An Initial Position Estimation Method for Dual Three-Phase IPMSM in Standstill/Free-Running States

Dual three-phase interior permanent magnet synchronous motors (DT-IPMSMs) are widely used in high-power and high-reliability applications, and accurate rotor polarity identification at startup is a critical prerequisite for their stable and efficient operation. This study aims to address the problem of initial position acquisition during the startup of DT-IPMSMs by proposing a simple and fast rotor polarity identification method. The proposed method is based on the high-frequency square-wave voltage injection (HFSWVI) in the vector space decomposition (VSD) space, where both the current and voltage are injected into the d-axis. The single-pulse direct current (DC) injection is used to alter the magnetic saturation. Then, the change rates of the d-axis high-frequency response current are compared before and after DC injection to identify the rotor magnetic polarity. In addition, a moving average filter (MAF) is applied to suppress the fluctuations in the current change rate, which increases the accuracy of polarity identification. Moreover, a simple compensation technique is designed to make the estimated d-axis current change smoothly when the estimated angle changes from N-pole to S-pole. The effectiveness of the proposed method is proved by the experimental results in both standstill and free-running states for the prototyped DT-IPMSMs. This method provides a practical and efficient solution for initial position identification of DT-IPMSMs, contributing to the advancement of control technology for dual three-phase motor systems in related fields.