Power limit of the Surface-Mounted Permanent Magnet Synchronous Motor drive system

The Surface-Mounted Permanent Magnet Synchronous Motor(SM-PMSM) is commonly used on electric vehicles. The wide operating speed range of the drive system is demanded for the electric vehicle. In order to research the operating speed range of SM-PMSM drive system, the power limit during the speed range of the SM_PMSM drive system was studied. To analyse the power limit, the mathematical model and the simulation model were established. Both the mathematical analysis and the computer simulation indicated that as the current ratio λ of the equivalent exciting current to the current limit is different, the power limit during the speed range of the drive system were different. As λ > 1, the power limit have not the constant power segment, and there was the speed limit which increased with λ decreasing. As λ <; 1, the power limit have the constant power segment, and there was not the speed limit, but the maximum power limit was smaller than λ > 1. As λ = 1, the speed has not the limitation and the maximum of the power limit is infinitely near to those of λ > 1.