New flux weakening control for surface mounted permanent magnet synchronous machine using gradient descent method

This paper presents a new flux weakening algorithm for a surface mounted permanent magnet synchronous machine. A current reference is modified by a controller in order to achieve a flux weakening. The current reference modification is determined by the d-q currents and the output voltage using the gradient descent method. The proposed method consists of two parts, the determination of the flux weakening region and the current reference modification. The flux weakening region is determined by the angle between the constant torque direction and the voltage decreasing direction, and the current reference is modified by the voltage magnitude and the flux weakening direction according to the flux weakening region. This method is possible to be applied to the infinite speed drive system as well as the finite speed drive system.