Compensation for Rotor Position Estimation Error due to Cross-Coupling Magnetic Saturation in Signal Injection Based Sensorless Control of PM Brushless AC Motors

This paper proposes a simple method for reducing the rotor position estimation error caused by cross-coupling magnetic saturation between the d- and q-axes when signal injection based sensorless control is applied to a brushless AC (BLAC) motor. The error in the estimated rotor position, which results when conventional signal injection sensorless control is employed, is analyzed. Based on an improved model of a BLAC motor which accounts for the influence of dq-axis cross-coupling on the high-frequency components of the incremental winding inductances, as deduced by either finite element analysis or from measurements, an improved signal injection based sensorless scheme is proposed. Its effectiveness is demonstrated by measurements on a BLAC motor having an interior permanent magnet rotor.