This paper proposes a new sensorless control strategy based on a Sliding Mode Observer (SMO) for a non-sinusoidal seven phase PMSMs. This strategy, based on all harmonics contained in the back-EMF, is compared to the classical sensorless control strategy using only the fundamental of back-EMF signal. As the novel sensorless control strategy estimate the rotor position by using different harmonics, it can lead to a good torque response compared to the classical strategy, specially in transient states. Therefore, in order to define the appropriate sensorless control strategy for the non-sinusoidal seven-phase PMSM, each sensorless control strategy will be highlighted in terms of robustness to the speed variation and torque ripple. Simulation results will be shown to verify the feasibility of the proposed methods.