This paper presents a sensorless and stable control method for a five-phase permanent magnet synchronous motor (PMSM). At first, a model of a five-phase PMSM is presented. After that a stability study has been performed by the analysis of the eigenvalues of the state transition matrix of the linearized PMSM model about an operating point. The results show that the machine speed response is unstable for input frequencies below the machine rated frequency. Finally, an open-loop V/f stabilization algorithm which ensures the stability of the system over a wide range of speed is presented.