Robust cascade H infinity control of BLDC motor systems using fixed-structure two degrees of freedom controllers designed via genetic algorithm

A robust control technique is proposed to regulate the current and angular velocity in typical brushless direct current (BLDC) motors. The proposed technique relies on two degree-of-freedom (2-DOF) H infinity control with loop shaping in which the structure of the two controllers and the loop shaping function are pre-specified parametrically (i.e., attain a fixed-structure). This consideration allows for striking a desirable balance between control effectiveness and controllers’ simplicity safeguarding feasibility of practical implementation. It further allows for using standard genetic algorithm (GA) for searching optimal controller parameters. Herein, two 2-DOF fixed-structure H infinity control structures are used in cascade to regulate BLDC motor response in time and in frequency domain subject to internal and external disturbances. Simulation results pertaining to a model of a particular commercial BLDC motor derived through standard system identification demonstrate the applicability and robustness of the proposed control technique to changes to internal BLDC resistance and external BLDC payload. It is shown that the proposed technique is more robust than optimal cascade 1-DOF PID control treated as a special case of the proposed technique.