Multiphase (more than three phases) drives possess several advantages over conventional three-phase drives, such as reducing the amplitude and increasing the frequency of torque pulsations, reducing the rotor harmonic currents, reducing the current per phase without increasing the voltage per phase, lowering the dc-link current harmonics, and higher reliability. By increasing the number of phases it is also possible to increase the power /torque per ampere for the same volume machine. Another important feature of multi-phase drives is ensuring optimal and acceptable performance in unbalanced supply conditions due to interruption of one or even two phases, which has increased the acceptance of this type of drive in various industries. In this paper, speed control without mechanical sensor of six-phase induction machines in single-phase interruption conditions is presented using the second-order sliding mode control method. In this control method, the reference model theory is used to estimate the machine speed in order to improve the drive performance. The simulation results show that the method has an acceptable performance under unbalanced machine supply conditions and speed control will be performed well.