Optimized Current and Speed Fractional-Order PID Control in Electrical Drives

Fractional-order PID controllers are suitably designed for cascade control of permanent magnet synchronous motor drives. The stator current and the speed are controlled in two nested loops. Six parameters characterizing the two controllers (the proportional, integral, and derivative gains, the non-integer orders of integration and differentiation, and a filter time constant) are determined by optimizing different cost criteria for the two loops. To this aim, a particle swarm optimization is applied in a single step, instead of performing two successive steps, the first for the inner loop, the second for the external loop. Simulation by an accurate model confirms effectiveness of the approach and shows improvements with respect to PID optimized controllers.