Six-step operation has many advantages in permanent-magnet synchronous machine (PMSM) drives such as maximum power utilization and widened flux-weakening region. However, due to the maximum utilization of inverter output, saturation of current regulator makes it difficult to maintain instantaneous current control capability. Accordingly, in most of conventional research studies, the six-step operation has been implemented by voltage angle control without current regulation, whose dynamic performance is quite unsatisfactory. This paper proposes a control scheme for the six-step operation of PMSM with enhanced dynamic performance of current control. By collaborative operation of dynamic overmodulation, flux weakening, and a technique for enhanced dynamic performance, the six-step operation is realized without losing instantaneous current control capability. Simulations and experiments are carried out to verify the effectiveness of the proposed control scheme. The experimental results show 17% extension of the constant torque region and 27% enhancement of torque capability at three times of the base speed. Index Terms-Current control, flux weakening, motor drives, overmodulation, permanent-magnet synchronous machines (PMSMs), six-step operation. NOMENCLATURESuperscript s Stationary reference frame. Superscript r Synchronously rotating rotor reference frame. Superscript * Reference value. P Number of poles. ω r Electrical rotor speed. V * s Magnitude of voltage reference. V s1 Fundamental component of inverter output voltage. v r ds , v r qs d−q components of inverter output in rotor reference frame. i r ds , i r qs d−q components of phase current in rotor reference frame. R s Stator resistance. L ds , L qs d−q components of stator self-inductance.

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