基于模型的SCR控制策略和故障诊断策略研究

发布时间：2018-02-10 20:22

本文关键词： 柴油机SCR后处理系统非线性模型自适应滑模观测器反步法基于模型的OBD策略　出处：《西南交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：近年来随着人们生活质量的日益提高以及城市的快速发展,机动车的尾气排放问题日益严重。本文以柴油机选择性催化还原(Selective Catalytic Reduction,SCR)后处理系统为研究对象,对SCR催化器化学反应机理进行了系统的研究并建立了 SCR催化器模型,设计了基于模型的SCR控制策略和车载故障诊断(On-Board Diagnostics,OBD)策略,并分别在发动机欧洲稳态循环(European Steady Cycle,ESC)和欧洲瞬态循环(European Transient Cycle,ETC)工况下进行了验证,主要内容如下:(1).SCR催化器非线性建模。首先对SCR催化器的化学反应机理进行了系统的研究,为了便于建模,沿着气流轴线方向将SCR催化器分为数个理想的SCR单元,基于连续搅拌釜式反应器(Continuous Stirred Tank Reactor,CSTR)方法,结合 Arrhenius定理和质量守恒定律,建立了 SCR催化器的化学反应动力学模型、温度模型和床温模型等,并对SCR催化器的化学反应动力学模型的敏感性、稳定性和可观性进行了分析。随后,分别在发动机ESC和ETC工况下对模型进行了验证。(2).SCR催化器的状态观测器设计。首先对自适应滑模观测器进行了简单介绍,然后,设计了基于自适应滑模观测器的SCR催化器状态观测器,并利用Lyapunov稳定性理论对观测器的稳定性和鲁棒性进行了证明,最后,观测器的可靠性在发动机ESC和ETC工况下得到了验证。(3).基于模型的SCR闭环控制策略开发。提出了基于模型的SCR尿素喷射闭环控制策略,采用"前馈控制器+SCR储氨状态控制"的闭环反馈控制结构,其中前馈控制采用MAP图标定和模型计算相结合的控制器结构,根据尿素溶液的理论需求量进行前馈控制;根据SCR催化器沿着气流轴线方向的储氨状态分布规律,以及催化器模型的结构特点,利用反步法设计了 SCR储氨状态控制器,对SCR催化器沿着气流轴线方向的储氨状态分布进行控制,因而,SCR储氨状态控制实现减少氮氧化物(Nitrogen Oxide,NOx)排放的同时避免氨泄漏造成的二次污染。在发动机ESC和ETC工况下的实验验证结果表明,所提出的基于模型的SCR闭环控制策略可以有效降低NOx排放同时减少氨泄漏量。(4).基于模型的OBD策略开发。首先重点分析了 SCR系统几种常见的故障类型,接着对其中几种典型的故障类型设计了基于模型的OBD故障诊断策略,并对发生SCR催化器下游温度传感器和NOx传感器故障、催化器老化以及尿素喷嘴堵塞这四个最具代表性的故障模式时,基于模型的OBD策略和闭环控制策略的工作性能进行了重点验证,验证表明所提出的基于模型的SCR控制策略和OBD策略是有效的。
[Abstract]:In recent years, with the increasing improvement of people's quality of life and the rapid development of cities, the problem of vehicle exhaust emission is becoming more and more serious. In this paper, the selective Catalytic reduction (SCR) aftertreatment system of diesel engine is taken as the research object. The chemical reaction mechanism of SCR catalytic converters is systematically studied, and the model of SCR catalytic converters is established. The SCR control strategy based on the model and the on-board diagnostics strategy of on-board fault diagnosis are designed. The nonlinear modeling of the catalytic converters is as follows: 1. The chemical reaction mechanism of the SCR catalytic converters is studied systematically at first, which is verified under the conditions of the engine steady state cycle Steady cycle SCR and the European transient cycle European Transient cycle converter respectively, the main contents of which are as follows: 1 / 1 / 1.SCR catalytic converters are modeled as follows: (1) the chemical reaction mechanism of the SCR catalytic converters is studied systematically. In order to facilitate modeling, SCR catalytic converters are divided into several ideal SCR units along the direction of air flow axis. Based on continuous Stirred Tank reactor method, Arrhenius theorem and mass conservation law are combined. The chemical reaction kinetics model, temperature model and bed temperature model of SCR catalyst were established. The sensitivity, stability and observability of the chemical reaction kinetics model of SCR catalyst were analyzed. The design of the state observer of the model is verified under the conditions of engine ESC and ETC respectively. Firstly, the adaptive sliding mode observer is introduced briefly, and then the adaptive sliding mode observer is introduced. The SCR catalytic converter state observer based on adaptive sliding mode observer is designed, and the stability and robustness of the observer are proved by Lyapunov stability theory. The reliability of the observer is verified under the conditions of engine ESC and ETC. The model-based SCR closed-loop control strategy is developed. A model-based SCR urea injection closed-loop control strategy is proposed. The closed-loop feedback control structure of "feedforward controller SCR ammonia storage state control" is adopted, in which the feedforward control adopts the controller structure which combines MAP icon determination and model calculation, and carries out feedforward control according to the theoretical demand of urea solution. According to the state distribution of ammonia storage in SCR catalytic converters along the direction of air flow axis and the structural characteristics of catalytic converters model, a SCR state controller for ammonia storage is designed by using the backstepping method. The distribution of ammonia storage state of SCR catalytic converter along the axis of air flow is controlled. Therefore, SCR state control for ammonia storage can reduce nitrogen oxide nitrogen oxide no _ x emissions while avoiding secondary pollution caused by ammonia leakage. The experimental results under ESC and ETC conditions show that, The proposed model-based SCR closed-loop control strategy can effectively reduce NOx emissions and reduce ammonia leakage. The model-based OBD strategy is developed. Firstly, several common fault types in SCR system are analyzed. Then, a model-based OBD fault diagnosis strategy is designed for several typical fault types, and the downstream temperature sensor and NOx sensor fault of SCR catalyst are analyzed. The performance of the model-based OBD strategy and the closed-loop control strategy are mainly verified when the catalytic converter is aging and the urea nozzle clogging is the most typical fault mode. The results show that the proposed model based SCR control strategy and OBD strategy are effective.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U464.172;X734.2

【相似文献】