Pulsating signal injection-based sensorless initial rotor position detection of PMSM using three symmetrical injection axes

This paper investigates the performance limits of pulsating carrier signal injection method in detecting the initial rotor position of permanent magnet synchronous motors (PMSMs). To eliminate the influence of motor parameter variations and signal delays, a novel signal extraction algorithm by simultaneously demodulating the two orthogonal response currents in the estimated rotor frame is proposed. On this basis, an improved method using three symmetrical injection axes (0°, 120° and 240°) is presented to determine the rotor shaft position, which not only accelerates the detection procedure but also minimizes the dead zone effects without any compensation strategies. Besides, to identify the magnetic polarity, the magnetic saturation effects on the saliency is considered. Finally, the effectiveness of the improved approach is verified by experiments when the motor is at standstill.