Design and implementation of an observer-based state feedback controller for a pseudo direct drive

A pseudo direct drive (PDD) permanent magnet (PM) machine, realised by a mechanical and magnetic integration of a PM machine and a magnetic gear can achieve torque densities in excess of 60 kNm/m³. Since the torque in the PDD machine is transmitted to the load through a relatively low-stiff magnetic gear, undesirable speed/position oscillations become significant. This study addresses the pertinent issues associated with PDD operation and control. A full-state feedback (SFBK) control strategy has been employed and the feedback gains are optimally tuned by genetic algorithm against a defined performance index and under torque, current and voltage limits. To realise this control strategy at low cost, a reduced order observer has been designed and implemented to reconstruct the system states required for the SFBK control. It has been shown that the proposed control strategy and tuning method are effective in suppressing torsional oscillation, and for improving PDD servo operation and control performance. Experimental results have demonstrated the effectiveness of the proposed control technique.