Cascade Fuzzy Control System for Boiler Superheated Steam Temperature

Abstract: The information of cascade fuzzy control system for boiler superheated steam temperature is provided by excellent flowmeter and flowmeter manufacturers. 1 Introduction The temperature of superheated steam is one of the important indicators of boiler operation quality. If the temperature of superheated steam is too high, it may cause damage to the high pressure parts of superheaters, steam pipes and steam turbines; steam turbine. For more flowmeter manufacturers to select models and price quotations, you are welcome to inquire. The following is the article details of cascade fuzzy control system for boiler superheated steam temperature. 1 Introduction The temperature of superheated steam is one of the important indicators of boiler operation quality. If the temperature of superheated steam is too high, it may cause damage to the high pressure parts of superheaters, steam pipes and steam turbines; The increase of the axial thrust of the steam turbine causes the overload of the thrust bearing, and also causes the steam humidity of the final stage of the steam turbine to increase, thereby reducing the internal efficiency of the steam turbine and aggravating the erosion of the blades. Therefore, during the operation of the boiler, the superheated steam temperature must be kept stable near the specified value. In general power plants, the inlet steam temperature of the high temperature superheater is changed by changing the flow rate of desuperheating water, thereby affecting the outlet steam temperature of the superheater. Since the superheater lines of large boilers are very long, it is an object of pure lag with large inertia. At present, most of the power plants use the differential of the leading steam temperature as a supplementary signal system for boiler superheated steam temperature regulation. Its system schematic diagram is shown in Figure 1. In view of the characteristics of large inertial delay and slow feedback of the adjusted amount of the adjustment channel of the superheated steam temperature adjustment object, find an intermediate signal from the object adjustment channel that responds faster than the adjusted amountθ1 as a complementary signal to the regulator to improve the dynamics of the subject's modulation channel. Dynamic time regulator according toθThe differential sum of 1θ2 These two signals act. but at static (after the end of the conditioning process)θ1 no longer changes, then dθ/dt=O, at this time the superheater steam temperatureθ2 must be restored to the given value. In actual use, the intermediate signalθThe introduction of 1 does improve the dynamic characteristics of the control system to a certain extent. However, due to the mutual influence of various production equipment during the operation of the system, random disturbances cause the superheated steam temperature.θ2 fluctuations. For units with a single unit capacity of 300,000, the rated superheated steam temperature is 540°C±5 ℃, under frequent load changes and other unstable conditions, especially when the load has a large change range, the fluctuation of the superheated steam temperature even exceeds the allowable range of change, affecting the safe production of the power plant. At the same time, these fluctuations are unpredictable and cannot be described by precise mathematical models. Considering that the fuzzy control does not require an accurate mathematical model of the object, it has good robustness and is especially suitable for large delay, time-varying, and nonlinear situations. According to the actual situation, we propose a cascade fuzzy control system for boiler superheated steam temperature. 2. Design of control scheme Cascade regulation system is one of the effective methods to improve regulation quality of large inertia and pure lag system. Its control system is shown in Figure 2. F in Figure 2 is the desuperheating water flow control valve. In order to ensure the rapidity of the auxiliary loop and the intermediate variable does not require no difference, the auxiliary regulator adopts proportional regulation; the main loop adopts a hybrid fuzzy controller. In addition to eliminating the disturbance outside the secondary ring as soon as possible, it can also correct the steam temperature deviation to ensure the accuracy of the steam temperature control. 3 Fuzzy Control Algorithms In this control scheme, the main regulator adopts a hybrid fuzzy controller, that is, a conventional proportional-integral control and a two-dimensional fuzzy controller are connected in parallel. The basic block diagram of the 2D fuzzy controller is shown in Figure 3. The subsets of controller fuzzy variables are defined as: E={NB, NM, NS, ZO, PS, PM, PB} DE={NB, NM, NS, ZO, PS, PM, PB} U={NB, The corresponding universe of NM, NS, ZO, PS, PM, PB} quantization processing is as follows: E={-3,-2,-1,0,1,2,3}DE={-3,-2,-1 , 0, 1, 2, 3} U={-3, -2, -1, 0, 1, 2, 3} The membership functions of the fuzzy sets of input quantities E, DE and output U are triangles. The fuzzy decision-making of the controller adopts the Mamdani-type inference algorithm, and the inverse fuzzy adopts the Centroid method to obtain the precise control output u1. Conventional n-regulator algorithm: the output of the hybrid fuzzy controller is u=u1+u2. Combining the fuzzy control with the conventional PI regulator in this way makes the control system not only have the advantages of flexible fuzzy control, fast response and strong adaptability, but also has the characteristics of high PI control accuracy. 4. Simulation analysis The mathematical models of the controlled process of the main and secondary loops are respectively: using MATLAB simulation software to simulate and compare the two systems. Key people under MATLABCommandWindow“simulink”, enter the SIMULINK visual dynamic system simulation environment. The SIMULINK component library is used to build the simulation block diagram of superheated steam temperature control with leading differential signal and the simulation block diagram of superheated steam temperature cascade fuzzy control. In the former system, Kp is set to 2, Ti is set to 10, while in the cascade fuzzy control system, the secondary loop Kp is set to 3.5, and the quantization factors Ke, Kec, and Ku of the fuzzy control in the main loop are 2.2, respectively. 0.6 and 1. In its PI control, Kp=0.2, Ti=10. The simulation results show that the superheated steam temperature cascade fuzzy control system has better control effect than the steam temperature control system with leading differential signal. It can be seen from the response curve that the former has no overshoot, fast response, small static error and high corresponding precision. When the parameters or structure of the object of the cascaded fuzzy control system change, it can maintain the rapidity of response and the excellent performance of no static error and no overshoot, and has strong robustness and adaptability. The control strategy proposed in this paper provides a unique control scheme for superheated steam temperature control in power plants. The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Cascade Fuzzy Control System for Boiler Superheated Steam Temperature'

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