Incremental multivariable predictive functional control and its application in a gas fractionation unit

The control of gas fractionation unit(GFU) in petroleum industry is very difficult due to multivariable characteristics and a large time delay.PID controllers are still applied in most industry processes.However,the traditional PID control has been proven not sufficient and capable for this particular petro-chemical process.In this work,an incremental multivariable predictive functional control(IMPFC) algorithm was proposed with less online computation,great precision and fast response.An incremental transfer function matrix model was set up through the step-response data,and predictive outputs were deduced with the theory of single-value optimization.The results show that the method can optimize the incremental control variable and reject the constraint of the incremental control variable with the positional predictive functional control algorithm,and thereby making the control variable smoother.The predictive output error and future set-point were approximated by a polynomial,which can overcome the problem under the model mismatch and make the predictive outputs track the reference trajectory.Then,the design of incremental multivariable predictive functional control was studied.Simulation and application results show that the proposed control strategy is effective and feasible to improve control performance and robustness of process.

增量式多变量预测函数控制及其在气体分馏装置中的应用

针对传统的比例-积分-微分(PID)控制应用于多变量、大滞后的复杂过程时无法获得满意控制效果的问题,该文提出一种增量式多变量预测函数控制(IMPFC)算法。该算法利用过程阶跃响应数据建立增量式传递函数矩阵模型,采用单点线性化方法直接递推出过程预测输出,并对控制增量进行优化求解,解决了位置式预测函数控制算法对控制量约束的不足,使控制量变化更加平缓。通过对预测输出误差和未来的设定值进行多项式拟合,克服了模型失配问题,使预测输出更接近于参考轨迹。在气体分馏装置中的应用表明,该文方法具有良好的跟踪性、鲁棒性和抑制干扰的能力,其控制品质优于传统PID控制。