Q-axis Current Reverse Control of Variable Flux Memory Machines With High Salient Ratio During Magnetization Process for Speed Fluctuation Reduction

For variable flux memory machine (VFMM) with high salient ratio, a negative torque occurs when applying a positive
d
-axis current (
i_d
) pulse to magnetize the machine under positive
q
-axis current (
i_q
), causing a large speed drop. Since traditional speed controllers tend to increase
i_q
at this point to increase the speed, unfortunately the higher
i_q
will generate stronger negative torque and further exacerbate the speed drop. To deal with this unique problem, a novel
q
-axis current reverse control (QCRC) concept is proposed to achieve non-negative torque by reversing
i_q
current during the period of negative torque occurrence. Specifically, based on QCRC concept, three control methods are newly designed, including look-up-table-based QCRC method (Method I), disturbance observer assistance + Method I (Method II) and disturbance-observer-based QCRC method (Method III). A supertwisting sliding mode torque observer is newly structured as the disturbance observer. Furthermore, a linear active-disturbance-rejection-based feedforward decoupling current controller is utilized to improve the current tracking performance, and the effect of its intrinsic time delay is also investigated. Finally, the effectiveness and feasibility of the proposed three control methods are validated through experimental measurement on a separated series-parallel VFMM.