Deep Flux-Weakening Operation for a Surface-Mounted Permanent-Magnet Synchronous Motor Based on an Automated Working Path for the d-axis Current with Floating Conversion Point

This paper presents a new method of automatically formulating path of d-axis current command of surface-mounted permanent-magnet synchronous motor to realize deep flux-weakening operation. The theoretical deduction for flux-weakening regime has been reviewed, and a three segment d-axis current command control strategy with decoupling current control is proposed, which includes maximum torque per ampere, basic flux-weakening and simplified deep flux-weakening mode. The adopted path of utilizing d-axis current command is described in detail. One of its remarkable advantages is that the corresponding converting points between the basic flux-weakening and simplified deep flux-weakening mode can be generated by the given speeds, resulting in the fact that the values of the current floating conversion point and the path connected by the point are far less than the current maximum so as to save the energy in a certain extent. Another prominent merit of the design is to first satisfy the need of d-axis current with gliding property at converting point so that deep flux-weakening and high speed operation can be successfully realized. Finally, the results of MATLAB test have been shown and analyzed which demonstrate the advantages for achieving a wide speed range with safe field weakening.