On the Mixed H2/H∞ Loop-Shaping Tradeoffs in Fractional-Order Control of the AVR System

—This paper looks at frequency domain design of a fractional order (FO) PID controller for an Automatic Voltage Regulator (AVR) system. Various performance criteria of the AVR system are formulated as system norms and is then coupled with an evolutionary multi-objective optimization (MOO) algorithm to yield Pareto optimal design trade-offs. The conflicting performance measures consist of the mixed H2/H∞ designs for objectives like set-point tracking, load disturbance and noise rejection, controller effort and as such are an exhaustive study of various conflicting design objectives. A fuzzy logic based mechanism is used to identify the best compromise solution on the Pareto fronts. The advantages and disadvantages of using a 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.