This article discusses a proportional-integral-derivative controller circuit for an unstable system with a delay in a parallel control structure. The parallel control structure has two separate controllers for tracking tasks and suppressing load disturbances. The considered controller is developed on the basis of a direct synthesis approach by choosing a separate reference model with feedback. The proposed design method is applicable to both the lower and the high-level unstable process without model reduction in the higher order process. The effectiveness of the proposed method is demonstrated through example modeling and comparison with methods published in the literature.

Keywords: proportional-integral-derivative regulator circuit, direct synthesis, reference model, design method