This thesis proposes a six-step operation strategy of direct self control (DSC) method for an interior permanent magnet synchronous motor (IPMSM) based on torque angle. Conventional DSC method for induction motors (IMs) have been researched for railway applications because it has advantages about the control high-power traction drives and it is possible to guarantee the extension of the voltage limit through a six-step inverter operation. Conversely, IPMSM controlled via conventional DSC methods based on IMs is not able to be appropriately controlled through a six-step operation as torque angle control is not considered. Furthermore, the rotation of synchronous frame causes the phase error at high speeds owing to the low-frequency modulation index and the time delay of the digital controller. This thesis presents a stator flux estimation method that is based on the current model but also considers the torque angle and a heterodyning process, whereby the phase discordance is controlled to zero. The effectiveness of the proposed DSC method was verified through experimental results.
