滑模控制在火电机组脱硝控制中的应用研究

发布时间：2019-05-27 09:35

【摘要】：火电机组SCR脱硝系统的非线性、时滞和时变特性,给实际控制增加了难度。近来随着大气环境的恶化,对火电机组氮氧化物的排放标准愈加严格,对SCR脱硝系统控制性能的要求也更高,因此有必要寻求性能良好的控制算法。滑模控制自提出以来,由于极强的鲁棒性,在非线性、时变系统控制中效果良好,因而受到广泛关注,已成功应用于机器人、航空航天等领域。本文在完成大唐洛阳双源热电厂改造项目中脱硝系统改造的基础上,对脱硝系统的特性和现阶段脱硝系统控制中存在的问题进行了分析。随后,从理论与应用相结合的角度出发,针对滑模控制的性能和抖振等方面进行了理论研究及算法改进,并将研究成果应用于SCR脱硝系统。具体工作如下:针对脱硝系统的非线性、大时滞和时变等特性,根据Smith预估器补偿滞后的特性和滑模控制鲁棒性强的特点,将滑模控制器与Smith预估器结合起来应用于SCR脱硝系统。针对滑模控制器的抖振,将其看作噪声,采用低通滤波器进行滤波,得到平滑的控制信号,然而滑模控制的鲁棒性与切换增益相关,切换增益越大时鲁棒性越强,上述方法在外部扰动大于切换增益时,存在稳态误差,采用积分滑模面解决这一问题。针对积分滑模面在初始误差较大时造成系统超调大的问题,采用时变积分滑模面,使系统状态从初始时刻位于滑模面,然而仍无法减小超调,因此提出条件积分型滑模面改进积分滑模面,使积分作用仅发生在滑模面附近的边界层内,从而避免了初始误差的影响,保证了跟踪精度,获得了较好的暂态性能,针对实际系统不确定性上界未知的情况,采用自适应律自动调节切换增益,设计了基于Smith预估的自适应条件积分型滑模控制器,并通过仿真验证了该控制器的鲁棒性。
[Abstract]:The nonlinear, time-delay and time-varying characteristics of SCR denitrification system of thermal power unit make the actual control more difficult. Recently, with the deterioration of atmospheric environment, the emission standard of nitrogen oxides for thermal power units has become more stringent, and the control performance of SCR denitrification system is also higher, so it is necessary to find a control algorithm with good performance. Since the sliding mode control was proposed, because of its strong robustness and good effect in nonlinear and time-varying system control, sliding mode control has been widely concerned and has been successfully used in robots, aerospace and other fields. Based on the retrofit of denitrification system in Datang Luoyang Shuangyuan Thermal Power Plant, the characteristics of denitrification system and the problems existing in the control of denitrification system at present are analyzed in this paper. Then, from the point of view of the combination of theory and application, the performance and buffeting of sliding mode control are studied theoretically and the algorithm is improved, and the research results are applied to SCR denitrification system. The concrete work is as follows: according to the nonlinear, large time delay and time varying characteristics of denitrification system, according to the characteristics of compensation lag of Smith predictor and strong robustness of sliding mode control, The sliding mode controller and Smith predictor are combined to apply to SCR denitrification system. Aiming at the buffeting of sliding mode controller, it is regarded as noise, and a smooth control signal is obtained by using low pass filter to obtain smooth control signal. however, the robustness of sliding mode control is related to switching gain, and the larger the switching gain is, the stronger the robustness is. When the external disturbance is larger than the switching gain, there is a steady-state error in the above method, and the integral sliding mode surface is used to solve this problem. In order to solve the problem that the system overshoot is caused by the initial error of the integral sliding mode surface, the time-varying integral sliding mode surface is adopted so that the state of the system is located on the sliding mode surface from the initial time, but it is still impossible to reduce the overshoot. Therefore, the conditional integral sliding mode surface is proposed to improve the integral sliding mode surface, so that the integral action only occurs in the boundary layer near the sliding mode surface, thus avoiding the influence of the initial error, ensuring the tracking accuracy and obtaining better transient performance. In order to solve the problem that the upper bound of the uncertainty of the actual system is unknown, the adaptive conditional integral sliding mode controller based on Smith prediction is designed by using the adaptive law to automatically adjust the switching gain, and the robustness of the controller is verified by simulation.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP273;TM621

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