Method for testing service life of power device of converter equipment

Abstract

The invention discloses a method for testing the service life of a power device of converter equipment. The service life test method comprises the following steps: constructing an acceleration model of the converter equipment in a running state, obtaining an acceleration factor in the running state, and obtaining an actual test duration according to a design life in the running state and the acceleration factor in the running state, carrying out an acceleration experiment on the power device of the current equipment in a running state according to the actual test duration; wherein the acceleration model in the operation state is constructed according to the temperature, humidity and electric stress conditions of the converter equipment in the operation state, and the electric stress is obtained according to the ratio of the added experimental voltage to the actual working voltage. According to the method, the service life of the power device in the operation state is evaluated in combination with influence factors of the climate environment and the electrical condition on the power device, the design requirement of current equipment is met, and the evaluation result is reliable.

Description

Technical Field

[0001] The invention relates to a method for testing the service life of a power device of a current conversion device. Background Art

[0002] As the core semiconductor components of photovoltaic inverters and energy storage converters, power devices such as IGBTs play the role of rectifying and inverting electric energy to achieve AC grid connection of new energy power generation and charging and discharging of energy storage batteries. Therefore, power devices such as IGBTs will fully benefit from the rapid development of green electricity and energy storage. The performance and reliability of power semiconductor devices directly affect the efficiency of new energy power generation and the service life of inverters / converters, and their performance and reliability requirements are very strict. With the vigorous development of the new energy industry, the power semiconductor industry has also developed. Faced with many brands and models of power semiconductor devices, photovoltaic inverters must be scientific and rigorous in their selection of such devices. They need to evaluate the devices according to the specifications and quality assurance information of the product design, and the test and verification plan must also be reasonably formulated to ensure that the design quality requirements are met and the cost of over-investment is reduced to optimize the competitiveness of the product.

[0003] At present, the evaluation of power semiconductor devices in photovoltaic inverters, especially the life assessment part, is mainly based on the test reports provided by suppliers and the temperature rise, double pulse and reliability tests of the whole machine. However, the rationality of the life assessment of such devices in photovoltaic inverters based on these test contents is still insufficient. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a service life test method for power devices of power conversion equipment, which combines the factors affecting power devices such as climate environment and electrical conditions to evaluate the service life of power devices in operation, which is more in line with the design requirements of current equipment and the evaluation results are more reliable.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for testing the service life of power devices of a current conversion device comprises the following steps: constructing an acceleration model of the current conversion device in an operating state, obtaining an acceleration factor in an operating state, obtaining an actual test duration according to a design life in an operating state and the acceleration factor in an operating state, and performing an acceleration test on the power devices of the current device in an operating state according to the actual test duration; wherein the acceleration model in an operating state is constructed according to temperature, humidity and electrical stress conditions of the current conversion device in an operating state, and the electrical stress is obtained according to the ratio of an added experimental voltage to an actual working voltage.

[0007] In a preferred embodiment, the electrical stress V Af =(V stress / V normal ) β ; Among them, V stress is the accelerating test voltage, V normal is the actual working voltage, and β is the voltage acceleration constant.

[0008] In a preferred embodiment, the acceleration factor Af1 in the running state is obtained according to the following formula (1):

[0009] Af1=exp[E a / k B ×(1 / T u -1 / T t )] × (H a / H u ) n × (V stress / V normal ) β (1)

[0010] Among them, E a represents the activation energy, k B is the Boltzmann constant, T u is the typical operating absolute temperature, T t is the absolute temperature of the accelerated experiment, H u is the relative humidity of the operating environment, H a Relative humidity is used to accelerate the experiment, and n is a model parameter determined by the corrosion of the power device.

[0011] In a specific and preferred embodiment, n=1-5, β=1.

[0012] In a preferred embodiment, the service life test method also includes the following steps: constructing an acceleration model of the converter device in a non-operating state, obtaining an acceleration factor in the non-operating state, obtaining an actual test duration based on the design life in the non-operating state and the acceleration factor in the non-operating state, and performing an acceleration experiment on the power device of the current device in the non-operating state according to the actual test duration; wherein the acceleration model in the non-operating state is constructed based on the temperature shock condition of the converter device in the non-operating state.

[0013] In a more preferred embodiment, the acceleration factor Af2 in the running state is obtained according to the following formula (2):

[0014] Af2=(ΔT t / ΔT u ) m × (f u / f t ) p × e B(1 / Tu-1 / Tt) (2)

[0015] Where, ΔT t is the temperature difference of the accelerating experimental condition, ΔT u is the temperature difference under actual use conditions, m is the model constant, and f u is the number of cycles per unit time under actual use conditions, f t To accelerate the number of cycles per unit time under experimental conditions, p and B are both model constants, T u is the maximum temperature of each cycle under actual use conditions, T t The maximum temperature of each cycle of the accelerated test conditions.

[0016] In a specific and preferred embodiment, it is characterized in that the converter device is a photovoltaic inverter, the power device is an IGBT, m=1.9, p=1 / 3, and B=1414.

[0017] In a more preferred embodiment, after the accelerated test in the non-operating state, the test sample is visually inspected. If there is no abnormality in the appearance, the power factor, current harmonics, DC component, efficiency and temperature of the device after thermal balance are tested, and whether the design life is met is determined based on the results.

[0018] In a preferred embodiment, after the accelerated test under the operating state, the test prototype is subjected to a low-temperature test. After the test is completed, it is confirmed whether the test prototype has any hardware damage and whether it can operate normally. Then, the power factor, current harmonics, DC component, efficiency and temperature test of the device after thermal balance are performed, and it is determined whether the design life is met based on the results.

[0019] In a preferred embodiment, during the accelerated experiment, multiple test prototypes are tested simultaneously, and the test time is the ratio of the actual test time to the number of prototypes.

[0020] The above solution adopted by the present invention has the following advantages:

[0021] The service life testing method of the power device of the converter equipment of the present invention can measure the service life of the power device of the converter equipment in the operating state, considers the comprehensive influence of the climatic environment and the electrical stress environment received by the machine in the operating state, and conducts accelerated experiments, which is more in line with the design requirements of converter equipment such as photovoltaic inverters, and the life assessment is more reliable, and the assessment scheme is more reasonable. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The method of this embodiment is mainly for optimizing the measurement and verification scheme of power semiconductor devices of power conversion equipment such as photovoltaic inverters. The power conversion equipment is typically a photovoltaic inverter or an energy storage converter; the power device is typically a switch tube such as an IGBT, which is a device that plays a role of rectification and inversion in the power conversion equipment, and is used to realize the AC grid connection of new energy power generation equipment or the charging and discharging of energy storage batteries.

[0024] The service life test method of the power device of the converter device of this embodiment mainly includes: service life evaluation in the operating state and service life evaluation in the non-operating state. The evaluation method and principle are described in detail below.

[0025] 1. Operation status

[0026] The machine is affected by the combined effects of the climate environment and the electrical stress environment during operation, and this embodiment performs a comprehensive evaluation.

[0027] 1. The impact of the operating environment on power devices during product operation:

[0028] 1.1 High temperature: Power devices may age, metal may oxidize, and solder may crack or come loose.

[0029] The working temperature of the photovoltaic inverter is closely related to the ambient temperature around the photovoltaic inverter. When the ambient temperature is high or heat dissipation is difficult, the heat energy generated by the photovoltaic inverter is difficult to dissipate, which will increase the temperature rise of the power device. Since power semiconductor devices have a certain operating temperature range, if their limit temperature is exceeded, the working state will change, the life will be shortened or even damaged. The reliability discipline has such a rule definition that the life will be reduced by half for every 10°C increase in temperature. Therefore, the following high temperature acceleration model is combined for life assessment:

[0030] A f =exp[E a / k B ×(1 / T u -1 / T t )]

[0031] in:

[0032] A f : The acceleration factor of the acceleration condition relative to the use environment

[0033] E a : Activation energy, in eV; in this embodiment, it specifically refers to the activation energy of damage to the power device, which is measured according to the aging test, and the reference value can be 0.5 to 2.0 eV;

[0034] k B: Boltzmann constant, 8.62E-05 Unit: eV / k

[0035] T u : Typical operating absolute temperature, in Kelvin (K)

[0036] T t : Absolute temperature of accelerated experiment, the unit is Kelvin (K).

[0037] 1.2 Low temperature: Power devices will become brittle and physically shrink, electrical and mechanical properties will change, and physical parameters will change.

[0038] 1.2.1. Temperature performance: Low temperature environment may affect the performance of electronic components inside the photovoltaic inverter, such as reducing the efficiency and life of power semiconductor switching devices and increasing resistance losses. Under low temperature conditions, the open circuit voltage of the components will increase, and the voltage of the photovoltaic inverter system will also increase accordingly. High open circuit voltage will cause the inverter to have the risk of overvoltage protection shutdown, which will seriously affect the performance of the photovoltaic inverter.

[0039] 1.2.2. Start-up characteristics: Under extremely low temperatures, the start-up time and output stability of the photovoltaic inverter may be affected.

[0040] The impact of low temperature on photovoltaic inverters is smaller than that of high temperature. Most of the current power semiconductor devices use advanced designs and materials, and have good low-temperature adaptability. There is no relevant acceleration model for the life assessment of power devices affected by low temperature. For low-temperature environments, corresponding test plans can be formulated based on product specifications and industry standards.

[0041] 1.3 Humidity: Power devices will absorb moisture, resulting in degradation of physical properties, reduced electrical strength, and reduced insulation resistance.

[0042] As the "heart" of photovoltaic inverters, power semiconductor devices need to work reliably for many years under various complex working conditions. Due to the conductivity and corrosiveness of water molecules, high humidity environments have a very large negative impact on the long-term reliable operation of power semiconductor devices. According to the statistical analysis of failure information of power semiconductor devices in the field of a large number of different applications in the past, it is found that when other external conditions are similar, the failure rate in the rainy season is significantly higher. Therefore, it is very important to evaluate the application of power semiconductor devices in high humidity environments.

[0043] For life assessment under humidity, a test plan is developed in combination with the following humidity acceleration model.

[0044] Af=Luse / Laccelerated=AH u -n / AH a -n =(H a / H u ) n

[0045] in:

[0046] Af: Acceleration factor

[0047] n: unknown model parameter (range: 1 to 5, recommended value: 3), which is determined by the corrosion characteristics

[0048] H u : Relative humidity of the operating environment, in %

[0049] H a : Accelerated test relative humidity, unit is %.

[0050] 1.4 Electrical conditions: If the operating voltage and power during power operation exceed the derating requirements, hardware damage may occur easily.

[0051] Power semiconductor devices are subject to challenges from voltage stress during operation. Therefore, appropriate electrical insulation design is the key to ensuring such reliability. By adopting effective isolation and shielding measures, the adverse effects of voltage stress on power devices can be reduced. Maintaining the voltage balance between various power semiconductor devices in the system and the stability of the power supply are essential to improving the reliability of the entire system. Reasonable circuit design, perfect power management and voltage monitoring technology can help solve these problems and improve the reliability of power semiconductor devices. In actual verification, accelerated life assessment can be performed based on the electrical stress conditions of the product in field applications. The following model can be applied.

[0052] V Af =(V stress / V normal ) β

[0053] in:

[0054] V Af : Voltage acceleration factor

[0055] V stress : Acceleration test voltage

[0056] V normal： Actual working voltage

[0057] β: voltage acceleration constant, the default value is 1.

[0058] 2. Specific test plan

[0059] According to the temperature, humidity and electrical stress conditions of the converter equipment in the operating state, an acceleration model of the converter equipment in the operating state is constructed to obtain the acceleration factor in the operating state. According to the design life in the operating state and the acceleration factor in the operating state, the actual test duration is obtained. According to the actual test duration, an acceleration experiment is performed on the power devices of the current device in the operating state.

[0060] Specifically, the acceleration factor Af1 under the running state is obtained according to the following formula (1):

[0061] Af1=exp[E a / k B ×(1 / T u -1 / T t )] × (H a / H u ) n × (V stress / V normal ) β (1)

[0062] Formula (1) comprehensively evaluates the life of the power device under operating conditions based on the climate environment and electrical stress environment of the test sample.

[0063] After the accelerated test under the running state, the test sample is subjected to a low-temperature test. After the test is completed, it is confirmed whether the test sample has any hardware damage and whether it can operate normally. Then the power factor, current harmonics, DC component, efficiency and temperature test of the device after thermal balance are carried out, and it is determined whether the design life is met based on the results.

[0064] Furthermore, during the accelerated experiment, multiple test prototypes are tested simultaneously, and the test time is the ratio of the actual test time to the number of prototypes.

[0065] 2. Non-operating state

[0066] When not in operation, the photovoltaic inverter is mainly affected by the climate environment. In addition, the humidity has little effect on this situation. Therefore, we only focus on the impact of temperature shock on the product. Before the temperature shock test, we collect the key parameters of the prototype, such as power factor, current harmonics, DC component, efficiency and the temperature of related components after the thermal balance of the prototype, to ensure that these parameters meet the product specifications and relevant safety requirements.

[0067] 1. Temperature shock acceleration model

[0068] Temperature shock can cause the structural strength of the device to decrease or fail, and damage the sealing of the device. By simulating the impact of external temperature changes on power semiconductor devices, the overall structure and materials of the device or module can be verified. In particular, the IGBT power module is a system composed of different materials. When heated and cooled, the thermal expansion coefficients of different materials vary greatly, and the mechanical stress on the two interfaces during heating or cooling is greater.

[0069] The temperature shock test mainly tests the material properties of the device. It can consider the impact of temperature changes in the external environment on the device when the machine is not running. The following model can be used to evaluate the life:

[0070] Af=(ΔT t / ΔT u ) m (f u / f t ) n e B(1 / Tu-1 / Tt)

[0071] Af: acceleration factor

[0072] ΔT t : Temperature difference under accelerated experimental conditions

[0073] ΔT u : Temperature difference under actual use conditions

[0074] m: Model constant (lead: 1.9, lead-free: 2.65). Select the lead parameter based on the product design.

[0075] f u :Number of cycles per unit time under actual use conditions (number of cycles per 24 hours)

[0076] f t : The number of cycles per unit time under accelerated experimental conditions (number of cycles per 24 hours)

[0077] n: Model constant (lead: 1 / 3, lead-free: -0.136). Select the lead parameter based on the product design.

[0078] B: Model constant (lead: 1414, lead-free: 2185), select the lead parameters based on the product design.

[0079] T u : The maximum temperature of each cycle under actual use conditions

[0080] T t : The maximum temperature of each cycle of accelerated test conditions.

[0081] 2. Specific test plan

[0082] An acceleration model of the converter device in a non-operating state is constructed to obtain an acceleration factor in the non-operating state, an actual test duration is obtained based on the design life in the non-operating state and the acceleration factor in the non-operating state, and an acceleration experiment is performed on the power devices of the current device in the non-operating state according to the actual test duration; wherein the acceleration model in the non-operating state is constructed based on the temperature shock condition of the converter device in the non-operating state.

[0083] Specifically, the acceleration factor Af2 under the running state is obtained according to the following formula (1):

[0084] Af2=(ΔT t / ΔT u ) m × (f u / f t ) p × e B(1 / Tu-1 / Tt) (2)

[0085] Where, ΔT t is the temperature difference of the accelerating experimental condition, ΔT u is the temperature difference under actual use conditions, m is the model constant, and f u is the number of cycles per unit time under actual use conditions, f t To accelerate the number of cycles per unit time under experimental conditions, p and B are both model constants, T u is the maximum temperature of each cycle under actual use conditions, T t The maximum temperature of each cycle of the accelerated test conditions.

[0086] Furthermore, the current conversion device is a photovoltaic inverter, the power device is an IGBT, m=1.9, p=1 / 3, and B=1414.

[0087] After the accelerated test in the non-operating state, the test sample is visually inspected. If there is no abnormality in the appearance, the power factor, current harmonics, DC component, efficiency and temperature of the device after thermal balance are tested. Based on the results, it is determined whether the design life is met.

[0088] Furthermore, during the accelerated experiment, multiple test prototypes are tested simultaneously, and the test time is the ratio of the actual test time to the number of prototypes.

[0089] Application Examples

[0090] The life of power semiconductor devices (IGBT) in photovoltaic inverter applications is evaluated based on the two states of machine operation and non-operation, and a corresponding plan is formulated assuming that the design life of the product is 10 years.

[0091] Non-operating state: Calculate the acceleration factor Af2 according to the above formula (2).

[0092] Specifically, combined with the environmental conditions of the product in multiple areas, the high temperature at the site can reach 45°C, the low temperature can reach -15°C, the temperature difference is 60°C, and the number of temperature cycles at the site is 2 times every 24 hours. The test conditions are as follows: the high temperature is set to 100°C, the low temperature is -40°C, the temperature difference is 140°C, the dwell time of each temperature is 30 minutes, and the temperature change time is less than 5 minutes. It can be cycled 23.8 times every 24 hours. Based on the above information, the acceleration factor Af2 is 5.46.

[0093] The number of temperature shocks on site in 10 years is: 10×365×2=7320 times, and the accelerated test needs to be performed 7320 / 5.46=1340 times.

[0094] Test duration: 1340 / 23.8=56 days.

[0095] After the temperature shock test is completed, the sample is visually inspected. If there is no abnormality in appearance, the power factor, current harmonics, DC component, efficiency and temperature test of related components after the prototype is thermally balanced are conducted to check whether the product specifications and safety requirements are met. Based on the results, it is determined whether the design life requirements are met.

[0096] Running status: Calculate the acceleration factor Af1 according to the above formula (1).

[0097] Specifically, for a photovoltaic inverter with a system voltage of 1000V, the setting conditions are the conditions for field application, the ambient temperature is not more than 40℃ on average, the humidity is not more than 75%RH on average, the system voltage is normally 650V, the test conditions can be set to a high temperature of 60℃, a humidity of 95%RH, a system operating voltage of 850V, and an acceleration factor Af1=19.75

[0098] Product testing time: 10×365 / 19.75=185 days.

[0099] Low temperature: Since there is no corresponding acceleration model, the product specification and product industry standard requirements can be combined to formulate a low temperature of -25°C (minimum operating temperature) and a light load (10% rated power) power cycle test for 30 days.

[0100] After the above tests are completed, confirm that the machine has no hardware damage and can operate normally, and test the power factor, current harmonics, DC component, efficiency and the temperature of related components after the prototype is thermally balanced to ensure that these parameters meet the product specifications and relevant safety requirements.

[0101] Furthermore, in the above-mentioned accelerated experiments, for the accelerated tests of temperature shock and high temperature, high humidity + voltage stress, the number of machines can be increased to shorten the test cycle. It is recommended that the number of prototypes be 2 to 3, and the test cycle can be divided by 2 or 3.

[0102] The method of this embodiment is based on the product specifications of the photovoltaic inverter, the conditions for the product's on-site application, and the design life of the product. The test and verification scheme is reasonably formulated to ensure that the design quality requirements are met, reduce excessive cost investment, and optimize the competitiveness of the product.

[0103] As shown in this specification and claims, the terms "comprises" and "include" only indicate the inclusion of the steps and elements that have been clearly identified, and these steps and elements do not constitute an exclusive list, and the method or device may also include other steps or elements. The term "and / or" as used herein includes any combination of one or more of the relevant listed items.

[0104] It should be noted that, unless otherwise specified, when a feature is referred to as being "fixed" or "connected" to another feature, it may be directly fixed or connected to the other feature, or it may be indirectly fixed or connected to the other feature. In addition, the descriptions of up, down, left, right, etc. used in the present invention are only relative to the relative positional relationship of the various components of the present invention.

[0105] The above embodiment is only for illustrating the technical concept and features of the present invention, and is a preferred embodiment. Its purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for testing the service life of a power device of a converter device, characterized in that: The method comprises the following steps: constructing an acceleration model of the converter device under operation, obtaining an acceleration factor under operation, obtaining an actual test duration according to the design life under operation and the acceleration factor under operation, and performing an acceleration test on the power device of the current device under operation according to the actual test duration; wherein the acceleration model under operation is constructed according to the temperature, humidity and electrical stress conditions of the converter device under operation, and the electrical stress is obtained according to the ratio of the added experimental voltage to the actual working voltage.

2. The service life testing method according to claim 1, characterized in that: The electrical stress V Af =(V stress / V normal ) β ; Among them, V stress is the accelerating test voltage, V normal is the actual working voltage, and β is the voltage acceleration constant.

3. The service life testing method according to claim 1 or 2, characterized in that: The acceleration factor Af1 under the running state is obtained according to the following formula (1): Af1=exp[E a / k B ×(1 / T u -1 / T t )] × (H a / H u ) n × (In stress / V normal ) β (1) Among them, E a represents the activation energy, k B is the Boltzmann constant, T u is the typical operating absolute temperature, T t is the absolute temperature of the accelerated experiment, H u is the relative humidity of the operating environment, H a Relative humidity is used to accelerate the experiment, and n is a model parameter determined by the corrosion of the power device.

4. The service life testing method according to claim 3, characterized in that: n＝1～5，β＝1。 5. The service life testing method according to claim 1, characterized in that: The service life test method also includes the following steps: constructing an acceleration model of the converter device in a non-operating state, obtaining an acceleration factor in the non-operating state, obtaining an actual test duration based on the design life in the non-operating state and the acceleration factor in the non-operating state, and performing an acceleration experiment on the power device of the current device in the non-operating state according to the actual test duration; wherein the acceleration model in the non-operating state is constructed based on the temperature shock condition of the converter device in the non-operating state.

6. The service life testing method according to claim 5, characterized in that: The acceleration factor Af2 under the running state is obtained according to the following formula (2): Af2=(ΔT t / ΔT u ) m × (f u / f t ) p × e B(1 / Tu-1 / Tt) (2) Where, ΔT t is the temperature difference of the accelerating experimental condition, ΔT u is the temperature difference under actual use conditions, m is the model constant, and f u is the number of cycles per unit time under actual use conditions, f t To accelerate the number of cycles per unit time under experimental conditions, p and B are both model constants, T u is the maximum temperature of each cycle under actual use conditions, T t The maximum temperature of each cycle of the accelerated test conditions.

7. The service life testing method according to claim 6, characterized in that: The current conversion device is a photovoltaic inverter, the power device is an IGBT, m=1.9, p=1 / 3, and B=1414.

8. The service life testing method according to claim 5, characterized in that: After the accelerated test in the non-operating state, the test sample is visually inspected. If there is no abnormality in the appearance, the power factor, current harmonics, DC component, efficiency and temperature of the device after thermal balance are tested. Based on the results, it is determined whether the design life is met.

9. The service life testing method according to claim 1, characterized in that: After the accelerated test under the running state, the test sample is subjected to a low-temperature test. After the test is completed, it is confirmed whether the test sample has any hardware damage and whether it can operate normally. Then the power factor, current harmonics, DC component, efficiency and temperature test of the device after thermal balance are carried out, and it is determined whether the design life is met based on the results.

10. The service life testing method according to claim 1 or 5, characterized in that: During the accelerated experiment, multiple test prototypes are tested at the same time, and the test time is the ratio of the actual test time to the number of prototypes.