This paper compares the non-modulated square-wave voltage injection-based and sinusoidal voltage injection-based polarity detection methods applicable in sensorless PMSM drives. A quadratic PMSM model extension is presented that serves as a basis for the polarity detection techniques. The comparison includes the polarity-dependent current components produced by the injected signals, the design parameters related to the injected signal features and their effect on the probability of correct polarity detection. The performance differences and possible application areas are also discussed.