This paper systematically reviews the impact of the parameter variation on the power-speed characteristic of the interior permanent magnet synchronous machine while running with vector current control methods. The authors attempt to study the impact of the stator resistive drop, variation of the magnet flux-linkage, saturation, cross-coupling, and the reduced DC bus voltage on the voltage limits and trajectories for motoring and generation modes. Primarily, the stator resistive drop causes the difference in the base speeds of motoring and generation modes. On the other hand, the reduction in the DC bus voltage affects the starting point of the pseudo-constant power speed range. The saturation and cross-coupling affects the motoring and generation similar way by distorting the voltage limit ellipses and trajectories.