Abstract: A technique to improve iron utilization and power density in the five-phase induction motor with concentrated full-pitch windings structure is presented in this paper, which is realized through third harmonic current injection to optimize air-gap flux density distribution and stator current waveform. Sliding Mode Observer with stator resistance identification is adopted to achieve sensorless vector control for high transient response performance, by using the rotor flux estimation for direct rotor flux orientation in the wide speed range. The proposed method with third harmonic current injection is achieved to reshape the flat-topped waveforms for air-gap flux distribution and stator current, while conventional method focuses on the flux density optimization, neglecting the stator current distortion. A five-phase induction motor drive with low DC link is constructed, and experimental results verify the feasibility of the sensorless vector control strategy with improved harmonic injection