精馏塔多通道对角矩阵解耦控制仿真

在化工生产中,许多单元操作的控制涉及至少2个被控变量,因此产生至少2个以上的控制回路。在该类具有多个控制回路的多变量控制系统中,同一被控对象上的多个控制回路,在实现其各自的控制目标时,将发生相互作用和相互影响。精馏塔是化工等行业中广泛使用的高耗能分离设备,为满足工艺要求和节能,需将塔顶和塔底产品流控制在设计值,即双成分控制。通常,利用回流量和加热量作操纵变量分别控制塔顶和塔底产品的组成。不过,回流量的变化也会影响塔底产品的组成,加热量的改变也会影响塔顶产品的组成。当采用温度作为反映产品组成的间接指标时,塔顶和塔底温度控制回路具有强烈的耦合作用,会导致系统不稳定。一个简单有效的方法就是解出耦合,因此,本文先介绍了一种基于对角矩阵的温度解耦控制方案,并在MATLAB/Simulink平台进行了控制仿真。结果显示:与两个独立PID回路控制相比,对角矩阵解耦控制不仅能达到更优的控制效果,还具有极强的对象特性鲁棒性。

Simulation of multi-channel control of a distillation column based on diagonal matrix decoupling

In the chemical processes,many unit operations capable of manufacturing or refining a production typically require to control at least two variables.There are,therefore,usually at least two control loops to contend with.Systems with more than one control loop are known as multi-input multi-output(MIMO) or multivariable systems,in which different loops may interact in trying to achieve their respective objectives.Distillation columns,which are widely used for separation and refining operations,require a phenomenal amount of energy for their operation.Minimization of energy usage is possible if the compositions of both the top and the bottom product streams are controlled to their design values,i.e.,dual composition control.A common scheme is to use reflux flow to control top product composition while heat input is used to control bottom product composition.However,changes in reflux also affects bottom product composition and component fractions in the top product streams are also affected by changes in heat input.When the temperature is used as the indirectly controlled variable,the temperature control loops of the column top and the column bottom have strong coupling and therefore cause system instability.A simple approach to dealing with coupling between loops,i.e.,diagonal matrix decoupling,is first introduced.Its objective is to eliminate completely the effects of loop interactions by the specification of compensation networks known as decouplers.Then,such a scheme is simulated in Matlab/simulink.This results reveal that compared with the double single-loop PID control,the diagonal matrix decoupling control can not only achieve better control performance,but also has strong robustness of the controlled object.