Virtual line-shafting control for permanent magnet synchronous motor systems using sliding-mode observer

This study presents a novel observer-based electronic line-shafting control strategy for permanent magnet synchronous motor systems. Adopting the sliding-mode variable structure technology, the proportional–integral speed controller for every servo unit is designed, followed by design of two cascades connected observers, in order to improve the system synchronisation performance when a large load disturbance occurs. The load torque observer transmits the observed load torque value instead of the calculated one back to the virtual shafting, which reflects the dynamic relationships of all the virtual or slave shafts more accurately. Another load torque derivative observer feeds the observed value forward to the corresponding sliding-mode controller for reducing the switching gain. The proposed control system is proved stable by Lyapunov stability theory, and simulation results show the strategy is effective on reducing sliding-mode chattering and achieving higher synchronisation precision.