For electric vehicles an applied control of PMSM is the flux weakening operation for extending the region over nominal speed on nominal voltage. This paper deals with these questions and its impacts. Proved methods increase the torque angle and the d axis directed component of the stator current vector reduces the main flux, but the eddy current loss developing in magnets became significant. These impacts and their reduction need several investigations. This paper preents the possibilities and limits of flux-weakening for a given PMSM, and gives a usable optimum control strategy on nominal power's region by varied speeds.