Mode Transition of Synchronous Optimal Modulation for High-Speed PMSM Drives

Mode transition of synchronous optimal modulation (SOM) associated with changes in pulse number or pulse pattern can cause large transient overshoots of current in high-speed permanent magnet synchronous machine drives. In this article, an in-depth and detailed analysis of the mode transition of SOM for the classic two-level inverter fed high-speed PMSM drives is presented, from the perspectives of transient current errors, optimal switching vector patterns and optimal flux trajectories. Based on the gained insights and general properties of SOM, a novel smooth and fast SOM mode transition scheme is proposed. The proposed method can start the mode transition at any position of a voltage space vector and complete the transition within 1/6 fundamental cycle, between any two SOM modes, i.e., different pulse numbers and continuous sets of optimal switching angle. Moreover, the proposed transition is very simple and almost adds no cost to the drive system. Extensive simulations and experiments have been performed to validate the effectiveness of the proposed mode transition scheme in all the representative conditions.