Stabilizing unstable operating points is an effectiveway to enhance process benefits and safety

which motivates the development for a variety of advanced control strategies. The washout filter-aided controller (WFC)

originally used for electric power system and aircraft

has been introduced to adjust the dynamic behavior of chemical process. However

the parameter tuning method faces two major limitations:the dimension of operating variables must be equal to or greater than that of state variables and only one positive real eigenvalue exists in the open loop system. To overcome the two limitations

this paper proposes a new parameter tuning method

so that theWFC is applicable in most chemical processes. By solving a constrained optimization problem

the controller parameters are determined under the constraint that the reassignment of the eigenvalues of the unstable desired operating point can satisfy the stability condition. Thus parts of the equilibrium manifold including the desired operating point are stabilized without affecting the shape of the equilibrium manifold. Finally

the effectiveness of the WFC improved by the proposed parameter tuning method is illustrated through a case study for propanediol anaerobic fermentation.