The speed regulation of the frequency converter realizes constant pressure air supply, reliable operation, constant system pressure and good control effect. The most important thing is to achieve high efficiency and energy saving. At the same time, the soft start of the motor is adopted by the inverter, which reduces the equipment consumption and prolongs the service life of the air compressor. The frequency converter can better adjust the stability of the parameters such as pressure, flow and temperature of the system, which plays an important role in improving the working performance of the compressor and prolonging the working life of the system.
In the gas supply system, we used two air compressors for power frequency operation and another air compressor for standby to ensure normal system air supply. Therefore, the configuration of the air compressor can be regarded as a 2/3G voting system, that is, when two or more of the three variable frequency air compressors work normally, the system works normally. Figure 2 shows the reliability block diagram of the system.
Figure 2 Reliability diagram of the variable-voltage constant-pressure gas supply system The reliability block diagram describes the reliability relationship between the function of the system and the various components of the system. It indicates that the system must perform the specified functions and which components must work normally.
The reliability of the filter is R1; the reliability of the motor is R2; the reliability of the air compressor is R3; the reliability of the gas storage tank is R4; the reliability of the control box is R5, the reliability of the variable frequency constant pressure gas supply system The reliability equation RS is .
RS = R1R2.
3 j=2 3 j R j 3(1-R3)
3-j R4R5R1(1).
2 The selection and evaluation method of reliability feature quantity.
2.1 The selection and evaluation method of single machine reliability feature quantity.
The reliability feature quantity is a parameter capable of characterizing the reliability of the product, such as the working life, strength, and the like of the product. The selection of the reliability feature quantity is based on the specific properties of each component and refers to past experience.
2.2 System reliability assessment method.
2.2.1 Filter, the control box should adopt the reliability confidence limit method of the exponential series system.
Let the reliability of the series system of i-index components be R, the test data of the i-th unit product is i, ri, i is the total test time, and ri is the number of failures. When the total test time between the i components is not much different, then the lower confidence limit of R is.
RL=(1-)
1/min when.
When li=1 i=0, e xp- r+1(1- 1 9(r+1)
+ ur 3r+1)
3 when.
When li=1 i0 (2).
Where: confidence level =. ii = 1 i / i (3).
Where i is the number of successes of the i-th unit product, and i is the number of failures of the i-th unit product.
Min=min(1,2,#,l),=min. li=1 rii/.li=1 ri,.
Li=1 i/l. li=1 ri0,r=. li=1 ri/i,i=i/t,i=1,2,#,l,u are the quantiles of the standard normal distribution.
2.2.2 The gas storage tank shall adopt the normal distribution double-sided confidence limit method. It is assumed that the product characteristic value X is from the same population of independent random samples of sample size n, x1, #xn, given the confidence level. When unknown, for the upper (lower) limit of the given characteristic value, the reliability one-side confidence lower limit is required.
Calculate the coefficient K according to the upper (lower) limit of the eigenvalue. When the upper limit U is specified, K= UX S(4)
When the lower limit L is specified, K = XL S (5).
From the given confidence level, sample size n and calculated K value, the K-factor table (GB4885-85, 1985) is inversely checked, that is, the reliability of the characteristic value X is unilaterally limited.
2.2.3 Use the fiducial method to find the approximate confidence limits of the air compressor voting system.
It is assumed that the 2/3G voting system consisting of air compressors consists of three identical exponential life-type components that are independent of each other. The reliability of the components is R3, and the reliability of this 2/3G voting system is R=.
3 i=2 3 i R j 3<1-R3> 3-i. Let (zi, i) be the experimental data obtained for the i-th component, zi is the number of trials of the i-th unit product, i is the number of successes of the i-th unit product, and fi is the number of failures of the i-th unit product, and There is zi=i+fi. The commonly used fiducial method in engineering.
The approximate lower confidence limit of the voting system is obtained.
51, No. 3, Yang Ling et al.: Reliability analysis modeling of variable frequency constant pressure gas supply system.
E(Ri)=i i+1 zi, E(R 2 i)=i i+2 zi(6).
Therefore, the reliability approximation limit RL of the system reliability is solved.
n= E(R)-E(R 2)
E(R 2)-
Where IRL(s,F)= 1 B(s,F)
RL 0 R S-1(1-R)
F-1. dR is called incomplete #-function; n, s is called the success or failure test number of the system (n test times, s success number), and can be checked by GB4087.3 table using linear interpolation method to obtain reliability trust approximation limit.
3 Reliability evaluation method of variable frequency constant pressure gas supply system.
It can be seen from the reliability block diagram of the variable frequency constant pressure air supply system that the reliability of the 2/3G voting system, the gas storage tank, the control box and the filter composed of the filter, the motor and the air compressor in the system is a series relationship. . Since each unit product of the variable-frequency constant-pressure gas supply system is differently distributed and converted into a success or failure type product, the system can be regarded as a series of six success or failure products, and then the reliability limit of the reliability of the calculation system is calculated. .
A system in which k success or failure products are connected in series, the test data of the i-th unit product is ni, si, ni is the number of trials of the i-th unit product, si is the number of success of the i-th unit product, and fi is The number of failures of the i-th unit product, and ni=si+ fi. In order to determine the lower confidence limit of the system reliability at the confidence level, the Lindstrom-Madden method is popular in engineering.
-M method, ie.
N=min1%i%n ni F=N1-& ni=1 si ni.
F x=0 N x R Nx 1-R x =1-(8).
In the formula, N and F are the equivalent test number and failure number of the system respectively. Usually, F is a non-integer. You can check the GB4087.3 table to obtain the lower confidence limit by linear interpolation.
A more complex series system, the unit products that make up the system are often of different distribution types, such as success or failure products, Weibull products, exponential life products, and possibly normal life products. In order to adopt the LM method for system reliability evaluation, it is required that each unit product constituting the system must be success or failure test data. In this regard, Professor Zheng Zhongguo of Peking University solved the problem of converting non-successful test data into equivalent success or failure test data, and proved the existence and uniqueness of the solution of this transformation.
4 System reliability calculation and result analysis.
According to the relevant technical data and MATLAB software simulation and calculation, the reliability and reliability of each component in the variable frequency constant pressure gas supply system are given and the test results are converted into success or failure test data.
5 Conclusion.
In this paper, by analyzing the working principle of the variable frequency constant pressure gas supply system, the reliability of the variable frequency constant pressure gas supply system is modeled by the reliability theory, and the quantitative evaluation result of the system reliability is given by the LM method. Design has an important guiding role.
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