On the Mixed Loop-Shaping Tradeoffs in Fractional-Order Control of the AVR System

This paper looks at frequency domain design of a fractional-order (FO) proportional-integral differential (PID) controller for an automatic voltage regulator (AVR) system. Various performance criteria of the AVR system are formulated as system norms and are then coupled with an evolutionary multiobjective optimization (MOO) algorithm to yield Pareto optimal design tradeoffs. The performance measures consist of mixed H₂/H_∞ design objectives, such as the set-point tracking, load disturbance, and noise rejection controller effort, which are an exhaustive set of conflicting control objectives. A fuzzy logic-based mechanism is used to identify the best compromise solution on the Pareto fronts. The advantages and disadvantages of using an FOPID controller over the conventional PID controller, which are popular for industrial use, are enunciated from the presented simulations. The relevance and impact of FO controller design from the perspective of the dynamics of AVR control loop is also discussed.