Smooth and Fast Mode Transition of Synchronous Optimal Modulation for Two-Level Inverter Fed High-Speed PMSM Drives

Synchronous optimal modulation (SOM) can minimize current distortions for high-speed permanent magnet synchronous machine (PMSM) drives when the ratio of switching frequency to fundamental frequency (SFR), also known as pulse number is limited. However, the mode transition associated with changes in pulse number or pulse pattern can cause large transient overshoots of current. To solve this problem, this paper presents a novel smooth and fast transition scheme. The proposed method is based on the analysis of optimal switching vector patterns (OSVPs) and optimal flux trajectories (OFTs) of SOM and the two general properties identified in the analysis. It can start the mode transition at any position of a voltage space vector and complete the transition within 1/6 fundamental cycle. The smooth and fast mode transition can be achieved 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 add no cost to the drive system. Extensive simulation and experiments on a high-speed prototype machine have been performed and the proposed method validated.