Variable-flux machine (VFM) is designed to solve the problems of energy crisis and environmental pollution for traditional automotive industry

which satisfies the requirements of high-efficiency operation of new energy vehicle driving machines in a wide speed range. The development of VFM system and its key technologies were reviewed. First

the application background and operating principle of VFMs were introduced. Then

the topologies

advantages

and disadvantages of various VFMs (including VFMs using AC flux-adjustment coils

DC flux-adjustment coils

and mechanical structures) were analyzed

and the structure characteristics and design methods of different VFMs were summarized. Finally

in view of the special working principle of VFMs and the requirements of on-line parameter identification

flux-adjusting current control

and torque ripple suppression during load and on-line flux-adjustment operations

the control strategies specific to VFMs (including flux observer

current and torque control strategies

flux-adjustment

and speed regulation strategies) were summarized. The theoretical method

implementation approach

system structure

advantages

and disadvantages of various control strategies of VFMs were analyzed. Results show that the air-gap magnetic field of VFMs could be adjusted to expand the speed range and improve the efficiency of machines in high-speed range. By adopting advanced control methods

the on-line flux-adjustment and speed regulation could be realized

and the system could operate efficiently and steadily with torque ripple and flux-adjusting loss reduced. Thus

with the development of VFM topologies and related technologies

VFMs have great application prospects in the fields of electric vehicles and numerically controlled machines

and will become one of the key technologies in the future development of new energy fields.