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

Abstract

For variable flux memory machine (VFMM) with high salient ratio, a negative torque occurs when applying a positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_d</i> ) pulse to magnetize the machine under positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> ), causing a large speed drop. Since traditional speed controllers tend to increase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> at this point to increase the speed, unfortunately the higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> will generate stronger negative torque and further exacerbate the speed drop. To deal with this unique problem, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current reverse control (QCRC) concept is proposed to achieve non-negative torque by reversing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> 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 super-twisting sliding mode torque observer (STSMTO) is newly structured as the disturbance observer. Furthermore, a linear active-disturbance-rejection-based feedforward decoupling (LADR-FFD) 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 (SSP-VFMM).