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Fuzzy decoupling control of mixed gas pressure and calorific value

1 introduction

at present, most soaking pits in the rolling system of Baotou Iron and steel company use the method of burning mixed gas to heat billets. The so-called mixed gas is to mix blast furnace gas (relatively low calorific value, also known as lean gas) and coke oven gas (relatively high calorific value, also known as rich gas) in a certain proportion, and use the computer system to realize automatic control, so as to stabilize the calorific value and pressure of the mixed gas of each steel rolling user, ensure the temperature of the heating furnace, so that the billet can be evenly heated to ensure the quality of steel rolling. However, in actual production (taking 2 gas mixing station as an example), the automatic control system of mixed gas has not really achieved the expected control goal. The site is still dominated by simple conventional instrument PID control system or manual operation, so the pressure and calorific value of mixed gas fluctuate greatly, resulting in large energy consumption and environmental pollution. This paper will propose a new fuzzy intelligent decoupling control to solve this problem

2 production process of blast furnace and coke oven mixed gas

the 2 ＃ mixing station of Baotou Steel metering Department mixes blast furnace gas and coke oven gas and sends them to blooming mill, rail beam mill, wire rod mill and other users after being pressurized by the presser. The production process of direct mixing of blast furnace and coke oven gas is shown in Figure 1. It can be seen from Figure 1 that the input is the pressure and flow of blast furnace gas and coke oven gas, and the output is the pressure and calorific value of mixed gas. In addition, due to the parabolic relationship between the opening of the gas butterfly valve and the gas pressure and flow, if one of the input blast furnace gas or coke oven gas changes, it will not only affect the pressure of the mixed gas, but also affect its calorific value. Therefore, the process of mixing gas can be regarded as a multivariable system with nonlinear strong coupling, multi input and double output

3 fuzzy controller design

3.1 controller design principle

for the process of mixed gas, on the one hand, its time response delay is large, on the other hand, its mathematical model changes with the working condition of the gas object, so it is difficult to establish an accurate mathematical model, so it is more appropriate to adopt fuzzy control. Based on the above discussion of the fuzzy controller theory, combined with the specific production process of mixed gas, the overall structure of the controller can be established, as shown in Figure 2: 3.2 fuzzy control principle

set E as the deviation, EC as the deviation change rate, and u as the control function. If Pb, PM, PS, PZ, NZ, NS, nm, Nb are used to indicate that the E value is positive, median, positive small, positive zero, negative zero, negative small, negative medium and negative large respectively; Use PB, PM, PS, Z, NS, nm, Nb to indicate that EC and U values are positive, median, positive small, zero, negative small, negative medium, negative large. The fuzzy control rules can be summarized from the control experience, as shown in Table 1. The above control rules can be described by 21 fuzzy statements:

however, the input and output of the actual system are continuous and accurate quantities, so first of all, e, EC and u should be fuzzed into a certain fuzzy quantity. Define its fuzzy subset, give its universe, and determine the correspondence theory B0 of each fuzzy variable - the outer dimension of carton width (CM); Then, the off-line fuzzy reasoning synthesis algorithm is used to calculate the corresponding fuzzy control. Here, the fuzzy subsets of E, EC and u are defined as:

{e} = {NB is very low, nm is low, NS is low, NZ is slightly low, PZ is slightly high, PS is high, PM is high, Pb is very high}

{EC} = {NB decreases very quickly}

{we work partner recruitment is hot, NM decreases rapidly, s decreases slightly, Z is moderate, PS rises slightly, PM rises rapidly, Pb rises very quickly}

{u} = NB quickly opens the valve, and nm medium speed open valve, NS micro open the valve, Z maintain, PS micro in 2020, the utilization ratio of degradable green packaging materials will reach 50%, close the valve, PM medium speed close the valve, Pb fast close the valve 、

membership function adopts triangle function. This system adopts Mamdani reasoning method, which is widely used in fuzzy control system. The total reasoning output of the system can only be obtained after accurate calculation. In fact, it is still a synthetic reasoning method

4 decoupling control scheme

the mixed gas system is a multi input and dual output system. The control quantity has a direct or indirect impact on the output pressure and calorific value, that is, there is a strong coupling between them, which seriously affects the stability of the mixed gas pressure and calorific value. In order to reduce the fluctuation of the mixed coal pressure and calorific value, the decoupling link must be introduced. Because the mathematical model of the control system is difficult to establish, a simple decoupling method is adopted here, that is, the azimuth coupling link in the document according to the query word is introduced between the pressure and flow control λ 12， λ 21. Make the pressure and flow control respectively:

then when λ 12， λ When 21 is 0, ut = CT, up = CP, there is no decoupling between pressure and flow control; And when λ 12， λ When 21 is 1, ut = CP, up = CT, which corresponds to the limit coupling. λ 12， λ The actual value of 21 is between 0 and 1, which needs to be determined by test, and then written into the computer. When controlling λ 12， λ 21 press

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