A thermal design method based on high power density PCB board

Abstract

The application provides a high-power-density PCB-based thermal design method, which comprises the following steps: firstly, a power loss mathematical model of a heat source on a PCB is established, and a PCB thermal simulation model is established according to the power loss mathematical model; secondly, chip-level, board-level and system-level thermal analysis is performed on the PCB according to the thermal simulation result; then, thermal-structure improvement is performed on the PCB according to the thermal analysis result, so that the power density of the PCB is improved while the heat dissipation capacity is ensured; finally, a heat dissipation device is added to the improved PCB corresponding to the heat source, and the structure parameters of the heat dissipation device are optimized through a genetic algorithm. The method can improve the power density of the PCB, so that the system has good heat dissipation capacity and high thermal reliability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal design, and particularly relates to a thermal design method based on a high-power-density PCB (Printed Circuit Board). BACKGROUND

[0002] PCB boards are widely used in various fields such as national defense, aerospace, new energy vehicles and daily production, and the performance of a system mainly depends on a PCB board, so the optimization of the performance of a PCB board is very important in both military and civilian fields. With the wide application of PCB boards in various fields, the market demand for PCB boards is increasing, and higher requirements are put forward for the size, weight and power density of PCB boards. Due to the development trend of miniaturization and high power density of PCB boards, the overall design of the PCB boards faces problems such as heat dissipation, electromagnetic compatibility and insulation. A large number of studies have shown that the proportion of equipment failure caused by high temperature is as high as 55%, and the failure rate increases exponentially with the increase of temperature. Therefore, while improving the power density of the PCB board, how to ensure good heat dissipation performance is the key and difficulty of the thermal design of the PCB board. SUMMARY

[0003] The application provides a thermal design method based on a high-power-density PCB board, solves the problem that high power density and strong heat dissipation capability are difficult to be compatible, and realizes the dual goals of good heat dissipation and high power density of the system.

[0004] In order to achieve the above-mentioned purpose, the application provides a thermal design method based on a high-power-density PCB board, which comprises the following steps

[0005] A power loss mathematical model of a heat source on the PCB board is established, and a thermal simulation model of the PCB board is established according to the power loss mathematical model;

[0006] According to the simulation result of the thermal simulation model, chip-level, board-level and system-level thermal analysis is performed on the PCB board, the chip-level thermal analysis is used to determine the working condition of the PCB board with high heat dissipation capability, the board-level thermal analysis is used to determine the device layout of the PCB board with high heat dissipation capability, and the system-level thermal analysis is used to determine the system structure with high heat dissipation capability and the heat dissipation effect under different environmental conditions;

[0007] According to the thermal analysis result, the thermal-structure of the PCB board is improved, and the power density of the PCB board is improved while ensuring the heat dissipation capability;

[0008] A heat dissipation device is added to the heat source on the improved PCB board, and the structure parameters of the heat dissipation device are optimized by using a genetic algorithm.

[0009] Further, the heat source is a switching device, and the switching device comprises a plurality of IGBT modules, and the power loss mathematical model of each IGBT module is

[0010]

[0011] wherein P DC , P DC-Tr , P DC-Dio are the total on-state power loss of the IGBT module, the on-state loss of the IGBT and the on-state loss of the antiparallel diode respectively, r T-Tr , r T-Dio are the on-state resistances of the IGBT, the antiparallel diode respectively, V T0-Tr , V T0-Dio are the threshold voltages of the IGBT, the antiparallel diode respectively, M is the modulation ratio, I m is the current amplitude, P SW , P SW-Tr , P SW-Dio are the total switching power loss of the IGBT module, the switching loss of the IGBT and the switching loss of the antiparallel diode respectively, f s is the switching frequency, E on , E off are the turn-on energy loss, turn-off energy loss of the IGBT, E rr is the switching energy loss of the antiparallel diode.

[0012] Further, the thermal simulation model deletes the circuits and devices for signal transmission, ignores the circuits and devices with small loss, and sets the thermal resistance values and power loss values of the remaining devices according to the data provided in the data manual and the calculation results of the power loss mathematical model.

[0013] Further, the chip-level thermal analysis determines the working condition with high heat dissipation capacity of the PCB board by changing the working condition control parameters of the switching device to simulate the heat change of the PCB board under different working conditions; the board-level thermal analysis determines the device layout of the PCB board to make the temperature distribution uniform and the overall temperature lowest by adjusting the device position to simulate the highest temperature and heat distribution of the PCB board; and the system-level thermal analysis determines the structure form and working environment of the PCB board by adjusting the environmental conditions and the structure form of the PCB board in the system to analyze the heat transformation of the system.

[0014] Further, the thermal-structural improvement method of the PCB board is to design the PCB board as a multi-layer structure.

[0015] Further, the PCB board is designed as a double-layer structure, and the double-layer structure transfers heat through interlayer gap heat convection, the interlayer gap heat convection transfers heat through heat convection in a large space with small gas flow resistance, and the interlayer gap heat convection transfers heat through heat conduction in a narrow space with large gas flow resistance, and the thermal resistance of the heat convection is

[0016]

[0017] wherein D is the thickness of the air layer, S is the heat transfer area, h 空气 is the air heat transfer coefficient;

[0018] The thermal resistance of the heat conduction is

[0019]

[0020] wherein R1 is the thermal resistance of the lower circuit board to the air, R2 is the thermal resistance of the air to the upper circuit board, S1 and S2 are the surface areas of the upper and lower circuit boards respectively, h 水平 is the horizontal natural heat transfer coefficient.

[0021] Further, the demarcation range of the large-space heat transfer and the small-space heat transfer of the interlayer gap is determined by calculating the thermal resistance of the double-layer structure, and the heat transfer mode of the double-layer structure is determined according to the distance between the double-layer structure boards.

[0022] Further, the upper board of the PCB is arranged with low-power devices, and the upper and lower surfaces of the lower board are arranged with high-power devices, so that the heat sources of the upper and lower boards are avoided to overlap and the power devices of the lower board are avoided to be shielded by the upper board.

[0023] Further, the heat dissipation device for the heat source is a columnar heat sink and a fan, the heat source is installed on the lower surface of the lower board, the columnar heat sink is installed vertically downward close to the heat source, and the fan is installed vertically downward close to the columnar heat sink.

[0024] Further, the genetic algorithm is used to optimize the structure parameters of the heat dissipation device, and the method is as follows

[0025] The substrate thickness d, the needle column diameter L and the air volume V are selected as the optimization variables, the constraint range of each variable is determined, and the optimization mathematical model is established as

[0026]

[0027] A quadratic response surface model is constructed as

[0028] T=50.4-0.073d-10.698L-0.842V+0.043d 2 +2.198L 2 +0.019V 2 +0.145dL+0.0005dV-0.108LV

[0029] The population size, evolution generation number, crossover probability and mutation probability are set, and the genetic algorithm is used to optimize the heat dissipation device.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] 1. The thermal design method system is comprehensive: a three-level combination of chip-level, board-level and system-level thermal analysis method is adopted to more comprehensively guide thermal design, and has systematicness and comprehensiveness.

[0032] 2. High universality: the thermal design method is applicable to thermal design of different types of PCBs, and has high universality.

[0033] 3. Wide application of finished products: through thermal design of high-power density motor driver, the design goal of smaller size, lighter weight and higher power density is realized, and it is more suitable for application scenarios with limited space.

[0034] 4. High thermal reliability: through thermal design of high-power density motor driver, the heat dissipation capacity of the driver is enhanced, and the thermal reliability of the equipment is improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] The included drawings are used to provide a further understanding of the embodiments of the present application, constitute a part of the specification, serve to illustrate the embodiments of the present application, and explain the principles of the present application together with the text. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0036] Figure 1 The thermal design method principle block diagram of high-power density PCB provided for the specific embodiments of the present application;

[0037] Figure 2 The thermal simulation flowchart provided for the specific embodiments of the present application;

[0038] Figure 3 The chip-level thermal analysis temperature curve provided for the specific embodiments of the present application, wherein (a) is the temperature of the inverter under different voltages, and (b) is the temperature of the inverter under different switching frequencies;

[0039] Figure 4 The PCB temperature cloud map of different device layouts provided for the specific embodiments of the present application;

[0040] Figure 5 The PCB temperature thermal simulation and experimental curve under different working conditions provided for the specific embodiments of the present application;

[0041] Figure 6 The double-layer structure layout improvement schematic diagram of the motor driver PCB provided for the specific embodiments of the present application;

[0042] Figure 7 The genetic algorithm flowchart for optimizing the structure parameters of the heat dissipation device provided for the specific embodiments of the present application;

[0043] Figure 8 The schematic diagram of the motor driver PCB product provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0044] The embodiment of the present application is described in detail below. In the following description, for the purpose of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced in other embodiments that depart from these specific details.

[0045] It should be noted that, in order to avoid obscuring the present application due to unnecessary details, only the device structure and / or processing steps closely related to the scheme of the present application are shown in the drawings, and other details not closely related to the present application are omitted.

[0046] The present application provides a thermal design method based on high power density PCB, as shown in the figure, comprising the following steps: Figure 1

[0047] 1. Establish a power loss mathematical model of the main heat source on the PCB, and establish a PCB thermal simulation model based on the power loss mathematical model.

[0048] The thermal simulation model is the basis of PCB thermal analysis and thermal design. Taking high power density PCB as the research object, a power loss mathematical model of the main heat source is established, and a relatively accurate thermal simulation model is established based on the power loss mathematical model of the main heat source.

[0049] On a conventional PCB, the main heat source is generally a switching device on the board, so the present application mainly models the power loss of the switching device.

[0050] Finally, the thermal simulation model is simulated, and the feasibility of the thermal simulation model is verified through experiments.

[0051] 2. According to the simulation results of the thermal simulation model, perform chip-level, board-level, and system-level thermal analysis on the PCB, determine the working condition with strong heat dissipation capacity of the PCB through chip-level thermal analysis, determine the device layout of the PCB with good heat dissipation capacity through board-level thermal analysis, and determine the system structure with high heat dissipation capacity and the heat dissipation effect under different environmental conditions through system-level thermal analysis.

[0052] ​According to the simulation result of the thermal simulation model, the chip-level, board-level and system-level thermal analysis is carried out for the high power density PCB board. The thermal analysis of the chip-level influencing factors is mainly to explore the factors affecting the power loss of the switching device, that is, to explore the heat change of the PCB board under different working conditions; the thermal analysis of the board-level influencing factors is to explore the influence of different device layout on the temperature distribution of the PCB board; the thermal analysis of the system-level influencing factors is to explore the system heat change caused by different external environments and different system structures (the system refers to the overall device assembled with the PCB board).

[0053] 3. According to the thermal analysis result of step 2, the thermal-structure improvement is carried out on the PCB board to ensure that the PCB board meets good heat dissipation capacity while improving the power density of the PCB board.

[0054] In order to realize the dual goals of good heat dissipation and high power density of the PCB board, the thermal-structure improvement is carried out on the PCB board according to the chip-level, board-level and system-level thermal analysis, the PCB board can be designed as a multi-layer structure, and the layout design of each layer of components is carried out to improve the power density, and the feasibility of the improvement measures is verified through simulation and experiment.

[0055] 4. On the improved PCB board, heat dissipation devices are added corresponding to the main heat source, and the structure parameters of the heat dissipation devices are optimized by genetic algorithm.

[0056] The heat dissipation device in the application includes two heat dissipation parts of air cooling and cold plate, and the selected structure parameters to be optimized are the substrate thickness d, the needle column diameter L and the air volume V.

[0057] Through the thermal-structure improvement measures, the thermal reliability of the improved PCB board is effectively ensured, and in order to further improve the heat dissipation performance, more direct and effective external heat dissipation devices such as heat sinks and fans need to be used for optimization. Based on the above analysis, the heat dissipation optimization is carried out on the main heat source, the power switching device, the heat dissipation effect of the improved PCB board is analyzed by various types of heat sinks, the heat dissipation mode of the needle column heat sink combined with air cooling is selected, the genetic algorithm is combined with the heat sink structure optimization problem, the optimal heat sink structure is obtained and simulation and experiment verification are carried out.

[0058] The technical scheme of the application will be described in detail below in combination with a specific embodiment.

[0059] The thermal design method of the high power density PCB board provided by the application takes a high power density motor driver PCB board as an example, which can effectively improve the heat dissipation performance of the driver while improving the power density of the driver, including the following steps:

[0060] (1) Thermal simulation model establishment

[0061] The high-power-density motor driver PCB mainly includes rectifiers, inverters, DSP controllers, orthogonal encoders, simulators and various protection circuits, wherein the inverter is a typical switching device and is a main heat source.

[0062] According to the component selection of the motor driver structure, the key heat source is determined to be the inverter, and a power loss mathematical model of the inverter is established.

[0063] The inverter, as a representative of switching devices, is usually composed of six IGBT modules, each of which is divided into IGBT and anti-parallel diode, both of which are periodically in the on or off state. In a control cycle, the power loss generated by the IGBT and the anti-parallel diode is divided into on-state loss and switching loss, and the power loss mathematical model of an IGBT module is:

[0064]

[0065]

[0066] Among them, P DC , P DC-Tr , P DC-Dio are the total on-state power consumption of the IGBT module, the on-state loss of the IGBT and the anti-parallel diode, r T-Tr , r T-Dio are the on-state resistances of the IGBT and the anti-parallel diode, V T0-Tr , V T0-Dio are the threshold voltages of the IGBT and the anti-parallel diode, M is the modulation ratio, I m is the current amplitude, P SW , P SW-Tr , P SW-Dio are the total switching power consumption of the IGBT module, the switching loss of the IGBT and the anti-parallel diode, f s is the switching frequency, E on , E off are the turn-on energy loss and turn-off energy loss of the IGBT, and E rr is the switching energy loss of the anti-parallel diode.

[0067] The above mathematical model is used to calculate the power loss of an IGBT module, and the power loss of an inverter is the sum of the power losses of the six IGBT modules. For other switching devices, the combination is carried out according to the number of IGBT modules, for example, a rectifier is composed of four IGBT modules, and the power loss of a rectifier is the sum of the power losses of the four IGBT modules.

[0068] Based on the power loss mathematical model, a relatively accurate thermal simulation model is established to analyze the thermal simulation of the motor driver and to verify the experiment. By comparing the highest temperature and heat distribution of the simulation and the experiment, the feasibility of the thermal simulation model can be verified.

[0069] To improve the calculation efficiency, the signal transmission part needs to be deleted in the process of establishing the thermal simulation model, and the auxiliary circuits and devices with small loss are ignored. The thermal resistance values and power loss values of the remaining devices are set according to the data provided by the data manual and the calculation results of the power loss mathematical model.

[0070] The signal transmission part specifically refers to the DSP peripheral signal transmission circuit, the quadrature encoder, the simulator connection circuit, etc. The above parts are mainly used for the generation of PWM signal, the input of motor feedback signal, the input of control algorithm, and the connection of PC interface, etc. The auxiliary circuits and devices mainly include 400V to 15V converter, 15V to 5V converter, 5V to 3.3V converter, and 3.3V isolation power supply.

[0071] As shown in Figure 2 , the thermal simulation process includes establishing a physical model, applying a load, model mesh division, setting solving parameters, and processing simulation results. The specific method of thermal simulation is a known technology, which will not be described here.

[0072] (2) Three-level thermal analysis

[0073] (2.1) The thermal analysis of chip-level influencing factors mainly explores the factors affecting the power loss of switching devices. Considering the variables of the power loss mathematical model, different bus voltages and switching frequencies are selected for inverter thermal simulation. The simulation and experimental temperatures are shown in FIGS. Figure 3 (a) and (b). It can be seen from the figures that the inverter heat is positively correlated with the bus voltage and switching frequency, i.e., as the bus voltage and switching frequency increase, the inverter heat also increases linearly. The experimental data and simulation data both maintain linear growth. Considering that the heat emitted by the devices around the inverter will cause the temperature of the inverter to rise during the actual experiment, the experimental value will be slightly higher than the simulation value, but the temperature difference between the two is not more than 1°C. It can be considered that the simulation data and experimental data are consistent and reliable.

[0074] According to the simulation and experimental results, the appropriate working conditions of the PCB board can be selected to some extent, i.e., selecting more appropriate switching frequency, bus voltage, and other chip-level influencing factors. Under the allowable conditions, the working condition with better heat dissipation effect is selected to enhance the thermal reliability of the PCB board and prolong its service life.

[0075] (2.2) Thermal analysis of board-level influencing factors is to explore the influence of different device layouts on the temperature distribution of the PCB board. In order to explore the influence of layout on temperature distribution, according to the thermal simulation process, five power switch devices with a power of 5W are placed on the PCB board. Except for the power switch device at the center position, the remaining power switch devices need to be placed in parallel or staggered, and then gradually move towards the center power switch device. Observe the changes of the maximum temperature and heat distribution of the PCB board in this process, and the simulation results are shown in the accompanying Figure 4 From the figure, the following conclusions can be drawn: when the power switch devices are placed dispersedly at the edge, the temperature distribution on the board is extremely uneven, which can easily cause thermal stress problems, thereby causing the PCB board to bend or the device to fall off; when the power switch devices are too concentrated, although the temperature distribution becomes uniform, the overall temperature will rise, and when the power switch devices move from a suitable distance with a lower temperature to the most concentrated situation, the maximum temperature of the PCB board rises by 8℃, which will cause the thermal reliability to decrease; the staggered placement of power switch devices is better than parallel placement, and the temperature can be reduced by about 3℃, but when too concentrated, the difference between staggered placement and parallel placement of power switch devices is not large. The above conclusions can guide the subsequent thermal layout optimization of the motor driver to some extent.

[0076] By analyzing the layout of the device on the PCB board, the temperature distribution is uniform and the overall temperature is the lowest.

[0077] (2.3) Thermal analysis of system-level influencing factors is to explore the heat changes of the motor driver caused by different external environments and driver structures. First, analyze the influence of external environment temperature changes on the temperature distribution of the motor driver PCB board. According to formula (3), the temperature of each switch device on the PCB board is:

[0078] T 器件 =T 环境 +ΔT (3)

[0079] Where T 环境 is the ambient temperature, and ΔT is the temperature change of the switch device caused by power loss.

[0080] From formula (3), it can be seen that the device temperature will change with the change of the environment temperature. In order to verify this principle, three different working conditions are selected to explore the influence of different environment temperatures on the inverter heat. Working condition 1 is bus voltage U cc = 100V, switching frequency f s = 10kHz, rated load; working condition 2 is U cc = 100V, f s = 10kHz, no load; working condition 3 is U cc = 200V, f s = 10kHz, rated load, and the corresponding thermal simulation and experiment are as follows Figure 5The simulation results are shown in the figure. It can be seen from the figure that the inverter heat increases linearly with the increase of the ambient temperature in three working conditions, and the simulation values are consistent with the experimental values. By comparing working condition 1 and working condition 2, it can be seen that although the relative error of the two working conditions is only less than 1℃, it can be seen that the increase of the load will cause the temperature rise of the inverter, which is consistent with the theoretical analysis. By comparing working condition 1 and working condition 3, it can be seen that the temperature change caused by changing the bus voltage is more obvious than that caused by changing the load. The increase of the bus voltage will cause the temperature rise of the inverter. According to the temperature influence of the environment on the system, the appropriate working environment of the PCB board can be guided to some extent to enhance the thermal reliability of the PCB board, prolong its service life, and determine the maximum environmental temperature range that the PCB board can withstand.

[0081] Then the influence of the structure change of the motor driver on the temperature distribution of the PCB board is analyzed. The traditional PCB board structure is mostly single-layer, which has the characteristics of simple design, large size, and unclear high-low power boundary. In order to improve the overall power density of the system, it is easier to distinguish high-low power modules, so the traditional PCB board is changed to a double-layer board structure. The double-layer PCB board structure conducts heat through interlayer gap heat convection. The interlayer gap heat convection conducts heat through heat convection in a large space with small gas flow resistance, and conducts heat through heat conduction in a narrow space with large gas flow resistance. The thermal resistances of the two heat transfer modes are shown in equations (4) and (5):

[0082]

[0083]

[0084] In the formula, D is the air layer thickness, S is the heat transfer area, h 空气 is the air heat transfer coefficient, R1 is the thermal resistance from the lower circuit board to the air, R2 is the thermal resistance from the air to the upper circuit board, S1 and S2 are the surface areas of the upper and lower circuit boards, h 水平 is the horizontal direction natural heat transfer coefficient. According to the formula, when large space heat convection occurs, within a certain distance, the larger the distance, the larger the thermal resistance, and the worse the heat dissipation effect. When small space heat conduction occurs, within a certain distance, the larger the circuit board surface area, the smaller the thermal resistance, and the better the heat dissipation effect. In addition, in the case of small space heat conduction, when the board spacing is shortened to a certain value, the space layer thickness has little effect on the heat dissipation effect, that is, the temperature of the temperature measurement point no longer changes.

[0085] By comparing the simulation results with the change trend presented by the above analysis, the dividing range of large space heat transfer and small space heat transfer can be obtained, and then according to the actual board spacing, it can be determined whether the system analysis should be large space heat convection or small space heat conduction.

[0086] (3) Thermal structure improvement

[0087] According to the above chip-level, board-level and system-level thermal analysis, the motor driver is thermally and structurally improved. First, the motor driver PCB board is changed to a two-layer board structure to reduce the volume of the driver. Then, the components are adjusted according to the board-level influencing factor analysis. Finally, the improved motor driver is simulated and experimented to verify the feasibility of the improvement measures.

[0088] The DSP controller module, quadrature encoder module, emulator module and protection circuit module and other small power modules below 15V are located on the upper layer board and are simply laid out. The rectifier, inverter and other high-power modules are placed on the lower layer board. The high-power chip PS21765 in the inverter is placed on the back of the lower layer PCB board to reduce the volume. Since each high-power module has more devices and a larger size than the small power module, the upper layer board is smaller than the lower layer board. In addition, since the rectifier module devices are high and concentrated on the left side of the lower layer board, the upper and lower layer boards are placed right-aligned.

[0089] Due to the height limitation of each device on the PCB board, the minimum layer spacing of the two-layer PCB board is above 1.4cm. Therefore, when the motor driver is thermally analyzed, the large space thermal convection heat transfer is mainly considered. To avoid heat accumulation, the circuit on the upper layer board of the driver is rearranged based on the three-layer thermal analysis results to enhance the natural convection heat dissipation capacity of the driver. The layout improvement scheme is as follows: the DSP controller module, quadrature encoder module, emulator module and protection circuit module and other small power modules below 15V on the upper layer board are placed around the most serious heat-emitting inverter on the lower layer board to avoid overlapping of heat sources; the relative positions of the upper and lower layer boards are adjusted to avoid the situation that the power modules on the lower layer board are blocked by the upper layer board, causing poor heat dissipation and heating of the upper layer board by thermal convection. The specific layout improvement is shown in Figure 6 Finally, the improved motor driver is simulated and experimented to verify the feasibility of the improvement measures.

[0090] (4) External heat dissipation device

[0091] To further improve the heat dissipation performance of motor driver, forced air cooling and cold plate heat dissipation are combined to optimize the heat dissipation of the main heat source, inverter. The specific heat dissipation device is columnar heat sink and fan. The placement method is to place the columnar heat sink and fan vertically downward in turn next to the IGBT on the back of the lower layer plate. The IGBT and columnar heat sink are heat-conducting with silver silicon grease and other adhesive materials, and the heat dissipation device is further reinforced with screws. The heat of IGBT can be transferred to the heat sink through heat conduction, and then dissipated through the heat convection path with air. The columnar heat sink has basic structural parameters such as substrate thickness, needle column diameter, substrate thickness, needle column height, and the fan has basic structural parameters such as air volume, length, width, and height. According to the single factor control variable method, the structural parameters affecting the heat dissipation performance of the heat dissipation device are explored, which is convenient for subsequent selection of the largest structural parameters for optimization.

[0092] To make the heat dissipation effect of the heat dissipation device optimal, the genetic algorithm is used to optimize the structural parameters of the heat dissipation device, and the process is shown in Figure 7 The substrate thickness d, needle column diameter L and air volume V are selected as optimization variables, and the constraint range of each variable is determined. Since there is a nonlinear relationship between each variable and the optimization target, a proxy model is constructed for multivariate optimization design, and the optimization mathematical model is

[0093]

[0094] Then a quadratic response surface model is constructed, as shown in equation (7). Through variance analysis, the regression coefficient of the quadratic response surface model reaches 0.9971, which meets the requirement of response surface error greater than 0.9, and the accuracy of the quadratic response surface model can be verified.

[0095]

[0096] The genetic algorithm is used to optimize the heat dissipation device, with population size of 10, evolution number of 500, crossover probability of 0.4 and mutation probability of 0.2. The final optimization result is d = 2.9963 mm, L = 1.7685 mm, V = 16.8216 CFM and T = 32.8748 ℃.

[0097] Finally, a high-power-density motor driver is produced through thermal design, and the structure diagram of the finished product is as follows: Figure 8The motor driver is changed to a two-layer board structure with higher power density. The DSP module, encoder module, emulator module and protection circuit module and other small power modules below 15V are located on the upper layer board, and the rectification, inversion and other high power modules are placed on the lower layer board. The high power chip PS21765 in the inversion module and the additional heat dissipation device are placed on the back of the lower PCB board to reduce the volume, and the feasibility of the thermal design is verified through simulation and experiment, realizing the dual goals of good heat dissipation and high power density.

[0098] The design method can be applied to the thermal design of high power density PCB board, and the high power density motor driver of permanent magnet synchronous motor AC driving system is taken as an example for related thermal design. The finished motor driver is suitable for permanent magnet synchronous motor AC driving system with light weight, small size and high efficiency, realizing various performances of the motor including starting, rotating speed, variable speed, stopping and the like; a mathematical model of power loss of the switching device is established, and the calculation result is used to establish a thermal simulation model, so that the thermal simulation model is more accurate; a thermal analysis method combining chip level, board level and system level is adopted, which more comprehensively guides the thermal design; the genetic algorithm is used to solve the optimal structure of the additional heat dissipation device, so that the heat dissipation effect of the thermal design is maximized; through the thermal design method of high power density PCB board, the motor driver has good heat dissipation capacity and high thermal reliability.

[0099] Features described and / or illustrated with respect to one embodiment above can be used in the same or similar manner in one or more other embodiments, and / or in combination with or in place of features in other embodiments.

[0100] It should be emphasized that the term "comprises / comprising" when used in this text refers to the presence of a feature, whole, step or component, but does not exclude the presence or addition of one or more other features, whole, step, component or combination thereof.

[0101] Many of the features and advantages of the embodiments are apparent from the detailed description, and thus, the appended claims should be construed to include all features and advantages falling within the true spirit and scope of the embodiments. In addition, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the embodiments of the present application to the exact construction and operation described and illustrated, and accordingly, all suitable modifications and equivalents can be resorted to, falling within the scope of the embodiments.

[0102] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0103] The portions of the disclosure not specifically described herein are well known to those skilled in the art.

Claims

1. A thermal design method based on high power density PCB boards, characterized in that, Includes the following steps Establish a mathematical model of power loss of heat source on PCB board, and establish a thermal simulation model of PCB board based on the power loss mathematical model. Based on the simulation results of the thermal simulation model, chip-level, board-level, and system-level thermal analyses are performed on the PCB board. The chip-level thermal analysis is used to determine the operating conditions with high heat dissipation capacity of the PCB board. The board-level thermal analysis is used to determine the component layout of the PCB board with high heat dissipation capacity. The system-level thermal analysis is used to determine the system structure with high heat dissipation capacity and the heat dissipation effect under different environmental conditions. Based on the thermal analysis results, the PCB board was improved in terms of thermal structure to increase the power density of the PCB board while ensuring heat dissipation capacity. On the improved PCB board, heat dissipation devices are added to the corresponding heat sources, and the structural parameters of the heat dissipation devices are optimized by a genetic algorithm. The chip-level thermal analysis simulates the heat changes of the PCB board under different operating conditions by changing the operating control parameters of the switching devices, and determines the operating conditions with high heat dissipation capacity of the PCB board; the board-level thermal analysis simulates the highest temperature and heat distribution of the PCB board by adjusting the position of the devices, and determines the PCB board device layout to achieve uniform temperature distribution and the lowest overall temperature; the system-level thermal analysis analyzes the heat transformation of the system by adjusting the environmental conditions and the structural form of the PCB board in the system, and determines the PCB board structure and working environment. The PCB board is designed with a double-layer structure; The boundary between heat transfer in the large and small spaces between the layers is determined by calculating the thermal resistance of the double-layer structure, and the heat transfer mode of the double-layer structure is determined based on the distance between the double-layer structure plates. The upper layer of the PCB is arranged with low-power devices, and the lower layer is arranged with high-power devices on both sides. The upper and lower layers should avoid overlapping of heat sources and avoid the power devices on the lower layer being blocked by the upper layer.

2. The thermal design method based on high power density PCB board according to claim 1, characterized in that, The heat source is a switching device, which includes several IGBT modules. The mathematical model for the power loss of each IGBT module is as follows: Among them, P DC P DC-Tr P DC-Dio These represent the total on-state power consumption of the IGBT module, the on-state loss of the IGBT, and the on-state loss of the anti-parallel diode, respectively. T-Tr r T-Dio The on-state internal resistances of the IGBT and the anti-parallel diode are V, respectively. T0-Tr V T0-Dio These are the threshold voltages of the IGBT and the anti-parallel diode, respectively; M is the modulation ratio; I... m P is the current amplitude. SW P SW-Tr P SW-Dio These represent the total switching power consumption of the IGBT module, the switching loss of the IGBT, and the switching loss of the anti-parallel diode, respectively. s E is the switching frequency. on E off E represents the energy loss during IGBT turn-on and turn-off. rr This refers to the switching energy loss of the anti-parallel diode.

3. The thermal design method based on high power density PCB board according to claim 2, characterized in that, The thermal simulation model removes circuits and devices used for signal transmission, ignores circuits and devices with low losses, and sets the thermal resistance and power loss values ​​of the remaining devices based on the data provided in the datasheet and the calculation results of the power loss mathematical model.

4. The thermal design method based on high power density PCB board according to claim 1, characterized in that, The method for improving the thermal-structural properties of the PCB board is to design the PCB board as a multi-layer structure.

5. The thermal design method based on high power density PCB board according to claim 1, characterized in that, The double-layer structure transfers heat through interlayer convection. In large spaces with low gas flow resistance, interlayer convection occurs via heat transfer; in convection within confined spaces with high gas flow resistance, heat transfer occurs via heat conduction. The thermal resistance of convection is... Where D is the air layer thickness, S is the heat transfer area, and h 空气 It is the thermal conductivity of air; The thermal resistance of heat conduction is Where R1 is the thermal resistance from the lower circuit board to the air, R2 is the thermal resistance from the air to the upper circuit board, S1 and S2 are the surface areas of the upper and lower circuit boards, respectively, h 水平 It is the natural heat transfer coefficient in the horizontal direction.

6. The thermal design method based on high power density PCB board according to claim 1, characterized in that, The heat dissipation device added to the heat source is a columnar radiator and a fan. The heat source is installed under the lower plate. The columnar radiator is installed vertically downward close to the heat source, and the fan is installed vertically downward close to the columnar radiator.

7. The thermal design method based on high power density PCB board according to claim 6, characterized in that, The method for optimizing the structural parameters of the heat dissipation device using a genetic algorithm is as follows: The substrate thickness d, pin diameter L, and airflow V are selected as optimization variables. The constraint range of each variable is determined, and an optimization mathematical model is established. Construct a quadratic response surface model for T=50.4-0.073d-10.698L-0.842V+0.043d 2 +2.198L 2 +0.019V 2 +0.145dL+0.0005dV-0.108LV The population size, number of generations, crossover probability, and mutation probability are set, and a genetic algorithm is used to optimize the heat dissipation device.

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