利用NO_x传感器的NH_3交叉敏感实现SCR系统闭环控制

Feedback Control of SCR System by Cross-Sensitivity of NO_x Sensor to NH_3

介绍了目前常用的氮氧化物(NOx)传感器的测量原理和特性,并以NOx传感器对氨(NH3)交叉敏感这一特性为出发点,设计了基于NOx传感器的氨泄漏量闭环控制器(FBC).比较了4种常见的前馈控制策略,然后针对闭环控制需求对传感器信号进行相应的数值处理,使得信号具有更佳的线性特征,从而能够对排气中的NH3进行有效区分.建立了选择性催化还原(SCR)系统喷射量的闭环控制模型,通过奈奎斯特稳定性判据和试验确定了最终的控制参数,实现了闭环控制的稳定.SCR系统响应性能试验的结果表明:闭环控制策略能够在120,s内完成对干扰的调整.排放测试表明:该闭环控制方法在大多数试验条件下可行,应用此策略的SCR系统在ESC和ETC测试循环下的NOx平均转化效率分别能够达到82.4%和77.3%,NH3平均泄漏量在10×10-6以下.

The measuring principle and characteristics of nitrogen oxide(NOx)sensor are introduced and a feedback controller(FBC)based on the cross-sensitivity of NOx sensor to ammonia(NH3)was developed. Four feed forward control strategies are compared first,then the sensor output signal is changed by using mathematical manipulation because FBC needs a linear signal,which makes the NOx sensor more effective at NH3 measurement. A feedback control model was established and its control parameters were quantified on the basis of experimental and Nyquist stability criterion. Response test results show that FBC can compensate disturbance and adjust operation within 120,s. Emission tests showed that the closed loop control method is feasible under most of the test conditions,NOx conversion efficiency of selective catalytic reduction(SCR)system is 82.4% and 80.3% in ESC and ETC test while the leakage of NH3 is under 10×10-6 on average.