Fractional slot concentrated winding (FSCW) structure of induction motors contains abundant magnetomotive force harmonics in the air gap. Direct starting of the motor will result in huge inrush current and high torque ripple. Selecting an appropriate motor starting method ensures the necessary energy for starting the motor while minimizing costs and improving efficiency. This paper investigated two different starting methods for induction motors based on the FSCW structure: hard start and soft start. The full voltage method (hard start) was the simplest method but it might adversely affect motor lifespan. Alternatively, reduced voltage and frequency start (soft start) could reduce energy consumption during starting. First, the mathematical model of the induction motor was established based on winding theory. The starting torque and the impact of non-dominant pole-pair harmonic magnetic fields on torque ripple were analyzed under both hard and soft start conditions using electromagnetic torque theory. Then, the expression of the electromagnetic torque was derived using the virtual displacement method. Finally, the electromagnetic torque and torque ripple under the two starting methods were discussed based on the electromagnetic torque theory. In addition, the feasibility and stability of soft start were verified through theoretical calculation, finite element simulation and experimental validation.