Phase Inductance and Rotor Position Estimation for Sensorless Permanent Magnet Synchronous Machine Drives at Standstill

Sensorless control is a common control method used in variable speed drive applications with permanent magnet synchronous machines (PMSMs). In these drive systems, phase inductance (i.e., ${q}$ - and ${d}$ -axis inductance) is the key parameter in designing current controllers. Additionally, the rotor position is essential for coordinate transformation during the motor startup. This paper presents the two offline methods of 1) line-to-line voltage injection and 2) stator qd voltage injection of sensorless PMSM drives for the estimation of phase inductance and initial rotor position, respectively. A distinct feature of the proposed methods is that they estimate both inductance and rotor position using the same algorithm. These methods were experimentally verified using an interior PMSM (IPMSM) and a surface-mounted PMSM (SPMSM). Because of the use of a least-squares algorithm, only a limited number of voltage vectors are required to achieve reasonable accuracy for measuring inductance. However, the accuracy of the estimated position was linearly proportional with the number of voltage vectors injected. Furthermore, the position error for IPMSM was found to be smaller than that for SPMSM.