components within the inverter, the air temperature inside the cavity, the cooling water temperature distribution, and, most critically, the surface temperatures of the module chips. These temperature distribution results guided the heat dissipation design of compact, distributed water-cooled inverters with high protection ratings.

[0025] Preferred method: Step 1, the electro-thermal coupling calculation, includes the following detailed operating procedures: First, a three-dimensional model of the copper busbar was established. When assigning material properties to the model, attention was paid to how these properties change with temperature. The characteristic-temperature curves were confirmed and assigned using methods such as consulting material libraries, conducting research, or experimentation, preparing for the next step of electro-thermal coupling simulation. In the electro-thermal coupling of the copper busbar, its conductivity σ and constant-pressure heat capacity C were confirmed. p Relative permittivity ε r Density ρ, thermal conductivity λ T The temperature-dependent curve is then assigned. Subsequent material properties are all given with temperature consideration.

[0026] Secondly, an electric field needs to be added. The contact resistance R at the copper busbar overlap needs to be considered. Contact This resistance value was obtained experimentally. In the model, at the copper busbar overlap, the projection surface of the connecting bolt gasket on the copper busbar interface is equivalent to the current conduction region, given the surface resistivity ρ. surface The remaining copper busbar contact points are set to be electrically insulated. Surface resistivity ρ surface It can be determined by the contact resistance R Contact The calculation yields the following formula: ρ surface =R Contact ·S In the formula: ρ surface — Surface resistivity, Ω·mm 2 ; R Contact —Contact resistance, Ω; S – Total area of ​​the equivalent conductive region of contact resistance, mm 2 .

[0027] The formula for calculating the total area of ​​the equivalent conductive region with contact resistance is as follows:

[0028] Where: P — the number of equivalent conductive regions for contact resistance; S n —The area of ​​the equivalent conducting region of the nth contact resistance.

[0029] After setting current or potential values ​​at both ends of the copper busbar, the entire structure is meshed. The mesh is further refined in the equivalent conductive region of the contact resistance, while other parts are automatically meshed based on the physical field. Electric field calculations can then be performed to obtain the current density J distribution of the copper busbar under the influence of contact resistance.

[0030] The next step is to establish a thermal field model along the heat transfer path. This involves creating a model of an epoxy resin plate pressed onto a copper busbar, assigning it a constant-pressure heat capacity C. p Density ρ, thermal conductivity λ TMaterial properties, etc. Modeling of the air inside the inverter cavity is not performed at this step. Add a thermal field, specifying the surface heat transfer coefficient h at the heat exchange interface between the copper busbar, epoxy resin plate, and air. Set the air temperature T. amb .

[0031] Finally, the electric and thermal fields are coupled, and a Joule thermal physics field is added. The remaining part of the model is automatically meshed based on the physics field. The current density distribution has already been calculated in the electric field, and Joule heating is calculated based on this. Step-by-step calculations enhance the model's convergence. Finally, the temperature distribution on the copper busbar and epoxy resin plate is obtained.

[0032] Preferred method: Step 2, the flow-heat coupling calculation includes the following detailed operation methods: A model is built along the heat transfer path, including the IGBT module, thermal grease, inverter housing (flow channel shell), and flow channels (cooling water). A chip model of the same size and location is built based on the chip's position and size within the IGBT module. An equivalent model of the structure between the chip and the bottom surface of the copper substrate is established, referring to the junction-to-shell thermal resistance R in the IGBT module manual. thJC As the equivalent model's thermal resistance, a surface is given on the mating surface between the IGBT module's copper substrate and the heatsink mounting surface. This surface is the same size as the copper substrate, coincidentally positioned with it, and its thickness is set within the thermal field. Models of the inverter housing (flow channel shell) and the flow channel (cooling water) are then established. All models are assigned a constant-pressure heat capacity C. p Thermal conductivity λ T Material properties such as density ρ, and thermal grease and cooling water materials also require an additional dynamic viscosity μ. The thermal conductivity λ of the equivalent model between the chip and the mounting surface. T The following calculation formula is given: λ T =L / (R thJC∙ S) In the formula: λ T — Thermal conductivity of the equivalent model between the chip and the mounting surface, W / (m·K); RthJC—Equivalent thermal resistance of the equivalent model between the chip and the bottom surface of the copper substrate, i.e., the junction-case thermal resistance of the IGBT module, K / W; L—Length of the heat transfer path from the chip to the bottom surface of the copper substrate, in meters; S – Heat transfer area, which in this model is the area of ​​the copper substrate of the IGBT module, in meters. 2 .

[0033] Add a thermal field. Continue modeling the thermal paste by setting up the thermal contact. Define a layer thickness d in the thermal contact based on the thickness of the thermal paste applied to the copper substrate and the heatsink mounting surface. s Set the coolant inflow surface and assign a temperature T. inSet the coolant outlet surface. Provide a heat source based on the chip's heat dissipation rate P under calculated operating conditions.

[0034] Add a flow field, set the coolant inflow surface and give a flow rate Q, and set the coolant outflow surface. Different flow fields can be selected based on different turbulence equations. Couple the flow field and thermal field, and add a non-isothermal flow multiphysics field. Begin mesh generation. Select fine or extremely fine mesh on the chip structure and flow channels; the remaining parts are automatically meshed based on the physics field. The multiphysics calculation is also performed step-by-step: first, initialize the wall distance; then, perform steady-state flow field calculations; and finally, couple the thermal field calculations. This yields the temperature distribution on the copper substrate surface under coolant heat dissipation. The following calculations are then performed: T chip-max =T plate-max +R thJC *P chip -273.15 In the formula: T chip-max —The highest temperature on the chip, in °C; T plate-max —Highest temperature on the heat spreader, °C; P chip —Chip thermal efficiency, W.

[0035] This embodiment is merely an exemplary description of the present invention and does not limit its scope of protection. Those skilled in the art can make partial changes to it, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A high protection class compact distributed marine water-cooled frequency converter thermal simulation method, characterized in that, The method comprises the following steps: S1, electric-thermal coupling calculation: electric-thermal coupling calculation is carried out mainly on the copper bar, a copper bar electric field model and a thermal field model are established, the influence of the contact resistance on the current density and the joule heat generated thereby are considered in the modeling process, and the electric-thermal coupling material properties of the model are given with temperature variation, and the temperature distribution of the copper bar and the epoxy resin plate is calculated; S2, flow-thermal coupling calculation: flow-thermal coupling calculation is carried out from the IGBT module to the radiator coolant, an equivalent model from the IGBT to the radiator and a flow field model are established, a thermal contact method is used to establish a radiator silicone grease model, a turbulent flow equation is used and the accuracy of the equation is verified by experiment, and the temperature distribution of the copper base surface is calculated; S3, thermal field calculation of the remaining heat sources: for the capacitors, control boards and other remaining heat sources, an air domain in the frequency converter cavity and each heat source model are established, the air temperature in the frequency converter cavity and the frequency converter shell temperature are obtained through natural convection heat dissipation and conduction heat dissipation calculation; S4, electric field-flow field-thermal field three-field coupling calculation: the calculation results of steps S1 to S3 are integrated, a whole geometric model is established, electric field, flow field, thermal field and mutually coupled physical fields are added, boundary conditions are summarized and mesh is divided, and then calculation is started, and finally the surface temperature of each device in the frequency converter, the air temperature in the cavity, the cooling water temperature distribution and the module chip surface temperature are obtained.

2. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 1, characterized in that, The step S1 specifically comprises the following sub-steps: S1.1, establishing a three-dimensional model of the copper bar, querying a material library, researching or testing to obtain the conductivity σ, constant voltage heat capacity C p , relative dielectric constant ε r , density ρ, thermal conductivity λ T of the copper bar with temperature change curves and assigning the model; S1.2, at the lap joint of the copper bar, the projection surface of the connecting bolt gasket on the copper bar interface is equivalent to the current conduction area, the contact resistance R Contact is obtained through testing, the surface resistivity ρ surface is calculated and assigned, and the remaining contact positions of the copper bar are set as electrically insulated. S1.3, a copper bar on the compression epoxy resin plate model, give its constant pressure heat capacity C p , density ρ, thermal conductivity λ T Material properties, on the copper bar, epoxy resin plate and air heat transfer interface to set the surface heat transfer coefficient h and air temperature T amb ; S1.4, coupling electric field and thermal field, adding joule heat physical field, refining grid in the equivalent conduction area of contact resistance, and automatically dividing grid in the remaining part, and calculating the temperature distribution of the copper bar and the epoxy resin plate in steps.

3. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 2, characterized in that, The surface resistivity p in step S1.2 surface The surface resistivity p in step S1.2 surface = R Contact · S The total area S of the contact resistance equivalent conduction areas is calculated by the formula where P is the number of contact resistance equivalent conduction areas, S n is the area of the nth contact resistance equivalent conduction area.

4. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 1, characterized in that, Step S2 specifically includes the following sub-steps: S2.1, establishing a model along the heat transfer path, including IGBT module, heat dissipation silicone grease, frequency converter shell, flow channel, establishing a chip model at the same position according to the chip position and size in the IGBT module, and establishing an equivalent model of the structure between the chip and the bottom surface of the copper base, taking the IGBT module junction-shell thermal resistance R thJC as the equivalent model thermal resistance; S2.2, assigning constant pressure heat capacity C p , thermal conductivity λ T , and density ρ material properties to all models, and additionally assigning dynamic viscosity μ to the heat dissipation silicone grease and cooling water, wherein the thermal conductivity λ T of the equivalent model between the chip and the mounting surface is calculated by the formula λ T =L / (R thJC∙ S), L is the heat transfer path length from the chip to the bottom surface of the copper base, and S is the area of the IGBT module copper base; S2.3, add a thermal field, set the thickness d of the thermal grease layer by thermal contact s , set the temperature T of the inflow surface and the outflow surface of the cooling liquid, and give the heat source according to the heat dissipation rate P of the chip under the calculated working condition; in S2.4, add a flow field, set the inflow and outflow of the cooling liquid, select a turbulent flow equation, couple the flow field and the thermal field, and add a non-isothermal flow multi-physics field, and perform step-by-step wall distance initialization calculation, flow field steady-state calculation, and thermal field coupling calculation to obtain the temperature distribution of the copper substrate surface.

5. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 4, characterized in that, The turbulent flow equation in step S2.4 includes k-ε equation and k-ω equation, the adaptability of different turbulent flow equations is verified by experiment, and the optimal equation is selected.

6. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 4, characterized in that, Step S2 also includes calculating by formula T chip-max = T plate-max + R thJC * P chip - 273.15 The maximum temperature of the computing chip, where T chip-max is the maximum temperature on the chip, T plate-max is the maximum temperature on the heat spreader, P chip is the chip heat dissipation rate.

7. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 1, characterized in that, Step S3 specifically includes the following sub-steps: S3.1, establishing thermal field models of capacitors, copper bars and control boards, and assigning heat dissipation rates to each model; S3.2, establishing an air domain flow field model in the frequency converter cavity, assigning air properties, and setting the gravity direction according to the actual arrangement direction of the frequency converter; S3.3, coupling thermal field and flow field, adding non-isothermal flow multi-physical field, and calculating the air temperature in the frequency converter cavity and the frequency converter shell temperature.

8. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 1, characterized in that, Step S4 specifically includes the following sub-steps: S4.1, integrating the model contents of steps S1 to S3, establishing a whole geometric model of the frequency converter, giving material properties of the whole model, and the material properties all consider temperature dependence; S4.2, adding electric field, flow field, thermal field and mutually coupled joule heat, non-isothermal flow physical field, and transferring the joule heat calculation result to the non-isothermal flow physical field as a heat source for coupling calculation; S4.3, summarizing the boundary conditions of steps S1 to S3, including current or potential in the electric field, contact resistance, inlet and outlet positions in the flow field, inlet and outlet flow, ambient temperature, inlet water temperature, equivalent thermal resistance and heat dissipation rate of the heat source in the thermal field; S4.4, refining grid in the equivalent conduction area of contact resistance, chip structure and flow channel, and automatically dividing grid in the remaining part according to the physical field, and starting three-field coupling calculation.

9. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 8, characterized in that, In step S4.4, the chip structure and the flow channel are processed by using extremely refined grids, and the contact resistance equivalent conduction area is processed by using refined grids, and the grid refinement density is adjusted according to the simulation convergence requirement.

10. The high protection class compact distributed marine water-cooled frequency converter thermal simulation method according to claim 1, characterized in that, In steps S1 to S4, the material property assignment of all models is based on a characteristic-temperature curve, which is obtained by querying a material library, testing by experiment or industry research.

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