Flux-Weakening Control of Novel Hybrid-Excited Permanent Magnet Machines

For hybrid-excited permanent magnet machines, both the field excitation current and the d-axis current can be utilized to adjust the flux-linkage, which offers more flexible control parameters for flux-weakening operation. In this paper, three flux-weakening control methods, i.e. utilizing field excitation current alone (Method-I), utilizing armature current alone (Method-II), and optimal method (Method-III), are proposed and compared. All three methods can achieve the same torque in the constant-torque region by the same enhanced field excitation current. In the flux-weakening region, Method-I exhibits low torque and limited operating speed range. The operating speed range can be further extended by Method-II and Method-III. In addition, Method-III can provide a higher efficiency in flux-weakening region than Method-II since the copper loss of field winding can be decreased in proportion to the reduction of field excitation current. Those flux-weakening control methods are verified by experimental results.