Method for predicting service life of power device under low air pressure

Abstract

The invention provides a method for predicting the service life of a power device under low air pressure, and the method comprises the following steps: obtaining the environment parameters of the environment where the power device to be tested is located, the environment parameters at least comprising air pressure and environment temperature; determining a heat transfer coefficient of a radiator surface of the to-be-tested power device based on the environmental parameters of the environment where the to-be-tested power device is located; determining equivalent thermal resistance from the radiator to air based on the heat transfer coefficient of the radiator surface of the to-be-tested power device; the shell temperature and the junction temperature of the power device are determined based on the equivalent thermal resistance from the radiator to the air, and the inelastic strain rates of the welding layer of the power device and the welding layer of the substrate are determined according to the shell temperature and the junction temperature; determining the cycle life of the power device based on the strain values of the welding layer of the power device and the welding layer of the substrate; it can be effectively guaranteed that the predicted life and the actual life of the power device basically tend to be consistent in the low-pressure environment, and safe and stable operation of a photovoltaic power generation system is effectively guaranteed.

Description

Technical Field

[0001] The invention relates to an analysis method for a power device, and in particular to a life prediction method for a power device under low pressure. Background Art

[0002] In photovoltaic power generation, power devices are the core components of photovoltaic power converters, and their reliability affects the stability of the photovoltaic system. Plateau areas above 3,000 meters above sea level are rich in solar energy resources and are the main gathering places for photovoltaic power generation. However, with the increase in altitude, the air pressure decreases, the heat transfer capacity of the air decreases, and the thermal fatigue degradation of power devices accelerates, resulting in a shortened life of power devices under low pressure conditions, thus affecting the stability of the photovoltaic power generation system.

[0003] In the prior art, the life prediction method for power devices in photovoltaic systems is generally based on indoor accelerated aging experiments. This method does not take into account the impact of low pressure on the life of power devices. If directly applied, the predicted life of the power devices will be higher than the actual life, resulting in failure of the power devices, thereby affecting the safe and stable operation of the converter subsystem in the entire photovoltaic system.

[0004] Therefore, in order to solve the above technical problems, it is urgent to propose a new technical means. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for predicting the life of a power device under low pressure. The heat transfer coefficient of the heat sink of the power device is determined based on the air pressure value and temperature information of the low-pressure environment in which the power device is located, and then the shell temperature and junction temperature of the power device are determined by the heat transfer coefficient, so as to evaluate the life of the power device. This can effectively ensure that the predicted life of the power device in a low-pressure environment is basically consistent with the actual life, and effectively ensure the safe and stable operation of the photovoltaic power generation system.

[0006] The present invention provides a method for predicting the life of a power device under low pressure, comprising the following steps:

[0007] Acquire environmental parameters of the environment in which the power device to be tested is located, the environmental parameters at least including air pressure and ambient temperature;

[0008] Determine the heat transfer coefficient of the heat sink surface of the power device to be tested based on the environmental parameters of the environment in which the power device to be tested is located;

[0009] Determine the equivalent thermal resistance from the heat sink to the air based on the heat transfer coefficient of the heat sink surface of the power device to be tested;

[0010] The case temperature and junction temperature of the power device are determined based on the equivalent thermal resistance from the heat sink to the air, and the inelastic strain rate of the solder layer of the power device and the solder layer of the substrate are determined from the case temperature and the junction temperature;

[0011] The cycle life of the power device is determined based on the strain values ​​of the solder layer of the power device and the solder layer of the substrate.

[0012] Furthermore, the cycle life of the power device is determined by the following method:

[0013]

[0014] in: Indicates the cycle life of the substrate solder layer of the power device, Indicates the cycle life of the chip solder layer of the power device, C 11 Indicates the fatigue ductility coefficient of the substrate solder layer of the power device, C 12 Indicates the fatigue ductility index of the substrate solder layer of the power device, Indicates the inelastic strain rate of the substrate solder layer of the power device; C 21 Indicates the fatigue ductility coefficient of the chip solder layer of the power device, C 22 Indicates the fatigue ductility index of the chip solder layer of the power device, Represents the inelastic strain rate of the chip solder layer of the power device.

[0015] Further, the inelastic strain rate of the chip solder layer of the power device and the inelastic strain rate of the substrate solder layer are determined as follows:

[0016]

[0017] Where: K A represents the setting coefficient, Q1 and Q2 represent the activation energy, where the activation energy refers to the energy threshold that needs to be overcome for the internal microstructure (such as dislocation, grain boundary, etc.) of the chip solder layer of the power device to undergo irreversible deformation (such as dislocation slip, void nucleation). Represents the stress coefficient of the substrate solder layer of the power device, Represents the equivalent stress of the substrate solder layer of the power device, m A1 represents the strain sensitivity coefficient of the substrate solder layer of the power device, R represents the universal gas constant, T C (P a ) represents the case temperature of the power device, T J (P a ) represents the junction temperature of the power device, Represents the strain of the substrate solder layer, Represents the stress coefficient of the chip solder layer of the power device, Represents the equivalent stress of the chip solder layer of the power device, m A2 Represents the strain sensitivity coefficient of the chip solder layer of the power device.

[0018] Furthermore, the case temperature T of the power device is determined by the following method: C (P a ):

[0019]

[0020] Where: P loss Represents the power device loss, T cmax Indicates the maximum case temperature of the power device during the power pulse period, R th,ch It represents the thermal resistance from the power device case to the power device heat sink, C th,ch represents the heat capacity from the power device housing to the power device heat sink, t represents the temperature change time of the power heat sink, T h (P a ) represents the temperature of the heat sink of the power device, t p Indicates that the temperature of the power device heat sink reaches the maximum value T hmax Duration, t d Indicates the duration of the high level of the power pulse of a power device in one cycle.

[0021] Furthermore, the junction temperature T of the power device is determined by the following method: J (P a ):

[0022]

[0023] Where: T jmax Indicates the maximum junction temperature of the power device during the power pulse period; R th,jc Indicates the thermal resistance from the PN junction of the power device to the power device case, C th,jc It represents the thermal capacitance from the PN junction of the power device to the case of the power device.

[0024] Further, the temperature T of the heat sink of the power device is determined by the following method: h (P a ):

[0025]

[0026] Where: T hmax Indicates the maximum temperature of the heat sink of the power device during the power pulse cycle, R th,ha (P a ) represents the equivalent thermal resistance from the heat sink of the power device to the ambient air, C th,ha It represents the heat capacity from the heat sink of the power device to the ambient air, T a Indicates the ambient temperature of the power device.

[0027] Furthermore, the equivalent thermal resistance R from the heat sink to the air of the power device is determined by the following method: th,ha (P a ):

[0028]

[0029] in:

[0030] R th,hai (P a ) represents the equivalent thermal resistance from the ith surface of the heat sink of the power device to the air, h hai (P a ) is the heat transfer coefficient from the ith surface of the power device heat sink to the air, A i It represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink of the power device. When i is 2, it represents the lower surface of the heat sink of the power device. When i is 3 to 6, it represents the side surface of the heat sink of the power device.

[0031] Furthermore, the heat transfer coefficient of the heat sink surface of the power device is determined by the following method:

[0032] When i is 1:

[0033]

[0034] When i is 2:

[0035]

[0036] When i is 3 to 6:

[0037]

[0038] Where: K a (P a ) represents the thermal conductivity of air, L s Represents the characteristic length of the upper and lower surfaces of the heat sink of the power device, L h is the vertical height of the side surface of the heat sink of the power device, Ra(P a ) represents the Prandtl number, Pr(P a ) represents the Rayleigh number;

[0039]

[0040] Where: β represents the volume expansion coefficient of air, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the acceleration of gravity, R represents the universal gas constant, c a represents the specific heat capacity of air, ΔT represents the air temperature deviation, P aIndicates the air pressure value of the environment where the power device is located.

[0041] Beneficial effects of the present invention: Through the present invention, the heat transfer coefficient of the heat sink of the power device is determined based on the air pressure value and temperature information of the low-pressure environment in which the power device is located, and then the shell temperature and junction temperature of the power device are determined by the heat transfer coefficient, and then the life of the power device is evaluated. It can effectively ensure that the predicted life of the power device in the low-pressure environment is basically consistent with the actual life, and effectively ensure the safe and stable operation of the photovoltaic power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0043] Figure 1 It is a flow chart of the present invention.

[0044] Figure 2 It is a schematic diagram of a power supply and a heat sink of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below:

[0046] The present invention provides a method for predicting the life of a power device under low pressure, comprising the following steps:

[0047] S1. Obtaining environmental parameters of the environment in which the power device to be tested is located, the environmental parameters including at least air pressure and ambient temperature;

[0048] S2. Determine the heat transfer coefficient of the heat sink surface of the power device to be tested based on the environmental parameters of the environment in which the power device to be tested is located;

[0049] S3. Determine the equivalent thermal resistance from the heat sink to the air based on the heat transfer coefficient of the heat sink surface of the power device to be tested;

[0050] S4. Determine the case temperature and junction temperature of the power device based on the equivalent thermal resistance from the heat sink to the air, and determine the inelastic strain rate of the solder layer of the power device and the solder layer of the substrate from the case temperature and junction temperature;

[0051] S5. Determine the cycle life of the power device based on the strain value of the solder layer of the power device and the solder layer of the substrate. Through the present invention, the heat transfer coefficient of the heat sink of the power device is determined based on the pressure value and temperature information of the low-pressure environment in which the power device is located, and then the shell temperature and junction temperature of the power device are determined by the heat transfer coefficient, and then the life of the power device is evaluated, which can effectively ensure that the predicted life of the power device in a low-pressure environment is basically consistent with the actual life, and effectively ensure the safe and stable operation of the photovoltaic power generation system.

[0052] In this example, in step S5, the cycle life of the power device is determined by the following method:

[0053]

[0054] in: Indicates the cycle life of the substrate solder layer of the power device, Indicates the cycle life of the chip solder layer of the power device, C 11 Indicates the fatigue ductility coefficient of the substrate solder layer of the power device, C 12 Indicates the fatigue ductility index of the substrate solder layer of the power device, Indicates the inelastic strain rate of the substrate solder layer of the power device; C 21 Indicates the fatigue ductility coefficient of the chip solder layer of the power device, C 22 Indicates the fatigue ductility index of the chip solder layer of the power device, Represents the inelastic strain rate of the chip solder layer of the power device. The power device includes a semiconductor chip and a substrate. The semiconductor chip is packaged on the substrate through a solder layer, and the substrate of the power device also has a solder layer, which is mainly composed of copper foil and ceramic plates. The cycle life of the above two solder layers is often difficult to determine in a low-pressure environment. The above method can accurately determine the cycle life in a low-pressure environment. After the two cycle lives are determined, the two cycle lives can be used as input in the Comsol simulation software to obtain the cycle life during the entire power period. The processing process of the Comsol simulation software obtaining the cycle life during the entire power period through the cycle life of the substrate solder layer of the power device and the cycle life of the chip solder layer is a prior art and will not be repeated here.

[0055] In this example, the inelastic strain rate of the chip solder layer of the power device and the inelastic strain rate of the substrate solder layer are determined as follows:

[0056]

[0057] Where: K A represents the setting coefficient, Q1 and Q2 represent the activation energy, where the activation energy refers to the energy threshold that needs to be overcome for the internal microstructure (such as dislocation, grain boundary, etc.) of the chip solder layer of the power device to undergo irreversible deformation (such as dislocation slip, void nucleation). Represents the stress coefficient of the substrate solder layer of the power device, Represents the equivalent stress of the substrate solder layer of the power device, m A1 represents the strain sensitivity coefficient of the substrate solder layer of the power device, R represents the universal gas constant, T C (P a ) represents the case temperature of the power device, T J (P a ) represents the junction temperature of the power device, Represents the strain of the substrate solder layer, Represents the stress coefficient of the chip solder layer of the power device, Represents the equivalent stress of the chip solder layer of the power device, m A2 Indicates the strain sensitivity coefficient of the chip solder layer of the power device;

[0058] Specifically, the case temperature T of the power device is determined by the following method: C (P a ):

[0059]

[0060] Where: P loss Indicates the loss of the power device. The loss of the power device can be determined by the voltage and current of the power device. This is the existing technology. cmax Indicates the maximum case temperature of the power device during the power pulse period, R th,ch It represents the thermal resistance from the power device case to the power device heat sink, C th,ch represents the heat capacity from the power device housing to the power device heat sink, t represents the temperature change time of the power heat sink, T h (P a ) represents the temperature of the heat sink of the power device, t p Indicates that the temperature of the power device heat sink reaches the maximum value T hmax Duration, t d It indicates the duration of the high level of the power pulse of the power device in one cycle. The power pulse of the power device refers to the power device working in the form of pulse current during operation.

[0061] The junction temperature T of the power device is determined by the following method: J (P a ):

[0062]

[0063] Where: T jmax Indicates the maximum junction temperature of the power device during the power pulse period; R th,jc Indicates the thermal resistance from the PN junction of the power device to the power device case, C th,jc It represents the thermal capacitance from the PN junction of the power device to the case of the power device.

[0064] Determine the temperature T of the heat sink of the power device by the following method h (P a ):

[0065]

[0066] Where: T hmaxIndicates the maximum temperature of the heat sink of the power device during the power pulse cycle, R th,ha (P a ) represents the equivalent thermal resistance from the heat sink of the power device to the ambient air, C th,ha It represents the heat capacity from the heat sink of the power device to the ambient air, T a Indicates the ambient temperature of the power device.

[0067] Determine the equivalent thermal resistance R from the heat sink to the air of the power device by the following method: th,ha (P a ):

[0068]

[0069] in:

[0070] R th,hai (P a ) represents the equivalent thermal resistance from the ith surface of the heat sink of the power device to the air, h hai (P a ) is the heat transfer coefficient from the ith surface of the power device heat sink to the air, A i represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink of the power device. When i is 2, it represents the lower surface of the heat sink of the power device. When i is 3 to 6, it represents the side surface of the heat sink of the power device. Figure 2 As shown, Figure 2 The heat sink of the power device is equivalent to a rectangular parallelepiped, and each heat sink can be equivalent to a corresponding rectangular parallelepiped.

[0071] The heat transfer coefficient of the heat sink surface of the power device is determined by the following method:

[0072] When i is 1:

[0073]

[0074] When i is 2:

[0075]

[0076] When i is 3 to 6:

[0077]

[0078] Where: K a (P a ) represents the thermal conductivity of air, L s The characteristic lengths of the upper and lower surfaces of the heat sink of the power device are represented by Figure 2It can be seen that the characteristic lengths of the upper and lower surfaces of the power device are equal; L h is the vertical height of the side surface of the heat sink of the power device, Ra(P a ) represents the Prandtl number, Pr(P a ) represents the Rayleigh number;

[0079]

[0080] Where: β represents the volume expansion coefficient of air, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the acceleration of gravity, R represents the universal gas constant, c a represents the specific heat capacity of air, ΔT represents the air temperature deviation, P a Indicates the atmospheric pressure value of the environment where the power device is located, μ a is the dynamic viscosity.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for predicting the life of a power device under low pressure, characterized in that: The following steps are involved: Acquire environmental parameters of the environment in which the power device to be tested is located, the environmental parameters at least including air pressure and ambient temperature; Determine the heat transfer coefficient of the heat sink surface of the power device to be tested based on the environmental parameters of the environment in which the power device to be tested is located; Determine the equivalent thermal resistance from the heat sink to the air based on the heat transfer coefficient of the heat sink surface of the power device to be tested; The case temperature and junction temperature of the power device are determined based on the equivalent thermal resistance from the heat sink to the air, and the inelastic strain rate of the solder layer of the power device and the solder layer of the substrate are determined from the case temperature and the junction temperature; The cycle life of the power device is determined based on the strain values ​​of the solder layer of the power device and the solder layer of the substrate.

2. The method for predicting the life of a power device under low pressure according to claim 1, characterized in that: The cycle life of the power device is determined by the following method: in: Indicates the cycle life of the substrate solder layer of the power device, Indicates the cycle life of the chip solder layer of the power device, C 11 Indicates the fatigue ductility coefficient of the substrate solder layer of the power device, C 12 Indicates the fatigue ductility index of the substrate solder layer of the power device, Indicates the inelastic strain rate of the substrate solder layer of the power device; C 21 Indicates the fatigue ductility coefficient of the chip solder layer of the power device, C 22 Indicates the fatigue ductility index of the chip solder layer of the power device, Represents the inelastic strain rate of the chip solder layer of the power device.

3. The method for predicting the life of a power device under low pressure according to claim 2, characterized in that: The inelastic strain rate of the chip solder layer of the power device and the inelastic strain rate of the substrate solder layer are determined as follows: Where: K A represents the setting coefficient, Q1 and Q2 represent the activation energy, Represents the stress coefficient of the substrate solder layer of the power device, Represents the equivalent stress of the substrate solder layer of the power device, m A1 represents the strain sensitivity coefficient of the substrate solder layer of the power device, R represents the universal gas constant, T C (P a ) represents the case temperature of the power device, T J (P a ) represents the junction temperature of the power device, Represents the strain of the substrate solder layer, Represents the stress coefficient of the chip solder layer of the power device, Represents the equivalent stress of the chip solder layer of the power device, m A2 Represents the strain sensitivity coefficient of the chip solder layer of the power device.

4. The method for predicting the life of a power device under low pressure according to claim 3, characterized in that: Determine the case temperature T of the power device by the following method: C (P a ): Where: P loss Represents the power device loss, T cmax Indicates the maximum case temperature of the power device during the power pulse period, R th,ch It represents the thermal resistance from the power device case to the power device heat sink, C th,ch represents the heat capacity from the power device housing to the power device heat sink, t represents the temperature change time of the power heat sink, T h (P a ) represents the temperature of the heat sink of the power device, t p Indicates that the temperature of the power device heat sink reaches the maximum value T hmax Duration, t d Indicates the period during which a power device is subjected to a power pulse.

5. The method for predicting the life of a power device under low pressure according to claim 3, characterized in that: The junction temperature T of the power device is determined by the following method: J (P a ): Where: T jmax Indicates the maximum junction temperature of the power device during the power pulse period; R th,jc Indicates the thermal resistance from the PN junction of the power device to the power device case, C th,jc It represents the thermal capacitance from the PN junction of the power device to the case of the power device.

6. The method for predicting the life of a power device under low pressure according to claim 4 or 5, characterized in that: Determine the temperature T of the heat sink of the power device by the following method h (P a ): Where: T hmax Indicates the maximum temperature of the heat sink of the power device during the power pulse cycle, R th,ha (P a ) represents the equivalent thermal resistance from the heat sink of the power device to the ambient air, C th,ha It represents the heat capacity from the heat sink of the power device to the ambient air, T a Indicates the ambient temperature of the power device.

7. The method for predicting the life of a power device under low pressure according to claim 6, characterized in that: Determine the equivalent thermal resistance R from the heat sink to the air of the power device by the following method: th,ha (P a ): in: R th,hai (P a ) represents the equivalent thermal resistance from the ith surface of the heat sink of the power device to the air, h hai (P a ) is the heat transfer coefficient from the ith surface of the power device heat sink to the air, A i It represents the area of ​​the i-th surface of the heat sink of the power device. When i is 1, it represents the upper surface of the heat sink of the power device. When i is 2, it represents the lower surface of the heat sink of the power device. When i is 3 to 6, it represents the side surface of the heat sink of the power device.

8. The method for predicting the life of a power device under low pressure according to claim 7, characterized in that: The heat transfer coefficient of the heat sink surface of the power device is determined by the following method: When i is 1: When i is 2: When i is 3 to 6: Where: K a (P a ) represents the thermal conductivity of air, L s Represents the characteristic length of the upper and lower surfaces of the heat sink of the power device, L h is the vertical height of the side surface of the heat sink of the power device, Ra(P a ) represents the Prandtl number, Pr(P a ) represents the Rayleigh number; Where: β represents the volume expansion coefficient of air, v represents the kinematic viscosity of air, M represents the average molar mass of air, g represents the acceleration of gravity, R represents the universal gas constant, c a represents the specific heat capacity of air, ΔT represents the air temperature deviation, P a Indicates the atmospheric pressure value of the environment where the power device is located, μ a is the dynamic viscosity.

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