Step stress test method and system for electric energy meter under combined action of temperature, humidity and stress

Abstract

The present invention discloses a method and system for step stress testing of electric energy meters under the combined action of temperature, humidity and stress. The method includes establishing a degradation model in the temperature and humidity accelerated stress model of the electric energy meter and establishing an acceleration model in the temperature and humidity accelerated stress model of the electric energy meter according to temperature and humidity information; obtaining the temperature and humidity stress limit of the electric energy meter by using a preliminary experiment; determining the stress applied in each test according to the temperature and humidity stress limit of the electric energy meter; determining the minimum time for applying each test stress according to the acceleration model; and performing a double cross step stress test according to the determined degradation model, the stress applied in each test and the minimum time for applying each test stress. The present invention can make up for the shortcomings of the traditional constant stress test method in terms of high sample size requirements and long test time, effectively shorten the time of the accelerated degradation test of the electric energy meter, reduce the test cost, and improve the test efficiency.

Description

Technical Field

[0001] The invention relates to a step stress test method and system for an electric energy meter under the combined action of temperature, humidity and stress, belonging to the technical field of reliability assessment. Background Art

[0002] As an important part of the smart grid, the smart energy meter is also the final node of the smart grid. Accelerating the development of smart energy meters is of great significance to the realization of informatization, automation and interactivity of the power grid. With the improvement of technology and the rapid development of smart grids, the construction of electricity information collection systems has become more and more complete. As a basic element of the electricity information collection system, the smart energy meter has the functions of data measurement, collection, transmission and simple analysis. Taking into account the environmental and component quality factors, affected by the production time, process and batch, there are differences in the life of the installed meters. In addition, the prototype test of the meter before leaving the factory has strict requirements from the perspective of time, equipment, environment and experience of the test personnel. Therefore, how to accurately and conveniently predict the life and reliability of the meter is an urgent problem to be solved.

[0003] Accelerated degradation test can make full use of the useful information of the product in the degradation test process, and extrapolate the degradation data of the product under high stress level to normal stress level through corresponding methods, so as to evaluate the performance indicators of the product. Compared with constant stress accelerated degradation test, the advantage of step stress accelerated degradation test is that the test samples are less than constant stress accelerated degradation test, and it has higher efficiency than constant stress accelerated degradation test.

[0004] Since the step stress accelerated degradation test is still in the exploratory development stage, there is a lack of relevant national standards. Therefore, a step stress test method for electric energy meters under the combined action of temperature and humidity stress is proposed to help fill the relevant gaps and provide necessary conditions and foundation for the subsequent effective evaluation of its reliability and service life under temperature and humidity environmental stress. This method can shorten the test cycle, improve the test efficiency, reduce the test cost, and solve the problem of partial reliability evaluation of electric energy meters under temperature and humidity environmental stress. Summary of the invention

[0005] Purpose of the invention: In order to solve the problem of partial reliability assessment of electric energy meters under environmental stress involving temperature and humidity, the present invention provides a step stress test method for electric energy meters under the combined action of temperature and humidity stress.

[0006] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A step stress test method for an electric energy meter under the combined action of temperature, humidity and stress comprises the following steps:

[0008] Step 1: Obtain the temperature and humidity information in the test environment.

[0009] Step 2: Establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter based on the temperature and humidity information.

[0010] Step 3: Establish an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information.

[0011] Step 4: Use preliminary experiments to obtain the temperature and humidity stress limits of the electricity meter.

[0012] Step 5: Determine the stress to be applied in each test according to the temperature and humidity stress limit of the electric energy meter.

[0013] Step 6: Determine the minimum stress application time for each test based on the acceleration model.

[0014] Step 7, performing a double cross step stress test according to the determined degradation model, each test applied stress and each test stress applied minimum time.

[0015] Preferably: the formula for determining the minimum time for applying each test stress in step 6 is as follows:

[0016]

[0017] Where D min is the minimum test time, χ 2 (α,2r+2) is the chi-square distribution, α is the confidence level, 2r+2 is the degree of freedom, r is the total number of test failures, Y is the required service life, N is the test sample size, F is the cumulative failure rate, is the electromagnetic interference stress level under the use conditions, Indicates the percentage relative humidity under the conditions of use, Expressed as percentage relative humidity under stress conditions, represents the power, represents the activation energy, represents the Boltzmann constant, represents the thermodynamic temperature under stress conditions, Indicates the thermodynamic temperature under operating conditions.

[0018] Preferably: the degradation model in step 2 is:

[0019] ;

[0020] Where X(t) represents the performance degradation, t represents the time, μ represents the drift parameter, σ represents the diffusion coefficient, B(t) represents the standard Brownian motion, ε represents the random measurement error, ε(t) is independent and identically distributed and has ε~N(0,σ ε 2), is the expected drift parameter, is the drift parameter variance, is the random measurement error variance.

[0021] Preferably, in step 5, the normal working stress and the limit stress of the electric energy meter are substituted into the applied stress formula to determine the applied stress, and the applied stress formula is as follows:

[0022] ;

[0023] In the formula, S1, S2, and S3 are three stress levels, S0 is the upper limit of normal working stress, S max is the maximum working stress, is an intermediate variable.

[0024] Preferably: the method for obtaining the temperature and humidity stress limits of the electric energy meter by using a preliminary experiment in step 4: conducting a preliminary experiment on electric energy meters of the same specification and batch as the electric energy meter to be tested, and obtaining the temperature limit stress and humidity limit stress of the electric energy meter respectively.

[0025] Optimum: The electromagnetic interference stress level formula is as follows:

[0026] ;

[0027] in, is the electromagnetic interference stress level under the use conditions, is the interference voltage.

[0028] Another object of the present invention is to provide a step stress test system for an electric energy meter under the combined action of temperature, humidity and stress, which is used to implement the step stress test method for an electric energy meter under the combined action of temperature, humidity and stress, and comprises an input unit, a degradation model unit, an acceleration model unit, a temperature and humidity stress limit unit, an applied stress determination unit, a stress application minimum time unit, and a double cross step stress test unit, wherein:

[0029] The input unit is used to obtain temperature and humidity information in the test environment.

[0030] The degradation model unit is used to establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter according to the temperature and humidity information.

[0031] The acceleration model unit is used to establish an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information.

[0032] The temperature and humidity stress limit unit is used to obtain the temperature and humidity stress limit of the electric energy meter by using a preliminary experiment.

[0033] The stress determination unit is used to determine the stress to be applied in each test according to the temperature and humidity stress limit of the electric energy meter.

[0034] The stress application minimum time unit is used to determine the minimum stress application time for each test according to the acceleration model.

[0035] The double cross step stress test unit is used to perform a double cross step stress test according to a determined degradation model, stresses applied in each test and minimum stress application time in each test.

[0036] Another object of the present invention is to provide a computer system, comprising a memory and a processor, wherein the memory is used to store computer programs / instructions. The processor is used to execute the computer programs / instructions to implement the step stress test method of an electric energy meter under the combined action of temperature, humidity and stress.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] Firstly, the temperature and humidity stress limit of the electric energy meter is obtained by preliminary experiment, and then the double cross step stress test method is used to accelerate the degradation test of the electric energy meter through calculation. This method can make up for the shortcomings of the traditional constant stress test method in terms of high sample size requirements and long test time, effectively shorten the time of the accelerated degradation test of the electric energy meter, reduce the test cost, improve the test efficiency, and solve the problem of partial reliability evaluation of the electric energy meter under the environmental stress involving temperature and humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention is a flow chart of a step stress test of an electric energy meter under the combined effects of temperature, humidity and stress. DETAILED DESCRIPTION

[0040] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0041] The present invention designs a step stress test method for an electric energy meter under the combined action of temperature, humidity and stress, establishes a degradation model in the temperature and humidity accelerated stress model of the electric energy meter based on the Wiener process; establishes an acceleration model in the temperature and humidity accelerated stress model based on the generalized Eyring model; obtains the temperature and humidity stress limit of the electric energy meter by using a preliminary experiment; substitutes the normal working stress and the limit stress of the electric energy meter into the applied stress calculation formula to determine the applied stress of each test; substitutes each factor into the stress time calculation formula to determine the minimum time for applying each test stress; and uses a double cross step stress test method to perform an accelerated degradation test on the electric energy meter, such as Figure 1 As shown, the specific steps include:

[0042] Step 1: Obtain the temperature and humidity information in the test environment.

[0043] Step 2: Establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter based on the temperature and humidity information.

[0044] The Wiener process is used to describe the degradation process of the electric energy meter, and the influence of measurement error is considered in the degradation model.

[0045] Usually, the performance degradation of a product will show an increasing trend away from the original point. Then this random motion process away from the original point can be described by adding a drift term to the standard Brownian motion. The specific expression of the performance degradation process is as follows:

[0046] (1)

[0047] Where X(t) represents the performance degradation, μ is the drift parameter, σ is the diffusion coefficient, and B(t) is the standard Brownian motion.

[0048] Due to the limitations of the signal acquisition equipment and the unavoidable interference of environmental factors, the final collected electric energy meter signal data will be affected by random errors. Therefore, in order to ensure the accuracy of the model, the influence of measurement errors must be considered in the degradation model. Let ε represent the random measurement error, ε(t) is independent and identically distributed and has ε~N(0,σ ε 2 ). Then the performance degradation model expression after adding the measurement error term on the basis of the above model is as follows:

[0049] (2)

[0050] Where X(t) represents the performance degradation, t represents the time, μ represents the drift parameter, σ represents the diffusion coefficient, B(t) represents the standard Brownian motion, ε represents the random measurement error, ε(t) is independent and identically distributed and has ε~N(0,σ ε 2 ), is the expected drift parameter, is the drift parameter variance, is the random measurement error variance.

[0051] According to the properties of the Wiener process, the probability density function can be expressed as:

[0052] f ( Δ x ( t )) = 1 σ 1 2 π Δ t exp [ − ( Δ x ( t ) − μ 1 Δ t ) 2 2 σ 1 2 Δ t ] (3)

[0053] In the formula, represents the probability density, represents the incremental change in performance degradation, Indicates the change time, represents the standard deviation of performance degradation, Represents the mean performance degradation.

[0054] The corresponding cumulative distribution function is:

[0055] (4)

[0056] In the formula, represents the cumulative distribution function, represents the probability,

[0057] Correspondingly, the reliability function R(t) of the electric energy meter is:

[0058] (5)

[0059] Where R(t) represents the reliability of the electric energy meter.

[0060] Step 3: Establish an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information.

[0061] The generalized Eyring model further considers the influence of factors such as material properties, working conditions, activation energy, etc. on the performance degradation rate of the test sample. The specific form is as follows:

[0062] (6)

[0063] In the formula, Indicates the characteristic parameters related to the performance degradation rate of the electric energy meter, Indicates the performance degradation rate of the electric energy meter. represents the thermodynamic temperature, represents the thermodynamic temperature-related parameter, represents the activation energy, represents the Boltzmann constant, Indicates the second parameter related to the performance degradation rate of the electric energy meter. represents stress other than temperature, Indicates the third parameter related to the performance degradation rate of the electric energy meter.

[0064] On the basis of the generalized Eyring model, let S = log (RH), where RH represents relative humidity, let m = 0, and do not consider the interaction between temperature and humidity, that is, γ3 = 0, the model can be further simplified, and the acceleration model is:

[0065] (7)

[0066] This model is also called the Peck model, and the corresponding acceleration factor formula is:

[0067] (8)

[0068] In the formula, represents the acceleration factor, Relative humidity, represents the activation energy, represents the Boltzmann constant, represents the thermodynamic temperature, Indicates the percentage relative humidity under the conditions of use, Expressed as percentage relative humidity under stress conditions, represents the power, Indicates the thermodynamic temperature under the conditions of use, represents the thermodynamic temperature under stress conditions. Activation energy E a =0.7, n=3.

[0069] By establishing an acceleration model based on the generalized Eyring model and calculating the acceleration factor, the foundation is laid for the subsequent calculation of determining the stress application time.

[0070] Step 4: Use preliminary experiments to obtain the temperature and humidity stress limits of the electricity meter.

[0071] A preliminary experiment is carried out on electric energy meters of the same specification and batch as the electric energy meters to be tested, and the temperature limit stress and humidity limit stress of the electric energy meters are obtained respectively.

[0072] Ensure that other stresses in the test environment are the stress magnitudes under normal working conditions of the smart energy meter and remain unchanged. According to the structural characteristics of the smart energy meter and previous assembly and working experience, determine the initial stress, step size, and step duration of the step stress test. The energy meter is left to stand for 3 minutes between steps, and the working status is continuously monitored and the status parameters of the energy meter are recorded. When approaching the working limit stress, the step size is appropriately adjusted down. When the energy meter fails at a certain step and the stress is adjusted back to the previous step, the faulty meter resumes normal operation. This stress is the limit stress of the energy meter, and then the normal working stress upper limit S0 and the maximum working stress S max .

[0073] Step 5: Determine the stress to be applied in each test.

[0074] Substitute the normal working stress and limit stress of the electric energy meter into the applied stress formula to determine the applied stress. The applied stress formula is as follows:

[0075] (9)

[0076] In the formula, S1, S2, and S3 are three stress levels, S0 is the upper limit of normal working stress, S max is the maximum working stress, is an intermediate variable.

[0077] Step 6: Determine the minimum stress application time for each test based on the acceleration model.

[0078] The formula for determining the minimum time for applying each test stress is as follows:

[0079] (10)

[0080] Where D min is the minimum test time (in hours), χ 2 (α,2r+2) is a chi-square distribution, Y is the required service life (in hours), α is the confidence level, α is the value of 1-CL, CL is the maximum confidence level, 2r+2 is the degree of freedom, r is the total number of test failures, is the comprehensive environmental factor, N is the test sample size, F is the cumulative failure rate, and AF is the acceleration factor.

[0081] When considering the combined effects of multiple physical fields, temperature, humidity and electromagnetic stress will be coupled and superimposed on each other, affecting the validity of the accelerated reliability test results. Therefore, the comprehensive environmental factors of electromagnetic interference must be considered to solve the problem of test result deviation caused by the coupling of multiple physical fields. The formula for the comprehensive environmental factors of electromagnetic interference is as follows:

[0082] (11)

[0083] (12)

[0084] in, is a comprehensive environmental factor. is the electromagnetic interference stress level under the use conditions, is the interference voltage. According to formula (12), the electromagnetic interference stress level is: when the interference voltage is less than or equal to 500V, E c Equal to 1; when the interference voltage is greater than 500 and less than or equal to 1000V, E c Equal to 2; when the interference voltage is greater than 1000 and less than or equal to 2000V, E c Equal to 3; when the interference voltage is greater than 2000 and less than or equal to 4000V, E c Equal to 4; when the interference voltage is greater than 4000, E c Equals 5.

[0085] Then substitute formula (11) and formula (8) into formula (10) and simplify:

[0086] (12)

[0087] That is, the formula for the minimum time of applying each test stress is:

[0088] (13)

[0089] Where D min is the minimum test time, χ 2 (α,2r+2) is the chi-square distribution, Y is the required service life, α is the confidence level, 2r+2 is the degree of freedom, r is the total number of test failures, N is the test sample size, F is the cumulative failure rate, is the electromagnetic interference stress level under the use conditions, Indicates the percentage relative humidity under the conditions of use, Expressed as percentage relative humidity under stress conditions, represents the power, represents the activation energy, represents the Boltzmann constant, represents the thermodynamic temperature under stress conditions, Indicates the thermodynamic temperature under operating conditions.

[0090] Step 7, performing a double cross step stress test according to the determined degradation model, each test applied stress and each test stress applied minimum time.

[0091] The acceleration factor obtained in step 3, the limit stress obtained in step 4, the applied stress obtained in step 5, and the minimum stress application time obtained in step 6 are summarized to form a complete double cross step stress test scheme as shown in Table 1, and then a double cross step stress test is carried out.

[0092] Table 1 Experimental plan

[0093] Stress No. Temperature(℃) humidity(%) Acceleration Factor AF Minimum stress application time (h) <![CDATA[S0]]> 80 85 238 798 <![CDATA[S1]]> 87 85 372 510 <![CDATA[S2]]> 87 90 442 430 <![CDATA[S3]]> 95 90 721 263 <![CDATA[S max ]]> 95 95 848 224

[0094] In another embodiment, a step stress test system for an electric energy meter under the combined action of temperature, humidity and stress is provided, which is used to implement the step stress test method for an electric energy meter under the combined action of temperature, humidity and stress, and includes an input unit, a degradation model unit, an acceleration model unit, a temperature and humidity stress limit unit, an applied stress determination unit, a stress application minimum time unit, and a double cross step stress test unit, wherein:

[0095] The input unit is used to obtain temperature and humidity information in the test environment.

[0096] The degradation model unit is used to establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter according to the temperature and humidity information.

[0097] The acceleration model unit is used to establish an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information.

[0098] The temperature and humidity stress limit unit is used to obtain the temperature and humidity stress limit of the electric energy meter by using a preliminary experiment.

[0099] The stress determination unit is used to determine the stress to be applied in each test according to the temperature and humidity stress limit of the electric energy meter.

[0100] The stress application minimum time unit is used to determine the minimum stress application time for each test according to the acceleration model.

[0101] The double cross step stress test unit is used to perform a double cross step stress test according to a determined degradation model, stresses applied in each test and minimum stress application time in each test.

[0102] In another embodiment, a computer system is provided, including a memory and a processor, wherein the memory is used to store computer programs / instructions, and the processor is used to execute the computer programs / instructions to implement the step stress test method of the electric energy meter under the combined action of temperature, humidity and stress.

[0103] The present invention can make up for the shortcomings of the traditional constant stress test method, that is, the high sample quantity requirement and the long test time, effectively shorten the time of the accelerated degradation test of the electric energy meter, reduce the test cost, and improve the test efficiency.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A step stress test method for an electric energy meter under the combined action of temperature, humidity and stress, characterized in that: The following steps are involved: Step 1, obtaining temperature and humidity information in the test environment; Step 2: Establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter according to the temperature and humidity information; Step 3, establishing an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information; Step 4, using a preliminary experiment to obtain the temperature and humidity stress limit of the electric energy meter; Step 5, determining the stress to be applied in each test according to the temperature and humidity stress limit of the electric energy meter; Step 6, determining the minimum application time of each test stress according to the acceleration model; The formula for determining the minimum time for applying each test stress is as follows: Where D min is the minimum test time, χ 2 (α,2r+2) is the chi-square distribution, α is the confidence level, 2r+2 is the degree of freedom, r is the total number of test failures, Y is the required service life, N is the test sample size, F is the cumulative failure rate, is the electromagnetic interference stress level under the use conditions, Indicates the percentage relative humidity under the conditions of use, Expressed as percentage relative humidity under stress conditions, represents the power, represents the activation energy, represents the Boltzmann constant, represents the thermodynamic temperature under stress conditions, Indicates the thermodynamic temperature under the conditions of use; Step 7, performing a double cross step stress test according to the determined degradation model, each test applied stress and each test stress applied minimum time.

2. The step stress test method for electric energy meter under the combined action of temperature, humidity and stress according to claim 1 is characterized in that: The degradation model in step 2 is: ； Where X(t) represents the performance degradation, t represents the time, μ represents the drift parameter, σ represents the diffusion coefficient, B(t) represents the standard Brownian motion, ε represents the random measurement error, ε(t) is independent and identically distributed and has ε~N(0,σ ε 2 ), is the expected drift parameter, is the drift parameter variance, is the random measurement error variance.

3. The step stress test method for electric energy meter under the combined action of temperature, humidity and stress according to claim 2 is characterized in that: In step 5, the normal working stress and the limit stress of the electric energy meter are substituted into the applied stress formula to determine the applied stress. The applied stress formula is as follows: ； In the formula, S1, S2, and S3 are three stress levels, S0 is the upper limit of normal working stress, S max is the maximum working stress, is an intermediate variable.

4. The step stress test method for electric energy meter under the combined action of temperature, humidity and stress according to claim 3 is characterized in that: The method for obtaining the temperature and humidity stress limits of the electric energy meter by using a preliminary experiment in step 4 is: conducting a preliminary experiment on electric energy meters of the same specification and batch as the electric energy meter to be tested, and obtaining the temperature limit stress and humidity limit stress of the electric energy meter respectively.

5. The step stress test method for electric energy meter under the combined action of temperature, humidity and stress according to claim 4 is characterized in that: The electromagnetic interference stress level formula is as follows: ； in, is the electromagnetic interference stress level under the use conditions, is the interference voltage.

6. A step stress test system for electric energy meters under the combined action of temperature, humidity and stress, characterized by: The method for implementing the step stress test of an electric energy meter under the combined action of temperature, humidity and stress as described in any one of claims 1 to 5 comprises an input unit, a degradation model unit, an acceleration model unit, a temperature and humidity stress limit unit, an applied stress determination unit, a stress application minimum time unit, and a double cross step stress test unit, wherein: The input unit is used to obtain temperature and humidity information in the test environment; The degradation model unit is used to establish a degradation model in the temperature and humidity accelerated stress model of the electric energy meter according to the temperature and humidity information; The acceleration model unit is used to establish an acceleration model in the temperature and humidity acceleration stress model of the electric energy meter according to the temperature and humidity information; The temperature and humidity stress limit unit is used to obtain the temperature and humidity stress limit of the electric energy meter by using a preliminary experiment; The stress determination unit is used to determine the stress to be applied in each test according to the temperature and humidity stress limit of the electric energy meter; The stress application minimum time unit is used to determine the minimum stress application time for each test according to the acceleration model; The double cross step stress test unit is used to perform a double cross step stress test according to a determined degradation model, stresses applied in each test and minimum stress application time in each test.

7. A computer system, characterized in that: It includes a memory and a processor, the memory is used to store computer programs / instructions; the processor is used to execute the computer programs / instructions to implement the step stress test method of the electric energy meter under the combined action of temperature and humidity stress as described in any one of claims 1-5.

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