H_∞ model matching two-degree-of-freedom control with adaptive torque ripple cancellation for high performance direct drive systems

This study presents a novel adaptive robust control scheme to achieve a fast and accurate tracking performance in direct-drive (DD) systems under parameter and load uncertainties. The control combines an outer loop based on H_∞ model matching (MM) in a two-degree-of-freedom (2-DOF) control structure, with an adaptive cancellation loop to increase torque ripple suppression further for improved tracking performance. A modified H _∞ MM 2-DOF approach is taken by designing both the feedback loop and reference controller to achieve an improved tracking performance in the sense of H_∞ MM criterion with integral action, while the robustness of the system is naturally satisfied by the 2-DOF control structure. Experimental results taken on a permanent magnet synchronous motor (PMSM) driven directdrive system demonstrate a good tracking performance under a variety of reference trajectories. The results also demonstrate the robustness of the method against payload uncertainties and torque pulsations, except for the cogging torque components around the corner frequency. To improve attenuation of cogging torque terms further, the H_∞ based outer loop is combined with an adaptive cancellation scheme derived based on the Lyapunov criteria. The developed adaptive robust control scheme demonstrates an improved robustness and tracking performance over a large frequency range.